Introduction

Prematurity of adrenal function is recognized as transient adrenocortical insufficiency of prematurity (TAP) or glucocorticoid responsive hypotension in preterm infants [1–3]. In Japan, late-onset circulatory collapse (LCC) was recognized in 2000, and tentative diagnostic criteria were established. In the established criteria, LCC is defined as acute-onset hypotension or oliguria occurring after the transitional period. The incidence of LCC in very low birth weight (VLBW) infants and extremely low birth weight infants is 6.3%, and 11.6%, respectively [4]. Prematurity of adrenal function is an important cause of LCC, and certain drugs, including levothyroxine, may be related to the onset of LCC; however, the etiology remains unclear [5]. The reported incidence of LCC varies among Japanese perinatal centers; however, the cause of such center variation remains unclear [6].

We hypothesized that perinatal and neonatal factors may be related to LCC in preterm infants and these factors could affect center variation in the incidence of LCC. This study attempted to identify the perinatal and neonatal factors associated with LCC in extremely preterm (EP) infants, and to estimate the factors related to center variation in the incidence of LCC in Japan using the nationwide database of the Neonatal Research Network, Japan (NRNJ).

Materials and methods

Study subjects

VLBW infants (40,806) born between 2003 and 2012 were registered in the NRNJ database (Fig 1(A)). EP infants born between 2008 and 2012 were included in this study because the definition of LCC has been widely recognized in Japanese perinatal centers since 2008. Infants who died within 6 days were excluded according to the definition of LCC. Infants with congenital anomalies, whose sex was undetermined, or whose records were missing data on LCC were also excluded. Consequently, 8,260 EP infants who were born at 22–27 weeks of gestation in 2008–2012 were included in the base study population. In addition, we selected infants from 68 perinatal centers that contained more than 50 EP infants per center during the study period in order to examine the factors related to center variation in incidence of LCC (Fig 1(B)). This study was approved by the Central Internal Review Board of Tokyo Women’s Medical University, where a secretariat of the Neonatal Research Network, Japan (NRNJ) is located; all data were collected and stored anonymously. The institutions enrolled in the study of the NRNJ are described in the Acknowledgements. Jichi Medical University had the approval for participation in the study. All data were fully anonymized before they were accessed by any of the authors.

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Fig 1. Study subjects.

(A) Study subjects for the perinatal and neonatal factors related to LCC. (B) Study subjects for the center variation in the incidence of LCC. VLBW, very low birth weight; LCC, late-onset circulatory collapse; EP, extremely preterm.

https://doi.org/10.1371/journal.pone.0198518.g001

Results

1. Comparison of the perinatal characteristics between the LCC and non-LCC groups

The LCC and non-LCC groups included 1,501 and 6,759 cases, respectively. The incidence of LCC in EP infants was 18.1%. According to univariate analyses, the GA and BW were significantly lower and the proportions of SFD, male sex, and ANS use were significantly higher in the LCC group than in the non-LCC group (Table 1). After adjusting for the covariates, multivariate analyses revealed low GA, SFD, male sex, and ANS use to be significantly associated with an increased risk of LCC.

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Table 1. The perinatal characteristics in the LCC and non-LCC groups and the odds ratios for LCC.

https://doi.org/10.1371/journal.pone.0198518.t001

2. Comparison of the neonatal morbidities and interventions in the LCC and non-LCC groups

The mortality rate at discharge was 7.4%, and did not differ between the LCC and non-LCC groups to a statistically significant extent. The causes of death included sepsis, NEC, chronic lung disease, IVH and congenital anomaly (in descending order). According to univariate analyses, the proportions of all neonatal morbidities, except for IVH and NEC, were significantly higher in the LCC group than in the non-LCC group (Table 2). The proportions of all neonatal interventions were also significantly higher in the LCC group than in the non-LCC group. After adjusting for the covariates, multivariate analyses revealed RDS, CLD at 36 weeks, PVL, ROP, HFOV use, PN, and RBC transfusion to be significantly associated with an increased risk of LCC and that NEC was significantly associated with a decreased risk of LCC.

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Table 2. Neonatal morbidities and interventions in the LCC and non-LCC groups and the odds ratios for LCC.

https://doi.org/10.1371/journal.pone.0198518.t002

3. The relationship between the SIR of LCC and the SIRs of perinatal and neonatal factors in each perinatal center

The median number of subjects in each center was 85 (IQR 70–123). Two centers were excluded because their SIRs of LCC (3.71 and 3.19) were considered to be outlying values. The SIR of LCC ranged from 0.05 to 2.94 among 66 perinatal centers. The SIR of LCC was not significantly correlated with the SIRs of any perinatal factors, including SFD, male sex, and ANS use (Fig 2). Conversely, the SIR of LCC in each center showed significant positive correlations with the SIRs of PVL, ROP, HFOV use and RBC transfusion in the corresponding center.

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Fig 2. The relationship between the SIRs of LCC and perinatal and neonatal factors in each center.

SIR, standardized incidence ratio; SFD, small for date; ANS, antenatal steroid use; RDS, respiratory distress syndrome; CLD, chronic lung disease; PDA, patent ductus arteriosus; PVL, periventricular leukomalacia; NEC, necrotizing enterocolitis, ROP, retinopathy of prematurity; HFOV, high- frequency oscillating ventilation; PN, parenteral nutrition; RBC, red blood cell.

https://doi.org/10.1371/journal.pone.0198518.g002

Discussion

We examined the perinatal and neonatal factors associated with LCC in EP infants using the NRNJ database. GA, SFD, male sex, ANS use, RDS, CLD at 36 weeks, PVL, NEC, ROP, HFOV use, PN and RBC transfusion significantly correlated with LCC. The center variation for LCC remained after standardizing the incidence at every 2 weeks of gestation. The SIR of LCC significantly correlated with the SIRs of PVL, ROP, HFOV use and RBC transfusion.

The incidence of LCC in EP infants was approximately 18% in this study. The perinatal factors significantly associated with LCC included GA, male sex, SFD and ANS use. Previous studies showed that GA was inversely related to the serum cortisol level in the early postnatal period [9–11]. Furthermore, an adrenocorticotropic hormone (ACTH) test showed that the ability to synthesize cortisol was limited in infants of <30 weeks of gestational age [12]. Their immaturity of the hypothalamic-pituitary-adrenal (HPA)-axis and enzymes in the adrenal cortex may lead to adrenocortical insufficiency in infants born at a lower GA. SFD infants also showed higher cortisol levels in the early postnatal period, and blunted HPA-axis responses to stressors [11, 13]. The conditions of SFD infants are similar to those of lower GA infants. ANS use, which suppresses the neonatal adrenal function transiently in the early period after birth, is known to be a cause of TAP [1, 14]. LCC partially overlapped with TAP; thus our results correlated with previous reports.

The neonatal factors significantly related to LCC were RDS, CLD at 36 weeks, PVL, NEC, ROP, HFOV use, PN and RBC transfusion. RDS, CLD at 36 weeks and HFOV use reflected severe respiratory dysfunction. Ng, et al. reported that very low birth weight infants who required mechanical ventilation support showed a weak HPA-axis response on CRH tests at 7 days of age [15]. Severe respiratory dysfunction was thought to be related to the weak response of the HPA-axis and thus, might be the cause of the significant correlation with LCC. With regard to HFOV use, a high mean airway pressure might reduce the cardiac output and thereby cause hypovolemia, leading to circulatory collapse [4].

Regarding LCC onset, most EP infants develop LCC around 25–30 weeks of gestation because LCC generally occurs around third postnatal week [16, 17]. The periventricular avascular area is still present at that time, and the ischemic area due to LCC might result in PVL. Kobayashi, et al. reported LCC to be a risk factor for late-onset cystic PVL, which correlates with our results [18]. The onset of ROP generally occurs at around 30 weeks of gestation and peaks at 36–38 weeks of gestation [19]. Considering the timing of the onset, LCC is thought to mostly occur before ROP. The circulatory fluctuation and lung edema due to LCC increase the supply of oxygen and thus worsen ROP. Contrary to our expectations, NEC was related to a significant decrease in the risk of LCC. This might explain the high mortality rate in NEC patients in the neonatal period. Infants suffering from severe NEC might die before the onset of LCC. Most of these cases were included in the non-LCC group, which may be why NEC was negatively correlated with LCC. Because our study population was sufficiently large, we also calculated the OR and 99% CI for each factor using univariate and multivariate logistic regression analyses (S1 Table). The results did not differ from the results shown in Tables 1 and 2, with the exception of the significance of CLD at 36 weeks in the multivariate logistic regression analysis.

To investigate the center variation in the incidence of LCC, we standardized the incidence ratio of LCC for every 2 weeks of gestation, to equalize subjects’ background difference among centers. To standardize the incidence ratio of LCC for every week of gestation, SFD, and a male sex is desirable; however, the number of subjects in each center was insufficient. The center variation in the incidence of LCC remained after standardization for every 2 weeks of gestation. Furthermore, the SIR of LCC was not significantly correlated with the SIRs of any perinatal factors. We thus concluded that the center variation in the incidence of LCC was not based on differences in the subjects’ perinatal background among centers. The SIR of LCC significantly correlated with the SIRs of PVL, ROP, HFOV use and RBC transfusion in the corresponding centers. The decision of HFOV use was made by the physician at each center, depending on each center’s respiratory management protocol. Thus it might be one of the reasons for the center variation in the incidence of LCC.

The strength of our study is considered to be that large number of the EP infants who developed LCC after the definition of the diagnostic criteria were included and compared with non-LCC infants using the NRNJ database. However, this study is associated with some limitations. First, the timelines of the individual neonatal morbidities and interventions were unknown because our study was retrospective and due to the nature of the database. We therefore could not examine causal associations among the factors. Second, the database did not include a number of factors suspected to cause LCC, including thyroid hormone replacement therapy [5].

In conclusion, GA, SFD, male sex, ANS use, RDS, CLD at 36 weeks, PVL, NEC, ROP, HFOV use, PN, and RBC transfusion were significantly correlated with LCC in EP infants who were registered in the NRNJ database. PVL, ROP, HFOV use and RBC transfusion were found to correlate with the center variation in the incidence of LCC. Prospective studies should be performed to clarify the pathophysiological relationship between these factors and LCC.

Supporting information

Acknowledgments

Institutions enrolled in the study of the Neonatal Research Network, Japan, were as follows: Sapporo City General Hospital, Asahikawa Kosei General Hospital, Engaru-Kosei General Hospital, Kushiro Red Cross Hospital, Obihiro-Kosei General Hospital, Tenshi Hospital, NTT Higashinihon Sapporo Hospital, Nikko Memorial Hospital, Nayoro City General Hospital, Sapporo Medical University, Asahikawa Medical University, Aomori Prefectural Central Hospital, Iwate Medical University, Iwate Prefectural Ofunato Hospital, Iwate Prefectural Kuji Hospital, Iwate Prefectural Ninohe Hospital, Sendai Red Cross Hospital, Akita Red Cross Hospital, Tsuruoka Municipal Shonai Hospital, Yamagata University, Yamagata Prefectural Central Hospital, Fukushima Medical University, Takeda General Hospital, Fukushima National Hospital, Tsukuba University, Tsuchiura Kyodo Hospital, Ibaraki Children's Hospital, Dokkyo Medical University, Jichi Medical University, Ashikaga Red Cross Hospital, Gunma Children's Medical Center, Kiryu Kosei General Hospital, Fuji Heavy Industries Health Insurance Society Ota Memorial Hospital, Gunma University, Saitama Children's Medical Center, Nishisaitama-chuo National Hospital, Saitama Medical University Saitama Medical Center, Kawaguchi Municipal Medical Center, Jichi Medical University Saitama Medical Center, Asahi General Hospital, Chiba Kaihin Municipal Hospital, Kameda Medical Center, Tokyo Women's Medical University Yachiyo Medical Center, Juntendo University Urayasu Hospital, Tokyo Metropolitan Children's Medical Center, Tokyo Women's Medical University, Aiiku Hospital, Nihon University Itabashi Hospital, National Center for Global Health and Medicine, Tokyo Medical University, Teikyo University, Showa University, Japan Red Cross Medical Center, National Center for Child Health and Development, Tokyo Metropolitan Otsuka Hospital, Toho University, Tokyo Metropolitan Bokuto Hospital, Tokyo Jikei Medical University, Tokyo Medical and Dental University, Saint Luku’s International Hospital, Juntendo University, Sanikukai Hospital, Katsushika Red Cross Hospital, Yokohama Rosai Hospital, Yokohama City University Medical Center, St. Marianna University School of Medicine Hospital, Kanagawa Children's Medical Center, Tokai University, Kitazato University, Odawara Municipal Hospital, Nippon Medical School Musashi Kosugi Hospital, Saiseikai Yokohamashi Tobu Hospital, National Hospital Organization Yokohama Medical Center, Yamanashi Prefectural Central Hospital, Nagano Children's Hospital, Shinshu University, Iida Municipal Hospital, National Hospital Organization Shinshu Ueda Medical Center, Saku General Hospital, Niigata University, Niigata Prefectural Central Hospital, Niigata Municipal Hospital, Nagaoka Red Cross Hospital, Koseiren Takaoka Hospital, Toyama Prefectural Central Hospital, Toyama University, Ishikawa Medical Center for Maternal and Child Health, Kanazawa Medical University, Kanazawa Medical Center, Fukui Prefectural Hospital, Fukui University, Gifu Prefectural General Medical Center, National Hospital Organization Nagara Medical Center, Takayama Red Cross Hospital, Seirei Hamamatsu Hospital, Shizuoka Saiseikai Hospital, Shizuoka Children's Hospital, Hamamatsu Medical University, Numazu Municipal Hospital, Yaizu City Hospital, Fujieda Municipal General Hospital, Nagoya Red Cross Daini Hospital, Nagoya University, Nagoya Red Cross Daiichi Hospital, Toyohashi Municipal Hospital, Nagoya City West Medical Center, Anjo kosei Hospital, Tosei General Hospital, Komaki Municipal Hospital, TOYOTA Memorial Hospital, Okazaki Municipal Hospital, Konan Kosei Hospital, National Mie Central Medical Center, Ise Red Cross Hospital, Yokkaichi Municipal Hospital, Otsu Red Cross Hospital, Shiga University of Medical Science Hospital, Nagahama Red Cross Hospital, Uji Tokushukai Hospital, The Japan Baptist Hospital, Kyoto University, Kyoto Red Cross Daiichi Hospital, National Maizuru Medical Center, Fukuchiyama City Hospital, Kyoto Prefectural University of Medicine Hospital, Kyoto City Hospital, Mitsubishi Kyoto Hospital, Yodogawa Christian Hospital, Osaka Medical Center and Research Institute for Maternal and Child Health, Osaka University, Takatsuki General Hospital, Kansai Medical University, Osaka City General Hospital, Osaka City Sumiyoshi Hospital, Aizenbashi Hospital, Toyonaka Municipal Hospital, National Cerebral and Cardiovascular Center, Kitano Hospital, Saiseikai Suita Hospital, Chifune Hospital, Bellland General Hospital, Rinku General Medical Center, Osaka Red Cross Hospital, Yao Municipal Hospital, Osaka General Medical Center, Osaka City University, Hyogo Prefectural Kobe Children's Hospital, Kobe University, Kakogawa West City Hospital, Saiseikai Hyogoken Hospital, Kobe City Medical Center General Hospital, Hyogo College of Medicine Hospital, Himeji Red Cross Hospital, Toyooka Public Hospital, Hyogo Prefectural Awaji Medical Center, Nara Medical University, Wakayama Medical University, Tottori Prefectural Central Hospital, Tottori University, Shimane Prefectural Central Hospital, Matsue Red Cross Hospital, Kurashiki Central Hospital, Tsuyama Central Hospital, Kawasaki Medical School Hospital, National Hospital Organization Okayama Medical Center, Okayama Red Cross Hospital, Hiroshima City Hiroshima Citizens Hospital, Hiroshima Prefectural Hospital, Hiroshima University, Tsuchiya General Hospital, National Hospital Organization Kure Medical Center, Yamaguchi University, Yamaguchi Grand Medical Center, Tokushima University, Tokushima Municipal Hospital, Kagawa University, National Hospital Organization Kagawa Children's Hospital, Matsuyama Red Cross Hospital, Ehime Prefectural Central Hospital, Kochi Health Science Center, St.Mary's Hospital, National Kyushu Medical Center, Kurume University, Kitakyushu Municipal Medical Center, University of Occupational and Environmental Health, Fukuoka University, Kyushu University, Iizuka Hospital, National Hospital Organization Kokura Medical Center, National Hospital Organization Saga Hospital, National Hospital Organization Nagasaki Medical Center, Kumamoto City Hospital, Kumamoto University, Oita Prefectural Hospital, Almeida Memorial Hospital, Nakatsu Municipal Hospital, Miyazaki University, National Hospital Organization Miyakonojo Medical Center, Kagoshima City Hospital, Imakiire General Hospital, Okinawa Prefectural Nanbu Medical Center & Children’s Medical Center, Okinawa Prefectural Chubu Hospital, Naha City Hospital, Okinawa Red Cross Hospital.