RESUMEN
Anesthesia for thoracic surgery is most commonly performed with the patient in the lateral decubitus position, with nondependent hemithorax comprising the operation field. When one-lung ventilation is employed, the nondependent lung is nonventilated and collapsed, while the dependent lung is ventilated. Consequently one-lung ventilation creates an obligatory right to left transpulmonary shunt through the nondependent nonventilated lung. Therefore one-lung ventilation results in a much larger alveolar-arterial oxygen tension-difference P(A-a)O2 and lower PaO2 than does two-lung ventilation. The present study was to evaluate oxygenation effect of selective CPAP to nondependent lung in the 17 thoracic surgical patients. Arterial blood gases were analysed, systolic blood pressures and heart rates were measured at following stages. Stage I; lateral decubitus position before chest opening Stage II; 15 min after chest opening and one lung ventilation stage III; 15 min after application of selective CPAP 5 cmHO to the nondependent lung stage IV; 40 min after application of selective CPAP 5 cmHO to the nondependent lung The results were as follows: 1) In stage II, the value of PaO2 was significantly lower as compared to that in stage I(224.9+/-78.0 vs 418.2+/-63.1 mmHg, P<0.01). 2) In stage III and IV, the values of PaC4 were significantly higher.as compared to that in stage II(333.8+/-97.1, 364.5+/-88.6 vs 224,9+/-78.0 mmHg, P<0.01). 3) In stage III, the value of PaCO2 was significantly lower as compared to that in stage II(37.1+/-2.9 vs 38.2+/-2.7 mmHg, P<0.05). 4) In stage IV, the value of pH was significantly lower as compared to that in stage III(7.37+/-0.05 vs 7.38+/-0.05 P<0.05). 5) Systolic blood pressures and heart rates remained unchanged at all times. We concluded that application of 5 cmHO CPAP to the nondependent lung during one-lung ventilation is one of most efficacious maneuvers to increase PaO2, accompanying less surgical interference.