This is of particular importance in patients who have not had previous anaesthetics. A number of conditions have an inherited component, but may not be evident from the patient's history. Examples include:
Some drugs showsignificant interactions with anaesthetic agents, while others may have significant withdrawal effects
| Drug group | Comments |
|---|---|
| Cardiovascular | |
| ACE inhibitors | Hypotensive effects may b potentiated by anaesthetic agents. Relatively long halflives mean that sudden withdrawal tends not to produce haemodynamic effects.BNF |
| Angiotensin II antagonists | May be associated with severe hypotension. Consider stopping treatmen 24hrs pre-op. Exmaples include Losartan and Valsartan. BNF |
| Antihypertensives | The following may result in significant hypotension, and necessitate extreme care in dosing. |
| Clonidine / dexmedetomidine | Allows reduction in dose of anaesthetic agents |
| Guanethidine | Potentiates the effects of sympathomimetics |
| Reserpine | Depletes norepinephrine stores, so attenuating the action of pressor agents acting via norepinephrine release. |
| β-blockers | Negative inotropic effects potentiate by anaesthetic agents.Acute withdrawal may precipitate angina, VE's or MI |
| Calcium channel blockers | |
| Verapamil | Reduces AV conduction and excitability. Interact with volatile agents to produce bradycardias and reduced CO. |
| Diltiazem/Nifedipine | Negative inotropic effects and vasodilatiation giv rise to hypotesion. May augement the action of competitive muscle relaxants. Acutewithdrawal may exacerbate angina. |
| Digoxin | |
| Magnesium | Potentiates muscle relaxants |
| Quinidine | Can potentiate neuromucular blockers, notable suxamethonium |
| CNS | |
| Anticonvulsants | Liver enzyme induction may lead to increased requirements for anaesthetic agents. Avoid enflurane. Caution with propofol. Sudden withdrawal may produce rebound convulsions. |
| Benzodiazepines | Additive effect with CNS depressant drugs and competitive neuro-muscular blockers. Effects of suxamethonium may be antagonized. |
| MAOIs | React with opiods causing coma or CNS excitement. Severe hypertensive responses to pressor agents. Treatment of regional anaesthetic-induced hypotension may be difficult, especially as indirect sympathomimetics (e.g. ephedrine) are contraindicated due to unpredicatble and exagerated release of norepinephrine. Adverse effects do not always occure, but recommed to withdraw drugs 2-3 weeks before surgery and use alternative medication. |
| Tricyclic antidepressants | Inhibit the metabolism of catecholamines, increasing the likelihood of arrythmias. Imipramine potentiates cardiovascular effects of ephedrine. Delay gastric emptying. |
| Phenothiazines / Butyrophenones | Potentiate other hypotensive agents |
| Lithium | Potentiates non-depolarizing muscle relaxants - consider switching to other agents 48-72 hrs pre-op, but note that sudden cessation is not recommended. Lithium toxicity is increased by hyponatraemia. |
| L-DOPA | Risks of tachycardia and arrythmais with halothane. Actions anatagonised by droperidol. Exacerbates hyperglycaemia in diabetes. Debatable as to whether should be stopped on day of surgery. |
| Antibiotics | |
| Aminoglycosides | Potentiate neuromuscular blockade - effects may be partially antagonized by calcium. |
| Sulphonamides | Potentiate thiopentone |
| Misc | |
| Anticoagulants | Absolute CI to some regional techniques |
| Organophosphorus insecticides / antimitotic agents | Inhibition of plasma cholinesterase. Caution with suxamethonium. |
| OCP | Either discontinue 4 weeks pre-op or arrange for DVT prophylaxis |
Smoking is said to increase to chances of post-op morbidiy sixfold. Carbon monoxide has a short half-life and abstinence for 12 hours may result in a significant increase in oxygen carrying capacity. Cessation of smoking for 6 weeks may result in a reduction in bronchoconstriction and mucous secretion.
| FBC |
Patients of Afro-carribean origin should have a documented sickle-cell status. |
| U&Es |
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| Blood glucose | Patients with diabetes, CVS disease or those taking steroids. |
| LFT's |
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| Coagulation screen |
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| ECG |
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| CXR |
|
| PFTs | PEFR, FVC, FEV1 should be measured in all patients with significant dyspnoea on mild to moderate exercise. |
| ABGs | Required for all patients with dyspnoea at rest and patients scheduled for thoracotomy. A PaO2 of less than 9kPa combined with dyspnoea at rest is the most sensitive indicator of the need for post-op mechanical ventilation. |
Prediction and Management of Difficult Tracheal Intubation.
Role of short mandibular ramus v receeding jaw.