Anaesthesia: Introduction and preoperative assessment

In the first of a four part series, Jonathan Behar and colleagues tell us how to assess patients in the lead up to an operation

Inducing a state of unconsciousness is dangerous without correct preparation, and it is the role of the anaesthetist to assess and optimise the patient's fitness before their operation. An anaesthetist is also responsible for safe induction into, maintenance of, and emergence from anaesthesia and for postoperative care (including sufficient pain management). In this series we explore preoperative, perioperative, and postoperative care and look at regional anaesthesia. Other key roles of the anaesthetist, such as pain management and intensive care, are covered elsewhere.

History and examination are crucial in the anaesthetic assessment, as are the appropriate investigations, which depend on the patient's perceived health. These will guide the type of anaesthesia and the timing of surgery. An anaesthetist should have an overall picture of the patient's anaesthetic risk, and any comorbid conditions should be optimised before surgery.

History

Active problems and symptoms

Anaesthetic drugs have profound effects on the cardiovascular and respiratory systems-the main focus of questioning is therefore about cardiac or respiratory problems. Ask about chest pain, breathlessness (including orthopnoea and paroxysmal nocturnal dyspnoea), ankle swelling, and palpitations. Cough, sputum, recurrent infections, and any clues indicating obstruction of the airways (chronic obstructive pulmonary disorder or asthma). An excellent indicator of cardiorespiratory function is tolerance of exercise. Indeed, one scale of the New York Heart Association grades severity of heart disease by functional impairment.¹ The key question with any patient is "Are they as well as they can be?" If not, what can be done to improve the patient's condition?

A patient's stomach must be empty to reduce any risk of aspiration-ward staff must be aware to keep the patient nil by mouth (no food or drink). Of course, this advice only refers to patients undergoing elective surgery. Emergency procedures require a different strategy. Any systemic upset with fever, reduced appetite, weight loss, and malaise are also important markers of health. And if your patient is a woman of childbearing age, check she isn't pregnant.

Medical and family history

Note any past conditions, including management and outcome. Remember some active problems, such as hepatitis and HIV, may require staff in theatre to take extra precautions. Ask about any previous procedures, anaesthetic problems (difficult intubation or postoperative complications), and any unexpected admissions to intensive care. Knowledge of any hereditary conditions that cause anaesthetic problems is invaluable because they only manifest while under anaesthesia-for example, malignant hyperpyrexia and cholinesterase abnormalities.

Malignant hyperpyrexia, a genetic abnormality of muscle, causes a substantial increase in metabolism and body heat. This response is often triggered by inhaled anaesthetics and can be dangerous. Suxamethonium apnoea occurs in patients who have abnormally low plasma cholinesterase, the enzyme that breaks down the drug. As a result, the action of suxamethonium (a paralysing agent) is prolonged, with dangerous consequences; these patients will require special care. Other conditions that may also cause a problem include porphyria and haemophilia.

Drug history

This includes current drugs (name, dose, route, frequency) and allergies (especially to penicillins or latex). Prescribed drugs may need to be continued, stopped completely, and changed in dose or route of administration.

Cigarette smokers are difficult to anaesthetise because their upper airways are sensitive to the dry gases and their risk of hypoxia is greater.² A smoking history (recorded in pack years) is a must. Alcohol history and illicit drug misuse should always be asked-the former because induction of liver enzymes by alcohol may shorten the action of anaesthetic drugs. The latter may show additional problems-for example, intravenous drug users, who often have difficult venous access, are at risk of septicaemia, and may have withdrawal symptoms if their regular drug regimen is stopped.

Drugs that may cause problems include antibiotics, the oral contraceptive pill, and steroids. Some antibiotics prolong the action of muscle relaxant drugs, which may be a problem in the postoperative period. Taking the combined oral contraceptive pill is a risk factor for developing deep vein thrombosis, and, usually, patients are asked to stop taking it six weeks before surgery and to use alternative contraception. Patients taking steroids long term need adequate cover during the operation because a sudden reduction in dose may induce a hypotensive crisis (because of the depleted endogenous production of steroid).

Physical examination

Airway assessment

How easy or difficult it will be to intubate a patient depends on these important points. Do they have a short neck and small mouth? Are they obese, and to what extent can they open their mouth? Is there any soft tissue swelling at the back of the mouth or any limitations in neck flexion or extension (rheumatoid arthritis or ankylosing spondylitis)?

The Mallampati scoring system uses a simple visual scale to grade each patient based on the visual vertical distance between the tongue and soft palate or uvula at the back of the pharynx (fig 1). Grade I shows a large vertical distance between the uvula and the base of the tongue, and you could imagine that this patient is a lot easier to intubate than a patient with a grade IV score.

(adapted from http://anestit.unipa.it/siaarti/mallampa.htm )

Fig 1 The Mallampati scoring system. A simple visual scale to grade patients by visual vertical distance between the tongue and soft palate or uvula at the back of the pharynx

A general systems examination must be done to pick up any abnormalities-for example, heart murmur, abnormal breath sounds, abdominal masses, skeletal malformations such as kyphoscoliosis, previous scars, and any local skin infection.

Vital signs

With the exception of emergency surgery, patients should be haemodynamically stable and their vital signs normal before starting anaesthesia (see box).

Investigations

The medical assessment, prescribed drugs, and planned procedure will determine which tests are needed (in accordance with hospital guidelines). Ask yourself whether the result of the test is going to alter the patient's management? Ordering unnecessary tests is neither helpful nor cost effective. Commonly used investigations are discussed below.

Urine dipstick or analysis-Invaluable in detecting undiagnosed diabetes or urinary tract infection.

Haematology-Haemoglobin should be checked when the history or examination indicates anaemia or when the proposed operation is expected to cause substantial blood loss. Clotting and platelet function is relevant for the many patients who take aspirin. Sickle cell tests can be ordered in higher risk ethnic groups-for example, Afro-Caribbeans. The decision about whether to cross match serum (to be used in transfusion) or to order group and save (kept ready in reserve) should be judged on the current haematology status of the patient as well as the estimated blood loss.

Biochemistry-Deranged electro­lytes are common in procedures, and it is usual to measure the urea, creatinine, and electrolytes before any major operation. Renal function is important because it may influence the choice of drugs given.

Lung function-Chest radiographs are not routinely ordered and are usually limited to patients with substantial cardiac or respiratory disease, depending on local policy. Radiographs of the cervical spine, to determine any instability, are useful in patients with rheumatoid arthritis because almost 90% of patients have some degree of involvement.³ Also, patients with ankylosing spondylitis can have a semifused spinal column, and the anaesthetist should bear this in mind when extending the patient's neck during intubation. Spirometry tests are a good measure of pulmonary physiology and are useful in patients with obstructive or restrictive patterns of disease-for example, asthma may be reversible with bronchodilators.

Heart function-An electrocardiogram can identify underlying ischaemia or previous infarction and also abnormalities in heart rhythm. It should be taken in anyone with cardiovascular risk factors-for example, hypertension, smoking, high cholesterol, significant family history, diabetes, and obesity. Exercise stress testing and echocardiography are reserved for patients in whom a further cardiac assessment is needed before deciding whether or not to proceed.

Risk assessment

The information gathered above is used to predict the patient's absolute mortality after anaesthesia and surgery and therefore to assess whether the risk of surgery is proportional to the benefit the patient is likely to derive from the procedure.

The scale of the American Society of Anesthesiologists assesses the patient's physical fitness for anaesthesia and is widely accepted around the world (table 1).

In addition to this score, the Goldman cardiac risk index assesses the likelihood of perioperative cardiac events in patients having non-cardiac surgery.⁴ The leading cause of postoperative death is from myocardial infarction. The overall risk is the sum of scores for nine independent factors (table 2).

Patients who scored more than 25 had a 56% incidence of death, with a 22% incidence of severe cardiovascular complications. Patients with scores below 25 had a 4% incidence of death, with a 17% incidence of severe cardiovascular complications. Patients with a minimal score (below six) had a 0.2% incidence of death, with a 0.7% incidence of severe cardiovascular complications.⁴

Preoperative optimisation

Cardiovascular system

We have listed some common cardiac problems and the suggested clinical approach.
• People who have had an acute coronary syndrome within the past three months are at great risk of a perioperative myocardial infarction, with a mortality of more than 30%. The risk is sufficiently reduced to proceed at six months
• Uncontrolled hypertension (180/100 mm Hg) and uncontrolled cardiac failure are both contraindications to surgery. Diastolic blood pressure greater than 110 mm Hg is associated with a high risk of infarction, and surgery should be postponed until the hypertension is controlled
• Short acting antihypertensives should be replaced with longer acting ones (for example, atenolol) and these should not be stopped during the surgery
• Prophylactic antibiotics are required if there is a risk of infective endocarditis
• Arrhythmias, such as atrial fibrillation, need to be well controlled before proceeding
• Volume depletion is common in preoperative patients (starved, nasogastric tube aspiration, and bowel preparation) and this requires quick identification and treatment.

Lung function and surgery

Remember that postoperative pain and altered diaphragmatic function contribute to a reduction in functional residual capacity (FRC) of at least 40%.⁵⁶

FRC=ERV+RV

(ERV-the expiratory reserve volume-is the additional volume of air that can be forcibly exhaled after a normal expiration. RV-the residual volume-is the air remaining in the lungs even after a maximal expiration; it cannot be expired no matter what the effort.)

This means that after the operation there is a reduced lung reserve, and, therefore, for the safe induction of a patient an adequate lung function needs to be obtained preoperatively. People with asthma tend to have problems with the expiratory phase of breathing because of obstruction of the airways (from hypersensitivity and inflammation) and this can be optimised with a b2 agonist, such as salbutamol. Also, long term smokers are at a much greater risk of post­operative atelectasis (collapse of lung tissue) as well as pneumonia. Encouraging these patients to stop smoking for as little as 24 hours before anaesthesia can optimise oxygenation of their tissues because the carbon monoxide in cigarette smoke, which reduces oxygen transport by up to a quarter, has a short half life.

"I've got a cold doctor-is it still OK to have the surgery?" The presence of an upper respiratory tract infection, particularly in children, often complicates the decision about whether or not to proceed. Excess secretions and mucous plugging can compromise the airway in the perioperative period. Upper respiratory tract infections are especially common in the winter, but usually only patients with key risk factors relating to their breathing (prematurity or airway obstruction) will have their procedure postponed.

Other considerations

Fluid shifts are almost inevitable, and volume depletion is important to recognise and treat. Patients with diabetes should be first on the operating list and should have regular glucose monitoring; they usually need a change to their route of insulin administration (subcutaneous to intravenous infusion). Patients with uncontrolled hyperthyroidism are at risk of developing a "thyroid storm," and their resting pulse on the morning of surgery should be fewer than 80 beats/min.⁸ Regurgitation and aspiration can be dangerous (remember the lower oesophageal sphincter is less competent in the unconscious patient). Be vigilant of patients not properly fasted or anyone at higher risk-for example, patients with hiatus hernia, bowel obstruction, oesophageal pouch, upper gastrointestinal bleeding, obesity, and pregnancy. These patients require antiacid and antiemetic drugs.

Preoperative preparation

Adults must be starved of solids for six hours to minimise any risk of aspiration during induction. A general anaesthetic will suppress the protective cough and gag reflexes. Water may be allowed up to two hours before elective surgery. This guidance refers only to elective surgery. Antibiotic prophylaxis needs discussion with the surgical team; the type and dose of antibiotic will depend on the location and nature of the procedure as well as the patient's general health. It is good practice to review all of the patient's drugs-some need to be stopped preoperatively (aspirin), others can be continued (b blockers). Patients taking anticoagulants are often switched to an intravenous infusion of heparin during the procedure mainly because of the ability to titrate the drug with the patient's response (as opposed to one dose of subcutaneous injection of low molecular weight heparin).

The risk stratification and management guidelines for thromboembolism prophylaxis are beyond the scope of this series, but attention should be paid to compressive stockings, sufficient hydration, and mobility before and after the surgery as well as heparin. Note, however, that in patients having a regional anaesthetic for their procedure, anticoagulation (for deep vein thrombosis prophylaxis) can be associated with vertebral canal bleeding and so specific guidelines regarding the type and timing of prophylaxis are crucial.

Consent

Acquisition of consent is the responsibility of the surgeon doing the procedure but often the teams' house officer has the job of getting hold of that critical signature for the go ahead. All surgical procedures carry risk but should all of these be mentioned to the patient, including the small print? Clearly, going through every risk possible is excessive, unhelpful, and inefficient. The key to remember is that the patient must make an informed, uncoerced decision based on the information given to them, once they have weighed up the advantages and disadvantages of the operation. Remember the ABCs:

Anatomical-They need the nature of the procedure explained (simple diagrams are often helpful) as well as the likely position of any scars when they wake up.

Benefits-Compare the advantages of going ahead with the risks of doing nothing. Include any statistics you know relating to the natural progression or prognosis of the problem without surgical intervention.

Chronology-Discuss the sequence of events in brief, such as any premedication, what they will be feeling when they wake up, and the expected duration of the procedure and hospital stay.

Complications -It is difficult to know exactly what to include and what to leave out. Certainly the common risks to any surgical procedure are a good start (haemorrhage, infection, wound dehiscence, operative failure), and this can be followed by risks specific to the procedure. Again, start with the more common possibilities (events you expect to happen), and then mention any rare but serious dangers so the patient is aware of all the possibilities. Minor complications refer to damage to dentition or postoperative nausea and vomiting and events that occur when anaesthesia seems to have been without incident. Major problems refer to potential life threatening events, such as a stroke or aspiration pneumonia.

These guidelines relate to surgical consent-epidurals and other specific procedures will need to be consented for by the anaesthetist doing the procedure.

Remember that patients on the whole are dreadful at assessing risk-they may be more likely to be involved in a road traffic crash than suffer one of the adversities of surgery but they still cross the road everyday.

Jonathan M Behar, final year medical student, affiliation
Email: jonathanbehar@gmail.com
Petrut Gogalniceanu , final year medical student, Royal Free and University College Medical School, London
Email: peter_gogalniceanu@yahoo.co.uk
Lesley Bromley, consultant anaesthetist director of postgraduate medical education, University College London Hospitals NHS Foundation Trust
Email: lesley.bromley@uclh.nhs.uk


studentBMJ 2007;15:1-44 January ISSN 0966-6494

Competing Interests: None declared

1. Criteria Committee of the New York Heart Association. Nomenclature and criteria for diagnosis of diseases of the heart and great vessels. 9th ed. Boston, MA: Little, Brown, 1994: 253-6.
2. Dennis A, Curran J, Sherriff J, Kinnear W. Effects of passive and active smoking on induction of anaesthesia. Br J Anaesth 1994;73:450-2.
3. Rawlins BA, Girardi FP, Boachie-Adjei O. Rheumatoid arthritis of the cervical spine. Rheum Dis Clin North Am 1998;24:55-65.
4. Goldman L, Caldera DL, Nussbaum SR, Southwick FS, Krogstad D, Murray B, et al. Multifactorial index of cardiac risk in noncardiac surgical procedures. N Engl J Med 1977;297:845-50.
5. Ali J, Weisel RD, Layug AB, Kripke BJ, Hechtman HB. Consequences of post-operative alterations in respiratory mechanics. Am J Surg 1974;128:376-82.
6. Craig DB. Post-operative recovery of pulmonary function. Anesth Analg 1981;60:46-52.
7. Rodrigo C. The effects of cigarette smoking on anaesthesia. Anesth Prog 2000;47:143-50.
8. Lee SL. Hyperthyroidism. New Kork: eMedicine, 2006. www.emedicine.com/med/topic1109.htm (accessed 12 Dec 2006)

       

           

	Responses published this month

Articles	Responses
EDITORIALS Anaesthesia: Introduction and preoperative assessment       Jonathan Behar, Petrut Gogalniceanu, Lesley Bromley (January 2007)	Jonathan Behar (January 11th 2007) Read this response

	EDITORIALS Anaesthesia: Introduction and preoperative assessment       Jonathan Behar, Petrut Gogalniceanu, Lesley Bromley (January 2007)
	Jonathan Behar (January 2007)       FY1 - Medicine/Surgery, North Middlesex Hospital, Edmonton, London Jonathan Behar
	Re: Anaesthetics series (part I) The writers wish to correct an error made during the publishing of this piece. On page 12, there is a paragraph that refers to the Mallampati scoring system - a visual scale to assess the difficulty in intubating a patient. It refers to figure 1 which is supposed to be a diagram of this visual scale. It is unfortunately the wrong table. We cannot add these diagrams to the rapid response section online but the diagram can be found through a simple internet search. If any more information is required about this, please don't hesitate to contact us via jonathanbehar@gmail.com