You are caring for a patient with a history of COAD who is requiring 70% humidified oxygen via a facemask. You are monitoring his response to therapy by observing his colour, degree of respiratory distress and respiratory rate. The patient’s oxygen saturations have been between 95% and 98%. In addition, the doctor has been taking arterial blood gases. What is the reason for this?

  • Oximeters may be unreliable under certain circumstances, e.g. if tissue perfusion is poor, if the environment is cold and if the patient’s nails are covered with nail polish.

  • Arterial blood gases should be sampled if the patient is receiving >60% oxygen.

  • Pulse oximeters provide excellent evidence of oxygenation, but they do not measure the adequacy of ventilation.

  • Arterial blood gases measure both oxygen and carbon dioxide levels and therefore give an indication ofboth ventilation and oxygenation