Effect of positive end-expiratory pressure on the pressure gradient of venous return in hypovolemic patients under mechanical ventilation

Abstract

To assess the effects of positive end-expiratory pressure (PEEP) on central venous pressure (CVP) and common iliac venous pressure (CIVP), and the difference between CVP and CIVP [D(c-i)VP] in hypovolemic patients under mechanical ventilation. From May 2007 to May 2009, 30 acute hypovolemic adult patients undergoing mechanical ventilation in intensive care unit (ICU) were enrolled. The patients were randomly divided into three groups, and PEEP with 0, 5, 10 cm H(2)O (1 cm H(2)O=0.098 kPa) levels were used respectively. Ten mechanically ventilated patients with similar basic clinical conditions but normal blood volume were selected randomly as the control group. CVP, CIVP and D(c-i)VP were measured and recorded at each PEEP level in both groups. The patients' heart rate, mean artery pressure and respiratory pressure data were also collected. The correlation analysis was used to analyze relationship between CVP and CIVP and between the changes in venous pressure and the changes in respiratory pressure. (1)CVP increased significantly when PEEP level was elevated in the study group. When PEEP was 0, 5 and 10 cm H(2)O, the CVP was (1.3+/-0.9), (3.1+/-1.3) and (4.5+/-1.3) mm Hg, respectively (1 mm Hg=0.133 kPa, all P<0.01). Whereas, in the control group, the changes in CVP was small. At 0, 5 and 10 cm H(2)O PEEP levels, CVP was (6.9+/-1.3), (7.2+/-1.2) and (8.0+/-1.5) mm Hg, respectively, but when CVP at PEEP0 and PEEP5 was compared with that of PEEP10, the difference was significant (P<0.01 and P<0.05). There was slight increase of CIVP in both groups when PEEP was elevated. D(c-i)VP was increased significantly in the study group compared with control group (all P<0.01). But the value was gradually decreased when with elevation of PEEP. When PEEP level was elevated from 0 to 10 cm H(2)O, D(c-i)VP value was lowered from (4.9+/-1.7) mm Hg to (2.8+/-1.4) mm Hg. No significant difference in D(c-i)VP was found in the control group. The D(c-i)VP values in the control group were equal or lower than 1.5 mm Hg at three PEEP levels. (2)No relationship was found between CVP and CIVP at each PEEP level in the study group (r(1)=0.236, r(2)=0.299, r(3)=0.262, all P>0.05), but there was a statistically significant correlation between CVP and CIVP in the control group (r(1)=0.485, r(2)=0.679, r(3)=0.748, all P<0.05). The findings suggest that it may not be appropriate to use CVP or CIVP to evaluate the patients' blood volume and effect of volume resuscitation in the hypovolemic patients undergoing mechanical ventilation in combination with PEEP.