Preoperative Assessment Of Fitness For Anaesthesia And Surgery

Cardiovascular system

Cardiac risk factors

Numerous studies have attempted to define the aetiological factors associated with perioperative cardiac complications and several risk assessment indices have been published. Patients may be classified as low risk (<3%), intermediate (3-10%) or high risk (>10%) of major adverse cardiac events. Major risk factors are:

• myocardial infarction within previous 3 (major risk) or 6 (moderate risk) months;

• unstable angina;

• untreated cardiac failure;

• significant aortic valve stenosis;

• untreated hypertension. Relative risk factors are:

• prior myocardial infarction;

• jugular vein distension (or S3 gallop);

• ventricular ectopic beats/min;

• emergency surgery;

• significant medical impairment: PaO2 < 60 mmHg, PaCO2 > 50 mmHg and K < 3 mmol/l;

• chronic liver impairment.

Postoperative cardiac complications result from patients with impaired physiological reserve being unable to cope with the stresses of the perioperative period. Factors impinging on the physiological reserve include:

• myocardial depression from sepsis and anaesthetic agents;

• variable pre- and after-load due to fluid shifts associated with disease, surgery and fluid replacement regimens;

• reduction in oxygen transport secondary to myocardial depression, intrapulmonary shunting, blood loss and pain-or drug-induced hypoventilation;

• miscellaneous factors such as hypotension, acidosis, tachycardia, fluctuating blood levels of therapeutic agents.

Ischaemic heart disease

Recent consensus guidelines from the USA (American Heart Association and American College of Physicians) plus research in Europe has produced algorithms to assist evaluation of at-risk patients prior to non-cardiac surgery (American College of Physicians, 1997; Chassot et al., 2002).

Myocardial infarction

The risk of perioperative myocardial infarction is most strongly correlated with previous infarction history (Table 1.3) or the

Table 1.3. Risk of myocardial infarction.

• No previous infarction

0-5%

• Acute myocardial infarction >6 months previously

6%

• Myocardial infarction 3-6 months ago

10%

• Infarction <3 months ago

30%

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