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Informing the patient

Often, the anesthetist has only a brief time in which to develop a relationship with the patient and one of the most important things is to explain the events the patient will experience in the perioperative period, avoiding technical jargon, followed by an opportunity to ask questions. Most patients will want to know how long they are to be starved prior to surgery, both in terms of eating and drinking. It is important that they are given clear instructions regarding the arrangements for taking their normal medications and whether they can have a small amount of water to take tablets. If a premedication is prescribed, the approximate timing route of administration and likely effects should be discussed. The choice of anesthetic technique rests with the anesthetist, but most patients appreciate some details of what to expect. The induction of general anesthesia is most commonly achieved by an I.V. injection through an indwelling cannula, producing rapid loss of consciousness. If regional anesthesia is used, it should be pointed out that remaining conscious throughout is to be expected unless some form of sedation is to be used. If large numbers of invasive monitoring devices are to be used prior to anesthesia, the procedures should be described in such a way as to not alarm or frighten the patient. Most patients will ask about their immediate recovery. For most, this will be in a recovery ward or a similar unit. It is advisable to warn about the possibility of drains, catheters and drips as their presence may be misinterpreted by the patient as indicating unexpected problems. Where postoperative care is planned to take place in the intensive care unit, the patient should be told what to expect and, if at all possible, be given the opportunity to visit the unit a few days before and meet some of the staff. Finally, it is important to reassure patients about postopetative pain control. They will need to be informed of the technique to be used, particularly if it requires their co-operation, for example a patient-controlled analgesia device (see page 122). As consent for anesthesia becomes a separate entity (currently it is included in the consent for surgery), the information given to the patient and the time this takes is likely to increase in order that consent is truly informed.

Premedication

Premedication originally referred to drugs administered to facilitate the induction and maintenance of anesthesia (literally, preliminary medication). Nowadays, premedication refers to the administration of any drugs in the period prior to induction of anesthesia. Consequently, a wide variety of drugs are used with a variety of aims. The 6 As of premedication Anxiolysis Amnesia Anti-emetic Antacid

Anti-autonomic

Analgesic ANXIOLYSIS The most commonly prescribed drugs are the benzodiazepines. They produce a degree of sedation and amnesia, are well absorbed from the gastrointestinal tract and are usually given orally, 45-90 minutes preoperatively. Those most commonly used include temazepam 20-30 mg, diazepam 10-20 mg lorazepam 2-4 mg. Other agents include phenothiazines (promazine), antihistamines (promethazine, trimeprazine) and B-blockers in-patients who suffer from excessive somatic manifestations of anxiety, for example tachycardia. A preoperative visit and explanation is often as effective as drugs at alleviating anxiety and sedation does not always mean lack of anxiety. AMNESIA Some patients specifically request that they do not wish to have any recall of the events leading up to anesthesia and surgery. This is usually accomplished by administration of lorazepam, which will provide anterograde amnesia. ANTI-EMETIC (REDUCTION OF NAUSEA AND VOMITING) Nausea and vomiting may follow the administration of opioids either pre- or intraoperatively. Certain types of surgery are associated with a higher incidence of postoperative nausea and vomiting, for example gynecology. Drugs with useful anti-emetic properties include: ANTACID (MODIFY pH AND VOLUME OF GASTRIC CONTENTS) Patients are starved preoperatively to reduce the risk of regurgitation and aspiration of gastric acid. Patients who have received opiates preoperatively or present as emergencies, particularly if in pain, will have delayed gastric emptying and those a hiatus hernia are at an increased risk of regurgitation. A variety of drug combinations are used to try and increase the pH and reduce the volume. An alternative is aspiration of gastric contents via a naso- or orogastric tube. ANTI-AUTONOMIC (BLOCK ATONOMIC REFLEXES) Parasympathetic reflexes Excessive vagal activity, causing profound bradycardias, may be seen following : The anticholinergic agents atropine and glycopyrrolate ate used to protect against the occurrence of bradycardias and although used preoperatively they are most effective when administered intravenously at induction. They are also used to prevent excessive secretion of saliva associated with the presence of objects in the mouth, for example and oropharyngeal airway. Sympathetic reflexes Increased sympathetic activity can be seen at intubation causing tachycardia and hypertension. This is undesirable in certain patients, for example those with ischemic heart disease or raised intracranial pressure. These responses can be attenuated by the use of B-blockers administered orally preoperatively (e.g. atenolol) or intravenously at induction (e.g. esmolol). An alternative is to administer potent analgesics at induction of anesthesia, for example fentanyl or alfentanil. ANALGESIA Although the oldest form of premedication, analgesic drugs are now generally reserved for patients who are in pain preoperatively and they are best administered intramuscularly. The most commonly used are morphine, pethidine and fentanyl. Morphine was widely used for its sedative effects but is relatively poor as an anxiolytic and has largely been replaced by the benzodiazepines. In addition, opiates have a range of unwanted side effects including, nausea, vomiting, respiratory depression and delayed gastric emptying. MISGELLANEOUS A variety of other drugs are commonly administered prophylactically prior to anesthesia and surgery, for example:

In addition to these are the patient’s own regular medications, which should be taken as instructed by the anesthetist (Table 1.6).

MEDICATION AND ANESTHETIC ANENTS

Drug group Comments 1 Angiotensin-converting Potent vasodilators. Synergistic with the effects of enzyme (ACE) inhibitors: anesthetics causing hypotension Captopril Enalapril 2 Antibiotics: Synergistic with neuromuscular blocking drugs Aminoglycosides prolonging length of block. Renal toxicity with long Polymixins term therapy or combination with some diuretics

3 Anticoagulatnts: Increased risk of hemorrhage during intubation, (a) Oral: warfare, insertion of central lines, local/regional nicoumalone anesthesia, surgery, insertion of a nasogastric tube (b) IV: heparin

4 Anticonvulsants: Potent inducers of hepatic enzymes, may need Barbiturates increased does of induction agents and opioids

Phenytoin Carbamazepine 5 Benzodiazepines Wide variety of drugs with varying half-lives. Tolerance common. Additive effect with other CNS depressants. A withdrawal syndrome may be precioitated if flumazenil, a specific benzodiazepine antagonist, is administered 6 B-blockers Negative inotropic effects may combine with

 

Atenolol Metoprolol Oxprenolol Propranolol Sotalol and others

 

7 Calcium antagonists:

Diltiazem Nifedipine Verapamil

　

8 Digoxin

　

9 Diuretics: Thiszides Loop diuretics 10 Lithium

　 　

 

Negative inotropic effects may combine with Vasodilatation caused by anesthetic agents to Produce hypotension. The pulse rate is a poor guide To blood loss intraoperatively 　 Isoflurane, enflurane and halothane are non- Specific calcium antagonists. Effects additive, producing hypotension. Verapamil may cause bradycardias secondary to decreased atrioventricular conduction Toxicity common, predisposing to arrhythmias, potentiated by suxamethonium Hypokalaemia causing dysrhythmias and prolonging neuromuscular blockade. Hyponatraemia Prolongs the effects of non-depolaring neuromuscular blocking drugs 　 11. Monoamine oxidase inhibitors (MAOIs): isocaboxazid phenelzine tranylcypromine 12 Steroids 　 　 　 13 Tricyclic Antidepressants 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 Uncommon but potentially fatal interaction with opioids, particularly pethidine, and all Sympathomimetics. Must be stopped at least 2 weeks before surgery 　 Hypotension at induction of anesthesia. supplementary doses required for patients on long- term treatment or if taken in the past 3 months, due to adrenocortical suppression Potentate the effects of exogenous catecholamines causing arrhythmias, e.g. adrenaline, where it is used as a vasoconstrictor in local anesthetics or to reduce bleeding

　 　 　 　 　 　 　 　 　 　

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