Hypoxia and Oxygen Therapy

With Dr. Lauren Troy, Respiratory Physician at Royal Prince Alfred Hospital, New South Wales, Australia.

Introduction

The hypoxic patient is a common issue that many junior doctors will face when on the wards. Hypoxia can significantly contribute to a patient’s morbidity and mortality and must be managed early. It is therefore important that the junior doctor has a structured approach to the hypoxic patient and sound knowledge of oxygen therapies available for their patients in the hospital setting.

The definition of hypoxaemia: PaO2 less than 80mmHg. Hypoxia and hypoxaemia are often used interchangeably.

The five major cause of hypoxia are split into two major categories base on the alveolar-arterial gradient(AA)

• Normal AA gradient (<15mmHg)
  • Low FiO2
  • Hg. CNS depression such as in opiate use, sleep apnoea
• Widened AA gradient (>15mmHg)
  • VQ mismatch (ventilation – perfusion – pneumonia, asthma
  • Shunt; the extreme version of VQ mismatch
  • Diffusion Limitation; e.g. in pulmonary fibrosis

Case

You are a junior doctor on night shift. You are asked by the nursing staff to review an 86-year-old female patient who is day 2 post total hip replacement. The nurse is asking you to review the patient in regards to her low O2 saturations of 92% on room air.