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: Theresa Olasveengen, Janet Bray

CoSTR Citation

Nehme Z, Cash R, Dicker B, de Caen A, Perkins G, Dewan M, Dassanayake V, Raffay V, Vaillancourt C, Olasveengen T, Tjelmeland I, Kleinman M, Bray J, on behalf of the International Liaison Committee on Resuscitation (ILCOR) Basic Life Support Task Force. Chest compression-to-ventilation ratios for cardiopulmonary resuscitation: A systematic review Consensus on Science with Treatment Recommendations [Internet] Brussels, Belgium: International Liaison Committee on Resuscitation (ILCOR) Basic Life Support Task Force, 2024 November 11. 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 led by the Basic Life Support Task Force (Ashoor 2017 112 – PROSPERO CRD42016047811) and conducted by the Knowledge Synthesis Unit at St Michael’s Hospital, Toronto, Canada with involvement of clinical content experts. The review team examined the Ashoor at al. 2017 systematic review and noted a high number of studies that were not identified in the search strategy used. Additionally, the Ashoor review included unadjusted data and some meta-analyses that had considerable heterogeneity.

For the present review, the team revised and re-executed the search strategy from database inception to October 20, 2024. Evidence for adult and pediatric literature was sought and considered by the Basic and Paediatric Life Support Task Forces. Since that time, additional scientific literature was published after the completion of the systematic review and identified by the Basic Life Support Task Force and is described before the justifications and evidence to decision highlights section of this CoSTR. These data were considered when formulating the Treatment Recommendations. The current review also excluded studies reporting unadjusted data and meta-analyses were reconsidered where there was significant heterogeneity between included studies.

Systematic Review

Nehme Z, Cash R, Dicker B, de Caen A, Perkins G, Dewan M, Dassanayake V, Raffay V, Vaillancourt C, Olasveengen T, Tjelmeland I, Kleinman M, Bray J, on behalf of the International Liaison Committee on Resuscitation (ILCOR) Basic Life Support Task Force. Chest compression-to-ventilation ratios for cardiopulmonary resuscitation: A systematic review [in progress]

PICOST

The PICOST (Population, Intervention, Comparator, Outcome, Study Designs and Timeframe)

Population: Adults and children with out-of-hospital cardiac arrest (OHCA)

Intervention: Any cardiopulmonary resuscitation (CPR) ratio delivered by emergency medical services (EMS)

Comparators: Eligible comparator groups include a CPR ratio different from the one in the intervention arm delivered by EMS. Comparator groups that receive no CPR or compared manual CPR with mechanical CPR were excluded from the review. Studies including automated CPR or any use of mechanical devices will only be included if administered to all treatment arms.

Outcomes: Favourable neurological survival (as measured by cerebral performance category or modified Rankin Score) at discharge or 30-days and at any time interval after 30-days; Survival to discharge or 30 days survival; Survival to any time interval after discharge or 30 days survival; Return of spontaneous circulation (ROSC); Quality of life as measured by any indicator or score.

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. Unpublished studies (e.g., conference abstracts, trial protocols) are excluded. Studies without a comparator group, reviews, and pooled analyses were excluded. Observational studies that only reported unadjusted data were also excluded. All relevant publications in any language are included as long as there was an English abstract.

Timeframe: Literature search was conducted from database inception to October 20, 2024

PROSPERO Registration CRD42024559318

Consensus on Science

A search strategy was executed using Medline and the Cochrane Central Register of Controlled Trials. The broader search identified 11,442 non-duplicate titles, of which 19 studies were deemed relevant and underwent full-text review. We excluded five studies (Rae 2006 2760, Hung 2010 569, Becker 2008 22, Hinchey 2010 348, Bigham 2011 979) comparing patient outcomes between the 2005 and 2000 resuscitation guideline periods, because they either did not specify changes to compression ventilation (CV) ratios or did not adopt changes to CV ratios. Six additional studies were excluded as they only provided unadjusted estimates of the effect of implementing a new CV ratio (Robinson 2010 1648, Aufderheide 2010 1357, Maisch 2010 998, Lick 2011 36, Schewe 2015 232, Yanagawa 2010 340). The remaining eight studies examined the impact of the 2005 resuscitation guideline changes, where changes to CV ratios were made in combination with other bundled intervention. The studies consisted of seven retrospective cohort studies, including six uncontrolled before-and-after designs (Olasveengen 2009 407, Kudenchuk 2012 1787, Steinmetz 2008 908, Garza 2009 2597, Sayre 2009 469, Hostler 2007 446) and one time series analysis (Deasy 2011 984), and one prospective study (Berdowski 2010 1101). Four of the eight studies originated from North America, while the others were from Australia, Norway, Denmark, and the Netherlands. Two studies included patients of all ages while five included adults only (age not reported in one study). None of the eight studies included specifically reported the effect of CV ratios on paediatric populations.

Favourable neurological survival at discharge or 30-days

For the critical outcome of favourable neurological survival at discharge or 30-days, we identified very low certainty evidence (downgraded for risk of bias and serious indirectness) from two cohort studies (Kudenchuk 2012 1787, Berdowski 2010 1101). In one cohort study of 3960 initially non-shockable OHCA (Kudenchuk 2012 1787), the implementation of the 2005 resuscitation guidelines consisting of a CV ratio of 30:2 (among other interventions) was associated with an improvement in neurologically favourable survival at hospital discharge (Cerebral Performance Category score 1–2) compared to a prior period consisting of a CV ratio of 15:2 (OR 1.56, 95% CI: 1.11, 2.18). In another cohort study of 522 initially shockable OHCA (Berdowski 2010 1101), patients treated under the 2005 resuscitation guidelines consisting of a CV ratio of 30:2 (among other interventions) was associated with no change in neurologically favourable survival at 30-days (Cerebral Performance Category score 1–2) compared to patients treated under the 2000 guidelines consisting of a CV ratio of 15:2 (OR 0.50, 95% CI: 0.20, 1.25).

Survival to hospital discharge or 30-day survival

For the critical outcome of survival to hospital discharge or 30-day survival, we identified very low certainty evidence (downgraded for risk of bias and serious indirectness) from six cohort studies (Steinmetz 2008 908, Olasveengen 2009 407, Sayre 2009 469, Garza 2009 2597, Deasy 2011 984, Kudenchuk 2012 1787). Due to significant variation in included populations, the bundled interventions used, and concerns regarding serious indirectness of CV ratios on the reported outcomes, a meta-analysis was not undertaken. A summary of findings is described below:

1. CV ratio 30:2 vs 15:2: Five studies (Steinmetz 2008 908, Olasveengen 2009 407, Sayre 2009 469, Deasy 2011 984, Kudenchuk 2012 1787) involved retrospective before-after analyses of the implementation of the 2005 resuscitation guidelines, consisting of a CV ratio of 30:2 (compared to 15:2) among other resuscitation practice changes. In three cohort studies of OHCA from all rhythms, the implementation of a CV ratio of 30:2 compared to 15:2 improved the risk-adjusted odds of survival in Sayre 2009 469 (AOR 1.8 (95% CI: 1.2, 2.7) and Steinmetz 2008 908 (AOR 2.5, 95% CI: 1.4, 4.6), but not in Olasveengen 2009 407 (AOR 1.42, 95% CI: 0.79, 2.57). For OHCA with initially shockable rhythms, Deasy 2011 984 reported an improvement in the risk-adjusted odds of survival to hospital discharge with a CV ratio of 30:2 compared with 15:2 (AOR 1.62, 95% CI: 1.33-1.98), which was completely attenuated after adjustment for the temporal trend (AOR 1.07, 95% CI: 0.71, 1.62). In OHCA patients with initial non-shockable rhythms, the implementation of a CV ratio of 30:2 compared to 15:2 increased the risk adjusted odds of survival in Kudenchuk 2012 1787 (AOR 1.53, 95% CI: 1.14, 2.05), but not in Deasy 2011 984 (AOR 1.19, 95% CI: 0.82, 1.73).
3. CV ratio 50:2 vs 5:1: A before-after study (Garza 2009 2597) of 200 bystander witnessed OHCA from initial shockable rhythms reported an improvement in survival to hospital discharge following the implementation of a bundled change in resuscitation practice consisting of a CV ratio of 50:2 compared to 5:1 (AOR 2.17, 95% CI: 1.26-3.73).

Survival to 12 months

For the critical outcome of survival to 12-months, we identified very low certainty evidence (downgraded for risk of bias and serious indirectness) from one cohort study (Kudenchuk 2012 1787) of 3960 OHCA patients with initially non-shockable rhythms which showed an improvement in the odds of survival to 12-months with a CV ratio of 30:2 compared to 15:2 (AOR 1.85, 95% CI: 1.29–2.66).

Return of spontaneous circulation

For the critical outcome of return of spontaneous circulation, we identified very low certainty evidence (downgraded for risk of bias and serious indirectness) from one cohort study (Hostler 2007 446) of 1243 OHCA patients which showed no change in the risk-adjusted odds of return of spontaneous circulation with a CV ratio of 30:2 compared to 15:2 (OR 1.31, 95% CI: 0.99, 1.73).

Treatment Recommendations

We suggest a compression–ventilation ratio of 30:2 compared with any other compression–ventilation ratio in adult patients in cardiac arrest (weak recommendation, very low-certainty evidence).

Justification and Evidence to Decision Framework Highlights

• In making this recommendation, the task force placed a high priority on consistency with our 2005, 2010, 2015 and 2020 treatment recommendations and the findings identified in this review, which suggest that the bundle of care (which included changing to a CV ratio of 30:2 from 15:2) resulted in more lives being saved.
• We note that there would likely be substantial resource implications (e.g., reprogramming, retraining) associated with a change in recommendation, and an absence of any data addressing our critical outcomes to suggest our current recommendation should be changed.
• As all the studies identified in this review were undertaken around the time of the 2005 resuscitation guideline changes, the task force felt there was little benefit in further reviews examining a CV ratio of 15:2. Future studies and reviews should focus on the benefit of longer compression to ventilation ratios, compared to the current recommendation of 30:2.
• All studies included in this review suffered from serious indirectness, where a change to CV ratio was delivered or introduced as part of a bundle of care consisting of other changes, such as increases in CPR duration cycles, removal of stacked shocks, removal of post-shock rhythm checks and fewer interruptions to chest compressions. It is possible that the benefits observed in these studies are not related to a change in CV ratio, but other changes occurring at the same time.
• It is also possible that the effects attributed to the change in CV ratio may be the result of temporal improvements in patient outcomes. Deasy (2011 984) reported an improvement in the risk-adjusted odds of survival to hospital discharge with a CV ratio of 30:2 compared with 15:2, but this was completely attenuated after adjustment for the temporal trend. Only two of the eight included studies attempted to control for the pre-intervention trend in patient outcomes.
• The task force excluded from this review five studies (Rae 2006 2760, Hung 2010 569, Becker 2008 22, Hinchey 2010 348, Bigham 2011 979) comparing patient outcomes between the 2005 and 2000 resuscitation guideline periods, because they either did not specify changes to CV ratios or did not adopt changes to CV ratios. In one study (Rae 2006 2760), an improvement in survival to hospital discharge was observed in bystander witnessed OHCA from initial shockable rhythms after the implementation of the 2005 resuscitation guidelines without adopting the change to 30:2.

Knowledge Gaps

Current knowledge gaps include but are not limited to:

1. What is the true effect 30:2 versus 15:2 without any other concurrent changes in practice?
2. Is there a benefit of longer compression to ventilation ratios compared to 30:2?
3. What is the ability of CPR providers to deliver two effective ventilations during the short allotted pause in chest compressions during CPR?
4. Is there a ratio-dependent critical volume of air movement required to maintain oxygenation?

ETD summary table: BLS 2202 Compression ventilation ratios Et D

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