[Successful management of a patient for cardiac surgery with difficulty in weaning from cardiopulmonary bypass by using both isosorbide dinitrate and olprinone hydrochloride].

A 57-year-old man with mitral stenosis underwent mitral valve plasty under general anesthesia. He had a history of cerebral infarction. Although he was with atrial fibrillation, his left ventricular function was good. Preoperative coronary angiography revealed no significant coronary stenosis. Induction of anesthesia and the surgical procedure had been uneventful, but the patient had difficulty to wean the patient from cardiopulmonary bypass because of unexpected low cardiac output syndrome. O1-prinone hydrochloride, a newly developed phosphodiesterase III inhibitor, was initiated in addition to high doses of dopamine and dobutamine. This increased the amplitude of the electrocardiogram and caused ST elevation of the lead II. A full dose of isosorbide dinitrate was administered intravenously to differentiate coronary artery spasm from coronary air embolism. This drastically improved the ventricular function and mixed venous oxygen saturation, and weaning from CPB was finally accomplished. The heart showed hypercontraction and inotropes were tapered gradually without further cardiac events. Although there are various etiologies for low cardiac output syndrome after CPB, the possibility of myocardial ischemia must be the first consideration. Full pharmacological support must be tried before initiating a mechanical assist modality. Coronary dilators, nitrates in particular, and phosphodiesterase III inhibitors are promising agents in such cases.

Expiratory asynchrony in proportional assist ventilation.

One of the proposed advantages of proportional assist ventilation (PAV) has been the automatic synchrony between the end of the patient's inspiratory effort and the ventilator cycle (i.e., expiratory synchrony). However, recent clinical studies have shown a prolonged ventilator inspiratory time or even a "runaway" phenomenon with the normal use of PAV. We hypothesize that control-system delay may account for this, because in reality there is always some degree of delays between control-system's input and output in all ventilators. Computer simulation study to date has not taken into account the potential effect of control-system delay on expiratory synchrony. We therefore created a computer model in which the parameter of control-system delay time was introduced. We found that significant expiratory asynchrony may occur with this more realistic model of PAV. The ventilator flow termination may fall behind the completion of the patient inspiration by as long as 0.33 seconds under the selected simulation conditions. The inspiratory termination delay time is in proportion to the control-system delay time, the respiratory time constant, and the assist gain settings. In conclusion, this model indicates that due to the unavoidable control-system delay in the ventilators, expiratory asynchrony may be an inherent shortcoming associated with PAV.