To view this site you must be a
veterinarian surgeon or nurse.
Are you a Veterinary Surgeon or Veterinary Nurse?

No

Pain, what a Pain! How Locoregional Anaesthesia can Improve the Outcome and Welfare of Veterinary Patients (Part 1)

It is widely accepted that the reduction of pain, or analgesia, assists in a patient’s recovery from surgery. For this purpose, and to be most effective, analgesia should be instigated at the premedication phase, maintained across the surgery and continued well into the recovery phase. 

The use analgesia prior to any procedure that is likely to cause pain is known as pre-emptive analgesia.

The administration of several analgesic agents with different modes of action (e.g. opioids, non-steroidal anti-inflammatory drugs (NSAIDs) and local anaesthetics) is known as multimodal analgesia. This technique can target more than one point in the nervous system, thus making the control of pain more effective. 

Why Locoregional Anaesthesia? 

Local anaesthesia is the reversible loss of sensation in a localised area of the body caused by the depression of excitation in nerve endings or inhibition of the conduction process in peripheral nerves (Covino and Vassallo, 1976). Where local anaesthetic is used to desensitise a region of the patient’s body, the term locoregional anaesthesia (LRA) is often employed.

There has been an increase in the popularity of LRA techniques within the veterinary profession over recent years and in human medicine it is well recognised that the use of local anaesthesia reduces the time to discharge versus the use of systemic analgesia alone. In addition to this, the appropriate application of local anaesthesia is likely to reduce the dose of anaesthetic required for both induction and maintenance. This in turn leads to less cardiopulmonary depression, reduces post-operative pain scores and results in a faster more stable recovery, increasing the likelihood of a safer anaesthetic (Taylor and Robertson, 2004; Caniglia et al. 2012; Romano et al. 2015).

How to Perform Locoregional Anaesthesia and Drugs to Consider

LRA may be performed either via a ‘blind’ technique, where the needle is placed in an appropriate location based on anatomical knowledge of nerve location, or via a ‘guided’ technique using ultrasound or electrical stimulation needles. Whilst a ‘guided’ approach may improve the accuracy of your peripheral nerve block (PNB), if the technique is to be practiced safely, it is vital that the clinician has a thorough appreciation for the associated anatomy. Iatrogenic nerve injury occurs in a reported one in 10,000 cases in human medicine following perineural analgesia and similar injuries are also reported in the veterinary literature (Forterre et al. 2007; Murdoch and Michou, 2015).

The drugs used for LRA mainly fall within three classes, these include:

  1. local anaesthetics, 
  2. opioids,
  3. and alpha2-adrenergic receptor agonists (alpha2-agonists).

Local anaesthetics are the primary drug class used for LRA although opioids and alpha2-adrenergic agonists may be added in certain circumstances. In general, preservative free drugs are preferred, especially when used intra-articularly or epidurally to avoid potential preservative related toxic effects (Borer-Weir, 2014).

1. Local Anaesthetics

Local anaesthetics elicit their effects via blockade of sodium ion channels on nerve axons, this prevents sodium ion influx and blocks nerve action potential and propagation of nerve impulse transmission.

Local anaesthetics are an unusual class of drug as their site of application is also their site of action. As a result, systemic absorption controls both the duration and offset of action (Borer-Weir, 2014). Systemic absorption of local anaesthetics is affected by:

  1. injection site,
  2. drug dosage,
  3. presence of added vasoconstrictor,
  4. or the pharmacological profile of the drug itself.

Common examples include:

Drug Lidocaine hydrochlorideBupivacaine hydrochloride
Time to onset 2-5 minutes5-10 minutes
Duration of action 1-1.5 hours4-8 hours
Dose 3-4 mg/kg1-2 mg/kg
Maximum safe dose 10 mg/kg (Dogs)
6 mg/kg (Cats)
2 mg/kg (Dogs and Cats)
Comments Licensed formulations available.
Combined with epinephrine which can prolong the anaesthetic effect.
No current UK licence for use in veterinary species.


Table 1.
(Adapted from Dugdale, 2001 and Duke-Novakovski, 2016).

Toxic doses (see Table 1.) for these drugs exist and so their judicious use is recommended. Toxicity mainly results from inadvertent intravenous injection and so given the proximity of blood vessels to nerves it is vitally important to aspirate before injecting any local anaesthetic. 

Signs of toxicity mainly include depression, sedation, seizure like activity and hypotension through cardiovascular depression.

Commercially available infusions of 20% lipid emulsion can be used at a dose of 1.5-3ml/kg administered over 30 minutes to treat toxicity from overdose of local anaesthetics (O’Brein et al. 2010). The mechanism of action is currently unknown, but theories include:

  • By the stimulation of a ‘lipid plasma phase’ which attracts the lipid soluble local anaesthetic therefore reducing the amount of free drug within the plasma (Borer-Weir, 2014).
  • By increasing myocardial calcium through fatty acid provision therefore countering the negative inotropic effects of the local anaesthetic.
  • By preventing inhibition of the enzyme responsible for the transport of fatty acids, used for oxidative phosphorylation, into myocardial cells (Duke-Novakovski, 2016).

2. Opioids

Morphine is the opioid that is most often used in LRA techniques, and there is increasing evidence to suggest that there are opioid receptors on the peripheral terminals of sensory nerves (Borer, 2006). Low doses of morphine are required when used in this manner, typically 0.1mg/kg providing local analgesia when used epidurally (Borer, 2006). The upregulation of opioid receptors that occurs within inflamed joints means that opioids will also exert an analgesic effect when injected intra-articularly (Lindegaard et al. 2010). 

3. Alpha2- agonists

The addition of an alpha2- agonist to local anaesthetic when used as a peripheral nerve block has also found to have beneficial effect. For example, Lamont and Lemke, 2008 found that the addition of medetomidine to mepivacaine prolonged both motor and sensory blockade after radial nerve block in dogs.

Please note that not all the drugs discussed in this article are licenced for use in small animals despite their frequent use in veterinary practice. Their use is the responsibility of the administering veterinary surgeon following an appropriate risk/benefit analysis in each case and in line with the cascade.

Please keep an eye out for Part 2 where we will discuss some of the more common practical applications of LRA in veterinary practice.

Article by
Dr. Dan Cripwell
BSc (Hons) BVSc CertAVP (EM) PgCert (VPS) MRCVS

Veterinary Technical Advisor UK
RCVS Recognised Advanced Veterinary Practitioner

Originally published: Thursday, 31st May 2018
Last updated: Thursday, 14th June 2018

References

  • Borer, K. 2006. Local analgesic techniques in small animals. In practice. 28(4): 200-207.
  • Borer-Weir, K., 2014. Analgesia. In Veterinary Anaesthesia (Eleventh Edition): 101-133.
  • Caniglia, A.M., Driessen, B., Puerto, D.A., Bretz, B., Boston, R.C., Larenza, M.P. 2012. Intraoperative antinociception and postoperative analgesia following epidural anesthesia versus femoral and sciatic nerve blockade in dogs undergoing stifle joint surgery. Journal of the American Veterinary Medical Association. 241: 1605–1612.
  • Covino, B. G., and Vassallo, H. G. 1976. Local Anesthetics: Mechanisms of Action and Clinical Use. New York, San Francisco, London: Grune & Stratum.
  • Duke-Novakovski, T. 2016. Pain management II: local and regional anaesthetic techniques. In: BSAVA manual of canine and feline anaesthesia and analgesia (Third Edition). John Wiley & Sons.
  • Dugdale, A., 2011. Veterinary anaesthesia: principles to practice. John Wiley & Sons.
  • Forterre, F., Tomek, A., Rytz, U., Brunnberg, L., Jaggy, A. and Spreng, D. 2007. Iatrogenic sciatic nerve injury in eighteen dogs and nine cats (1997–2006). Veterinary surgery. 36(5): 464-471.
  • Lamont, L.A. and Lemke, K.A. 2008. The effects of medetomidine on radial nerve blockade with mepivacaine in dogs. Veterinary anaesthesia and analgesia. 35(1): 62-68.
  • Lindegaard, C., Gleerup, K.B., Thomsen, M.H., Martinussen, T., Jacobsen, S. and Andersen, P.H. 2010. Anti-inflammatory effects of intra-articular administration of morphine in horses with experimentally induced synovitis. American journal of veterinary research. 71(1): 69-75.
  • Murdoch, A.P. and Michou, J.N. 2016. The effect of loco-regional anaesthesia on motor activity induced by direct stimulation of the sciatic nerve in dogs. The Veterinary Journal. 209: 139-143.
  • O'Brien, T.Q., Clark-Price, S.C., Evans, E.E., Di Fazio, R. and McMichael, M.A. 2010. Infusion of a lipid emulsion to treat lidocaine intoxication in a cat. Journal of the American Veterinary Medical Association237(12): 1455-1458.
  • Romano, M., Portela, D.A., Breghi, G. and Otero, P.E. 2016. Stress‐related biomarkers in dogs administered regional anaesthesia or fentanyl for analgesia during stifle surgery. Veterinary anaesthesia and analgesia. 43(1): 44-54.
  • Taylor, P.M. and Robertson, S.A. 2004. Pain management in cats—past, present and future. Part 1. The cat is unique. Journal of Feline Medicine and Surgery6(5): 313-320.

Keep reading... More news items that may interest you.

Buprenorphine: it’s not all static in rabbits

Opioids are well known for causing gastrointestinal stasis in mammalian species. This recent paper examined the effects of a single high dose of buprenorphine on the rabbit gastrointestinal tract using non-invasive imaging techniques.

Read On...

Caesarean Section Survival Guide. Part 1: Physiology & Pre-anaesthetic Considerations.

In the first instalment of this 2-part review Karen examines the physiological changes that occur during pregnancy and how those adjustments can affect the selection of anaesthetic protocols for the increasingly common Caesarean section.

Read On...

Cardiac arrest - the human factor

Cardiac arrest in dogs and cats is, thankfully, relatively rare. However, when it does happen it can have devastating consequences for the animal, owner and the veterinary team. This study examined the common causalities leading up to a cardiac arrest with the aim of changing protocols to improve outcomes.

Read On...

Are you Using Safety Checklists in your Practice?

In this article, Carl focuses on the benefits of introducing a safety checklist in practice to reduce patient morbidity, mortality and to improve communication between members of the veterinary team. The article contains links to the AVA safety checklist as well as a link to a customisable list that you can adapt to your practice needs. 

Read On...

The Big Chill - Temperature Management in Sedated and Anaesthetised Patients

The effects of hypothermia are very far reaching throughout the peri-anaesthetic process. In this article, James takes us through the interesting mechanisms of body cooling and warming, the clinical relevance of hypothermia and what we can do to prevent it.

Read On...

Keeping the Finger on the Pulse -  Nuances in CV Monitoring

All patients are exposed to the risks associated with general anaesthesia. Continuously monitoring anaesthetised patients maximises patients safety and wellbeing. In this article, Dan takes us through the common monitoring techniques that provide information about the cardiovascular status of your patient. 

Read On...

Effect of Maropitant on Isoflurane Requirements & Postoperative Nausea & Vomiting

Despite being widely recognized in humans, postoperative nausea and vomiting (PONV), and the role of maropitant in reducing inhalational anaesthetic requirements have been poorly documented in dogs. This recent study evaluates PONV and isoflurane requirements after maropitant administration during routine ovariectomy in bitches.

Read On...

New! Alfaxan® Multidose Now Available

We are happy to announce we have enhanced our anaesthesia and analgesia portfolio with the introduction of Alfaxan®Multidose for dogs, cats and pet rabbits.

Read On...

Sevoflurane requirement in dogs premedicated with medetomidine and butorphanol

Little information is available about the effect that different doses of medetomidine and butorphanol may have when using sevoflurane for maintenance of anaesthesia in dogs. This recent study evaluates heart rate and median sevoflurane concentration required at different dose rates.

Read On...

Capnography II - What happened to the elephants? A summary of abnormal traces

In this second article of the capnography series, James provides a guide to a few of the most common traces that you will encounter during surgery. Scroll to the end of the article to download a printable capnography cheatsheet. 

Read On...

Pain, what a Pain! (Part 2) – Practical Tips On How To Perform Dental Nerve Blocks In Companion Animal Practice

In this second article of the Pain, what a Pain! series, Dan takes us through the LRA techniques associated with dental and oral surgery. In this article, you will find practical tips and pictures on common dental nerve blocks as well as safety concerns to consider.

Read On...

​Peri-anaesthetic mortality and nonfatal gastrointestinal complications in pet rabbits

This recent retrospective study looks at the cases of 185 pet rabbits admitted for sedation or general anaesthetic and evaluates the incidence and risk factors contributing to peri-anaesthetic mortality and gastrointestinal complications.

Read On...

Perspectives on Premeds – Opioids

Perspectives on Premeds is a series of articles touching on different pharmacological, physiological and clinical aspects of pre-anaesthetic medication. This second article aims to provide a refresher on opioids.

Read On...

Effects of Dexmedetomidine with Different Opioid Combinations in Dogs

Read the highlights of a recently published research paper that evaluates cardiorespiratory, sedative and antinociceptive effects of dexmedetomidine alone and in combination with morphine, methadone, meperidine, butorphanol, nalbuphine and tramadol. 

Read On...

Preoxygenation Study Highlights

This study evaluates the effectiveness of two methods of preoxygenation in healthy yet sedated dogs and the impact of these methods on time taken to reach a predetermined haemoglobin desaturation point (haemoglobin saturation (SpO2) of 90%) during an experimentally induced period of apnoea.

Read On...

Capnography – Not Just a Load of Hot Air

Capnography is the measurement of inhaled and exhaled carbon dioxide (CO2) concentration. The graphical illustration of CO2 within respired gases versus times is known as the capnogram.

Read On...

Perspectives on Premeds – Alpha-2 Agonists

Perspectives on Premeds is a series of articles touching on different pharmacological, physiological and clinical aspects of pre-anaesthetic medication. This first article aims to provide a refresher on α2 agonists.

Read On...

We are ‘injecting’ a bit of fun into BSAVA Congress!

We will be ‘injecting’ a bit of fun into BSAVA Congress on our stand (stand 702).

Read On...

Alfaxan - now licensed for use in pet rabbits

Jurox Animal Health is delighted to announce that Alfaxan is now licensed for cats, dogs and pet rabbits. This is an exciting advance and could change the way rabbits are anaesthetised in the U.K.

Read On...

Best Practice Rabbit Anaesthesia Roadshows

Jurox Announces eight country wide events on Best Practice Rabbit Anaesthesia

Read On...

Considerations in Rabbit Anaesthesia at the 2017 London Vet Show

Jurox to host talks on Considerations in Rabbit Anaesthesia at the 2017 London Vet Show.

Read On...

Vets needing more support for anaesthesia

Jurox research reveals that veterinary professionals have questions about their anaesthetic protocols

Read On...
Repeatable. Reliable. Relax.