Non-invasive continuous renal tissue oxygenation monitoring to identify preterm neonates at risk for acute kidney injury

ADVANCE: a biomedical informatics approach to investigate acute kidney injury in infants

BACKGROUND

Acute kidney injury (AKI) occurs in up to half of infants admitted to the neonatal intensive care unit (NICU) and is associated with increased risks of death and more days of mechanical ventilation, hospitalization, and vasopressor drug support. Our objective was to build a granular relational database to study the impact that AKI has on infants admitted to Level-IV NICUs.

METHODS

A relational database was created by linking data from the Children's Hospitals Neonatal Database with AKI-focused data from electronic health records from 9 centers.

RESULTS

The current cohort consists of 24,870 infants with a median (IQR) gestational age of birth of 37 weeks (32 weeks, 39 weeks), and a median birth weight of 2.720 kg (1.750 kg, 3.310 kg). There was a male predominance with 14,214 (57%) males. In all, 2434 (9.8%) of the mothers were of Hispanic ethnicity. The maternal race breakdown of the cohort was as follows: 741 (3.0%) Asian, 5911 (24%) Black, and 14,945 (60%) White. Overall mortality was 5.8%.

CONCLUSION

The ADVANCE relational database is an innovative research tool to rigorously study the epidemiology of AKI in a large national cohort of infants admitted to Level-IV NICUs involved in the Children's Hospital Neonatal Consortium.

IMPACT

We used a biomedical informatics approach to build a relational database to study acute kidney injury in infants. We highlight our methodology linking Children's Hospital Neonatal Consortium and electronic health record data from nine neonatal intensive care units. The ADVANCE relational database is a granular and innovative research tool to study risk factors and in-hospital outcomes of acute kidney injury and mortality in a vulnerable patient population.

Correlation of Renal Tissue Oxygenation to Venous, Arterial, and Capillary Blood Gas Oxygen Saturation in Preterm Neonates

OBJECTIVE

The aim of the study is to assess the correlation of renal regional tissue saturation of oxygen (RrSO2) measured by near-infrared spectroscopy (NIRS) in preterm neonates to venous oxygen saturation (SvO2) obtained from umbilical venous catheters (UVCs), arterial oxygen saturation (SaO2) obtained from umbilical artery catheters (UACs), and capillary oxygen saturation (ScO2) from capillary heel blood draws.

STUDY DESIGN

A secondary analysis of a prospective RrSO2 monitoring study in preterm neonates born <32 weeks gestational age. Neonates with any blood gas obtained during RrSO2 monitoring were included. RrSO2 was compared with simultaneous O2 saturation using non-parametric Mann Whitney U-test and Spearman correlation coefficient.

RESULTS

In 35 neonates, 25 UVC, 151 UAC, and 68 heel capillary specimens were obtained. RrSO2 was lower than the median SvO2 (58.8 vs. 78.9, p <0.01), SaO2 (51.0 vs. 93.2, p <0.01), and ScO2 (62.2 vs. 94.25, p <0.01). RrSO2 values correlated to both SaO2 and ScO2 (r = 0.32; p <0.01, r = 0.26; p = 0.03), but not SvO2 (r = 0.07; p = 0.74).

CONCLUSION

In this secondary analysis, RrSO2 was consistently lower than blood gas O2 saturations and correlated with SaO2 and ScO2 but not SvO2. Lack of a correlation to SvO2 could be due to the small UVC sample size limiting statistical power. Future studies should prospectively evaluate if RrSO2 truly primarily reflects venous oxygenation in preterm neonates.

KEY POINTS

· Renal oxygenation correlates with arterial and capillary oxygen saturation.. · Renal oxygenation did not correlate with venous oxygenation from umbilical venous catheters.. · Studies are needed to determine if renal oxygenation primarily reflects venous or arterial oxygen..

Renal Oxygen Saturations and Acute Kidney Injury in the Preterm Infant with Patent Ductus Arteriosus

OBJECTIVE

Decreased near-infrared spectroscopy (NIRS) measures of renal oxygen saturation (Rsat) have identified preterm infants with a hemodynamically significant patent ductus arteriosus (hsPDA). NIRS may further identify infants at risk for acute kidney injury (AKI) in a population with concern for hsPDA.

STUDY DESIGN

Review of infants ≤29 weeks' gestation undergoing NIRS and echocardiography due to concern for hsPDA. The hsPDA was defined by two of the following: moderate-large size, left to right shunt, aortic flow reversal, left atrial enlargement. AKI was defined by neonatal modified Kidney Disease Improving Global Outcomes (KDIGO). Rsat and cerebral saturation (Csat), averaged over 1 hour, were evaluated for the 24-hour period around echocardiography.

RESULTS

Among 77 infants, 29 (38%) had AKI by neonatal modified KDIGO criteria. hsPDA was found on echocardiography in 59 (77%). There were no differences in hsPDA in infants with and without AKI (p = 0.1). Rsat was not associated with AKI (p = 0.3). Infants on dopamine had less Rsat variability (p < 0.01).

CONCLUSION

Rsat prior to echocardiography did not discriminate AKI in this cohort of preterm infants at risk for hsPDA; however, data may not capture optimal timing of Rsat measurement before AKI.

KEY POINTS

· No Rsat value was found to be associated with the development of AKI.. · The optimal timing of Rsat measurement should be evaluated in infants at risk for hsPDA.. · NIRS bedside monitoring of Csat and Rsat measures may be useful in trending perfusion patterns.. · Identification of those at high risk for AKI may allow for more careful kidney function monitoring..

Transfusion strategies for neonates: current perspectives

Background

Blood transfusion intervention has been proven to be a crucial therapeutic aid for preterm infants with serious morbidities such as sepsis, intraventricular hemorrhage, and cardiopulmonary insufficiencies. However, blood transfusion practices have also been shown to cause significant adverse outcomes, which may negate the therapeutic effect of the intervention. To address the varying policies regarding the administration of blood products, healthcare professionals have adopted a consensus-based approach. The absence of a standard protocol has resulted in conflicting outcomes in previous clinical studies.

Objective

This study aimed to evaluate the effectiveness of blood transfusion practices in preterm infants by analyzing past clinical research and identifying the current trends that have emerged as a result of recent trials.

Results

Recent trials have demonstrated comparable trends in mortality rates and other primary outcomes, including retinopathy of prematurity, intraventricular hemorrhage, bronchopulmonary dysplasia, and brain injury, following transfusion of blood products in both groups. Nevertheless, employing restrictive thresholds rather than adopting a liberal approach can reduce these outcomes.

Conclusion

The current literature does not provide clear support for either technique as opposing and contradictory results are evident. However, there is a slight inclination toward the restrictive transfusion threshold due to recent trials, which warrants further in-depth investigation into this issue.

Understanding Near-Infrared Spectroscopy: An Update

Near-infrared spectroscopy (NIRS) is a novel technology that uses infrared light to noninvasively and continuously measure regional oxygen extraction in real time at the bedside. Neonatal research using this device supports its use as an adjunct to routine cardiovascular monitoring because NIRS serves as a surrogate marker for end-organ perfusion and can detect minute changes in cerebral, intestinal, and kidney tissue beds. Multiple conditions affecting premature infants are frequently associated with hypoperfusion; therefore, methods to detect early tissue-specific perfusion alterations may substantially improve the clinician's ability to intervene and prevent further deterioration.

Arch watch: current approaches and opportunities for improvement

Coarctation of the aorta (CoA) is a ductus arteriosus (DA)-dependent form of congenital heart disease (CHD) characterized by narrowing in the region of the aortic isthmus. CoA is a challenging diagnosis to make prenatally and is the critical cardiac lesion most likely to go undetected on the pulse oximetry-based newborn critical CHD screen. When undetected CoA causes obstruction to blood flow, life-threatening cardiovascular collapse may result, with a high burden of morbidity and mortality. Hemodynamic monitoring practices during DA closure (known as an "arch watch") vary across institutions and existing tools are often insensitive to developing arch obstruction. Novel measures of tissue oxygenation and oxygen deprivation may improve sensitivity and specificity for identifying evolving hemodynamic compromise in the newborn with CoA. We explore the benefits and limitations of existing and new tools to monitor the physiological changes of the aorta as the DA closes in infants at risk of CoA.

Renal tissue oxygenation and development of AKI in preterm neonates born < 32 weeks' gestational age in the first week of age

OBJECTIVE

To evaluate the relationship between regional renal saturation of oxygen (RrSO2) changes and serum creatinine (SCr) during the first eight days of age for preterm neonates born < 32 weeks' gestational age.

DESIGN

Post-hoc analysis of multicenter prospectively measured neonatal RrSO2 values collected during the first 8 days of age in neonates born at < 32 weeks' gestation. Acute kidney injury (AKI) was defined by the neonatal modified Kidney Disease: Improving Global Outcomes (KDIGO) criteria. Variables were compared between groups of neonates with and with AKI.

RESULTS

One hundred nine neonates were included and 561 SCr values were obtained. Eight participants developed AKI by SCr criteria. A 10-percentage point increase in mean %RrSO2 was associated with a 40% decrease in risk of AKI (95%CI: 9.6-61%; p = 0.016).

CONCLUSIONS

Increases in mean %RrSO2 in neonates born at < 32 weeks' GA were associated with a decreased risk of AKI. These findings support the design of further prospective trials utilizing RrSO2 monitoring to evaluate new therapies or clinical protocols to prevent and treat neonatal AKI.

Routine Diaper Change Alters Kidney Oxygenation in Premature Infants: A Non-A Priori Analysis

BACKGROUND

Reduction in oxygen delivery to developing kidneys of premature infants may be an important source for acute kidney injury in premature infants.

PURPOSE

To describe changes in continuous kidney oxygenation (RrSO 2 ) measures before, during, and after routine diaper changes.

METHODS

Non-a priori analysis of a prospective cohort that received continuous measurement of RrSO 2 with near-infrared spectroscopy (NIRS) over the first 14 days of life demonstrating acute RrSO 2 drops surrounding diaper changes.

RESULTS

In total, 26 of 38 (68%) infants (≤1800 g) from our cohort exhibited acute drops in RrSO 2 that temporally correlated with diaper changes. Mean (SD) RrSO 2 baseline prior to each diaper change event was 71.1 (13.2), dropped to 59.3 (11.6) during diaper change, and recovered to 73.3 (13.2). There was a significant difference between means when comparing baseline to diaper change ( P < .001; 95% CI, 9.9 to 13.8) and diaper change to recovery ( P < .001; 95% CI, -16.9 to -11.2). The mean decrease in RrSO 2 during diaper change averaged 12 points (17%) below 15-minute RrSO 2 mean prior to diaper change, with quick recovery to prediaper change levels. No decreases in SpO 2 , blood pressure, or heart rate were documented during the intermittent kidney hypoxic events.

IMPLICATIONS FOR PRACTICE AND RESEARCH

Routine diaper changes in preterm infants may increase the risk for acute reductions in RrSO 2 as measured by NIRS; however, the impact on kidney health remains unknown. Larger prospective cohort studies assessing kidney function and outcomes related to this phenomenon are needed.

An Exploratory Review on the Potential of Artificial Intelligence for Early Detection of Acute Kidney Injury in Preterm Neonates

A preterm birth is a live birth that occurs before 37 completed weeks of pregnancy. Approximately 15 million babies are born preterm annually worldwide, indicating a global preterm birth rate of about 11%. Up to 50% of premature neonates in the gestational age (GA) group of <29 weeks' gestation will develop acute kidney injury (AKI) in the neonatal period; this is associated with high mortality and morbidity. There are currently no proven treatments for established AKI, and no effective predictive tool exists. We propose that the development of advanced artificial intelligence algorithms with neural networks can assist clinicians in accurately predicting AKI. Clinicians can use pathology investigations in combination with the non-invasive monitoring of renal tissue oxygenation (rSO2) and renal fractional tissue oxygenation extraction (rFTOE) using near-infrared spectroscopy (NIRS) and the renal resistive index (RRI) to develop an effective prediction algorithm. This algorithm would potentially create a therapeutic window during which the treating clinicians can identify modifiable risk factors and implement the necessary steps to prevent the onset and reduce the duration of AKI.

Renal oximetry for early acute kidney injury detection in neonates with hypoxic ischemic encephalopathy receiving therapeutic hypothermia

BACKGROUND

Neonates with hypoxic ischemic encephalopathy (HIE) receiving therapeutic hypothermia are at high risk of acute kidney injury (AKI).

METHODS

We performed a two-site prospective observational study from 2018 to 2019 to evaluate the utility of renal near-infrared spectroscopy (NIRS) in detecting AKI in 38 neonates with HIE receiving therapeutic hypothermia. AKI was defined by a delayed rate of serum creatinine decline (< 33% on day 3 of life, < 40% on day 5, and < 46% on day 7). Renal saturation (Rsat) and systemic oxygen saturation (SpO2) were continuously measured for the first 96 h of life (HOL). Renal fractional tissue oxygen extraction (RFTOE) was calculated as (SpO2 - Rsat)/(SpO2). Using renal NIRS, urine biomarkers, and perinatal factors, logistic regression was performed to develop a model that predicted AKI.

RESULTS

AKI occurred in 20 of 38 neonates (53%). During the first 96 HOL, Rsat was higher, and RFTOE was lower in the AKI group vs. the no AKI group (P < 0.001). Rsat > 70% had a fair predictive performance for AKI at 48-84 HOL (AUC 0.71-0.79). RFTOE ≤ 25 had a good predictive performance for AKI at 42-66 HOL (AUC 0.8-0.83). The final statistical model with the best fit to predict AKI (AUC = 0.88) included RFTOE at 48 HOL (P = 0.012) and pH of the infants' first postnatal blood gas (P = 0.025).

CONCLUSIONS

Lower RFTOE on renal NIRS and pH on infant first blood gas may be early predictors for AKI in neonates with HIE receiving therapeutic hypothermia. A higher resolution version of the Graphical abstract is available as Supplementary information.

The Potential Use of Near- and Mid-Infrared Spectroscopy in Kidney Diseases

Traditional renal biomarkers such as serum creatinine and albuminuria/proteinuria are rather insensitive since they change later in the course of the disease. In order to determine the extent and type of kidney injury, as well as to administer the proper therapy and enhance patient management, new techniques for the detection of deterioration of the kidney function are urgently needed. Infrared spectroscopy is a label-free and non-destructive technique having the potential to be a vital tool for quick and inexpensive routine clinical diagnosis of kidney disorders. The aim of this review is to provide an overview of near- and mid-infrared spectroscopy applications in patients with acute kidney injury and chronic kidney disease (e.g., diabetic nephropathy and glomerulonephritis).

Intraoperative renal desaturation and postoperative acute kidney injury in older patients undergoing liver resection: A prospective cohort study

STUDY OBJECTIVE

To determine the association between intraoperative renal tissue desaturation as measured using near-infrared spectroscopy and increased likelihood of developing postoperative acute kidney injury (AKI) in older patients undergoing hepatectomy.

DESIGN

A multicenter prospective cohort study.

SETTING

The study was conducted at two tertiary hospitals in China from September 2020 to October 2021.

PATIENTS

157 older patients (≥ 60 years) undergoing open hepatectomy surgery.

INTERVENTIONS AND MEASUREMENTS

Renal tissue oxygen saturation was continuously monitored during operation using near-infrared spectroscopy. The exposure of interest was intraoperative renal desaturation, defined as at least 20% relative decline in renal tissue oxygen saturation from baseline. The primary outcome was postoperative AKI, defined using the Kidney Disease: Improving Global Outcomes criteria according to the serum creatinine criteria.

MAIN RESULTS

Renal desaturation occurred in 70 of 157 patients. Postoperative AKI was observed in 23% (16/70) and 8% (7/87) of patients with versus without renal desaturation. Patients with renal desaturation were at higher risk of AKI than patients without renal desaturation (adjusted odds ratio 3.41, 95% confidence interval: 1.12-10.36, p = 0.031). Predictive performance was 65.2% sensitivity and 33.6% specificity for hypotension alone, 69.6% sensitivity and 59.7% specificity for renal desaturation alone, and 95.7% sensitivity and 26.9% specificity for combined use of hypotension and renal desaturation.

CONCLUSIONS

Intraoperative renal desaturation occurred in >40% in our sample of older patients undergoing liver resection and was associated with increased risk of AKI. Intraoperative near-infrared spectroscopy monitoring enhances the detection of AKI.

Use of Renal Near-Infrared Spectroscopy and Urinary Neutrophil Gelatinase-Associated Lipocalin Monitoring as Indicators of Acute Kidney Injury in Pediatric Cardiac Surgery

Acute kidney injury (AKI) is a common complication following cardiac surgery under cardiopulmonary bypass (CPB) in children. A prospective study for examining urinary neutrophil gelatinase-associated lipocalin (NGAL) and renal near-infrared spectroscopy (NIRS) trends during AKI was conducted among pediatric patients undergoing cardiac surgery with CPB. Urinary NGAL showed a significant difference between intensive care unit admission (0 h) and 2 h post-admission (p < 0.001) and remained significant up to 4 h (p < 0.05). The renal NIRS in the AKI group showed a significant rate of decrease and lower values during the intraoperative period (p < 0.05). The cumulative median saturation of renal regional saturation of oxygen (rSO2) during CPB was 1637.5% min in the AKI group and 943.0% min in the non-AKI group. The median renal rSO2 scores at a reduction of 20% and 25% were significantly higher (p < 0.001) in the AKI group. Our results suggest that monitoring renal rSO2 scores and limiting their decline might be useful in preventing AKI. The combination of NGAL, renal rSO2, and renal rSO2 scores might be useful in the early diagnosis of AKI during pediatric cardiac surgery.

Renal oxygenation measured by near-infrared spectroscopy in preterm neonates in the first week

OBJECTIVE

To describe renal regional saturation of oxygen (RrSO₂) values during the first week of life for preterm neonates born at <32 weeks gestational age (GA).

METHODS

RrSO₂ values recorded over the first week of life using near-infrared spectroscopy were retrospectively analyzed in this two-center cohort study of preterm infants without known congenital anomalies of the kidney.

RESULTS

A cohort of 109 neonates with a median GA of 26.9 weeks and a median of 120 (IQR: 87-141) hours of continuous RrSO₂ monitoring were included. Separately fitted trends in RrSO₂ did not differ (p = 0.52) between sites and demonstrated a consistent decrease in RrSO₂ by 20 points (95% CI: 9.6-30.1) during the first 60 h of life, followed by a stabilization of RrSO₂ thereafter. RrSO₂ baseline trends increased by 2.1 (95% CI: 0.8-3.3) percentage points for each additional week GA between 24 and 32 weeks GA.

CONCLUSIONS

Despite differences in adjusted RrSO₂ values between sites, profiles over time are consistent, allowing for the determination of RrSO₂ trajectories in preterm infants. This expected pattern of RrSO₂ changes in the first week may help guide future investigations and interventions to identify and reduce kidney injury in the preterm neonate.

IMPACT

Renal regional saturation of oxygen (RrSO₂) slowly decreases during the first 60 h of age in <32-week preterm neonates. While site differences were identified with respect to absolute values, RrSO₂ trends from two different centers were not different. Lower gestational age neonates have lower RrSO₂ levels during the first week.

Clinical impact of severe acute kidney injury on post-operative and brain injury outcomes in preterm infants following surgical necrotizing enterocolitis

BACKGROUND

To evaluate post-operative outcomes and white matter injury (WMI) using brain MRI at term equivalent in neonates with and without severe acute kidney injury (AKI) following surgical necrotizing enterocolitis (NEC).

METHODS

A retrospective cohort study comparing neonates with severe (Stage 2/3) vs. other (no AKI/Stage 1) AKI using KDIGO classification with multivariable models assessing this association in the context of multiple systemic comorbidities.

RESULTS

Of 103 neonates with surgical NEC, 60 (58%) had severe AKI. Those with severe AKI had lower birth weight (BW; 715 vs. 950 g; p = .023), more frequently treated with indomethacin (18.3 vs. 2.4%); p = .014), higher CRP levels at 24 h after NEC onset (14.4 [6.4-19.8] vs. 4.8 [1.6-13.4]; p = .005), higher presence of cholestasis (73.3 vs. 51.2%); p = .023), later age of NEC onset (14 vs. 7 d); p = .004), longer length of bowel resected (14.9 vs. 4.3 cm); p = .011), longer post-operative ileus days (14 vs. 9 d); p < .001), longer post-operative days at starting enteral feedings (15 vs. 10 d; p < .001), longer days of attainment of full enteral feedings (75 vs. 44.5 d; p = .008) and longer length of stay (140.5 vs. 94 d; p = .028) compared to those without severe AKI. Compared to infants without AKI by serum creatinine, those with AKI had significantly more cases of white matter abnormality (WMA; 90 vs. 36.6%; p < .001) and retinopathy of prematurity (63.9 vs. 35.3%; p = .017). In addition, the presence of AKI Stage 2 and 3 by serum creatinine was independently associated with higher odds of sustaining severe WMI level on an ordinal scale (OR = 6.2; 95% CI = (1.1-35.5); p = .041).

CONCLUSIONS

Neonates with severe AKI following surgical NEC were more likely to experience longer post-operative morbidity and higher WMI by MRI at term.

[Value of intestinal regional oxygen saturation and C-reactive protein in the diagnosis of necrotizing enterocolitis in preterm infants]

OBJECTIVES

To study the clinical value of intestinal regional oxygen saturation (rSO₂) and C-reactive protein (CRP) in the diagnosis of necrotizing enterocolitis (NEC) in preterm infants.

METHODS

A prospective observational study was conducted among the preterm infants who were hospitalized in Children's Hospital Affiliated to Anhui Medical University, from October 2020 to December 2021, with 22 infants in the NEC group and 35 infants in the non-NEC group. Intestinal rSO₂ was monitored 24 hours after a confirmed diagnosis of NEC in the NEC group, and serum CRP levels were measured before anti-infection therapy. In the non-NEC group, intestinal rSO₂ monitoring and serum CRP level measurement were performed at the corrospording time points. The two groups were compared in terms of intestinal rSO₂ and serum CRP level. The receiver operating characteristic (ROC) curve was used to analyze the value of intestinal rSO₂ alone, serum CRP alone, and intestinal rSO₂ combined with CRP in the diagnosis of NEC in preterm infants.

RESULTS

Compared with the non-NEC group, the NEC group had a significantly lower level of intestinal rSO₂ (P<0.05) and a higher serum CRP level (P<0.05). The ROC curve analysis showed that intestinal rSO₂ had an optimal cut-off value of 50.75% in the diagnosis of NEC in preterm infants, with a sensitivity of 81.8%, a specificity of 85.7%, and an area under the ROC curve (AUC) of 89.4%; CRP had an optimal cut-off value of 12.05 mg/L in the diagnosis of NEC in preterm infant, with a sensitivity of 72.7%, a specificity of 74.3%, and an AUC of 74.8%; intestinal rSO₂ combined with CRP had a sensitivity of 90.9%, a specificity of 77.1%, and an AUC of 91.9% in the diagnosis of NEC. The AUC of intestinal rSO₂ alone in the diagnosis NEC was higher than that of CRP (P<0.05). There was no significant difference in the AUC between intestinal rSO₂ alone and intestinal rSO₂ combined with CRP (P>0.05).

CONCLUSIONS

The value of intestinal rSO₂ in the diagnosis NEC is higher than that of CRP, and is equivalent to that of the combination of intestinal rSO₂ and CRP in preterm infants.

Renal tissue oxygenation after caffeine administration in preterm neonates

BACKGROUND

Caffeine has been associated with reduced rates of acute kidney injury (AKI) in preterm neonates. The effect of caffeine on preterm neonatal renal regional saturation of oxygen (RrSO₂) is unknown.

METHODS

RrSO₂ was recorded continuously in neonates < 32 weeks' gestation until 7 days of age with INVOS™ neonatal near-infrared spectroscopy (NIRS) sensors. Baseline RrSO₂ values were established by averaging the saturations in the 20 min prior to caffeine administration. Subgroup analysis was performed based on pre-caffeine RrSO₂ averages. Change in RrSO₂ was recorded at 0.5, 1, 2, 3, 4, 6, and 12 h after maintenance caffeine administration.

RESULTS

Of 35 eligible neonates, 31 (median gestational age 28.4 weeks) received 156 caffeine doses (median 8 mg/kg). Analysis of combined doses showed no significant changes in RrSO₂ after caffeine administration at any time. However, neonates with baseline 20-29.9% had significant increases from 1 to 12 h (range of increase 5.9-13.9%), and those with baseline 30-39.9 had significant increases at 1 h (8.06%, p < 0.05).

CONCLUSIONS

Maintenance caffeine dosing increased RrSO₂ in neonates with low RrSO₂ in the first week. Further research is needed to determine the effect of loading doses of caffeine and if increases in RrSO₂ correlate with improved clinical kidney outcomes.

IMPACT

Caffeine administration is associated with increased renal tissue oxygenation in preterm neonates with low baseline values under 40%. The most significant renal tissue oxygenation changes occur in the first 3 h after IV caffeine administration. With recent studies suggesting low RrSO₂ values in preterm neonates are associated with AKI, caffeine should be studied as a potential therapeutic for this common and complex morbidity in preterm neonates.

Advances in Neonatal Acute Kidney Injury

In this state-of-the-art review, we highlight the major advances over the last 5 years in neonatal acute kidney injury (AKI). Large multicenter studies reveal that neonatal AKI is common and independently associated with increased morbidity and mortality. The natural course of neonatal AKI, along with the risk factors, mitigation strategies, and the role of AKI on short- and long-term outcomes, is becoming clearer. Specific progress has been made in identifying potential preventive strategies for AKI, such as the use of caffeine in premature neonates, theophylline in neonates with hypoxic-ischemic encephalopathy, and nephrotoxic medication monitoring programs. New evidence highlights the importance of the kidney in "crosstalk" between other organs and how AKI likely plays a critical role in other organ development and injury, such as intraventricular hemorrhage and lung disease. New technology has resulted in advancement in prevention and improvements in the current management in neonates with severe AKI. With specific continuous renal replacement therapy machines designed for neonates, this therapy is now available and is being used with increasing frequency in NICUs. Moving forward, biomarkers, such as urinary neutrophil gelatinase-associated lipocalin, and other new technologies, such as monitoring of renal tissue oxygenation and nephron counting, will likely play an increased role in identification of AKI and those most vulnerable for chronic kidney disease. Future research needs to be focused on determining the optimal follow-up strategy for neonates with a history of AKI to detect chronic kidney disease.

Normal regional tissue oxygen saturation in neonates: a systematic qualitative review

BACKGROUND

The aim of this systematic qualitative review was to give an overview of reference ranges defined as normal values or centile charts of regional tissue oxygen saturation measured by near-infrared spectroscopy (NIRS) in term and preterm neonates.

METHODS

A systematic search of MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials was performed. Additional articles were identified by manual search of cited references. Only human studies in neonates were included.

RESULTS

Nineteen studies were identified. Eight described regional tissue oxygen saturation during fetal-to-neonatal transition, six during the first 3 days after birth, four during the first 7 days after birth, and one during the first 8 weeks after birth. Nine described regional tissue oxygen saturation in term, nine in preterm neonates, and one in both. Eight studies published centile charts for cerebral regional tissue oxygen saturation, and only five included large cohorts of infants. Eleven studies described normal values for cerebral, muscle, renal, and abdominal regional tissue oxygen saturation, the majority with small sample sizes. Four studies of good methodological quality were identified describing centile charts of cerebral regional tissue oxygen saturation.

CONCLUSIONS

In clinical settings, quality centile charts are available and should be the preferred method when using NIRS monitoring.

IMPACT

Near-infrared spectroscopy (NIRS) enables a bed-side non-invasive continuous monitoring of tissue oxygenation. When using NIRS monitoring in a clinical setting, centile charts with good quality are available and should be preferred to normal values. High-quality reference ranges of regional tissue oxygenation in term and preterm born neonates are an important step toward routine clinical application of NIRS.