Arterial CO2 tension

Both chronic and acute respiratory failure are accompanied by elevation of Paco2 above its normal level of 5.3 kPa (40 mmHg). A feature of patients with deteriorating chronic obstructive airways disease is the slow rise in Paco2 compensated by renal retention of bicarbonate. Usually, there is a rise in bicarbonate (normal range

23-28 mmol/l) of about 4 mmol/l for every 1.3-kPa (10-mmHg) rise in Paco2. With acute exacerbations secondary to infection and increased sputum production, sharp increases in Paco2 occur which exceed the ability of the kidney to compensate and precipitate severe respiratory acidosis.

Where expertise allows, nasal ventilation may avert the need for intubation ( ,U.dw.a.,dia.eL┬ži(, but mechanical ventilation should be introduced in appropriately chosen patients with arterial pH levels below 7.2 and evidence of exhaustion. In acute respiratory failure, elevation of Paco2 is also a useful marker for the introduction of respiratory support; an irreversible respiratory acidosis with an arterial pH below 7.2 is usually considered intolerable. However, severely asthmatic patients provide an exception to this rule, with ventilation being introduced at lower or even normal levels of Paco2 if other indications are present (e.g. obtunded, fatigued, falling Pao2).

Sleep Apnea

Sleep Apnea

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