Complications During Anaesthesia
CAUSES OF COMPLICATIONS
AVOIDANCE OF COMPLICATIONS
preoperative assessment, investigation and counselling of the patient
preoperative checking of equipment and the assurance of backup equipment
the availability of an appropriately trained assistant
preoperative consultation with more experienced personnel, where necessary, regarding the most appropriate anaesthetic technique
Monitoring
Monitoring systems have been designed to detect and prevent complications during anaesthesia. Aspects of the patient should be monitored that are likely to deviate from the norm, or that are dangerous if they deviate from the norm. The Association of Anaesthetists of Great Britain and Ireland (AAGBI) has produced guidelines stipulating the acceptable minimum level of intraoperative monitoring (see Ch 16).
MANAGEMENT OF COMPLICATIONS
Generic Management of Complications
In general, complications should be dealt with through a sequence of:
1. Continual vigilance and monitoring
2. Recognition of the evolution of a problem
3. Creation of a list of differential diagnoses
4. Choice of a working diagnosis, which is either the most likely or the most dangerous possibility
5. Treatment of the working diagnosis
6. Assessment of the response of the problem to the treatment administered
7. Refinement of the list of differential diagnoses, especially if the response has not been as expected
8. Confirmation or elimination of the choice of working diagnosis; if the response to treatment has been unexpected then replacement with a more likely working diagnosis is indicated
Respiratory System
Table 43.1 details the common causes of respiratory obstruction during anaesthesia. Obstruction may occur at any point from the gas delivery system through the patient’s airway and bronchi to the expiratory parts of the breathing system and the scavenging tubing. It is common and potentially very dangerous. The commonest sites for obstruction are the larynx (e.g. laryngospasm), the tracheal tube (e.g. biting or secretions) and the bronchi (e.g. bronchospasm). Respiratory obstruction causes inadequate ventilation and impaired gas exchange. This causes hypercapnia, hypoxaemia and reduced uptake of volatile anaesthetic agent. Respiratory obstruction prevents the mass inflow of ambient gas which occurs during apnoea and thus produces hypoxaemia more rapidly than does apnoea with an open airway.
Management: Any significant airway obstruction should be treated by gentle, manual ventilation of the patient’s lungs with oxygen. Location of the site of obstruction should be sought urgently. In the absence of a laryngeal mask airway (LMA) or tracheal tube, apposition of the tongue and pharyngeal soft tissue is a common cause of upper airway obstruction. This may be overcome by a jaw lift or neck extension. It may require the use of an oro- or nasopharyngeal airway, although these devices may themselves provoke laryngospasm or pharyngeal abrasion. Absolute obstruction suggests an equipment problem. Easy passage of a suction catheter through the tracheal tube confirms its patency. If obstruction persists and no obvious cause is identified, then the tracheal tube or laryngeal mask may be the site of obstruction and should be replaced.
The most common airway complication is partial respiratory obstruction during spontaneous ventilation or during assisted manual ventilation in the absence of a formal (equipment) airway. A gentle jaw thrust, head tilt and chin lift usually clear a partially obstructed airway, and insertion of an oropharyngeal or nasopharyngeal airway resolves almost all of the remainder. In the rare situation of complete inability to ventilate the patient’s lungs manually, and after equipment failure has been excluded, the insertion of a laryngeal mask airway or tracheal tube may be necessary. Allowing the patient to awaken is prudent if there is no urgency to proceed with the operation. If it is necessary to continue the operation or if the patient cannot be wakened, and insertion of a laryngeal mask airway and tracheal tube have proved impossible, then it becomes necessary to establish a surgical airway. This may take the form of a cricothyroid cannula, a surgical cricothyrotomy or an emergency tracheostomy. These procedures must be learned and practised before the occurrence of the incident. They are technically demanding and are themselves potentially life-threatening to the patient if performed inexpertly (see Ch 22).
Laryngospasm
Management: Where possible, airway and surgical stimulation should be avoided during light anaesthesia and the lateral position should be used for control of secretions during extubation and transfer. Surgical stimuli should be anticipated and anaesthetic depth should be adjusted accordingly. The anaesthetist should remove the stimulus to laryngospasm, administer 100% oxygen and provide a clear airway. Gentle pharyngeal suction should be applied. Where appropriate, anaesthetic depth may be increased by administration of an intravenous anaesthetic agent and the lungs ventilated manually, applying continuous positive airway pressure (CPAP). Most episodes of laryngospasm respond to this treatment. If laryngospasm persists and hypoxaemia ensues, a small dose of succinylcholine (e.g. 25 mg in adults) relaxes the vocal cords and allows manual ventilation and oxygenation. A full dose of succinylcholine may be given if tracheal intubation is indicated, but this is usually unnecessary. Doxapram, an analeptic and respiratory stimulant, has also been used successfully in the treatment of laryngospasm.
Bronchospasm
Management: Bronchospasm during anaesthesia results in hypercapnia, hypoxaemia and pulmonary gas trapping, which may cause hypotension (through reduction in left ventricular preload). Management is aimed at preventing hypoxaemia, and resolving the bronchospasm. Initially, 100% oxygen should be given, anaesthesia deepened if appropriate and any aggravating factors removed (e.g. the tracheal tube should be repositioned and surgery stopped). If further treatment is necessary, a bronchodilator should be given in increments according to the response. Recommended drugs include intravenous aminophylline (up to 6 mg kg−1) or salbutamol (up to 3 μg kg−1). Volatile anaesthetic agents and ketamine are also effective bronchodilators. Adrenaline is indicated in life-threatening situations and may be given via the tracheal tube. Steroids and H1-receptor antagonists have no immediate effect but may be indicated in the later management of severe cases of bronchospasm.
Complications Associated with Tracheal Intubation
Poor management of difficult intubation is a significant cause of morbidity and mortality during anaesthesia. Sequelae include dental and airway trauma, pulmonary aspiration, hypoxaemia, brain damage and death. Table 43.2 shows the commonest causes of difficulty in intubation. The single most important cause is an inexperienced or inadequately prepared anaesthetist and the difficulty is often compounded by equipment malfunction. The anatomical features associated with difficult laryngoscopy are listed in Table 43.3. Of these, the atlanto-occipital distance is the best predictor of difficulty but requires a lateral cervical X-ray. Many of these factors are normal anatomical variations, but extreme abnormalities do occur. A cluster of normal variations in an apparently healthy patient may be sufficient to cause major difficulties in laryngoscopy.
TABLE 43.3
Anatomical Factors Associated with Difficult Laryngoscopy
Short, wide, muscular neck
Protruding incisors
High, arched palate
Receding lower jaw
Poor mobility of the mandible
Increased anterior depth of mandible
Increased posterior depth of mandible (reduces jaw opening, requires X-ray)
Decreased atlanto-occipital distance (reduces neck extension, requires X-ray)
Management: Preoperative examination of the airway (Table 43.4) is essential. Identification of patients with a potentially difficult airway (see Tables 43.2 and 43.3) before anaesthesia allows time to plan an appropriate anaesthetic technique. The Mallampati test is a widely used and simple classification of the pharyngeal view obtained during maximal mouth opening and tongue protrusion (see pp. 455–456). In practice, this test suggests a higher likelihood of difficult laryngoscopy if the posterior pharyngeal wall is not seen. The predictive value of this test may be strengthened if the thyromental distance (the distance between the thyroid cartilage prominence and the bony point of the chin during full head extension) is less than 6.5 cm.
TABLE 43.4
Preoperative Assessment of the Airway
General appearance of the neck, face, maxilla and mandible
Jaw movement
Head extension and neck movement
Teeth and oropharynx
Soft tissues of the neck
Recent chest and cervical spine X-rays
Previous anaesthetic records
Mallampati classification
Thyromental distance
Premedication with an antisialagogue reduces airway secretions. This is advantageous before inhalational induction and essential for awake fibreoptic laryngoscopy to maximize the effectiveness of topical local anaesthesia. An anxiolytic may also be given (but is contraindicated in patients with airway obstruction, e.g. caused by burns, trauma, tumour or infection affecting the larynx or pharynx). The presence of a trained assistant is essential and the availability of an experienced anaesthetist and a ‘difficult intubation’ trolley with a range of equipment such as bougies, a variety of laryngoscopes and tracheal tubes, and cricothyrotomy needles is desirable (see Ch 22).
A variety of options exists for the patient in whom a difficult laryngoscopy is anticipated. If the procedure can be carried out under local or regional anaesthesia, then this technique should be used as the first choice (see Ch 24). However, the patient, anaesthetist and equipment must be prepared for general anaesthesia in case a complication arises.
If general anaesthesia is necessary for the procedure, or if the patient refuses local or regional anaesthesia despite a frank discussion of the risks, then steps must be taken to secure the airway safely. Unless tracheal intubation is essential for airway protection or to enable muscle relaxation and ventilation, the use of an artificial airway such as the laryngeal mask with spontaneous ventilation is usually a safe technique. If intubation is essential, the appropriate anaesthetic technique depends on the anticipated degree of difficulty, the presence or absence of airway obstruction and the risk of regurgitation of gastric fluid. The management of the patient in whom difficulties with airway management are anticipated is detailed in Ch 22.
The safest anaesthetic technique may usually be chosen from the following clinical examples.
1. Patients with an increased risk of regurgitation and aspiration (e.g. full stomach, intra-abdominal pathology, pregnancy). An inhalational induction is inappropriate in these patients. Regional anaesthesia is preferable in the parturient (see Ch 35). Preoxygenation and a rapid sequence induction with succinylcholine can be used if there is little anticipated difficulty. If intubation is unsuccessful, no further doses of neuromuscular blocking drug should be used, the patient allowed to wake and further assistance sought. If there is a high degree of anticipated difficulty, an awake technique is recommended (see below).
2. Patients with little anticipated difficulty and no airway obstruction (e.g. mild reduction of jaw or neck movement). After a sleep dose of intravenous induction agent and confirmation of the ability to ventilate the lungs manually by mask, succinylcholine may be given to provide the best conditions for tracheal intubation. If difficulty is encountered, the patient is allowed to wake up and the procedure replanned. Where appropriate, anaesthesia is deepened by spontaneous ventilation using a volatile agent and alternative techniques to facilitate tracheal intubation used (see Ch 22).
3. Patients with severe anticipated difficulty and no airway obstruction (e.g. severe reduction of jaw or neck movement). Appropriate techniques include inhalational induction with sevoflurane or the use of fibreoptic laryngoscopy either in the awake patient or after inhalational induction. Neuromuscular blocking drugs must not be used until the ability to ventilate the lungs manually and view the vocal cords is confirmed.
4. Patients with airway obstruction (e.g. burns, infection, trauma). An inhalational induction may be used; otherwise an awake technique should be considered. Neuromuscular blocking drugs should not be used until tracheal intubation is confirmed.
5. Extreme clinical situations. Tracheostomy performed under local anaesthesia may be the safest technique.
Failed Intubation
Poor management of failed intubation is a significant cause of serious morbidity and mortality. The aims of management are to maintain oxygenation and prevent aspiration of gastric contents. The ‘failed intubation drill’ is now established as an important skill for safe anaesthetic practice. An early decision to use a failed intubation protocol and to call for assistance is essential, because continued attempts at tracheal intubation may result in trauma to the airway, pulmonary aspiration or hypoxaemia (see Ch 22). The obstetric patient is a special case and is considered in Chapter 35.
If the airway is obstructed and ventilation is inadequate during management of a failed intubation, then insertion of an LMA should be considered (see Figs 22.3–22.5). It has been used successfully to provide an airway and allow ventilation when attempts to intubate the trachea and ventilate the lungs by other means have failed. Alternatively, it may be possible to pass a small-diameter tracheal tube or a bougie through the LMA into the trachea; a variant of the LMA, the intubating LMA (ILMA) is designed specifically to facilitate tracheal intubation. The LMA should not be regarded as providing protection against pulmonary aspiration, although it is claimed that the ProSeal™ LMA, which has a rearward port for the downward passage of a gastric tube or the upward passage of gastric contents, is better in this regard. The oesophageal obturator airway and similar devices are alternatives in an emergency, but there are doubts about their efficacy and there have been reports of misplacement and oesophageal rupture associated with their use. A recent innovation is an ILMA which incorporates a video camera and LCD screen, allowing direct visualization of the introduction of a tracheal tube through the larynx.
Aspiration of Gastric Contents
Management: At-risk patients should be managed actively to prevent the aspiration of gastric contents. The volume and acidity of the gastric contents should be reduced as far as possible. Preoperative fasting, histamine H2-receptor blockers and a gastric prokinetic drug (e.g. metoclopramide) are recommended. If general anaesthesia is essential, then the trachea must be intubated. Most commonly, this is achieved using a rapid-sequence induction with cricoid pressure (see Ch 37), but awake intubation is advisable if difficulty in intubation is predicted. During emergence, the tracheal tube should not be removed until protective airway reflexes are regained when the patient is awake.
Hypoxaemia
Hypoxaemia is an inadequate partial pressure of oxygen in arterial blood. Hypoxia is oxygen deficiency at the tissue level. A practical classification of the causes of hypoxaemia is shown in Table 43.5. Hypoxaemia threatens tissues globally and, if allowed to persist, risks permanent damage to those organs most delicately dependent upon continued oxygen supply. The first organs to be damaged, most commonly, are the brain and heart, and any pathological impairment of their blood supply increases the risk of early and permanent damage. There is no categorically safe or unsafe level of arterial oxygen tension (PaO2). The risk presented by a level of hypoxaemia is dependent upon the patient’s haemoglobin concentration, cardiac output, state of hydration, concurrent disease processes (especially vasculopathic diseases) and the duration of exposure to the lowered PaO2. In general, few patients are harmed by arterial oxyhaemoglobin saturations of greater than 80%, but clearly, this low level provides very little margin for safety should any other complication occur. Most anaesthetists choose to set the arterial oxygen saturation alarm limits on the pulse oximeter at 92–94%.
Management: Hypoxaemia occurring during anaesthesia is almost invariably treatable and its complications are preventable. Cyanosis should seldom be witnessed by the vigilant anaesthetist because the routine use of pulse oximetry allows early detection and treatment of hypoxaemia. If hypoxaemia is detected, the following drill should be instituted.