Current methods of anticoagulation monitoring: Heparin is usually monitored with the APTT (activated partial thromboplastin time) method. It tests the time it takes for your blood to clot [14].

Problems with method: Can’t always accurately predict things. Current methods are the best we have, but technology is not good enough yet [15].

Other methods, such as activated clotting time (ACT) and anti-factor XA are used, though they are not as accurate, or do not provide enough information [15].

A balance is needed to prevent bleeding and clotting. Anticoagulation tests are needed to determine how much anticoagulant to use, however, these tests are not always accurate. Current methods are limited and not good enough [14].

Test results vary among individual, and test procedure varies among ECMO centers. The standard range of test results may not accurately predict the clotting time for different individuals [13],[16].

Our criteria:

  1. Accurate blood clot formation time prediction. 
  2. Does not interfere with body activities.
  3. Detect blood clots through their chemical or physical property [13]. 
  4. Affordable. 
  5. Constant monitoring.
  6. Compatible Biomaterial for the Tubing used in the ECMO machine

 

Accurate prediction of

coagulation time

Accurate prediction of

coagulation time
  • We must ensure our testing method accurately predicts if a patient’s blood is likely to clot
  • Various testing array is used to ensure accuracy
  • Scan different body parts to ensure no unnoticed clots
  • Blood tests prior to surgery are recommended to determine clotting time of patient and that will allow us to determine how much anticoagulant is initially needed
  • The color Doppler ultrasound is used as the last resort to see if any blood clot has already formed
Safety
  • Monitoring can’t be too invasive
  • Blood is taken from the tube connecting to the ECMO, not additional penetration needed to the patient’s skin for blood sample collection
  • None of the arrays should interfere with the normal body activity
  • No additional reagents injected into the patient
Biomaterial of the tube to prevent coagulation of blood within tubes

Biomaterial of the tube to prevent coagulation of blood within tubes
  • Must mimic human blood vessels
  • Cannot change the qualities of the blood (make it thinner or add foreign species) (sterile)
  • Blood must be able to flow through freely and coagulate as it normally would, without any interference
Constant Monitoring
  • aPTT tests would be performed every 6 hours
  • D-dimer tests would be performed every 6 hours
  • The results would be sent to a program that would alert the doctor if something was wrong
  • If the aPTT and D-dimer tests disagree an ultrasound will be used
Limitations

Limitations
  • Must consider intervals at which blood will be drawn
  • What is a healthy amount of blood to be drawn?
  • Is actual real-time required?
  • At what point does a clot become a problem?
  • Must ensure that blood pressure is relatively stable
  • Accuracy of aPTT test and D-dimer test are not always accurate, ultrasound with good operating protocol may have higher accuracy but can be costly
Cost
  • Constant D-dimer and aPTT tests will cost a lot after several uses
  • New ECMO tubing would have to be made (cannot use normal PVC + plasticizer)
  • The ultrasound machine needs to be small enough to be portable
Contraindication
  • Patients with impaired blood coagulation ability such as Hemophilia, Von Willebrand disease, and clotting factor deficiencies;[18]
  • Patients on medication such as such as antihistamines, vitamin C (ascorbic acid), aspirin, and chlorpromazine;[19] may not respond to these tests.

 

 

figure 2

Various anticoagulants used in ECMO devices and their monitoring methods[13].

 

References

  • [11]Zeibi Shirejini, Saeedreza, et al. “Current and future strategies to monitor and manage coagulation in ECMO patients.” Thrombosis Journal, vol. 21, no. 1, 2023, https://doi.org/10.1186/s12959-023-00452-z.
  • [12]Kumar G, Maskey A. Anticoagulation in ECMO patients: an overview. Indian J Thorac Cardiovasc Surg. 2021 Apr;37(Suppl 2):241-247. doi: 10.1007/s12055-021-01176-3. Epub 2021 Mar 23. PMID: 33967447; PMCID: PMC8062644.
  • [13]Chlebowski, M.M., Baltagi, S., Carlson, M. et al. Clinical controversies in anticoagulation monitoring and antithrombin supplementation for ECMO. Crit Care 24, 19 (2020). https://doi.org/10.1186/s13054-020-2726-9
  • [14]Tung Phi Nguyen, Xuan Thi Phan, Dai Quang Huynh, Ha Thi Viet Truong, Yen Nguyen Hai Le, Tuan Manh Nguyen, Quan Quoc Minh Du, Thao Phuong Le, Hai Ngoc Truong, Thi Thi Ho, Thao Thi Ngoc Pham, “Monitoring Unfractionated Heparin in Adult Patients Undergoing Extracorporeal Membrane Oxygenation (ECMO): ACT, APTT, or ANTI-XA?”, Critical Care Research and Practice, vol. 2021, Article ID 5579936, 7 pages, 2021. https://doi.org/10.1155/2021/5579936
  • [15]Lee, S., Chaturvedi, A. Imaging adults on extracorporeal membrane oxygenation (ECMO). Insights Imaging 5, 731–742 (2014). https://doi.org/10.1007/s13244-014-0357-x
  • [16]https://www.hopkinsmedicine.org/health/conditions-and-diseases/coagulation-disorders#:~:text=Coagulations%20disorders%20are%20conditions%20that,thrombosis%20are%20all%20coagulations%20disorders
  • [17] https://www.testing.com/tests/partial-thromboplastin-time-ptt-aptt/