Effect of ablated bronchial blood flow on survival rate and pulmonary function after burn and smoke inhalation in sheep
Introduction
Severe burn is very traumatic, especially when the injury is associated with smoke inhalation. This combination greatly increases morbidity and mortality [1], [2]. After smoke inhalation, there is a rapid appearance of hyperaemia in the upper airway of humans and sheep [3], [4], [5]. Hyperaemia of the airway is the most effective way of diagnosing smoke inhalation [6]. Pulmonary oedema has been directly related to smoke-inhalational injury, as evidenced by an increase in extravascular lung water and lung lymph flow after inhalational injury [7], [8], [9], [10], [11]. Smoke inhalation has also been shown to cause an increase in microvascular permeability to protein in the pulmonary and bronchial circulations [8], [9], [10], [12].
These physiological alterations in the pulmonary microvasculature are delayed in onset, and the peak of increased microvascular permeability was observed around 24 h after injury [13]. In contrast, there is a marked increase in bronchial blood flow immediately after inhalational injury [3], [14]. Because the increased bronchial blood flow largely enters the pulmonary vasculature through pre-capillary anastomoses with the pulmonary microcirculation [15], [16], [17], it has been suggested that the bronchial circulation plays a significant role in the spread of injury from the airway of the lung to the parenchyma [11], [18]. Reduction of the bronchial artery circulation reduced lung oedema formation after inhalation in the anaesthetised canine model [11] and in a conscious sheep model [10], [18]. For this, we performed 96-h survival experiments and analysed the regional tissue blood flow. The present study was undertaken to provide a detailed analysis of pulmonary function at 96 h after injury and to estimate the 96-h survival rate. We hypothesised that ablation of the bronchial artery would not only reduce pulmonary injury following combination burn and inhalational injury, but would also allow survival to 96 h with weaning from ventilatory support.
Section snippets
Materials and methods
Twelve adult female sheep (30–40 kg) were cared for in the investigative intensive care unit at our institution. The experimental procedure was approved by the Animal Care and Use Committee of the University of Texas Medical Branch. The guidelines of the National Institutes of Health and American Physiological Society for animal care were strictly followed. The investigative intensive care unit is accredited by The Association for the Assessment and Accreditation of Laboratory Animal Care
Results
Fig. 1 shows the regional blood flow changes measured with fluorescent-coloured microspheres. In the trachea, burn and smoke-inhalation injury significantly increased in both injection and sham groups (ablation group–baseline: 0.18 ± 0.04 vs. 6 h: 1.25 ± 0.22; sham group–baseline: 0.15 ± 0.02 vs. 6 h: 1.67 ± 0.16 ml g−1 tissue). The regional blood flow at 6 h in the trachea was 6.9 and 11 times higher than at baseline, and the ablation of the bronchial artery did not reduce the acute regional blood flow
Discussion
The systemic circulation of the lung supplies nutrients to the airways, blood vessels and supporting structures. The bronchial circulatory system has been thought to play a significant role in certain physiological functions such as warming and humidification of inspired air [26]. Normally, the bronchial circulation comprises ∼1–3% of cardiac output [19], [22]. In several disease states, including pulmonary artery obstruction, congenital pulmonary atresia, chronic bronchiectasis and chronic
Acknowledgements
We thank Jeffrey D. Meserve for his editorial assistance and Nettie Biondo and John R. Salsbury for their technical assistance.
This work was supported by the National Institute for General Medical Sciences Grant GM66312, GM060688 and Grants 8954, 8450 and 8460 from the Shriners of North America.
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