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LETTER TO THE EDITOR

Spinal Block with 1.5 mg Hyperbaric Bupivacaine: Not Successful for Everyone

Department of Pharmacology and Anesthesiology; University of Padova, Italy; micarron{at}libero.it

To the Editor:

A recent report by Wassef et al. (1) described successful spinal block with 1.5 mg bupivacaine for short perianal surgery. Our department has been conducting investigational protocols on spinal anesthesia (2,3) including a dose-finding study with hyperbaric bupivacaine for perianal surgery. Fifty-four of 160 planned patients with perianal pathologies (hemorrhoids, fistulas, anal lesions) have been recruited and randomly assigned to receive 2, 3, 4, or 5 mg of hyperbaric 0.5% bupivacaine intrathecally. Protocol stipulations include switching failed spinal to general anesthesia and termination of a dose-group for failure rates greater than 20% at interim analyses.

From the available data, block efficacy by bupivacaine seems dose-dependent: low at 2 mg (20%), near maximal (90%) at 3 mg, and maximal (100%) at the highest doses. At 2 mg, specifically, bupivacaine provides a block (i.e., pin-prick anesthesia of S₄ dermatome [86 ± 37 min], inability of walking [129 ± 18 min] and of voiding [184 ± 36 min]) that is effective for surgery only in one of five patients. For this reason, 2 mg bupivacaine will not be tested further under this protocol.

Recovery times reported by Wassef et al. in their 1.5 mg bupivacaine group are similar to those found in our 2 mg group. Only two patients in the 1.5 mg group by Wassef et al. (1) (5%) required intraoperative sedation and analgesics to alleviate "discomfort," whereas we had an 80% failure rate in our 2 mg group. After the publication by Wassef et al., we asked the drug manufacturer (Recordati Chemical Pharmaceutical Industry, Milan, Italy) to check the actual concentration of bupivacaine. An HPLC analysis on three unopened vials (batch number 018, expiration date June 2009) yielded a 97%–103% of the labeled amount (mean bupivacaine concentration 4.94 mg/mL). Our patient population seems to be similar to the Wassef et al. groups as far as clinical features and had no significant pain symptoms before surgery. All spinal anesthetics were performed by staff anesthesiologists experienced with the technique. "Clusters" of failed spinals even with higher doses of bupivacaine (9–12 mg) can be found in the literature (4–6). In those cases, authors were not able to find a clear reason for the failure and their hypothetical explanations dealt with the "heat intolerance" of bupivacaine or patient related factors such as diabetes or other anatomical or biochemical abnormalities (6,7) that may cause resistance to local anesthetics. We reviewed charts and blood tests of our patients and none of them has diabetes. We did not test sensitivity to local anesthetics in individual patients.

Failure of spinal anesthesia occurred only at a 2 mg dose of bupivacaine suggesting that, at least in our patients, this dose may be not sufficient to ensure intraoperative analgesia for perianal surgery in all patient populations, a finding worth of note.

REFERENCES

1. Wassef MR, Michaels EI, Rangel JM, Tsyrlin AT. Spinal perianal block: a prospective, randomized, double-blind comparison with spinal saddle block. Anesth Analg 2007;104:1594–6[Abstract/Free Full Text]
2. Carron M, Innocente F, Veronese S, Miotto D, Pilati P, Rossi CR, Ori C. Subarachnoid anesthesia for loco-regional antiblastic perfusion with circulatory block (stop-flow perfusion). Minerva Anestesiol 2006;72:37–45[Web of Science][Medline]
3. Carron M, Freo U, Innocente F, Veronese S, Pilati P, Jevtovic-Todorovic V, Ori C. Recovery profiles of general anesthesia and spinal anesthesia for chemotherapeutic perfusion with circulatory block (stop-flow perfusion). Anesth Analg. In press
4. Calthorpe N. Inadequate spinal anaesthesia with 0.5% Marcain Heavy (Batch 2016). Int J Obstet Anesth 2004;13:131[Web of Science][Medline]
5. Wood M, Ismail F. Inadequate spinal anaesthesia with 0.5% Marcain Heavy (Batch 1961). Int J Obstet Anesth 2003;12:310–1[Medline]
6. Smiley RM, Redai I. More failed spinal anesthetics with hyperbaric bupivacaine. Int J Obstet Anesth 2004;13:131–4[Web of Science][Medline]
7. Hoppe J, Popham P. Complete failure of spinal anaesthesia in obstetrics. Int J Obstet Anesth 2007;16:250–5[Web of Science][Medline]

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