Induction of anaesthesia using a co-induction technique is a simple method that may improve the safety and quality of anaesthesia administered.
This blog details some of the benefits of co-induction and explains how to use the technique in domestic species.
Co-induction of anaesthesia is a technique that uses more than one drug together (e.g. fentanyl and propofol, diazepam and ketamine, etc.).
Benefits of a co-induction technique include:
- Smaller dose requirements for each drug, therefore, minimising their adverse physiological effects
- Reduction / avoidance of inappropriate side effects that occur when a drug is used to induce anaesthesia on its own
- Smoother induction and easier intubation
1. Smaller dose requirement
The addition of a drug such as fentanyl, diazepam or midazolam to propofol for anaesthetic induction of small animals results in a lower dose requirement for propofol. Propofol results in dose-dependent cardiorespiratory depression which may result in adverse effects such as hypotension, hypoventilation and post-induction apnoea. Opioids such as fentanyl, and benzodiazepines such as diazepam and midazolam, produce minimal cardiorespiratory depression. However, their use alongside propofol at induction means that a smaller dose of propofol is required to achieve adequate anaesthetic depth, thus minimising the cardiorespiratory depression produced. This may be particularly important during the anaesthesia of geriatric animals, or those with pre-existing diseases.
2. Reduction / avoidance of unwanted drug effects
When used alone for anaesthetic induction ketamine produces muscle rigidity and may cause excitement. Combining ketamine with a benzodiazepine tranquilliser with a muscle relaxant effect such as diazepam or midazolam, offsets the muscle rigidity and allows for a smooth calm anaesthetic induction. In large animals such as horses and cattle, an alpha-2 adrenergic agonist such as xylazine may be chosen instead or in addition to a benzodiazepine. Xylazine also produces sedation and muscle relaxation (but its use in small animal anaesthesia has been linked to increased mortality rates, therefore its use is reserved for large animals only).
3. Smoother induction and easier intubation
The addition of drugs with a sedative/tranquillising effect, that also minimise airway reflexes or are cough suppressants helps to produce a calm induction and smooth placement of an endotracheal tube. Avoidance of coughing and irritation during intubation is especially important in animals that may be suffering increased intracranial pressure. Drugs with these effects include fentanyl, midazolam and lidocaine.
How to perform co-induction
The sedative/tranquilliser drug being used for co-induction alongside an anaesthetic agent such as propofol is often administered intravenously first in small animals so that the propofol can then be slowly titrated to effect. However, when using benzodiazepines for co-induction, recent studies have shown that administration of a small amount of propofol (1 mg/kg) then the benzodiazepine, then continuing to titrate propofol until the desired anaesthetic depth is achieved, will help to avoid any excitement/dysphoria that benzodiazepines may produce in healthy small animals.
In large animals, and when ketamine and a benzodiazepine are used in combination, both drugs are usually mixed in the same syringe in order to produce the smoothest anaesthetic induction. It should be noted however that some brands of diazepam may not mix well with other drugs, and so may have to be administered immediately prior on its own.
Suggested doses / combinations (small animals)
Fentanyl 2 mcg/kg IV just prior to induction with propofol IV to effect
Propofol 1mg/kg IV, then midazolam 0.2mg/kg, then propofol IV to effect
Propofol 1mg/kg IV, then diazepam 0.2 – 0.4 mg/kg, then propofol IV to effect
Medetomidine 1 mcg/kg IV just prior to induction with propofol IV to effect
Dexmedetomidine 0.5 mcg/kg IV just prior to induction with propofol IV to effect
Diazepam 0.25 mg/kg + Ketamine 5mg/kg IV combined in the same syringe
- Covey-Crump & Murison (2008). Fentanyl or midazolam for co-induction of anaesthesia with propofol in dogs. Veterinary Anaesthesia and Analgesia 35 pages 463-472
- Ko et al. (2006). Effects of intravenous diazepam of microdose medetomidine on propofol-induced sedation in dogs. Journal of the American Animal Hospital Association 42 pages 18-27
- Sanchez et al. (2013). Effects of altering the sequence of midazolam and propofol during co-induction of anaesthesia.Veterinary Anaesthesia and Analgesia 40 pages 359-66
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