Transcutaneous Near-infrared Spectroscopy Research Articles

Evaluation of machine learning algorithms for noninvasive intracranial pressure estimation using near infrared spectroscopy as a covariate.

Intracranial pressure (ICP) is a vital parameter that is continuously monitored in patients with severe brain injury and imminent intracranial hypertension. To estimate intracranial pressure without intracranial probes based on transcutaneous near infrared spectroscopy (NIRS). We developed machine learning based approaches for noninvasive intracranial pressure (ICP) estimation using signals from transcutaneous near infrared spectroscopy (NIRS) as well as other cardiovascular and artificial ventilation parameters. In a patient cohort of 25 patients, with 22 used for model development and 3 for model testing, the best performing models were Fourier transform based Transformer ICP waveform estimation which produced a mean absolute error of 4.68 mm Hg (SD = 5.4) in estimation. We did not find a significant improvement in ICP estimation accuracy by including signals measured by transcutaneous NIRS. We expect that with higher quality and greater volume of data, noninvasive estimation of ICP will improve.

Evaluation of transcutaneous near-infrared spectroscopy for early detection of cardiac arrest in an animal model

Sudden cardiac arrest (SCA) is a leading cause of mortality worldwide. The SCA-to-resuscitation interval is a key determinant of patient outcomes, highlighting the clinical need for reliable and timely detection of SCA. Near-infrared spectroscopy (NIRS), a non-invasive optical technique, may have utility for this application. We investigated transcutaneous NIRS as a method to detect pentobarbital-induced changes during cardiac arrest in eight Yucatan miniature pigs. NIRS measurements during cardiac arrest were compared to invasively acquired carotid blood pressure and partial oxygen pressure (PO2) of spinal cord tissues. We observed statistically significant decreases in mean arterial pressure (MAP) 64.68 mmHg ± 13.08, p < 0.0001), spinal cord PO2 (38.16 mmHg ± 20.04, p = 0.0028), and NIRS-derived tissue oxygen saturation (TSI%) (14.50% ± 3.80, p < 0.0001) from baseline to 5 min after pentobarbital administration. Euthanasia-to-first change in hemodynamics for MAP and TSI (%) were similar [MAP (10.43 ± 4.73 s) vs TSI (%) (12.04 ± 1.85 s), p = 0.3714]. No significant difference was detected between NIRS and blood pressure-derived pulse rates during baseline periods (p > 0.99) and following pentobarbital administration (p = 0.97). Transcutaneous NIRS demonstrated the potential to identify rapid hemodynamic changes due to cardiac arrest in periods similar to invasive indices. We conclude that transcutaneous NIRS monitoring may present a novel, non-invasive approach for SCA detection, which warrants further investigation.

NEAR-INFRARED SPECTROSCOPY FOR MONITORING DISTAL LIMB PERFUSION DURING PEDIATRIC MINIMAL INVASIVE CARDIAC SURGERY FOR CONGENITAL HEART DEFECTS

Introduction Acute femoral artery occlusion due to remote access bypass (femoral arterial cannulation), is a routine for pediatric minimal invasive cardiac surgery and prevention of leg ischemia is necessary. This technique requires peripheral vessel cross clamping, which may lead to transient perfusion deficit of the lower extremities.Strategies to prevent muscle necrosis or development of compartment syndrome include invasive or non-invasive monitoring of tissue oxygen saturation of involved extremity. A variety of means are utilized, to assess lower extremity (LE) perfusion – including pulse palpation, pulse oximetry, subjective assessment of LE by colour, temperature etc. Regional oxygen saturation measured by near-infrared spectroscopy (NIRS), used as a potential surrogate of cerebral and somatic mixed venous oxygen saturation-is a noninvasive tool to continuously monitor LE perfusion. We sought to evaluate the safety of peripheral arterial cannulation by using NIRS in such subset of patients. Methods We evaluated 50 pediatric patients, weight 10-30kg, age 3-12years, divided in: Group A (N=25), - underwent peripheral femoral artery cannulation for remote access perfusion for MICS, group B (N=25), receive conventional sternotomy incision. All patients were monitored by transcutaneous NIRS (placed on calves of both legs) for quality control of distal leg perfusion during cardiopulmonary bypass. Baseline NIRS value, followed by continuous NIRS values were recorded. Total creatinine kinase (CK) and serum myoglobin levels, mid-thigh and mid -calf circumference (to rule out compartment syndrome), were measured at preoperatively, 6hour and 24hour after surgery. Intra-operatively, all hemodynamic parameters along with blood gas parameters like PH, PO2, PCO2, SCVO2, lactate etc. were recorded at baseline, on bypass, clamp on, clamp off and off bypass period. Total CPB time, ventilation duration, hospital and ICU stay were also recorded. Results The baseline NIRS comparable in group A (72.6±6.86) over cannulated versus (71.76±4.05), contralateral leg, while, in group B, it was (69.96±5.75 vs.69.84±5.50). During clamping of femoral artery in Group A, NIRS dropped to 39.12±5.60 (vs. baseline), while it remained stable in the contralateral leg and group B patients. After successful implantation of the distal leg perfusion, the NIRS normalized to baseline within 5 to 7 minutes. Myoglobin and CK levels increased in both the groups, more so in Group A. There were no clinical side effects from increased CK or myoglobin. None of our patients had residual vascular complications. ±±±± Discussion We speculate that remote CPB with direct femoral artery cannulation can be safely used in pediatric patients- with a body weight 10-30 kg and CPB time less than 60 minutes- without increasing operative morbidity and complications. When prolonged CPB time is expected probably one should change the MICS policy by adding selective distal leg perfusion to minimize the complications

Transcutaneous near-infrared spectroscopy (NIRS) for monitoring kidney and liver allograft perfusion.

The use of transcutaneous near-infrared spectroscopy (NIRS) for monitoring the perfusion of kidney and liver allografts has been proposed in the last years. This device might detect an early decrease in allograft oxygenation allowing prompt detection of vascular complications. A systematic review of the literature about the use of transcutaneous NIRS in monitoring allograft perfusion was performed according to the PRISMA guidelines. The authors screened 1313 papers. The search yielded five pertinent articles. Three of them reported the experience of NIRS in kidney transplantation and the other two dealt with its use in liver transplantation, for a total of 55 paediatric patients and 121 adults. In the studies concerning kidney transplantation, NIRS measurements were significantly related to serum creatinine, estimated glomerular filtration rate (eGFR), urinary neutrophil gelatinase-associated lipocalin (u-NGAL), serum lactate, resistive index assessed by Doppler-ultrasonography and systolic blood pressure. The two studies dealing with liver transplantation found a significant decrease in liver regional oxygenation, assessed by NIRS, before the occurrence of vascular complications. Preliminary studies have related NIRS monitoring to kidney and liver allograft perfusion, both in adults and children. Further investigation is needed to establish the normal range of NIRS values and the factors influencing NIRS monitoring.

Noninvasive monitoring of central venous oxygen saturation by jugular transcutaneous near-infrared spectroscopy in pediatric patients undergoing congenital cardiac surgery

Background and aimIn patients undergoing congenital cardiac surgery, it is crucial to maintain oxygen demand-consumption balance. Central venous oxygen saturation (ScvO2) is a useful indicator of oxygen demand and consumption balance which is an invasive method. Near-infrared spectroscopy (NIRS) is a noninvasive, continuous monitoring technique that measures regional tissue oxygenation. NIRS that is placed over the internal jugular vein cutaneous area (NIRSijv) has the potential to show ScvO2 indirectly. In this study, we aimed to determine the correlation between ScvO2 with NIRSijv in pediatric patients undergoing congenital cardiac surgery.Materials and methodsFifty children participated in the study. Four patients were excluded for the inability of internal jugular vein (IJV) catheterization due to technical difficulties. After anesthesia induction, NIRS probes were placed on the IJV site with ultrasound guidance for the measurement of continuous transcutaneous oxygen saturation. The catheter insertion was also done through the IJV from the other side using ultrasound guidance. Cerebral oxygenation monitoring was done using NIRS with a single pediatric probe placed on the right forehead. Values of NIRSijv, cerebral NIRS (NIRSc) and ScvO2, were recorded at certain times until postoperative 24th hour.ResultsData were collected at 8 different time points. There was a significant correlation between ScvO2 and NIRSijv in all measurement time points (r = 0.91), (P = 0.001). The mean bias between ScvO2 and NIRSijv was 2.92% and the limits of agreement were from 11% to –5.2%. There was a moderate correlation between ScvO2 and NIRSc (r = 0.45), (P = 0.001). The mean bias between ScvO2 and NIRSc was 2.7% and the limits of agreement were from +26% to –20%.ConclusionIn this study, we found a strong correlation between ScvO2 and NIRS measurements taken from the internal jugular vein site. Accordingly, continuous noninvasive monitoring with transcutaneous NIRSijv can be an alternative method as a trend monitor for the central venous oxygen saturation in pediatric cardiac patients undergoing congenital cardiac surgery.

Spinal cord perfusion protection for thoraco-abdominal aortic aneurysm surgery.

Spinal cord ischemia (SCI) is a devastating complication after open or endovascular aortic repair for thoracoabdominal aortic disease. The underlying pathogenesis is not fully understood but appears multifactorial. Multiple spinal cord protection strategies and monitoring techniques are currently utilized with variable results seen. The purpose of this review is to summarize important and recent findings related to cause, monitoring and impact of multiple spinal cord protection strategies. Recent data suggests collateral blood flow as the major determinant of spinal cord perfusion instead of individual intercostal vessels, potential role of transcutaneous near-infrared spectroscopy for monitoring of spinal cord perfusion and positive impact of implementing multimodal spinal cord protection strategies on reducing the risk of SCI. SCI leading to paraplegia is a multifactorial complication that remains a major concern in complex aortic surgeries. Although there are no sufficient data to document the efficacy of spinal cord protection techniques individually, their effect on lowering the risk of SCI is most evident when used concomitantly using a multimodal approach that encompasses the perioperative and early postoperative period.

Prospective Evaluation of Predictors of Testis Atrophy After Surgery for Testis Torsion in Children

To prospectively correlate pain duration, red scrotal skin, ultrasound appearance of testis, and intraoperative testis color to future testis atrophy after acute testicular torsion. Patients 2 months-18 years old with unilateral acute scrotum were consecutively enrolled in a National Institutes of Health transcutaneous near-infrared spectroscopy study, with a subgroup analysis of the true torsion group. Presence or absence of red scrotal skin, pain duration, testicular heterogeneity on preoperative ultrasound, and intraoperative testis color based on a novel visual chart 5 minutes after detorsion were recorded. All testes underwent orchiopexy regardless of appearance. Percent volume difference between normal and torsed testicles on follow-up ultrasound was compared between patients with and without risk factors. Thirty of 56 patients who had surgical detorsion underwent scrotal ultrasound at a mean of 117 days after surgery. A color of black or hemorrhagic 5 minutes after detorsion, pain duration >12 hours, and heterogeneous parenchyma on preoperative ultrasound were associated with significant testis volume loss in follow-up compared with normal testis. All patients with a black or hemorrhagic testis had >80% volume loss. Erythematous scrotal skin was not significantly associated with smaller affected testis volume in follow-up. Based on the high atrophy rate, orchiectomy can be considered for testes that are black or hemorrhagic 5 minutes after detorsion. Pain duration >12 hours and parenchymal heterogeneity on preoperative ultrasound were also associated with testis atrophy. Red scrotal skin was not a reliable predictor of atrophy and should not delay exploration.

Can transcutaneous near infrared spectroscopy detect severe hepatic ischemia: a juvenile porcine model.

Vascular complications following pediatric liver transplantation occur in 8-10% of cases, and no continuous, non-invasive monitoring for this problem exists. Near infrared spectroscopy (NIRS) allows non-invasive, continuous, transcutaneous assessment of hemoglobin oxygenation (StO2 ) 1-4 cm below the skin surface. We hypothesized that transcutaneous NIRS would be able to detect severe hepatic ischemia, and tested this in an animal model using 15-20 kg and 5-7 kg juvenile pigs. Direct liver surface and transcutaneous hepatic tissue hemoglobin oxygen saturation (StO2 ) were measured during occlusions of the hepatic artery and portal vein. Changes in hepatic delivery of oxygen (HepDO2 ) were calculated for each ischemic challenge and compared to changes in direct liver surface (DirHepStO2 ) and transcutaneous liver StO2 measurements (CutHepStO2 ). In the 15-20 kg animals during complete occlusion, CutHepStO2 decreased by 6.0(±4.9)%, whilst DirHepStO2 decreased by 83.7(±7.2)%. In the 5-7 kg animals during complete occlusion, CutHepStO2 decreased by 27.4(±8.5)%, whilst DirHepStO2 decreased by 82.8(±4.6)%. Transcutaneous hepatic StO2 monitoring cannot reliably detect severe hepatic ischemia in a juvenile porcine model, although a stronger and potentially useful signal is seen in 5-7 kg pigs. Trials of this technology should be currently restricted to situations where the organ is less than 1 cm from the skin surface, corresponding to infants of <10 kg.

Transcutaneous near-infrared spectroscopy for monitoring spinal cord ischemia: an experimental study in swine.

We aimed to assess the ability of near-infrared spectroscopy (NIRS) to detect spinal cord ischemia, and to evaluate changes in regional oxygen saturation (rSO2) following recovery of spinal cord circulation and cerebrospinal fluid drainage. Four 12-month-old female swine weighing 28.7-29.5kg were acquired for this study. NIRS probes were placed along the midline of the upper (T6/7) and lower (T9/T10) thoracic vertebrae. The thoracic aorta was clamped distal of the left subclavian artery to induce spinal ischemia. Aortic cross-clamping was maintained for 30min. Fifteen minutes after aortic de-clamping, the cerebrospinal fluid drainage catheter was opened to air, and cerebrospinal fluid drainage was initiated. Following aortic clamping, rSO2 in both upper and lower regions of the spinal cord decreased by 15% within 5min and by 20% within 10min (relative change). After aortic de-clamping, rSO2 values in both regions returned to baseline within 5min. No changes in rSO2 in either the upper or lower vertebrae were observed following initiation of cerebrospinal fluid drainage. Histological analysis revealed that ischemic changes had occurred in all spinal levels. NIRS may be used to detect decreases in and recovery of spinal cord circulation following aortic clamping and de-clamping, whereas it may not reflect minor changes in spinal cord circulation due to cerebrospinal fluid drainage. Further clinical studies are required to investigate the potential for NIRS as an index of spinal cord circulation.

Optical diagnosis of lower urinary tract infection: A pilot study in children

Conventionally, diagnosis of lower urinary tract infection (LUTI) is made on the basis of history, urine microscopy and culture. But there are limitations to this methodology especially in children and special populations where there is difficulty in obtaining a full history and details of clinical symptoms. The aim of this study was to determine if monitoring bladder wall oxygenation as a measure of bladder mucosal inflammation using transcutaneous near-infrared spectroscopy (NIRS) allows detection of the presence or absence of LUTI in children. A convenience sample of children referred to a pediatric urology clinic with an acute LUTI and a control group were studied. Diagnosis was confirmed by history, physical examination, laboratory investigations, and urine culture. Participants had transcutaneous measurement of an absolute measure of tissue oxygen saturation (TSI%) in their bladder wall, and a quadriceps muscle control site, using a spatially resolved (SR) wireless NIRS device. Average measures of bladder wall TSI% (B.TSI%) and quadriceps TSI% (Q.TSI%) and their differences (TSI.diff) were calculated and compared between those with LUTI and controls by performing a two-way repeated analysis of variance. Thirty-four patients met the inclusion criteria (LUTI n = 12 and controls n = 22). Comparing LUTI to controls B.TSI% and TSI.diff values were significantly higher in the LUTI group (p < 0.0001), while Q.TSI% values were not significantly different. Optical monitoring of bladder wall oxygenation is feasible in children. In this study a significant difference was evident in a SR NIRS-derived measure of absolute oxygen saturation in the bladder wall between children with UTI diagnosed by conventional testing methods, and those in a control group without infection. SR-NIRS monitoring of bladder wall oxygenation may offer a rapid and non-invasive means of bedside screening for LUTI where history and/or clinical signs are not available or adequate.

MP8-03 OPTICAL DIAGNOSIS OF LOWER URINARY TRACT INFECTION: A PILOT STUDY IN CHILDREN.

You have accessJournal of UrologyInfections/Inflammation of the Genitourinary Tract: Kidney & Bladder1 Apr 2014MP8-03 OPTICAL DIAGNOSIS OF LOWER URINARY TRACT INFECTION: A PILOT STUDY IN CHILDREN. Babak Shadgan, A.M. Kajbafzadeh, Lynn Stothers, Macnab Andrew, and Mark Nigro Babak ShadganBabak Shadgan More articles by this author , A.M. KajbafzadehA.M. Kajbafzadeh More articles by this author , Lynn StothersLynn Stothers More articles by this author , Macnab AndrewMacnab Andrew More articles by this author , and Mark NigroMark Nigro More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2014.02.346AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Lower urinary tract infection (LUTI) is a common and important urological condition that requires early diagnosis and treatment. Diagnosis is based on history and clinical symptoms confirmed by positive urine culture, which although feasible for the general population, it is not readily applicable in young children and individuals with neurogenic bladder where a reliable history and changes in sensation are lacking. As UTI-induced bladder inflammation is associated with an increase in perfusion and oxygen consumption, an optical method akin to oximetry capable of detecting changes in bladder oxygenation could provide early detection of LUTI. OBJECTIVE To determine if monitoring bladder oxygenation as a measure of bladder mucosal inflammation using transcutaneous near-infrared spectroscopy (NIRS) allows detection of the presence or absence of LUTI in children. METHODS A convenience sample of children referred to a pediatric urology clinic with an acute LUTI, and a control group, were studied. Diagnosis was confirmed by history, physical examination, laboratory investigations and culture. Participants had transcutaneous measurement of an absolute measure of tissue oxygen saturation (TSI%) in their bladder wall, and a quadriceps muscle control site, using a wireless NIRS device. RESULTS Thirty-four patients met the inclusion criteria (LUTI n=12 and controls n=22). Comparing LUTI to controls B.TSI% and TSI.diff values were significantly higher in the LUTI group (p<0.0001), while Q.TSI% values were not significantly different. CONCLUSIONS NIRS optical monitoring of an absolute measure of bladder wall oxygenation (TSI%) may offer a means of screening for LUTI where history and/or clinical signs are not available or adequate. Non UTI Group UTI Group Significance Q.TSI% Mean 67.9 70.4 P=0.20 SD (+ -) 6.5 5.4 Range 56.2-78.9 60.7-75.6 B.TSI% Mean 66.8 80.8 p=< 0.0001 SD (+ -) 7.3 5.9 Range 49.1-77.1 70.5-89.9 TSI diff Mean -1.1 10.4 P< 0.0001 SD (+ -) 3 3.9 Range -5.8-2.6 5.2-16.7 © 2014FiguresReferencesRelatedDetails Volume 191Issue 4SApril 2014Page: e75 Advertisement Copyright & Permissions© 2014MetricsAuthor Information Babak Shadgan More articles by this author A.M. Kajbafzadeh More articles by this author Lynn Stothers More articles by this author Macnab Andrew More articles by this author Mark Nigro More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Effect of cerebral circulatory arrest on cerebral near‐infrared spectroscopy in pediatric patients

The aim was to investigate whether cerebral transcutaneous near-infrared spectroscopy (NIRS) or two-site NIRS is a suitable monitoring tool to detect or confirm a cerebral circulatory arrest in pediatric intensive care unit (PICU) patients. Prospective single-center pediatric observational study. Simultaneous NIRS measurements over forehead (cNIRS, crS02) and kidney (rNIRS, rrSO2), at the same time, the cardiac output were determined by transthoracic echocardiography. Area under the curve (AUC) in the receiver-operating curve (ROC) was analyzed for NIRS regarding cerebral circulatory arrest. There were two groups of patients (weight 2.1-73 kg): Group A: patients with intact cerebral perfusion (n = 36). Group B: patients with cerebral circulatory arrest (n = 8) proven by Doppler ultrasound scan or perfusion scintigraphy. There was no difference in cardiac output between the groups. PICU mortality for Group A was 3/36 (8.3%), for Group B 8/8, (100%). Mean cNIRS values were significantly higher with 68.92 (SEM = 2.54, SD = 15.25) in Group A compared with 34.63 (SEM = 5.36, SD = 15.15) in Group B (P < 0.001). ROC analysis for cNIRS detecting cerebral circulatory arrest was significant (AUC 0.948, 95% confidence interval 0.876-1.000, SE = 0.037, P < 0.001). Discrimination was optimal at 46 for cNIRS, at 36.5 for the difference rNIRS-cNIRS and at 0.5646 for the quotient cNIRS/rNIRS. The probability of a cerebral circulatory arrest was 77.8% (cNIRS) and 87.5% (combinations of cNIRS and rNIRS) at these cutoffs. cNIRS did detect cerebral circulatory arrest with high sensitivity. Specificity was, however, not high enough to confirm a cerebral circulatory arrest.

Pressures, Flow, and Brain Oxygenation During Plateau Waves of Intracranial Pressure

Plateau waves are common in traumatic brain injury. They constitute abrupt increases of intracranial pressure (ICP) above 40 mmHg associated with a decrease in cerebral perfusion pressure (CPP). The aim of this study was to describe plateau waves characteristics with multimodal brain monitoring in head injured patients admitted in neurocritical care. Prospective observational study in 18 multiple trauma patients with head injury admitted to Neurocritical Care Unit of Hospital Sao Joao in Porto. Multimodal systemic and brain monitoring of primary variables [heart rate, arterial blood pressure, ICP, CPP, pulse amplitude, end tidal CO₂, brain temperature, brain tissue oxygenation pressure, cerebral oximetry (CO) with transcutaneous near-infrared spectroscopy and cerebral blood flow (CBF)] and secondary variables related to cerebral compensatory reserve and cerebrovascular reactivity were supported by dedicated software ICM+ ( www.neurosurg.cam.ac.uk/icmplus) . The compiled data were analyzed in patients who developed plateau waves. In this study we identified 59 plateau waves that occurred in 44% of the patients (8/18). During plateau waves CBF, cerebrovascular resistance, CO, and brain tissue oxygenation decreased. The duration and magnitude of plateau waves were greater in patients with working cerebrovascular reactivity. After the end of plateau wave, a hyperemic response was recorded in 64% of cases with increase in CBF and brain oxygenation. The magnitude of hyperemia was associated with better autoregulation status and low oxygenation levels at baseline. Multimodal brain monitoring facilitates identification and understanding of intrinsic vascular brain phenomenon, such as plateau waves, and may help the adequate management of acute head injury at bed side.

Validation of transcutaneous NIRS monitoring of bladder hemodynamics and oxygenation using a rabbit model

Transcutaneous near infrared spectroscopy (NIRS) is a recognized means of non-invasively monitoring changes in the concentration of oxygenated and deoxygenated hemoglobin in tissue. However in applications of this technique to the bladder, because the combined thickness of the detrusor muscle and the wall of the organ is only a few millimeters, the question arises whether the trends and variations in hemoglobin concentration detected transcutaneously reflect physiologic changes occurring in the detrusor or are influenced by the effect of overlying tissue on the NIRS signal. In this study a rabbit model was used so that NIRS data could be collected transcutaneously and then with the optical probe applied directly the anterior bladder wall after surgical exposure of the organ, and the data compared. Studies were done with an Oxymon dual channel spectrometer on 6 anaesthetized New Zealand white rabbits using interop- tode distances adjusted for the two measurement sites, a consistent bladder filling and emptying protocol, and exposure to a brief period of controlled hypoxia (oxygen saturation decrease to 80%). Consistent data were obtained from transcutaneous and direct bladder wall measurements which confirms that transcutaneous NIRS monitoring does reflect changes occurring within the detrusor muscle in the anterior bladder wall. Hence, transcutaneous monitoring in humans using appropriate methodology and inter-optode spacing can be expected to avoid any potentially con- founding signals from tissues in the abdominal wall overlying the bladder.

Blood flow index using near-infrared spectroscopy and indocyanine green as a minimally invasive tool to assess respiratory muscle blood flow in humans

Near-infrared spectroscopy (NIRS) in combination with indocyanine green (ICG) dye has recently been used to measure respiratory muscle blood flow (RMBF) in humans. This method is based on the Fick principle and is determined by measuring ICG in the respiratory muscles using transcutaneous NIRS in relation to the [ICG] in arterial blood as measured using photodensitometry. This method is invasive since it requires arterial cannulation, repeated blood withdrawals, and reinfusions. A less invasive alternative is to calculate a relative measure of blood flow known as the blood flow index (BFI), which is based solely on the NIRS ICG curve, thus negating the need for arterial cannulation. Accordingly, the purpose of this study was to determine whether BFI can be used to measure RMBF at rest and during voluntary isocapnic hyperpnea at 25, 40, 55, and 70% of maximal voluntary ventilation in seven healthy humans. BFI was calculated as the change in maximal [ICG] divided by the rise time of the NIRS-derived ICG curve. Intercostal and sternocleidomastoid muscle BFI were correlated with simultaneously measured work of breathing and electromyography (EMG) data from the same muscles. BFI showed strong relationships with the work of breathing and EMG for both respiratory muscles. The coefficients of determination (R(2)) comparing BFI vs. the work of breathing for the intercostal and sternocleidomastoid muscles were 0.887 (P < 0.001) and 0.863 (P < 0.001), respectively, whereas the R(2) for BFI vs. EMG for the intercostal and sternocleidomastoid muscles were 0.879 (P < 0.001) and 0.930 (P < 0.001), respectively. These data suggest that the BFI closely reflects RMBF in conscious humans across a wide range of ventilations and provides a less invasive and less technically demanding alternative to measuring RMBF.

Transcutaneous near-infrared spectroscopy for detection of regional spinal ischemia during intercostal artery ligation: Preliminary experimental results

Real-time information about regional spinal cord ischemia can guide intraoperative management and reduce the risk of paraplegia after thoracic aortic surgery. We hypothesized that near-infrared spectroscopy could provide such information during intercostal and lumbar artery ligation in pigs. Transcutaneous near-infrared spectroscopic sensors were placed in the midline over the upper and lower thoracic vertebrae of 4 progressively larger pigs (weight range 21-70 kg). After the entire aorta was exposed, segmental arteries from T6 through L1 were sequentially ligated while regional oxygen saturation was monitored. Decreases in regional oxygen saturation were calculated as percentage changes from baseline. The degrees of ischemia in the upper and lower spinal cord were compared histopathologically. Baseline regional oxygen saturations were similar in the upper (68.8% +/- 9.0%) and lower (68.0% +/- 11.5%, P = .82) cord. After ligation, however, regional oxygen saturation levels were significantly lower in the lower cord (41.3% +/- 10.1%) than in the upper cord (64.8% +/- 9.3%, P = .037). The regional oxygen saturation had decreased by 39.0% +/- 11.5% in the lower cord but only by 6.3% +/- 7.6% in the upper cord (P = .026). This difference was confirmed microscopically: upper-cord sections had fewer ischemic neurons (8.8 +/- 9.4) than did lower-cord sections (21.3 +/- 13.6, P = .002). Intraoperative spinal cord ischemia was detectable with near-infrared spectroscopy in pigs weighing as much as 70 kg. The potential utility of this technique in patients undergoing thoracic aortic surgery warrants investigation.

Tissue oxygenation monitoring during major pediatric surgery using transcutaneous liver near infrared spectroscopy

The aim of the study was to compare liver tissue oxygenation determined by near infrared spectroscopy (NIRS) with central venous oxygen saturation (SvO(2)) and intestinal perfusion as measured by gastric intramucosal pH (pHi) in pediatric surgical patients. Twenty children undergoing craniofacial surgery with expected major intraoperative blood loss were studied. NIRS tissue oxygenation index (TOI(Liver)) and pHi values were recorded. Arterial blood gas analysis and SvO(2) were assessed from periodically taken blood samples. Data are presented as ranges (median) and were compared using linear regression analysis. Sensitivity and specificity of the intra-individual changes in TOI(Liver) to predict falling SvO(2) or pHi values were calculated. Patients age ranged from 0.79 to 8.27 years (1.92 years). TOI(Liver) ranged from 41.5 to 77.4% (61.5%), gastric pHi from 7.13 to 7.60 (7.37) and SvO(2) from 51 to 86% (74%). Among patients only moderate correlation was found between TOI(Liver) and SvO(2) (r = 0.594, P < 0.0001) and gastric pH(i) (r = 0.502, P < 0.0001). Intra-individual measured TOI(Liver) values, however, demonstrated close correlation with SvO(2) values (r = 0.680 to 0.976) but a varying correlation with gastric pHi values (r = 0.055 to 0.972). Sensitivity/specificity of TOI(Liver) to predict decreasing SvO(2) or gastric pHi values were 76.4/73.4% and 67.4/62.7% respectively. TOI(Liver) provided a better trend monitor of central venous oxygen saturation than gastric intramucosal pH. Because of its limited sensitivity and specificity to indicate deterioration of SvO(2), liver tissue oxygenation measured by transcutaneous NIRS does not provide additional practical information for clinical management.

Transcutaneous glucose measurement using near-infrared spectroscopy during hypoglycemia.

To analyze a transcutaneous near-infrared spectroscopy system as a technique for in vivo noninvasive blood glucose monitoring during euglycemia and hypoglycemia. Ten nondiabetic subjects and two patients with type 1 diabetes were examined in a total of 27 studies. In each study, the subject's plasma glucose was lowered to a hypoglycemia level (approximately 55 mg/dl) followed by recovery to a glycemic level of approximately 115 mg/dl using an intravenous infusion of insulin and 20% dextrose. Plasma glucose levels were determined at 5-min intervals by standard glucose oxidase method and simultaneously by a near-infrared spectroscopic system. The plasma glucose measured by the standard method was used to create a calibration model that could predict glucose levels from the near-infrared spectral data. The two data sets were correlated during the decline and recovery in plasma glucose, within 10 mg/dl plasma glucose ranges, and were examined using the Clarke Error Grid Analysis. Two sets of 1,704 plasma glucose determinations were examined. The near-infrared predictions during the fall and recovery in plasma glucose were highly correlated (r = 0.96 and 0.95, respectively). When analyzed during 10 mg/dl plasma glucose segments, the mean absolute difference between the near-infrared spectroscopy method and the chemometric reference ranged from 3.3 to 4.4 mg/dl in the nondiabetic subjects and from 2.6 to 3.8 mg/dl in the patients with type 1 diabetes. Using the Error Grid Analysis, 97.7% of all the near-infrared predictions were assigned to the A-zone. Our findings suggest that the near-infrared spectroscopy method can accurately predict plasma glucose levels during euglycemia and hypoglycemia in humans.