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Ann Thorac Surg 2003;75:1140-1144
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

Preliminary evaluation of the arctic sun temperature-controlling system during off-pump coronary artery bypass surgery

^a Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA
^b Department of Surgery, Division of Cardiac Anesthesiology and Critical Care Medicine, Duke University Medical Center, Durham, North Carolina, USA

Accepted for publication September 28, 2002.

^* Address reprint requests to Dr Newman, Department of Anesthesiology, Box 3094, Duke University Medical Center, Durham, NC 27710, USA.
e-mail: newma005{at}mc.duke.edu

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
BACKGROUND: Maintaining normothermia during off-pump coronary artery bypass (OPCAB) surgery is a challenge not met by currently available medical devices and strategies. The purpose of this study was to determine the efficacy of a new thermoregulatory device, the Arctic Sun temperature-controlling circulating fluid adhesive pad system, in preventing hypothermia during OPCAB surgery.

METHODS: Thirteen consenting patients undergoing OPCAB had their temperature managed using the Arctic Sun^TM system. They were matched with 23 consenting control OPCAB patients whose temperature was maintained with standardized, conventional therapy (elevated ambient operating room temperature, warmed intravenous fluids, and a convective forced air warming system placed under the surgical drapes). Nasopharyngeal temperature (recorded at 1-minute intervals) was compared between the two groups by analysis of both the time and area under the curve for a temperature less than 36°C.

RESULTS: Multivariate linear regression analysis revealed that the average amount of hypothermia in the Arctic Sun group was significantly less than in the control group, both for time spent less than 36°C (20.7 vs 121.3 minutes, p = 0.0004) and for area under the curve less than 36°C (11.8°C vs 78.1°C x minutes, p = 0.0001).

CONCLUSIONS: The Arctic Sun temperature-controlling system is more effective than conventional warming methods in preventing hypothermia during OPCAB surgery.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
Managing temperature during cardiac surgery presents the operative team with a number of monitoring and treatment challenges. Despite extensive investigation, the optimal temperature during surgery is not known. Because hypothermia may have both detrimental and beneficial effects, many different temperature management strategies have been utilized during cardiac surgery [1, 2]. Unique to the setting of conventional cardiac surgery is the operating team’s ability to modulate temperature utilizing the heat exchanger in the cardiopulmonary bypass (CPB) pump, thereby lowering temperature during times of potential hypoperfusion (and ischemic risk) and then returning it to normal before the end of CPB. This capability does not exist, however, with off-pump coronary artery bypass graft (OPCAB) surgery. In OPCAB surgery, a patient’s temperature is influenced by the same environmental sources of heat loss that many other non-CPB surgical patients encounter. Additionally, because of an open thorax and extremities exposed for vascular conduit harvest, maintaining normothermia can be difficult.

Although it is not clearly known what the optimal temperature during OPCAB should be, efforts to maintain normothermia are generally instituted. These techniques include maintaining an elevated (and often uncomfortable) ambient operating room temperature, warming ventilated gases and intravenous fluids, water blankets, and forcing warm convective air over nonexposed portions of the body. These techniques have produced variable success. The purpose of this study was to assess the efficacy of the Arctic Sun^TM (MediVance, Inc, Louisville, CO) temperature-controlling system, which circulates temperature-controlled water through hydrogel energy transfer pads under negative pressure to prevent hypothermia (36°C) during OPCAB surgery.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
Patient selection
After Institutional Review Board approval, written informed consent was obtained from 20 patients undergoing OPCAB surgery between January and June 2000. The control group consisted of a matched group of 23 OPCAB patients with similar surgery times treated during the same period of time and who consented to participate in a concurrent epidemiological study. Because of changes to the planned surgical procedure before the operation but after patient consent, 5 patients underwent conventional on-bypass coronary artery bypass graft surgery (CABG) and thus were excluded from further study. Another 2 patients did not complete the study because of changes in their procedures (1 to an aortic aneurysm repair with CPB and 1 to a thoracotomy approach for OPCAB). Exclusion criteria included age less than 21 years, the anticipated requirement for CPB, known hypersensitivity to any other skin contact medical device or product, participation in any other investigational drug or device study, or any other condition that could limit the application of the Energy Transfer Pads.

Procedure
A standardized anesthetic approach including midazolam (0.02 to 0.1 mg/kg), fentanyl (5 to 10 µg/kg), and pancuronium (0.01 mg/kg) with isoflurane (0.5% to 1.0%) maintenance was used in all patients. Nasopharyngeal temperature monitoring was established after endotracheal intubation. Nasopharyngeal temperature was continuously measured and recorded every minute on the automated anesthesia record system (SATURN; North American Draeger, Telford, PA). Procedure length was defined as the time from the first recorded temperature in the operating room until the patient was transferred to the intensive care unit (ICU). OPCAB procedures included the use of a myocardial stabilization device (Octopus; Medtronic, Inc., Minneapolis, MN) and placement of a partial occlusion clamp on the ascending aorta for proximal vein graft anastamosis.

Temperature management
Nasopharyngeal temperature was measured (to the nearest 0.1°C) at 1-minute intervals in both the treatment and control groups after induction of anesthesia and intubation. Temperatures utilized in the subsequent analysis included those recorded after a 5-minute stabilization period until temperature monitoring discontinuation for transfer to the ICU.

The energy transfer pads were placed on the posterior portions of the torso and legs of subjects in the treatment group before induction of anesthesia. The pads were connected to the control module that circulates temperature-controlled water to maintain a preset target temperature after induction of anesthesia. A target temperature of 36.8°C, approximately normothermia in these patients, was chosen to attempt to maintain normothermia and prevent hypothermia and hyperthermia. The pads incorporate a biocompatible and highly conductive hydrogel material that adheres to the patient’s skin. The pads are designed to simulate water immersion, thereby providing effective energy transfer to and from the patient.

Temperature in the control group was managed through the standardized institutional practice of warming intravenous fluids, increasing the operating room temperature to 24°C to 28°C and using a convective forced air warming system with a U-shaped blanket (Progressive Dynamics Medical, Inc, Marshall, MI) under the surgical drapes.

Hypothermia was defined as a nasopharyngeal temperature less than 36°C before the conduct of the trial and quantified by measuring the area under the curve for a temperature less than 36°C (AUC < 36°C) for each subject as well as the time (minutes) that the temperature was less than 36°C. Temperature area less than 36°C considers both magnitude and duration of hypothermia and has a unit of degrees x minutes. For example, 1° x min could mean 1°C below 36 for 1 minute, or 0.5°C below 36 for 2 minutes; a 2°C x min could mean 1°C below 36 for 2 minutes, or 0.5°C below 36 for 4 minutes. The secondary outcome, time less than 36°C, is a simple count of minutes below 36°C. A cutoff of 36°C was used as a stringent criteria to effectively differentiate between temperature management strategies. Mean temperature and temperature before leaving the operating room were also compared.

Statistical methods
Patient demographics were compared between groups using a Student’s t test for continuous variables and Fisher’s exact tests for categorical variables. A linear regression analysis was performed to examine the relationship between treatment group (Arctic Sun or control) and temperature area less than 36°C. Multivariate analyses were performed to allow for effect modification due to the inclusion of covariates. The following predictors were tested as covariates: length of procedure, diabetes, gender, number of grafts, age, body mass index, and left ventricular ejection fraction (LVEF). As a secondary analysis, number of minutes less than 36°C was also examined as an outcome. The same multiple regression model was used as described above.

For each case, cumulative extent of hypothermia (AUC < 36°C) was calculated for the procedure. The mean cumulative hypothermia area in each group was graphed for descriptive purposes.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
The demographic characteristics of both groups are shown in Table 1. There were no significant differences between the treatment and control groups. The control group had 121.3 (31 to 205) minutes (median and interquartile range) less than 36°C, whereas the treatment group had 20.7 (0 to 24) minutes (median and interquartile range) (p = 0.0001). As shown in Figure 1, the amount of hypothermia (quantified as the temperature area < 36°C x min) was significantly greater in the control group compared with the Arctic Sun group (78.1°C x min vs 11.8°C x min; p = 0.0004). Table 2 shows that this significant group effect remained even after controlling for the length of procedure and the presence of diabetes (r² = 0.50, p = 0.0004). Gender, number of grafts, age, body mass index, and LVEF were all nonsignificant covariates. Number of minutes less than 36°C also shows a significant treatment effect after controlling for length of procedure and diabetes (r² 0.5, p = 0.0001, Table 2). Gender, number of grafts, age, body mass index, and LVEF were all nonsignificant as covariates of time less than 36°C. Results are summarized in Table 2. As the individual cases progressed, the accumulated temperatures less than 36°C became increasingly divergent between the two groups, reflecting that the treatment group remained normothermic whereas the control group progressively cooled or were not rewarmed to the same extent (Fig 2). Mean temperature by treatment group was also different, being lower in the control than in the treatment group (control: mean, 35.95; SD, 0.49 vs treatment: mean, 36.43, SD, 0.30; p = 0.04).

View larger version (12K): [in this window] [in a new window]   Fig 1. Hypothermia, as assessed by the AUC less than 36°C, in patients undergoing off-pump coronary artery bypass utilizing conventional temperature strategies or the Arctic Sun system. The degree of hypothermia, as assessed by the AUC for temperature less than 36°C (AUC < 36) was lower in the group utilizing the Arctic Sun temperature-controlling system versus the conventional temperature management (Control) group (p = 0.0004). AUC = area under the curve; + = mean value.

View larger version (13K): [in this window] [in a new window]   Fig 2. The cumulative hypothermia (AUC < 36) in the Arctic Sun group was lower than the conventional temperature management (Control) group. AUC = area under the curve.

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

Our results show that the Arctic Sun temperature-controlling system establishes or restores normothermia better than conventional temperature management methods during OPCAB surgery. Although the optimal body temperature for OPCAB surgery is not known, normothermia has been considered a goal, particularly to aid in the timely extubation of these patients. In addition, perioperative hypothermia has been linked to increased infection rates, excessive bleeding due to adverse coagulation profiles, cardiac dysrhythmias, decreased drug metabolism, and increased time to extubation [3–7]. A further advantage of this system is its unique ability to warm the patient in the relatively cool environment of the operating room. This allows the surgical team to keep the ambient room temperature comfortably cool without the concern of allowing the patient to become excessively hypothermic.

The primary limitation of the study is the nonrandomized design, which could have introduced unmeasured bias. To minimize this possibility, we standardized anesthetic and surgical management and included patients of similar procedure length. In addition, we performed a multivariable linear regression taking into account length of procedure, gender, diabetes, number of grafts, age, body mass index, and LVEF. Multivariable analysis allowed us to effectively determine if other patient or operative factors may have contributed to the differences we observed between the groups. Even after accounting for other covariates, management with the Arctic Sun device was associated with a substantially lower degree of hypothermia, both AUC less than 36 and time less than 36°C. As predicted by our definition of hypothermia, length of procedure was also a significant factor, with longer procedures producing a higher degree and duration of hypothermia. Interestingly, diabetes was also associated with greater degrees of hypothermia, potentially as a result of decreased ability to regulate peripheral temperature due to loss of autoregulation.

An effective, precise, thermoregulatory system that transfers energy effectively to and from the patient may also be used to modulate temperature in other ways; it has the potential to either raise or lower patient temperature to a predetermined target. Mild to moderate hypothermia is still commonly utilized in conventional CABG surgery for its putative organ protective abilities, particularly in neuroprotection [2]. Whereas the efficacy of hypothermic strategies in cardiac surgery have been questioned [8], still, the ability to rapidly and safely lower temperature and similarly return it to normal while avoiding hyperthermia is a beneficial development.

In summary, the Arctic Sun temperature-controlling system effectively reduced the amount of hypothermia during OPCAB surgery. This may have significant advantages both in this setting and others.

	Acknowledgments

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
This research project was funded by an educational grant from MediVance Incorporated, Louisville, CO. The authors thank Yvonne M. Connelly, MA, MPH, for editorial assistance with the manuscript.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
^* The members of the Neurologic Outcome Research Group of the Duke Heart Center are listed in Appendix 1. The Cardiothoracic Anesthesiology Research Endeavors (C.A.R.E.) Investigators are listed in Appendix 2.

	Appendix 1

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
Neurologic Outcome Research Group of the Duke Heart Center
Director
Joseph P. Mathew, MD; Co-Director: James A. Blumenthal, PhD

Anesthesiology
John V. Booth, MD, Hilary P. Grocott, MD, Steven E. Hill, MD, Joseph P. Mathew, MD, Mark F. Newman, MD, J.G. Reves, MD, Debra A. Schwinn, MD, Mark Stafford-Smith, MD, David Warner, MD, Madan Kwatra, PhD, Bonita L. Funk, RN, E.D. Derilus, BS, Jason Hawkins, RN, BSN, I. Lee McClurkin, BA, RN, Terri Moore, BA, Chonna Campbell, BS, Amanda Cheek, AS, Roger L. Hall, AAS, Tanya Kagarise BS, Jerry L. Kirchner, BS, Satarah Latiker, BS, Erich Lauff, BA, Charles R. Peters, MA, Meredith Prince, Joe Russell, RN, Debra L. Whiteheart, BS, Regina DeLacy, BA, William Hansley, BS, Yvonne M. Connelly, MA, MPH, Barbara Phillips-Bute, PhD, and William D. White, MPH

Behavioral medicine
Michael A. Babyak, PhD, James A. Blumenthal, PhD, Cardiology: Daniel B. Mark, MD, MPH, and Michael H. Sketch, Jr., MD

Neurology
Carmelo Graffagnino, MD, Daniel T. Laskowitz, MD, John R. Lynch, MD, Ann M. Saunders, PhD, Warren J. Strittmatter, MD, and Kathleen A. Welsh-Bohmer, PhD

Pathology
Ellen R. Bennett, PhD

Perfusion services
Greg Smigla, BS., CCP, and Ian Shearer, BS, CCP

Surgery
Robert W. Anderson, MD, Thomas A. D’Amico, MD, R. Duane Davis, MD, Donald D. Glower, MD, R. David Harpole, MD, James Jaggers, MD, Robert H. Jones, MD, Kevin Landolfo, MD, James E. Lowe, MD, Robert H. Messier, MD, Carmelo Milano, MD, Peter K. Smith, MD, Eric M. Toloza, MD, PhD, and Walter G. Wolfe, MD

	Appendix 2

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 
Cardiothoracic Anesthesia Research Endeavors (C.A.R.E.)
Director
Mark Stafford-Smith, MD; Co-Director: Joseph P. Mathew, MD

Anesthesiology
Mark J. Bennett, MD, John V. Booth, MD, Fiona M. Clements, MD, Norbert de Bruijn, MD, Katherine Grichnik, MD, Hilary P. Grocott, MD, Steven E. Hill, MD, Joseph P. Mathew, MD, Mark F. Newman, MD, Mihai V. Podgoreanu, MD, Debra A. Schwinn, MD, Mark Stafford-Smith, MD, Madhav Swaminathan, MD, and Ian J. Welsby, MD

	References

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments Appendix 1 Appendix 2 References

 

1. The Warm Heart Investigators. Randomized trial of normothermic versus hypothermic coronary bypass surgery. Lancet 1994;343:559-563.[Medline]
2. Martin T.D., Craver J.M., Gott J.P., et al. Prospective, randomized trial of retrograde warm blood cardioplegia: myocardial benefit and neurologic threat. Ann Thorac Surg 1994;57:298-302.[Abstract]
3. Leslie K., Sessler D.I. The implications of hypothermia for early tracheal extubation following cardiac surgery. J Cardiothorac Vasc Anesth 1998;12:30-34.[Medline]
4. Sessler D.I., Kurz A., Lenhardt R. Re: Hypothermia reduces resistance to surgical wound infections. Am J Surg 1999;65:1193-1196.
5. Taylor C.A. Surgical hypothermia. Pharmacol Ther 1988;38:169-200.[Medline]
6. Rohrer M.J., Natale A.M. Effect of hypothermia on the coagulation cascade. Crit Care Med 1992;20:1402-1405.[Medline]
7. Staab D.B., Sorensen V.J., Fath J.J., et al. Coagulation defects resulting from ambient temperature-induced hypothermia. J Trauma-Inj Infect Crit Care 1994;36:634-638.
8. Grigore A.M., Grocott H.P., Mathew J.P., et al. The rewarming rate and increased peak temperature alter neurocognitive outcome after cardiac surgery. Anesth Analg 2002;94:4-10.[Abstract/Free Full Text]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Kevin P. Landolfo Mark F. Newman Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Stanley, T. O. Articles by Newman, M. F. Search for Related Content PubMed PubMed Citation Articles by Stanley, T. O. Articles by Newman, M. F. Related Collections Minimally invasive surgery