Comparison of Three Rewarming Methods in a Postanesthesia Care Unit

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Comparison of Three Rewarming Methods in a Postanesthesia Care Unit

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atients who undergo surgical procedures frequently feel very cold in postanesthesia care units (PACUs), and they report marked discomfort associated with hypotliermia. Although most patients generally can- tolerate moderate hypothermia for brief periods, unrecognized or prolonged hypothermia can constitute a significant clinical risk for some patients during the early postoperative period.’ Shivering in response to hypothermia increases patients’oxygen demands by as much as 400% and places elderly patients and patients with underlying cardiovascular disorders at increased risk for cardiovascular complications.2 Managing patients who shiver and are unable to self-regulate their body temperatures after surgery is challenging. Perioperative nurses must discover effective interventions to decrease the duration and severity of postoperative hypothermia, enhance

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patients’ comfort, and potentially decrease postoperative complications. I M P r m S FOR SllJDY

Nurses in our PACU at Memorial Sloan-Kettering Cancer Center (MSKCC), New York, had documented that 58% of patients who underwent thoracotomy or laparotomy procedures had PACU admission temperatures that were less than 36” C (96.8’ F). Concerned about the deleterious effects of postoperative hypothermia, we designed this study to determine if the application of reflective blankets and reflective head coverings could be effective nursing interventions in rewarming patients after surgery. We sought to answer the research question, “Is there a difference in the time patients require to reach normothermia based on which of three PACU nursing interventions they receive?’ The three interventions consisted of covering patients in the PACU with two warmed thermal blankets A B S T R A C T Postoperative hypothermia is problematic because patients in and a hospital bedspread (ie, postanesthesia care units (PACUs) often feel very cold, and unrecogstandard PACU care); two warmed thermal blankets, a nized or prolonged postoperative hypothermia can aggravate patients’ underlying cardiovascular disorders. The researchers compared three reflective blanket, and a hospital methods of rewarming PACU patients who had undergone laparotomy bedspread; or two warmed thermal blankets, a procedures. Patients were assigned randomly to three groups. Each patient in group one received the standard PACU rewarming intervenreflective blanket, a hospital bedtion (ie, Mb warmed thermal blankets and a hospital bedspread). Each spread, and a reflective head covering. patient in group two received the standard PACU rewarming intervenWe defined an effective PACU tion plus a reflective blanket. Each patient in group three received the standard PACU rewarming intervention plus a reflective blanket and a rewarming intervention as one that reflective head covering. Nurses measured patients‘ vital signs on reduced the duration of patients’ admission to the PACU and every 15 minutes thereafter until patients‘ postoperative hypothermia, desublingual temperatures reached 36”C (96.W F). No signlficant tem- creased patients’ time in the PACU, perature differences occurred among patients in the three groups, but increased patients’ comfort levels, an inverse relationship existed between patients‘ PACU admission and decreased patients’ risks for temperatures and the time they required to reach normothermia. AORN postoperative complications, and we hypothesized that the effectiveness J 65 (March 1997)597-601.

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JUNE HERSHEY, R N ; CORA VALENCIANO, R N ; MARILYN BOOKBINDER, RN

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of these three interventions would differ. For the purposes of this study, we used the following operational definitions. We defmed hypothermia as a sublingual temperature of less than 36" C (96.8" F), normothermia as a sublingual temperature of 36" C (96.8" F), and reflective blanket and reflective head covering as covers made of reflective aluminized material that are used to reduce radiant heat loss. ~lunER€Vlrn

A primary PACU nursing intervention is to facilitate patients' return to normothermia.? Shivering increases postoperative patients' oxygen demands and can cause airway obstructions and increased somnol e n ~ e Simultaneous .~ metabolic response to surgery and recovery from anesthesia often result in increased metabolic rates and myocardial workload^.^ Maintenance of homeostasis is important in postoperative patients, especially those with compromised pulmonary functions who have undergone abdominal and thoracic surgical procedures and who are at risk for cardiovascular complications. The infusion of cold IV fluids, application of cold skin prep solutions, and extensive exposure of body surfaces in the intraoperative period contribute to patients' postoperative hypothekia.6 The combination of open body cavities, cool OR temperatures, and the effects of general anesthesia are significant factors in the development of intraoperative hypothermia.' Researchers have investigated methods to reduce intraoperative hypothermia. One study documented that administering heated humidified anesthetic gases maintained normothermic adult surgical patients' body temperatures and rewarmed hypothermic adults during general anesthesia.8 A decade ago, several groups of researchers reported the effectiveness of reflective blankets in maintaining adult patients' body temperatures during ~ u r g e r yOther .~ researchers have documented that application of reflective head coverings helps maintain neonates' body temperatures.IO Even with intraoDerative temDerature-maintenance interventions, many patients arrive in PACUs with body temperatures less than 36" C (96.8" F). In 1980, a nurse researcher studied various interventions to rewarm 198 adult PACU patients. Sixty percent of these patients had body temperatures less than 36" C (96.8" F) when they were admitted to the PACU, and patients older than 60 years had significantly longer durations of hypothermia than younger patients. This researcher also noted that patients who had general anesthesia returned to normothermia faster than those who had regional anesthesia, but noted no significant differences among patients who received radiant heat lamp treatments, thermal blankets with warmed bath blankets.

warmed bath blankets that were changed every 30 minutes, or room-temperature bath blankets only.lI Other researchers have documented the effectiveness of applying head coverings and reflective blankets to patients during surgery. l 2 We were unable to find controlled studies that had tested the effectiveness of reflective materials in rewarming PACU patients. As our literature review did not answer our question, we designed this study to compare the efficacy of three PACU nursing interventions in rewarming adult postoperative patients. SeUDY Mrmoo5 We conducted the study in the 23-bed PACU at MSKCC, which is a 565-bed comprehensive cancer center that has 17 ORs. More than 11,000 surgical procedures are performed at MSKCC each year. The hospital's institutional review board reviewed our study protocol and waived the requirement to obtain informed consent because all patients would receive, at a minimum, standad PACU care (ie, two warmed thermal blankets and hospital bedspreads); other investigators had not experienced complications using the same type of reflective blanket to prevent inkaoperative heat loss; the electronic thermometer was standard equipment in our PACU; oral temperature measurements using this specific electronic thermometer had correlated moderately well ( r = .77, P < .0001) with tympanic temperatures in a previous study;'? and surgical staff members at our hospital regularly applied reflective head coverings to patients during the intraoperative period. Sample. Using a statistical power analysis, we determined that we would need a sample size of 48 patients per group to detect a medium effect size of F = .25 with 80% desired statistical power and a significance level of .05. Power is the probability of rejecting the null hypothesis (ie, that there would be no difference among patients in the three groups in the time required to reach normothermia). Effect size is a measure of how incorrect the null hypothesis is.14 Our study sample initially consisted of 144 adult patients between the ages of 20 and 60 years who had undergone laparotomy procedures, had received general anesthesia, were in stable condition, and had PACU admission temperatures less than 36" C (96.8' F). We eventually disqualified four of the 140 patients (ie, two in group one, two in group two) because of missing data. The principal investigator reviewed the OR schedule each day to identify potential patients for our study. 598

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We limited the study to patients who had undergone laparotomy procedures in an attempt to control for the effects of body surface exposure during surgery. As infants and elderly patients are known to generate and conserve their body temperatures less efficiently than other age groups,’5 we excluded them from the sample. We also excluded patients who had undergone previous radical oral surgical procedures and those who required controlled ventilation (ie, warmed oxygen) in the PACU because of the potential effects on sublingual temperature measurements. Most of the patients were women who had undergone traditional (ie, open) gynecologic procedures. Patients’ ages did not differ significantly among the three groups. Data collection. We used a specific type of electronic thermometer to measure patients’ temperatures. Members of our hospital’s biomedical electronics department established the reliability of this thermometer before it was used in the study and recalibrated it weekly during the study to ensure the accuracy of the sublingual temperature measurements. A staff member in our nursing research department used a table of random numbers to assign patients prospectively to one of the three study groups. As each eligible patient was admitted to the PACU, the investigator opened an envelope that contained the patient’s group assignment. The investigator and a PACU staff nurse measured the patient’s temperature, pulse, respirations, and blood pressure and repeated these measurements every 15 minutes until the patient’s sublingual temperature reached at least 36” C (96.8” F),which was a requirement for discharge from the PACU. The nurse placed the thermometer in the sublingual pocket of the patient’s oral cavity and held the thermometer in place while the temperature was measured. The investigator calculated the patient’s time to normothermia by recording the number of minutes that elapsed from PACU admission until the patient’s temperature reached 36” C (96.8” F). The investigator also obtained demographic data (eg, age, gender, body weight, length of time in the OR, presence of an endotracheal tube that was removed shortly after admission to the PACU, previous history of cardiovascular disease, preoperative and intraoperative vital signs, intraoperative electrocardiogram rhythm strip, incidence of shivering in the PACU, pain control methods) from the patient’s medical record during this time. Interventions. After the investigator and PACU nurse obtained the patient’s initial vital signs, the PACU nurse applied the rewarming intervention dictated by the patient’s group assignment. Each patient in group one received the standard PACU rewarming intervention (ie, two warmed thermal blankets and a hospital bedspread). Each patient in group two received the standard PACU rewarming intervention

plus an aluminized reflective blanket. Each patient in group three received received the standard PACU rewarming intervention plus an aluminized reflective blanket and reflective head covering. RESULTS

To test the hypothesis that durations of postoperative hypothermia differed among the three groups of patients, we performed a one-way analysis of variance, using a significance level of .05. There were no significant differences among the three nursing interventions and patients’ durations of hypothermia. We tested the assumptions underlying the technique that dealt with homogeneity of variance (ie, we performed an F test to determine if samples had the same variance) and normality. Although the results did not support the study hypothesis, patients in group two (ie, two warmed thermal blankets covered by a reflective blanket and then a hospital bedspread) reached normothermia an average of eight minutes faster than the patients in the other two groups (Table 1). We performed additional statistical tests to identify factors related to hypothermia. A Pearson’s Product Moment Correlation revealed a significant inverse relationship between patients’ PACU admission temperatures and the time they required to reach normothermia (r = -.54, P = .001). This finding indicates that patients with higher PACU admission temperatures require shorter times to reach normothermia. No significant differences existed between the time required to reach normothermia and age, gender, body weight, length of time in the OR, temporary presence of endotracheal tube on admission to the PACU, other vital signs, electrocardiogram rhythm, or pain medication. Patients who shivered (ie, 24% of the sample) reached normothermia significantly faster than those who did not shiver (t = 2.27, df= 138,P = .025). DISCUSSION

We conducted this controlled study to evaluate an innovative method of rewarming postoperative patients (ie, applying aluminized reflective blankets, hats, warmed thermal blankets, hospital bedspreads). The lack of statistically significant differences among the three nursing interventions suggests that applying aluminized reflective blankets over warmed thermal blankets does not expedite postoperative patients’ return to normothermia. The study patients’ PACU admission temperatures significantly affected the durations of their postoperative hypothermia, which suggests that it may be more effective to sustain patients’ body temperatures intraoperatively so that their PACU admission temperatures are closer to normal. The patients in our study who shivered returned to normothermia more quickly,

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Table 1 SELECTED PATIENT DEMOGRAPHICS AND PHYSIOLOGIC VARIABLES

Group one n=46

Group two n=46

184

233

20 1

13 (29%)

14 (30%)

15 (3 1"/o)

34.80 c (94.70 F) .76

34.8" C (94.7" F) .72

115.1 69.6

109.6 65.0

119.8 82.3

PACU admission blood pressures systolic <150 mm Hg diastolic > 90 mm Hg

90%

91%

94%

PACU admission pulse rates 60 to 100 beats per min

63%

74'/o

69%

PACU admission respiratory rates 12 to 24 breaths per min

9ao/o

98%

96%

Normal sinus rhythm demonstrated on admission to PACU

56%

70%

69%

Presence of shivering while in PACU

20%

26%

27%

Pain medication administered in PACU

67%

59%

67%

Characteristics Mean time in the OR (min) Endotracheal tube present when admitted to the postanesthesia care unit (PACU)

Temperature at admission to the PACU mean 35.0" C (95.0" .59 standard deviation Duration of hypothenio (min) mean standard deviation

F)

supporting other researchers' findingst6that shivering is a normal homeostatic response. The frequent occurrence of hypothermia in our PACU patients was the impetus for this study. Although statistical significance was not attained between the time needed for patients to reach normothermia and the three nursing interventions we tested, the study is significant clinically because it has increased our perioperative staff members' awareness of the need to prevent intraoperative and postoperative hypothermia. It is now routine practice at our hospital to begin warming interventions in the preoperative holding area by covering patients with warmed thermal blankets. During surgery, patients now lie on warmed water mattresses with their extremities covered with plastic drapes or cotton blankets. As a result of these practice changes, almost all surgical patients now are normothermic when they enter our PACU. UhlTATfONS

The patients in our study primarily were female and between 20 and 60 years of age. Only patients who underwent diagnostic laparotomy procedures

Group three n=4a

for suspected cancer were included. These factors may limit the generalizability of our findings. IMPUCATlOlYS #)R P R A M AND RESEARCH

Perioperative staff members need to minimize the risks associated with hypothermia by striving to maintain patients' normal body temperatures during surgery. Other perioperative nurse researchers should replicate our study using a wider variety of surgical patients and settings. Our study findings validate perioperative nurses' standard intervention of using warmed thermal blankets and hospital bedspreads as a cost-effective, safe, efficient method of increasing PACU patients' body temperatures and comfort levels. Forced-warm-air devices are being used to rewarm patients in many PACUs; however, reports of their safety17 and efficacy in rewarming postoperative patients are inconsistent.18 Perioperative nurse researchers have examined the use of simultaneous interventions (eg, increasing OR temperatures to 26.7" C [SOo F], covering patients' heads and extremities, applying warmed cotton blankets, using warmed IV and irrigation fluids) to prevent 600

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hypothermia or to rewarm surgical patients before transporting them to PACUs.l9 The application of multiple nursing interventions appears to be effective in preventing patients from developing intraoperative hypothermia and in rewarming postoperative patients,*O but additional research is needed to verify these observations. A

June Hershey, RN, BSN, OCN, is nurse manager, treatment room, Memorial Sloan-Kettering Cancer Center, New York. At the time of this study, she was a clinical nurse W,postanesthesia care unit, Memorial Sloan-Kettering Cancer Center. New York. NOTES 1. G J Slotman,E H Jed, K W Burchard, “Adverse effects of hypothermia in postoperativepatients,”American Journal of Surgery 149 (April 1985) 495-501. 2. M S Vaughan, “Nursing Treatment of Hypothermia in Adult Recovery Room PostsurgicalPatients” (Doctoral dissertation, University of Arizona, 1980). 3. Ibid. 4. M S Vaughan, R W Vaughan, R Cork, “Postoperativehypothermia in adults: Relationshipof age and shivering to rewarming,”Anesthesia and Analgesia 60 (October 1981) 746-751. 5. J L Rodriguez et al, “Morphine and postoperativerewarming in critically ill patients,” Circulation 68 (December 1983) 1238-1246. 6. H C Tausk, R Miller, R B Roberts, “Maintenanceof body temperature by heated humidifcation,” Anesthesia and Analgesia 55 (September/October 1976)719-723. 7. R H Moms, “Operatingroom temperature and the anesthetized,paralyzed patient,” Archives of Surgery 102 (February 1971)95-97. 8. D R Stone et al, “Adult body temperature and heated humidification of anesthetic gases during general anesthesia,”Anesthesia and AnaZgesia 60 (October 1981) 736-741. 9. M T Murphy, J M Lipton,

“Reductionof perioperativeheat loss using reflective drape,” poster presentation at the meeting of the American Society of Anesthesiologistsand the American College of Surgeons,Las Vegas, 17 Oct 1986; D L Bourke et al, “Intraoperativeheat conservation using a reflective blanket,”Anesthesiology 60 (February 1984) 151-154. 10. S L Molland, R C Kopf, personal communicationwith the authors, New York, 8 Aug 1991. 11. Vaughan, “Nursing Treatment of Hypothemia in Adult Recovery Room PostsurgicalPatients” (Doctoral dissertation,University of Arizona, 1980). 12. Murphy, Lipton, “Reductionof perioperativeheat loss using reflective drape;” Bourke et al, “Intraoperative heat conservationusing a reflective blanket,” 151-154; M T Blansett, “The effects of rewarming hypothermic postanesthesiapatients using Thermadrape covering, heat lamps, and warmed cotton blankets,”Journal of Post Anesthesia Nursing 5 (April 1990) 80-84. 13. Murphy, Lipton, “Reductionof perioperativeheat loss using reflective drape;” R S Ericson, S T Yount, “Comparisonof tympanic and oral temperaturesin surgical patients,” Nursing Research 40 (MarcWApril 1991) 90-93. 14. J Cohen, Statistical Power

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Cora Valenciano,RN,CPAN, is a clinical nurse 111,postanesthesia care unit, Memorial Sloan-Kettering Cancer Center, New York.

Marilyn Bookbinder, RN, PhD, is director of the nursing researchprogram, Memorial Sloan-Ketfering Cancer Center, New York, and adjunct assistant professor of nursing, New York University,New York. Analysisfor the Behavioral Sciences, second ed (Hillsdale,N J Lawrence Erl6aum Associates, 1988). 15. A C Borchartd, K E Fraulini, “Hypothermiain the postanesthetic patient,”AORN Journal 36 (October 1982) 648-660. 16. Vaughan, Vaughan, Cork, “Postoperativehypothermia in adults: Relationship of age and shivering to rewarming,” 746-751. 17. T Stevens, “Managingpostoperative hypothermia,rewarming, and its complications,”Critical Care Nursing Quarterly 16 (May 1993) 60-77. 18. M Giuffre et al, “Rewarming postoperativepatients: Lights, blankets, or forced warm air,”Journal of Post Anesthesia Nursing 6 (December 1991) 387-393. 19. D Dennison, “Thermalregulation of patients during the perioperative period,” AORN Journal 61 (May 1995) 827-832; L Lewis-Sims, “Minimizing patients’ hypothermia and bleeding after cardiac surgery,”AORN Journal 61 (April 1995) 731-736. 20. C Ellis-Stoll et al, “Effect of continuously warmed IV fluids on intraoperativehypothermia,”AORN Journal 63 (March 1996) 599-606; R D Howell et al, “Effects of two types of head coverings in the rewarming of patients after coronary artery bypass graft surgery,”Heart and Lung 2 1 (January 1992) 1-5.