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

No

Food for Thought: Pre-anaesthetic Fasting


Pre-anaesthetic fasting

INTRODUCTION

The practice of fasting patients prior to anaesthesia was instigated in human patients in 1946 when it was considered beneficial to give “nil by mouth” after midnight before the anaesthetic procedure1.  This was extrapolated to the veterinary patient and has been questioned little until recently. 

REGURGITATION, VOMITING AND ASPIRATION OF STOMACH CONTENTS 

Inhalation of gastric contents can result in mechanical obstruction to respiration and chemical inflammation.  In the dog regurgitation/vomiting can be a major cause of oesophagitis with the potential for subsequent development of oesophageal strictures. However, the incidence may be underestimated as the episodes tend to be “silent” and frequently go un-noticed.1 

Gastro-oesophageal reflux (GOR) in dogs is influenced by: age; type of surgery; volume of gastric contents at the time of anaesthesia; acidity of gastric contents; premedicant selection; induction/maintenance drugs; abdominal surgery1.  Dorsal recumbency and the duration of pre-operative fasting can also affect GOR2.  Pregnancy, obesity (both of which increase abdominal pressure) and high ASA scores may also influence GOR1

DURATION OF FASTING 

Recent studies on the duration of fasting in dogs have reported conflicting results: 

Savvas et al (2016) suggest a light meal (1/2 the daily rate of a canned food) 3 hours before anaesthesia can reduce GOR when compared to administering the same amount/type of food 10 hours before3.  This may be due to the volume of gastric contents at the time of anaesthetic induction not being significantly increased by feeding a light meal 3 hours before anaesthesia4

A recent paper by Viskjer et al (2017) demonstrated that a half-ration given 3 hours prior to anaesthesia was associated with 61% GOR and 48% regurgitation compared to fasting for 18 hours which resulted in 43% GOR and 11% regurgitation.  The authors state: “Consumption of a light meal 3 hours prior to anaesthesia was associated with significantly greater odds of reflux and regurgitation compared with overnight food withholding.” 

The current recommendation for adult patients by Bradbrook (2017) is to fast overnight unless the patient presents for urgent/emergency treatment.  However, fasting for greater than 10 hours can increase the acidity of stomach contents with the potential for oesophageal injury should regurgitation occur.4 A 6-8 hour fast is now considered sufficient.7

In the emergency situation attention should be directed towards minimising the risk of aspiration of regurgitated or refluxed gastric contents before the airway is secure, and also during recovery.6 

For paediatric patients the recommendation is a shorter period of fasting primarily due to the risk of hypoglycaemia, and due care should be taken in these patients during the anaesthetic process.6 Jolliffe (2011) suggests fasting of juveniles for 3-4 hours prior to anaesthesia and Bednarski (2015) advises 1-2 hours. 

RABBITS 

Rabbits are obligate nose-breathers and cannot vomit although they can regurgitate. They are hind-gut digesters, with digestible fibre being fermented in the caecum to produce volatile fatty acids (VFAs) which provide approximately 40% of the maintenance energy requirements of the rabbit.  Their high metabolic rate requires a constant intake of food and this continual supply of ingested fibrous material also assists in the maintenance of gut motility.

Rabbits should not be starved prior to general anaesthesia and hay should be available at all times.  Pellet/concentrate & fresh food items may be removed approximately 1 hour prior to induction to help minimise the presence of residual food particles in the oropharynx, and to decrease stomach volume in order to reduce pressure on the diaphragm.10 If assisted feeding is being performed the last feed should be approximately 30 minutes prior to premedication.11 

Once a premedicant/sedative has been administered all food items, including hay, should be removed so the rabbit does not become sedated with food still present in the oropharynx. Water bowls should also be removed at this time. 

Gastrointestinal support via prokinetics may be of value to the rabbit patient.  Ranitidine acts on the stomach, metaclopramide is a foregut prokinetic, and cisapride is a hindgut and general intestine prokinetic. All three may be administered orally and metoclopramide subcutaneously. Ranitidine can also be administered intravenously.12,13

Article by
Dr. Karen Heskin
BVSc CertSAO MRCVS

Veterinary Technical Manager, Jurox UK

Originally published: Thursday, 25th October 2018

References

  1. Ratopoulos D & Savvas I (2004). Preoperative fasting: “Nil per Os After Midnight” – Time to Change?  Proceedings of the WSAVA World Congress.
  2. Gelatos AD et al (1995). Gastro-oesophageal reflux during anaesthesia in the dog: the effect of preoperative fasting and premedication. Vet Rec.137(19): 479-83
  3. Savvas I, Ratopoulos D & Rallis T (2016). A “light meal” three hours preoperatively decreases the incidence of gastro-oesophageal reflux in dogs. J Am Anim Hosp Assoc. 52(6): 357-363
  4. Savvas I, Rallis T & Ratopoulos D (2009). The effect of pre-anaesthetic fasting time and type of food on gastric content volume and acidity in dogs. Veterinary Anaesthesia & Analgesia. 36: 539-546
  5. Viskjer S & Sjostrom (2017). Effect of the duration of food withholding prior to anaesthesia on gastro-oesophageal reflux and regurgitation in healthy dogs undergoing elective orthopaedic surgery.  Am J Vet Res. 78(2): 144-150
  6. Bradbrook C (June 2017).  Ask the expert. BSAVA Companion: 4-6
  7. Duke-Novakovski T, de Vries M & Setmour C (2016). BSAVA Manual of Canine and Feline Anaesthesia and Analgesia.
  8. Jolliffe C (2011) Approaches to anaesthesia protocols. Vet Times 41(42):12-18.
  9. Bednarski RM (2015) In: Grimm KA, Lamont LA, Tranquilli WJ, Greene SA, Robertson SA, editors. Lumb & Jones' Veterinary Anesthesia and Analgesia. 5th ed: 819-826
  10. Harcourt-Brown FM (2007). Gastric dilation and intestinal obstruction in 76 rabbits. Vet Rec 161 (12): 409-414
  11. Meredith A & Lord B (2014).  BSAVA Manual of Rabbit Medicine. 1st Edition.
  12. Hedley J, Saunders R, Tittle D, Miles S, Potter J, Stapleton N, Wren T, Gardener C, Edis A, Bertrand H (2017). Considerations for anaesthetising rabbits – Expert panel guidelines. Jurox UK.
  13. Longley L (2009). Risky rabbits: safe protocols and successful anaesthetic recovery. Vet Times Sept 21

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

Putting methadone in its place in your pain management.

In this article we examine why methadone could be considered the analgesic of choice for many of our patients and understand its importance in modern veterinary medicine. The article includes a link to a downloadable summary sheet.

Read On...

​Purr-fecting Pain Management

In this article summary we examine which of the two opioids, buprenorphine or butorphanol, provides the most appropriate analgesia following ovariohysterectomy in the cat.

Read On...

Perspectives on Premeds - Phenothiazines: from Mental Health to Premedication

In this article from the Perspectives on Premeds series, Karen takes us through the properties and uses of phenothiazines in modern veterinary practice.

Read On...

Methadone with Acepromazine - when is enough, enough?

This study looks at the effects of three methadone doses combined with acepromazine on sedation and some cardiopulmonary variables in dogs.

Read On...

AceSedate®, Our New Acepromazine, Available Now.

We have extended our anaesthesia and analgesia portfolio with the launch of AceSedate®. Containing the tried and trusted, long-acting sedative agent acepromazine as its active ingredient, AceSedate can be used for the premedication, sedation and tranquilisation of cats and dogs.

Read On...

Time: is 30 minutes long enough?

This recent study examined whether the application of EMLA cream, for 30 or 60 minutes, would be a useful tool to improve patient compliance prior to intravenous cannula placement in the veterinary clinical practice setting.

Read On...

Caesarean Section Survival Guide. Part 2: Anaesthetic Protocol Selection & Peri-operative Considerations.

In this second instalment of the 2-part article, we explore premedication, induction, maintenance & monitoring, recovery and analgesia for the Caesarean section patient.

Read On...

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...

No leeway for the spay: A comparison between methadone and buprenorphine for perioperative analgesia in dogs undergoing ovariohysterectomy.

This recent paper compares post-operative pain scores and requirement for rescue analgesia following premedication with methadone or buprenorphine, in combination with acepromazine or medetomidine, in 80 bitches undergoing ovariohysterectomy.

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...

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

In this first article out of a series of two, Dan takes us through an introduction and practical tips for appropriate local anaesthesia delivery. Find out why these anaesthesia techniques, that are well recognised in human medicine, have seen an increase in popularity in veterinary medicine over the recent years

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.