This document discusses automating the heart-lung machine used in open heart surgery. The heart-lung machine takes over the functions of the heart and lungs during surgery by pumping and oxygenating the blood. Currently, the heart-lung machine is operated manually which poses safety risks. The author presents a proof of concept for automating the control of the heart-lung machine using sensors to monitor the blood reservoir level and a computer to control the arterial pump speed to prevent the reservoir from emptying. Testing showed the sensor monitoring of the reservoir was accurate even with flow and vibration. Next steps proposed include integrating additional automation and monitoring of the blood circuit.

1. Automation of
Cardiopulmonary
Bypass
An Autopilot for the Heart-Lung
Machine
Kenneth Wilkerson

2. Theme
 Improving the safety of open-heart surgery
through automation of the heart-lung
machine

3. What is Cardiopulmonary Bypass?
 Removing heart & lungs from circulation
 Used during open heart surgery
 Heart stopped, opened
 E.G.:
 Coronary Artery Bypass Graft
 Valve repair/replacement
 Function taken over by a machine

4. What is a Heart-Lung Machine?
 Replaces function of heart and lungs
 Pump blood
 Oxygenate blood
 Set/maintain body temperature
 Other secondary functions

5. What is a Heart-Lung Machine?
 Key parts for primary purpose:
 Venous reservoir
 Arterial pump
 Heat exchanger
 Oxygenator
 Arterial filter
 Arterial-Venous (A-V) circuit

6. Key parts of heart-lung machine A-V Circuit

7. Early Heart-lung Machine

8. Modern Heart-Lung Machine

9. How is HLM operated?
 Manually
 Constantly monitored by a perfusionist
 Reservoir level
 Arterial line pressure
 Other
 Perfusionist also recording data
 Some sites automated

10. Attempts at automating
 1953 first successful use of HLM
 Within a few years attempt automating
 Measuring reservoir level
 Controlling pump based on reservoir level
 1990: first attempt to use computer
 Efforts continue

11. Why Automate?
 Improved safety
 Humans get tired, distracted;machines don’t
 Machines react faster
 Aviation automated before HLM
 Worst distraction scenario: reservoir empties,
pump air into patient
 Would you still need a person dedicated to
running HLM?

12. This Project
 Computer control of HLM
 Monitor Volume in venous reservoir
 Control speed of arterial pump
 Goal: do not allow reservoir level to drop
below critical level
 Proof of concept/feasibility study
 Description of possible next steps

13. Automated heart-lung machine
Reservoir
Autopilot
Arterial pump
Heat Heater-cooler
exchanger
Oxygenator Arterial filter

14. Test automated HLM

15. This Project: Technique
 Monitoring reservoir:
 Measure volume by weighing reservoir
 Suspend reservoir from strain gage
 Computer polls strain gage
 Control pump speed:
 Pump has connection for external control by
another pump (master-slave)
 Connect to D/A converter in computer
 Computer plays part of master

16. This Project – strain gage

17. Monitoring reservoir volume
 Why use this method?
 No blood contact
 Does not require modifying reservoir
 Easily adaptable to different bag reservoirs
 Other types of reservoirs have issues

18. Monitoring reservoir volume
 Tested three ways
 Maximum accuracy
 Effect of flow and vibration on accuracy
 Sensitivity to change in volume
 The tests cover patients from a small adult
female using a Cardiac Index of 1.8 to a
very large adult male using a Cardiac
index of 2.4

19. Cardiac Index
 Method of indexing blood flow to patient
size
 Size measured by Body Surface Area
 Calculated from height, weight
 E.g., CI 2.4 means 2.4 LPM per M2

20. This Project – simulated patient

21. Maximum accuracy
 Fill reservoir using graduated cylinder
 100ml to capacity in 100ml increments
 Strain gage reads to 0.01 Kg = 10ml
 Capacity is 1200ml
 Record value from strain gage
 Do three times to check repeatability

22. Maximum accuracy - Results
 Largest absolute error 0.01 Kg
 Largest percent error : 2.5 %
 0.01 Kg at 400ml
 Volumes < 400ml no error

23. Flow and Vibration
 Build basic circuit
 Use another reservoir to simulate patient
 Add different volumes to circuit
 1500ml to 3000ml
 500ml Increment
 Circulate at different flow rates
2 LPM to 7 LPM
 1 LPM increment

24. Flow and Vibration
 Take multiple readings from strain gage
 0.5 second interval
 Check variations in readings
 Results:
 Largest variation 0.03 Kg (1.12 to 1.15 Kg)
 Mostly variation 0.01
 Conclusion:
 Flow and vibration no effect on accuracy

25. Sensitivity to change
 Circulate at different flow rates
2 to 7 LPM, 1 LPM increment
 Fully or partially occlude input to reservoir
 Take readings of strain gage
 0.5 sec interval
 5 seconds
 Determine correlation coefficient

26. Sensitivity to change - Results
 Correlation coefficient: -0.91 to -1.00

27. Sensitivity to change – worst
Full occl. 4 LPM (67 ml/ sec)
1.5
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
1.05
1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ti m Seconds
e

28. Sensitivity to change – best
Full Occl. 7 LPM (120 ml/ sec)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ti m Seconds
e

29. Monitoring Reservoir -
Summary
 This method of monitoring volume is as
good as or better than standard of practice
which is the perfusionist reading the
volume from a scale on the side of
reservoir

30. Reservoir

31. Autopilot operator interface

32. Autopilot log
Max flow rate 1 LPM, min pct flow 50, low level 300, min level 100
700 1.2
600
1
500
0.8
reservoir level ml
400
flow rate LPM
Volume
0.6
Flowrate
300
0.4
200
0.2
100
0 0
1
2
3
4
5
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Time seconds

33. Demonstration
 Auto HLM demo

34. Overall results
 This method for automated control of a
heart-lung machine is feasible

35. Next steps
 How to build on this project
 Further automation of A-V circuit

36. Tasks – Part 1
 Modern pump
 Blood monitoring
 Gas flow and mixture
Reservoir
Autopilot
Arterial pump
Heat Heater-cooler
exchanger
Oxygenator Blood monitor Arterial filter

37. Modern pump
 Validate approach
 Tech support available
 Test over full range
 Stress test autopilot
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler
Oxygenator Blood monitor Arterial filter

38. Blood monitoring
 Inline, real-time
 PaO2, PaCO2, Sv02, Hgb
 Calc O2 consumption w/blood flow, show trend
 Tell if anesthesia wearing off
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler
Oxygenator Blood monitor Arterial filter

39. Gas flow and mixture
 Tighter control of blood gases
 Monitor gas/blood flow to O2 consumption ratio
 Detect impending oxygenator failure
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler
Oxygenator Blood monitor Arterial filter

40. Part 1 - result
 Key pieces automated
 Close attention of perfusionist
Reservoir
Autopilot
Arterial pump
Heat Heater-cooler
exchanger
Oxygenator Blood monitor Arterial filter

41. Tasks – Part 2
 Arterial line pressure
 Occluders
 Heater-cooler
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

42. Arterial line pressure
 Part of perfusionist scan
 High pressure requires stopping pump
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

43. Occluders
 Standard is scissor clamps
 Mainly used at initiation & termination
 Much to monitor
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

44. Heater-cooler
 Cool & rewarm blood w/heat exchanger
 From a few degrees to zero C
 Severe cooling means care rewarming
 Rewarm fast as possible without overheating
blood
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

45. Part 2 - result
 Allow autopilot to control initiation and
termination of bypass as well as monitor
Reservoir
Autopilot
Arterial pump
Heat exchanger Heater-cooler ALP monitor
Oxygenator Blood monitor Arterial filter

46. Part 2 – Autopilot operator interface

47. Part 3 – voice recognition
 More convenient in OR than mouse and
keyboard
 Quicker access
 Multiple locations
 Bluetooth headset

48. Voice recognition
 Two types of commands
 Normal– repeated back for confirmation
 Emergency – immediate execution

49. Voice recognition
 Sample normal dialog
 Perf: “autopilot increase blood flow zero point
five”
 Auto: “increase blood flow zero point five”
 Perf: “yes”
 Auto: “blood flow now at five point zero”

50. Voice recognition
 Sample emergency dialog
 Perf:“autopilot emergency stop”
 Auto: “pump stopped, gas flow stopped”

51. Overall design guidelines
 Perfusionist ultimate safety device
 Equipment will fail
 Always manual backup
 Switch quick and simple

52. References
 1. Austin Jon W., Harner David L.. The Heart-lung Machine and Related Technologies of Open Heart Surgery. Phoenix: Phoenix Medical Communications1986:7.
 2. Chronicle of Aviation, JL International Publishing Inc., 1992:462
 3. C CRAFOORD, B NORBERG, and A SENNING. Clinical studies in extracorporeal circulation with a heart-lung machine. Acta Chir Scand, Mar 1957; 112(3-4): 220-45.
 4. F OLMSTED, WJ KOLFF, and DB EFFLER. Three safety devices for the heart-lung machine. Cleve Clin Q, Jul 1958; 25(3): 169-76.
 5. Murray N. Andersen, M.D., James F Ulrich,P.E.,Christian V. Mouritzen, M.D. An automatic flow control system for extracorporeal circulation. Journal of thoracic and
Cardiovascular Surgery, Aug 1965;50(2):260-264
 6. A KANTROWITZ, S REINER, and D ABELSON. An automatically controlled, inexpensive pump-oxygenator.J. Thorac. Cardiovasc. Surg., Nov 1959; 38: 586-93.
 7. VINCENT L. GOTT, ROBERT D. SELLERS, RICHARD A. DeWALL, RICHARD L. VARCO, and C. WALTON LILLEHEI. A Disposable Unitized Plastic Sheet
Oxygenator for Open Heart Surgery. Chest, Dec 1957; 32: 615 - 625.
 8. Pierre M. Galletti M.D.,Ph.D,Gerhard A. Brecher, M.D.,Ph.D.. HEART-LUNG BYPASS, Principles and Techniques of Extracorporeal Circulation. Grune &
Stratton,1962:199
 9. Gerald Moss M.D.,Ph.D. A device to maintain automatically and continuously an absolute or relative constant weight of a subject or container during perfusion. Surgery,
June 1961
 10 . F. John Lewis,M.D., Sidney J. Horwitz, B.S.,Joseph B. Naines,Jr.,B.S. Semiautomatic control for an extracorporeal blood pump. Journal of thoracic and
Cardiovascular Surgery,March 1962,43(3):392-396
 11. James J. Roche, Irving Ungar,M.D.,Herman S. Coleman,M.D. An electric apparatus for rapid and precise regulation of the venous blood-reservoir height on heart-lung
machines. Surgery, September 1964,56(3):561-564
 12. Jeffrey B. Riley, B.A. CCT. A Technique for Computer Assisted Monitoring in the Management of Total Heart-lung Bypass. The Journal of Extra-Corporeal Technology,
1981, 13(1):171-176.
 13. Thomas Hankins, C.L.A.,C.C.P. Computer Assisted Bypass Management. The Journal of Extra-Corporeal Technology, 1980, 12(4):95-102
 14. J.B. Riley, M.B. Hurdle, B.A. Winn, P.A. Wagoner. Automation of Cardiopulmonary Bypass Data Collection. The Journal of Extra-Corporeal Technology,1985, 17(1):7-
12
 15. D. Gaillard,MD, C. Barraud,CCP, O. Bical, MD, L. Detoni,CCP, L.S. Montejo,MD,A. Venetti,MD. Use of an Extracorporeal Circulation Workstation During the Routine
Care of Cardiac Patients. Int J Artif Organs,1990 Feb,13(2):35-41
 16. N. Chauveau, W. Van Meurs, R. Barthelemy, J.P. Morucci. Automatic modules for extracorporeal circulation control. Int J Artif Organs, 1990,13(10):692-696
 17. Toshiyuki Beppu, ME, Yasuharu Imai, MD, Yasuhiro Fukui, PhD. A Computerized control system for cardiopulmonary bypass. The Journal of Thoracic and
Cardiovascular Surgery, 1995, 109(3):428-438
 18. US Patent No 7022099, A. Kenneth Litzie et al. Extracorporeal blood handling system with automatic flow control and methods of use. File: Mar 17, 2003, Issue: Apr 4,
2006
 19. Alfred H Stammers, Brian L Mejak.An update on perfusion safety: does the type of perfusion practice affect the rate of incidents related to cardiopulmonary bypass?.
Perfusion, 2001, 16:189-198
 20. Bryan V. Lich,CCP, D. Mark Brown, CCP. The Manual of Clinical Perfusion. Perfusion.com, Inc. 2004
 21. Glenn P. Gravlee MD, Richard F. Davis MD, Mark Kurusz CCP, Joe R. Utley MD. Cardiopulmonary Bypass Principles and Practice, second edtion. Lippincott Williams
& Wilkins 2000.
 22. Bryan V. Lich, CCP,D. Mark Brown CCP. The Manual of Clinical Perfusion, Second Edition Updated. Perfusion.Com 2004:47
 23. Glenn P. Gravlee MD, Richard F. Davis MD, Mark Kurusz CCP, Joe R. Utley MD. Cardiopulmonary Bypass Principles and Practice, second edtion. Lippincott Williams
& Wilkins 2000: 88
 24. Bryan V. Lich, CCP, D. Mark Brown CCP. The Manual of Clinical Perfusion, Second Edition Updated. Perfusion.Com 2004:71
 25. Bryan V. Lich, CCP, D. Mark Brown CCP. The Manual of Clinical Perfusion, Second Edition Updated. Perfusion.Com 2004:79

53. Acknowledgement
 Cardiovascular Science/Perfusion
department MWU Glendale, AZ