Oxygen Therapy and Respiratory Management

Physiological Mechanisms

The Bohr effect facilitates oxygen delivery to tissues by shifting the oxygen-hemoglobin dissociation curve rightward in response to increased CO2, decreased pH, and elevated temperature, while the Haldane effect enhances CO2 transport by increasing hemoglobin's CO2-carrying capacity when oxygen is released 1
Increases oxygen release at the tissue level when CO2, hydrogen ions, and temperature rise, shifting the dissociation curve rightward 1
Enhances oxygen availability to metabolically active tissues where CO2 production is highest 1
Decreases CO2 buffering capacity of hemoglobin when oxygen saturation increases 2, 3

The Haldane effect is the third most important mechanism causing hypercapnia when supplemental oxygen is administered to patients with chronic respiratory disease 2, 3, 4
V/Q mismatch remains the dominant mechanism: High-concentration oxygen reverses hypoxic pulmonary vasoconstriction (HPV), increasing blood flow to poorly ventilated units with high PACO2, thereby raising systemic PaCO2 4
Loss of hypoxic ventilatory drive contributes when PaO2 rises above 8 kPa (60 mmHg), though this effect plateaus above 13 kPa (100 mmHg) 4
The Haldane effect independently decreases hemoglobin's CO2 buffering capacity, contributing to CO2 retention 2, 3

Target PaO2 between 70-90 mmHg or SaO2 92-97% to avoid both hypoxemia and hyperoxia 5
Monitor arterial blood gases within 30-60 minutes after initiating oxygen therapy in at-risk patients 1
Never abruptly discontinue oxygen in patients who developed hypercapnia on supplemental oxygen 2, 3
Do not assume hypercapnia on oxygen is solely due to loss of hypoxic drive—V/Q mismatch and the Haldane effect are more important contributors 4
Do not target supranormal oxygen levels—increases above 13 kPa provide no ventilatory benefit and worsen V/Q matching 4