Effects Of Essential Hypertension On Postoperative Pain And Possible Mechanism

Part1Effects of untreated preoperative essential hypertension on postoperative pain after major abdominal surgeryObjective:Hypertension has been associated with hypoalgesia. This prospective study was designed to test the effects of untreated preoperative essential hypertension on postoperative pain intensity and morphine requirement in intravenous patient-controlled analgesia pumb after major abdominal surgery.Methods:One hundred and thirty-eight patients scheduled for abdominal surgery were included in this study. One hundred and thirty-one (62untreated essential hypertensives and69normotensives) completed the study. All patients received standardized anaesthetic with intraoperative fentanyl and patient-controlled analgesia with morphine for48hours postoperatively as the only analgesics. Pain intensity scores, cumulative morphine requirement, and side-effects were recorded until48hours postoperatively.Results:All patients with essential hypertension had systolic hypertension,91.9%having grade1severity and8.1%patients grade2severity.16.1%of essential hypertensive patients had elevated diastolic blood pressure. Essential hypertensive patients had significantly lower total postoperative morphine requirement (P<0.01), and significantly lower verbal rating scale (VRS) postoperative pain intensity scores at rest (P<0.01) and with coughing (P<0.01) over48hours than normotensive patients. There were no postoperative differences in incidence of postoperative nausea (P=0.898), vomiting (P=0.907) and pruritus (P=0.251) between the two groups.Conclusion:Untreated essential hypertension is associated with significantly reduced total morphine requirement and pain intensity scores postoperatively. These morphine-sparing effects suggest hypertension-associated hypoalgesia in postoperative pam. Part2Effects of phosphorylated p38mitogen-activated protein kinase on incisional pain in spontaneously hypertensive ratsObjective:To investigate the changes of pain behaviour, Hindpaw Withdrawal Mechanical Threshold (HWMT), Hindpaw Withdrawal Thermal Latency (HWTL) and spinal phosphorylated p38mitogen-activated protein kinase in a model of incisional pain in spontaneously hypertensive rats (SHRs) and Wistar Kyoto rats (WKYs).Methods:Health adult male SHRs and WKYs weighing300～350gram were divided into two groups:group SHR and group WKY. A1-cm longitudinal incision was made in left hindpaw after anesthesia with2%sodium pentobarbital intraperitoneally (i.p.,40mg/kg body weight). The rats in each group were randomly subdivided into four groups according to time points (preoperative, one day postoperatively, three days postoperatively, five days postoperatively). After rats received a plantar incision surgery, Hindpaw Withdrawal Mechanical Threshold (HWMT) and Hindpaw Withdrawal Thermal Latency (HWTL) were determined by von Frey filaments and radiant heat, respectively, and the number of phosphorylated p38immunoreactive cells in spinal cord was quantified to determine p38activation at different time points after incision between the two groups.Results:There was no difference in the weight between the two groups (P>0.05). SHRs had significantly higher systolic blood pressure and diastolic blood pressure than WKYs (P<0.05). HWMT decreased after operation in both groups, and SHRs had significantly higher mechanical thresholds both preoperatively and postoperatively than WKYs (P<0.05). HWTL decreased after operation in both groups, but there was no significant difference in thermal Latency between the two groups both preoperatively and postoperatively (P>0.05). A significant decrease in number of phosphorylated p38immunoreactive cells was observed in spinal cord of SHRs from preoperative to5days after the incision (P<0.05).Conclusion:SHRs had higher mechanical thresholds both preoperatively and postoperatively than WKYs. Inhibition of p38MAPK maybe contributes to hypoalgesia in spontaneously hypertensive rats.