What intraoperative monitors would you use?

What intraoperative monitors would you use?

A general goal in these patients is to maintain intraoperative hemodynamics within 20% of preoperative values. Therefore, in addition to the standard intraoperative monitors, other monitors that should be considered include an intra-arterial line, a pulmonary artery catheter (PAC), and a TEE. An intra-arterial line would be the optimum way of monitoring blood pressure (BP) beat-to-beat. Although 40% of intraoperative ischemic episodes are not related to aberrations in hemodynamics, there are studies demonstrating that inadequate management of hemody-namic abnormalities may increase risk. Hypotension (BP <30% baseline for greater than 10 minutes) has been shown to be a strong predictor of PCE in one study. On the other hand, there are no studies demonstrating conclusively that hypertension is associated with adverse outcome. Tachycardia has not been definitely shown to be associated with PCE, although studies suggest a relationship.

The easiest technique for myocardial ischemia monitoring in the anesthetized patient is with a multiple-lead ECG. Monitoring precordial chest leads V₄ and V₅ detects greater than 90% of ischemic events that would be seen on a 12-lead ECG, but it has been reported to have as low as a 9% sensitivity compared with the gold standard (myo-cardial lactate extraction). ST-segment depressions and T-wave morphology changes are most commonly seen. However, there are patients in whom the ECG is not an effective intraoperative monitor of myocardial ischemia, such as those with LV hypertrophy, conduction abnormal-ities, and ventricular pacemaker dependence.

The development of V waves on the pulmonary artery wedge pressure waveform may be an indication of myocar-dial ischemia, but it is not sensitive or specific enough to be regarded as a reliable monitor for this purpose (Figure 3.1).

The utility of the PAC, however, extends beyond its ques-tionable ability to detect ischemia. It provides information about the patient’s intravascular volume status, a quantitative estimate of myocardial compliance, and allows for calcula-tion of cardiac output and other hemodynamic measure-ments, such as systemic vascular resistance and stroke volume. A PAC would be mandatory if this patient showed signs of CHF preoperatively.

The TEE is the most sensitive detector of intraoperative ischemia, and it is capable of detecting ischemia earlier than any other modality. However, studies have questioned its specificity. Specifically, it is not clear what TEE changes are predictive of ischemia and PCE. In the largest study of patients with or at-risk for CAD who were scheduled for noncardiac surgery, Mangano and Goldman (1995) did not find that LV wall motion abnormalities were predictive of ischemia or PCE. The TEE also provides physiologic information, such as estimates of LV ejection fraction and intravascular volume status, which may help with intraoperative management in patients with ventricular dysfunction.