CVP and PAoP measurements are discordant during fluid therapy after traumatic brain injury

The objective of the study was to compare measurements of central venous pressure (CVP) and pulmonary artery occlusion pressures (PAoP) as estimates of intravascular volume during the first 96 hours of fluid therapy after traumatic brain injury (TBI). One thousand five hundred ten simultaneous CVP and PAoP measurements from 31 patients entered into the National Acute Brain Injury Study: Hypothermia (NABISH:H) protocol were retrospectively compared. The effect of fluid administration and body temperature upon the paired measurements was statistically assessed. Agreement between CVP and PAoP values was poor. The CVP and PAoP were equal in only 11% of paired values. The CVP was always higher than PAoP in 1 patient, whereas PAoP always exceeded the CVP in 5 others. In 74% of the pairs, the PAoP was higher than the CVP, whereas in 15%, CVP was greater than PAoP. For any CVP measurement, the PAoP was either 3 mm Hg above or below the CVP in 67% of the pairs and at least 5 mm Hg above or below the CVP in 21% of the pairs. In 21 (68%) patients, PAoP was > or = 5 mm Hg above CVP in more than 4 readings, a clinically important difference. Discordance was not attributed to the fluid administered or to the temperature protocol. Neurological outcome appears affected by the volume of fluid administration. However, during initial therapy, estimates of intravascular volume provided by the CVP and PAoP are discordant. Although documented in other clinical conditions, the disparity noted here after TBI has not been previously reported. Assessment of intravascular volume to avoid hypovolemia should utilize other measurement techniques.