Epidural anesthesia: Simulated intravascular test dose with S(+) ketamine, lidocaine and adrenaline. A prospective, randomized, double blind and placebo controlled study☆

Abstract Objective The use of a test dose in epidural anesthesia is a safety recommendation. However, specificity and sensitivity of the drugs used with this indication have not been conclusive. The main objective of this study was to compare the effectiveness and the adverse effects of a simulated intravascular test dose of adrenaline, lidocaine and S(+)-ketamine. Material and methods A prospective, randomized, double blinded, placebo controlled study was designed. ASA I patients scheduled for elective surgery were included. These were randomized to the following study groups: S(+)-ketamine 0.5 mg kg −1 (S+K group), 5% lidocaine 1.5 mg kg −1 (L5% group), adrenaline 15 μg (ADR group), and physiological saline 3 ml (SF group; control group). An evaluation was made during the first 15 min after the study drug was administered. Variables including heart rate (HR) systolic and diastolic blood pressure (sBP and dBP), mean arterial pressure (MAP), and SpO 2 were recorded at 0 min (baseline) and at 2, 5, 8, 10 and 15 min after drug injection. An increase of at least 20 beats per minute (bpm) in relation to the baseline measurement was considered a positive result, as was an increase sBP >15 mm Hg. The clinical effects described as related to IV injection of the study drugs recorded were sedation-hypnosis, dizziness, nystagmus, metallic taste perception, perioral or facial paresthesias, tinnitus, as well as any other effect the patients mentioned. Sensitivity and specificity were calculated as was the percent increase in the parameters in order to see if these were clinically useful. Results A total of 80 patients, 20 per group, were included. The sBP, dBP, and MAP were significantly raised at the 2, 5, 8 and 10 min measurements in the S(+)K group compared to the rest of the groups ( p p Sensitivity and specificity were high, and significant in the S(+)K group from minute 2 to minute 8 compared with the placebo group, as well as percentage points differences in the same interval. There were significant differences in the incidence of sedation-hypnosis, nystagmus and dizziness, which were more frequent in the S(+)K group. There were no differences in the incidence of metallic taste, perioral and facial paresthesias or tinnitus. The effects in the S(+)K group always occurred before minute 5 after drug injection. Conclusion Both lidocaine and adrenaline at the scheduled doses showed low sensitivity and specificity as a simulated IV epidural test dose. S(+)-ketamine could be a feasible marker after accidental IV injection during epidural anesthesia or analgesia.