Are Changes in Diaphragm Thickness During Mechanical Ventilation Associated With Outcomes? A Prospective Multi-Centre Cohort Study
CCCF ePoster library. Sklar M. Oct 31, 2016; 150894; 16
Dr. Michael Sklar
Dr. Michael Sklar
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Topic: Clinical Trial

Are Changes in Diaphragm Thickness During Mechanical Ventilation Associated With Outcomes? A Prospective Multi-Centre Cohort Study


Sklar, Michael C1; Fan Eddy2; Herridge, Margaret S2; Vorona, Stefannie2; Dres Martin2;  Rittayamai, Nuttapol2;  Lanys, Ashley2;  Brace, Debbie3;  Murray, Alistair3; Urrea, Christian3;  Tomlinson, George W2;  Reid, Darlene3; Rubenfeld, Gordon D2; Kavanagh, Brian P2;   Brochard, Laurent J2; Ferguson, Niall D2; Goligher, Ewan C2.

1. Department of Anaesthesia, 2. Interdepartmental Division of Critical Care Medicine, the Department of Physiology, the Institute for Health Policy, Management and Evaluation, and the 3. Department of Physical Therapy, University of Toronto, Toronto, Canada



Abstract:

INTRODUCTION
Changes in diaphragm thickness (Tdi) are common during mechanical ventilation (MV) (1). However, the impact of changes in Tdi on clinical outcomes is unknown and it is uncertain whether targeting specific levels of inspiratory effort during MV would prevent changes in Tdi or accelerate liberation from MV. We aimed to determine whether changes in Tdi during the early course of MV are associated with impaired liberation from MV and to further establish the links between ventilator settings, patient inspiratory effort, changes in Tdi, and clinical outcomes.
 
METHODS
In 3 ICUs, Tdi and diaphragm thickening fraction (TF, a measure of inspiratory effort) were prospectively measured on a daily basis by ultrasound. Patients were classified according to the initial change in Tdi recorded on the first day that the change in Tdi exceeded 10% up to MV day 7. Patient characteristics, ventilator settings, severity of illness scores and outcomes in hospital were recorded. Predicted relationships were analyzed by multivariable regression modelling and causal mediation analysis.
 
RESULTS
We enrolled 212 patients (outcomes available for 207). Initial changes in Tdi occurred early in the course of MV (median MV day 3, IQR 3-5). Consistent with our previous findings (1), the rate and direction of change in Tdi over time were strongly associated with TF in this cohort (p< 0.001). Controlled MV was associated with an accelerated decline in Tdi (p=0.01) mediated by TF (proportion of effect mediated = 0.3, p< 0.01 for mediation effect). Both decreased and increased Tdi were associated with prolonged ventilator dependence (Table 1, Figure 1, log rank p< 0.001), even after adjusting for age, severity of illness, sepsis, and comorbidities. Mean TF below 15% or above 30% over the first 3 days of MV was associated with prolonged ventilator dependence in survivors (Figure 2, adjusted p=0.02) and a higher risk of complications of acute respiratory failure (adjusted p=0.02). The associations between mean TF and these outcomes were mediated by changes in Tdi (proportion mediated 0.44, p=0.05, and 0.29, p=0.02, respectively).
 
CONCLUSIONS
Early changes in diaphragm thickness following initiation of MV are associated with marked differences in clinical outcomes. Both insufficient and excessive inspiratory effort levels are associated with prolonged ventilator dependence due in part to changes in Tdi. Titrating ventilatory support to maintain TF between 15-30% might prevent changes in Tdi and accelerate liberation from MV.
 


References:

1. Goligher EC et al. Evolution of Diaphragm Thickness during Mechanical Ventilation. Impact of Inspiratory Effort. Am J Respir Crit Care Med 2015;192:1080–1088.
 



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