Pregnancy enhances the antinociceptive effects of extradural lignocaine in the rat

Sex, age, and genetics in anesthesia

PURPOSE OF REVIEW

Pharmacology is one of the corner stones of anesthesia. Outcome of anesthesia is related, in part, to both pharmacodynamics and pharmacokinetics of anesthetic drugs. Recent developments have indicated that among individuals, major differences exist in pharmacological effects. In this regard, sex, age, and genetic profile are increasingly considered to be of importance.

RECENT FINDINGS

For a number of anesthetic drugs, it has been demonstrated that sex differences influence their effects and thus can alter the outcome of anesthesia. Also other genetically determined differences than sex are important.

SUMMARY

In the future, it is expected that an individual's pharmacological needs will be based on age, sex, and genomics.

Anesthetic efficacy and pain induced by dental anesthesia: the influence of gender and menstrual cycle

OBJECTIVE

To assess the influence of the menstrual cycle and oral contraceptives on pain sensitivity and local anesthetic effectiveness.

STUDY DESIGN

Thirty volunteers were designated into 3 groups (n = 10): group 1, women using contraceptives; group 2, women not using contraceptives; and group 3, men. Groups 1 and 2 had a buccal infiltration of 2% lidocaine with 1:100,000 epinephrine at the upper-right canine during each one of the 5 phases of the menstrual cycle and group 3 at a randomly selected day. Pain threshold, latency period, and pulpal anesthesia were measured with an electrical pulp tester. Injection discomfort was recorded. Data were analyzed with Friedman and Kruskal-Wallis tests.

RESULTS

Pain threshold was higher in men; however, there were no significant differences (P > .05) in anesthetic duration and injection discomfort.

CONCLUSION

Injection discomfort and clinical effectiveness of local anesthetics are not related to sex, phases of the menstrual cycle, or use of oral contraceptives.

Spread of subarachnoid block, intraoperative local anaesthetic requirements and postoperative analgesic requirements in Caesarean section and total abdominal hysterectomy

BACKGROUND

Pregnancy is associated with a higher spread of subarachnoid anaesthesia and increased pain threshold. The study was designed to assess the spread of subarachnoid block and the intra- and postoperative analgesic requirements in pregnant vs non-pregnant women.

METHODS

We assessed the level of subarachnoid anaesthesia after 1.8 ml of hyperbaric lidocaine 5% and the postoperative analgesic requirements in women undergoing Caesarean section and undergoing abdominal hysterectomy (30 each group). Intraoperatively epidural ropivacaine was given as required. All patients received 10 ml of ropivacaine 0.2% epidurally 2, 10, and 24 h after operation and the VAS pain score was assessed. They also had access to patient controlled analgesia i.v. morphine.

RESULTS

Duration of surgery was 64 (13.7) vs 127 (33.8) min (P<0.0001) in the pregnant and non-pregnant groups. Ten minutes after subarachnoid injection, sensory block was higher by three dermatomes in the pregnant group (P<0.0001). Time to first ropivacaine dose was 37 (19.7) vs 19 (12.2) min (P<0.001) and the ropivacaine normalized for the duration of anaesthesia was 0.8 (0.6) vs 1.3 (0.5) mg(-1) (P=0.001) in the pregnant and non-pregnant groups, respectively. The time between the first and second ropivacaine dose was similar in the two groups (P=0.070). Fewer pregnant women (81 vs 100%) required ropivacaine intraoperatively (P=0.017). The VAS scores were similar but parturients consumed more i.v. morphine (33 (14) vs 24 (12) mg, P=0.016) during the first 24 h after operation.

CONCLUSIONS

Pregnant patients exhibited a higher level of subarachnoid sensory block and required more i.v. morphine after operation.

Does pregnancy increase the efficacy of lumbar epidural anesthesia?

Pregnancy has been reported to enhance the sensitivity of nerves to local anesthetics and to decrease anesthetic requirements during regional anesthesia. In this study, whether pregnancy increased the efficacy of lumbar epidural anesthesia was evaluated. Two populations (14 pregnant and 14 non-pregnant women) undergoing lumbar epidural anesthesia were studied and received 17 mL of 2% lidocaine-epinephrine (1: 200,000). The pain threshold response after repeated electrical stimulation was used to assess sensory blockade at the L2, S1 and S3 dermatomes. Motor blockade was evaluated using the Bromage score. Demographic data except for weight were comparable between the two groups. There was a significant difference in cephalad spread of anesthesia between the groups. No significant differences in pain threshold or onset of sensory blockade at the L2, S1 or S3 segments were found between the groups. The pain thresholds at the S1 and S3 dermatomes were significantly lower than that at L2 within each group. The mean onset times at the S1 and S3 dermatomes were significantly longer than that at L2 within each group. No differences in Bromage score were found between the groups. In pregnant women, cephalad spread of epidural anesthesia was facilitated but latency of blockade, density and motor blockade were not. It takes over 25 min to achieve satisfactory blockade at sacral segments. Those who perform lumbar epidural anesthesia alone for cesarean section should consider the use of additives (e.g. fentanyl, bicarbonate) to enhance the block, or a greater volume of local anesthetic.

Sex-related hormonal influences on pain and analgesic responses

Considerable evidence indicates sex-related differences in pain responses and in the effectiveness of various analgesic agents. Specifically, females are at greater risk for experiencing many forms of clinical pain and are more sensitive to experimentally induced pain relative to males. Regarding analgesic responses, nonhuman animal studies indicate greater opioid analgesia for males, while a limited human literature suggests the opposite. Though the mechanisms underlying these effects remain unclear, the influence of gonadal hormones on nociceptive processing represents one plausible pathway whereby such sex differences could emerge. The present article reviews the complex literature concerning sex steroid effects on pain responses and analgesia. First, nonhuman animal research related to hormonal effects on nociceptive sensitivity and analgesic responses is presented. Next, human studies regarding gonadal hormonal influences on experimental pain responses are reviewed. Several potential mechanisms underlying hormonal effects on nociceptive processing are discussed, including hormonal effects to both peripheral and central nervous system pathways involved in pain transmission. Finally, based on these findings we draw several conclusions and make specific recommendations that will guide future research as it attempts to elucidate the magnitude and importance of sex-related hormonal effects on the experience of pain.