Peri-Intubation Adverse Airway Events in Critically Ill Patients With Morbid and Super Obesity: A Retrospective Analysis

Obesity represents a major global health challenge, with prevalence steadily rising worldwide. Beyond its well-characterized metabolic and cardiovascular consequences, obesity poses significant challenges for airway management, particularly among critically ill patients requiring urgent tracheal intubation. The degree of obesity is clinically relevant: morbid obesity (BMI ≥40 kg/m²) is associated with anatomical and physiological alterations that markedly increase the risk of difficult airway and peri-intubation complications compared with patients with BMI <40 kg/m².

From an anatomical perspective, morbidly obese patients often present with a short, thick neck, increased cervical adiposity, and limited atlanto-occipital extension, complicating optimal positioning and glottic visualization during laryngoscopy. Redundant upper airway soft tissue, macroglossia, and higher Mallampati classes further impede mask ventilation and reduce pharyngeal patency. Secondary analyses of the international INTUBE cohort demonstrated that obese critically ill patients had a significantly higher prevalence of difficult airway predictors such as short neck, reduced mouth opening, and high Mallampati scores, compared with non-obese patients (74.3% - 35.7%, p<0.001). Similarly, in a large retrospective bariatric cohort, severe obesity independently increased the odds of difficult intubation when Cormack-Lehane grade IV (OR 8.9) or Mallampati IV (OR 5.1) were present.

Physiological derangements further compound these challenges. Elevated intra-abdominal pressure and cephalad diaphragm displacement reduce functional residual capacity (FRC) and expiratory reserve volume, leaving critically limited oxygen reserves during apnea. Increased oxygen consumption and basal metabolic rate shorten the safe apneic window, resulting in rapid desaturation if intubation is prolonged or requires multiple attempts. The INTUBE study reported that severe peri-intubation hypoxemia (SpO₂ <80%) occurred more frequently in obese versus non-obese critically ill patients (12.1% - 8.6%, p=0.01), and first-pass intubation failure strongly correlated with this complication. Even in optimized elective settings such as bariatric surgery, BMI >60 kg/m² significantly increased the risk of difficult intubation, despite high first-pass success rates (95.4%) and low complication rates.

These findings highlight that morbid obesity imposes both anatomical and physiological barriers to safe intubation. Critically ill patients with morbid obesity are uniquely vulnerable, with increased risks of failed first-pass attempts, severe hypoxemia, and potentially life-threatening complications. However, prospective evidence directly comparing peri-intubation outcomes among critically ill patients with BMI 40-50 versus ≥50 kg/m² remains limited.

While morbid obesity is an established risk factor, there is a compelling physiological rationale to suspect heterogeneity of risk within this category. Super obesity (BMI ≥50 kg/m²) may represent a distinct phenotype with more pronounced anatomical and physiological derangements. In elective bariatric populations, BMI >50 kg/m² has been linked to difficult mask ventilation and intubation, suggesting a threshold effect for extreme obesity [6]. Potential mechanisms include increased fat deposition in the neck and pharynx, further reductions in FRC, and higher prevalence of comorbidities such as obesity hypoventilation syndrome. Nonetheless, studies in elective settings remain inconclusive; for example, Mahmoud et al. found that neither super-obesity nor super-super-obesity independently predicted difficult intubation or mask ventilation, with high STOP-Bang and Mallampati scores emerging as the primary predictors.