Prehospital airway management- what is the gold standard?
by Dr Minh Le Cong
Peer reviewed by Dr Seth Trueger ( see end section for his helpful comments!)
Whilst this may seem a surprising area to be considered controversial, the reader should try to answer a simple question first before proceeding.
“What are the sentinel studies demonstrating a clear benefit in prehospital intubation and/or rapid sequence induction of anaesthesia for the trauma patient or the critically ill patient?”
Unfortunately this question cannot be simply answered as such studies do not exist. Some readers may argue that there is no point in trying to answer this question as tracheal intubation and rapid sequence induction are considered standard of care in hospital settings for critically ill and injured patients. Therefore the logic demands that if its good enough in hospital, so be it for prehospital settings. Many attempts to prove this in research have failed to demonstrate a clear benefit for trauma patients. In the traumatic head injury group, some studies demonstrate an advantage to prehospital intubation but many studies do not as well. The Paramedic MICA RSI trial in Victoria, Australia was one randomised controlled trial(4) examining the benefit of rapid sequence induction and intubation for head injured patients. At 6 month outcome, there was a barely significant advantage in neurologic condition in the prehospital RSI group. Unfortunately there was a significant increase in cardiac arrests in the prehospital RSI group, albeit no overall increase in mortality between control and treatment groups. The other RCT trial was in a paediatric population, and tracheal intubation without use of drugs was performed by paramedics who had limited training(5). This failed to demonstrate any benefit to prehospital intubation compared to bag/valve face mask ventilation.
Along the way in this debate has been the line of argument that only doctors should be performing prehospital RSI as allegedly paramedics do not have enough experience to do this safely. Certainly published research out of Europe and UK have demonstrated a much higher claimed success rate for prehospital RSI with little complications when performed by senior prehospital doctors compared with paramedics. The San Diego RSI trial added more cold water into the argument in favour of prehospital RSI by demonstrating a clear survival disadvantage for head injured patients undergoing paramedic led prehospital RSI. Careflight NSW Head Injury Retrieval Trial has been collecting randomised data examining this issue of the benefit of prehospital RSI by a helicopter borne critical care physician in the head injured patient compared to paramedic led road ambulance care. The HIRT trial began in 2005 and concluded in 2012. It was the largest RCT trial of its type in the world and failed to shed important information into this controversial area. There were no significant differences in mortality and neurologic outcomes between physician led care including prehospital RSI and road based paramedic care.
So where does the truth lie for prehospital airway management? The evidence suggests that the experience and training of the prehospital provider performing RSI and intubation does make a difference in minimising complications. Therefore regardless of the background of the retrieval provider, it seems common sense looking at the evidence to ensure they have adequate initial training and ongoing maintenance of their airway and anaesthetic skills. What this means in real terms is difficult to say as once again the evidence base into this area of “sufficient airway training and ongoing skills maintenance” is scant. One study out of the London HEMS retrieval service indicates that at least 6 months of formal hospital anaesthetics training is required to achieve a sufficiently high intubation success rate(6). Other published articles stipulate a minimum of at least one retrieval intubation per month to maintain skills or an initial successful completion of 57 intubations to achieve a intubation success rate of greater than 90%. It is the author’s opinion that prehospital RSI should be beneficial in most critically ill and injured patients when performed by providers who are experienced and maintain high level of skills maintenance and case volume. To become good at prehospital RSI you probably need to be doing it at least several times a week, with a well-rehearsed prehospital team/assistant , working from a well-trained standard operating procedure with a standard setup of drugs , monitoring and airway equipment. If you work in a retrieval service that does not provide sufficient volume of prehospital RSI cases, then unless you are maintaining your airway skills elsewhere such as hospital work, you are likely to suffer significant airway deskilling to the point of becoming substandard competency within a short period of time. Whilst your emergency airway skills will never reduce to the level of a novice, it seems fool hardy thinking to assume you will be as competent as a provider who is performing prehospital RSI 3-4 times more often than you are! Sports and human factors research clearly demonstrates this.
The obvious alternative question to consider in this topic is whether tracheal intubation is absolutely necessary for all critically ill and injured patients? Certainly the cardiac arrest research in the last 10 years has demonstrated consistently worse outcomes in arrested patients who were intubated compared with controls. The latest international resuscitation guidelines stipulate that a laryngeal mask airway is considered an advanced airway equal to a cuffed tracheal tube for the purposes of advanced life support. This issue has received virtually no attention in the anaesthetic or critical care research field apart from some case reports in the use of laryngeal mask airway for transport ventilation of neonates and in the failed intubation scenario for a trauma patient on retrieval. The author has published a prehospital intubation audit in which 3 cases of failed intubation were all successfully managed and transported using a laryngeal mask airway. Uncuffed paediatric tracheal tubes are in many services still considered standard of care for emergency intubation but what they offer for airway protection compared to the laryngeal mask airway, in particular the older Proseals or newer paediatric LMA Supremes, both with gastric drainage ports, is difficult to say and indeed prove. May there come a day in retrieval medicine whereby the paradigm in airway management has shifted to a focus on oxygenation instead of intubation, using RSI to insert primarily a supraglottic airway device such as a LMA and if oxygenation and ventilation are adequate then transporting with said device in situ?
An unsettlingly controversial topic in emergency anaesthetic and airway management circles for some time now has been the use of cricoid pressure during rapid sequence induction and intubation. Since 1961 when Dr Sellick reported his case series of cricoid pressure use in parturients to prevent gastric regurgitation, there has been only a handful of trials and articles purporting to examine the same issue. Surprisingly there have been little positive benefits demonstrated in reducing regurgitation and pulmonary aspiration events by applying cricoid pressure. An overview of all the literature published on this debate of benefit can be summed up by the fact that it is clear that training and a minimum standard in application of the correct technique of cricoid pressure is starkly lacking in provider training at any level or professional background. It is likely that this lack of proper uniform training is the reason why a clear benefit in the technique cannot be demonstrated.
Whilst it is anatomically plausible that cricoid pressure should prevent regurgitation during induction, it seems probable that improper technique and pressure often makes airway management more difficult, thereby negating any benefit from the technique in protecting against aspiration. One study performed by London HEMS indicated that the removal of cricoid pressure during difficult intubation , allowed success to be achieved in a significant number of cases. It certainly seems illogical that if cricoid pressure is removed to allow successful intubation then what is the point in applying it in the first place, if the primary desired outcome in your emergency airway intervention is to place the cuffed tube below the vocal cords as quickly as possible! It is the opinion of the author that cricoid pressure be used selectively in high risk cases for regurgitation such as bowel obstruction or haematemesis and if difficulty in intubation is encountered then removal of cricoid pressure should be undertaken. As well proper training using a simulated pressure model as well as regular anatomical review should be undertaken by all providers required to apply the technique.
An interesting growing controversy is developing over the preferred neuromuscular blocking agent in rapid sequence induction and intubation. For decades the agent of choice has remained suxamethonium due to is low cost, rapid onset of paralysis and excellent intubating conditions achieved. Its relatively quick offset of action, averaging 5-7 minutes has also made it preferred in the event of a failed intubation and need to awaken the patient with a difficult airway. It is clear now within the published emergency airway research that rocuronium when dosed appropriately (at least 1mg/kg) produces as good intubating conditions as suxamethonium within a comparable time of onset. There has been at least one study to suggest that suxamethonium’s depolarising action increases oxygen consumption and significantly shortens the safe apnoea time in the critically ill patient during RSI. Rocuronium avoids several of the contraindications to suxamethonium such as hyperkalaemic states, myopathies and malignant hyperthermia. Opponents of using rocuronium in RSI argue that due to its prolonged action , averaging 30-45 minutes after standard RSI dosing, that in the event of a cannot intubate, cannot ventilate scenario, then the inability to quickly awaken the patient and return them to a spontaneously breathing state is too much of a gamble.
The counter argument from an emergency airway perspective is that if a critically ill or injured patient requires a secured airway then regardless of a failed intubation or even the dreaded cannot intubate/cannot ventilate situation developing once rocuronium had taken effect, then an airway must be secured whether the patient resumes spontaneous breathing or not. In other words, do not live the myth that suxamethonium wearing off quickly enough will save your patient from hypoxic brain injury! If they need an emergent airway , then there is no point trying to waken them up once you have started your RSI process. In some respects it is argued it is better to use a long acting paralytic to ensure that in the event of a failed intubation, repeat intubation attempts and/or insertion of supraglottic devices or even the resort to a surgical airway is not made more difficult by a patient who starts to have a return of muscle tone and breathing , with complications of coughing and gagging. Experienced emergency clinicians will attest to the oft used method of repeated dosing of suxamethonium during a difficult RSI that proves that perhaps a longer acting agent initially is a better strategy in the first place! The availability of sugammadex, the reversal agent for rocuronium now offers an even quicker method of acute reversal of paralysis than the traditional notion of allowing suxamethonium wearing off. Near complete reversal of full paralysis using sugammadex can be achieved within 90 seconds compared to the 5-7 minute average duration of effect of one dose of suxamethonium. Unfortunately for now the cost of sugammadex is prohibitive, averaging $450 a dose for emergency reversal. Yet some retrieval services have stopped using suxamethonium and now stock rocuronium and sugammadex as their standard RSI paralytic and reversal agent. Notably the Queensland Ambulance Brisbane rapid response trauma road unit staffed by an emergency physician and paramedic have made this change. A whole generation of emergency doctors and anaesthetists have grown up using suxamethonium in RSI and therefore it is unlikely that this controversy will be settled any time soon. It remains a topic that the reader should consider carefully in their own practice.
References and Further reading:
(1) P Berlac et al. Pre-hospital airway management: guidelines from a task force from the Scandinavian Society for Anaesthesiology and Intensive Care Medicine. Acta Anaesthesiol Scand, 2008;52:897-907
(2) F Thomas et al. Difficult Airway Simulator Intubation Success Rates Using Commission on Accreditation of Medical Transport Systems Training Standards. Air Med J, 2011; 30(4):208-215.
(3) Davis et al. The Effect of Paramedic Rapid Sequence Intubation on Outcome in Patients with Severe Traumatic Brain Injury.Journal of Trauma, 2003;54:444-453
(4) Bernard et al. Prehospital Rapid Sequence Intubation Improves Functional Outcome for Patients With Severe Traumatic Brain Injury A Randomized Controlled Trial. Annals of Surgery,2010; 252(6):959-965.
(5) Gausche M, Lewis RJ, Stratton SJ, Haynes BF, Gunter CS, Goodrich, SM, et al. Effect of out-of-hospital pediatric endotracheal intubation on survival and neurological outcome: a controlled clinical trial. JAMA 2000;283:783-90.
(6) T Harris, D Lockey. Success in physician prehospital rapid sequence intubation: what is the effect of base speciality and length of anaesthetic training? Emergency Medicine Journal, 2011;28:225-229
(7) http://clinicaltrials.gov/ct2/show/NCT00112398 viewed on Tuesday 19th April 2011
(8) Wang et al. Out-of-Hospital Endotracheal Intubation Experience and Patient Outcomes. Annals Emerg Med,2010;55(6):527-537
(9) R Dawes,A Mellor. Prehospital anaesthesia. J R Army Med Corps, 2010;156(4 Suppl 1):S289-294
(10) . Egly et al. ASSESSING THE IMPACT OF PREHOSPITAL INTUBATION ON SURVIVAL IN OUT-OF-HOSPITAL CARDIAC ARREST. Prehospital Emergency Care, 2011;15(1):44-49
(11) M Le Cong. Flying doctor emergency airway registry: a 3-year, prospective, observational study of endotracheal intubation by the Queensland Section of the Royal Flying Doctor Service of Australia. Emergency Medicine Journal, 2010 ;Sept 15 published ahead of print
(12) Walls, RM. The emergency airway algorithms. In: Manual of Emergency Airway Management, 3rd edition, Walls, RM, Murphy, MF (Eds), Lippincott Williams and Wilkins, Philadelphia 2008. p.8.
(13) D Braude, M Richards. Rapid Sequence Airway (RSA) – a novel approach to prehospital airway management. Prehosp Emerg Care, 2007;11:250-252
(14) R Mackenzie,J French,S Lewis, A Steel. A pre-hospital emergency anaesthesia pre-procedure checklist. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine 2009, 17(Suppl 3):O26
(15) http://www.epmonthly.com/archives/features/no-desat-/ viewed on April 19th, 2011
(16) T C Mort. The supraglottic airway in the emergent setting : its changing role outside the operating room. Anesthesiology News Guide to Airway management, McMahon Publishing, 2011 : 59-71
(17) X Combes et al. Unanticipated difficult airway management in the prehospital emergency setting : Prospective validation of an algorithm. Anesth, 2011 ;114 (1):105-110
(18) S Weingart and R Levitan.Preoxygenation and prevention of desaturation during emergency airway management. Ann Emerg Med, 2011 : Nov 1 Epub ahead of print.
(19) http://www.bestbets.org/bets/bet.php?id=261 viewed on April 19th, 2011.
(20) D Ellis, T Harris, D Zideman.Cricoid pressure in emergency department rapid sequence intubations : a risk-benefit analysis. Annals Emerg Med, 2007;50(6):653-665.
(21) T Harris, D Ellis, L Foster, D Lockey. Cricoid pressure and laryngeal manipulation in 402 pre-hospital emergency anaesthetics: essential safety measure or a hindrance to rapid safe intubation? Resuscitation, 2010;81(7):810-816.
(22) Patanwala et al. Comparison of Succinylcholine and Rocuronium for First-attempt Intubation Success in the Emergency Department. Acad Emerg Med, 2011;18:11-14.
(23) Tang et al. Desaturation following rapid sequence induction using succinylcholine vs. rocuronium in overweight patients. Acta Anaesthesiol Scand 2011; 55: 203–208
Dr Seth Trueger comments :
re: prehospital intubation data
you should mention the big (?100K patients?) observational Japanese study showing best outcomes with intubation vs LMA etc
“It is likely that this lack of proper uniform training is the reason why a clear benefit in the technique cannot be demonstrated.” would change to “certainly possible” or “very plausible” (vs “likely”)
“Opponents of using rocuronium in RSI argue that due to its prolonged action , averaging 30-45 minutes after standard RSI dosing, that in the event of a cannot intubate, cannot ventilate scenario, then the inability to quickly awaken the patient and return them to a spontaneously breathing state is too much of a gamble.”