Conflict of Interest Declaration
The ILCOR Continuous Evidence Evaluation process is guided by a rigorous ILCOR Conflict of Interest policy. The following Task Force members and other authors were recused from the discussion as they declared a conflict of interest: none applicable
The following Task Force members and other authors declared an intellectual conflict of interest and this was acknowledged and managed by the Task Force Chairs and Conflict of Interest committees: none applicable.
CoSTR Citation
Bray J, Dassanayake V, Considine J, Scholefield B, Olasveengen TM on behalf of the International Liaison Committee on Resuscitation Basic Life Support Task Force and Paediatric Life support Task Force.
Starting CPR (ABC vs. CAB) for Cardiac Arrest in Adults and Children Consensus on Science with Treatment Recommendations [Internet] Brussels, Belgium: International Liaison Committee on Resuscitation (ILCOR) Basic Life Support Task Force. Available from: http://ilcor.org
Methodological Preamble and Link to Published Systematic Review
The continuous evidence evaluation process for the production of Consensus on Science with Treatment Recommendations (CoSTR) started with a systematic review of Basic Life Support conducted by BLS Task Force members, with the involvement of clinical content experts. Due to ongoing debate in the scientific literature regarding the merits of commencing chest compressions before ventilations, the decision was made to update the systematic review. Evidence for adult and pediatric literature was sought and considered by the Basic Life Support Task Force and the Pediatric Task Forces.
Traditionally, cardiopulmonary resuscitation (CPR) commenced with opening the airway and ventilations then, chest compressions (i.e. A-B-C). However, airway and breathing are technical skills and previous systematic reviews by the International Liaison Committee on Resuscitation (ILCOR) have found that starting CPR with compressions in simulation studies resulted in faster times to key elements of resuscitation (rescue breaths, chest compressions, completion of first CPR cycle). Observational research of changes to dispatcher CPR instructions and guidelines have also supported this approach in adults, with a change from A-B-C to compression-first and compression-focused CPR associated with a significant increase in rates of bystander CPR and patient survival.
Most international adult BLS guidelines now commence CPR with chest compressions before ventilations. However, paediatric guidelines vary, with different approaches in various jurisdictions.
Systematic Review
Webmaster to insert the Systematic Review citation and link to Pubmed using this format when it is available if published
Dassanayake V, Considine J, Scholefield B, Olasveengen TM, Bray J -on behalf of the International Liaison Committee on Resuscitation Basic Life Support Task Force and Paediatric Life support Task Force. ABC vs CAB on outcomes: A systematic review
PICOST
The PICOST (Population, Intervention, Comparator, Outcome, Study Designs and Timeframe)
Population: Adults and children in any setting (in-hospital or out-of-hospital) with cardiac arrest
Intervention: Commencing CPR with compressions first (30:2)
Comparators: Commencing CPR with ventilations first (2:30)
Outcomes: Critical: Survival with favorable neurological outcome at hospital discharge or 30-days, Survival at hospital discharge or 30 days, Survival with favourable neurological outcome to one-year, Survival to one-year, Event survival, Any ROSC. Important: Time to commencement of rescue breaths, Time to commencement of first compression, Time to completion of first CPR cycle, Ventilation rate, Compression rate, Chest compression fraction, Minute ventilation
Study Designs: Randomized controlled trials (RCTs) and non-randomized studies (non-randomized controlled trials, interrupted time series, controlled before-and-after studies, cohort studies) are eligible for inclusion. Simulation studies will be included if there are insufficient human studies. Relevant publications in any language are included as long as there is an English abstract. Unpublished studies (e.g., conference abstracts, trial protocols), animal studies, and studies of post-cardiac arrest debriefing or post-cardiac arrest feedback or dispatcher/telephone assisted CPR are excluded. Indirect evidence (e.g. studies examining resuscitation guideline changes and changes to dispatch protocols without examining the type of CPR delivered) will be excluded.
Timeframe: All years and all languages were included as long as there was an English abstract. Literature search updated from inception to 18th June 2024.
PROSPERO Registration CRD42024583890
Consensus on Science
This updated systematic review identified one new paediatric manikin simulation study1 (published with corrections2), in addition to the 4 manikin simulation studies3-6 found in the previous ILCOR reviews7-10. Of the 5 manikin studies found, 3 were randomised studies, one in adult5 and 2 in paediatric resuscitation1,4, and 2 were observational studies in adult resuscitation3,6.
For all critical outcomes: No human studies were identified.
For the important outcomes, we identified 5 studies.1,3-6 The overall certainty of evidence was rated as very low for all outcomes, downgraded for a very serious risk of bias and indirectness. The observational studies were both at a critical risk of bias due to confounding and the randomized controlled trials were all at critical risk of bias due to lack of blinding. Because of this and a high degree of heterogeneity, no meta-analyses could be performed and individual studies are difficult to interpret.
For the important outcome of time to commencement of chest compressions, we identified very-low-certainty evidence from: 1 cross-over paediatric manikin randomized study4 in 159 two-person teams, 1 adult manikin randomized study5 in 108 two-person teams and 2 adult manikin observational studies in 33 six-person teams(Kobayashi et al.2008) and 40 single rescuers6 All four studies found that C-A-B decreased the time to commencement of chest compressions. In the two randomized controlled trials4,5 in cardiac arrest scenarios the mean time to chest compressions was faster with C-A-B: 19.3± 2.6 seconds vs. 43.4 ±5.0 seconds; p < 0.054 and 25 ±9 seconds vs. 43 ± 16 seconds, p<0.001.5 The two adult-manikin observational studies found C-A-B sequence to be associated with shorter median time to chest compressions (16.0 seconds [IQR=14.0-26.0] vs. 42.0 [IQR=41.5-59.0]; p < 0.001)(Kobayashi et al.2008) and mean time to compressions (15.4 ±3.0 seconds vs. 36.0 ±4.1 seconds; p<0.001).6
For the important outcome of time to commencement of rescue breaths, we identified very-low-certainty evidence from 2 randomized manikin studies representing 108 two-person teams5 and 159 two-person teams.4 In cardiac arrest scenarios, mean time to ventilations started later with C-A-B: 28.4 ±3.1 seconds vs. 22.7 ±3.1 (p < 0.05)4 compared to a mean of 43 ± 10 seconds vs. 37 ± 15 seconds (p<0.001).5 In the respiratory arrest scenario, ventilation was started earlier when the C-A-B sequence was used (mean 19.1 ±1.5 s vs. 22.7 ± .1; p < 0.05).4
For the important outcome of time to completion of first CPR cycle (30 chest compressions and 2 rescue breaths), we identified low-certainty evidence (downgraded for risk of bias) from 1 randomized manikin study representing 108 two-person teams.5 The mean time to completion of the first resuscitation cycle (30:2) was shorter with C-A-B (48 ±10 seconds vs. 63 ±17 seconds; p<0.001). The clinical significance of this difference is unknown.
For the important outcome on ventilation rate, we identified one cross-over paediatric randomized manikin study with risk of bias and low-certainty evidence due to a lack of blinding, representing 28 two-person teams.1 The median number of ventilations delivered in the first minute of resuscitation were higher with the A-B-C sequence (delivering 5 rescue breaths before commencing chest compressions) (median 13 [IQR=12-15] vs. 10 [IQR=8-10]; p<0.05).
For the important outcome on compression rate, we identified 1 paediatric randomized manikin study in 28 two person teams1 and 1 adult observational study with very low certainty of evidence in 33 six person teams.3 There was no difference noted in the compression rate between the two sequences.
For the important outcomes on chest compression fraction (CCF) the same two studies1,25 identified the median CCF to be lower with the A-B-C (delivering 5 rescue breaths before commencing chest compressions) sequence (57% [IQR=54-64] vs. 66% [IQR=59-68]; p<0.001,1,2 which was significant compared to the observational study where there was no difference in the CCF.3
For the important outcome on minute alveolar ventilation in the first minute of resuscitation we identified one paediatric randomized manikin study with very low certainty of evidence.1 The alveolar ventilation in the first minute of resuscitation was higher with the A-B-C (delivering 5 rescue breaths before commencing chest compressions) sequence (median 370 mL [IQR=203-472] vs. 276 mL [IQR=140–360]; p<0.001).
Treatment Recommendations
In adults and children in cardiac arrest, we suggest commencing CPR with compressions rather than ventilations (weak recommendation, very-low-certainty evidence).
Justification and Evidence to Decision Framework Highlights
The majority of the existing evidence, in 5 manikin studies of very low quality, suggests:
- that starting CPR with compressions first results in faster times to key elements of resuscitation, such as time to commencement of chest compressions, time to start and complete the first cycle of compressions, and a higher chest compression fraction.
- One simulated study in pediatric resuscitation found that starting with compressions delayed the commencement of rescue breaths in cardiac arrest, but the difference was of questionable clinical significance. This minute delay in commencing rescue breaths may be acceptable given the decreased time to other elements of resuscitation seen with ABC. However, alveolar minute ventilation and the number of ventilations delivered in the first minute of resuscitation were higher with the A-B-C (delivering 5 rescue breaths before commencing chest compressions) sequence.
Indirect evidence from before-and-after OHCA registry studies in adults, which examined changes in dispatcher telephone CPR instructions11 and the implementation of guideline changes12,13, suggests that switching from the A-B-C to C-A-B approach was associated with increased rates of bystander CPR11 and improved patient outcomes.11-13 Similar data on in-hospital cardiac arrest show conflicting evidence in patient outcomes.14,15 One large registry study from Japan demonstrated increased bystander CPR rates in children with bystander-witnessed OHCAs after compression-only CPR was introduced.16 Whether the change in sequence to CAB by some ILCOR member councils has resulted in more infants and children receiving compression-only CPR overall is unknown, although available data continues to support the combination of compressions and breaths is needed for optimal pediatric CPR.17,18
While important uncertainties regarding timing and delays in initiation of the components of CPR (chest compressions, opening airway, and rescue breaths) remain and may not be readily extrapolated from manikin studies, in retaining this treatment recommendation in adults and adding children, the BLS and PLS task forces also considered:
- The benefits of a single training approach versus separate approaches for adults and children, recognizing regions currently using an A-B-C approach in children may incur additional short-term costs and resources to implement a C-A-B approach;
- Effective chest compressions generate cumulative coronary perfusion pressure, which falls to near zero when compressions stop. Therefore, early effective chest compressions are vital to establishing and maintaining coronary perfusion pressure19;
- Time to first compression is associated with better patient outcomes, including good neurological outcomes in adults20;
- Opening the airway and delivery of ventilations is technical, and bystanders, especially if untrained or minimally trained, are typically unable to deliver effective ventilations during simulated CPR21;
- Due to the public’s concerns with mouth-to-mouth ventilations,22 commencing CPR with airway and ventilations may result in no bystander CPR being provided;
- Further evidence suggests that delivering the A-B-C approach has more errors in CPR4; and that lay-bystanders prefer C-A-B, and it is easier to learn and retain4;
- The delivery of non-mouth-to-mouth ventilation requires the retrieval and preparation of equipment (e.g. bag-valve-mask, pocket mask), which, when multiple rescuers are present, can occur during chest compressions;
- The new treatment recommendation in children is about starting CPR and does not mean ventilation should not be provided in resuscitation;
- While the PLS Task Force appreciates that most cardiac arrest in infants and children have a respiratory etiology, the short delay in starting ventilation is unlikely to make a clinically significant difference in outcome;
- The PLS Task Force emphasized that further investigation is needed in children. This recommendation for infants and children was based on a single manikin study, and clinical data are lacking. Such data may be challenging to obtain and may take years to acquire.
Knowledge Gaps
- No human studies directly evaluating this question in any setting were identified. The Task Forces noted that Utstein-based registry data may be the only source of information to answer this question. Because different councils worldwide have adopted C-A-B vs. A-B-C, comparative studies of different registries may provide evidence to answer this question.
ETD summary table: BLS 2201 ABC vs CAB Et D
References
1. Suppan L, Jampen L, Siebert JN, Zund S, Stuby L and Ozainne F. Impact of Two Resuscitation Sequences on Alveolar Ventilation during the First Minute of Simulated Pediatric Cardiac Arrest: Randomized Cross-Over Trial. Healthcare (Basel). 2022;10:2451.
2. Suppan L, Jampen L, Siebert JN, Zund S, Stuby L and Ozainne F. Correction: Suppan et al. Impact of Two Resuscitation Sequences on Alveolar Ventilation during the First Minute of Simulated Pediatric Cardiac Arrest: Randomized Cross-Over Trial. Healthcare 2022, 10, 2451. Healthcare (Basel). 2023;11:1799.
3. Kobayashi M, Fujiwara A, Morita H, Nishimoto Y, Mishima T, Nitta M, Hayashi T, Hotta T, Hayashi Y, Hachisuka E and Sato K. A manikin-based observational study on cardiopulmonary resuscitation skills at the Osaka Senri medical rally. Resuscitation. 2008;78:333-9.
4. Lubrano R, Cecchetti C, Bellelli E, Gentile I, Loayza Levano H, Orsini F, Bertazzoni G, Messi G, Rugolotto S, Pirozzi N and Elli M. Comparison of times of intervention during pediatric CPR maneuvers using ABC and CAB sequences: a randomized trial. Resuscitation. 2012;83:1473-7.
5. Marsch S, Tschan F, Semmer NK, Zobrist R, Hunziker PR and Hunziker S. ABC versus CAB for cardiopulmonary resuscitation: a prospective, randomized simulator-based trial. Swiss Med Wkly. 2013;143:w13856.
6. Sekiguchi H, Kondo Y and Kukita I. Verification of changes in the time taken to initiate chest compressions according to modified basic life support guidelines. Am J Emerg Med. 2013;31:1248-50.
7. Olasveengen TM, Mancini ME, Perkins GD, Avis S, Brooks S, Castren M, Chung SP, Considine J, Couper K, Escalante R, Hatanaka T, Hung KKC, Kudenchuk P, Lim SH, Nishiyama C, Ristagno G, Semeraro F, Smith CM, Smyth MA, Vaillancourt C, Nolan JP, Hazinski MF, Morley PT and Adult Basic Life Support C. Adult Basic Life Support: International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. Resuscitation. 2020;156:A35-A79.
8. Olasveengen TM, Mancini ME, Perkins GD, Avis S, Brooks S, Castren M, Chung SP, Considine J, Couper K, Escalante R, Hatanaka T, Hung KKC, Kudenchuk P, Lim SH, Nishiyama C, Ristagno G, Semeraro F, Smith CM, Smyth MA, Vaillancourt C, Nolan JP, Hazinski MF, Morley PT and Adult Basic Life Support C. Adult Basic Life Support: 2020 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. Circulation. 2020;142:S41-S91.
9. Travers AH, Perkins GD, Berg RA, Castren M, Considine J, Escalante R, Gazmuri RJ, Koster RW, Lim SH, Nation KJ, Olasveengen TM, Sakamoto T, Sayre MR, Sierra A, Smyth MA, Stanton D, Vaillancourt C and Basic Life Support Chapter C. Part 3: Adult Basic Life Support and Automated External Defibrillation: 2015 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. Circulation. 2015;132:S51-83.
10. Perkins GD, Travers AH, Berg RA, Castren M, Considine J, Escalante R, Gazmuri RJ, Koster RW, Lim SH, Nation KJ, Olasveengen TM, Sakamoto T, Sayre MR, Sierra A, Smyth MA, Stanton D, Vaillancourt C and Basic Life Support Chapter C. Part 3: Adult basic life support and automated external defibrillation: 2015 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations. Resuscitation. 2015;95:e43-69.
11. Bray JE, Deasy C, Walsh J, Bacon A, Currell A and Smith K. Changing EMS dispatcher CPR instructions to 400 compressions before mouth-to-mouth improved bystander CPR rates. Resuscitation. 2011;82:1393-8.
12. Pasupula DK, Bhat A, Siddappa Malleshappa SK, Munir MB, Barakat A, Jain S, Wang NC, Saba S and Bhonsale A. Impact of Change in 2010 American Heart Association Cardiopulmonary Resuscitation Guidelines on Survival After Out-of-Hospital Cardiac Arrest in the United States. Circulation: Arrhythmia and Electrophysiology. 2020;13:e007843.
13. Garza AG, Gratton MC, Salomone JA, Lindholm D, McElroy J and Archer R. Improved patient survival using a modified resuscitation protocol for out-of-hospital cardiac arrest. Circulation. 2009;119:2597-605.
14. Mallikethi-Reddy S, Briasoulis A, Akintoye E, Jagadeesh K, Brook RD, Rubenfire M, Afonso L and Grines CL. Incidence and Survival After In-Hospital Cardiopulmonary Resuscitation in Nonelderly Adults: US Experience, 2007 to 2012. Circ Cardiovasc Qual Outcomes. 2017;10.
15. Wang CH, Huang CH, Chang WT, Tsai MS, Yu PH, Wu YW and Chen WJ. Outcomes of adults with in-hospital cardiac arrest after implementation of the 2010 resuscitation guidelines. Int J Cardiol. 2017;249:214-9.
16. Goto Y, Funada A, Maeda T and Goto Y. Temporal trends in neurologically intact survival after paediatric bystander-witnessed out-of-hospital cardiac arrest: A nationwide population-based observational study. Resusc Plus. 2021;6:100104.
17. Naim MY, Griffis HM, Berg RA, Bradley RN, Burke RV, Markenson D, McNally BF, Nadkarni VM, Song L, Vellano K, Vetter V and Rossano JW. Compression-Only Versus Rescue-Breathing Cardiopulmonary Resuscitation After Pediatric Out-of-Hospital Cardiac Arrest. J Am Coll Cardiol. 2021;78:1042-52.
18. Zhang X, Zhang W, Wang C, Tao W, Dou Q and Yang Y. Chest-compression-only versus conventional cardiopulmonary resuscitation by bystanders for children with out-of-hospital cardiac arrest: A systematic review and meta-analysis. Resuscitation. 2019;134:81-90.
19. Nassar BS and Kerber R. Improving CPR performance. Chest. 2017;152:1061-9.
20. Goh JL, Pek PP, Fook-Chong SMC, Ho AFW, Siddiqui FJ, Leong BS-H, Mao DRH, Ng W, Tiah L, Chia MY-C, Tham LP, Shahidah N, Arulanandam S and Ong MEH. Impact of time-to-compression on out-of-hospital cardiac arrest survival outcomes: A national registry study. Resuscitation. 2023;190:109917.
21. Beard M, Swain A, Dunning A, Baine J and Burrowes C. How effectively can young people perform dispatcher-instructed cardiopulmonary resuscitation without training? Resuscitation. 2015;90:138-42.
22. Bray JE, Smith K, Case R, Cartledge S, Straney L and Finn J. Public cardiopulmonary resuscitation training rates and awareness of hands-only cardiopulmonary resuscitation: a cross-sectional survey of Victorians. Emerg Med Australas. 2017;29:158-64.