J Extra Corpor Technol 2023 , 55 , 209 – 217 Ó The Author ( s ), published by EDP Sciences , 2023 https :// doi . org / 10.1051 / ject / 2023032
Available online at : ject . edpsciences . org
REVIEW ARTICLE
Our initial experience of monitoring the autoregulation of cerebral blood flow during cardiopulmonary bypass Leon Andersen ( Msc ) 1 , Micael Appelblad ( PhD ) 1 , Urban Wiklund ( PhD ) 2 , Nina Sundström ( PhD ) 2 , and Staffan Svenmarker ( PhD ) 1 ,*
1 Heart Centre , Department of Public Health and Clinical Medicine , Umeå University , 901 87 Umeå , Sweden 2 Department of Radiation Sciences , Radiation Physics , Biomedical Engineering , Umeå University , 901 87 Umeå , Sweden
Received 25 January 2023 , Accepted 5 July 2023
Abstract – Background : Cerebral blood flow ( CBF ) is believed to be relatively constant within an upper and lower blood pressure limit . Different methods are available to monitor CBF autoregulation during surgery . This study aims to critically analyze the application of the cerebral oxygenation index ( COx ), one of the commonly used techniques , using a reference to data from a series of clinical registrations . Method : CBF was monitored using nearinfrared spectroscopy , while cerebral blood pressure was estimated by recordings obtained from either the radial or femoral artery in 10 patients undergoing cardiopulmonary bypass . The association between CBF and blood pressure was calculated as a moving continuous correlation coefficient . A COx index > 0.4 was regarded as a sign of abnormal cerebral autoregulation ( CA ). Recordings were examined to discuss reliability measures and clinical feasibility of the measurements , followed by interpretation of individual results , identification of possible pitfalls , and suggestions of alternative methods . Results and Conclusion : Monitoring of CA during cardiopulmonary bypass is intriguing and complex . A series of challenges and limitations should be considered before introducing this method into clinical practice .
Key words : Cardiopulmonary bypass , Monitoring , Cerebral blood flow , Autoregulation , Near-infrared spectroscopy .
Introduction
Cerebral complications after cardiac surgery have a multifaceted background , often with serious consequences for the patient [ 1 ]. One risk factor is disturbances of the cerebral circulation during surgery , which may provoke the development of both stroke and delirium [ 1 – 3 ]. Cerebral blood flow ( CBF ) should under normal conditions be relatively insensitive to variations of the systemic mean arterial pressure ( MAP ), within a safe upper and lower blood pressure limit [ 3 – 5 ]. The theory of vasomotor control in relation to blood pressure was first demonstrated by Bayliss in 1902 [ 6 ] and later manifested by Lassen in 1959 [ 5 ]. This principle remains the dominating theory of CBF autoregulation to this day [ 7 , 8 ].
The brain represents about 2 – 3 % of the total body mass . Despite its relatively small weight it still receives approximately 15 % of the systemic blood flow . This disproportionally high CBF is explained by a high cerebral metabolically activity requiring about 20 % of available circulating oxygen [ 9 ]. As cerebral tissue stores limited energy explains why normal cerebral function depends on a continuous supply of oxygen .
* Corresponding author : staffan . svenmarker @ umu . se
How CBF is modulated to meet fluctuating cerebral oxygen demands was demonstrated by Jones and colleagues in 1981 [ 10 ]. Normal CBF in conscious humans is 50 mL / 100 g / min [ 9 ]. A decrease of 50 % causes neuronal damage and further reduction can lead to unconsciousness and permanent brain damage [ 9 , 11 ].
Clinically suitable methods to monitor cerebral autoregulation ( CA ) emerged during the mid-1990s [ 12 ]. The use of near-infrared spectroscopy ( NIRS ) has later been suggested as a non-invasive method to estimate the CBF [ 13 , 14 ]. The association between CBF and MAP is assessed by analyzing the correlation between slow waves in NIRS with those in MAP recordings . This association is referred to in the literature as the COx index . The hypothesis is that an increase in COx is indicative of disturbed CA . This technique to monitor CA in real-time recordings has been applied in many studies [ 3 , 4 , 13 , 15 – 18 ] and recently suggested as a reliable method to assess CA [ 19 ].
The present study aims to critically analyze and discuss the reliability and validity of the COx index as a measure of CA , where the properties of the COx index were illustrated using data from a series of patients undergoing cardiopulmonary bypass ( CPB ).
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