Blood-Gas and Hemodynamic Responses to Oxygen in Acute Myocardial Infarction

Abstract

Blood-gas (Pao_o2) and hemodynamic responses to the inhalation of oxygen were studied in 60 patients with acute myocardial infarction. Patients who were not in heart failure on admission and did not develop signs of heart failure within the next 5 days achieved the same Pao_o2 level while breathing 100% oxygen as did patients without acute myocardial infarction. Patients with pulmonary edema or cardiogenic shock had a very poor Pao_o2 response to oxygen inhalation. Patients in mild heart failure at the time of study and patients who developed heart failure subsequent to the study had a Pao_o2 response intermediate between the other two groups. This rise of Pao_o2 with oxygen correlated with the cardiac index and right atrial oxygen prior to inhalation of oxygen. Uncomplicated patients responded to inhalation of oxygen with a decrease of heart rate, cardiac index, stroke index, and cardiac work, and an increase of peripheral resistance. Patients in pulmonary edema or cardiogenic shock or with a low cardiac index or low Pao_o2 responded with only a slight increase in peripheral resistance. The Pao_o2 achieved while breathing oxygen appeared to determine the type of hemodynamic response to oxygen. Administration of oxygen to patients with acute myocardial infarction is useful in identifying latent heart failure and in predicting the subsequent clinical course of these patients.