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Minimal Safe Arterial Blood Flow During Selective Antegrade Cerebral Perfusion at 20° Centigrade
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Radiology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Thoracic Surgery.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Radiology.
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2011 (English)In: Annals of Thoracic Surgery, ISSN 0003-4975, E-ISSN 1552-6259, Vol. 91, no 4, 1198-1205 p.Article in journal (Refereed) Published
Abstract [en]

Background

Selective antegrade cerebral perfusion (SACP) enables surgery on the aortic arch, where cerebral ischemia may cause neurologic sequels. This study aims to identify the minimum arterial flow level to maintain adequate cerebral perfusion during SACP in deep hypothermia in the pig.

Methods

Two groups of pigs were subjected to SACP at 20°C α-stat. In group 1 (n = 6), flow was stepwise adjusted from 8-6-4-2-8 mL · kg−1 · min−1 and in group 2 (n = 5), flow was kept constant at 6 mL · kg−1 · min−1. Magnetic resonance imaging and spectroscopy were performed at each flow level together with hemodynamic monitoring and blood gas analysis. The biochemical marker of cerebral damage protein S100β was measured in peripheral blood.

Results

Decreased mixed venous oxygen saturation and increased lactate in magnetic resonance spectroscopy was seen as a sign of anaerobic metabolism below 6 mL · kg−1 · min−1. No ischemic damage was seen on diffusion-weighted imaging, but the concentrations of S100β were significantly elevated in group 1 compared with group 2 at the end of the experiment (p < 0.05). Perfusion-weighted imaging showed coherence between flow setting and cerebral perfusion, increase of blood volume across time, and regional differences in perfusion during SACP.

Conclusions

The findings suggest an ischemic threshold close to 6 mL · kg−1 · min−1 in the present model. Regional differences in perfusion during SACP may be of pathogenic importance to focal cerebral ischemia.

Place, publisher, year, edition, pages
2011. Vol. 91, no 4, 1198-1205 p.
Keyword [en]
cerebral perfusion
National Category
Physiology
Research subject
Thorax Surgery
Identifiers
URN: urn:nbn:se:uu:diva-147480DOI: 10.1016/j.athoracsur.2010.12.066ISI: 000288785800057PubMedID: 21353198OAI: oai:DiVA.org:uu-147480DiVA: diva2:400451
Funder
Swedish Research Council, k2010-64x-08268-23-3
Available from: 2011-02-25 Created: 2011-02-25 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Cerebral Perfusion and Metabolism during Experimental Extracorporeal Circulation
Open this publication in new window or tab >>Cerebral Perfusion and Metabolism during Experimental Extracorporeal Circulation
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Neurologic injuries are major causes of mortality and morbidity after cardiac surgery. This thesis aimed to investigate cerebral metabolism and perfusion abnormalities in pigs during hypothermic circulatory arrest, selective antegrade cerebral perfusion (SACP) and extracorporeal circulation following progressive venous stasis.

Hypothermic circulatory arrest induced a metabolic pattern consistent with overt ischaemia, which was absent following SACP. In contrast, metabolism during SACP was influenced by the perfusate temperature, where a colder perfusate (20 °C) preserved cellular metabolism and membrane integrity better than a warmer perfusate (28 °C).

The minimum SACP flow required to maintain metabolism during hypothermia at 20 °C was investigated with magnetic resonance imaging, protein S100β, near infrared spectroscopy and microdialysis. The findings suggested an ischaemic threshold close to 6 ml/kg/min in the present models. Furthermore, regional differences in perfusion with a hemispheric distribution were apparent at all flow levels and differed from earlier studies where the differences were uniform and followed a neuranatomical pattern.

Venus stasis following superior vena cava congestion produced measurable signs of impaired cerebral perfusion and patterns of cerebral ischaemia were evident in individual animals. As venous pressure increased, the mean arterial pressure stayed more or less unchanged, generating reduced cerebral perfusion pressure and consequently an increased risk of ischaemia, which may impair cerebral perfusion, especially in cases of compromised arterial flow during extracorporeal circulation.

In conclusion, cerebral metabolism and perfusion are influenced by temperature, SACP flow levels and venous congestion. In clinical practice, the regional differences in perfusion during SACP may be of pathogenic importance in focal cerebral ischaemia. Furthermore, the reduced superior vena cava cannula flow may pass undetected during bicaval cardiopulmonary bypass if the superior vena cava flow is not specifically monitored.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 649
Keyword
cerebral perfusion
National Category
Physiology
Research subject
Thorax Surgery
Identifiers
urn:nbn:se:uu:diva-147486 (URN)978-91-554-8016-5 (ISBN)
Public defence
2011-04-08, Enghovssalen, Hus 50,, Thoraxkliniken, Akademiska Sjukuset, 17185, Uppsala, 13:15 (Swedish)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2011-03-17 Created: 2011-02-25 Last updated: 2011-05-04Bibliographically approved
2. Quantitative Tracer Based MRI Perfusion: Potentials and Limitations
Open this publication in new window or tab >>Quantitative Tracer Based MRI Perfusion: Potentials and Limitations
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tracer based MRI perfusion measurements is a clinically useful tool to assess regional distributions of tissue blood flow and volume. The method may be based on any of the three relaxation mechanisms T1, T1 and T2*, the latter denoted DSC-MRI being the most common. The primary aim of this work was to study the feasibility of obtaining quantitative estimates using these methods.

1) Feasibility of DSC-MRI for kidneys using an iron oxide based contrast agent and the influence of secondary relaxation effects on the results, part of a clinical phase II trial: The method proved feasible and the underestimation induced by secondary relaxation can be corrected for by using a double echo sequence.

2) Influence of blood flow rate on risk factors for developing cerebral ischemia during cardio pulmonary bypass, measurements in pig with gadolinium based DSC-MRI: The results indicated an ischemic threshold level at a blood flow rate of approximately 6 ml/kg/min.

3) The ability of gadolinium based DSC-MRI to detect changes in global blood flow, experimental measurements in pig and numerical simulations: The results support that DSC-MRI can discriminate between global flow levels in the same subject given that all other parameters are kept constant. The results also indicate that calculated perfusion values are highly sensitive to the arterial deconvolution procedure.

4) Influence of differences in blood/tissue relaxivity and secondary relaxation for a gadolinium based contrast agent, measurements in pig and numerical simulations: The blood/tissue relaxivity ratio is not unity and the situation is complicated by secondary relaxation effects. Deconvolution regularization appears to partly counteract the overestimation induced by difference in blood/tissue relaxivity for DSC-MRI.

In summary, the fundamental assumption of equal blood and tissue relaxivity is experimentally shown to be invalid and the influence of this discrepancy is substantial. Several factors contribute to measurement errors, a combination of these factors can incidentally lead to additive errors or error cancellation based on a variety of experimental and analysis conditions. Given that the differences in blood/tissue relaxivity cannot readily be accounted for in a clinical setting, absolute perfusion quantification by tracer based MRI remains challenging if not impossible.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 761
Keyword
MRI, Perfusion, Contrast agent, Relaxivity
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Radiology
Identifiers
urn:nbn:se:uu:diva-171901 (URN)978-91-554-8330-2 (ISBN)
Public defence
2012-05-16, Auditorium Minus, Museum Gustavianum, Akademigatan 3, Uppsala, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2012-04-25 Created: 2012-03-29 Last updated: 2012-08-01Bibliographically approved

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Jonsson, OveMorell, ArvidLundström, ElinTovedal, ThomasThelin, StefanAhlström, HåkanBjörnerud, AtleLennmyr, Fredrik

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