What causes oxygen induced hypercapnia? To date we are aware of three different mechanisms: 1. Hypoxic drive – COPD patients’ respiratory rate is affected by pO2 levels (not only pCO2 as normal) 2. Ventilation/perfusion mismatch – the additional oxygen opens up flow to alveoli which are functioning poorly 3. Haldane effect – the additional oxygen makes hemoglobin release carbon dioxide Different researchers have different opinions about the magnitude of these different effects. Key takehomes 1. Always give oxygen to a hypoxic patient. Hypoxia is a fast killer, whereas you can sort out hypercapnia later 2. Normal respiratory rate doesn’t rule out hypercapnia, since there are several mechanisms at play. Follow repeated ABGs! 3. Oxygeninduced hypercapnia can affect patients with other chronic lung disease, not just COPD patients
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