Medical Student Notebook: Preoperative Anesthetic Considerations in Patients with Obesity Undergoing Surgery

| June 1, 2021

by Abraham Z Cheloff, MS

Mr. Cheloff is a medical student at Harvard Medical School in Boston, Massachusetts.

FUNDING: No funding was provided for this article.

DISCLOSURES: The author reports no conflicts of interest relevant to the content of this article.

ABSTRACT: As obesity continues to rise in the United States and worldwide, there is a greater need for anesthesiologists and surgeons alike to be attuned to the specific needs of this patient population during surgery, and to understand their unique physiology. Several recommendations exist surrounding the use of anesthesia in patients with overweight and obesity, but further data is needed to create best practices for how anesthesia is practiced in this patient population. In this review, we assess the current literature on anesthesia in patients with obesity and make recommendations for current practice. Furthermore, we recognize the current gaps in research, and suggest where additional data would be helpful in forming more substantial recommendations.

KEYWORDS: Obesity, bariatric surgery, anesthesia, perioperative

Bariatric Times. 2021;18(6):10–11.

The proportion of individuals with overweight and obesity globally has been increasing and is expected to continue to rise in the future. According to the World Health Organization, obesity worldwide has tripled since 1975, with over 13 percent of adults being classified as having obesity in 2016, and hundreds of millions of children age 5 to 19 years were classified as having obesity or overweight in the same year.1 This raises concern in the medical field, as obesity raises an individual’s risk of multiple conditions, including cardiovascular disease, diabetes, dyslipidemia, sleep apnea, and some cancers.2 However, obesity also raises concern during planned and emergent surgeries, for issues surrounding surgical planning, postoperative care,3 and anesthesia.4 Creating an anesthetic plan, one of the key roles that anesthesiologists play in keeping patients safe during a procedure, must include special considerations specific to a patient’s particular physiology, including whether or not they have overweight or obesity. Here, we will review some of the key concepts that anesthesiologists should consider as they create anesthetic plans for patients with overweight and obesity. 

Antibiotic Prophylaxis

Obesity has been linked with changes in human physiology affecting the ability to both prevent and fight infections. The mechanisms of this are not completely understood, though there are a number of potential factors, including immune system suppression, respiratory dysfunction, changed in circulation and healing, and comorbidities.5 However, data on the incidence and outcomes of specific infections, including postoperative infections, is lacking and remains a need in further research.6 There is, however, some data surrounding best practices for antibiotic usage in patients with obesity. Many antibiotics, but not all, require some sort of dosage adjustment in patients with overweight and obesity to account for changes in the pharmacokinetic and pharmacodynamic factors that would otherwise lead to overdosing or underdosing in this population.7,8 More specifically, cefazolin, a common antibiotic used for skin and soft tissue prophylaxis prior to surgery, was found to work well when a 2g dose is given.9 However, it should be noted that this recommendation comes from multiple studies that often use conflicting methodologies, and variability among patients with obesity is not necessarily considered in this recommendation. While there is data on other antibiotics, data is overall limited, sometimes with conflicting reports, leading to difficulty in dosing antibiotics appropriately when allergies or other contraindications to cefazolin are involved. Further research is needed to create full dosing guidelines for this population.

Pain Management

Acute pain treatment following surgery is similar in patients with obesity as other individuals, except that there is increased concern and consideration for patient safety. Many physicians consider opioids before, during, and after surgery as mainstays of treatment to keep patients comfortable. However, patients with obesity have an increased risk of opioid-induced ventilatory impairment, leading to increased perioperative morbidity and mortality.10 This risk, combined with the recommendations from enhanced recovery after surgery (ERAS) guidelines to limit opioid use after bariatric surgery has led to increased use of opioid-free analgesia for patients with obesity, who commonly undergo bariatric surgery.11 A retrospective study performed in a cohort of 9,246 patients having bariatric surgery between 2009 and 2017 showed fewer complications postsurgery if patients were given continuous deep neuromuscular block with complete opioid-free analgesia.12 There is good evidence, and recommendations currently suggest, that using opioid alternatives in patients with obesity is the safest option.

Anesthesia

Induction and maintenance of anesthesia in patients with obesity can be difficult given the changing pharmacodynamic and pharmacokinetic parameters of anesthetic agents commonly used. There is currently limited evidence regarding the best anesthetic plan to use in patients with obesity. A 2019 double-blind, randomized, controlled trial evaluated 183 patients undergoing bariatric surgery, randomized to either total intravenous anesthesia with propofol, or reparatory anesthesia with desflurane. The study found no significant differences between the two anesthetic types in regard to postoperative nausea, postoperative pain, time to awakening, or use of perioperative muscle relaxants for peritoneal stretch.13 This is in contrast to previous data, which had suggested more rapid and consistent recovery from anesthesia when using desflurane as opposed to propofol. There has been no resolution to this contradictory data, and so there are currently no protocols to guide anesthesia in patients with obesity. Rather, basic pharmacologic principles are used to guide anesthetic planning. Accommodations must be made for the increased distribution of drugs into adipose tissue, and increased renal clearance secondary to renal blood flow. Generally, drugs are dosed according to either lean or ideal body weight, and so calculations must be made to account the physiologic difference from these values to prevent over or under dosing of medications.14 Given the complicated nature of pharmacology and lack of evidence there are unfortunately no discreet guidelines, and so anesthesiologists must continue to account for these individual patient factors in each medication until more data is collected to suggest best practices.

Intubation and Ventilation Planning

The possibility of a failed intubation should be considered in all patients. However, obesity raises the chance of a difficult or failed intubation by 30 percent,15 though obesity itself is not a risk factor for difficult laryngoscopy. A recent observational study showed that in a small set of patients with obesity, conventional intubation was appropriate in most cases.16 However, this was the case when appropriate preparation and precautions were taken. Two of the common parameters used to assess for difficult intubation are the Mallampati score and neck circumference. A 2002 study on 100 patients with morbid obesity found that while morbid obesity itself was not a good predictor of difficult intubation, a Mallampati score of at least 3 and increasing neck circumference were both good predictors of difficult intubation in this population.17 To facilitate intubation, the “ramped” position should be used, elevating the patients shoulders and head.18 Given the reduced functional residual capacity (FRC), patients should be preoxygenated for several minutes after SPO2 reaches 100 percent,19 followed by rapid intubation to regain and maintain airway access.

Once a secure airway is achieved, proper planning of ventilation must occur to ensure adequate oxygenation through the length of the surgery. Individuals with obesity are at an increased risk of obstructive sleep apnea (OSA) and obesity hypoventilation syndrome (OHS), so patients with obesity should be screened for both conditions prior to surgery. OSA screen can occur via either a sleep study, which is preferred, or with the STOP-Bang/Berlin questionnaire if a study had not been performed. OHS can be screened with a venous HCO3– level.20 If a patient screens negative for these conditions, then positive end-expiratory pressure (PEEP) should be used during induction and intubation, with low tidal volumes throughout surgery. If a patient screens positive, then continuous positive airway pressure (CPAP) should be used prior to surgery, during induction and intubation, and immediately following extubation to keep patients well oxygenated.20

Conclusion

Patients with obesity undergo a wide variety of procedures and surgeries, and special conditions must be made for their changing physiology to ensure a smooth and safe anesthetic experience. Data is currently limited across many domains, and further research is needed to optimize anesthesia for this population and ensure that patients with obesity are being provided the best care possible. In the meantime, there is data to support multiple preoperative considerations as described to limit complications and prepare for them if they arise.

 

References

  1. World Health Organization. Obesity and overweight fact sheet. 2020. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight. Accessed April 12, 2021.
  2. Apovian CM. Obesity: definition, comorbidities, causes, and burden. Am J Manag Care. 2016;22(7 Suppl):s176–185.
  3. Ri M, Aikou S, Seto Y. Obesity as a surgical risk factor. Ann Gastroenterol Surg. 2018;2(1):13–21.
  4. Pouwels S, Buise MP, Twardowski P, et al. Obesity surgery and anesthesiology risks: a review of key concepts and related physiology. Obes Surg. 2019;29(8):2670–2677.
  5. Huttunen R, Syrjänen J. Obesity and the risk and outcome of infection. Int J Obes (Lond). 2013;37(3):333–340.
  6. Falagas ME, M. Kompoti, obesity and infection. Lancet Infect Dis. 2006;6(7):438–446.
  7. Meng L, Mui E, Holubar MK, Deresinski SC. Comprehensive guidance for antibiotic dosing in obese adults. Pharmacotherapy. 2017;37(11):1415–1431.
  8. Janson B, Thursky K. Dosing of antibiotics in obesity. Curr Opin Infect Dis. 2012;25(6):634–649.
  9. Grupper M, Nicolau DP. Obesity and skin and soft tissue infections: how to optimize antimicrobial usage for prevention and treatment? Curr Opin Infect Dis. 2017;30(2):180–191.
  10. Belcaid I, Eipe N. Perioperative pain management in morbid obesity. Drugs. 2019;79(11):1163–1175.
  11. Thorell A, MacCormick AD, Awad S, et al. Guidelines for perioperative care in bariatric surgery: enhanced recovery after surgery (ERAS) society recommendations. World J Surg. 2016;40(9):2065–2083.
  12. Mulier JP, Dillemans B. Anaesthetic factors affecting outcome after bariatric surgery, a retrospective levelled regression analysis. Obes Surg. 2019;29(6):1841–1850.
  13. Aftab H, Wang Fagerland M, Gondal G, et al. Pain and nausea after bariatric surgery with total intravenous anesthesia versus desflurane anesthesia: a double blind, randomized, controlled trial. Surg Obes Relat Dis. 2019;15(9):1505–1512.
  14. Sharma S, Arora L. Anesthesia for the morbidly obese patient. Anesthesiol Clin. 2020;38(1):197–212.
  15. Lundstrøm LH, Møller AM, Rosenstock C, et al. High body mass index is a weak predictor for difficult and failed tracheal intubation: a cohort study of 91,332 consecutive patients scheduled for direct laryngoscopy registered in the Danish Anesthesia Database. Anesthesiology. 2009;110(2):266–274.
  16. Kaya C, Bilgin S, Cebeci GC, et al. Anaesthetic management of patients undergoing bariatric surgery. J Coll Physicians Surg Pak. 2019;29(8): 757–762.
  17. Brodsky JB, Lemmens HJM, Brock-Utne JG, et al. Morbid obesity and tracheal intubation. Anesth Analg. 2002;94(3):732–736; table of contents.
  18. Soleimanpour H, Safari S, Sanaie S, et al. Anesthetic considerations in patients undergoing bariatric surgery: a review article. Anesth Pain Med. 2017;7(4):e57568–e57568.
  19. Jense HG, Dubin SA, Silverstein PI, O’Leary-Escolas U. Effect of obesity on safe duration of apnea in anesthetized humans. Anesth Analg. 1991;72(1):89–93.
  20. de Raaff CAL, de Vries N, van Wagensveld BA. Obstructive sleep apnea and bariatric surgical guidelines: summary and update. Curr Opin Anaesthesiol. 2018;31(1):104–109.

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