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16 Respiratory Physiology And Support
Treatment of carboxyhaemoglobin is about 90 minutes in 21% oxygen but
This patient was exposed to a fire in an enclosed environment—a his- decreases to 20–30 minutes in 100% oxygen).
tory that raises concern for an inhalation injury. Other findings includ- An inhalation injury is not commonly due to direct thermal injury
ing soot in the oropharynx and around the nares support the likelihood to the airways, but these injuries are associated with inhalation of toxic
of inhalation injury, whereas the findings of the cherry-red skin and by-products of combustion, which can result in airway oedema due
anxiety are consistent with carbon monoxide poisoning. to inflammation. Therefore, fluid resuscitation should be judicious
Carbon monoxide is a by-product of combustion. Inhaled carbon and the patient should have a bladder catheter placed to monitor urine
monoxide is rapidly transported across the alveolar membrane and output as an indicator of adequacy of hydration. Care should be taken,
preferentially binds to the haemoglobin molecule in place of oxygen. however, to avoid overhydration. At times, after fluid resuscitation, the
Binding of carbon monoxide to haemoglobin (carboxyhaemoglobin) airway can become oedematous, and one needs to monitor for airway
impairs unloading of O . Carboxyhaemoglobin is bright red, which obstruction, which may make a definitive airway more difficult.
2
explains the cherry-red skin color, and the tachypnea and anxiety Steroids have been used frequently in the past to attempt to decrease
suggest tissue (central nervous system) hypoxia. airway swelling. Their use, however, has not been shown to decrease
The most important first step in treating this patient is to the morbidity or mortality in patients with inhalation injury, and they
provide supplemental oxygen in high concentrations. High oxygen may increase the risk of infections. Similarly, prophylactic antibiotics
concentration accomplishes two goals: (1) it optimises oxygen have also not been shown to decrease pulmonary complications or
delivery to ameliorate tissue hypoxia, and (2) it accelerates unloading mortality in patients with inhalation injuries.
of carbon monoxide from the haemoglobin molecule (the half-life

Key Summary Points

1. The primary role of the lungs is to allow for exchange of 4. Severe derangements may overcome compensatory mechanisms,
respiratory gases (intake of oxygen and elimination of carbon resulting in hypoxia and acidosis.
dioxide). 5. Due to differences in lung maturation and respiratory mechanics,
2. Pulmonary function requires a balance of ventilation, gas neonates may be at increased risk of altered gas exchange.
transport, and blood flow.
6. Recognition and treatment of causes of dysfunction are key to
3. Surgical diseases can negatively impact gas exchange by improving patient outcomes.
altering any or all of these factors.

Suggested Reading

Cilley RE. Respiratory physiology and extracorporeal life support. In: Staub NC, Dawson CA, Pulmonary and bronchial circulation. In:
Oldham KT, Colombani PM, Foglia RP, Skinner M, eds. Principles and Gregor R, Windhorst U, eds. Comprehensive Human Physiology,
Practice of Pediatric Surgery. Lippincott Williams & Wilkins, 2005, Pp from Cellular Mechanisms to Integration. Springer-Verlag, 1996,
179–221. Pp 2071–2078.
Guyton AC, Hall JE. Respiration. In: Guyton AC, Hall JE, eds. Textbook West JB. Respiration. In: West JB, ed. Best and Taylor’s
of Medical Physiology, 10th ed. WB Saunders, 2000, Pp 432–492. Physiological Basis of Medical Practice, 11th ed. Williams and
Wilkins, 1985, Pp 546–613.
Piiper J, Respiratory gas transport and acid-base equlibrium in blood.
In: Gregor R, Windhorst U, eds. Comprehensive Human Physiology, Whipp BJ. Pulmonary Ventilation. In: Gregor R, Windhorst U, eds.
from Cellular Mechanisms to Integration. Springer-Verlag, 1996, Pp Comprehensive Human Physiology, from Cellular Mechanisms to
2051–2062. Integration. Springer-Verlag, 1996, Pp 2015–2036.
Piiper J. Pulmonary gas exchange In: Gregor R, Windhorst U, eds. Wilson JW, DiFiore JW. Respiratory physiology and care. In: Grosfeld
Comprehensive Human Physiology, from Cellular Mechanisms to JL, O’Neill JA, Coran AG, Fonkalsrud EW, eds. Pediatric Surgery,
Integration. Springer-Verlag, 1996, Pp 2037–2049. 6th ed. Mosby Elsevier, 2006, Pp 114–133.