Article, Cardiology

The introduction of an esophageal heat transfer device into a therapeutic hypothermia protocol: A prospective evaluation

a b s t r a c t

Background: Temperature management is a recommended part of post-resuscitation care of comatose survivors of cardiac arrest. A number of methods exist for temperature management, all of which have limitations. We aimed to evaluate the performance and ease of use of a new esophageal Heat transfer device (EHTD; Advanced Cooling Therapy, Chicago, IL, USA) for temperature management of adult survivors of cardiac arrest.

Methods: We performed a prospective study from March to June 2015. Our standard protocol uses servo- controlled water blankets supplemented with ice-cold saline in order to attain goal temperature (32?C-34?C) within 1 hour. We substituted the EHTD for our usual water blankets, then recorded temperature over time and adverse effects.

Main findings: A total of 14 patients were treated, with mean age 65.1 +- 13.7 years, and median weight 75.5 (70; 83) kg. Initial temperature was 35.3 +- 1.2?C. Mean Cooling rate during the induction phase was 1.12 +- 0.62?C/h, time to target temperature was 60 (41; 195) min and the volume of iced fluids infused was 1607 +- 858 ml (as compared with 2-2.5 L historically). The percentage of time outside target temperature range during the maintenance phase was 6.5% (0.0; 29.0). Rewarming rate was 0.22 (0.18; 0.31)?C/h. No major adverse effects were observed.

Conclusion: Using the EHTD, our patient population attained goal temperatures in one hour, the volume of ice- cold saline required to attain this cooling rate was decreased by one-third, and experienced a low percentage of time outside target temperature range and no major adverse effects.

(C) 2016 The Authors. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Temperature management is an important part of post-resuscitation care of comatose survivors of cardiac arrest. Therapeutic hypothermia has been a part of guidelines since 2005 [1,2], although controlled normothermia was as successful as TH in a large, prospective, random- ized study [3]. Both approaches to temperature management require the capability to control and, if necessary, induce changes to body tem- perature [2-4]. A number of methods exist for temperature management

Abbreviations: TH, therapeutic hypothermia; EHTD, esophageal heat transfer device; ICU, intensive care unit; CPC, cerebral performance category.

? SOURCE OF SUPPORT: The devices that were used in the study and article processsing

fee were provided by the manufacturer (Advanced Cooling Therapy, Chicago, Illinois). The manufacturer had no other involvement in the study.

?? Some of the data from this study were presented as an abstract at the ERC congress in

Prague in October 2015 (Markota A et al., Resuscitation 2015; 96: 138, doi: 10.106/ j.resuscitation.2015.09.328).

* Corresponding author. Medical Intensive Care Unit, University Medical Centre Maribor, Ljubljanska ulica 5, 2000 Maribor, Slovenia

E-mail address: [email protected] (A. Markota).

after cardiac arrest, all of which have limitations [5,6]. External, non- invasive temperature management methods require direct contact with 40-90% of patients’ skin, obstruct access to patient and are less efficient [4]. Intravascular methods are invasive in nature and expensive [5,7,8]. TH can be successfully induced via infusion of cold fluid, however, Fluid loading required to induce TH with this technique has been associated with negative effects on Ventilation parameters and greater use of di- uretics [4,9].

The esophageal heat transfer device (EHTD; Advanced Cooling Ther- apy, Chicago, Illinois) is a novel device designed as a silicone orogastric tube with 3 lumens: inflow and outflow lumens for Circulating water and an orogastric suction lumen [10]. It is connected to a generic exter- nal unit where water is cooled or heated according to differences be- tween a patient’s actual and desired temperature. It offers several potential advantages over external methods (greater heat conducting capability because of its proximity to the heart and great vessels, with less obstruction of access to the patient) and is minimally invasive when compared to intravascular methods [10-12].

We aimed to evaluate the performance and ease of use of the EHTD for temperature management of adult survivors of cardiac arrest after the introduction of the EHTD in our hospital.

http://dx.doi.org/10.1016/j.ajem.2016.01.028

0735-6757/(C) 2016 The Authors. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Materials and methods

Study design and setting

We performed a Prospective data collection in a tertiary medical in- tensive care unit (ICU) after the introduction of the EHTD in our hospi- tal, from March to June 2015. Institutional ethics committee approval (No 8-1/15) and patient/surrogate consent was obtained.

Study population

We included all comatose adult survivors of cardiac arrest, irre- spective of the initial recorded rhythm or location of arrest, treated with Targeted temperature management. We excluded patients with known or suspected esophageal deformity or evidence of esophageal trauma (eg, esophageal varices, history of esophagecto- my, previous swallowing disorders, achalasia, etc), known ingestion of acidic or caustic poisons within the prior 24 h, less than 40 kg of body mass, pregnancy, terminal disease and death likely b 24 h after admission.

Study intervention

Our standard protocol for targeted temperature management in co- matose survivors of cardiac arrest uses servo-controlled water blankets supplemented with ice-cold saline infusion in order to attain target temperature (32-34?C) within one hour [2,9]. In this study, we substituted the EHTD for our usual water blankets, then recorded tem- perature over time, and observed for any adverse effects. The EHTD is a silicone orogastric tube designed to enable transfer of heat to and from the patient through the esophagus via temperature-controlled water with an additional orogastric lumen [10]. The water circulates in a closed circuit via the inflow and the outflow lumens of the EHTD, with water temperature regulated by an external heat exchanger. We used an external unit with the lowest circulating water temperature of 13?C, rate of circulation 1.2 l/min and automated regulation of circulat- ing water temperature (CritiCool, MTRE, Rehovot, Israel) [13]. The EHTD was inserted using a laryngoscope by orogastric intubation to a depth of approximately 35 cm, after first connecting the EHTD to the external unit and turning on the water circulation to increase the rigidity of the device. Adequate placement was confirmed with auscultation above the stomach during insuflation of approximately 50 ml of air. Due to time constraint, locating the radioopaque tip of the device in stomach on chest radiograph was performed later, after the cooling had already started. Urinary bladder (Foley) or rectal temperature probes were placed for temperature measurement and feedback to the external heat exchange unit. Once inserted, the external unit was set to cooling mode. Intravenous infusion of iced fluids (normal saline or Ringer’s so- lution at 0?C-4?C) was started simultaneously at a predetermined vol- ume of 1000 ml if initial temperature was 34.1?C to 35?C, and 20 ml/ kg body weight (rounded to 500 ml) if N 35?C. Additional iced fluid was allowed if a goal temperature of 34?C or less was not achieved in 60 min after admission. During the maintenance phase, minor temper- ature fluctuations were defined as <= 0.5?C above or below target tem- perature range. No additional interventions were performed for minor temperature fluctuations. If temperature fluctuations were N 0.5?C, then additional external cooling/rewarming was allowed if temperature was above/below temperature range 32-34?C +- 0.5?C for more than 2 consecutive hours. Similarly, additional external cooling/rewarming was allowed if the rate of rewarming was above/below target rate (0.25?C-0.5?C/h) for more than 2 consecutive hours. Unwanted rewarming during the rewarming phase was defined as an increase of body temperature N 36.5?C at any point in time between 24 and 36 h after admission.

Measurements

We aimed to determine the cooling rate during the induction phase, to evaluate the feasibility of reaching a goal temperature of <= 34.0?C within 1 h, to measure the amount of intravenous iced fluids adminis- tered, to determine the time that Patient temperature was out of the target temperature range (32?C-34?C) during the maintenance phase, and to evaluate the feasibility of rewarming patients at a rate of 0.25?C-0.5?C/h. We also recorded any adverse effects, estimated the suc- cess rate of EHTD insertion, and recorded ICU survival, survival to hospi- tal discharge and neurological outcome of patients expressed in the Cerebral Performance Category scale [14].

Adverse effects were defined as: oral cavity, pharyngeal, esophageal or gastric injury or bleeding, dys- or odynophagia reported by patients, bradycardia b 30/min, the need for temporary transcutaneous or transvenous cardiac pacing, Aspiration pneumonia b 24 h after admis- sion, or any other adverse effect thought to be related to the use of EHTD. Patient temperature recording began with EHTD insertion and was recorded in 15 min intervals for the first hour and in hourly inter- vals until 36 h after admission. Unstructured interviews were per- formed with all nursing teams regarding workload associated with the device and any issues regarding the use of the EHTD in our clinical environment.

Data analysis

Descriptive statistics were performed. Cooling rate was derived by dividing the difference between each patients’ initial temperature and target temperature (34.0?C) with the time that was required to reach target temperature. The time that the temperature was out of the de- sired range was calculated from each patient’s data. Rewarming rate was derived by dividing the difference between each patient’s temper- ature at 24 h after admission and point in time when normothermia was achieved with the time that was required to reach normothermia. Sta- tistical analysis and presentation of results were performed using Microsoft Excel 2013 (Microsoft, USA) and SigmaPlot 11.0 (Systat Soft- ware Inc., USA).

Results

Baseline characteristics

A total of 14 patients were included from March to June 2015. Pa- tient characteristics are presented in Table 1. During this study period, 12 additional patients were admitted after successful cardiopulmonary resuscitation but were not treated with the EHTD: 4 were awake, 7 were not expected to survive 24 h, and one had suspected esophageal pathology (all patients with return of spontaneous circulation are

Table 1

Patient characteristics

Patient characteristics

Result

Age, mean (years +- SD)

65.1 +- 13.7

Male sex, n (%)

12 (86)

Weight, median (kg, IQR)

75.5 (70; 83)

Height, mean (cm +- SD)

174.1 +- 9.9

Initial temperature, mean (?C +- SD)

35.3 +- 1.2

body surface area, median (m2, IQR)

1.93 (1.83; 1.98)

Out-of-hospital cardiac arrest, n (%)

11 (78)

Initial rhythm VF/pVT, n (%)

9 (64)

Initial rhythm PEA/asystole, n (%)

5 (36)

Required noradrenaline, n (%)

13 (93)

Required neromuscular blocking agents, n (%)

13 (93)

Survival to hospital discharge, n (%)

7 (50)

good neurological outcome, n (%)

6 (43)

VF = ventricular fibrillation, pVT = pulseless ventricular tachycardia, PEA = pulseless electrical activity, ICU = intensive care unit.

admitted directly to our ICU, bypassing the emergency department, even in case comfort measures only are applied).

Main results

Details on each patient treated are shown in Table 2, and tempera- ture changes over time are shown in Figure. A mean of 1.6 (+-0.8) at- tempts were required for successful insertion of the EHTD. In all patients temperature was measured via the urinary bladder (Foley) catheter. A mean cooling rate during the induction phase of TH was

1.12 +- 0.62?C/h. A goal temperature of <= 34.0?C was achieved in a medi- an time of 60 (41.2; 195) minutes (Figure). The mean amount of intra- venous iced fluids infused was 1607 +- 858 ml (20.9 +- 9 ml/kg BW). In 6 patients target temperature was not achieved in 60 min after admission. The additional volume of intravenous iced saline was 500 ml for pa- tients no. 5, 8, 9, and 12, and 1000 ml for patients no. 2 and 14, and tar- get temperature was eventually achieved in all patients.

During the maintenance phase, the median percentage of time out- side the target range was 6.5% (0.0; 29.0). Overshoot cooling during the maintenance phase occurred in 2 patients with the lowest temperature being 31.2?C. In both cases, temperature returned to target range with- out additional interventions. Unwanted rewarming during the mainte- nance phase that required additional external cooling occurred in 4 patients. The duration of time that temperature was above target range was 9 h (patient No 1), 7 h (patient No 6), 5 h (patient No 8), and 8 h (patient No 9), and maximum temperatures during the episodes of unwanted rewarming were 35.1?C (patient No 1), 36.1?C (patient No 6), 34.6?C (patient No 8) and 35.2?C (patient No 9). Minor temperature fluctuations of b 0.5?C above target range occurred in additional 5 pa- tients. In these patients the temperature was controlled using the EHTD alone.

The median rate of rewarming was 0.22 (0.18; 0.31)?C/h (Figure). Additional External rewarming was required in one patient, who died after 4 days from cardiogenic shock and multiorgan failure.

One patient was found to have a superficial pharyngeal laceration one day after the removal of the EHTD. A local hemostatic agent was used and no additional procedures were necessary. One patient devel- oped radiographic signs of right lobe pneumonia within 24 h after ad- mission. One patient required temporary transvenous pacemaker insertion in the peri-arrest period before the insertion of EHTD or

initiation of cooling. Temporary pacemaker support was successfully discontinued after 2 h during ongoing cooling via EHTD. During treat- ment with the EHTD a total of 5 patients experienced episodes of atrial fibrillation, 5 patients suffered nonsustained ventricular tachycardia and one patient multiple episodes of ventricular tachycardia. Esophagogastroduodenoscopy was performed in 1 patient for indica- tions unrelated to the use of EHTD (preexistent microcytic anemia). Esophagogastroduodenoscopy was performed one day after removal of EHTD (the device was in situ for 3 days) and no changes were ob- served that could be attributed to EHTD (chronic hiatal hernia and chronic gastritis were present).

Patients who survived with good neurological outcome were interviewed for symptoms of dys- and odynophagia after discharge from the ICU and none were reported.

Seven patients (50%) survived to hospital discharge, 6 (43%) with Good neurologic outcome (CPC of 1-2) at discharge. Of 7 patients that did not survive, 5 died in the ICU setting. In 2 patients neurologic assess- ment was not possible due to early death in ICU. The EHTD was removed after 36 h in 5 patients. In 9 patients the device was left in situ after com- pletion of 36 h (mean duration 3.3 +- 1.0 days, with the longest being 5 days). The devices were inspected after removal and no major damage to the device, such as bulging, creases, surface degradation, etc., were visible.

Untill the removal of the EHTD it was the only orogastric or nasogas- tric tube used, and orogastric lumen of the device was used for applica- tion of therapy (eg. Dual antiplatelet therapy in patients with acute coronary syndrome) and for Enteral feeding. Nine patients were transported from the ICU with the device in-situ (e.g. for emergency coronary angiography, to radiology department), and no problems were encountered.

Unstructured interviews with nursing teams that worked with the device revealed that the device enabled good access to the patients (in- cluding oral hygiene), and the workload regarding temperature man- agement was felt to be decreased.

Discussion

We report here our initial experience with a novel temperature management device in a clinical setting where temperature manage- ment is important [15,16]. Initial case series have suggested favorable

Table 2

Main results

Patient

Initial bladder

Weight

Time to target

Cooling rate during the

Volume of fluids received

Time out of target range during the

Rate of

temperature

(kg)

temperature

induction phase (?C/h)

during the induction phase

maintenance phase (%)

rewarming

(?C)

(min)

(ml)

Altogether

Minor fluctuations (b0,5?C outside target range)

(?C/h)

1

35.2

56

45

1.6

1500

48

18

0.11

2

36.0

126

240

0.5

3500

0

0

0.10

3

34.4

69

15

1.6

1000

0

0

0.20

4

36.3

87

60

2.4

1500

4

4

0.32

5

35.1

80

180

0.4

2000

0

0

0.26

6

32.6

73

0

*

0

29

4

+

7

35.2

75

60

1.5

1500

13

13

0.30

8

36.0

91

300

0.4

2500

31

26

0.21

9

35.6

83

120

0.8

2000

36

9

0.25

10

34.8

76

30

1.6

1000

0

0

0.26

11

34.4

82

15

1.6

1000

4

4

0.63

12

36.6

59

180

0.9

1500

9

9

?

13

34.5

75

45

0.7

1000

17

17

0.26

14

37.8

70

360

0.6

2500

0

0

0.20

Medians (IQR)

or

Means

35.2 (34.5; 36.0)

75.5

(70;

83)

60 (41.2; 195)

1.12 +- 0.62

1607 +- 858

6.5 (0.0;

29.0)

4.0 (0.0; 13.0)

0.22 (0.18;

0.31)

(+-SD)

IQR = interquartile range, SD = standard deviation, * = no cooling rate was calculated because target temperature was present on admission, + = the patient was in normothermia when rewarming was initiated, ? = the patient never achieved normothermia during study period.

Figure. Temperature changes over time. Temperature changes during the induction, maintenance and rewarming phases from first measured temperature until 36 h after admission expressed as median values. Box plots indicate respective interquartile ranges, whiskers extend from 10th until 90th percentile.

temperature management in various conditions; our report is the first larger data set to be prospectively acquired [12,17].

Standard practice in our ICU is to use servo-controlled water blan- kets supplemented with ice-cold saline in order to attain goal tempera- ture (32?C-34?C) within one hour [5,18,19]. Although recent data has questioned the use of pre-hospital iced saline for induction of hypother- mia [9], fluid infusions are often required for early haemodynamic opti- misation in patients with Post-cardiac arrest syndrome [20-24]. Using the EHTD, we were able to utilize a smaller volume of iced fluids (1607 +- 858 mL, or 20.9 +- 9 mL/kg BW) than we typically utilize when using water blankets to attain goal temperature and smaller vol- ume compared to that as proposed by the guidelines at the time the study was performed (30 mL/kg BW) [2]. In a study performed in our site using the combination of intravenous cooling and water blankets, 2125 +- 694 ml were used to induce hypothermia [25]. During the in- duction of hypothermia we achieved a cooling rate of 1.12 (+-0.62)?C/

h. Similar rates have been achieved using intravascular devices or infu- sion of greater volumes of iced fluids [8,24,25]. In one of the largest re- cent studies to date, endovascular cooling devices were reported to have an average cooling rate of 0.39?C/h, while Surface cooling devices were reported to have an average cooling rate of 0.27?C/h [16]. Temper- ature control during the maintenance phase was comparable to intra- vascular cooling catheters [16].

The ability to gradually rewarm patients is important because of loss of protective effects of hypothermia electrolyte disturbances and an in- crease in insulin sensitivity in case of overly rapid rate of rewarming [3,4,26]. The EHTD enabled controlled rewarming with a median rate of 0.22 (0.18; 0.31)?C/h, which is comparable to intravascular devices [15,16]. We were unable to rewarm one patient despite supplementing the EHTD with additional external rewarming; that patient died in car- diogenic shock and multiorgan failure on day 4, suggesting that heat production was compromised by metabolic failure associated with irre- versible shock [27].

No serious adverse effects were observed in our study. The superfi- cial pharyngeal laceration appears likely to have been induced by oral hygiene procedures or laryngoscopy, which was used during placement of the EHTD to facilitate tongue displacement. Minor injuries to oral and pharyngeal mucosa occur in about 5% of laryngoscopy attempts [28]. The right sided pneumonia that presented within 24 h after admission was thought by the treating clinicians to be caused by aspiration prior to intubation. Pneumonia occurs in up to 40% of patients who undergo therapeutic hypothermia [29]. The incidence of supraventricular and ventricular dysrhythmias was also similar to previously published data for survivors of cardiac arrest [4,29].

Insertion of the EHTD was straightforward and was successful in all patients. All therapeutic and Diagnostic procedures (ECG, echocardiog- raphy, coronary angiography, brain CT, oral hygiene etc.) could be

performed with the device in-situ. The device was successfully used for application of therapy and for enteral feeding, obviating the need for additional naso- or oro-gastric feeding tube.

Limitations

Because our protocol utilizes cold saline to enhance the speed to goal temperature, we are unable to isolate the specific cooling rate of the EHTD. Nevertheless, when compared to our historical use of water blan- kets as the primary Temperature control modality, we found that we could reduce our use of cold saline by approximately one third [25]. Fu- ture iterations of our standard temperature management protocol may result in our abandoning the use of cold saline, enabling further charac- terization of the specific cooling rate of the EHTD. Also, we utilized an external heat exchange unit that attains a Low Temperature of circulat- ing water of 13?C, and a rate of circulation of 1.2 l/min, as compared to 4?C and 2.6 l/min in other external units [11,13,17,30]. Higher cooling rates and further improvements in temperature control might be ex- pected with a higher water flow rates and lower minimum tempera- tures. We did not formally study the clinician workload associated with the device; although informal interviews with nursing teams were performed, a standardized questionnaire would offer more granu- larity and validity.

To conclude, using the EHTD, our patient population attained goal temperatures in 1 hour, using approximately two-thirds the amount of ice-cold saline typically required to attain this cooling rate, and experiencing a low percentage of time outside target temperature range. The EHTD could potentially be a useful tool for targeted temper- ature management in survivors of cardiac arrest.

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