by ETS were observed. Statistical analyses were per-formed by one-way analysis of variance and Scheffe Ftest as post hoc comparisons for multiple comparisonsat a significance level of 0.05.

Lidocaine inhibited ETS-evoked contraction in aconcentration dependent manner. Lidocaine pre-treated with ONOO–1 showed a decreased inhibitoryeffect against ETS-evoked contraction (Figure A),although lidocaine pre-treated with decomposedONOO–1 did not. Lidocaine pre-incubated with SIN-1 decreased the inhibitory effect of lidocaine signifi-cantly in an incubation-time dependent manner,although SIN-1 without lidocaine did not affect ETS-evoked contraction (Figure B).

Several hypotheses have been proposed to explainlesser local anesthetic effects in acute inflammatory tis-sues:1 a reduction in the pH of inflammatory tissues,leading to an ionized form of the molecule which hasa lower activity; an increase in vascularity of theinflammatory area, resulting in a rapid removal of thelocal anesthetic from the site of injection; a localincrease in extracellular fluid due to increased vascularpermeability in inflammatory tissues, resulting in adilution of the local anesthetic solution; nerve hyper-

algesia (or hyperexcitability),5 whereby a nerveimpulse is transmitted to the brain following a lowerthan normal threshold stimulus; and certain inflam-matory mediators (e.g., prostaglandins, kinins, ade-nine nucleotides) which could reverse a localanesthetic nerve block partially. In addition to thesehypotheses, we present a decrease of the inhibitoryeffect of lidocaine by ONOO–1 as a new, possibleexplanation for this effect.

Ko Takakura MD PhD*Maki Mizogami MD PhD*Yasushi Ono MD*Kazuyuki Ooshima DDS*Ikunobu Muramatsu PhD†Asahi University School of Dentistry, Gifu, Japan*University of Fukui, Fukui, Japan†E-mail: takakura@dent.asahi-u.ac.jp

RReeffeerreenncceess 1 Jastak JT, Yagiela JA, Donaldson D. Choice of anes-

thetic technique and causes of anesthetic failure. In:Jastak JT, Yagiela JA, Donaldson D (Eds). LocalAnesthesia of the Oral Cavity. Philadelphia: WBSaunders; 1995: 275–85.

2 Punnia-Moorthy A. Buffering capacity of normal andinflamed tissues following the injection of local anaes-thetic solutions. Br J Anaesth 1988; 61: 154–9.

3 Muramatsu I, Nakanishi S, Fujiwara M. Comparisonof the responses to the sensory neuropeptides, sub-stance P, neurokinin A, neurokinin B and calcitoningene-related peptide and to trigeminal nerve stimula-tion in the iris sphincter muscle of the rabbit. Jpn JPharmacol 1987; 44: 85–92.

4 Crow JP, Beckman JS, McCord JM. Sensitivity of theessential zinc–thiolate moiety of yeast alcohol dehydro-genase to hypochlorite and peroxynitrite. Biochemistry1995; 34: 3544–52.

5 Rood JP, Pateromichelakis S. Local anaesthetic failuresdue to an increase in sensory nerve impulses frominflammatory sensitization. J Dent 1982; 10: 201–6.

Appropriate waiting time for noncar-diac surgery following coronary stentinsertion: views of Canadian anethesi-ologists

To the Editor:The insertion of a coronary stent is a common proce-dure for the treatment of patients with cardiovasculardisease. Anesthesiologists and cardiac surgeons are

440 CANADIAN JOURNAL OF ANESTHESIA

FIGURE A) Inhibition by lidocaine (0.2 - 20 mM) pre-treatedwith (open circles) or without (closed circles) peroxynitrite(ONOO-1) 1 mM on contractions produced by electrical trans-mural stimulation (ETS). B) Inhibition by lidocaine pre-incubatedwith N-ethyl-carbamine (SIN-1); (open circles). Inhibitory effectsof lidocaine alone were incubation time-independent (closed cir-cles). Contractions are expressed as mean ± SD of the percentageof ETS-induced contraction (100%) in eight experiments. *P <0.05 compared with zero minute incubation.

often faced with a dilemma about how long to waitbetween stent insertion and a subsequent surgical pro-cedure. Patients may be placed at risk by either a tooshort or too long waiting period. The American HeartAssociation along with the American College ofCardiologists recommend a minimum wait of twoweeks and suggest an ideal waiting period of four to sixweeks, although these guidelines are not based on ran-domized controlled trials.1 It is unclear whetherCanadian anesthesiologists are aware of these guide-lines. The aim of this survey was to describe the viewsof practicing anesthesiologists on the waiting times forelective surgery following insertion of a coronary stent.

A postal survey (along with a reminder eight weekslater) was sent to 2,167 Canadian anesthesiologists inMarch, 2003 seeking their views about the appropri-ate waiting time for unrelated elective surgery follow-ing insertion of a coronary stent. Responders werepresented with a clinical scenario (a 59-yr-old malewith a prior stent insertion, no comorbidities, whorequired an urgent aneurysm repair) and asked toreport a recommended waiting time for three differentlocations (left anterior descending, circumflex or rightcoronary arteries). They were also asked about theexistence of a policy on this issue in their departments.

The response rate was 46%. Most departments ofanesthesiology (97%) do not have an explicit policyregarding the appropriate waiting time between coro-nary stent insertion and elective surgery. Half of theresponders believed their departments ought to havesuch a policy. While there was no consensus aboutwhat this policy ought to be, the majority of thosewho wanted a policy felt that the minimum waitingtime should be four weeks following surgery (Table).Few anesthesiologists felt that the minimum waitingtime should be less than four weeks. A substantial pro-

portion (63%) of Canadian anesthesiologists wereunaware of published or unpublished literature,including published U.S. guidelines, about the appro-priate length of time between the insertion of a stentand a subsequent surgical procedure.

The implications of this study are: 1) Canadiandepartments of anesthesiology consider implementingan explicit policy that sets the waiting time for unre-lated, elective surgery following coronary stent inser-tion, to four weeks or greater; and 2) anesthesiologistsreview published U.S. recommendations.1

Lindsey Patterson FRCA

Duncan Hunter PhD

Andrea Mann BScQueen’s University, Kingston, CanadaE-mail: ljp@post.queensu.caSource of support: Queen’s University Faculty ofHealth Sciences Research Initiation Grant.

AAcckknnoowwlleeddggeemmeennttssDrs. Ted Ashbury, David Mark, Brian Milne, JoelParlow, and Chris Simpson for reviewing the ques-tionnaire. The Royal College of Physicians andSurgeons of Canada and the CanadianAnesthesiologists’ Society for providing the mailinglist. The anesthesiologists who took the time to com-plete the questionnaire. The Queen’s UniversityFaculty of Health Sciences Research Initiation Grantfor funding this research.

RReeffeerreennccee1 Eagle KA, Berger PB, Calkins H, et al. ACC/AHA

Guideline Update for Perioperative CardiovascularEvaluation for Noncardiac Surgery–ExecutiveSummary. A report of the American College ofCardiology/American Heart Association Task Force onPractice Guidelines (Committee to update the 1996Guidelines on Perioperative Cardiovascular Evaluationfor Noncardac Surgery). Anesth Analg 2002; 94:1052–64.

S100ß and postcardiac surgery neuro-logical dysfunction: reasons to disregardany link

To the Editor:Dr. Hall’s editorial1 in reference to the work byKanbak et al.,2 eloquently outlines the pitfalls of usingS100ß as a surrogate marker of postcardiac surgeryneurologic dysfunction. He explains why S100ß, a

CORRESPONDENCE 441

TABLE Suggested length of time before anesthetizing a patientfollowing coronary stent replacement

Number of weeks n (%)

0 weeks 13 3.81 week 12 3.52 weeks 87 25.33 weeks 13 3.84 weeks 127 36.95 weeks 52 15.16 weeks 13 3.87 weeks 2 0.68 weeks 7 2.012 weeks 16 4.724 weeks 2 0.6Total 344