Maintenance of anesthesia by use of an inhalant agent has been routinely used in clinical practice. Inhalant anesthesia has become popular in veterinary practice because anesthetic depth is easily and rapidly adjusted by changing vaporizer settings and fresh gas flow rates. Additionally, inhalant anesthetics have a favorable pharmacokinetic profile, allowing relatively rapid induction and recovery from anesthesia because anesthetic gas uptake and elimination occurs mainly via the lungs. However, one of the main concerns is the progressive cardiorespiratory depression observed with high doses of inhalant agents such as isoflurane.1 In most instances, the cardiovascular depression caused by inhalant agents at doses adjusted to maintain a moderate level of anesthesia is well tolerated in healthy animals undergoing elective procedures. However, highrisk patients or animals with severe systemic disease may have excessively depressed cardiovascular function if anesthesia is maintained with an inhalant alone. In this situation, balanced anesthesia techniques achieved by combining inhalant agents with drugs such as opioids or local anesthetics administered systemically may provide better cardiovascular stability by reducing inhalant agent requirements during anesthesia.2–8
Fentanyl is a short-acting synthetic opioid agonist at m receptors that has high lipid solubility and is approximately 100 times as potent as morphine.9 Because fentanyl has a rapid onset and a short duration of action, it is suitable for continuous infusion regimens. Although vagally mediated bradycardia often occurs, cardiovascular stability is present even when the drug is administrated in high dosages.4 Several studies3,4,8,10–13 reveal that fentanyl significantly reduces inhalant requirements in a variety of species, and there is evidence that greater hemodynamic stability is achieved when fentanyl is combined with inhalant agents in a balanced anesthesia technique.
Lidocaine is a local anesthetic that reversibly inhibits nerve conduction by blocking Na channels. It has been widely used in regional anesthesia techniques, such as nerve blocks and epidural anesthesia. It is also commonly used in the treatment of ventricular arrhythmias.14 There has been a renewed interest in the use of lidocaine infusions during anesthesia in dogs because its use reduces the MAC of inhalant anesthetics in several species.2,5–7,15 Even though studies2–7,10–13,15 reveal that lidocaine and fentanyl infusions reduce the amount of volatile agent required to maintain anesthesia in the laboratory setting as measured by use of classical MAC determinations, to our knowledge, there are no reports evaluating the inhalant-sparing effects of lidocaine or fentanyl in dogs undergoing surgical procedures.
The lidocaine infusion regimen used in the present study was based on a previous reporta in which lidocaine was administered at 1.5 μg/kg (0.68 μg/lb) over 1 minute, followed by a CRI of 250 μg/kg/min (113.6 μg/lb/min) in dogs anesthetized with propofol. The minimal infusion rate of propofol, calculated as the arithmetic mean of the infusion rate that prevented gross purposeful movement in response to a supramaximal noxious stimulation, was reduced by 21% when lidocaine was administered. In the present study, a loading dose of 5 μg of fentanyl/kg (2.27 μg/lb) was given over 1 minute, followed by a CRI of 0.5 μg/kg/min (0.23 μg/lb/min). On the basis of pharmacokinetic data, when fentanyl is given at a loading dose of 10 μg/kg (4.5 μg/lb), followed by a CRI of 0.7 μg/kg/min (0.32 μg/lb/min), a maximal reduction in inhalant requirements is expected.3,8,16
The purpose of the study reported here was to evaluate the isoflurane-sparing effects of lidocaine and fentanyl administered via CRI in dogs undergoing unilateral mastectomy because of mammary neoplasia.
Minimum alveolar concentration
Constant rate infusion
Systolic arterial pressure
Diastolic arterial pressure
Mean arterial pressure
End-tidal carbon dioxide
Mannarino R, Luna SPL, Massone F, et al. Minimal infusion rate (MIR), cardiorespiratory and pharmacokinetical study of a continuous infusion of propofol or propofol combined with lidocaine in dogs (abstr), in Proceedings. Assoc Vet Anaesth Autumn Meet 2004;75.
Acepran 0.2%, Lab Univet, São Paulo, Brazil.
Dimorf, Lab Cristália, Itapira, Brazil.
Angyocath, Beckton-Dickinson, São Paulo, Brazil.
Vetaset, Fort Dodge, Campinas, Brazil.
Compaz, Lab Cristália, Itapira, Brazil.
Isothane, Baxter, São Paulo, Brazil.
Model LF 2001, Lifemed, São Paulo, Brazil.
AS/3, Datex-Engstrom, Helsinki, Finland.
RapidLab 348, Bayer Healthcare, Tarrytown, NY.
Quick Cal calibration gas, Datex-Engstrom, Helsinki, Finland.
Conquest 2000, HB Hospitalar, São Paulo, Brazil.
Xylestesin 2%, Cristália, Itapira, Brazil.
Fentanest, Cristália, Itapira, Brazil.
Vaporizador Universal, HB Hospitalar, São Paulo, Brazil.
Profenid, Aventis, São Paulo, Brazil.
GraphPad Prism, version 4.00, GraphPad Software Inc, San Diego, Calif.
Himes RS Jr, DiFazio CA, Burney RG. Effects of lidocaine on the anesthetic requirements for nitrous oxide and halothane. Anesthesiology 1977;47:437–440.
Murphy MR & Hug CC Jr. The anesthetic potency of fentanyl in terms of its reduction of enflurane MAC. Anesthesiology 1982;57:485–488.
Ilkiw JE, Pascoe PJ, Haskins SC, et al. The cardiovascular sparing effect of fentanyl and atropine, administered to enflurane anesthetized dogs. Can J Vet Res 1994;58:248–253.
Muir WW III, Wiese AJ, March PA. Effects of morphine, lidocaine, ketamine, and morphine-lidocaine-ketamine drug combination on minimum alveolar concentration in dogs anesthetized with isoflurane. Am J Vet Res 2003;64:1155–1160.
Valverde A, Doherty TJ, Hernández J.. Effect of intravenous lidocaine on isoflurane MAC in dogs. Vet Anaesth Analg 2004;31:264–271.
Pypendop BH, Ilkiw JC. The effects of intravenous lidocaine administration on the minimum alveolar concentration of isoflurane in cats. Anesth Analg 2005;100:97–101.
McEwan AI, Anaes FC, Smith C, et al. Isoflurane minimum alveolar concentration reduction by fentanyl. Anesthesiology 1993;78:864–869.
Moon PF, Scarlett JM, Ludders JW, et al. Effect of fentanyl on the minimum alveolar concentration of isoflurane in swine. Anesthesiology 1995;83:535–542.
Hellyer PW, Mama KR, Shafford HL, et al. Effects of diazepam and flumazenil on minimum alveolar concentration for dogs anesthetized with isoflurane or a combination of isoflurane and fentanyl. Am J Vet Res 2001;62:555–560.
Criado AB, Gomez de Segura IA. Reduction of isoflurane MAC by fentanyl or remifentanil in rats. Vet Anaesth Analg 2003;30:250–256.
Coté E, Ettinger SJ. Electrocardiography and cardiac arrhythmias. In: Ettinger SJ, Feldman EC, eds. Veterinary internal medicine. St Louis: Elsevier Saunders, 2005;1040–1076.
Doherty TJ, Frazier DL. Effect of intravenous lidocaine on the minimum alveolar concentration in ponies. Equine Vet J 1998;30:300–303.
Murphy MR, Olson WA, Hug CC. Pharmacokinetics of 3H-1fentanyl in the dog anesthetized with enflurane. Anesthesiology 1979;50:13–19.
Eger EI, Saidman LJ, Brandstater B. Minimum alveolar anesthetic concentration: a standard of anesthetic potency. Anesthesiology 1965;26:756–763.
Steffey EP. Inhalation anesthetics. In: Thurmon JC, Tranquilli WJ, Benson WJ, eds. Lumb and Jones' veterinary anesthesia. 3rd ed. Baltimore: The Williams & Wilkins Co, 1996;297–329.
Eger EI, Saidman LJ, Brandslater B. Temperature dependence of halothane and cyclopropane anesthesia in dogs: correlation with some theories of anesthetic action. Anesthesiology 1965;26:764–770.
Regan MJ, Eger EI. Effect of hypothermia in dogs on anesthetizing and apneic doses of inhalation agents. Anesthesiology 1965;28:689–700.
Torske KE, Dyson DH, Pettifer G. End tidal halothane concentration and postoperative analgesia requirements in dogs: a comparison between intravenous oxymorphone and epidural bupivacaine alone and in combination with oxymorphone. Can Vet J 1998;39:361–369.
Dyson DH, James-Davies R.. Dose effect and benefits of glycopyrrolate in the treatment of bradycardia in anesthetized dogs. Can Vet J 1999;40:327–331.
Motomura S, Kissin I, Aultman DF, et al. Effects of fentanyl and nitrous oxide on contractility of blood-perfused papillary muscle of the dog. Anesth Analg 1984;63:47–50.
Liu PL, Feldman HS, Giasi R, et al. Comparative CNS toxicity of lidocaine, etidocaine, bupivacaine, and tetracaine in awake dogs following rapid intravenous administration. Anesth Analg 1983;62:375–379.
Skarda RT. Local and regional anesthetic techniques: dogs. In: Thurmon JC, Tranquilli WJ, Benson WJ, eds. Lumb and Jones' veterinary anesthesia. 3rd ed. Baltimore: The Williams & Wilkins Co, 1996;426–447.
Ngo LY, Tam YK, Tawfik S, et al. Effects of intravenous infusion of lidocaine on its pharmacokinetics in conscious instrumented dogs. J Pharm Sci 1997;86:944–952.