Nitrous Oxide Enhances the Level of Sensory Block Produced by Intrathecal Lidocaine

We examined the effect of nitrous oxide (N2 O) administration on the level of sensory block produced by intrathecal lidocaine in patients undergoing transurethral procedures.Twenty minutes after subarachnoid injection of 100 mg (5%) hyperbaric lidocaine, the level of block to pressure sensation was assessed. After establishing the baseline sensory block, patients were randomly assigned to receive either 50% nitrogen (control group) or 50% N2 O in oxygen for 10 min, and the sensory level was reassessed. All patients then received 35% oxygen for 5 min, and the level of block to pressure was assessed again. Changes were measured in centimeters and standardized by dividing those results by the height of patients (in centimeters). Ten minutes after nitrogen or N2 O administration, a 3.8-cm regression of sensory block was found in the control group, and a 1.8-cm cephalad increase was found in the treatment group (P < 0.0001). Discontinuation of N2 O for 5 min resulted in a rapid regression of the level of sensory block (4 cm in the N2 O group versus 1.9 cm in the control group, P < 0.0001). However, 5 min after discontinuation of N2 O, the overall regression of the sensory block in the control group, when measured from the baseline, was 5.7 cm versus 2.2 cm in the N2 O group (P < 0.001). The differences between the two groups before standardization are consistent with those after standardization (t = 9.02 at 10 min, t = 4.24 at 15 min, and t = 3.97 for the overall change at 15 min). The results suggest that inhalation of 50% N2 O enhances the level of sensory block produced by intrathecal lidocaine. ImplicationsWe measured the level of sensory block produced by subarachnoid anesthesia with lidocaine before and after inhalation of 50% nitrous oxide for 10 min. Nitrous oxide enhanced the level of subarachnoid anesthesia with minimal hemodynamic effects. These findings are of clinical importance when subarachnoid anesthesia subsides before the completion of surgery.(Anesth Analg 1997;85:1108-11

Assessment of the Level of Sensory Block After Subarachnoid Anesthesia Using a Pressure Palpator

In a cross-over study, we compared two methods of assessing the level of sensory block during subarachnoid anesthesiathe traditional pinprick sensation or a novel pressure palpator exerting a pressure of 650 g. Fifty patients scheduled for transurethral surgery under subarachnoid anesthesia were randomly assigned to be tested for spread of sensory block. In Group 1, the pressure palpator was followed by pinprick; in Group 2, the reverse sequence was used. Evaluation was performed 15 and 25 min after the subarachnoid injection of 2 mL of 5% lidocaine hyperbaric solution. In Group 1, the level of sensory block assessed with the pressure palpator was 1.7 +/- 3.2 cm (0.5 +/- 1.2 dermatomes) higher than that with the pinprick at 15 min, and 2.2 +/- 3.4 cm (0.6 +/- 1.0 dermatomes) higher than that with the pinprick 25 min after the block. In Group 2, the difference was accentuated. The level of sensory block assessed by pinprick 15 min after subarachnoid lidocaine was 5.7 +/- 4.8 cm (1.2 +/- 0.9 dermatomes) lower than the level with the pressure palpator, and 4.2 +/- 3.3 cm (0.9 +/- 0.6 dermatomes) lower than that with the pressure palpator at 25 min. In all instances, the pressure palpator gave a significantly higher assessment than the pinprick. We conclude that the pressure palpator, when preceded by the pinprick test, is associated with an increased threshold. This method may be useful in assessing the sensory block produced by subarachnoid anesthesia. ImplicationsA novel pressure palpator that maintains the integrity of the epidermis was used to assess the level of sensory block after subarachnoid anesthesia and was compared with the standard method of the pinprick sensation. This method assessed the block consistently higher than the pinprick method, but it may have advantages as a noninvasive sensory test.(Anesth Analg 1999;88:398-401

Preoperative gabapentin: the effect on ropivacaine subarachnoid block and hemodynamics

Gabapentin is an adjuvant analgesic and may enhance the spread of subarachnoid block. We investigated the effects of pretreatment with gabapentin on subarachnoid block characteristics and hemodynamics. Seventy patients undergoing transurethral procedures under subarachnoid anesthesia with 2.2 mL of 0.75% ropivacaine were randomly assigned to receive preoperatively 400 mg of gabapentin 6 hourly, up to a total dose of 1200 mg, or placebo. Sensory and motor blocks were assessed every 30 min until regression of sensory block to L4. At the same time intervals, systolic and diastolic arterial blood pressures and heart rate were recorded. There were no differences between groups in the sensory block levels or degree of motor block. Sensory block 150 min after the subarachnoid injection had regressed to L4 in 26 of 32 patients in the gabapentin group and in 25 of the 33 patients in the control group. Systolic arterial blood pressure was decreased in the gabapentin group (P = 0.002 for the main effect of group, and P = 0.03 at 60 min between the groups). The diastolic arterial blood pressure did not differ between the groups, but overall, the heart rate was more rapid in the gabapentin group (P = 0.002, but only for baseline values between the groups, P = 0.036). Pretreatment with gabapentin had no effect on the spread of sensory block or the regression of motor block but was associated with lower systolic arterial blood pressure values in patients undergoing subarachnoid anesthesia with ropivacaine

Preoperative gabapentin: the effect on ropivacaine subarachnoid block and hemodynamics

BACKGROUND: Gabapentin is an adjuvant analgesic and may enhance the spread of subarachnoid block. We investigated the effects of pretreatment with gabapentin on subarachnoid block characteristics and hemodynamics. METHODS: Seventy patients undergoing transurethral procedures under subarachnoid anesthesia with 2.2 mL of 0.75% ropivacaine were randomly assigned to receive preoperatively 400 mg of gabapentin 6 hourly, up to a total dose of 1200 mg, or placebo. Sensory and motor blocks were assessed every 30 min until regression of sensory block to L4. At the same time intervals, systolic and diastolic arterial blood pressures and heart rate were recorded. RESULTS: There were no differences between groups in the sensory block levels or degree of motor block. Sensory block 150 min after the subarachnoid injection had regressed to L4 in 26 of 32 patients in the gabapentin group and in 25 of the 33 patients in the control group. Systolic arterial blood pressure was decreased in the gabapentin group (P = 0.002 for the main effect of group, and P = 0.03 at 60 min between the groups). The diastolic arterial blood pressure did not differ between the groups, but overall, the heart rate was more rapid in the gabapentin group (P = 0.002, but only for baseline values between the groups, P = 0.036). CONCLUSION: Pretreatment with gabapentin had no effect on the spread of sensory block or the regression of motor block but was associated with lower systolic arterial blood pressure values in patients undergoing subarachnoid anesthesia with ropivacaine