1 Department of Congenital Heart Disease, Paediatric Cardiology and Paediatric Intensive Care Medicineand 2 Department of Anaesthesiology, Deutsches Herzzentrum Berlin, Augustenburger Platz 1,D-13353 Berlin, Germany
Corresponding author. E-mail: nagdyman@dhzb.de
Accepted for publication: April 12, 2003
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Abstract |
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Br J Anaesth 2003; 91: 00000
Keywords: brain, cerebral oxygenation; children; complications, circulatory arrest; heart, resuscitation; measurement techniques, near-infrared spectroscopy
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Introduction |
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The NIRO 300 (Hamamatsu Phototonics, Japan), which uses spatially resolved spectroscopy (SRS) as an algorithm,5 6 measures a tissue oxygenation index (TOI) and a tissue haemoglobin index (THI) as absolute values without the need to know a path-length factor. TOI reflects the ratio of k x HbO2/(k x HbO2 + k x HHb) and THI reflects the denominator k x HbO2 + k x HHb, where k is an unknown but constant tissue parameter.5 TOI represents the tissue saturation and is measured in percent, whereas THI is an absolute figure of the total haemoglobin but, due to the factor k, measured in arbitrary units. As it is an absolute value, its changes from one measuring point to another can be measured as a percentage. We describe our observations on cerebral NIRS monitoring in a patient who needed CPR during cardiac catheterization.
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Case report |
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The NIRS probe was placed on the forehead in the supraorbital region receiving reflected light from the frontal neocortex. The patient was given midazolam and ketamine i.v. Monitoring was by ECG and pulse oximetry. Blood pressure was measured non-invasively at intervals of 5 min. During the examination a catheter was introduced into the right atrium and through the atrial septal defect into the left atrium. This triggered a supraventricular tachycardia (heart rate=230 beats min1). A sudden decrease in HbO2, tHb, CytOx, TOI and THI was observed. Figure 1 shows how the NIRS values changed.
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Discussion |
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The reason for an increase in CytOx to values greater than baseline after restoration of spontaneous circulation remains unclear. A possible explanation could be the compensatory reoxygenation following an ischaemic period or the influence of mechanical ventilation with oxygen 100%.
NIRS has been studied in cardiac arrest in 18 patients arriving in an emergency department with circulatory arrest or shortly after restoration of spontaneous circulation.10 The authors reported that if regional cerebral oxygen saturation (SrO2) is small after cardiac arrest, there is a greater mortality. Recently published data11 describe cerebral oximetry in a patient with cerebral infarction and circulatory arrest, with a difference between the NIRS signals obtained from the centre of the stroke compared with the non-stroke areas. The saturation in an ischaemic area that is metabolically inactive can be normal because oxygen extraction does not occur from cerebral venous blood, which can also be from other adjacent brain regions that are perfused. Thus, the interpretation of NIRS data may be difficult in patients with cerebral stroke without the use of other imaging methods.11 Our data support observations of another report where SrO2 decreased from 60% to 41% in a patient with circulatory arrest.12 Systemic perfusion was restored with cardiopulmonary bypass and the changes during hypoxaemia were reversed. The authors inferred that NIRS might be useful to determine the effectiveness of CPR. None of the reports1012 that measured cerebral oxygenation during cardiac arrest commented on CytOx changes because they used a different transcranial NIRS monitoring system (INVOS 3100, Somanetics Inc., Troy, MI, USA). A recent study compared two different near-infrared spectrophotometers (INVOS 4100 and the NIRO 300) measuring cerebral oxygen saturation during changes of cerebral blood flow induced by carbon dioxide challenge.13 The INVOS 4100 and the NIRO 300 showed a significant linear correlation for values of SrO2 and TOI during carbon dioxide alteration, but BlandAltman analysis14 showed that the individual values and the relative changes displayed by the two devices were not equivalent.
Discrepancies between persisting bowel desaturation measured with NIRS and short episodes of systemic desaturation were reported in neonates.15 We could not measure the circulation and systemic saturation continuously to detect differences between cerebral and systemic saturations.
Studies of the relationship between cerebral measurements with other devices and regional cerebral oxygenation measured by spatially resolved NIRS give different results.16 17 Measurements of jugular bulb oxygen saturation (SjO2) measured by co-oximetry and TOI measured by NIRO 300, do not agree well despite a statistically significant correlation.16 The NIRS cerebral monitoring measures TOI in a small region of the cerebral microvasculature, whereas SjO2 reflects a more global measurement, so inhomogeneous distribution of blood or metabolic activity will reduce the agreement between the two methods.18 In addition, the TOI signal reflects an average of arterial (25%), capillary (5%) and venous (70%) blood. Cerebral cortex haemoglobin saturation, measured directly by the spatially resolved method, reflects predominantly the saturation of the intracranial venous compartment of circulation.17 Unfortunately, we did not have other measurements of brain oxygenation in our patient to verify that the decrease in TOI represented a change in cerebral oxygen saturation. SjO2 and TOI may measure different entities, so that although there is a significant correlation between SjO2 and TOI, the two measures are not interchangeable.16
Our observations show that non-invasive cerebral NIRS measurement gives useful real-time information on cerebral oxygenation during cardiac arrest and CPR and this deserves further investigation.
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Acknowledgement |
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References |
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