In order to treat pain optimally, the Emergency Medical Service (EMS) clinician needs to be able to make a reasonable estimation of the severity of the pain. It is hypothesised that various physiological parameters will change as a response to pain.

In a cohort of patients who were seen by EMS clinicians, to relate the patients' estimated intensity of pain to various physiological parameters.

Patients who called for EMS due to pain in a part of western Sweden were included. The intensity of pain was assessed according to the visual analogue scale (VAS) or the Numerical Rating Scale (NRS). The following were assessed the same time as pain on EMS arrival: heart rate, systolic and diastolic blood pressure, respiratory rate, moist skin and paleness.

In all, 19,908 patients (≥18 years), were studied (51% women). There were significant associations between intensity of pain and the respiratory rate (r = 0.198; p < 0.0001), heart rate (r = 0.037; p < 0.0001), systolic blood pressure (r = −0.029; p < 0.0001), moist skin (r = 0.143; p < 0.0001) and paleness (r = 0.171; p < 0.0001). The strongest association was found with respiratory rate among patients aged 18–64 years (r = 0.258; p < 0.0001).

In the prehospital setting, there were significant but weak correlations between intensity of pain and physiological parameters.

The most clinically relevant association was found with an increased respiratory rate and presence of pale and moist skin among patients aged < 65 years. Among younger patients, respiratory rate may support in the clinical evaluation of pain.