CliniCal anaesthesia

Risks associated with anaesthesiaRaja lakshmanan

Barrie Fischer

Abstractanaesthesia has undergone continuing development, with researchers

striving to improve its efficacy and safety. nevertheless there are still

risks associated with having an anaesthetic, ranging from the trivial and

self-limiting to major, permanent injury. the issue of risks associated

with anaesthesia has been highlighted in a series of publications for

patients by the Royal College of anaesthetists.

Keywords awareness; chest infection; confusion; dental damage;

equipment failure

A number of risks associated with anaesthesia are described in this issue, including anaphylaxis, cardiovascular risks, respiratory risks and nerve damage. A summary of the risks associated with anaesthesia, important risk factors and preventative measures are given in Table 1. The issue of risks associated with anaesthesia has been highlighted in a series of publications for patients by the Royal College of Anaesthetists.1

Shivering

Shivering is an involuntary process associated with both general and regional anaesthesia, and has an incidence as high as 1 in 4 (which may be slightly higher with central neuraxial blocks). The most common cause is a fall in the core body temperature (ther-moregulatory shivering). Anaesthetic drugs and exposure to a cool environment have an important role.2 Non-thermoregulatory shivering may be due to anaesthetic drugs, but is not attributed to a fall in temperature. It is more likely if there is associated postoperative pain.3

Although distressing, shivering is generally not dangerous. Treat-ment/prophylactic measures may be passive (minimizing exposure, blankets, heat–moisture exchanger) or active (heated blankets, intravenous fluid warmer, heated mattress). Drug treatment is generally not required, but if considered necessary, small doses of pethidine, tramadol and magnesium sulphate are effective.

Raja Lakshmanan, FRCA, is Specialist Registrar in Anaesthetics at the

Alexandra Hospital, Redditch. He qualified from Chennai, India. His

interests include regional anaesthesia, chronic pain and teaching.

Barrie Fischer, FRCA, is Consultant Anaesthetist at the Alexandra

Hospital, Redditch. He qualified from the University of Bristol and

trained in Truro, Cambridge and Cardiff. His main interests are the role

of regional anaesthesia in surgery and acute pain management.

anaesthesia anD intensiVe CaRe MeDiCine 8:11 44

Sore throat

The severity of sore throat varies from minor discomfort to severe continuous pain. The incidence is around 1 in 5–7 (fol-lowing endotracheal intubation) and 1 in 25 (following the use of a laryngeal mask airway).1 The use of additional nasal/oral tubes (e.g. nasogastric tube) increases the risk.

Sore throat may be caused by the direct irritation/damage on insertion of the device, pressure effects from an inflated cuff, or the use of instruments to place the tubes (laryngoscope, Magill’s forceps). These factors may be aggravated by a dry throat caused by anaesthetic gases or antisialogogues. Sore throat is more likely to occur in young women.

In most instances it resolves without any specific treatment. Simple measures such as gargling water and paracetamol are suffi-cient. If persistent after 2 days, further follow-up may be necessary.

Postoperative chest infection

Chest infection following surgery may be as common as 1 in 5 fol-lowing upper abdominal surgery,4 but is less common with other types of surgery. Other risk factors include poor general health, smoking, immobilization following surgery, urgency of the pro-cedure and age (more common at extremes of age). Interference with the natural barriers and poor protective reflexes (coughing/deep breathing) are important factors in the development of post-operative chest infections, which present as a painful cough with purulent/mucopurulent sputum associated with fever. Specific treatment for chest infection includes the use of antibiotics, chest physiotherapy (deep-breathing exercise), supplemental oxygen and early mobilization. In severe cases, non-invasive or invasive ventilation may be needed.

Prevention includes cessation of smoking (at least 6 weeks) before elective surgery, treatment of pre-existing chest infection, physiotherapy, and effective pain management.

Damage to teeth, lips and tongue

The incidence of dental damage that requires subsequent removal of teeth or repair is around 1 in 4500 general anaesthetics.5 The most frequently damaged teeth are the upper maxillary incisors. Risk factors include patient factors (difficult airway, pregnancy, obesity, and poor dentition), anaesthetic factors (general anaes-thetic, use of an artificial airway and endotracheal intubation) and surgical factors (e.g. ENT procedures). Mouth guards may be use-ful in patients with poor dentition. Dental damage ranges from minor chipping/cracking of the tooth to complete dislodgement. Damage may require repair, re-implantation or extraction. Dam-age to veneers, crowns or bridges also occurs and requires repair.

Lacerations or bruising to the lips or tongue are very common and they usually heal quickly. Very rarely, nerve damage to the tongue may occur due to pressure from airway devices. It is usu-ally temporary and recovery occurs spontaneously within weeks or months.

Postoperative nausea and vomiting

Postoperative nausea and vomiting (PONV) is a common prob-lem (as high as 1 in 3) following an anaesthetic (Anaesthesia and

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CliniCal anaesthesia

Summary of the risks associated with anaesthesia, important risk factors and preventative measures

Risk Incidence Important risk factors Prevention/treatment

shivering 1 in 4 exposure, drugs,

spinal/epidural

active and passive

warming methods

sore throat 1 in 5–7 (Cett)

1 in 25 (lMa)

airway instrumentation,

nasogastric tube

Regional anaesthesia, gargling,

paracetamol, antibiotics

(if needed)

Chest infection 1 in 5 (abdominal surgery) abdominal surgery, smoking,

immobilization, inadequate

analgesia

Cessation of smoking, chest

physiotherapy, analgesia, early

mobilization, oxygen, antibiotics

(as necessary)

Dental/oral damage Minor damage is common.

Damage requiring repair:

1 in 4500

Difficult airway, poor dentition,

airway instrumentation

avoid airway instrumentation,

regional anaesthesia if possible

POnV 1 in 3 Women, non-smokers, motion

sickness, previous POnV

Regional anaesthesia, tiVa,

anti-emetic agents

Ocular damage 1 in 600 (with eye protection) Prone position, prolonged

surgery, exposure

avoid exposure, use of gel/

ointment, eye protection pads

Confusion exact incidence unknown.

1 in 5 (>65 years) POCD

Old age, dementia, alcoholism,

general anaesthetic

Reassurance, use of familiar

objects and environment,

correction of reversible causes

awareness 1–2 in 1000 Moribund, alcoholism/substance

abuse, cardiac surgery, use of

muscle relaxants

Balanced anaesthesia,

agent-concentration monitoring,

processed eeG monitoring

(Bis, aeP)

equipment failure/disease

transmission

0.05% (regional)

0.23% (general anaesthetic)

human error, ent surgery Regular servicing, appropriate

monitoring, use of filters, use

of disposable equipment

Death/brain damage 1 in 100,000–185,000 Old age, emergency surgery,

moribund condition, major

surgery

Meticulous assessment,

appropriate choice of drugs

and equipment

aeP, auditory evoked potential; Bis, bispectral index; Cett, endotracheal tube; eeG, electroencephalogram; lMa, laryngeal mask airway; POCD, postoperative cognitive deficit; POnV, postoperative nausea and vomiting; tiVa, total intravenous anaesthesia

Table 1

intensive care medicine 7:12: 453). Risk factors may be separated into patient factors (children, women, non-smokers, history of motion sickness/PONV), surgical factors (abdominal surgery, ENT/ophthalmic procedures, prolonged duration) and pharmaco-logical factors (anaesthetic agents, including inhalational agents, opioid analgesics).6 Preoperative starvation and anxiety can also contribute to the risk. PONV is distressing to patients and may prolong the length of stay in hospital. Prevention includes use of anti-emetic agents, regional anaesthesia/total intravenous anaes-thesia (where possible), adequate hydration and slow build-up of oral feeds. Drugs used to combat PONV include antihistamines, antiserotonergic agents, dopamine antagonists, steroids and anticholinergics.

Ophthalmic injury

The most common type of damage to the eye is a corneal abra-sion, the incidence of which can be as high as 1 in 4 if no eye

anaesthesia anD intensiVe CaRe MeDiCine 8:11 450

protection is used (this decreases to 1 in 600 if eye protection is used).7 Rare injuries include pressure on the eyeball, result-ing in dislocation of the lens or even blindness (due to retinal detachment or pressure on the optic nerve). Duration of surgery, posture (prone position: 1 in 140 incidence of corneal abrasion), exposure and decreased tear production, all contribute to the development of corneal abrasion.

A corneal abrasion can be very painful. It usually heals after a few days without long-term effects. There may be a scar, which can affect vision to a variable extent depend-ing on the location on the cornea. If located in the centre of the cornea then there may be some long-term blurring of vision.

Prevention includes avoiding exposure of the eye. A hypo-allergic adhesive tape is usually used for this purpose; however, the tape may cause bruising around the eye on removal. Aque-ous gel or paraffin-based ointment may be necessary for some operations when the surgeon needs to look in the eyes during

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CliniCal anaesthesia

surgery. These substances can in turn cause irritation/congestion of the eye, lasting for a few hours.

Confusion

Confusion is common after major operations, especially in elderly people. There may be an associated change in the higher mental functions (postoperative cognitive deficit (POCD)). Typical symp-toms include disorientation to name, place, person and time, emotional disturbances, paranoid delusions, visual and auditory hallucinations. Although the exact cause is unknown, risk factors include advancing age, previous ill-health, poor memory, demen-tia, stroke, poor mobility, alcoholism and unfamiliar environment. It is more common following a general anaesthetic, although it can occur following regional anaesthesia. It can be difficult to identify POCD because of problems in objectively assessing the changes in the patient’s ability to carry out the tasks of daily life. 1 in 5 patients aged more than 60 years have measurable early, self-limiting POCD (1 week) after major non-cardiac surgery. Following cardiac surgery there is evidence that POCD can be prolonged or permanent.

Reversible factors need to be resolved (pain, infection, con-stipation, dehydration, hypoxia, inadequate nutrition, sleep disturbances, etc.). Simple measures can be the most helpful: frequent reorientation and reassurance, use of clocks, calendars and familiar objects, and appropriate room lighting (to follow a day/night cycle).

Awareness

Awareness is defined as becoming conscious during surgery (which may not be apparent immediately) due to an inappro-priately low level of anaesthesia for the degree of surgical stimu-lation. The incidence of patients experiencing some degree of awareness during some part of their anaesthetic is 1–2 in 1000.8 More than half these patients recollect sounds and conversations within the operating theatre; about 30% may feel pain and 25% may feel the presence of the endotracheal tube. This can result in long-term effects including anxiety, fear of anaesthesia, sleep disturbances, nightmares, flashbacks and post-traumatic stress disorder.

Risk factors include critically ill/moribund patients, hypoten-sion, prolonged heavy use of alcohol/opioids, use of neuromuscular blockers, cardiac surgery (1 in 100), emergency surgery for major trauma (1 in 20) and emergency caesarean section (4 in 1000).

It is important to take a detailed account of the patient’s experience. If there is evidence of awareness, a complete expla-nation, including any factors that may have increased the risk, should be given to the patient and documented in the notes. Counselling may be offered if considered necessary.

Prevention of awareness includes ensuring that anaesthetic equipment is working properly and that appropriate monitoring is used, including end-tidal/MAC levels of anaesthetic agent. Processed electroencephalogram monitors (bispectral index monitoring) may help in reducing the risk of awareness.9 Patients who have had an episode of awareness are at a slightly increased risk of awareness during their next anaesthetic. Regional anaes-thesia, where possible, supplemented by sedation precludes unintentional awareness.

anaesthesia anD intensiVe CaRe MeDiCine 8:11 45

Equipment failure/disease transmission

There is a low (0.05% with regional and 0.23% with general anaesthesia) risk of anaesthetic equipment failure. One-third of problems involve the anaesthetic machine (most common being leakage/disconnection of breathing system). They seldom cause any harm to patients. Human error has a role in around one-quarter of equipment problems. Formal equipment checks, appropriate monitoring, alarms, and vigilance by the anaesthetist will prevent most, if not all, of these problems. The anaesthetic machine should be serviced at regular intervals and a service record kept. It is the responsibility of the anaesthetist to check the equipment at the beginning of each session and before each new patient. Published guidelines are available and should be attached to every anaesthetic machine.10 Equipment failures that cause potential or actual harm should be reported as critical incidents. Back-up facilities (e.g. oxygen cylinder, intravenous anaesthetic agents, self-inflating bag for manual ventilation) need to be available and checked.

Anaesthetic equipment can transmit disease. Filters have been shown to prevent contamination of the breathing system, but the system may still need to be discarded after use in a patient with serious lung infection (e.g. tuberculosis). During tonsil-lectomy, it is recommended that all non-disposable equipment should be covered with a disposable protective sheath as there is a very rare risk of the new variant Creutzfeldt–Jakob prion being passed on by equipment because it resists current methods of decontamination.

Death or brain damage

Death or severe brain damage from general anaesthesia is extremely rare for healthy patients undergoing elective surgery (less than 1 in 100,000). The risk increases with age, type of sur-gery (major cardiac, thoracic, neurological, vascular and bowel surgery), urgency (increased risk with emergency surgery) and pre-existing comorbidity. Deaths caused by anaesthetic errors are very rare (about 1 in 100,000 for caesarean sections and 1 in 185,000 for other procedures).11

The risk of having a stroke that causes brain damage during or soon after general anaesthesia increases with age, history of previous stroke and for those having neurosurgery, head and neck surgery, carotid or cardiac surgery. Most strokes occur 2–10 days postoperatively and are due to the combined effects of surgery, anaesthesia and patient condition. The risks should be discussed with patients who are considered to be at high risk. Prevention includes thorough preoperative assessment, appro-priate choice of drugs and equipment, careful monitoring and constant vigilance. ◆

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