Background
A dysregulated host response to infection is a cornerstone of the pathophysiology of sepsis [
1,
2]. A dysregulated response alters vital signs such as body temperature (BT), heart rate (HR), blood pressure (BP), and respiratory rate (RR) [
3,
4]. Alterations such as hypothermia, fever, tachycardia, hypotension, or tachypnea tend to be associated with altered clinical outcomes [
5‐
9].
Elderly patients generally have a blunted host inflammatory response [
10‐
12], which could contribute to different associations between the vital signs and mortality between non-elderly and elderly patients, as observed in a variety of pathological settings [
13‐
15]. In sepsis, a single-center study with a limited sample size demonstrated that BT, as a component of the vital signs, is an independent predictor of mortality only in elderly patients [
13]. However, whether the relationships between altered vital signs and clinical outcomes differ between elderly and non-elderly patients remains unclear. Investigating and clarifying these differences might contribute to improving the quality of sepsis care, thus reducing mortality rates in critically ill septic patients.
Thus, we hypothesized that associations between initial vital signs and mortality are different for elderly and non-elderly patients with sepsis. Three large sepsis cohorts were investigated to assess the primary outcome of 90-day in-hospital mortality.
Discussion
In the present study, non-elderly sepsis patients with hypothermia (BT < 36.0 °C) had significantly increased mortality, and those with fever (BT ≥ 38.3 °C) had decreased mortality. In contrast, hypothermia and fever were not associated with altered mortality in elderly patients. Interestingly, the other vital sign values were not consistently associated with differences in the outcome in patients of any age. Thus, BT was distinct among the vital signs for its association with the clinical outcomes in the non-elderly, but not elderly, patients with sepsis.
The key finding of our analysis is that the association of BT alterations on mortality was only observed in the younger septic population as opposed to elderly patients. The meta-analytic technique showed that there was low heterogeneity (
I2 = 17%) in the association between hypothermia and mortality in non-elderly patients in the three cohorts (Fig.
3). In a secondary analysis, the opposite effect of fever was also only observed in non-elderly sepsis patients (Additional file
4: Figure S3 and Additional file
5: Figure S4). The changes in the association between the vital signs and mortality based on age have been investigated in several categories of critically ill patients. In blunt trauma, the presenting vital signs are less predictive of mortality in elderly patients as compared to the non-elderly [
14]. Additionally, vital signs are less predictive of in-hospital cardiac arrest in elderly patients as compared to the non-elderly [
15]. Since the significant associations of tachycardia and tachypnea on mortality in elderly patients were not replicated in the validation cohorts, we confirmed that BT alterations are uniquely predictive of mortality among the vital signs in non-elderly patients with sepsis but not in the elderly patients. Significant interactions with mortality between hypothermia or fever and age groups reinforced these findings.
In the current understanding of pathomechanism of sepsis-related BT changes, fever and hypothermia both have adaptive biological value for the host. In this context, fever is considered as an indicator of active (disease-fighting) strategy which may be beneficial in diseases of mild-to-moderate severity in a previously healthy host while hypothermia is a passive (disease-tolerating) strategy that is advantageous in severe forms of the disease, especially in the presence of comorbidities [
29‐
31]. Nevertheless, BT is not the cause but rather the indicator of the severity, thus consequently of the outcome of the disease. In our previous study employing the FORECAST and JAAMSR cohorts, with no distinction between the non-elderly and elderly sepsis patients, hypothermia was associated with poor clinical outcomes [
32,
33]. In another study of adult sepsis patients, hypothermia (< 36.0 °C) within 24 h from sepsis diagnosis was associated with a higher 28-day and 1-year mortality [
34]. Oppositely, increased BT in sepsis/septic shock patients admitted to an ICU within 24 h of hospital arrival was associated with decreased mortality [
35]. These reports were in line with our results in non-elderly patients.
Several factors could explain the difference in the relationships between the hypothermia and clinical outcome in elderly and non-elderly patients with sepsis. The physiology of fever generation and development of hypothermia is complicated; however, reduced production of pyrogenic cytokines such as IL-6 and TNF-a may be related to the lower incidence of fever seen in elderly septic patients [
36,
37]. Comorbidities such as stroke, which was a higher prevalence in the elderly group in this study, may comprise neurological deficits that could impair thermoregulatory/inflammatory reflexes [
38,
39]. Decreased heat production due to reduced muscle mass and increased heat radiation due to a reduced fat mass and blunted peripheral vasoconstriction capacity might be related to the lower BTs [
40]. Observational studies have indeed reported that higher age populations have lower BTs and smaller diurnal BT variations [
41,
42], which is consistent with our results. Lower BT and altered BT response in elderly septic patients as the result of age-related physical and functional deterioration may mitigate the hypothermic/febrile effects on clinical outcomes.
There were several limitations to the present study. First was the descriptive nature of the observational study. The primary findings were validated using two independent cohorts, which included multiple centers and patients of different ancestry; however, these do not prove a causal link. Second limitation of the study was the absence of data on variables that may have confounded BT measurement, including temperature measurement site and whether patients received antipyretics or targeted temperature management. Third was on the retrieval of vital signs. The vital signs corresponding to the APACHE II score were analyzed in the present study. However, according to the APACHE II scoring, a temperature as lower than 34 °C receives 1 point, whereas fever higher than 38.9 °C receives 3 points. Therefore, patients presenting both hypothermia and fever were more likely to be categorized in the fever group, which may have influenced the results. In addition, since the analyzed data were only in the first 24 h after the diagnosis of sepsis, it is unclear whether the duration of hypothermia or temperature changes over time affects the outcome. Another limitation could be the absence of established criteria for defining elderly patients. In this study, we applied the currently accepted standards in literature [
20‐
22]. The analyses in the age cutoff of 70 and 80 years yielded the same conclusion, which could help strengthen the results of this study.
Acknowledgements
We thank Prof. Toshiaki Iba, MD, PhD, for advice on this project. We also thank all contributors of the JAAM FORECAST group.
The following are the investigators of the JAAM FORECAST Group: Nagasaki University Hospital (Osamu Tasaki), Osaka City University Hospital (Yasumitsu Mizobata), Tokyobay Urayasu Ichikawa Medical Center (Hiraku Funakoshi), Aso Iizuka Hospital (Toshiro Okuyama), Tomei Atsugi Hospital (Iwao Yamashita), Hiratsuka City Hospital (Toshio Kanai), National Hospital Organization Sendai Medical Center (Yasuo Yamada), Ehime University Hospital (Mayuki Aibiki), Okayama University Hospital (Keiji Sato), Tokuyama Central Hospital (Susumu Yamashita), Fukuyama City Hospital (Susumu Yamashita), JA Hiroshima General Hospital (Kenichi Yoshida), Kumamoto University Hospital (Shunji Kasaoka), Hachinohe City Hospital (Akihide Kon), Osaka City General Hospital (Hiroshi Rinka), National Hospital Organization Disaster Medical Center (Hiroshi Kato), University of Toyama (Hiroshi Okudera), Sapporo Medical University (Eichi Narimatsu), Okayama Saiseikai General Hospital (Toshifumi Fujiwara), Juntendo University Nerima Hospital (Manabu Sugita), National Hospital Organization Hokkaido Medical Center (Yasuo Shichinohe), Akita University Hospital (Hajime Nakae), Japanese Red Cross Society Kyoto Daini Hospital (Ryouji Iiduka), Maebashi Red Cross Hospital (Mitsunobu Nakamura), Sendai City Hospital (Yuji Murata), Subaru Health Insurance Society Ota Memorial Hospital (Yoshitake Sato), Fukuoka University Hospital (Hiroyasu Ishikura), Ishikawa Prefectural Central Hospital (Yasuhiro Myojo), Shiga University of Medical Science (Yasuyuki Tsujita), Nihon University School of Medicine (Kosaku Kinoshita), Seirei Yokohama General Hospital (Hiroyuki Yamaguchi), National Hospital Organization Kumamoto Medical Center (Toshihiro Sakurai), Saiseikai Utsunomiya Hospital (Satoru Miyatake), National Hospital Organization Higashi-Ohmi General Medical Center (Takao Saotome), National Hospital Organization Mito Medical Center (Susumu Yasuda), Tsukuba Medical Center Hospital (Toshikazu Abe), Osaka University Graduate School of Medicine (Hiroshi Ogura, Yutaka Umemura), Kameda Medical Center (Atsushi Shiraishi), Tohoku University Graduate School of Medicine (Shigeki Kushimoto), National Defense Medical College (Daizoh Saitoh), Keio University School of Medicine (Seitaro Fujishima, Junichi Sasaki), University of Occupational and Environmental Health (Toshihiko Mayumi), Kawasaki Medical School (Yasukazu Shiino), Chiba University Graduate School of Medicine (Taka-aki Nakada), Kyorin University School of Medicine (Takehiko Tarui), Kagawa University Hospital (Toru Hifumi), Tokyo Medical and Dental University (Yasuhiro Otomo), Hyogo College of Medicine (Joji Kotani), Saga University Hospital (Yuichiro Sakamoto), Aizu Chuo Hospital (Shin-ichiro Shiraishi), Kawasaki Municipal Kawasaki Hospital (Kiyotsugu Takuma), Yamaguchi University Hospital (Ryosuke Tsuruta), Center Hospital of the National Center for Global Health and Medicine (Akiyoshi Hagiwara), Osaka General Medical Center (Kazuma Yamakawa), Aichi Medical University Hospital (Naoshi Takeyama), Kurume University Hospital (Norio Yamashita), Teikyo University School of Medicine (Hiroto Ikeda), Rinku General Medical Center (Yasuaki Mizushima), and Hokkaido University Graduate School of Medicine (Satoshi Gando).
Consortia
JAAM FORECAST Group
Osamu Tasaki, Yasumitsu Mizobata, Hiraku Funakoshi, Toshiro Okuyama, Iwao Yamashita, Toshio Kanai, Yasuo Yamada, Mayuki Aibiki, Keiji Sato, Susumu Yamashita, Kenichi Yoshida, Shunji Kasaoka, Akihide Kon, Hiroshi Rinka, Hiroshi Kato, Hiroshi Okudera, Eichi Narimatsu, Toshifumi Fujiwara, Manabu Sugita, Yasuo Shichinohe, Hajime Nakae, Ryouji Iiduka, Mitsunobu Nakamura, Yuji Murata, Yoshitake Sato, Hiroyasu Ishikura, Yasuhiro Myojo, Yasuyuki Tsujita, Kosaku Kinoshita, Hiroyuki Yamaguchi, Toshihiro Sakurai, Satoru Miyatake, Takao Saotome, Susumu Yasuda, Toshikazu Abe, Hiroshi Ogura, Yutaka Umemura, Atsushi Shiraishi, Shigeki Kushimoto, Daizoh Saitoh, Seitaro Fujishima, Junichi Sasaki, Toshihiko Mayumi, Yasukazu Shiino, Taka-aki Nakada, Takehiko Tarui, Toru Hifumi, Yasuhiro Otomo, Joji Kotani, Yuichiro Sakamoto, Shin-ichiro Shiraishi, Kiyotsugu Takuma, Ryosuke Tsuruta, Akiyoshi Hagiwara, Kazuma Yamakawa, Naoshi Takeyama, Norio Yamashita, Hiroto Ikeda, Yasuaki Mizushima, and Satoshi Gando.
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