|
|
Bariatric Surgery: The Needs of the Obese Patient
Hien Nguyen, MD*
Clinical Instructor
Minimally Invasive and
Bariatric Surgery
Department of Surgery
Johns Hopkins Medical Institutions
Baltimore, Maryland, USA
Michael Schweitzer, MD**
Associate Professor
Bariatric Surgery
Johns Hopkins Medical Institutions
Baltimore, Maryland, USA
Thomas H. Magnuson, MD***
Associate Professor
Director of Bariatric Surgery
Johns Hopkins Medical Institutions
Baltimore, Maryland, USA
B. Robert Gibson, MD****
Assistant Professor
Surgery/Critical Care Medicine
Department of Surgery
Johns Hopkins Medical Institutions
Baltimore, Maryland, USA
According to the Centers for Disease Control and Prevention (CDC), the regional prevalence of obesity (body mass index [BMI], calculated as weight in kilograms divided by height in meters squared, >30) can be as high as 25% and continues to increase.(1) Since 2007, more than 205,000 bariatric procedures have been performed.(2) One-quarter of the population is known to have obesity as a recognized risk factor for increased hospital morbidity and mortality,(3) and bariatric procedures have become more common; thus, critical care practitioners can expect to encounter more patients with obesity-related comorbidities. Therefore, a familiarity with these comorbidities and postoperative complications specific to the bariatric patient may aid clinicians in the critical care setting. A discussion of obesity-related cardiopulmonary pathology will be presented, as well as common postoperative critical complications such as venous thromboembolism (VTE), anastomotic leak and internal herniation.
The mortality rate of bariatric-specific procedures is between 0.14% and 0.35% in Bariatric Surgery Centers of Excellence. Despite this low mortality rate, acute complications such as hemorrhage, obstruction and anastomotic leak can occur in 5% to 10% of cases. When these complications do occur, they are less well tolerated than in the nonobese populace.(4) For example, Montravers et al found that bariatric patients admitted to the intensive care unit with sepsis can have a mortality rate as high as 33%.(5) Also, when critical illness does mandate ventilator support, obese patients tend to be ventilator-dependent for a longer period.(3)
It has been postulated that the increased morbidity, mortality and length of intensive care unit stay in the obese patient may arise from the physiologic strain on the cardiopulmonary system as much as from the obese state itself, as well as from obesity-related comorbidities. Common comorbidities associated with obesity – such as diabetes, hypertension and renal insufficiency – cause microvascular damage to the cardiopulmonary system. Furthermore, approximately 30 mL of blood are required per kilogram of adipose tissue.(8) This increased blood volume and metabolic requirement can lead to increased myocardial demand and can lower the threshold for symptomatic high-output cardiac failure in the extremely obese. At the other end of the spectrum, obesity-associated congestive heart failure results in abnormal diastolic function, left atrial enlargement and left ventricular hypertrophy.(7) The bariatric myocardium has a decreased relative number of adrenergic receptors,(9) thus response to beta-blockers and adrenergics may be attenuated, even when the dose is adjusted for weight.
Noninvasive blood pressure monitoring may be inaccurate, as standard- sized cuffs do not have the correct ratio of bladder size to arm circumference. In the acute setting, a more liberal use of an indwelling arterial catheter for hemodynamic monitoring is warranted. Anatomically, venous access in the obese patient has been notoriously difficult because of obscured anatomic landmarks and difficult intravascular cannulation. Of the various sites for central line access, the internal jugular vein has been shown to have the highest successful cannulation rate with the lowest incidence of associated complications.(10)As ultrasound guidance for bedside procedures is rapidly becoming the standard of care, ultrasoundamenable sites such as the internal jugular should be preferred.
The strain on the respiratory system caused by the obese state can be observed in the increased incidence of obstructive sleep apnea and obstructive lung disease in these patients. Obesity also contributes to a restrictive pulmonary physiology as well. Gattinoni et al discovered that an increasing BMI leads to a proportional decrease in functional residual capacity and pulmonary compliance, which results in increased work of breathing.(11) Consequently, calculated tidal volumes for intubated bariatric patients should be based on ideal body weight instead of actual body weight to avoid volutrauma and barotrauma. Providing positive endexpiratory pressure and frequent alveolar recruitment maneuvers may further improve pulmonary ventilation mechanics. Prior to assessment for endotracheal intubation, these patients may also benefit from noninvasive ventilatory support, such as bi-level or continuous positive airway pressure, as positive pressure may serve to open up airways partially collapsed from the restrictive effects of obesity. Because obese patients tend to have an increased neck diameter, the decision to perform a tracheostomy must be made with the realization that a longer tracheostomy tube and a sharper angle may be needed.
Increasing BMI is associated with an increased incidence of VTE in patients undergoing abdominal procedures,(14) as there is a linear relationship between the occurrence of VTE and increasing body weight,(15) with a six-fold increase in incidence of pulmonary emboli in patients with a BMI of 35 compared(16) to those with a BMI of 22. A possible mechanism for this increased risk may be due to the chronic inflammatory state in obese patients caused by secretion of proinflammatory cytokines by adipose tissue. These cytokines, such as tumor necrosis factor as well as activated interleukin-6, also can contribute to insulin resistance, increase oxidative stress and lead to endothelial cell dysfunction.(12) Furthermore, obesity is associated with increased levels of factors VII and VIII, von Willebrand factor, and fibrinogen,(13) which further increases VTE risk. Current prophylaxis strategy is multimodal and includes early ambulation, compression stockings, intermittent pneumatic compression devices and large-dose (40 mg) subcutaneous enoxaparin given every 12 hours, with the first dose given preoperatively.(21)
Gastrointestinal (GI) anastomotic leak following gastric bypass is found after 1% to 5% of procedures. Multiple intraoperative strategies have been employed to reduce the rate of leakage, but no clinical evidence definitively supports any one strategy. Symptoms of anastomotic leaks can be subtle and are rarely conclusive. The most sensitive bedside finding is tachycardia, but this is present in only 72% of leaks. Fever and abdominal pain are even less reliable indicators of anastomotic leaks at 63% and 54%, respectively. As clinical findings are subtle, reliance on radiographic imaging and re-exploration must be made. Yet, there is a wide range (22% to 75%) in the reported sensitivity of an upper GI contrast study. Weight limitations on computed tomography (CT) scanners can make them unavailable and, when used, this much vaunted modality has not demonstrated a high level of sensitivity in detecting anastomotic leaks in the immediate postoperative period.(17) In one study, combined upper GI and CT scans did not identify approximately 30% of patients later found to have anastomotic leaks.(18) Surgical re-exploration has demonstrated the highest sensitivity, specificity and accuracy for the definitive assessment of an anastomotic leak.(17) At repeat surgery, the most common source of leakage was the gastrojejunal anastomosis, associated with a mortality rate up to 25%.(5) When suspected, it is highly recommended that aggressive and early surgical intervention be considered for postoperative bariatric patients.
In bariatric-specific surgery, mesenteric internal hernia is the most common cause of bowel obstruction after a laparoscopic Roux-en-Y gastric bypass, while adhesions are the most common cause of obstruction in open bypass. Symptoms are vague and consist of intermittent abdominal pain, nausea and bloating before development of acute bowel obstruction. The incidence of obstruction is 4%, with internal herniation being the cause in 55% of these cases, which occur most frequently at the jejunojejunal anastomosis.(19) Radiographically, detection of a mesenteric “swirl” on CT scan is the most predictive sign of an internal hernia.(20) Increased numbers of obese patients are seen in the intensive care setting due to a higher prevalence in the population and the rapidly growing number of bariatric-related operations being performed. Therefore, it is increasingly incumbent upon the critical care practitioner to be familiar with the specific risks and complications associated with bariatric surgery and the obese patient. As understanding of the physiologic changes and common postoperative complications in this population grows, the ability to provide the Right Care, Right NowTM for this unique patient population will continue to improve.
References:
1. U.S. Obesity Trends. Centers for Disease Control and Prevention Web site. http://www.cdc.gov/nccdphp/dnpa/obesity/trends/html. Accessed on July 22, 2009.
2. Metabolic and bariatric surgery: fact sheet. American Society for Metabolic and Bariatric Surgery Web site. http://www.asbs.org/Newsite07/media/asbs_presskit.htm. Accessed July 22, 2009.
3. El-Solh A, et al. Morbid obesity in the medical ICU. Chest. 2001;120:1989-1997.
4. Pories WJ. Bariatric surgery: risks and rewards. J Clin Endocrinol Metab. 2008;93(11 Suppl 1):S89-96.
5. Kermarrec N, et al. High mortality rate for patients requiring intensive care after surgical revision following bariatric surgery. Obes Surg. 2008;18:171-178.
6. Jones R, et al. The Effects of Body Mass Index on Lung Volumes. Chest. 2006;130:827–833.
7. Movahed MR, et al. Obesity is associated with left atrial enlargement, E/A reversal and left ventricular hypertrophy. Exp Clin Cardiol. 2008 Summer;13:89-91.
8. Alexander JK. The cardiomyopathy of obesity. Prog Cardiovasc Dis. 1985;27:325–333.
9. Merlino G, et al. Lymphocyte beta-adrenergic receptors in young subjects with peripheral or central obesity: relationship with central haemodynamics and left ventricular function. Eur Heart J. 1994;15:786–792.
10. Gilbert TB, et al. Facilitation of internal jugular venous cannulation using an audio-guided Doppler ultrasound vascular access device: results from a prospective, dual-center, randomized, crossover clinical study. Crit Care Med. 1996;24:2053–2058.
11. Pelosi P, et al. The effects of body mass on lung volumes, respiratory mechanics, and gas exchange during general anesthesia. Anesth Anal. 1998;87:654-660.
12. Olusi SO. Obesity is an independent risk factor for plasma lipid peroxidation and depletion of erythrocyte cytoprotectic enzymes in humans. Int J Obes Relat Metab Disord. 2002;26:1159-1164.
13. Mertens I, et al. Obesity, haemostasis and the fibrinolytic system. Obes Rev. 2002;3:85-101.
14. Heit JA. Venous thromboembolism epidemiology: implications for prevention and management. Semin Thromb Hemost. 2002;28(Suppl 2):3-13.
15. Eichinger S, et al. Overweight, obesity, and the risk of recurrent venous thromboembolism. Arch Intern Med. 2008;168:1678-1683.
16. Kabrhel C, et al. Prospective Study of BMI and the Risk of Pulmonary Embolism in Women. Obesity (Silver Spring). 2009. In press.
17. ASMBS Clinical Issues Committee. ASMBS guideline on the prevention and detection of gastrointestinal leak after gastric bypass including the role of imaging and surgical exploration. Surg Obes Relat Dis. 2009;5:293-296.
18. Gonzalez R, et al. Diagnosis and contemporary management of anastomotic leaks after gastric bypass for obesity. J Am Coll Surg. 2007;204:47-55.
19. Gandhi AD, et al. Elective laparoscopy for herald symptoms of mesenteric/internal hernia after laparoscopic Roux-en-Y gastric bypass. Surg Obes Relat Dis. 2009;5:144-149; discussion 149.
20. Iannuccilli JD, et al. Sensitivity and specificity of eight CT signs in the preoperative diagnosis of internal mesenteric hernia following Roux-en-Y gastric bypass surgery. Clin Radiol. 2009;64:373-380.
21. Scholten DJ, et al. A comparison of two different prophylactic dose regimens of low molecular weight heparin in bariatric surgery. Obes Surg. 2002;12:19–24.
22. O’Brien JM Jr, et al. Sepsis. Am J Med. 2007;120:1012-1022.
Disclosures:
*Author has no disclosures to report
**Author has no disclosures to report
***Author has no disclosures to report
****Author has no disclosures to report
|
|
|
|
|
| |
|
|
| |
|
|
|
