In some studies, the failure rate of non-invasive positive pressure ventilation (CPAP, BiPAP) in acute exacerbations of COPD has been as high as 50%
When setting the ventilator in patients with COPD, keep in mind that the majority have chronic ventilatory failure with a chronic compensatory respiratory acidosis
Pearl: Look at the serum bicarbonate level obtained from a recent period of stability
A recent serum bicarbonate level can provide an indirect indication of the patient's baseline PaCO2 if you have no prior ABGs
Rather than target a PaCO2 of 40 mm Hg, manipulate the ventilator to target the patient's baseline serum bicarbonate or a pH of 7.35 - 7.38.
References
Ward NS, Dushay KM. Clinical concise review: Mechanical ventilation of patients with chronic obstructive pulmonary disease. Crit Care Med 2008;36:1614-9.
