Upper limb muscle strength and endurance as predictors of successful extubation in mechanically ventilated patients : a predictive correlational study

Abstract

Mechanical ventilation temporarily replaces or supports breathing in the critically ill patient. Prolonged mechanical ventilation is associated with an increase in nosocomial infections, respiratory muscle weakness and intensive care unit acquired weakness (ICU-AW). Since the inception of mechanical ventilators, successful weaning and extubation failure has always been a challenge that physiotherapists, nurses and physicians grapple with. Due to the complexity of determining extubation readiness 10% to 20% of patients still fail extubation and therefore predictors for successful extubation are paramount. Different parameters including, rapid shallow breathing index (RSBI), partial pressure of arterial oxygen to fraction of inspired oxygen ratio (PaO2/FiO2 ratio) and maximum inspiratory pressure (MIP) were used to predict extubation readiness, but none could be used in isolation. Failed extubation increases the intensive care unit (ICU) length of stay, the hospital length of stay, the financial costs and it decreases the patient’s functional ability, muscle strength and health-related quality of life (HRQOL).

Early mobilisation and rehabilitation according to a patient centred program are essential to decrease the development of peripheral muscle weakness and respiratory muscle weakness. Previous research studies demonstrated associations between respiratory muscle weakness and peripheral muscle weakness as well as possible associations between successful extubation, exercise endurance and upper limb muscle strength respectively.

The aim of this study was to determine if upper limb muscle strength and exercise endurance can be used by physiotherapists as predictors of successful extubation in mechanically ventilated patients. The statistical objective of this study was to develop a prediction equation based on upper limb muscle strength and exercise endurance for outcome of extubation.

A total of 463 patients were recruited from the medical and trauma ICU’s of a large Academic hospital. Fifty seven of these patients were eligible for testing. Peripheral and respiratory muscle strength was evaluated using the Oxford grading scale, Medical Research Council score (MRC-score), handgrip dynamometer and MIP. Exercise endurance was tested while patients were riding the MOTOmed® letto2 cycle ergometer for six minutes with the upper limbs.

In an attempt to determine whether upper limb muscle strength and exercise endurance can predict successful extubation, a prediction equation was developed. Univariable logistic analysis was performed to identify the marginal significant and significant factors to be included in the multivariable logistic regression analysis to develop the final prediction equation. The predictive ability of the prediction equation was assessed using cross validation. Testing was based on a 0.05 level of significance. Data analysis employed STATA version 15.1 software.

The results demonstrated that the exercise endurance (time the patient rode actively) (P = 0.005), general body muscle strength (MRC-score: P = 0.007) and number of days ventilated (P = 0.005) were associated with successful extubation. The handgrip strength (P = 0.061), MIP (P = 0.095) and muscle strength of the sternocleidomastoid (P = 0.053) and trapezius muscles (P = 0.075) were marginally associated with successful extubation. The muscle strength of the deltoid (P = 0.273) and pectoralis major muscles (P = 0.327) were not significantly associated with successful extubation. Due to multicollinearity between muscle strength and exercise endurance, elimination of factors were done. The newly developed prediction equation only included the exercise endurance and the number of days ventilated as the other factors did not contribute to the predictive value of the equation. This newly developed prediction equation had a sensitivity of 81.82% and a specificity of 77.14% to predict successful extubation.

Conclusion: Exercise endurance can be used as predictor of successful extubation in mechanically ventilated patients when physiotherapists apply the newly developed prediction equation ŷ = -1.0064 – (0.17 x active time) + (0.230 x ventilator days) and the value for ŷ is less than or equal to -0.282. Theoretically the equation indicated that if the number of days the patient is ventilated decrease and the exercise endurance increase the risk to fail extubation will decrease. Clinically, successful extubation reduce the ICU length of stay, hospital length of stay and the development of ICU-AW. It increases the patients’ functional level and HRQOL, therefore the findings of this study have the potential to impact positively on patient outcomes.