Effects of Perioperative Hypothermia on Extubation,Recovery Time,and Postoperative Shivering in Breast Surgery

Abstract

Women undergoing breast surgery seem to be under the risk for hypothermia (central body temperature <36°) due to the uncertainty caused by the preoperative preparation time and the variety of operations, leading to neglect of warming precautions. The study examines the perioperative hypothermia (PH) in breast surgery and the relationships between the depth of decrease in body temperature and individual or clinical variables. This prospective, cross-sectional, observational study includes 120 female patients 18–65 years of age who were given general anesthesia for breast surgery. The incidence of hypothermia was 68.1%. The given patients were discriminated as body temperature <36°, hypothermia was significantly related with lower weight, body mass index, American Society of Anesthesiology (ASA) score, baseline body temperatures, higher extubation, and recovery times. When patients' temperature decreases by >1 or 1.5°, lower age and longer durations of operation and anesthesia were also significant variables. The incidence of shivering is quite high at temperatures below 36°C or at 1 and 1.5°C reductions from baseline (72.7%, 84%, 94.1%, respectively). Body temperature changes of the patients had no effect on nausea–vomiting and pain scores. It turned out that the incidence of PH and shivering is high in women who underwent breast surgery. We think that the depth of decrease in body temperature should be taken into account when evaluating the predictors or clinical consequences of hypothermia, except for the 36°C limit for body temperature.

Introduction

Perioperative hypothermia (PH) defined as core temperature <36°C, has a wide-ranging incidence of 17–90% and is associated with significant morbidities (Akers et al., 2019; Sessler, 2008). Factors, including anesthesia, surgery, and the patient's personal characteristics may lead to a decrease in temperature by 0.5–1.5° in the first half hour, and even up to 6° afterward (Kurz, 2008; Vural et al., 2018). The range of physiological response thresholds increases to 2–4° under anesthesia (Riley and Andrzejowski, 2018). In parallel with the depth of hypothermia, the severity of deterioration in coagulation, wound healing, immune functions, tissue oxygenation, and drug metabolism functions increases (Horosz and Malec-Milewska, 2013; Reynolds et al., 2008; Sessler, 2016). Although recommended as one of the basic rules in the guidelines, only 40% of the patients under general anesthesia were warmed, and body temperature was measured in 20%. These incidences are 20% and 6%, respectively, in patients undergoing regional anesthesia (Torossian, 2007).

Breast cancer is a significant global health problem, necessitating a high frequency of surgical interventions for diagnosis or treatment. A considerable proportion of these interventions involve younger women. The multitude of variables inherent to the process, such as preoperative preparation, perioperative radiological–pathological examinations, prosthesis applications, addition of axillary dissection, contribute to the uncertainty of surgical and anesthesia durations. This uncertainty, combined with the challenge of maintaining the patient's upper body warmth during surgery, predisposes patients to hypothermia. Consequently, the focus of this study is on PH in breast surgery and the associations between the degree of body temperature decrease and various individual or clinical variables.

Materials and Methods

Selection of patients

In accordance with the decision dated November 28, 2018 and numbered 18-11.1T/25 from the Clinical Research Ethics Committee of the University Faculty of Medicine, a prospective, cross-sectional, observational study was undertaken from January 2019 through March 2020. The cohort comprised 120 female patients, 18–65 years of age, classified as American Society of Anesthesiology (ASA) I–II, who underwent elective breast surgery under general anesthesia and provided informed consent. The study excluded those who declined participation or wished to withdraw at any stage, as well as individuals with body temperatures >37.5°C or <36°C in the preoperative period, or those diagnosed with coronary artery disease, heart failure, liver, kidney or endocrine disorders (thyroid hormone disorder, diabetes, etc.), respiratory diseases (asthma, chronic obstructive pulmonary disease, etc.), anemia, and/or known drug allergies.

Preparations, anesthesia protocol, and recordings

During preoperative anesthesia consultations, patients were apprised of the study protocol, and written consent was obtained from those agreeing to participate. Before entering the operation room, 20 Gauge cannula was inserted into the antecubital vein of the arm opposite to the surgery site for single breast operations, and the arm not undergoing axillary dissection in bilateral breast surgeries. Initial tympanic membrane measurements were taken to establish each patient's basal body temperature using a Covidien Genius 2 (Covidien IIc, Mansfield, MA). On arrival in the operating room, patients were premedicated with 30 μg/kg of midazolam and underwent monitoring for electrocardiography, noninvasive blood pressure, and peripheral arterial oxygen saturation. The operating room temperature was maintained at 22 ± 1°C throughout the surgery.

All patients were orotracheally intubated following standard anesthesia induction protocols. Intravenous (IV) induction of anesthesia was achieved with 2–3 mg/kg propofol, 1 μg/kg fentanyl, and 0.6 mg/kg rocuronium. General anesthesia was maintained with O₂–Air–Sevoflurane and remifentanil (0.5–1.0 μg/[kg·min]), end-tidal carbon dioxide levels kept between 34 and 36 mmHg. A temperature probe, monitored by a GE B650 Healthcare device (Helsinki, Finland), was advanced 35–40 cm into the lower third of the esophagus to track temperature measurements throughout the operation.

Upon the completion of sterile draping, a warming device (Medtronic, Covidien WarmTouch 6000 Warming Unit, MN) delivering a 40°C hot air flow was utilized from the foot extremities until patient recovery was complete. Remifentanil dosage was adjusted by ±25% to maintain intraoperative hemodynamic stability in cases of hypotension or hypertension (±20% of baseline systolic blood pressure) and tachycardia or bradycardia (heart rate >100 or <50 minutes). For postoperative analgesia, 10 mg/kg of IV paracetamol was administered ∼10 minutes before the commencement of skin suturing, and 1 mg/kg of tramadol was administered intramuscularly upon placement of the final suture. After the removal of the esophageal probe, temperature monitoring ceased. Upon completion of the surgical procedure, 2 mg/kg of sugammadex was administered for neuromuscular antagonism. The duration from cessation of the inhalation agent to extubation was noted as the extubation time. The recovery time was defined as the period until a Modified Aldrete recovery score of ≥9 was achieved postextubation (Aldrete, 1995).

Data recorded on the case report form encompassed patient age, body weight, height, body mass index, ASA score, type of surgery performed, durations of operation and anesthesia, total IV fluid volume, dosages of muscle relaxant (rocuronium) and opioid (remifentanil), as well as the body and operating room temperatures taken at 5-minute intervals.

Patients were initially classified into two groups based on whether their intraoperative central body temperature fell below 36°C (hypothermic) (primary objective). Subsequently, they were satisfied into four subgroups according to the degree of body temperature decrease (Stage I < 0.5°C, Stage II ≤0.5–<1°C, Stage III ≤1–<1.5°C, and Stage IV ≥1.5°C, secondary objective). Staging was determined by the difference between the patient's basal body temperature and the lowest intraoperative body temperature recorded.

Postoperative parameters, including pain, shivering, nausea, and vomiting were evaluated in patients whose cardiac (electrocardiogram), respiration (pulse oximetry), consciousness, fever, blood pressure, and pulse follow-up were monitored every 15 minutes for a period of 4–6 hours after admission to the postoperative care unit. Pain intensity was assessed 30 minutes postoperatively using the Visual Analog Scale (VAS, 0–100 mm scale, 0: no pain, 100 mm: most severe pain known) and recorded in the case report form (Gunusen et al., 2011). Patients who registered a VAS score >40 patients received a single intramuscular (IM) dose of 1 mg/kg diclofenac IM. Shivering was evaluated 15 minutes postoperatively using a 4-point scale: 0: no shivering; 1: piloerection without observable muscle activity, peripheral vasoconstriction, or unexplained peripheral cyanosis; 2: continuous observable muscle activity in one muscle group; 3: observable muscle activity in more than one muscle group; and 4: generalized muscle activity throughout the body (Crossley and Mahajan, 1994).

Nausea and vomiting were recorded on a 3-point scale (1: no nausea or vomiting, 2: nausea alone, and 3: nausea and vomiting) within the first postoperative hour (Gunusen et al., 2011). Patients who experienced nausea were administered 4 mg of intravenous ondansetron.

Statistics

Data analysis was conducted using the IBM-SPSS 25.0 statistical package (IBM Statistical Package for the Social Sciences Corp., Armonk, NY). Categorical data are presented as frequency (n) and percentage (%), whereas continuous variables are expressed as mean ± standard deviation (mean ± SD). The Shapiro–Wilk test was employed to assess the normal distribution of continuous data. Cross-group comparisons for data conforming to normal distribution were performed using a one-way analysis of variance (ANOVA), with post hoc multiple comparisons being undertaken by Bonferroni or Kruskal–Wallis binary comparison tests. Correlations between the variables were evaluated using the Pearson's correlation test. Continuous variables not adhering to a normal distribution were analyzed with the Mann–Whitney U test, and cross-sectional data were compared using Pearson's Chi-square test. A p-value of <0.05 was established as the threshold for statistical significance.

Results

Technical difficulties and data omissions during the study led to the exclusion of 7 out of 120 patients. Consequently, the statistical evaluation was conducted on the data from the remaining 113 patients, all of whom were female.

Hypothermia was detected in 68.1% of the patients (77/113 patients). The mean baseline body temperature and intraoperative lowest body temperature were 36.5 (SD 0.3) and 35.58 (SD 0.7), respectively. Donor characteristics, including age, height, weight, body mass index, anesthesia, and surgery-related variables are presented in Table 1. Considering all the females included in the analysis, the mean age was 49.2 (SD 9.1) years. Among them, 51 patients (45.1%) were ASA I, 62 patients (54.9%) were ASA II. Various surgical procedures were performed: partial mastectomy and sentinel lymph node biopsy in 44 patients, total mastectomy and sentinel lymph node biopsy in 16 patients, axillary dissection with mastectomy in 27 patients, and mammoplasty in 26 patients. The mean durations of the operation and anesthesia were 112 (SD 36) and 122 (SD 37) minutes, respectively. Following the cessation of anesthesia, the mean time to extubation was 401 (SD 198) seconds, with a mean recovery time of 577 (SD 250) seconds.

Table 1.

Comparison of the Study Variables in the Presence of Hypothermia

	All patients n = 113	With hypothermia n = 77	Without hypothermia n = 36	p
Age (years)	49.2 ± 9.1	48.8 ± 9.1	49.9 ± 9.1	0.534
Weight (kg)	68.9 ± 10.5	67.3 ± 11.2	72.2 ± 8.2	0.011
Height (cm)	163.1 ± 5.9	163 ± 6	163 ± 5	0.835
BMI (kg/m²)	25.8 ± 3.3	25.2 ± 3.4	27 ± 2.7	0.003
ASA				0.033
I	51	40	11
II	62	37	25
Duration of anesthesia (minutes)	122 ± 37	126 ± 38	112 ± 52	0.065
Duration of operation (minutes)	112 ± 36	116 ± 37	103 ± 31	0.086
<120 (n)	77	45	32	0.535
≥120 (n)	36	24	12
Total fluid infused (mL)	962 ± 375	994 ± 372	892 ± 375	0.181
Total remifentanil dose (mcg)	819 ± 477	847 ± 523	761 ± 358	0.312
Total rocuronium dose (mg)	48.5 ± 9.9	50 ± 10	46 ± 8	0.064
Extubation time (seconds)	401 ± 198	440 ± 221	318 ± 134	0.000
Recovery time (seconds)	577 ± 250	636 ± 259	450 ± 173	0.000
Nausea–vomiting score (n, %)				0.986
1 (none)	88	60	28
2 (nausea only)	25	17	8
Shivering score (n, %)	50.4%	72.7%	2.7%	0.000
0	56	21	35
1	33	32	1
2	23	23	0
3	1	1	0
Pain score (VAS)	33.4 ± 13.1	34.3 ± 12.9	31.4 ± 14.8	0.291
Baseline body temperature (°C)	36.5 ± 0.3	36.4 ± 0.3	36.7 ± 0.3	0.000
Lowest body temperature (°C)	35.6 ± 0.7	35.3 ± 0.5	36.3 ± 0.3	0.000

Bold values indicate p < 0.05.

All data presented with n and mean ± SD.

ASA, American Society of Anesthesiology; BMI, body mass index; SD, standard deviation; VAS, Visual Analog Scale.

Patients were bifurcated into two groups: those with hypothermia and those without (Table 1). The hypothermic patients had significantly lower body weights (67.3 [11.2] vs. 72.2 [8.2] kg, p = 0.011), lower body mass index (BMI) (25.2 [3.4] vs. 27 [2.7] kg/m², p = 0.003), lower ASA (I/II) scores (40/37 vs. 11/25, p = 0.033), lower baseline body temperature (36.4 [0.3] vs. 36.7 [0.3]°C, p = 0.000), and lower intraoperative lowest body temperature (35.3 [0.5] vs. 36.3 [0.3]°C, p = 0.000). However, these patients experienced significantly longer extubation and recovery times (440 [221] vs. 318 [134] seconds, p = 0.000 and 636 [259] and 450 [173] seconds, p = 0.000) and higher Shivering score (72.7% vs. 2.7%, p = 0.000) compared with patients without hypothermia. There was no correlation observed between hypothermia (<36°C of body temperature) and nausea–vomiting. A moderately significant correlation was noted between basal body temperature and intraoperative lowest body temperature (r = 0.580, p = 0.000).

The study variables were segmented into four stages based on the decrement of body temperature by 0.5° (Table 2). The differential between basal body temperature and the lowest intraoperative body temperature showed a decline of <0.5° in 28 patients (24.7%), 0.5 ≤ to <1° in 43 patients (38%), 1 ≤ to <1.5° in 25 patients (22.3%), and >1.5° in 17 patients (15%). The groups were assessed through ANOVA and Bonferroni post hoc tests. The intervariable differences became significant at stage IV. The mean age (44.3 vs. 47.1 years), mean duration of operation (139 vs. 107 and 103 minutes), mean duration of anesthesia (149 vs. 117 and 113 minutes), mean volume of IV fluid (1226 vs. 911 and 852 mL), extubation time (632 vs. 281 and 372 and 447 minutes), and recovery time (915 vs. 417 and 516 and 629 minutes) in stage IV were significantly different when juxtaposed against stages I, II, and III, respectively. Upon examining early postoperative clinical scores, the shivering score at stage IV was considerably higher than those at stages I and II (94.1% vs. 44.2% and 3.5%, respectively).

Table 2.

Comparison of Variables of Patients Distinguished According to Each 0.5°C Decrease in Body Temperature

	Stage I	Stage II	Stage III	Stage IV	p
	<0.5°C	≤0.5–<1°C	≤1–<1.5°C	≥1.5°C
	n = 28	n = 43	n = 25	n = 17
Age (years)	47.1 ± 8.5	51.9 ± 8.9	50 ± 9.02	44.3 ± 8.7^†	0.019
Weight (kg)	71.0 ± 9.8	70.4 ± 9.5	66.7 ± 11.3	65 ± 12.2	0.143
Height (cm)	163.5 ± 5.4	163.2 ± 5.2	163.7 ± 6.4	163.1 ± 5.9	0.586
BMI (kg/m²)	26.5 ± 3.1	26.4 ± 3	24.8 ± 3.4	24.9 ± 3.6	0.087
ASA (%)					0.008
I	10	14	16	12
II	18	29	9	5
Duration of operation (minutes)	107 ± 32	103 ± 39	113 ± 30	139 ± 30^*,^†	0.005
Duration of anesthesia (minutes)	117 ± 33	113 ± 40	124 ± 32	149 ± 31^*,^†	0.005
Total iv fluid volume (mL)	911 ± 419	852 ± 362	1027 ± 286	1226 ± 318^*,^†	0.003
Total remifentanil dose (mcg)	809 ± 415	671 ± 328	896 ± 542	1100 ± 655	0.105
Total rocuronium dose (mg)	46.2 ± 8.9	46.3 ± 8.7	52.4 ± 9.3	52.1 ± 13	0.308
Extubation time (seconds)	281 ± 141	372 ± 148	447 ± 216^*	632 ± 198^*,^†,≠	0.000
Recovery time (seconds)	417 ± 170	516 ± 170	629 ± 228^*	915 ± 230^*,^†,≠	0.000
Nausea–vomiting score (n, %)					0.378
1 (none)	21 (75)	32 (74.4)	19 (76)	16 (94.1)
2 (nausea only)	7 (25)	11 (25.6)	6 (24)	1 (5.9)
Shivering score (n, %)	3.5%	44.2%	84%	94.1%	0.000
	27	24	4	1^*^†
0	0	17	13	3
1	1	2	8	12
2	0	0	0	1
3
4
Paine score (VAS)	33.6 ± 13.1	29.3 ± 12.6	36.4 ± 12.9	38.8 ± 15.4	0.88

Data: n (%), mean ± SD; bold values indicate p < 0.05.

Significant intragroup comparisons: ^*Stage I versus Stage IV, ^†Stage II versus Stage IV, ^≠Stage III versus Stage IV.

ASA, American Society of Anesthesiology; BMI, body mass index; SD, standard deviation; VAS, Visual Analog Scale.

No significant differences were observed between the patient groups when stratified according to the 0.5° decrease in body temperature with respect to weight, height, BMI, total doses of remifentanil and neuromuscular blocking drugs (NMBD), nausea–vomiting, and pain scores.

Pearson's correlation analysis demonstrated weak-to-moderate relationships between the variables for all patients (Table 3).

Table 3.

Pearson Correlations Between the Study Variables, Including All Patients

	Duration of anesthesia		Duration of operation		Lowest body temperature		Extubation time		Recovery time
	r	p	R	p	r	p	R	p	r	p
Age (years)	0.059	0.538	0.053	0.579	0.126	0.183	0.134	0.157	0.065	0.49
Weight (kg)	0.098	0.302	0.088	0.355	0.291	0.002	−0.181	0.055	−0.177	0.06
Height (cm)	0.200	0.034	0.194	0.04	0.169	0.073	−0.165	0.082	−0.094	0.32
BMI (kg/m²)	0.002	0.982	0.007	0.939	0.271	0.004	−0.135	0.153	−0.173	0.068
Duration of anesthesia (minutes)		1	0.998	0.000	−0.243	0.01	0.365	0.000	0.304	0.001
Duration of operation (minutes)	0.998	0.000		1	−0.240	0.01	0.366	0.000	0.301	0.001
Total IV fluid (mL)	0.727	0.000	0.725	0.000	−0.228	0.015	0.263	0.005	0.263	0.005
Total remifentanil dose (mcg)	0.565	0.000	0.560	0.000	−0.152	0.108	0.207	0.028	0.197	0.036
Total rocuronium dose (mg)	0.372	0.000	0.367	0.000	−0.194	0.04	0.158	0.094	0.155	0.1
Lowest body temperature (°C)	−0.243	0.01	−0.240	0.01		1	−0.554	0.000	−0.623	0.000

Bold values indicate p < 0.05.

BMI, body mass index; NMBD, neuromuscular blocker drug; r, Pearson's correlation coefficient.

The durations of the anesthesia and the operation showed significant correlations with height, total volume of infused fluid, total remifentanil, and NMB doses. The duration of the anesthesia was inherently more closely related to the duration of the operation (r = 0.998).

The lowest body temperature showed significant correlations with body weight (r = 0.291), BMI (r = 0.271), duration of anesthesia (r = 0.243), duration of operation (r = 0.240), total fluid volume (r = 0.228), NMBD dose (r = 0.194), extubation time (r = −0.554), and recovery time (r = −0.623).

Both extubation time and recovery time demonstrated similar relationships with duration of anesthesia, duration of operations, total fluid volume, total remifentanil dose, and lowest body temperature (p < 0.05 for all). However, these times were not significantly correlated with age, weight, height, BMI, and total NMBD dose.

The impacts of varying levels of body temperature decline on extubation and recovery times were evaluated through ANOVA and Bonferroni post hoc tests. Taking into account the difference between the basal body temperature and the lowest body temperature, we observed a decrease of <0.5° in 28 patients (24.7%), a decrease between 0.5° and <1° in 43 patients (38%), a decrease between 1° and <1.5° in 25 patients (22.3%), and a decrease of >1.5° in 17 patients (15%). Upon a decline in body temperature by 1° or more, a statistically significant prolongation in extubation and recovery times was observed (Table 3). Moreover, extubation time displayed a strong correlation with recovery time (r = 0.914, p = 0.000) (not replaced as table data).

Discussion

In our study, the incidence of hypothermia, noted as 68.1%, is substantially high among patients undergoing breast tumor surgery. Patients presenting with hypothermia were classified within the realm of mild hypothermia (34–36°C), with an average minimum temperature of 35.3° (SD 0.5) (Kurz, 2008).

Predictors for hypothermia

General anesthesia inhibits the hypothalamus, leading to impaired thermoregulation and vasodilation (Riley and Andrzejowski, 2018). The core body temperature, typically regulated to within a few tenths of a degree, tends to decrease rapidly by 0.5–1.5° in the first hour of surgery, cumulating in a total decrease of 2–6° (Sessler, 2016). In a study involving 3132 patients under general anesthesia, the incidence of hypothermia in each hour within the first 4 hours postanesthesia induction was found to be 17.8%, 36.2%, 42.5%, and 44.1%, respectively (Yi et al., 2017). Various factors such as lower ambient temperature, the use of cold IV and irrigation fluids, application of cold solutions for skin preparation, blood product transfusions, types and extended duration of surgeries and anesthesia, older age, male gender, higher BMI, comorbidities, compromised hemodynamic status, lower basal body temperature, and the absence of active patient warming have been associated with hypothermia (Akers et al., 2019; Kurz, 2008; Horosz and Malec-Milewska, 2013; Yi et al., 2017; Miyazaki and Hoka, 2019; Collins et al., 2019; Duman and Yılmaz, 2016; Li et al., 2020).

In this present study, heating the residual body surface with a single heating device (forced-air with 40°), maintaining the operating room temperature at 22°C, the type of the anesthesia, and female gender remained constant for all patients. During breast tumor surgery, the evaluation of tumor mass and lymphadenopathy through ultrasonographic, scintigraphic, or X-ray methods often results in increased open upper body surface and extended operation duration due to the need for surgical intervention on either single or double breasts also potential axillary region involvement. The attempt to maintain body temperature by forced-air warming over the lower half of the body appears to be inadequate. Incorporation of active warming methods, such as under-body or fluid warming techniques, in combination with our forced-air warming method, seems to mitigate the incidence of hypothermia in these patients with mild hypothermia (Chen et al., 2019; Moola and Lockwood, 2011; Rauch et al., 2021). This absence of heating becomes increasingly critical under prolonged surgery and anesthesia conditions, as clearly demonstrated in the Stage IV patient group.

Even though it holds greater importance in urological surgeries involving high-volume irrigation (whose volume was not measured in our study), the use of irrigation fluid during extended surgeries also likely contributes to body temperature decrease (Tekgul et al., 2015).

Our patient population, consisting of women who underwent approximately two-hour breast surgery, was primarily younger, with normal body measurements and had a low ASA grade (I-II). Upon examining the patients, we noticed that in hypothermic patients (central body temperature < 36°C), basal body temperature, body weight, BMI, and ASA grades were significantly lower, a finding consistent with previously reported studies (Duman and Yılmaz, 2016; Yi et al., 2017). It is recognized that subcutaneous fat tissue plays a protective role against hypothermia. The ASA grade, ranging from 2 to 5, is acknowledged as a determinant of hypothermia risk, with the risk increasing as the grade escaletes (Riley and Andrzejowski, 2018). A study incorporating various surgeries under general anesthesia, revealed an association between ASA score and hypothermia in univariate analysis, although this connection was not found significant in multivariate analysis (Vural et al., 2018 ). In our study, patients with lower ASA grades were significantly overrepresented in the hypothermic groups, as demonstrated by both patient comparisons.

To safeguard patients from PH, maintenance of basal body temperature is critical, as suggested by the thermal care bundles recommended for implementation from the preoperative period (Duff et al., 2018). The hypothermic group presented a lower basal temperature. In addition to younger age, elongated durations of anesthesia and operations, increased amount of IV fluid, amplified doses of opioids, and NMBDs were also not identified as significant variables when comparing patient temperatures below 36°.

Perioperative complications and their severity are known to amplify as hypothermia intensifies. Therefore, we postulate that in multifactorial perioperative inadvertent hypothermia studies, patient classification based solely on body temperatures <36°C may be inadequate to comprehensively understand the results. Unlike the differentiation pattern observed in hypothermia, significant variables between groups divided on a 0.5° temperature drop included age, durations of the surgery and anesthesia, amount of fluid infused, and ASA grades, all of which were significant in hypothermia classification. The fourth group, characterized by a body temperature decrease of 1.5° or more, included patients who were younger, had lower ASA scores, longer operation and anesthesia times, and higher fluid requirements compared with groups with body temperature decreases below 1°. Elderly patients are reported to be more susceptible to hypothermia and its complications during major surgeries due to a lower vasoconstriction threshold compared with younger individuals (Kasai et al., 2002; Li et al., 2020; Moola and Lockwood, 2011).

The association between surgery duration and hypothermia became significant when comparing patient temperatures with decreases exceeding 1.5° and those with decreases below 1°. Pearson's correlation also disclosed significant associations between prolonged surgery and anesthesia durations with the lowest body temperatures (p = 0.01 for both). These correlations appeared similar for body temperatures <36°, a finding that diverges from other studies (Li et al., 2020). When classifying patients according to each 0.5° decrease in body temperature, body measurements, total doses of opioid and NMBDs did not differentiate the patients undergoing breast surgery. Although surgery durations seemed prolonged, the fact that average rocuronium and remifentanil doses did not significantly increase might be interpreted as decreased requirements with the reduction of body temperature in patients. As expected, there was a strong positive correlation between the total amount of IV fluid administered and the duration of the surgeries (r = 0.725, p = 0.000) during breast surgery.

Clinical effects of hypothermia

Multivariate interactions between patient characteristics, surgical conditions, and hypothermia prevention methods influence both the incidence of hypothermia and associated outcome variables. In the present study, the clinical outcomes of hypothermia were assessed based on extubation and recovery times, as well as shivering, nausea–vomiting, and pain scores.

Intraoperative hypothermia is one of the significant factors associated with delayed extubation and recovery. According to a study by Nivatpumin et al. (2010), which classified patients based on a body temperature threshold of 35°, there was no significant difference between the two groups regarding extubation and recovery times. This suggests that the selected body temperature cutoff for patient classification may affect the target outcomes. Taking into account the progression of perioperative temperature balance, minimizing operation and anesthesia duration emerges as a crucial factor in preventing hypothermia or reducing its severity. Intraoperative hypothermia results from vicious cycles incited by the extension of the operation and anesthesia durations and the effects of anesthetic drugs, which together impair heat production and enhance heat loss mechanisms (Riley and Andrzejowski, 2018). The impact of body heat loss on extubation time can be attributed to alterations in the pharmacokinetics and pharmacodynamics of anesthetic drugs (Rauch et al., 2021; Torossian, 2007).

However, in our study of patients undergoing balanced general anesthesia comprising an inhalation anesthetic, an opioid and a nondepolarizing NMBD, the correlation between opioid and NMBD doses and extubation and recovery times became evident only when temperature loss exceeded 1.5°.

In our female-only study population, factors influencing outcome variables varied depending on patient classification and data evaluation method. Pearson's correlation demonstrated that patient extubation and recovery times were associated with the durations of anesthesia and surgery, total IV fluid volume, remifentanil dose, and the lowest recorded body temperature. Among these, the most strongly correlated parameter with extubation and recovery times was the lowest body temperature. However, when patients are separated based on the definition of hypothermia, weight, BMI, and lower ASA scores are seen to significantly contribute to prolonged extubation and recovery times. Upon classifying patients according to body temperature reduction levels, factors accompanying extended extubation and recovery times included younger age, lower ASA score, longer durations of anesthesia and surgery, and total fluid volume. Extubation and recovery durations significantly increased when temperature dropped >1°, but body size variables were unaffected. Extubation and recovery times were not influenced by total rocuronium doses.

The lack of significant differences in rocuronium doses among groups, combined with the use of fast-acting sugammadex to counteract rocuronium's effects, may have negated any impact of rocuronium on clinical outcomes. An examination of the relationship between total remifentanil volume and extubation and recovery durations using the Pearson's correlation test revealed a mild yet significant positive association. However, when patients were classified according to their body temperatures, remifentanil doses did not significantly differ.

Consequently, our study also evaluated whether hypothermia influenced postoperative shivering score, nausea–vomiting score, and pain score. Postoperative shivering has been reported to occur in 20–70% of patients under general anesthesia (Eberhart et al., 2005). Hypothermia instigates shivering as an aftermath of the use of inhalation agents, opioids, and nondepolarizing neuromuscular blockers in general anesthesia (Baran et al., 2019; Röhm et al., 2006). Moreover, intraoperative remifentanil infusion has been implicated in augmenting postoperative shivering through the induction of hyperalgesia (Song et al., 2014). Tekgul et al. (2015) reported that adult hypothermic patients who were not warmed experienced shivering (23.3% vs. 50%) and protracted recovery. Xu et al. (2004) suggested that maintaining normothermia and curtailing shivering can be effectively achieved with warmed IV fluid and compressed hot air flow heating systems in patients 21–69 years of age undergoing abdominal surgery. Sessler et al. (1991) posited that factors related to surgery, stress, or pain might precipitate postoperative shivering.

Duman and Yılmaz (2016) disclosed that 71.4% of their hypothermic patients undergoing orthopedic surgery experienced shivering. Our study found that shivering score was the only variable affected in our patient group. In both evaluation methodologies, shivering score was significantly associated with decreased body temperature. Shivering, which was observed in 50.4% of all patients and 72.7% of hypothermic patients, escalated to 94.1% in those with a temperature drop exceeding 1.5°, indicating a considerably high incidence.

The multifactorial etiology of postoperative symptoms complicates the interpretation of associations between hypothermia, and the frequencies of nausea, vomiting, and pain scores. Ma et al. (2017) found that elderly patients undergoing 3-hour hip replacement had shorter extubation times, lower VAS scores, and less common shivering, but there were no intergroup differences in terms of nausea and vomiting. PH, when accompanied by the prolonged duration of action of hypnotic drugs and neuromuscular blockers, can result in an increased frequency of vomiting and shivering (Aydın et al., 2019). Despite classification based on body temperature values, no association was found between nausea–vomiting scores and hypothermia in patients who underwent breast surgery. Similarly, no correlation could be discerned between pain scores and hypothermia in our female patients who underwent breast surgery. We hypothesize that this might be attributable to the efficacy of the postoperative analgesic method we employed.

A significant limitation of this study is the absence of neuromuscular or anesthesia depth monitoring the study. Doses of anesthetic, analgesic, and muscle relaxants were determined through clinical judgment to ensure patient immobility and hemodynamic stability.

In conclusion, our study reveals that the incidence of hypothermia and shivering is strikingly high in female patients undergoing breast surgery. The degree of body temperature reduction should be taken into account when evaluating the predictors or clinical outcomes of hypothermia, beyond the threshold of 36°. Accordingly, we propose that patients undergoing breast surgery warrant the implementation of thermal care bundle that incorporates various heating methodologies.

Footnotes

Authors' Contributions

H.C.H.: conceptualization, data collection, data analysis writing—original draft, formal analysis, writing—review and editing, and investigation. M.N.D.: data collection, and writing—review and editing. I.G.: conceptualization, investigation, methodology, and writing—review and editing. Ö.Y.Ö.: data collection. A.T.: data collection. S.U.: writing—original draft, formal analysis, and writing—review and editing.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

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