Acute versus subacute haemorrhagic shock evaluated in an isolated perfused rat lung model

Introduction

Volume resuscitation of haemorrhagic shock (HS) may lead to delayed apparition of shock lung. We compared acute versus subacute grade IV HS with and without volume resuscitation in an isolated blood-perfused and ventilated lung rat model.

Methods

Male Sprague Dawley rats were anaesthetised with isoflurane, fentanyl and pancuronium, tracheotomised and ventilated with a volume controlled ventilator. After 300 U/kg i.v. heparin, grade IV HS was induced by withdrawing 30 ml/kg blood with a roller pump in four groups of 10 rats (acute HS with and without volume resuscitation, subacute HS with and without volume resuscitation). A 5th group without HS served as control. Volume resuscitation consisted of infusion of Ringer Lactate (three times the volume of blood withdrawn) over 30 min, starting 60 min after initiation of HS. Mean arterial pressure (MAP) dropped from 75 mmHg to 10 mmHg in the acute HS, and from 75 to 25 mmHg in the subacute HS. MAP recovered initial values at the end of resuscitation in the rats submitted to the subacute but not to the acute HS. Ventilation parameters were maintained constant. The isolated lung circuit was primed and perfused with the blood of a donor rat.

Results

Acute HS with volume resuscitation was not associated with significant alterations in any of the measured variables of the perfused lung. In contrast, acute HS without volume resuscitation resulted in the most striking alterations in lung mechanics, haemodynamics, as well as weight changes. Subacute HS independently of volume resuscitation showed only moderate and non significant changes. See Figure 1 opposite.

Figure 1

Mean ± SE values of data measured at 60 min after reperfusion of the isolated lungs of control rats (black bars), acute HS with resuscitation (white bars), acute HS without resuscitation (light grey bars), subacute HS with resuscitation (dark grey bars), subacute HS without resuscitation (hatched bars). V_PEF/V_T = volume of peak expiratory flow over tidal volume, an index of airway resistance. ^*P < 0.05.

Conclusions

Our results demonstrate that pulmonary injury following non resuscitated HS depends principally on the intensity and not on the volume of blood loss, and that during subacute HS even of grade IV, volume resuscitation is of minimal benefit.