Efficacy of lung recruitment maneuver on shunt fraction and oxygenation in one lung ventilation during sevoflurane anaesthesia

ABSTRACT

Deterioration of gas exchange during one lung ventilation [OLV] is caused by both total collapse of the nondependent lung and partial collapse of the dependent lung. It was demonstrated that an alveolar recruitment strategy [ARS] improves lung function during general anesthesia in supine patients. The objective of this article was to study the impact of this ARS on arterial oxygenation in patients undergoing OLV for lobectomies. Twelve patients undergoing open lobectomies were studied at three time points [1] during two- lung ventilation [TLV], [2] during OLV before, and [3] after ARS. The ARS maneuver was done as follows Peak inspiratory pressure [PIP] and PEEP were sequentially increased from 30/10 to 35/15 in steps. Every level of pressure was maintained during 1 minute. The recruitment pressure of 40/20 cm H[2]O was applied for 1 minute. The ARS took approximately 5 min. Airway pressures were then gradually decreased, returning to baseline settings but maintaining a PEEP level of 8 cm H[2]O. After the ARS was completed, the ventilator was, set back to volume control. The percent of shunt fraction was calculated using the formula Qs/Qt=CcO[2]-CaO[2]/CcO[2]-CvO[2]. Hemodynamic parameters [HR, MAP, CVP, MPAP and Paw] were measured at three time points [TLV, OLV [pre], OLV[ARS] there was significant decrease of MAP [p<0.03] after recruitment in relation to pre-recruitment. Also there was significant increase of MPAP after recruitment [p<0.002] in relation to OLVpre. The paw increased significantly [p<0.04] at OLV[ARS] in relation to OLVpre. Pa 02 was statistically significant lower during OLV before [120 +/- 65] compared with OLV after the recruitment 266 +/- 83 [p <0.01] and to TLV 348 +/- 77, [P< 0.001]. Pao2 values of the one recruited lung were not significant from the ones during TLV. Shunt fraction was calculated using a standard formula based on the three compartment model proposed by Riley and colleagues, it is increased significantly from 15.4 +/- 6.0 in TLV to 29.3 +/- 8.3 in OLV pre [p<0.003] Alveolar recruitment of the dependent lung augments Pa02 values during one-lung ventilation and corrects the percent of increased shunt fraction of the dependent lung