Reduced inspiratory muscle endurance following successful weaning from prolonged mechanical ventilation.
OBJECTIVE
Respiratory muscle weakness and decreased endurance have been demonstrated following mechanical ventilation. However, its relationship to the duration of mechanical ventilation is not known. The aim of this study was to assess respiratory muscle endurance and its relationship to the duration of mechanical ventilation.


METHODS
Prospective study.


METHODS
Tertiary teaching hospital ICU.


METHODS
Twenty subjects were recruited for the study who had received mechanical ventilation for > or = 48 h and had been discharged from the ICU.


METHODS
FEV1, FVC, and maximal inspiratory pressure (P(I(max)) at functional residual capacity were recorded. The P(I(max)) attained following resisted inspiration at 30% of the initial P(I(max)) for 2 min was recorded, and the fatigue resistance index (FRI) [P(I(max)) final/P(I(max))initial] was calculated. The duration of ICU length of stay (ICULOS), duration of mechanical ventilation (MVD), duration of weaning (WD), and Charlson comorbidities score (CCS) were also recorded. Relationships between fatigue and other parameters were analyzed using the Spearman correlations (rho).


RESULTS
Subjects were admitted to the ICU for a mean duration of 7.7 days (SD, 3.7 days) and required mechanical ventilation for a mean duration of 4.6 days (SD, 2.5 days). The mean FRI was 0.88 (SD, 0.13), indicating a 12% fall in P(I(max)), and was negatively correlated with MVD (r = -0.65; p = 0.007). No correlations were found between the FRI and FEV1, FVC, ICULOS, WD, or CCS.


CONCLUSIONS
Patients who had received mechanical ventilation for > 48 h have reduced inspiratory muscle endurance that worsens with the duration of mechanical ventilation and is present following successful weaning. These data suggest that patients needing prolonged mechanical ventilation are at risk of respiratory muscle fatigue and may benefit from respiratory muscle training.
Chang
Angela T
AT
Division of Physiotherapy, The University of Queensland, St. Lucia, QLD 4072, Australia. a.chang@shrs.uq.edu.au
Boots
Robert J
RJ
Brown
Michael G
MG
Paratz
Jennifer
J
Hodges
Paul W
PW
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance; D012121:Respiration, Artificial / Q000009:adverse effects*; D012132:Respiratory Muscles / Q000503:physiopathology*; D013997:Time Factors; D015300:Ventilator Weaning