Mechanical CPR and the LINC trial

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.

Bottom Line

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.

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