PEEP-INDUCED DISCREPANCY BETWEEN PULMONARY ARTERIAL WEDGE PRESSURE AND LEFT ATRIAL PRESSURE - EFFECTS OF CONTROLLED VS SPONTANEOUS VENTILATION AND COMPLIANT VS NON-COMPLIANT LUNGS IN THE DOG

Pulmonary-artery (PA) wedge pressure (P(paw)) is usually considered to be an accurate reflection of left atrial pressure (P(la)). Recent reports had demonstrated that during controlled positive-pressure ventilation (CV) in normal lungs, a progressive increase in positive end-expiratory pressure (PEEP) produced a progressive positive P(paw)-P(la) discrepancy when the PA catheter tip was positioned vertically above the left atrium (LA). In seven anesthetized dogs the P(paw)-P(la) relationship (as transmural pressures) was studied at PEEP = 0, 5, 10, 15, and 20 torr, in two ways: 1) in compliant lungs with the PA catheter tip above the LA, CV was compared with spontaneous ventilation (SV); 2) during CV with PA catheter tip both above (C(up)) and below (C(down)) the LA compliant lungs were compared with noncompliant lungs. A 35 per cent decrease in static pulmonary compliance was induced by administering oleic acid, 0.06 ml/kg, intravenously, and 0.01 N HCl, 5 ml, intratracheally. In compliant lungs with the PA catheter tip above the LA during CV, P(paw) was significantly greater than P(la) at PEEP ≥ 5 torr and equalled PEEP when PEEP ≥ 10 torr, whereas during SV, P(paw) did not differ significantly from P(la) at any PEEP. During CV in compliant lung, P(paw) recorded from C(up) and C(down) was significantly greater than P(la) at PEEP ≥ 5 and PEEP ≥ 15 torr, respectively. During CV in noncompliant lung, P(paw) recorded from C(up) and C(down) was significantly greater than P(la) at PEEP ≥ 10 and PEEP ≥ 15 torr, respectively. The P(paw)-P(la) difference from C(up) at PEEP ≥ 10 torr was significantly less in noncompliant lung than in compliant lung. It is concluded that SV affords complete protection of the P(paw)-to-P(la) relationship even at high PEEP, whereas a decrease in pulmonary compliance affords moderate protection of the P(paw)-to-P(la) relationship. These results are important because they further our ability to assess the accuracty of P(paw) during varying clinical situations.