Preoperative Atelectasis and Its Impact on Oxygen Saturation in Obese Patients Undergoing Bariatric Surgery

Pulmonary atelectasis is often present in obese patients even before surgery. This study aimed to assess the prevalence and extent of preoperative atelectasis in obese individuals undergoing bariatric surgery and to investigate whether variations in preoperative oxygen saturation (Spo2) values in a seated position on room air are related to the extent of atelectasis when positioned supine.

The research involved a cross-sectional study at a specialized center for laparoscopic bariatric surgery. Preoperative chest CT scans were analyzed by a senior radiologist to quantify atelectasis as a percentage of total lung volume, defining atelectasis as present when the affected volume was 2.5% or greater. Prevalence ratios and odds ratios were calculated to relate atelectasis prevalence and coverage to increasing obesity categories. Inverse probability weighting assessed the total, direct, and indirect effects of body mass index (BMI) on preoperative Spo2, including the degree of mediation by atelectasis. E-values were calculated to estimate the strength of potential unmeasured confounders.

The results demonstrated:

• Among 236 patients with a median BMI of 40.3 kg/m², the overall prevalence of atelectasis was found to be 32.6%. 
• The prevalence varied by BMI category: 12.7% for 30-35 kg/m², 28.3% for 35-40 kg/m², 12.3% for 40-45 kg/m², 48.4% for 45-50 kg/m², and 100% for those with a BMI of 50 kg/m² or higher. 
• Only the higher BMI categories (≥45 kg/m²) showed a significantly increased prevalence of atelectasis compared to the 30-35 kg/m² group.
• Atelectasis accounted for 70.2% of the variation in preoperative Spo2 levels, with 81.5% of the effect of BMI on Spo2 values below 96% mediated by atelectasis.

Thus, the study concluded that the prevalence and extent of atelectasis significantly increased with higher BMI, particularly in patients with a BMI of 45 kg/m² or more. Preoperative atelectasis plays a significant role in mediating the influence of BMI on Spo2 levels in the seated position while breathing room air.

Source: Mancilla-Galindo J, Ortiz-Gomez JE, Pérez-Nieto OR, De Jong A, Escarramán-Martínez D, Kammar-García A, Ramírez Mata LC, Díaz AM, Guerrero-Gutiérrez MA. Preoperative Atelectasis in Patients with Obesity Undergoing Bariatric Surgery: A Cross-Sectional Study. Anesth Analg. 2024 Aug 23. doi: 10.1213/ANE.0000000000007166. Epub ahead of print. PMID: 39178161.