Decrease In Tissue Oxygenation Index Research Articles

Cerebral tissue oxygenation response to brain irradiation measured during clinical radiotherapy.

Cancer therapy treatments produce extensive changes in the physiological and morphological properties of tissues, which are also individual dependent. Currently, a key challenge involves developing more tailored cancer therapy, and consequently, individual biological response measurement during therapy, such as tumor hypoxia, is of high interest. This is the first time human cerebral haemodynamics and cerebral tissue oxygenation index (TOI) changes were measured during the irradiation in clinical radiotherapy and functional near-infrared spectroscopy (fNIRS) technique was demonstrated as a feasible technique for clinical use in radiotherapy, based on 34 online patient measurements. Our aim is to develop predictive biomarkers and noninvasive real-time methods to establish the effect of radiotherapy during treatment as well as to optimize radiotherapy dose planning for individual patients. In particular, fNIRS-based technique could offer an effective and clinically feasible online technique for continuous monitoring of brain tissue hypoxia and responses to chemo- and radiotherapy, which involves modulating tumor oxygenation to increase or decrease tumor hypoxia. We aim to show that fNIRS is feasible for repeatability measuring in patient radiotherapy, the temporal alterations of tissue oxygenation induced by radiation. Fiber optics setup using multiwavelength fNIRS was built and combined with a medical linear accelerator to measure cerebral tissue oxygenation changes during the whole-brain radiotherapy treatment, where the radiation dose is given in whole brain area only preventing dosage to eyes. Correlation of temporal alterations in cerebral haemodynamics and TOI response to brain irradiation was quantified. Online fNIRS patient measurement of cerebral haemodynamics during clinical brain radiotherapy is feasible in clinical environment, and results based on 34 patient measurements show strong temporal alterations in cerebral haemodynamics and decrease in TOI during brain irradiation and confirmed the repeatability. Our proof-of-concept study shows evidently that irradiation causes characteristic immediate changes in brain tissue oxygenation. In particular, TOI seems to be a sensitive parameter to observe the tissue effects of radiotherapy. Monitoring the real-time interactions between the subjected radiation dose and corresponding haemodynamic effects may provide important tool for the researchers and clinicians in the field of radiotherapy. Eventually, presented fNIRS technique could be used for improving dose planning and safety control for individual patients.

Physiological Responses to Intermittent Endurance Exercise with Blood Flow Restriction in the Moderate Intensity Domain

Blood flow restriction (BFR) endurance training may induce both endurance and strength improvements. However, there is no consensus on the ideal BFR endurance exercise prescription in order to balance the physiological and perceptual responses. PURPOSE: The purpose of this investigation was to examine the physiological responses, as well as the perceived exertion in responses to a range of BFR endurance protocols. METHODS: Participants randomly performed 7 exercise protocols: 50% of the difference between peak oxygen uptake (VO2) and ventilatory threshold (VT) (∆50%), 90%, 80%, and 70% of VT with and without BFR. Each protocol consisted of two sets of five work intervals (2 minutes work, 1 minute rest) separated by 5 minutes of recovery. Pulmonary VO2 was recorded breath-by-breath, muscle activation (vastus medialis (VM), vastus lateralis (VL)) was assessed by surface electromyography (sEMG), microvascular oxygenation (tissue oxygenation index (TOI)) was assessed by near-infrared spectroscopy (NIRS), and level of perceived exertion (RPE) was assessed using the Borg scale. The last 30 seconds of intervals 5 and 10 were used for analysis. sEMG data were normalized to baseline cycling (20 watts). TOI during each condition was analyzed compared to baseline cycling and then expressed as change from baseline (arbitrary units) to compare between conditions. RESULTS: The ∆50% protocol resulted in a higher end exercise (interval 10) VO2 compared to all other conditions, no other differences in VO2 were observed. No sEMG differences were observed between conditions (VL- p = 0.24, VM- p = 0.33) or between interval 5 and 10. All BFR conditions resulted in a decrease in TOI from baseline. TOI was greater for all BFR conditions (70%BFR = -36.4 ± 21.9, 80%BFR = -40.4 ± 6.5, 90%BFR = -44.7±7.25) compared to the non-BFR conditions (70% = +4.3 ± 20.2, 80% = +11.8 ± 5.5, 90% = +7.25). No differences in TOI between ∆50 (-36.93 ± 10.8) and any BFR conditions were observed. RPE was greater during 90%BFR (18.0 ± 0) and 80%BFR (17.1 ± 1.1) compared to 70% (11.3 ± 0.6) and 90% (13.0 ± 0). No differences were observed between 70%BFR (14.6 ± 0.6) and non-BFR conditions. CONCLUSION: This study demonstrated that cycling with the addition of BFR at an intensity equivalent to 70% of VT may provide a balance between physiological strain and perceived exertion.

Prophylactic infusion of phenylephrine is effective in attenuating the decrease in regional cerebral blood volume and oxygenation during spinal anesthesia for cesarean section

BackgroundHypotension induced by spinal anesthesia for cesarean section causes a decrease in maternal regional cerebral blood volume and oxygenation. We used near-infrared spectroscopy to determine whether prophylactic infusion of phenylephrine attenuates these decreases. MethodsSixty patients undergoing bupivacaine spinal anesthesia for cesarean section were randomly divided into one of three intravenous infusion groups: saline (P0), phenylephrine 25 (P25) or 50 µg/min (P50). Mean arterial pressure, heart rate and near-infrared spectroscopy measurements were made at one-minute intervals for 20 minutes, and oxyhemoglobin, deoxy-hemoglobin and total-hemoglobin concentrations and tissue oxygenation index were determined. Mean changes in the values between baseline and each measurement time after intrathecal injection were compared. ResultsSignificant decreases in mean arterial pressure were seen in group P0 compared to P25 and P50 (P <0.01). Heart rate decreased in a dose-dependent manner during phenylephrine infusion (P0 vs. P25 and P50, P25 vs. P50; P <0.05). Significantly higher total-hemoglobin levels were observed in the phenylephrine groups versus the P0 group (P <0.01). The largest decrease in tissue oxygenation index was found in the P50, followed by P0 and P25 groups (P0 vs. P25 and P50, P25 vs. P50; P <0.05). ConclusionProphylactic infusion of phenylephrine, especially at 25 µg/min, can effectively suppress decreases in regional cerebral blood volume and regional cerebral blood oxygenation after induction of spinal anesthesia for cesarean section.

Characterizing the profile of muscle deoxygenation during ramp incremental exercise in young men

This study characterized the profile of near-infrared spectroscopy (NIRS)-derived muscle deoxygenation (Δ[HHb]) and the tissue oxygenation index (TOI) as a function of absolute (PO(ABS)) and normalized power output (%PO) or oxygen consumption (%VO(2)) during incremental cycling exercise. Eight men (24 ± 5 year) each performed two fatigue-limited ramp incremental cycling tests (20 W min(-1)), during which pulmonary VO(2), Δ[HHb] and TOI were measured continuously. Responses from the two tests were averaged and the TOI (%) and normalized Δ[HHb] (%Δ[HHb]) were plotted against %VO(2), %PO and PO(ABS). The overall responses were modelled using a sigmoid regression (y = f ( 0 ) + A/(1 + e(-(-c+dx)))) and piecewise 'double-linear' function of the predominant adjustment of %Δ[HHb] or TOI observed throughout the middle portion of exercise and the 'plateau' that followed. In ~85% of cases, the corrected Akaike Information Criterion (AIC(C)) was smaller (suggesting one model favoured) for the 'double-linear' compared with the sigmoid regression for both %Δ[HHb] and TOI. Furthermore, the f ( 0 ) and A estimates from the sigmoid regressions of %Δ[HHb] yielded unrealistically large projected peak (f ( 0 ) + A) values (%VO(2p) 114.3 ± 17.5; %PO 113.3 ± 9.5; PO(ABS) 113.5 ± 9.8), suggesting that the sigmoid model does not accurately describe the underlying physiological responses in all subjects and thus may not be appropriate for comparative purposes. Alternatively, the present study proposes that the profile of %Δ[HHb] and TOI during ramp incremental exercise may be more accurately described as consisting of three distinct phases in which there is little adjustment early in the ramp, the predominant increase in %Δ[HHb] (decrease in TOI) is approximately linear and an approximately linear 'plateau' follows.

Do Changes In Vastus Lateralis Muscle Oxygenation Reflect The Leg Vascular Response To Sympathetic Stimulation?

Changes in local muscle oxygenation, measured by near-infrared spectroscopy (NIRS), have been used to assess the vascular response to sympathetic stimulation. Changes in muscle oxygenation have been shown to reflect changes in forearm vascular resistance. If such a relationship existed in the leg, NIRS derived muscle oxygenation could potentially be used as an index of the vascular response to sympathetic stimulation during large muscle mass dynamic exercise in humans. PURPOSE: To determine whether changes in vastus lateralis muscle oxygenation reflect changes in femoral vascular resistance during sympathetic stimulation. METHODS: Healthy, male volunteers (mean ± SD; Age: 25 ± 3 yrs; Height: 175 ± 4 cm; Body Mass: 76 ± 13 kg; n=6) performed a cold-pressor test (CPT) on 3 separate occasions with at least 24 hours between tests. After a 5 min supine baseline period, subjects placed their hand in ice water (-1°C) for 5 min, followed by a 5 min recovery period. Mean arterial pressure (MAP) was calculated on a beat-by-beat basis from the blood pressure waveform using finger photoplethysmography (Finometer; Finapres Medical Systems). Femoral artery blood flow was measured continuously via Doppler ultrasound (Vivid-I; GE Medical). Femoral vascular resistance (FVR; mmHg·mL·min-1) was calculated. Vastus lateralis muscle oxygenation (Tissue oxygenation index (TOI); %) was determined by NIRS (Hamamatsu Photonics, NIRO 200). CPT trials were time-aligned and averaged and the peak response of each variable was calculated as a percent change from the supine baseline value. Differences between the peak changes in TOI and FVR were determined by T-test, whereas the relationship between variables was determined by Pearson Product correlation. RESULTS: The peak decrease in TOI (13 ± 5 %) was significantly lower (p<0.001) than the peak increase in FVR (133 ± 73%). Additionally, the change in TOI was not correlated with the change in FVR (r=0.275, p=0.60). CONCLUSION: These data indicate that the changes in vastus lateralis muscle oxygenation do not reflect the leg vascular response to sympathetic stimulation. Supported by NSERC, Canada.

Cerebral Oxygenation Is Depressed During Sleep in Healthy Term Infants When They Sleep Prone

Prone sleeping is a major risk factor for the sudden infant death syndrome and is associated with lower blood pressure and impaired arousability from sleep, both of which may be signs of cerebral hypoxia. However, the impact of sleep position on cerebral oxygenation during infancy remains unknown. We assessed the effects of sleeping position, sleep state, and postnatal age on cerebral oxygenation by measuring tissue oxygenation index (TOI) during the first 6 months of infancy. Seventeen healthy term infants (8 girls and 9 boys) were recruited as study participants. Infants were studied at ages 2 to 4 weeks, 2 to 3 months, and 5 to 6 months by use of daytime polysomnography, with additional measurements of blood pressure (Finometer, FMS Finometer Medical Systems, Amsterdam, Netherlands) and tissue oxygenation index (TOI) (NIRO 200 spectrophotometer, Hamamatsu Photonics KK, Tokyo, Japan). In infants who slept in the prone position, TOI was lower in both quiet sleep (QS) and active sleep (AS) at age 2 to 4 weeks and in QS at age 2 to 3 months (P < .05). TOI was lower in AS compared with QS in infants aged 2 to 4 weeks (P < .05). When the infants reached 5 to 6 months of age, TOI was greater in AS (P < .05), as there was a profound decrease in TOI during QS (P < .05) over this period. No relationship was identified between blood pressure and TOI at any age. In healthy infants cerebral oxygenation is reduced during sleep in the prone position. This reduction may underpin the reduced arousability from sleep exhibited by healthy infants who sleep prone, a finding that provides new insight into potential risks of prone sleeping and mechanisms of sudden infant death syndrome.

Vastus lateralis oxygenation dynamics during maximal fatiguing concentric and eccentric isokinetic muscle actions

The present study aimed to assess whether high intensity exhaustive eccentric (ECC) exercise was associated with a greater decrease in muscle oxygenation compared to high intensity exhaustive concentric (CON) exercise during maximal isokinetic knee extensions. On two separate days, ten recreationally active participants performed maximal isokinetic concentric (KE CON) and eccentric (KE ECC) knee extension exercises at 60° s −1 until exhaustion. Muscle oxygenation profile and activity were acquired continuously from the vastus lateralis (VL) muscle using near-infrared spectroscopy, along with surface electromyography (sEMG). The torque output was significantly greater during KE ECC ( P < 0.01). Total time to exhaustion was longer in ECC condition ( P < 0.01). The decrease in tissue oxygenation index observed between the beginning and end-exercise values was significantly greater during KE ECC than during KE CON ( P < 0.05) while total haemoglobin volume did not differ significantly. KE ECC resulted in a significant increase in end-exercise integrated sEMG ( P < 0.05). We propose that the associated higher intramuscular pressure may have compressed blood vessels and led to a greater decrease in tissue oxygenation index. The observed end-exercise increase in neural drive during KE ECC may have occurred to prevent from muscle performance decrease. These results suggest that, over time, repeated maximal ECC actions induce a greater O 2 extraction compared to maximal CON actions.

319 Effects of Blood Sampling on Cerebral Tissue Oxygenation Index (TOI) in VLBW Infants: Venepuncture Versus Heel Lance

Background and aims: In term neonates venepuncture is considered less painful than heel lance for blood sampling. Here, we compared the effects of venepuncture and heel lance blood sampling in preterm infants < 1500 g birth weight. Methods: Twenty infants (median [range] birth weight 855 [355 - 1470] g, gestational age 28 [24 - 32] weeks) were studied during sequentially performed venepuncture and heel lance blood sampling. Heart rate and arterial oxygen saturation were registered continuously. Cerebral tissue oxygenation index (TOI) was measured by near infrared spectroscopy. Cerebral fractional oxygen extraction (FOE) was calculated. Results: During both procedures, heart rate increased and TOI decreased significantly. The decrease in TOI was significantly larger during venepuncture (from 64 [45-99]% to 57 [47-95%]) than during heel lance blood sampling (from 68 [51-99]% to 63 [47-99] %, p=0.05). Arterial oxygen saturation decreased and FOE increased during venepuncture only. Conclusions: Our results indicate that - in contrast to term neonates - for preterm infants venepuncture is more stressful than heel lance blood sampling.

Comparison between maximal lengthening and shortening contractions for biceps brachii muscle oxygenation and hemodynamics

Eccentric contractions (ECC) require lower systemic oxygen (O2) and induce greater symptoms of muscle damage than concentric contractions (CON); however, it is not known if local muscle oxygenation is lower in ECC than CON during and following exercise. This study compared between ECC and CON for changes in biceps brachii muscle oxygenation [tissue oxygenation index (TOI)] and hemodynamics [total hemoglobin volume (tHb)=oxygenated-Hb+deoxygenated-Hb], determined by near-infrared spectroscopy over 10 sets of 6 maximal contractions of the elbow flexors of 10 healthy subjects. This study also compared between ECC and CON for changes in TOI and tHb during a 10-s sustained and 30-repeated maximal isometric contraction (MVC) task measured immediately before and after and 1-3 days following exercise. The torque integral during ECC was greater (P<0.05) than that during CON by approximately 30%, and the decrease in TOI was smaller (P<0.05) by approximately 50% during ECC than CON. Increases in tHb during the relaxation phases were smaller (P<0.05) by approximately 100% for ECC than CON; however, the decreases in tHb during the contraction phases were not significantly different between sessions. These results suggest that ECC utilizes a lower muscle O2 relative to O2 supply compared with CON. Following exercise, greater (P<0.05) decreases in MVC strength and increases in plasma creatine kinase activity and muscle soreness were evident 1-3 days after ECC than CON. Torque integral, TOI, and tHb during the sustained and repeated MVC tasks decreased (P<0.01) only after ECC, suggesting that muscle O2 demand relative to O2 supply during the isometric tasks was decreased after ECC. This could mainly be due to a lower maximal muscle mass activated as a consequence of muscle damage; however, an increase in O2 supply due to microcirculation dysfunction and/or inflammatory vasodilatory responses after ECC is recognized.

Influence of external cardiac pacing on cerebral oxygenation measured by near-infrared spectroscopy in children after cardiac surgery

The brain of children in the early period after repair of congenital heart defects with cardiopulmonary bypass (CPB) may be more vulnerable to hemodynamic changes because of impaired cerebral autoregulation. During postoperative testing of the external temporary safety pacer, we performed desynchronizing ventricular pacing (VVI) while monitoring cerebral oxygenation using near-infrared spectroscopy (NIRS). We prospectively investigated 11 children (6 girls, 5 boys). Mean age was 6.1 months (+/-3.8 months) and mean weight: 5.3 kg (+/-1.5 kg). We performed measurements at four study steps: baseline I, VVI pacing, baseline II and atrial pacing (AOO) to exclude effects of higher heart rate. We continuously measured the effects on hemodynamic and respiratory parameters as well as on cerebral tissue oxygenation index (TOI). Hemoglobin difference (HbD) was calculated as a parameter for cerebral blood flow (CBF). Ventricular pacing leads to a significant decrease in arterial blood pressure and central venous saturation accompanied by an immediate and significant decrease in TOI (63.3% +/- 7.6% to 61.5% +/- 8.4% [P < 0.05]) and HbD (0.51 +/- 1.8 micromol.l(-1) to -2.9 +/- 4.7 micromol.l(-1) [P < 0.05]). Cardiac desynchronization after CPB seems to reduce CBF and cerebral oxygenation in children.

The Effect on Cerebral Tissue Oxygenation Index of Changes in the Concentrations of Inspired Oxygen and End-Tidal Carbon Dioxide in Healthy Adult Volunteers

A variety of near-infrared spectroscopy devices can be used to make noninvasive measurements of cerebral tissue oxygen saturation (ScO2). The ScO2 measured by the NIRO 300 spectrometer (Hamamatsu Photonics, Japan) is called the cerebral tissue oxygenation index (TOI) and is an assessment of the balance between cerebral oxygen delivery and utilization. We designed this study to investigate the effect of systemic and intracranial physiological changes on TOI. Fifteen healthy volunteers were studied during isocapneic hyperoxia and hypoxemia, and normoxic hypercapnea and hypocapnea. Absolute cerebral TOI and changes in oxy- and deoxyhemoglobin concentrations were measured using a NIRO 300 spectrometer. Changes in arterial oxygen saturation (SaO2), ETCO2, heart rate, mean arterial blood pressure (MBP), and middle cerebral artery blood flow velocity (Vmca) were also measured during these physiological challenges. Changes in cerebral blood volume (CBV) were subsequently calculated from changes in total cerebral hemoglobin concentration. Baseline TOI was 67.3% with an interquartile range (IQR) of 65.2%-71.9%. Hypoxemia was associated with a median decrease in TOI of 7.1% (IQR -9.1% to -5.4%) from baseline (P < 0.0001) and hyperoxia with a median increase of 2.3% (IQR 2.0%-2.5%) (P < 0.0001). Hypocapnea caused a reduction in TOI of 2.1% (IQR -3.3% to -1.3%) from baseline (P < 0.0001) and hypercapnea an increase of 2.6% (IQR 1.4%-3.7%) (P < 0.0001). Changes in SaO2 (P < 0.0001), ETCO2 (P < 0.0001), CBV (P = 0.0003), and MBP (P = 0.03) were significant variables affecting TOI. Changes in Vmca (P = 0.7) and heart rate (P = 0.2) were not significant factors. TOI is an easy-to-monitor variable that provides real-time, multisite, and noninvasive assessment of the balance between cerebral oxygen delivery and utilization. However, TOI is a complex variable that is affected by SaO2 and ETCO2, and, to a lesser extent, by MBP and CBV. Clinicians need to be aware of the systemic and cerebral physiological changes that can affect TOI to interpret changes in this variable during clinical monitoring.

Use of the Liver Tissue Oxygenation Index as a Noninvasive Parameter of Intestinal Ischemia in Rabbits

The tissue oxygenation index (TOI), measured by spatially resolved spectroscopy (SRS), reflects the ratio between oxygenated and deoxygenated tissue hemoglobin. We investigated whether liver TOI is a noninvasive parameter for early detection of intestinal ischemia. In seven adult New Zealand rabbits the superior mesenteric artery (SMA) and vein were exposed by laparotomy. The SRS probe was attached at the skin above the liver to calculate the TOI. The bowel (SbO(2)) and peripheral (SpO(2)) oxygen saturation were continuously measured. The SMA was occluded, creating small bowel ischemia for 90 minutes. Then reperfusion was started for 1 hour. The median TOI and interquartile range (IQR) of the TOI were calculated. A paired Wilcoxon test was used to evaluate changes in the liver TOI and SpO(2) during ischemia and reperfusion. The median TOI was 54.3% (IQR 8) at the start of ischemia, 54.9% (IQR 9) after 30 minutes, 51% (IQR 11) after 60 minutes, and 50.3% (IQR 10) after 90 minutes. The median TOI values were 46.3% (IQR 5) after 30 minutes of reperfusion and 41.2% (IQR 5) after 60 minutes. The decrease in TOI became significant (p < 0.05) after 90 minutes of ischemia. The SpO(2) was stable during the experiment. A significant decrease in liver TOI was seen after 90 minutes of occlusion of the SMA and is likely to be the consequence of bowel ischemia. The further decrease after reperfusion might reflect reperfusion injury. Liver TOI may be a new tool for noninvasive early detection of intestinal ischemia and reperfusion. Further study is needed to confirm these findings.

Clinical application of cerebral oxygenation monitoring during aortic aneurysm operation

To analyze the correlation between cerebral oxygenation and cerebral complications after aortic aneurysm operation and to evaluate the protective effects of DHCA and/or ASCP during aortic aneurysm operation. Thirty patients with aortic aneurysm, 24 with Stanford type A dissection, 4 with Stanford type B dissection, 1 with degenerative aneurysm in ascending and arch aorta, and 1 with false aneurysm in thoraco-abdominal aorta, 23 males and 7 females, aged 44 +/- 12, underwent aorta operation with circulatory arrest were alternatively allocated to two groups: 22 patients underwent aortic arch replacement under deep hypothermic circulatory arrest (DHCA) plus antegrade selective cerebral perfusion (ASCP), and 8 patients underwent descending thoracic aorta replacement under DHCA only. There was no significant difference in the lowest core temperature, hematocrit at lowest core temperature, and velocity of rewarming between these 2 groups. Near-infrared spectroscopy (NIRS) was used to continuously monitor the cerebral tissue oxygenation index (TOI) percutaneously. The mean circulatory arrest time in the DHCA + ASCP group was 23.25 min, significantly longer than that of the DHCA group (16.67 min, P = 0.022). Cerebral complication occurred in 8 patients after aortic operation (complication group). The baseline TOI of the complication group was 70% +/- 5%, and the maximum decrease in TOI was 58% +/- 8%; and the baseline TOI of the non-complication group was 69% +/- 8%, and the maximum decrease in TOI was 55% +/- 8%; however, there were no significant differences between these 2 groups (both P > 0.05). The TOI decrease was more significant in the DHCA group than in the DHCA + ASCP group. During circulatory arrest, the levels of TOI were higher than the baseline level all along in the ASCP group and were lower than the baseline level 3 to 10 minutes after arrest in the DHCA group. The duration of TOI less than the baseline level in the DHCA group was significantly longer than that in the ASCP group. Mild decrease of TOI is not significantly correlated to the occurrence of complication. DHCA + ASCP is more effective in brain protection compared with only DHCA.

Cerebral ischemia caused by obstructed superior vena cava cannula is detected by near-infrared spectroscopy

Objective: Bicaval venous cannulation is being used with increasing frequency in neonates and infants to avoid circulatory arrest. However, superior vena cava (SVC) cannula obstruction may result in cerebral ischemia with no change in blood pressure or mixed venous O 2 saturation. The authors hypothesized that near-infrared spectroscopy (NIRS) would allow noninvasive detection of SVC cannula obstruction. Methods: Fifteen Yorkshire piglets (9.07 ± 0.20 kg) underwent total cardiopulmonary bypass (CPB) (100 mL/kg/min, pH-stat strategy, hematocrit of 20%) with ascending aortic and bicaval cannulations. Femoral arterial and SVC pressure were monitored as well as mixed venous O 2 saturation. NIRS monitoring of tissue oxygenation index (TOI) as well as oxyhemoglobin and deoxyhemoglobin (HHb) was undertaken. Animals were cooled to an esophageal temperature of 25°C over 20 minutes. CPB flow was reduced to 50 mL/kg/min for 20 minutes. Animals then underwent a 60-minute study period of continuous CPB at 50 mL/kg/min with manipulation of the SVC cannula: group 1, open; group 2, partial occlusion; and group 3, complete occlusion. Animals were rewarmed to 37°C at full flow with the SVC cannula open. Cerebral blood flow was assessed at onset of CPB, at end of cooling, at end of low flow, at end of SVC manipulation period, and at end of rewarming using radioactive microspheres. Results: CBF decreased to 27.9 ± 1.5 mL/min/100 g with complete occlusion ( p < 0.01 v group 1: 39.7 ± 1.9, group 2, 38.3 ± 2.0 mL/min/100 g) with no change in arterial pressure or mixed venous saturation. There were also significant differences in cerebral oxygen delivery between group 3 and other groups ( p < 0.01). SVC pressure increased to 19.5 ± 4.5 and 32.5 ± 3.1mmHg with partial and complete occlusion. NIRS indicated significant cerebral ischemia with a decrease in TOI ( p < 0.05; group 3 v group 1 and 2) and an increase in HHb ( p < 0.05; group 3 v group 1). At the end of the study, significant acidosis was found in group 3 compared with group 1 ( p < 0.05). Conclusion: SVC cannula obstruction causes cerebral ischemia with no change in blood pressure or venous oxygen saturation. In view of the difficulties and risks of CVP monitoring in babies, it is recommended to use other monitoring modalities such as NIRS to assess adequacy of cerebral perfusion if bicaval cannulation is used in neonates and infants.