Hipoksemi

Hipoksemi, also known as hypoxemia, is a lower-than-normal level of oxygen in arterial blood. It is typically defined by a PaO2 below 80 mmHg or an arterial oxygen saturation (SaO2) below about 95% on room air, though exact thresholds vary with age, altitude, and clinical context.

Causes of hipoksemi include conditions that impair oxygen transfer from the lungs to the blood. These include hypoventilation, diffusion impairment, ventilation-perfusion (V/Q) mismatch, and intrapulmonary or intracardiac shunts. Common etiologies are pneumonia, acute respiratory distress syndrome, chronic obstructive pulmonary disease exacerbations, pulmonary embolism, heart failure, and chest wall disorders. Exposure to high altitude and certain dyshemoglobinemias, such as carbon monoxide or methemoglobinemia, can also produce hypoxemia even when lung function appears normal.

Pathophysiology involves reduced oxygen delivery to tissues. When PaO2 falls or oxygen content in the blood decreases, cellular oxygen delivery declines, which can lead to tissue hypoxia and organ dysfunction if not corrected. The body may respond with increased ventilation and heart rate; chronic hypoxemia can cause secondary polycythemia and pulmonary vasoconstriction.

Diagnosis relies on arterial blood gas measurements (PaO2 and SaO2) and pulse oximetry (SpO2). The alveolar-arterial gradient, chest imaging, and tests to identify the underlying cause help guide management. Treatment aims to correct the hypoxemia and treat the cause, typically with supplemental oxygen to maintain SpO2 in the low to mid-90s. More severe cases may require noninvasive or invasive ventilation. Specific situations, such as CO poisoning or methemoglobinemia, require targeted therapies like hyperoxia with consideration of hyperbaric oxygen or methylene blue, respectively.

Prognosis depends on the cause and the timeliness of therapy; chronic or severe hypoxemia is associated with higher morbidity and mortality.