Haemodynamic and volumetric response to tidal volume and positive end expiratory pressure variation in acute lung injury/acute respiratory distress syndrome patients

Introduction

Tidal volume limitation and incremental positive end expiratory pressure (PEEP) correlates with improved survival in acute respiratory distress syndrome (ARDS) [1], but the impact on haemodynamic response is not well established [2, 3].

Aim of study

To evaluate (1) the haemodynamic and volumetric response to incremental changes of tidal volume and (2) the haemodynamic and volumetric response to incremental changes of PEEP.

Materials and methods

Twenty acute lung injury (ALI)/ARDS patients were mechanically ventilated and connected to an integrated monitoring system (PICCO system; Agilent) by a fiberoptic arterial catheter (pv 2014L16) and a central venous catheter. All patients were randomised to receive mechanical ventilation with an incremental tidal volume (TV) (6, 8, 10 and 12 ml/kg at ZEEP) (group A) or TV = 6 ml/kg and incremental PEEP (5, 10 and 15 cmH₂O) (group B). At every change of respiratory parameters the main haemodynamic and volumetric data were evaluated. Cardiac output (CO) was evaluated continuously online. All data are expressed as the mean ± SD. The ANOVA test was used to compare changes at different TV and at incremental levels of PEEP. P < 0.05 was considered statistically significant.

Results

Tables 1 and 2 report the main hemodynamic changes during different ventilation patterns. Volumetric parameters did not change during the study, but the intrathoracic blood volume index (ITBVI) correlated with CO at every step (r = 0.73, P < 0.001, Spearman correlation).

Table 1

Table 2

Conclusion

• (1) TV ≥ 10 ml/kg decreases either the CO or the mean arterial pressure (MAP). (2) PEEP 15 ≥ cmH₂O decreases CO. (3) Mechanical ventilation with TV ≤ 6 ml/kg and PEEP 10 ≤ cmH₂O has minimal impact on the cardiovascular system. (4) Optimisation of ITBVI may improve the cardiovascular response to mechanical ventilation adjustment.