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23rd May 2022
The presence of contrast agent pooling (CAP) is strongly associated with a subsequent in-hospital cardiac arrest one hour later, according to the findings of a retrospective analysis by a team from the Department of Emergency Medicine, Far Eastern Memorial Hospital, New Taipei City, Taiwan.
Within emergency departments, computed tomography (CT) scans are a widely used imaging modality for the detection of a number of conditions such as blood clots, kidney stones, head injuries etc. Prior to a CT and irrespective of the reason for the scan, radiologists ensure that a patient is clinically stable. However, despite the appearance of clinical stability, there are case reports of patients who experience a cardiac arrest while undergoing a CT scan.
Interestingly, these reports have also described some characteristic features on the scan. The first case to be reported was in 2002 and the authors identified the presence of contrast agent pooling in the dependent parts of the right side of the body, including the venous system and the right lobe of the liver. This likely occurs due to a pump failure of the heart, leading to stasis of blood in the dependent organs of the body.
Moreover, once the heart stops pumping, there is a drop in both arterial and venous pressures and because the contrast agent is heavier than blood, CAP occurs in the dependent portions of the venous system.
Although this CAP sign has been reported in several cases, but clearly it not a common phenomenon, it remains uncertain as to whether the presence of CAP has any potential prognostic value for an imminent in-hospital cardiac arrest.
For the present study, the researchers performed a retrospective analysis of all patients admitted to their hospital and who underwent a CT scan and then experienced an in-hospital cardiac arrest and collected both demographic and clinical data for these patients.
The occurrence of the CAP sign on a chest or abdominal scan was recorded and was defined by accumulation of the contrast agent in the renal, hepatic vein or dependent part of the liver, or if there was contrast agent layering over the vena cava.
The primary outcome of interest was the accuracy of the CAP sign in predicting an imminent cardiac arrest (defined as within 1 hour after the CT scan).
CAP sign and cardiac arrest
A total of 128 patients with a mean age of 69 years (60.2% male) were included in the analysis, among whom, 8.6% were positive for the CAP sign on a CT scan.
With respect to the primary outcome, the accuracy of the CAP sign in predicting cardiac arrest was 85.94% (95% CI 78.69 – 91.45%) and the positive predictive value was 64%. Additionally, the CAP sign was significantly associated with a cardiac arrest within 1 hour (odds ratio, OR = 7.35, 95% CI 1.27 – 42.59).
The authors concluded that the CAP sign could be viewed as an imaging feature of circulatory failure and its presence should be taken as a warning sign to clinicians to allow them to provide timely interventions for critically ill patients.
Lee YH et al. Contrast Agent Pooling (C.A.P.) sign and imminent cardiac arrest: a retrospective study BMC Emerg Med 2022
7th March 2022
Neurofilament light is the best biomarker for the assessment of brain injury in patients who experience hypoxic ischaemic brain injury (HIBI) after the return of spontaneous circulation following a cardiac arrest. This was main finding of a systematic review and meta-analysis by a team from the Division of Critical Care Medicine, Vancouver General Hospital, Vancouver, Canada.
Hypoxic-ischaemic brain injury, represents a recognised consequence of cardiac arrest. For example, in one study examining the cause of death after an out-of-hospital cardiac arrest, it was found that neurological injury was responsible for two-thirds of all deaths.
In fact, HIBI after cardiac arrest is a leading cause of mortality and long-term neurologic disability in survivors. Moreover, patients with HIBI are at a high risk for secondary brain injury from, for example, brain oedema, tissue ischaemia and haematoma expansion.
Biomarkers can be used to identify those at risk through the provision of prognostic information and two such marker, neuron specific enolase (NSE) and S-100B are released following injury to neurons and glial cells, respectively and their blood values are presumed to correlate with the extent of HIBI following a cardiac arrest.
Others include neurofilament light (which reflects white matter damage) and tau although the relative prognostic value of these biomarkers has not been evaluated.
For the present analysis, the Canadian team searched electronic databases for studies using biomarkers including neuron specific enolase, S100 beta, S100 calcium binding protein, tau and neurofilament light.
They included only those for which at least one of the biomarkers was used to prognosticate the neurological outcome for patients with HIBI after a cardiac arrest. The team calculated the summary receiver operating characteristic curve (SROC) for each biomarker at 48 hours after the cardiac arrest and used this as the primary outcome measure.
Subgroup analysis was performed comparing with targeted temperature management (TTM), which is a recognised method designed to minimise post-anoxic injury and improving neurological outcome after cardiac arrest.
Neurofilament light and predictive value for neurological outcomes
A total of 86 studies with 10, 567 patients and a mean age of 62.8 years (73.6% male) were included in the final analysis.
In terms of the SROC, neurofilament light had the highest area under the curve (AUC) for predictive value of unfavourable neurological outcomes, with a value of 0.92 (95% CI 0.84 – 0.97), followed by tau with an AUC of 0.89 (95% CI 0.71 – 0.97). This was higher than neuron-specific enolase (AUC = 0.84) and S100 calcium (AUC = 0.85).
When compared with TTM, SROC curves were calculated for each biomarker and the results did not differ appreciably and neurofilament light still had the highest AUC (0.92, 95% CI 0.86 – 0.95).
The authors concluded that neurofilament light which is a biomarker for white matter damage, was associated with the highest accuracy to predict unfavourable neurological outcomes in those with HIBI after a cardiac arrest.
Hoiland RL et al. Neurologic Prognostication After Cardiac Arrest Using Brain Biomarkers: A Systematic Review and Meta-analysis. JAMA Neurol 2022