At present, this "basic life support" chapter is a discussion of compression-only CPR, reflecting the interest of the college examiners. Question 15 from the first paper of 2010 asked the candidates not to critically evaluate compression only CPR per se, but to critique the use of this technique as a replacement of the current guidelines. A brief lucid introduction to this topic is available from LITFL. In short, compression-only CPR seems sound theoretically (as it minimises interruption to compressions) and experimentally (many arrested animals can testify to its efficacy). However, human data for improved outcomes is lacking. The major benefit may be the increase in participation among squeamish rescuers.
Rationale for the use of compression-only CPR
- Compression-only CPR dispenses with recommendation to interrupt CPR for breaths, arguing that mouth to mouth peri-arrest ventilation it is unneccessary at best and counterproductive at worst.
- In cardiac arrest, cardiac output is the rate-limiting step of oxygen delivery
- Compressions create enough passive circulation for adequate gas mixing to occur
- Breath pauses in compressions may be counterproductive (as they allow cardiac output to decrease)
- The amount of gas required by the lung is relatively small, because the cardiac output is relatively poor with external cardiac compressions (thus, the extra breath is squandered, if the circulation though the pulmonary capillaries is inadequate).
- At rest, there is enough gas in the lung to support some gs exchange during CPR. Animal studies have demonstrated that even with a totally occluded airway one can perform compression-only CPR for about 6.5 minutes with no difference in neurological outcome (Kern et al, 1998)
- Interruptions in CPR (for breaths or for anything) are known to decrease cerebral perfusion and the chances or ROSC or favourable neurologicl outcome, and much of CPR training revolves around minimising the interruption of compressions.
- Reluctance to provide mouth-to-mouth may discourage all CPR attempts in lay rescuers
- Easier to teach
- Easier to perform as a single rescuer
- Definitely better than no CPR
- May encourage grossed-out lay rescuers to provide some CPR, rather than no CPR
- Uninterrupted compressions may be of better quality
- Supporting data is mainly from animal studies
- Positive pressure ventilation may be essential in drowning, pulmonary oedema, airway obstruction, etc.
- Asphyxia is a major cause of cardiac arrest in children, and for this reason the AHA still recommends ventilation as a part of paediatric CPR (Neumar et al, 2015). Two large database studies among children have found worse 30-day outcomes with compression-only CPR.
Evidence for physiological efficacy of compression-only CPR
Epidemiological evidence in support of compression-only CPR
- Using the entirety of Japan as a prospective cohort, Iwami et al (2015) found that the nationwide dissemination of compression-only CPR practice was associated with an increased survival from out-of-hospital cardiac arrest, because the participation in CPR by bystanders increased from 17.4% to 39.3%.
- On a rather grim note, dispatch operator advice to perform compression-only CPR seems to actually increase bystander participation in CPR, from 62% to 70% ( Shimamoto et al, 2015). This of course implies that in 30-40% of cases the bystander refuses to help, just standing there pointlessly while the arrested patient turns grey.
Current status of Australian recommendations
- The ARC still recommends a 30:2 compression-ventilation ratio. "The ARC has extensively reviewed the recently published evidence and does not consider it to be of sufficient magnitude to warrant a change in the current guidelines"
- The ARC also recommends you provide compression-only CPR if you are for some reason unwilling to provide proper CPR.
- In general, the ARC encourages anything that increases the number of cardiac arrest patients receiving CPR, "but not to the abandonment of conventional CPR".