Emergency Anaesthesia
PREOPERATIVE ASSESSMENT
During the preoperative visit a past medical and drug history is elicited. In particular, the patient’s degree of cardiorespiratory reserve should be established, even if there is no formal diagnosis of cardiovascular or respiratory disease. The presence and severity of symptoms suggestive of reduced reserve such as angina, productive cough, orthopnoea or paroxysmal nocturnal dyspnoea should be sought. The patient’s functional capacity is of useful prognostic value and can be simply quantified in terms of metabolic equivalents (METs). 1 MET is a unit of resting oxygen consumption and appropriate questioning can allow an estimate of the patient’s maximal oxygen consumption capacity (VO2 max) (Table 37.2 and Ch 18 [Table 18.1]). A patient who is unable to perform activity at 4 METs or more is at increased risk of perioperative cardiac complications.
TABLE 37.2
MET Score | Approximate Level of Activity |
1 | Dress, walk indoors |
2 | Light housework, slow walk |
4 | Climb one flight of stairs |
6 | Moderate sport eg golf or dancing |
10 | Strenuous sport or exercise |
Assessment of Circulating Volume
Extracellular Volume Deficit
TABLE 37.4
Indices of Extent of Loss of Extracellular Fluid
Percentage Body Weight Lost as Water | mL of Fluid Lost per 70 kg | Signs and Symptoms |
Over 4% (mild) | Over 2500 | Thirst, reduced skin elasticity, decreased intraocular pressure, dry tongue, reduced sweating |
Over 6% (mild) | Over 4200 | As above, plus orthostatic hypotension, reduced filling of peripheral veins, oliguria, low CVP, apathy, haemoconcentration |
Over 8% (moderate) | Over 5600 | As above, plus hypotension, thready pulse with cool peripheries |
10–15% (severe) | 7000–10 500 | Coma, shock followed by death |
THE FULL STOMACH
Gastric Emptying
TABLE 37.5
Situations in Which Vomiting or Regurgitation May Occur
Full stomach
With absent or abnormal peristalsis
Peritonitis of any cause
Postoperative ileus
Metabolic ileus: hypokalaemia, uraemia, diabetic ketoacidosis
Drug-induced ileus: anticholinergics, those with anticholinergic side-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
TECHNIQUES OF ANAESTHESIA
Phase I – Preparation
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 pressure is still effective at reducing regurgitation even with a nasogastric tube in situ.
Clear oral antacids (e.g. sodium citrate) may be used to raise the pH of gastric contents immediately before induction. However, this also increases gastric volume. Particulate antacids should not be used, as they may be very damaging to the airway if aspirated. The preoperative administration of H2-receptor antagonists consistently raises gastric pH and may reduce the chance of chemical pulmonary injury occurring in the event of inhalation. Although this is standard practice in obstetric anaesthesia, few anaesthetists employ these measures for emergency general surgery. The regimens available are described in Chapter 35.