The first time I saw the Thumper performing CPR on a patient I thought “well, that makes sense.” Since then we have seen other devices, most notably the Zoll AutoPulse and the Physio-Control LUCAS. It was disappointing to many in 2005 when the AutoPulse trial was halted early due to harm. 1 Although four-hour survival was similar between groups, the hospital discharge survival rate in the manual CPR group was 9.9% compared to 5.8% in the mechanical CPR group. Many hypotheses were proposed to explain the results, which included Hawthorne effect, prolonged device deployment time, and enrollment bias. Last month, the results of the LUCAS in Cardiac Arrest (LINC) trial were published in JAMA, breathing new life into the mechanical vs manual CPR debate. 2
Study Methodology and Results
6 month survival was 8.5% and 8.1% for mechanical vs manual CPR respectively
The LINC trial was a multicenter, randomized trial, which enrolled 2,589 cardiac arrest patients in Europe into either a mechanical CPR or manual CPR arm.
- The primary outcome measure was survival after four hours.
- Secondary outcomes included neurologic function at ICU discharge, hospital discharge, 1 month, and 6 months.
- There was no significant difference in any of the outcome measures between the two groups.
- 4-hour survival rate: Mechanical compression group (23.6%) versus the conventional CPR group (23.7%)
- 6-month survival rate: Mechanical compression group (8.5%) versus conventional CPR group (8.1%)
- 6-month good neurologic status (based on Cerebral Performance category of 1 or 2): Mechanical compression group (99%) versus conventional group (94%)
- There are some discrepant details:
- The mechanical CPR group received 3 minute cycles of compressions as opposed to 2 minutes in the manual group (so rescuer fatigue would not be an issue)
- In the mechanical CPR group, defibrillations were given to all patients after 90 seconds of compression without rhythm check to reduce interruptions in compressions (as an unnecessary shock was thought to have less harm than interruptions).
Prehospital CPR is a unique entity
Manual CPR performance in the field creates unique challenges for EMTs and paramedics. In the hospital, the patient generally remains on a gurney with adequate staff to rotate every two minutes per the AHA standards. In a six-story walkup apartment, the situation is different: the initial team consists of two people, one of which needs to gather information, ventilate, obtain access, and give medications while the other does compressions. This is after they just carried their equipment up six flights of stairs. Maybe they have upset or angry bystanders to control as well. Eventually backup arrives, which may only be another pair of providers.
Many of these resuscitations are pronounced in the field, but not all. On scene, a mechanical CPR device can free up a provider to perform other tasks. During transport, however, is where the benefit of mechanical CPR truly emerges. Imagine performing compression in a stairwell, stopping on each landing to “catch-up” compressions since you can’t carry the person and do compressions simultaneously. Imagine performing compressions in an elevator on an upright patient because there is not enough room to lay the patient flat. Imagine standing up unrestrained in a moving ambulance driving lights and sirens through traffic to perform compressions on a patient.
None of these situations lend towards effective compressions, and some are even dangerous to providers. This is the reality of prehospital care that cannot be nicely quantified, and this is why proof of equivalency in neurologic outcomes between manual and mechanical CPR is so important.
The LUCAS device can provide effective and uninterrupted compressions during the entire EMS scene and transport experience. Although the LINC trial demonstrated that mechanical CPR is equivalent to manual CPR, mechanical compressions may reduce the risk of injury to providers without compromising patient outcome. From the perspective of the EMS arena, mechanical CPR may be more than just equivalent.
Expert Peer Review
Mechanical CPR is a concept that simply makes sense. Why not use a machine that creates the simple up and down motion of traditional CPR to free up providers to do other interventions? For years we’ve worked to maximize the quality of compressions. Rate is important so use a metronome or keep a song in your head that mimics the rate (the most frequently referred to is “Stayin’ Alive” by the Beegees but others have been cited). Humans get tired so let’s switch providers frequently. Pauses in CPR to check for pulse, cardiovert etc are bad. Unfortunately, based on Salim Rezaie’s ALiEM post and Scott Weingart’s peer review, it doesn’t look like hands-on defibrillation is ready for prime time. The device, however, allows for shocks to be delivered while compressions are administered. Solving these human factors with a simple automated device makes sense but does it work?
The two studies cited here by Dr. Kivlehan suggest these devices don’t help. The first study from 2005 demonstrated harm with an increased mortality rate in the group receiving treatment from the mechanical device. The more recent study (LINC trial) demonstrated equivalence of the LUCAS device with traditional CPR. Additionally, some advantages were given to the device: no blinding (clearly can’t be done), longer cycles of compressions (debatable advantage – increases pauses in traditional group), shock given without pulse check (decreases pauses in compressions). Bottom-line, though, is that there was no benefit in the primary outcome of survival at four hours.
Dr. Kivlehan, and many others, argues that use of this device is safer in the prehospital setting because compressions can continue while the patient is being carried, loaded or driven to the ED without interruptions and without harm to providers. I’m not a prehospital provider but it seems to me that patients without ROSC in the field shouldn’t be transported. This is supported by a recent study in Critical Care showing that only 0.49% of patients without ROSC in the field had a good neurologic outcome. A longer commentary on this paper can be found on Ryan Radecki’s EM Lit of Note site.
So what’s the real bottom line on mechanical devices? At this point in time, there’s no data that supports their use over traditional compressions. That being said, I guarantee there will be more studies looking for benefit. Why? The LUCAS device costs roughly $15,000. That’s a big price tag. Proving a benefit will lead to huge device sales. One in every ambulance in NYC (about 300 on the street at any one time) would carry a price tag of $4.5 million. How many should each hospital have? There’s a lot of money around this device but no numbers to support it’s widespread adoption.
For more information on the LUCAS trial, please see Rory Spiegel’s post on EM Lit of Note.
- Hallstrom A, Rea TD, Sayre MR, et al. Manual Chest Compression vs Use of an Automated Chest Compression Device During Resuscitation Following Out-of-Hospital Cardiac Arrest: A Randomized Trial. JAMA 2006 Jun 14 (295)22:2620-2628. Pubmed
- Rubertsson S, Lindgren E, Smekal D, et al. Mechanical Chest Compressions and Simultaneous Defibrillation vs Conventional Cardiopulmonary Resuscitation in Out-of-Hospital Cardiac Arrest: The LINC Randomized Trial. JAMA 2013 Nov 17 [Epub ahead of print]. Pubmed
- Goto Y, Maeda T, Nakatsu-Goto, Y. Neurological outcomes in patients transported to hospital without prehospital return of spontaneous circulation after cardiac arrest. Critical Care 2013; 17:R274 doi: 10.1186/cc13121 [Open Access]