hypoxæmi

Hypoxæmi, or hypoxemia, is a lower-than-normal level of oxygen in arterial blood. It is defined by a decreased partial pressure of oxygen in arterial blood (PaO2) and/or reduced arterial oxygen content. At sea level, normal PaO2 is about 75–100 mmHg; hypoxæmia is commonly defined as PaO2 below 80 mmHg, with more severe pathology often recognized when PaO2 falls to about 60 mmHg or lower or SaO2 drops below 90%. Hypoxæmia can lead to tissue hypoxia if oxygen delivery to tissues is inadequate.

Diagnosis relies on arterial blood gas analysis and pulse oximetry. ABG provides PaO2, PaCO2, pH and oxygen content, while SpO2 estimates oxygen saturation. ABG thresholds are used in clinical decision-making, but interpretation must consider altitude, age, and comorbidity.

Causes fall into several categories: impaired oxygen transfer due to ventilation-perfusion mismatch (e.g., COPD, pulmonary embolism), diffusion impairment (fibrosis, edema), shunt (atelectasis, ARDS), and hypoventilation (drug overdose, neuromuscular weakness) or high altitude. Chronic hypoxaemia can cause polycythemia and pulmonary hypertension.

Management aims to correct inadequate oxygen delivery and treat the underlying cause. Supplemental oxygen is first-line for most hypoxemias, with non-invasive or invasive ventilation reserved for more severe cases or respiratory failure. Oxygen delivery must be carefully titrated in certain conditions to avoid hypercapnia or oxygen toxicity. Prognosis depends on the cause and severity; timely treatment improves outcomes.