E-CPR in Cardiac Arrest due to Accidental Hypothermia Using Intensivist Cannulators: A Case Series of Nine Consecutive Patients

Introduction

Severe accidental hypothermia (AH), defined as an involuntary decline in core temperature to <28 °C, ¹ accounts for an average of over 1300 deaths per year in the United States (US).^2,3 Extracorporeal Cardiopulmonary Resuscitation (E-CPR) use is associated with improved outcomes, ⁴ and is recommended in current guidelines.^1,5,6

Prior publications reporting the success of E-CPR for cardiac arrest due to AH have described cannulation techniques performed primarily by cardiovascular surgeons^7–12 with a neurologically intact survival ranging from 26.5% ⁹ to up to 90% ¹³ at established centers. To our knowledge, none of the studies was performed in the United States using intensivist physicians (IPs) as cannulating proceduralists.

In 2017, we created an intensivist led extracorporeal life support (ECLS) team using IPs as cannulators for both veno-venous (V-V) and V-A ECLS. E-CPR is part of our ECLS program, and IPs respond to all cardiac arrests arriving in the Emergency Department (ED). We aimed to evaluate the use of E-CPR for patients undergoing out-of-hospital cardiac arrest (OHCA) due to AH in the United States at a center with IPs as cannulators.

Methods

Results

Nine patients were identified with OHCA due to AH as the indication for initiation of V-A ECLS. The patient characteristics and initial biological data are presented in Table 1.

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Table 1.

Patient Characteristics and Initial Biological Data.

Patient	Age	Sex	Cause of hypothermia	Witnessed (Yes/No)	Initial rhythm	Core temperature (celsius)	pH	Lactate (mmol/L)	Potassium (mmol/L)	EtOH (mg/dL)	Time from arrest to cannulation (min.)	Time from arrival to cannulation (min.)	Time to temp >34 °C (min.)	HOPE Score (%)
1	23	M	Exposure/immersion	No	VF	24	6.8	17.7	2.9	0	261	71	280	72
2	27	M	Exposure	Yes	PEA	23	6.7	4.4	5.6	0	49	44	85	62
3	41	M	Exposure	Yes	VF	24.7	7.29	10.1	3.8	577	60	34	220	69
4	49	M	Exposure	Yes	VF	22.6	7.09	11.6	4.4	306	34	64	575	76
5	54	M	Exposure	No	VF	24.1	6.8	15	3.9	26	31	24	130	77
6	56	M	Exposure	Yes	VF	25.4	6.8	20	4.9	19	21	53	535	60
7	60	M	Exposure	Yes	VF	22	7.1	7.6	4.2	—	37	39	160	76
8	65	M	Exposure	Yes	VF	25.2	7.2	8.5	4.5	176	19	32	115	66
9	60	M	Exposure	Yes	VF	24.5	7.1	6.8	2.8	288	17	17	3	92

There was no ethanol level measured for patient number 7. EtOH denotes Ethanol, HOPE Hypothermia Outcome Prediction after ECLS, PEA Pulseless Electrical Activity, VF Ventricular Fibrillation.

The average age was 48 years old. All patients were male. All arrests involved exposure in a cold weather environment with one patient having a simultaneous water immersion event. Seven arrests (78%) were witnessed. All patients were in active cardiac arrest during cannulation for V-A ECLS. Three patients developed cardiac arrest in the field, two arrested during ground transport, and four patients had cardiac arrest shortly after arrival in the ED. For the six patients who developed cardiac arrest prior to arrival, the mean time from cardiac arrest to arrival in the ED was 55.5 min (range 5 to 180 min). The mean time from cardiac arrest to initiation of ECLS was 58 min (range 17 to 251 min). For the four patients that arrested after arrival, the mean time from ED arrival to the initiation of ECLS was 42 min. The mean initial core temperature was 23.8 degrees Celsius (range 22-24.4 degrees Celsius). The initial rhythm was ventricular fibrillation (VF) in 8 patients and pulseless electrical activity (PEA) in one. Four patients had a blood alcohol content above 80 mg/dL, the legal limit for impaired driving in the state of New Mexico. The mean initial pH was 6.98 and the mean lactate was 11.3 mmol/dL (range 4.4-17.7 mmol/dL). The mean HOPE ⁷ score survival predictability was 72.2% (range 60-92%).

Patient outcomes are presented in Table 2. The mean duration of ECLS was 39.1 h (range 2-109). The mean hospital length of stay was 10.2 days (range 1.3 to 20.7). Five patients were discharged home, 2 patients were discharged to an acute rehabilitation facility, 1 patient was transferred to a skilled nursing facility, and 1 patient was transferred to a Veteran's Administration hospital. All nine patients had a CPC score of 1 or 2 at the time of discharge or transfer.

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Table 2.

Patient Outcomes.

Patient	Survival to discharge (Y/N)	Duration of ECLS (hrs)	Hospital length of stay (days)	Discharge destination	Cerebral Performance Category at discharge
1	Y	72	19.8	Acute rehab	2
2	Y	31	11.5	Home	1
3	Y	29	3.8	Home	1
4	Y	26	9.3	Acute rehab	1
5	Y	109	20.7	Skilled nursing facility	2
6	Y	6	1.3	Home	1
7	Y	52	15.2	Transfer to VA hospital	2
8	Y	2	3.2	Home	1
9	Y	25	7	Home	1

ECLS denotes Extracorporeal Life Support.

Discussion

We present nine consecutive patients over a 4-year period that presented with cardiac arrest due to AH treated with ECLS who survived with a favorable neurological outcome. To our knowledge, this is the largest report of consecutive patients with cardiac arrest due to AH with a 100% favorable neurological outcome. This occurred despite prolonged downtimes, relatively advanced age, and markedly elevated lactate levels, all of which would be associated with poor survival in other forms of cardiac arrest ¹⁶ and E-CPR. ¹⁷

In an analysis performed by Pasquier et al, ⁷ the average duration of CPR prior to cannulation was 106 min in survivors and 120 min in nonsurvivors, a statistically significant difference. The average time from arrest to cannulation in their study was 120 min, with an overall survival rate of 37%. In our series, one patient was transferred to two facilities while undergoing CPR prior to ECLS cannulation and therefore had a CPR duration of 251 min. If that patient is excluded, the average time from cardiac arrest to cannulation was 34 min. This was enabled by the availability of an IP for cannulator at all times as part of our hospital's E-CPR program, which likely contributed to the high survival rate seen in this case series.

It should be noted, however, that three of the patients were cannulated after a duration of CPR longer than the sixty minutes recommended by the ELSO ¹⁵ and all survived with a favorable neurologic outcome. This is consistent with prior data^7,9 indicating that duration of CPR, though inversely correlated with survival, is not prohibitive, and in our study one patient survived with a favorable outcome after nearly four hours of CPR. In fact, neurologically intact survival after cardiac arrest from AH after over six hours of CPR has been reported. ¹⁸ Potassium levels have been shown to be informative in determining whether or not resuscitation should continue in cardiac arrest due to AH. ⁷ In this case series, all patients had normal or nearly normal potassium levels and none had potassium levels above 12 mmol/L, a criteria for withholding ECLS for cardiac arrest due to AH at our center. ¹ The HOPE score, an established prediction model for survival in hypothermic cardiac arrest, ⁷ predicted a high likelihood of survival in the patients in this series.

Mean duration of ECLS support in our patients was 39.1 h (1.6 days), which is shorter than the 78 h (3.25 days) reported in other survivors of E-CPR. ¹⁹ Further, the mean hospital length of stay was 10.3 days, which is substantially lower than the hospital length of stay seen in other studies involving E-CPR for OHCA. ²⁰ This is likely due to the more immediate reversibility of hypothermia as a cause of cardiac arrest, as well as the relative lack of need for interventions other than rewarming.

The state of New Mexico is a high-desert environment that often sees temperatures well above freezing during the day, even in mid-winter. At night the temperature rapidly drops, often well below freezing. This creates an environment where people may be comfortable outside during the day but rapidly develop hypothermia at night, leading to a relatively high frequency of cardiac arrests due to AH. In similar geographic regions, a readily available, rapidly deployable E-CPR program may be useful.

At our center, employing IPs as cannulators enabled the development of a rapidly deployable E-CPR program. The use of IPs for cannulation has been shown to be safe and effective^21,22 and there were no cannulation complications in this series. Using IPs as cannulators may decrease response time due to the lack of competing operating room obligations. Our IPs are also the primary managers of patients on ECLS and manage the patients from time of admission to discharge. This may contribute to the high survival seen in this series.

Limitations

This is a single-center case series with no control group, so it is impossible to determine whether standard rewarming would generate similar outcomes, although the outcomes in our case series are superior to those reported in cohorts without E-CPR. ²³ The cohort in this study was also entirely male, all were found outdoors, and a majority had an elevated blood alcohol level. Hence, this group does not represent the wide variety of patients that are known to present with hypothermic arrest, such as victims of avalanche or prolonged immersion. Further, though the patients in our cohort did not have clinically apparent neurological deficits at discharge, we were not able to perform long-term follow-up or neuroimaging to evaluate for milder forms of cognitive impairment. However, prior evidence suggests minimal cognitive impairment in this patient population. ¹¹

Conclusion

We present the largest reported case series of consecutive patients with cardiac arrest due to AH who all survived with a favorable neurologic outcome after being treated with an intensivist-led E-CPR system. Larger cohort studies are needed to further elucidate the effect this E-CPR system may have on survival in OHCA due to AH.