Acute hemorrhagic shock decreases airway resistance in anesthetized rat

Abstract

Bayat S, Albu G, Layachi S, Portier F, Fathi M, Peták F, Habre W. Acute hemorrhagic shock decreases airway resistance in anesthetized rat. J Appl Physiol 111: 458 -464, 2011. First published May 19, 2011 doi:10.1152/japplphysiol.00024.2011We studied the relation between changes in pulmonary and systemic hemodynamics to those in the airway resistance, respiratory tissue mechanics, and thoracic gas volume (TGV) following acute hemorrhage and blood reinfusion in rats. Forced oscillation technique was used to measure airway resistance (Raw), respiratory tissue damping, and elastance at baseline and after stepwise 1-ml blood withdrawals up to 5 ml total, followed by stepwise reinfusion up to full restoration. Mean systemic (Pam) and pulmonary arterial pressures and suprarenal aortic blood flow were measured at each step. In supplemental animals, plethysmographic TGV, Pam, and respiratory mechanics measurements were performed. Blood volume loss (BVL) led to proportional decreases in Raw (66.5 Ϯ 8.8 vs. 44.8 Ϯ 9.0 cmH 2O·s·l Ϫ1 with 5 ml, P Ͻ 0.001), Pam, and aortic blood flow. In contrast, tissue damping increased significantly (1,070 Ϯ 91 vs. 1,235 Ϯ 105 cmH 2O/l, P ϭ 0.009 with 5 ml BVL), whereas tissue elastance did not change significantly. TGV significantly increased with acute BVL (3.7 Ϯ 0.2 vs. 4.2 Ϯ 0.2 ml, P ϭ 0.01). Stepwise reinfusions produced opposite changes in the above parameters, with Raw reaching a higher value than baseline (P ϭ 0.001) upon full volume restoration. Both adrenalin (P ϭ 0.015) and noradrenalin levels were elevated (P ϭ 0.010) after 5-ml blood withdrawal. Our data suggest that the decreases in Raw following BVL may be attributed to the following: 1) an increased TGV enhancing airway parenchymal tethering forces; and 2) an increase in circulating catecholamines. The apparent beneficial effect of a reduction in Raw in acute hemorrhagic shock is counteracted by an increase in dead space and the appearance of peripheral mechanical heterogeneities due to de-recruitment of the pulmonary vasculature.

Respiratory consequences of perioperative complications related to anaesthesia

“…15,16 In common with previous findings, the blood loss in the present study led to bronchodilation, which is most probably due to the compensatory increase in thoracic gas volume and/or the elevated levels of circulatory catecholamines. 8 Our findings add to what is known from a different model of haemorrhage that does not induce Fluid replacement with blood, colloid or crystalloid 37 the severe hypovolaemia characteristic of hidden, leaky blood loss during major surgery.…”

“…Alternatively, the depressed Raw may be attributed to the presence of bronchoactive mediators in the sequestered blood, with the particular importance of increased levels of adrenaline and noradrenaline in the withdrawn and subsequently re-administered blood. 8 In contrast to autologous blood, colloid completely reversed the haemorrhage-induced bronchodilation. This illustrates the interaction between circulatory changes and airway mechanics, with recovery of the original airway geometry following restoration of normovolaemia.…”

“…Among the respiratory adverse effects during anaesthesia and intensive care, bronchoaspiration poses a major challenge for health professionals [7,8]. This syndrome has been reported to cause a high incidence of morbidity and mortality, involving up to 90 % of the affected patients, depending on the extent of the involved lung regions [9][10][11][12][13].…”

“…This syndrome has been reported to cause a high incidence of morbidity and mortality, involving up to 90 % of the affected patients, depending on the extent of the involved lung regions [9][10][11][12][13]. Inhalation of the gastric contents into the lower respiratory tract induces a number of pulmonary syndromes, described originally by Mendelson et al, including acute aspiration pneumonitis caused by the acidity subsequent to chemical injury [14], and aspiration pneumonia resulting from the inhalation of pathogenic bacteria [7,8,15].…”

“…[5][6][7] We have recently shown that acute hypovolaemic shock and subsequent resuscitation with autologous blood affects respiratory mechanics. 8 Although surgical procedures are associated with a more controlled but sustained blood loss that also requires fluid replacement therapy, the respiratory consequences of this have not been explored. The administration of blood products is often regarded as the gold standard therapy, with the main aim of maintaining oxygen transport capacity.…”