Time to change thinking on ‘cricoid pressure’

April 19, 2014 by  
Filed under All Updates, EMS, ICU, Resus

Here’s my take on the role of ‘cricoid pressure’ in critical care intubation.


Cautionary notice: This post represents my opinion on a topic about which airway practitioners seem to be divided. It is deliberately provocative in order to stimulate thinking and to challenge assumptions. It is not meant to offend or to divide professions or specialties, who seem to be spread over both sides of the question anyway.

As with all posts, I strongly recommend you follow your institutional policy regarding clinical practice and follow the advice of your supervisors. This is not a postgraduate training program. It’s a guy on the internet.

Okay I am now SO tired of endless circular arguments about cricoid pressure like those currently taking place on the FOAMcc Google Plus Community.

As I see it, ‘cricoid pressure’ should not be considered the standard of care in critical care rapid sequence intubation. The potential for harm (proven) vastly outweighs any likelihood of benefit (unproven).

Some practitioners argue that because it has traditionally been considered standard of care in operating room-based practice, and additionally because some guidelines recommend its use in anaesthesia, then it should be applied as a standard for critical care intubation outside the operating room. And they maintain this stance while simultaneously acknowledging the validity of evidence that it frequently is poorly applied outside the OR, and that it often significantly impairs the view on laryngoscopy. They reassure us that ‘you can always remove it if you get a bad view’ (I know, that makes me face-palm too).

Consider the weakness of this argument. While the rest of the critical care world has been espousing the goal of optimising first pass laryngoscopy success over the last decade, these unwitting promulgators of muppetry are recommending a technique that they admit can reduce first pass success unless it’s removed. So, in a critical resuscitation setting, where everything we’ve learned and taught in the last few years demonstrates the importance of human factors, simplicity, and reducing cognitive load, these ‘CP’ proponents are happy to commit an extra member of the team (where’s this person coming from in an ED, prehospital, ward or rural clinic setting exactly?) to a useless technique that someone then has to remember to get them to remove – thus invoking an additional cognitive step during a time of heightened cognitive demand (failed laryngoscopy) for NO proven benefit and a list of potential harms that have been so well described elsewhere over and over. This argument displays comparably breathtaking ignorance to the one that promulgates the use of propofol for induction because you can give a ‘metaraminol chaser’ afterwards to recover the blood pressure (at the likely expense of blood flow).

An unsurprising but at the same time very reassuring observation is that consultant anaesthetists who simultaneously specialise in critical care (intensive care and/or prehospital & retrieval medicine), such as Drs John Hinds, Pete Sherren, Anthony Lewis, Per Bredmose, and Geoff Healy (all of whom know far more about anaesthetising the critically ill than I ever will) will argue forcefully and eloquently AGAINST the use of cricoid pressure, demonstrating this isn’t about anaesthetists versus other specialists, its about something else – perhaps resuscitationists versus non-resuscitationists, or evidence-based practitioners versus dogma-based practitioners.

Since cricoid pressure in critical care settings is often poorly applied, displaces the oesophagus sideways (that it’s supposed to be occluding), compresses the airway (preventing tube passage), and distorts the airway (inhibiting larygoscopic view), it could be argued that it isn’t the ‘pure’ cricoid pressure one would desire in the operative setting anyway. Because of that, I don’t think we should call it ‘cricoid pressure’ any more. Just as U.S. emergency physicians successfully engineered a culture shift by rebranding ‘rapid sequence induction of anaesthesia’ (when it’s all about the anaesthesia, because the patient needs an operation) to ‘rapid sequence intubation’ (it’s all about drug assisted intubation, because the patient needs resuscitative airway protection or improved gas exchange), I think as critical care providers we must take ownership of this farcical situation and rebrand the assault on the airways of our critically ill patients by would-be chicken bombers who appear not to grasp the environmental and human factors that we devote our careers as resuscitationists to mastering.

So my call to arms is this: resuscitationists, you must stop ‘feeding the bears’ in this ‘debate’ and OWN the terminology. Join me in the rebranding of this destructive manoeuvre that slows down, or retards, effective airway management. From this day forward, we are not calling it cricoid pressure any more. Ladies and gentlemen, fellow resuscitationists, my suggestion, my request, is that we now refer to it as manual Routine Esophageal Transposition with Airway Restriction and Distortion. I know that’s a mouthful, but the good news is this: it abbreviates to a memorable acronym, which is ‘manual RETARD’. Of course, this could well be construed as offensive, so you must put the emphasis on the final syllable, as in the verb ‘to retard’ (to delay or set back).

Let the debate go away, unless both sides are talking about the same thing: manual ‘RETARD’, or until some new evidence arises that proves me wrong, in which case I will savour the slice of humble pie as long as it’s coated in the sauce of real science.

Breaking with tradition in paediatric RSI

April 8, 2014 by  
Filed under All Updates, EMS, ICU, Kids, Resus

‘Traditional’ rapid sequence induction of anaesthesia is often described with inclusion of cricoid pressure and the strict omission of any artifical ventilation between paralytic drug administration and insertion of the tracheal tube. These measures are aimed at preventing pulmonary aspiration of gastric contents although there is no convincing evidence base to support that. However it is known that cricoid pressure can worsen laryngoscopic view and can occlude the paediatric airway. We also know that children desaturate quickly after the onset of apnoea, and although apnoeic diffusion oxygenation via nasal cannula can prevent or delay that, in some cases it may be preferable to bag-mask ventilate the patient while awaiting full muscle relaxation for laryngoscopy.

A Swiss study looked at 1001 children undergoing RSI for non-cardiac surgery. They used a ‘controlled rapid sequence induction and intubation (cRSII)’ approach for children assumed to have full stomachs. This procedure resembled RSI the way it is currently done in many modern critical care settings, including the retrieval service I work for:

  • No cricoid pressure
  • Ketamine for induction if haemodynamically unstable
  • A non-depolarising neuromuscular blocker rather than succinylcholine
  • No cricoid pressure
  • Gentle facemask ventilation to maintain oxygenation until intubation conditions achieved
  • Intubation with a cuffed tracheal tube
  • Still no cricoid pressure

The authors comment:

The main finding was that cRSII demonstrated a considerably lower incidence of oxygen desaturation and consecutive hemodynamic adverse events during anesthesia induction than shown by a previous study on classic RSII in children. Furthermore, there was no incidence of pulmonary aspiration during induction, laryngoscopy, and further course of anesthesia.

Looks like more dogma has been lysed, and this study supports the current trajectory away from traditional teaching towards an approach more suitable for critically ill patients.

Controlled rapid sequence induction and intubation – an analysis of 1001 children
Paediatr Anaesth. 2013 Aug;23(8):734-40


BACKGROUND: Classic rapid sequence induction puts pediatric patients at risk of cardiorespiratory deterioration and traumatic intubation due to their reduced apnea tolerance and related shortened intubation time. A ‘controlled’ rapid sequence induction and intubation technique (cRSII) with gentle facemask ventilation prior to intubation may be a safer and more appropriate approach in pediatric patients. The aim of this study was to analyze the benefits and complications of cRSII in a large cohort.

METHODS: Retrospective cohort analysis of all patients undergoing cRSII according to a standardized institutional protocol between 2007 and 2011 in a tertiary pediatric hospital. By means of an electronic patient data management system, vital sign data were reviewed for cardiorespiratory parameters, intubation conditions, general adverse respiratory events, and general anesthesia parameters.

RESULTS: A total of 1001 patients with cRSII were analyzed. Moderate hypoxemia (SpO2 80-89%) during cRSII occurred in 0.5% (n = 5) and severe hypoxemia (SpO2 <80%) in 0.3% of patients (n = 3). None of these patients developed bradycardia or hypotension. Overall, one single gastric regurgitation was observed (0.1%), but no pulmonary aspiration could be detected. Intubation was documented as ‘difficult’ in two patients with expected (0.2%) and in three patients with unexpected difficult intubation (0.3%). The further course of anesthesia as well as respiratory conditions after extubation did not reveal evidence of ‘silent aspiration’ during cRSII.

CONCLUSION: Controlled RSII with gentle facemask ventilation prior to intubation supports stable cardiorespiratory conditions for securing the airway in children with an expected or suspected full stomach. Pulmonary aspiration does not seem to be significantly increased.

Palpating neonatal tracheal tubes

April 6, 2014 by  
Filed under All Updates, EMS, ICU, Kids, Resus

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infant-intubate-iconAfter neonatal intubation, the incidence of malposition of the tip of the tracheal tube is fairly high.

A technique was evaluated involving palpation of the tube tip in the suprasternal notch, which in this small study was superior to insertion length based on a weight-based nomogram.

The suprasternal notch was chosen because it anatomically corresponds to vertebral level T2, close to the optimal position at the mid-tracheal point. Correct position on the chest radiograph was defined as any position <0.5 cm above the interclavicular midpoint and more than 1 cm above the carina.

During tracheal tube placement, the tip was gently palpated in the suprasternal notch with the index or little finger of the left hand while holding the body of the tube with the fingers of the right hand. The tube tip was adjusted until the bevelled edge was just palpable in the the suprasternal notch.

Digital palpation of endotracheal tube tip as a method of confirming endotracheal tube position in neonates: an open-label, three-armed randomized controlled trial.
Paediatr Anaesth. 2013 Oct;23(10):934-9


OBJECTIVE: To compare the malposition rates of endotracheal tubes (ETTs) when the insertional length (IL) is determined by a weight-based nomogram versus when IL is determined by palpation of the ETT tip.

DESIGN: Open-label, randomized controlled trial (RCT).

SETTING: Level III neonatal intensive care unit (NICU).

SUBJECTS: All newborn babies admitted in NICU requiring intubation.

INTERVENTIONS: Subjects were randomly allocated to one of three groups, wherein IL was determined by (i) weight-based nomogram alone, (ii) weight-based nomogram combined with suprasternal palpation of ETT tip performed by specially trained neonatology fellows, or (iii) combination of weight-based and suprasternal methods by personnel not specially trained.

PRIMARY OUTCOME: Rate of malposition of ETT as judged on chest X-ray (CXR).

RESULTS: Fifty seven babies were randomized into group 1(n = 15), group 2 (n = 20), and group 3 (n = 22). The proportion of correct ETT placement was highest in group 2, being 66.7%, 83.3%, and 66.7% in groups 1 through 3, respectively (P value = 0.58). No complication was attributable to palpation technique.

CONCLUSION: Suprasternal palpation shows promise as a simple, safe, and teachable method of confirming ETT position in neonates.

Atropine for Paediatric RSI?

April 5, 2014 by  
Filed under All Updates, EMS, ICU, Kids, Resus

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paedRSIdrugiconIn some areas it has been traditional to pre-medicate or co-medicate with atropine when intubating infants and children, despite a lack of any evidence showing benefit. It is apparently still in the American Pediatric Advanced Life Support (PALS) Provider Manual when age is less than 1 year or age is 1–5 years and receiving succinylcholine. However it is not recommended with rapid sequence intubation in the British and Australasian Advanced Paediatric Life Support manual and course.

A French non-randomised observational study compares intubations with and without atropine in the neonatal and paediatric critical care setting. Atropine use was associated with significant acceleration of heart rate, and no atropine use was associated with a higher incidence of new dysrhythmia, the most common being junctional rhythm, but with none appearing to be clinically significant.

The incidence of the most important peri-intubation cause of bradycardia – hypoxia – is not reported. It is also not clear how many intubation attempts were required. The authors admit:

it is not possible using our methodology to deduce whether bradycardia was due to hypoxia, laryngoscopy, or sedation drugs.

Actual rapid sequence was rarely employed – their use of muscle relaxants was low – making this difficult to extrapolate to modern emergency medicine / critical care practice.

My take home message here is that this study provides no argument whatsoever for the addition of atropine in routine RSI in the critically ill child. Why complicate a procedure with an unnecessary tachycardia-causing drug when the focus should be on no desat / no hypotension / first look laryngoscopy?

The Effect of Atropine on Rhythm and Conduction Disturbances During 322 Critical Care Intubations
Pediatr Crit Care Med. 2013 Jul;14(6):e289-97


OBJECTIVES: Our objectives were to describe the prevalence of arrhythmia and conduction abnormalities before critical care intubation and to test the hypothesis that atropine had no effect on their prevalence during intubation.

DESIGN: Prospective, observational study.

SETTING: PICU and pediatric/neonatal intensive care transport.

SUBJECTS: All children of age less than 8 years intubated September 2007-2009. Subgroups of intubations with and without atropine were analyzed.

INTERVENTION: None.

MEASUREMENT AND MAIN RESULTS: A total of 414 intubations were performed in the study period of which 327 were available for analysis (79%). Five children (1.5%) had arrhythmias prior to intubation and were excluded from the atropine analysis. Atropine was used in 47% (152/322) of intubations and resulted in significant acceleration of heart rate without provoking ventricular arrhythmias. New arrhythmias during intubation were related to bradycardia and were less common with atropine use (odds ratio, 0.14 [95% CI, 0.06-0.35], p < 0.001). The most common new arrhythmia was junctional rhythm. Acute bundle branch block was observed during three intubations; one Mobitz type 2 rhythm and five ventricular escape rhythms occurred in the no-atropine group (n = 170). Only one ventricular escape rhythm occurred in the atropine group (n = 152) in a child with an abnormal heart. One child died during intubation who had not received atropine.

CONCLUSIONS: Atropine significantly reduced the prevalence of new arrhythmias during intubation particularly for children over 1 month of age, did not convert sinus tachycardia to ventricular tachycardia or fibrillation, and may contribute to the safety of intubation.

High Flow Nasal Cannulae In Paediatric Retrieval

April 2, 2014 by  
Filed under All Updates, EMS, ICU, Kids

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High Flow Nasal Cannulae (HFNC) oxygen therapy was introduced in paediatric interfacility retrievals undertaken by the Mater Children’s PICU Retrieval Team in Queensland, Australia. In 793 under 2 year olds, HFNC was associated with a reduction in infants receiving invasive or non-invasive ventilation. 77% of the patients had bronchiolitis.

The rationale for this treatment is explained as:

Owing to the inherent properties of the infant respiratory system with small airways and high chest compliance, the risk of developing atelectasis is high in bronchiolitis. HFNC therapy applied early in the disease process may prevent progression of the disease and maintain normal lung volumes, thereby preventing atelectasis. As a result, the functional residual capacity can be maintained and work of breathing reduced, which may stabilize the patient sufficiently to avoid the need for intubation. For this purpose we used flow rates of 2 L/kg/min which have been shown to result in a positive end-expiratory pressure of 4–5 cmH2O

Read more on high-flow nasal cannula oxygen therapy.

High-flow nasal cannula (HFNC) support in interhospital transport of critically ill children
Intensive Care Med. 2014 Feb 15. [Epub ahead of print]


BACKGROUND: Optimal respiratory support for interhospital transport of critically ill children is challenging and has been scarcely investigated. High-flow nasal cannula (HFNC) therapy has emerged as a promising support mode in the paediatric intensive care unit (PICU), but no data are available on HFNC used during interhospital transport. We aimed to assess the safety of HFNC during retrievals of critically ill children and its impact on the need for invasive ventilation (IV).

METHODS: This was a retrospective, single-centre study of children under 2 years old transported by a specialized paediatric retrieval team to PICU. We compared IV rates before (2005-2008) and after introduction of HFNC therapy (2009-2012).

RESULTS: A total of 793 infants were transported. The mean transport duration was 1.4 h (range 0.25-8), with a mean distance of 205 km (2-2,856). Before introduction of HFNC, 7 % (n = 23) were retrieved on non-invasive ventilation (NIV) and 49 % (n = 163) on IV. After introduction of HFNC, 33 % (n = 150) were retrieved on HFNC, 2 % (n = 10) on NIV, whereas IV decreased to 35 % (n = 162, p < 0.001). No patients retrieved on HFNC required intubation during retrieval, or developed pneumothorax or cardiac arrest. Using HFNC was associated with a significant reduction in IV initiated by the retrieval team (multivariate OR 0.51; 95 % CI 0.27-0.95; p = 0.032).

CONCLUSIONS: We report on a major change of practice in transport of critically ill children in our retrieval system. HFNC therapy was increasingly used and was not inferior to low-flow oxygen or NIV. Randomized trials are needed to assess whether HFNC can reduce the need for IV in interhospital transport of critically ill children.

i-STAT® analysis of intraosseous aspirate

March 6, 2014 by  
Filed under All Updates, EMS, ICU, Kids, Resus

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In the absence of vascular access we may resort to sending intraosseous aspirates for analysis, but in some laboratories there is concern that the samples can block autoanalysers.

A study on haematology/oncology patients undergoing diagnostic bone marrow aspiration showed clinically acceptable agreement between venous and intraosseous measurements for pH, base excess, sodium, ionised calcium and glucose using an an i-STAT® point-of-care analyser.

Key points are:

  • The first 1-2 ml should be discarded (as in this study)
  • Lactate hasn’t been assessed
  • These patients weren’t critically ill

Analysis of bloodgas, electrolytes and glucose from intraosseous samples using an i-STAT® point-of-care analyser
Resuscitation. 2014 Mar;85(3):359-63


BACKGROUND: Intraosseous access is used in emergency medicine as an alternative when intravenous access is difficult to obtain. Intraosseous samples can be used for laboratory testing to guide treatment. Many laboratories are reluctant to analyse intraosseous samples, as they frequently block conventional laboratory equipment. We aimed to evaluate the feasibility and accuracy of analysis of intraosseous samples using an i-STAT(®) point-of-care analyser.

METHODS: Intravenous and intraosseous samples of twenty children presenting for scheduled diagnostic bone marrow aspiration were analysed using an i-STAT(®) point-of-care analyser. Sample types were compared using Bland Altman plots and by calculating intraclass correlation coefficients and coefficients of variance.

RESULTS: The handheld i-STAT(®)point-of-care analyser proved suitable for analysing intraosseous samples without technical difficulties. Differences between venous and intraosseous samples were clinically acceptable for pH, base excess, sodium, ionised calcium and glucose in these haemodynamically stable patients. The intraclass correlation coefficient was excellent (>0.8) for comparison of intraosseous and intravenous base excess, and moderate (around 0.6) for bicarbonate, sodium and glucose. The coefficient of variance of intraosseous samples was smaller than that of venous samples for most variables.

CONCLUSION: Analysis of intraosseous samples with a bedside, single-use cartridge-based analyser is feasible and avoids the problem of bone marrow contents damaging conventional laboratory equipment. In an emergency situation point-of-care analysis of intraosseous aspirates may be a useful guide to treatment.

Is 4 Joules per kg enough in kids?

March 5, 2014 by  
Filed under All Updates, EMS, Guidelines, ICU, Kids, Resus

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glash-sim-paed-face-smResearchers from the Iberian-American Paediatric Cardiac Arrest Study Network challenge the evidence base behind defibrillation shock dose recommendations in children.

In a study of in-hospital pediatric cardiac arrest due to VT or VF, clinical outcome was not related to the cause or location of arrest, type of defibrillator and waveform, energy dose per shock, number of shocks, or cumulative energy dose, although there was a trend to better survival with higher doses per shock. 50% of children required more than the recommended 4J per kg and in over a quarter three or more shocks were needed to achieve defibrillation.

 

Shockable rhythms and defibrillation during in-hospital pediatric cardiac arrest
Resuscitation. 2014 Mar;85(3):387-91


OBJECTIVE: To analyze the results of cardiopulmonary resuscitation (CPR) that included defibrillation during in-hospital cardiac arrest (IH-CA) in children.

METHODS: A prospective multicenter, international, observational study on pediatric IH-CA in 12 European and Latin American countries, during 24 months. Data from 502 children between 1 month and 18 years were collected using the Utstein template. Patients with a shockable rhythm that was treated by electric shock(s) were included. The primary endpoint was survival at hospital discharge. Univariate logistic regression analysis was performed to find outcome factors.

RESULTS: Forty events in 37 children (mean age 48 months, IQR: 7-15 months) were analyzed. An underlying disease was present in 81.1% of cases and 24.3% had a previous CA. The main cause of arrest was a cardiac disease (56.8%). In 17 episodes (42.5%) ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT) was the first documented rhythm, and in 23 (57.5%) it developed during CPR efforts. In 11 patients (27.5%) three or more shocks were needed to achieve defibrillation. Return of spontaneous circulation (ROSC) was obtained in 25 cases (62.5%), that was sustained in 20 (50.0%); however only 12 children (32.4%) survived to hospital discharge. Children with VF/pVT as first documented rhythm had better sustained ROSC (64.7% vs. 39.1%, p=0.046) and survival to hospital discharge rates (58.8% vs. 21.7%, p=0.02) than those with subsequent VF/pVT. Survival rate was inversely related to duration of CPR. Clinical outcome was not related to the cause or location of arrest, type of defibrillator and waveform, energy dose per shock, number of shocks, or cumulative energy dose, although there was a trend to better survival with higher doses per shock (25.0% with <2Jkg(-1), 43.4% with 2-4Jkg(-1) and 50.0% with >4Jkg(-1)) and worse with higher number of shocks and cumulative energy dose.

CONCLUSION: The termination of pediatric VF/pVT in the IH-CA setting is achieved in a low percentage of instances with one electrical shock at 4Jkg(-1). When VF/pVT is the first documented rhythm, the results of defibrillation are better than in the case of subsequent VF/pVT. No clear relationship between defibrillation protocol and ROSC or survival has been observed. The optimal pediatric defibrillation dose remains to be determined; therefore current resuscitation guidelines cannot be considered evidence-based, and additional research is needed.

The ‘Magic Eye®’ method of rhythm assessment

February 9, 2014 by  
Filed under Acute Med, All Updates, EMS, ICU, Resus

Are you someone who tries to determine whether an ECG trace is ‘irregularly irregular’ by drawing little dots on a piece of paper level with the R waves to see if they are evenly spaced? I’d done that for years until I read this fantastic suggestion, which I’ve been following for over a year now.

In the 1990s there was a popular series of posters and books called ‘Magic Eye‘. These contained a ‘random dot autostereogram‘ which appeared as a mish-mash of coloured dots, but when you stared at it for a while the illusion of a 3D image would emerge. They looked a bit like this (although this one won’t work at such reduced resolution):

Image Credit: Wikimedia Commons

Image Credit: Wikimedia Commons

Dr Broughton and colleagues from Cambridge, UK, discovered that this technique, which involves forcing a divergent gaze to get repeating patterns to appear to overlap, can be applied to an ECG trace.

Stereoviewing an ECG trace causes successive QRS complexes to visually overlap and produce a new image. As Broughton and colleagues point out:

When achieved, this will lead to one of three outcomes. Entirely regular rhythms will ‘click’ into place as a new image at fixed depth. Rhythms with only mild irregularity may be stereoviewable, and if so, will appear to show successive QRS complexes at subtly varying depths. Rhythms with marked irregularity will not be stereoviewable, instead (in our experience) merely giving the viewer sore eyes after several failed viewing attempts.”

The authors assert that this can be applied to continuous ECG monitors, although unless you are really good at stereoviewing while moving your head/eyes horizontally, you should really freeze the trace on the screen first.

The ‘Magic Eye®’ method of rhythm assessment
Anaesthesia. 2012 Oct;67(10):1170-1

Not finding a difference doesn’t prove equivalence

January 28, 2014 by  
Filed under Acute Med, All Updates, EMS, Resus

Image from http://www.physio-control.com/

The recent LINC trial was a randomised controlled trial comparing a mechanical chest compression device (LUCAS) with manual CPR(1). “No significant difference” was found for any of the main outcome measures considered.

So do you think the LINC trial demonstrated that mechanical CPR using the LUCAS device is equivalent, or at least not inferior, to manual CPR?

This was an interesting and important trial for those of us who manage prehospital cardiac arrest patients. In some social media discussions, it appears to have been interpreted by some as evidence that they are equivalent resuscitative techniques or that LUCAS is not inferior to manual CPR.

LINCdata

However, unless you see a p-value less than 0.05 in the table above, (issues of multiple hypotheses testing aside) no evidence of anything was demonstrated; not of difference and certainly not of equivalence. When faced with 2-sided p values >5%, investigators often conclude that there is “no difference” between the treatments, leading to an assumption among readers that the treatments are equivalent. A better conclusion is that there is “no evidence” of a difference between treatments (see opinion piece by Sackett, 2004(2)). In order to determine if treatments are equivalent, equivalence must be tested directly.

How can we test for equivalence?
First, we must define equivalence. It is crucial that this definition is provided a priori i.e. defined before the data are examined. As the focus of the LINC study was on superiority the investigators did not offer an a priori definition of equivalence. However, the CIRC study(3), conducted some time earlier and similar in design, did. (This study examined an alternative mechanical CPR device, the Zoll AutoPulse).

When establishing equivalence between treatments, instead of the more customary null hypothesis of no difference between treatments, the hypothesis that the true difference is equal to a specified ‘delta’ (δ) is tested (4).

To analyse the LINC results to look for equivalence, we can derive our delta values from the CIRC study, which as we’ve said did offer an a priori definition of equivalence. For the purpose of illustration, we will use the risk-difference stopping boundaries calculated for the CIRC study, rather than the odds ratio based equivalence margins, on the grounds of greater simplicity and clinical appropriateness. Therefore, we set our equivalence margins at -δ=-1.4% and δ=1.6%, meaning, where LUCAS fared no worse than manual CPR by 1.4% and no better by 1.6%, we will consider the two techniques equally efficacious. Thus, we will declare equivalence between LUCAS and manual CPR if the 2-sided 95% CI for the treatment difference lies entirely within -1.4% and 1.6%, and noninferiority if the one-sided 97.5% CI for the treatment difference (equivalent to the lower limit of the two-sided 95% CI) lies above -1.4%. (5).

These concepts and how they differ from a traditional comparison are more readily appreciated graphically (Fig. 1).

Figure 1. Two one-sided test procedure and the equivalence margin in equivalence/noninferiority testing between LUCAS and manual CPR

1a Traditional comparative study, such as the LINC trial, shows results with confidence intervals that show no evidence of a difference as they encompass 0.

LINCtradcomp

1b. Using equivalence margins (-δ and δ) derived from a similar study (CIRC), we show that the LINC trial does not demonstrate that LUCAS and manual CPR are equally efficacious, since the 95% CI do not lie completely within the equivalence margins.

LINCequiv
1c. The one sided CI lies above -δ for some outcomes, allowing us to declare non-inferiority on those measures.
LINCnoninf

Conclusion
The presentation of the LINC trial’s results shows no evidence of a difference in outcomes between mechanical and manual CPR, which is not the same as showing they are equivalent or that mechanical CPR is non-inferior. However if we re-examine their data using equivalence margins (-δ, δ) derived from a similar study (CIRC), there is some evidence that the LUCAS device is not inferior to manual CPR (but not necessarily equivalent) with respect to longer term good neurological outcome.

References

1. Rubertsson S, Lindgren E, Smekal D, er al. Mechanical Chest Compressions and Simultaneous Defibrillation vs Conventional Cardiopulmonary Resuscitation in Out-of-Hospital Cardiac Arrest
JAMA. 2014 Jan 1;311(1):53-61

2. Sackett D. Superiority trials, non-inferiority trials, and prisoners of the 2-sided null hypothesis
Evid Based Med 2004;9:38-39 [Open Access]

3. Lerner EB, Persse D, Souders CM, et al. Design of the Circulation Improving Resuscitation Care (CIRC) Trial: a new state of the art design for out-of-hospital cardiac arrest research
Resuscitation. 2011 Mar;82(3):294-9

4. Dunnett CW, Gent M. Significance testing to establish equivalence between treatments, with special reference to data in the form of 2X2 tables. Biometrics. 1977 Dec;33(4):593-602

5. Piaggio G, Elbourne DR, Pocock SJ, et al. Reporting of noninferiority and equivalence randomized trials: extension of the CONSORT 2010 statement. JAMA. 2012;308(24):2594-604. [Open Access]

London Trauma Conference Day 4

December 15, 2013 by  
Filed under All Updates, EMS, ICU, Resus, Trauma

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London Trauma Conference Day 4 by Dr Louisa Chan

It’s the last day of the conference and new this year is the Neurotrauma Masterclass running in parallel with the main track which focuses on in-hospital care.

We heard a little from Mark Wilson yesterday. He believes we are missing a pre-hospital trick in traumatic brain injury. Early intervention is the key (he has data showing aggressive intervention for extradural haemorrhage in patients with fixed dilated pupils has good outcomes in 75%).

Today he taught us neurosurgery over lunch. If you have a spare moment over then go to his website and you too can learn how to be a brain surgeon!

Dr Gareth Davies talks about Impact Brain Apnoea. Many will not heard of this phenomenon. Clinicians rarely see patients early enough in their injury timeline to witness

Essentially this term describes the cessation of breathing after head injury. It has been described in older texts (first mentioned in 1894!) The period of apnoea increases with the severity of the injury and if non fatal will then recover to normal over a period of time. Prolonged apnoea results in hypotension.

This is a brain stem mediated effect with no structural injury.

The effect is exacerbated by alcohol and ameliorated by ventilatory support during the apnoeic phase.

Associated with this response is a catecholamine surge which exacerbates the cardiovascular collapse and he introduces the concept of Central Shock.

So how does this translate into the real world?

Well, could we be miscategorising patients that die before they reach hospital as succumbing to hypovolaemic when in fact they had central shock?

These patients essentially present with respiratory arrest, but do well with supported ventilation. Identification of these patients by emergency dispatchers with airway support could mean the difference between life and death.

Read more about this at: http://www.sciencedirect.com/science/article/pii/S0025619611642547

Prof Monty Mythen spoke on fluid management in the trauma patient after blood (not albumin, HES or colloids) and Prof Mervyn Singer explained the genetic contribution to the development of MODS after trauma.

LTC-BrohiProf Brohi gave us the lowdown on trauma laparotomies – not all are the same! With important human factors advice:

1. Task focus kills
2. Situational awareness saves lives
3. The best communication is non verbal
4. Train yourself to listen

Prof Susan Brundage is a US trauma surgeon who has been recruited into the Bart’s and the London School of Medicine and the Royal College of Surgeons of England International Masters in Trauma Sciences for her trauma expertise.

She tells us that MOOCs and FOAM are changing education. Whilst education communities are being formed, she warns of the potential pitfalls of this form of education with a proportion of participants not fully engaged.

The Masters program is growing and if you’re interested you can read more here.

This has been a full on conference, with great learning points.

Hopefully see you next year!

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