Effect of smoke inhalation on viscoelastic properties and ventilation distribution in sheep

1 Paediatric Intensive Care Unit, The Children's Hospital, Westmead, New South Wales; 2 Critical Care Research Group and 3 Biological Research Facilities, The Prince Charles Hospital, Chermside, Queensland; 4 Queensland Radiation Institute and 5 Paediatric Intensive Care Unit, Mater Children's Hospital, South Brisbane, Queensland, Australia Submitted 29 December 2005 ; accepted in final form 16 March 2006 Smoke inhalation injuries are the leading cause of mortality from burn injury. Airway obstruction due to mucus plugging and bronchoconstriction can cause severe ventilation inhomogeneity and worsen hypoxia. Studies describing changes of viscoelastic characteristics of the lung after smoke inhalation are missing. We present results of a new smoke inhalation device in sheep and describe pathophysiological changes after smoke exposure. Fifteen female Merino ewes were anesthetized and intubated. Baseline data using electrical impedance tomography and multiple-breath inert-gas washout were obtained by measuring ventilation distribution, functional residual capacity, lung clearance index, dynamic compliance, and stress index. Ten sheep were exposed to standardized cotton smoke insufflations and five sheep to sham smoke insufflations. Measured carboxyhemoglobin before inhalation was 3.87 ± 0.28% and 5 min after smoke was 61.5 ± 2.1%, range 50–69.4% ( P < 0.001). Two hours after smoke functional residual capacity decreased from 1,773 ± 226 to 1,006 ± 129 ml and lung clearance index increased from 10.4 ± 0.4 to 14.2 ± 0.9. Dynamic compliance decreased from 56.6 ± 5.5 to 32.8 ± 3.2 ml/cmH 2 O. Stress index increased from 0.994 ± 0.009 to 1.081 ± 0.011 ( P < 0.01) (all means ± SE, P < 0.05). Electrical impedance tomography showed a shift of ventilation from the dependent to the independent lung after smoke exposure. No significant change was seen in the sham group. Smoke inhalation caused immediate onset in pulmonary dysfunction and significant ventilation inhomogeneity. The smoke inhalation device as presented may be useful for interventional studies. electrical impedance tomography; functional residual capacity; lung clearance index; dynamic compliance; stress index Address for reprint requests and other correspondence: A. Schibler, Paediatric Intensive Care Unit, Mater Children's Hospital, South Brisbane, 4101 QLD, Australia (e-mail: andreas.schibler{at}mater.org.au )