Assessment of the circulation

Physical examination is valuable in the postoperative period and provides prompt diagnosis of pneumothorax or acute valvular insufficiency, for example, but low cardiac output states are not recognized consistently from clinical signs. Oliguria and metabolic acidosis are also unreliable in this connection. There is a need for direct assessment of myocardial performance by invasive monitoring in some patients.

Routine monitoring includes ECG, direct arterial pressure, right atrial pressure, urine output, and core and peripheral temperatures. More complex monitoring, while providing more information, carries more risk to the patient and should be used only where benefit balances risk. Thus opinions vary widely on the use of the pulmonary artery catheter in these patients. Direct measurement of filling pressures and cardiac output provides information unavailable by any other single intervention and can form the basis for rational use of vasoactive drugs and support of the circulation. However, the complications and costs of these devices are not insignificant, and there is no hard evidence of their use improving outcome.

Cardiac output may be measured less invasively using an esophageal Doppler probe which provides a beat-to-beat display of flow in the descending aorta and calculates analogs for filling pressures and resistances.

Myocardial and valvular performance are increasingly assessed using transesophageal echocardiography which provides accurate estimates of cardiac filling, contraction, and ejection fraction, although it requires considerable expertise and the equipment is costly. Use of this technique to assess regional wall motion abnormalities is more controversial.

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