Impact of Obesity in Critical Illness

Abstract

The prevalence of obesity is rising worldwide. Adipose tissue exerts anatomic and physiological effects with significant implications for critical illness. Changes in respiratory mechanics cause expiratory flow limitation, atelectasis, and V̇/Q̇ mismatch with resultant hypoxemia. Altered work of breathing and obesity hypoventilation syndrome may cause hypercapnia. Challenging mask ventilation and peri-intubation hypoxemia may complicate intubation. Patients with obesity are at increased risk of ARDS and should receive lung-protective ventilation based on predicted body weight. Increased positive end expiratory pressure (PEEP), coupled with appropriate patient positioning, may overcome the alveolar decruitment and intrinsic PEEP caused by elevated baseline pleural pressure; however, evidence is insufficient regarding the impact of high PEEP strategies on outcomes. Venovenous extracorporeal membrane oxygenation may be safely performed in patients with obesity. Fluid management should account for increased prevalence of chronic heart and kidney disease, expanded blood volume, and elevated acute kidney injury risk. Medication pharmacodynamics and pharmacokinetics may be altered by hydrophobic drug distribution to adipose depots and comorbid liver or kidney disease. Obesity is associated with increased risk of VTE and infection; appropriate dosing of prophylactic anticoagulation and early removal of indwelling catheters may decrease these risks. Obesity is associated with improved critical illness survival in some studies. It is unclear whether this reflects a protective effect or limitations inherent to observational research. Obesity is associated with increased risk of intubation and death in SARS-CoV-2 infection. Ongoing molecular studies of adipose tissue may deepen our understanding of how obesity impacts critical illness pathophysiology.

Keywords: adiposity; artificial respiration; logistics; patient outcome assessment; physiology.

Figure 1

Summary of pathophysiological and management challenges relevant to critically ill patients with obesity. Some challenges are relevant across the obesity severity spectrum, whereas others may predominantly affect patients with more severe obesity (BMI > 40-50 kg/m²). Figure created with BioRender.com. DJD = degenerative joint disease; FRC = functional residual capacity; GFR = glomerular filtration rate; IAP = intraabdominal pressure; LVH = left ventricular hypertrophy; PEEP = positive end-expiratory pressure; RV = right ventricle; t_1/2 = half-life; V_d = volume of distribution.