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Effect of Preoperative Forced-Air Warming on Postoperative Temperature and Postanesthesia Care Unit Length of Stay
Effect of Preoperative Forced-Air Warming on Postoperative Temperature and Postanesthesia Care Unit Length of Stay SONDRA FETTES, MSN, RNC; MARY MULVAINE, BSN, CNOR, CRNFA; ELAINE VAN DOREN, PhD, RN
ABSTRACT Unintended hypothermia in the surgical patient has been linked to numerous postoperative complications, including increased risk for surgical site infection, increased oxygen demands, and altered medication metabolism. The lack of literature on the subject was part of the impetus for perioperative nurses in one hospital to conduct a quality improvement project to evaluate the effectiveness of preoperative warming on patients’ postoperative temperatures. We randomly assigned 128 patients to either a group that received a forced-air warming blanket preoperatively or a group that did not. Our results showed that prewarming patients before surgery did not have an effect on patients’ postoperative temperatures. AORN J 97 (March 2013) 323-328. Ó AORN, Inc, 2013. http://dx.doi.org/10.1016/j.aorn.2012.12.011 Key words: perioperative hypothermia, postoperative complications, preoperative warming, forced-air warming.
F
eeling cold is often reported by patients to be one of the most uncomfortable aspects of surgery. In addition, since the 1990s, the literature has shown that the cold environment in the OR can have a detrimental effect on patients.1-3 For example, hypothermia has been linked to numerous postoperative patient complications that include, but are not limited to, an increased risk for surgical site infection, an increase in the patient’s oxygen needs, and alterations in medication metabolism.1-7 The literature concentrates on approaches used in the intraoperative and postoperative environments to decrease hypothermia for patients.1-5 In our small community hospital in Marshall, Michigan, a group
of perioperative nurses decided to examine whether warming patients before their surgical procedures would positively affect their postoperative temperatures. Some of the nurses assumed that prewarming a patient before surgery would have a positive effect on the patient’s postoperative temperature; others felt that intraoperative warming was adequate to maintain normothermia. We conducted a review of literature that provided limited evidence regarding warming in the preoperative area.1,3,4,7 Most of the literature we found discussed the effects of using improved temperature management intraoperatively.2,5,6,8-10 With this
http://dx.doi.org/10.1016/j.aorn.2012.12.011
Ó AORN, Inc, 2013
March 2013
Vol 97 No 3
AORN Journal j 323
March 2013 Vol 97 No 3
void in the literature, we felt the need to study the situation before developing a policy and procedure regarding prewarming. Adding a preoperative warming protocol has the potential to increase costs from increased nursing activity and warming blanket replacement costs because the blankets would be used for longer periods.
LITERATURE REVIEW Hypothermia is described as a core body temperature below 96.8 F (36 C), and it is common for patients to become hypothermic during a surgical procedure.1-7 Health care providers know that the temperature of the ORs, patients’ exposed skin and open body cavities, and the use of cold solutions during surgery contribute to hypothermia.1,5,6 In addition, certain patient characteristics (ie, age, gender, body mass index [height and weight], general health status) are known to affect body temperature.3 In the past, clinicians considered this form of hypothermia to be inadvertent and a normal consequence of surgery that was not cause for great concern.2 The common intervention was to rewarm the patient on his or her admission to the postanesthesia care unit (PACU).2 More recently, Scott and Buckland2 indicated that hypothermia is still common and that 70% of patients may be hypothermic on admission to the PACU. In addition to inadvertent hypothermia, some surgical procedures (eg, coronary artery bypass surgery) use planned hypothermia to decrease complications; but both types of hypothermia have been associated with postoperative complications.1-7 Some of the physiological changes that can occur with hypothermia include n
altered medication and protein metabolism; alterations in serum potassium levels; n shivering, which can increase oxygen demand by 400% to 500%; n peripheral vasoconstriction; and 2 n altered tissue perfusion.
FETTESdMULVAINEdVAN DOREN Recently, the trend has been to prevent inadvertent hypothermia. In our search of the literature, we found that most of the interventions discussed focused on intraoperative warming of patients.1,5-7 A systematic review by Scott and Buckland2 examined studies on decreasing patient complications by preventing hypothermia. All of the studies they reviewed discussed intraoperative warming interventions, but only five of 26 studies included preoperative warming interventions. Although the review by Scott and Buckland2 indicated that these latter studies generally lacked methodology and measurement consistency, they concluded that there is evidence that responding to correct hypothermia before the intraoperative period is beneficial. A systematic review by Sajid et al1 looked at 25 studies, 19 of which were randomized controlled trials. These studies discussed the effects of intraoperative and postoperative warming, but they did not discuss the effects of preoperative warming.1 Many studies indicated that the majority of instances of intraoperative hypothermia are caused by the redistribution of heat after the administration of anesthesia.1-5 In their seminal article from 1995, Sessler et al3 indicated that 81% of the heat reduction in their test patients was a result of core-to-peripheral redistribution of body heat after the induction of anesthesia. As a result of such information, Bitner et al8 hypothesized that hypothermia may result in longer patient stays in the PACU as well as other postoperative complications. They implemented a process to warm patients preoperatively by using forced-air warming blankets.8 The results of their study indicated that the number of patients arriving in the PACU with a temperature below 96.4 F (35.8 C) dropped from 61% to 37%.8
n
324 j AORN Journal
OUR PROJECT We compared the temperature of patients undergoing surgery who did not receive forced-air warming before induction of anesthesia with
PREOPERATIVE WARMING patients who did receive forced-air warming before anesthesia. Our guiding questions were n
Will forced-air warming techniques used before surgery decrease the number of patients presenting to the PACU in a hypothermic state? n Will prewarming patients before surgery decrease the length of stay in the PACU? We defined hypothermia as a core temperature below 96.8 F (36 C),1-7 as measured by a temporal artery-scanning thermometer. This instrument has been documented as accurate to 0.2 F (0.1 C), and using it has been established as an accurate means to monitor core body temperature.9 We defined warming as the placement of a forced-air warming blanket set at a medium or 100 F (37.8 C) setting. Inclusion and Exclusion Criteria To be included in this project, participants had to be between the ages of 18 and 85 years, speak English, be able to sign for informed consent, and have an American Society of Anesthesiologist’s Physical Status Classification of I to III.11 Patients in our project underwent the following surgeries: n n n n n n
exploratory laparotomy; colorectal surgery; total joint replacements (including hip and knee); spinal and chest procedures; total abdominal hysterectomy; and robotic-assisted nephrectomy, prostatectomy, and cystectomy.
We excluded potential participants from the project if they had known thyroid disease, autonomic dysfunction (eg, dysautonomia or Shy-Drager syndrome), Cushing syndrome, or documented peripheral vascular disease. Variations in core body temperature are often seen in patients with these diseases, and, because temperature was a study variable, we decided to exclude these patients. We also excluded patients with admission temperatures higher than 37.5 C (99.5 F) or less than
www.aornjournal.org
36.5 C (97.7 F) and those with a known infection with fever or a surgical site infection. Design, Setting, and Sampling We used a prospective, pretest/posttest design with random assignment. The setting was an independently owned, MagnetÒ status, community hospital with 77 acute care beds located in the Midwest. After receiving institutional review board approval, we approached a convenience sample of 146 patients for initial consent at the point of preoperative teaching and testing. The RNs providing preoperative teaching explained the study and obtained informed consent. After they obtained the patient’s consent to participate in the study, the nurses randomly assigned participants to the intervention or control group by using the last two digits of the patient’s account numbers and random integers. If the two-number combination was on the sheet of 65 randomized number sets, then the patient was placed in the intervention group; if the pair of numbers was not on the randomized sheet, then the patient was placed in the control group. The nurse then placed a sealed envelope with the appropriate protocol, a data collection sheet, and the signed consent on the patient’s chart. On the day of admission to the preoperative surgical area, the admitting nurse confirmed that the patient was still willing to participate. Five individuals dropped out of the study at that time, because they verbalized that they were already uncomfortably warm before or shortly after being given the warming blanket. For the other participants, the admitting nurse opened the envelope and ensured that the blanket was turned on for the intervention group participants. Both groups received one warmed cotton blanket per standard protocol. An additional three participants had their surgery cancelled, and the admission nurse did not recognized 10 patients as participants in the project. Thus, a total of 128 participants or 88% of the convenience sample of 146 individuals provided AORN Journal j 325
FETTESdMULVAINEdVAN DOREN
March 2013 Vol 97 No 3
TABLE 1. Demographic Characteristics of the Sample All participants (N ¼ 128) Gender Male Female Age in years (mean) American Society of Anesthesiologists Physical Status Classification I II III Body mass index in kg/m2 (mean)
Warming blanket (n ¼ 54)
Test and value c2; P ¼ .407
60 68 58.7
8 114 6 33
data. We had conducted a power analysis before data collection to determine the necessary sample size. We based our calculations on a two-tailed t test to detect a significant difference in mean temperature between the intervention and control groups at a significance level of 5%. To detect a moderate effect size of 0.5 with 80% power, a sample size of 64 patients in each group was deemed necessary. Our project resulted in 54 participants in the intervention group and 74 participants in the control group. Although we reached the total desired sample size, the uneven distribution between groups is a limitation of the project. The demographic characteristics of the sample are presented in Table 1. There were no significant differences between the two groups based on gender (c2 ¼ 0.688, P ¼ .407), age (t ¼ 0.333, P ¼ .740), body mass index (t ¼ 0.834, P ¼.406), American Society of Anesthesiologists Physical Status Classification (Fisher exact test, P ¼ .392), or hospital admission temperature (t ¼ -0.185, P ¼ .853). Instrumentation We used a temporal artery-scanning thermometer to determine patients’ temperatures. This instrument has been documented to be accurate to 0.2 F (0.1 C). The thermometers used in the surgical 326 j AORN Journal
No warming blanket (n ¼ 74) 37 37 59
23 31 58.4
3 68 3 33.5
5 46 3 32.3
t test; P ¼ .740 Fisher exact test; P ¼ .392
t test; P ¼ .406
areas are checked for accuracy before the first use, but the brand of thermometer we used is designed to stay calibrated permanently and not require routine recalibration.9 We used forced-air warming blankets set at the 100 F (37.8 C) setting (ie, medium) for warming. Safety features such as self-test sequences, temperature alarms, system failure turn-off devices, higher than programmed temperature shutdown circuits, and mechanisms to verify temperature output all make these warming blankets reliable and safe for use.10 Procedures On the day of surgery, when a participant arrived in the outpatient surgery area, the admission nurse opened the sealed envelope that had been placed on the chart by the nurse who obtained consent. The envelope contained information that determined in which group the participant belonged. All the patients had a forced-air warming blanket open and in place. The blanket went with the patient to the OR and then to the PACU; this ensured that the PACU nurses performing postoperative temperature measurements did not know who was in the intervention group and who was in the control group. For control group participants, the forced-air warming blanket was not turned on. The normal routine in our hospital is to follow AORN standards
PREOPERATIVE WARMING
www.aornjournal.org
TABLE 2. Temperatures and Length of Stay Between Groups
Means Patient temperature on admission to the outpatient department Patient temperature on exiting the preoperative area Patient temperature on admission to the postanesthesia care unit Postanesthesia care unit length of stay
No warming blanket (n ¼ 74)
Warming blanket (n ¼ 54)
Test and value
98.2 F (36.7 C)
98.2 F (36.7 C)
t test; P ¼ .853
98.4 F (36.8 C)
98.6 F (37 C)
t test; P ¼ .314
98.0 F (36.6 C)
98.1 F (36.7 C)
t test; P ¼ .314
52.5
55.1
Mann-Whitney test; P ¼ .526
for preventing hypothermia 5 in the surgical patient, which includes using intraoperative warming and forced-air warming, and warming IV and irrigation fluids. In addition to these intraoperative interventions, our team places a warm cotton blanket on all patients in the preoperative area for comfort. For the intervention group, approximately one hour before surgery, the preoperative nurse placed a forced-air warming blanket on the patient and set it on medium. The nurses took the patient’s temperature in the preoperative, intraoperative, and postoperative care areas. The nurses turned the blankets on for both groups in the surgical suite to help maintain normothermia. Throughout the preoperative, intraoperative, and postoperative period, the nurses followed standard policies and procedures for observing and monitoring the patient. No patients experienced adverse temperature events; however, two participants in the study group asked that the blanket be removed because they felt too warm. RESULTS AND FINDINGS We entered temperature data into the statistical program12 and analyzed the data for the project’s two questions. The question “Will using forcedair warming techniques before surgery decrease the number of patients presenting to the PACU in a hypothermic state?” was not supported (Fisher exact test; P ¼ .508). There also was no significant difference in the mean temperatures
when participants exited the preoperative area. The second question “Will prewarming patients before surgery decrease the length of stay in the PACU?” also was not supported. The median PACU times, 50 minutes for the intervention group and 49 minutes for the control group, were not statistically significant (Mann-Whitney test, P ¼ .545). Statistical results are provided in Table 2. LIMITATIONS Although this quality improvement project used an established method to investigate the effects of prewarming, there were limitations. The sample size was one of the largest in the literature to date, but the differences in the group sizes could have affected the statistical outcomes. Another issue was the lack of patients with hypothermia in either control or intervention groups. The literature reviewed, before we initiated this project, was published on or around the time that the Centers for Medicare & Medicaid Services quality measure on PACU temperatures for colorectal surgical patients was published.13 This ruling focuses on the need to keep patients warm, which placed increased attention on intraoperative care to minimize heat loss. These changes could account for the significant difference between the 60% to 70% hypothermia identified in the literature and the 1% observed during our project. Lastly, nurses may have given additional warm cotton blankets
AORN Journal j 327
FETTESdMULVAINEdVAN DOREN
March 2013 Vol 97 No 3
to patients in the preoperative area, further confounding the temperature readings. However, this is thought to be unlikely given the limited time patients spend in that area. CONCLUSION Maintaining normothermia is not only important for the comfort of surgical patients, it affects surgical outcomes. Our quality improvement project supports the study by Burns et al6 that showed that prewarming does not significantly affect patient temperature on arrival to the PACU. Based on our findings, we do not recommend further research on patient prewarming to decrease PACU time but suggest that nurses consider the effect of adequate warming on long-term patient complications, such as postoperative infections. An area for further study might be the effect that prewarming has on patient satisfaction. Our participants frequently commented on how nice it was to be warm. We also recommend strengthening our study approach by reducing the limitations of unequal group size and confounding variables. Editor’s note: Magnet is a registered trademark of the American Nurses Credentialing Center, Silver Spring, MD. References 1. Sajid MS, Shakir AJ, Khatri K, Baid MK. The role of perioperative warming in surgery: a systematic review. Sao Paulo Med J. 2009;127(4):231-237. 2. Scott EM, Buckland R. A systematic review of intraoperative warming to prevent postoperative complications. AORN J. 2006;83(5):1090-1113. 3. Sessler DI, Schroeder M, Merrifield B, Matsukawa T, Cheng C. Optimal duration and temperature of prewarming. Anesthesiology. 1995;82(3):674-681. 4. Andrzejowski J, Hoyle J, Eapen G, Turnbull D. Effect of prewarming on post-induction core temperature and the incidence of inadvertent perioperative hypothermia in patients undergoing general anaesthesia. Br J Anesth. 2008;101(5):627-631. 5. Recommended practices for the prevention of unplanned perioperative hypothermia. In: Perioperative Standards and Recommended Practices. Denver, CO: AORN, Inc; 2012:365-378. 6. Burns SM, Piotrowski K, Caraffa G, Wojnakowski M. Incidence of postoperative hypothermia and the relationship
328 j AORN Journal
7.
8.
9.
10.
11.
12. 13.
to clinical variables. J Perianesth Nurs. 2010;25(5): 286-289. Kiekkas P, Karga M. Prewarming: preventing intraoperative hypothermia. Br J Perioper Nurs. 2005;15(10): 444-451. Bitner J, Hilde L, Hall K, Duvendack T. A team approach to the prevention of unplanned postoperative hypothermia. AORN J. 2007;85(5):921-929. Exergen Temporal ArteryThermometer TAT-5000: a kinder, gentler way to take a temperature, 2006. Exergen Corporation. http://www.exergen.com/tathermometry/ Specifications-TAT-5000-REV-5-12-11a.pdf. Accessed December 11, 2012. Life-Air 1000, Hypothermic Therapy System, 2007. Progressive Dynamics Inc. http://www.progressivedyna micsmedical.com/pdf/life_air_owners.pdf. Accessed December 11, 2012. ASA Physical Status Classification System. American Society for Anesthesiologists. http://www.asahq.org/Ho me/For-Members/Clinical-Information/ASA-PhysicalStatus-Classification-System. Accessed December 11, 2012. PASW StatisticsÒ Version 18.0. Chicago, IL: SPSS, Inc; 2008. CMS Core Measure SCIP: Surgical Care Improvement Project. http://wwwsjhlex.org/documents/Physicians/ SCIP_Poster_Full_Size.pdf. Accessed December 11, 2012.
Sondra Fettes, MSN, RNC, is the director of nursing research and Magnet at Oaklawn Hospital, Marshall, MI. Ms Fettes has no declared affiliation that could be perceived as posing a potential conflict of interest in the publication of the article. Mary Mulvaine, BSN, CNOR, CRNFA, is an RN first assistant in the OR at Oaklawn Hospital, Marshall, MI. Ms Mulvaine has no declared affiliation that could be perceived as posing a potential conflict of interest in the publication of the article. Elaine Van Doren, PhD, RN, is the associate dean for Undergraduate Programs and an associate professor at Kirkhof College of Nursing, Cook-DeVos Center for Health Sciences, Grand Valley State University, Allendale, MI. Dr Van Doren has no declared affiliations that could be perceived as posing a potential conflict of interest in the publication of the article.
ABSTRACT Unintended hypothermia in the surgical patient has been linked to numerous postoperative complications, including increased risk for surgical site infection, increased oxygen demands, and altered medication metabolism. The lack of literature on the subject was part of the impetus for perioperative nurses in one hospital to conduct a quality improvement project to evaluate the effectiveness of preoperative warming on patients’ postoperative temperatures. We randomly assigned 128 patients to either a group that received a forced-air warming blanket preoperatively or a group that did not. Our results showed that prewarming patients before surgery did not have an effect on patients’ postoperative temperatures. AORN J 97 (March 2013) 323-328. Ó AORN, Inc, 2013. http://dx.doi.org/10.1016/j.aorn.2012.12.011 Key words: perioperative hypothermia, postoperative complications, preoperative warming, forced-air warming.
F
eeling cold is often reported by patients to be one of the most uncomfortable aspects of surgery. In addition, since the 1990s, the literature has shown that the cold environment in the OR can have a detrimental effect on patients.1-3 For example, hypothermia has been linked to numerous postoperative patient complications that include, but are not limited to, an increased risk for surgical site infection, an increase in the patient’s oxygen needs, and alterations in medication metabolism.1-7 The literature concentrates on approaches used in the intraoperative and postoperative environments to decrease hypothermia for patients.1-5 In our small community hospital in Marshall, Michigan, a group
of perioperative nurses decided to examine whether warming patients before their surgical procedures would positively affect their postoperative temperatures. Some of the nurses assumed that prewarming a patient before surgery would have a positive effect on the patient’s postoperative temperature; others felt that intraoperative warming was adequate to maintain normothermia. We conducted a review of literature that provided limited evidence regarding warming in the preoperative area.1,3,4,7 Most of the literature we found discussed the effects of using improved temperature management intraoperatively.2,5,6,8-10 With this
http://dx.doi.org/10.1016/j.aorn.2012.12.011
Ó AORN, Inc, 2013
March 2013
Vol 97 No 3
AORN Journal j 323
March 2013 Vol 97 No 3
void in the literature, we felt the need to study the situation before developing a policy and procedure regarding prewarming. Adding a preoperative warming protocol has the potential to increase costs from increased nursing activity and warming blanket replacement costs because the blankets would be used for longer periods.
LITERATURE REVIEW Hypothermia is described as a core body temperature below 96.8 F (36 C), and it is common for patients to become hypothermic during a surgical procedure.1-7 Health care providers know that the temperature of the ORs, patients’ exposed skin and open body cavities, and the use of cold solutions during surgery contribute to hypothermia.1,5,6 In addition, certain patient characteristics (ie, age, gender, body mass index [height and weight], general health status) are known to affect body temperature.3 In the past, clinicians considered this form of hypothermia to be inadvertent and a normal consequence of surgery that was not cause for great concern.2 The common intervention was to rewarm the patient on his or her admission to the postanesthesia care unit (PACU).2 More recently, Scott and Buckland2 indicated that hypothermia is still common and that 70% of patients may be hypothermic on admission to the PACU. In addition to inadvertent hypothermia, some surgical procedures (eg, coronary artery bypass surgery) use planned hypothermia to decrease complications; but both types of hypothermia have been associated with postoperative complications.1-7 Some of the physiological changes that can occur with hypothermia include n
altered medication and protein metabolism; alterations in serum potassium levels; n shivering, which can increase oxygen demand by 400% to 500%; n peripheral vasoconstriction; and 2 n altered tissue perfusion.
FETTESdMULVAINEdVAN DOREN Recently, the trend has been to prevent inadvertent hypothermia. In our search of the literature, we found that most of the interventions discussed focused on intraoperative warming of patients.1,5-7 A systematic review by Scott and Buckland2 examined studies on decreasing patient complications by preventing hypothermia. All of the studies they reviewed discussed intraoperative warming interventions, but only five of 26 studies included preoperative warming interventions. Although the review by Scott and Buckland2 indicated that these latter studies generally lacked methodology and measurement consistency, they concluded that there is evidence that responding to correct hypothermia before the intraoperative period is beneficial. A systematic review by Sajid et al1 looked at 25 studies, 19 of which were randomized controlled trials. These studies discussed the effects of intraoperative and postoperative warming, but they did not discuss the effects of preoperative warming.1 Many studies indicated that the majority of instances of intraoperative hypothermia are caused by the redistribution of heat after the administration of anesthesia.1-5 In their seminal article from 1995, Sessler et al3 indicated that 81% of the heat reduction in their test patients was a result of core-to-peripheral redistribution of body heat after the induction of anesthesia. As a result of such information, Bitner et al8 hypothesized that hypothermia may result in longer patient stays in the PACU as well as other postoperative complications. They implemented a process to warm patients preoperatively by using forced-air warming blankets.8 The results of their study indicated that the number of patients arriving in the PACU with a temperature below 96.4 F (35.8 C) dropped from 61% to 37%.8
n
324 j AORN Journal
OUR PROJECT We compared the temperature of patients undergoing surgery who did not receive forced-air warming before induction of anesthesia with
PREOPERATIVE WARMING patients who did receive forced-air warming before anesthesia. Our guiding questions were n
Will forced-air warming techniques used before surgery decrease the number of patients presenting to the PACU in a hypothermic state? n Will prewarming patients before surgery decrease the length of stay in the PACU? We defined hypothermia as a core temperature below 96.8 F (36 C),1-7 as measured by a temporal artery-scanning thermometer. This instrument has been documented as accurate to 0.2 F (0.1 C), and using it has been established as an accurate means to monitor core body temperature.9 We defined warming as the placement of a forced-air warming blanket set at a medium or 100 F (37.8 C) setting. Inclusion and Exclusion Criteria To be included in this project, participants had to be between the ages of 18 and 85 years, speak English, be able to sign for informed consent, and have an American Society of Anesthesiologist’s Physical Status Classification of I to III.11 Patients in our project underwent the following surgeries: n n n n n n
exploratory laparotomy; colorectal surgery; total joint replacements (including hip and knee); spinal and chest procedures; total abdominal hysterectomy; and robotic-assisted nephrectomy, prostatectomy, and cystectomy.
We excluded potential participants from the project if they had known thyroid disease, autonomic dysfunction (eg, dysautonomia or Shy-Drager syndrome), Cushing syndrome, or documented peripheral vascular disease. Variations in core body temperature are often seen in patients with these diseases, and, because temperature was a study variable, we decided to exclude these patients. We also excluded patients with admission temperatures higher than 37.5 C (99.5 F) or less than
www.aornjournal.org
36.5 C (97.7 F) and those with a known infection with fever or a surgical site infection. Design, Setting, and Sampling We used a prospective, pretest/posttest design with random assignment. The setting was an independently owned, MagnetÒ status, community hospital with 77 acute care beds located in the Midwest. After receiving institutional review board approval, we approached a convenience sample of 146 patients for initial consent at the point of preoperative teaching and testing. The RNs providing preoperative teaching explained the study and obtained informed consent. After they obtained the patient’s consent to participate in the study, the nurses randomly assigned participants to the intervention or control group by using the last two digits of the patient’s account numbers and random integers. If the two-number combination was on the sheet of 65 randomized number sets, then the patient was placed in the intervention group; if the pair of numbers was not on the randomized sheet, then the patient was placed in the control group. The nurse then placed a sealed envelope with the appropriate protocol, a data collection sheet, and the signed consent on the patient’s chart. On the day of admission to the preoperative surgical area, the admitting nurse confirmed that the patient was still willing to participate. Five individuals dropped out of the study at that time, because they verbalized that they were already uncomfortably warm before or shortly after being given the warming blanket. For the other participants, the admitting nurse opened the envelope and ensured that the blanket was turned on for the intervention group participants. Both groups received one warmed cotton blanket per standard protocol. An additional three participants had their surgery cancelled, and the admission nurse did not recognized 10 patients as participants in the project. Thus, a total of 128 participants or 88% of the convenience sample of 146 individuals provided AORN Journal j 325
FETTESdMULVAINEdVAN DOREN
March 2013 Vol 97 No 3
TABLE 1. Demographic Characteristics of the Sample All participants (N ¼ 128) Gender Male Female Age in years (mean) American Society of Anesthesiologists Physical Status Classification I II III Body mass index in kg/m2 (mean)
Warming blanket (n ¼ 54)
Test and value c2; P ¼ .407
60 68 58.7
8 114 6 33
data. We had conducted a power analysis before data collection to determine the necessary sample size. We based our calculations on a two-tailed t test to detect a significant difference in mean temperature between the intervention and control groups at a significance level of 5%. To detect a moderate effect size of 0.5 with 80% power, a sample size of 64 patients in each group was deemed necessary. Our project resulted in 54 participants in the intervention group and 74 participants in the control group. Although we reached the total desired sample size, the uneven distribution between groups is a limitation of the project. The demographic characteristics of the sample are presented in Table 1. There were no significant differences between the two groups based on gender (c2 ¼ 0.688, P ¼ .407), age (t ¼ 0.333, P ¼ .740), body mass index (t ¼ 0.834, P ¼.406), American Society of Anesthesiologists Physical Status Classification (Fisher exact test, P ¼ .392), or hospital admission temperature (t ¼ -0.185, P ¼ .853). Instrumentation We used a temporal artery-scanning thermometer to determine patients’ temperatures. This instrument has been documented to be accurate to 0.2 F (0.1 C). The thermometers used in the surgical 326 j AORN Journal
No warming blanket (n ¼ 74) 37 37 59
23 31 58.4
3 68 3 33.5
5 46 3 32.3
t test; P ¼ .740 Fisher exact test; P ¼ .392
t test; P ¼ .406
areas are checked for accuracy before the first use, but the brand of thermometer we used is designed to stay calibrated permanently and not require routine recalibration.9 We used forced-air warming blankets set at the 100 F (37.8 C) setting (ie, medium) for warming. Safety features such as self-test sequences, temperature alarms, system failure turn-off devices, higher than programmed temperature shutdown circuits, and mechanisms to verify temperature output all make these warming blankets reliable and safe for use.10 Procedures On the day of surgery, when a participant arrived in the outpatient surgery area, the admission nurse opened the sealed envelope that had been placed on the chart by the nurse who obtained consent. The envelope contained information that determined in which group the participant belonged. All the patients had a forced-air warming blanket open and in place. The blanket went with the patient to the OR and then to the PACU; this ensured that the PACU nurses performing postoperative temperature measurements did not know who was in the intervention group and who was in the control group. For control group participants, the forced-air warming blanket was not turned on. The normal routine in our hospital is to follow AORN standards
PREOPERATIVE WARMING
www.aornjournal.org
TABLE 2. Temperatures and Length of Stay Between Groups
Means Patient temperature on admission to the outpatient department Patient temperature on exiting the preoperative area Patient temperature on admission to the postanesthesia care unit Postanesthesia care unit length of stay
No warming blanket (n ¼ 74)
Warming blanket (n ¼ 54)
Test and value
98.2 F (36.7 C)
98.2 F (36.7 C)
t test; P ¼ .853
98.4 F (36.8 C)
98.6 F (37 C)
t test; P ¼ .314
98.0 F (36.6 C)
98.1 F (36.7 C)
t test; P ¼ .314
52.5
55.1
Mann-Whitney test; P ¼ .526
for preventing hypothermia 5 in the surgical patient, which includes using intraoperative warming and forced-air warming, and warming IV and irrigation fluids. In addition to these intraoperative interventions, our team places a warm cotton blanket on all patients in the preoperative area for comfort. For the intervention group, approximately one hour before surgery, the preoperative nurse placed a forced-air warming blanket on the patient and set it on medium. The nurses took the patient’s temperature in the preoperative, intraoperative, and postoperative care areas. The nurses turned the blankets on for both groups in the surgical suite to help maintain normothermia. Throughout the preoperative, intraoperative, and postoperative period, the nurses followed standard policies and procedures for observing and monitoring the patient. No patients experienced adverse temperature events; however, two participants in the study group asked that the blanket be removed because they felt too warm. RESULTS AND FINDINGS We entered temperature data into the statistical program12 and analyzed the data for the project’s two questions. The question “Will using forcedair warming techniques before surgery decrease the number of patients presenting to the PACU in a hypothermic state?” was not supported (Fisher exact test; P ¼ .508). There also was no significant difference in the mean temperatures
when participants exited the preoperative area. The second question “Will prewarming patients before surgery decrease the length of stay in the PACU?” also was not supported. The median PACU times, 50 minutes for the intervention group and 49 minutes for the control group, were not statistically significant (Mann-Whitney test, P ¼ .545). Statistical results are provided in Table 2. LIMITATIONS Although this quality improvement project used an established method to investigate the effects of prewarming, there were limitations. The sample size was one of the largest in the literature to date, but the differences in the group sizes could have affected the statistical outcomes. Another issue was the lack of patients with hypothermia in either control or intervention groups. The literature reviewed, before we initiated this project, was published on or around the time that the Centers for Medicare & Medicaid Services quality measure on PACU temperatures for colorectal surgical patients was published.13 This ruling focuses on the need to keep patients warm, which placed increased attention on intraoperative care to minimize heat loss. These changes could account for the significant difference between the 60% to 70% hypothermia identified in the literature and the 1% observed during our project. Lastly, nurses may have given additional warm cotton blankets
AORN Journal j 327
FETTESdMULVAINEdVAN DOREN
March 2013 Vol 97 No 3
to patients in the preoperative area, further confounding the temperature readings. However, this is thought to be unlikely given the limited time patients spend in that area. CONCLUSION Maintaining normothermia is not only important for the comfort of surgical patients, it affects surgical outcomes. Our quality improvement project supports the study by Burns et al6 that showed that prewarming does not significantly affect patient temperature on arrival to the PACU. Based on our findings, we do not recommend further research on patient prewarming to decrease PACU time but suggest that nurses consider the effect of adequate warming on long-term patient complications, such as postoperative infections. An area for further study might be the effect that prewarming has on patient satisfaction. Our participants frequently commented on how nice it was to be warm. We also recommend strengthening our study approach by reducing the limitations of unequal group size and confounding variables. Editor’s note: Magnet is a registered trademark of the American Nurses Credentialing Center, Silver Spring, MD. References 1. Sajid MS, Shakir AJ, Khatri K, Baid MK. The role of perioperative warming in surgery: a systematic review. Sao Paulo Med J. 2009;127(4):231-237. 2. Scott EM, Buckland R. A systematic review of intraoperative warming to prevent postoperative complications. AORN J. 2006;83(5):1090-1113. 3. Sessler DI, Schroeder M, Merrifield B, Matsukawa T, Cheng C. Optimal duration and temperature of prewarming. Anesthesiology. 1995;82(3):674-681. 4. Andrzejowski J, Hoyle J, Eapen G, Turnbull D. Effect of prewarming on post-induction core temperature and the incidence of inadvertent perioperative hypothermia in patients undergoing general anaesthesia. Br J Anesth. 2008;101(5):627-631. 5. Recommended practices for the prevention of unplanned perioperative hypothermia. In: Perioperative Standards and Recommended Practices. Denver, CO: AORN, Inc; 2012:365-378. 6. Burns SM, Piotrowski K, Caraffa G, Wojnakowski M. Incidence of postoperative hypothermia and the relationship
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to clinical variables. J Perianesth Nurs. 2010;25(5): 286-289. Kiekkas P, Karga M. Prewarming: preventing intraoperative hypothermia. Br J Perioper Nurs. 2005;15(10): 444-451. Bitner J, Hilde L, Hall K, Duvendack T. A team approach to the prevention of unplanned postoperative hypothermia. AORN J. 2007;85(5):921-929. Exergen Temporal ArteryThermometer TAT-5000: a kinder, gentler way to take a temperature, 2006. Exergen Corporation. http://www.exergen.com/tathermometry/ Specifications-TAT-5000-REV-5-12-11a.pdf. Accessed December 11, 2012. Life-Air 1000, Hypothermic Therapy System, 2007. Progressive Dynamics Inc. http://www.progressivedyna micsmedical.com/pdf/life_air_owners.pdf. Accessed December 11, 2012. ASA Physical Status Classification System. American Society for Anesthesiologists. http://www.asahq.org/Ho me/For-Members/Clinical-Information/ASA-PhysicalStatus-Classification-System. Accessed December 11, 2012. PASW StatisticsÒ Version 18.0. Chicago, IL: SPSS, Inc; 2008. CMS Core Measure SCIP: Surgical Care Improvement Project. http://wwwsjhlex.org/documents/Physicians/ SCIP_Poster_Full_Size.pdf. Accessed December 11, 2012.
Sondra Fettes, MSN, RNC, is the director of nursing research and Magnet at Oaklawn Hospital, Marshall, MI. Ms Fettes has no declared affiliation that could be perceived as posing a potential conflict of interest in the publication of the article. Mary Mulvaine, BSN, CNOR, CRNFA, is an RN first assistant in the OR at Oaklawn Hospital, Marshall, MI. Ms Mulvaine has no declared affiliation that could be perceived as posing a potential conflict of interest in the publication of the article. Elaine Van Doren, PhD, RN, is the associate dean for Undergraduate Programs and an associate professor at Kirkhof College of Nursing, Cook-DeVos Center for Health Sciences, Grand Valley State University, Allendale, MI. Dr Van Doren has no declared affiliations that could be perceived as posing a potential conflict of interest in the publication of the article.