Relationship between superior (P_SVC), inferior (P_IVC) vena cava and bladder (P_CYST) pressure

Introduction

Measurements of P_IVC have been reported to allow a fairly reliable assessment of CVP. On the other hand, in patients with abdominal hypertension, P_IVC has been reported to reflect P_CYST. We studied the relationship between Pivc and a) Psvc, b) intra-abdominal pressure measured in the urinary bladder (Pcyst).

Methods

We obtained simultaneous measurements of Psvc, Pivc and Pcyst in 27 critically ill hemodynamically stable patients under mechanical ventilation (81 sets of measurements). Phlebostatic zero and pubic symphysis were at the same level. Measurements were divided in two groups: Group A (Pcyst = Psvc, n = 39). Group B (Pcyst < Psvc, n = 42). Statistics were performed with paired t-test and Pearson correlation.

Results

a) Pivc was significantly higher than Psvc (15.7 ± 0.5 vs 14.9 ± 0.6, P = 0.008), with r = 0.87. Pivc was significantly higher than Pcyst (15.7 ± 0.5 vs 13.6 ± 0.7, P = 0.000), with r = 0.61. b) In Group A, Pivc was significantly higher than Psvc (15.8 ± 0.9 vs 13.4 ± 0.9, P = 0.000), with r = 0,89. There was a significant difference between Pivc and Pcyst (15.8 ± 0.9 vs 17.3 ± 0.8, P = 0.030), with r = 0.85. c) In Group B there was no significant difference between Pivc and Psvc (15.7 ± 0.7 vs 15.8 ± 0.8, P = 0.877) r = 0.91. Pivc was significantly higher than Pcyst (15.7± 0.7 vs 10.2 ± 0.7, P = 0.000), with r = 0.62.

Conclusions

When Pcyst < Psvc, Pivc reflects Psvc and not Pcyst. When Pcyst > Psvc, Pivc does not allow an accurate assessment either of Pcyst or of Psvc but becomes highly correlated with Pcyst.