Anaesthesia for endoscopy

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Chapter 29 ANAESTHESIA FOR ENDOSCOPY

KEY POINTS

• Patients do not need a deep level of anaesthesia, only moderate sedation—drug-induced depression of consciousness.
• A review of medications and results of investigations is necessary, in particular the presence of hepatic or renal impairment, which affects drug clearances and half-lives.
• All patients need reliable intravenous access, oxygen, pulse oximetry, accessible Ambu bag, emergency drugs, reversal drugs for benzodiazepines and narcotics and access to an electrocardiogram (ECG) and defibrillator.
• Sedation for endoscopy requires a combination of drugs. Midazolam, fentanyl and propofol are used in varying amounts to increase the comfort and tolerance of the patient to the procedure.

INTRODUCTION

In order to undertake upper or lower gastrointestinal endoscopy patients must be anaesthetised in some way. They do not need a deep level of anaesthesia, only moderate sedation—drug induced depression of consciousness. The purpose of this chapter is to give an outline of patient assessment (see Chapter 28 for more information), monitoring and drugs used in order to sedate patients undergoing procedures.

PATIENT ASSESSMENT

• Identification and introduction of anaesthetist to patient.
• Appropriate medical assessment of patient, especially cardiovascular and respiratory history (questionnaires are often helpful).
• Ask about previous sedation, anaesthetics, allergies, fasting and damaged or loose teeth (this is of particular interest for upper endoscopy).
• Clinical examination, review of medications and results of investigations. Hepatic and renal impairment are particularly relevant as they affect drug clearances and half-lives.

MONITORING CHECKLIST

• All patients need reliable intravenous access.
• All should have oxygen.
• All patients should have pulse oximetry.
• Pulse rate should be palpated and recorded.
• Blood pressure should be recorded.
• Electrocardiogram (ECG) and capnography may be required if cardiovascular or respiratory history.
• There should be an ambubag nearby (or means of inflating lungs).
• Emergency drugs.
• Reversal drugs for benzodiazepines and narcotics.
• Access to ECG and defibrillator.

ANAESTHESIA AND SEDATION

Anaesthesia should only be performed by medical practitioners with appropriate training in airway management and resuscitation.

Sedation for endoscopy requires a combination of drugs. Midazolam, fentanyl and propofol are used in varying amounts to increase patient comfort and tolerance of the procedure.

The use of narcotics and benzodiazepines avoids coughing in upper endoscopy and withdrawal response for colonoscopy.

Midazolam

Midazolam has anxiolytic, sedative-hypnotic and anticonvulsant activities. This is the benzodiazepine of choice because it has a rapid onset and ultra-short duration of action and has no active metabolites.

Midazolam is given intravenously with very rapid onset of action ranging from 15–20 seconds to a few minutes.

Midazolam is metabolised in the liver, thus there may be a need to decrease the dose if liver failure is present or expect a longer duration of action.

In the event of overdose, seen by respiratory depression, flumazenil, a specific benzodiazepine receptor antagonist, can be given. The plasma half-life of flumazenil is very short (2–5 min), so repeat doses may be required. The dosage is 0.1–0.2 mg boluses of up to 3 mg until reversal is seen.

Fentanyl

Fentanyl is a synthetic narcotic. It is eighty times more potent than morphine, yet has a much shorter duration of action. The plasma half-life of fentanyl is 20 minutes. It has a high hepatic extraction ratio (i.e. metabolism is dependent on liver blood flow). Fentanyl is haemodynamically stable, such that administration maintains blood pressure, and is generally safe to use in patients with impaired cardiovascular function.

Fentanyl dosages are individualised on a patient-to-patient basis. Doses may start with 10 μg boluses in older patients, and 25 μg boluses in young healthy people.

Overdose is often seen as a triad of coma, respiratory depression and pinpoint pupils. After establishing an airway, ventilation and administration of an opioid antagonist is required. Naloxone 0.01 mg/kg is the antagonist of choice. Patients may experience rebound sympathetic nervous system overdrive, which can result in dysrhythmias and pulmonary oedema. Naloxone’s duration is very short so repeat doses or an infusion may be required.

Propofol

Propofol is an induction agent. It has a very short plasma half-life of 2–8 minutes. Its metabolism is also dependent on liver blood flow and it has inactive metabolites.

Propofol is less haemodynamically stable than fentanyl. It drops the blood pressure and can cause a reflex increase in heart rate and should be used with caution in patients with ischaemic heart disease. It can also lead to transient apnoea, and thus needs to be titrated slowly.

Propofol dosage is 10–20 mg boluses until its effect are seen. Propofol should not be used patients allergic to egg or soya bean. Thiopentone is a suitable alternative in this instance.

There is no reversal agent for propofol, but the effects are very short acting so maintain the airway, ventilation and blood pressure whilst needed and the patient will soon regain consciousness.

Thiopentone

Thiopentone is a barbiturate. It is used less and less these days because it has a longer duration of action than propofol (40 min). It has much slower metabolism and 30% is excreted in the urine. Thus in endoscopy, which is done as a day surgery procedure, people awaken more slowly.

Thiopentone decreases blood pressure, increases heart rate and, thus, increases myocardial oxygen demand. Severe cardiovascular disease is a relative contraindication for thiopentone use.

SUMMARY

• Do a patient assessment—assess previous health, allergies, medications. Patient preparation is key.
• Check fasting status and provide informed consent (Figure 29.1).
• Examination—focus on the airway, and the respiratory and cardiovascular states.
• Monitoring—oxygen saturation, intravenous access, supplemental oxygen, pulse and blood pressure.
• Sedation—know your drugs: midazolam, fentanyl, propofol.
image

FIGURE 29.1 Preparing for conscious sedation.

FURTHER READING

Bailey PL, Zuccaro GJr. Sedation for endoscopic procedures: Not as simple as it seems. Am J Gastroenterol. 2006;101:2008-2010.

Rex DK. Review article: moderate sedation for endoscopy: sedation regimens for non-anesthesiologists. Aliment Pharmacol Ther. 2006;24:163-171.

Ristikankare M, Julkunen R, Heikkinen M, et al. Sedation, topical pharyngeal anesthesia and cardiorespiratory safety during gastroscopy. J Clin Gastroenterol. 2006;40:899-905.

Waring JP, Baron TH, Hirota WK, et al. Guidelines for conscious sedation and monitoring during gastrointestinal endoscopy. Gastrointest Endosc. 2003;58:317-322.

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