Lack of cardiopulmonary reserve is a more important predictor of perioperative death than cardiac ischaemia. It has long been observed that high risk patients who survive surgery have greater compensatory increases in cardiovascular and oxygen transport measurements than patients who die - non-survivors are unable to compensate for the added metabolic and cardiorespiratory demands of surgery and die of multiple organ failure. High risk patients are those who are most critically ill at the time of surgery or who face major surgery.
In the preoperative period, high risk patients have an increased incidence of severe physiological impairment as measured by a PA catheter. In many patients the baseline values can be improved by relatively simple measures, for example giving fluid or inotropes. Previous studies have shown that careful invasive monitoring of high risk patients in the perioperative period improves outcome. More recently,
"preoptimisation" or screening to see which patients could benefit from giving therapy preoperatively has also been shown to improve outcome.
In one study, patients underwent preoperative invasive cardiovascular monitoring with a PA catheter and were classified as groups 1 (normal) to 4 (severe physiological impairment). All of group 1 survived surgery. Groups 2 and 3 had moderate physiological impairment, which could be corrected with simple measures. Their mortality was 85%. In group 4, with uncorrectable physiological impairment, seven patients had lesser surgery and survived, 19 were cancelled, and all 8 who went ahead with the planned surgery died. In another study, patients were divided in to three groups. Group 1 was assessed using a PA catheter and treated with fluid loading, afterload reduction, and/or inotropes 12 hours preoperatively. Group 2 was investigated and treated 3 hours preoperatively, and group 3 was the control (no PA catheter). The aim was to achieve a PAOP of 8-15 mmHg, cardiac index > 2 8 litres per minute m-2, and SVR < 1100 dyn.s cm-5. Patients with a PA catheter and subsequent intervention had significantly fewer adverse intraoperative events and less overall mortality.
Based on studies like this, practice is moving in the direction of invasive cardiac monitoring in high risk patients before major surgery in order to correct pre-existing physiological impairment and to improve compensatory responses. This illustrates the general importance of adequate resuscitation before major surgery.
Echocardiography does not appear to be a useful predictor of perioperative cardiac events, although a reduced ejection fraction correlates with an increased risk of perioperative pulmonary oedema.
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