Anesthesia And Monitoring Guidelines - AAHA

2020 Anesthesia and Monitoring Guidelinesequipment, and drug availability should be considered throughoutanesthesia, have been identified during preanesthetic screeningthe entire anesthetic plan.of geriatric dogs.10To further minimize patient risk, use of an anesthesia-surgery·Breed/Size: Few breed-specific anesthesia “sensitivities” havechecklist (available at aaha.org/anesthesia) helps prevent practicesbeen identified. Greyhounds may have prolonged recoveriesfrom committing critical oversights and errors in the peri- andafter receiving some anesthetics such as barbiturates and mayintraoperative periods. These patient safety checklists can be createdexperience hyperkalemia associated with general anesthesia.11,12for every sedation or general anesthesia procedure, as part of theBreeds affected by the multiple drug resistance mutation 1patient’s medical record.(now ABCB1 or adenosine triphosphate binding cassette subfamily B member 1) gene mutation should receive reducedStep 1: Preanesthetic Evaluation and Plan Considerationsdosages of acepromazine and potentially butorphanol.13 Con-Preanesthetic Evaluationversely, breed-specific anatomy or propensity for underlyingThe preanesthetic patient evaluation is critical for patient safety as itconditions commonly impact anesthesia. For instance, brachy-promotes identification of individual risk factors and underlyingcephalic dogs and cats are more prone to upper airway obstruc-physiologic changes or pathologic compromise that will impact thetion, and brachycephalic breeds have been shown to haveanesthetic plan. Factors to be evaluated include the following:higher airway-related anesthetic complication rates compared·History: Identify risk factors such as known medical conditionswith nonbrachycephalic breeds.14 Some breeds of dogs (e.g.,and previous adverse drug responses. Clarify the use of allCavalier King Charles spaniel) and cats (e.g., Maine Coon)prescribed and over-the-counter medications (e.g., aspirin,may be predisposed to cardiac disease.15 Other breed-relatedherbal products, cannabidiol, and supplements) to avoid ad-diseases that may impact anesthesia, such as collapsing tracheaverse drug interactions.9 Note any abnormal clinical signs, bothin many small-breed dogs, breed-related renal or hepatic dys-acute and chronic, with individual questions specifically di-function, low intra-erythrocyte potassium concentrations inrected at the cardiovascular, respiratory, gastrointestinal, ner-the Shiba Inu, and drug metabolism in cats, should also bevous, and musculoskeletal/mobility systems. Records should beconsidered.16 Breed-related size can also impact anesthesia.6evaluated for previous anesthetic events, and client communi-Very small/toy-breed dogs and all cats are at increased riskcation should include specific questions regarding satisfactionfor anesthetic complications because they are more prone towith previous anesthetics and recoveries. A smooth recoveryhypothermia and may be more difficult to intubate and mon-may be noted in the hospital, but the patient may go home anditor. These patients may experience volume overload if a meansexhibit abnormal behaviors such as lethargy, nausea, vomiting,to deliver precise fluid volume (e.g., syringe pumps, buretrols,restlessness, and vocalization, which could indicate pain oretc.) is not instituted and are more easily overdosed if high-other complications that need to be addressed.concentration drugs, high-volume syringes, or high-volumePhysical examination: A thorough physical examination shouldbags of fluid are used. Giant-breed dogs can be at increasedbe completed and documented within 12–24 hr previous torisk because they are more commonly overdosed when milli-anesthesia and repeated just prior to anesthesia if acute clinicalgram per kilogram dosing versus body surface area dosingchanges occur. Failure to record a physical exam was reportedis used.Temperament: Fear, anxiety, and stress can be exhibited in·to increase the odds for death in dogs.4··Age: Although age is not a disease, disease processes occurmany ways, including aggression, hiding, fleeing, or freez-more commonly in aged patients, and physiologic systemsing. When any of these behaviors are exhibited, the patientcan be immature in neonatal and pediatric patients. Advancedmay benefit from medication administered at home to pro-or very young age can increase anesthetic risk because of al-vide anxiolysis and reduce fear prior to travel to the hospi-tered responses to drugs caused by changes or immaturity intal. An aggressive temperament can limit the preanestheticcardiovascular, respiratory, renal, hepatic, and neurological sys-evaluation or make examination prior to sedation impossi-4–6Examples include the inability to mount a robust phys-ble. This can impair the ability to detect abnormalities andiologic response to hypotension or hypothermia in thesemay increase anesthetic risk. Anxious patients often requireage groups. Neonatal and pediatric patients may also be im-high doses of sedatives or tranquilizers, which may causepacted by hypoglycemia and geriatrics by impaired cognitiverespiratory and cardiovascular depression. For elective pro-function. A fairly high percentage of health abnormalities,cedures, consider rescheduling with a plan to manage anx-including those that might cause a cancellation of or change iniety before admission to the clinic. Conversely, a quiet ortems.JAAHA.ORG3

Medications the Day of Anesthesia”). Individual patient diagPotential Anesthesia Risk Factors andnostics may include a minimum database of laboratory analysisActions to Mitigate Risk(complete blood count, chemistry panel, urinalysis) andPreanesthesia conditions for which correctivecould include other components such as blood pressureintervention is advisable to critical(BP), electrocardiogram (ECG), and imaging modalities likeechocardiogram or ultrasound. For example, BP should beAnxietyroutinely measured in patients with renal, cardiovascular,Painand endocrine disorders. Currently, dogs eating a grain-Hypoglycemia BG ,60 mg/dLfree diet should undergo an echocardiogram to evaluateHypothermia ,998Fcardiac contractility as a result of the potential link betweenAnemia (depending on severity and chronicity)dilated cardiomyopathy and grain-free diets.17 There is noDehydrationevidence to indicate the minimum timeframe between lab-Life-threatening cardiac arrhythmiasoratory analysis and anesthesia. A reasonable timeframeElectrolyte and acid–base dyscrasias (K .6.0 mEq/L, pHis #3–6 mo if values were normal and the patient is clini-,7.2)cally healthy. If either lab values or the patient’s health isCyanosisabnormal, repeat diagnostics should be performed immedi-Congestive heart failureately prior to anesthesia.Oliguria, anuriaPneumothoraxActions to mitigate risk during anesthesiaOther Plan Considerations·Type of Procedure: In addition to patient temperament andPreanesthetic physical exam and documentationcomorbidities, consider the level of procedural invasiveness, du-Premedication to reduce stress, decreased anesthetic re-ration of surgery, and anticipated pain level. General anesthesiaquirementsDedicated anesthetistIV catheter to facilitate IV administration of medicationsRecommendations for Chronic Medications the Day ofOxygen supplementation and monitoring of respiratoryAnesthesia*function (RR, ETCO2, SpO2)Continue medications as scheduled:Monitoring of cardiovascular function (HR, BP)··Assessing cardiac rhythm (ECG)Monitoring and support of normal body temperatureThyroid medication: thyroid supplement or methimazoleBehavioral and analgesic medications: sudden withdrawalof these medications is not advisedBG, blood glucose; BP, blood pressure; ECG, electrocar-····diogram; ETCO2, end-tidal carbon dioxide; HR, heartDiscontinue the day of anesthesia:rate; RR, respiratory rate; SpO2, percentage of hemoglo-·Continued patient support and monitoring in recoveryDocumentation of patient parameters during anesthesiaand recovery (anesthesia record)bin saturated with oxygen.Oral anxiolytics: to reduce fear and anxietyCardiac medications: pimobendan, furosemideAntibioticsSteroids: should not be abruptly stoppedAntihypertensive medication, especially ACE inhibitors:enalapril, benazepril8·Anticoagulants: may need to be discontinued 2 wk priorto anesthesia based on risk of bleeding·depressed animal may require lower drug dosages for seda-Administer based on specific recommendations to owner:tion or anesthesia.·Patient Diagnostics: Risk factors and specific patient concernsprovide a framework for developing individualized anesthesiapatients because of risk of hypoglycemia*List is not all-inclusive but focuses on medications stronglyplans and may indicate the need for additional diagnostic test-recommended to either administer or cease.ing, stabilization before anesthesia, or adjustments in chronicACE, angiotensin-converting enzyme.medications (see textbox “Recommendations for Chronic4Insulin: full dose should not be administered to fastedJAAHA 56:2 Mar/Apr 2020

2020 Anesthesia and Monitoring Guidelineswith airway control is required for long, invasive, and/or poten-be 0.05% (1 in 1,849, 95% confidence interval [CI] 0.04–0.07%) intially painful procedures (dentistry, elective ovariohysterectomydogs and 0.11% (1 in 895, 95% CI 0.09–0.14%) in cats, with deathor castration, or orthopedic procedure) and for any patient withmost frequently occurring in the first 3 hr postoperative.6,18 Al-airway compromise or undergoing airway surgery. Sedation maythough this can be concerning, fears can be alleviated with as-be appropriate for shorter (,30 min) and less invasive proce-surance that the anesthesia team will consider multiple factorsdures (e.g., diagnostic procedures, joint injections, suture re-including health status, breed, age, expected pain level, and sur-moval, and minor wound management) in healthy patients.gical plan when making an individualized anesthesia plan for theirHowever, heavy sedation is not suitable for all patients andpet. Tailoring each patient’s anesthetic plan to their specific needs5may actually increase the odds for anesthesia-related death.allows the anesthesia team to provide optimum care, includingFor instance, in older, medically compromised patients, briefpatient-specific anesthetic monitoring performed by a dedicatedgeneral anesthesia is preferable because it is less stressful andanesthetist. The anesthesia team should clearly communicate tomore controlled than sedation. Some procedures may limit phys-the pet owner that these measures will decrease the likelihoodical access to the patient (e.g., oral or ophthalmic procedures),of anesthetic complications both during the procedure and in thenecessitating individualized plans for monitoring, catheter ac-recovery period.cess, etc.··Pain management and patient comfort is generally very con-Clinical Staff Training: Trained clinical staff are essential for safecerning to the pet owner and should be emphasized as an integralanesthesia. The number of trained staff and the level at whichpart of each patient’s anesthetic plan. Pet owners should be reassuredthey are trained will also impact efficiency and scheduling. Inthat multiple modalities will be used to minimize patient discomfortaddition, staff training can positively impact specific areas ofand stress level prior to leaving home, in hospital, and during re-anesthesia; for instance, staff training in local and regional an-covery at home. The pet may require analgesics and anxiolyticsesthesia techniques will help facilitate their perioperative use.administered at home, and the benefits of these drugs shouldTime of Day: Increased anesthetic risk has been documentedbe explained. The overarching goal for client communication is tofor procedures occurring late in the day or after normalensure that the pet owner is confident that the anesthesia team hashours.4,6 This is because of a combination of inadequate timethe compassion, skills, and technology to provide the safest possiblefor stabilization, limited staff availability, and staff fatigue. Theanesthesia for their pet.fact that many procedures are also emergency or urgent, versusscheduled or elective, is also associated with an increase in thePhase 2: Day of Anesthesiarisk of anesthetic death.5,6 Nonemergency procedures may beStep 1: Anesthesia Begins at Homebest performed during the next available regular clinic dayThe pet owner begins the continuum of anesthesia with fasting the petwhen time for preparation and planning is adequate. Whenand administering medications as directed by the anesthesia team.possible, critical patients should be anesthetized early in theAlthough not all evidence is in agreement, in general, the recommendedday to allow adequate time for anesthetist-supported recovery.fast duration for healthy adult patients has decreased. The change isbased on clinical experience and experimental evidence of shorterStep 2: Client Communication/Educationfasting benefits, including a lower incidence of gastroesophageal refluxOnce the initial plan is formulated, pertinent information regarding(GER). An abbreviated fast is particularly important for diabetic andthe anesthetic procedure and pet-specific risk factors should beneonatal patients (Figure 1). Most medications currently adminis-discussed with the pet owner. Because of safety concerns, pet ownerstered to the pet should be continued on the day of anesthesia, butare sometimes hesitant to authorize discretionary procedures re-there are exceptions, especially for some cardiac medications (seequiring general anesthesia, such as preventive dental care or diag-textbox “Recommendations for Chronic Medications the Day ofnostic imaging. This concern is best alleviated with appropriateAnesthesia”). Analgesic drugs (e.g., nonsteroidal anti-inflammatorycommunication between the veterinary team and the pet owner,drugs [NSAIDs]) may be among the drugs that the patient is al-along with education of the pet owner regarding the entire anestheticready receiving or may be started immediately prior to the procedure.process. Additional resources are available at aaha.org/anesthesia.If the patient experiences motion sickness, maropitant should beCommunication with the pet owners should include a fullconsidered for administration before the patient is transported to thedescription of the anesthetic procedure and a discussion of potentialhospital to prevent vomiting. Anxiolytic drugs should definitely berisks prior to obtaining written, preprocedural consent. In healthyadministered for all fractious/aggressive/fearful patients and should bedogs and cats, the risks of anesthetic-related death were estimated tostrongly considered for patients that develop any level of fear, anxiety,JAAHA.ORG5

FIGURE 1Feeding and treatment recommendations for dogs and cats prior to anesthesia.or stress during a visit to the veterinary hospital. Gabapentin andcarbon dioxide (CO2) by the patient. The machine and thetrazodone are commonly used for this purpose. Dosages for thesebreathing circuit become part of the patient’s respiratory system andand other previsit pharmaceuticals are listed in Figure 2.can support, if working correctly, or impair, if working incorrectly,respiratory function. Two essential safety features to have on everyStep 2: Equipment Preparationanesthetic machine are (1) an in-circuit manometer and (2) a safetyPrior to the start of any general anesthesia or sedation-only pro-pop-off valve (see examples at aaha.org/anesthesia). A manometercedure, it is critical to ensure that all equipment and monitors areallows safe delivery of manual and mechanical breaths, enables leakturned on, are functioning, and have undergone appropriate safetychecking of the seal of the ETT cuff within the trachea, and allowschecks. All necessary equipment, including the anesthesia machine,for a visual indication of rise in airway pressure. Safety pop-offbreathing circuit, endotracheal tube (ETT), intubation tools (e.g.,valves prevent excessively high airway pressure and potential baro-laryngoscope), and anesthetic monitors, should be prepared. An-trauma. These can be installed on most anesthesia machines for useesthetic equipment is considered “life-critical” because the well-with both types of breathing circuits.being of patients can be adversely affected if the equipment is notAnesthesia personnel have a responsibility to understand thefunctioning optimally or is used incorrectly. Anesthesia machines,proper use and function of, and be able to set up, check, and trou-paired with breathing circuits (nonrebreathing circuit [NRC] orbleshoot, all necessary equipment prior to use. Equipment setuprebreathing circuit [RC]), are designed to deliver oxygen (O2) andshould be guided by checklists (found at aaha.org/anesthesia) thatinhalant anesthetic to the patient and to prevent rebreathing ofdictate general equipment preparation tasks for the day (e.g., fill the6JAAHA 56:2 Mar/Apr 2020

2020 Anesthesia and Monitoring GuidelinesFIGURE 2Anxiolytic, sedation, and premedication medications.CO2 absorbent canisters) and specific preparation tasks for each pa-may be roughly daily or weekly, depending on the anesthesia casetient (e.g., pressure check the anesthesia machine prior to each use).load.Step 2aStep 2bEnsure that O2 levels in the E-tank or hospital supply tank are .200Connect the breathing circuit to the machine. When choosing apsi or that the oxygen generator is functioning properly. Fill thebreathing circuit, note that NRCs are commonly used for cats andvaporizer with liquid inhalant. If the patient will be breathingsmall dogs (patients ,3–5 kg [6.6–11 lbs]) because, compared withthrough an RC, change the CO2 absorbent after 8 hr of use, whichRCs, they cause less resistance to breathing and have low equipmentJAAHA.ORG7

dead space, both of which are important considerations in smallmeasure ensures that oxygen is flowing to the patient and that therepatients. Excessive equipment dead space leads to rebreathing of CO2is minimal risk of inhalant leakage. For this step, the adjustableand subsequent hypercarbia/hypercapnia. Dead space should be keptpressure limiting, also called the pop-off valve, must be closed.to a minimum and should be #2–3 mL/kg, which is #20% of totalOcclude the end of the breathing circuit and increase the O2 flow totidal volume. The patient end of breathing circuits (where mixing ofraise the machine circuit pressure to 20–30 cm H20 on the ma-inspired and expired gases occurs) is a common source of dead space.nometer. The oxygen should be turned off, and the pressure ma-Pediatric circuits, which have low dead space, are recommended fornometer should remain steady. If no leak is detected, open theuse in smaller patients. Rebreathing of CO2 in the NRC is preventedpop-off valve, and then release the breathing circuit occlusion. Ifby high O2 flow rates, which also allows for a faster turnover in thea leak is detected, pull the machine from use and initiate trou-change of anesthetic depth when adjusting the vaporizer setting. Thus,bleshooting procedures.the O2 flow should be w200–400 mL/kg/min when using NRCs.19Flow adequacy should be monitored with a capnograph and adjustedStep 2dto keep the inspired CO2 to ,5 mm Hg. If any occlusion occurs inEnsure proper setup of the scavenging system to limit or eliminatethe expiratory limb of the circuit, the relatively high oxygen flow ratespersonnel exposure to inhalant gases. The Occupational Safetyused in NRCs will cause rapid pressurization of the entire system andand Health Administration provides advisory guidelines, althoughcan lead to airway damage and/or circulatory collapse within minutes.some US states have specific regulations regarding control of wasteIn addition, the oxygen flush valve should never be used in a patientanesthetic gases. Active scavenging systems are far more effectivebreathing through an NRC because it directs a high-pressure flowthan passive scavenging systems (e.g., activated charcoal canis-directly into the patient’s

However, the use of guidelines, checklists, and training can decrease the risk of anesthesia-related adverse events. These tools should be used not only during the time the patient is unconscious but also before and after this phase. The framework for saf