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Erschienen in:
06.03.2019 | Editorial
Cerebral oximetry in cardiac arrest: a potential role but with limitations
Erschienen in: Intensive Care Medicine | Ausgabe 6/2019
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In patients with cardiac arrest (CA) cerebral oximetry has emerged as a real-time indicator of oxygen delivery to the brain which could be used to optimise cerebral oxygenation during and after cardiopulmonary resuscitation (CPR) (Table 1). Near-infrared spectroscopy (NIRS) emits infrared light (700–950 nm wavelength), which is not absorbed significantly by melanin in the skin and enables non-invasive monitoring of the regional haemoglobin oxygen saturation in the brain (rSO2). NIRS electrodes are placed on the scalp above the frontal cortex and the sampling volume is located about 2 cm underneath the skull [1]. Since about 70% of the sampled blood is venous, normal rSO2 is approximately 60–80%. Unlike arterial pulse oximetry, rSO2 can still be measured when blood flow is nonpulsatile or even absent, enabling NIRS to be used during CA. Unlike the electroencephalogram, NIRS is not susceptible to motion artefact generated by CPR.
Table 1
Cerebral oximetry (rSO2) in cardiac arrest
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Potential applications
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Results/advantages
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Limitations
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Monitoring brain oxygenation
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NIRS measures the regional oxygen saturation (rSO2) by analysing the intensity of infrared light backscattered from tissue located about 2 cm underneath a probe placed on the frontal scalp
rSO2 can be detected even when flow is nonpulsatile or absent, as in cardiac arrest
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Prediction of ROSC during CPR
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In a systematic review of 26 studies [2], the averaged mean rSO2 in patients with ROSC was 41 ± 12% vs. 30 ± 12% for those without ROSC (p = 0.009)
In a study on 183 IHCA [3], a ≥ 65% rSO2 cut-off had 99 [95–100]% specificity for ROSC, while a ≤ 25% rSO2 cut-off had 100 [94–100]% specificity for no ROSC
In a study on 329 OHCA, a 15% increase of rSO2 during CPR was the best predictor of ROSC (OR 4.88 [2.79–8.54])
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There was a wide overlap of averaged rSO2 values between ROSC and no-ROSC studies
High specificities only at the extremes of the distribution. The relevant sensitivities were low (21 [12–33]% and 13 [8–21]%, respectively)
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Targeting MAP to optimise cerebral perfusion after resuscitation
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Optimal MAP is defined as the one which minimises the correlation coefficient (COX) between MAP and rSO2 (optimal autoregulation)
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There are no interventional studies showing that targeting a specific MAP improves neurological outcome after CPR
The relationships between rSO2, CBF and neurological outcome are not fully understood and deserve further investigation
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