Concise review on anaesthetic considerations & emergency management techniques in brachycephalic patients for successful anaesthesia

Introduction

Brachycephalic dogs with BOAS (Brachycephalic Obstructive Airway Syndrome) are twice as likely to have anesthetic complications as non-brachycephalic dogs primarily dyspnoea, regurgitation & aspiration pneumonia, occurring in the postoperative period (Grubb, 2022) [8] . Anaesthesia is a pre-requisite for most of the surgical procedures, so that surgeons can perform surgical intervention with maximum precision and sagacity (Muhammad et al., 2009) [17] . Surgical general anaesthesia is the state of anaesthesia that provides unconsciousness, amnesia, muscular relaxation and hypoalgesia sufficient for painless surgery (Grimm et al., 2015, Novakovski et al., 2017) [7,18] . There is no single drug available that can fulfil all the quality of anaesthesia as a result concept of balanced anaesthesia is developed that includes use of a combination of anaesthetic agents with different mechanisms of action. Balanced anaesthesia included four different phases: 1. Preanaesthesia, 2. Induction, 3. Maintenance 4. Recovery. Preanaesthetic & sedative drugs (anticholinergics, alpha-2 agonists, narcotics, benzodiazepines) calms the patient, induce sedation, decreases salivation, airway secretions, provide muscle relaxation, analgesia promote smooth induction and recovery from anaesthesia (Tranquilli et al., 1999, Novakovski et al., 2017) [26,18] .

Preanaesthetic considerations (patient assessment & preparation):

A full medical assessment starts with proper collection of history of patient which includes deworming, vaccination status, ongoing medications, any history of pre-existing disease, any history of surgery at past, history of food or medicinal allergy, epilepsy, anxiety medication. Any history of hospitalization within last one month. History of feeding schedule and common foods are given. Patient risk assessment should be done by assessing vitals like-rectal temp., heart rate, respiration rate, NIBP monitoring, SpO 2 etc., observing patient behavioral responses with cardiopulmonary (ECG, ECHO, chest X-ray, abdominal USG, endoscopy) & haemato-biochemical (CBC, LFT, KFT, blood glucose profile, thyroid profile) analysis. [2] . Using known drugs by the anaesthesiologist is highly advised as it increase safety window for patients. In the discussion section an example of a balanced anaesthetic protocol will be prepared based on the different research parameters for a hypothetical brachycephalic patients undergoing for a surgical protocol. Commonly available drugs in veterinary anaesthesia field in Indian markets are includesDiscussion: Selection of drugs for an will be done from the above listed drugs to make a balanced anaesthetic protocol so it can cover all the aspects of anaesthetic triad (analgesia, unconsciousness & muscle relaxation). Selection of these drugs are purely based on clinical experience and it's not an universal protocol. Any anaesthesiologist can select and create any anaesthetic protocol by considering preanaesthetic assessment and surgical procedure of respected patient. Here in this hypothetical anaesthetic protocolglycopyrrolate is taken as a preanaesthetic, butorphanol as premedicant analgesics, midazolam as sedative & muscle relaxant, combination of ketamine & propofol commonly known as ketofol @ (1:1) ratio for induction and finally isoflurane with 100% oxygen as inhalant anaesthetic for maintenance of anaesthesia. Here in this protocol selection of drugs are done purely based on clinical experience of using drugs, their availability also considering their combined pharmacological effects in different body systems as well as different clinical & physiological parameters.

Reason to choose glycopyrrolate as premedicant:

Anticholinergic agents are used as preanaesthetics in veterinary practice to reduce salivation and bronchial secretions and to block the effects produced by agents who stimulate the parasympathetic system. Premedication with glycopyrrolate provides better CV stability and decreases cardiac arrhythmias which is caused by atropine and also decreases excessive salivation and bradycardia. It has more rapid onset of action than atropine and has a powerful and prolonged anti-sialagogue activity and is about five times as potent as atropine (Hall et al., 2001; Lemke, 2001) [9,15] . Glycopyrrolate administration as preanaesthetic leads to dryness of muzzle and nostrils and it also blocked vegal mediated bradycardia caused by alpha-2 agonist like xylazine (Potliya et al., 2015) [20] . Glycopyrrolate is long acting drug and provides better cardiovascular stability than atropine.

Reason to choose butorphanol as premedicant analgesics:

Butorphanol is a agonist/antagonist opioid group of drug can be used to produce dose dependent analgesia (2-6 hours) to control moderate pain with mild sedation effect in combination with other drugs. (Grimm et al., 2015) [7] . Butorphanol Produces light to moderate level of sedation with short-duration analgesia and minimal to no respiratory effects (Grubb, 2022) [8] . Combination of butorphanol, midazolam and alfaxolone in Beagles and concluded that this drug combination resulted in excellent recoveries (Seo et al., 2015) [24] .

Reason to choose midazolam as sedation & muscle relaxation agent:

Midazolam is a water soluble agent shows rapid onset of action with minimal negative cardiovascular & respiratory effects unlike alpha-2 agonists and also shows anticonvulsant properties. It is less irritant and short acting in nature compared to diazepam. The coadministration of midazolam with propofol decreased the total dose of propofol needed for induction of anesthesia in sedated healthy dogs (Hopkins et al., 2014) [11] . Midazolam causes dose-dependent significant decrease in the MAC value of isoflurane which may be due to the centrally mediated sedative effect or its spinally mediated antinociception or both together (Seddighi et al., 2011) [22] . Midazolam is a short acting benzodiazepines with higher potency (3times) than diazepam and produce profound sedation when combined with opioids.

Reason to choose ketofol as induction agent: Combination of ketamine and propofol known as Ketofol; administered either individually or by mixing in a single-syringe offering the benefits of both the agents, and for reducing the adverse effects of either agent alone (Lee and Lee, 2016) [14] . The anaesthetic duration of propofol could be enhanced when used in combination with ketamine hydrochloride (Van Natta and Rex, 2006) [27] . The cardiovascular effects of ketamine and propofol are opposite in action from each other, thus balancing each other out when they combined together for anaesthesia (Arora, 2007) [1] . Combo of ketamine and propofol can reduce unwanted adverse effects of both drugs, since these drugs act on different extremesexcitation and depression, respectively (Mair et al., 2009) [16] . IV shots of ketofol @ 2mg/kg each drug produces effective anaesthesia which can be maintain by introducing ketofol @ 1 mg/kg each drug alternative to inhalation anaesthesia (Saikia et al., 2016) [21] . Admixture of ketamine and propofol helps to mask the side effects of the individual drugs which increase the safety and efficacy without changing the haemodynamic stability of the patient when used as general anaesthetic in dog (Shinde et al., 2018) [25] . [10,19] . A greater degree of respiratory depression of a longer duration is seen with propofol than with thiopental (Larisa et al., 2008) [13] . None of these agents individually provides all the components of anaesthesia like adequate muscle relaxation, analgesia & unconsciousness. By considering all these factors ketofol is preferred over propofol, ketamine, etomidate and alfaxolone.

Reason to choose isoflurane as maintenance agent:

Maintenance of anaesthesia can either be done by TIVA technique by inhalant anaesthesia (isoflurane and sevoflurane) technique in dogs. After induction intubation is done by inserting proper sized cuffed endotracheal tube and connecting it with anaesthetic machine for supply of anaesthetic agent and for fresh gas flow (Grimm et al.. 2015) [7] . The MAC value of isoflurane in dogs was between 1.28% and 1.30%. Isoflurane is one of the common inhalant anaesthetic for maintenance of anaesthesia. It is not considered as nephrotoxic as methoxyflurane. Maintenance of anaesthesia with isoflurane in acepromazine-propofol induced dogs had no adverse effects on haematobiochemical and physiological parameters and has smooth and fast recovery from anaesthesia (Kulkarni, 2012) [12] . Recovery from anaesthesia from isoflurane maintenance is very smooth and rapid and very less recovery complications are observed. Maintenance with isoflurane is easy and safe although it did not provide any analgesia in painful procedures, so administration of analgesics in pre or intraoperative period is necessary (Sen and Kilic, 2018) [23] . trauma in these patients. Topical anaesthetic gel like lox 2% is applied to the surface of ET tube before intubation, it acts as a lubricant as well as reduce laryngospasm leads to an easy intubation. Crash cart contains all essential drugs, anaesthetic drugs and their antagonists. Positioning of patient during anaesthesia (lateral, ventro-dorsal or dorsoventral position) is mostly depends on which surgical procedure is to be performed, easy access of anatomical area involved with surgery. But some measures are taken related to positioning to avoid respiratory distress like keeping the head & neck in extended position which improves airflow and reduce the chances of respiratory distress. During anaesthetic procedure eye drops or NS drops are applied to the eyes at a regular intervals (15-20 mins). To control hypothermia inside the OT room heater, hot water bag, warm IV fluid therapy these techniques can be implemented.

Anaesthetic monitoring & emergency management approach:

Most of the anaesthetic deaths occur during recovery period and postoperative mortality rate is 47% in canines (Brodbelt et al. 2008) [4] . Death in canines occurs within first 24 hours after the operation are called as anaesthetic death, makes the post-operative period a high risk time (Gil and Redondo 2013) [6] . Hypoventilation, hypotension, hypercapnia, hypoxemia and ventricular arrhythmias are common complications during anaesthesia which leads to other complications and death during recovery (Gaynor et al. 1999; Bednarski et al. 2011) [5,2] . Anaesthetic death has correlation with ASA status of animal, species, age, type of operation, anaesthetic drugs used, where it was observed that low ASA score was low death rate while the death rate of animals with higher ASA score was higher (Bille et al. 2012) [3] . Before induction of anaesthesia functioning of suction machine, anaesthetic [18] .

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