Changes In HbO Research Articles

Cerebral oxygenation during cardiopulmonary bypass measured by near-infrared spectroscopy: Effects of hemodilution, temperature, and flow

Objective: To determine the effects of hemodilution, PaCO 2, PaO 2, arterial pressure, and temperature on cerebral oxygenation during mild hypothermic cardiopulmonary bypass (CPB). Participants: Fourteen patients electively scheduled for cardiac surgery. Interventions: Oxyhemoglobin (HbO 2), deoxyhemoglobin (Hb), hemoglobin differential (Hb-diff = HbO 2-Hb), and oxidized cytochrome aa 3 (CtO 2) were measured with nearinfrared spectroscopy (NIRS) during CPB. Results: With onset of CPB, a significant decrease in HbO 2(median, −4.55 μmol/L; 25th to 75th percentile, −5.5 to −3.1; p < 0.05), Hb-diff (median, −3.88 μmol/L; 25th to 75th percentile, −4.7 to −1.9; p < 0.05), and CtO 2 (median, −0.05 μmol/L; 25th to 75th percentile, −0.15 to 0; p < 0.001) occurred. The simultaneous decrease in arterial hemoglobin concentration (from 11.7 to 8.5 g/100 mL, p < 0.005) correlated significantly with changes in HbO 2 ( r 2 = 0.71; p < 0.001), Hb-diff( r 2 = 0.59; p < 0.005), and CtO 2 ( r 2 = 0.57; p < 0.005). After 24 minutes of CPB, the largest decline in HbO 2 (−5.03 μmol/L) and Hb-diff (−5.68 μmol/L) was recorded, whereas CtO 2 showed no changes during cooling. During CPB, Hb and Hb-diff significantly correlated with the duration of CPB, PaO 2 and PaCO 2. Conclusions: In early stages of CPB, a diminished cerebral oxygen supply was found, which may be caused by acute hemodilution. Despite an increased extraction of oxygen as demonstrated by the decrease in Hb-diff, cerebral energy balance reflected by CtO 2was maintained within a safe range during cooling. Because NIRS measures regional cerebral oxygenation, it is useful as an adjunct to global measures in the early noninvasive detection of cerebral hypoxia.

Quantitative assessment of changes in blood CO(2) tension mediated by the haldane effect.

Adequate assessment of circulatory and gas-exchange interactions may involve the quantification of the Haldane effect (HE) and of the changes in blood PCO(2) mediated by changes in Hb-O(2) saturation and O(2)-linked CO(2) binding. This is commonly prevented by the complexity of the involved calculations. To simplify the task, a large series of patient measurements has been processed by regression analysis, thus developing an accurate fit for this quantification (v-a) PCO(2)HE + 0.460 [(a-v) HbO(2)]0.999e0.015(PvCO(2))-0.852(Hct) (n = 247, r(2) = 0. 99, P << 0.001), where (v-a)PCO(2 HE) is the reduction in venous PCO(2) (Pv(CO(2)), Torr) allowed by the chemical binding of CO(2) in blood due to the HE (Torr), (a-v)HbO(2) is the arteriovenous difference in Hb-bound O(2) (ml/dl), and Hct is hematocrit fraction. Values of (v-a)PCO(2 HE) estimated by this expression compared well with the results of previously published experiments. This formula is useful in assessing the impact of HE on Pv(CO(2)) and venoarterial PCO(2) gradient and the survival advantage offered by HE in extreme conditions. Use may be extended to all investigative and clinical settings in which changes in blood O(2) saturation and O(2)-linked CO(2) binding must be converted into the corresponding changes in dissolved CO(2) and PCO(2).

Hemodynamic evaluation by using near infrared spectroscopy during carotid endarterectomy

To evaluate the hemodynamic changes during carotid endarterectomy, we compared changes in oxyhemoglobin levels with changes in the internal carotid artery flow and the somatosensory evoked potential (SEP). In 40 of 42 patients, the oxyhemoglobin level, measured in the frontal area on the operated side using near infrared spectroscopy (NIRS), decreased immediately after cross-clamping the internal carotid artery and returned to the preclamping level after the clamp was removed. There was no linear relationship between the internal carotid flow and the decrement in the oxyhemoglobin level after carotid clamping. Nineteen patients (45%) had a large internal carotid flow (> or =90 mL/min), but a small decrease in the oxyhemoglobin level (<0.04 in index); presumably these patients had adequate collateral circulation. Eight patients (19%) had a large internal carotid flow and a marked decrease in the oxyhemoglobin level (> or =0.04); presumably these patients had insufficient collateral circulation. The changes in oxyhemoglobin and SEP after carotid clamping agreed in 77.5% of the patients; however, in the other 22.5%, the disparity between the two factors indicated different causes of cerebral ischemia following carotid clamping. A marked decrease in oxyhemoglobin without a significant change in SEP suggests ischemia predominantly in the frontal area, whereas a small decrease in oxyhemoglobin and a significant change in SEP suggest ischemia predominantly in the somatosensory pathway or cortex. In conclusion, the relationship between the internal carotid flow and the change in HbO(2) provides information about the collateral circulation. Simultaneous monitoring of NIRS and SEP is useful for assessing of the pattern of cerebral ischemia during carotid clamping.

Effects of indomethacin and hyperventilation on cerebral hemodynamics and oxygenation in newborn piglets.

We investigated the effect of indomethacin (INDO) and hyperventilation (HV) on cerebral hemodynamics and oxygenation in newborn piglets using near-infrared spectroscopy (NIRS). A total of 10 piglets aged 7-10 days were divided into 2 groups. INDO (Experimental group; 0.2 mg/kg i.v.) or saline (Control group) was administered after steady state, then each group was hyperventilated (pCO2; 20 mm Hg). Cerebral oxyhemoglobin concentrations (HbO2) significantly decreased immediately after INDO administration compared to controls (p < 0.01). This decrease continued for 15 min. During HV, HbO2 remained low compared to the steady state (p < 0.05) in the experimental group. Total hemoglobin concentrations (HbT) decreased simultaneously with HbO2. In the control group, no changes in HbO2 or HbT were observed after saline administration, and only a slight decrease in HbO2 was observed during the 5 minutes' HV compared to the steady state. No changes in cytochrome aa3 (Cytaa3) were observed in either group during 100% O2 inhalation. We conclude that INDO decreased HbO2 and HbT by vasoconstriction, but that HV did not further aggravate this tendency. Great care should be taken when using INDO for newborn neonates.

Effects On Cerebral Perfusion Of Blood Withdrawal And Infusion Through The Umbelical Arterial (UAC) And Venous Catheters (UVC) In Preterm Infants† 1079

Objectives. To compare, using cerebral near-infrared spectroscopy (NIRS), the effects of blood withdrawal (W) and infusion (I) via, respectively, UAC with tip in the thoracic aorta and UVC. Method Twelve infants of 30 weeks (25-33) gestational age, 1175 g (760-1690) birth weight, mechanically ventilated for RDS were studied at 19 hours (2-25) postnatal age. The protocol involved W, through UAC of 3 ml/kg blood in 30 seconds, followed by I at the same rate, after recovery of the NIRS trace. The procedure was repeated 3 times for UAC and 3 times for UVC. NIRS (NIRO 500, Hamamatsu Photonics), a technique based on the differential absorption of NIR light by hemoglobin and cytochrome aa3 (CytO2), depending on their oxidation state, was used to assess changes in cerebral blood volume (DCBV), calculated from total hemoglobin, oxy- (DHbO2), deoxy-(DHb) hemoglobin and CytO2, time of max variation and recovery (from start of W and I). Vital parameters, including mean arterial blood pressure (MABP) were continuously measured. Results No significant change in Hb or CytO2, heart rate, pCO2 or pO2 was seen. Concordant changes in HbO2 and CBV indicate modifications of cerebral blood flow. MABP increased significantly during I-UVC and decreased during W-UVC. A positive correlation between MABP and CBV changes during W-UVC(r2 =0.41, p = 0.036) was observed. Conclusion Blood withdrawal and infusion via UVC cause significant MABP changes and related CBV oscillation which could potentially precipitate germinal matrix hemorrhage in preterm infants; utilizing the UAC this effect may be reduced or altogether avoided. Table

The use of near infrared spectroscopy (NIRS) in children after traumatic brain injury: a preliminary report.

Children commonly develop diffuse cerebral swelling after traumatic brain injury (TBI) which is believed due to a secondary response to the injury. Near infrared spectroscopy (NIRS), a continuous, direct, and noninvasive monitor of cerebral oxygenation and cerebral blood volume (CBV), could be helpful in understanding these secondary responses. The aims of our study were to determine whether NIRS used in children with severe TBI will provide insight into the pathophysiology of injury. Ten children (1 mo to 15 years old) with severe TBI (admission GCS < or = 7) were continuously monitored by NIRS by placing optodes over the frontalparietal region. Relative values of oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and total hemoglobin (THb) were obtained and compared to intracranial pressure (ICP), mean arterial pressure (MAP), electroencephalography (EEG), and arterial PCO2 (PaCO2). Episodes of intracranial hypertension (ICP > 20 Torr [T]), changes in ICP > 10 T, changes in PaCO2 > or = 8 T, and changes in MAP > 20 T frequently resulted in changes in HbO2, Hb, and THb. Hyperventilation with decreased PaCO2 always resulted in cerebral oxygen desaturation irregardless of ICP. Often, high ICP correlated with increased THb and HbO2 indicating increased CBV and cerebrovascular dilatation. In two children, posttraumatic seizures were preceded by an unexplained rapid cerebral hyperoxygenation several hours prior to the onset of the clinical seizures. NIRS reliably detects changes in cerebral hemodynamics in children and may be used to further understand the etiology of the diffuse cerebral swelling seen in children after severe TBI.

Near-Infrared Spectroscopy Demonstrates Changes In Cerebral Blood Volume, Oxygenation, And Metabolism In Premature Neonates During Bolus Gavage Feeding† 974

Objective: To determine whether bolus gavage feeding (GF) causes changes in the cerebral vascular or metabolic status of premature neonates detectable by Near-Infrared Spectroscopy (NIRS). Background: Although GF is a routine neonatal practice, its effect on the premature infant's brain is unknown. NIRS is a safe, portable, noninvasive technique which monitors cerebrovascular and metabolic status by determining changes in cerebral concentrations of oxygenated hemoglobin (HbO), deoxygenated hemoglobin (HbR), total hemoglobin (THb) and oxidized cytochrome aa3 (cytaa3). THb is an index of cerebral blood volume and cytaa3 is the terminal electron acceptor in the mitochondrial respiratory chain whose redox status reflects cerebral metabolism. Methods: Fourteen premature infants (24-32 wk GA) receiving intermittent GF were studied 20 min before and up to 1h following a GF. NIRS and systemic parameters (SaO2, HR, RR) were monitored and recorded throughout the study. Eight infants were fed by intermittently passed orogastric tube (OGT) and six were fed by indwelling OGT. Changes in NIRS parameters were determined during OGT insertion and after bolus feed relative to pre-GF values. Data were analyzed during OGT insertion and during defined 5 min intervals following feeding, and analyzed by ANOVA for repeated measures, p<0.05. Results: OGT insertion decreased cerebral HbO and cytaa3 in 6/8 infants. THb was also decreased in 4/6 of these infants. Within 20 min of the feed infusion, THb decreased from baseline in 11/14 infants. In 8/11 of these infants, HbO and HbR were also decreased. Conclusions: Cerebral HbO and cytaa3 decreased during OGT insertion. In infants in whom THb also decreased during OGT insertion, changes in HbO and cytaa3 may be related to diminished cerebral blood flow. Decreased THb, HbO, and HbR after bolus feeds suggest that cerebral blood flow may decrease due to spanchnic steal. These findings highlight the cerebrovascular and metabolic reactivity of premature infants during routine nursery procedures. These changes in cerebral circulation and metabolism are detectable by NIRS but are not clinically evident or detected by routine monitoring. The significance of these changes in the preterm infant's brain is unknown and warrants further study.

Can cerebrovascular reactivity be measured with near-infrared spectroscopy?

We used near-infrared spectroscopy (NIRS) to monitor the cerebral oxygenation changes during CO2 reactivity tests. Fifty healthy volunteers were examined (age range, 19 to 68 years). The monitored parameters were as follows: transcranial Doppler (TCD) time-averaged middle cerebral artery flow velocity end-tidal CO2 (EtCO2); change in concentration of cerebral oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and total hemoglobin; mean arterial blood pressure; peripheral arterial oxygen saturation (SaO2); and extracranial tissue perfusion with the use of cutaneous laser-Doppler flowmetry. The examination protocol included both hypercapnia and hypocapnia. The cerebrovascular reactivity indexes were calculated as follows: TCD, relative change in flow velocity per 1 kPa increase in EtCO2; NIRS, absolute change in HbO2, Hb, and total hemoglobin concentration (micromoles per liter) per 1 kPa increase in EtCO2. Mean middle cerebral artery flow velocity was found to be 58 cm/s at a mean baseline EtCO2 of 4.7 kPa. Mean cerebrovascular reactivities were as follows: TCD, 24%/kPa (SEM, 1.1); HbO2, 2.06 mumol/L per kilopascal (SEM, 0.08); Hb, -0.63 mumol/L per kilopascal (SEM, 0.09); and total hemoglobin concentration, 1.44 mumol/L per kilopascal (SEM, 0.1). Statistical analysis revealed significant correlation between reactivities calculated with the use of NIRS and TCD (P < .001). Although some fluctuations were observed in SaO2 and laser-Doppler flux, they were not correlated with either EtCO2 or NIRS. NIRS signal changes in HbO2, Hb, and total hemoglobin concentration are very sensitive to alterations in EtCO2, which are largely independent of extracranial tissue perfusion. NIRS may be developed as an alternative method for testing cerebrovascular reactivity and may be of particular clinical importance when the ultrasound window is poor.

Reduction of Cytochrome aa3 Measured by Near-Infrared Spectroscopy Predicts Cerebral Energy Loss in Hypoxic Piglets

Near-infrared spectroscopy is a noninvasive monitoring technique that allows quantitative measurement of changes in cerebral oxygenated Hb (HbO2), deoxygenated Hb (Hb), total Hb, and oxidized cytochrome aa3 (CytO2). Changes in cerebral Hb oxygenation and CytO2 have been measured in human neonates and infants under a variety of conditions. However, the association of these measurements with cerebral high-energy phosphate loss is not known. We studied simultaneous changes in cerebral HbO2, Hb, total Hb, and CytO2 by near-infrared spectroscopy and changes in nucleoside triphosphate (NTP, mostly ATP) and phosphocreatine (PC) concentrations and intracellular pH by in vivo 31P-labeled magnetic resonance spectroscopy. Four-wk-old piglets (n = 8) underwent sequential hypoxic episodes of increasing severity (inspired O2 concentration, 12, 8, 6, 4, and 0%). Animals were anesthetized and mechanically ventilated. At all levels of hypoxia, cerebral HbO2 decreased, and Hb increased. Loss of PC or NTP was not observed until inspired O2 concentration was decreased to less than 12%. With such severe hypoxia, hypotension, intracellular acidosis, and increasingly severe PC and NTP depletions occurred. Decreases in PC and NTP correlated closely with decreased CytO2 and arterial blood pressure (p < 0.0001) but not with changes in HbO2 and Hb. In conclusion, cerebral hypoxemia is readily detected by near-infrared spectroscopy as a decrease in HbO2 and an increase in Hb. However, relative changes in cerebral HbO2 and Hb have low predictive value for cerebral energy failure. Reduction of CytO2 is highly correlated with decreased brain energy state and may indicate impending cellular injury.

CEREBRAL CHANGES IN CYTOCHROME aa3 AS AN INDICATOR OF BILIRUBIN UNCOUPLING OF OXIDATIVE PHOSPHORYLATION

The flow of electrons from substrates through the mitochondria respiratory chain to cytochrome aa3 (Cyt aa3) and O2 provides the energy for ATP production by oxidative phosphorylation (OXPHOS). Bilirubin by uncoupling OXPHOS interfers with this process. This should result in an increased flow of electrons and therefore a tendency for Cyt aa3 to become more reduced. A near-infrared, multiwavelength, differential spectrophotometer was used to test whether hyperbilirubinemia alone or in association with hyperosmolar opening (HOSMO) of blood brain barrier (BBB) can affect the redox state of Cyt aa3. Eight anaesthetized rats, m.wt = 229 g were studied. Following achievement of a steady state of 30% inspired O2 the rats received an IV infusion of bilirubin, dissolved in 0.1 N NaOH, 4% albumin in 1 M PO4 buffer sol., calculated to reach a Se. bili.conc. of 30 mg/dl. Hyperbilirubinemia alone caused a slight or no reduction in Cyt aa3 oxygenated lib (HbO2) or blood volume (BV), However, in combination with HOSMO of BBB with IV infusion of 1.6M arabinose sol., there was a significant reduction of Cyt aa3, 26–47% of total labile signal, smaller changes in HbO2 and an increase in BV. A second dose of arabinose caused an exaggeration of these changes. Similar studies with 5 newborn piglets yielded similar results. We conclude that changes in the redox state of Cyt aa3 can be developed as an index of bilirubin toxicity. Near-infrared spectroscopy may be used to amplify clinical and biochemical findings and assess the risks of hyperbilirubinemia.

Fetal and neonatal cerebral oxygen monitoring with NIRS: theory and practice

Near infra-red spectroscopy (NIRS) is a comparatively new method for monitoring the oxygenation in blood and tissue in the brain of the fetus and the neonate. Absorption of light in the wavelength range 700–1000 nm through such tissue is measured, which is then used to calculate changes in the concentration of cerebral oxygenated and de-oxygenated haemoglobin (HbO 2 and Hb) and hence cerebral blood volume (CBV). Studies carried out on several groups of newborn babies have shown clear changes in HbO, Hb and CBV with hypoxia and bradycardia. These changes may well have implications in the occurrence of hypoxic/ischaemic brain injury. Intra partum NIR measurements on the fetal brain have demonstrated clear changes in HbO 2, Hb and CBVm, coinciding with the onset of contractions.

Mechanism of the effect of alkalosis on maximum oxygen uptake in hypoxic exercise

Maximum oxygen uptake (V̇ O 2max ) of rats is increased in alkalosis; this increase is larger in hypoxic than in normoxic exercise (Gonzalez et al. (1991b). J. Appl. Physiol., 71: 1050–1056). The objective of the present experiments was to determine the mechanism of this phenomenon. NaHCO 3 (0.3 M, 9 mmol/kg) was given 15 min before exercise to rats acclimated to P b 380 Torr for 3 weeks (HxBic) and to normoxic rats (NxBic). Additional groups of acclimated and normoxic rats received 0.3 M NaCl (HxNaCl and NxNaCl, respectively). Hx rats exercised at P i O 2 ≈ 70 Torr ; Nx rats at P i O 2 ≈ 140 Torr . V̇ O 2max was higher after NaHCO 3 than after NaCl; this effect was larger in hypoxia. The increase in V̇ O 2max was mediated through an increased arterio-venous oxygen concentration difference ((Ca - Cv) O 2 ), due, in turn, to a higher Ca O 2 without changes in Cv O 2 . (Ca - Cv) O 2 after NaHCO 3 was larger in hypoxia because a change in pH results in a larger change in HbO 2 saturation at the values prevalent in arterial blood of the hypoxic rats ( i.e. P O 2 ∼ 40–50 Torr, S O 2 50–60%), than at either the values of normoxic arterial blood or of venous blood during maximum exercise. These results suggest that an increase in hemoglobin-oxygen affinity improves oxygen uptake in the lungs during hypoxia, without hindering its release in the tissues, and therefore has a beneficial effect in hypoxic exercise.