Background and objective: Dynamic indices represented by systolic pressure variation and pulse pressure variation have been demonstrated to be more accurate than filling pressures in predicting fluid responsiveness. However, the literature is scarce concerning the impact of different ventilatory modes on these indices. We hypothesized that systolic pressure variation or pulse pressure variation could be affected differently by volume‐controlled ventilation and pressure‐controlled ventilation in an experimental model, during normovolaemia and hypovolaemia.
Method: Thirty‐two anaesthetized rabbits were randomly allocated into four groups according to ventilatory modality and volaemic status where G1‐ConPCV was the pressure‐controlled ventilation control group, G2‐HemPCV was associated with haemorrhage, G3‐ConVCV was the volume‐controlled ventilation control group and G4‐HemVCV was associated with haemorrhage. In the haemorrhage groups, blood was removed in two stages: 15% of the estimated blood volume withdrawal at M1, and, 30 min later, an additional 15% at M2. Data were submitted to analysis of variance for repeated measures; a value of P < 0.05 was considered to be statistically significant.
Results: At M0 (baseline), no significant differences were observed among groups. At M1, dynamic parameters differed significantly among the control and hypovolaemic groups (P < 0.05) but not between ventilation modes. However, when 30% of the estimated blood volume was removed (M2), dynamic parameters became significantly higher in animals under volume‐controlled ventilation when compared with those under pressure‐controlled ventilation.
Conclusions: Under normovolaemia and moderate haemorrhage, dynamic parameters were not influenced by either ventilatory modalities. However, in the second stage of haemorrhage (30%), animals in volume‐controlled ventilation presented higher values of systolic pressure variation and pulse pressure variation when compared with those submitted to pressure‐controlled ventilation.
*University of São Paulo, School of Medicine, Laboratory of Medical Investigation LIM/08‐Anaesthesiology, São Paulo, Brazil
†University of São Paulo, School of Veterinary Medicine, Department of Surgery, São Paulo, Brazil
¶University of São Paulo, School of Medicine, Hospital das Clínicas, Division of Anaesthesia, São Paulo, Brazil
‡University of São Paulo, School of Medicine, Hospital das Clínicas, Heart Institute, Anaesthesia Department and Surgical ICU, São Paulo, Brazil
Correspondence to: José Otávio Costa Auler Junior, Instituto do Coração (Incor) – Hospital das Clínicas da FMUSP, Av. Dr. Enéas de Carvalho Aguiar 44, 2° and. CEP 05403‐000 São Paulo, Brazil. E‐mail: email@example.com; Tel/Fax: +55 11 3069 5232
Accepted for publication 1 January 2008
First published online 8 February 2008