Peri-operative lidocaine infusion: IV in Horses (Equis) | Vetlexicon
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Peri-operative lidocaine infusion: IV

ISSN 2398-2977

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Introduction

  • A large multi-centered epidemiological study investigating peri-operative equine fatalities, demonstrated a significantly higher peri-operative mortality rate in horses, compared to small animals and humans. The reasons for the high incidence of deaths have not been fully elucidated, however limitations in current equine anesthetic techniques are almost certainly a contributing factor.
  • In horses, anesthesia is commonly maintained using high concentrations of volatile agents that have significant depressant effects on the equine cardiovascular (CVS) system.
  • In man and small animals multi-modal techniques have evolved:
    • Anesthesia is maintained with a combination of intravenous and volatile agents.
    • These techniques combine anesthetic agents with different specific actions to provide unconsciousness, muscle relaxation and analgesia.
    • This enables the dose of each individual agent to be reduced and minimizes adverse side effects, particularly on the cardiovascular system.
  • In man potent opioids are an integral part of the anesthetic protocol, providing analgesia throughout surgery with minimal cardiovascular side effects.
  • Unfortunately potent opioids have excitatory side effects in horses that render them problematic for clinical use. Limb fracture is relatively common during stormy recoveries from anesthesia in the horse. Horses that attempt to stand early in the recovery period, when ataxic, are obviously at greater risk. There could be many explanations for this agitation, however peri-operative pain is probably a significant factor. Current equine anesthetic protocols provide poor peri-operative analgesia compared to those used in man and small animals.
  • Therefore, incorporation of an intravenous agent that provides peri-operative analgesia and reduces the concentration of volatile agent required to maintain anesthesia into anesthetic regimens, may have significant advantages.
  • Lidocaine   Lidocaine  , administered by continuous IV infusion (systemically), appears to provide both analgesia and a volatile agent sparing effect. Currently studies investigating the use of lidocaine by infusion during anesthesia, in horses and other species, are limited. However the results appear to be promising, with systemic lidocaine providing improved peri-operative analgesia with minimal cardiovascular side effects.

Studies in man

  • Intravenous lidocaine has been used peri-operatively in man as a supplement to general anesthesia.
  • More recently systemic lidocaine has been administered to treat chronic pain, particularly pain of neuropathic origin.

Studies in horses

  • Systemic administration of lidocaine during anesthesia in horses has undergone limited evaluation.
  • One study investigated the effect of intravenous lidocaine on the minimum alveolar concentration (MAC) of halothane:
    • Lidocaine decreased MAC of halothane in a dose dependent manner, demonstrating a halothane-sparing effect.
    • Plasma concentrations of lidocaine administered at two different infusion rates (low and high) were measured. Concentrations varied between 1-3 ug/ml and 3-7 ug/ml respectively <2 h after the start of the infusion, suggesting that the lidocaine concentration gradually increased with time.
  • Another study used EEG changes as a marker for nociception (pain) during anesthesia and surgery to investigate the antinociceptive (analgesic) effects of intravenous lidocaine as an adjunct to halothane anesthesia in ponies during castration; lidocaine abolished EEG changes during castration suggesting an analgesic action.
  • In both of these investigations the infusion of lidocaine was associated with good CVS stability. These studies highlight the potential for systemic lidocaine to be incorporated into clinical equine anesthetic protocols.

Mechanism of action

  • Lidocaine hydrochloride is a widely used local anesthetic agent. Local anesthetic agents applied directly to nerve fibers block conduction of action potentials by modifying sodium channels in the cell membrane.
  • The mechanisms whereby systemic lidocaine exerts an analgesic action have not been fully elucidated. Both peripheral and central sites of action have been proposed.
  • Peripherally, lidocaine analgesia may result from specific peripheral blockade of ectopic discharges in neurones involved in nociception. A direct action of lidocaine on spinal transmission in the spinal cord has also been suggested, although the cellular mechanism of such a spinal action is not clear.
  • The relationship between plasma lidocaine concentration and analgesic efficacy in man has been determined and suggests that there may be a divergence in the specificity of the analgesic action of systemic lidocaine according to the nature of the pain inducing process.
  • It appears that low concentrations of lidocaine are effective at suppressing neuropathic pain, while higher concentrations suppress both neuropathic and ischemic pain, eg pain produced by a tourniquet placed around the arm.
  • The greater efficacy of systemic lidocaine, against neuropathic pain, may reflect the changes in neuronal sodium channels that occur in chronic pain states.

Uses

  • Lidocaine   Lidocaine  can be administered continuously by IV infusion as an adjunct to maintenance of anesthesia with volatile agents (such as halothane   Halothane  or isoflurane   Isoflurane  ). Two infusion regimens have been described:
    • 5 mg/kg-1 lidocaine loading dose, 100 ug/kg/min-1 continuous intravenous infusion (HIGH DOSE).
    • 2.5 mg/kg-1 lidocaine loading dose, 50 ug/kg/min-1 continuous intravenous infusion (LOW DOSE).
  • The loading dose of lidocaine is administered slowly over 15 min.

Advantages

  • Improved peri-operative analgesia.
  • Reduction in the concentration of volatile agent needed to maintain anesthesia (decreased CVS side effects).
  • Good CVS stability during the lidocaine infusion.

Disadvantages

  • Limited data has been published describing this technique, although anecdotal evidence suggests that the use of lidocaine infusions during anesthesia in horses is increasing.
  • Potential for hypotension during administration of the lidocaine loading dose if it is given too quickly. This can be effectively managed by administration of an inotrope such as dobutamine   Dobutamine  .
  • Although the CVS stability during this technique appears to be good in healthy horses, there are limited data regarding use of the technique in very CVS compromised patients such as horses presented for exploratory laparotomy   Abdomen: laparotomy  .
  • Potential for accumulation of lidocaine if a prolonged infusion is given (>2 h), with a risk of prolonged recovery from anesthesia. After 2 h infusion of the higher dose rate (100 ug/kg/min-1) the infusion rate should be halved (50 ug/kg/min-1).

Time required

Preparation

  • Approximately 15 min to prepare the syringes of lidocaine for bolus administration and injection and calculate the bolus dose and infusion rate.
  • It is advisable to place a second jugular venous catheter after induction of anesthesia solely for the administration of lidocaine.
  • Once the loading dose of lidocaine is started, there is minimal extra time requirement during anesthesia.

Decision taking

Criteria for choosing test

  • It is desirable to improve both peri-operative analgesia and minimize the administration of high doses of volatile agents during every equine anesthesia, therefore the administration of lidocaine by IV infusion could be integrated into most routine anesthetic protocols involving maintenance of anesthesia with volatile agents.
  • Length of procedure: the loading dose of lidocaine must be administered over 15 min, therefore for procedures shorter than 20-30 min the administration of lidocaine is unwarranted.
  • Many anesthetics for elective procedures on healthy horses are shorter than 2 h. Administration of lidocaine at the high dose infusion rate is appropriate (5 mg/kg-1 loading dose, followed by 100 ug/kg/min-1 infusion).
  • When the duration of anesthesia is longer than 2 h, the lidocaine infusion rate should be halved (50 ug/kg/min-1).
  • Foals (<12 weeks old):
    • There is no data pertaining to plasma concentrations of lidocaine following systemic administration of lidocaine in foals during anesthesia, therefore caution must be exercised using this technique in young animals.
    • It is probable that lidocaine accumulates more quickly in younger animals   →   higher plasma concentrations. This is not an absolute contraindication to lidocaine administration, but the low dose infusion rate should be used and the infusion rate reduced according to assessment of depth of anesthesia and cardiovascular status in the individual patient.
  • Colic patients:
    • Systemic lidocaine administration is an appropriate technique for horses presented for exploratory laparotomy however, the CVS effects of lidocaine in animals with severe CVS compromise have not been evaluated.
    • Attempts should be made to stabilize blood pressure as far as possible before administration of the loading dose of lidocaine and blood pressure should be monitored carefully. Extra inotropic support with dobutamine may be required.
    • The potential role of lidocaine as a prokinetic agent after colic surgery is being increasingly investigated.

Requirements

Personnel

Anesthetist expertise

  • The anesthetist should be comfortable with assessing the depth of anesthesia in horses during volatile agent anesthesia and direct arterial blood pressure monitoring.

Materials required

Minimum equipment

  • Lidocaine loading dose and infusion:
    • Apparatus to deliver the loading dose of lidocaine and infusion accurately and continuously is required.
    • This is usually a syringe driver (capable of holding a 50 ml syringe) or a volumetric infusion pump.
    • The loading dose is a relatively large volume of 2% lidocaine (125 ml/500 kg horse), therefore if a syringe driver is used, this will necessitate changing the syringe 3 times during a 15 min period.
  • Anesthetic monitoring equipment   Anesthesia: monitoring - overview  :
    • Direct arterial blood pressure monitoring.
    • This facilitates maintenance of CVS stability with inotropic support (dobutamine) during administration of the loading dose of lidocaine.

Minimum consumables

  • Lidocaine hydrochloride (without adrenaline) 2% solution:
    • 140 ml in total is required for a 500 kg horse administered the high dose infusion rate for 2 h.
  • 50 ml syringe and extension tube:
    • Administration of the loading dose is easier if the total calculated volume is prepared in advance of anesthesia and drawn up in 2-3 50 ml syringes.

Preparation

Technique

Approach

Step 1 - Standard method

  • Systemic lidocaine administered by continuous intravenous infusion is an adjunct to maintenance of anesthesia with volatile agents.
  • Published studies have administered the lidocaine in combination with halothane following induction of anesthesia with thiopental   Thiopental  or thiopental and guaifenesin   Guaifenesin  . However there are no contraindications for the use of lidocaine with other combinations of drugs for induction of anesthesia (such as alpha-2-adrenoreceptor agonists and ketamine   Ketamine hydrochloride  ) or other volatile agents, eg isoflurane.
  • The loading dose of lidocaine is given at the start of anesthesia following placement of an arterial catheter for direct arterial blood pressure monitoring. The loading dose is immediately followed by the continuous intravenous infusion.

Example

  • A worked example is given to demonstrate calculation of the loading dose and infusion rates of lidocaine for a 500 kg horse administered at the high dose infusion rate:

Step 2 - Calculate the loading dose of lidocaine

  • Loading dose of lidocaine: 5 mg/kg-1.
  • Loading dose: 5 x 500 = 2500 mg.
  • Volume of lidocaine hydrochloride 2% loading dose: 2500/20 = 125 ml.
  • Rate of administration of the loading dose: 125 ml over 15 min = 500 ml/h.

Step 3 - Calculate the rate of the continuous intravenous infusion

 
  • Lidocaine infusion rate: 100 ug/kg/min-1.
  • Lidocaine infusion rate: 100 x 500 x 60/1000 mg/h = 3000 mg/h-1.
  • Infusion rate for lidocaine hydrochloride 2% = 150 ml/h-1.

Step 4 - Prepare syringes

 
  • Prepare the syringes of lidocaine for the loading dose and continuous infusion.

Core procedure

 

Step 1 - Preparation

 
  • The horse is anesthetized and direct arterial blood pressure monitoring   Anesthesia: monitoring - cardiac output and blood pressure  is established.
  • Administration of the loading dose is facilitated if a second intravenous catheter is placed in the jugular vein and reserved solely for the administration of lidocaine.

Step 2 - Administration of the lidocaine loading dose and infusion

 
  • The loading dose of lidocaine is given over 15 min at the calculated rate.
  • The blood pressure is carefully monitored   Anesthesia: monitoring - cardiac output and blood pressure  during the infusion. Blood pressure can be supported by the administration of dobutamine and an increased infusion rate of isotonic fluid, eg Hartmann's solution, if necessary, although it is normally well maintained in healthy horses.
  • The lidocaine will reduce the concentration of volatile agent required to maintain anesthesia so the vaporizer setting may be reduced, judged on clinical assessment of depth of anesthesia.
  • One study found that the high dose infusion reduced MAC halothane by 50-70%, indicating that there may be a substantial reduction in volatile agent requirement.

Step 3 - Continuous infusion of lidocaine

 
  • The continuous infusion of lidocaine is started immediately after the end of the lidocaine loading dose.
  • The infusion is continued until the end of anesthesia, the rate is reduced by half (50 ug/kg/min-1) should the anesthesia extend for longer than 2 h.
  • Blood pressure is monitored and inotropic support given as necessary (see above), although cardiovascular stability is usually good.
  • Expect that the concentration of volatile agent can be gradually reduced as the infusion continues, this is judged based on clinical assessment of anesthetic depth.

Exit

 

Step 1 - Cessation of anesthesia/infusion

 
  • Administration of lidocaine is stopped at the end of anesthesia, there is no need to stop the lidocaine infusion prematurely.
  • Recovery from anesthesia   Anesthesia: recovery - overview  may be more prolonged due to the "anesthetic effect" of the lidocaine.
  • The post-operative analgesic effects of lidocaine in horses are unknown, therefore additional analgesia using other classes of analgesic agents, eg NSAIDs   Therapeutics: anti-inflammatory drugs  or opioids, must be provided.

Aftercare

Immediate Aftercare

Fluid requirements

  • Monitoring during recovery from anesthesia after the administration of lidocaine is routine.

Outcomes

Complications

  • Hypotension during administration of the lidocaine loading dose can be managed by the administration of dobutamine   Dobutamine  in combination with increased infusion of an isotonic solution such as Hartmann's solution. There is probably a greater risk of hypotension in patients with existing CVS compromise.
  • Hypotension during the continuous lidocaine infusion.
  • Hypotension during anesthesia of horses maintained with volatile agents is common, and may possibly occur during administration of lidocaine. Check that the administered concentration of volatile agent is not high, ie the horse is too deeply anesthetized, and if possible reduce the concentration of volatile agent. Increase the level of inotropic and fluid infusion support.

Summary

  • There is currently limited published clinical information about the clinical use of peri-operative lidocaine infusion in horses, although there is anecdotal evidence that they are being increasingly used in anesthetic practice.
  • Lidocaine administered systemically appears to provide good intra-operative analgesia and an anesthetic sparing effect, allowing the concentration of volatile anesthetic agent to be reduced. This has advantages of both improved CVS stability and peri-operative pain management.
  • In the future it is likely that this technique will become more widespread and contribute to improvements in current clinical equine anesthetic techniques.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Valverde A et al (2010) Comparison of cardiovascular function and quality of recovery in isoflurane-anaesthetised horses administered a constant rate infusion of lidocaine or lidocaine and medetomidine during elective surgery. Equine Vet J 42 (3), 192-199 PubMed.
  • Williams J M et al (2010) Effect of intravenous lidocaine administration on laminar inflammation in the black walnut extract model of laminitis. Equine Vet J 42 (3), 261-269 PubMed.
  • Koppert W, Ostermeirer N, Sittl R, Weidner C & Schmelz M (2000) Low-dose lidocaine reduces secondary hyperalgesia by a central mode of action. Pain 85 (1-2), 217-224 PubMed.
  • Doherty T & Frazier D (1998) Effect of intravenous lidocaine on halothane minimum alveolar concentration in ponies. Equine Vet J 30 (4), 300-303 PubMed.
  • Ferrante F, Paggioli J, Cherukuri S & Arthur G (1996) The analgesic response to intravenous lidocaine in the treatment of neuropathic pain. Anesthesia and Analgesia 82 (1), 91-97 PubMed.
  • Wallace M, Dyck J, Rossi S & Yaksh T (1996) Computer controlled lidocaine infusion for the evaluation of neuropathic pain after peripheral nerve injury. Pain 66 (1), 69-77 PubMed.
  • Waterman A (1996) Equine anesthesia - HBLB workshop. Equine Vet J 28 (1), 10-14 WileyOnline.
  • Johnston G, Taylor P & Holmes M (1995) Confidential enquiry of perioperative equine fatalities (CEPEF-1) - Preliminary results. Equine Vet J 27 (3), 193-200 PubMed.
  • Pascoe P, Black W, Claxton J & Sanson R (1991) The pharmacokinetics and locomotor activity of alfentanil in the horse. J Vet Pharmacol Therap 14 (3), 317-325 PubMed.
  • Tanelian D & MacIver M (1991) Analgesic concentrations of lidocaine suppress tonic A-delta and C fiber discharges produced by acute injury. Anesthesiology 74 (5), 934-936 PubMed.
  • Kastrup J, Petersen P, Dejgard A, Angelo H & Hilsted J (1987) Intravenous lidocaine infusion - A new treatment of chronic painful diabetic neuropathy. Pain 28 (1), 69-75 PubMed.
  • Woolf C & Wiesenfeld-Hallin Z (1985) The systemic administration of local anaesthetics produces a selective depression of C-afferent fibre evoked activity in the spinal cord. Pain 23 (4), 361-374 PubMed.
  • Boas R, Covino B & Shahnarian A (1982) Analgesic responses to IV lignocaine. British J Anesthesia 54 (5), 501-505 PubMed.
  • Bartlett E & Hutaserani O (1961) Xylocaine for the relief of postoperative pain. Anesthesia and Analgesia 40, 296-304 PubMed.
  • DeClive-Lowe SD, Desmond J & North J (1958) Intravenous lignocaine anesthesia. Anesthesia 13 (2), 138-146 PubMed.

Other sources of information

  • Murrell J (2001) Spontaneous EEG Changes in the Equine Surgical Patient. In: PhD Thesis. University of Bristol, UK.
  • Taylor P (2000)Is Intravenous Anaesthesia in Horses Better than Volatile Agents?In:Proceedings of the Association of Veterinary Anesthetists - Spring 2000 Conference. Cambridge, UK.