hipoxemia

Hipoxemia is a lower-than-normal level of oxygen in the arterial blood, typically reflected by a reduced partial pressure of oxygen (PaO2) or lower oxygen saturation (SaO2). It is important to distinguish hipoxemia from hypoxia; hipoxemia refers to the oxygen content in the blood, while hypoxia describes insufficient oxygen delivery to tissues.

Causes and mechanisms of hipoxemia fall into several categories. Alveolar hypoventilation reduces the amount of oxygen entering the lungs and can raise carbon dioxide levels. Diffusion impairment occurs with interstitial or fibrotic lung disease that slows oxygen transfer. Ventilation-perfusion (V/Q) mismatch and intrapulmonary shunts, including anatomic or physiologic right-to-left shunts, reduce the efficiency of oxygen uptake. A low inspired oxygen tension, such as at high altitude or under certain anesthetic conditions, can also cause hipoxemia. Diseases commonly associated with hipoxemia include COPD, pneumonia, pulmonary edema, acute respiratory distress syndrome (ARDS), interstitial lung disease, and heart failure.

Diagnosis is typically made by arterial blood gas analysis and pulse oximetry. PaO2 values below about 80 mmHg at sea level and/or SaO2 below roughly 90% on room air indicate hipoxemia, with severity categorized by PaO2 levels. In critical care, the PaO2/FiO2 ratio is used to assess oxygenation, particularly in conditions like ARDS.

Management focuses on correcting hypoxemia and treating the underlying cause. Supplemental oxygen is the mainstay of therapy, with targets individualized by condition (often aiming for SpO2 around 92–96%, or 88–92% in certain chronic obstructive disease cases). Escalation to noninvasive or invasive ventilation may be necessary for respiratory failure. Long-term oxygen therapy may be required in chronic hypoxemia due to lung or heart disease. Prognosis depends on the cause, severity, and duration of hipoxemia.