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Premedication
Clinical anaesthesia
Premedication
and reduce salivation has been abandoned with the advent of modern intravenous and inhalational agents, which have far fewer side effects and a faster onset. Other factors have also influenced modern practice and reduced the use of a sedative premedication: • increasing use of day-case surgery • same-day admissions – patients often do not find a bed until just before surgery and the preoperative visit is rushed • changes to the surgical list, making the timing of drug delivery difficult. Despite these changes, the main aims of premedication are: • anxiolysis • analgesia (systemic and topical) • anti-emesis • risk reduction specific to the patient or the type of surgery (antihypertensives, antacids, antisialogogues, antibiotic cover). The decision as to which premedication to prescribe (if any) is made at the time of the preoperative visit. As well as assessing the patient for any pre-existing conditions, the anaesthetist should also issue clear instructions as to which of the patient’s current medicines should be given preoperatively. Although there are exceptions, most drugs should be continued right up to the time of the operation and restarted immediately afterwards.
Charlotte Steeds Robert Orme
Abstract The aims of premedication are anxiolysis, analgesia, anti-emesis and to reduce perioperative risk to the patient (e.g. with antihypertensives, antacids and antisialogogues). Many factors have contributed to the decline in premedicant prescription, including changes in anaesthetic agents and short postoperative stays. As well as considering premedication as part of the preoperative visit, the anaesthetist should review the patient’s current medications and decide which drugs should be continued during the perioperative period. In general, most drugs are given on the morning of surgery, but there are important exceptions, some of which may require discontinuation before hospital admission (e.g. clopidogrel). Insulin and steroids may need parenteral supplementation. Anxiolytics are less commonly prescribed than other premedications but are useful for some cases. Benzodiazepines are the most frequently used anxiolytic agents. Analgesics are sometimes prescribed, especially in the daysurgery setting, since paracetamol and non-steroidal anti-inflammatory drugs reduce perioperative opioid requirements. Caution must be taken when considering the use of cyclo-oxygenase-2 inhibitors, because of their association with increased risk of myocardial infarction and stroke. Topical analgesics are used in children to lessen the pain of cannulation. Anti-emetics, though commonly given at induction, can be prescribed as a premedicant. Consideration should also be given to the perioperative use of β-adrenoreceptor antagonists for patients undergoing major surgery. Antacids (e.g. H2-receptor antagonists and proton-pump inhibitors) should be prescribed for patients at risk from aspiration of gastric contents. Antisialogogues are rarely needed but may be indicated for awake fibre-optic intubation.
Drugs for continuation or discontinuation in the perioperative period Cardiovascular drugs: antihypertensives, anti-anginal, and antiarrhythmic agents are best continued to reduce haemodynamic instability and the risk of myocardial ischaemia. The continuation of angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists is controversial because of the risk of profound hypotension under anaesthesia. These drugs are usually best omitted on the day of surgery. Diuretics should be omitted if there are concerns about volume depletion and hypokalaemia or if regional anaesthesia is to be used when the patient is awake. Anticoagulants: warfarin should be stopped 5–7 days preoperatively, and be converted to heparin, depending on the initial reason for treatment. Unfractionated heparin infusions should be stopped 6 hours before surgery, and the activated partial prothrombin time checked immediately before surgery. Low molecular weight heparin should be given at least 12 hours before surgery. A full clotting screen should be checked preoperatively when anticoagulants have been used. Aspirin and clopidogrel may need to be omitted before surgery; however, clopidogrel should not be stopped if the patient has had a drug-eluting coronary stent inserted within the past year, as there is a risk of stent occlusion.
Keywords analgesia; anti-emesis; anxiolytics; premedication; steroids
Premedication can be defined as the administration of medication before anaesthesia. The practice of premedication has changed substantially in recent years. The use of strongly sedative drugs, such as morphine and hyoscine, to aid smooth induction
Charlotte Steeds, MBBS, FFARCSI, is Specialist Registrar in Anaesthesia at the Royal United Hospital, Bath. She is currently spending a year in Chronic Pain Management. She qualified at University College London and is in training in Anaesthesia in the Bristol region.
Respiratory drugs: bronchodilators should be continued up to the time of surgery. Inhaled β2-adrenoceptor agonists can be given immediately before theatre to reduce risk of bronchospasm.
Robert Orme, MBChB, FRCA, is Consultant Anaesthetist with an interest in Intensive Care at Cheltenham General Hospital. He trained in anaesthesia in Exeter, Dunedin and Oxford. He has developed a specific interest in echocardiography in the ICU. His current research interest is in ventilator-associated pneumonia.
Drugs acting on the central nervous system generally need to be continued. However, there are some exceptions. Tricyclic antidepressants can have important drug interactions and increase the risk of arrhythmias and hypotension. They should not be stopped abruptly. Monoamine oxidase inhibitors (MAOIs) have
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
393
© 2006 Elsevier Ltd. All rights reserved.
Clinical anaesthesia
important interactions with pethidine and indirectly acting sympathomimetic drugs (e.g. ephedrine). Irreversible MAOIs should be stopped 2 weeks preoperatively, and a shorter-acting agent prescribed. Lithium may potentiate the effect of neuromuscular blocking agents and should be stopped 1–3 days before major surgery. However, it may be continued for minor surgery, whilst electrolytes are monitored.
have effect if given too late. The patient may also be left with a ‘hangover’ from the sedative effect of their anxiolytic premedication, which may delay recovery from anaesthesia. Nevertheless, anxiolysis and sedation may be required in particular groups of patients (e.g. children, those with learning difficulties) and before major surgery (e.g. cardiac surgery) to cover the period that the patient spends in the anaesthetic room whilst invasive monitoring is put in place. For major surgery, the sedative ‘hangover’ is less of a problem because the patient may be transferred to intensive care postoperatively. Benzodiazepines are the most commonly used anxiolytic agent, and act as agonists at receptors closely linked to the γ- aminobutyric acid receptor, increasing entry of chloride ions to hyperpolarize the synaptic membrane. The anxiolytic agents commonly used are summarized in Table 2. It is important to ensure that informed consent has been obtained before the administration of a sedative drug.
Metabolic and endocrine drugs: patients with diabetes mellitus undergoing moderate or major surgery will require an intra venous insulin regimen. For people with type 2 diabetes having minor surgery, omit oral hypoglycaemic agents on the morning of surgery, and put the case first on the list. Steroids: patients on 10 mg prednisolone or more per day within 3 months of surgery will need perioperative supplementation, as outlined in Table 1 (see Further Reading). Anxiolysis Anxiety is very common before surgery, and can be unpleasant for the patient. In many cases patient’s fears can be alleviated at the preoperative visit. However, some patients request or require a pharmacological solution to this problem. Most drugs used for anxiolysis are sedative and can also provoke amnesia. There are usually problems with the timing of drug administration as the drug may not have sufficient time to
Analgesia In theory, the use of analgesics before surgery (‘pre-emptive analgesia’) aims to reduce total analgesic requirements, possibly sparing the need for opioid administration in recovery. Whether or not it is clinically effective is controversial. However, the increase in day surgery has driven the development of multimodal analgesia, using a combination of opioids, paracetamol and non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDs have received much publicity in recent years. Conventional non-selective NSAIDs inhibit at least two isoforms of the enzyme cyclo-oxygenase (COX): COX-1 and COX-2. COX-1 is expressed continuously in most tissues, and in the stomach catalyses production of prostaglandins that protect the gastric mucosa. COX-2 is less widely expressed, but is readily induced when tissues are exposed to inflammatory stimuli. As inhibition of COX-1 is thought to be the main way in which conventional NSAIDs cause adverse effects, such as gastric irritation, specific COX-2 inhibitors, known as coxibs, were developed. However, selective inhibition of COX-2 proved to be more complex than at first suggested as both isoforms may be important in the maintenance of vascular homeostasis and regulation of platelet function. In September 2004, evidence of an increased risk of myocardial infarction and stroke in patients who had been taking rofecoxib for more than 18 months led to its withdrawal worldwide. In addition, coxibs have a high ‘number needed to treat’ (about 140 patients) to prevent a single gastrointestinal bleed (see Further Reading). Based on current evidence, the Committee on Safety of Medicines advise that coxibs should not be given to patients with ischaemic heart disease or cerebrovascular disease. Of the currently available coxibs, only parecoxib has a licence for postoperative pain. It may be given intravenously at a dose of 40 mg on induction. Traditional NSAIDs include diclofenac 50–100 mg given orally or rectally, and ibuprofen 400 mg given orally. Paracetamol can be used as a premedication at 1 g in adults orally or rectally. In children, it is commonly used as a loading dose preoperatively at 20–30 mg/kg orally or 30-40 mg/kg rectally. Remember, it is necessary to seek patient and, if appropriate, parental consent to administer rectal medications under anaesthesia. Topical anaesthetic creams are commonly prescribed for children before cannulation, and are applied under an occlusive
Recommendations for perioperative steroid supplementation Type of surgery
Dose of steroid cover
Minor
Usual dose of corticosteroid on morning of surgery plus 25 mg hydrocortisone at induction Resume normal medication postoperatively Usual dose of corticosteroid on morning of surgery and 25 mg hydrocortisone at induction Then: 25 mg i.v. 8 hourly for 48–72 hours postoperatively; or 100 mg/24 hours infusion, stopped at 24–48 hours. Then resume normal preoperative dose Usual dose of corticosteroid on morning of operation plus 25 mg hydrocortisone at induction Then: 25 mg i.v. 8 hourly for 48–72 hours postoperatively; or 100 mg/24 hours infusion, stopped at 48–72 hours. Then resume normal preoperative dose
Moderate
Major
i.v., intravenously
Table 1
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
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© 2006 Elsevier Ltd. All rights reserved.
Clinical anaesthesia
Frequently used anxiolytic agents for premedication Class
Drug
Route
Dose
Preoperative timing
Notes
Benzodiazepines
Temazepam
Oral
10.0–30.0 mg
1 hour
Midazolam
Oral Intramuscular Intranasal/sublingual
0.50 mg/kg 2.0–10.0 mg 0.20 mg/kg
1 hour 20–40 min 20–30 min
Lorazepam
Oral
2 hours
Diazepam
Oral
0.05 mg/kg. Maximum 4.0 mg 2.0–10.0 mg
Zopiclone
Oral
3.75–7.50 mg
1 hour
Tablet or elixir. Short duration of action (90 min) Solutions of 2 or 5 mg/ml available. Bitter taste needs disguising. Useful in children Can cause marked amnesia Long half-life. Active metabolites Hypnotic
Non-benzodiazepines
2 hours
Table 2
dressing. EMLA (eutectic mixture of local anaesthetics) contains 2.5% lidocaine and 2.5% prilocaine, and is applied 60–90 minutes before cannulation. Ametop is a 4% tetracaine gel, works within 30–45 minutes and is effective for 4–6 hours.
Antihypertensives Many patients who present for surgery are hypertensive, and the anaesthetist often has to decide whether or not to proceed with surgery. Currently, it is felt that patients with mild or moderate hypertension and no evidence of coronary artery disease or end-organ damage may safely undergo surgery without delay. However, for patients with severe hypertension (systolic pressure ≥ 180 mm Hg and/or diastolic pressure ≥ 110 mm Hg) it is appropriate to defer surgery if possible, whilst blood pressure is controlled. Efforts must be made to check that any preoperative hypertension is not an isolated reading and any recommendation to postpone elective surgery must be balanced against the urgency of the planned operation.
Anti-emesis Postoperative nausea and vomiting is one of the most unpleasant experiences for the patient undergoing anaesthesia. Generally, anti-emetic agents are now given intravenously at induction of anaesthesia and are no longer prescribed as premedication. A combination of agents works more effectively than monotherapy. A brief summary of the anti-emetic drugs is shown in Table 3.
Drugs available for the prevention of postoperative nausea and vomiting Class
Mode of action
Drugs
Dose
Notes
Antidopaminergic agents
Antagonize dopamine receptors in the CTZ. Extrapyramidal side effects, especially in children and young adults Selective antagonists at muscarinic receptors Antagonism at H1-receptors
Phenothiazines (e.g. prochlorperazine)
5.0–20.0 mg p.o. or 12.5 mg i.m.
Metoclopramide
10.0 mg p.o., i.m. or i.v.
Anti-adrenergic, anticholinergic and antihistamine effects Also used as a prokinetic
Hyoscine
0.30–0.60 mg i.m.
Cyclizine
Granisetron
1.0 mg/kg p.o., i.m. or i.v. Max 50.0 mg 16.0 mg p.o. 1 hour preoperatively or 4.0 mg i.v. at induction 1.0 mg at induction
Dexamethasone
4.0–8.0 mg p.o. or i.v.
Anticholinergic agents Antihistamines 5-HT3 receptor antagonists
Steroids
Act peripherally and centrally at the CTZ
Mechanism unclear
Ondansetron
Sedating and peripheral antimuscarinic effects Peripheral antimuscarinic effects Side effects: headache, constipation, flushing and altered liver enzymes. Expensive compared with other agents
5-HT3, 5-hydroxytryptamine; CTZ, chemoreceptor trigger zone; i.m., intramuscularly; i.v., intravenously; p.o., orally
Table 3
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
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© 2006 Elsevier Ltd. All rights reserved.
Clinical anaesthesia
The anaesthetist should also consider the benefits of perioperative β-adrenoreceptor blockade in patients undergoing major surgery who are at risk from perioperative myocardial ischaemia. Cardiac risk should be assessed to identify which patients should be treated. Ideally, treatment should be started before hospital admission.
• metoclopramide – 10 mg orally or intravenously is used as a prokinetic agent to reduce gastric volume Antisialogogues An antisialogogue (glycopyrrolate 200 μg intramuscularly or intravenously) may be desirable before ketamine anaesthesia and awake fibre-optic intubation.
Antacids Decreasing gastric residual volume to less than 25 ml and raising pH to more than 2.5 may reduce the morbidity associated with pulmonary aspiration of gastric contents. Antacids should be considered for patients who are particularly at risk, such as those who are obese, pregnant, those who have diabetes or a hiatus hernia. In addition, oral administration of clear fluids up to 2 hours before surgery decreases gastric residual volume and acidity. Drugs commonly used are: • ranitidine – an H2-receptor antagonist, 150 mg orally or 50 mg intravenously 2 hours preoperatively. An additional dose the night before surgery increases efficacy • omeprazole – a proton-pump inhibitor, 20–40 mg orally 2 hours preoperatively or 40 mg by intravenous infusion • sodium citrate – a non-particulate antacid, 30 ml orally 10 minutes preoperatively is effective for up to 45 minutes
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
Antibiotics These agents will be required for patients with certain cardiac lesions or prosthetic valves undergoing procedures associated with bacteraemia. They can be given at induction, or prescribed on the ward preoperatively. The British National Formulary (http://www.bnf.org) has guidance for specific procedures. ◆
Further reading Taking stock of coxibs. Drug Ther Bull 2005; 43: 1–6. Howell S J, Sear J W, Foёx P. Hypertension, hypertensive cardiac disease and cardiac risk. Br J Anaesth 2004; 92: 570–83. Nicholson G, Burrin J M, Hall G M. Peri-operative steroid supplementation. Anaesthesia 1998; 53: 1091–1104.
396
© 2006 Elsevier Ltd. All rights reserved.
Premedication
and reduce salivation has been abandoned with the advent of modern intravenous and inhalational agents, which have far fewer side effects and a faster onset. Other factors have also influenced modern practice and reduced the use of a sedative premedication: • increasing use of day-case surgery • same-day admissions – patients often do not find a bed until just before surgery and the preoperative visit is rushed • changes to the surgical list, making the timing of drug delivery difficult. Despite these changes, the main aims of premedication are: • anxiolysis • analgesia (systemic and topical) • anti-emesis • risk reduction specific to the patient or the type of surgery (antihypertensives, antacids, antisialogogues, antibiotic cover). The decision as to which premedication to prescribe (if any) is made at the time of the preoperative visit. As well as assessing the patient for any pre-existing conditions, the anaesthetist should also issue clear instructions as to which of the patient’s current medicines should be given preoperatively. Although there are exceptions, most drugs should be continued right up to the time of the operation and restarted immediately afterwards.
Charlotte Steeds Robert Orme
Abstract The aims of premedication are anxiolysis, analgesia, anti-emesis and to reduce perioperative risk to the patient (e.g. with antihypertensives, antacids and antisialogogues). Many factors have contributed to the decline in premedicant prescription, including changes in anaesthetic agents and short postoperative stays. As well as considering premedication as part of the preoperative visit, the anaesthetist should review the patient’s current medications and decide which drugs should be continued during the perioperative period. In general, most drugs are given on the morning of surgery, but there are important exceptions, some of which may require discontinuation before hospital admission (e.g. clopidogrel). Insulin and steroids may need parenteral supplementation. Anxiolytics are less commonly prescribed than other premedications but are useful for some cases. Benzodiazepines are the most frequently used anxiolytic agents. Analgesics are sometimes prescribed, especially in the daysurgery setting, since paracetamol and non-steroidal anti-inflammatory drugs reduce perioperative opioid requirements. Caution must be taken when considering the use of cyclo-oxygenase-2 inhibitors, because of their association with increased risk of myocardial infarction and stroke. Topical analgesics are used in children to lessen the pain of cannulation. Anti-emetics, though commonly given at induction, can be prescribed as a premedicant. Consideration should also be given to the perioperative use of β-adrenoreceptor antagonists for patients undergoing major surgery. Antacids (e.g. H2-receptor antagonists and proton-pump inhibitors) should be prescribed for patients at risk from aspiration of gastric contents. Antisialogogues are rarely needed but may be indicated for awake fibre-optic intubation.
Drugs for continuation or discontinuation in the perioperative period Cardiovascular drugs: antihypertensives, anti-anginal, and antiarrhythmic agents are best continued to reduce haemodynamic instability and the risk of myocardial ischaemia. The continuation of angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists is controversial because of the risk of profound hypotension under anaesthesia. These drugs are usually best omitted on the day of surgery. Diuretics should be omitted if there are concerns about volume depletion and hypokalaemia or if regional anaesthesia is to be used when the patient is awake. Anticoagulants: warfarin should be stopped 5–7 days preoperatively, and be converted to heparin, depending on the initial reason for treatment. Unfractionated heparin infusions should be stopped 6 hours before surgery, and the activated partial prothrombin time checked immediately before surgery. Low molecular weight heparin should be given at least 12 hours before surgery. A full clotting screen should be checked preoperatively when anticoagulants have been used. Aspirin and clopidogrel may need to be omitted before surgery; however, clopidogrel should not be stopped if the patient has had a drug-eluting coronary stent inserted within the past year, as there is a risk of stent occlusion.
Keywords analgesia; anti-emesis; anxiolytics; premedication; steroids
Premedication can be defined as the administration of medication before anaesthesia. The practice of premedication has changed substantially in recent years. The use of strongly sedative drugs, such as morphine and hyoscine, to aid smooth induction
Charlotte Steeds, MBBS, FFARCSI, is Specialist Registrar in Anaesthesia at the Royal United Hospital, Bath. She is currently spending a year in Chronic Pain Management. She qualified at University College London and is in training in Anaesthesia in the Bristol region.
Respiratory drugs: bronchodilators should be continued up to the time of surgery. Inhaled β2-adrenoceptor agonists can be given immediately before theatre to reduce risk of bronchospasm.
Robert Orme, MBChB, FRCA, is Consultant Anaesthetist with an interest in Intensive Care at Cheltenham General Hospital. He trained in anaesthesia in Exeter, Dunedin and Oxford. He has developed a specific interest in echocardiography in the ICU. His current research interest is in ventilator-associated pneumonia.
Drugs acting on the central nervous system generally need to be continued. However, there are some exceptions. Tricyclic antidepressants can have important drug interactions and increase the risk of arrhythmias and hypotension. They should not be stopped abruptly. Monoamine oxidase inhibitors (MAOIs) have
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
393
© 2006 Elsevier Ltd. All rights reserved.
Clinical anaesthesia
important interactions with pethidine and indirectly acting sympathomimetic drugs (e.g. ephedrine). Irreversible MAOIs should be stopped 2 weeks preoperatively, and a shorter-acting agent prescribed. Lithium may potentiate the effect of neuromuscular blocking agents and should be stopped 1–3 days before major surgery. However, it may be continued for minor surgery, whilst electrolytes are monitored.
have effect if given too late. The patient may also be left with a ‘hangover’ from the sedative effect of their anxiolytic premedication, which may delay recovery from anaesthesia. Nevertheless, anxiolysis and sedation may be required in particular groups of patients (e.g. children, those with learning difficulties) and before major surgery (e.g. cardiac surgery) to cover the period that the patient spends in the anaesthetic room whilst invasive monitoring is put in place. For major surgery, the sedative ‘hangover’ is less of a problem because the patient may be transferred to intensive care postoperatively. Benzodiazepines are the most commonly used anxiolytic agent, and act as agonists at receptors closely linked to the γ- aminobutyric acid receptor, increasing entry of chloride ions to hyperpolarize the synaptic membrane. The anxiolytic agents commonly used are summarized in Table 2. It is important to ensure that informed consent has been obtained before the administration of a sedative drug.
Metabolic and endocrine drugs: patients with diabetes mellitus undergoing moderate or major surgery will require an intra venous insulin regimen. For people with type 2 diabetes having minor surgery, omit oral hypoglycaemic agents on the morning of surgery, and put the case first on the list. Steroids: patients on 10 mg prednisolone or more per day within 3 months of surgery will need perioperative supplementation, as outlined in Table 1 (see Further Reading). Anxiolysis Anxiety is very common before surgery, and can be unpleasant for the patient. In many cases patient’s fears can be alleviated at the preoperative visit. However, some patients request or require a pharmacological solution to this problem. Most drugs used for anxiolysis are sedative and can also provoke amnesia. There are usually problems with the timing of drug administration as the drug may not have sufficient time to
Analgesia In theory, the use of analgesics before surgery (‘pre-emptive analgesia’) aims to reduce total analgesic requirements, possibly sparing the need for opioid administration in recovery. Whether or not it is clinically effective is controversial. However, the increase in day surgery has driven the development of multimodal analgesia, using a combination of opioids, paracetamol and non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDs have received much publicity in recent years. Conventional non-selective NSAIDs inhibit at least two isoforms of the enzyme cyclo-oxygenase (COX): COX-1 and COX-2. COX-1 is expressed continuously in most tissues, and in the stomach catalyses production of prostaglandins that protect the gastric mucosa. COX-2 is less widely expressed, but is readily induced when tissues are exposed to inflammatory stimuli. As inhibition of COX-1 is thought to be the main way in which conventional NSAIDs cause adverse effects, such as gastric irritation, specific COX-2 inhibitors, known as coxibs, were developed. However, selective inhibition of COX-2 proved to be more complex than at first suggested as both isoforms may be important in the maintenance of vascular homeostasis and regulation of platelet function. In September 2004, evidence of an increased risk of myocardial infarction and stroke in patients who had been taking rofecoxib for more than 18 months led to its withdrawal worldwide. In addition, coxibs have a high ‘number needed to treat’ (about 140 patients) to prevent a single gastrointestinal bleed (see Further Reading). Based on current evidence, the Committee on Safety of Medicines advise that coxibs should not be given to patients with ischaemic heart disease or cerebrovascular disease. Of the currently available coxibs, only parecoxib has a licence for postoperative pain. It may be given intravenously at a dose of 40 mg on induction. Traditional NSAIDs include diclofenac 50–100 mg given orally or rectally, and ibuprofen 400 mg given orally. Paracetamol can be used as a premedication at 1 g in adults orally or rectally. In children, it is commonly used as a loading dose preoperatively at 20–30 mg/kg orally or 30-40 mg/kg rectally. Remember, it is necessary to seek patient and, if appropriate, parental consent to administer rectal medications under anaesthesia. Topical anaesthetic creams are commonly prescribed for children before cannulation, and are applied under an occlusive
Recommendations for perioperative steroid supplementation Type of surgery
Dose of steroid cover
Minor
Usual dose of corticosteroid on morning of surgery plus 25 mg hydrocortisone at induction Resume normal medication postoperatively Usual dose of corticosteroid on morning of surgery and 25 mg hydrocortisone at induction Then: 25 mg i.v. 8 hourly for 48–72 hours postoperatively; or 100 mg/24 hours infusion, stopped at 24–48 hours. Then resume normal preoperative dose Usual dose of corticosteroid on morning of operation plus 25 mg hydrocortisone at induction Then: 25 mg i.v. 8 hourly for 48–72 hours postoperatively; or 100 mg/24 hours infusion, stopped at 48–72 hours. Then resume normal preoperative dose
Moderate
Major
i.v., intravenously
Table 1
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
394
© 2006 Elsevier Ltd. All rights reserved.
Clinical anaesthesia
Frequently used anxiolytic agents for premedication Class
Drug
Route
Dose
Preoperative timing
Notes
Benzodiazepines
Temazepam
Oral
10.0–30.0 mg
1 hour
Midazolam
Oral Intramuscular Intranasal/sublingual
0.50 mg/kg 2.0–10.0 mg 0.20 mg/kg
1 hour 20–40 min 20–30 min
Lorazepam
Oral
2 hours
Diazepam
Oral
0.05 mg/kg. Maximum 4.0 mg 2.0–10.0 mg
Zopiclone
Oral
3.75–7.50 mg
1 hour
Tablet or elixir. Short duration of action (90 min) Solutions of 2 or 5 mg/ml available. Bitter taste needs disguising. Useful in children Can cause marked amnesia Long half-life. Active metabolites Hypnotic
Non-benzodiazepines
2 hours
Table 2
dressing. EMLA (eutectic mixture of local anaesthetics) contains 2.5% lidocaine and 2.5% prilocaine, and is applied 60–90 minutes before cannulation. Ametop is a 4% tetracaine gel, works within 30–45 minutes and is effective for 4–6 hours.
Antihypertensives Many patients who present for surgery are hypertensive, and the anaesthetist often has to decide whether or not to proceed with surgery. Currently, it is felt that patients with mild or moderate hypertension and no evidence of coronary artery disease or end-organ damage may safely undergo surgery without delay. However, for patients with severe hypertension (systolic pressure ≥ 180 mm Hg and/or diastolic pressure ≥ 110 mm Hg) it is appropriate to defer surgery if possible, whilst blood pressure is controlled. Efforts must be made to check that any preoperative hypertension is not an isolated reading and any recommendation to postpone elective surgery must be balanced against the urgency of the planned operation.
Anti-emesis Postoperative nausea and vomiting is one of the most unpleasant experiences for the patient undergoing anaesthesia. Generally, anti-emetic agents are now given intravenously at induction of anaesthesia and are no longer prescribed as premedication. A combination of agents works more effectively than monotherapy. A brief summary of the anti-emetic drugs is shown in Table 3.
Drugs available for the prevention of postoperative nausea and vomiting Class
Mode of action
Drugs
Dose
Notes
Antidopaminergic agents
Antagonize dopamine receptors in the CTZ. Extrapyramidal side effects, especially in children and young adults Selective antagonists at muscarinic receptors Antagonism at H1-receptors
Phenothiazines (e.g. prochlorperazine)
5.0–20.0 mg p.o. or 12.5 mg i.m.
Metoclopramide
10.0 mg p.o., i.m. or i.v.
Anti-adrenergic, anticholinergic and antihistamine effects Also used as a prokinetic
Hyoscine
0.30–0.60 mg i.m.
Cyclizine
Granisetron
1.0 mg/kg p.o., i.m. or i.v. Max 50.0 mg 16.0 mg p.o. 1 hour preoperatively or 4.0 mg i.v. at induction 1.0 mg at induction
Dexamethasone
4.0–8.0 mg p.o. or i.v.
Anticholinergic agents Antihistamines 5-HT3 receptor antagonists
Steroids
Act peripherally and centrally at the CTZ
Mechanism unclear
Ondansetron
Sedating and peripheral antimuscarinic effects Peripheral antimuscarinic effects Side effects: headache, constipation, flushing and altered liver enzymes. Expensive compared with other agents
5-HT3, 5-hydroxytryptamine; CTZ, chemoreceptor trigger zone; i.m., intramuscularly; i.v., intravenously; p.o., orally
Table 3
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
395
© 2006 Elsevier Ltd. All rights reserved.
Clinical anaesthesia
The anaesthetist should also consider the benefits of perioperative β-adrenoreceptor blockade in patients undergoing major surgery who are at risk from perioperative myocardial ischaemia. Cardiac risk should be assessed to identify which patients should be treated. Ideally, treatment should be started before hospital admission.
• metoclopramide – 10 mg orally or intravenously is used as a prokinetic agent to reduce gastric volume Antisialogogues An antisialogogue (glycopyrrolate 200 μg intramuscularly or intravenously) may be desirable before ketamine anaesthesia and awake fibre-optic intubation.
Antacids Decreasing gastric residual volume to less than 25 ml and raising pH to more than 2.5 may reduce the morbidity associated with pulmonary aspiration of gastric contents. Antacids should be considered for patients who are particularly at risk, such as those who are obese, pregnant, those who have diabetes or a hiatus hernia. In addition, oral administration of clear fluids up to 2 hours before surgery decreases gastric residual volume and acidity. Drugs commonly used are: • ranitidine – an H2-receptor antagonist, 150 mg orally or 50 mg intravenously 2 hours preoperatively. An additional dose the night before surgery increases efficacy • omeprazole – a proton-pump inhibitor, 20–40 mg orally 2 hours preoperatively or 40 mg by intravenous infusion • sodium citrate – a non-particulate antacid, 30 ml orally 10 minutes preoperatively is effective for up to 45 minutes
ANAESTHESIA AND INTENSIVE CARE MEDICINE 7:11
Antibiotics These agents will be required for patients with certain cardiac lesions or prosthetic valves undergoing procedures associated with bacteraemia. They can be given at induction, or prescribed on the ward preoperatively. The British National Formulary (http://www.bnf.org) has guidance for specific procedures. ◆
Further reading Taking stock of coxibs. Drug Ther Bull 2005; 43: 1–6. Howell S J, Sear J W, Foёx P. Hypertension, hypertensive cardiac disease and cardiac risk. Br J Anaesth 2004; 92: 570–83. Nicholson G, Burrin J M, Hall G M. Peri-operative steroid supplementation. Anaesthesia 1998; 53: 1091–1104.
396
© 2006 Elsevier Ltd. All rights reserved.