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Importance of Noninvasively Measured Respiratory Muscle Overload Among the Causes of Hospital Readmission of COPD Patients^*

^* From the Servicio de Neumología (Dr. González), Hospital Clínico Universitario de Valencia, Valencia, Spain; and the Universidad de Valencia (Drs. Servera and Marín), Valencia, Spain.

Correspondence to: Cruz González, MD, Servicio de Neumología, Hospital Clínico Universitario de Valencia, Avda Blasco Ibáñez 17, E-46010 Valencia, Spain; e-mail: cruz.gonzalez{at}uv.es

Abstract

Aim: To evaluate the influence of respiratory muscle overload and right cardiac overload among the possible risk factors of hospital readmission in a 1-year follow-up of a cohort of patients with moderate-to-severe COPD.

Methods: A total of 112 COPD patients who were admitted consecutively to the hospital for acute exacerbation. At hospital discharge, we evaluated the conventional clinical and functional determinations in addition to the pressure-time index (PTI), which is obtained using the equation PTI = (Pawo/PImax) x (TI/TTOT) x 100, where Pawo represents the mean airway pressure measured at the mouth during spontaneous breathing, PImax is the maximal inspiratory pressure, TI is the inspiratory time, and TTOT is the total breathing cycle time. A cardiac echo-Doppler examination was carried out when patients were in stable condition and presented clinical signs of right cardiac overload prior to inclusion in the study.

Results: Multivariate analysis showed that the use of long-term oxygen therapy (LTOT) and high PTI (> 0.25) were independently related to the risk of hospital readmission. Patients receiving LTOT had higher PaCO₂ (p < 0.05), FEV₁ percent predicted (p < 0.05), FVC percent predicted (p < 0.05), and PaO₂ (p < 0.05), and had higher PaCO₂ (p < 0.05). An elevated systolic pulmonary arterial pressure (> 40 mm Hg) was also independently related, but only 28 patients had echo-Doppler data that could be used.

Conclusions: At hospital discharge, noninvasively measured respiratory muscle overload as well as the use of LTOT were associated with an increased risk of hospital readmission for exacerbation in patients with moderate-to-severe COPD.

Key Words: acute exacerbation • COPD • readmission • respiratory muscle overload • right cardiac overload