Modifying Cardiopulmonary Bypass Machine for Pediatric Patients Pumped and Ready Group 5: Kelsey Henderson, Kr ishane Suresh, Kaylee McCormack, Holly Rollin

Department of Chemical Engineering, Auburn University, Auburn, AL, USA

When a patient undergoes open-heart cardiopulmonary bypass surgery, the

blood is transferred to an artificial heart lung machine which receives the deox-

ygenated blood from the patient, oxygenates it, and returns it to the body. This

allows surgeons to temporarily stop the heart while they perform the necessary

repairs. Since most heart lung machines (HLM’s) are designed for adults, and

simply scaling down the machines for pediatric versions may cause unwanted

complications, new designs for pediatric HLM’s are typically considered.

Minimize priming volume of system Select tubing diameters that maintain laminar flow Optimize diameter of tubing to minimize shear stress Minimize length of tubing to reduce effects of shear stress Optimize for cost and safety of process for patient Analyze and select ideal process components

1. Laminar flow 2. Differences between male and female negligible 3. Constant density

Modifications and Analysis

Design Schematics

References

Assumptions

Conclusions

Cost and Safety Analysis

Component Analysis

Other necessary components: arterial filter, cannulae, PVC tubing, air removal device & monitor.

Patient

Classification

Patient age

(years)

Body Surface

Area (m2)

Aortic Annulus

Diameter (m)

Blood Flow

Velocity (m/s)

Blood Flow

Rate (m3/s) Shear Stress

(N/m2)

Infant/Toddler 0 – 5 0.41 0.0087 0.57 3.39 x 10-5 0.915

Child/Tween 5 - 13 1.10 0.0143 0.595 9.55 x 10-5 0.585

Adult 13 + 1.65 + 0.0201 0.575 1.83 x 10-4 0.400

Table 1: Patient classifications based on various given

Fig 1: Based on these analyses a membrane oxygenator, a centrifugal pump, and a pressurized reservoir were selected as the ideal system components for each of our rede-signed systems.

0

50

100

150

200

0 2 4

Prim

ing V

olume

(mL)

Tubing Length (m)

Tube Length vs Priming Volume

Separate SystemIntegrated System

0

50

100

150

200

250

0.0

0.5

1.0

1.5

2.0

2.5

1/8 3/16 1/4 5/16 3/8

Pri

min

g V

olum

e (m

L)

Shea

r St

ress

(P

a)

Tube Diameter (in)

Tube Diameter vs Shear Stress and Priming Volume

Shear Stress

Optimal ShearStress

PrimingVolume

Final Design Specifications

Minimized priming volume of system by optimizing length and diameter of tubing

Laminar flow maintained for all tubing sizes Optimized diameter and length of tubing to minimize shear stress Optimized for cost and safety of process for patient Analyzed and selected ideal process components as shown

4. Temperature changes negligible 5. Newtonian fluid (constant viscosity) 6. Tubing surfaces can be considered smooth

0500

100015002000

1/8 3/16 1/4 5/16 3/8 7/16 1/2 9/16

Rey

no

lds

Nu

mb

er

Tube Diameter (in)

Tube Diameter vs. Reynolds Number

InfantChild

Fig 7

Fig 8

$32,500

$24,375

$1,000

$24,375

$0

$5,000

$10,000

$15,000

$20,000

$25,000

$30,000

$35,000

Non-Integrated(conventional HLM)

Integrated (mini-HLM)

Cos

t (U

SD

)

Cost Comparison of Non-Integrated and Integrated HLMs Startup Costs

Variable Costs

Figures 7 & 8, from Mozol, K., et al., compare groups M and C. Group M contains infants who underwent surgery with the miniaturized HLM, while group C used the conventional HLM. Figure 9, displays the comparison of start up and variable costs for the two designs compiled from data found during research.

Fig 9

Design 1 (Integrated) Design 2 (Standard) Design 3 (Integrated) Design 4 (Standard) Volumetric Flow Rate (mL/min) 700 700 700 700

Length of Tubing (m) 1 3 1 3 Diameter of Tubing (in) 1/4 1/4 5/16 5/16

Head of pump (cm) 14.361 34.052 6.096 14.161 Shear Stress (Pa) 0.813 0.813 0.416 0.416

Priming Volume (mL) 110.653 149.959 128.458 203.374

Table 2: Critical data for each of the final four designs

1. Arens J., Schnoring H., Reisch. F., et al: Development of a miniaturized heart-lung machine for neonates with congenital heart defect. ASAIO Journal 2008. 2. Viscosity and Density of Blood. http://www.unc.edu/~tammyj/Viscosity.htm (accessed December 2, 2014).

3. Wedro, Benjamin. Pediatric Vital Signs: Get a Helpful Chart. http://www.emedicinehealth.com/pediatric_vital_signs/article_em.htm (accessed December 2, 2014).

4. Mozol K., Haponiuk I., Byszewski A., Maruszewski B.: Cost—effectiveness of mini-circuit cardiopulmonary bypass in newborns and infants undergoing open heart surgery. Kardiologia Polska 2008; 66:9. 5. Perfusion.com. Equipment Sales. http://www.perfusion.com/services/clinical/equipment/equipment-sales (accessed Nov. 30. 2014). 6. Pfuntner, A., Wier L., Steiner C. Cost of Hospital Stays in the United States, 2010. Agency for Healthcare Research and Quality [Online] 2013, 145, 2. http://www.hcup-us.ahrq.gov/reports/statbriefs/sb146.pdf (accessed Nov. 30, 2014).

Fig 4: Optimization of tube length with respect to prim-ing volume

Fig 6: Maintenance of laminar flow through varying tube diameter

Fig 5: Optimization of tube diameter with re-spect to shear stress and priming volume

Fig 3: Standard Heart Lung Machine

Fig 2: Integrated Heart Lung Machine

Membrane Oxygenator vs. Bubble Oxygenator

Centrifugal Pumps vs. Positive Displacement Pumps

Pressurized Reservoir vs. Vented Reservoir

Background and Significance

Goals and Parameters

Patient Specifications