Conditions rendering patients at increased anaesthetic risk
- Difficult airway
- Obesity
- Cardiac disease
- Respiratory disease
- Gastrointestinal disease
- Renal failure
- Diabetes
- Haematological disorders
- Allergic reactions
Cardiovascular disease
- Several scoring systems exist for stratifying cardiac risk prior to non-cardiac surgery
- Simple to use and identify patients in need of further investigation
Eagle index
- One point allocated for each of:
- History of myocardial infarction of angina
- Q wave on preoperative ECG
- Non-diet controlled diabetes mellitus
- Age more than 70 years
- History of ventricular arrhythmia
- If total score is:
- No points = low risk
- 1 or 2 points = intermediate risk
- More than 2 points = high risk
- Low risk patients require no further investigation
- Intermediate risk patients require exercise ECG and thallium scan
- High risk patients require coronary angiography prior to major surgery
Revised cardiac risk index
- One point allocated for each of:
- High-risk surgery
- Ischaemic heart disease
- History of congestive heart failure
- History of cerebrovascular disease
- Insulin therapy for diabetes mellitus
- Renal impairment
- Risk of major cardiac event during surgery:
- No points = 0.5%
- 1 point = 1.3%
- 2 points = 4%
- More than 2 points = 10%
Myocardial Infarction
- Elective surgery should be deferred for 6 months after a myocardial infarct
- Risk factors for postoperative myocardial re-infarction:
- Short time since previous infarct
- Residual major coronary vessel disease
- Prolonged or major surgery
- Impaired myocardial function
- Risk or postoperative re-infarction after a previous MI is:
- 0-3 months is 35%
- 3-6 months is 15%
- More than 6 months is 4%
- 60% of post operative myocardial infarcts are silent
- The mortality of re-infarction is approximately 40%
Hypertension
- In patients with hypertension need to assess
- Degree of hypertension
- Presence of end organ damage
- Risk of cardiovascular morbidity is increased in untreated or poorly controlled hypertension
- Risk is present if diastolic pressure is greater than 95 mmHg
- Elective surgery should be cancelled if diastolic pressure is greater than 120 mmHg
Respiratory disease
- Patients with lung disease are at increased risk of respiratory complications
- The complications include:
- Bronchospasm
- Atelectasis
- Bronchopneumonia
- Hypoxaemia
- Respiratory failure
- Pulmonary embolism
- In addition to routine preoperative investigations need to consider
- Chest radiography
- Spirometry
- Arterial blood gases
- Upper respiratory tract infections increase the risk postoperative chest complications
- Elective surgery should be deferred for 2-4 weeks
Smoking
- Doubles the risk of pulmonary complications
- Increased risk persists for 3-4 months after stopping smoking
- Smoking increases blood carboxyhaemoglobin
- Increased carboxyhaemoglobin persists for 12 hours after last cigarette
Obesity
- Morbidity and mortality after all surgery is increased in the obese
- Risk is increased even in the absence of other disease
- Body mass index (BMI) is best measure of degree of obesity
- BMI = Weight (Kg) / height (m)2
- Normal BMI = 22-28
- BMI greater than 28 equates to significantly overweight
- BMI greater than 35 equals morbid obesity
- Patients are at risk of numerous complications
- ITU or HDU bed may be required postoperatively
Cardiovascular
- Hypertension
- Ischaemic heart disease
- Cerebrovascular disease
- Deep venous thrombosis
- Difficult vascular access
Respiratory
- Difficult airway
- Difficult mechanical ventilation
- Chronic hypoxaemia
- Obstructive sleep apnoea
- Pulmonary hypertension
- Postoperative hypoxaemia
Other complications or problems
- Gastro-oesophageal reflux
- Abnormal liver function
- Insulin resistance and Type 2 diabetes
- Poor postoperative pain control
- Unpredictable pharmacological responses
Diabetes mellitus
- Pre and perioperative management depends on severity of disease.
Diet controlled diabetes
- No specific precautions.
- Check blood sugar and consider Glucose-Potassium-Insulin (GKI) infusion if >12 mmol/l.
Oral hypoglycaemics
- Stop long acting sulphonylureas (e.g. chlorpropamide) 48
hours prior to surgery
- Short acting agents - omit on morning of operation
- Restart when eating normally
- Consider GKI infusion for major surgery
Insulin dependent diabetes
- Convert long acting insulins to 8-hourly Actrapid
- Place early on operating list
- Give GKI infusion until eating normally
GKI infusion
- Made up as:
- 15 u insulin
- 10 mmol potassium chloride
- 500 ml 10% dextrose
- Infused at a rate of 100 ml /hr.
Obstructive Jaundice
Operative morbidity and mortality is increased in patients with obstructive jaundice due
to:
- Coagulation disorders
- Reduces the absorption of fat soluble vitamins
- Reduces production of factors II, VII, IX, X
- Disorders can be reversed with Fresh Frozen Plasma or Vitamin K
- Reduced wound healing
- Increased risk of infection
- Hepato-renal syndrome
- Acute renal failure in patient with jaundice
- Probably due to systemic endotoxaemia
- Requires adequate hydration and diuretics
- Value of mannitol unproven
- Altered drug metabolism
- Half life of many analgesics is prolonged (e.g. morphine).
Chronic renal failure
- Chronic renal failure affects multiple organ systems
- Effects that need to be considered by both surgeons and anesthetists include
- Electrolyte disturbances
- Impaired acid-base balance
- Anaemia
- Coagulopathy
- Impaired autonomic regulation
- Protection of veins, shunts and fistulae
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