Prehospital anaesthesia is fundamentally different from planned anaesthesia in the operating theatre. In the prehospital setting such as the air ambulance, it becomes an emergency and an unplanned procedure, as the patient's medical history is often unknown, and it is assumed that the patient is not fasting. Acute hypoxia or hypovolemia is common in this patient clientele and requires special care in the choice of anaesthesia.
The spatial conditions in the patient's home environment, in public spaces, as well as in the ambulance, helicopter, or air ambulance are problematic and incomparable to those in the operating theatre. This poses a challenge to the attending physician, as well as the supporting staff, who are trained inconsistently, depending on the country. For this reason, comprehensive exercise of the team with simulator-based training is essential.
In order to perform prehospital anaesthesia safely, the colleagues involved need not only sound knowledge of the physiology and pathophysiology of emergency anaesthesia, but also of team leadership, decision-making and other factors of communication, the so-called "soft skills".
Jörn Adler is the Medical Supervisor at Luxemborg Air Rescue in Luxembourg
To discuss all these aspects, the author of this article has searched the international literature and compiled the results. Various aspects of the Canadian, English and German guidelines for prehospital anaesthesia are discussed as examples:
Aspect Crew Resource Management
The above-mentioned peculiarities, such as time pressure, difficult general conditions, non-fasting and unstable patients are factors that lead us to expect an increased rate of difficult intubations. Therefore, it seems more important to create standard conditions, if possible, and to establish a standardised procedure. An airway algorithm and checklists can help to increase safety here.
First team time-out or the “10 for 10”
This refers to a "10-second break to plan the next 10 minutes”. Once the indication for induction of anaesthesia and intubation has been established, it must now be communicated within the team — why anaesthesia is necessary, where it will be performed, how will it prepared, and what tasks will be assigned to the team members. The preparation time should be used for preoxygenation.
Goal: Optimisation of the framework conditions
Despite the time pressure during emergency intubation, standard conditions should be established whenever possible. Conditions are always better in a well-lit ambulance than on the street or in the patient's bathroom, for example.
In any case, minimum requirements should be warranted, The suction unit should be easily accessible and its functionality checked; a safe, or better two well-running venous accesses should be established, standard monitoring with SpO2, ECG, non-invasive blood pressure measurement and capnometry should be available and ventilation with increased FiO2 should be possible.
The patient should be positioned optimally in an improved Jackson position. If injuries to the cervical spine are suspected, manipulations of the cervical spine should be avoided or minimised. Under manual inline fixation, these patients can be gently intubated with the aid of the hyper angulated blade of the video laryngoscope. In obese patients, it may be helpful to elevate the entire upper body (ramped position).
The best possible preoxygenation of the patient also increases the window of opportunity for action in the rescue service, should the airway unexpectedly appear difficult. The aim of preoxygenation is denitrogenating, i.e., replacing the nitrogen component of the functional residual capacity (FRC) with oxygen to create an intrapulmonary oxygen reservoir.
Medication for induction of anaesthesia
A potent fast-acting analgesic, a suitable hypnotic and a fast-acting muscle relaxant are needed for the induction of anaesthesia. An essential prerequisite for low-risk intubation is ensuring sufficient depth of anaesthesia. Insufficient depth of anaesthesia is the most common cause of difficult intubation and significantly increases the risk of vomiting and aspiration.
For certain patients, too shallow anaesthesia is also dangerous for other reasons. For example, all patients at risk of increased intracranial pressure such as traumatic brain injury (SHT) or intracranial haemorrhage (ICB) may develop coughing, pushing and other defensive reactions during intubation, which can have a devastating effect. It is often forgotten that the unconscious patient does not necessarily imply the absence of reflex. Deep anaesthesia is needed for these cases.
On the other hand, deep anaesthesia is associated with a high risk of further haemodynamic deterioration, especially in the presence of cardiocirculatory instability and hypovolemia.
Clear recommendations for certain substances or even fixed dosages are not possible due to the interindividual differences of the patients.
The German guideline "Preclinical emergency anaesthesia" (14) suggests various protocols for typical preclinical situations as:
- Isolated traumatic brain injury, stroke and intracranial haemorrhage
- Hypertensive pulmonary edema, hypoxia and NIV failure
- Cardiogenic shock, hypotension and hypoxia
- Respiratory insufficiency
- Trauma: hypovolemia
Second team time-out
Pre Rapid Sequence Induction check involves the following — are all preparations completed? Who injects the drugs? Who hands over the materials for intubation? How will the procedure be communicated? Who will cater to questions from the team?
Implementation of the RSI
After completing the monitoring and securing two venous accesses, if possible, the completeness of the required material should be checked. This includes an operational video laryngoscope with Macintosh and hyper-angulated blades, an endotracheal tube with a guide, stylet and/or bougie, material for fixation of the tube, a running suction pump, a resuscitation bag with mask, capnography, and a stethoscope.
The planned fallback levels for the difficult airway must be ready: Laryngeal mask / laryngeal tube (Plan B) and the coniotomy set (Plan C). After the rapid injection of the analgesic, the hypnotic (in reverse order only in the case of ketamine) and the muscle relaxant, intermediate should be suspended in adult RSI. However, if the SpO2 is poor or cannot be measured, the patient must be ventilated carefully until the drugs take effect.
Capnography is indispensable and required in 100 per cent of all emergency anaesthesia. Specially under difficult conditions, the immediate detection of a false intubation by means of capnometry is lifesaving for the patient.
Managing difficult airways
The difficult airway is not the subject of this lecture but should be briefly addressed since the induction of anaesthesia and airway management belong together. Difficult airway describes a situation in which endotracheal intubation does not succeed without problems.
The various guidelines differ in their approach — but in summary, the principles are similar. In any case, there should be a fallback level. It is also highly emphasised that securing the airway by means of an endotracheal tube is not paramount in all cases, but much rather the oxygenation of the patient. Here is a synthesis of different guidelines:
The German guideline emergency anaesthesia recommends using the video laryngoscope if available. The non-experienced user (less than 100 intubations under the supervision of a specialist and after that min. 10 intubations per year) should primarily use a video laryngoscope with a Macintosh-like blade. The experienced user should use a hyper-angulated blade.
If intubation is not successful, the first step is to ensure oxygenation. A step-by-step approach is recommended.
Step 1: Mask ventilation, ideally using a double C-grip or double manual bale handle.
Step 2: A second intubation attempt may be useful if conditions can be optimised. This may mean deepening the anaesthesia, optimising positioning, improving relaxation or using a different blade or blade size. It may also include an external laryngeal manoeuvre such as the BURP (Backward-Upward-Rightward-Pressure) manoeuvre. It should be noted that repeated intubation attempts without optimisation of the situation by the same person are not useful and endanger the patient.
Step 3: If intubation is still not successful, the procedure must be changed. The next stage of relapse is supraglottic airway devices such as the laryngeal mask (LM) or the laryngeal tube (LT). Only LM and LT of the second generation should be used.
Step 4: If this is unsuccessful or if the patient cannot be intubated or ventilated in the "Cannot Ventilate, Cannot Intubate” (CVCI) situation, surgical access to the airway is
unavoidable as the last option. In an emergency, access is as a coniotomy via the opening of the cricothyroid ligament.
References available on request.
Jörn Adler is the Medical Supervisor at Luxemborg Air Rescue in Luxembourg. He will be speaking at the Anaesthesia & Pain Management conference at Arab Health 2023.