Male and female, older and younger patients feel pain differently, say Australian researchers, which may have significant implications for 2 physiological pain assessment methods currently under development.
According to physicians at the University of Western Australia and Royal Perth Hospital a patient's gender and, to a lesser extent, age have an effect on the body's autonomic and hemodynamic responses to pain, including heart rate variability and sympathovagal balance. Specifically, men showed greater cardiac sympathetic activity and a stronger response to higher pain levels than women did.
These findings, published in the June issue of the European Journal of Anaesthesiology, are important because 2 new methods of measuring pain tap the sympathovagal balance for their assessments, without taking sex or age into account.
The new methods, skin conductance and the surgical stress index, have yet to be fully validated. But they may be potentially useful in assessing the nociceptive/anti-nociceptive balance in perioperative patients.
Skin conductance assesses sympathetically controlled sweat gland filling. The surgical stress index measures changes in both the plethysmographic pulse wave amplitude and the heartbeat interval - essentially assessing the peripheral and cardiac sympathetic-parasympathetic balance. Both methods attempt to monitor pain, whether solely or in part, by assessing sympathetic tone.
Both methods sidestep the limitations of pain assessment through patient cooperation with score systems such as the visual analogue or the numeric rating scale, which fail those patients who are uncommunicative, anesthetized, sedated or very young. But the researchers suggest that incorporating data about age and sex may improve their accuracy.
"For current clinical practice, our results suggest that changes in [heart rate] cannot be used as meaningful discriminators of levels of acute post-operative pain," the study's authors write, "and that blood pressure in this context may only be useful in male patients."
Rob Murphy
