Background

Variations in intrathoracic pressure interfere with venous return and cardiac output (CO). Inspiratory fall in central venous pressure (CVP) traces (ifCVP) during spontaneous breathing have been recommended for cardiovascular fluid responsiveness (CFR) evaluation. We recently described the usefulness of CVP wave amplitude variation (pressoric vena cava collapsibility index, Cvc_i) during mechanical ventilation for CFR estimation in critically ill patients. There are no data about the Cvc_i evaluation during spontaneous breathing.

Objective

To test the hypothesis that Cvc_i can be used for CFR evaluation during spontaneous ventilation.

Methods

In six male, anesthetized, intubated and spontaneous breathing dogs, CO measurements and CVP waves were registered through a Swan–Ganz catheter while the mean arterial pressure (MAP) was measured through an intraarterial catheter.

After baseline measurements a graded hemorrhage was performed in 10% quota until 50% of the estimated volemia. The total shed blood volume was then re-infused in the same quota. Measurements of the heart rate (HR), CO, MAP, CVP, ifCVP, and Cvc_i are performed in every bleeding and re-infusion step. The Cvc_i was calculated with the following formula: Cvc_i(%) = [(CVPP_exp - CVPP_ins)/CVPP_exp] × 100, using the inspiratory (CVPP_ins) and expiratory central venous pulse pressure (CVPP_exp). ifCVP = CVP measured in the 'a' wave base at expiration minus CVP measured in the 'a' wave base at inspiration. Correlations among the CO and other variables were performed using the Spearman coefficient test.

Results

See Table 1. The correlations encountered were: CO and SvO₂ (r = 0.94, P < 0.001); CO and Cvc_i (r = 0.61, P < 0.04); and CO and ifCVP (r = -0.02, P < 0.9).

Conclusion

We conclude that a pressoric vena cava collapsibility index may be used to detect cardiovascular fluid responsiveness during spontaneous ventilation.