Posture and central venous pressure measurement in circulatory volume depletion.

The effect of posture on central venous pressure (CVP) was studied in 16 patients with circulatory volume depletion before and after fluid replacement. At presentation, measurement of CVP when supine did not reflect circulatory volume depletion, with a mean (SEM) of 0.1 cm H2O (0.6), but when sat at 45 degrees the CVP showed a striking fall in all patients to -9.7 cm H2O (1.1). After fluid replacement, the CVP was 2.3 cm H2O (0.4) when supine, and -0.4 cm H2O (0.4) at 45 degrees. In the assessment of circulatory volume depletion, CVP should be measured with the patient sat at 45 degrees, if possible: measurement of CVP in a supine patient may not detect or severely underestimate circulatory volume depletion.