Very-low-dose ketamine (0.05 mg . kg(-1) . h(-1)) potentiated morphine-ropivacaine analgesia and reduced postthoracotomy pain.

N-methyl-D-aspartate (NMDA) receptor antagonists enhance opioid-induced analgesia. The plasma concentration of ketamine, an NMDA receptor antagonist that enhances epidural morphine-and-bupivacaine-induced analgesia, is not known. We examined 24 patients with lung carcinoma or metastatic lung tumor who underwent video-assisted thoracic surgery in a placebo-controlled, double-blind manner 4 h after emergence from anesthesia. The morphine + ketamine group (n = 8) and morphine + placebo group (n = 8) received 5 mL volume of 2.5 mg morphine and 0.25% bupivacaine and the placebo + ketamine group (n = 8) received 5 mL volume of saline and 0.25% bupivacaine epidurally at the end of skin closure. Four hours after this anesthesia, in the morphine + ketamine and placebo + ketamine groups, ketamine was administered to successively maintain a stable plasma ketamine concentration of 0, 10, 20, 30, 40, and 50 ng/mL by a target-controlled infusion device, and patients assessed the levels of pain at rest, pain on coughing, somnolence (drowsiness), and nausea using a 100-mm visual analog scale (VAS). In the morphine + placebo group, a placebo (saline) was similarly administered instead of ketamine. In the morphine + ketamine group, the VAS scores for pain at rest and pain on coughing significantly decreased on ketamine administration at a plasma concentration of 20 ng/mL or larger compared with the respective baseline VAS scores (P < 0.05 each). In the placebo + ketamine group, the VAS scores for pain at rest and pain on coughing did not significantly change at any plasma concentration of ketamine as compared to the morphine + placebo group. In the morphine + ketamine group, a plasma concentration of ketamine larger than 20 ng/mL did not further reduce VAS scores for pain at rest and pain on coughing. The VAS scores for drowsiness were comparable among the three groups at any plasma concentration of ketamine. Ketamine at a plasma concentration of 20 ng/mL or larger may enhance epidural morphine-and-bupivacaine-induced analgesia. As an adjunct with epidural morphine-and-bupivacaine and considering the safety of small doses, the minimal plasma concentration of ketamine given IV may be approximately 20 ng/mL.

CPTs are significantly reduced after parturition. However, this reduction does not appear to be significantly correlated with the reduction in serum progesterone levels.

Ropivacaine, 1%, administered in the lower thoracic epidural space, induces sensory blockade to cold and pinprick in the S1 dermatome more frequently than 2% mepivacaine.

The effects of intravenous oxytocin on thoracic epidural pressure during cesarean section were studied in 90 parturients (American Society of Anesthesiologists physical atatus class I or II) after obtaining informed consent. The subjects were randomized to either a control (control group; n=30), bolus (bolus group; n=30) or drip treatment group (drip group; n=30). The subjects were anesthetized with 11 approximately 12 mg of intrathecal isobaric bupivacaine (0.5%). An epidural catheter placed at Th 11/12 was connected to a pressure transducer to continuously monitor thoracic epidural pressure. Ten units of oxytocin were administered over 30 seconds in the bolus group and over 5 minutes in the drip group after fetus delivery. We analyzed epidural pressure, mean blood pressure, and heart rate, until 5 minutes after fetus delivery. Epidural pressures in both bolus and drip groups increased after fetus delivery compared with control group (P<0.0001). Epidural pressure immediately after placental delivery in the bolus group was higher than in the control group (p<0.0001) and epidural pressure at 5 minutes after fetus delivery in the drip group was higher than in the control group (p=0.0452). There were no significant differences in changes in blood pressure and heart rate among the three groups. We concluded that the increase in epidural pressure with intravenous administration of oxytocin 10 units over 5 minutes was lower than with intravenous administration of oxytocin 10 units over 30 seconds after fetus delivery.