, Amy Gospel2, Andrew Griffiths3 and Jeremy Henning4
(1)
Intensive Care Unit, James Cook University Hospital, Middlesbrough, UK
(2)
Tyne and Wear, UK
(3)
The York Hospital, Middlesbrough, UK
(4)
James Cook University Hospital, Middlesbrough, UK
By the end of this chapter you should:
Know the indications and contraindications for pre-hospital anaesthesia (PHA)
Understand the significance of aspiration
Appreciate the risks and benefits of PHA
Know the factors to consider before undertaking PHA
The decision to escalate airway management from basic to advanced is not always clear-cut. The primary aim must always be to maintain reliable airway patency and ensure adequate oxygenation and ventilation in order to prevent hypoxia and hypercarbia. The airway is also at risk from aspiration or soiling from upper airway debris if the laryngeal reflexes are incompetent or rendered ineffective by drugs. In these cases, or if clear indications exist, consideration should be given to endotracheal intubation (Boxes 2.1 and 2.2).
Box 2.1: Indications for PHA
To Maintain reliable airway patency
Ventilatory insufficiency –
SpO2 <92 % despite O2 or impending respiratory collapse due to exhaustion.
To control PaCO2 when raised ICP is a concern
Preventing Aspiration – Loss of airway reflexes/Glasgow coma scale (GCS) rapidly falling or <9.
Patients requiring repeated sedation for safe management – they present a danger to themselves or attending staff
Humanitarian reasons – Severe injuries/pain unlikely to be relieved without excessive doses of opioid.
Box 2.2: Contraindications to PHA
Inexperienced team or inadequate equipment
Known anaphylaxis to one of the drugs required for intubation (although there may be an alternative).
Patient anatomy or airway swelling/distortion – making successful intubation unlikely (Rapid transfer to hospital is preferred; cricothyroidotomy under local anaesthesia may be the safest technique if respiratory failure develops)
Croup or epiglottitis – failed intubation attempts may leave a critical situation – adrenaline (epinephrine) nebulisers and rapid transfer to hospital preferred.
2.1 Significance of Aspiration
Many patients with a reduced GCS are intubated to ‘protect their airway’. The aim is to remove the potential for aspiration in someone who has lost their airway reflexes. The significance of aspiration in the pre-hospital environment is unclear. The risk of aspiration is dependent on both the absence of effective airway reflexes and the presence of something to aspirate (e.g. blood or gastric contents). Death due to aspiration usually occurs in two ways: Large aspirates may cause upper or lower airway obstruction and asphyxiation. Smaller volumes may lead to early hypoxia with subsequent brain death or multiorgan failure. Small aspirates may also cause pneumonia or pneumonitis, with death secondary to sepsis or acute respiratory distress syndrome (ARDS).
2.1.1 Incidence, Morbidity and Mortality of Aspiration
The incidence of aspiration in non-survivors from trauma has been reported to be up to 55 % (where aspiration was defined as the presence of blood, vomit or other material in the upper respiratory tract at post-mortem) (Yates 1977). Ottosson (1985) noted that 20 % of road traffic fatalities had evidence of aspiration, however, it was suggested that the aspiration did not alter the final outcome, as all victims except one had virtually unsurvivable injuries. McNicholl (1994) looked at 239 patients who sustained major trauma (injury severity score >15) and reached hospital alive. Fifteen patients (6 %) aspirated; all before ambulance arrival, and all subsequently died. All of these patients had either severe brain injury or were considered unsalvageable.
So, although Yates’ study could suggest that aspiration may be a major contributor to trauma deaths, other studies suggest it is simply a marker of injury severity and an indicator of poor outcome (i.e. more severely injured patients, who are more likely to die, are more prone to aspiration).
In one study of intubation, the incidence of aspiration in those intubated on scene was shown to be significantly greater (50 % vs. 22 %) compared with those intubated in the Emergency department (ED) (Ufberg et al. 2005). As paramedics tend to only intubate those with very low GCS pre-hospital, this may simply confirm that those who are most severely injured are likely to have aspirated by the time a pre-hospital team arrives. This appears to be supported by Lockey et al (2013), who presented a series of 400 patients intubated by a physician led pre-hospital trauma team in London. They found that 177 patients (44 %) had gross airway contamination at the time of intubation. Patients with GCS 3–8 were significantly more likely to have a contaminated airway (57 %) compared with patients of GCS 9–15 (34 %). The contamination was predominantly from upper airway blood (78 %) rather than gastric content and much of this may have appeared in the oropharynx during induction, secondary to ongoing bleeding in facial injuries. Vadeboncoeur et al (2006) noted that aspiration had occurred in 72/269 (27 %) of head-injured patients with GCS <9, prior to intubation. There was only one reported case of aspiration during intubation.
It should now be appreciated that strong pre-hospital evidence to recommend intubation as a means to prevent aspiration and reduce mortality does not exist and that aspiration is likely to have already occurred in the majority of those at risk.
There will be a number of patients, however, whose GCS may be deteriorating (combined with a reduction in protective airway reflexes) and who may become at risk of aspiration during transfer due to the presence of blood from facial trauma or regurgitation of gastric contents. In these patients the following statistics should be considered: Perioperative aspiration is associated with around 4 % mortality (Kluger and Short 1999; Warmer et al. 1993), and patients who aspirate have a longer Intensive Care Unit stay and poorer neurological outcome (Bronchard et al. 2004) when compared with those that do not, despite comparable injuries.
Given this information, it would seem reasonable to try and prevent aspiration where possible.
2.2 Laryngeal Mask Airway (LMA) vs. Endotracheal Tube (ETT)
In patients who have evidence of airway soiling, the majority of debris originates from the mouth or nose, with a low incidence of soiling from gastric contents (McNicholl 1994; Lockey et al. 1999, 2013). This suggests that a laryngeal mask airway (LMA), which provides some protection from soiling from above, may provide reasonable protection in the majority. It will certainly provide more airway protection than when ventilating with only a bag-valve-mask (BVM). It should be remembered, however, that the act of inserting an LMA without prior administration of drugs may provoke vomiting or regurgitation. As a rule, if the level of consciousness has allowed the placement of an oropharyngeal airway, an LMA will usually be tolerated.
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