Identifying at risk patients

In this section you will cover four questions. Which of my patients: 

  • might predictably be difficult to ventilate?
  • might predictably desaturate?
  • are more likely to regurgitate and potentially aspirate?
  • might predictably drop their blood pressure?

Pre-procedural airway evaluation is vital in order to address the first question. Table 3 lists several factors that may be associated with difficulty in airway management. A single factor in isolation may not be significant, but two or more should prompt you to reconsider your strategy.

You may find the simple pneumonic BOOTS helpful:

  • Beard
  • Obese
  • Older patient
  • Toothless
  • Snores?

Learning Bite:

In your preparation for conscious sedation always ask yourself whether you are confident you can ventilate the patient using a bag and mask

Fasting is not needed for minimal sedation, sedation with nitrous oxide/ oxygen mixtures alone, or moderate sedation where verbal contact is maintained.For an emergency procedure in someone who is not fasted, base the decision to proceed with sedation on the urgency of the procedure and the target depth of sedation. The joint RCoA/RCEM report2 recommends that careful judgement is required when assessing the risk of aspiration in relation to the urgency of a proposed procedure. The key factors to consider are:

  • The urgency of the proposed procedure. In many life or limb threatening situations (e.g. cardioversion of a cardiac arrhythmia causing significant cardiovascular compromise, or an orthopaedic procedure to correct distal limb ischaemia) the patient is unable to wait and the main question becomes the choice of sedation/anaesthetic technique rather than the possibility of deferment.
  • The proposed depth and duration of sedation. Longer periods of sedation, greater sedation depth and airway interventions may stimulate airway reflexes (coughing, hiccoughs or laryngospasm) and gastro-intestinal motor responses (gagging or recurrent swallowing) leading to gastric distension, regurgitation or vomiting.
  • Patient factors – conditions such as raised intracranial pressure, hiatus hernia and gastrointestinal obstruction are known to delay gastric emptying, and these patients may be at greater risk. Gastric emptying may also be delayed in patients who have previously undergone upper gastrointestinal surgery, in those recently injured or receiving opioids, and in pregnancy. Morbidly obese patients may be at risk, because the intra-abdominal pressure is higher and the incidence of hiatus hernia is greater than in non-obese patients. The timing of food intake in relation to the injuries also important.

For those un-starved patients needing deeper levels of sedation (for prosthetic hip relocation for example), ensure pre-oxygenation is maximised and consider employing apnoeic oxygenation* so as to minimise the need for bag-valve-mask ventilation (which when delivered may insufflate the stomach and increase the likelihood of regurgitation).More recently, American College of Emergency Physicians policy 2014 on procedural sedation5 makes the following level B** recommendation: do not delay procedural sedation in adults or paediatrics in the ED based on fasting time. Pre-procedural fasting for any duration has not demonstrated the reduction in the risk of aspiration when administering procedural sedation and analgesia.

*Apnoeic oxygenation – high flow oxygen delivered via nasal prongs once sedated – This is covered in a proposed RCEM learning module – Advanced Procedural Sedation.

**Level B recommendation – based on evidence from one of more class of evidence II studies or strong consensus of class of evidence III studies.

Learning Bite

Before proceeding with sedation of an unstarved patient a senior emergency physician with level 2 sedation training (see section 6) should be present.

The American Society of Anaesthesiologists classification (table 1) is widely used to describe the physical status of patients. Sensibly employed it should help you identify those patients who might become hypoxic (question 2) or hypotensive (question 4). You may wish to consult with senior anaesthetic colleagues regarding those patients classified as III or higher. Neurological conditions, notably myasthenia gravis and cerebral palsy, are worthy of special mention as patients with these conditions may be more sensitive to sedative agents, as are the elderly in general.

Table 3: Airway assessment procedures for sedation and analgesia
History:

Previous problems with anaesthesia or sedation (look in the hospital and ED records if possible)

Stridor, snoring or sleep apnoea

Advanced rheumatoid arthritis

Chromosomal abnormality (e.g. trisomy 21)

Physical Examination:

Habitus

Significant obesity (especially involving the neck and facial structure)

Head and neck

Short neck, limited neck extension, decreased hyoid-mental distance (<3cm in an adult),

neck mass, cervical spine disease or trauma, tracheal deviation, dysmorphic facial features

(e.g. Pierre-Robin syndrome), excessive facial hair

Mouth

Small opening (<3cm in an adult, edentulous, protruding incisors, high arched palate, macroglossia, tonsillar hypertrophy and nonvisibule uvula)

Jaw

Micrognathia, retrognathia, trismus and significant malocclusion

Table 1: American Society of Anesthesiologists Physical Status Classification
Class Description Examples
I Normal, healthy patient
II Mild systemic disease Asthma, controlled diabetes
III Moderate systemic disease Stable angina, diabetes with hyperglycaemia, moderate chronic obstructive pulmonary disease
IV Severe systemic disease Unstable angina, diabetic ketoacidosis
V Moribund
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