Each year an estimated 165,000 people in the United States have an out-of-hospital cardiac arrest, and many more undergo in-hospital resuscitation [
In spite of the data and guidelines hospitals in the United States have been slow to adopt therapeutic hypothermia in the routine management of comatose postcardiac arrest patients [
This was a longitudinal comparative study of consecutive comatose postcardiac arrest survivors, who were treated with our institution’s hypothermia protocol (see the appendix). All patients were sedated and paralyzed to ensure comfort and prevent shivering. Target core temperature measured by bladder temperature was 32.0–34.0°C for 24 hours followed by spontaneous or passive rewarming over 12 hours. The start of the 24-hour cooling period was designated as the time of the written order to initiate the therapeutic hypothermia protocol and included the organizational time required for setting up the surface or endovascular cooling equipment and for the catheter insertion. All patients had bladder temperatures recorded hourly from the initiation of the cooling protocol. This study was approved by our institutional review board.
The study spanned the time period between February 2004 and September 2006 (~2.5 years). Between February 2004 and February 2005, hypothermia was induced using cold-water-circulating cooling blankets (Mul-T-Blanket with Gaymar Medi Therm III, Gaymar Industries, Orchard Park, NY) and ice bags. In February 2005 our institution converted to endovascular cooling using the Celsius Control System (Innercool Therapies, San Diego, CA) catheter. This catheter system has a feedback loop controlling target temperature by using a temperature sensing esophageal probe. In patients who underwent endovascular cooling, surface cooling was initiated until the catheter could be inserted. Patients did not receive ice-cooled intravenous fluids. The catheter was removed at the end of the 24-hour cooling period, and spontaneous or passive rewarming occurred over 12 hours.
The performance of endovascular versus surface-based cooling was compared by assessing the following variables: (1) number of hourly recordings in target temperature range (32–34°C) during the 24-hour cooling period, (2) time elapsed from the written orders to initiate the cooling protocol and the target temperature achieved (time required to insert the catheter was included in this time period), and (3) frequency of predefined adverse events possibly related to hypothermia or the use of an endovascular catheter or surface cooling technique during the first 7 days after cardiac arrest. Data was collected using the patients’ medical records. Details of the diagnostic criteria for adverse events may be found at the bottom of Table
Baseline characteristics and adverse events during the first week in the endovascular-(
Characteristic/adverse event | Endovascular number (%) | Surface number (%) | ||
---|---|---|---|---|
Mean age (years) | .28 | |||
Sex (males) | 18 (69%) | 12 (80%) | .22 | |
Mean weight (kg) | .15 | |||
Duration of the arrest (min) | 31 | 24 | .13 | |
Ventricular fibrillation arrests | 12 (46%) | 1 (7%) | .008 | |
Median time from arrest to initiation of cooling protocol (min) | 277 | 481 | .16 | |
Median Bladder T at initiation of cooling (°C) | 36.4 | 36.4 | .76 | |
Renal failure on admissionb | 10 (38%) | 10 (67%) | .06 | |
Hypotensionc | 10 (38%) | 4 (27%) | .21 | |
Bradycardiad | 18 (69%) | 8 (53%) | .16 | |
Other arrhythmias | 6 (23%) | 4 (27%) | .28 | |
New infection in 1st week | 16 (62%) | 8 (53%) | .23 | |
Pneumonia | 14 (54%) | 7 (47%) | .23 | |
Sepsis | 1 (4%) | 0 (0%) | .63 | |
Pancreatitis | 0 (0%) | 0 (0%) | — | |
Renal failure 1st weeke | 6 (23%) | 4 (27%) | .25 | |
Hemodialysis | 1 (4%) | 1 (7%)f | .48 | |
Coagulopathyg | 6 (23%) | 4 (27%) | .77 | |
Groin hematoma | 0 (0%) | N/A | — | |
Skin injury | 0 (0%) | 0 (0%) | — | |
Transfusion pRBC | 6 (23%) | 4 (27%) | .28 | |
Transfusion of platelets | 1 (4%) | 0 (0%) | .63 | |
Seizuresh | 2 (8%) | 2 (13%) | .33 | |
Deep venous thrombosisi | 3 (12%) | 1 (7%) | .38 | |
Pulmonary embolism | 1 (4%) | 0 (0%) | .63 |
a
Continuous variables were analyzed with the Wilcoxon Rank-Sum test. Categorical variables were analyzed with the Fisher’s exact test. Group differences were considered significant at
Forty-one cardiac arrest patients underwent hypothermia between February 2004 and September 2006 at our hospital: 15 with surface and 26 with endovascular cooling. In five patients in whom hypothermia was considered using endovascular cooling, surface cooling was used instead, because of a failed attempt at catheter placement (
Hourly bladder temperature recordings of each patient from the time point that the cooling protocol was initiated to the end of active cooling (24 hours). (a) Endovascular-cooled group (
The results of this study demonstrate that temperature control using the Celsius Control System Innercool catheter is more accurate in keeping patients in the target temperature range than surface cooling with ice bags and cooling blankets. Two similar studies also found that endovascular cooling is superior to surface cooling in maintaining a target temperature [
We felt that a pragmatic comparison between the two cooling methods in our study was the most appropriate and decided to compare them from the time point that it was decided to initiate the cooling protocol to reaching target temperature, hence including the organizational time required to implement each one of the two cooling techniques. After all, if one technique cools patients faster than another, but requires more time to initiate because of process issues, its apparent benefit may be negated. We observed a trend to reach target temperatures faster in the endovascular-cooled group despite the additional time required to move the patient to an intensive care unit bed or the cardiac catheterization laboratory prior to insertion of the catheter. Furthermore, sometimes a neurointensivist traveled from home to place the catheter. Adjunct cooling methods, such as ice-cooled intravenous fluid infusions, might have decreased the time to target temperature in both groups but were not used during the study period [
There was a trend towards better neurologic outcomes in the endovascular group. This finding may be based on imbalances in baseline characteristics and should not be interpreted as a suggestion of better clinical outcomes with endovascular cooling. Further, with increasing familiarity with the use of hypothermia at our institution, the time from arrest to initiation of cooling protocol decreased over time and tended to be less in the endovascular group. Thus, data of this study cannot be used to compare the clinical benefit of endovascular with surface cooling.
While this study did not specifically measure nursing satisfaction with the two cooling techniques, part of the reason we changed to endovascular cooling from surface cooling was that the nursing staff found the surface method very labor intensive. The application and removal of the ice bags and cooling blankets to maintain the target temperature was difficult and time consuming for the nursing staff. Despite the nurses efforts some patients would remain above or below the target range. The endovascular method, once in place, frees the nurse to focus on other duties, because temperature is automatically maintained in target range. Both techniques require an additional piece of equipment to be in the patient’s room and make transporting a patient more cumbersome. Special attention must be paid by the nurse when turning or transporting the endovascularly cooled patient as the patient’s leg must be kept straight on the insertion side. For the physician the endovascular technique is more labor intensive, and for those unfamiliar with the device it will require procedural training for placement.
Limitations of this study include its nonrandomized design and imbalances in the baseline characteristics between the two groups; however, we intended to compare performance of cooling technologies and not patient outcome. It is possible that newer, more sophisticated surface cooling technology, such as adhesive surface devices with patient temperature feedback to computer-controlled temperature management systems, performs even better than endovascular cooling techniques. Similarly, there may also be differences in performance among various commercially available cooling catheters. Other studies have reported effective temperature control and safety with the Icy catheter and CoolGard system [
Endovascular cooling to mild-to-moderate hypothermia is feasible in comatose postcardiac arrest patients. When compared with conventional surface cooling it is more accurate in maintaining target temperature, but it is not faster in terms of reaching target temperature, because of time lost to logistic issued associated with catheter insertion and setting up the cooling console. Further studies are needed to assess if differences in cooling accuracy translate into better clinical outcomes.
The authors have reported no conflicts of interest. The use of the Celsius Control System Innercool catheter for cooling postcardiac arrest patients is offlabel usage of the device.
This is adapted from the University of California San Francisco hypothermia after cardiac arrest cooling protocol with permission.
Age 18 years or older.
Women must be over 50 or have a negative pregnancy test.
Cardiac arrest with return of normal sinus rhythm.
Persistent coma as evidenced by no eye opening to pain after resuscitation (no waiting period required).
Blood pressure can be maintained at least at 90 mm Hg systolic either spontaneously or with fluid and pressor (no aortic balloon pump unless approved by cardiology).
Modified Rankin scale 0–2 prior to the arrest.
Any other overt reason to be comatose (e.g., sedating drugs, drug overdose, status epilepticus).
Pregnancy.
A known terminal illness preceding the arrest.
Known pre-existing coagulopathy or bleeding.
Pre-existing do not intubate code status and patient not intubated as part of the resuscitation efforts
Hypothermia should be initiated as quickly as possible. For out-of-hospital arrests the ED attending in conjunction with the neurocritical care/stroke team will make the decision to implement the protocol. For in-hospital arrests, the neurocritical care/stroke team in conjunction with the CCU or ICU fellow in charge of the patient will make the decision.
Page Neurology resident in house for immediate neurological assessment prior to pharmacologic paralysis. Do not delay initiation of cooling pending assessment.
Immediately place ice bags under the armpits, next to the neck, on the torso and limbs.
Temperature sensing Foley catheter should be placed, otherwise rectal or tympanic temperatures should be used (in that order) until Foley placement.
Two cooling blankets should be used, one under and one over the patient. Both should be set to maximum cooling.
The room thermostat should be turned off.
Administer midazolam and fentanyl for sedation or other sedatives as ordered by the primary team.
Once sedation is started and effective, give a vecuronium bolus, then continuous drip for paralysis or other paralyzing agent as ordered by the primary team. Titrate the drip to keep 1–2/4 twitches on train of four.
Patients should be on sliding scale insulin to maintain glucose between 151–200 mg/dL, daily aspirin, pressors to maintain blood pressure, and any antiarrhythmics as necessary. Place nasogastric tube for meds.
Patients may receive other cardiac interventions including systemic thrombolysis, anticoagulation, and urgent cardiac catheterization interventions as needed. Hypothermia should proceed concurrent with these interventions.
Once the patient reaches 34°C, remove the ice packs and top cooling blanket if necessary. The goal is for the patient’s temperature to remain between 32–34°C.
Begin passive rewarming 24 hours after the beginning of cooling (not 24 hours after target temperature is reached). The goal is to reach 36.5–37°C (If temperature increases over 37.5°C restart cooling blankets).
Turn room thermostat up to normal. Discontinue cooling blankets. May use regular blankets. Do not use warm air blankets unless temperature not at 36°C after 12 hours of passive rewarming.
Paralysis, then sedation, may be discontinued after rewarming to 36.5°C.
The neurocritical care/stroke team should be paged as part of the standard protocol for considering hypothermia following cardiac arrest. The neurocritical care/stroke team will evaluate the patient for endovascular cooling.
External cooling should be initiated immediately as per the standard protocol, pending evaluation for endovascular cooling. Patient must be able to tolerate large-bore catheter (as large as 14 F) into the inferior vena cava via a femoral vein.
If possible inform family members of the procedure and its risks and benefits and make a note of this in the chart.
Equipment needed for endovascular cooling:
innercool console, console-related equipment, cooling catheter equipment.
The neurocritical care/stroke team will place the endovascular catheter. Cooling will then be initiated using the innercool console to a target temperature of 33°C for 24 hours. All external cooling elements may be discontinued. Rewarming will take place passively over 12 hours to a target temperature of 36.5–37°C.
An abdominal X-ray should be obtained following placement of the catheter, but initiation of the endovascular cooling should not be delayed pending the result of the study.
Sedation, paralytics and mechanical ventilation should be employed as part of the standard hypothermia after cardiac arrest protocol.
Patients may receive other cardiac interventions, including systemic thrombolysis, anticoagulation and urgent cardiac intervention as needed.
The neurocritical care team will remove the catheter at the end of the 24-hour cooling period.
Start heparin subcutaneously 5000 unit q 12 hours, 12 hours after the catheter is removed.