[Does Swan-ganz catheter help in weaning from controlled ventilation after mitral valve replacement?]

The difference between oxygen consumption during spontaneous and controlled ventilation represents the oxygen cost of breathing. Swan-Ganz catheters enable oxygen consumption to be calculated as the product of cardiac index by arteriovenous oxygen concentration. This method was used in 25 patients on the day after anaesthesia and mitral valve replacement to predict the success of weaning from mechanical ventilation. Four patients could not be weaned: one for pulmonary reasons, one for neurological reasons and two because of their cardiac status. Whether weaning was successful or not, oxygen consumption did not change significantly during spontaneous respiration; concomitantly lactacidaemia remained stable. Two patients had an oxygen consumption below the physiological threshold (115 ml.min-1.m-2): one could be weaned, but not the other. Haemodynamic parameters did not change significantly during weaning. Thus, measurement of oxygen consumption through a Swan-Ganz catheter does not predict the success of weaning after mitral valve replacement, but the catheter can diagnose a low cardiac output needing treatment before weaning.