Effects of acute on chronic respiratory failure on hypercapnia and 3-month survival.

BACKGROUND: There is a lack of information on respiratory function and mechanics after COPD exacerbations. STUDY
OBJECTIVES: To find their role in short-term survival and occurrence of chronic hypercapnia after these events. PATIENTS AND
INTERVENTIONS: Seventy-three COPD patients recovering from a recent severe exacerbation underwent evaluation of breathing pattern, breathing mechanics, lung function, and arterial blood gas levels at the time of discharge from a respiratory ICU (RICU).
RESULTS: The 3-month mortality rate after RICU discharge was 11%. The percent of ideal body weight (%IBW) [R = 6.04; p = 0.01] and occlusion pressure (R = 5.41; p = 0.02) provided significant distinction between deceased patients and survivors; the final discriminant equation showed that %IBW was able to predict patient death or survival with an accuracy of 90%. With decreasing order of power, the ratio of inspiratory time to total breathing cycle time (Ti/Ttot) [R = 8.87; p = 0.003], pressure-time product of the inspiratory muscles (R = 7.12; p = 0.009), maximal esophageal pressure (R = 6.00; p = 0.01), esophageal pressure (R = 5.50; p = 0.02), Pa(O2)/fraction of inspired oxygen (R = 4.72; p = 0.03), and pressure time index (PTI) [R = 4.57; p = 0.03] provided a significant distinction between hypercapnia and normocapnia at discharge. The discriminant equation, including Ti/Ttot and PTI, could correctly separate hypercapnic or normocapnic patients with an accuracy of 76%.
CONCLUSIONS: In COPD patients who are recovering from a severe exacerbation, hypercapnia is strongly related to inspiratory muscle work, strength, and breathing pattern; and only body weight predicts short-term survival.