Automated Blood Aspiration
Blood samples must be automatically obtained to perform tests for heparin levels [21]
Current heparin monitoring protocol is an aPTT test every six hours and TEG every twelve hours [28]
Design Constraints:
- Flow rate
- Flow rate is dependent on tubing diameter
- High rate causes cell shearing [22]
- Low rate causes blood clotting [22]
- Volume of blood drawn
- ACT tests require at least 15 μL of blood [26]
- Blood loss of over 10% can cause a decrease in the amount of oxygen delivered to tissue [27]
- Blood loss of over 20% can decrease arterial pressure [27]
Methods:
- Continuous
- Pros
- Tubing will not need to be flushed out
- No shut-off system required
- Cons
- Draws too much blood
- Cannot dispose of test material easily
- Pros
- At Intervals
- Pros
- More control over volume drawn
- Gives time for test material disposal
- Cons
- Requires an electronic valve
- Requires regular flushing of tubing
- Pros
Biocompatibility
Surface biocompatibility is necessary for the tubing in the heparin monitoring system [29]
- Circulating Blood
- In order to conserve the volume of blood drawn, blood must be able to flow back into the patient
- Non-biocompatible tubing material could be picked up and delivered into the body
- Anticoagulation
- The tubing must have a means to prevent clotting within the tubing system
- Currently, this is often achieved by a coating of heparin [30]
Bleeding Controlling System
![](https://you.stonybrook.edu/tempnamegroup2/files/2020/09/ECMO-Fig_cropped-300x197.jpg)
Anticoagulation controlling systems in ECMO cause bleeding and haemorrhage complications. [22]
Design Constraints:
- Prevent Coagulopathic Haemorrhage [24]
- Control constant blood loss
- Measure platelets [24, 25]
- Prevent significant changes in blood pressure
- Vasoconstriction
Solution:
- Incorporation of a system that preserves coagulation levels in the ECMO circuit.
- Carry out hemoglobin tests
Limitations:
- Interference with other components in ECMO
- Oxygenator
- Lack of monitoring systems
- Blood clotting.
- Time consuming
- An estimate amount of platelets.
Image Source: https://www.pennmedicine.org/for-health-care-professionals/for-physicians/physician-education-and-resources/clinical-briefings/2017/june/ecmo-as-bridge-to-lung-transplant
[21]: Extracorporeal Life Support Organization. “ELSO Anticoagulation Guideline.” (2014). https://www.elso.org/Portals/0/Files/elsoanticoagulationguideline8-2014-table-contents.pdf
[22]: Hathcock, J. J. (2006). “Flow effects on coagulation and thrombosis.” Arterioscler Thromb Vasc Biol 26(8): 1729-1737.
[23]: Mulder, M. et al. “ECMO and anticoagulation : a comprehensive review.” (2018). https://nvic.nl/sites/nvic.nl/files/pdf/review_22.pdf
[24]: Esper SA, Welsby IJ, Subramaniam K, Jet al. Adult extracorporeal membrane oxygenation: an international survey of transfusion and anticoagulation techniques. Vox Sanguinis. 2017.
[25]: Balle, C.M., et al., Platelet Function During Extracorporeal Membrane Oxygenation in Adult Patients. Front Cardiovasc Med, 2019. 6: p. 114.
[26]: Craig S. Kitchens, B. M. A. a. C. M. K. (2007). Consultative Hemostasis and Thrombosis (Second Edition): Elsevier.
[27]: Kreimeier, U. (2000). Pathophysiology of fluid imbalance. Crit Care, 4 Suppl 2, S3-7. doi:10.1186/cc968
[28]: Colman, E., et al., Evaluation of a heparin monitoring protocol for extracorporeal membrane oxygenation and review of the literature. Journal of Thoracic Disease, 2019. 11(8): p. 3325-3335
[29]: Pieri, M., Turla, O. G., Calabro, M. G., Ruggeri, L., Agracheva, N., Zangrillo, A., & Pappalardo, F. (2013). A new phosphorylcholine-coated polymethylpentene oxygenator for extracorporeal membrane oxygenation: a preliminary experience. Perfusion, 28(2), 132-137. doi:10.1177/0267659112469642
[30]: Marasco, S. F. (2008). Review of ECMO (extra corporeal membrane oxygenation) support in critically ill adult patients. Heart Lung Circ, S41-47.