History: This middle-aged obese man was admitted following a motor vehicle crash. Previous health was good.
Examination: His major injury was chest trauma with a small right pneumothorax and at least five fractured ribs on the right. There was no head or neck injury. Abdomen was soft. He was haemodynamically stable with BP 130/80 and pulse 90/min. Heart sounds were normal. Respiratory distress was present. Respiratory rate was 30/min. Saturation was 95% on high flow oxygen via face mask.
Investigations: Na+ 138, K+ 3.9, Cl- 103, Total CO2 21, glucose 13.6, urea 5.5, creatinine 0.10 (all in mmol/l). CT scan of abdomen was normal. Urinalysis was not reported. Arterial blood gases were collected soon after arrival.
A respiratory acid-base disorder is likely given the trauma and clinical evidence of respiratory distress. There is no indication of a metabolic acid-base disorder. If the patient had been shocked then a lactic acidosis would need to be considered. The patient has not been intubated and ventilated yet. Ventilated patients may be over-ventilated intitially resulting in an iatrogenic respiratory alkalosis.
This man has an acute respiratory acidosis due to acute chest trauma. This patient has respiratory failure and requires intubaton and ventilation.
In acute trauma affecting previously healthy patients, the commonest acid-base problem is a respiratory one related to chest or head trauma, pain, or airway obstruction. Shocked patients may develop a lactic acidosis. Resuscitation of patients with large volumes of saline can cause a hyperchloraemic acidosis.
The medical history of acutely injured patients may not be known initially, but pre-existing medical disorders are often present, and indeed could be the cause of the crash (e.g. if the patient had lost consciousness).