Pulmonary artery diastolic and wedge pressure relationships in critically ill and injured patients

To study pulmonary artery wedge pressure (PAWP) and pulmonary artery diastolic pressure (PADP) relationships, we measured these simultaneously with cardiac outputs 1922 times in 128 patients who were critically ill or in an intensive care unit. In 356 (18.5%) of the readings, the PAWP exceeded the PADP, indicating that the PAWP reading might be erroneous. In 106 (5.5%) of these readings, the PAWP was 6.0 mm Hg or more higher than the PADP, indicating that the PAWP was almost certainly erroneous. In virtually all instances in which this discrepancy was recognized, changing the position of the catheter tip provided a PAWP value equal to or lower than the PADP. On the other extreme, in 49 (30%) of the patients, the PADP was 6.0 mm Hg or more higher than the PAWP. The pulmonary vascular resistance in these patients averaged (+/- SD) 257 +/- 145 dyne/s/cm-5 (normal, 80 to 160 dyne/s/cm-5). The mean pulmonary vascular resistance in the other 74 patients was significantly lower (158 +/- 72 dyne/s/cm-5). The mortality rate with the increased PADP-PAWP gradients was 59% (24/49). This was significantly higher than the mortality rate (34%, or 27/79) seen with lower PAWP-PADP gradients. Thus, the relationship between the PADP and PAWP should be examined closely in critically ill patients. A PAWP higher than the PADP indicates that the PAWP measurement may be erroneous. On the other hand, if the PADP exceeds the PAWP by 6.0 mm Hg or more, the patient has probably developed pulmonary hypertension and has a much poorer prognosis.