Emergency and trauma anaesthesia

Patients scheduled for elective surgery are usually in optimal physical and mental condition, with a definitive surgical diagnosis; any coexisting medical disease is defined and well controlled. These patients have often discussed plans for surgery and anaesthesia (including postoperative care) in advance and may be better prepared from a psychological perspective for the challenges of the perioperative period. In contrast, the patient with a surgical emergency may have an uncertain diagnosis and uncontrolled coexisting medical disease, in addition to any physiological derangements resulting from their surgical pathological condition. In the emergency setting, preparation for theatre focusses on identifying, correcting or optimising (where possible) any major physiological abnormalities. In addition, the anaesthetist must be prepared for potential complications arising because of the nature of emergency surgery or anaesthesia. These include vomiting and regurgitation, hypovolaemia, haemorrhage, electrolyte disturbances, acute kidney injury and adverse reactions to drugs in the emergency situation.

Preoperative assessment

Thorough preoperative anaesthetic assessment of the emergency surgical patient is very important. This requires adequate and accurate preoperative evaluation of the patient's general condition, with attention to specific problems that may influence anaesthetic management. The likely surgical diagnosis and the extent and urgency of the proposed surgery must be discussed with surgical and medical colleagues preoperatively. The urgency for surgery is most helpfully conveyed using a recognised classification system, such as the one created by the National Confidential Enquiry into Patient Outcome and Death (NCEPOD) ( Table 44.1 ). The nature and urgency of the planned surgery dictate the extent of preoperative preparation and anaesthetic technique. The classification is useful in prioritising cases on the emergency list.

Table 44.1

NCEPOD classification of surgical urgency

Code	Category	Description	Target time to theatre	Expected location	Examples	Typical procedures
1	Immediate	Immediate (A) lifesaving or (B) limb- or organ-saving intervention Resuscitation simultaneous with surgical intervention	Within minutes of decision to operate	Next available operating theatre – ‘break in’ to existing lists, if required	Ruptured aortic aneurysm Major trauma to abdomen or thorax Fracture with major neurovascular deficit	Repair of ruptured aortic aneurysm Laparotomy/thoracotomy for control of haemorrhage
2	Urgent	Acute onset or deterioration of conditions that threaten life, limb or organ survival; fixation of fractures; relief of distressing symptoms	Within hours of decision to operate and normally once resuscitation complete	Daytime ‘emergency list’ or Out-of-hours emergency theatre (including at night)	Compound fracture Perforated bowel with peritonitis Critical organ or limb ischaemia Penetrating eye injury	Debridement plus fixation of fracture Laparotomy for perforation
3	Expedited	Stable patient requiring early intervention for a condition that is not an immediate threat to life, limb or organ survival	Within days of decision to operate	Elective list which has ‘spare’ capacity or Daytime emergency list (not at night)	Tendon and nerve injuries Stable and non-septic patients for wide range of surgical procedures	Repair of tendon and nerve injuries Excision of tumour with potential to bleed or obstruct
4	Elective	Surgical procedure planned or booked in advance of routine admission to hospital	Planned	Elective theatre list booked and planned before admission	Encompasses all conditions not classified as immediate, urgent or expedited	Joint arthroplasty

NCEPOD, National Confidential Enquiry into Patient Outcome and Death.

During the preoperative assessment, the history must be focused and highlight areas that are likely to influence choice of anaesthetic technique, postoperative care and any potential complications. Emergency patients may often be obtunded because of their illness, so a history may have to be elicited from various sources, such as the patient's previous notes and/or relatives or carers.

It is important to ensure that all the history taken from the patient before emergency surgery is just as thorough as for elective surgery (see Chapter 19 ) including:

medical and surgical history;
previous anaesthetic history (especially previous airway problems or admissions to ICU);
drug history (especially use of anticoagulants and antiplatelet agents);
drug allergies;
correct identification of fasting times (the same guidelines apply as for elective patients (see Chapter 22 ), though in extreme surgical emergencies the patient may need to proceed to theatre before these fasting times are achieved);
social history; and
functional history, including assessment of metabolic equivalents (METs) (see Chapter 19 ).

Depending upon the urgency of surgery, the physical examination may be targeted to identify significant cardiorespiratory dysfunction or any abnormalities that might lead to technical difficulties during anaesthesia. Valuable information about the patient's condition can also be obtained from the bedside observations chart. In particular, trends in physiological variables such as blood pressure, heart rate, respiratory rate and oxygen saturations may signal a deteriorating condition and even impending decompensation.

Cardiovascular system

Basal lung crepitations, pitting oedema and raised jugular venous pressure signify impaired ventricular function and limited cardiac reserve, which significantly increase the risks of emergency surgery and anaesthesia. It is also important to exclude arrhythmias and heart sounds indicative of valvular heart disease, as these influence the patient's response to physiological challenges and thus anaesthetic management. Any significant arrhythmias need to be identified and managed preoperatively.

Respiratory system

Assessment of respiratory function is particularly difficult, as the patient in pain (with or without peritoneal irritation) may be unable to cooperate with pulmonary function testing.

Airway

The standard clinical tests of airway assessment should be used (see Chapter 23 ) and any previous anaesthetic charts consulted if available. A history of difficult tracheal intubation is of considerable significance; however, a past record of easy tracheal intubation does not guarantee future success. In emergency anaesthesia, airway difficulties may be caused by the patient's usual anatomy but also surgical pathological conditions such as dental abscesses, trauma, bleeding or haematoma. If RSI is contemplated, then contingency plans are required for management of the patient in the event of failure to intubate the trachea. If a high degree of difficulty in tracheal intubation is anticipated, then an awake technique may be necessary (see Chapter 23 ).

The final stage of the preoperative assessment is to review any relevant laboratory investigations, including ECG, blood tests, radiological imaging and arterial blood gases where appropriate. The guidelines for preoperative investigations in the elective setting (see Chapter 19 ) should be viewed as the minimum requirements, with most emergency patients routinely requiring additional tests depending on their underlying pathological condition and physiological status. The availability of blood products should be checked if necessary and urgent requests should be made for any additional tests which may influence patient management.

Assessment of circulating volume

Assessment of intravascular volume is essential, as underestimated or unrecognised hypovolaemia may lead to circulatory collapse during induction of anaesthesia, which attenuates the sympathetically mediated increases in arteriolar and venous constriction as well as reducing cardiac output. In any patient in whom fluid is sequestered or lost (e.g. peritonitis, bowel obstruction) or in whom haemorrhage has occurred (e.g. ectopic pregnancy), the anaesthetist should try to quantify the circulating blood and extracellular fluid volumes and correct any deficits.

Intravascular volume deficit

Blood loss may be assessed using the patient's history and any measured losses, but more commonly the anaesthetist must rely on clinical evaluation of the patient's current cardiovascular status. Profound circulatory shock with hypotension, poor peripheral perfusion, oliguria and altered cerebration is easy to recognise. However, a more careful assessment is needed to recognise the early manifestations of haemorrhage, such as tachycardia and cutaneous vasoconstriction. Useful indices include heart rate, blood pressure (especially pulse pressure), the state of the peripheral circulation, pyrexia and urine output. In young, healthy adults, arterial pressure may be an unreliable guide to volume status because compensatory mechanisms can prevent a measurable decrease in arterial pressure until more than 30% of the patient's blood volume has been lost. In such patients, attention should be directed to pulse rate, skin circulation and a narrowing pulse pressure. In elderly patients with widespread arterial disease, limited cardiac reserve and a rigid vascular tree (fixed total peripheral resistance), signs of severe hypovolaemia may become evident when blood volume has been reduced by as little as 15%. However, as baroreceptor sensitivity decreases with age, elderly patients may exhibit less tachycardia for any degree of volume depletion.

Although clinical evaluation remains the most important and most commonly used guide to intravascular volume management, non-invasive and minimally invasive methods of cardiac output measurement can be used (see Chapters 17 and 30 ). These techniques may be of particular benefit in guiding the immediate resuscitation of frail or critically ill patients in theatre.

Extracellular volume deficit

Assessment of extracellular fluid volume deficit is difficult. Guidance may be obtained from the nature of the surgical condition, duration of impaired fluid intake and presence and severity of symptoms associated with abnormal losses (e.g. vomiting). At the time of the earliest radiological evidence of intestinal obstruction, there may be 1500 ml of fluid sequestered in the bowel lumen (so-called ‘third space losses’). If the obstruction is well established and vomiting has occurred, the extracellular fluid deficit may exceed 3000 ml. Table 44.2 describes some of the clinical features seen with varying degrees of severity of extracellular fluid losses. Considerable fluid losses must occur before clinical signs are apparent, and these signs are often subjective in more minor degrees of extracellular fluid deficit. In addition to clinical signs, laboratory investigations may also indicate extracellular fluid volume deficit. Haemoconcentration results in increased haemoglobin concentration and packed cell volume. As dehydration becomes more marked, renal blood flow diminishes, reducing renal clearance of urea and consequently increasing the blood urea concentration. Patients with moderate volume contraction exhibit a ‘prerenal’ pattern of uraemia characterised by an increase in blood urea out of proportion to any increase in serum creatinine concentration. Under maximal stimulation from antidiuretic hormone (ADH) and aldosterone, conservation of sodium and water by the kidneys results in excretion of urine of low sodium concentration (0–15 mmol L ^–1 ) and high osmolality (800–1400 mosmol kg ^–1 ).

Table 44.2

Clinical signs of the extent of extracellular fluid deficit

Body weight lost as water	Fluid lost (ml kg ^–1 )	Signs and symptoms
4%–6% (mild)	>35	Thirst Reduced skin elasticity Decreased intraocular pressure Dry tongue Reduced sweating
6%–8% (mild)	>70	As above, plus: Orthostatic hypotension Reduced filling of peripheral veins Oliguria Apathy Haemoconcentration
8%–10% (moderate)	>80	As above, plus: Hypotension Thready pulse with cool peripheries
10%–15% (severe)	100–150	Coma, shock followed by death

Once the extent of blood volume or extracellular fluid volume loss has been estimated, deficits should be corrected with the appropriate intravenous fluid. The overall priority is to maintain adequate tissue perfusion and oxygenation; therefore correction of intravascular deficit takes precedence. Hypovolaemia as a result of blood loss should be treated with a balanced crystalloid solution (such as Hartmann's solution) until packed red cells (PRCs) are available (see Chapter 12 ). Resuscitation is usually guided by clinical indices of circulating volume status and organ perfusion. High-risk surgical patients undergoing major surgery may benefit from the use of (non-invasive) cardiac output measuring devices to direct fluid resuscitation towards predetermined goals for cardiac output and systemic oxygen delivery (goal-directed therapy; see Chapter 30 ). Extracellular fluid deficit is usually corrected after the correction of any intravascular deficit, by adjusting maintenance fluid infusion rates. Losses from vomiting or gastric aspirates are best replaced by crystalloid solutions containing an appropriate potassium supplement. Hartmann's solution is often used, although hypochloraemia is an indication for saline 0.9% (with additional potassium). Lower GI losses, such as those caused by diarrhoea or intestinal obstruction, are normally replaced volume for volume with Hartmann's solution.

The full stomach

Vomiting or regurgitation of gastric contents, followed by aspiration into the tracheobronchial tree whilst protective laryngeal reflexes are obtunded, is one of the most common and most devastating hazards of emergency anaesthesia. Vomiting is an active process that occurs in the lighter planes of anaesthesia. Consequently, it is a potential problem during induction of, or emergence from, anaesthesia but should not occur during maintenance if anaesthesia is sufficiently deep. In light planes of anaesthesia, the presence of vomited material above the vocal cords stimulates spasm of the cords (laryngospasm). In contrast to vomiting, regurgitation is a passive process that may occur at any time, is often ‘silent’ (i.e. not apparent to the anaesthetist) and, if aspiration occurs, may have clinical consequences ranging from minor pulmonary sequelae to fulminating aspiration pneumonitis and acute respiratory distress syndrome (ARDS). Regurgitation usually occurs in the presence of deep anaesthesia or at the onset of action of neuromuscular blocking agents (NMBAs), when protective laryngeal reflexes are absent. The most important factors determining the risk and degree of gastric regurgitation are lower oesophageal sphincter function and residual gastric volume, which itself is largely determined by the duration of fasting and rate of gastric emptying. Risk factors for vomiting and/or regurgitation during anaesthesia are shown in Box 44.1 .

Box 44.1

Situations in which vomiting or regurgitation may occur during anaesthesia

Full stomach

With absent or abnormal peristalsis

Peritonitis of any cause
Postoperative ileus
Metabolic ileus (e.g. hypokalaemia, uraemia, diabetic ketoacidosis)
Drug-induced ileus (e.g. anticholinergics or agents with anticholinergic effects)

With obstructed peristalsis

Small or large bowel obstruction
Gastric carcinoma
Pyloric stenosis

With delayed gastric emptying

Diabetic autonomic neuropathy
Fear, pain or anxiety
Late pregnancy
Opioids
Head injury

Other causes

Hiatus hernia
Oesophageal strictures – benign or malignant
Pharyngeal pouch

Lower oesophageal sphincter

The lower oesophageal sphincter (LOS) is a 2–5 cm length of oesophagus with a higher resting intraluminal pressure situated just proximal to the cardia of the stomach. The sphincter relaxes during oesophageal peristalsis to allow food into the stomach but remains contracted at other times. The structure cannot be defined anatomically but may be detected using intraluminal pressure manometry. The LOS is the main barrier preventing reflux of gastric contents into the oesophagus. Many drugs used in anaesthetic practice affect the resting tone of the LOS. Reflux is related not to the LOS tone per se, but to the difference between gastric and LOS pressures; this is termed the barrier pressure. Drugs that increase the barrier pressure (e.g. cyclizine, anticholinesterases, α-adrenergic agonists and metoclopramide) decrease the risk of reflux. Anticholinergic drugs, ethanol, tricyclic antidepressants and opioids all reduce LOS pressure, and it is reasonable to assume that these drugs increase the tendency to gastro-oesophageal reflux.

Gastric emptying

Gastric emptying results from peristaltic waves sweeping from the cardia to pylorus at a rate of approximately three per minute. The rate of gastric emptying is significantly delayed if the mixture reaching the duodenum is very acidic or hypertonic (the inhibitory enterogastric reflex), but both the nervous and humoral elements of this regulating mechanism are still poorly understood. Many pathological conditions reduce gastric emptying (see Box 44.1 ). It is important to understand that the stomach is never ‘empty’. In the absence of any of these factors, it is reasonably safe to assume that the risks of regurgitation and aspiration are minimised, provided that solids have not been ingested within the previous 6 h, with only fluids consumed up to 2 h before anaesthesia, and provided that normal peristalsis is occurring. This is the usual case for elective surgical patients. However, in emergency surgery it may be necessary to induce anaesthesia before an adequate period of starvation occurs. In addition, the patient's surgical condition is often accompanied by delayed gastric emptying or abnormalities of peristalsis. In these circumstances, even if the usual period of fasting has been observed it cannot be assumed that the risks of aspiration have been minimised.

In patients who have sustained a significant trauma injury, gastric emptying virtually ceases because of the combined effects of fear, pain, shock and treatment with opioid analgesics. In these patients the interval between ingestion of food and the injury is a more reliable index of residual stomach volume than the period of fasting observed since injury. A patient's sensation of hunger should not be used to indicate an empty stomach; sensations of hunger and satiety are complex and are unreliable indicators of stomach volume. There is currently a considerable interest in bedside ultrasonography as an objective tool in determining the volume of gastric contents, and its use may become more widespread in the coming years.

Injury from the regurgitation/aspiration of gastric contents results from three different mechanisms: chemical pneumonitis (from acid material), mechanical obstruction from particulate material and bacterial contamination. Aspiration of liquid with a pH less than 2.5 is associated with a chemical burn of the bronchial, bronchiolar and alveolar mucosa, leading to atelectasis, pulmonary oedema and reduced pulmonary compliance. Management after aspiration is discussed in Chapter 27 .

Anaesthetic techniques

It is important to recognise any patient who may have significant gastric residue and who is in danger of regurgitation (and therefore aspiration). For emergency surgical procedures, if general anaesthesia is necessary, then tracheal intubation is common practice, with an RSI routine if there is significant risk of aspiration.

Preinduction

Although it may be necessary to postpone surgery in the emergency patient to obtain investigations and resuscitate with i.v. fluids, there is usually little benefit in terms of reducing the risk of aspiration of gastric contents; the risk of aspiration must be weighed against the risk of delaying an urgent procedure. Although not completely effective, insertion of a nasogastric tube to decompress the stomach and to provide a low-pressure vent for regurgitation may be helpful. Aspiration through the tube may be useful if gastric contents are liquid, as in bowel obstruction, but is less effective when contents are solid. Cricoid force (see Chapter 23 ) is still effective at reducing regurgitation even with a nasogastric tube in situ. In patients who have any haemodynamic instability preoperatively, consider the use of invasive arterial blood pressure monitoring before induction of anaesthesia. These patients may well go on to need vasopressor infusions (e.g. metaraminol, noradrenaline) intraoperatively and so placing a CVC should be considered either before the patient is anaesthetised or, more commonly, immediately after induction.

Induction

The conduct of RSI is discussed in detail in Chapter 23 , and this is the technique used most often for the patient with a full stomach. One of the main disadvantages of the RSI technique is the haemodynamic instability that may result if the dose of induction agent is excessive (hypotension, circulatory collapse) or inadequate (hypertension, tachycardia).

Thiopental has long been regarded as the i.v. induction agent of choice for RSI. It provides a rapid loss of consciousness with a clearly defined endpoint. A dose of 4–5 mg kg ^–1 can reliably be predicted to be sufficient for healthy young patients, but much less (1.5–2 mg kg ^–1 ) is required in the older, frail or hypovolaemic patient. In the critically ill patient with a metabolic acidaemia, the unbound fraction of the drug is increased, and this will reduce dose requirements. Ketamine (1–2 mg kg ^–1 ) has a slower speed of onset and poorly defined endpoint compared with thiopental. However, it causes the least cardiovascular depression of any induction agent and has now become the agent of choice in severely shocked patients. In comparison, propofol 2–5 mg kg ^–1 causes greater suppression of laryngeal reflexes and may be more familiar to junior anaesthetists because of its everyday use in anaesthesia for elective procedures. However, propofol causes more cardiovascular depression than thiopental and ketamine and should be used with caution in the emergency setting. Intravenous anaesthetic agents are detailed in Chapter 4 .

Opioids are often injected along with intravenous anaesthetics at induction of anaesthesia for elective surgery, but ‘classical’ teaching was that they should be omitted during RSI despite their potential benefits. This was largely because of concerns about delaying the onset of spontaneous respiration in the event of failed tracheal intubation. However, shorter-acting drugs such as alfentanil are now widely used as part of an RSI to reduce induction agent doses and to help obtund the sympathetic response to laryngoscopy, particularly in conditions such as pre-eclampsia (see Chapter 43 ) or traumatic brain injury (see Chapter 40 ).

Inhalational induction

If there is reasonable doubt about the ability to perform successful tracheal intubation or to maintain a patent airway in a patient with a full stomach (e.g. the patient with facial trauma, epiglottitis or bleeding tonsil), an inhalational induction may be used with oxygen and sevoflurane. When the patient has reached a deep plane of anaesthesia, laryngoscopy is performed followed by an attempt at tracheal intubation during spontaneous ventilation. Traditionally the patient was placed in the left lateral, head-down position, but current practice favours sitting the patient up and using cricoid force. When anaesthesia is sufficiently deep, a rapid-onset NMBA is injected and the trachea intubated. This technique may be used in any older, frail patients who may not tolerate i.v. induction agents.

Awake fibreoptic intubation

Tracheal intubation with a fibreoptic intubating laryngoscope is often the preferred technique in those patients who are likely to develop refractory airway obstruction when loss of consciousness occurs (e.g. trismus from dental abscess) or who are known or suspected to pose difficulties with tracheal intubation. The procedure is discussed in detail in Chapter 23 .

Regional anaesthesia

The use of regional anaesthesia is increasing in the UK, partly because of the growth in the practice of ultrasound-guided regional anaesthetic techniques. Many regional techniques are ideal for emergency procedures on the extremities (e.g. to reduce fractures or dislocations) and are discussed in detail in Chapter 25 . Brachial plexus block by the axillary, supraclavicular or interscalene approach works well for orthopaedic manipulations or surgical procedures involving the upper extremity. It satisfies surgical requirements for analgesia, muscle relaxation and immobility. There are minimal effects on the cardiovascular system, and there is a prolonged period of analgesia postoperatively. For regional anaesthesia of the lower extremity, available techniques include subarachnoid, epidural and sciatic/femoral blocks. Spinal and epidural blocks are contraindicated if there is doubt about the adequacy of extracellular fluid or vascular volumes, as large decreases in arterial pressure may result from the associated pharmacological sympathectomy.

It is a common surgical misconception that subarachnoid or epidural anaesthetic techniques are safer than general anaesthesia for patients in poor physical condition. It must be emphasised that for the inexperienced anaesthetist, these techniques are invariably more dangerous than general anaesthesia for the patient with moderate to major trauma or any intra-abdominal emergency condition.

Maintenance of anaesthesia

If RSI has been performed, the patient's lungs are gently ventilated manually whilst heart rate and blood pressure measurements are repeated to assess the cardiovascular effects of the drugs used and of the stimulus of tracheal intubation. Capnography is essential throughout anaesthesia and gives valuable information about perfusion and ventilation of the lungs. When there is evidence of return of neuromuscular transmission (by clinical signs or from a nerve stimulator) as suxamethonium is degraded, a non-depolarising NMBA is administered. The choice depends on the patient's condition and the effect of the induction of anaesthesia on the patient's cardiovascular status. Both rocuronium and atracurium are appropriate drugs for routine use, although the pharmacokinetics of atracurium make it the logical choice for the older patient. Atracurium has virtually no cardiovascular effects in clinical doses and is useful if there is any doubt about renal function.

After induction of anaesthesia, the tracheal tube is connected to a mechanical ventilator and minute volume adjusted to produce normocapnia. Ventilators are now increasingly sophisticated and incorporate a choice of ventilation modes. The choice is usually between pressure- or volume-controlled ventilation. It can be difficult to predict ventilator requirements, but initial settings should aim to produce a tidal volume of 6–8 ml kg ^–1 . The inspiratory flow rate should be adjusted to minimise peak airway pressure (target < 30 cmH ₂ O), and the capnograph waveform and pressure volume loops should be inspected regularly to guide the further adjustment of ventilator settings. Maintenance of core temperature is a very important aspect of intraoperative management; core temperature should be monitored throughout the procedure and hypothermia avoided whenever possible (see Chapter 13 ).

Before the initial surgical incision is made, analgesia may be supplemented by incremental i.v. doses of opioids. It is important to be familiar with the pharmacokinetics and pharmacodynamics of all agents used and to be aware that these may change during emergency anaesthesia, when acute circulatory changes or impaired organ function often occur.

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