Mechanical Cardiopulmonary Resuscitation During In‐Hospital Cardiac Arrest

In‐hospital cardiac arrest (IHCA) strikes ≈300 000 hospitalized patients every year in the United States alone. ¹ High‐quality cardiopulmonary resuscitation (CPR) is a critical component of IHCA resuscitation care and is associated with higher rates of survival and reduced neurocognitive disability. As such, optimizing the quality of CPR during IHCA is a key priority emphasized in scientific statements from the American Heart Association and international cardiac arrest guidelines. ² , ³ Despite these educational efforts, studies have shown that CPR quality during IHCA remains suboptimal, likely because of a range of factors including rescuer fatigue during prolonged resuscitation; interruptions in CPR during defibrillation, intubation, and other intra‐arrest interventions; and inadequate depth and rate of chest compressions. ⁴ , ⁵

In contrast to conventional delivery of manual CPR, mechanical CPR devices represent a potentially appealing alternative as they can provide uninterrupted chest compressions at appropriate rate and depth and are not limited by human performance variability and fatigue. During prolonged resuscitation efforts, these devices can free team members for other tasks and potentially reduce room crowding. Currently available devices include the Lund University Cardiopulmonary Assist System (LUCAS, Stryker Medical, Kalamazoo, MI), the Autopulse (ZOLL Medical Corporation, Chelmsford, MA), and the Thumper (Michigan Instruments, Grand Rapids, MI). These devices use a piston, band, or vest to externally compress the thoracic cavity. ⁶ However, the use of these devices is not without disadvantages, including the need to pause CPR for device deployment and a risk of traumatic injuries from the devices themselves. The majority of high‐quality studies comparing mechanical CPR to manual CPR have been performed in the setting of out‐of‐hospital cardiac arrest (OHCA) and have not found a benefit of mechanical CPR over manual CPR. ⁷ , ⁸ , ⁹ The data comparing the effectiveness of mechanical CPR devices in IHCA are much more limited (Table 1). ¹⁰ , ¹¹ In the absence of robust clinical trial data, members of hospital cardiac arrest committees must weigh the risks, benefits, and costs of whether, how, and when to integrate these technologies into their IHCA response. Given these data, the American Heart Association states that “the use of mechanical CPR devices by trained personnel may be beneficial in settings where reliable, high‐quality manual compressions are not possible or may cause risk to personnel,” but the guidelines do not give specific consideration for the use of mechanical CPR during IHCA. ² In this Perspective, we present a summary of current data on the use of mechanical CPR during IHCA to inform these decisions.

Table 1.

Summary of Three Randomized Controlled Trials of Mechanical Cardiopulmonary Resuscitation Use in In‐Hospital Cardiac Arrest

Author	Year	Design	Intervention	Device	Number of cases	Primary outcome	Results
Couper	2021	Multicenter, feasibility RCT	3:1 Randomization mechanical vs manual CPR	Lund University Cardiopulmonary Assist System	127 patients with IHCA	Proportion of eligible participants who were successfully randomized	55% of eligible participants recruited. No difference when comparing rates of ROSC, survival to discharge, or survival with a good neurological outcome at 6 mo.
Halperin	1993	Single‐center RCT	1:1 Randomization mechanical vs manual CPR	Thoracic‐vest system	34 patients with IHCA	ROSC	ROSC rate higher in mechanical vs manual CPR (47% vs 18%).
Taylor	1978	Single‐center RCT	1:1 Randomization mechanical vs manual CPR	Piston‐driven CPR device	30 patients with IHCA	1‐hour survival	No difference in 1‐hour survival between mechanical vs manual CPR (38% vs 42%)

CPR indicates cardiopulmonary resuscitation; IHCA, in‐hospital cardiac arrest; RCT, randomized controlled trial; and ROSC, return of spontaneous circulation ¹² , ¹³ , ¹⁴

Studies Comparing Survival After IHCA With Mechanical CPR Versus Conventional CPR

Few studies have focused on barriers to high‐quality CPR during IHCA, where impediments are likely to differ substantially from those seen during OHCA. In addition to differences in the patient populations who experience IHCA compared with OHCA, the provider response to IHCA also differs considerably. Given the resources available in the hospital setting, CPR is typically started earlier than in OHCA, prolonged CPR by a single individual is unusual, and survival rates are often higher than in OHCA. Given these differences, the results from studies of mechanical CPR during OHCA may not be generalizable to cardiac arrests occurring in the in‐hospital environment.

Few randomized controlled trials (RCTs) have examined whether mechanical CPR has a survival benefit over conventional manual CPR during IHCA. Most of these trials failed to demonstrate superiority of mechanical CPR over conventional CPR, consistent with OHCA trials of mechanical CPR. The most robust of these was COMPRESS‐RCT, an RCT that randomized 127 patients in a 3:1 ratio to mechanical CPR versus conventional CPR. ¹² Although mortality was not the primary outcome, no difference was found between mechanical CPR and conventional CPR when comparing rates of teturn of spontaneous circulation (ROSC; 28% versus 25%), survival to hospital discharge (4% versus 4%), or survival with a good neurological outcome at 6 months (1.0% versus 0%). ¹² However, this study was limited by low survival in both arms and lower‐than‐expected recruitment. There are 2 published prior RCTs of mechanical CPR use in IHCA, which served as preliminary efficacy studies describing novel mechanical CPR devices. ¹³ , ¹⁴ Neither of these trials found a difference in survival between mechanical CPR or manual CPR, although one study found that the use of mechanical CPR was associated with higher rates of ROSC and survival at 1 hour. However, no patients in this trial survived to hospital discharge. ¹³ , ¹⁴ Another RCT, performed by Lu and colleagues, enrolled only patients who experienced cardiac arrest in the emergency department and as such represented a very specific arrest population. ¹⁰ , ¹¹ , ¹⁵ Several observational studies have also been published comparing patients with IHCA who received mechanical CPR and those who received conventional CPR. However, these observational studies should be interpreted with caution because of the high risk of bias, particularly from confounding by indication as the responding providers may be unlikely to start mechanical CPR in cases of IHCA that they deem to be futile, and additional confounding from immortal time bias as patients who receive mechanical CPR have not attained ROSC by the time the responding team members apply mechanical CPR devices. Therefore, current evidence does not support routine use of mechanical CPR for all in‐hospital resuscitation events.

Potential Benefits of Mechanical CPR During IHCA in Special Situations

In‐hospital cardiac arrest teams can become large owing to the need to circulate compressors. Use of a mechanical CPR device can, in theory, allow for members of the team to leave the room, potentially requiring fewer individuals to be present during resuscitation efforts. This may be an important factor in settings where human resources might be limited. The issue of crowding became particularly relevant during the COVID‐19 pandemic, where viral aerosolization during CPR was a central concern during IHCA events. As such, many hospital systems acquired mechanical CPR devices during the pandemic to reduce exposure of health care workers. ¹⁶

IHCA During Cardiac Procedures

Cardiac arrest can sometimes occur as a complication during cardiac catheterization procedures. The underlying cause of arrest in these situations could be acute myocardial infarction or a complication of the procedure itself (eg, coronary artery dissection), both of which require rapid intervention. Therefore, high‐quality resuscitative measures (CPR and defibrillation) need to be combined with immediate efforts to reestablish coronary blood flow (eg, angioplasty and stenting of the infarct related artery). Given these dual objectives, providing high‐quality CPR during a cardiac catheterization procedure can be especially challenging. Moreover, limited space around the fluoroscopy unit and radiation exposure also creates barriers for effective CPR. Mechanical CPR devices are attractive in this setting as they avoid radiation exposure to the team members and can ensure ongoing CPR while the underlying cause of the arrest can be promptly addressed. ¹⁷ Several mechanical CPR devices have been designed to be partially radiolucent to facilitate such interventions. ¹⁸ In recent years, there has been growing enthusiasm for extracorporeal membrane oxygenation (ECMO) for use in refractory cardiac arrest, largely based on the positive findings from the advanced reperfusion strategies for patients with out‐of‐hospital cardiac arrest and refractory ventricular fibrillation (ARREST) trial. ¹⁹ Resuscitation in the ARREST trial was facilitated with the use of the Lund University Cardiopulmonary Assist System device to provide continuous CPR during prolonged transport and ECMO cannulation. Although the potential for ECMO as a strategy for refractory IHCA remains unclear, mechanical CPR devices could play an adjunctive role similar to OHCA, in selected patients considered for ECMO for refractory IHCA while the ECMO team is mobilized.

Potential Risks of Mechanical CPR

Delays in CPR for Device Application

The use of mechanical CPR in IHCA does not come without risks. The time required to apply mechanical CPR devices can lead to delays in initiation of CPR during the early phase of cardiac arrest when the likelihood of achieving ROSC may be greatest. Prolonged pauses could potentially have a substantial impact on the likelihood of achieving ROSC but are not widely reported in the published literature. In the setting of RCTs, relatively short deployment times have been reported, highlighting that delays can be minimized with appropriate training. For example, in the COMPRESS‐RCT, the mean pause durations for backplate and upper portion deployment were 7.3 seconds and 9.8 seconds respectively, which highlights the importance of ongoing training of resuscitation teams in the use of mechanical CPR devices when such devices are used as a standard part of IHCA resuscitation practice. ¹²

Injuries From Mechanical CPR

Several studies have demonstrated traumatic injuries associated with the use of mechanical CPR, which range from relatively benign injuries to life‐threatening or fatal ones. Such injuries are commonly caused by CPR, whether manual or mechanical and include fractures of ribs and sternum as well as damage to organs such as the liver, heart, and lungs. A recent meta‐analysis suggested that mechanical CPR may be associated with an increased risk of rib fractures as well as heart and liver injuries. ²⁰ Such injuries may be caused by poor placement or migration of the device during resuscitation. The risks of CPR pauses and injuries may be mitigated by ongoing high‐quality training of cardiac arrest teams in the correct use of mechanical CPR devices, although whether such training reduces such complications has not been rigorously studied.

The efficacy of mechanical CPR for IHCA remains incompletely understood. Several knowledge gaps remain that, when answered, might help to clarify the population who should receive mechanical CPR, where in the hospital it should be used, and how best to implement a mechanical CPR program. Some of these are highlighted in Table 2.

Table 2.

Examples of Key Knowledge Gaps in the Use of Mechanical CPR During IHCA Events

Knowledge gap	Example questions
Which populations might benefit the most from mechanical CPR?	Do outcomes from mechanical CPR use in IHCA differ between different inpatient settings or cardiac arrest rhythms? (eg, cardiac arrest in procedural settings, emergency department) Does use of mechanical CPR improve success of interventional procedures such as extracorporeal membrane oxygenation cannulation or coronary catheterization? Does deployment of mechanical CPR earlier during a resuscitation lead to better outcomes compared with manual CPR? Is mechanical CPR more useful in situations with limited human resources?
High‐quality mechanical CPR	Who should apply the mechanical CPR device? At what point during the resuscitation effort should the device be applied? Can the efficacy and safety of mechanical CPR devices be improved with simulation training or pit‐crew model of IHCA?
IHCA dynamics	Does use of mechanical CPR during IHCA improve team dynamics, communication, coordination, and leadership? Does use of mechanical CPR affect postevent attitudes of the resuscitation team?
Implementation of mechanical CPR	What barriers and facilitators exist to the implementation of mechanical CPR in the inpatient setting? Is mechanical CPR cost effective?

CPR indicates cardiopulmonary resuscitation; and IHCA, in‐hospital cardiac arrest.

Conclusion

Optimizing the quality of CPR remains a crucial factor to improve survival rates from IHCA. Although an this is an attractive solution, studies have not demonstrated the superiority of mechanical CPR compared with conventional CPR during IHCA. Although use of these devices may have a place in specific resuscitation scenarios, the current evidence does not support a strategy for routine use of mechanical CPR devices for in‐hospital resuscitation. More research is needed to establish how the balance of risks and benefits of mechanical CPR use differs in IHCA when compared with OHCA.

Sources of Funding

Dr. Girotra is currently supported the National Heart, Lung, and Blood Institute (R56HL158803, R01HL160734).

Disclosures

Dr Abella holds equity and research funding from VOC Health, a company developing novel COVID testing. He also holds research funding and has received speaking honoraria from Zoll and Becton Dickinson. For the remaining authors, no conflicts of interest were declared. Dr Girotra has received funding from the American Heart Association for editorial work.