Joke Vanderhaegen

Cerebral Tissue Oxygenation and Regional Oxygen Saturation Can Be Used to Study Cerebral Autoregulation in Prematurely Born Infants

The coupling of cerebral intravascular oxygenation (dHbD) with mean arterial blood pressure (MABP) was taken as a reflection of autoregulation assuming constant arterial oxygen content. However, this method is sensitive to movement artifacts. We examined whether the cerebral tissue oxygenation index (cTOI) and regional oxygen saturation (rScO2) may replace dHbD and changes in total Hb (dHbT), respectively. Correlation (COR) and coherence (COH) were used to measure the agreement of MABP with rScO2/dHbT and cTOI/dHbD. dHbD/cTOI and dHbT/rScO2 recordings of, respectively, 34 and 20 preterm infants in need for intensive care were studied during the first days of life. dHbD and cTOI were obtained with the NIRO300 and rScO2 and dHbT with the INVOS4100. Invasive MABP was measured continuously. COR and COH scores of MABP versus dHbD/dHbT were compared with the corresponding ones by replacing dHbD/dHbT by cTOI/rScO2, respectively. Generally, no significant score differences were found for dHbD/cTOI. Differences for dHbT/rScO2 were slightly larger but still within the normal variation of the parameters. Differences become insignificant when restricting calculations to epochs of larger variation in MABP (>10 mm Hg). Hence, we suggest that cTOI and rScO2 can be used to study cerebral autoregulation in newborns.

Cerebral and Systemic Hemodynamic Effects of Intravenous Bolus Administration of Propofol in Neonates

Objectives: To assess variability of systemic hemodynamics and its covariates following bolus propofol administration in (pre)term neonates, and to analyze the effect of propofol on cerebral tissue oxygenation index (TOI) and fractional tissue oxygen extraction measured by near-infrared spectroscopy. Methods: In (pre)term neonates, we recorded mean arterial blood pressure (MABP), saturation (SaO2), heart rate (HR) and TOI from 5 min before up to 60 min after intravenous bolus propofol (3 mg kg–1) administration during elective chest tube removal. Covariate analysis included postmenstrual age (PMA ≤ or >37 weeks), postnatal age (PNA ≤ or >10 days), comedication (fentanyl +/– midazolam) and congenital cardiopathy (yes/no). Fractional tissue oxygen extraction was calculated as (SaO2 – TOI)/SaO2. Results: Twenty recordings in 19 neonates were assessed. Following propofol administration, an abrupt, minor decrease in HR and SaO2 was seen with fast recovery, while MABP decreased up to 1 h. TOI decreased during the first 3 min, reflecting an imbalance between cerebral oxygen delivery and demand. Despite sustained decrease in MABP, TOI then returned to baseline, suggesting a better balance between oxygen delivery and demand. PNA ≤10 days, comedication and absence of cardiopathy were associated with more subtle decreases in cerebral oxygenation and faster recovery. Conclusions: Propofol-induced decrease in HR, SaO2 and cerebral oxygenation is short lasting while a decrease in MABP is observed up to 60 min. The variability in the effects of propofol is influenced by PNA, comedication or cardiopathy. Near-infrared spectroscopy can be used to assess hemodynamic effects of hypnotics on the cerebral oxygenation.

Surgical closure of the patent ductus arteriosus and its effect on the cerebral tissue oxygenation

Aim: Surgical patent ductus arteriosus (PDA) ligation is considered after failure or contraindication of medical treatment. Till now ligation of the PDA has been associated with low morbidity and mortality although recently concerns have been raised about the possible association of ductal clipping and neurodevelopmental abnormalities later in life. By means of near‐infrared spectroscopy (NIRS), we analysed the changes in the cerebral tissue oxygenation index (TOI) and fractional tissue oxygen extraction (FTOE) at the time of clipping as well as after clipping.

The effect of changes in tPCO2 on the fractional tissue oxygen extraction – as measured by near-infrared spectroscopy – in neonates during the first days of life

The cerebral fractional oxygen extraction (FOE) reflects the balance between cerebral oxygen delivery (OD) and consumption (VO(2)). PCO(2) affects the cerebral blood flow (CBF): hypocapnia decreases CBF and OD and increases FOE. We recently showed that the fractional tissue oxygen extraction (FTOE) reflects FOE and hypothesized that a decrease in tPCO(2) increases FTOE. In this study we looked at the effect of changes in tPCO(2) on FTOE. We analysed 23 measurements in 13 neonates with birth weight below 1500 g and need for intensive care. Exclusion criteria were congenital malformations or cerebral complications. The tissue oxygenation index (TOI), tPCO(2), mean arterial blood pressure (MABP), heart rate (HR) and peripheral oxygen saturation (SaO(2)) were continuously recorded for 4h during the first days of life and FTOE was calculated. Over the whole group we found a significant negative (r=-0.227) correlation between tPCO(2) and FTOE and a significant positive (r=0.258) correlation between tPCO(2) and TOI. After correction for MABP these correlations remained significant. Over the whole group we found a significant positive correlation between tPCO(2) and TOI and a significant negative correlation between tPCO(2) and FTOE, which remained significant after correction for MABP. This implies that tPCO(2) influences the cerebral oxygenation independently of MABP. We therefore believe that for the interpretation of cerebral oxygenation in mechanically ventilated neonates during the first days of life continuous measurements of tPCO(2) are needed. Moreover we suggest FTOE to become a continuous parameter in the clinical setting for the non-invasive measurement of the neonatal brain oxygenation.

Impaired Cerebral Autoregulation Using Near-Infrared Spectroscopy and Its Relation to Clinical Outcomes in Premature Infants

The concordance between the change in the Mean Arterial Blood Pressure (MABP) and the Cerebral Blood Flow (CBF) is studied using the Correlation, Coherence and Partial Coherence methods in order to detect Impaired Cerebral Autoregulation in Neonates. The presence of impaired autoregulation is assessed by the use of the Critical Percentage of Recording Time (CPRT). The changes in CBF are reflected by the measurement of changes in cerebral intravascular oxygenation (HbD), regional cerebral oxygen saturation (rSO(2)), and cerebral tissue oxygenation (TOI), as measured by Near-Infrared Spectroscopy (NIRS) (INVOS4100 and NIRO300). The relation between impaired autoregulation and long term clinical outcomes in premature infants is studied.

Estimation of Muscle Fatigue Using Surface Electromyography and Near-Infrared Spectroscopy

This study looks at various parameters, derived from surface electromyography (sEMG) and Near Infrared Spectroscopy (NIRS) and their relationship in muscle fatigue during a static elbow flexion until exhaustion as well as during a semidynamic exercise.We found a linear increasing trend for a corrected amplitude parameter and a linear decreasing slope for the frequency content of the sEMG signal. The tissue oxygenation index (TOI) extracted from NIRS recordings showed a four-phase response for all the subjects. A strong correlation between frequency content of the sEMG signal and TOI was established. We can conclude that both sEMG and NIRS give complementary information concerning muscle fatigue.

The partial coherence method for assessment of impaired cerebral autoregulation using near-infrared spectroscopy: potential and limitations.

The most important forms of brain injury in premature infants are partly caused by disturbances in cerebral autoregulation. As changes in cerebral intravascular oxygenation (HbD), regional cerebral oxygen saturation (rSO(2)), and cerebral tissue oxygenation (TOI) reflect changes in cerebral blood flow (CBF), impaired autoregulation can be measured by studying the concordance between HbD/rSO(2)/TOI and the mean arterial blood pressure (MABP), assuming no changes in oxygen consumption, arterial oxygen saturation (SaO(2)), and in blood volume. We investigated the performance of the partial coherence (PCOH) method, and compared it with the coherence method (COH). The PCOH method allows the elimination of the influence of SaO(2) on HbD/rSO(2)/TOI in a linear way. We started from long-term recordings measured in the first days of life simultaneously in 30 infants from three medical centres. We then compared the COH and PCOH results with patient clinical characteristics and outcomes, and concluded that PCOH might be a better method for assessing impaired autoregulation.

New Measurements For Assessment Of Impaired Cerebral Autoregulation Using Near-Infrared Spectroscopy

Some preterm infants have poor cerebral autoregulation. The concordance between cerebral intravascular oxygenation (HbD), computed as the difference between oxygenated (HbO2) and deoxygenated (Hb) haemoglobin, and mean arterial blood pressure (MABP) reflects impaired autoregulation. As HbD is not an absolute value, we developed mathematics to prove that the cerebral tissue oxygenation (TOI), an absolute signal computed as the ratio of HbO2 to total haemoglobin (Hb+HbO2), may replace HbD. In the meantime, we attempt to theoretically predict the true level of autoregulation of a patient by defining a critical percentage of the signal recording time (CPRT). 20 preterm infants with need for intensive care were studied in the first days of life. HbD and TOI were obtained with the NIRO-300 (Hamamatsu, Japan). Invasive MABP was measured continuously. All mathematics showed a strong similarity between HbD and TOI.

The Effect of Glycaemia on the Cerebral Oxygenation in Very Low Birthweight Infants as Measured by Near-Infrared Spectroscopy

The cerebral tissue oxygenation index (TOI) and fractional tissue oxygen extraction (FTOE) reflect the cerebral oxygenation. We studied the effect of glycaemia on the TOI and FTOE, as measured by near-infrared-spectroscopy (NIRS). We continuously measured TOI, glycaemia, mean arterial blood pressure (MABP), saturation (SaO(2)) and transcutaneous carbon dioxide pressure (tPCO(2)) for at least 4 h during the first week of life in neonates with gestational age (GA) < 32 weeks and weight < 1500 g. FTOE was calculated. 24 measurements in 11 neonates were analyzed. We found a significant negative correlation (r = -0.077; p = 0.0344) between glycaemia and TOI, also after correction for MABP, SaO(2) and tPCO(2) (r = -0.118; p = 0.002) and a significant positive correlation between glycaemia and FTOE (r = 0.147; p < 0.000) which remained significant after correction for MABP and tPCO(2) (r = 0.116; p = 0.001). Our results indicate that in neonates during the first days of life glycaemia - even within the normal ranges and after correction for MABP, SaO(2) and tPCO(2) - influences the cerebral oxygenation.

How do patients between the age of 65 and 75 use a web-based decision aid for treatment choice in localized prostate cancer?

This study was designed to evaluate the use of a web‐based decision aid by a 65plus patient group in their decision‐making process for treatment of localized prostate cancer. Of particular interest was the use of technology features such as patients’ statements, comparative tables, and a values clarification tool.