These devices first appeared in Question 14 from the first paper of 2015. The candidates were offered a picture of two such devices, and asked about their role in resuscitation. Specifically, the college wanted to see whether the trainees could identify advantages and disadvantages for these devices. Specific literature was not asked about; however the model answer mentioned four trials:
Other useful reseources include:
Rationale for automated mechanical CPR
This stuff below comes from an early study of mechnical CPR, by Hallstrom et al (the ASPIRE trial, JAMA 2006). The study itself was weirdly designed (primary outcome was survival 4 hours after arrest) but the justifications for the use of automated CPR devices were well researched, and can be found in the introduction of that article. In brief:
- High quality CPR is important to resuscitation outcome
- Interruptions of CPR degrade the chance of successful defibrillation (widely believed fact, best known from experimental pig data).
- However, rescuers must pause compressions so that they themselves do not get defibrillated. Similarly, rescuers need to pause compressions to escape the beams of radiation while fluoroscopic screening takes place (eg. for angiography or placement of ECMO catheters).
- Rescuer fatigue degrades the quality of CPR over time (over the first two minutes, irrespective of your training or age the rate of correct compression performance decreases from a mean of around 80% to a mean of around 25%)
- Chest compressions are a repetitive mechanical task, in contrast to the other cognitively intense tasks which are required from rescue personnel. Some might say that diversion of personnel to the task of performing CPR is a waste of their skills.
- Ergo, it makes sense to outsource the task of CPR to a largely radiolucent device which suffers neither fatigue nor electrical shock.
Theoretical advantages of mechanical CPR
- CPR is of uniform (presumably, high) quality.
- CPR is not interrupted for defibrillation.
- Angiography or ECMO cannulation may take place with CPR in progress.
- The device is more portable than a group of rescuers.
Disadvantages of mechanical CPR
- The device takes time to set up.
- An incorrectly aligned device might actually perform poorer compressions than a rescuer, because a rescuer corrects their own position.
- There may be more injuries: in the CIRC trial for example the rate of rib fractures was almost doubled (from 31 to 69 of ~ 2100 patients), and the risk of pneumothrax increased by a third (those guys were using the Zoll machine)
- Other theoretical injury patterns include liver, lung, spleen and stomach lacerations, as well as mediastinal or aortic trauma. It is assumed that this will not be seen with normal human CPR because the humans perform weaker CPR on average , i.e. the machine is so effective that it is too effective.
Device design and distinguishing features
- The Zoll Autopulse is a load-distributing compression band, which compresses the heart as well as the rest of the thorax.
- The LUCAS Device is a motorised piston (all the load is directed at the heart).
- Comparsions of the two techniques have so far only been run in porcine models of VF. Among the fibrillating pigs, there was no histopathological difference in the degree of lung injury. The LUCAS device may be superior to the AutoPulse in terms of cardiac output and end-tidal CO2 (again in pigs), but there does not seem to be any difference in coronary perfusion.
Evidence for (or against) the use of these devices
- A review article by Gates et al (2015) summarises the date from the abovelisted clinical trials (as well as a few others).
- In brief:
- Five eligible studies were found: ASPIRE, CIRC, LINC, PARAMEDIC and another one so far not mentioned by Smekal et al (2011). CHEER was not included or some reason, and it is unclear whether it was not captured by the search strategy or whether it was excluded by ineligibility.
- Two trials evaluated the AutoPulse device, and three evaluated the LUCAS device.
- Heterogeneity of trial design and poor transparency of methodology made this analysis difficult. For example, in the PARAMEDIC trial, only 40% of the mechanical CPR group actually received mechanical CPR.
- The meta-analyses did not suggest any advantage for any of the outcomes.
- This 2018 Cochrane review by Wang et al did not find any significant benefit after analysis of 11 trials, and concluded that these devices were "a reasonable alternative to manual chest compressions".
Pragmatic role in clinical practice
Who cares about clinical trial data, one might belligerently yell. Patient selection is the key. Someone somewhere will benefit. Certainly the college wanted their trainees to "summarise the role of these devices in clinical practice", implying that they indeed have some role to play.
- Use where CPR will be prolonged, and consistent quality will be required
- Cardiac arrest due to hypothermia
- Cardiac arrest following thrombolysis for PE or MI
- Use where rescuers are few, or unskilled:
- Pre-hospital setting
- Rural and regional setting
- Use where space is limited
- Aeromedical retrieval
- Ambulance transport
- Interventional radiology suite
- Use as a part of a larger ECPR bundle a'la CHEER