Recovery profile of spinal local anesthetics

Introduction: Surgical procedures previously considered too lengthy for the ambulatory setting (e.g. ACL repair) are now being done under spinal anesthesia. The complete recovery profile (ambulation, voiding, complete block resolution) of tetracaine and bupivicaine are now of clinical interest, but are not available in the literature. Methods: After 1RB approval and written informed consent, 12 volunteers (10 males, 2 females), age 36.6 + 1.0 yrs (range: 32-44) underwent spinal anesthesia on three separate occasions with three local anesthetics in random order and in a double blind fashion: lidocaine 100mg, bupivicaine 15mg, and tetracaine 15mg in hyperbaric solutions. The subarachnoid space was entered via the L2-3 interspace using a 24 G Sprotte spinal needle. Each local anesthetic solution was diluted in an equal volume of CSF and injected with the needle oriented cephalad. The level of analgesia to pin-prick was determined with a safety pin moving cephalad in the mid-clavicular line until a dermatome was reached where the pin felt as sharp as over an unblocked dermatome (shoulder). The level of analgesia was then recorded as one dermatome caudad to this point. Testing was performed every five minutes. Results are presented as means + SD. Times to ambulation, voiding and complete resolution of sacral analgesia were noted. MANOVA Wilks' lamda test and Bonferroni method, where appropriate, were used to test for differences among local anesthetics. A p<0.05 was considered significant. Results: 2 segment 4 segment time to time to time to regression regression ambulatio void resolution (min) (min) n (hr) (hr) (hr) (range) (range) (range) Lidocaine 59±11 74±14* 2.9±1* 3.3±1* 3.9±1.4* (.8 - 4.3) Jl 5) (1.5-6) Tetracaine 70±13 93±18 6.2 ± 2* 6.4 ± 2 9.1 ± 3.5" (3 - 9) (3-8.5) (3-14) Bupivacaine 60+15 84 ± 22 4.8±1.4* 5.9±1.4 7.3±1.7* (2.4-7) (3-8) (3-9.5) *bupivacaine < tetracaine # lidocaine < tetracaine or bupivacaine & Lidocaine < Tetracaine Discussion: Times to 2 and 4 segment regression are not different between tetracaine and bupivacaine, however times to ambulation and complete resolution of the block are significantly shorter with bupivicaine. The recovery profiles of the three local anesthetics studied were widely variable between subjects, resulting in some overlap of time to meeting discharge criteria. For ambulatory anesthesia, times to 2 and 4 segment regression may not accurately predict time to readiness for discharge after spinal anesthesia.