Anaesthesia Outside the Operating Theatre

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Anaesthesia Outside the Operating Theatre

G eneral anaesthesia outside the operating theatre suite is often challenging for the anaesthetist, because specialized environments pose unique problems. In hospital, the anaesthetist must provide a service for patients with standards of safety and comfort which are equal to those in the main operating department. Outside the hospital, this level of service is more dependent on location and available resources.

ANAESTHESIA IN REMOTE HOSPITAL LOCATIONS

In-hospital remote locations include radiology, radiotherapy, the Accident and Emergency (A & E) department and wards with areas designated for procedures such as ECT, assisted conception, cardioversion and intrathecal chemotherapy administration.

General Considerations and Principles

Anaesthetists are frequently required to use their skills (e.g. administer anaesthesia, analgesia, sedation, resuscitate, cannulate, etc.) outside the familiar operating theatre environment. When requests are made for anaesthetic intervention in remote locations, there are multiple considerations which the anaesthetist must be aware of. These include the following.

1. Appropriate personnel. Only senior experienced anaesthetists who are also familiar with the particular environment and its challenges should normally administer anaesthesia in remote locations. Additional skilled anaesthetic help may not be readily available compared with an operating theatre suite and patients are often challenging, e.g. paediatric or critically ill.

2. Equipment. The remote clinical area may not have been designed with anaesthetic requirements in mind. Anaesthetic apparatus often competes for space with bulky equipment (e.g. scanners) and, in general, conditions are less than optimal. Monitoring capabilities and anaesthetic equipment should be of the same standard as those used in the operating department. In reality, such equipment may not be readily available and the equipment used is often the oldest in the hospital. Nevertheless, the monitoring equipment should meet the minimum standards set by the Association of Anaesthetists of Great Britain and Ireland (AAGBI, 2006). The anaesthetist who is unfamiliar with the environment should spend time becoming accustomed to the layout and equipment. Compromised access to the patient and the type of monitors used during the procedure require careful consideration. Advanced planning helps to prepare for unanticipated scenarios. Clinical observation may be limited by poor lighting.

3. Patient preparation. Preparation of the patient may be inadequate because the patient is from a ward where staff are unfamiliar with preoperative protocols, or patients may be unreliable, e.g. those presenting for ECT.

4. Assistance. An anaesthetic assistant (e.g. operating department practitioner) should be present, although this person may be unfamiliar with the environment. Maintenance of anaesthetic equipment may be less than ideal. Consequently, the anaesthetist must be particularly vigilant in checking the anaesthetic machine, particularly because it may be disconnected and moved when not in use. Empty gas cylinders need to be replaced in older suites without piped gases, and also the anaesthetist must ensure the presence of drugs, spare laryngoscope and batteries, suction and other routine equipment.

5. Communication. Communication between staff of other specialities and the anaesthetist may be poor. This may lead to failure in recognizing each other’s requirements. Education programmes for non-anaesthesia personnel regarding the care of anaesthetized patients may be of benefit.

6. Recovery. Recovery facilities are often non-existent. Anaesthetists may have to recover their own patients in the suite. Consequently, they must be familiar with the location of recovery equipment including suction, supplementary oxygen and resuscitation equipment. Alternatively, patients may be transferred to the main hospital recovery area. This requires the use of routine transfer equipment which should ideally be available as a ‘pack’ kept alongside monitoring equipment and a portable oxygen supply. This avoids searching for various pieces of equipment which may delay transfer, and ensures that nothing is forgotten. The pack should be regularly checked and maintained.

There should be a nominated lead anaesthetist responsible for remote locations in which anaesthesia is administered in a hospital. This individual should liaise with the relevant specialities, e.g. radiologists, psychiatrists, to ensure that the environment, equipment and guidelines are suitable for safe, appropriate and efficient patient care.

Anaesthesia in the Radiology Department

In most hospitals, members of the anaesthetic department are called upon to anaesthetize or sedate patients for diagnostic and therapeutic radiological procedures. These procedures include ultrasound, angiography, computed tomography (CT) scanning and magnetic resonance imaging (MRI). The major requirement of all these imaging techniques is that the patient remains almost motionless. Thus, general anaesthesia may be necessary when these investigations and interventions are performed in children, the critically ill or the uncooperative patient. The presence of pain or prolonged procedures may also be an indication for anaesthesia.

Radiological studies may require administration of conscious sedation. This term describes the use of medication, often given by a non-anaesthetist, to alter perception of painful and anxiety-provoking stimuli while maintaining protective airway responses and the ability to respond appropriately to verbal command. Medical personnel responsible for the sedation should be familiar with the effects of the medication and skilled in resuscitation (including airway management). All the equipment and drugs required for resuscitation should be readily available and checked regularly. It is undesirable for a single operator to be responsible for both the radiological procedure and administration of sedation because there is the potential to be distracted from one responsibility and to allow side-effects to go untreated. Ideally, different individuals should be responsible for each of these tasks. Guidelines for prescribing, evaluating and monitoring sedation should be readily available. Chloral hydrate may be used in young children and benzodiazepines, opioids or propofol in adults. Patients should be starved before sedation and vital signs monitored and documented.

Iodine-containing intravascular contrast agents are used routinely during angiographic and other radiological investigations. The anaesthetist must always be aware of the risk of adverse reactions to contrast dyes. In recent years, low-osmolarity contrast media have been introduced; these cause less pain and have fewer toxic effects than the older contrast agents, but are more expensive. Factors contributing to the development of adverse reactions include speed of injection, type and dose of contrast used and patient susceptibility.

Coronary and cerebral angiography are associated with a high risk of reaction. Other major risk factors include allergies, asthma, extremes of age (under 1 and over 60 years), cardiovascular disease and a history of previous contrast medium reaction. Fatal reactions are rare, occurring in about 1 in 100 000 procedures. Nausea and vomiting are common and reactions may progress to urticaria, hypotension, arrhythmias, bronchospasm and cardiac arrest. Treatment of allergic reactions depends on the severity of the reaction. This usually consists of fluids, oxygen and careful monitoring. An anaphylaxis protocol should be readily available along with adrenaline, antihistamines, steroids and fluids, preferably as an ‘anaphylaxis kit’. Adequate hydration is important, because patients undergoing contrast dye procedures usually have an induced osmotic diuresis, which may exacerbate pre-existing renal dysfunction. Patients at particular risk are dehydrated patients, those with chronic renal dysfunction and patients in the recovery phase of acute renal failure for which renal replacement therapy has been required. In these patients, even small doses of contrast may cause sufficient deterioration to necessitate further haemofiltration. Some intensive care units have a policy of giving acetylcysteine with a fluid load up to 1 h before the scan, with a further dose after the scan to protect against contrast-induced nephropathy. A urinary catheter may be useful for patients undergoing long procedures.

Healthcare workers are exposed to X-rays in the radiology and imaging suites. The greatest source is usually from fluoroscopy and digital subtraction angiography. Although the patient dose is high, ionizing radiation from a CT scanner is relatively low because the X-rays are highly focused. Radiation intensity and exposure decrease with the square of the distance from the emitting source. The recommended distance is 2–3 m. This precaution, together with lead aprons, thyroid shields and movable lead-lined glass screens, keeps exposure at a safe level. A personal-dose monitor should be worn by personnel who work frequently in an X-ray environment.

Computed Tomography

General Principles: A CT scan provides a series of tomographic axial ‘slices’ of the body. It is used most frequently for intracranial imaging and for studies of the thorax and abdomen and is the investigation of choice in the evaluation of major trauma when whole body CT may be used in place of plain X-rays. Each image is produced by computer integration of the differences in the radiation absorption coefficients between different normal tissues and between normal and abnormal tissues. The image of the structure under investigation is generated by a cathode ray tube and the brightness of each area is proportional to the absorption value.

One rotation of the gantry produces an axial slice or ‘cut’. A series of cuts is made, usually at intervals of 7 mm, but this may be larger or smaller depending on the diagnostic information sought. The first-generation scanners took 4.5 min per cut, but the newest scanners take only 2–4 s.

The circular scanning tunnel contains the X-ray tube and detectors, with the patient lying stationary in the centre during the study. The procedure is noisy and patients are occasionally frightened or claustrophobic.

Anaesthetic Management: Computed tomography is non-invasive and painless, requiring neither sedation nor anaesthesia for most adult patients. A few patients may require conscious sedation to relieve fears or anxieties. However, patients who cannot cooperate (most frequently paediatric and head trauma patients or those who are under the influence of alcohol or drugs) or those whose airway is at risk may need general anaesthesia to prevent movement, which degrades the image. Anaesthetists may also be asked to assist in the transfer from the ICU and in the care of critically ill patients who require CT scans.

General anaesthesia is preferable to sedation when there are potential airway problems or when control of intracranial pressure (ICP) is critical. Because the patient’s head is inaccessible during the CT scan, the airway needs to be secured. In the majority of situations, tracheal intubation is more appropriate than the use of a laryngeal mask airway (e.g. full stomach). The scan itself requires only that the patient remains motionless and tolerates the tracheal tube. If ICP is high, controlled ventilation is essential to maintain normo- or hypocapnia.

Because these patients are often in transit to or from critical care areas or A & E, a total intravenous technique with neuromuscular blockade is usually the technique of choice with tracheal intubation and controlled ventilation. Use of volatile anaesthetic agents during the scan is also acceptable but may involve changing from one technique to another for transfer. In addition, the anaesthetic machine may be left unplugged when not in use in the scanner and reconnecting and checking it may be distracting and time-consuming. A portable ventilator with CO2 monitoring removes the need to change breathing systems. If the scan is likely to take a long time, it may be advisable to change from cylinder to piped oxygen supply to conserve supplies for transfer. Anaesthetic complications while in the scanner include kinking of the tracheal tube or disconnection of the breathing system, particularly during positioning and movement of the gantry, hypothermia in paediatric patients and disconnection of drips and lines during transfer. In addition, in the trauma setting, patients may become markedly unstable during movement on to the scanning table, and emergency drugs and fluids should be readily available. If, during the scan, the anaesthetist is observing the patient from inside the control room, it is imperative that alarms/monitors have visual signals which may be seen easily.

Stereotactic-guided surgery is possible using CT scanners although this has largely been replaced by frameless image guidance systems which allow tumour localization in the theatre suite from an existing scan. Most procedures involve aspiration or biopsy of intracranial masses in eloquent or important motor areas to give a tissue diagnosis with minimal risk to surrounding structures. The patient may either be anaesthetized in the theatre suite and then transferred to the CT scanner or anaesthetized in the scanner itself. Advantages of the former are induction of anaesthesia in a familiar environment with assistance and equipment readily available; the disadvantage is that the patient then must be transferred to the CT scanner and back again to theatre. The advantage of inducing anaesthesia in the CT scanner is that the need for initial transfer is removed, but there are the risks already outlined of anaesthesia in a remote location. Pins are used to hold a radiolucent frame around the head and then coordinates are mapped onto the frame from the scan to allow precise location of the tumour. Application of the frame via the pins is painful and access to the patient and airway with the frame attached inside the scanner is difficult.

Magnetic Resonance Imaging

General Principles: Magnetic resonance imaging (MRI) is an imaging modality which depends on magnetic fields and radiofrequency pulses for the production of its images. The imaging capabilities of MRI are superior to those of CT for examining intracranial, spinal and soft tissue lesions. MRI differentiates clearly between white and grey matter in the brain, thus making possible, for example, the in vivo diagnosis of demyelination. It may display images in the sagittal, coronal, transverse or oblique planes and has the advantage that no ionizing radiation is produced.

An MRI imaging system requires a large magnet in the form of a tube which is capable of accepting the entire length of the human body. A radiofrequency transmitter coil is incorporated in the tube which surrounds the patient; the coil also acts as a receiver to detect the energy waves from which the image is constructed. In the presence of the magnetic field, protons in the body align with the magnetic field in the longitudinal axis of the patient. Additional perpendicular magnetic pulses are applied by the radiofrequency coil; these cause the protons to rotate into the transverse plane. When the pulse is discontinued, the nuclei relax back to their original orientation and emit energy waves which are detected by the coil. The magnet is over 2 m in length and weighs approximately 500 kg. The magnetic field is applied constantly even in the absence of a patient. It may take several days to establish the magnetic field if it is removed and this is only done in an emergency because it is very expensive to shut down the field. The magnetic field strength is measured in tesla units (T). One tesla is the field intensity generating 1 Newton of force per 1 ampere of current per 1 metre of conductor. One tesla equals 10 000 gauss; the earth’s surface strength is between 0.5 and 1.0 gauss. MRI strengths usually vary from 1 to 3 T although some research facilities have scanners which may produce fields up to 9.4 T. The force of the magnetic field decreases exponentially with distance from the magnet and a safety line at a level of 5 gauss is usually specified. Higher exposure may result in pacemaker malfunction and unscreened personnel should not cross this level. At 50 gauss, ferromagnetic objects become dangerous projectiles. The magnetic fields present are strong static fields which are present all around the magnet area, and fast-switching and pulsed radiofrequency fields in the immediate vicinity of the magnet.

The final MR image is made from very weak electromagnetic signals, which are subject to interference from other modulated radio signals. Therefore, the scanner is contained in a radiofrequency shield (Faraday cage). A hollow tube of brass is built into this cage to allow monitoring cables and infusion lines to pass into the control room. This is termed the waveguide.

Anaesthetic Management:

STAFF SAFETY: Staff safety precautions are essential. The supervising MR radiographer is operationally responsible for safety in the scanner and anaesthetic staff should defer to him or her in matters of MR safety. Screening questionnaires identify those at risk and training should be given in MR safety, electrical safety, emergency procedures arising from equipment failure and evacuation of the patient. Anaesthetists should also understand the consequences of quenching the magnet and be aware of recommendations on exposure and the need for ear protection. Long-term effects of repeated exposure to MRI fields are unknown, and pregnant staff should be offered the option not to work in the scanner. All potentially hazardous articles should be removed, e.g. watches, bleeps and stethoscopes. Bank cards, credit cards and other belongings containing electromagnetic strips become demagnetized within the vicinity of the scanner and personal computers, pagers, phones and calculators may also be damaged.

PATIENT SAFETY: Metal objects within or attached to the patient pose a risk. Jewellery, hearing aids or drug patches should be removed. Absolute contraindications include implanted surgical devices, e.g. cochlear implants, intraocular metallic objects and metal vascular clips. Pacemakers remain an absolute contraindication in most settings although some patients with a pacemaker have undergone scanning under tightly controlled conditions when the benefit has been deemed to outweigh the risk. Metallic implants, e.g. intracranial vascular clips, may be dislodged from blood vessels. Programmable shunts for hydrocephalus may malfunction because the pressure setting may be changed by the magnetic field, leading to over- or underdrainage. The use of neurostimulators such as spinal cord stimulators for chronic pain is increasing. These devices may potentially fail or cause thermal injury on exposure to the magnetic field. Each must be considered individually, some may be safe if strict guidelines are adhered to. Joint prostheses, artificial heart valves and sternal wires are safe because of fibrous tissue fixation. Patients with large metal implants should be monitored for implant heating. A description of the safety of various devices is available on dedicated websites. All patients should wear ear protection because noise levels may exceed 85 dB.

Other unique problems presented by MRI include relative inaccessibility of the patient. In most scanners, the body cylinder of the scanner surrounds the patient totally; manual control of the airway is impossible and tracheal intubation or use of a laryngeal mask airway is essential when general anaesthesia is necessary. The patient may be observed from both ends of the tunnel and may be extracted quickly if necessary. Because there is no hazard from ionizing radiation, the anaesthetist may approach the patient in safety.

EQUIPMENT: The magnetic effects of MRI impose restrictions on the selection of anaesthetic equipment. Any ferromagnetic object distorts the magnetic field sufficiently to degrade the image. It is also likely to be propelled towards the scanner and may cause a significant accident if it makes contact with the patient or with staff. Terminology regarding equipment used in the MRI scanner has now changed from ‘MR compatible’ or ‘MR incompatible’ to ‘MR conditional’, ‘MR safe’ or ‘MR unsafe’. MR conditional equipment is that which poses no hazards in a specified MR environment with specified conditions of use. The conditions in which it may be used must accompany the device and it may not be safe to use it outside these conditions, e.g. higher field strength or rate of change of the field. MR safe equipment is that which poses no safety hazard in the MR room but it may not function normally or may degrade the image quality. Consideration needs to be given to replacing equipment if a scanner is replaced by one of higher field strength.

The layout of the MRI room/suite determines whether the majority of equipment needs to be inside the room (and therefore MR conditional or safe), or outside the room with suitable long circuits, leads and tubing to the patient. Suitable anaesthetic machines and ventilators are manufactured and may be positioned next to the magnetic bore to minimize the length of the breathing system. They require piped gases or special aluminium oxygen and nitrous oxide cylinders. Consideration also needs to be given to intravenous fluid stands, infusion pumps and monitoring equipment, including stethoscopes and nerve stimulators. Laryngoscopes may be non-magnetic, but standard batteries should be replaced with non-magnetic lithium batteries. Laryngeal mask airways without a metal spring in the pilot tube valve should be available.

All monitoring equipment must be appropriate for the environment. Technical problems with non-compatible monitors include interference with imaging signals, resulting in distorted MRI pictures, and radiofrequency signals from the scanner inducing currents in the monitor which may give unreliable monitor readings. Special monitors are available or unshielded ferromagnetic monitors may be installed just outside the MRI room and used with long shielded or non-ferromagnetic cables (e.g. leads may be fibreoptic or carbon fibre cable). Ambient noise levels are such that visual alarms are essential. The 2010 AAGBI guidelines on services for MRI suggest that monitoring equipment should be placed in the control room outside the magnetic area. A non-invasive automated arterial pressure monitor, in which metallic tubing connectors are replaced by nylon connectors, should be used. Distortion of the ECG may occur, which interferes with arrhythmia and ischaemia monitoring. Interference may be reduced by using short braided leads connected to compatible electrodes placed in a narrow triangle on the chest. There should be no loops in cables because these may induce heat generation and lead to burns. Side-stream capnography and anaesthetic gas concentration monitoring require a long sampling tube, which leads to a time delay of the monitored variables. The use of 100% oxygen during the scan should be indicated to the radiologist reporting the images because this may produce artefactually abnormal high signal in CSF spaces in some scanning sequences.

CONDUCT OF ANAESTHESIA: The indications for general anaesthesia during MRI are similar to those for CT. In addition, the scanner is very noisy and, in general, the patient lies on a long thin table in a dark, confined space within the tube (typical diameter 50–65 cm). This may cause claustrophobia or anxiety-related problems which may require sedation or anaesthesia. Obese patients cannot be examined in this small magnetic bore. A complex scan may take up to 20 min and an entire examination more than 1 h. Open scanners have been developed and some are available which allow the patient to stand up, allowing a greater range of patients to be scanned. Outside normal working hours, only neuraxial scanning is usually performed, for acute brain or spinal cord evaluation.

Anaesthesia is induced usually outside the MRI room in an adjacent dedicated anaesthetic area where it is safe to use ferromagnetic equipment (distal to the 5 gauss line). Most patients benefit from the use of short-acting drugs because these are associated with rapid recovery and minimal side-effects. Sedation of children by organized, dedicated and multidisciplinary teams for MRI has been shown to be safe and successful. However, general anaesthesia allows more rapid and controlled onset, with immobility guaranteed. All patients must be transported into the magnet area on MRI-appropriate trolleys. During the scan, the anaesthetist should ideally be in the control room but may remain in the scanning room in exceptional circumstances if wearing suitable ear protection. If an emergency arises, the anaesthetist needs to be aware of the procedure for rapid removal of the patient to a safe area.

Occasionally, ICU patients may require scanning. Careful planning is required and screening checklists should be used. Non-essential infusions should be discontinued and essential infusions may need to be transferred to MR safe pumps. This may induce a period of instability in the patient while the infusions are being moved and high requirements for drugs such as vasopressors may be a relative contraindication to scanning. The tracheal tube pilot balloon valve spring should be secured away from the scan area. Pulmonary artery catheters with conductive wires and epicardial pacing catheters should be removed to prevent microshocks. Simple central venous catheters appear safe if disconnected from electrical connections, etc. All anaesthetized patients, especially infants, are at risk from hypothermia because the MRI room may be cold.

Gadolinium-based contrast agents are used in MR and are generally safe, with a high therapeutic ratio. However, the use of these contrast agents in patients with renal failure may precipitate a life-threatening condition called nephrogenic systemic fibrosis. If the GFR is less than 30 mL min− 1 per 1.73 m2, only minimal amounts of contrast should be given (if deemed absolutely necessary). No more should be given for at least 7 days.

MRI-guided surgery is a new, highly specialized form of surgery which may continue to be developed. It offers surgeons radiological images of the tissues immediately beyond their operative field. This makes use of an open-configuration scanner rather than the traditional closed tubular scanner. The absence of ionizing radiation places less restriction on the duration of staff presence, but the anaesthetic considerations are similar to those of the traditional MRI scanner and the anaesthetist and all the related equipment including surgical instruments are required to be in the vicinity of the scanner and therefore compatible with a magnetic field. Surgery which has been performed in this environment includes endoscopic sinus surgery and neurosurgery.

Diagnostic and Interventional Angiography

General Principles: Direct arteriography using percutaneous arterial catheters is used widely for the diagnosis of vascular lesions. Catheters are usually inserted by the Seldinger technique via the femoral artery in the groin and injection of contrast medium provides images which are viewed by conventional or digital subtraction angiography. In addition, it is becoming increasingly common to consider vessel embolization both in the elective preoperative setting (e.g. vascular tumours or malformations) and in the emergency management of major haemorrhage (e.g. major trauma or massive obstetric or gastrointestinal haemorrhage). The procedure involves the injection of an embolic material to stimulate intravascular thrombosis, resulting in occlusion of the vessel. There is a risk of distal organ damage if the blood supply is completely occluded. Non-invasive angiographic techniques used with CT or MRI have reduced the need for direct arteriography for diagnosis of some vascular lesions. The advent of spiral and double helical CT scanners allows whole vascular territories to be mapped within 30 s and produces superior images, including three-dimensional pictures. MRI is sensitive to the detection of flow and, together with more sophisticated scanning and data collection techniques, is used increasingly for assessment of vascular structures.

Anaesthetic Management: Most angiographic procedures may be carried out under local anaesthesia, with sedation if necessary during more complex investigation. If the procedure is likely to be prolonged, general anaesthesia may be more appropriate; the same applies to nervous patients, those unable to cooperate and children. Complete immobility is required during the investigation and particularly if any interventional procedures are to be performed. Sedation to augment local anaesthesia must be avoided in the presence of intracranial hypertension, because the increased PaCO2 leads to vasodilatation and a further increase in ICP; in addition, vasodilatation results in poor-quality angiography. Major trauma patients and those with life-threatening haemorrhage are nearly always sedated, with ventilation controlled, before arrival in the angiography suite. The drawbacks of general anaesthesia include prolonging the time taken for the investigation and increasing the cost and risks associated with anaesthesia. Moreover, the patient is unable to react to misplaced injections and alert staff to untoward reactions.

Adequate hydration is essential for patients undergoing angiography because they are often fasted and the contrast medium causes an osmotic diuresis. Intravenous cannulae and monitor leads may require extensions to enable the anaesthetist to remain at an acceptable distance from the patient, to minimize exposure. This also allows the anaesthetist to remain outside the range of movement of the imaging machine.

Complications of Angiography

Interventional Neuroradiology: Cerebral angiography may be used to demonstrate tumours, arteriovenous malformations, aneurysms, subarachnoid haemorrhage and cerebrovascular disease. Since the ISAT (International Subarachnoid Aneurysm Trial) in 2002 (which compared coiling in patients with a ruptured aneurysm of good clinical grade with surgical clipping) showed a favourable initial outcome, endovascular treatment has become the technique of choice for most patients. Detachable coils are used to pack the aneurysm to prevent rebleeding. These patients are often systemically unwell as a result of subarachnoid haemorrhage and may be profoundly cardiovascularly unstable during induction of anaesthesia. A thorough preoperative assessment should be made, including cardiovascular, respiratory, neurological and metabolic status. The risk of complications is generally increased in the elderly and those with pre-existing vascular disease, diabetes, stroke or transient ischaemic attacks. Many of these patients have intracranial hypertension and cerebral vasospasm; consequently, control of arterial pressure and carbon dioxide tension is essential. Obtunding the pressor response to tracheal intubation and careful positioning to avoid increasing central venous pressure are necessary to prevent elevation of intracranial pressure. A relaxant/IPPV technique with ventilation to mild hypocapnia (PaCO2 = 4.5–5.0 kPa) is usually used. A moderate reduction in PaCO2 causes vasoconstriction of normal vessels, slows cerebral circulation and contrast medium transit times and improves delineation of small vascular lesions.

Transient hypotension and bradycardia or asystole may occur during cerebral angiography with contrast dye injection. This usually responds to volume replacement and atropine. Complications during interventional neuroradiology include haemorrhage from rupture of the vessel, which may necessitate reversal of anticoagulation with protamine, and ischaemia as a result of thromboembolism (e.g. clot forming around the catheter tip), vasospasm, embolic material or hypoperfusion. Heparin and glycoprotein IIb/IIIa inhibitors (e.g. abciximab) may be required if an occlusive clot forms. All complications may occur rapidly and with devastating results. Occasionally, urgent craniotomy may be required.

Cardiac Catheterization: General anaesthesia is required mainly for children (rarely in adults because sedation is usually adequate). In children (premature neonates to teenagers), congenital heart disease may cause abnormal circulations and intracardiac shunts, which often present with cyanosis, dyspnoea, failure to thrive and congestive heart failure. Patients may also have coexisting non-cardiac congenital abnormalities. Neonatal patients may be deeply cyanotic and critically ill. Initial echocardiography often gives a diagnosis but catheterization is required for treatment or determining the possibility of surgery. These radiological procedures include pressure and oxygen saturation measurements, balloon dilatation of stenotic lesions (e.g. pulmonary valve), balloon septostomy for transposition of the great arteries and ductal closure.

The ideal anaesthetic technique would not produce myocardial depression, would avoid hypertension and tachycardia, preserve normocapnia and maintain spontaneous respiration of air. All techniques have their limitations. Positive-pressure ventilation causes changes in pulmonary haemodynamics and therefore influences measurements of flow and pressure. Spontaneous respiration with volatile agents may not be suitable for patients with significant myocardial disease. The onset of action of anaesthetic drugs is affected by cardiac shunts and congestive failure. Contrast medium in the coronary circulation may cause profound transient changes in the ECG. Therefore, ECG and invasive arterial pressure monitoring should be used to allow rapid assessment of arrhythmias and hypotension. Children with cyanotic heart disease may be polycythaemic, thereby predisposing to thrombosis.

Anaesthesia for Radiotherapy

Adults may require general anaesthesia for insertion of intracavity radioactive sources to treat some types of tumour. The commonest tumours to be treated in this way are carcinoma of the cervix, breast or tongue. These procedures are undertaken in the operating theatre and the anaesthetic management is similar to that for any type of surgery in these anatomical sites. These patients may require more than one anaesthetic for radiotherapy treatment. The anaesthetist may be exposed to radiation and appropriate precautions should be taken.

Radiotherapy is used increasingly in the management of a variety of malignant diseases which occur in childhood. These include the acute leukaemias, Wilms’ tumour, retinoblastoma and central nervous system tumours. High-dose X-rays are administered by a linear accelerator and all staff must remain outside the room to be protected from radiation.

Anaesthesia in paediatric radiotherapy presents several problems.

Before treatment begins, the fields to be irradiated are plotted and marked so that the X-rays may be focused on the tumour to avoid damaging the surrounding structures. This procedure requires the child to remain still for 20–40 min and takes place in semi-darkness. Radiotherapy treatment is of much shorter duration; two or three fields are irradiated for 30–90 s each. Anaesthesia or sedation may be required for both the focusing and the administration of radiation.

Anaesthetic Management

Frequently, these children have a Hickman line in situ to ensure reliable intravenous access for a range of medications and blood sampling. This makes induction of anaesthesia far simpler and avoids repeated i.v. cannulation, which may become technically difficult and also increasingly distressing for the patient, parent and anaesthetist. The dead space volume of Hickman lines must always be remembered and an attempt made to keep them clean. Failure to flush these lines immediately after administering drugs may lead to disastrous consequences when the anaesthetic drugs are flushed into the bloodstream at a later time. Inhalational induction with the child sitting on the parent’s knee is an alternative technique. Agents such as ketamine are unsatisfactory because sudden movements may occur and excessive salivation may risk airway compromise.

When anaesthesia has been induced, the child is placed on a trolley and anaesthesia maintained with nitrous oxide, oxygen and volatile agent delivered via a laryngeal mask. No analgesia is required and tracheal intubation is generally not necessary. There is virtually no surgical stimulation and patients may be maintained at relatively light anaesthetic levels, allowing for rapid emergence and recovery. Monitoring during radiotherapy requires the patient, anaesthetic monitors and equipment to be observed continuously by closed-circuit television.

The same principles apply when anaesthetizing children for other oncology procedures such as bone marrow aspiration, lumbar puncture and administration of intrathecal chemotherapy. This often takes place in a dedicated suite on the oncology ward and patients attend as day cases to avoid the need to come to operating theatre. It is helpful to keep records of how best to manage these children both physically and emotionally to allow continuity and minimize the impact on the child and its family.

Anaesthesia for Electroconvulsive Therapy

Electroconvulsive therapy (ECT) is controlled electrical stimulation of the central nervous system to cause seizures. It is often administered in a dedicated ward area within a psychiatric hospital. Indications include severe depression, including postnatal depression and certain psychoses. The mechanism of the therapy remains unknown. The electrical stimulus applied transcutaneously to the brain results in generalized tonic activity for about 10 s followed by a generalized clonic episode lasting up to 1 min or more. The hand-held electrodes are placed in the bifrontotemporal region for bilateral ECT, or with both electrodes over the non-dominant hemisphere for unilateral therapy. The duration of the seizure may be important for outcome and depends on age, stimulus site, stimulus energy and drugs, including anaesthetics. Seizure activity lasting 25–50 s is optimal for the antidepressant effect. Treatment may initially be 2 or 3 times per week for 3 weeks. Contraindications include increased intracranial pressure, recent cerebrovascular accident, phaeochromocytoma, cardiac conduction defects, and cerebral or aortic aneurysms. The risks from ECT and anaesthesia need to be balanced against potential benefits. Drug interactions with tricyclic antidepressants, monoamine oxidase inhibitors and lithium should be considered and managed appropriately. Seizures cause parasympathetic followed by sympathetic discharge, producing bradycardia followed by tachycardia and hypertension. Myocardial and cerebral oxygen demands increase and cardiac arrhythmias and changes in blood pressure of variable magnitude and significance, depending on any underlying medical conditions (e.g. hypertension, coronary artery disease, peripheral vascular disease), may be precipitated. Emergence agitation, nausea, headache and fracture dislocations are other described complications.

Anaesthesia

The patient may be a poor historian because of the psychiatric condition, so a careful preoperative evaluation is essential, including dentition, reflux and fasting status. Anaesthesia with neuromuscular blockade is necessary to reduce physical and psychological trauma. The anaesthetic technique should allow a rapid recovery. Routine anaesthetic equipment and minimum standards of monitoring should be available. Pretreatment with glycopyrrolate may be useful to reduce bradycardia and oral secretions. After preoxygenation, an intravenous induction agent and a neuromuscular blocker are administered. A bite block is inserted when mask ventilation with oxygen is achieved and then the stimulus is applied to produce a seizure. Intubation of the trachea would be required in late pregnancy or other full-stomach situations. Ventilation should continue until the patient is breathing, because hypoxia and hypercapnia may shorten the seizure.

Propofol is the most commonly used intravenous anaesthetic agent, replacing methohexital in this role. If seizure activity is deemed inadequate, etomidate is sometimes used, although consideration must be given to the potential effect of adrenal suppression with repeated administration. Recovery is also likely to be less rapid. Thiopental is used occasionally but may shorten the duration of the seizure. Sevoflurane has no advantages when compared with intravenous agents and is generally more time-consuming to administer.

Partial neuromuscular blockade is required to allow monitoring of the duration of the peripheral seizure and to reduce physical symptoms in an attempt to help to avoid trauma and minimize post-seizure muscle pain. Succinylcholine is often used in a dose of 0.5 mg kg−1 because it has a short duration. Subsequent doses for ECT may be modified as appropriate. Use of other neuromuscular blockers (e.g. mivacurium) may necessitate short post-procedural artificial ventilation and may not be as effective in preventing muscle contractions.

Cardiovascular drugs such as esmolol or labetalol may be required to minimize the acute haemodynamic changes of ECT in high-risk patients.

Anaesthetic drug administration and the patient’s response should be accurately recorded, as in other anaesthetic situations. This is particularly important with ECT because the therapy is repeated frequently over several weeks. Each individual responds differently to the drugs used and consistent conditions are required to obtain the best ECT stimulus response.

Anaesthesia in the Accident and Emergency Department

Anaesthetists’ involvement in the Accident and Emergency (A & E) department varies among hospitals, depending on the skills of the resident A & E medical staff. The following clinical conditions usually require an anaesthetist to attend the A & E department.

The anaesthetist attending A & E should be trained and experienced enough to manage these seriously ill patients. As in other remote locations, trained anaesthetic assistance is mandatory. Equipment and monitoring should match the minimum standard agreed for the main operating theatres. Although the anaesthetist should ideally be available continuously (assuming the A & E department is admitting patients), there may be a delay if he or she is busy in theatre or ICU. Therefore, the emergency physician or A & E doctor may sometimes have provided the initial care of the patient. In these situations, it is essential for the anaesthetist to obtain appropriate handover information and to check the patient/equipment carefully before accepting responsibility, e.g. before transferring the patient for CT scan or to the ICU.

ANAESTHESIA IN THE PRE-HOSPITAL ENVIRONMENT

The difficulties described in giving anaesthesia outside the operating theatre are compounded when working outside the hospital and the AAGBI has produced a safety guideline for pre-hospital anaesthesia. Anaesthetic intervention may be life-saving in specific situations. However, these situations are relatively infrequent and it can result in harm if performed poorly. It should only be performed by appropriately trained personnel with similar standards as those expected in hospital. There should also be a robust clinical governance structure integral to every pre-hospital service including audit, appraisal, case review, standard algorithms and a clearly defined lead clinician. Hospital staff may find themselves providing care in several situations:

Each of these situations has different clinical and logistical issues but there are some common areas. For this chapter, the main example used is that of hospital staff attending a road accident. Working safely in the pre-hospital environment demands consideration of hazards at the scene and of the roles of the other emergency services.

For example, at a road accident, potential hazards include:

Personal Preparation for Working in the Pre-Hospital Environment

It is unreasonable to expect hospital staff to get into an ambulance and attend a road accident and function effectively without training and preparation. The road accident is also a remote and unsupervised location and hospitals should deploy only staff with the correct clinical background to work in these situations.

Preparation includes having appropriate safety clothing and equipment such as:

For people attending ballistic incidents, this needs to include ballistic helmets and body armour.

Staff also need insurance to cover travelling to and from the incident, and working at the incident. Advice on suitable equipment may be found on the British Association for Immediate Care (BASICS) website: http://www.basics.org.uk

Team Working

Hospital personnel at an incident are there to support the Ambulance Service and they need to know whom to report to and how to work with ambulance staff and police. In addition, the Fire Service may be present to manage hazards and provide cutting equipment if needed for extrication. The police are present to coordinate the incident and the area around it, managing traffic flow and protecting evidence at the scene.

While everyone is concentrating their efforts on saving and treating the casualties, hospital staff need to understand that the other emergency services have their own roles, and the management of the incident continues after they and the casualties have left the scene.

Interservice working is addressed by the Major Incident Medical Management and Support (MIMMS) Course run by the Advanced Life Support Group: http://www.alsg.org and described in the MIMMS manual.

Working at the Scene

On arriving at an incident, the anaesthetist should report to the senior ambulance person, who has called the hospital flying squad or immediate care practitioner for a reason, such as:

They may also provide an explanation of what has happened, from which the mechanism of injury may be inferred and likely injuries anticipated.

Problems likely to be encountered are:

Logistical Considerations

The aim is to move the patient in the best clinical condition possible to the most appropriate hospital in the shortest time possible. In reality, a series of compromises is needed. Before carrying out any procedure, the clinician on the scene needs to ask:

Decisions such as these depend on many factors, including the overall situation, travel time to hospital, availability of ambulances and the needs of other casualties.

Clinical Considerations

Airway: The main issue is oxygenation. As in hospital practice, simple methods should be tried first, such as chin lift, jaw thrust, oral airway, nasopharyngeal airway and laryngeal mask.

Tracheal intubation may be desirable in a casualty at risk of aspiration or with a severe head injury but this may not be practical if access to the casualty is restricted. Simple methods should be used first and the situation reassessed because access to the casualty may be improved (e.g. when the roof of the car has been cut off or when the casualty has been released from the vehicle). The NCEPOD Report from 2007 highlighted the deficiencies in airway management in trauma and emphasized the need for pre-hospital anaesthesia when appropriate. Rapid-sequence induction (RSI) with oral intubation is usually the technique of choice but this should be performed only by appropriately trained individuals with adequate resources. A surgical cricothyroidotomy is an alternative definitive airway if tracheal intubation is not possible.

Children are a separate group in whom the threshold for RSI and tracheal intubation should be high (i.e. tracheal intubation should generally be used only if other techniques have failed) because not all anaesthetists are familiar with the management of small children. The risk:benefit ratio should be considered and most can be treated with simple airway interventions.

Anaesthetic and Analgesic Techniques

The principles of emergency anaesthesia are discussed in Chapter 37. In the pre-hospital environment, the same principles apply. Techniques which are familiar to the anaesthetist should be used. If the technique causes problems (e.g. apnoea or airway obstruction), the anaesthetist should have adequate access to the patient for appropriate management.

Intravenous Anaesthesia: Rapid-sequence induction using an i.v. anaesthetic agent may be the technique of choice to allow airway protection and control of ventilation in the injured casualty. Appropriate agents include ketamine, etomidate and propofol but with the dose moderated according to the casualty’s haemodynamic status. Before embarking on general anaesthesia, the anaesthetist should consider such issues as:

Ideally, there should be four people available to perform intubation, assist the anaesthetist, provide manual in-line stabilization and perform cricoid pressure.

Pre-oxygenation should be performed as in the standard hospital setting. If the casualty is combative and aggressive as a result of low GCS or the effects of drugs or alcohol, consideration may be given to carefully titrated sedation to allow adequate preoxygenation to take place rather than a ‘smash and grab’ approach which may result in significant hypoxaemia.

Even with a supine casualty on the roadside, laryngoscopy and successful tracheal intubation are often more difficult than in the anaesthetic room. A bougie or introducer should always be immediately to hand. In bright sunlight, it is difficult to see the light from the laryngoscope bulb in a casualty’s airway and an assistant may be posted between the sunlight and the casualty. There should be a well rehearsed failed intubation plan. Tracheal tube placement should be confirmed using capnography and the tube should be secured so as not to impair venous drainage of the head and neck. Anaesthesia should be maintained with midazolam or propofol either as intermittent boluses or infusions, although infusion pumps are rarely to hand. Ventilation should aim to produce normocapnia and consideration should be given to the adequacy of the oxygen supply. Clinical assessment and monitoring should be employed continuously and recorded as fully as practicable. Observations should include:

Transfer to Hospital

The choice of hospital is decided usually by the medical and ambulance staff on scene and relayed to ambulance control. Ambulance control or the personnel on scene should contact the hospital so that the receiving team is placed on standby and receives as much information about the casualty (or casualties) as possible in advance.

A checklist for transfer includes the following:

image Is the airway secured for transport? A tracheal tube or laryngeal mask should to be tied or taped in place.

image Is oxygen being provided in adequate quantities?

image Is breathing adequate or is assistance required? If the patient’s lungs are being ventilated using a mechanical ventilator, is the power capacity (gas, electricity or battery) adequate for the journey? Is there a back-up such as a self-inflating bag?

image Is external bleeding controlled? Are i.v cannulae/catheters taped securely in place? What variables have been selected (arterial pressure and/or pulse) as indicators of resuscitation requirements?

image If the patient has a reduced GCS, have remediable causes such as hypovolaemia or hypoglycaemia been considered?

image Are splints secured? Is spinal immobilization in place (where indicated)? Has a check been made that straps from splints and spinal immobilization devices are not interfering with respiration?

image Is the patient being kept warm with blankets?

image Is appropriate monitoring in place?

In some situations, it is necessary to ignore much of this preparation and ‘load and go’ as fast as possible, e.g. some stabbing or gunshot incidents in which the overriding need is surgical intervention.

Civilian helicopter ambulances provide a fast method of transporting a patient to hospital but these have some limitations. The attending staff may be unfamiliar with working in a helicopter, the space around the casualty is restricted compared with a ground ambulance and the environment is noisy; also, a second ambulance journey is often required at many UK hospitals to transport the patient from the helicopter landing site to the A & E department.

FURTHER READING

AAGBI. Recommendations for standards of monitoring during anaesthesia and recovery. The Association of Anaesthetists of Great Britain and Ireland, 2006.

AAGBI. Pre-hospital Anaesthesia. The Association of Anaesthetists of Great Britain and Ireland, 2009.

AAGBI. Provision of anaesthetic services in MRI units. Anaesthesia. 2010;65:766–770.

Advanced Life Support Group. Major incident medical management and support, second ed. London: BMJ Books, 2002.

Ding, Z., White, P.F. Anesthesia for electroconvulsive therapy. Anesth. Analg. 2002;94:1351–1364.

Greaves I., Porter K., eds. Pre-hospital medicine: the principles and practice of immediate care. London: Arnold, 1999.

Hashimoto, T., Gupta, D.K., Young, W.L. Interventional neuroradiology – anesthetic considerations. Anesthesiol. Clin. North America. 2002;20:347–359.

Holleran R.S., ed. Air and surface patient transport: principles and practice, third ed., St Louis: Mosby, 2003.

Trauma: Who Cares? National Confidential Enquiry into Patient Outcome and Death, 2007.

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