Lung and Diaphragm Ultrasound as Predictors of Success in Weaning from Mechanical Ventilation

Tenza-Lozano E,  Llamas-Alvarez A, Jaimez-Navarro E et al.

Critical Ultrasound Journal. 2018; 10: 12. doi: 10.1186/s13089-018-0094-3

Aim of Study

‘To assess the reliability and accuracy of lung and diaphragm ultrasound for predicting successful weaning in general critical care patients on mechanical ventilation.’

Design and Location

Elche General university Hospital, Spain

2 studies combined:

1. A cross sectional concordance study (Interobserver agreement study)
2. prospective cohort study.

Methodology

• Cross sectional concordance study (Interobserver agreement study):
  2 sonographers, 50 ITU consecutive patients – measured diaphragm thickening index (TI) and modified Lung Ultrasound Score (LUSm) within 5 hours of each other.
• Prospective cohort study (predictive accuracy study) :
  Physician blinded to results
  All patients on mechanical ventilation between 15^th January 2016 to 15^th April 2017. (separate participants from Study 1) n=69 with signed consent form, > 18 years, >24hours on mechanical ventilation and appropriate for weaning.
  LUSm and TI measured on spontaneous breathing test – pressure support ventilation with PEEP.

Primary Outcome

Concordance between sonographers with LUSm and TI measurements

Assess reliability in TI and LUSm in predicting successful wean from mechanical ventilation.

Statistics

StatsDirect v3.0.194

Cross sectional concordance study – Medians, interquartile ranges, percentages

• Continuous data – unpaired Students t test, Mann-Whitney U test and Wilcoxon test
• Categorical data – chi-squared or Fisher’s exact test
• LUSm – quadratic weighted kappa coefficient
• TI – intraclass correlation coefficient, Bland-Altman Method

Prospective cohort study

• Area under the curve, sensitivities, specificities, likelihood ratios,
• Binary logistic regression as independent variables

Results

Interobserver agreement study :

• LUSm – Quadratic weight kappa valve for LUSm = 0.95 (95% CI = 0.92-0.98) –> substantial interobserver agreement
• TI – ICC 0.78 – 95% CI 0.65-0.87 –> moderate-good interobserver agreement,

Prospective Cohort study:

• No significant difference in baseline characteristics
• Statistically significant variables between successful wean and failed: COPD, time on mechanical ventilation, o2 saturations, ICU mortality, hospital mortality, ICU stay.
• LUSm – 3 point difference
• TI – 11% difference

Prognostic accuracy – LUSm >7, TI <24% indicates increased risk of weaning failure.

Conclusions/Discussions

Interobserver agreement excellent for LUSm and good/moderate for TI.

Low TI or high LUSm indicates increased risk of weaning failure.

Despite LUSm being a new parameter, comparable with LUS in other papers.

Findings consistent with similar papers

Stated Limitations from the Study

Small sample size

Standardisation of ultrasound technique required, definitions required (failed wean) and protocol required

Discussion from Journal Club Meeting (?Change of Practice)

Value of study: what additional benefit will ultrasound give to current practice?

More data required regarding TI/sample sizes/numbers of sonographers

Whose remit does this fall under – anaesthetics/ITU/dedicated sonography or radiology team

Summary by Dr A Harris. Journal Club Meeting 04 April 2019.

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