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
• At Intervals
  • Pros
    • More control over volume drawn
    • Gives time for test material disposal
  • Cons
    • Requires an electronic valve
    • Requires regular flushing of tubing

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

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

[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.