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IN PRACTICE | May 2020 197

Preanaesthetic screening in dogs and catsBackground: Preparation before performing general anaesthesia is essential. In order to comprehensively plan and execute safe anaesthesia, it is vital to quantify anaesthetic risk. However, currently there is limited veterinary literature that collates anaesthetic-related, patient-related and procedural-related risks.

Aim of the article: This article highlights previously reported perioperative factors contributing to morbidity and mortality in small animals, as well as important considerations to factor in based on the patient history and findings on clinical examination. It also discusses the current opinions on blood screening and diagnostic imaging.

Jacques Ferreira qualified from the University of Pretoria, South Africa,

in 2011. He went on to complete a residency in veterinary anaesthesia before moving to the University of Liverpool, where he was a lecturer between 2016 and 2018. He is currently a veterinary anaesthetist at the Willows Veterinary Centre and Referral Service in Solihull.

KEY LEARNING OUTCOMESAfter reading this article, you should understand:

▢ Perioperative factors that contribute to mortality and morbidity in small animals;

▢ Classification of physical status in preanaesthetic patients; ▢ The importance of performing preanaesthetic assessments; ▢ Current opinions on preanaesthetic screening and how to adapt

this based on surgical procedure; ▢ The use of point-of-care ultrasound for diagnostic imaging.

doi: 10.1136/inp.m1448

in screening all patients before sedation or anaesthesia, and thereby ensure the assimilation of a tailored perianaesthetic plan (AVA 2018). Similarly to AAGBI guidelines, the AVA safety checklist highlights the need to identify risk based on history and clinical findings. Unfortunately, further explanation is lacking.

Differentiating low-risk and high-risk patients for anaesthesiaAnaesthesia induces substantial stress on various organ systems in the body and therefore the presence of disease or reduced health raises the risk of adverse perianaesthetic outcomes (Portier and Kazue 2018). Considering this, the ability to differentiate patients according to their magnitude of illness would be beneficial in aiding with perianaesthetic risk profiling. In human anaesthesia, stratification of patients in this manner is performed using the American Society of Anaesthesiologists (ASA) physical status classification system, which has demonstrated a good correlation with perioperative mortality (Wolters and others 1996, McMillan and Brearely 2013). In veterinary anaesthesia, similar findings have been observed, where patients assigned a higher ASA grade have been associated with increased risk of death (Brodbelt and others 2008; Portier and Kazue 2018).

The ASA scoring system is essentially an ordinal rating scale, which classifies a patient’s health status based on simple descriptors. The ASA has been adapted for veterinary anaesthesia (Table 1) and has five categories. These range from grade one, assigned to healthy patients presenting for an elective procedure (eg, castration) to grade five, assigned to patients with severe systemic derangement involving a number of organ systems. These would result in a moribund presentation with minimal chance of survival despite surgery (eg,

PERIOPERATIVE mortality in veterinary practice has improved in the past decade, but the rate is still considerably higher than that observed in human anaesthesia (Brodbelt and others 2008). In the UK, substantial effort is made to streamline human patients according to perceived anaesthetic risk before they undergo anaesthesia, by making use of the Association of Anaesthetists of Great Britain and Ireland (AAGBI) guidelines (Mortimer and others 2001). The AAGBI guidelines are intended to improve perioperative outcomes by primarily focusing on: ■■ identification of potential anaesthetic difficulties and existing medical conditions,■■ improving safety by assessing and where possible quantifying risk, ■■ allowing planning of perioperative care.

In veterinary science, the Association of Veterinary Anaesthesia (AVA) have published anaesthetic safety checklists (https://ava.eu.com/resources/checklists/) in which a number of pre-anaesthetic questions pertaining to the patient requiring anaesthesia have been formulated. The questionnaire is intended to aid the clinician

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severe sepsis secondary to pyometra) (Clarke and others 2014). The ASA is not a complete system and should not be used as the sole method for assigning anaesthetic risk (McMillan and Brearely 2013; Hosgood and Scholl 1998).

ASA limitationsThe foremost limitation with the scoring system relates to the degree of interobserver variability, which has resulted in, at best, fair agreement when different clinicians assign a grade to the same patient (McMillan and Brearely 2013). Furthermore, the assigning to a patient of an ASA score of one or two does not significantly change the likelihood of a patient suffering perianaesthetic complication (PAC), demonstrating relatively poor sensitivity at lower scores (Hosgood and Scholl 1998, Brodbelt and others 2015).

A third limitation of the scoring system is the inability to incorporate procedure-related risks to the final score (McMillan and Brearely 2013). Such an example has been demonstrated in a study comparing cervical and thoracolumbar spinal surgery in dogs. The study reported that increased risk of mortality was directly attributed to the site of surgery and procedure performed, highlighting the importance of taking this into consideration (Posner and others 2014).

A fourth limitation to using ASA score alone to assign perianaesthetic risk is deciding on whether signalment should influence the score allocated. For example, should age be a contributor to ASA (Hosgood and Scholl 1998). Similarly, the relevance of breed-specific (eg, Labrador retriever and brachycephalic breeds) considerations is not necessarily incorporated in the ASA model (Gil and others 2013, Ponser 2016).

ASA classification is simple and quick to perform,

however it cannot be the sole method for assigning perianaesthetic risk to veterinary patients. In addition to ASA, patient history, signalment, intended procedure(s), available facilities and personnel experience should be taken into account when qualifying risk and deciding on the patient’s perianaesthetic plan.

Performing thorough preanaesthetic assessments in dogs and catsClinically relevant history and current health status in veterinary patients is vital. This is particularly important as there is a high degree of heterogeneity, with some patients presenting for the first time for an elective procedure (eg, castration or ovariohysterectomy), compared to others which have chronic comorbidities and a comprehensive medical history.

Patient historyA comprehensive patient history is important and should not be overlooked. Table 2 outlines some important details that should be acquired from the patient history. Assimilating a thorough history will guide the clinician towards any abnormal organ(s) function to investigate during the clinical examination and subsequent pre-anaesthetic diagnostic tests.

In addition to establishing a recent clinical frame of reference from which to interpret any relevant findings on clinical examination, acquiring a comprehensive history regarding any concurrent medication relevant to anaesthesia is important. Certain pharmaceuticals will have a marked effect on a dog’s sensitivity to anaesthetic agents and/or risk for PAC (Defranscesco 2014, Dell’osa and Jaensch 2016). Such an example is the analgesic robenacoxib, which may reduce the requirements of

Table 1: Classification of physical status in preanaesthetic patients (Brodbelt and others 2015)

Grade (ASA) Physical status Clinical examples

Grade ASA I Normal (non-brachycephalic) healthy patients

Castration/neutering Simple fracture repair

Grade ASA II Mild systemic disease Brachycephalic/geriatric considered otherwise healthyCardiac murmur (grade 1-2)Dehydration – mild (4-6 per cent)Gastrointestinal disease – mild/stable

Grade ASA III Severe systemic disease Anaemia – moderateBrachycephalic with mild respiratory/gastrointestinal signsEpilepsy – uncontrolled/unstablePulmonary/renal disease – patient compensating

Grade ASA IV Severe systemic disease, constant threat to life

Cardiac arrhythmia – severe/uncontrolledDehydration – severe (>10 per cent)EndotoxaemiaHepatic disease – uncontrolled/unstable

Grade ASA V Moribund patient, not expected to survive without operation

Intracranial haemorrhageMultiple organ dysfunction Severe sepsis/traumaTerminal malignancy

ASA American Society of Anaesthesiologists

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sevoflurane to maintain anaesthetic depth in dogs by up to 10 to 15 per cent (Tamura and others 2013). It is also important to determine when the medication was last administered (Tamura and others 2013). In dogs, the incidence of intraoperative hypotension is greater when the angiotensin-converting enzyme (ACE) inhibitor enalapril is administered within 90 minutes of undergoing general anaesthesia (Dell’osa and Jaensch 2016). Taking this into consideration, dogs administered enalapril on the day of surgery may require more intensive monitoring and/or have elective procedures delayed by 24 hours until the vasoactive effects of the drug are minimal.

SignalmentPatient signalment is important when compiling your perianaesthetic plan. Notably, species, breed, age and weight should be taken into account (Coleman and others 2016), as interspecies mortality varies considerably in veterinary anaesthesia (Brodbelt and others 2008). Mortality for dogs undergoing anaesthesia ranges from 0.14 to 0.19 per cent. In cats, the risk is comparatively greater with a mortality of 0.20 to 0.27 per cent being reported (Brodbelt and others 2007, 2008).

Breed differencesBreed differences may predispose patients to greater risk of PAC, and this was subtly demonstrated in a recent retrospective study quantifying PAC in brachycephalic dogs. Grunheld and others (2018) concluded that the greater the severity of brachycephalic-related clinical signs, the greater the risk for PAC, particularly during the anaesthetic recovery period.

Brachycephalic obstructive airway syndrome (BOAS) involves congenital anatomical abnormalities of the upper respiratory tract, such as, stenotic nares,

elongated soft palate, everted laryngeal ventricles, laryngeal collapse and hypoplastic trachea. These predispose to respiratory compromise and altered autonomic nervous system responses (ie, increased vagal tone) (Kaye and others 2017).

In addition to anatomical differences, breed-specific drug idiosyncrasies have been reported. One such example is the report of opioid-induced dysphoria in certain breeds of dogs (Table 3) (Kongara 2018). Likewise, in Alaskan breeds, increased opioid sensitivity has been observed, and revising of the dose rates in these dogs may be warranted (Kongara 2018).

Breed-specific organ dysfunction, such as sick sinus syndrome (SSS), is a particularly challenging comorbidity to diagnose. SSS is characterised by intermittent sinoatrial standstill manifesting as severe bradycardia or syncope (Ward and others 2016). In severe cases, pacemaker implantation may be required, and as highlighted in a case of West Highland white terriers, abnormal heart rate and rhythm should not be ignored (Ward and others 2017). Von Willebrand disease in dobermanns is a congenital dysfunction. This genetically inherited disease affects primary haemostasis, predisposing to severe haemorrhagic diatheses. This may be potentially life threatening during routine procedures such as ovariohysterectomy or orchiectomy (Brooks and others 2001).

Table 3 lists common breeds at risk of PAC; however, it is not exhaustive and readers are encouraged to familiarise themselves with any breed-specific considerations before anaesthetising breeds not commonly encountered.

AgeExtremes of age is another signalment-related consideration which may pose anaesthesia-related challenges. Altered physiology, physical size and comorbidities may potentially contribute to PAC.

Very young patients (under 8 to 12 weeks old) have immature organ function predisposing to other complications, including hypoglycaemia, hypothermia, respiratory depression, hypotension, electrolyte abnormalities and increased sensitivity to anaesthetic and analgesic agents (Grubb and others 2015). Geriatric patients (seven years and older in dogs, 12 years and older in cats) are considered predisposed to PAC. However, there appears to be limited correlation between chronological age and physiological age (Perrin 2009).

Assigning additional risk for PAC solely based on a dog’s age has been previously questioned; it has been suggested that the risk of PAC doubles in geriatric versus non-geriatric dogs (Hosgood and Scholl 1998, Posner and others 2014). Importantly, age as a factor was significantly worse at predicting PAC than increasing the ASA score by a factor of one (Hosgood and Scholl 1998). Considering this,

Table 2: Parameters to consider preanaesthesia when taking a patient’s history (Posner 2016)Parameter Points of interest

Medical history Current medication, vaccination status, polytrauma

Preanaesthetic preparedness

Fasting, owner consent

Activity and interaction

Willingness to interact (animals and owners)

Central nervous system

Mentation, history of seizures, changes to exercise tolerance, sudden loss of conciousness, chronic coughing (time of day), respiratory effort, stertor or stridor

Gastrointestinal Appetite, drinking frequency, vomiting, regurgitation, abnormal faeces colour/consistency

Urogential Reproductive status, water intake and urination

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clinicians should be mindful that older patients are more likely to have comorbidities, thus warranting thorough preanaesthetic screening.

Body conditionBody condition is an important consideration when designing a perianaesthetic plan. Obesity is a common comorbidity of dogs and cats. Altered organ function in obese patients is common and predisposes to clinical signs such as hypertension, hypoventilation and hypoxaemia. These can all be particularly life threatening when undergoing anaesthesia and may further predispose to an increased risk of perianaesthetic mortality (Brodbelt 2009, Love 2015).

Recently, concern with overdosing of anaesthetic agents in obese dogs has been demonstrated by a reduction in propofol dose requirements when the dose was calculated based on total body weight. Due to these findings, it is currently recommended to calculate anaesthetic dose based on an animal’s lean body mass and the difficulty of formulating an anaesthetic plan in this cohort of patients has been highlighted (Boveri and others 2013).

Clinical examinationThe clinical examination is still the fundamental tool for assessing a patient before they undergo general anaesthesia. The importance of a comprehensive, repeatable and concise clinical examination is undisputed. It helps the clinician to construct a clinical picture on the current status of the patient, which may or may not compliment the clinical history. The clinical examination should take into account the intended surgical or

diagnostic procedure requiring an anaesthetic, with the goal of highlighting potential patient-related risk factors that may require further investigation beforehand. Table 4 describes common organ-specific findings that may be indicative of disease, as well as suggested further investigations to be performed. Box 1 demonstrates the importance of performing a thorough clinical examination by demonstrating the rationale for further investigation of abnormal findings before general anaesthesia is performed.

Is there a role for routine preanaesthetic blood testing?Clinical examination provides a large amount of information regarding the status of the animal on presentation; however, further diagnostics are often required to qualify and quantify disease progression, degree of organ dysfunction and ultimate anaesthetic risk. Taking this into consideration, it would appear reasonable to perform routine haematological and biochemistry screening in all patients undergoing anaesthesia (Dell’osa and Jaensch 2016).

Unfortunately, routine screening detecting previously undiagnosed concomitant disease has been reported in only three per cent of people, six per cent of dogs and 19 per cent of cats undergoing anaesthesia (Dell’osa and Jaensch 2016). Due to the low incidence of significant findings, the indiscriminate laboratory testing of all patients before anaesthesia has rightly been questioned. Trials investigating pre-general anaesthetic screening in dogs and cats have demonstrated conflicting results, with one paper advising against

Table 3: Breed-specific perianaesthetic considerations

Breed Perianaesthetic considerations Reference(s)

Alaskan breeds Predisposed to opioid-induced dysphoria Kongara 2018

Brachycephalic Brachycephalic obstructive airway syndrome (BOAS)Predisposed to regurgitation

Kaye and others 2017Dias and others 2016

Collies MDR-1 gene mutation, therefore sensitive to: penothiazines, morphine, macrocyclic lactones

Mealey 2004

Dobermann Genetic predisposition to Von Willebrand disease (type 1)Risk of preclinical dilated cardiomyopathy

Brooks and others 2001Wess and others 2017

Greyhound Unpredictable drug sensititivty and dosing intervals, above average PCV, low BWC and low platelet count, functional murmurs, aortic stenosis, high blood pressure, high GFR, high serum creatinine, low T4 and fT4, high risk of postoperative bleeding (slow clot kinetics and low clot strength)

Vilar and others 2008

Labrador retriever Predisposed to opioid-induced dysphoriaAt risk of laryngeal paralysis

Sinclair 2018Broome and others 2000

Rottweiler At risk of laryngeal paralysis Sinclair 2018

Schaunzers, West Highland white terriers

At risk of sick sinus syndrome (SSS) Ward and others 2016

GFR Glomerular filtration rate; MDR Multi-drug resistance; PCV Packed cell volume; T4 Thyroxine (fT4 free thyroxine)

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Table 4: Abnormal clinical findings, possible underlying causes and possible further investigations required in dogs and cats before formulating a perianaesthetic plan

Body system Examination Relevant findings Possible causes Further investigations

Body condition Skin tent Increased tenting Increased water lossDecreased water uptake

PCV and TSPUrinalysisMucus membranes Tacky mucus membranes

Lean muscle mass Cachexic Decreased protein synthesis (eg, hepatopathy)Increased protein secretion (eg, PLE, PLN)Increased protein catabolism (eg, hyperthyroidism)

Serum albuminRenal and hepaticEnzyme activityTSH + T4UrinalysisAbdominal ultrasonography

Obese Dietary endocrinopathy See endocrine

Cardiovascular Heart auscultation Muffled heart sounds Pericardial effusion, pleural effusion, space occupying lesion

Thoracic radiographyTFAST

Murmur Physiological cardiac disease Echocardiography

Arrhythmia (including bradyarrhythmias, and tachyarrhythmias)

Cardiac disease, respiratory disease, shock, pain, electrolyte abnormalities

Thoracic/abdominal radiography, echocardiography, ECG, pain score, lactate serum biochemistry/electrolytes

Peripheral pulse palpitation

Absent/deficit Decompensated heart failureShock

Thoracic radiography, echocardiography, check mucus membrane colour, CRT

Mucus membrane colour Pale, brick red Anaemia, haemorrhage, shock PCV and TSP, AFAST and TFAST, lactate

Capillary refill time < 1 second, > 1 second Shock, pain PCV and TSP, FAST, lactate, pain score

Respiratory Rate > 30 breaths/min< 12 breaths/min

Pulmonary disease, pain, pleural effusion, cardiovascular disease

Thoracic radiography, pain score, ECG, TFAST

Work of breathing Abdominal effortAbducted elbowsExtended neck

Upper/lower airway diseasePulmonary disease, cardiac diseasePain

Upper airway exam, thoracic radiography, echocardiography, TFAST, arterial blood gas

Breathing pattern and noise

Shallow and rapid Increased expiratory/inspiratoryStertor, stridor

Pleural diseaseUpper and lower airway diseasePulmonary diseaseCardiac disease

Pain score

Postural change Reluctant to lie down

Mucus membrane colour Cyanotic

Thoracic auscultation Referred/abnormal lung sounds eg, crackles, borborygmi

Pulmonary/cardiac diseaseSpace occupying lesion eg, stomach

Thoracic radiographyFAST

Hepatic Mucus membrane colour Icterus (jaundice) Prehepatic, hepatic, post-hepatic Serum biochemistry, bile acid, abdominal ultrasound, serum glucose

Mentation Depressed, seizures Hepatic encephalopathy, hypoglycaemia

Blood urea nitrogen, ammonia, serum glucose

Body condition score Cachexic Hypoalbuminaemia Serum biochemistry

Petechiae Clotting abnormality Clotting factor deficiency Haematology, clotting tests, TEG

Renal Urinalysis Urine-specific gravity Prerenal, renal, postrenal Haematology, serum biochemistry and electrolytes

Endocrine Body condition score Obese Hypothyroidism, hyperadrenocorticism

T4 and TSH, dexamethasone suppression test, serum biochemistry and electrolytes, systolic blood pressure

Cachexic Hyperthyroidism, diabetes mellitus T4 and TSH, blood glucose, glucose fructosamine

Hydration status Dehydrated Hypoadrenocorticism Serum biochemistry and electrolytes

CRT Cardiac resynchronisation therapy; ECG Electrocardiogram; FAST Focused assessment sonography for trauma (A abdominal, T thoracic); PCV Packed cell volume; PLE Protein losing

enteropathy; PLN Protein losing nephropathies; TEG Thromboelastography; TSH Thyroid stimulating hormone; TSP Total serum protein; T4 Thyroxine

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routine testing and a second paper advocating it (Joubert 2007, Alef and others 2008). An ideal screening test has a high sensitivity and specificity to minimise the incidence of false results being reported (Webb and others 2012).

Unfortunately, the greater the sensitivity of a screening test the lower its specificity, increasing the likelihood of dogs having abnormal blood results. In a trial of 53 dogs considered healthy on clinical examination, routine haematology, serum biochemistry, urinalysis and abdominal ultrasound before they underwent general anaesthesia were performed (Webb and others 2012). Routine blood and urine testing were highly sensitive, reporting a 54 per cent incidence of occult abnormalities requiring further investigation. Interestingly, the addition of abdominal ultrasound further increased the incidence of detected abnormalities to 64.2 per cent.

The limitation of such findings is the potential for these poorly specific tests to over-report abnormal findings in healthy animals. This was demonstrated in a trial in which approximately 95 per cent of the 772 dogs and cats investigated had at least one or more blood test result outside of the reference range; however, only 0.9 per cent of this cohort was ultimately diagnosed with a previously unknown disease (Davies and Kawaguuchi 2014).

These findings illustrate one of the limitations of pre-general anaesthetic testing in all animals. A high prevalence of abnormalities on pre-general anaesthetic blood tests may be due to narrow reference ranges in conjunction with normal inter-population variability, resulting in over-reporting of abnormal findings (Dell’osa and Jaensch 2016).

Secondly, in the case of otherwise healthy animals, greater cost and time is required from both the clinician and owner in order to perform additional tests required to rule out the high percentage of false positives.

A caveat to this rationale is the use of pre-general anaesthetic screening in geriatric patients (Joubert 2007). In a study performed in 101 geriatric dogs (ie, over the age of seven), 30 new diagnoses were made based on the findings on pre-general anaesthetic screening (haematology, serum biochemistry and urinalysis). The most common diseases diagnosed were neoplasia, chronic kidney disease and hyperadrenocorticism (Joubert 2007). Interestingly, of the 30 new diagnoses, 15 of the dogs had anaesthesia delayed or cancelled.

The number of cases in which the outcome of pre-general anaesthesia screening delayed or cancelled surgery was relatively low. This is significant considering the presence of a ‘previously undiagnosed’ neoplasia may abolish the necessity of undergoing an elective procedure (eg, routine dentistry) and the presence of previously undiagnosed disease (ie, chronic kidney disease and Cushing’s disease) may require stabilisation before the animal undergoes anaesthesia. Once again, abnormal pre-general anaesthesia screening in the absence of clinical signs or supporting history in these patients was not considered sufficient motivation for delaying anaesthesia.

Similarly, the influence of patient history, clinical examination findings and pre-general anaesthesia laboratory screening on its potential to alter anaesthetic risk has been compared in dogs. Alef

BOX 1: ‘SHELLEY’ THE SHIVERING DOGShelley is a neutered female Labrador retriever. She weighs 26 kg and is nine years and 11 months old. She requires sedation for abdominal ultrasonography.Clinical history: Intermittent vomiting (two day duration)InappetentSporadic eyelid and skin twitchingRelevant clinical findings:Tachycardia (>160 beats per minute)Arrhythmia on auscultationAberrant skin twitches Plan: perform electrocardiogram to qualify tachycardia Diagnosis: sinus tachycardia with dropped ST segment (interval between ventricular depolarisation and repolarisation)Plan: serum biochemistryRelevant biochemistry results: Ionised serum calcium: 0.64 (1.12-1.40 mmol/l)Urea: 15.8 (3.5-9.3 mmol/l)Creatinine: 292 (44-155 mmol/l)Plan:

■■ Delay sedation/anaesthetic■■ Commence intravenous fluids■■ Supplement with calcium gluconate■■ Re-assess biochemistry■■ Investigate the cause for the underlying hypocalcaemia

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and others (2008) demonstrated that patient history had a far greater bearing on risk allocation pre-general anaesthesia, when compared to clinical examination and pre-general anaesthesia laboratory screening. This once again stresses the importance of obtaining a thorough patient or clinical history to help decide which blood tests would be appropriate be perform.

To conclude, in otherwise non-geriatric healthy patients undergoing routine elective procedures (eg, orchiectomy), the use of routine pre-general anaesthesia blood testing may not be necessary. Instead, the clinician should be guided by patient history and clinical findings (Table 4), with the addition of pre-general anaesthesia blood testing where appropriate. The exception is in cases where non-routine surgery is to be performed.

Adapting preanaesthetic screening based on a surgical procedureDepending on the intended surgery, thorough pre-general anaesthesia screening may be required. Noteworthy cases include: ■■ Organ-specific surgery in which normal function may be attenuated perioperatively;■■ In high risk surgery with potentially life threatening complications; ■■ Where timing of surgery may affect outcome;■■ Where serial testing is required to assess response to surgery.

In general, any surgical procedure requiring invasive surgical attention to a particular organ or organ system will have organ-specific pre-general anaesthesia screening. Such an example would be thoracic surgery in which pre-general anaesthesia haematology and thoracic radiology is essential. Additional arterial blood gas analysis may be indicated in the case of suspected pulmonary disease and if monitoring of pulmonary function perioperatively is required (Robinson and others 2013).

Support for pre-general anaesthesia screening in high-risk surgeries has been explored in dogs and a number of prognostic indicators of survival have

been summarised in Table 5. A further requirement for pre-general anaesthesia screening is in cases where the intended surgery carries reasonable risk of significant complications. One such example is maxillofacial surgery in which the risk for life-threatening haemorrhage is considerable (Verstraete 2005).

Pre-general anaesthesia haematology and cross-matching is essential in order to establish blood loss allowances before a blood transfusion and to ensure the compatible blood product is available at the time of surgery (Verstraete 2005).

Pre-general anaesthesia blood testing may also guide the clinician as to the type of surgery required. In dogs with cholestasis, dogs requiring emergency cholecystectomy due to complete obstruction were noted to have higher pre-general anaesthesia serum bilirubin levels when compared to dogs with only cholestasis (Burns and others 2014). Identifying cholestasis in dogs before surgery provides the clinician with the opportunity to delay surgery in order to adequately resuscitate and stabilise the dog prior to anaesthesia, thereby limiting adverse events.

The need for pre-general anaesthesia blood testing in order to establish a current clinical picture helps to prognosticate outcomes from emergency surgery (Green and others 2011). This is particularly important in dogs presenting with gastric dilatation volvulus (Green and others 2011). A greater chance for survival to discharge was reported in dogs in which more than 50 per cent reduction in lactataemia was observed during the initial 12-hour period from admission (Green and others 2011).

It is thus logical to assume that the efficiency with which the preanaesthetic resuscitation of the patient is performed is critical, and pre-general anaesthesia establishment of baseline values against which to compare both intra-operative and postoperative management will aid in guiding resuscitation with greater accuracy.

Safely imaging conscious patients requiring preanaesthetic screeningOne of the challenges associated with pre-screening patients undergoing anaesthesia is the requirement for sedation or general anaesthetic in order to perform diagnostic imaging. Considering this limitation, the use of point-of-care ultrasound (POCUS) has been adapted from human anaesthesia as an alternative imaging modality not requiring anaesthesia or sedation.

POCUS is performed at the bedside and facilitates acquisition of near-immediate ultrasound images in real time. The findings may directly correlate with the patient’s presenting signs and symptoms indicative of the current status of disease (Moore and Copel 2011).

The adoption of POCUS within the veterinary fraternity was initially incorporated in the triage

Table 5: Predictors of survival in high-risk surgery in dogs (Hardie and others 1995)

Variable Survival Non-survival

Age (years) 5 7.33

Hospital days 1.74 2.67

PCV (per cent) 41 35

TP (gm/dl) 6.08 5.57

Platelet count (platelet/μl) 367,342 284,750

Albumin (gm/dl) 2.80 2.42

Bilirubin (gm/dl) 0.32 2.28

Number of concurrent diseases 0.91 2.17

PCV Packed cell volume; TP Total serum protein

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of dogs and cats presenting with trauma, and was termed focused assessment sonography for trauma (FAST) (McMurray and others 2016). FAST involves rapid, systemic assessment of specific sites within the thorax and abdomen, using free fluid (pericardial, peritoneal, pleural fluid) as an indicator of trauma-related injury (McMurray and others 2016) (Fig 1). Abdominal FAST (AFAST) and thoracic FAST (TFAST) (Fig 2) have demonstrated usefulness in detecting free fluid in dogs with blunt trauma, with the added benefit of providing a means of repeated measures to course the progression or resolution of trauma-induced injury (McMurray and others 2016).

More recently, the use of POCUS has been tailored to evaluate organ-specific parenchymal, intraluminal and interfacial detail. Presence of artefacts and changes in shape or echogenicity may be characteristic of organ-specific disease, and when observed in real time they can provide important information pertaining to organ function (Ward and others 2017).

Considering the predominance of PAC being attributed to the cardiorespiratory system, the use of POCUS focused on the thoracic cavity (ie, bedside lung ultrasound examination [BLUE] and focused echocardiography [ECHO]) may be of particular benefit during preanaesthetic screening (Brodbelt and others 2008). The vet BLUE protocol employs four bilaterally applied lung views in order to accurately diagnose and characterise pulmonary disease (Lisciandro 2014).

For assessment of the cardiac system, development of the ECHO has been described. ECHO allows quick identification and comparison of all cardiac chambers, assessment of ventricular contractility and characterisation of cardiac pathology, such as mitral valve endocardiosis (Defranscesco 2014) .

In addition to the cardiorespiratory system, POCUS provides a means by which to assess other systems, for example the urinary system (Lisciandro and Fosgate 2017). In a recently published trial, the use of POC cystocolic ultrasonographic determinations of the bladder length, width and

height measurements have been incorporated into a simple equation which accurately predicts bladder volume (Lisciandro and Fosgate 2017). Serial measurements of bladder volume (only accurate in patients who have not voided their bladder) provides a non-invasive method for determining urine output, a key indicator of renal perfusion and/or function (Lisciandro and others 2017).

Summary Thorough screening of all animals before general anaesthesia is essential in order to tailor perianaesthetic management plans to each individual patient. The fundamentals of pre-general anaesthesia testing still relies on the assimilation of an accurate patient history, conduction of a thorough clinical examination and selection of appropriate pre-general anaesthesia testing. Routine blood testing in all animals does not appear to be essential in all cases; however, strategic testing of animals based on historical and clinical findings as well as considering the intended surgical procedure will yield the most value. Recent advances in POCUS is creating new methods to safely assess conscious animals and may compliment pre-general anaesthesia screening in high-risk patients in the future.

ReferencesALEF, M., VON PRAUN, F. & OECHTERING, G. (2008) Is routine pre-anaesthetic haematological and biochemical screening justified in dogs? Veterinary Anaesthesia Analgesia 35, 132-140AVA (2018) Guidelines for safer anaesthesia. https://ava.eu.com/resources/anaesthesia-guidelines. Accessed April 1 2020BOVERI, S., BREARELY, J. & DUGDALE, A. (2013) The effect of body condition on propofol requirement in dogs. Veterinary Anaesthesia Analgesia 40, 449-454BRODBELT, D. C., PFEIFFER, D. U., YOUNEY, L. E. & WOOD, J. L. N. (2007) Risk factors for anaesthetic-related death in cats: results from the confidential enquiry into perioperative small animal fatalities (CEPSAF). British Journal of Anaesthesia. 99, 617-623BRODBELT, D., BLISSITT, K., HAMMOND, R., NEATH, P., YOUNG, L., PFEIFFER, D. & WOOD, J. (2008) The risk of death: the confidential enquiry into perioperative small animal fatalities. Veterinary Anaesthesia Analgesia 35, 365-373BRODBELT, D. C. (2009) Perioperative mortality in small animal

FIg 1: Focused assessment sonography trauma (FAST) scan being performed in a dog

FIg 2: Ultrasound image of the heart obtained during a thoracic focused assessment sonography for trauma FAST (TFAST) scan of a dog

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view to estimate urinary bladder volume in dogs and cats. Journal of Veterinary Emergency and Critical Care 27, 713-717LOVE, L. (2015) Perioperative physiology and pharmacology in the obese small animal patient. Veterinary Anaesthesia and Analgesia 42, 119-32MCMILLAN, M. & BREARELY, J. (2013) Assessment of the variation of in American society of anaesthesiologist physical status classification assignment in small animal anaesthesia. Veterinary Anaesthesia Analgesia 40, 229-236MCMURRAY, J., BOYSEN, S. & CHALHOUB, S. (2016) Focused assessment with sonography in nontraumatized dogs and cats in the emergency and critical care setting. Journal of Veterinary Emergency and Critical Care 26, 64-73MEALEY, K. (2004) Therapeutic implications of the MDR-1 gene. Journal of Veterinary Pharmcology and Therapeutics 27, 257-64MOORE, C. L. & COPEL, J. A. (2011) Point-of-care ultrasonography. New England Journal of Medicine. 364, 749-757MORTIMER, A., VAUGHN, R., BASSETT, A. & WODDHEAD, K. (2001) Preoperative assessment and patient preparation – the role of the anaesthetist. Association of Anaesthesia of Great Britain andIreland. pp 5-7PERRIN, T. (2009) The business of urban animals survey: the facts and statistics on companion animals in Canada. Canadian Veterinary Journal 50, 48-52PORTIER, K. & KAZUE, I. K. (2018) The ASA status classification: What is the evidence for recommending its use in veterinary anesthesia? A systematic review. Frontiers of Veterinary Science 5, 204POSNER, L., MARIANI, C., SWANSON, C., ASAKAWA, M., CAMPBELL, N. & KING, A. (2014) Perianaesthetic morbidity and mortality in dogs undergoing cervical and thoracolumbar spinal surgery. Veterinary Anaesthesia Analgesia 41, 137-144POSNER, L. P. (2016) Preanaesthetic assessment and preparation. In BSAVA manual of canine and feline anaesthesia and analgesia, 3rd edn. Eds T. Duke-Novakovski, T, M. de Vries, C. Seymour. British Small Animal Veterinary Association. pp 6-12ROBINSON, R., CHANG, Y., SEYMOUR, C. & PELLIGRAND, L. (2013) Predictors of outcome in dogs undergoing thoracic surgery (2002-2011). Veterinary Anaesthesia and Analgesia 41, 259-268SINCLAIR. M. (2018) Pharmacologic and clinical application of sedatives. Analgesia and anaesthesia for the ill or injured dog and cat. Eds K. Mathews, M. Sinclair, A. Steele, T. Grubb. Wiley. pp 112-114TAMURA, J., ITAMI, T., ISHIZUKA, T., ITAMI, T., ISHIZUKA, T. & MIYOSHI, K. (2013) Sparing effects of robenacoxib on the minimum alveolar concentration for blunting adrenergic response (MAC-BAR) of sevoflurane in dogs. Journal of Veterinary Medical Science 76,113-117VERSTRAETE, F. J. (2005) Mandibulectomy and maxillectomy. Veterinary Clinics of North America: Small Animal Practice. 35, 1009-1039VILAR, P., COUTO, C., WESTENDORF, N., LAZBIK, C. & MARIN, L. (2008) Thromboelastographic tracings in retired racing greyhounds and in non-greyhound dogs. Journal of Veterinary Internal Medicine 22, 374-379WARD, J. L., DEFRANCESCO, T. C., TOU, S. P., ATKINS, C. E., GRIFFITHS, E. H. & KEENE, B. W. (2016) Outcome and survival in canine sick sinus syndrome and sinus node dysfunction: 93 cases (2002-2014). Journal of Veterinary Cardiology 18, 199-212WARD, J. L., LISCIANDRO, G. R., KEENE, B .W., TOU, S. P. & DEFRANCESCO, T. C. (2017) Accuracy of point-of-care lung ultrasonography for the diagnosis of cardiogenic pulmonary oedema in dogs and cats with acute dysponea. Journal of the American Veterinary Medical Association. 250, 666-675WEBB, J. A., KIRBY, G. M., NYKAMP, S. G. & GAUTHIER, M. J. (2012) Ultrasonographic and laboratory screening in clinically normal mature golden retriever dogs. Canadian Veterinary Journal 53, 626-630WESS, G., DOMENECH, O., DUKES-MCEWAN, J., HAGGSTROM, J. & GORDON S. (2017) European society of veterinary cardiology screening guidelines for dilated cardiomyopathy in dobermann. Journal of Veterinary Cardiology 19, 405-415WOLTERS, U., WOLF, T., STUTZER, H. & SCHRODER, T. (1996) ASA classification and perioperative variables as predictors of postoperative outcome. British Journal of Anaesthesia 77, 217-222

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SELF-ASSESSMENT: PREANAESTHETIC SCREENING IN DOGS AND CATSIn Practice partners with BMJ OnExamination to host self-assessment quizzes for each clinical article. These can be completed online at inpractice.bmj.com

Answers: (1) d, (2) d, (3) a, (4) d, (5) b

1. Which of the following factors does not directly affect the American Society of Anaesthesiologists (ASA) physical status classification system grade?a) Active haemorrhageb) Mitral valve insufficiencyc) Congestive heart failured) Emergency laparotomye) Renal failure

2. Which of the following factors has been linked to an increased risk perianaesthetic mortality?a) Speciesb) Extremes of agec) Low haematocritd) All of the abovee) None of the above

3. Which of the following diseases are Labrador retrievers predisposed to?a) Laryngeal paralysisb) Sick sinus syndrome

c) Hypocoagulabilityd) All of the abovee) None of the above

4. Routine preanaesthesic blood testing is warranted in which of the following patients?a) In patients requiring preanaesthetic

stabilisationb) In geriatric patientsc) In patients undergoing invasive surgery, with

a high risk of haemorrhaged) All of the abovee) None of the above

5. Which of the following risk factors have been associated with survival in patients undergoing high-risk surgery?a) Serum creatinineb) Normal haematocritc) High bilirubind) Presence of less than three comorbiditiese) Low albumin

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