Anaesthetic sedation for gastrointestinal endoscopy
Dr G M Andrew, BA (Hons), MBBS
Rapid strides have been made in gastro-intestinal endoscopy (gastroscopy, colonoscopy, ERCP, and related techniques) in the last thirty years. Gastro-intestinal endoscopy, once largely diagnostic, has evolved such that therapeutic procedures are often performed at the same time. This may prevent the need for major surgery. Safe and effective sedation has been a major factor in the development of therapeutic endoscopy. However, not all patients require sedation for endoscopic procedures. Some patients are quite comfortable with no sedation, or only minimal sedation, depending on the type and duration of the procedure.
Patients usually have three major concerns prior to endoscopy - the outcome of the procedure (could it be cancer?), complications of the procedure, and most importantly the question "Doctor, how much will I feel the procedure?" or "Will it hurt?" With modern sedation and careful monitoring the great majority of patients will feel comfortable during the procedure.
Before the Endoscopy
It is most likely that you will have your endoscopy in a day surgery unit in a public or private hospital. During the procedure an anaesthetist or sedationist (doctor or nurse trained in sedation and resuscitation) will be present throughout the procedure to provide monitoring of your level of consciousness, your cardiorespiratory state and provide the right amount of anaesthetic sedation to keep you comfortable throughout.
Prior to the procedure, you will meet the doctor giving the sedation. You will be asked (by the doctor or nursing staff) to provide your medical history, including the reason you are having the test, whether you have heart or lung disease (including asthma, angina or heart failure), liver or kidney disease, gastro-intestinal bleeding or other bleeding problems, or anaemia. The anaesthetist will wish to ensure you have fasted (i.e. not had food or drink) for the required number of hours before the procedure. A brief physical examination may be performed. If you are dehydrated, intravenous fluids may be administered. The doctor will wish to know your allergies and a list of your medications.
This is the time to ask any questions you may have regarding the sedation. An intravenous cannula or needle will be placed in the back of the hand or forearm. This is for the administration of intravenous sedative drugs.
During the Endoscopy
When you are wheeled into the procedure room, you will be connected to monitoring equipment which is essential when sedative agents are to be used. Monitoring detects early signs of impaired lung or heart function resulting from the sedatives, permitting early correction, thus maximising patient safety. Years ago, the anaesthetist would monitor the patient by checking skin colour, pulse rate, and rate of breathing. Modern equipment, in combination with careful clinical observation, can do much better than this.
You will also be given a mask or some type of oxygen delivery system to increase the level of oxygen in the air that you are breathing - this is now standard for endoscopic procedures. Oxygen will continue throughout the procedure. When you are asleep you may be aware of suction in the mouth or throat, which is used to remove any unwanted secretions.
Pulse oximeters are the most important monitors to have been developed in the last fifteen years. They should be used in every endoscopy procedure room, and be available in recovery areas.
The pulse oximeter measures the differential absorption of red and infra-red light by oxygenated and deoxygenated haemoglobin. A light emitting diode, located in a fingertip probe, sends a light wave through the tissues and monitors the reflected wavelengths coming back as the blood passes through the capillaries. The pulse rate and oxygen level (saturation) of haemoglobin in the blood can be measured. All healthy patients will have an oxygen saturation greater than 96% when breathing room air. If the oxygen saturation in the blood drops, the machine will alarm, and the anaesthetist will undertake measures to correct the situation to avoid an emergency.
Blood Pressure and ECG Monitoring
These measures are also frequently used when sedative agents are given, particularly in elderly patients or patients who have a cardiac history. The ECG is useful for detecting cardiac rhythm abnormalities (arrhythmias) and insufficiency of blood supply to the heart muscle (cardiac ischaemia).
A typical print-out from a patient monitor is shown below. The top tracing is an ECG, the bottom tracing the pulse rate. The monitor also shows continuously the pulse rate, the last blood pressure recording, and the oxygen saturation.
Sedative and Anaesthetic Agents Used in Endoscopy
In the ideal situation, the patient should be lightly sedated (i.e. drowsy but still able to be woken), pain free and cooperative, unable to remember the procedure, and free of anxiety and fear.
The features of an ideal drug for sedation for endoscopy include:
· Anxiolytic (reduces anxiety)
· Amnestic (reduces memory of the procedure)
· Analgesic (takes away pain)
· Rapid onset of action
· Predictable sedative effects, in proportion to the dose
· Safe over a wide range of doses
· Water soluble and free of pain or irritation on injection
· Rapid recovery with no hangover
No single agent has all these properties, and therefore 2 or even 3 drugs are commonly used. Sedation is often achieved using a benzodiazepine, in combination with an opioid for pain relief and a barbiturate-like hypnotic agent if deeper sedation is required.
All the agents used cause a mild temporary depression of lung function, and some mild temporary effects on the heart, particularly when used in combination. This reinforces the need for adequate monitoring by direct observation and monitoring equipment.
These cause sedation but have no effect on pain. The original benzodiazepine used in day surgery and endoscopy was diazepam. However, the plasma elimination half-life for diazepam has been estimated at between 24 and 57 hours, and its breakdown metabolites also have sedative properties. This means that it takes a long time to recover from the effects, which often last until the next day. It is therefore an unsuitable agent for day procedures.
A newer sedative agent, called MIDAZOLAM, is now very commonly used. This is a short-acting benzodiazepine with useful amnesia for events during the procedure (it does not cause amnesia for events before or after the procedure). The plasma elimination half-life is one tenth that of diazepam, and therefore it is cleared from the blood very quickly. Furthermore the breakdown products (metabolites) are short lived, and have no sedative properties. The dosages range from 1mg to about 10mg.
Midazolam has few side effects and if they occur they are very rarely serious. Depression of breathing is the most important. Others include an itchy nose, rash, dizziness, anxiety, irritability, vivid dreams, twitching movements. Midazolam should not be used in patients with myasthenia gravis, acute glaucoma, and patients known to be allergic to this class of drug. It should be used with caution in patients with serious lung diseases particularly chronic obstructive airways disease.
Pregnancy: while midazolam is not thought to cause fetal malformations in humans, it should be avoided in the first 3 months of pregnancy unless the potential benefits outweigh the risks.
Lactation: midazolam is excreted in breast milk and should be avoided in breastfeeding mothers. Alternatively a breast pump can be used and the milk discarded for the first few hours after the procedure.
These are for pain relief. The short acting opioid fentanyl (or its relative alfentanil) is often used in combination with midazolam. The effect of fentanyl lasts for about thirty minutes and provides good relief from pain. The major side effect is depression of breathing. The rate and depth of breathing decreases within a minute or so of the drug being injected. A drop in pulse rate (bradycardia) may also occur. Dosage is in the range 1 - 1.5 ug/kg, with lower doses in the elderly or in impaired renal function or hepatic function. Lower doses may be required in patients with lung and heart diseases and in patients on the newer type 2 MAOI drugs (a type of antidepressant medications). Fentanyl is contraindicated in patients taking the older type 1 MAOI drugs.
Pregnancy: the safe use of fentanyl has not been established in the first 3 months of pregnancy, and therefore it should be used only where the potential benefits outweigh possible risks.
Lactation: it is not known if fentanyl is excreted in breast milk and fentanyl should be avoided in breastfeeding mothers, or precautions taken to prevent the baby receiving any fentanyl (see above).
Propofol and other hypnotic agents
Barbiturates have been used for many years to put people to sleep at the start of an operation (often called 'induction'). Propofol is a newer non-barbiturate short acting anaesthetic induction drug which, due to its rapid onset of action and short recovery period, is ideally suited for endoscopy sedation. It amplifies the sedative effects of the other analgesic and hypnotic agents, and causes profound sedation, depending on the dose.
In summary, propofol is a 'stronger' drug than midazolam in producing sedation, which makes it very useful, but a greater level of monitoring is required. Propofol causes pain in the arm on injection in about 30% of patients but this passes off in a minute or so.
Pregnancy: propofol should not be used in pregnancy.
Lactation: propofol should not be used in breastfeeding mothers.
Reversal of sedation
Normally the recovery from the effects of the above agents is gradual and pleasant. However, specific antagonists for the benzodiazepines and for opioid narcotics are available for use in emergencies and (rarely) electively - these reverse the effects of the above drugs very quickly.
Flumazenil is a specific benzodiazepine receptor antagonist which acts within seconds. Naloxone is an opioid antagonist which reverses the respiratory and analgesic effects of opioids.
After the endoscopy
Usually you will be regaining conscious awareness just as you are being wheeled to the recovery area. You may be attached to the same monitors as were used in the procedure area. You will be closely monitored at this time by experienced nursing staff, who will check your blood pressure and vital signs frequently. This is a time to relax and gradually awaken. A long awaited cup of tea and a light meal may be provided about an hour after your procedure. Often it is wise to eat only lightly for the rest of the day following an endoscopic procedure.
You will be fit for discharge when you are wide awake, have had some food, and are able to get up, get dressed, and walk around without any unsteadiness. Another person should accompany you home. You must not drive or use machinery for the remainder of the day.
For the remainder of that day (and sometimes the next, if you still feel tired and unsteady),
do not -
- drive a motor vehicle
- use machinery that requires judgement or skill
- drink alcohol
- cook (because of the risk of burns)
- take sedative medication unless prescribed by your doctor
- sign legal documents
- make major financial decisions
- be the only person in charge of children or other dependent individuals.