Heated Humidified Breathing Circuit Rewarming in Hypothermic Post Cardiopulmonary Bypass Patients.
Phase: NA
Conditions: Hypothermia, Rewarming
Sponsor: Duke University

 
 
 
 
 
 
 
 
Heated Humidified Breathing Circuit Rewarming in Hypothermic Patients after 
Cardiopulmonary Bypass 
 
NCT03697122 
 
Document Date: 02/25/2019 
 
 

Heated Humidified Breathing Circuit Rewarming in Hypothermic Patients after 
Cardiopulmonary Bypass 
 
Purpose of the Study 
  
Our primary objective is to assess whether use of Heated Humidified breathing circuits (HHBC) 
decreases time to normothermia (≥ 36.5 °C). 
Our secondary objectives are to assess whether use of HHBC shorten time to extubation, 
improve coagulopathy, decrease bleeding, and metabolic derangements seen with hypothermia. 
We propose the hypothesis that:  Rewarming hypothermic patients (≤ 35 °C) admitted to the 
CTICU following cardiac surgery with CPB, using HHBC in addition to conventional forced air warming 
blankets will shorten time to normothermia. 
 
Background & Significance 
 
To reduce the rising cost of cardiac operations, researchers have studied early extubation as a 
means to shorten ICU length of stay, and favorably influence patients’ health outcomes. In the process, 
various nursing ICU protocols have been developed to facilitate the expedient tracheal extubation of 
patients, taking into account hemodynamic status, mediastinal drainage, urine output, patient 
temperature (rewarming from induced hypothermia), and other factors. 
  
Hypothermia on admission to the ICU following CPB is common. Cooling and rewarming during 
CPB and takes considerable time and contributes to the post-procedural coagulopathy and physiologic 
perturbations. 
  
Rewarming in the postoperative period after hypothermic CPB is often associated with 
hemodynamic and ventilatory instability. Temperature changes, PaCO2 values, and mechanical 
ventilation were observed for the first 12 hours in the ICU in 73 patients who had undergone cardiac 
surgery with hypothermic CPB. Mean rectal temperature increased from 34.7 to 38.3 degrees C over the 
first 8 hr after admission to the ICU. The temperature curve was sigmoid rather than linear, and the 
most rapid rate of temperature increase occurred 2-4 hours after admission. During rewarming, the 
most common abnormality of PaCO2 on mechanical ventilation was acute respiratory acidosis (PaCO2 
greater than 45 mmHg, pH less than 7.35), which occurred in 42% of patients. 
  
After disconnecting from CPB the body is allowed to self-equilibrate. The normal 
vasoconstriction response is impaired by the administered anaesthesia. Hence, heat distribution takes 
place from the warm core to the colder periphery. This causes an afterdrop: a decrease in the 
temperature of the core organs. After-drop may contribute to post-operative complications of 
hypothermia such as shivering, coagulopathy, increased myocardial stress, increased wound 
infections,metabolic acidosis, delayed extubation and prolonged ICU length of stay. 
  
The current standard of rewarming patients in the ICU is to use forced air heating blankets. 
Forced-air blankets reduce the core temperature afterdrop by 60%. However, heat-balance data 
indicate that this reduction resulted primarily because forced-air heating prevented the typical decrease 
in body heat content after discontinuation of CPB, rather than by reducing redistribution. They do not 
lead to clinical relevant changes in deep thigh temperature, or toe perfusion. The extra heat especially 
favors core temperature. This is underlined by the decrease in postoperative leg blood flow, suggesting 
that the majority of the warmed blood leaving the heart flows to core organs and not to the periphery. 

A recent Cochrane review showed that active warming, particularly forced air warming, appears 
to offer a clinically important reduction in mean time taken to achieve normothermia (normal body 
temperature between 36°C and 37.5°C) in patients with postoperative hypothermia. However, high-
quality evidence on other important clinical outcomes is lacking; therefore it is unclear whether active 
warming offers other benefits or harms. High-quality evidence on other warming methods is also 
lacking; therefore it is unclear whether other rewarming methods are effective in reversing 
postoperative hypothermia. 
  
Regarding HHBC, Hyungseok et al recently showed that a heated humidifier is more effective in 
preventing intraoperative core temperature decrease in elderly patients than a heat moisture exchanger 
alone. Sooyong et al showed that a decrease in core temperature from anesthetic induction to 120 
minutes after induction was lower in the HHBC group in patients undergoing hip arthroscopy. Park et al 
showed that HHBC influences heat redistribution in early period of thyroid surgery and can lessen the 
magnitude of the decrease in core body temperature. Frank et al showed that the delivery of warmed, 
humidified O2 via nasal canula accelerates core rewarming rate by approximately two-fold in mildly 
hypothermic postoperative patients. A recent fellow QI project used HHBC during rewarming of patients 
in the operating room following DHCA procedures found that it significantly attenuated the temperature 
afterdrop upon separation from CPB when compared to standard airway circuits. 
  
Design & Procedures 
 
Hypothermia (≤ 35 °C) after cardiac surgery using CPB is not uncommon. To avoid complications 
associated with hypothermia, and due to absence of shivering when patient is sedated, and harmful 
effects of shivering when patient is awake, clinicians resort to active warming devices. Forced air 
warming devices are the most commonly utilized, but occassionally heated humidified breathing circuits 
are used as well. We plan to use both warming devices on study patients, and compare them with a 
historical cohort that has used forced air warming device only. 
On admission to CTICU, if temperature ≤ 35 °C, we will attempt to recruit the patient. Patients 
are intubated and sedated on admission to the CTICU after cardiac surgery, so informed consent will be 
obtained from the patient's next of kin or power of attorney. After consent is obtained, the clinical 
provider will ask the patient's nurse to place a lower body forced air warming device and set to 38 °C, 
and ask the respiratory therapist to set up and connect a heated humidified breathing circuit. 
Admission temperature and other vital signs will be recorded per CTICU standards. Other 
patient management decisions (ie medication changes, laboratory assessments…etc) per direction of 
ICU providers. Core temperature and location (esophageal, nasopharyngeal, bladder, rectal, blood) will 
be recorded every 15-30 minutes until normothermia reached (36.5 °C), then record per CTICU 
standard. Record active warming methods in nursing flow sheets (i.e. Forced air warming blanket and 
heated humidified breathing circuit). Record other vital signs, medications, extubation time, hourly 
chest tube output, and patient data per unit policy. Alert Respiratory therapy once normothermia (36.5 
°C) has been achieved for discontinuation of HHBC. 
 
Selection of Subjects 
  
For the prospective part of the study: 
 

Inclusion Criteria: 
Adult patients (18-85 years old) Admitted to CTICU following cardiac surgery using CPB. 
Admission temperature ≤ 35.0 °C. 
  
Exclusion Criteria: 
Patients admitted to ICU on ECMO support. 
  
For the retrospective part of the study: 
 
We will be matching the 14 prospective patients who received both ANAPOD and forced warm air with 
28 retrospective ones who presented with hypothermia that were treated with forced warm air alone 
without ANAPOD. Criteria should include: 
 
• 
Hypothermic Patients (Temp < 35C) undergoing cardiac surgery under CPB who received forced 
warm air alone. 
• 
Temp at time of ANAPOD application would be our reference point. 
• 
Type of surgery 
• 
Patient’s BMI 
• 
Deep hypothermic arrest 
 
Subject Recruitment and Compensation 
 
All adult patients (18-85 years old) Admitted to CTICU following cardiac surgery using CPB, with 
an admission temperature ≤ 35.0 °C will be considered for recruitment. 
Both males and females and all demographic groups will be included. 
  
Patients are intubated and sedated on admission to the CTICU after cardiac surgery, so informed 
consent will be obtained from the patient's next of kin or power of attorney by one of the patient's care 
providers or study personnel. 
  
Approximately 14 patients will be included in the prospective recruitment of patients. Data will 
be matched with a historical cohort of 28 patients (2:1 matching). 
  
No compensation will be offered. 
  
Consent Process 
  
Typically, patients remain intubated and sedated until hypothermia resolves. Patients will not be 
able to consent for themselves for this study. Informed consent will be obtained from next of kin / 
power of attorney. 
 
Risk/Benefit Assessment 
 
Heated humidified breathing circuits are being used clinically to avoid / treat hypothermia both 
in the OR and the ICU. We aim to examine if this clinical practice provides additional benefit to the 
forced warm air devices. Risks associated with heated humidified breathing air includes: possible 
inefficient warming of body temperatures, thermal inlury to airways, excessive heathing (hyperthermia). 

There is also a potential risk of loss of confidentiality. Every effort will be made to keep your 
information confidential, but this cannot be guaranteed. Those risks can be minimized by frequent 
monitoring and documentation of both the device temperature as well as the patient temperature every 
15-30 minutes to avoid over heating, and make sure active rewarming is stopped when temperature of 
patient exceeds 36 C. 
If patient's power of attorney declined to participate in the study, only forced air warming will 
be used for active rewarming of patient. 
Possible benefit if using warm humidified air is more effective in rewarming patients when 
combined with forced warm air devices than when using forced warm air devices alone, hypothermia 
will resolve quicker, potentially minimizing complications associated with hypothermia such as 
coagulopathy, shivering, metabolic derangements, etc.  
  
Data Analysis & Statistical Considerations 
 
Descriptive statistics will be used to evaluate patient demographics and clinical characteristics. 
Descriptive statistics will be summarized as mean ± (SD) or median (interquartile range) for continuous 
variables and group frequencies (%) for dichotomous or categorical variables. 
As all patients are expected to achieve normotherma within the study period, the primary 
outcome of time to normothermia will be analyzed as a numeric outcome variable.Following validation 
of distributional assumptions we will compare the time to normothermia between the two groups via t-
test or Wilcoxon rank sum test as appropriate. It is expected that the patients will reach normothermia 
between 45 minutes and 6 hours after admission to the ICU. 
By using a 2:1 matching ratio and a moderate level of variability (SD=1.3 hours) a study of 14 
prospectively enrolled patients and 28 retrospectively matched patients would attain 82% power to 
detect a 1.25 hour difference between time to normothermia in the two groups at alpha level 0.05. 
Secondary numeric outcomes such as time to extubation, time to normal PH, and coagulopathy 
lab values will be analyzed by t-test or Wilcoxon rank sum test as appropriate.Differences in categorical 
outcomes between treatment groups such as shivering will be analyzed via chi-square or fisher exact 
tests.As the patients will be matched on key confounders no further adjustment is expected to be 
necessary, so the moderate sample size should not limit the primary analysis.Potential subgroup analysis 
may be conducted in an exploratory analysis to determine if the treatment effect of ANAPOD warming is 
different by procedure type or patient/surgical characteristics.