Near infrared spectroscopy and abdominal compartmental syndrome in neonates

ABSTRACT Background and Aims Abdominal compartmental syndrome considered the most common cause of postoperative mortality in neonates scheduled for surgical repair of congenital abdominal wall defect. This study aimed primarily to observe the renal and cerebral rSO2 variation during and after surgical reduction, while secondarily to analyze correlations with other perfusion markers of intra-abdominal hypertension. Patients and methods A randomized, prospective, cohort study was piloted in a tertiary care pediatric surgery center from February 2017 to march 2021 where 20 neonates scheduled surgical repair of congenital abdominal wall defects. Near-infrared spectroscopy (NIRS) measurements of regional tissue oxygenation (rSO2) fluctuations performed using the two-channel mode, channel 1 for cerebral monitoring (C rSO2) and channel 2 for renal monitoring (R rSO2), and calculating differences intraoperative as well as postoperative. Results Intra-operative C and R ΔrSO2 had a significant positive correlation with an intraoperative post-ductal SPO2 and MABP changes, while a significant negative correlation was noted with serum lactate level and capillary refill time. Postoperative C ΔrSO2 showed a negative correlation with postoperative serum lactate level, whereas postoperative R ΔrSO2 had a positive correlation with postoperative post-ductal SPO2 changes, and negative correlations with postoperative capillary refill time changes. Pathological intraoperative ΔrSO2 had a statistically significant relation with intraoperative post-ductal SPO2, MABP, capillary refill time, serum lactate level, postoperative serum creatinine level, and postoperative vasoactive-ventilation-renal (VVR) score. Conclusion : NIRS is an efficient non-invasive monitor of cerebral and tissue perfusion, evaluating tissue microcirculation, and considered an early warning for detecting abdominal compartment syndrome (ACS) in neonates.


Introduction
Ventral abdominal wall defects involve multiple congenital malformations including gastroschisis and omphalocele, which are common anomalies relative to ectopia cordis, bladder exstrophy, and cloacal exstrophy. [1] The combined prevalence of omphalocele and gastroschisis is one case per 3,500 newborns. [2] Gastroschisis defined as uncovered abdominal visceral herniation through a full-thickness abdominal wall defect [3]. In contrast, omphalocele is a central abdominal wall defect in which the protruded abdominal contents are covered in a thin sac [4].
Abdominal compartment syndrome (ACS) considered the most common postoperative complication, especially with herniated visceral reintegration surgery, defined as intra-abdominal hypertension associated with one or more organs dysfunction. [5] Intraabdominal hypertension (IAH), defined as increased intra-abdominal pressure (IaP) >12 mmHg, lead to ventilatory and circulatory compromises in critically ill neonates [6], there is no accredited standard technique for IaP measurement in neonatal surgery [7].
End organ perfusion usually assessed by clinical signs as capillary refill time, urine output, heart rate, base excess, lactate concentration, and blood pressure [8]. However, early perfusion disorders detection required to improve therapeutic outcome is difficult to be achieved using clinical signs alone. [9] Near infrared spectroscopy was first described in 1977 by Jobsis [10] as a continuous non-invasive method of tissue oxygenation assessment. Regional oxygen saturation (rSO2) measuring the percentage of oxygenated hemoglobin in a target tissue, can detect microcirculatory dysfunctions. [11] The renal oxygen values considered a sensitive indicator for cardiac output changes, while cerebral oxygen values are relatively stable due to cerebral autoregulation mechanisms. [12] Recent studies estimated the validity of simultaneous monitoring of cerebral and renal oxygen tension in prediction of subclinical hypoperfusion. [13] The vasoactive-ventilation-renal (VVR) score introduced in 2015 as a novel predictor of postoperative prognosis in neonates [14], based on the measurement of inotropic support required to provide hemodynamic stability, markers of the pulmonary, and renal systems. [15] The aim of the present study primarily was to observe the renal and cerebral rSO2 variation and pathological values during and after surgical reduction of neonatal viscera procedures, while secondarily to analyze correlations with other perfusion markers including MAP, pH, lactate concentration, and vasoactive-ventilation-renal score.

Patients and methods
A randomized, prospective, cohort study piloted in a tertiary care pediatric surgery center from February 2017 to march 2021 after the approval of the regional ethical committee.
A written informed approval was attained from the parents for the contribution of their infants in this study. The sample size was approved to be appropriate by the Department of Statistics, Medical Research Institute, Alexandria University, Egypt. [16] Twenty full-term neonates of both sex, weighing 3-5 kg, scheduled for congenital abdominal wall defect repair, whereas infants had hemodynamic instability, cyanic heart disease, and very low body weight (VLBW) were excluded from the study. All infants were assessed preoperatively with complete history taking, clinical examination and routine laboratory investigations.
On arrival to operating theater the neonate was attached to multichannel monitor including continuous electrocardiogram, heart rate, pulse oximeter (pre-ductal SPO2 of Rt upper limb, post-ductal SPO2 of Lt lower limb), noninvasive arterial blood pressure, and capnography (EtCO2) after endotracheal tube (ETT) insertion.
Near infrared spectroscopy measurements were performed with a continuous wave system (INVOS 5100 C, Somanetics, Troy, MI, USA), used the two-channel mode, with channel 1 for cerebral monitoring and channel 2 for renal monitoring. Cerebral (C) sensor positioned on the forehead (below the hairline) and a renal (R) sensor on the neonate's lower back (right side) between T10 and L2, accurate localization of right kidney performed using ultrasound curvilinear transducer with a frequency ranging between 5 and 7.5 MHz. [17] All infants had general anesthesia induced by incremental concentrations of sevoflurane (2%-4%) with oxygen and 24 gauge intravenous cannula was inserted and secured.
To facilitate insertion of endotracheal tube, rocuronium 0.6 mg/kg and fentanyl 1 µg/kg was given. Demographic information (chronological age, gestational age, sex, and weight), the hemodynamic and respiratory monitoring done by HR, MABP, pre-ductal SpO2, and post-ductal SpO2 recording every 15 min intraoperative, while postoperative values were documented hourly for first 6 h, later every 3 h for 18 h.
Near infrared spectroscopy measurements were achieved by a continuous wave system. Cerebral (C rSO2), renal (R rSO2), and rSO2 variations (ΔrSO2) [ΔrSO2 = ((rSO2measured − rSO2initial)/ rSO2initial) × 100 (%), initial C rSO2 and R rSO2 value on arrival to the operating theater on room air] values were simultaneously recorded and calculated along with hemodynamics and respiratory parameters. Pathological ΔrSO2 defined by a 20% or more decrease of measured rSO2, compared to initial rSO2 values.
Capillary refilling time defined as time required for return of circulation to blanched area achieved by applying sustained pressure with index finger soft bad for 5 s on forehead.
Capillary refill time and lactate concentrate were recorded every 6 h and mean value was calculated.

Statistical analysis
Data were coded, reviewed and analyzed using the SPSS version 25.0 (Armonk, NY: IBM Corp). Quantitative data were expressed as median and Data is expressed as median (min -max), bpm; beat per minute, MABP; mean arterial blood pressure, CrSO2; cerebral regional oxygen saturation, RrSO2; renal regional oxygen saturation. F; Friedman test, pairwise comparison was done using Wilcoxon ranked test P; p value between groups p1; p value between preoperative and intraoperative p2; p value between preoperative and postoperative p3; p value between intraoperative and postoperative range as the data was not normally distributed. Qualitative data were expressed as frequency and percentage. Friedman test was used to assess the difference between more than two related groups and Wilcoxon ranked test was used for the pairwise comparison. Mann Whitney test was used to test the significant difference between two independent variables and Pearson Correlation (r) was used to measure the strength of a linear association between two continuous variables. P value below than 0.05 was considered significant.

Results
A total of 32 patients were screened for eligibility; 22 patients met inclusion criteria and were approached to participate, and two infants died before surgery (Flowchart 1). Flowchart 1. Flow diagram.
Eight infants had primary closure of abdominal wall defects (one case of gastroschisis and seven cases of omphalocele), and six infants required a silo pouch stoma for gradual reintegration of the herniated viscera (five cases of gastroschisis and one case of omphalocele), then complete closure accomplished, respectively, on 10, 11 and 13 days post-initial surgery (Table 1), whereas the mean duration of surgeries was about 95 ± 72 minutes.

Cerebral and renal rSO2 variations and correlations with other perfusion markers
Cerebral rSO2 values presented a statistically significant upsurge during intra-operative and postoperative period compared to initial values (p1 = 0.004*, p2 < 0.001*, p3 = 0.742), however, R rSO2 values had a statistically insignificant decline noted throughout an intraoperative and postoperative times (F = 0.757, P value = 0.685) as reported in (Table 2).

Pathological ΔrSO2 incidence and relations with other perfusion markers
Pathological ΔrSO2 observed intra-operative in six infants, three cases had both pathological C and R ΔrSO2 occurred during progressive visceral reduction, whereas three cases showed isolated pathological R ΔrSO2 occurred with trial of abdominal wall closure, so silo pouch stoma used to permit progressive reintegration of the herniated viscera, as it was critical to achieve the reintegration in one surgical step.
The analysis of the present data documented a statistically significant relation between incidence of intraoperative pathological ΔrSO2 and intraoperative post-ductal SPO2, MABP, capillary refill time, serum lactate level, postoperative serum creatinine level, and postoperative VVR score, while no relation was found between pathological ΔrSO2 and any of the other parameters studied as presented in (Table 5).

Discussion
Abdominal compartmental syndrome causes increased mortality and morbidity in neonatal intensive care, intra-abdominal hypertension associated with regional renal and mesenteric hypoperfusion. [19] Early diagnosis of IAH can prevent progression to ACS and improve postoperative outcomes. [20] Previous literature data revealed that no absolute reference values for NIRS measures due to interindividual variations; however, a 20% decrease of the initial rSO2 was established that is a sign of tissue  ; intraoperative cerebral regional oxygen saturation variation, Intra RΔrSO2; intraoperative renal regional oxygen saturation variations.
hypoperfusion [21], while an absolute value of cerebral rSO2 < 50% associated with hypoxic brain injury evident in radiological imaging and risk of disability [22]. An upsurge of cerebral rSO2 noted intraoperative and postoperative resulted from high fraction of inspired oxygen (FiO2) and elevated PIP (>20 mmHg) applied to maintain effective ventilation during the increased abdominal pressure, in agreement with the present results Beck et al. [23] studied changes of regional oxygen saturation during neonatal digestive surgeries and concluded that cerebral auto-regulation and high ventilation pressure were the reasons of stable CrSO2.
Intra-operative C and R rSO2 variations had a significant positive correlation with an intraoperative post-ductal SPO2 and MABP changes, while a significant negative correlation was noted with serum lactate level and capillary refill time.
Sood et al. [24] reported that regional saturation variations reflect global saturation and MAP variations. Whereas Kaufman et al. [25] documented negative correlation between serum lactate levels and splanchnic rSO2 levels. They reported that rSO2 considered an index for systemic oxygenation and perfusion of infants after congenital heart surgery.
Postoperative C rSO2 variations showed a negative correlation with postoperative serum lactate level whereas postoperative R rSO2 variations had a positive correlation with postoperative post-ductal SPO2 changes, and negative correlation with postoperative capillary refill time changes. Al Tayar et al. [26] concluded that cerebral rSO2 considered a noninvasive predictor of shock. While Balakrishnan et al. [27] assessed low somatic NIRS values in relation to other hemodynamic parameters in the critically ill children and found a positive correlation between low somatic NIRS values and early implication of life-saving interventions.
An intraoperative pathological ΔrSO2 observed in 30% of included infants occurred with trial of abdominal wall closure and had a strong relation with other perfusion markers. Conforti et al. [28] studied NIRS values in neonates had congenital diaphragmatic hernia (CDH) repair and concluded that reduction of herniated viscera induced intra-abdominal hypertension, which could worsen regional abdominal tissue oxygenation.
The present study verified the strong relation between the incidence of pathological ΔrSO2 which necessitates circulatory as well as ventilatory support and increased postoperative morbidity measured by  Post CΔrSO2; postoperative cerebral regional oxygen saturation variation, Post RΔrSO2; postoperative renal regional oxygen saturation variations.   Pathological ΔrSO2; pathological regional oxygen saturation variations, Intra; intraoperative, MABP; mean arterial blood pressure, VVR; vasoactive ventilation renal score.
VVR score. Cashen et al. [30] documented the value of vasoactive-inotropic score as predictor of morbidity and mortality in neonates undergoing cardiac surgery.

Conclusion
NIRS is an efficient non-invasive monitor of cerebral and tissue perfusion, evaluating tissue microcirculation, and considered an early warning for detecting abdominal compartment syndrome (ACS) in neonates.

Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Ethics approval and consent to participate
The present study was approved by the ethical committee of Faculty of Medicine, Alexandria University (IRB no. 00007570, FWA no. 00018702). A consent to participate was obtained as well.

Consent for publication
Written informed consent was obtained from the parents for publication of this article and any accompanying tables/ images. The copies of the written consents are available for review by the Editor of this journal upon request.

Availability of data and material
All data supporting the study are presented in the manuscript or available upon request.