Menoufia Medical Journal

ORIGINAL ARTICLE
Year
: 2016  |  Volume : 29  |  Issue : 2  |  Page : 240--246

Renal failure index and assessment of renal function in asphyxiated newborns


Maha A Tawfik, Ahmed T Mahmoud, Osama H Elnggar 
 Department of Pediatrics, Faculty of Medicine, Menoufiya University, Menoufiya, Egypt

Correspondence Address:
Osama H Elnggar
14 Ahmed Mousa Blabel St. Quesna, Menoufiya, 32631
Egypt

Abstract

Objective: To assess the renal failure index (RFI) in asphyxiated neonates in relation to other clinical and laboratory findings among those with acute renal failure, whether prerenal or intrinsic renal failure. Background: Asphyxia is an important cause of morbidity and mortality among neonates. It leads to multiorgan dysfunction and redistribution of cardiac output to maintain cerebral, cardiac and adrenal perfusion while potentially compromising renal, gastrointestinal and skin perfusion. Thus, acute renal failure is recognized as a complication of birth asphyxia. Materials and Methods: This case–control study included 80 neonates divided into two groups: the patient group (40 babies with perinatal asphyxia) and the control group (40 normal babies). In all patients, hypoxic ischemic encephalopathy staging (Sarnat and Sarnat) was performed. Blood and urinary parameters for renal function were assessed in all newborns, and fractional excretion of sodium (FENa) and the RFI were also calculated. The results obtained were analyzed and compared within subgroups using the computer program statistical package for social science, version 16. Results: Acute renal failure was noted in 19 patients in the patient group (47.5%): 16 of them (40%) had prerenal failure and three had intrinsic renal failure (7.5%). FENa and the RFI were found to be the most useful in evaluating babies with renal failure, as these derived renal indices were more reliable than individual parameters. FENa and RFI increased with increasing hypoxic ischemic encephalopathy staging. Conclusion: Perinatal asphyxia is an important cause of neonatal acute renal failure, which is predominantly prerenal failure. FENa and RFI are useful parameters for assessing the renal function in these neonates and can be used to differentiate prerenal failure from intrinsic renal failure, and thus helps in proper management.



How to cite this article:
Tawfik MA, Mahmoud AT, Elnggar OH. Renal failure index and assessment of renal function in asphyxiated newborns.Menoufia Med J 2016;29:240-246


How to cite this URL:
Tawfik MA, Mahmoud AT, Elnggar OH. Renal failure index and assessment of renal function in asphyxiated newborns. Menoufia Med J [serial online] 2016 [cited 2020 Aug 4 ];29:240-246
Available from: http://www.mmj.eg.net/text.asp?2016/29/2/240/192449


Full Text

 Introduction



Asphyxia remains a common problem in neonatal nursery and is a significant cause of morbidity and death in term and preterm neonates. Asphyxia can lead to multiorgan dysfunction and redistribution of the cardiac output, compromising the renal perfusion, and therefore, acute renal failure (ARF) is common in asphyxiated neonates [1],[2].

Early recognition of renal failure is important in babies with hypoxic ischemic encephalopathy (HIE) to facilitate appropriate fluid and electrolyte management as it may even lead to irreversible cortical necrosis if prolonged. Diagnosis of ARF is difficult in neonates as many of the established clinical and biochemical parameters are unreliable in this age group. However, fractional excretion of sodium (FENa) and the renal failure index (RFI) were found to be the most useful in evaluating babies with renal failure as these renal indices are more reliable than individual parameters [3].

The aim of this study was to assess the RFI in asphyxiated neonates in relation to other clinical and laboratory findings among those with ARF, whether prerenal or intrinsic renal failure.

 Materials and Methods



Eighty neonates were recruited in this case–control study from patients admitted to the neonatal intensive care units of the Pediatric department, Menoufiya University Hospital and Banha Children Hospital, spanning the period from May 2012 to April 2013. Informed written parental consents were taken according to the rules of the local ethical committee. The neonates were divided into two groups: the patient group (group I) consisted of 40 babies with perinatal asphyxia, including 32 male and eight female babies (31 full-term babies and nine preterm babies) and the control group (group II) consisted of 40 normal babies, including 34 male and six female babies (26 full-term babies and 14 preterm babies).

The study included babies born with perinatal asphyxia as evidenced by delayed first cry (more than 5 min), Apgar score up to 6 at 5 min or the presence of postnatal clinical complications attributed to perinatal asphyxia such as abnormal neurological signs or severe metabolic acidosis (pH ≤ 7) [4].

Babies were excluded if they had one or more of the following features: congenital malformations including renal or cardiovascular anomalies, chromosomal abnormalities, inborn errors of metabolism and/or significant illness (e.g. septicemia, pathological hyperbilirubinemia).

HIE staging (Sarnat and Sarnat) was performed [4].

On the first day of life, venous blood samples (2.5 ml) were collected and sent for complete blood count, C-reactive protein estimation and arterial blood gases. On the third day of life, 3 ml of venous blood was collected for the estimation of electrolytes (sodium, potassium), blood urea and serum creatinine. Twenty-four hour urine samples were simultaneously collected on the third day using commercially available pediatric urine bags and sent for the estimation of 24-h urine sodium and creatinine. Care was taken to prevent leakage and contamination of the urine with stool. In addition, the following renal indices were calculated:

[INLINE:1]

Criteria adopted for defining ARF in neonates were oliguria less than 0.5 ml/kg/h or serum creatinine more than 2 SD above the mean value for the gestational age [5]. ARF was considered prerenal if FENa was up to 2.5 and intrinsic if FENa was greater than 2.5 [6].

Statistical analysis was carried out with the help of 'statistical package for the social sciences', version 16 program (SPSS 16.0.1 – November 2007; SPSS Inc. Company version 17 software programs (SPSS Inc., Chicago, Illinois, USA), SBAS (Hong Kong) Ltd, Unit 1804, 18/F, Westlands Centre, 20 Westlands Road, Quarry Bay, Hong Kong); various renal parameters were compared within subgroups as well as with controls. For values that followed a normal distribution, the independent t-test was performed, and for parameters that were non-normally distributed, the Mann–Whitney test was performed. All statistical analyses were carried out and P value less than 0.05 was considered significant. P value less than 0.01 was considered highly significant in all analyses.

 Results



The current study included 80 neonates who were divided into two groups: patient and control. The patient group (group I) consisted of 40 neonates suffering from birth asphyxia, including 32 male and eight female babies (31 full-term babies and nine preterm babies) with mean gestational age 37.0 weeks ± 2.16 SD and mean birth weight 2.85 kg ± 0.516 SD. The control group (group II) consisted of 40 neonates, including 34 male and six female babies (26 full-term babies and 14 preterm babies) with mean gestational age 36.8 weeks ± 1.96 SD and mean birth weight 2.79 kg ± 0.626 SD ([Table 1] and [Table 2]).{Table 1}{Table 2}

Among the 40 babies in the patient group, all cases had delayed first cry (more than 5 min) and low Apgar score (≤6 at 5 min) as evidences of occurrence of asphyxia, whereas 17 patients (42.5%) had meconium-stained umbilical stump, 27 patients (67.5%) developed convulsions and 26 patients(65%) had metabolic acidosis ([Table 3]). According to the Sarnat and Sarnat scoring system, seven patients had HIE I (17.5%), 25 patients had HIE II (62.5%) and eight patients had HIE III (20%).{Table 3}

In the patient group, 21 patients (52.5%) had no renal failure, whereas 19 patients (47.5%) developed ARF: 16 patients (40%) had prerenal failure and three patients (7.5%) had intrinsic renal failure ([Table 4]). The 19 patients with ARF were distributed as 12 patients with HIE II and seven patients with HIE III ([Table 5]).{Table 4}{Table 5}

Blood chemistry showed that there was a highly significant difference in serum sodium, serum potassium, blood urea and serum creatinine between the patient and the control groups, showing that there was hyponatremia, elevated blood urea and elevated serum creatinine in the patient group (P< 0.01), whereas the serum potassium level was normal in the patient and the control groups, but was significantly higher in the patient group (P< 0.05).

Comparison of blood chemistry parameters among patients with ARF and patients without ARF showed that blood urea and serum creatinine were significantly higher in patients with ARF and serum sodium was significantly lower in patients with ARF. Blood chemistry parameters in patients showed no significant difference between patients with prerenal failure and patients with intrinsic failure ([Table 6]).{Table 6}

Urine chemistry showed that there was a highly significant increase in the urine sodium level in the patient group compared with the control group (P< 0.01) and there was a significant increase in the urine creatinine level in the patient group compared with the control group (P< 0.05). Comparison of the urine chemistry among patients with ARF and patients without ARF showed that the urine output and the urine creatinine was significantly lower in patients with ARF (P< 0.05), whereas the urine sodium was higher in cases with ARF, but without a significant difference between both groups (P > 0.05). Urine sodium was significantly higher in patients with intrinsic renal failure (P< 0.05) ([Table 7]).{Table 7}

Renal indices (RFI and FENa) were significantly higher in patients compared with controls (P< 0.05); they were significantly higher in patients with ARF compared with patients without ARF (P< 0.05), and were significantly higher in patients with intrinsic renal failure compared with patients with prerenal failure (P< 0.05) ([Table 8]).{Table 8}

There was a significant increase in the mean values of blood urea, serum creatinine, urine sodium, FENa and RFI as the HIE staging progressed (P< 0.05). There was a significant decrease in the mean values of urine output as the HIE staging progressed (P< 0.05) ([Table 9]). Significant correlation between blood, urine chemistries and HIE was found ([Table 10]). The RFI was greater than 2.6 in all patients with intrinsic renal failure and up to 2.6 in 15 of the 16 patients with prerenal failure. At this cutoff point, the sensitivity was 93.8% and the specificity was 100% ([Table 11]).{Table 9}{Table 10}{Table 11}

 Discussion



Multiorgan dysfunction is a recognized result of perinatal asphyxia as hypoxia, and ischemia can cause change to almost every tissue and organ of the body [4]. As kidneys are very sensitive to oxygen deprivation, renal insufficiency may occur due to hypoxic ischemic episodes, which if prolonged may lead to irreversible cortical necrosis [7].

This study was designed to assess the RFI in asphyxiated neonates in relation to other clinical and laboratory findings among those with ARF, whether prerenal or intrinsic renal failure.

The frequency of ARF in the patient group of our study was 47.5% (19 of the 40 cases); among the 19 patients with ARF, four patients had oliguric renal failure and 15 patients had nonoliguric renal failure; this is in agreement with Gupta et al. [6] who found that the incidence of ARF in asphyxiated neonates was 47.14%, and among them, 21.21% were oliguric renal failure and 78.78% were nonoliguric renal failure. However, Aggarwal et al. [8] showed that the incidence of ARF was 56%, and among them, 42% were oliguric and 58% were nonoliguric. Nouri et al. [9] observed that the incidence of ARF among asphyxiated neonates was 17.2% and predominantly nonoliguric. Mohan and Pai [0] noticed that the incidence of ARF in birth asphyxia was 72%, and among them, 44% had oliguric renal failure and 56% had nonoliguric renal failure. Kaur et al. [1] found that ARF developed in 9.1% of infants with moderate asphyxia and 56.0% of infants with severe asphyxia, making a total incidence of 41.7%.

Among the 19 patients with ARF in our study, 16 patients (84.2%) had prerenal failure and three patients (15.8%) had intrinsic renal failure.

The mean blood urea and creatinine in our study were significantly higher in patients as compared with controls (P = 0.001), and this was in agreement with Gupta et al. [6] and Aggarwal et al. [8]. In the current study, the mean serum sodium level was significantly lower in patients compared with controls (P = 0.001), and this was in agreement with Gupta et al. [6]. In contrast, the serum potassium level was significantly higher in patients as compared with controls (P = 0.001), whereas Gupta et al. [6] found that the serum potassium was comparable in the two groups. Also, the mean urine sodium level was significantly higher in patients as compared with controls (P = 0.001), whereas Karlo and Koner [3] found that there was no significant difference in the urine Na level between the two groups.

In the current study, the mean urine creatinine level was significantly higher in patients as compared with controls (P = 0.005), and this was in agreement with the study by Karlo and Koner [3]. However, the mean urine output was significantly lower in patients as compared with controls (P = 0.001) in contrast to Gupta et al. [6] who found that the urine output had no significant difference between the two groups.

In the current study, the mean blood urea and serum creatinine were significantly higher in patients with ARF compared with patients without ARF (with both P = 0.001). The serum Na was significantly lower in patients with ARF (with P = 0.04), whereas the serum K was comparable in the two groups. Karlo and Koner [3] found that blood urea, serum creatinine and serum Na and K had a strong correlation with ARF.

In our study, the mean urine creatinine was significantly lower in patients with ARF compared with patients without ARF (with P = 0.038), and the urine output was significantly lower in patients with ARF compared with patients without ARF (with P = 0.001), whereas there was no significant difference in the urine sodium between the two groups.

In our study, blood chemistry parameters (blood urea, serum creatinine and serum Na and potassium) in patients showed no significant difference between patients with prerenal failure and patients with intrinsic failure. In contrast, regarding the urine chemistry, urine sodium was significantly higher in patients with intrinsic renal failure (with P = 0.038) and urine creatinine showed no significant difference between patients with prerenal failure and patients with intrinsic renal failure.

In the current study, FENa and RFI were significantly higher in patients compared with controls (with P = 0.001 for both parameters) and were significantly higher in patients with ARF compared with patients without ARF (with P = 0.001 in both parameters). FENa and RFI were significantly higher in patients with intrinsic renal failure, showing their importance in the differentiation between patients with intrinsic renal failure and patients with prerenal failure in agreement with the study by Karlo and Koner [3]. In our study, the FENa and the RFI were found to be the most useful in evaluating babies with renal failure in this study, meaning that these derived renal indices were more reliable than individual parameters.

Gupta et al. [6] found that there was an increasing trend in the concentration of blood urea and serum creatinine as the HIE staging progressed, and this agrees with the current study, which showed that there was a significant decrease in the mean values of urine output as the HIE staging progressed (P = 0.001). In contrast, Gupta et al. [6] found that the urine output was slightly less in neonates with severe birth asphyxia, but it was statistically insignificant when compared with cases of mild and moderate asphyxia in contrast to the current study, which showed a significant increase in the mean values of urine sodium as the HIE staging progressed (P = 0.017). In our study, there was a significant increase in the mean values of FENa and RFI as the HIE staging progressed; this is in agreement with the study by Karlo and Koner [3].

In the current study, the relation between the occurrence of ARF and its type with HIE staging showed that the incidence of ARF increased as the HIE staging progressed, ranging from 0% in patients with HIE grade I to 48% (12/25) in patients with HIE grade II and reaching 87.5% (7/8) in patients with HIE grade III. This is in agreement with the study by Gupta et al. [6], who found that the incidence of ARF increased as the HIE staging progressed. In the current study, the incidence of intrinsic renal failure among patients with renal failure increased with progress of HIE reaching from 0% in patients with HIE grade II to 42.9% (3/7) in patients with HIE grade III. This is in agreement with the study by Karlo and Koner [3], who found that intrinsic renal failure was more likely with increasing HIE staging. The outcome of the patient group is not included in this study and is to be assessed in further research studies.

 Conclusion



Perinatal asphyxia is an important cause of neonatal ARF. ARF in birth asphyxia is predominantly prerenal failure. FENa and RFI are useful parameters for assessing the renal function in babies with perinatal asphyxia and can be used to differentiate prerenal failure from intrinsic renal failure, and thus help in deciding the proper management.

 Acknowledgements



Author contributions: Concepts: Maha Atef Tawfek, Ahmed Thabet Mahmoud. Design: Maha Atef Tawfek, Ahmed Thabet Mahmoud. Definition of intellectual content: Maha Atef Tawfek, Ahmed Thabet Mahmoud. Literature search: Maha Atef Tawfek, Ahmed Thabet Mahmoud. Clinical studies: Maha Atef Tawfek, Ahmed Thabet Mahmoud, Osama Hamed Elnggar. Experimental studies: Maha Atef Tawfek, Ahmed Thabet Mahmoud, Osama Hamed Elnggar. Data acquisition: Maha Atef Tawfek, Ahmed Thabet Mahmoud, Osama Hamed Elnggar. Data analysis: Maha Atef Tawfek, Ahmed Thabet Mahmoud, Osama Hamed Elnggar. Statistical analysis: Maha Atef Tawfek, Ahmed Thabet Mahmoud, Osama Hamed Elnggar. Manuscript preparation: Maha Atef Tawfek, Ahmed Thabet Mahmoud, Osama Hamed Elnggar. Manuscript editing: Maha Atef Tawfek, Ahmed Thabet Mahmoud. Manuscript review: Maha Atef Tawfek, Ahmed Thabet Mahmoud.

Conflicts of interest

There are no conflicts of interest.[11]

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