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Background The effects of acute respiratory versus metabolic acidosis on the myocardium and their consequences on adrenoceptor stimulation remain poorly described. We compared the effects of metabolic and respiratory acidosis on inotropy and lusitropy in rat myocardium and their effects on the responses to α- and β-adrenoceptor stimulations. Methods The effects of acute respiratory and metabolic acidosis (pH 7.10) and their interactions with α and β-adrenoceptor stimulations were studied in isolated rat left ventricular papillary muscle (n=8 per group). Intracellular pH was measured using confocal microscopy and a pH-sensitive fluorophore in isolated rat cardiomyocytes. Data are mean percentages of baseline±SD. Results Respiratory acidosis induced more pronounced negative inotropic effects than metabolic acidosis did both in isotonic (45±3 versus 63±6%, P Conclusion Acute metabolic and respiratory acidosis induce different myocardial effects related to different decreases in intracellular pH. Only metabolic acidosis impairs the positive inotropic effect of β-adrenergic stimulation.

Background Positive end-expiratory pressure (PEEP) may reduce cardiac output and total hepatic blood flow after liver transplantation. Pulse pressure variation is useful in predicting the PEEP-induced decrease in cardiac output. The aim of the study was to examine the relationships between stroke volume variations (SVV) obtained with the Vigileo monitor (Edwards Lifesciences, Irvine, CA), and the hemodynamic effects of PEEP. Methods Over 2 yr, patients presenting an acute lung injury or an acute respiratory distress syndrome in the 72 h after liver transplantation were prospectively enrolled. Patients were monitored with a pulmonary artery catheter (stroke volume) and with the Vigileo system (stroke volume and SVV). Measurements were performed in duplicate, first during zero end-expiratory pressure and then 10 min after the addition of 10 cm H2O PEEP. Results Twenty-six patients were included. Six patients were excluded from analysis. On PEEP, SVV and pulse pressure variation increased significantly and stroke volume decreased significantly. PEEP-induced changes in stroke volume measured by pulmonary artery catheter were significantly correlated with SVV (r = 0.69; P < 0.001) and pulse pressure variation on zero end-expiratory pressure (r = 0.66, P < 0.001). PEEP-induced decrease in stroke volume measured by pulmonary artery catheter > or = 15% was predicted by an SVV > 7% (sensitivity = 100%, specificity = 80%) and by a pulse pressure variation > 8% (sensitivity = 80%, specificity = 100%). PEEP-induced changes in stroke volume measured by pulmonary artery catheter and Vigileo device were correlated (r = 0.51, P < 0.005). Conclusions SVV obtained with Vigileo monitor is useful to predict decrease in stroke volume induced by PEEP. Moreover, this device is able to track changes in stroke volume induced by PEEP.