A 30-year-old man with no significant past medical history was admitted to ED from a house fire started by a piece of faulty electrical equipment. There were superficial skin burns only but some evidence of a possible inhalation injury with singed nasal hairs and a hoarse voice. Coughing resulted in expectoration of carbonaceous sputum with some haemoptysis. Arterial blood gas analysis revealed a PaO₂ of 10.4 kPa on 40% oxygen a carboxyhaemoglobin level of 18%.

Semi-elective endotracheal intubation was performed using an uncut orotracheal tube. Ventilatory parameters were adjusted to give a tidal volume of 6-8 ml/kg and plateau pressure of less than 30 cmH₂0. Recruitment manouveres were performed to give an optimum compliance in the region of 40-50 ml/cmH₂0 with a positive end-expiratory pressure of 8 H₂0. The inspired fraction of oxygen was kept high (i.e. greater than 60%) until there was a fall of the carboxyhaemoglobin level to less than 5% at which point downwards titration was performed as guided by a target SpO₂ of 94%.

Fibreoptic bronchoscopy was performed approximately six hours after admission to intensive care which demonstrated carbonaceous colonisation of the lower respiratory tract and areas of erythematous and denuded epithelium. Within 12 hours of intubation significant oedema of the face and upper airway had developed. A restrictive fluid regimen was instituted and there was gradual resolution of this swelling over the next 3 days. At this time, gas exchange was satisfactory and the patient was successfully extubated before being discharged to the high-dependency unit.

How is inhalational injury managed on the ICU?

Steven Shepherd

Smoke inhalation injury is a long-established contributor to morbidity and mortality after burns.^1,2 Effective assessment is compounded by exposure to the large number of products of combustion, hence it is not possible to accurately qualify or quantify exactly which or how much toxin a patient has been exposed to. The incidence of inhalation injury in burns patients who require hospitalisation ranges from 20-30% and at least 30% of those with inhalation injury die.³

The most reliable indicator in current use of the impact of inhalation injury is the PaO₂/FiO₂ ratio but this may be affected by a number of other variables including the efficacy of mechanical ventilation, the time since initiation of resuscitation and contribution of carboxyhaemoglobin.³ As regards the latter variable, whilst easily measured with modern blood gas technology it only describes the contribution of one component of smoke and often normalises before transfer to a burn centre with high flow oxygen and time.^3,4 Admission bronchoscopy may offer a safe and effective diagnostic modality.⁵

Inhalational injury is a chemical insult rather than a thermal tracheobronchiolitis.⁶ Those with an associated inhalation injury often exhibit more pronounced hypotension and require more extensive fluid resuscitation. Respiratory care of these patients is focussed upon adequate bronchial toilet including physiotherapy or therapeutic bronchoscopy to prevent atelectasis, early ambulation, lung-protective ventilatory strategies and the use of pharmacological adjuncts.⁷ The use of nebulised heparin and N-acetylcysteine has been shown to attenuate both acute lung injury and the progression to adult respiratory distress syndrome in ventilated patients.⁸ It has been suggested that this regimen inhibits airway fibrin clot formation, produces mucolysis and has bronchodilatory effects.⁸ Given the complex pathogenesis involved in the development of this condition, the use of anti-oxidants may have a role.⁹

No particular mode of traditional ventilation has been shown as particularly efficacious in the management of this injury.¹⁰ High-frequency oscillatory ventilation has, however, been shown to be perhaps beneficial if instituted early in inhalation injury; this benefit was not borne out if instituted as a rescue therapy in established respiratory failure.¹¹ A protocolised bundle of care appears to offer significant benefits.^3,10

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Lessons Learnt

The management of inhalation injury necessitates careful assessment, ventilation and rehabilitation to prevent long-term sequelae. The use of nebulised bronchodilators and heparin was not considered in this case and could have offered significant benefits. Similarly, consideration to transfer to a regional burns centre could have been considered.

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References

1. Shirani KZ, Pruitt BA, Mason AD. The influence of inhalation injury and pneumonia on burn mortality. Annals of Surgery. 1987 Jan;205(1):82–7.
2.  Ryan CM, Schoenfeld DA, Thorpe WP, Sheridan RL, Cassem EH, Tompkins RG. Objective estimates of the probability of death from burn injuries. N. Engl. J. Med. 1998 Feb 5;338(6):362–6.
3.  Hassan Z, Wong JK, Bush J, Bayat A, Dunn KW. Assessing the severity of inhalation injuries in adults. Burns. 2010 Mar;36(2):212–6.
4.  Lange M, Cox RA, Enkhbaatar P, Whorton EB, Nakano Y, Hamahata A, et al. Predictive role of arterial carboxyhemoglobin concentrations in ovine burn and smoke inhalation-induced lung injury. Exp. Lung Res. 2011 May;37(4):239–45.
5.  Ryan CM, Fagan SP, Goverman J, Sheridan RL. Grading inhalation injury by admission bronchoscopy. Critical Care Medicine. 2012 Apr;40(4):1345–6.
6.  Albright JM, Davis CS, Bird MD, Ramirez L, Kim H, Burnham EL, et al. The acute pulmonary inflammatory response to the graded severity of smoke inhalation injury*. Critical Care Medicine. 2012 Apr;40(4):1113–21.
7.  Mlcak RP, Suman OE, Herndon DN. Respiratory management of inhalation injury. Burns. 2007 Feb;33(1):2–13.
8.  Miller AC, Rivero A, Ziad S, Smith DJ, Elamin EM. Influence of Nebulized Unfractionated Heparin and N-Acetylcysteine in Acute Lung Injury After Smoke Inhalation Injury. Journal of Burn Care & Research. 2009 Mar;30(2):249–56.
9.  Yamamoto Y, Sousse LE, Enkhbaatar P, Kraft ER, Deyo DJ, Wright CL, et al. γ-Tocopherol Nebulization Decreases Oxidative Stress, Arginase Activity, and Collagen Deposition After Burn and Smoke Inhalation in the Ovine Model. Shock. 2012 Dec;38(6):671–6.
10.  Schwartz SJ, Pantle H, McQuay N. Inhalation Injuries. ICU Director. 2011 Oct 18;2(5):163–71.
11.  Cartotto R, Walia G, Ellis S, Fowler R. Oscillation after inhalation: high frequency oscillatory ventilation in burn patients with the acute respiratory distress syndrome and co-existing smoke inhalation injury. Journal of Burn Care & Research. 2009 Jan;30(1):119–27.