doi: 10.1111/j.1742-6723.2007.00921.x Emergency Medicine Australasia (2007) 19, 207–212

© 2007 The AuthorsJournal compilation © 2007 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine

Blackwell Publishing AsiaMelbourne, AustraliaEMMEmergency Medicine Australasia1742-6731© 2006 The Authors; Journal compilation © 2006 Australasian College for Emergency Medicine and Australasian Society forEmergency Medicine2007193207212Xxxx XxxxEvaluation of cricoid pressure task trainingP May and C Trethewy

Correspondence: Dr Peter May, Department of Emergency Medicine, Tamworth Base Hospital, Tamworth, NSW 2340, Australia. Email: peter.may@hnehealth.nsw.gov.au

Peter May, B.Med (Hons), FRACGP, Emergency Registrar; Christopher Trethewy, MB BS, FACEM, DEMT, Emergency Physician.

ORIGINAL RESEARCH

Practice makes perfect? Evaluation of cricoid pressure task training for use within the algorithm for rapid sequence induction in critical carePeter May and Christopher TrethewyDepartment of Emergency Medicine and Critical Care, Tamworth Base Hospital, Tamworth, New South Wales, Australia

Abstract

Objective: To assess task training in cricoid pressure application suitable for incorporation into thealgorithm for rapid sequence induction in acute care.

Method: A blinded prospective direct observational study of 110 critical care staff of two hospitalsin regional New South Wales. Each participant was instructed to apply blinded cricoidforce within the target range of 30–40 N to a cricoid model mounted on a weighing scaleand the result recorded. After up to 3 min of unblinded practice without coaching on thesame model a repeat blinded application of force was recorded. The pre- and post-intervention results were compared.

Results: At the pre-intervention stage, 22 participants (20%) applied initial pressure within thetarget range, increasing to 57 (52%) at the post-intervention stage (χ2 = 24.19, d.f. = 1,P < 0.01; odds ratio [OR] = 0.23; 95% confidence interval [CI] 0.12–0.44). The post-intervention results show a significant improvement in the number of participants achiev-ing the target range in both nursing (χ2 = 20.42, d.f. = 1, P < 0.01; OR = 0.18; 95% CI 0.08–0.42) and medical subgroups (χ2 = 4.68, d.f. = 1, P = 0.03; OR = 0.34; 95% CI 0.11–1.02).The number applying force sufficient to prevent regurgitation, that is 30 N or greater, rosefrom 71 to 97 (65% to 88%) (χ2 = 17.02, d.f. = 1, P < 0.01; OR = 0.24; 95% CI 0.11–0.51).The number applying in excess of 44 N fell from 41 to 25 (37% to 21%) (χ2 = 5.54, d.f. = 1,P < 0.02; OR = 2.02; 95% CI 1.08–3.81).

Conclusion: The application of cricoid force by critical care staff can be significantly improved by upto 3 min of practice on a simple task trainer.

Key words: biofeedback trainer, cricoid force, cricoid pressure, rapid sequence induction, task trainer.

P May and C Trethewy

208 © 2007 The AuthorsJournal compilation © 2007 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine

Introduction

Since first described by Sellick in 1961 the applicationof cricoid pressure (hereafter referred to as cricoid force)has become widely accepted as a key component inrapid sequence induction (RSI).1–4 The AustralianResuscitation Council states that ‘personnel potentiallyinvolved in emergency airway management should becompetent in this manoeuvre’.2

Recently Clark and Trethewy reported that only 25%of ED staff applied cricoid force within the prescribedrange.5 These findings add to a compelling body ofevidence that cricoid force is generally inadequatelyapplied. It has been shown among anaesthetic staff thatcommonly used descriptors of cricoid force are inade-quate, knowledge of the prescribed force is poor, as fewas 20% are able to achieve the prescribed range, andfurthermore, that despite effective training in its appli-cation, cricoid force remains a skill that is poorlyretained.4,6–13

To achieve its purpose in preventing gastro-pharyngeal regurgitation and aspiration applied cricoidforce must occlude the oesophageus at the level of thecricoid cartilage, maintaining an effective upper oesoph-ageal pressure in excess of intragastric pressure. It hasbeen demonstrated that the upper oesophagus can beoccluded by the correct application of cricoid force at orin excess of 30 newtons (N).14–16 Wraight et al. extrapo-lated from his research that a force of 44 N wouldsuffice for instances of above average intragastricpressure.14

Force in excess of 44 N carries an increased risk ofairway obstruction, which becomes significant shouldthere be a failure to intubate. This level of force mightdirectly impede intubation and is implicated in somecase reports of soft tissue injury.3,17–19 Few commenta-tors routinely recommend the ‘gold standard’ of 44 N,and the generally accepted target range for cricoid forceis as 30–40 N3,14–16,20

There is debate over the effectiveness and poten-tial risk in the application of cricoid force in RSI.3,17–22

For this debate to be carried forward it is necessaryto demonstrate that applied cricoid force in the criti-cal care setting actually prevents aspiration. A pre-requisite for this research is confidence that theforce applied to the cricoid in the active arm of anytrial achieves at least 30 N and, ideally, is less than44 N.

Our study investigated the utility of task trainingthat could be easily incorporated into RSI for improveddelivery of cricoid force.

Method

With the approval of the ethics committee of the HunterNew England Area Health Service, a prospective directobservational study was undertaken in July 2005among 110 critical care staff at two hospitals in regionalNew South Wales (Tamworth Base and Armidale).

A literature review indicated that 25% of the studypopulation could be reasonably expected to apply cri-coid force within the target range.4,6–13,16 Assuming a90% confidence interval (CI), 102 participants wererequired to give the study sufficient power. We enrolledall the critical care medical and nursing staff on dutyin the ED and ICU during the study period. Consent wasobtained from each. There were no exclusions. No par-ticipant was enrolled twice.

The device under study was a plastic modelhuman larynx mounted on a set of self-calibratingdigital postage scales (Hycom SW series, a range of0.000–10.000 kg, resolution of 0.005 kg) (Fig. 1). Theuse of such devices for this purpose has been vali-dated.5,9–13,17,18,23,24 The model was placed on a firm benchin the work area at a height comfortable for the stand-ing participant, simulating a supine patient on a height-adjustable resuscitation bed.

A single pre- and post-intervention measurement ofcricoid force was recorded. The one-handed techniquewas employed, with the thumb and middle finger moul-ded to the anterolateral aspects of the cricoid model.Each participant was instructed to apply vertical forceto the model cricoid ring, depressing the scale towithin the target range of 3.060–4.075 kg, equating to

Figure 1. The model larynx mounted on a postage weighingscale.

Evaluation of cricoid pressure task training

© 2007 The AuthorsJournal compilation © 2007 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine

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30–40 N.16 An initial measurement was taken with theparticipant blinded. Each participant was immediatelyinformed of their result and instructed to familiarizethemselves with the target range by unblinded practicewith the device for up to 3 min. A second blinded mea-surement was then taken. The de-identified data wereimmediately entered on a spreadsheet and the partici-pant’s name was recorded on a separate roll. No coach-ing in technique was given at any stage.

The data were subjected to statistical analysis usingEpiInfo 3.3.2 12.0.1, the χ2-test was applied whereappropriate.

Results

The study group comprised 110 critical care staff, ofwhom 74 were nursing and 36 were medical.

The range of force applied prior to the interventionwas from 0.38 kg (3.7 N) to in excess of 10 kg (98.1 N)(beyond the range of the instrument). Following theintervention the range was from 2.41 kg (23.7 N) to6.10 kg (59.8 N) (Table 1).

Twenty-two (20%) participants applied force withinthe target range of 30–40 N prior to the intervention; 39(36%) applied below 30 N (Fig. 2). Following theintervention 57 (52%) applied force within the targetrange (Fig. 2) (χ2 = 24.19, d.f. = 1, P < 0.01; odds ratio[OR] = 0.23; 95% CI 0.12–0.44). This statistically signif-icant difference in cricoid force application was evidentin both the nursing (χ2 = 20.42, d.f. = 1, P < 0.01;OR = 0.18; 95% CI 0.08–0.42) and the medicalsubgroups (χ2 = 4.68, d.f. = 1, P = 0.03; OR = 0.34; 95%CI 0.11–1.02) (Figs 3,4, respectively).

The number applying force at or beyond 30 N rosefrom 72 (65%) to 97 (88%) (χ2 = 17.02, d.f. = 1, P < 0.01;OR = 0.24; 95% CI 0.11–0.51). The number applyingforce in excess of 44 N fell from 41 (37%) to 25 (23%)(χ2 = 5.54, d.f. = 1, P < 0.02; OR = 2.02; 95% CI 1.08–3.81).

Discussion

The present study demonstrates that the application ofcricoid force can be improved by task training suitablefor incorporation into the RSI algorithm.

Our study follows on from the recent work of Clarkand Trethewy who used the same model to demonstratethat the application of cricoid force by emergency staffwas accurate in only 25%.5 This number correlates withprevious research in anaesthesia and is in keeping withour own data wherein only 20% of critical care staffachieved the target range of 30–40 N (Fig. 2).4,6–13

Table 1. Applied cricoid force, pre- and post-intervention, allparticipants (n = 110)

Parameters Pre-interventionvalues

Post-interventionvalues

Mean (kg) 4.2 3.9Median (kg) 3.6 3.9Range (kg) 0.38–>10 2.41–6.19Standard deviation 2.14 0.78Variance 4.6 0.6

Figure 2. Applied cricoid force, pre- (- -�- -) and post-intervention (–�–), all participants.

Application of Force All Participants

39

22

49

13

57

40

0

10

20

30

40

50

60

<3.060 3.060–4.075 >4.075

Kilograms

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Figure 3. Applied cricoid force, pre- (- -�- -) and post-intervention (–�–), medical staff.

Application of Cricoid Force by Doctors

12

10

14

7

19

10

0

2

4

6

8

10

12

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16

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<3.060 3.060–4.075 >4.075

Kilograms

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ts

P May and C Trethewy

210 © 2007 The AuthorsJournal compilation © 2007 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine

Our results show that practice on a model larynxmounted on a post office weighing scale over a maxi-mum of 3 min, without coaching, resulted in positivechanges in three parameters of cricoid force delivery: anincrease in the number who immediately achieved thetarget range, an increase in the number who applieda protective force of 30 N or greater and a decrease inthe number of participants applying cricoid force inexcess of 44 N. Each of these parameters is of clinicalsignificance.

The risk of aspiration during RSI might be increasedif inadequate cricoid force is delivered. The applicationof cricoid force results in a fall in lower oesophagealsphincter tone, whereas suxamethonium-induced fascic-ulations produce a rise in mean intragastric pres-sure.20,25–27 Previous research has demonstrated thataccurately applied cricoid force in excess of 30 Noccluded the upper oesophagus, creating an effectivebarrier to regurgitation and aspiration.14–16 AlthoughWraight et al. extrapolated from their research that aforce of 44 N would prove protective in situations ofelevated intragastric pressure, most commentators rec-ommend 30–40 N as the target range.3,14–16 Our interven-tion brought about a statistically significant increase inthe number of critical care staff who applied cricoidforce both within this target range (P < 0.01), andin excess of 30 N (P < 0.01), that is, in the numberwho applied protective force (Table 1, Figs 2–4).These improvements in target range application wereobserved in both the medical and nursing subgroups.

An upper limit for cricoid force in the paralysedpatient has not been determined, and is probably uniqueto each patient and situation. However, it has beenclaimed that force in excess of 44 N might distort thelarynx, impede intubation, and possibly cause softtissue injury.3,17–20 Our data demonstrated a reductionin the number who applied force in excess of 44 N(P < 0.02).

There are four potential limitations in the presentstudy: the decision to pool participants from the ED andICU; the assumption that cricoid force within the pre-scribed range is protective against aspiration; theassumption that the force applied to the model will bereproduced on the patient; and the assumption that thatforce will be sustained until the airway is secured.

There were two reasons for enrolling staff from boththe ED and ICU. First, in each hospital there is someexchange of staff between the two areas. Second, thepurpose of the study was to assess the efficacy of thedevice for improving the application of cricoid forcewithin the context of critical care. In comparison withfasted individuals having planned surgery, patientsrequiring emergent intubation within these critical careenvironments are accepted as being at an increased riskof aspiration.28 No anaesthetic personnel were enrolledin the present study.

The assumption that cricoid force, properly appliedwithin the target range will prevent aspiration remainsto be proven. To date the research defining the targetrange has been limited to identifying the pressurerequired to occlude the oesophagus, and has beenconducted on already intubated surgical patients,supported by research on cadavers.14–16 There is no con-trolled research demonstrating a change in the actualrate of aspiration in patient groups subjected to cricoidforce during tracheal intubation. Definitive clinicalresearch is necessary and can be undertaken; however,without an intervention such as ours such research willsuffer from having applied cricoid forces below targetrange in about 35% of the control arm.4–13 Our interven-tion reduced this number to 12%.

The application of models such as this one has beenvalidated.5,9–13,17–20,23,24 Applied force was the variableunder study, and as such was independent of the objectto which it was applied. Other task trainers could havebeen used. We chose this device because of its ease ofuse, low cost, portability and its capacity to provideimmediate, accurate and easily understood biofeedback.

With respect to the final assumption, Meek et al. stud-ied six operating theatre assistants and found, with theelbow flexed, that the prescribed range of force could

Figure 4. Applied cricoid force, pre- (- -�- -) and post-intervention (–�–), nursing staff.

Application of Cricoid Force by Nurses

27

12

35

6

38

30

0

5

10

15

20

25

30

35

40

<3.060 3.060–4.075 >4.075

Kilograms

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© 2007 The AuthorsJournal compilation © 2007 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine

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be maintained for 2–4 min, or up to 8 min with theelbow extended.24 Recognizing that these intervals fitwithin the usual time frame for RSI we made no attemptto reproduce his work.

The critical care patient is by definition at a height-ened risk of aspiration. This risk might be escalated byinadequate technique in the application of cricoid force.Therefore we recommend that the team member nomi-nated to apply cricoid force in RSI be solely tasked.27,29,30

He/she should practise on a task trainer such as theweighing scale used in the present study during the pre-oxygenation phase and immediately apply that force tothe patient. Such practice can be expected to achievecricoid force within the prescribed range in 52%and a force protective against aspiration in 88% ofapplications.

Such an approach would seem to be the only practicalmeans of meeting the recommendation of The Austra-lian Resuscitation Council.2 Moreover, by achieving agreater uniformity in the application of force in excessof 30 N, the way might be cleared for studies into thetrue incidence of aspiration in the context of RSI incritical care. These studies might better define whatrange of cricoid force is protective.

Conclusion

The application of cricoid force within a prescribedrange is an accepted, but poorly executed part of RSI.4–13

Although practice might not perfect it, our researchestablishes that task training on a simple model larynxmounted on post office scales for 3 min significantlyimproves the application of target force. Such practicecould be easily incorporated into the existing algorithmfor RSI.

Acknowledgements

The enthusiastic assistance of the critical care staffs ofTamworth Base and Armidale Hospitals is gratefullyacknowledged. Dr Christian Alexander, SeniorResearch Fellow, Hunter New England Area RuralTraining Unit provided invaluable statistical support.Special thanks to Dr Jennifer May, GP Academic Uni-versity Department of Rural Health, for her assistancewith the study design and manuscript, and Ms KerryCuskelly, Coordinator, Library Services, Hunter-NewEngland Health Service, Tamworth for her ready assis-tance with the referencing.

Author contributions

Both authors contributed equally to the study.

Competing interests

The authors have no industrial links or affiliations rel-evant to the conduct of this research. There were nofinancial grants or other sources of funding for thisresearch.

Accepted 16 October 2006

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