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Relaxation rate of the inspiratory muscles and prediction of extubation outcome in prematurely born infants

Presented at the Neonatal Society 2016 Autumn Meeting.

Dassios T1, Kaltsogianni O1, Greenough A2,3

1 King’s College Hospital NHS Foundation Trust, London
2 Division of Asthma, Allergy and Lung Biology, MRC-Asthma UK Centre in Allergic Mechanisms of Asthma, King’s College London, UK
3 National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy’s and St Thomas’ NHS Foundation Trust and King’s College London; UK

Background: The functional state of the inspiratory muscles and the risk for muscle fatigue can be assessed by measuring the rate of relaxation of the inspiratory muscles. We aimed to assess whether the inspiratory muscle time constant of relaxation (τ) predicted extubation outcome in mechanically ventilated, premature infants.

Methods: Forty-six mechanically ventilated premature infants with a median gestational age of 26 [interquartile range (IQR) 25-29] weeks were prospectively studied. τ was calculated from the reciprocal of the slope of the airway pressure decline as a function of time. Measurements of τwere done during 5 to 10 minutes of a spontaneous breathing test (SBT) within thirty minutes prior to extubation. During the first and last minute of the spontaneous breathing trial τ 1 and τ 2respectively were assessed and the difference between them was calculated (Δτ).

Results: The median τ 2 was significantly higher in infants that failed extubation [20.7 (IQR 12.9-34.7)] compared to infants that succeeded extubation [8.2 (IQR 6.2-17.8), p=0.002]. The median Δτ was significantly higher in infants that failed extubation [10.3 (IQR 4.4-23.9)] compared to infants that succeeded extubation [-1.63 (IQR -5.7-0.3), p=0.001]. Extubation failure was associated with τ 2 (p=0.011) and Δτ (p=0.010) after correcting for postmenstrual age, patent ductus arteriosus and intraventricular haemorrhage. Receiver operator characteristic curve analysis demonstrated that τ 2 and Δτ predicted extubation failure with an area under the curve of 0.790 and 0.937 respectively. A Δτ of +1.02 predicted extubation failure with 94% sensitivity and 83% specificity.

Conclusion: The inspiratory muscle time constant of relaxation during a SBT was significantly greater in infants who failed extubation and could be used to predict extubation outcome in prematurely born infants.

Corresponding author: theodore.dassios@kcl.ac.uk

Goldstone JC, Green M, Moxham J. Maximum relaxation rate of the diaphragm during weaning from mechanical ventilation. Thorax. 1994;49(1):54-60.

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