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Brain injury markers in blood predict signs of hypoxic ischaemic encephalopathy on head computed tomography after cardiac arrest

Open AccessPublished:December 20, 2022DOI:https://doi.org/10.1016/j.resuscitation.2022.12.006

      Abstract

      Background/Aim

      Signs of hypoxic ischaemic encephalopathy (HIE) on head computed tomography (CT) predicts poor neurological outcome after cardiac arrest. We explore whether levels of brain injury markers in blood could predict the likelihood of HIE on CT.

      Methods

      Retrospective analysis of CT performed at 24–168 h post cardiac arrest on clinical indication within the Target Temperature Management after out-of-hospital cardiac arrest-trial. Biomarkers prospectively collected at 24- and 48 h post-arrest were analysed for neuron specific enolase (NSE), neurofilament light (NFL), total-tau and glial fibrillary acidic protein (GFAP). HIE was assessed through visual evaluation and quantitative grey-white-matter ratio (GWR) was retrospectively calculated on Swedish subjects with original images available.

      Results

      In total, 95 patients were included. The performance to predict HIE on CT (performed at IQR 73–116 h) at 48 h was similar for all biomarkers, assessed as area under the receiving operating characteristic curve (AUC) NSE 0.82 (0.71–0.94), NFL 0.79 (0.67–0.91), total-tau 0.84 (0.74–0.95), GFAP 0.79 (0.67–0.90). The predictive performance of biomarker levels at 24 h was AUC 0.72–0.81. At 48 h biomarker levels below Youden Index accurately excluded HIE in 77.3–91.7% (negative predictive value) and levels above Youden Index correctly predicted HIE in 73.3–83.7% (positive predictive value). NSE cut-off at 48 h was 48 ng/ml. Elevated biomarker levels irrespective of timepoint significantly correlated with lower GWR.

      Conclusion

      Biomarker levels can assess the likelihood of a patient presenting with HIE on CT and could be used to select suitable patients for CT-examination during neurological prognostication in unconscious cardiac arrest patients.

      Introduction

      Signs of hypoxic ischaemic encephalopathy (HIE) on head computed tomography (CT) or magnetic resonance imaging (MRI) are guideline recommended predictors of poor neurological outcome after cardiac arrest.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Sandroni C.
      • D'Arrigo S.
      • Cacciola S.
      • et al.
      Prediction of poor neurological outcome in comatose survivors of cardiac arrest: a systematic review.
      HIE on CT is qualitatively assessed through visual evaluation of generalised oedema and quantitatively calculated from grey-white-matter ratio (GWR).
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      Reduced GWR is a 100% specific predictor of poor neurological outcome but lacks consensual thresholds and standardised methods for interpretation, resulting in varying levels of sensitivity.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Sandroni C.
      • D'Arrigo S.
      • Cacciola S.
      • et al.
      Prediction of poor neurological outcome in comatose survivors of cardiac arrest: a systematic review.
      • Keijzer H.M.
      • Hoedemaekers C.W.E.
      • Meijer F.J.A.
      • Tonino B.A.R.
      • Klijn C.J.M.
      • Hofmeijer J.
      Brain imaging in comatose survivors of cardiac arrest: Pathophysiological correlates and prognostic properties.
      • Oh J.H.
      • Choi S.P.
      • Wee J.H.
      • Park J.H.
      Inter-scanner variability in Hounsfield unit measured by CT of the brain and effect on gray-to-white matter ratio.
      • Streitberger K.J.
      • Endisch C.
      • Ploner C.J.
      • et al.
      Timing of brain computed tomography and accuracy of outcome prediction after cardiac arrest.
      • Cristia C.
      • Ho M.L.
      • Levy S.
      • et al.
      The association between a quantitative computed tomography (CT) measurement of cerebral edema and outcomes in post-cardiac arrest-a validation study.
      Certain MRI sequences may be more sensitive to acute structural damage than CT, but is more expensive and offers limited possibilities to monitor haemodynamically and respiratory unstable patients during the extended examination.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      There is currently no method to guide the choice of suitable neuroimaging modality.
      Elevated levels of neuron specific enolase (NSE) ≥60 ng/ml at 48 or 72 h (h) post-arrest is another predictor of poor neurological outcome and has previously been associated with HIE on CT.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Moseby-Knappe M.
      • Pellis T.
      • Dragancea I.
      • et al.
      Head computed tomography for prognostication of poor outcome in comatose patients after cardiac arrest and targeted temperature management.
      The novel brain injury markers neurofilament light (NFL) and total-tau have shown superior prognostic accuracy to NSE at 24–72 h.
      • Sandroni C.
      • D'Arrigo S.
      • Cacciola S.
      • et al.
      Prediction of poor neurological outcome in comatose survivors of cardiac arrest: a systematic review.
      • Mattsson N.
      • Zetterberg H.
      • Nielsen N.
      • et al.
      Serum tau and neurological outcome in cardiac arrest.
      • Moseby-Knappe M.
      • Mattsson N.
      • Nielsen N.
      • et al.
      Serum Neurofilament Light Chain for Prognosis of Outcome After Cardiac Arrest.
      • Hoiland R.L.
      • Rikhraj K.J.K.
      • Thiara S.
      • et al.
      Neurologic Prognostication After Cardiac Arrest Using Brain Biomarkers: A Systematic Review and Meta-analysis.
      Astrocytic glial fibrillary acidic protein (GFAP) is an early marker of glial injury and increased astrocytic activity.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Bazarian J.J.
      • Biberthaler P.
      • Welch R.D.
      • et al.
      Serum GFAP and UCH-L1 for prediction of absence of intracranial injuries on head CT (ALERT-TBI): a multicentre observational study.
      • Ebner F.
      • Moseby-Knappe M.
      • Mattsson-Carlgren N.
      • et al.
      Serum GFAP and UCH-L1 for the prediction of neurological outcome in comatose cardiac arrest patients.
      The earliest guideline recommended timepoint for NSE evaluation is 48 h, which is a timepoint where all four biomarkers mentioned above have demonstrated reasonable prognostic accuracies.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Mattsson N.
      • Zetterberg H.
      • Nielsen N.
      • et al.
      Serum tau and neurological outcome in cardiac arrest.
      • Moseby-Knappe M.
      • Mattsson N.
      • Nielsen N.
      • et al.
      Serum Neurofilament Light Chain for Prognosis of Outcome After Cardiac Arrest.
      • Ebner F.
      • Moseby-Knappe M.
      • Mattsson-Carlgren N.
      • et al.
      Serum GFAP and UCH-L1 for the prediction of neurological outcome in comatose cardiac arrest patients.
      NFL has additionally demonstrated excellent predictive performance for neurological outcome already at 24 h.
      • Wihersaari L.
      • Ashton N.J.
      • Reinikainen M.
      • et al.
      Neurofilament light as an outcome predictor after cardiac arrest: a post hoc analysis of the COMACARE trial.
      CT performed from biomarker sampling and up to 7 days after cardiac arrest were considered eligible for prognostication.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      The aim of this study was to describe the association between brain injury marker levels in blood and signs of HIE on CT. We examined whether biomarker levels at 24- and 48 h could be used as an individualised decision aid for determining whether CT is likely sufficient for HIE diagnosis. This could reduce the number of neuroradiological examinations necessary to predict neurological outcome in unconscious patients after cardiac arrest and enable wisely spent resources in post-arrest care.

      Materials and methods

      Study population

      Retrospective analysis of the prospective Target Temperature Management after out-of-hospital cardiac arrest (TTM)-trial, which included adult unconscious patients with presumed cardiac cause of arrest.
      • Moseby-Knappe M.
      • Pellis T.
      • Dragancea I.
      • et al.
      Head computed tomography for prognostication of poor outcome in comatose patients after cardiac arrest and targeted temperature management.
      • Nielsen N.
      • Wetterslev J.
      • Cronberg T.
      • et al.
      Targeted temperature management at 33°C versus 36°C after cardiac arrest.

      Biomarkers

      Brain injury markers in blood prospectively collected at 24- and 48 h after randomisation were analysed after trial completion.
      • Nielsen N.
      • Wetterslev J.
      • Cronberg T.
      • et al.
      Targeted temperature management at 33°C versus 36°C after cardiac arrest.
      • Stammet P.
      • Collignon O.
      • Hassager C.
      • et al.
      Neuron-Specific Enolase as a Predictor of Death or Poor Neurological Outcome After Out-of-Hospital Cardiac Arrest and Targeted Temperature Management at 33°C and 36°C.
      NSE concentrations were measured using COBAS e601 line with electrochemiluminescence immunoassay (ECLIA) kit (Roche Diagnostics).
      • Stammet P.
      • Collignon O.
      • Hassager C.
      • et al.
      Neuron-Specific Enolase as a Predictor of Death or Poor Neurological Outcome After Out-of-Hospital Cardiac Arrest and Targeted Temperature Management at 33°C and 36°C.
      All samples were tested for haemolysis and discarded if positive, as previously described.
      • Stammet P.
      • Collignon O.
      • Hassager C.
      • et al.
      Neuron-Specific Enolase as a Predictor of Death or Poor Neurological Outcome After Out-of-Hospital Cardiac Arrest and Targeted Temperature Management at 33°C and 36°C.
      NFL and total-tau concentrations were measured using an ultrasensitive single molecule array (SimoaTM) method (Quanterix Billerica, MA), with a homebrew kit and a human total-tau kit respectively.
      • Mattsson N.
      • Zetterberg H.
      • Nielsen N.
      • et al.
      Serum tau and neurological outcome in cardiac arrest.
      • Moseby-Knappe M.
      • Mattsson N.
      • Nielsen N.
      • et al.
      Serum Neurofilament Light Chain for Prognosis of Outcome After Cardiac Arrest.

      Quanterix. Scientific Principle of Simoa (Single Molecule Array) Technology [Internet]. https://www.quanterix.com/whitepapers-appnotes/scientific-principle-simoa-single-molecule-array-technology/. Accessed 03-24-21.

      • Rissin D.M.
      • Kan C.W.
      • Campbell T.G.
      • et al.
      Single-molecule enzyme-linked immunosorbent assay detects serum proteins at subfemtomolar concentrations.
      GFAP concentrations were measured using sandwich enzyme-linked immunosorbent assay (ELISA) (Banyan Biomarkers).

      Neuroimaging

      CT was performed according to clinical indication. Primary outcome was signs of HIE on CT, qualitatively assessed by on-site radiologists through visual evaluation of generalised oedema as previously described.
      • Nielsen N.
      • Wetterslev J.
      • Cronberg T.
      • et al.
      Targeted temperature management at 33°C versus 36°C after cardiac arrest.
      These results were available during clinical decision-making. Quantitative GWR was retrospectively evaluated on original scan images from Swedish sites by a radiology resident with approximately-3 years of experience (ML), blinded to clinical data.
      • Lang M.
      • Nielsen N.
      • Ullén S.
      • et al.
      A pilot study of methods for prediction of poor outcome by head computed tomography after cardiac arrest.
      16 regions of interest (ROI) of approximately 0.1 cm2 (60 pixels) were used to calculate the GWR as previously described by Metter et al.
      • Metter R.B.
      • Rittenberger J.C.
      • Guyette F.X.
      • Callaway C.W.
      Association between a quantitative CT scan measure of brain edema and outcome after cardiac arrest.
      For scatter plot illustrations, neurological outcome at 6 months was dichotomized into good (Cerebral Performance Category scale (CPC) 1–2) or poor (CPC 3–5).
      • Teasdale G.
      • Jennett B.
      Assessment of coma and impaired consciousness. A practical scale.

      Statistical analysis

      The predictive capacity of biomarker levels at 24- and 48 h was assessed for CT examinations performed at 24–168 and 48–168 h, respectively. The earliest timepoint was chosen to explore the predictive capacity of early decision-making and the latter was determined by the earliest guideline recommended timepoint for NSE analysis in neurological prognostication after cardiac arrest.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      Kruskal Wallis statistical test was used for comparing binary outcome (presence/absence of HIE). Spearman’s rank-order correlation test was used for continuous outcome (GWR). The performance to predict HIE on CT was evaluated by area under the receiving operating characteristic curve (AUC).
      • Hosmer D.W.
      • Lemeshow S.
      • Sturdivant R.X.
      Applied Logistic Regression.
      Significance levels and 95% confidence intervals were calculated through bootstrap procedure (N = 2000 iterations). Biomarker cut-off levels to predict HIE were assessed by Youden index, for optimal sensitivity and specificity. Cut-offs were evaluated by positive predictive value (PPV; percentage of correctly confirmed HIE in patients with elevated biomarker levels) and negative predictive value (NPV; percentage of correctly excluded HIE in patients with low biomarker levels). To improve the readability of graphic illustrations the axes of the biomarker levels were transformed by log10. Scatter plots separated by neurological outcome were used to illustrate individual patients.
      P-values ≤ 0.05 were considered statistically significant. All statistical analyses were performed in R version 4.1.2.

      Results

      In total, 95 patients had available biomarker levels at 24 or 48 h and available CT scan results at 24–168 h, of which 27 patients from Swedish sites had available GWR measurements (Table 1, Fig. S1, Fig S2). All biomarker levels were significantly higher in patients with HIE on CT as compared to patients without HIE, p < 0.001 (Fig. S3, Fig. S4, Table S2, Table S3).
      Table 1Demographics of study population.
      Biomarkers 24 h

      CT 24-168 h
      Biomarkers 48 h

      CT 48-168 h
      Included

      (n=94)
      Excluded

      (n=845)
      Included

      (n=75)
      Excluded

      (n=864)
      Baseline data
      Age years65.0 (58.0-72.0)65.0 (56.0-73.0)65.0 (59.0-71.0)65.0 (56.0-73.0)
      Male73 (77.7)688 (81.4)58 (77.3)703 (81.4)
      Time to ROSC minutes26 (20-43)25 (17-39)26 (20-43)25 (17-39)
      Initial shockable68 (72.3)661 (78.2)56 (74.7)673 (77.9)
      GCS-M 1-3 on day 449/86 (57.0)179/683 (26.2)41/73 (56.2)187/696 (26.9)
      Head CT examinations
      Time to scan hours

      Missing Data
      77.5 (52.0-112.0)3.0 (1.0-10.75)

      615
      91.0 (73.0-115.5)3.0 (1.0-23.0)

      615
      Normal32 (34.0)196/263 (74.5)24 (32.0)204/282 (72.3)
      Signs of HIE46 (48.9)32/263 (12.2)38 (50.7)40/282 (14.2)
      Biomarkers
      NSE ng/ml34.9 (19.6-66.9)22.4 (14.8-38.6)68.4 (23.3-130.4)20.0 (12.7-46.3)
      NFL pg/ml1459.6 (209.5-3283.3)83.2 (28.6-834.8)3222.6 (670.4-7909.1)115.7 (36.8-2032.3)
      Total-tau pg/ml8.8 (3.9-39.5)4.2 (1.8-13.0)28.4 (6.3-118.4)3.6 (1.5-28.4)
      GFAP pg/ml99.7 (47.2-1041.3)48.3 (22.2-115.3)123.2 (66.8-2066.2)52.3 (24.7-139.7)
      Neurological outcome at six months
      Good 1-2 CPC21 (22.3)419 (49.6)15 (20.0)425 (49.2)
      Poor 3-5 CPC73 (77.7)420 (49.7)60 (80.0)433 (50.1)
      Results presented as median (IQR) for numeric variables and as count of numbers (%) for ordinal variables. ROSC = Return of spontaneous circulation. GCS-M = Glasgow Coma Scale Motor on day 4 (72–96 h post-arrest), 1–3 = no reaction to pain stimulus, abnormal extension or flexion, hence eligible for prognostication of neurological outcome according to current guidelines.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      HIE = Hypoxic-ischaemic encephalopathy. CPC = Cerebral Performance Categories (1–2 = good outcome, no or moderate neurological deficit, 3–5 = poor outcome, severe deficit, unresponsive wakefulness or death) at 6 months.
      • Teasdale G.
      • Jennett B.
      Assessment of coma and impaired consciousness. A practical scale.
      The total amount of included patients was 95, one patient had available biomarker levels at 48 h only.

      Predictive performance

      The performance of biomarkers at 24 h to predict HIE on CT (performed at IQR: 52.0–112.0 h) was similar for all biomarkers AUC NSE 0.72 (0.61–0.83), NFL 0.79 (0.69–0.89), total-tau 0.77 (0.68–0.87), GFAP 0.81 (0.73–0.98) (Fig. 1A). The performance at 48 h and CT performed at IQR: 73–116 h was also without significant difference; AUC NSE 0.82 (0.71–0.94), NFL 0.79 (0.67–0.91), total-tau 0.84 (0.74–0.95), GFAP 0.79 (0.67–0.90) (Fig. 1B).
      Figure thumbnail gr1
      Fig. 1A-B. Performance of biomarker levels to predict signs of HIE. Significance level and 95% CI calculated by bootstrap procedure, (N = 2000 iterations). A. Biomarker levels at 24 h and CT scans performed at 24–168 h post arrest, N = 88. B. Biomarker levels at 48 h and CT scans performed at 48–168 h post arrest, N = 67.

      Optimal cut-offs for prediction

      Youden Index derived cut-offs for predicting presence or absence of HIE at 48 h were: NSE 48 ng/ml, NFL 2549 pg/ml, total-tau 17 pg/ml and GFAP 96 pg/ml (Table 2). Patients with biomarker levels below cut-offs had very low likelihood of HIE on CT (NPV 77.3–91.7%). Patients with biomarker levels elevated beyond cut-offs had high likelihood of HIE on CT (PPV 73.3–83.7%). Cut-off levels at 24 h had lower predictive accuracy for NSE and total-tau whereas NFL and GFAP had similar predictive performance as compared to 48 h. A sensitivity analysis on patients still unconscious at day 4 was performed with similar results (Table S1).
      Table 2Youden calculated cut-offs at 24- and 48 h. Results are presented with 95% CI. PPV = Positive Predictive Value; percentage of correctly confirmed hypoxic-ischaemic encephalopathy (HIE) in patients with elevated biomarker levels. NPV = Negative Predictive Value; percentage of correctly excluded HIE in patients with low biomarker levels. Sensitivity: percentage of all patients with signs of HIE that had biomarker levels elevated beyond this cut-off. Specificity: percentages of all patients without HIE that had biomarker levels below this cut-off. TP = True Positive, elevated biomarkers and signs of HIE on CT. FP = False Positive; elevated biomarker levels without signs of HIE. TN = True Negative, low biomarkers and no signs of HIE. FN = False Negative; low biomarker levels and signs of HIE on CT.
      BiomarkersOptimal thresholdPPVNPVSensitivitySpecificityTPFPTNFN
      24 hNSE ng/ml32.168.1 (53.8-79.6) %68.3 (53.0-80.4) %71.1 (56.6-82.3) %65.1 (50.2-77.6) %32152813
      NFL pg/ml720.074.1 (61.1-83.99 %85.3 (69.9-93.6) %88.9 (76.5-95.2) %67.4 (52.5-79.5) %4014295
      Total-tau pg/ml6.271.7 (58.4-82.0) %80.0 (64.1-90.0) %84.4 (71.2-92.3) %65.1 (50.2-77.6) %3815287
      GFAP pg/ml82.074.0 (60.5-84.1) %78.9 (63.7-88.9) %82.2 (68.7-90.7) %69.8 (54.9-81.4) %3713308
      48 hNSE ng/ml48.382.9 (68.7-91.5) %84.6 (66.5-93.9) %89.5 (75.9-95.8) %75.9 (57.9-87.8) %347224
      NFL pg/ml2548.680.5 (66.0-89.8) %80.8 (62.1-91.5) %86.8 (72.7-94.3) %72.4 (54.3-85.3) %338215
      Total-tau pg/ml17.483.7 (70.0-91.9) %91.7 (74.2-97.7) %94.7 (82.7-98.5) %75.8 (57.9-87.8) %367222
      GFAP pg/ml95.873.3 (59.0-84.0) %77.3 (56.6-89.9) %86.8 (72.7-94.3) %58.6 (40.7-74.5) %3312175
      ESICM guideline1 NSE ng/ml 48 h6078.9 (65.8-90.5) %75.9 (55.6-85.8) %81.1 (63.7-88.9) %73.3 (57.9-87.8) %307228

      GWR

      Elevated biomarker levels at 24 h significantly correlated with reduced GWR (ρ24 h = negative 0.40–0.62), p < 0.05. At 48 h elevated NSE, NFL and total-tau significantly correlated with reduced GWR (ρ48h = negative 0.44–0.69), p < 0.05 (Fig. 2). GFAP presented with larger spread in biomarker levels, likely affecting the correlation coefficient and significance level.
      Figure thumbnail gr2
      Fig. 2Correlation of biomarker levels and quantitative GWR. Scatterplot separated by neurological outcome at 6 months after cardiac arrest; (yellow circles; good outcome, CPC 1–2, black triangles; poor outcome, CPC 3–5).
      • Teasdale G.
      • Jennett B.
      Assessment of coma and impaired consciousness. A practical scale.
      GWR = Grey-White-Matter Ratio, score closer to 1 indicates pathological extinction of normal attenuation difference. A-D, biomarkers 24 h, CT 24–168 h: NNSE = 25, NNFL = NTotal-Tau = NGFAP = 27. Spearman’s rank-order correlation test: NSE ρ24h = −0.42 p = 0.04, NFL ρ24h = −0.40 p-value = 0.04, Total-tau ρ24h = −0.49 p-value = 0.010, GFAP ρ24h = −0.62 p-value < 0.001. E-H, biomarkers at 48 h, CT 48–168 h: NNSE = 19, NNFL = NGFAP = NTotal-Tau = 21. Spearman’s rank-order correlation test: NSE ρ48h = −0.69 p = 0.001, NFL ρ48h = −0.44 p-value = 0.04, Total-tau ρ48h = −0.45 p-value = 0.04, GFAP ρ48h = −0.37 p-value > 0.05.

      Discussion

      In this retrospective analysis we present results suggesting that biomarker levels in blood can be used to predict signs of HIE on CT, a highly specific predictor of poor outcome after cardiac arrest. By using biomarker levels as an individualised decision aid to select suitable neuroimaging modality for adequate neurological prognostication, repeated examinations may be avoided – which could save resources and avoid additional risks for patients.
      We explored predictive performances of biomarkers at 24- and 48 h. According to international guidelines CT performed prior to 48 h is also of prognostic relevance, although its sensitivity in prediction has been reported to vary based on timing.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Streitberger K.J.
      • Endisch C.
      • Ploner C.J.
      • et al.
      Timing of brain computed tomography and accuracy of outcome prediction after cardiac arrest.
      • Lang M.
      • Nielsen N.
      • Ullén S.
      • et al.
      A pilot study of methods for prediction of poor outcome by head computed tomography after cardiac arrest.
      • In Y.N.
      • Lee I.H.
      • Park J.S.
      • et al.
      Delayed head CT in out-of-hospital cardiac arrest survivors: Does this improve predictive performance of neurological outcome?.
      By using biomarker levels at 24 h post-arrest more patients could be individually assigned to suitable neuroimaging modality with lower yet acceptable accuracy.
      We found that the optimal cut-off for NSE to predict signs of HIE on CT at 48 h was 48 ng/ml. Patients with biomarker levels ≥48 ng/ml were most often sufficiently examined with CT. Patients with NSE levels <48 ng/ml had very low likelihood of HIE on CT and we therefore suggest MRI to be considered for these patients to adequately map the extent of structural damage. This cut-off may reasonably apply on first examinations as well as for repeated neuroimaging on patients with early normal CT and delayed awakening.
      • Streitberger K.J.
      • Endisch C.
      • Ploner C.J.
      • et al.
      Timing of brain computed tomography and accuracy of outcome prediction after cardiac arrest.
      • Moseby-Knappe M.
      • Pellis T.
      • Dragancea I.
      • et al.
      Head computed tomography for prognostication of poor outcome in comatose patients after cardiac arrest and targeted temperature management.
      • In Y.N.
      • Lee I.H.
      • Park J.S.
      • et al.
      Delayed head CT in out-of-hospital cardiac arrest survivors: Does this improve predictive performance of neurological outcome?.
      NFL, total-tau and GFAP are not yet routinely available, which limits their clinical use. As their availability increase, their concentrations could also be used to guide decisions on neuroimaging modality. The applicability of this decision aid is determined by the accessibility to prompt biomarker analysis.
      The correlation of elevated biomarker levels and reduced GWR aligns with the results of qualitatively measured HIE on CT. Due to the lack of clinically established cut-off values for GWR and considering the small sample size, we decided to not perform any further calculations on prognostic accuracy.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Oh J.H.
      • Choi S.P.
      • Wee J.H.
      • Park J.H.
      Inter-scanner variability in Hounsfield unit measured by CT of the brain and effect on gray-to-white matter ratio.
      Strengths of this study include the prospective sampling and retrospective analysis of biomarker levels to avoid bias caused by having the analysis results upon clinical decision making as well as the blinded GWR assessements.
      • Mattsson N.
      • Zetterberg H.
      • Nielsen N.
      • et al.
      Serum tau and neurological outcome in cardiac arrest.
      • Moseby-Knappe M.
      • Mattsson N.
      • Nielsen N.
      • et al.
      Serum Neurofilament Light Chain for Prognosis of Outcome After Cardiac Arrest.
      • Ebner F.
      • Moseby-Knappe M.
      • Mattsson-Carlgren N.
      • et al.
      Serum GFAP and UCH-L1 for the prediction of neurological outcome in comatose cardiac arrest patients.
      • Nielsen N.
      • Wetterslev J.
      • Cronberg T.
      • et al.
      Targeted temperature management at 33°C versus 36°C after cardiac arrest.
      • Stammet P.
      • Collignon O.
      • Hassager C.
      • et al.
      Neuron-Specific Enolase as a Predictor of Death or Poor Neurological Outcome After Out-of-Hospital Cardiac Arrest and Targeted Temperature Management at 33°C and 36°C.
      Limitations include selection of poor outcome patients, limited sample size, known interrater and inter-scanner variability and lack of standardised approach for GWR-interpretation.
      • Nolan J.P.
      • Sandroni C.
      • Böttiger B.W.
      • et al.
      European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care.
      • Oh J.H.
      • Choi S.P.
      • Wee J.H.
      • Park J.H.
      Inter-scanner variability in Hounsfield unit measured by CT of the brain and effect on gray-to-white matter ratio.
      • Streitberger K.J.
      • Endisch C.
      • Ploner C.J.
      • et al.
      Timing of brain computed tomography and accuracy of outcome prediction after cardiac arrest.
      • Lang M.
      • Nielsen N.
      • Ullén S.
      • et al.
      A pilot study of methods for prediction of poor outcome by head computed tomography after cardiac arrest.
      Analysis of novel biomarkers were performed with research grade assays.
      • Nielsen N.
      • Wetterslev J.
      • Cronberg T.
      • et al.
      Targeted temperature management at 33°C versus 36°C after cardiac arrest.

      Conclusion

      Biomarker levels can be used to predict the likelihood of HIE on CT and may clinically be used to select suitable neuroimaging modality in unconscious patients after cardiac arrest. Patients with elevated biomarker levels often present with signs of HIE on CT. For patients with low biomarker levels, the likelihood of HIE on CT is very low and other guideline recommended tools for prognostication may instead be considered.

      Funding

      Funding for the study was provided by the Swedish Research Council, Swedish Heart Lung Foundation, Arbetsmarknadens Försäkringsaktiebolag Insurance Foundation, the Skåne University Hospital Foundations, the Gyllenstierna-Krapperup Foundation, and governmental funding of clinical research within the Swedish National Health System, the County Council of Skåne; the Swedish Society of Medicine; the Koch Foundation; TrygFonden (Denmark); European Clinical Research Infrastructures Network; Thelma Zoega Foundation; Stig and Ragna Gorthon Foundation; Thure Carlsson Foundation; Hans-Gabriel and Alice Trolle-Wachtmeister Foundation for Medical Research; Lions Research fund Skåne; South Swedish Hospital Region Research Funds; the Swedish Brain Foundation; the Lundbeck Foundation; and the Torsten Söderberg foundation at the Royal Swedish Academy of Sciences. KB is supported by the Swedish Research Council (#2017-00915), the Alzheimer Drug Discovery Foundation (ADDF), USA (#RDAPB-201809-2016615), the Swedish Alzheimer Foundation (#AF-930351, #AF-939721 and #AF-968270), Hjärnfonden, Sweden (#FO2017-0243 and #ALZ2022-0006), the Swedish state under the agreement between the Swedish government and the County Councils, the ALF-agreement (#ALFGBG-715986 and #ALFGBG-965240), the European Union Joint Program for Neurodegenerative Disorders (JPND2019-466-236), the National Institute of Health (NIH), USA, (grant #1R01AG068398-01), and the Alzheimer’s Association 2021 Zenith Award (ZEN-21-848495). HZ is a Wallenberg Scholar supported by grants from the Swedish Research Council (#2018-02532), the European Research Council (#681712 and #101053962), Swedish State Support for Clinical Research (#ALFGBG-71320), the Alzheimer Drug Discovery Foundation (ADDF), USA (#201809-2016862), the AD Strategic Fund and the Alzheimer's Association (#ADSF-21-831376-C, #ADSF-21-831381-C and #ADSF-21-831377-C), the Olav Thon Foundation, the Erling-Persson Family Foundation, Stiftelsen för Gamla Tjänarinnor, Hjärnfonden, Sweden (#FO2019-0228), the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860197 (MIRIADE), the European Union Joint Programme – Neurodegenerative Disease Research (JPND2021-00694), and the UK Dementia Research Institute at UCL (UKDRI-1003).

      Role of the Funder/Sponsor

      The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

      CRediT authorship contribution statement

      Alice Lagebrant: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Writing – original draft, Visualization. Margareta Lang: Conceptualization, Methodology, Investigation, Resources, Writing – original draft. Niklas Nielsen: Conceptualization, Methodology, Investigation, Resources, Writing – original draft, Supervision, Project administration, Funding acquisition. Kaj Blennow: Investigation, Formal analysis, Resources, Writing – review & editing. Josef Dankiewicz: Investigation, Resources, Writing – review & editing. Hans Friberg: Investigation, Resources, Writing – review & editing. Christian Hassager: Investigation, Resources, Writing – review & editing. Janneke Horn: Investigation, Resources, Writing – review & editing. Jesper Kjaergaard: Investigation, Resources, Writing – review & editing. Mikael A. Kuiper: Investigation, Resources, Writing – review & editing. Niklas Mattsson-Carlgren: Investigation, Resources, Writing – review & editing. Tommaso Pellis: Investigation, Resources, Writing – review & editing. Christian Rylander: Investigation, Resources, Writing – review & editing. Roger Sigmund: Investigation, Resources, Writing – review & editing. Pascal Stammet: Investigation, Resources, Writing – review & editing. Johan Undén: Investigation, Resources, Writing – review & editing. Henrik Zetterberg: Investigation, Formal analysis, Resources, Writing – review & editing. Matt P. Wise: Investigation, Resources, Writing – review & editing. Tobias Cronberg: Conceptualization, Methodology, Investigation, Resources, Writing – original draft, Supervision, Project administration, Funding acquisition. Marion Moseby-Knappe: Conceptualization, Methodology, Investigation, Resources, Writing – original draft, Supervision, Project administration, Funding acquisition.

      Conflicts of interest

      KB has served as a consultant, at advisory boards, or at data monitoring committees for Abcam, Axon, BioArctic, Biogen, JOMDD/Shimadzu. Julius Clinical, Lilly, MagQu, Novartis, Ono Pharma, Pharmatrophix, Prothena, Roche Diagnostics, and Siemens Healthineers, and is a co-founder of Brain Biomarker Solutions in Gothenburg AB (BBS), which is a part of the GU Ventures Incubator Program, outside the work presented in this paper. HZ has served at scientific advisory boards and/or as a consultant for Abbvie, Alector, ALZPath, Annexon, Apellis, Artery Therapeutics, AZTherapies, CogRx, Denali, Eisai, Nervgen, Novo Nordisk, Pinteon Therapeutics, Red Abbey Labs, reMYND, Passage Bio, Roche, Samumed, Siemens Healthineers, Triplet Therapeutics, and Wave, has given lectures in symposia sponsored by Cellectricon, Fujirebio, Alzecure, Biogen, and Roche, and is a co-founder of Brain Biomarker Solutions in Gothenburg AB (BBS), which is a part of the GU Ventures Incubator Program (outside submitted work).
      No other conflicts of interest were reported.

      Appendix A. Supplementary data

      The following are the Supplementary data to this article:
      • Supplementary data 1

        Figure S1. Flow chart for inclusion of biomarkers at 24 h. Figure S2. Flow chart for inclusion of biomarkers at 48 hFigure S3 A-D. Biomarker levels at 24 h separated by presence of HIE on CT (24-168 h). Figure S4 A-D. Biomarker levels at 48 h separated by presence of HIE on CT (48-168 h). Table S1. Sensitivity analysis: Youden calculated cut-offs at 24- and 48 h for modified population. Table S2. Detailed description of biomarker outliers of NFLTable S3. Detailed description of biomarker outliers of GFAP.

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