ANAESTHETIC MORTALITY RATES
Let’s talk about anaesthetic mortality rates.
How good are we Vets regarding anaesthetic mortality compared to our colleague human doctors?
Well, in human anaesthesia, as you can see, the mortality has been estimated at around 0.02 to 0.002%, while in veterinary medicine, anaesthesia mortality is estimated as well.
The first study developed in the 80s about canine species registers anaesthetic mortality of 0.24 in healthy dogs.
Another study published in 2008, that was performed on almost a hundred thousand dogs in the UK. In this study, the risk of death due to anaesthesia and sedation is estimated to be 1 out of 1800 in healthy dogs and 1 out of 75 in sick dogs.
The author classified healthy dogs and cats ASA grades 1 or 2, whereas critical dogs or sick dogs were classified (ASA) 3 to 5.
We can see that mortality is double if the patient is classified ASA 3, 4 or 5, which is quite scary compared to human medicine, but it is somewhat expected. We can also see a reduction of the risk, but we are still superior if we compare it with human medicine.
It means that we are doing well, we are doing good, we are improving, but we still have much to improve.
ANAESTHETIC MORTALITY FACTORS
We need to take into account the anaesthetic related mortality. As I mention before, every few years, mortality studies come out.
The research study we discussed previously, published in 2008, and the conclusions are fascinating.
According to this article, different factors can affect anaesthetic mortality.
Body condition score is an important factor; very obese or cachectic animals are at a higher risk of anaesthesia associated mortality as well as age, very young or very old animals.
It was found that animals classified ASA 3, 4 or 5 were associated with a higher risk of mortality, which is expected.
The recovery period is very crucial. The study observes that some patients died during the recovery period, and it was established as a critical time.
The first 3 hours after extubation is a crucial time regarding anaesthetic mortality.
In emergency cases, time is a limiting factor, and we have to go quickly to surgery, which was also a factor increasing the anaesthetic risk.
Finally, a very interesting point is out of hours. Out of hours was highlighted as an important factor associated with an exhausted staff or personnel or associated with the fact that there are few people at the practice or fewer people at the practice or people that do not necessarily know where surgical instruments are or other material needed are located in practice or in the surgical room.
It’s essential to be aware of these factors and recognise them to establish and evaluate the anaesthetic risk.
THE ASA (American Society Anesthesiologists)SYSTEM
ASA system classifies the patients only based on the scriptures of the current state of health without taking into account all the variables, such as the type of procedures or location of procedures.
At present, patients are divided into six categories, of which the first five are relevant for veterinary medicine. For each of these categories, an E stands for Emergency, and it is added if the procedure is urgent.
ASA PS ClassificationDefinitionAdult Examples, Including, but not Limited to:Pediatric Examples, Including but not Limited to:Obstetric Examples, Including but not Limited to:ASA IA normal healthy patientHealthy, non-smoking, no or minimal alcohol use.Healthy (no acute or chronic disease), normal BMI percentile for age.ASA IIA patient with mild systemic diseaseMild diseases only without substantive functional limitations. Current smoker, social alcohol drinker, pregnancy, obesity (30<BMI<40), well-controlled DM/HTN, mild lung disease.Asymptomatic congenital cardiac disease, well controlled dysrhythmias, asthma without exacerbation, well controlled epilepsy, non-insulin dependent diabetes mellitus, abnormal BMI percentile for age, mild/moderate OSA, oncologic state in remission, autism with mild limitations.Normal pregnancy*, well controlled gestational HTN, controlled preeclampsia without severe features, diet-controlled gestational DM.ASA IIIA patient with severe systemic diseaseSubstantive functional limitations; One or more moderate to severe diseases. Poorly controlled DM or HTN, COPD, morbid obesity (BMI ≥40), active hepatitis, alcohol dependence or abuse, implanted pacemaker, moderate reduction of ejection fraction, ESRD undergoing regularly scheduled dialysis, history (>3 months) of MI, CVA, TIA, or CAD/stents.Uncorrected stable congenital cardiac abnormality, asthma with exacerbation, poorly controlled epilepsy, insulin dependent diabetes mellitus, morbid obesity, malnutrition, severe OSA, oncologic state, renal failure, muscular dystrophy, cystic fibrosis, history of organ transplantation, brain/spinal cord malformation, symptomatic hydrocephalus, premature infant PCA <60 weeks, autism with severe limitations, metabolic disease, difficult airway, long term parenteral nutrition. Full term infants <6 weeks of age.Preeclampsia with severe features, gestational DM with complications or high insulin requirements, a thrombophilic disease requiring anticoagulation.ASA IVA patient with severe systemic disease that is a constant threat to lifeRecent (<3 months) MI, CVA, TIA or CAD/stents, ongoing cardiac ischemia or severe valve dysfunction, severe reduction of ejection fraction, shock, sepsis, DIC, ARD or ESRD not undergoing regularly scheduled dialysis.Symptomatic congenital cardiac abnormality, congestive heart failure, active sequelae of prematurity, acute hypoxic-ischemic encephalopathy, shock, sepsis, disseminated intravascular coagulation, automatic implantable cardioverter-defibrillator, ventilator dependence, endocrinopathy, severe trauma, severe respiratory distress, advanced oncologic state.Preeclampsia with severe features complicated by HELLP or other adverse event, peripartum cardiomyopathy with EF <40, uncorrected/decompensated heart disease, acquired or congenital.ASA VA moribund patient who is not expected to survive without the operation.Ruptured abdominal/thoracic aneurysm, massive trauma, intracranial bleed with mass effect, ischemic bowel in the face of significant cardiac pathology or multiple organ/system dysfunction.Massive trauma, intracranial hemorrhage with mass effect, patient requiring ECMO, respiratory failure or arrest, malignant hypertension, decompensated congestive heart failure, hepatic encephalopathy, ischemic bowel or multiple organ/system dysfunction.Uterine rupture.ASA VIA declared brain-dead patient whose organs are being removed for donor purposes.Source: https://www.asahq.org/standards-and-guidelines/asa-physical-status-classification-system
* Although pregnancy is not a disease, the parturient’ s physiologic state is significantly altered from when the woman is not pregnant, hence the assignment of ASA 2 for a woman with uncomplicated pregnancy. **The addition of “E” denotes Emergency surgery: (An emergency is defined as existing when delay in treatment of the patient would lead to a significant increase in the threat to life or body part).
In this table, you can find clinical examples for each ASA grade. I hope this is helpful to better classify your patients according to the ASA classification and hopefully improve the way you do anaesthesia.
METHODICAL APPROACH
How should we perform our anaesthetic evaluation?
One of the most important factors is that we should have a methodical approach, an approach that we use with every patient and we are confident with.
We are going to split it into different parts. The First will be patient history, and second will be a physical examination, and the third will be other complementary tests.
The first part, as we said, considers complete patient history.
We will take into account the species, if the animal is wild or domesticated, the animal’s size or behaviour, breed, age, sex, and that is very important we could ask if the animal is pregnant.
In definitive, or in conclusion, as complete as we can.
PATIENT HISTORY
As previously mentioned, we aim to find or diagnose pre-clinic or sub-clinic diseases by knowing the patient history.
It is important to ask, for example, how is the animal’s appetite is our patient drinking or urinating too much, how is their exercise tolerance, so they have any syncope, history of collapse, familial genetics diseases as well or is our patient taking any medications which could potentially affect our anaesthesia, how is his vaccination status.
The next question is quite important from my point of view:
Prior anaesthetic, do they have any allergies?
Do they have any complications that we could potentially prevent during this anaesthesia and also reasons for surgery or for the procedure.
The reason for anaesthesia or sedation is not always for a surgical procedure, but it could also be for a diagnostic procedure.
METHODICAL APPROACH
The second part of our methodical approach to pre-anaesthetic evaluation is physical examination.
Here we could ask if we could take into account the cardiovascular, respiratory, neurologic, urinary system, and integumentary system, which is skin mainly.
PHYSICAL EXAMINATION
It’s helpful to have a systematic method always to try to perform your physical examination systematically.
That way, you will reduce the number of findings that you could miss.
Do not focus only on the reasons for surgery. It is common for Vets to focus on the reasons for surgery, try to avoid that while it is important to develop a systematic approach for your physical examination.
Physical examination should include physical observation, for example, skin condition, body condition score, and palpate abdomen, spine, linfonodos.
Thoracic auscultation including lungs, trachea, heart and abdominal auscultation.This is just an example of how to perform a physical examination in a systematic way.
So we could start with body weight and body conditions score to follow with a physical exam and organ systems.
We could start with the respiratory system, evaluating breathing pattern, breathing effort, thoracic auscultation and mucous membrane colour. We could follow with cardiovascular systems, cardiac auscultation, pulse palpation.
Central nervous system: we need to evaluate, assess their medical status, gait, presence of pain or other parts; cranial reflexes are quite interesting for us as well from the anaesthesia point of view.
We can carry out the abdomen, renal, hepatic, gastrointestinal system. For example, if the patient has abdominal pain, if the patient is jaundice, musculoskeletal system, so palpation of the different muscular groups or muscular complexes.
Integumentary system, skin conditions which could reflect many systemic diseases, very often endocrine nature diseases, and we can finish with rectal temperature.
OTHER TESTS
In human medicine as well as in veterinary medicine, a series of standardised tests have to be performed on patients before each anaesthesia and surgery.
The routine test is defined as the test commissioned by the protocol in all patients independently of the results of clinical evaluation.
For example, in the absence of any clinical indications or specific purpose.
The objective of these routine tests is to obtain more information regarding the health condition of any individual to be subject to anaesthesia or surgery.
Some of the factors that have to be associated with the request of evidence in this indiscriminately are the insecurity on the part of the anaesthetist, the confidence of a higher number of tests we can safely perform anaesthesia.
Obviously some legal protection, and the fear that the patient postpones the surgery due to the lack of information in front of that surgery.
This is mainly based on human medicine.
Should we do these tests on our patients in veterinary medicine? So, let’s have a look at that.
BLOOD TEST
There are a couple of papers where this question is partially answered.
They have found that if you haven’t found anything in your pre-anaesthetic evaluation so far, with your patient history or physical examination, a routine blood test would not be required in dogs less than 6 or 7 years old.
If these dogs have a routine pre-anaesthetic haematological or biochemistry, it was unlikely to find an abnormality, and this could potentially delay the anaesthetic procedure.
It’s important to say that this is not mandatory.
The Owner could be offered the possibility to perform a blood test on their pets every time if that is the protocol you have in your practice.
The take-home message here is that if the Owner declines to perform a blood test on a patient who needs an anaesthetic procedure, you could continue the anaesthetic procedure with the support of this evidence.
What about animals above seven years old?
It has been found out in around about 30% to 60% of patients blood abnormalities that could potentially indicate the presence of a pre-clinic disease which would be sufficient to explain the patient’s clinical signs or could ultimately delay or cancel the imaging diagnostic test or procedure in which anaesthetic procedure is necessary.
This is quite an interesting observation for us to take in our practices.
ELECTROCARDIOGRAM
What about ECG? What about an electrocardiogram?
Well, pre-anaesthetic EGCs are often included in the pre-anaesthetic evaluation in human medicine, but should we do that in our patients?
Three years ago, we studied pre-anaesthetic electrocardiogram findings in more than 700 dogs, and we compared that with pre-anaesthetic complications.
This is a retrospective study that was presented during the world conference in veterinary anaesthesia in Venice, Italy.
ECGs that showed abnormalities were about 521 out of 700, therefore almost 74% of them. These were rhythm abnormalities or any kind of wave morphology abnormalities.
The most common arrhythmia was sinus tachycardia. We couldn’t find any relationship between sinus tachycardia and anaesthetic complications, so we can conclude that this is not clinically relevant in order to reduce anaesthetic risks.
All the arrhythmia detected in this study could have been diagnosed with a physical examination, including cardiac auscultation and pulse palpation.
So its diagnostic is not exclusive to ECG.
In conclusion, good cardiac auscultation should be enough to detect a life-threatening arrhythmia which could potentially lead to anaesthetic complications.
If an arrhythmia is detected during cardiac auscultation, that is a fair reason to perform proper ECG in order to identify what type of arrhythmia you are dealing with.
IMAGING-POCUS
What about imaging?
Well, the use of a point of care ultrasound or POCUS has been adapted from human medicine, human anaesthesia, as an alternative imaging modality not requiring anaesthesia or sedation.
This approach was initially incorporated in the triage of dogs and cats presenting with trauma and it was called Toast or A fast, which stands for thoracic or abdominal POCUS assessment sonography for trauma.
POCUS techniques can be used to evaluate organ-specific parenchyma intraluminal or interfacial detail, mainly focused on the cardiorespiratory system evaluating lung and heart.
For more information, please read this super useful paper published this year in the journal ‘InPractice’ by Jacques Ferreira.
ANAESTHETIC RISK
As a reminder, when we are evaluating the anaesthetic risk, the ASA physical status or the ASA classification is not the same as anaesthetic risk.
If we would like to assess the anaesthetic risk, we should take into account different factors such as the type of procedure. For example, it is not the same sedation for an abdominal ultrasound than general anaesthesia for thoracotomy.
We should also evaluate or take into account the ability of both surgeon and anaesthetist, which play an important role when talking about the anaesthetic risk and finally, the ASA physical status of our patient.
Taking into account all these factors, we should be able to calculate we evaluate the anaesthetic risk and be ready for any anticipated or not anticipated complications as well as to keep the Owner informed about such anaesthetic risk.
CHOICE OF ANAESTHETIC TECHNIQUE
The choice or assessment of the anaesthetic risk will ultimately lead your choice of the anaesthetic technique that will depend on the patient, so this is what we have been talking about in this webinar, procedures to be done.
For example, it is amenable to regional anaesthesia, and what you have available, so the drugs and the equipment that you have available.
With these three is the way you will probably choose your anaesthetic technique.
TAKE-HOME MESSAGE
As take-home message the assessment of the anaesthetic risk, the preparation is what we are aiming when preparing a pre-anaesthetic evaluation.
Do it please in a systematic fashion, remember patient history, physical examination and other complementary tests if you consider them necessary.
Finally, as we just said, with pre-anaesthetic evaluation, the procedure and what we have available, we can hopefully make our choices regarding the anaesthetic protocol.