Prone Positioning Improves Pulmonary Function in Obese Patients During General Anesthesia

Abstract

We investigated the effects of prone position on functional residual capacity (FRC), the mechanical properties (compliance and resistance) of the total respiratory system, lung and chest wall, and the gas exchange in 10 anesthetized and paralyzed obese (body mass index more than 30 kg/m2) patients, undergoing elective surgery. We used the esophageal balloon technique together with rapid airway occlusions during constant inspiratory flow to partition the mechanics of the respiratory system into its pulmonary and chest wall components. FRC was measured by the helium dilution technique. Measurements were taken in the supine position and after 15-30 min of prone position maintaining the same respiratory pattern (tidal volume 12 mL/kg ideal body weight, respiratory rate 14 breaths/ min, fraction of inspired oxygen [FIO2]0.4). We found that FRC and lung compliance significantly (P < 0.01) increased from the supine to prone position (0.894 +/- 0.327 L vs 1.980 +/- 0.856 L and 91.4 +/- 55.2 mL/cm H2O vs 109.6 +/- 52.4 mL/cm H2O, respectively). On the contrary, the prone position reduced chest wall compliance (199.5 +/- 58.7 mL/cm H2O vs 160.5 +/- 45.4 mL/cm H2O, P < 0.01), thus total respiratory system compliance did not change. Resistance of the total respiratory system, lung, and chest wall were not modified on turning the patients prone. The increase in FRC and lung compliance was paralleled by a significant (P < 0.01) improvement of PaO2 from supine to prone position (130 +/- 31 vs 181 +/- 28 mm Hg, P < 0.01), while PaCO2 was unchanged. We conclude that, in anesthetized and paralyzed obese subjects, the prone position improves pulmonary function, increasing FRC, lung compliance, and oxygenation.

Morbid obesity and the prone position: a case report

“…7 In the prone position, if the abdomen is allowed to hang freely, respiratory mechanics, lung volumes, and oxygenation are improved in ventilated normal weight patients, 8 -10 and in mild to moderately obese patients (average BMI ϭ 34, range 30 -46). 11 To date, there are no reports of patients as large as ours being ventilated in the prone position. Without changing tidal volume or F i O 2 , our patient's arterial O 2 tension (P a O 2 ) increased from 363 mmHg (supine) to 448 mmHg (prone) during the procedure.…”

Perioperative management of the severely obese patient: a selective pathophysiological review

“…A frequently cited paper from 1996 studied only ten consecutive patients with BMI 30-40 but showed an improvement in FRC, lung compliance, and oxygenation in the prone position compared with the supine position. 105 Of importance, emphasis was placed on obtaining free abdominal movement, with weight taken on the chest wall and pelvis. The tidal volume used in the study would be considered high by today's standards, i.e., 12 mLÁkg -1 , and PEEP was not mentioned.…”

Perioperative Complications in Obstructive Sleep Apnea Patients

“…Supine positioning, often required following surgery, may worsen OSA in half of OSA patients [52]. In addition, the combination of obesity and supine positioning may lead to decrements in lung volume, increasing the propensity for upper airway collapse [53] as well as worsening gas exchange [54]. Residual effects of anesthetics can further aggravate decrements in functional residual capacity and oxygenation, potentially leading to more apneic events and hypoxemia [55].…”