CLOSED MITRAL VALVOTOMY AND ELECTIVE VENTILATION IN THE POSTOPERATIVEPERIOD - EFFECT OF MILD HYPERCARBIA ON RIGHT-VENTRICULAR FUNCTION

Objectives: It is customary to extubate patients immediately after clo sed mitral valvotomy. These patients often have deranged respiratory f unction caused by chronic lung congestion. The left ventricular functi on may also be subnormal after valvotomy in some patients. Therefore, elective ventilation for some duration in the postoperative period can be beneficial to these patients. This work is an attempt to find whet her elective ventilation should be preferred over immediate extubation in these patients. Design: A prospective randomized study. Setting: T he study was performed in a tertiary care hospital, and the patients a re referred from the northern states of India. Participants: One hundr ed patients undergoing elective closed mitral valvotomy were included in the initial part of the study. Ten more patients were studied to ev aluate the effect of mild hypercarbia on right ventricular function af ter closed mitral valvotomy. Interventions: One hundred patients were divided into two groups of 50 each. Group 1 consisted of patients in w hom the neuromuscular blockade was reversed at the end of surgery with neostigmine and atropine and the trachea was extubated. In group 2, t he residual neuromuscular paralysis was not reversed and the patients were electively ventilated in the postoperative period for an average duration of 5 hours and 29 minutes +/- 1 hour and 58 minutes. In all t he patients in both the groups, electrocardiogram, direct arterial blo od pressure, and oxygen saturation were continuously monitored, and ar terial blood gases were measured intermittently throughout the study p eriod. Because the results showed that there was mild hypercarbia, 30 minutes after extubation in group 1, 10 more patients were studied to evaluate the effect of mild hypercarbia on right ventricular function after surgery. Patients were ventilated after surgery (F1O2 = 1) to ma intain normocarbia (PaCO2 38.6 +/- 3.4 mmHg). Mild hypercarbia (PaCO2 51.5 +/- 3.7 mmHg) followed by normocarbia (PaCO2 40 +/- 2.5 mmHg) was induced by adjusting the ventilator rate with a constant tidal volume . Standard hemodynamic measurements were performed at each stage. Meas urements and Main Results: Although all the patients maintained satisf actory and stable hemodynamics in the postoperative period, the PaCO2 at the end of 30 minutes of extubation was significantly higher in gro up 1 (48.1 +/- 5.3 mmHg) as compared with group 2 (40.2 +/- 4.3 mmHg, p < 0.001). Mild hypercarbia significantly increased pulmonary vascula r resistance (p < 0.01), mean pulmonary arterial pressure (p < 0.001), right ventricular stroke work (p < 0.01), right ventricular systolic pressure (p < 0.01), and right ventricular end-diastolic pressure (p < 0.001). The effect was not totally reversible with CO2 washout as all parameters except right ventricular end-diastolic pressure and pulmon ary vascular resistance continued to remain significantly higher when normocarbia was restored. The significant changes in systemic hemodyam ics produced by hypercarbia were increases in cardiac index, mean arte rial pressure, and pulmonary capillary wedge pressure. Conclusions: Av oidance of even mild hypercarbia, therefore, appears advisable in the early postoperative period because of potential impedence to right ven tricular ejection. Continuous monitoring of end-tidal CO2 and frequent blood gas analyses should be practiced, and elective ventilation shou ld be considered in patients with long-standing disease and pulmonary hypertension. (C) 1995 by W.B. Saunders Company