Continuous assessment of labour pain using handgrip force

BACKGROUND Assessment of dynamic changes in painful experiences, such as labour, using conventional rating scales (eg, numerical rating scale [NRS]) has limitations. An alternative for continuous pain evaluation could be a signal generated by voluntary action of the parturient. Remifentanil administration for obstetric analgesia could be improved by these dynamic measures of labour pain. In the present study, handgrip force was measured by a dynamometer to signal labour pain. OBJECTIVES To evaluate: whether continuous monitoring of labour pain using handgrip force allows for determination of pain measurement during contractions; and the correlation between handgrip force and pain intensity on NRS. METHODS The present observational, single-centre study included 43 parturients. After calibration of the dynamometer for individual hand muscle strength, pain was recorded during early and late labour using a dynamometer and an NRS. The primary end point was the correlation coefficient between NRS ratings and peak intensity recorded by the dynamometer. RESULTS All dynamometer-registered readings were also registered by the external tocogram. All contractions recorded by external tocogram were also registered by the dynamometer. Handgrip force was moderately correlated with pain scores on the NRS. Mean handgrip force during contractions had the highest correlation coefficient (Pearson's r=0.67) compared with peak handgrip force (r=0.56) and area under the curve of handgrip force (r=0.55). CONCLUSIONS Pain intensity and duration can be assessed continuously using handgrip force measured via a dynamometer. The feedback of intensity and duration of pain could optimize patient-controlled remifentantil application for obstetric analgesia and other situations of highly variable pain intensity.