Preoperative atelectasis in patients with obesity undergoing bariatric surgery: a cross-sectional study
Authors: Mancilla-Galindo Javier , Ortiz-Gomez Jesus Elias , Pérez-Nieto Orlando Rubén , De Jong Audrey , Escarramán-Martínez Diego , Kammar-García Ashuin , Mata Luis Carlos Ramírez , Díaz Adriana Mendez , Guerrero-Gutiérrez Manuel Alberto 
Published: January 2024

Background

Pulmonary atelectasis is present even before surgery in patients with obesity. No study has reported the prevalence of preoperative atelectasis in obese patients to date. We aimed to estimate the prevalence and extension of preoperative atelectasis in patients with obesity undergoing bariatric surgery and to determine if variation in preoperative SpO2 values in the seated position at room air is explained by the extent of atelectasis coverage in the supine position.

Methods

Cross-sectional study in a single center specialized in laparoscopic bariatric surgery. Preoperative chest computed tomographies were reassessed by a senior radiologist to quantify the extent of atelectasis coverage as a percentage of total lung volume. Patients were classified as having atelectasis when the affection was ≥2.5%, to estimate the prevalence of atelectasis. Crude and adjusted prevalence ratios (PR) and odds ratios (OR) were obtained to assess the relative prevalence of atelectasis and percentage coverage, respectively, with increasing obesity category. Inverse probability weighting was used to assess the total, direct (not mediated), and indirect (mediated through atelectasis) effects of BMI on preoperative SpO2, and to quantify the magnitude of mediation (proportion mediated).

Results

In 236 patients with a median BMI of 40.3 kg/m2(IQR: 34.6–46.0, range: 30.0–77.3), the overall prevalence of atelectasis was 32.6% (95%CI: 27.0–38.9) and by BMI category: 30-35 kg/m2, 12.7% (95%CI: 6.1–24.4); 35-40 kg/m2, 28.3% (95%CI: 17.2–42.6); 40-45 kg/m2, 12.3% (95%CI: 5.5–24.3); 45-50 kg/m2, 48.4% (95%CI: 30.6–66.6); and ≥50 units, 100% (95%CI: 86.7–100). Compared to the 30-35 kg/m2group, only the categories with BMI ≥45 kg/m2had significantly higher relative prevalence of atelectasis — 45-50 kg/m2, aPR=3.52 (95%CI: 1.63–7.61) and ≥50 kg/m2, aPR=8.0 (95%CI: 4.22–15.2) — and higher odds of greater atelectasis percentage coverage: 45–50 kg/m2, aOR=7.5 (95%CI: 2.7–20.9) and ≥50 kg/m2, aOR=91.5 (95%CI: 30.0–279.3). Atelectasis percent alone explained 70.2% of the variation in preoperative SpO2. The proportion of the effect of BMI on preoperative SpO2 values <96% mediated through atelectasis was 81.5% (95%CI: 56.0–100).

Conclusions

The prevalence and extension of atelectasis increased with higher BMI, being significantly higher at BMI ≥45 kg/m2. Preoperative atelectasis mediated the effect of BMI on SpO2 at room air in the seated position. The high prevalence of atelectasis before surgery and their impact on SpO2 could be important factors to consider when deciding ventilation strategies during surgery and for the interpretation of the clinical significance of postoperative atelectasis.

Key points

Question: What is the prevalence of preoperative atelectasis in patients undergoing bariatric surgery and are changes in the preoperative peripheral saturation of oxygen (SpO2) at room air in the seated position explained by the extent of atelectasis coverage on chest CT in the supine position?

Findings: Preoperative atelectasis were highly prevalent (32.6%, 95%CI: 27.0–38.9) in patients with obesity and a BMI above 45 kg/m2was associated with a higher relative prevalence and atelectasis percentage coverage, the latter of which alone explained 70.2% of the variation in SpO2, with 81.5% (95%CI: 56.0-100) of the effect of BMI on SpO2 <96% mediated through atelectasis.

Meaning: Pulmonary atelectasis are detectable before surgery in obese patients and largely explain decreased preoperative SpO2 values, which could be an important factor to consider when interpreting postoperative atelectasis and for deciding perioperative ventilation strategies.