Relationship between pulmonary hemodynamics and arterial pH and carbon dioxide tension in critically ill patients.

To ascertain the clinical significance of derangements in arterial pH and arterial carbon dioxide tension (PaCO2) in modifying pulmonary arterial pressures and pulmonary vascular resistance in critically ill patients, the relationship between these two sets of variables was evaluated in 75 patients. No significant differences in pulmonary hemodynamic values were found among patients with acidemia, a normal pH, or alkalemia, even at extreme pH values; and there was no consistent relationship between PaCO2 and each of the pulmonary hemodynamic measurements. In patients who initially had a normal pH but subsequently developed acidemia or alkalemia, there was also no significant correlation between changes in pH and pulmonary hemodynamic values. We conclude that abnormalities of pulmonary hemodynamic values in seriously ill patients are usually due to factors other than acid-base derangements. Of practical importance is the observation that the predictability of the pulmonary arterial wedge pressure from the pulmonary arterial diastolic pressure is not invalidated by acid-base disturbances.