Heated Humidified Breathing Circuit Rewarming in Hypothermic Post Cardiopulmonary Bypass Patients.

Study Overview
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Brief Summary
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Hypothermia on admission to the intensive care unit (ICU) following cardiopulmonary bypass (CPB) is common. The investigators propose that rewarming hypothermic (≤ 35 C) patients admitted to the intensive care unit following procedures using CPB with heated humidified breathing circuits (HHBC) in addition to conventional forced air warming blankets will shorten time to normothermia. Secondarily it may shorten time to extubation, improve coagulopathy, and metabolic derangements seen with hypothermia.

Detailed Description
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Hypothermia on admission to the intensive care unit (ICU) following cardiopulmonary bypass (CPB) is common. Cooling and rewarming during CPB and deep hypothermic circulatory arrest (DHCA) takes considerable time and contributes to the post-procedural coagulopathy and physiologic perturbations. Core body parts (trunk and head) rewarm more quickly than peripheral parts (extremities). 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 such as shivering, coagulopathy, increased myocardial stress, increased wound infections, metabolic acidosis, delayed extubation and prolonged ICU length of stay (LOS). The use of the active warming via traditional methods (ie forced air warming blankets) and Heated Humidified breathing circuits (HHBC) via ANAPOD Heated Humidification System® (ANAPOD) may shorten time to normothermia. Secondarily it may shorten time to extubation, improve coagulopathy, and metabolic derangements seen with hypothermia. Sample and Study Design- The investigators will prospectively collect data for 14 enrolled non-patients who will receive active warming via both forced air warming blankets and Heated Humidified breathing circuits (HHBC). Retrospective data will be obtained retrospectively for 28 matched patients from two years prior to initiation of the trial, who received warming only via forced air warming blankets. Data Collection Plan- Data will be extracted and collected by the Duke Department of Anesthesiology IT analyst, who will review and extract information from the patient's chart via Epic/ Maestro Care, or manually if necessary. Data Evaluation- 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 normothermia within the study period, the primary outcome of time to normothermia will be analyzed as a numeric outcome variable. Following validation of distributional assumptions the investigators 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 prospective group (active warming via traditional methods (ie forced air warming blankets) and Heated Humidified breathing circuits (HHBC) via ANAPOD Heated Humidification System® (ANAPOD), and the retrospective group (active warming via traditional methods (ie forced air warming blankets only) 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 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.

Official Title
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Heated Humidified Breathing Circuit Rewarming in Hypothermic Post Cardiopulmonary Bypass Patients.

Conditions
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Hypothermia, Rewarming

Intervention / Treatment
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* Device: Heated Humidified Breathing Circuit and Forced Air Blanket


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Admission to intensive care unit following surgical procedure involving cardiopulmonary bypass. Admission temperature ≤ 35.0 C. Exclusion Criteria: Patients placed on extracorporeal membrane oxygenation intra-operatively, or during first 24 hours after ICU admission. Any additional surgical procedures in the first 24 hours days after initial surgery e.g. Chest exploration for bleeding, Open Chest, Non-cardiac surgery such as colectomy for ischemic gut, etc.

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Intervention Model: Single Group Assignment
Interventional Model Description: The intervention group has only one arm. All patients will use active warming via traditional methods (ie forced air warming blankets) and Heated Humidified breathing circuits (HHBC) via ANAPOD Heated Humidification System® (ANAPOD). Those patients will be matched with a retrospective historical cohort of patients that received active warming via traditional methods only (forced air warming blankets).
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: HHBC and Forced Air Warming<br>Patients admitted to intensive care unit hypothermic (≤ 35 C) following surgical procedures involving cardiopulmonary bypass. Will be rewarmed with heated humidified breathing circuits (ANAPOD) and standard forced air warming blankets. | Device: Heated Humidified Breathing Circuit and Forced Air Blanket<br>* Heated humidified breathing circuits (ANAPOD) will be set up and managed by respiratory therapist in standard fashion defined by the manufacturer. Temperate will be set at 41C. Forced air warming blankets will be set at 42C for duration of rewarming.<br>* Other names: ANAPOD;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Time to Normothermia | Core temperature normothermia defined as >=36.5 C. | up to 24 hours post admission to intensive care unit | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Time to Extubation | Time from admission to time of extubation. Followup was truncated at 24 hours and if patient had not been extubated at that time they were assigned a value of 24 hours. | up to 24 hours post admission to intensive care unit | 
| Coagulopathy as Measured by Need for Transfusion of Blood Product | Assessed via number of transfusions of red blood cells, fresh frozen plasma, platelets, cryoprecipitate. | 24 hours post admission to intensive care unit | 
| Metabolic Derangement as Measured by Time to Normal pH | Assessed via blood gas analysis. Normal pH defined as 7.35-7.45. | up to 24 hours post admission to intensive care unit | 
| Number of Subjects With Abnormal Coagulopathy as Measured by Laboratory Assessment of Prothrombin Time | Laboratory assessment of Prothrombin Time with normal defined as 9.5-13.1 seconds. | 24 hours post admission to intensive care unit | 
| Number of Subjects With Abnormal Coagulopathy as Measured by Laboratory Assessment of INR | Laboratory assessment of international normalised ratio (INR) with normal defined as 0.9-1.1. | 24 hours post admission to intensive care unit | 
| Number of Subjects With Abnormal Coagulopathy as Measured by Laboratory Assessment of Act Partial Thromboplastin Time | Laboratory assessment of Act Partial Thromboplastin Time with normal defined as 26.8-37.1 seconds. | 24 hours post admission to intensive care unit | 
| Number of Subjects With Abnormal Coagulopathy as Measured by Laboratory Assessment of Fibrinogen. | Laboratory assessment of fibrinogen levels with normal defined as 213-435 mg/dL. | 24 hours post admission to intensive care unit | 
| Number of Subjects With Abnormal Coagulopathy as Measured by Laboratory Assessment of Platelet Count | Laboratory assessment of platelet count with normal defined as 150 - 450 x10ˆ9/L. | 24 hours post admission to intensive care unit | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Cardiopulmonary bypass, Afterdrop, Deep Hypothermic Circulatory Arrest, Heated Humidified Breathing Circuit