Comparison of pulse pressure variation in swine experimental models of hypovolemic shock with and without controlled positive invasive mechanical ventilation

Introduction

Pulse pressure variation (DPP) is a very good method to predict the improvement in oxygen delivery in circulatory failure states after volume expansion. However, this method has been validated only in patients under sedation plus controlled positive pressure invasive mechanical ventilation (PCV). Our understanding of this method in patients under spontaneous ventilation remains unclear.

Materials and methods

In 10 male domestic pigs the pulmonary arterial pressure, aortic arch pressure, femoral arterial pressure (PP) and cardiac output by thermodilution technique were measured in four different stages: (I) basal, in spontaneous ventilation; (II) after controlled hemorrhage to simulate the hypovolemic shock in spontaneous ventilation; (III) in a hypovolemic shock state but now under PCV and breath muscle paralyzation with pancuronium; (IV) after volemic resuscitation under PCV (thiopental plus fentanyl plus pancuronium). The means and medians were compared by the ANOVA and TURKEY tests respectively; P < 0.05 was considered statistically significant. DPP was calculated in all stages by the formula: DPP = (100 × (maximalPP - minimalPP)/(maximalPP + minimalPP)/2), where maximalPP = (maximal systolic pressure - maximal diastolic pressure) and minimalPP = (minimal systolic pressure - minimal diastolic pressure).

Results

The means of DPP under spontaneous ventilation were statistically significantly higher than in other stages of the experiment, respectively: 22.3%; 42.27%; 21.8% and 10.48% with P = 0.039. After the PCV the DPP got back to basal values, without volemic resuscitation. The lowest value were achieved after volume expansion with P = 0.001 compared with stage II.

Conclusion

The DPP in hypovolemic shock in spontaneous ventilation is higher than under PCV. It is important to find the cutoff value that has a best relationship to the response to volume resuscitation.