Reliability, validity and usability of the K-force® grip dynamometer to evaluate handgrip-strength in patients with intensive care unit-acquired weakness.

Objective: Handgrip dynamometry is recognised as a method for evaluating volitional muscle strength in the intensive care, but conventional handgrip dynamometers cannot accurately measure grip strength in very weak patients. The aim of this study was to determine the reliability, validity and usability of the K-force^® grip in patients with intensive care unit-acquired weakness.

Design: Evaluation of measurement properties of the K-force^® grip.

Setting: Two Intensive Care Units in The Netherlands.

Participants: Patients diagnosed with intensive care unit-acquired weakness according to a Medical Research Council sum score <48.

Intervention & main measures: Intra- and inter-rater reliability of the K-force^® grip were assessed using the intraclass correlation coefficient. Concurrent validity was examined using calibration weights. The usability was evaluated with the System Usability Scale.

Results: Intra-rater reliability showed an intraclass correlation coefficient of 0.987 for the dominant hand and 0.972 for the non-dominant hand. Inter-rater reliability showed coefficients of 0.944 for the dominant hand and 0.942 for the non-dominant hand. There was a perfect correlation (r = 1) between the K-force® grip and the calibration weights. The usability of the K-force® grip was rated excellent by 11 healthcare professionals with a System Usability Scale score of 86.

Conclusions: The K-force^® grip is a promising new tool for the evaluation of muscle strength in intensive care unit-acquired weakness patients who are too weak to use conventional hand dynamometers.