A. Ewen et al., HYPERALGESIA DURING SEDATION - EFFECTS OF BARBITURATES AND PROPOFOL IN THE RAT, Canadian journal of anaesthesia, 42(6), 1995, pp. 532-540
Subhypnotic doses of thiopentone are considered to possess antianalges
ic or hyperalgesic properties In this study, we have tested the hypoth
esis that the coincidence of sedation and hyperalgesia is a property o
f both barbiturate and non-barbiturate anaesthetic agents. In a random
ized, prospective blinded study the effects of slow (20 min) iv infusi
ons of thiopentone, pentobarbitone, methohexitone or propofol on nocic
eptive threshold were measured in rats by tail pressure analgesimetry
and compared with saline-infused control animals. Nociceptive threshol
ds were correlated with measurements of plasma drug concentrations and
behavioural assessments, Comparison of pre-infusion nociceptive thres
hold with the lowest threshold obtained during drug infusion revealed
decreases in all four treatment groups. As a percentage of the pre-inf
usion values, the decreases were: thiopentone: 42.5% (P < 0.001), pent
obarbitone: 27.8% (P = 0.014), methohexitone: 24.9% (P = 0.013), propo
fol: 21.6% (P = 0.006). There were no changer in nociceptive threshold
in the control groups. The relationship between nociceptive threshold
and plasma drug concentration was usually characterized by an initial
decline followed by a rise in nociceptive threshold as the plasma con
centration and degree of sedation increased The results support the hy
pothesis that hyperalgesia is a property of different anaesthetic agen
ts when administered at sub-hynotic concentrations.