Obesity, defined as a body mass index (BMI) at or above 30 kg/m2, has become an “epidemic” according to contemporary researchers.1 The Centers for Disease Control and Prevention (CDC) recognized the obesity epidemic as a national problem in 1999, when it published a series of maps showing rapid changes in the prevalence of obesity.2 Even before obesity began costing the United States over $117 billion per year in medical costs,1 medical providers had been aware of the increased medical risks for obese patients. In fact, research as early as the 1960s acknowledged the effects of obesity on complications following general anesthesia.3 The worldwide increase in obesity has required anesthesiology practitioners to take further considerations while their patients undergo various procedures.
For one, obesity can affect accuracy of anesthesia dosing. Because of large differences between lean body weight (LBW) and total body weight (TBW) in obese patients,4,5 the pharmacokinetics (i.e., the way drugs are absorbed by the body) and pharmacodynamics (i.e., the effects of drugs and their mechanisms of action) of anesthetic drugs are altered.5 For example, several researchers have debated whether dosage adjustments in obese patients for Propofol, a common injectable general anesthetic, should be based on LBW or TBW.4-6 For many other anesthesia drugs, such as opioids7 and inhaled anesthetics,6 best practices for obese patients remain unclear. Overall, the complexity of obese patients’ altered lipid levels can affect dosing of anesthetic drugs in unpredictable ways.
Additionally, obese patients often show comorbidity, or the simultaneous presence of more than one chronic medical condition. Disorders that are comorbid with obesity, such as obstructive sleep apnea (OSA),8 can cause poor outcomes in anesthesiology. Some studies show that OSA and obesity may even share genetic risk factors,9,10 which may make OSA common in obesity and thus affect anesthesia for obese patients. Given that OSA is marked by upper airway blockages, brief periods of breathing cessation and lack of oxygenation,11 it can have harmful effects on anesthesia administration. In obese patients, who have more fatty tissue in the larynx, poor respiratory outcomes during anesthesia include intubation failure and respiratory obstruction soon after extubation.12 Also, the provision of opioids during procedures can add further respiratory and arousal depression, resulting in more issues for patients who already face obesity and OSA.12 Given the respiratory problems associated with OSA and obesity, anesthesiologists must keep in mind positioning of obese patients, using regional anesthesia, monitoring vital signs vigilantly and minimizing oxygen loss during anesthesia.
OSA and pharmacological changes only represent two of the main issues faced by obese patients undergoing anesthesia. Other challenges the anesthesiologist must confront include issues with cardiac, respiratory and metabolic systems and perioperative management (before and after surgery).14 Many studies also address complications facing certain populations with obesity and specific situations in which anesthesia may be necessary. For example, patients with obesity have increased complications during pregnancy and childbirth, a higher rate of caesarean sections and potential for difficulties with emergency anesthesia.15 Thus, the data suggest that epidural anesthesia during labor be well-planned and administered early and often.15-17 Other research has focused on anesthesia management in obese children, which involves careful preanesthesia assessment, changes in drug selection and consideration of comorbidities.18-20 Further studies have addressed the potential advantages and disadvantages of using regional instead of general anesthesia in obese patients when appropriate,6,21 as well as the effects obesity may have on regional anesthesia techniques.6,21,22 Evidently, anesthetic management of patients with obesity may vary based on patients’ ages, stages of gestation and types of anesthesia.
The obesity epidemic has effects on the pharmacology and risks of anesthesia administration. Anesthesia providers who care for patients with obesity must account for altered body weight, comorbidities that affect airway function and factors such as pregnancy, childhood and anesthesia location. As obesity affects more patients worldwide, anesthesiology practitioners must take more precautions before, during and after administering anesthetic drugs.
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