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Investigation

• Chest Radiograph: A relatively non-specific test although cardiomegaly and venous congestion associated with cardiac failure can be detected.

• ECG: A normal resting ECG does not exclude the presence of ischaemic heart disease. Ambulatory ECG during the 48 h prior to surgery in patients with known coronary artery disease has shown silent ischaemic episodes in 18-40% of patients. However, in the absence of symptoms and signs of coronary disease, there is good correlation between a normal resting ECG and an uneventful preoperative course.

• Stress ECGs: A significant correlation with the development of preoperative complications is shown in patients who:

- show ischaemic changes during exercise;

- are unable to reach 85% of their predicted maximum heart rate during exercise.

• Isotopic scanning: Thallium scanning can determine the ventricular ejection fraction. An ejection fraction of <0.30 correlates with a significantly increased risk of perioperative myocardial infarction.

• Transthoracic echocardiography ( TTE): This can detect abnormalities of the ventricular contractility and valve function.

• Coronary angiography: This provides definitive evidence of the degree and extent of coronary occlusion and is essential before coronary bypass surgery.

Hypertension

Hypertension is present in approximately 20% of adult patients and the definition of hypertension has changed with greater realisation of the deleterious effects of even modest long-term elevation of blood pressure (BP; Table 1.5).

Mild controlled hypertension in isolation appears to pose no additional operative risk, but uncontrolled hypertension (Stage 3 or 4) has an increased risk of congestive cardiac failure, myocardial ischaemia and unplanned admission to critical care units perioperatively.

Antihypertensive medication should not be discontinued prior to surgery. However, there have been reports of significant induction hypotension in patients treated with angiotensin converting enzyme (ACE) inhibitors. Clinical practice varies, with some authors advocating cessation of ACE inhibitors on the day prior to surgery whilst others continue therapy. Elective surgery should be curtailed if the diastolic BP exceeds 115mmHg as a diastolic BP >120mmHg has a well-documented association with perioperative complications. In the emergency situation, intra-arterial monitoring and control of BP using intravenous beta-blockers or glyceryl trinitrate (GTN) should be employed. Management of hypertensive patients during surgery is complicated by their exaggerated responses to noxious stimuli such as pain or endotracheal intubation. Management principals:

• Assessment and optimisation of BP control.

• Assessment of associated pathology:

- coronary disease;

- congestive failure;

- renal dysfunction;

- peripheral vascular disease.

• Anaesthetic management (refer to Chapter 2):

- accurate monitoring of BP;

- management of intubation hypertension;

- observation of intraoperative hypertension or signs of ischaemia;

- avoidance of large swings in BP or periods of prolonged hypotension.

• Postoperative management (refer to Chapter 3):

- optimal pain control - non-steroid anti-inflammatory drugs (NSAIDs) should be used cautiously, if at all, in patients on angiotensin 2 receptor blockers and diuretics because of a significant risk of development of renal impairment;

- BP management prior to return of oral medication. Congestive cardiac failure

Untreated congestive cardiac failure has a high association with postoperative morbidity and is a contraindication to elective surgery. If emergency surgery is necessary in the presence of poorly controlled heart failure, monitoring of left and right ventricular filling pressures will be necessary and consideration should be given to postoperative respiratory support. Patients with treated cardiac failure are at low risk of complications, provided medication is maintained over the preopera-tive period. The fluid shifts associated with spinal and epidural anaesthesia may precipitate pulmonary oedema in the preop-erative period and may be controlled by leg elevation or bandaging, as well as judicious doses of vasoconstrictors such as metaraminol.

Valvular heart disease

Undetected valvular heart disease, especially aortic stenosis, has a high association with postoperative morbidity. In addition to impaired cardiac function, associated organ pathology such as pulmonary, hepatic and renal dysfunction may occur. Clinical assessment is based on history, exercise tolerance and auscultation. The New York Heart Association classification

Table 1.6. New York Heart Association classification of patients with heart disease.

1 Asymptomatic

2 Symptoms with ordinary activity but comfortable at rest

3 Symptoms with minimal activity but comfortable at rest

4 Symptoms at rest of patients with heart disease is a useful index of functional impairment (Table 1.6).

Assessment requires either TTE, TOE or cardiac catheteri-sation to determine pressure gradients across the valves. In general, preoperative management of the patient with valve disease involves prophylactic antibiotics, because of the increased risk of bacterial endocarditis, and meticulous attention to fluid management, as well as specific therapy for individual heart problems.

Respiratory system

Risk factors

A list of risk factors which increase the incidence of postoperative pulmonary complications exists in an analogous manner to that for cardiac complications.

- preoperative symptoms of respiratory disease,

- preoperative history of chronic obstructive airways disease (COAD),

- preoperative productive cough,

- cigarette smoking,

- poor nutrition,

- obesity,

- abnormal chest examination,

- abnormal chest X-ray.

• Surgery and anaesthesia:

- thoracic and upper abdominal surgery,

- anaesthesia >3h.

Certain techniques improve preoperative pulmonary performance and reduce the incidence of complications:

• bronchodilator therapy,

• pre- and postoperative chest physiotherapy,

• optimal analgesia,

• cessation of smoking 6-8 weeks prior to major surgery,

• use of the incentive spirometer as an adjunct to physiotherapy,

• early ambulation,

• prophylactic antibiotics if chest infection is present.

Assessment of respiratory function

Clinical history should elicit exercise tolerance, type and productivity of cough and any precipitating factors of respiratory distress, such as lying flat. Examination includes auscultation and percussion of the chest and an assessment of airway patency. Bedside clinical testing of respiratory function provides valuable information, especially in situations where laboratory testing may not be readily available:

• breathlessness on walking a few metres around the ward usually represents decreased cardiopulmonary reserve;

• inability to count beyond 20 at a single inspiration quantifies dyspnoea;

• accompanying the patient during stair climbing verifies the degree of exertional dyspnoea.

Laboratory testing accurately quantifies the degree of impairment as well as recording effects of therapy such as bron-chodilator administration. The commonest tests are:

• Spirometry which measures the volumes of exhaled gas per unit time. The commonly assessed parameters are:

- forced vital capacity (FVC);

- forced expiratory volume (FEV1);

- FEV/FVC ratio: usually >85%; <50% indicates that postoperative ventilation is more likely;

- maximum mid-expiratory flow rate (MMEFR);

- peak expiratory flow rate (PEFR) which measures airflow obstruction at high flow rates.

• Arterial blood gas estimation provides information as to baseline levels of gas transfer and helps guide therapy.

Indicators of significant risk of postoperative respiratory failure are:

The COAD

The term COAD includes a group of destructive lung diseases generally caused by smoking and characterised by dyspnoea of progressive severity, airflow obstruction and cough. The destructive process leads to hypoxaemia and hypercarbia. Historically, the disease was separated into chronic bronchitis (predominantly obstructive disease) and emphysema (predominantly destructive disease), but they are now generally grouped together, reflecting the fundamentally similar patho-physiology. Intercurrent chest infections are common and right ventricular dysfunction is seen in up to 50% of patients with COAD.

Any increase in quantity or change in appearance of sputum may be indicative of developing infection. Assessment of the severity of COAD requires knowledge of the degree of exercise impairment. The distance a patient can walk on the flat or the number of flights of stairs which can be climbed before developing dyspnoea gives a measure of exercise tolerance. Other conditions such as hip disease or intermittent claudication can limit the value of this clinical test. Some anaesthetists walk up the stairs with patients to verify these facts.

Tests of airflow limitation quantitate the level of impairment. FEV1 is the most commonly used although the MMEFR is more sensitive. The response to p2 selective agonists such as salbutamol should be ascertained prior to surgery. As with asthma, the patient should take their aerosol with them to the operating room for use prior to surgery. Phosphodiesterase inhibitors (theophyline) are second-line therapy as the narrow therapeutic dose range means toxic symptoms may occur. Ipratropium bromide (atrovent) combined with selective p2 agonists may give improved and prolonged benefit compared with p2 agonists alone. Intraoperative arterial blood gas monitoring is advisable in patients with severe COAD and baseline values on room air, prior to surgery and assist planning postoperative care.

Patients with COAD are prone to desaturation during sleep and this has important implications for postoperative care and may contribute to the incidence of myocardial infarction in the early postoperative days. Physiotherapy commencing pre-operatively significantly improves the outcome, especially in patients with significant sputum production. Regional anaesthesia, particularly for lower abdominal, limb and vascular surgery, is useful in this group of patients.

Asthma

Asthma is a syndrome of heightened bronchial reactivity to a variety of stimuli, resulting in airflow obstruction of variable severity. The overall incidence in the population is 4% and this is increasing worldwide. Therapy involves the use of bron-chodilators alone or in combination with anti-inflammatory agents. Maintenance steroid use is increasing in asthma medication and inhaled steroids cause fewer systemic problems than oral steroids due to their poor absorption from the lungs. Suppression of adrenal function may occur with oral steroid therapy and this may last for up to 3 years after cessation of therapy.

Clinical assessment

In known asthmatics, it is essential to elicit provoking factors, frequency of attacks, length of hospitalisation required and the drug therapy, especially steroid use. Physical examination may be unremarkable between attacks.

Respiratory function test

Spirometry should be performed to assess FVC and FEV1. Spirometry also allows assessment of the response to bron-chodilators. Arterial blood gases and chest X-rays are not routinely necessary. Some centres recommend routine full blood testing to detect eosinophilia but this is not universal.

Preoperative preparation requires optimisation of drug therapy and estimation of baseline respiratory function, allowing grading of severity of asthma:

• Mild asthma (no hospitalisation): Maintain routine therapy and administer selective p2-agonist (salbutamol) via aerosol prior to surgery.

• Moderate asthma (some functional impairment, routine use of bronchodilators): Maintain routine therapy and administer selective p2-agonist (salbutamol) via nebuliser prior to surgery.

• Severe asthma (significant impairment, current bron-choconstriction): Corticosteroids should be used (e.g. hydrocortisone 1-3mg/kg) 2h prior to surgery in addition to inhaled p2-agonist therapy.

Upper respiratory tract infections

The significance of upper respiratory tract infections (URTIs) on the outcome of surgery has been argued. There is an increase in bronchial reactivity associated with URTI and thus postponement of surgery in asthmatic patients is prudent. In non-asthmatic adults, no effect on outcome has been found. In children, no agreement has been reached on the advisability of postponement of elective surgery during URTIs.

Obstructive sleep apnoea

Patients with obstructive sleep apnoea (OSA) have episodes of upper airways obstruction associated with arterial oxygen desaturation. OSA is defined as the cessation of airflow for longer than 10 s despite continued ventilatory efforts, at least 5 times per hour of sleep. Desaturation during sleep results in bradycardia and ventricular ectopic beats and eventually systemic and pulmonary hypertension develops. The incidence of OSA appears to be increasing with approximately 2-4% of the population affected. It is commoner in males and in the obese (>60% with OSA are obese). OSA causes episodes of daytime sleepiness and an increase in accidental injuries. At the preoperative interview patients or their partners may volunteer symptoms, but all obese patients should be questioned for occult OSA. Sleep studies should be performed to quantitate the severity of OSA and evaluate therapy prior to surgery. If surgery cannot be delayed, the patient should be assumed to have OSA and managed accordingly. Regional anaesthesia, if practical, is a good option and sedative drugs, particularly benzodiazepines should be avoided. If patients have their own continuous positive airway pressure (CPAP) apparatus this should be brought to hospital with them prior to surgery and postoperative care in a high dependancy unit is advisable.

Central nervous system

Epilepsy

Patients with grand mal epilepsy are at increased risk of fitting in the perioperative period due to:

• inadequate blood levels of anticoaconvulsants because of fasting or impaired absorption due to surgical pathology;

• excitatory effects of some anaesthetic agents or delay in recommencing oral medications.

At the preoperative interview the frequency of attacks, any precipitating circumstances, and current medications should be documented. Anti-epileptic agents should be taken on the morning of surgery and if oral therapy cannot be resumed postoperatively, parenteral anti-epileptic agents should be commenced.

Dementia

The increasing population of elderly patients has increased the number of patients with Alzheimer's dementia and vascular dementia presenting for surgery. The commonest co-morbidities encountered in dementia patients are COAD and atherosclerotic cardiovascular disease. It is common for a deterioration in cognitive function to occur in the perioperative period and this may take weeks to resolve. Neuroleptic drugs appear to increase the incidence of cognitive disorders perioperatively. Patients with chronic brain syndromes pose several problems in preoperative assessment:

• Consent, to be valid, should be signed by the person responsible under the relevant law of the jurisdiction involved or be referred to the local Guardianship Board (or similar).

• Accurate history taking may be impossible and medications may not be remembered. Increased time may be required to allow access to previous medical histories from other hospitals.

• Patient anxiety may lead to extreme agitation and restlessness. Sedative agents injudiciously given may worsen this agitation.

• Underlying pathological processes affecting other organ systems (alcoholism, severe peripheral vascular disease or chronic syphilis) or physical factors (head injury with flexion deformities, bed sores or low-grade urinary tract infections) must be taken into account during surgery and anaesthesia.

Renal system

Chronic renal failure

Patients with chronic renal failure pose many problems for the surgeon and anaesthetist because of the frequency with which surgery is necessary in these patients and the many associated medical problems present in this group:

• Cardiovascular:

- Hypertension and associated complications.

- Chronic anaemia due to ureamia and reduced erythropoietin levels. Haemoglobin (Hb) levels of 7-10g/l are normal in patients with chronic renal failure and injudicious transfusion may precipitate cardiac failure. The patient's weight is a useful guide to the level of hydration in an emergency when dialysis may not be possible prior to surgery.

- Associated retinopathy, microvascular disease or auto-nomic dysfunction should be considered.

• Acid-base and metabolic:

- Metabolic acidosis.

- Hyperkalemia: Serum potassium >6 mmol/l requires dialysis prior to surgery to prevent further rises during the preoperative period. Factors which may increase serum potassium include the use of suxamethonium, administration of blood and hypoventilation. In all but dire emergencies, correction of potassium prior to surgery can be accomplished by dialysis, glucose-insulin therapy or Resonium enemas.

- Hypocalcaemia due to vitamin D deficiency.

- Hypermagnesaemia.

- Inability to manage a water load.

- Concurrent use of immunosuppressants and decreased phagocyte effectiveness combine to increase perioperative risk of sepsis.

- Coagulopathy may be present due to reduced platelet adhesiveness. International Normalised Ratio (INR) and antiprothrombin time (APTT) are usually normal.

• Arteriovenous fistula:

- The presence of vascular access fistulas for haemodialysis in the upper limbs limits venous access for non-invasive blood pressure (NIBP) monitoring and drug administration during anaesthesia and recovery. Protection of the function of these fistulas from pressure and periods of hypotension (which may cause clotting of the fistulae) requires continual vigilance until the patient has fully regained consciousness.

• Miscellaneous:

- Delayed gastric emptying (uraemia) and increased gastric acidity increase the risk of reflux and aspiration. Preoperative use of H2 receptor blockers or proton pump inhibitors is recommended.

- The majority of renal patients have associated hypertension and medication should be continued through the preoperative period. Oral hypoglycaemics should be discontinued the night before surgery and insulin should be managed as discussed in the section on diabetes. Renal failure decreases clearance (but not loading dose) of many drugs. If gentamycin or other aminoglycosides are necessary, blood levels should be monitored perioperatively. Metabolic changes in chronic renal failure affect clearance of NSAID's, pancuronium, pethidine (norpethidine accumulation) and enflurane which should be avoided.

• Transplanted patients:

- Immunosuppressants increase infection risk, steroids increase osteoporosis and risk of pathological fractures. The transplanted kidney is at risk of physical damage during positioning or rejection if immunosuppressants are withheld perioperatively.

Liver

The commonest causes of liver impairment are viral (hepatitis B and C), toxicity (alcohol, paracetamol) and autoimmune disease (primary biliary cirrhosis, autoimmune hepatitis).

Liver failure can be classified by the acuity (i.e. the interval between the onset of jaundice and the development of encephalopathy:

• Hyperacute: within 7 days.

• Subacute: within 28 days to 6 months.

• Chronic: >6 months. Pathophysiological features include:

• Haematological: coagulation should be checked because many patients will have impaired coagulation due to clotting factor deficiency and impaired platelet function.

• Respiratory: pleural effusions or ascites may impair breathing and increase aspiration risk.

• Cardiovascular: cardiomyopathy (alcoholic and haemochro-matosis) should be excluded.

• CNS: encephalopathy is commonest in acute and can be graded:

- Grade 0: alert and orientated.

- Grade 1: drowsy but orientated.

- Grade2: drowsy and disorientated.

- Grade 3: agitated and aggressive.

- Grade4: unrousable to deep pain.

• Pharmacological effects include prolongation of muscle relaxants (suxamethonium, mivacurium, vecuronium and rocuronium), as well as accumulation of fentanyl and morphine. Non-steroidal agents should be avoided because of the increased risk of gastrointestinal (GI) bleeding in patients with impaired coagulation.

Assessment of liver function: Serum bilirubin and albumin plus prothrombin time (PT) are markers of global hepatic dysfunction, whilst elevated levels of transaminases can occur with minor liver damage. The Childs-Pugh classification for patients with cirrhosis indicates an increasing chance of hepatic failure.

Endocrine system

Diabetes

Approximately 2.5% of the population have diabetes with the incidence rising in patients >80 years old. The majority (>90%) have non-insulin-dependent diabetes mellitus (NIDDM or Type II diabetes).

Assessment of the diabetic patient undergoing surgery should include:

• Cardiovascular system: Microvascular disease is widespread in diabetic patients with between 15% and 60% of insulin-dependent diabetics having ECG changes. This microvascular disease is frequently associated with left ventricular dysfunction.

• Hypertension: This is present in over 60% of diabetic patients. Autonomic neuropathy is an uncommon but serious complication of diabetes with impaired cardiovascular responses to exercise and stress. Orthostatic hypotension is a reliable indicator of the presence of autonomic neuropathy.

• Peripheral vascular disease: This is frequently present and these patients are at risk of vascular occlusion during periods of hypotension or hypovolaemia.

• Renal disease: This is common in diabetic patients with glomerulosclerosis, papillary necrosis and ultimately chronic renal failure.

Preoperative management of blood glucose is necessary to prevent ketosis and acidosis, volume depletion due to osmotic diuresis or complications associated with undetected hypogly-caemia, especially brain cell damage or pulmonary aspiration, whilst unconscious. Blood sugar should be estimated, usually by the finger-prick method, since urine sugar estimations are too unreliable during periods of fluctuating blood sugar and variable urine output.

• For major surgery in insulin-dependent diabetes patients: insulin-dextrose-potassium infusion is a reliable regimen. Frequent blood sugar monitoring is important to avoid potentially dangerous periods of hypoglycaemia. Follow-up in the perioperative period and consultation between anaesthetist, surgeon and physician is essential.

• For minor surgery in insulin-dependent diabetes patients: half of the normal morning insulin requirement is given and a 5% dextrose infusion is commenced. If oral feeding does not recommence within 4-6 h, conversion to the regimen as for major surgery should be instituted.

• For minor surgery in NIDDM patients: withhold oral hypo-glycaemic agent on the morning of surgery. Blood sugar should be monitored throughout the preoperative period.

• Emergency surgery in diabetics: is frequently undertaken against a background of either infection or acidosis and hyperglycaemia. Meticulous attention to blood glucose control and fluid balance are essential.

Hypothyroidism

Subclinical hypothyroidism affects an estimated 2-8% of the population and this incidence rises to 16% in females over 60 years. Patients with clinical hypothyroidism should be rendered euthyroid prior to elective surgery, because of their increased sensitivity to anaesthetic agents which may cause delayed awakening. L-thyroxine can be given as 50 ^g/day initially followed by 150-200 ^g/day as a maintenance dose. In elderly patients or those with coronary disease, reduced doses are recommended.

Hyperthyroidism

Medical control of hyperthyroidism using beta-blockers and antithyroid drugs (propylthiouracil or similar) is necessary prior to elective surgery to avoid serious complications such as:

• Thyroid storm, which is an acute episode of profound thyroid hyperactivity associated with tachycardia, pyrexia and cardiac arrhythmias. If untreated, this condition has a high mortality rate.

• Precipitation of angina, myocardial infarction or cardiac failure.

• Tachyarrhythmias, episodes of paroxysmal atrial fibrillation (AF) occur in nearly 25% of hyperthyroid patients.

If emergency surgery is indicated in hyperthyroid patients, the following precautions are necessary,

• intravenous administration of antithyroid drugs;

• indwelling arterial monitoring;

• sedating premedication to allay anxiety;

• avoidance of drugs which may provoke tachycardia, such as ketamine, pancuronium, atropine;

• use of beta-blockade to control heart rate during endotra-cheal intubation and surgical incision;

• adequate depth of anaesthesia to ablate noxious stimuli;

• good postoperative pain control.

Adrenal insufficiency

Two types of adrenal insufficiency exist,

• Primary (Addison's disease) with inadequate levels of glucocorticoids, mineralocorticoids and androgens. Signs include fatigue, anorexia, cutaneous pigmentation and hypotension with hyponatremia and hyperkalaemia.

• Secondary due to inadequate levels of corticotropin-releasing hormone (CRH) or adrenocorticotrophic hormone (ACTH) due to corticosteroid use or hypothalamic or pituitary disease.

Normal cortisol secretion is 25-30 mg/day rising to 75-150 mg with stress such as surgery and peaking at 200-500 mg/day with severe stress. A dose equivalent of prednisolone 20 mg/day for at least 3 weeks in the last year will produce some adrenal suppression. Recommendations for steroid replacement perioperatively vary widely. A suggested regime is,

• minor surgery IV hydrocortisone 25 mg;

- intraoperatively, IV hydrocortisone 75-150 mg;

- postoperatively, IV hydrocortisone 50 mg 8 h for 1 day, then 25 mg 8 h for 1 day.

Acute Addisonian crisis is rare and presents with,

• severe nausea, vomiting and abdominal pain;

• hypotension with hypovolaemia.

Management involves treatment of cause (if possible), glucocorticoids and fluids. Inotropes are relatively ineffective in Addisonian crisis if steroids are not given.

Phaeochromocytoma

These are catecholamine secreting tumours of chromatin cells. Noradrenaline secretion predominates in most cases, but in 15% of cases adrenaline secretion is predominant. Presenting signs include hypertension either constant or paroxysmal, headache, sweating and palpitations. Catecholamine-induced cardiomyopathy may also be present. Management prior to surgery involves alpha-blockade with phenoxybenzamine or prazocin for between 3 days and 2 weeks. Beta-blockers may be added to alpha-blockade if necessary. Echocardiography to exclude cardiomyopathy is advisable.

Haematology

Anaemia

Chronic anaemia (Hb < 9 g/l) should be corrected prior to elective surgery, because the anaemic patient has reduced oxygen carrying capacity reserve to compensate for intraoperative blood loss. In addition, compensatory mechanisms for the reduced oxygen carrying capacity, such as:

• Increased cardiac output:

- peripheral vasodilation (microvascular control mechanisms);

- reduced blood viscosity.

• Increased oxygen extraction:

- shift of haemoglobin dissociation curve to the right;

- local tissue acidosis;

may encroach on cardiac reserve. Correction to Hb 10 g/l is advised using supplemental iron for elective surgery. If transfusion to correct chronic anaemia is necessary when surgery is more urgent, caution is required if >1 unit/day is administered in case pulmonary oedema is precipitated, and packed cells are used in preference to whole blood. Intraoperative blood loss should be promptly replaced and factors increasing postoperative oxygen requirements (especially shivering) should be avoided.

Patients with sickle cell anaemia are at increased risk of sickle cell crises during anaesthesia:

• hypoxic episodes,

• dehydration associated with prolonged fasting of increased fluid losses.

Although hydroxyurea has been used to stimulate HbF production which reduces the incidence and severity of sickle cell crises, this work is still in the experimental stages due to concerns regarding mutagenesis and leukemogenesis. Patients from countries with endemic sickle cell disease should be screened prior to surgery.

Coagulation and haemostasis

Coagulation disorders

It is vital to diagnose and appropriately manage patients with these disorders. Some of them are obscure, some of them can be elucidated from the history. A history must be taken of previous operations or spontaneous episodes of bleeding, perhaps from the gums or following trivial injuries. Drug and family history are also essential. Bruising or petechiae may be present on examination. Detection of some conditions will emerge from results of simple routine tests such as PT, partial thromboplastin time (PTT), thrombin time (TT) and platelet count.

In most cases the expert help of a clinical haematologist will be required. In cases that are difficult to interpret, it is better to anticipate and take precautionary measures than to call for help when disaster has struck. Bleeding disorders may be congenital or acquired:

• Congenital defects include clotting factors as in haemophilia and von Willebrand's disease, congenital platelet disorders and vessel wall defects such as hereditary haemorrhagic telangiectasia.

• Acquired disorders include clotting factor disorders resulting from drugs such as anticoagulants, antibiotics and liver disease. Disseminated intravascular coagulopathy (DIC) may complicate sepsis, haemolysis, antibody-antigen complex reactions and advanced neoplasia. Platelet function is notably reduced by aspirin and NSAIDs and in liver, kidney and myeloproliferative disorders. Platelets numbers are reduced in autoimmune thrombocytopaenia, hypersplenism and aplastic anaemia. The integrity of the vessel walls is reduced after taking steroids, in vasculitis and in malnutrition.

Patients on maintenance treatment with anticoagulants who are to undergo operation are at risk from bleeding but if their anticoagulants are stopped they are at risk of thrombosis. Before minor operations it is usual to stop oral warfarin for 2 days preoperatively and to start it immediately afterwards. Those having extensive procedures or with, for example, prosthetic heart valves, should stop warfarin and be maintained on heparin subcutaneously or by intravenous infusion under the supervision of a haematologist. In some cases, an operation may need to be performed as an emergency, or a patient may have bled as a result of taking anticoagulants. In these cases, the anticoagulant effects should be reversed with vitamin K, fresh frozen plasma (FFP) or concentrated clotting factors - again under the guidance of a haematologist.

Patients with coagulation disorders usually need to have blood or blood products available during surgical procedures, such as plasma-reduced cells, platelet transfusions, FFP cryo-precipitate (which contains fibrinogen, fibronectin and factor VIII) or coagulation factor concentrates. They may, however, have atypical antibodies.

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