The cutaneous sympathetic blockade associated with labour epidural analgesia: a quasi-experimental study conducted during labour and after delivery.

BACKGROUND

The mechanisms contributing to epidural-related maternal hyperthermia remain unclear. One explanation is that blockade of cholinergic sympathetic nerves prevents active vasodilation and sweating. However, it is not known how labour epidural analgesia affects cutaneous sympathetic function. The aim of this study was to test the hypothesis that labour epidural analgesia inhibits cholinergic and noradrenergic function in the lower, but not the upper, limbs.

METHODS

Twenty women (mean age [range]:33 yr [21-48]) receiving epidural analgesia had upper and lower limb cutaneous sympathetic skin responses assessed during labour (epidural) and after delivery (control). Responses were evoked with auditory stimuli delivered through headphones. Sudomotor skin responses (cholinergic function) were recorded with Ag/AgCl electrodes on the hand and foot (median [range]). Vasomotor skin responses (noradrenergic function) were recorded with laser Doppler flowmetry on the finger and toe (median [range]).

RESULTS

Sudomotor skin response amplitude was less during labour in both the hand (epidural: 0.05 mV [0.00-1.87] vs control: 0.69 mV [0.02-3.73]; P=0.013) and the foot (epidural: 0.00 mV [0.00-0.92] vs control: 0.53 mV [0.05-2.79]; P<0.001). Vasomotor skin response reduction rate was less during labour in the toe (epidural: 6.3% [0.0-41.8] vs control: 18.2% [0.0-53.3]; P<0.001) but was not different between visits in the finger (epidural: 7.9% [0.0-29.9] vs control: 5.0% [0.0-29.8]; P=0.242).

CONCLUSIONS

Labour epidural analgesia can inhibit cholinergic sympathetic outflow to 90% of the body surface. Cholinergic sympathetic blockade could prevent women offloading heat generated during labour. The distribution of cutaneous sympathetic blockade varied among individuals. Cholinergic sympathetic blockade distribution is a potential contributing factor to epidural-related maternal hyperthermia.