Oxygenators Pt 2

How can you tell if oxygenator is failing?

• PO2 continues to fall even with increased FiO2

• PCO2 continues to increase despite increased gas flow rate

• Progressive increase in pressure across oxygenator

What are oxygenator change-outs assocaited with?

Increased morbidity and mortality

How do you confirm your oxygenator is failing?

Calculate the oxygen transfer and compare it to the expected oxygen transfer of the oxygenator

DO₂= Q x (Ca - Cv)

Algorithm for failure identification of oxygenator

Oxygenation safety algorithm

How do you test blood path integrity of oxygenator?

Liquid pressure test

What is liquid pressure test for oxygenator blood path integrity?

Subject blood path of the device to 1.5 times the maximum pressure for 6 hours to determine leakage and increase pressure gradually

What is liquid pressure test for heat exchanger?

Subject the heat exchanger fluid path to 1.5 times maximum pressure for 6 hours

How do you test gas path integrity?

Subject the gas pathway to 1.5 times the maximum recommended pressure limit for 10 minutes

What is static prime volume for oxygenator?

Minimum volume of fluid residing in the oxygenator after priming at zero flow

How do you calculate carbon dioxide transfer?

F * (% change CO2)

What is rated blood flow?

Maximum flow at which oxygenation can yield 95% O2 saturation with 65% O2 saturation at venous inlet

What is carbon dioxide reference blood flow?

Flow rate in which CO2 content is decreased by 38mL/L of blood flow

What is oxygen reference blood flow?

Flow rate in which O2 content is increased by 45 mL/L of blood flow

What is reference blood flow?

Lowest CO2 reference flow, O2 reference flow, manufacturer’s recommended blood flow

What is index of hemolysis?

Quantity of plasma-free hemoglobin generated in vitro per 100 L of blood pumped through the oxygenator

What is initial priming volume?

Volume of blood to fill oxygenator and heat exchanger to the manufacturer’s recommended minimal reservoir volume

What is maximum operating volume?

Volume of blood contained in the device at the maximum reservoir level recommended by the manufacturer at the reference blood flow

What is minimum operating volume?

Minimum volume contained in the venous reservoir recommended by the manufacturer at the reference blood flow

How do you choose the size of your oxygenator?

Based on patient’s blood flow and rated blood flow for the oxygenator

Why do we use hypothermia?

Decreased basal metabolic rate which protects cerebral and myocardia

What is le chatelier’s principle?

When an environment stresses equilibrium, the equilibrium will shift to relieve the stress

What are the modes of heat transfer?

• Conduction

• Convection

• Radiation

How does conduction work?

Energy exchange by direct contact from one mass to another

What is convection?

Occurs within a fluid by mixing one portion of a fluid within another

How does radiation work?

Electromagnetic radiation emitted from the surface of a body that has been thermally excited

What is heat capacity?

Amount of heat required to raise its temperature by 1C

What is specific heat?

Heat capacity of 1 gram of substance

What does it mean it heat capacity is high?

It requires more heat to raise its temperature

How do you calculate heat transfer per unit time?

What are most heat exchangers made of?

Stainless steel

What are ideal characteristics of heat exchanger?

• Counter current flow

• Larger surface area

Why is aluminum not used as often for heat exchanger?

• Poor biocompatibility, must be coated

• Presence of aluminum micro emboli seen

What is Fourier’s law of heat flow?

Rate of heat transfer between water and blood is proportional to

• Temperature gradient

• Surface area

• Ability of material to transfer heat

Q = -KD (dT)/(dx)

How should you limit gas emboli formaiton?

Limit gradient to 8-10 C

Why should you always do water test first with heat exchanger?

Dissipates static electricity charges that may develop in the roller head

What is the coefficient of heat exchange?

How do we increase heat flow?

• Countercurrent flow

• Creating chevrons to promote mixing and larger surface area

• Minimizing thickness without sacrificing integrity

• Increase time in pathway

What should you maintain gradient between arterial and venous blood?

<8 during cooling

What is the average performance factor range at the rated flow in a heat exchanger?

0.4-0.8

What type of water can you put in heat exchanger?

Distilled water

What type of heat transfer does our heat exchanger use?

Conduction

What is k (thermal conductivity) of stainless steel?

311

How does solubility of gases change as we cool?

Solubility increases and gases go into solution

What is max temp for perfusate?

37 C - should never go over because it can cause brain injury

How to calculate gas transfer?

How do you calculate heat exchanger performance?