L . Andersen et al .: J Extra Corpor Technol 2023 , 55 , 209 – 217 213
Figure
4 . A summary of the variance for MAP , rSO 2 ( A ) and the COx index ( B ) defined by the interpatient ( 1 – 10 ) individual ratio between the mean value and the standard deviation expressed in percent .
Figure
5 . Boxplots showing COx sorted in bins of MAP including all patients ( n = 10 ). COx = 0.4 ( green dotted line ). The boxplot illustrates the interquartile range ( IQR ) and the median value ( horizontal line ). Whiskers represent minimum and maximum values . o = 3 rd quartile + 1.5 * IQR and 1 st quartile �1.5 * IQR . * = 3 rd quartile + 3.0 * IQR and 1 st quartile �3.0 * IQR .
the focus is to identify the lower and upper limits of MAP , i . e ., within what range of MAP CA is intact . Such a limit was identified in 1 out of 10 patients in our series , with a lower blood pressure limit of 55 mmHg for COx > 0.4 as reference ( Figure 5 ). An accompanied higher blood pressure limit was , however , not detected in any subject , why a “ safe window ” of MAP could not be established . In this patient , loss of CA lasted for 11 min , a value representing a summary of 15 independent short time intervals , which is important to bear in mind . In fact , it would seem reasonable to detect thresholds of abnormal CA in all patients , especially for lower blood pressure limits , since episodes of hypotension are frequent during a CPB procedure . The MAP ranged between 46 mmHg and 63 mmHg in our series but , individual MAP recordings as low as 23 mmHg were observed , contrasted by relative hypertensive events up to
95 mmHg . Why this full range of MAP recordings was unable to identify blood pressure limits for the maintenance of CA may raise the question – s about method ’ s validity .
An overview of the COx index relative bins of MAP including all patients is shown in Figure 5 . This indicates that CA was maintained over the entire span of blood pressure . It should however be underlined that the presentation disguises patients ’ individual COx values indicating loss of CA exemplified in Figure 6 . Nevertheless , it gives a fair illustration of the COx index distribution . MAP ranged between 30 mmHg and 90 mmHg in our patients , still , the COx method signaled sustained CA . This finding alone raises questions about the method ’ s sensibility . The other plausible answer to this puzzling result would be to question the role of MAP in relation to CA during CPB [ 31 , 32 ].