PEEP-induced Discrepancy Between Pulmonay Arterial Wedge Pressure and Left Atial Pressure

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Abstract
Pulmonary-artery (PA) wedge pressure (Ppaw) is usually an accurate reflection of left atrial pressure (Pla). During controlled positive-pressure ventilation (CV) in normal lungs, a progressive increase in positive end-expiratory pressure (PEEP) produced a progressive positive Ppaw-Pla discrepancy when the PA catheter tip was positioned vertically above the left atrium (LA). In 7 anesthetized dogs the Ppaw-Pla relationship (as transmural pressures) was studied at PEEP = 0, 5, 10, 15 and 20 torr, in 2 ways: in compliant lungs with the PA catheter tip above the LA, CV was compared with spontaneous ventilation (SV): during CV with PA catheter tip both above (Cup) and below (Cdown) the LA, compliant lungs were compared to noncompliant lungs. A 35% decrease in static pulmonary compliance was induced by administering oleic acid, 0.06 ml/kg, i.v., and 0.01N HCl, 5 ml, intratracheally. In compliant lungs with the PA catheter tip above the LA during CV, Ppaw was significantly greater than Pla at PEEP .gtoreq. 5 torr and equalled PEEP when PEEP .gtoreq. 10 torr, and during SV, Ppaw did not differ significantly from Pla at any PEEP. During CV in compliant lung, Ppaw recorded from Cup and Cdown was significantly greater than Pla at PEEP .gtoreq. 5 and PEEP .gtoreq. 15 torr, respectively. During CV in noncompliant lung, Ppaw recorded from Cup and Cdown was significantly greater than Pla at PEEP .gtoreq. 10 and PEEP .gtoreq. 15 torr, respectively. The Ppaw-Pla difference from Cup at PEEP .gtoreq. 10 torr was significantly less in noncompliant lung than in compliant lung. SV affords complete protection of the Ppaw-to-Pla relationship even at high PEEP, and a decrease in pulmonary compliance affords moderate protection of the Ppaw-to-Pla relationship. Assessment of the accuracy of Ppaw during varying clinical situations was demonstrated.