INTRODUCTION — Surgical procedures on the spine and spinal cord are common and are performed for a wide variety of conditions. They range in complexity from minimally invasive, single-level decompression to highly complex, multi-stage extensive reconstruction. Operative procedures for degenerative spine disease and herniated disks are most common in those under 60 years of age, while those over 60 years of age most commonly undergo spine surgery for spinal stenosis [1].

Anesthesia providers will increasingly care for patients having spine surgery as the population ages and clinical innovation and technological advancement continue. This topic will discuss preoperative evaluation and intraoperative management of adult patients having elective spine surgery. Selection of patients for surgical treatment and options for surgical treatment are discussed to a greater extent in other topics. (See "Lumbar spinal stenosis: Treatment and prognosis", section on 'Surgical treatment' and "Subacute and chronic low back pain: Surgical treatment", section on 'Indications for spinal surgery'.)

PREOPERATIVE EVALUATION — Preoperative evaluation should focus on assessment of the airway and the respiratory, cardiovascular, musculoskeletal, and neurologic organ systems.

●Airway evaluation – Airway management for patients presenting for spine surgery may be difficult, particularly when surgery on the upper thoracic or cervical spine is planned. These patients may present with diseases that distort airway anatomy or restrict neck or jaw movement, such as osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, neuromuscular disorders, and previous radiation of the head or neck. In addition, these patients may have instability of the cervical spine, which will affect the choice of intubation technique. (See 'Airway management' below.)

Airway evaluation and management are discussed more fully separately. (See "Airway management for induction of general anesthesia", section on 'Airway assessment'.)

●Pulmonary evaluation – Patients scheduled for spine procedures may have conditions that affect pulmonary function. Significant spinal deformity may result in restrictive respiratory physiology, with decreases in vital capacity and total lung capacity, and in some cases pulmonary hypertension and cor pulmonale. Although rarely required, in addition to routine preoperative respiratory assessment, pulmonary function testing and arterial blood gas analysis may be indicated for patients having complex spine procedures, especially for thoracic spine procedures requiring a thoracotomy and use of a double lumen endotracheal tube. Results may help predict the effects of one lung ventilation and thereby help plan the surgical approach.

●Cardiovascular evaluation – Cardiovascular compromise may be the result of the pathology for which spine surgery is being performed, such as pulmonary hypertension in patients with severe kyphoscoliosis. In addition, many patients presenting for spine surgery are unable to exercise and cannot provide functional assessment. Preoperative cardiac evaluation should take into account both patient factors and the invasiveness of the planned surgery. When evaluating cardiac perioperative risk, most spine surgeries involving fusion and instrumentation should be classified as intermediate-risk procedures [2-4]. One- or two-level decompression without fusion is classified as low-risk. Preoperative cardiac evaluation is discussed more fully separately. (See "Evaluation of cardiac risk prior to noncardiac surgery".)

Most spine surgery is performed in the prone position, which is associated with reduction of cardiac index of 12 to 24 percent compared with supine, the result of reduction of venous return and left ventricular compliance in the prone position. Therefore, the degree of preexisting cardiac dysfunction may affect decisions about anesthesia technique and monitoring. (See 'General anesthesia' below and "Evaluation of cardiac risk prior to noncardiac surgery" and 'Positioning' below.)

Specific comorbid conditions, particularly pulmonary hypertension and congestive heart failure, are highly associated with perioperative adverse events after spine surgery, and surveillance for these conditions should occur in the preoperative evaluation [5].

●Musculoskeletal evaluation – Some patients having spine surgery have coexisting conditions that make surgical positioning challenging. The patient should be asked about range of motion of joints prior to anesthesia, as limitations may affect decisions about positioning. Skin should be examined and bruises or signs of injury documented preoperatively. (See 'Positioning' below.)

●Neuromuscular evaluation – Existing motor and sensory neurologic deficits should be recognized and documented prior to surgery. Knowledge of existing deficits is essential for accurate surveillance and diagnosis of new postoperative deficits. Existing motor deficits may impact both the choice of neuromuscular blocking agent and the site of assessment of the extent of neuromuscular blockade. (See 'Neuromuscular blocking agents' below.)

●Laboratory evaluation – Existing comorbidities and invasiveness of the anticipated procedure should dictate preoperative laboratory evaluation. Laboratory testing is usually unnecessary for single-level decompressive procedures performed in patients with limited comorbid disease. We perform a baseline hemoglobin, platelet count, serum creatinine and blood bank type and screen for surgical procedures that involve more than two vertebral levels, vertebral fusion and/or instrumentation, or require osteotomies. If significant blood loss is expected, consultation with the blood bank may be required in advance of surgery if the type and screen shows antibodies that will delay cross match.

●Preoperative autologous blood donation – Preoperative autologous blood donation (PAD) is not routine but can be considered for patients scheduled for spinal surgery expected to result in more than 500 to 1000 mL blood loss. PAD as well as options for intraoperative blood conservation are discussed separately. (See "Surgical blood conservation: Preoperative autologous blood donation" and "Surgical blood conservation: Blood salvage" and 'Intraoperative blood salvage' below.)

ENHANCED RECOVERY AFTER SURGERY (ERAS) — Protocols focused on enhanced recovery are typically initiated in the pre-operative setting. ERAS principles are generally applicable to patients undergoing a wide variety of surgical interventions. ERAS protocols for spine surgery have been published, and like other major surgery, benefits of reduced opioid use and length of stay have been reported, without an increase in adverse effects [6-9]. (See "Anesthetic management for enhanced recovery after major surgery (ERAS) in adults".)

PREMEDICATION — Premedication should be chosen as it would be for patients having other types of surgery. Some general considerations include the following:

●Sedatives and opioids should be titrated to effect; patients having spine surgery are often taking opioid medication for pain and may require higher doses of opioids as part of premedication.

●If flexible scope intubation is planned, we administer an anticholinergic medication, glycopyrrolate 0.2 mg intravenously (IV) or atropine 0.4 mg IV, to dry secretions for patients who will tolerate the tachycardia that may result.

●If multimodal pain control is planned, preoperative administration of acetaminophen 1000 mg orally (PO) or IV, gabapentin 300 to 600 mg PO, or pregabalin 75 to 150 mg PO, with doses adjusted for older patients and for those with renal dysfunction, may be indicated. (See "Management of acute perioperative pain", section on 'Strategy for perioperative pain control'.)

●For patients at risk for aspiration of gastric contents, we premedicate one hour before surgery with an H2 blocker (eg, famotidine 20 mg IV) or a proton pump inhibitor (eg, pantoprazole 40 mg IV) to reduce gastric volume and acidity.

CHOICE OF ANESTHETIC TECHNIQUE — General anesthesia is most commonly used for spine surgery, but regional anesthesia is an option for one- or two-level lumbar laminectomy or disc surgery.

Regional anesthesia — Regional anesthesia has been used for lumbar discectomy and laminectomy. Though epidural anesthesia is occasionally used, more commonly spinal anesthesia is an acceptable alternative for selected patients without contraindications to its use, and when the surgeon agrees. Contraindications to spinal anesthesia include patient refusal, severe spinal stenosis, history of intracranial hypertension, coagulopathy, systemic infection or infection at the site of needle placement, arachnoiditis, and severe hypovolemia.

Spinal anesthesia for lumbar surgery can be performed with a variety of techniques and medications. It can be done in the sitting or lateral position using isobaric or hyperbaric local anesthetic, with or without the addition of opioid or epinephrine. Our usual practice is as follows:

●We consider spinal anesthesia for patients who will tolerate lying prone for the duration of surgery after assessing the patient's level of anxiety and range of motion of the neck, shoulders, and arms.

●We generally avoid spinal anesthesia for patients for whom we would anticipate difficult airway management; should an airway emergency occur, the patient may have to be turned supine and the airway rapidly secured. (See "Airway management for induction of general anesthesia", section on 'Prediction of the difficult airway'.)

●After routine monitors are applied, spinal anesthesia is performed as usual under sterile technique using a pencil point spinal needle (eg, 25 gauge Whitacre, 24 gauge Sprotte) in the sitting position, though the lateral decubitus position may be used in some cases. (See "Overview of neuraxial anesthesia".)

●We inject 3 mL of 0.5% bupivacaine without epinephrine over 5 to 10 seconds, with the dose modified according to patient factors (eg, height, age, body mass index).

●The patient is positioned prone on chest supports, arms on arm boards, padded and abducted to <90 degrees. (See 'Positioning' below.)

●Most patients are lightly sedated with either small doses of midazolam (eg, 1 to 2 mg) and fentanyl or propofol as necessary, aiming to avoid respiratory depression.

●Adequate level of anesthesia is confirmed prior to skin preparation to allow for change in anesthetic plan if necessary.

●If necessary, the surgeon supplements the anesthetic with a subarachnoid injection of 1 mL of 0.5 percent isobaric bupivacaine using a pencil point spinal needle under direct vision in the surgical field.

Several randomized trials have compared regional anesthesia with general anesthesia for lumbar microdiscectomy or laminectomy [10-14]. No clear difference in morbidity or mortality has been identified, though several short-term benefits of regional anesthesia have been demonstrated. A literature review of 11 trials comparing general with regional anesthesia for lumbar surgery showed modest reduction in hypertension and tachycardia, reduction in postoperative pain, and reduction in postoperative nausea and vomiting [12]. Similarly, a meta-analysis of eight randomized controlled trials that compared spinal with general anesthesia for lumbar spine surgery reported reductions in intraoperative hypertension and tachycardia, analgesic requirement in the post anesthesia care unit, and nausea and vomiting in the first 24 postoperative hours, with spinal anesthesia [15].

General anesthesia

Intravenous access — Spine surgery may result in massive blood loss. For multilevel spinal fusion, instrumentation, and tumor surgery, we place two large bore intravenous (IV) catheters (14 or 16 gauge) or a rapid infusion catheter. We use a fluid warmer in the line connected to the largest IV.

Hemodynamic monitoring — Standard monitors (blood pressure monitoring, pulse oximetry, electrocardiogram, end expired carbon dioxide, and temperature) are used for all patients having general anesthesia. The decision to employ a more advanced monitoring technique depends on the patient's medical status, the expected length of surgery, and the anticipated blood loss. An arterial catheter may be placed for close blood pressure monitoring or for repeated blood sampling and is used for most major spine procedures, such as multilevel fusion and tumor surgery.

Central venous or, rarely, pulmonary artery catheter placement may be necessary for patients who will require high-level cardiac monitoring or central administration of vasoactive medication.

Induction agents — Induction of anesthesia with IV medication is suitable for most patients scheduled for elective spine surgery. Occasionally, induction is performed with inhalation of a volatile anesthetic. This technique is used in adults with difficult intravenous access or when maintenance of spontaneous ventilation is preferred.

When neuromonitoring is planned for spine surgery, inhalational agents can significantly decrease the amplitude and increase the latency of evoked potential responses. Inhalational agents should be used with caution, if at all, for induction of anesthesia for cases requiring neurophysiologic monitoring [16]. (See 'Neurophysiologic monitoring' below.)

The most common IV induction agents used to achieve unconsciousness and apnea are propofol, ketamine, and etomidate. Methohexital, a short-acting barbiturate, may be used in selected circumstances (eg, for patients with egg allergy). Induction agents are discussed more fully separately. (See "Induction of general anesthesia: Overview" and "General anesthesia: Intravenous induction agents".)

Neuromuscular blocking agents — Neuromuscular blocking agents (NMBAs) are commonly administered to facilitate endotracheal intubation after induction of anesthesia. Choice of NMBA for intubation and relaxation during surgery must take into account the plan for neuromonitoring, if applicable. (See 'Neurophysiologic monitoring' below.)

●Nondepolarizing NMBAs – The commonly used nondepolarizing NMBAs rocuronium, vecuronium, atracurium, and cisatracurium are intermediate-duration NMBAs. Onset and duration depend on the dose, but for typical intubating doses, onset of paralysis occurs in three to five minutes, and recovery to 25 percent of baseline twitch height occurs in 30 to 45 minutes (table 1). If neuromonitoring is not planned, nondepolarizing NMBA can be used for intubation, to facilitate surgical positioning, and for muscle relaxation during surgery.

●Depolarizing NMBA – Succinylcholine is a depolarizing NMBA with onset of action of an intubating dose (1 mg/kg IV) within 60 seconds, and though recovery is variable, appreciable neuromuscular function returns within six to eight minutes. When neuromonitoring is planned, succinylcholine may be used for intubation, with no further NMBA administered, to allow for baseline motor testing within a few minutes of intubation. However, succinylcholine is contraindicated for some patients who are likely to present for spine surgery, such as patients with some neuromuscular disorders (eg, muscular dystrophies) and significant denervation lesions. Use of succinylcholine in such patients can cause severe, potentially life-threatening hyperkalemia. Duration of action of succinylcholine may be markedly prolonged in patients with atypical or low serum concentrations of pseudocholinesterase, the plasma enzyme that metabolizes succinylcholine.

●Remifentanil intubation – Remifentanil, an ultra-short-acting opioid, is particularly useful for intubation for cases with contraindications to succinylcholine and when the prolonged duration of action of nondepolarizing NMBAs is undesirable. For a high-dose remifentanil intubation, the administration of propofol (2 mg/kg IV) plus remifentanil (4 to 5 mcg/kg IV) provides good to excellent intubating conditions at 2.5 minutes after induction [17]. Doses should be adjusted for older patients and those with comorbidities. We give ephedrine (10 mg IV) along with the propofol for this type of induction to avoid the profound bradycardia and hypotension that may result from this dose of remifentanil.

Airway management — The strategy for airway management for general anesthesia for spine surgery depends on the expected degree of difficulty with mask ventilation, supraglottic airway device ventilation, endotracheal intubation, and the stability of the cervical spine.

●Awake versus asleep intubation – Endotracheal intubation before induction of anesthesia (awake intubation) is indicated for the patient at high risk of aspiration of gastric contents if intubation is difficult, when all methods of airway management are likely to be difficult, and when neurologic assessment after intubation is required. (See "Management of the difficult airway for general anesthesia in adults", section on 'Awake intubation'.)

●Choice of intubation technique – The choice of airway technique or device for intubation is generally determined by the expertise of the clinician and the availability of airway devices. Use of a familiar technique by an experienced clinician is most likely to succeed. While the flexible fiberoptic bronchoscope is most commonly used for awake intubation, increasingly video laryngoscopes are used for intubation after induction for patients with difficult direct laryngoscopy. Strategy for airway management for general anesthesia, flexible fiberoptic intubation, and techniques for difficult airway management are discussed more fully separately. (See "Airway management for induction of general anesthesia" and "Management of the difficult airway for general anesthesia in adults".)

For most patients, a single-lumen endotracheal tube will be adequate for airway protection, ventilation, and anesthetic delivery. The lateral approach to the thoracic spine via a thoracotomy incision may require lung isolation with a double-lumen endotracheal tube or a bronchial blocking device. When a double-lumen endotracheal tube is used, it may be replaced by a single-lumen tube if postoperative ventilation is required.

Positioning — Patient position for spine surgery depends on the spinal level and the surgical approach. The surgical plan may require repositioning during the procedure. Goals of positioning are the avoidance of injury to the eyes, peripheral nerves, and bony prominences, as well as maintenance of low venous pressure at the surgical site. If neuromonitoring with motor evoked potentials is to be used, bilateral bite blocks should be placed between molars after intubation, making sure the tongue and lips will not be injured with jaw clench. Bite blocks should be taped in place and rechecked once the patient is turned prone. Warming blankets should be used as the surgical site permits. (See "Patient positioning for surgery and anesthesia in adults".)

●Cervical spine surgery – The patient's arms are usually tucked at the sides for cervical procedures. Anterior procedures are usually done with the patient's head on a padded head rest. For posterior cervical procedures or for procedures requiring intraoperative traction, the Mayfield device with skull pins is often used. The endotracheal tube should be securely taped out of the way of the surgical field. Eyes should be protected from pressure and covered with occlusive dressings or tape.

When arms will be tucked at the sides, either in the supine or prone positions, adequate IV access should be obtained prior to final positioning. Plastic IV clamps should be removed, and rigid IV tubing connectors should be padded prior to arm tuck. After the arms are tucked, IV flow should be confirmed. The arms and hands should be padded in anatomic positions with gel or foam positioning devices, making sure there is no pressure on the ulnar groove at the elbow.

Cervical spine procedures are rarely performed in the sitting position. If the sitting position is planned, the patient should be monitored for venous air embolism with precordial Doppler or transesophageal echocardiography, and central venous catheter should be placed for possible air aspiration. Venous air embolism is discussed more fully separately. (See "Intraoperative venous air embolism during neurosurgery".)

●Thoracic spine surgery – The anterior approach to spine surgery requires a thoracotomy with the patient in the lateral position. A double-lumen endotracheal tube may be required to allow deflation of one lung for surgical exposure. Posterior thoracic spine surgery is done in the prone position with the head on a foam or gel head rest, in the horseshoe head rest of the Mayfield apparatus, or with skull pins. Depending on the level of the surgery, arms will be either tucked at the sides or placed with the shoulders at 90 degrees with the arms on arm rests.

●Lumbar spine surgery – The anterior approach to the lumbar spine requires a laparotomy, which is done in the supine position, while posterior procedures require the prone position.

●The prone position – Posterior procedures are usually performed with the patient in the prone position. Most patients are anesthetized on a stretcher while supine and then rolled prone onto the operating table after intubation. Prior to the turn the eyes are covered with tape or clear plastic adhesive dressing, bite blocks are placed, and an oral or nasal temperature probe is placed, as is an orogastric tube, if necessary. If the patient's head is to be supported on a foam headrest, the headrest is placed over the patient's face while supine, making sure that the eyes and nose are free in the respective openings in the device, and turned in place. After turning prone and frequently during surgery the eyes, nose, and periorbital areas should be checked to make sure they are not compressed.

In anticipation of the turn, we administer 100 percent oxygen to prevent desaturation while ventilation is interrupted. Intravenous tubing and arterial line transducer tubing should be positioned along the patient's side to avoid dislodgement while turning. Monitoring cables may be disconnected for the turn but should be replaced as soon as possible. We maintain either pulse oximetry or invasive blood pressure monitoring throughout the turn and positioning whenever possible.

Turning the patient should be coordinated among the anesthesia care provider, the surgeon, and the other individuals helping with positioning. The breathing circuit should be disconnected at the last possible moment and for as briefly as possible. During the turn, the patient's neck should be kept in a neutral position. The arm on which the patient is rolling over should be along the patient's side throughout to prevent injury.

Special attention should be paid to the endotracheal tube when positioning prone. The tube can move in or out and can kink with positioning, especially if the neck is flexed for surgical exposure. After turning prone, the ability to ventilate, bilateral breath sounds, and blood pressure should be confirmed immediately before the stretcher is taken out of the operating room, on the chance that a quick return to the supine position might be necessary. Once the patient is prone, the breathing circuit should be supported to avoid traction on the endotracheal tube. We usually use an elastic tourniquet to tie the elbow of the breathing circuit to the bed frame, making sure that the endotracheal tube is supported in a way that does not pull on the lips. If repositioning during surgery is planned, the endotracheal tube and circuit must be protected from dislodgement.

For lumbar and lower thoracic surgery in the prone position, arms may be tucked at the sides or placed in the "prone superman" or "surrender" position. Peripheral nerve injury related to arm position is rare, but one study found reversible upper-extremity somatosensory evoked potential (SSEP) changes in up to 7 percent of patients with arm abduction versus 2 percent with arms at the sides [18]. Ninety degrees or less of arm abduction without tension on the shoulder musculature should be the goal when positioning prone. Hips and knees should be slightly flexed and supported on pillows or pads, without pressure on the fibular heads. The face, ears, breasts, iliac crests, and genitalia should be positioned to avoid compression and padded if appropriate. If a Foley catheter is in place, it should be hanging free after positioning without traction on the genitalia.

Prone positioning can result in variable effects on cardiovascular physiology. Most commonly, there is a reduction in cardiac index, which has been attributed to reduction in venous return to the heart and reduced left ventricular compliance as a result of increased intrathoracic pressure [19-21]. Abdominal compression in the prone position can cause vena caval compression, reduction in venous return with resultant hypotension, venous stasis, and increased pressure in the epidural venous plexus. (See "Patient positioning for surgery and anesthesia in adults", section on 'Physiologic effects of prone positioning'.)

Reduced intraabdominal pressure is directly correlated with reduced blood loss during spine surgery [22]. There are a number of padding systems, surgical frames, and operating tables used for prone positioning. Regardless of the type of frame used, those that allow positioning so that the abdomen is free from compression and maintain or reduce intraabdominal or bladder pressure are associated with reduced blood loss [23].

Maintenance of anesthesia — Like many surgical procedures, a balanced anesthetic approach consisting of a volatile or intravenous anesthetic with intravenous opioid administration is safe and effective for spine surgery. The use of neurophysiologic monitoring may dictate the choice of anesthetic agents. (See 'Neurophysiologic monitoring' below.)

The decision to extubate at the end of surgery or delay extubation is discussed below. (See 'Extubation' below.)

BLOOD LOSS DURING SPINAL SURGERY — Major spine surgery can result in significant, and occasionally massive, blood loss. The severity of blood loss increases with increased number of spinal levels fused, age over 50, obesity, surgery for tumors, increased intraabdominal pressure in the prone position, and the performance of transpedicular osteotomy [24-27]. A number of organizations have developed guidelines for transfusion for various clinical scenarios, including the perioperative period. These are discussed in more detail separately. (See "Indications and hemoglobin thresholds for red blood cell transfusion in the adult".)

Perioperative transfusion — The decision to transfuse must reflect the patient's comorbidities and the clinical situation in the operating room, including the rate of blood loss. For most patients, we prefer using a restrictive transfusion strategy (ie, giving less blood, transfusing at a lower Hgb level, and aiming for a lower target Hgb level) rather than a liberal transfusion strategy (ie, giving more blood and transfusing at a higher Hgb level). For most hemodynamically stable medical and surgical patients, we suggest considering transfusion at a Hgb of 7 to 8 g/dL. Some patients may tolerate a lower Hgb level. Rationale, risks of transfusion, and transfusion thresholds are discussed more fully separately. (See "Indications and hemoglobin thresholds for red blood cell transfusion in the adult".)

The potential for significant blood loss during spine surgery dictates the intravenous access required for these procedures, affects the monitoring used, and affects preoperative preparation for blood conservation measures. We place two large bore intravenous catheters and arterial catheters for most patients having multilevel spinal fusion or tumor surgery. Surgical blood conservation strategies include those designed to reduce blood loss and those that reduce the transfusion of allogeneic blood once hemorrhage has occurred.

Reduction of blood loss — Intraoperative blood loss can be reduced by careful positioning to avoid venous congestion at the surgical site, by meticulous surgical technique, by the use of antifibrinolytic agents, and by intraoperative hemodilution. Induced hypotension is no longer recommended for patients having spine surgery [28,29].

Antifibrinolytics — Antifibrinolytics have been successfully used for decades in many surgical populations. In orthopedic surgical patients, the use of the lysine analogs tranexamic acid (TXA) and epsilon-aminocaproic acid (EACA) are effective when administered as a single dose [30] and when used in multiple dose regimens (ie, multiple boluses or bolus plus infusion) [31]. The available literature regarding the use of these agents and their dosing regimen in spine surgery is limited, and antifibrinolytic benefits related to a given drug and its dosing regimen are likely surgical procedure specific. Recommendations presented here are based on available meta-analyses and pharmacokinetic properties of the antifibrinolytic medications.

In spine surgery patients, both TXA and EACA have been shown to consistently reduce estimated blood loss, the need for transfusion, and the total amount of blood transfused when compared with controls [32-35]. There is insufficient evidence to recommend an ideal time to stop the infusion (end of skin closure or extension into the postoperative period). The side effect profiles for both agents have not been shown to cause substantial morbidity or increase the risk of thromboembolic events. For spine fusion cases, we administer either tranexamic acid or epsilon-aminocaproic acid, as follows:

●TXA – Bolus 10 mg/kg IV, followed by infusion 2 mg/kg/hour IV, discontinued at the end of the procedure, dose of maintenance infusion reduced for patients with renal insufficiency

●EACA – Bolus 100 mg/kg IV, followed by infusion 10 to 15 mg/kg/hour, discontinued at the end of the procedure

We do not administer antifibrinolytics for patients who will undergo a vascular anastomosis (eg, flap coverage of wound) or free fibula grafting, or who have a hypercoagulable condition.

Intraoperative hemodilution — We do not routinely use intraoperative hemodilution for spine surgery. Acute normovolemic hemodilution is a blood conservation technique that entails the removal of blood from a patient shortly after induction of anesthesia, with maintenance of normovolemia using crystalloid and/or colloid replacement. The amount of blood removed varies between one and three units (450 to 500 mL constitutes one unit), although larger volumes may be withdrawn safely in certain circumstances. The blood is infused into the patient during or shortly after the surgical procedure.

The principle behind intraoperative hemodilution is that fewer red blood cells are lost during surgery because the hemoglobin of the shed blood is lower. This technique is safest when used in a healthy young adult who starts with a relatively high hemoglobin level and can tolerate anemia. It may be useful for Jehovah's Witness patients who may consent to the technique if the blood is maintained in a closed-circuit system.

The effect of intraoperative hemodilution on reduction of allogeneic transfusion is likely to be small. Intraoperative hemodilution is discussed more fully separately. (See "Surgical blood conservation: Acute normovolemic hemodilution".)

Induced hypotension — The use of controlled hypotension is not recommended in patients undergoing spine surgery. Induced hypotension has historically been advocated as a mechanism to reduce blood loss during a variety of surgical procedures. Reduced wound blood flow as a result of lower arterial blood pressure has been the mechanism cited for reduction in blood loss. However, epidural venous plexus pressure and intraosseous pressure, both important determinants of blood loss in spine surgery, are independent of arterial blood pressure [28].

The most important reason to avoid the use of induced hypotension is the potential for end-organ ischemia [29,36]. In particular, patients with severe spinal stenosis are at risk for spinal cord ischemia and should be maintained during anesthesia at or near their usual blood pressure. In addition, spinal instrumentation and distraction can reduce spinal cord perfusion and result in ischemia. Therefore, adequate arterial blood pressure should be maintained during instrumented spinal surgery as one measure to avoid neurologic damage. Vasopressor infusion is an effective intervention to maintain mean arterial pressure during spine surgery and does not adversely impact postoperative renal function [37]. We routinely administer phenylephrine via infusion (0.1 to 0.8 mcg/kg/minute) to maintain a satisfactory intraoperative mean arterial pressure.  

In addition, visual loss is a rare but potentially devastating postoperative complication of prone spinal surgery. Ischemic optic neuropathy is the most common cause of postoperative visual loss associated with spine surgery. Although the causes of ischemic optic neuropathy have not been fully elucidated, tissue edema with reduced perfusion of the optic nerve is a suggested etiology. Use of deliberate hypotension has not been associated with the development of postoperative visual loss; however, optimization of hemodynamics with maintenance of perfusion pressure of the optic nerve is recommended. (See 'Visual loss after spine surgery' below and "Postoperative visual loss after anesthesia for nonocular surgery".)

Reduction of allogeneic transfusion — In addition to the use of a restrictive transfusion strategy, the use of allogeneic blood products can be reduced by intraoperative cell salvage and by preoperative autologous blood donation.

Preoperative autologous blood donation — Preoperative autologous donation (PAD) is the most popular and widely used of the autologous blood conservation options, which also include preoperative hemodilution and blood salvage. Interest in all forms of autologous transfusion, particularly PAD, increased in response to the Acquired Immune Deficiency Syndrome (AIDS) epidemic and has substantially diminished now that the safety of blood products has improved.

Assuming that the donor is not bacteremic at the time of donation and/or there are no clerical errors resulting in the inadvertent transfusion of the wrong unit of blood, the patient is protected against hemolytic, febrile, or allergic transfusion reactions; alloimmunization to erythrocyte, leukocyte, platelet, or protein antigens; and graft-versus-host disease. Patients unsuitable for preoperative autologous donation include those with significant cardiac disease of all types and those with active infection, especially if it can be associated with bacteremia. Benefits and risks and indications and contraindications to preoperative autologous donation are discussed separately. (See "Surgical blood conservation: Preoperative autologous blood donation".)

Intraoperative blood salvage — A 2010 Cochrane database report found that for orthopedic surgery, intraoperative cell salvage reduces both exposure to allogeneic blood and the number of units of blood transfused [38]. Intraoperative blood salvage complements other methods of blood conservation and may be particularly useful in patients who are expected to have substantial intraoperative bleeding but are unable to donate autologous blood prior to surgery. Some Jehovah's Witnesses who will not accept blood transfusion will accept autologous blood transfusion with a closed collection and administration system. Given the high cost of current technology, it becomes cost effective compared with allogeneic blood transfusion when ≥2 units of blood can be salvaged and reinfused. Intraoperative blood salvage is discussed in greater depth separately. (See "Surgical blood conservation: Blood salvage".)

ANALGESIA FOR MAJOR SPINE SURGERY — Pain after one- or two-level decompressive procedures may be controlled with a relatively low-dose opioid along with other analgesics, but multilevel spine surgery may require an intensive postoperative pain control regimen. In addition, many of these patients are opioid tolerant, making postoperative pain control more challenging. For most patients undergoing spine surgery, we recommend a multimodal approach to perioperative pain control. (See "Management of acute perioperative pain".)

Our approach — We typically use the following multimodal strategy for postoperative pain control for major spine surgery. Doses and details appear below. (See 'Options for analgesia' below.)

●Preoperative

•Acetaminophen, oral

•Gabapentin for patients who take a gabapentinoid daily and not taken on the day of surgery (usual patient dose)

•Oral opioid for patients who take opioids daily and not taken on the day of surgery (usual patient dose)

●Intraoperative

•Ketamine infusion for opioid-tolerant patients

•Acetaminophen 1000 mg IV at six hours after the preoperative dose, if applicable

•Local anesthetic wound infiltration by the surgeon

●Postoperative

•Oral opioids if tolerated, IV patient-controlled analgesia (PCA) if necessary, without background infusion, and avoiding IV bolus opioid

•Acetaminophen, orally if tolerated, IV if necessary, every six hours

•Ketorolac at the discretion of the surgeon,

•Continued ketamine infusion, if used, as needed

•Gabapentin for patients who were taking gabapentin preoperatively, usual dose

Some surgeons prefer to administer neuraxial opioids either via intrathecal or epidural injection, performed under direct vision by the surgeon.  

Some of our surgeons prefer that we place a transversus abdominis plane (TAP) block for patients who have anterior spine surgery.

Options for analgesia — In addition to opioids, components of multimodal perioperative pain management for spine surgery may include nonopioid analgesics and regional anesthesia techniques.

●Opioids – Most patients who have spine surgery require postoperative opioids. As a general rule we attempt to use oral opioids. Patients who undergo major spine surgery often require parenteral opioids via PCA.

●Ketamine – The use of ketamine as an analgesic adjunct has been shown to reduce postoperative opioid requirements [39,40]. For opioid naïve patients undergoing spine surgery, intraoperative use of ketamine by infusion does not offer benefit over standard management [41]. However, perioperative ketamine may be beneficial for patients whose pain is expected to be difficult to control postoperatively (eg, patients who are opioid-tolerant). For opioid tolerant patients undergoing spine fusion, we administer ketamine, 0.5 mg/kg intravenous (IV) bolus, followed by an infusion 10 mcg/kg/minute. This practice is supported by a randomized, prospective study of 102 opioid tolerant patients with chronic pain having spine surgery, which found that ketamine administered at these doses resulted in reduced short- and long-term (up to six weeks) opioid consumption without an increase in side effects [42]. In another randomized controlled trial, postoperative ketamine (0.2 mg/kg IV bolus, followed by infusion at 2 mcg/kg/minute for 24 hours) reduced opioid consumption after major spine surgery in opioid tolerant patients (hydromorphone 0.007 mg/kg/hour versus 0.011 mg/kg/hour), to levels that were similar to the opioid consumption in opioid naïve patients [43].

●Gabapentinoids – Gabapentinoids (gabapentin, pregabalin) reduce postoperative pain, opioid consumption, and some opioid-related adverse effects after surgery when used as a preoperative adjunctive analgesic [44,45]. However, gabapentinoids are associated with increased risks of sedation [46], respiratory depression [47,48], and potentiation of the respiratory depressant effects of opioids [49].

The opioid sparing benefits of gabapentinoids and effective doses may vary across surgical procedures. In one study of patients undergoing discectomy and decompression, gabapentin 600 mg within two hours prior to surgery has been associated with reduced visual analog score and opioid consumption [50]. Studies suggest that higher preoperative doses of gabapentin (900 to 1500 mg as compared with 300 to 600 mg) [51] and pregabalin (150 mg compared with 75 mg) [52] are more effective at reducing postoperative opioid consumption and pain scores after spinal fusion. Continuing administration in the postoperative period is likely to be more effective than a single preoperative dose of either of these medications [53].

We do not routinely administer gabapentin or pregabalin as part of our standard preoperative analgesic regimen for gabapentinoid naïve patients. For patients taking gabapentinoids chronically, we continue the morning dose as scheduled on the day of surgery, and monitor with postoperative pulse oximetry for patients who are likely to receive perioperative opioids, because of increased potential for sedation and respiratory depression. (See "Management of acute perioperative pain", section on 'Gabapentinoids'.)

Doses of gabapentinoids should be adjusted for comorbidities and for older patients.

●Acetaminophen – Acetaminophen, administered either orally, rectally, or parenterally, can be used as part of a multimodal pain control regimen after spine surgery. A meta-analysis of randomized trials found that the addition of acetaminophen (intravenous or oral) to morphine following major surgery resulted in a small, but statistically-significant, decrease in morphine use postoperatively [54]. Oral acetaminophen 650 to 1000 mg can be administered preoperatively and continued postoperatively when oral intake is tolerated. The usual dose of IV acetaminophen for patients over 50 kg is 650 mg every four hours or 1000 mg every six hours, not to exceed 4 g per day. (See "Management of acute perioperative pain", section on 'Intravenous acetaminophen' and "Management of acute perioperative pain", section on 'Acetaminophen'.)

●Intravenous nonsteroidal antiinflammatory drugs (NSAIDs) – We use intravenous (IV) ketorolac as part of multimodal pain control in the first 48 hours after spine surgery for patients without contraindications to its use, who have no additional risk factors for nonunion (eg, smoking, long-term NSAID use), and in consultation with the surgeon. We administer 15 to 30 mg IV every six to eight hours up to four total doses depending on renal function, avoiding ketorolac administration for patients with creatinine ≥2 mg/dL. For patients ≥65 years of age, we reduce the dose to 15 mg IV every six to eight hours, maximum daily dose of 60 mg, with maximum duration of treatment, combined oral and parenteral, of five days.

Ketorolac has been administered by intraoperative and postoperative bolus and as part of patient-controlled analgesia regimens [52] and has been shown to reduce postoperative opioid consumption and side effects [55-58]. However, some studies have shown that NSAIDs may adversely affect bone healing.

A 2010 systematic review and meta-analysis of 11 case-control and cohort studies, which compared 2067 NSAID-exposed patients with 9984 non-exposed controls, found that the degree of risk (pooled odds ratio [OR]) for nonunion was significantly elevated in NSAID-exposed patients when both moderate quality studies of long-bone fractures and higher-quality studies of spinal fusion were analyzed together (OR 3.0, 95% CI 1.6-5.6) [59]. However, when only the higher-quality studies were considered, a significant increase in risk was not observed (OR 2.2, 95% CI 0.8-6.3). There were no randomized trials that qualified for inclusion in the meta-analysis.

One study included in this systematic review retrospectively analyzed the use of ketorolac as an adjunctive analgesic after spinal fusion surgery, limited to 1.5 mg/kg/day for 48 hours [60]. There was no significant effect on ultimate fusion rates or pseudoarthrosis following posterior spinal fusion and instrumentation.

●Intrathecal opioid – Intrathecal morphine, administered preoperatively or intraoperatively at a dose of less than 20 mcg/kg for pediatrics and 0.4 mg for adults, has been shown to be safe and to provide improved visual analog scale (VAS) scores and opioid-sparing properties in both adults and adolescents for up to 24 hours after spine surgery [61,62]. Intrathecal hydromorphone has also been used for postoperative pain control [63,64], though its use in spine surgery has not been studied, and optimal doses are not established. For non-spine surgery, a typical dose range for intrathecal preservative free hydromorphone is 75 to 150 mcg.

We do not routinely administer intrathecal opioids for analgesia after spine surgery. Some surgeons prefer to administer intrathecal long-acting opioid (eg, 0.1 to 0.2 mg), under direct vision during surgery.

●Epidural analgesia – Continuous epidural analgesia using opioid and/or local anesthetic has been shown to provide superior analgesia [65] and reduced opioid requirement after major spine surgery, compared with intravenous patient controlled analgesia [66,67]. Both single and double epidural catheter techniques have been reported, with the double catheter technique proving more efficacious for procedures involving multiple vertebral levels [65,68]. The optimal concentration, dose, and method of administration of epidural drugs have not been established.

At our institution, for selected patients the surgeon places an epidural under direct vision just prior to wound closure and tunnels the catheter such that the insertion site is as lateral to the incision as possible.

Epidural local anesthetic administration can cause motor block, which may complicate postoperative neurologic assessment. For patients who have an epidural catheter placed, we administer opioid as the initial dose (hydromorphone 0.5 to 1 mg), and await the postoperative neurologic examination. If necessary, low-dose local anesthetic is added postoperatively, adjusted as needed. This may require a reduction in local anesthetic concentration or infusion rate, or discontinuation of the infusion. (See "Management of acute perioperative pain", section on 'Epidural analgesia with local anesthetics and opioids'.)

●Peripheral nerve blocks – The role of peripheral nerve blocks for postoperative analgesia after major spine surgery is unclear. Use of erector spinae plane (ESP) blocks for analgesia after spine surgery has been reported, with conflicting results with respect to pain scores and opioid consumption, and overall a lack of high quality data [69-71]; the author does not use ESP blocks in this setting. ESP block is discussed separately. (See "Thoracic nerve block techniques", section on 'Erector spinae plane block'.)

TAP blocks and quadratus lumborum blocks are other types of interfascial plane blocks, commonly used for analgesia after abdominal surgery. For patients who have anterior lumbar spine surgery and when requested by the surgeon, we perform bilateral TAP blocks (20 mL bupivacaine 0.25% with epinephrine for each side). (See "Abdominal nerve block techniques", section on 'Transversus abdominis plane (TAP) blocks' and "Abdominal nerve block techniques", section on 'Quadratus lumborum block'.)

●Local anesthetic infiltration – Peri-incisional infiltration of long acting local anesthetics (eg, bupivacaine, ropivacaine) improves pain scores and decrease analgesic use after surgery, and is recommended by the American Society of Anesthesiologists Task Force on Acute Pain Management [72]. At our institution, surgeons infiltrate the wound with, 0.5% bupivacaine or liposomal bupivacaine. Limited evidence suggests that liposomal bupivacaine injected for local infiltration may improve postoperative analgesia compared with saline but liposomal bupivacaine is not clearly superior to aqueous bupivacaine [73]. Use of liposomal bupivacaine is discussed in detail separately. (See "Clinical use of local anesthetics in anesthesia", section on 'Sustained release bupivacaine'.)

POSTOPERATIVE CARE — Both patient and procedural factors correlate with perioperative morbidity and mortality and should be taken into consideration when developing a plan for postoperative care.

Extubation — The most common indication for intensive care unit (ICU) admission after spine surgery is the need for ventilatory support. Airway and facial edema commonly occur during long procedures in the prone position and with administration of large volumes of intravenous fluid. The patient with significant airway edema is at risk for airway obstruction after extubation. The decision to extubate must take into account the duration of surgery, blood loss and fluid replacement, the surgical procedure performed as it relates to the potential for airway compromise, and patient factors such as obesity or sleep apnea that make airway obstruction more likely.

Though specific patient and surgical factors affect the decision to extubate, in general our approach to extubation after spine surgery is as follows:

●Patients who have had general anesthesia for one- or two-level decompression in the prone position are routinely extubated at the end of the procedure.

●Patients who have had surgery lasting more than four hours in the prone position are assessed after turning supine at the end of the procedure. If there is significant facial edema, extubation may be delayed, even for a short period in the operating room. The patient is positioned with the head elevated to 30 degrees to allow edema to recede. When the patient is extubated, if there has been significant edema we extubate over a tube changer.

●Patients who have had surgery in the prone position with significant blood loss (>2000 mL); large volume resuscitation with crystalloid, colloid, and blood products; or who have had anterior-posterior spine surgery remain intubated and receive postoperative care in the ICU.

Retrospective studies have shown correlation between operative duration, intravascular volume replacement, obesity, and number of levels of spinal surgery and the decision to delay extubation at the end of surgery [74-76]. Most patients who required delayed extubation after spine fusion procedures will be extubated in the first 24 hours postoperatively. However, even a limited period of postoperative mechanical ventilation is associated with a higher incidence of postoperative pneumonia [74].

Some procedures confer especially high risk of postoperative airway edema, such as anterior-posterior cervical spine surgery. These procedures usually last more than eight hours, with the majority of the procedure performed with the patient in the prone position. In addition, these procedures can result in >1000 mL blood loss and involve surgery and tissue dissection on structures around the airway. All of these factors make airway edema more likely.

Postoperative disposition — Patients with limited comorbid disease undergoing uncomplicated decompressive procedures may be candidates for short-stay or even outpatient surgery. Patients having more complex spinal surgery require inpatient, and in some cases ICU, postoperative care. Morbidity and mortality after spinal fusion can approach 23 and 0.5 percent, respectively, and up to 10 percent of lumbar spine fusion patients will require care in an ICU [77]. Factors independently associated with increased morbidity after spine surgery include advanced age, male sex, and increased comorbidity burden. Specific comorbid conditions highly associated with perioperative adverse events include pulmonary hypertension, congestive heart failure, renal failure, and presurgical coagulopathy [78].

Long procedures (longer than five hours), combined anterior/posterior spinal procedures, and some procedures involving only the anterior spine, particularly anterior thoracic procedures, are associated with increased perioperative complications and mortality when compared with posterior spine procedures [5,79]. Risk factors for extended hospital length of stay and dismissal to a health care facility other than home after adult spinal deformity surgery include advanced age, osteoporosis, the need for blood transfusion and three level osteotomies [80].    

SPECIAL CONSIDERATIONS

Neurophysiologic monitoring — Perioperative neurologic injury is a feared complication of major spine surgery. Multimodal intraoperative neuromonitoring (IONM), including motor evoked potential (MEP), somatosensory evoked potential (SSEP), and electromyography (EMG), is often used to monitor spinal cord function during surgery on the cord or the vertebral column. Multimodal IONM is recommended for spine surgery where the spinal cord or nerve roots are deemed to be at risk [81].

While neurologic injury can cause changes in recorded potentials, other factors can interfere with interpretation. Confounding factors that can occur during surgery include inhalational anesthetics, hypothermia, hypotension, hypoxia, anemia, and preexisting neurologic lesions. Inhaled anesthetics such as isoflurane, sevoflurane, and nitrous oxide can reduce the amplitude and prolong the latency of SSEP and can completely abolish MEP. Neuromuscular blocking agents (NMBAs) also abolish motor evoked potentials and cannot be used when monitoring. Intravenous anesthetics such as propofol, barbiturates, and opioids have less of an effect on monitoring, though very deep anesthesia, even with propofol, can affect waveforms.

Neuromonitoring during surgery and anesthesia, and anesthetic strategy during neuromonitoring, are discussed more fully separately. (See "Neuromonitoring in surgery and anesthesia", section on 'Anesthetic effects on neuromonitoring' and "Neuromonitoring in surgery and anesthesia", section on 'Anesthetic strategy'.)

Visual loss after spine surgery — Visual loss after spinal fusion surgery is a rare but devastating complication with a reported incidence of 0.017 to 0.1 percent [82-84]. The major causes of visual loss in this patient population include ischemic optic neuropathy (ION), central retinal artery occlusion (CRAO), and retinal vein occlusion (RVO). CRAO and RVO are attributed to embolic load and/or direct globe compression, emphasizing the need to protect the eyes from direct pressure while in the prone position. (See "Postoperative visual loss after anesthesia for nonocular surgery".)

ION almost universally results in permanent visual loss. In 2012, the Postoperative Visual Loss (POVL) Study Group reported the findings [85] of their multicenter case control study that used data from known ION cases registered in the American Society of Anesthesiologists POVL Registry and control cases from 17 United States academic medical centers. Independent risk factors for the development of ION include male sex, obesity, use of the Wilson frame (head lower than the heart), longer anesthetic time, greater estimated blood loss, and lower percent of colloid in the nonblood fluid replacement. Using these risk factors and the reported incidence of POVL from ION in the literature, the POVL Study Group created a risk prediction model that may help surgeons and anesthesia providers modify their care plans and define the risk of ION to patients [85].

Risk modification strategies for ION after prone spine surgery should include positioning with the head level with or above the heart, minimizing anesthetic duration and blood loss; the use of both colloids and crystalloids for intravascular volume replacement; monitoring hemoglobin periodically during cases with significant blood loss; and optimization of hemodynamics with maintenance of blood pressure within 20 percent of baseline. Patients scheduled for historically lengthy (longer than four hours) spine surgery in the prone position should be informed of the small but increased risk of ION [86]. When possible, staging of long procedures should be considered.

Staging complex spine procedures — Procedures requiring a combined approach (anterior-posterior) to the spine are commonly longer in duration and are associated with significant blood loss and increased postoperative complications when compared with procedures requiring an isolated anterior or posterior approach. Depending on the planned procedure, the anterior portion can include ureteral stenting, laparotomy, colonic and vascular mobilization, bony exposure, and osteotomies. The posterior portion, again depending on the surgery, can include tumor resection and spinal stabilization procedures.

The anterior and posterior portions of these procedures can be done sequentially during one anesthetic or can be staged with the two approaches performed days apart. Literature comparing outcomes during and after staged or sequential spine procedures is conflicting [87-91]. Planning for these potentially long and complicated procedures requires collaboration between surgery and anesthesia, including plans for postoperative care, giving consideration to staging spine procedures in an effort to reduce prolonged procedures with significant blood loss. A collaborative approach has been endorsed by the American Society of Anesthesiologists and the North American Neuro-Ophthalmology Society and supported by the North American Spine Society [92,93].

SUMMARY AND RECOMMENDATIONS

●General anesthesia is most commonly used for spine surgery. Regional anesthesia is possible for one- or two-level decompression or discectomy. For patients who will tolerate lying prone, for whom we do not anticipate difficulty with airway management, and with a willing surgeon, we sometimes administer spinal anesthesia. (See 'Regional anesthesia' above.)

●Airway management may be difficult for patients having spine surgery, who may present with instability of the cervical spine, decreased range of motion of the neck, or conditions that distort airway anatomy. Video laryngoscopy, flexible fiberoptic bronchoscopy, and, occasionally, awake intubation may be required. (See 'Airway management' above.)

●Anesthetic agents and neuromuscular blocking agents affect neuromonitoring for spinal surgery. If somatosensory and motor evoked potential monitoring is planned, we suggest total intravenous anesthesia rather than inhalational anesthesia. For these patients, we also use succinylcholine or remifentanil for intubation rather than longer-acting agents to allow monitoring within minutes of intubation. (See 'Neurophysiologic monitoring' above.)

●Blood loss may be significant or even massive for some spine procedures. We place two large bore intravenous catheters or a rapid infusion catheter and use invasive monitoring (eg, arterial line) for long procedures and for those in which we anticipate significant blood loss. For all patients having prone spine surgery, patients should be positioned to minimize intraabdominal pressure as a measure to reduce blood loss. For patients undergoing spinal fusion, we suggest administration of tranexamic acid or epsilon aminocaproic acid and the use of intraoperative cell salvage (Grade 2B). (See 'Intravenous access' above and 'Hemodynamic monitoring' above and 'Antifibrinolytics' above and 'Intraoperative blood salvage' above.)

●Positioning for surgery should be meticulous, avoiding abdominal compression and pressure on eyes, bony prominences, peripheral nerves, breasts, and genitalia. The head should be positioned level with or above the level of the heart whenever possible to reduce venous congestion and edema of the face, airway, and periorbital tissues. (See 'Positioning' above.)

●Pain after one- or two-level decompressive procedures may be controlled with a relatively low-dose opioid along with other analgesics. For patients undergoing major spine surgery, pain may be severe and requires a multimodal approach to pain control. In addition to opioids, we administer perioperative acetaminophen, gabapentin for patients already taking it, and intraoperative ketamine for opioid tolerant patients. We also administer intravenous ketorolac, in consultation with the surgeon. (See 'Analgesia for major spine surgery' above and 'Our approach' above.)

●The plan for postoperative care for patients having major spine surgery may include delayed extubation and intensive care, especially after long procedures with significant blood loss and large-volume fluid resuscitation. We delay extubation in patients at risk for edema and airway obstruction. (See 'Postoperative care' above.)

●Postoperative visual loss is a rare but devastating complication of prone spinal fusion. Patients should be positioned to avoid direct pressure on the eye. We also use the following precautions in an effort to minimize postoperative visual loss (see 'Visual loss after spine surgery' above and "Postoperative visual loss after anesthesia for nonocular surgery", section on 'Strategies for prone spine surgery'):

•Position the head level with or above the level of the heart

•Use colloids as well as crystalloids to maintain euvolemia

•Maintain the blood pressure within 20 percent of baseline

•Monitor the hemoglobin periodically during cases with significant blood loss

•Stage long procedures when possible