Effects of continuous negative abdominal pressure on intrathoracic blood shift with and without increased intra-abdominal pressure: experimental study

We set out to investigate whether continuous negative abdominal pressure (CNAP) may produce blood shift from the intrathoracic compartment, and whether this effect would be influenced by abdominal pressure. We investigated eight sedated, paralysed and mechanically ventilated pigs (19.4 ± 4 kg). Blood shift was assessed by measuring intrathoracic blood volume (ITBV; PiCCO Pulsion), and central venous pressure (CVP). Measurements were taken before (Pre), a few seconds and 15 min after CNAP (-20 cmH₂O; Life Care – Nev 100, Respironics) was applied on the abdomen (CNAP 1 and CNAP 2, respectively), and after CNAP was relieved (Post). The sequence of measurements was taken with and without abdominal hypertension. This was induced by means of helium (He) insufflation targeted to a value of 25 mmHg (24.7 ± 5.5 direct peritoneal measurement), corresponding to a bladder pressure of 29 ± 4 cmH₂O. Basal and He measurements were randomised with respect to time. Results are shown in Table 1.

Table 1

CVP was correlated with ITBVI (R² = 0.818, P < 0.001, multiple linear regression).

We conclude that CNAP induces a blood shift from the intrathoracic compartment. Blood shift is greater without abdominal hypertension.