1.1: PREOPERATIVE ASSESSMENT

An anaesthesia provider must assess every patient prior to surgery. There are two main goals: to evaluate the status and stability of the patient’s health, and to anticipate and minimize possible complications of anaesthesia and surgery. With this structured assessment the anaesthesia provider can decide if the patient needs further assessment and optimization before surgery, when the surgery can be safely scheduled, the choice of anaesthetic technique and the post-operative disposition for the patient, e.g. day case, inpatient or intensive care.

The timing of assessment may be determined by screening tools that triage patients depending on variables such as; the presence of significant medical conditions, older age,multiple medications, more complex surgery, previous anaesthesia complications and difficulty with communication. Healthy low surgical risk patients may be seen on the day of surgery, whilst higher risk patients should be assessed well in advance at a preanesthesia clinic.

Both anaesthesia and the surgical stress response cause significant physiological changes.Understanding the physiological changes is necessary for preoperative risk assessment, preoperative optimization and for the conduct of anaesthesia. The most important physiological changes attributable to anaesthesia are respiratory and cardiovascular variations, though all body systems are affected. The magnitude of the surgical stress response is proportional to the magnitude of surgical injury and triggers endocrine and inflammatory responses. Endocrine stress responses include increases in growth hormone,renin, angiotensin, catecholamines, cortisol and antidiuretic hormone. Together these promote the catabolism of glucose and acute-phase proteins, and salt and water retention.The inflammatory response, primarily driven by the release of cytokines, initiates both local and systemic changes.

As patient populations become increasingly older, they present with increasing numbers and severity of comorbidities, particularly non-communicable diseases, the decision to operate may become complex. Anesthesia providers may need to involve other clinicians,and in partnership with the patient, determine whether surgery should proceed, be postponed pending optimization or changed to a lesser procedure including a non-surgical alternative if possible.

The pre-anaesthetic consultation should include conformation of the patient’s identity, the proposed procedure and the site or side, a medical history, which may be assisted by questionnaires, and a review of previous anaesthesia records. Patients should be provided with information of significance regarding the anaesthetic and informed consent obtained.

Medical History

Many medical illnesses may complicate the course of anaesthesia. The anaesthesia provider must take a focused medical history including why the patient is having the surgery and the urgency of surgery.

The anaesthesia provider must evaluate past and concurrent illnesses. Cardio vascular diseases include , cardiac failure, murmurs, arrhythmias, valvular disease, Ischaemic heart disease and previous deep venous thrombosis or pulmonary embolism. Patients with cardiac failure are at increased risk of major adverse cardiac events and should receive medical optimization prior to surgery. Undiagnosed murmurs are a common finding. Systolic murmurs occur as a result of aortic stenosis/sclerosis, mitral or tricuspid regurgitation or a hyperdynamic state. Patients with an abnormal ECG or who are symptomatic should have further investigation. All undiagnosed diastolic murmurs are pathological and need evaluation. Arrhythmias such as symptomatic bradycardias and tachycardias, Mobitz II and 3rd degree heart block all increase perioperative risk. Patients with newly diagnosed atrial fibrillation should have non-urgent surgery delayed. Ischaemic heart disease is a major risk factor for perioperative myocardial infarction and death. Preoperative assessment needs to balance the urgency of surgery, the severity of Ischaemic heart disease and the risk of major adverse cardiac events. Patients need to be assessed for the risk of venous thromboembolism (VTE). Those receiving long-term VTE prophylaxis may require cessation of anticoagulant medication or a perioperative bridging strategy. Patients with recent VTE should have all non-urgent surgery delayed.

Postoperative pulmonary complications are a major cause of perioperative morbidity and mortality. The anaesthesia provider should inquire about respiratory diseases including asthma, chronic obstructive pulmonary disease, tuberculosis, smoking and obstructive sleep apnoea (OSA). Chronic kidney disease, severe liver disease and endocrine diseases such as diabetes mellitus, thyroid disease and adrenal disorders all increase postoperative morbidity and mortality. Both anaemia and malnutrition are common in patients presenting for surgery and significantly increases perioperative risk. Ideally, these need to be evaluated early enough to allow for diagnosis and treatment.

Patients with known or suspected preoperative cognitive dysfunction should be assessed for the risk of postoperative delirium. The anesthesia provider should also ask about medications, allergies, and fasting time and evaluate the patient’s risk of a cardio vascular complication with non-cardiac surgery.

Evaluation of cardiac risk prior to non-cardiac surgery

Patients with a myocardial infarct within 60 days, unstable angina, decompensated cardiac failure, high-grade arrhythmias or high-grade valvular disease (particularly aortic or mitral stenosis) require surgery deferral and referral for evaluation and optimization. These patients are at a very high risk of perioperative myocardial infarction, cardiac failure or cardiac death.

All patients should have an assessment of their cardiac functional status. This can be done by inquiring about the patient’s level of physical activity, expressed in metabolic equivalents(1 MET is defined as 3.5 ml O2 uptake/kg per minute, which is the normal oxygen consumption at rest).

 

Mets	Activity
1	Eating, getting dressed, walking indoors
2	Showering, walking down eight steps
3	Walking on a flat surface for one or two blocks
4	Walking up two lights of stairs
5-9	Walk > 4 m/h or 6 km/h, heavy housework, moderate recreational activity
>10	Participate in strenuous sports

The functional capacity to achieve 4 METs without symptoms was previously thought to be a good prognostic indicator, however patients may not accurately self-report METs and subjective assessment may result in the misclassification of high-risk patients as low risk.The Duke Activity Status Index (DASI) is the sum of values for 12 activity questions. The Physiological and Operative Severity Score for the enUmeration of Mortality and Morbidity(POSSUM) uses 12 physiological and six operative variables. There are many other risk stratification tools available, and most are available online. They may be applicable to specific or heterogeneous groups of patients, specific or multiple types of surgery and specific or generalized outcomes. Of clinical importance, the accuracy of risk stratification tools may be diminished when applied to patient/surgery/outcome populations for which they have not been validated. Additionally, most calculate 30-day mortality risk as their primary outcome, but other outcomes like inability to return to independent living are very important consequences to the patient in their decision-making, and should also be considered.

Several preoperative cardiovascular risk assessment tools, including the revised cardiac risk index (RCRI), or the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) are available online and provide greater sensitivity and specificity for determining the risk of a major adverse cardiac event (MACE). In general, according to the guidelines, patients with a risk for MACE lower than 1% require no further cardiac testing before surgery.

Medications

A complete medication history, including prescription and herbal/complementary medications, should be obtained. There are significant variations in recommendations for the perioperative management of patient’s medications though as a general rule most medications can be continued. Drugs known to cause morbidity if withdrawn abruptly must be continued.

In general, the cardiovascular medications: beta blockers, alpha 2 agonists, calcium channel blockers, diuretics and digoxin either confer potential benefits or present minimal adverse effects or may result in negative consequences with acute withdrawal and all should usually be continued.

Theoretically angiotensin converting enzyme (ACE) inhibitors and angiotensin 2 receptor blockers (ARB) could result in prolonged hypotension by dampening the renin-angiotensin system. Their omission on the day of surgery may be considered for patients who do not require them for the management of heart failure or poorly controlled hypertension and may protect the patient from acute kidney injury. Contrary to previous recommendations,the introduction of prophylactic beta-blocker therapy in non-cardiac surgery to improve perioperative outcome is now not advocated for those not already on this therapy. Medications used to treat pre-existing conditions such as histamine 2 blockers, proton pump inhibitors, thyroid medications and pulmonary beta agonists, anticholinergics and leukotriene inhibitors should also be continued. Most psychotropic agents should be continued, with the exception of monoamine oxidase inhibitors, which require collaboration between anesthetist and psychiatrist to avoid adverse effects from interactions with vasoactive medications used during anaesthesia. Aspirin’s irreversible inhibition of platelet cyclooxygenase may increase the risk of haemorrhagic complications but may also reduce the risk of perioperative vascular complications. The perioperative benefits and risks of aspirin depend on the indication for aspirin and the planned surgery. Patients scheduled for closed space procedures e.g. intracranial, intramedullary spine, intraocular or possibly prostate surgery should have aspirin withheld for 5-10 days before surgery and recommenced as soon as possible. Patients receiving aspirin for definitive guideline based primary or secondary indication and scheduled for non closed-space or non-prostate surgery should continue aspirin.

Herbal/complementary preparations should all be ceased two weeks prior to surgery as they are of unknown purity, do not improve surgical outcomes and may have negative effects including clotting abnormalities and adverse interactions with anaesthesia.

Drugs that require specific perioperative management include anticoagulants, steroids and diabetic medications and will require discussions between the physician, anaesthesia provider and surgeon to plan their perioperative administration or cessation and recommencement.

Allergy and Drug Reactions

The anaesthesia provider must ask the patient about unusual, unexpected or unpleasant reactions to drugs. True allergic reactions are uncommon but any drug that has caused a skin reaction, facial or oral swelling, shortness of breath, choking, wheezing or hypotension should be considered to have caused an allergic response and must be avoided.

Perioperative IgE mediated anaphylaxis most frequently occurs after induction of anaesthesia and is often due to neuromuscular blocking agents or Beta-lactam antibiotics. IgE mediated atopy, allergic asthma and other non-allergic conditions such as chronic urticarial or mastocytosis are not risk factors for IgE mediated drug allergy.

There is no evidence to avoid propofol, which contains egg lecithin, in patients with egg, soy or peanut food allergy. Cases of propofol allergy have been reported however the allergic determinant is likely to be the isopropyl group or phenol ring.

Anaesthetic History

All previous anaesthetic notes should be reviewed. Good anaesthetic notes will include responses to drugs, ease of mask ventilation and endotracheal intubation and any anaesthetic complications. Patients should be asked about their prior anesthetics, postoperative analgesia management and their history of postoperative nausea and vomiting (PONV). Several preoperative assessment tools for predicting PONV, including the Apfel score have been published.

Risk- estimation for PONV by the Apfel-score

Risk Points	1	2	3	4
Risk risk estimation (%)	20	40	60	80

Risk factors: 1 point each for female gender, non-smoking, postoperative use of opioids and previous PONV or a history of motion sickness.

Family History

The anaesthesia provider should ask if anyone in the family has experienced problems with anaesthesia; for example, unexpected postoperative admission to an intensive care unit or unexplained death.

Smoking and Alcohol 

Smoking increases the risk of perioperative morbidity and mortality in a dose-dependent manner. Quitting smoking before surgery reduces the risk. Evidence varies as to the optimum time to quit; however the longer the period of cessation (at least 4–8 weeks)before surgery, the greater the benefit. Anaesthesia providers should quantify the patient’s smoking pack years, advise smokers to quit and refer patients for smoking cessation support. Patients should be screened for problem drinking and alcohol dependence. Those at risk of alcohol withdrawal may need referral before surgery. Cessation of alcohol consumption for 6-8 weeks before surgery, in problem drinkers, decreases morbidity.

Pregnancy 

Pregnancy should be excluded in all women of reproductive age, prior to surgery. If pregnant, all elective surgery should be postponed until after delivery and time sensitive surgery should be scheduled during the second trimester.

Physical Examination

The anaesthesia provider must perform a focused physical examination including all vital signs, weight height and calculated body mass index (BMI). This examination must pay special attention to the patient’s airway, cardiovascular and respiratory systems.

Patients should be assessed for loose, damaged or artifical teeth, which are at increased risk of damage during anaesthesia. The maxillary incisors are the most commonly injured tooth during laryngoscopy, though the insertion of any oral airway or supraglottic device may damage any vulnerable teeth. The severity of dental damage ranges from minimal enamel damage to crown or root fracture and complete tooth avulsion. An unrecognized dislodged tooth may be inhaled causing pneumonia, abscess or bronchiectasis.

Every patient’s airway must be assessed to determine how difficult it may be to perform mask ventilation, insert a supraglottic airway, intubate and/or perform front of neck airway access. This assessment includes measuring mouth opening, neck flexion and extension and the distance from the mandible to the thyroid cartilage and looking in the mouth. Airway assessment should include an assessment of other physiological factors that could alter management, such as a full stomach, intolerance of apnoea or cardiovascular instability.Respiratory examination should look for signs of upper airway obstruction, bronchospasm,infection or obstructive sleep apnoea.

Cardiovascular examination is particularly focused on determining the hydration status of the patient (heart rate, blood pressure, postural drop, any signs of dehydration), signs of cardiac failure and cardiac valve abnormalities. Patients who have a low blood pressure and tachycardia may respond to intravenous fluid resuscitation before commencing surgery/anaesthesia.

Body mass index (BMI) is commonly used to classify obesity as it is easily calculated,however BMI does not not describe the distribution of body tissue or metabolic state. The terms ‘apples’ and ‘pears’ are commonly used to describe predominantly central(abdominal/visceral) and peripheral adipose tissue, respectively. The WHO defines central obesity as a waist circumference >102 cm and >88 cm for men and women, respectively, orin the Asian population as a waist circumference >90 cm and >80 cm for men and women,respectively. Central obesity has associated greater risks of difficulty in airway,cardiovascular disease, metabolic syndrome, cardiovascular disease, and perioperative risk.Health conditions associated with obesity include obstructive sleep apnoea, hypertension,left ventricular failure, right ventricular failure, conduction abnormalities, and diabetes.

WHO classification of obesity and ASA grades

Category	BMI kg/m^2	ASA
Underweight	<18.5	1
Normal weight	18.5 - 24.9	1
Overweigh	≥25	1
Pre-Obese	25 - 29.9	1
Obese	≥30	1
Class 1	≥30–34.9	1
Class 2	≥35–39.9	2
Class 3	≥40	3

 

Obesity increases perioperative risk significantly when BMI is ≥40 kg/m², or when associated with significant comorbidities.Other descriptors of size include ideal body weight (IBW) which estimates fat-free mass in kg based on equations only using height, so does not take into account the additional lean weight weight associated with obesity and adjusted body weight (ABW) which estimates fat-free mass in kg based on equations that attempt to take into account the additional lean weight associated with obesity.

IBW male = 50 kg+(0.91x(height in centimetres-152.4))

IBW female = 45.5kg+(0.91x(height-152.4))

ABW = IBW in kg+0.4(actual body weight in kg-IBW in kg)

At this stage, the anaesthesia provider may have diagnosed several problems that require further investigation and treatment before surgery.

 

Investigations

Preoperative investigations should be performed selectively based on the patient’s health,the planned procedure and the likelihood that the test result will alter management or help with risk assessment. Generally, for low risk procedures, no investigations are necessary unless the patient has a new, unstable or worsening condition.

 

Documentation

Communication and documentation are essential components of preoperative assessment. The preoperative assessment should be documented on a preoperative assessment form.

 

ASA Classification

It is useful to assign an American Society of Anesthesiologists (ASA) classification, although not designed as a risk predictor tool; it is widely used as a broad descriptor of anaesthetic risk.

ASA 1: a normal healthy person

ASA 2: a patient with mild systemic disease

ASA 3: a patient with severe systemic disease limiting activity but not incapacitating

ASA 4: a patient with incapacitating systemic disease that is a constant threat to life

ASA 5: an extremely ill patient who is not expected to live 24 hours with or without an operation

 

Recommendation

The anaesthesia clinician must decide:

If the patient is in optimal medical condition.

How urgent the surgery is.

If surgery can be delayed until the patient is in the best possible condition. 

What the best anaesthetic technique for the patient and planned surgery is.

How to care for the patient after surgery (e.g. disposition, analgesia).

 

Finally, the anaesthesia provider must discuss the anaesthetic technique and risks with the patient and/or guardian, answer any questions or concerns and obtain informed consent for anaesthesia and related procedures. All choices should be made in partnership with the patient in a truly shared decision-making process.