Physiology of ECMO Flashcards by Alpha Healy

Our bodies depend on…

Delivering the appropriate amount of oxygen to each cell

The ability of each cell to take-up and consume the proper amount of oxygen

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What ECMO will do to help

Drain venous blod
provide a pump for cardiac output
oxygenate and remove CO2 via an artificial lung
maintain temperature via a heat exchanger
returning blood to the patient via a:
vein (VV) or an artery (VA)

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ECMO Physiological Goals

Improve blood O2 delivery
Remove CO2
allow normal aerobic metabolism to take place while “resting” the lungs
provide cardiac and/or respiratory support as necessary

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What are the two places of gas exchange we look at ?

Pulmonary respiration

Tissue respiration

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Pulmonary respiration

refers to the gas exchange between blood and inspired gas

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Tissue respiration

refers to the exchange of oxygen and carbon dioxide at cellular level

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Aerobic Tissue Oxygenation

In order for tissues to engage in aerobic metabolism they need oxygen
allows conversion of glucose to ATP
Get 36 moles ATP per mole glucose

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Anaerbic Tissue Oxygenation (Hypoxia)

If not enough oxygen is available, we have anaerobic metabolism
Get 2 moles ATP per mole glucose and production of lactate

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4 principle hemodynamic processes

O2 content
O2 delivery
o2 consumption
o2 reserve/return

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Oxygen Content Equation (CaO2)

CaO2 = 1.34* HGb* SaO2 +(0.003 *paO2100)

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What is 1.34 in the oxygen content equation?

the amount of oxygen (ml at 1 atm) bound per gram of hemoglobin

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What is the 0.003 in the oxygen content equation?

represents the amount of oxygen dissolved in plasma

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WHat is the primary way to increase oxygen content?

Hemoglobin

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O2 Delivery Equation (DO2)

Available Oxygen x Delivery Rate

Arterial Content x Cardiac Output

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What is normal DO2?

600 cc/min/m2

(900-1000) cc/min

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How do we assess the effectiveness of oxygen transport?

Arterial and mixed venous blood gas determination (central lab)
Noninvasive pulse oximetry
Invasive mixed venous saturation monitoring
Continuous indwelling arterial blood gas monitoring
Point of care blood gas monitoring
Transcutaneous po2 monitoring
transcutaneous meausre of local tissue oxygen saturation

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Continuous indwelling arterial blood gas monitoring

20 gauge fiberoptic probe that measures pH, pCO2 and PO2

conflicting results on accuracy/very expensive/ no commerical units

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Transcutaneous PO2 monitirng

meausres oxygen tension of heated skin (43C) more problems than worth so not commonly used clinically

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How Does the Body Compensate

Increased cardiac output
Extract more oxygen from hemoglobin at the systemic capillaries
increase amount of hemoglobin and red cell mass

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Increased cardiac output

primary phsyiology response

healthy heart: 15-25 L/min

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Extract more oxygen from the hemoglobin at the systemic capillaries

decrease venous saturation to 32%

below 32% anaerobic metabolism and metabolic acidosis start

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Increase amount of hemoglobin and red cell mass

takes weeks to develop

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Oxygen Consumption

the difference between the deliveyr and what is returned

AVO2 difference = Ca-Cv

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Study These Flashcards

the oxygen concentration of arterial blood (oxygenated blood)

the oxygen concentration of venous blood (deoxygenated blood)

Oxygen Consumption is a function of....

Cardiac output difference in oxygen content b/w arterial and venous blood VO2 = CO x 1.34 x Hb (SaO2 - SvO2) 10

Oxygen Consumption (O2 Demand)

150 cc/min/m2 | 200-240 cc/min

Oxygen Extraction Ratio

VO2/Do2 x 100 Ratio of oxygen uptake to delivery Usually 20-30% uptake is kept constant by increasing extraction when delivery drops

Conditions that may affect tissue extraction

Excessive tissue requirements Demand > Supply Inability of body to use oxygen Impaired oxygen unloading at the capillary level

Demand > Supply

oxygen demand higher than system can provide hypermetabolism/systemic inflammatory response syndrome (post CPB) sepsis/ malignant hyperthermia

Why would the body not be able to use oxygen?

Toxic hypoxia | sepsis/cyanide or ethanol toxicity

Why would the body have impaired oxygen unloading at the capillary level?

Alkalemia/Hypocarbia | Administration of large amounts of banked blood

Conditions that may affect tissue oxygenation

Inadquate blood flow decresaed oxygen saturation of arterial hemoglobin severe anemia

Inadequate blood flow

ischemic hypoxia | -obstruction lesions of blood vessels/peripheral vascular disease

Decreased oxygen saturation of arterial hemoglobin

hypoxemic hypoxia inadequate oxygen transfer from lungs to blood -hypoxemia most common cause (PaO2 less than 60 mmHg) / carbon monoxide poisoning / methemoglobinemia

Severe anemia

anemic hypoxia deificiency ofh emoglobin molecules hemorrhage / nutritional deficiencies/dilution

Oxygen Reserve (RO2)

oxygen reserve can be described as what's left after consumption has taken place venous gases returning ot the heart it is essentially a build in phsyiological buffer

Normal Oxygen Reserve

450 cc/min/m2 | 700-800 cc/min

Carbon Dioxide

produced as part of the metabolic process and has an emission rate that is dependent on the level of activity while co2 is not normally harmful, the concentration of CO2 can act as a marker for the adequacy of ventilation

CO2 is produced where

at the tissue

CO2 is picked up by what

the capillary

ECMO will provide

oxygenation carbon dioxide removal maintenace of PH

ECMO will have the ability to _______ and ______ both oxygenation and carbon dioxide removal.

Assist and control

V-V ECMO

Oxygenated blood returned to the right side of hte heart (preoxygenated)

V-A ECMO

oxygenated blood returned to the left side of the heart (as normal)

Oxygenation is controlled on ECMO via ....

an O2 blender Control of FIO2 Monitor PaO2

If you increase FiO2 % = ______ PaO2 (mmHg)

increase

Carbon Dioxide Removal

controlld by gas flowing across a membrane (LPM) Blows off CO2 from the membrane Monitor pCO2 (mmHg)

Increase gas flow = ____ pCO2 (mmHg)

decrease

Gas to BF ratio of ____ when intiating ECMO

An increase in GBFR (more sweep) results in _____ pCO2

lower

A decrease in GBFR (less sweep) results in _____ pco2

higher

Cool stuff to know about gases

The body attempts to control PH Respiratory centers control pCO2 metabolic processes control carbonic acid cycle Hence ABG problems are referred to as metabolic or respitaory

Modified Henderson Hasselbach Equation

pH = 6.1 + log ([HCO3-]/0.03 x pCO2)

pH is proportional to .....

HCO3-

pH inversely proportion to....

CO2

Carbonic Acid Cycle

Carbonic acid is an intermediate step in the transport of CO2 out of the body via respiratory gas exchange H20 + Co2(g) H2CO3 (carbonic acid) H+ + HCO3-

The goal of ECMO is to....

rest the body

Physiology of ECMO Flashcards

(58 cards)