INTRODUCTION — Bariatric operations are performed as an effective method to reduce obesity and obesity-linked medical illnesses. Operating on obese patients is challenging because of anatomic and physiologic characteristics and comorbidities of obese patients. However, the risk of serious intraoperative and in-hospital complications and mortality rates are relatively low when the surgery is performed by experienced surgeons with an institutional investment in bariatric programs.

Adverse intraoperative events (AIEs) are a risk factor for serious postoperative complications (eg, pulmonary embolus, myocardial infarction) [1,2]. In addition, postoperative complication rates vary with surgical approach, such as fewer complications with the laparoscopic approach than the open approach [3]. Complications also vary based upon type of procedure, such as fewer complications with the laparoscopic sleeve gastrectomy (LSG) and adjustable gastric band (LAGB) than the laparoscopic Roux-en-Y gastric bypass (LRYGB) [3-7].

This topic will review the major perioperative (intraoperative and in-hospital postoperative) complications and mortality rates of the more common bariatric surgical procedures, including laparoscopic and open Roux-en-Y gastric bypass (RYGB), LAGB, LSG, and biliopancreatic diversion with duodenal switch (BPD-DS).

A description of bariatric procedures, indications and preoperative management, short-time medical outcomes, and long-term complications of laparoscopic operations are reviewed as separate topics.

●(See "Bariatric procedures for the management of severe obesity: Descriptions".)

●(See "Bariatric surgery for management of obesity: Indications and preoperative preparation".)

●(See "Outcomes of bariatric surgery".)

●(See "Bariatric operative procedures: Thirty-day morbidity and mortality".)

●(See "Late complications of bariatric surgical operations".)

●(See "Complications of laparoscopic surgery".)

●(See "Laparoscopic Roux-en-Y gastric bypass".)

●(See "Laparoscopic sleeve gastrectomy".)

OPERATIVE CHALLENGES — Operating on the obese individual can be technically challenging even for the most experienced anesthesia and surgical teams. Anatomic and physiologic characteristics of obesity are associated with difficult intubations and drug management, while the thicker abdominal wall and visceral adipose tissue can obscure visualization of critical structures during surgery.

●Airway management – Airway management, including mask ventilation and intubation, can be arduous in morbidly obese patients. The risk of a difficult direct laryngoscopy is six times higher than that of the nonobese general population and is proportional to the larger circumference of the neck [8-13]. Other physical attributes that increase the difficulty of airway management include limited flexion and/or extension of the cervical spine, restricted mouth opening, and redundant oral tissue. (See "Intraoperative management of adults with obstructive sleep apnea".)

●Altered drug pharmacokinetics – In addition, morbid obesity alters the pharmacokinetics of lipophilic anesthetics (eg, barbiturates, benzodiazepines). The anesthetic management of the obese patient is reviewed separately. (See "Anesthesia for the patient with obesity".)

●Respiratory dynamics – High pressures required to insufflate the abdomen during laparoscopic bariatric surgery can result in increased intrathoracic pressures and decreased functional capacity, pneumothorax, extraperitoneal insufflation, gas embolism, and surgical emphysema [14]. (See "Anesthesia for the patient with obesity".)

●Body habitus – Obese patients have a variety of factors that render surgical operations technically challenging, such as a thick abdominal wall (more often identified in obese women) or extensive visceral fat (more often found in obese men) [15].

INTRAOPERATIVE COMPLICATIONS — The rate of intraoperative complications varies with the complexity of the procedure, ranging in contemporary reports from <1 to 5 percent [1,2,16]. For example, based upon retrospective reviews of three large bariatric surgery databases, the Bariatric Outcomes Longitudinal Database (BOLD), which includes information on 78,951 patients [16]; the Longitudinal Assessment of Bariatric Surgery (LABS) database, which includes 5882 patients [1]; and the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) database, which includes 110,000 patients [6], the overall rate of adverse intraoperative events ranges from 0.69 to 5.0 percent. However, when specific procedures from the LABS database were evaluated, the adverse intraoperative event (AIE) rate was 7.3 percent for open Roux-en-Y gastric bypass (ORYGB) operations, 5.5 percent for laparoscopic RYGB (LRYGB) operations, and 3.0 percent for laparoscopic adjustable gastric band (LAGB) procedures [1]. The sleeve gastrectomy (SG) appears to be somewhere between the LRYGB and LAGB in terms of efficacy and safety [17].

In addition, an AIE, along with conversion from a laparoscopic to an open procedure, increases the risk for serious postoperative complications (eg, pulmonary embolus, myocardial infarction) [1,2]. Patients who experience an AIE are more than twice as likely to develop a major postoperative complication compared with patients without an adverse event (8.8 versus 3.9 percent, p <0.001). (See 'Conversion to open procedure' below.)

Laparoscopic procedural complications — The most common intraoperative complications for LRYGB and LAGB operations based upon the LABS database include [1]:

●Anesthesia events (1.0 percent)

●Instrument/equipment failure (0.8 percent)

●Bowel injury (0.8 percent)

●Hepatic injury (0.4 percent)

●Anastomosis revision (0.3 percent)

●Splenic injury (0.2 percent)

●Major blood vessel injury (0.1 percent)

In addition, previous intra-abdominal operations can create extensive adhesions, and abdominal wall procedures (ie, abdominoplasty) can restrict insufflation and reduce the visible surgical field. (See "Abdominal access techniques used in laparoscopic surgery".)

Trocar placement, blind insertion of the laparoscopic instruments, the torque required to safely maneuver laparoscopic instruments, electrosurgical injury, or excess traction/manipulation of organs can contribute to some of the more common intraoperative laparoscopic complications.

Laparoscopic access-related injuries — Abdominal access can be challenging in the patient with a thick abdominal wall; however, all types of entry access can be safely performed by experienced surgeons [18-21]. Based upon 17 randomized trials that included 3040 patients, there was no statistical difference in the rates of major complications (eg, vascular or solid organ injury) for open or closed (Veress needle, standard or optical trocar) laparoscopic entry techniques [21]. Many bariatric surgeons prefer a combined approach. They first obtain a pneumoperitoneum using the Veress needle technique through Palmer’s point, then place a port in the left upper quadrant using an optical view method. Access techniques and access-related complications for laparoscopic procedures are reviewed separately. (See "Abdominal access techniques used in laparoscopic surgery", section on 'Peritoneal access'.)

Many structures are at risk of injury, including major vessels and solid and hollow organs, during the introduction of the trocar or Veress needle. Some injuries can be life-threatening. In the supine position, the aorta and inferior vena cava are only 2 to 3 cm below the skin, so blind entry here can result in a major vascular injury. Obese patients tend to have a longer distance but may require more force to access the peritoneum because of the amount of subcutaneous tissue. Subsequently, they can still be at risk for vascular injuries. When using the Veress needle technique in obese patients, the left upper quadrant is preferred for initial placement (Palmer's point). The aspiration test, the saline drop test, and an opening pressure of less than 10 mmHg should all be used to confirm proper placement of the needle. When using the Hassan technique for patients with a large amount of subcutaneous fat, the incision should be made large enough to identify the abdominal wall fascia and peritoneum. The area beneath the Veress needle insertion site inside the abdomen should be inspected for injuries during the initial laparoscopic evaluation of the abdomen [18-21].

Bowel injury, such as a puncture or laceration, can occur with insertion of a Veress needle, trocar, lysis of adhesions, or dissection. (See "Complications of laparoscopic surgery", section on 'Gastrointestinal puncture' and "Complications of laparoscopic surgery", section on 'Gastrointestinal injury'.)

Splenic injury — The spleen can be injured during weight loss surgery, especially during a laparoscopic sleeve gastrectomy (LSG), but bleeding can usually be controlled with hemostatic agents, and splenectomy is rarely required [22]. (See "Complications of laparoscopic surgery", section on 'Major vessels'.)

In addition, patients with cirrhosis, especially if found incidentally, have a higher risk of splenic vein bleeding, and consideration should be given to aborting the operation, especially if previously undiagnosed gastric varices are found. (See "Cirrhosis in adults: Overview of complications, general management, and prognosis" and "Hemostatic abnormalities in patients with liver disease" and "Portal hypertension in adults".)

Portal vein, inferior vena cava injuries — Intraoperative injury to the portal vein and inferior vena cava is rare during bariatric operations but can lead to rapid exsanguination [23]. If thrombosis of the portal vein occurs following an injury, these patients may require liver transplantation [23], or it can lead to mesenteric venous thrombosis. (See "Complications of laparoscopic surgery", section on 'Major vessels' and "Acute portal vein thrombosis in adults: Clinical manifestations, diagnosis, and management".)

Bowel ischemia — During the performance of RYGB or biliopancreatic diversion with duodenal switch (BPD-DS) procedures in particular, ischemia of the bowel may result if the root of the mesentery containing the major mesenteric vessels is compromised or undermined during transection of the small bowel [24-27].

The following examples illustrate when bowel ischemia may occur during bariatric operations:

●Twisting the mesentery and/or mesenteric root while creating a retrocolic pathway for the Roux limb

●Creating tension on the Roux limb when performing a gastrojejunal anastomosis

●Incising the mesentery of the biliopancreatic limb or Roux limb at an angle such that blood flow to an end of intestinal limb is compromised

●Closing the mesenteric defect with overly generous amounts of tissue between sutures

Internal hernias at Petersen's defect (between the Roux limb mesentery and the transverse colon mesentery with a retrocolic Roux limb passage), through the transverse mesocolon itself in a retrocolic anastomosis, or the jejunojejunostomy site can also lead to ischemia, and, therefore, these defects must be closed (figure 1). (See "Late complications of bariatric surgical operations", section on 'Internal hernias'.)

An antecolic limb does not rule out the possibility of a future internal hernia through this potential space.

Solid viscus organs — The liver can be injured during bariatric surgical procedures because of its close proximity to the stomach (figure 2 and figure 3), especially during vertical sleeve gastrectomy (figure 4) [22]. Bleeding can usually be controlled with hemostatic agents, and a partial hepatectomy is rarely required [22]. Management of intraoperative splenic and hepatic injuries is discussed separately. (See "Management of intra-abdominal, pelvic, and genitourinary complications of colorectal surgery", section on 'Splenic injury'.)

Conversion to open procedure — As with any laparoscopic operation, surgeon comfort and patient safety should dictate whether or not a procedure should be completed laparoscopically, particularly if any intraoperative complications occur. Based upon the retrospective review of 77,406 laparoscopic RYGB procedures in the BOLD database, the conversion rate to an open procedure was 0.8 percent [16]. Conversion to an open procedure is one of the strongest risk factors for serious complications after laparoscopic bariatric procedures [2]. (See "Complications of laparoscopic surgery", section on 'Conversion to an open procedure'.)

Open procedural complications — Open bariatric surgical procedures are associated with similar intraoperative challenges and complications as discussed for laparoscopic procedures, with the exception of insufflation and trocar-related injuries. Injury to adjacent organs (eg, spleen), twisting of the mesentery, hemorrhage, and laceration of bowel wall can occur with open procedures as described with laparoscopic procedures. (See 'Laparoscopic procedural complications' above.)

Based upon the retrospective review of 504 patients in the BOLD database undergoing an open RYGB, the overall adverse intraoperative event was 7.3 percent [1]. The most common adverse intraoperative complications for open procedures included:

●Revision of anastomosis (2.0 percent)

●Bowel injury (1.0 percent)

●Instrument/equipment failure (0.6 percent)

●Anesthesia events (0.4 percent)

●Hepatic injury (0.2 percent)

●Major blood vessel injury (0.2 percent)

A trial that included 155 obese patients randomized to laparoscopic or open RYGB found a significantly higher rate of intraoperative blood loss for patients managed by an open procedure compared with a laparoscopic procedure (395 versus 137 mL) [28]. Intraoperative blood transfusion was required in 3.9 percent of patients undergoing the open procedure and none undergoing a laparoscopic procedure. Finally, venous thromboembolic events seem to occur at a higher rate after an open procedure [29].

Misconstruction — Misconstruction of a Roux-en-Y bypass or a BPD-DS (figure 5) can occur during a laparoscopic or open approach. Proper bowel orientation must be maintained to avoid misconstruction.

Misconstructions of the Roux-en-Y bypass with an anastomosis between the distal aspect of the biliopancreatic limb and the gastric pouch have been reported and lead to chronic bilious vomiting ("Roux-en-O") (image 1 and image 2 and figure 6 and figure 7) [30]. Other examples of misconstruction include Roux limb inversion (image 3 and figure 8) and short Roux limb (figure 9 and image 4).

PREVENTING INTRAOPERATIVE COMPLICATIONS

●Preoperative evaluation – A thorough preoperative assessment of comorbid illnesses (eg, diabetes, hypertension, cirrhosis, obstructive sleep apnea) and effective preoperative management as well as an assessment of anesthetic risks must be performed prior to the operative procedure. Higher risk of morbidity is noted in male bariatric patients, those with a body mass index (BMI) >50 kg/m², those with dysmetabolic syndrome, and those over age 65 [31]. Immobile or functionally dependent patients, in particular, have a very high risk of complications [32]. (See "Bariatric surgery for management of obesity: Indications and preoperative preparation", section on 'Preoperative assessment'.)

●Instrument and equipment condition – Prior to the patient receiving an anesthetic, the surgeon and appropriate operating room personnel should examine all instruments for availability and function. The usual length of laparoscopic equipment is 38 cm long, but lengths up to 43 cm are available for laparoscopic instruments, surgical energy devices, and staplers. It would be important for the surgeon to know if his or her hospital has such equipment at its disposal. (See "Instruments and devices used in laparoscopic surgery".)

●Proper placement of trocars – Torque that occurs from improperly placed trocars can be minimized by repositioning or adding additional ports. For example, for a patient with a very large abdomen, it may be difficult to access the gastroesophageal junction and infracolic abdomen to perform a Roux-en-Y gastric bypass (RYGB) anastomosis. In this setting, the use of additional ports would likely facilitate the procedure (figure 10). (See "Abdominal access techniques used in laparoscopic surgery", section on 'Foregut surgery'.)

●Tension-free anastomosis – Tension on the gastrojejunal anastomosis when performing an RYGB is a risk factor for anastomotic leak (figure 11). A retrocolic, retrogastric approach creates the least amount of tension on the anastomosis (figure 12). While the antecolic, antegastric route may be technically easier to perform, this route may also create a greater amount of tension on the anastomosis. Bariatric surgeons should be comfortable with performing both Roux limb routes. (See "Bariatric procedures for the management of severe obesity: Descriptions", section on 'Roux-en-Y gastric bypass'.)

●Defining a plane between adhesions and bowel – Regardless of whether adhesions are lysed with an electrosurgical device or scissors, defining and maintaining a clear plane of dissection will minimize risk to the bowel wall. Prompt identification of injury and primary repair of the inadvertent laceration will minimize the risk of a subsequent leak. If the procedure cannot be safely performed laparoscopically because of dense adhesions, conversion to an open approach may enable better visualization and safer lysis of adhesions. (See "Complications of laparoscopic surgery", section on 'Gastrointestinal injury'.)

IN-HOSPITAL POSTOPERATIVE MORBIDITY — In-hospital complications include anastomotic leaks, hemorrhage, deep venous thrombosis, pulmonary embolism, and cardiovascular and pulmonary (eg, pneumonia, respiratory failure) complications [28,33-44]. The risk of a major complication immediately after the operation ranges from approximately 0.2 to 10 percent in contemporary series, depending upon patient comorbid illnesses, type of procedure, surgical approach (laparoscopic or open), and surgeon expertise [3,16,35,36,45-47].

Anastomotic leak — The anastomotic leak remains the most dreaded technical complication of bariatric surgery and is one of the most challenging complications of weight loss surgery [28,36-42,48-52]. The risk of a leak ranges from 0.8 to 6 percent depending on procedures chosen as well as technical and patient factors involved [16,46,53,54]. As examples:

●The Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) database shows a leak rate of about 0.8 percent in over 93,000 patients who underwent laparoscopic sleeve gastrectomy [55].

●The MBSAQIP database shows a 1.6 percent leak rate in over 41,000 patients who underwent laparoscopic Roux-en-Y gastric bypass [55].

In revisional bariatric surgery, the risk of anastomotic leak approaches 35 percent [53].

Most leaks after bariatric surgery occur early, generally within the first week after surgery but also after the patient has been discharged [46]. Therefore, vigilant follow-up during the first 30 days is recommended for that group of patients.

The clinical presentation of an anastomotic leak can be subtle and requires vigilance for signs such as low-grade fevers, respiratory compromise, and/or unexplained sustained tachycardia greater than 120 bpm [56]. These signs may also be present in the setting of pulmonary embolism.

A leak may be radiographically confirmed by barium swallow or contrast computed tomography (CT) (image 5 and image 6) [57]. Several studies of patients undergoing upper gastrointestinal (GI) series on postoperative day 1 show a 3 percent leak rate [58,59]. Whether postoperative upper gastrointestinal series should be ordered routinely or selectively remains controversial [57,60,61]. In our practice, we do not routinely perform an upper GI series after bariatric surgery, unless there are clinical signs suggesting a leak or the case is technically difficult.

If a leak is suspected clinically, emergency surgical exploration should be performed, even if the imaging is negative, given the rapid progression to sepsis in the severely obese patient with comorbidities [60,62]. Any patient with unexplained but persistent tachycardia requires immediate exploration to rule out a leak. A negative exploration that does not reveal a leak should not be considered a complication but rather evidence of good surgical judgment. Multiple studies have shown that re-exploration is safe when compared with missing or delaying the treatment of a leak [63-65]. In experienced hands, surgical exploration and management of a leak is often feasible via a laparoscopic approach.

The surgical principles in treating a leak include (figure 13):

●Broad-spectrum antibiotic coverage

●Identification and repair of the defect

●Irrigation and control of contamination

●Wide external drainage of the contaminated area

●Enteral access for feeding, most commonly a gastric feeding tube placed in the gastric remnant

Percutaneous drainage of a contained fluid collection may be an option in patients who are hemodynamically stable [64]. Surgical therapies for a persistent gastric leak are technically difficult and often unsuccessful. New approaches using minimally invasive endoscopic repair techniques appear safe and effective in some patients. These include use of glue [66], placement of covered stents across the leak [67], or placement of clips to close the opening [68]. Again, these options are only open if the patient is clinically stable; unstable patients with a leak should undergo immediate surgical exploration, washout, and either repair or better control of the leak.

Many different intraoperative techniques have been used to decrease the incidence of leaks. Over-sewing staple lines, buttressing materials for the staple line, and fibrin glue have been used, but there is no evidence that these methods reliably decrease the leak rate after Roux-en-Y gastric bypass (RYGB) [69-76] or sleeve gastrectomy (SG) [77].

Methylene blue dye or endoscopy can be used intraoperatively to test for a leak during a gastric bypass or SG. For the dye test, methylene blue tinged saline is injected via the nasogastric tube while the bowel distal to the gastrojejunostomy is gently occluded. A leak is detected by the presence of methylene blue around the staple line. Alternatively, the pouch can be evaluated for a leak under direct visualization with an endoscope. For endoscopy evaluation, the gastrojejunostomy or sleeve is submerged in saline and the Roux limb or distal stomach is gently occluded, then the endoscope is used to insufflate the pouch. The presence of air bubbles in the saline around the pouch during insufflation indicates a leak may be present.

In SG patients, a sleeve leak may be the symptom of a kink, stenosis, or twist in the sleeve that causes an increase in intraluminal pressure resulting in the leak. These etiologies must be investigated, ruled out, and treated, or else the leak will not close.

Hemorrhage — Significant hemorrhaging after bariatric surgery has been described in 0.4 to 4.0 percent of patients [3,28,36-42,47]. (See 'Open procedural complications' above.)

Bleeding can occur from the gastric or short gastric vessels during dissection of the greater curve. Most of the bleeding problems associated with a sleeve gastrectomy occur from the staple line after transection of the stomach [78-80]. The bleeding is most likely a result of the large staples used for the thick tissue in the distal stomach. Large staples are not adequate to seal small vessels [81]. This has led many surgeons to reinforce the staple line by over-sewing, buttressing, or both [82].

Early bleeding typically can also occur from an anastomosis; more commonly, intraluminal bleeding occurs. Patients frequently present with tachycardia, a decreased hematocrit, hematochezia, or melena [43]. Such bleeding typically resolves without surgical intervention but may require transfusion of blood products and reversal of anticoagulation [36,37,40]. Careful endoscopic examination and therapy is appropriate for ongoing bleeding with high transfusion requirements. Surgery is reserved for hemodynamic instability, intraluminal bleeding not amenable to endoscopic therapy (eg, staple line of the excluded stomach), extraluminal bleeding, or continued bleeding despite restoration of normal coagulation status [43,44]. Patients with early postoperative bleeding had a longer hospital admission (4.8 versus 3.0 days, p <0.001) and a higher mortality rate (7.1 versus 0.9 percent, p <0.01) compared with patients without an early bleed [47].

Venous thromboembolism — Based upon the information from the aforementioned databases, the overall incidence of a venous thromboembolism (VTE) including deep vein thrombosis (DVT) and pulmonary embolism (PE) ranges from 0.17 to 0.4 percent [6,83]. Of the 260 patients who developed a VTE, most occurred following discharge; 2 percent occurred intraoperatively and 25 percent occurred prior to hospital discharge. VTE identified in patients undergoing an RYGB and AGB was 0.46 and 0.14 percent, respectively. The highest rates of VTE were identified in 4 percent of patients undergoing a biliopancreatic diversion (BPD) and 2.2 percent of patients undergoing a BPD with duodenal switch (BPD-DS). The incidence of VTE was 0.29 percent for laparoscopic procedures and 1.2 percent for open procedures.

Risk factors for VTEs include body mass index (BMI) >50 kg/m², a history of a VTE, a history of a hypercoagulable disorder, pulmonary hypertension, venous stasis disease, poor functional status, open or revision surgery, and operative time >3 hours [84,85].

The most common risk factors associated with fatal PE include severe venous stasis disease, BMI >60, truncal obesity, and obesity-hypoventilation syndrome [85,86]. Patients undergoing revision bariatric surgery are at a higher risk of a VTE [29]. (See "Clinical presentation, evaluation, and diagnosis of the nonpregnant adult with suspected acute pulmonary embolism" and "Treatment, prognosis, and follow-up of acute pulmonary embolism in adults" and "Clinical presentation and diagnosis of the nonpregnant adult with suspected deep vein thrombosis of the lower extremity".)

Diagnosis of PE in morbidly obese patients can be problematic because use of standard diagnostic modalities (such as a nuclear lung scan, CT angiography, pulmonary angiography, and/or lower extremity duplex scan) may not be physically feasible in extremely obese patients. Immediate anticoagulation is prescribed for patients for whom there is a high level of clinical suspicion. In patients in whom anticoagulation is contraindicated, a mechanical filter can be placed in the inferior vena cava to lower the risk of continued clot embolization (see "Placement of vena cava filters and their complications"). However, per the MBSAQIP data, the use of an inferior vena cava (IVC) filter even in high-risk patients did not seem to have a protective benefit [87].

A single optimal strategy for preventing VTE in the bariatric surgery setting has not been established [88]. Most bariatric surgeons use both pneumatic compression devices in conjunction with subcutaneous unfractionated or low-molecular-weight heparin and ambulation on the day of surgery [89]. The current American Society of Bariatric and Metabolic Surgeons (ASMBS) guidelines regarding thromboprophylaxis state that all bariatric patients receive mechanical prophylaxis and are ordered for early ambulation. Additionally, the surgeon may routinely use pharmacologic prophylaxis of either low-molecular-weight heparin or unfractionated heparin [84]. In one retrospective study of over 24,000 patients undergoing bariatric procedures, low-molecular-weight heparin was more effective than unfractionated heparin in preventing postoperative VTE while not increasing the rate of bleeding [90].

Preoperative risk stratification may be a useful tool for identifying high-risk patients for more aggressive prophylaxis [91]. In patients identified preoperatively as high risk for PE, due to previous medical history of VTE, PE, or venous stasis disease, or inability to ambulate (ie, wheelchair-bound), perioperative chemoprophylaxis of low-molecular-weight heparin or unfractionated heparin may be prescribed for an extended period even after discharge from the hospital. As the average time to developing a VTE is 21 to 28 days, many bariatric surgeons continue chemoprophylaxis for six weeks postoperatively. The use of preoperatively placed IVC filters is associated with higher rates of VTE, PE, other complications, and death. Their routine use is discouraged [92].

Prevention of postoperative VTE is reviewed in detail separately. (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients" and "Prevention of venous thromboembolism in adult orthopedic surgical patients".)

Myocardial infarction — The incidence of a postoperative myocardial infarction after a bariatric operation is approximately 0.2 percent [3]. (See "Perioperative myocardial infarction or injury after noncardiac surgery".)

Pulmonary complications — Major postoperative pulmonary complications include pneumonia and acute respiratory failure. Atelectasis is common after all types of surgery that require general anesthesia and is more prevalent in the morbidly obese.

The following studies illustrate the incidence rates and risks for pulmonary complications and the sequelae:

●Based upon a retrospective review of the Bariatric Outcomes Longitudinal Database (BOLD) database, the overall incidence of postoperative pneumonia was 0.4 percent [16]. The incidence of pneumonia was significantly higher for patients treated with a BPD-DS (n = 1545) compared with patients treated with a gastric bypass (0.9 versus 0.4 percent, p = 0.001).

●In a retrospective review of the National Inpatient Sample database that included 304,515 patients undergoing a bariatric operation, the overall rate of acute respiratory failure (ARF) was 1.35 percent [93]. The incidence was higher with an open compared with a laparoscopic procedure (3.87 versus 0.94 percent), gastric bypass procedures compared with procedures that did not include gastric bypass (1.54 versus 0.82 percent), and for patients with preoperative heart failure, chronic renal failure, peripheral vascular disease, chronic obstructive pulmonary disease (COPD), tobacco smoking, and diabetes. ARF is associated with a significantly higher in-hospital mortality rate compared with those who do not develop the complication (5.69 versus 0.04 percent). (See 'Mortality' below.)

●In a retrospective review of the American College of Surgeons' National Surgical Quality Improvement program that included 32,889 bariatric surgical patients, the incidence of pneumonia and ARF was 0.6 percent each [94]. While the incidence is relatively low, patients with pulmonary complications were more likely to have additional in-hospital complications (eg, surgical site infections, PE, myocardial infarction), and length of stay was significantly longer (six versus three days, median length of stay). The 30 day mortality rate for patients with pneumonia ARF was significantly higher compared with patients without the complication (4.3 versus 0.16 percent and 13.7 versus 0.10 percent, respectively). (See 'Mortality' below.)

Specific risk factors for pneumonia included new or preoperative medical history of heart failure, COPD, bleeding disorder, tobacco smoking history, increasing age, open versus laparoscopic operation, and RYGB and BPD-DS when compared with LAGB.

Specific risk factors for ARF included COPD, percutaneous coronary intervention, diabetes, increasing age, prolonged anesthetic time, open versus laparoscopic operation, and RYGB and BPD-DW when compared with laparoscopic AGB.

Early ambulation and incentive spirometry after surgery are important to decrease the incidence of pulmonary complications. Preoperative identification of the presence of significant obstructive sleep apnea and initiation of continuous positive airway pressure (CPAP) therapy also reduce the risk of pulmonary complications in the postoperative period [95]. CPAP should be used in the early postoperative period if it is clinically necessary without concern of causing a leak. (See "Overview of the management of postoperative pulmonary complications" and "Clinical presentation and diagnosis of obstructive sleep apnea in adults".)

Surgical site infections — Surgical site infections (SSIs), which often are localized to the incision but can extend into deeper tissues, are the most common nosocomial infection and are found in 2 to 5 percent of surgical operations in the United States [96-98]. SSIs are associated with substantial morbidity, mortality, prolonged hospital stay, and increased cost of care [99-101].

The BOLD study reported an overall incidence of SSIs of 1.1 percent [16]. Rates of wound infection are significantly greater for open gastric bypass procedures (10 to 15 percent) compared with laparoscopic (3 to 4 percent) procedures [23,28,37]. The incidence of wound infection in open cases can be decreased by almost 50 percent if the fascia is closed in a running fashion rather than in an interrupted manner [102]. Among laparoscopic techniques, rates of wound infection vary depending upon the technique used, with a higher rate of wound infections associated with the use of circular stapling devices to create the gastrojejunostomy, mostly due to the fact that a larger incision of 2.0 to 2.5 cm is needed to introduce the circular stapler into the abdomen [103,104]. Interestingly, the rate of organ space infection was lower in patients receiving an SG than an RYGB [6].

Signs of wound infections include unexplained fever, fluctuance, erythema, or drainage. Treatment consists of opening the affected area for drainage of infected fluid or pus, debridement of any devitalized tissue, and antibiotics if the surrounding skin suggests signs of cellulitis. (See "Complications of abdominal surgical incisions".)

The incidence of wound infections can be decreased by perioperative administration of antibiotics. Data support the use of cefazolin, or in patients allergic to penicillins and cephalosporins, clindamycin PLUS one of the following: ciprofloxacin, levofloxacin, gentamicin, or aztreonam [105]. Choice of antibiotics is reviewed in more detail separately. (See "Antimicrobial prophylaxis for prevention of surgical site infection following gastrointestinal procedures in adults", section on 'Gastroduodenal procedures'.)

MORTALITY — The intraoperative mortality is dependent upon multiple factors, including the technical difficulty of selected procedure (for example, biliopancreatic diversion with duodenal switch [BPD-DS] is technically more difficult than laparoscopic adjustable gastric band [LAGB]), patient selection (eg, body habitus), presence of comorbid illnesses (eg, chronic obstructive pulmonary disease [COPD], congestive heart failure, dependent functional status), skill of the surgeon (learning versus expert), institutional resources, and volume of procedures performed [15]. While there are limited data available, the overall intraoperative mortality rates that are reported as well as the overall in-hospital mortality rates are typically <1 percent in most contemporary series [39,106-109].

The overall 30 day mortality rate after discharge also is relatively low and is discussed separately. (See "Bariatric operative procedures: Thirty-day morbidity and mortality".)

Pulmonary embolism (PE) remains the most common cause of mortality in the perioperative period after bariatric surgery and accounts for approximately 30 to 50 percent of deaths [34,110]. The mortality rate of a PE is dependent upon the severity of presentation and time to diagnosis/treatment and widely varies from 1 to 95 percent [111]. The majority of deaths occur within the first one to two hours after the embolism. (See "Overview of acute pulmonary embolism in adults" and "Treatment, prognosis, and follow-up of acute pulmonary embolism in adults".)

Other common, serious causes of in-hospital mortality include cardiac events, respiratory failure, and septic complications related to an anastomotic leak. Mortality associated with these adverse events includes:

●Cardiac complications, including myocardial infarction and cardiac failure, are a common cause of mortality in the perioperative period [112,113]. An analysis of 13,871 morbidly obese patients from a national registry reported that the mortality from cardiovascular events ranged from 12.5 to 17.6 percent [113]. (See "Management of cardiac risk for noncardiac surgery".)

●Acute respiratory failure accounts for approximately 11 percent of perioperative mortality after bariatric operations [51,113]. (See "Overview of the management of postoperative pulmonary complications".)

●Sepsis related to an anastomotic leak, if not diagnosed in a timely fashion, is associated with a mortality rate as high as 15 percent [53]. (See "Sepsis syndromes in adults: Epidemiology, definitions, clinical presentation, diagnosis, and prognosis".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Bariatric surgery".)

SUMMARY AND RECOMMENDATIONS

●The primary intraoperative challenges of bariatric surgery include airway management, drug pharmacokinetics for lipophilic anesthetics, and the technical aspects related to protecting the airway and performing a surgical procedure on an obese person. (See 'Operative challenges' above.)

●Although the risk of an adverse intraoperative event is low, an intraoperative event increases the risk of further postoperative morbidity. (See 'Intraoperative complications' above.)

●For patients undergoing bariatric surgery, we use perioperative pharmacologic thromboprophylaxis (eg, low-molecular-weight heparin) and mechanical thromboprophylaxis to prevent venous thromboembolism (VTE). Postoperatively, we encourage early ambulation. Longer-duration thromboprophylaxis (>24 hours) should be prescribed for patients who remain nonambulatory or who have other risk factors for a VTE. (See 'Venous thromboembolism' above.)

●In-hospital morbidity rates are low and include anastomotic leak, hemorrhage, venous thromboembolism, cardiac events, and surgical site infections. (See 'In-hospital postoperative morbidity' above.)

●Patients who develop unexplained, persistent tachycardia after bariatric surgery undergo re-exploration to rule out a leak even with a negative radiologic study. Hemodynamically unstable patients who do not have another cause (eg, myocardial infarction or pulmonary embolism) should be re-explored as well. (See 'Anastomotic leak' above.)

●The mortality rate associated with bariatric operations is low. The most common causes of early postoperative mortality include pulmonary embolism, leak, cardiac events, and sepsis. (See 'Mortality' above.)