Maintenance of anaesthesia

PerioPerative care

Maintenance of anaesthesiarobert thompson

andrew Severn

Abstractanaesthesia enables the performance of procedures otherwise intoler-

able to the patient. During the maintenance period, when such proce-

dures take place, the anaesthetist performs many simultaneous tasks

in a complex environment. these tasks include maintaining physiologi-

cal homeostasis, prevention of awareness and facilitation of surgical

activity. in particular, constant surveillance of the theatre environment

(concentrating on the patient, monitoring and surgery) is pivotal to in-

terpret observations in the context of the clinical situation and prompts

the anaesthetist to intervene when necessary. Factors that may affect

the quality and safety of maintenance of anaesthesia are the person-

nel administering the anaesthetic, environment, equipment available

and skills, both technical and non-technical, of the anaesthetist. critical

incidents often occur during the maintenance period and human error is

frequently implicated. thus constant vigilance and strategies to prevent

error and deal with crises are invaluable to the anaesthetist.

Keywords general anaesthesia; maintenance; monitoring; safety

Anaesthesia enables the performance of a procedure that would otherwise be intolerable to the patient. While this procedure is usually surgery, there are other situations in which anaesthesia is administered, for example, in radiological imaging and electro-convulsive therapy. There are specific hazards associated with these environments that will not be discussed here.

The early pioneers of anaesthesia recognized that maintenance of anaesthesia required skill in observing the effects of the anaes-thetic. John Snow, writing about an inhalational agent adminis-tered as a sole agent in 1847 said, ‘The point requiring most skill

Robert Thompson, FRCA, is Specialist Registrar in Anaesthesia at

Manchester Royal Infirmary, Manchester. He graduated from the

University of Manchester and is training in anaesthesia in the

North- West.

Andrew Severn, FRCA, is Consultant Anaesthetist in Lancashire. He is

interested in general anaesthesia and perioperative care, especially in

the older patient.

‘i suppose it was all right for me to start?’ he asked the

anaesthetist.

the Daily Telegraph rustled slightly in assent.

Gordon r. Doctor in the House. London: Michael Joseph, 1952.

aNaeStHeSia aND iNteNSive care MeDiciNe 8:9 37

and care in the administration of the vapour of ether is undoubt-edly to determine when it has been carried far enough’. His modern counterparts deal less with single agents than a ‘balanced’ anaes-thetic of hypnosis, analgesia and muscle relaxation, and they have electronic devices to help them. Clinical monitoring of a patient for signs of overdose is one of many tasks undertaken between induction and emergence: that period which we will describe as ‘maintenance’; the period in which surgery takes place.

Practical procedures (those skills that are assessed in train-ing) such as securing the airway and regional blocks are gener-ally performed at the beginning of the anaesthetic. Thus, most critical incidents are expected occur during this time. However, one study1 found that 48% of recorded critical incidents occurred during maintenance compared with only 25% at induction. So what does an anaesthetist do during maintenance? There is a popular misconception that the anaesthetist ‘switches off’ during this period. In reality, the operating theatre is a complex environ-ment and the anaesthetist performs many tasks.

What does the anaesthetist do during maintenance of anaesthesia?

There are a number of discrete activities performed during main-tenance of anaesthesia. These activities may be described as a sequence of events such as those seen during a primary hip replacement. They can form the basis of an answer to an exami-nation question ‘How do you ‘do’ a hip replacement?’ However, these are only the activities performed by the anaesthetist and do not account for the cognitive processes involved, many of which would result in the decision ‘not to intervene’.

An alternative way of looking at maintenance, and one which is not specific to any particular operation, is to think of the out-comes to be achieved during maintenance of anaesthesia. These are listed below:• Maintain physiological homeostasis• Facilitate surgery• Prevent awareness• Provide analgesia• Prevent complications• Keep records• Communicate with theatre team• Demonstrate skills to trainee staff• Prepare for the postoperative period

SurveillanceTo achieve the outcomes listed above, continuous surveillance of the theatre environment is required. The main components of interest to the anaesthetist are the patient, monitors and the sur-gical procedure or the ‘patient–equipment–surgery’ triangle.

The Association of Anaesthetists of Great Britain and Ireland (AAGBI) revised their recommendations for ‘minimum standards of monitoring’ in 2007 (Table 1).2 Of paramount importance is the presence of an appropriately trained individual throughout the conduct of the anaesthetic. This person must continuously assess equipment function and the patient through direct obser-vation and monitoring devices. Observation should be continued throughout the anaesthetic until recovery of consciousness.

Observation of surgery is necessary to enable an appropri-ate reaction to surgical ‘milestones’. With the example of hip

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PerioPerative care

Minimum standards of monitoring as described by AAGBI

Monitoring the anaesthetic equipment Monitoring the patient

Observation Monitoring devices

• o2 supply: o2 analyser

• Breathing system: reservoir bag, capnogragh

• vapour analyser

• infusion devices: alarms set, infusion site visible

• colour

• Pupil size

• chest wall movements/reservoir bag

• response to surgical stimuli

• Pulse

• Breath sounds

• Urine output

• Blood loss

• Pulse oximeter

• Non-invasive blood pressure

• ecG

• airway gases: o2, co2, vapours

• airway pressure

aaGBi, association of anaesthetists of Great Britain and ireland

Table 1

replacement, placement of cement may cause cardiovascular instability and hypoxaemia, and these complications should be anticipated. Common to many operations, appreciation of surgical bleeding helps early correction of hypovolaemia and anticipation of future fluid or blood product replacement.

An understanding of the theatre environment is known as ‘situation awareness’ and allows effective decision making and appropriate intervention. Observation is the first step in a chain of cognitive processes, followed by verification of monitored variables and interpretation in context of the clinical situation. Verification involves confirming or rejecting an abnormal vari-able by correlating the reading with other clinical information and checking monitoring devices.

As an example of how an anaesthetist might interpret data from monitoring in the context of the clinical situation, we consider end-tidal carbon dioxide analysis in detail (Table 2). Abnormalities of the carbon dioxide trace or reading may be an important warning of a number of impending dangers.

Abnormalities of the carbon dioxide value or trace may indi-cate an immediate threat to the patient, yet the list of differential diagnosis is so large that many conflicting remedial options have

Differential diagnosis of abnormalities of a capnograph

• Disconnected airway

• oesophageal intubation

• tracheal tube near the carina

• obstructed airway

• cardiac arrest

• Fat, air or venous embolism

• Low cardiac output

• inappropriate ventilator settings

• Hypo/hyperventilation

• excessive depth of anaesthesia

• Malignant hyperthermia

• Sepsis and rebreathing

Table 2


to be considered. It is essential that data from the monitor is interpreted in the context of the clinical situation and rapidly cross-referenced against other monitors (e.g. blood pressure, pulse or temperature). Furthermore, the information gained is a surrogate marker (the concentration of carbon dioxide in the expired gas) and not a direct reading of the parameter under investigation (cardiac output, alveolar minute volume). Thus, interpretation requires an understanding of the factors that may alter the concentration of carbon dioxide (e.g. change in minute volume, dead-space, carbon dioxide production) and a response that takes this understanding into consideration. The same logic applies to all electronic monitoring because monitors measure that which can be measured and not necessarily the variable that is needed for clinical management (Table 3).

Maintenance of homeostasisIn the conscious individual, homeostasis maintains parameters such as blood pressure, temperature and pH within set limits. Homeostatic mechanisms are dampened by anaesthetic agents, permitting deviation of physiological variables away from normal values. An anaesthetist takes control of many of the patient’s homeostatic functions to defend parameters such as circulating volume, respiratory gases and temperature. This has been described as assuming the role of the ‘patients’ replacement brain’.3

VentilationWith the obvious exception of muscle relaxants, the use of any anaesthetic agent is compatible with a decision to allow the patient to breathe spontaneously, although all agents cause a dose-dependent depression of the medullary centres controlling respiration with a resulting rise in arterial partial pressure of carbon dioxide (PaCO2). There is also a reduction in functional residual capacity (FRC). Irrespective of the mode of ventilation, (spontaneous or controlled) a secure and unobstructed airway, with minimal resistance to expiration, is required. The choice of airway used depends on the circumstances. A laryngeal mask airway may be a suitable alternative to endotracheal tubes for controlled ventilation, although the latter offer security from aspiration of stomach contents and accidental displacement at the cost of a higher incidence of sore throat and cardiovascular changes during insertion or removal.

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PerioPerative care

Surrogate electronic measurement of wellbeing during anaesthesia

Device What is measured Errors of assumption that may be made

carbon dioxide monitor concentration of co2 in expired gas equivalence with arterial co2

Pulse oximeter ratio between two forms of Hb equivalence with tissue o2 delivery

Blood pressure cuff Systolic and mean blood pressure relationship with cardiac output

accuracy of diastolic blood pressure

arterial cannula Systolic, mean and diastolic pressure

ecG rate and electrical activity of heart the presence of cardiac output

Normal oxygen delivery to heart

Lack of awareness

Skin thermometer Skin temperature equivalence with central temperature

central vein cannula Blood pressure in right atrium equivalence with left atrial pressure

relationship with left ventricular volume

relationship with blood volume

airway pressure Pressure within the breathing system appropriate tidal volume

integrity of breathing system

Hb, haemoglobin

Table 3

During maintenance of anaesthesia, the unobstructed move-ment of the chest wall is an important observation (at deeper levels of anaesthesia, spontaneous ventilation becomes dia-phragmatic and some paradoxical rib movement is seen). Excur-sions of the breathing-system reservoir bag give an indication of tidal volume. Providing these two clinical signs are grossly unchanged, end-tidal carbon dioxide analysis gives an indirect measure of the PaCO2. Controlled ventilation allows the anaes-thetist to manipulate the PaCO2 and to counteract the effects of anaesthesia on the FRC. It also allows for the application of positive-end expiratory pressure.

While these considerations apply predominantly to general anaesthesia, changes may occur during regional anaesthesia and cause embarrassment to both patient and anaesthetist unless they are considered. Critical reductions in FRC may be caused by a high spinal block that hinders intercostal movement, by positions such as lithotomy, or by the use of interscalene block that paralyses the phrenic nerve. These complications may take some time to manifest and may not be a problem until after sur-gery has started. Therefore, the professional who takes on the responsibility for monitoring patients under regional anaesthetic needs to be aware of these problems and able to intervene if they arise.

CirculationCardiovascular disturbance is caused by anaesthetic and surgi-cal factors such as blood loss, fluid shifts, anaesthetic agents and neuraxial blockade. Cardiac disease may affect the ability of the patient to tolerate such challenges. However, in most cases cardiovascular change is predictable and ECG and non-invasive blood pressure monitoring are sufficient to enable delivery of a safe anaesthetic.

In patients with significant co-morbidity or in whom surgery is expected to cause a large physiological derangement, more inva-sive measurement devices may be used such as invasive arterial


pressure monitoring or central venous pressure monitoring to guide fluid delivery. Advanced methods of monitoring cardiac output (e.g. oesophageal Doppler, LidCO or transoesophageal echocardiographic monitoring) may also be used. Urine output and capillary refill are also useful markers.

Hypovolaemia may be a consequence of preoperative star-vation, bowel preparation, ongoing fluid losses and blood loss. Emergency patients may be especially dehydrated or bleed-ing before surgery. The extent of hypovolaemia is difficult to gauge, and fluid replacement is often best guided by response to fluid challenges. The extent of blood loss may be estimated by clinical observation, weighing blood swabs and measuring blood in suction apparatus. The choice of fluid replacement is initially between crystalloid and colloid. The choice of solu-tions is wide and beyond the scope of this article. Significant blood loss may necessitate replacement of red blood cells, platelets and coagulation factors.4

NormothermiaAnaesthesia impairs the patient’s ability to regulate body tem-perature, and surgery exposes body surfaces and tissue from which heat loss can occur. The effects of wet drapes, cold infu-sion fluids and dry inspired gas exacerbate the natural tendency for temperature to decrease during surgery. Heat and moisture exchangers prevent the loss of heat from the respiratory tract by preventing the loss of (latent) heat via evaporation from the respiratory tract. Warming mattresses and fluid warmers also compensate for the inevitable heat loss.

Hypothermia causes many adverse effects, including shiver-ing, sympathetic stimulation, increased oxygen consumption, coagulopathy, immunosuppression, delayed wound healing and delayed metabolism of drugs. Whenever devices are used to pre-vent heat loss or provide warmth, their effectiveness must be measured. Pyrexial patients or those at risk of malignant hyper-thermia pose additional challenges for the anaesthetist.


PerioPerative care

Activity related to surgeryThe aim of many of the interventions made by the anaesthe-tist during the maintenance period is to facilitate surgery rather than preserve homeostasis (Table 4). These interventions may be simple (administration of a muscle relaxant during an intra-abdominal operation) or complex (single-lung ventilation during thoracic surgery).

There may be competing interests to consider regarding the position required for surgical access and the possible harm or danger to the patient. Positioning may be associated with a num-ber of complications. These complications may be systemic, including ventilatory compromise caused by cephalad displace-ment of the diaphragm in the Trendelenburg position and the reduction in venous return in the deckchair position. There may also be local complications such as eye injury and brachial plexus injury in the prone position.

Prevention of awarenessGeneral anaesthesia is maintained using inhalational or intrave-nous agents. Awareness during general anaesthesia may be con-sidered as ‘explicit’ and ‘implicit’ memory. Explicit awareness results in recall of events during anaesthesia whereas implicit awareness may not be recalled but may affect behaviour at a later time. Historically, awareness has been associated with the use of neuromuscular block and the subsequent paralysis. Thus, risk is increased during cardiac and obstetric surgery and where neuromuscular blockade is used in preference to other agents that may have adverse cardiovascular actions or effects on the fetus.


Inadequate depth of anaesthesia may be a consequence of equipment problems or an insufficient dose of anaesthetic agent, which occurs as a result of error or if low doses are used to prevent cardiovascular problems. Rarely, requirements for anaesthetic agents are increased in circumstances such as hyperthyroidism and acute amphetamine intake. Equipment problems include vapourizer or syringe-pump malfunction, and disconnections in the breathing system or intravenous line.

The anaesthetist is responsible for error, and pumps, vaporiz-ers, and breathing circuit cannulation sites should be monitored.

There is no safe and reliable monitor of depth of anaesthe-sia, and for the foreseeable future it must be considered a mat-ter of professional judgment by an appropriately trained person. Although there are experimentally determined endpoints for anaesthetic action described for inhalational agents (minimal alveolar concentration (MAC)) and intravenous agents (minimal infusion rate), they are described on the basis of their action on the population not on the individual patient. Furthermore, these endpoints relate to inhibition of movement, not the abolition of awareness.

Clinical signs: assessment of clinical signs such as movement and sympathetic stimulation (e.g. tachycardia, hypertension, tachypnoea, lacrimation and pupillary dilatation) may indicate light anaesthesia. Signs may be masked by medication (e.g. β-blockers) or medical conditions (e.g. autonomic neuropathy).

Dose of anaesthetic delivered is measured by end-tidal volatile concentration or by a computer for target-controlled infusion.

Interventions made by the anaesthetist during maintenance

Type of surgery Examples of intervention Possible complications

abdominal/pelvic • Muscle relaxation

• Positioning (trendelenberg)

• awareness

• anaphylaxis

• Postoperative residual blockade

• ventilatory embarrassment, regurgitation

• LvF

thoracic • Muscle relaxation

• Positioning (lateral for thoracotomy)

• Single-lung ventilation

• Hypoxaemia

• Hypercapnia

obstetric • administration of tocolytics • Hypotension

• Nausea

cardiac • anticoagulation for cardiopulmonary bypass

• toe assessment of cardiac function

• Bleeding

• anaphylaxis (especially protamine)

orthopaedic • Positioning (lateral, prone, deckchair)

eNt • induced hypotension for middle ear surgery

• Jet ventilation during airway surgery

• impaired cerebral perfusion

• Barotrauma

Neurosurgery • Positioning (prone, sitting, park bench)

• induced hypotension

• intraoperative wake up

• air embolism in sitting position

vascular • anticoagulation

• assessment of neurological function during carotid surgery

• Bleeding

LvF, left ventricular failure; toe, transoesophageal echocardiographic

Table 4


PerioPerative care

Minimum alveolar concentration is defined as the minimum concentration of inhalational agent at equilibrium to prevent movement in 50% of unpremedicated patients to a standard stimulus. Prevention of movement is due to an effect at the spi-nal level. This should be differentiated from prevention of recall, which occurs at the cerebral level. The dose of agent required to prevent recall is much lower and approximates to the dose required to suppress response to command (MAC awake),5 which is typically one-third of MAC. MAC-awake values should not be assumed to prevent awareness in an individual because MAC-awake prevents response to command in only 50% of a population, and individual MAC is dependent on many variables. Plasma or effect site concentrations of intravenous agents are estimated by computer models. These concentrations are derived from estimates of known pharmacokinetic data and the body weight of the patient.

Electronic monitoring of depth of anaesthesia: auditory evoked potentials and bispectral index use processed electroencephalog-raphy (EEG) to estimate depth of anaesthesia. As yet, no tech-nique approaches the specification of an ideal depth of anaesthesia monitor and none has gained widespread use. A consensus report of the American Society of Anaesthesiologists stated that the use of monitoring devices was not routinely indicated, but should be decided on a case by case basis by the practitioner.

Prevention of complicationsComplications during anaesthesia range from death to a tempo-rary sore throat. Many complications, such as idiosyncratic drug reactions and equipment failure, are unpredictable and identifi-cation depends on constant vigilance. However, the incidence of some complications can be minimized by attention to detail.

Peripheral nerve injury and skin ischaemia may be caused by poor patient positioning, compression of superficial nerves (e.g. ulnar nerve) and the use of tourniquets. Methods to prevent such injuries include careful positioning, the use of padding around vulnerable areas and care of pressure areas.

Taping eyelids shut or the use of ointment helps to prevent corneal abrasion, drying and direct trauma. Care must be taken not to exert direct pressure on the globe.

Record keepingAbout one-tenth of the maintenance period is spent complet-ing the anaesthetic record. The aims of keeping a record are described below.• To facilitate clinical care during anaesthesia. Preoperative checklists and regular noting of physiological variables may help identify problems and physiological trends may emerge. The record ensures that the handover of care to another anaesthetist is as complete as possible.• To provide information for future procedures. The anaesthet-ist can be warned of difficulties encountered during a previous anaesthesia, such as difficult intubation.• Reviewing care. This may be for legal or audit purposes.

The AAGBI published a recommended data set in 1996. Infor-mation recommended to be recorded includes patient assessment, personnel involved, urgency of procedure, preoperative checks, monitoring, airway device and breathing system, positioning, regional techniques, vital signs, drugs and fluids administered,


postoperative instructions, untoward incidents and hazard flags for future procedures.

Computerized record keeping possesses a number of advan-tages and has recently been recommended by the AAGBI.2 An electronic record is more accurate and detailed than a manual record, especially during critical events, when the record is completed retrospectively. Also the anaesthetist may spend less time completing an electronic record.

Preparation for the postoperative periodIn anticipation of the end of the surgical procedure, patients should received appropriate analgesia and anti-emetics. Post-operative analgesia, anti-emetics, fluids and oxygen should be prescribed, and deep vein thrombosis prophylaxis should be considered. Drugs given during the procedure that may impact on postoperative care should be transcribed onto the prescrip-tion chart. Specific instructions for postoperative care should be clearly noted.

Quality of anaesthesia

From a patient’s perspective, the quality of anaesthetic care means waking up safely and being free of pain, nausea, vomiting and not being able to recall of surgery. However, professionals attach the highest priority to safety, the prevention of adverse incidents and appropriate timely treatment of such events. Fac-tors that impact on patient safety are described below.

PersonnelThe presence of an appropriately trained anaesthetist is required throughout the surgical procedure. The level of supervision of trainee anaesthetists should always be noted in the anaesthetic record, and there must also be a trained person to provide exclu-sive assistance to that anaesthetist.

The handover of responsibility of patient care from one anaes-thetist to another may occur. The aspects of the conduct of the anaesthetic that have not been managed to perfection become problems for an anaesthetist taking over the care. These aspects may not be obvious at the moment of handover.

Recent practice has moved away from the medical model of anaesthetic care, with the training of non-physician anaesthe-tists (anaesthetic practitioners) in the UK. Their role is envisaged as providing anaesthesia under the supervision of a consultant who should be present at induction and emergence. While this is a novel idea in the UK, non-physician anaesthetists have been working in healthcare systems in other countries for many years.

EnvironmentThe concept of ergonomics may be applied to operating theatre layout and anaesthetic equipment design to improve safety. Monitors should be user-friendly and alarms easily identifiable so that the anaesthetist is quickly alerted to abnormal readings. The operating theatre layout should be such that the anaesthetist can simultaneously observe the monitors, patient and surgery. Items such as urine manometers, surgical suction bottles and used swabs should be visible. Access to the patient and equip-ment should not be hampered.

The operating theatre is not the only place where anaesthe-sia is conducted. Layout is usually less suited to anaesthetist’s


PerioPerative care

needs in other locations such as the radiology or vascular suite, where space may be limited and access to the patient impaired. Preparation with regard to layout and availability of equipment is important before embarking on procedures in these types of locations. In particular, the MRI scanner presents a unique set of problems and hazards as direct observation, monitoring and access to the patient is limited and only specially designed equip-ment is permitted near the scanner.

Non-technical skillsTraining in anaesthesia concentrates on the acquisition of knowl-edge and technical skills. However, other skills are necessary for the successful delivery of an anaesthetic. These are described as non-technical skills6 and comprise cognitive skills (situation awareness, prioritising, and descision making) and social skills (communication and team work). These skills are vital during the maintenance period of anaesthesia when the anaesthetist is responsible for the interpretation of large amounts of data in a complex environment and effecting appropriate responses.

Error in anaesthesiaCritical-incident reporting, root-cause analyses and ‘closed claims’ studies provide insight into the causes of error in anaes-thesia. The Australian Incident Monitoring Study1 described causative factors of error and failures to rescue a situation. Errors of judgment, fault of technique, inattention, haste, distraction, poor communication and failure to check equipment all featured in the report.

Error may be compounded by stress and fatigue. In a cri-sis, performance may be impaired by anxiety, workload, time


pressure and the presence of a complex situation not encountered before.7 Anaesthetists encounter such situations infrequently so are often poorly equipped to deal with them. The simulation of situations and knowledge of precompiled responses (e.g. Advanced Life Support) may help the anaesthetist prepare for real-life incidents. ◆

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8 © 2007 elsevier Ltd. all rights reserved.

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Maintenance of anaesthesia