Originally publsihed on the Vet Anaesthesia Blog 15 July 2016
The current (July 2016) issue of Veterinary Anaesthesia & Analgesia features two separate clinical studies investigating the use of lidocaine at induction in dogs. The findings are interesting and I thought it may be beneficial to briefly present the findings here (particularly for vets and nurse that don’t have access to this journal).
Endotracheal intubation has been shown to produce a reflex increase in systemic blood pressure and a cough response. These changes may be of little concern when anaesthetising healthy animals, however in animals with pre-existing cardiac, intra-cranial or ocular disease these effects may be detrimental should hypertension, elevated intra-cranial pressure, or elevated intra-ocular pressure result.
The first paper by Thompson & Rioja (1) from the University of Liverpool investigated IV or topical laryngeal lidocaine in 42 healthy dogs undergoing orthopaedic procedures. They aimed to assess how these treatments affected the cardiovascular and cough response to endotracheal (ET) intubation. Dogs were pre-medicated with methadone, then administered propofol IV until their lateral palpebral reflex was abolished and jaw relaxation was achieved. Dogs then received either a saline placebo, lidocaine 2mg/kg IV or topical 2% lidocaine (0.4mg/kg) sprayed onto the larynx. Further propofol IV was administered until ET intubation could be performed. Heart rate and mean arterial blood pressure (measured non-invasively using an oscillometric device) were measured after pre-med, just prior to lidocaine, just after lidocaine, and just after ET intubation. There was no change in heart rate or blood pressure in response to lidocaine administration by either route. However, ET intubation caused an increase in MAP in the saline placebo group, whereas MAP decreased in the lidocaine groups. Dogs in the saline placebo group were almost 10 times more likely to cough during ET intubation than those receiving IV lidocaine (7% versus 43%). There was no difference for total required propofol dose between the three groups. Topical lidocaine did not appear to attenuate the cough reflex, however the authors point out that their dose and timing may have contributed to lack of a response, as in people a higher dose is used and the drug administered prior to induction (possibly in people, but usually not tolerated in dogs!).
The second paper by Panti et al. (2) from various clinics in the UK investigated the effect of IV lidocaine on the cough response to ET intubation in 84 healthy dogs.Dogs were pre-medicated with ACP and methadone. They then received either saline placebo, or 1.5mg/kg lidocaine IV, immediately prior to induction of anaesthesia using propofol IV.The authors report a significant reduction in the incidence of coughing at ET intubation in dogs that received IV lidocaine compared to those that received saline (21% versus 45%). Again, there was no difference for total propofol dose between groups.
Arguably, a limitation of both studies is the use of an opioid (methadone) pre-medication. Opioids may attenuate cardiovascular reflexes, and have an anti-tussive effect (prevent coughing). However, in most clinical veterinary cases an opioid will be administered at pre-medication so it can also be argued that these studies represent a clinical scenario well.
The main conclusions to draw from these studies are that IV lidocaine at 1.5 – 2 mg/kg appears to attenuate the cough response to ET intubation in dogs. This may be beneficial in patients with intra-cranial (e.g. brain neoplasia) or ophthalmic disease (e.g. penetrating ocular foreign body). However, a sparing effect on the induction dose of propofol cannot be expected.
- Thompson KR & Rioja E (2016). Effects of intravenous and topical laryngeal lidocaine on heart rate, mean arterial pressure and cough response to endotracheal intubation in dogs. Veterinary Anaesthesia and Analgesia 43: 371-378
- Panti A, Cafrita IC & Clark L (2016). Effect of intravenous lidocaine on cough response to endotracheal intubation in propofol-anaesthetized dogs. Veterinary Anaesthesia and Analagesia 43:405-411
