Hemoglobin Concentration Affects Electroencephalogram During Cardiopulmonary Bypass: An Indication for Neuro‐Protective Values

Abstract

Hemodilution during cardiopulmonary bypass (CPB) is widely used to decrease transfusion and improve microcirculation but has drawbacks, such as diminished hemoglobin levels. Among others, reduced brain oxygenation accounts for neurological adverse outcomes after CPB. The aim of the present study was to ascertain if and how continuous electroencephalogram (EEG) during CPB is affected by hematocrit level and what should be the minimum value to avoid significant frequency band shifts on the EEG. A comparative study design was used with 16 subjects undergoing elective mitral valve repair/replacement. EEG was continuously recorded during the surgical procedure (from anesthesia induction to 20 min after CPB end). Data were marked at relevant time points (T0: before CPB start; T1: after 30 min from CPB beginning; T2: at CPB end), and the following 2 min EEG analyzed with a fast Fourier transform to obtain relative power for delta, theta, alpha, and beta bands. A general linear model for repeated measure was used to study interactions of time (T0, T1, and T2, EEG frequency band, and topographical distribution. The relative powers for each electrode were calculated and represented using topographic maps. Power spectrum differences between time points (T2-T1; T2-T0; T1-T0) were calculated for each electrode, and differences >10%, considered indicative of neuronal sufferance, were included in further analysis. Cutoff hemoglobin values that maximize the proportion of correctly classified EEG band shifts were obtained by previous definition were obtained. At T2, diffuse EEG slowing in delta and theta bands was detected; a minor slowing over anterior regions was evident at T1 for the theta band. Decrements in EEG power greater than 10% were detected only for the delta band at T2. Hemoglobin concentration levels at which no slowing increase was evident were 9.4 mg/dL (Ht: 28.2%) at T1 and 9.2 mg/dL (Ht: 27.6%) at T2. EEG burst-suppression pattern related to a lesser degree of slowing at T2. In conclusion, we propose hemoglobin cutoff levels that prevent EEG slowing indicative of neuronal sufferance. In addition, burst-suppression EEG patterns offer higher central nervous system protection as measured on EEG.

Postoperative Cognitive Decline After Cardiac Surgery: A Narrative Review of Current Knowledge in 2019

“…Furthermore, performing a deep hypothermic circulatory arrest on animal models stimulates neuronal death [56], for which human studies have demonstrated an association with pronounced POCD [57]. Hemodilution also has an impact on cognitive functions [19,58], i.e., intraoperative hematocrit levels between 15 to 17% and a greater than 12% decline in hematocrit level from the baseline level represent a threshold for POCD occurrence [59]. Additionally, intraoperative and early postoperative hypercoagulability may cause temporary occlusion of tiny brain blood vessels, which is associated with POCD development [60].…”

The relationship between neurocognitive decline and the heart‐lung machine

“…Despite these aforementioned studies suggesting that the heart-lung machine does not cause significant neurocognitive changes, multiple studies argue the opposite-one paper even suggests that 20% to 80% of people experience "neurocognitive dysfunctions" following CPB. 29 One study of 100 patients on CPB found that half of the sample developed neurological damage after recovering from anesthesia and that 43% had focal neurological damage like ischemia followed by behavioral abnormalities like confusion and delirium; while such signs normalized by discharge in most patients, 15% had signs of cerebral injury at the time of discharge. 30 The study linked these neurological problems to impaired cerebral perfusion, reporting that arterial pressures was significantly low in these patients during CPB.…”

Neuroprotective Strategies during Cardiac Surgery with Cardiopulmonary Bypass

“…However, hemodilution might also be disadvantageous as brain oxygen supply might be reduced if hematocrit is too low. This problem was addressed by a very recent study of Del Felice et al [70], who examined the influence of different hematocrit levels on cerebral EEG (electroencephalogram). From this study and others, it became evident that a hematocrit level of about 25% was not associated with an impaired outcome [71].…”