Assessment of Ventilation Distribution during Laparoscopic Bariatric Surgery: An Electrical Impedance Tomography Study

Abstract

Introduction. The aim of the study was to assess changes of regional ventilation distribution at the level of the 3rd intercostal space in the lungs of morbidly obese patients as a result of general anaesthesia and laparoscopic surgery as well as the relation of these changes to lung mechanics. We also wanted to determine if positive end-expiratory pressure of 10 cm H₂O prevents the expected atelectasis in the morbidly obese patients during general anaesthesia. Materials and Methods. 49 patients completed the examination and were randomized to 2 groups: ventilated without positive end-expiratory pressure (PEEP 0) and with PEEP of 10 cm H₂O (PEEP 10) preceded by a recruitment maneuver with peak inspiratory pressure of 40 cm H₂O. Impedance Ratio (IR) was utilized to examine ventilation distribution changes as a result of anaesthesia, pneumoperitoneum, and change of body position. We also analyzed intraoperative respiratory mechanics and pulse oximetry values. Results. In both groups general anaesthesia caused a ventilation shift towards the nondependent lungs which was not further intensified after pneumoperitoneum. Reverse Trendelenburg position promoted homogeneous ventilation distribution. Respiratory system compliance was reduced after insufflation and improved after exsufflation of pneumoperitoneum. There were no statistically significant differences in ventilation distribution between the examined groups. Respiratory system compliance, plateau pressure, and pulse oximetry values were higher in PEEP 10. Conclusions. Changes of ventilation distribution in the obese do occur at cranial lung regions. During pneumoperitoneum alterations of ventilation distribution may not follow the direction of the changes of lung mechanics. In the obese patients PEEP level of 10 cm H₂O preceded by a recruitment maneuver improves respiratory compliance and oxygenation but does not eliminate atelectasis induced by general anaesthesia.

Figure 1

Ventilation distribution in a spontaneously breathing patient (T1). Dependent lungs: ROI 1 and ROI 2; nondependent: ROI 3 and ROI 4. IR = ROI 1 + ROI 2/ROI 3 + ROI 4 = 1,11.

Figure 2

IR ratio (regional ventilation distribution) in groups PEEP 0 and PEEP 10 at T1–T5. PEEP 0: T1 versus T2, T2 versus T3, T2 versus T4, T2 versus T5, T3 versus T4, and T4 versus T5; all p < 0,002. PEEP 10: T1 versus T2, T2 versus T3, T2 versus T4, T3 versus T4, and T4 versus T5, p < 0,001 and T2 versus T5; p > 0,05 (NS). PEEP 0 versus PEEP 10: T1–T5; all p > 0,05 (NS).

Figure 3

Ventilation distribution in ROI 1–ROI 4 in group PEEP 0.

Figure 4

Ventilation distribution in ROI 1–ROI 4 in group PEEP 10.

Figure 5

Plateau pressure (Pplat) in PEEP 0 and PEEP 10 at T2–T5. PEEP 0: T2 versus T3, T2 versus T4, T2 versus T5, T3 versus T4, and T4 versus T5; all p < 0,003. PEEP 10: T2 versus T3, T2 versus T4, T2 versus T5, T3 versus T4, and T4 versus T5; all p < 0,006. PEEP 0 versus PEEP 10: T2–T5; all p < 0,029.

Figure 6

Static respiratory system compliance (Cstat) in PEEP 0 and PEEP 10 at T2–T5. PEEP 0: T2 versus T3, T2 versus T4, T2 versus T5, T3 versus T4, and T4 versus T5; all p < 0,018. PEEP 10: T2 versus T3, T2 versus T4, T2 versus T5, T3 versus T4, and T4 versus T5; all p < 0,002. PEEP 0 versus PEEP 10: T2–T5; all p < 0,006.

Figure 7

SpO₂ in PEEP 0 and PEEP 10 at T1–T5. PEEP 0: T1 versus T2, T2 versus T3, T2 versus T4, T2 versus T5, and T3 versus T4; p > 0,05 (NS) and T4 versus T5; p < 0,04. PEEP 10: T1 versus T2, T2 versus T3, T2 versus T4, T2 versus T5, T3 versus T4, and T4 versus T5; p > 0,05 (NS). PEEP 0 versus PEEP 10: T2–T5; all p < 0,018.