• Andrea Purro, Lorenzo Appendini, Carolina Polillo, Giovanni Musso, Claudio Taliano, Fabio Mecca, Roberto Colombo, and Giorgio Carbone.
• Emergency Department, Gradenigo Hospital, Turin, Italy. andrea.purro@h-gradenigo.it
• Intensive Care Med. 2009 Apr 1; 35 (4): 639-47.

ObjectiveThe purpose of this study is to investigate the respiratory mechanics, breathing pattern, and pressure-generating capacity of respiratory muscles during the early phases of an acute exacerbation of COPD.DesignProspective study.SettingDivision of Emergency Critical Care and Chronic Ventilator Unit.PatientsA total of 24 COPD patients: nine patients requiring ventilatory support because of acute respiratory acidosis due to COPD exacerbation (NPPV group, pH 7.28 +/- 0.02); seven patients successfully managed with medical therapy only (SB group, pH 7.39 +/- 0.04); eight clinically stable, long term mechanically ventilated, COPD patients (IPPV group).MeasurementsRespiratory mechanics during a period of unsupported breathing.ResultsA rapid shallow breathing, in the presence of a high drive to breath and a high diaphragmatic tension-time index (TT(di)), was found in NPPV and IPPV groups compared to the SB group (f/V (T) ratio: 118 +/- 43 and 137 +/- 65, respectively, versus 37 +/- 12 breaths/min/L; P (0.1): 5.0 +/- 1.0 and 5.4 +/- 1.4, respectively, versus 2.2 +/- 0.2 cmH(2)O, TT(di): 0.168 +/- 0.035 and 0.161 +/- 0.039, respectively, versus 0.057 +/- 0.033); at variance, PEEPi(dyn) was greater in IPPV compared to the other two groups. A significant relationship was observed between TT(di) ratio and f/V (T) (Rho 0.756).ConclusionDuring the early phases of an acute exacerbation, patients with COPD and acute respiratory failure had an imbalance between the decreased capacity of the respiratory muscles to generate pressure and the increased respiratory load. This imbalance was similar to that recorded in patients with COPD and chronic ventilatory failure. In both groups, the imbalance was associated with rapid shallow breathing. Among the mechanical constraints to ventilation, only PEEPi,dyn was different between acute and chronic patients with ventilatory failure.

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