Starting CPR (ABC vs. CAB) BLS 2201 TF SR

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 studies^3-6 found in the previous ILCOR reviews^7-10. Of the 5 manikin studies found, 3 were randomised studies, one in adult⁵ and 2 in paediatric resuscitation^1,4, and 2 were observational studies in adult resuscitation^3,6.

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 trials^4,5 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 studies^1,25 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 changes^12,13, 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

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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.

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