Transcript Document

PerfEd INTERNATIONAL
OXYGENATION PRINCIPLES
Michael S. Vinas, MA-HRM
Oxygen, the most abundant element on Earth
present on the Earth as gases (O2, O3, O4);
H2O, and in countless chemical formulas
Oxygen 1:4
• Oxygen, symbol O, colorless, odorless,
tasteless, slightly magnetic gaseous
element. On earth, oxygen is more
abundant than any other element.
Oxygen was discovered in 1774 by the
British chemist Joseph Priestley and,
independently, by the Swedish chemist
Carl Wilhelm Scheele; it was shown to
be an elemental gas by the French
chemist Antoine Laurent Lavoisier in his
classic experiments on combustion.
Oxygen 2:4
• Oxygen composes 21 percent by
volume or 23.15 percent by weight of
the atmosphere; 85.8 percent by
weight of the oceans (88.8 percent of
pure water is oxygen); and, as a
constituent of most rocks and minerals,
46.7 percent by weight of the solid
crust of the earth. Oxygen comprises 60
percent of the human body. It is a
constituent of all living tissues; almost
all plants and animals, including all
humans, require oxygen, in the free or
combined state, to maintain life.
Oxygen 3:4
• Three structural forms of oxygen are
known: ordinary oxygen, containing two
atoms per molecule, formula O2; ozone,
containing three atoms per molecule,
formula O3; and a pale blue,
nonmagnetic form, O4, containing four
atoms per molecule, which readily
breaks down into ordinary oxygen.
Three stable isotopes of oxygen are
known; oxygen-16 (atomic mass 16) is
the most abundant. It comprises 99.76
percent of ordinary oxygen and was
used in determination of atomic weights
until the 1960s.
Oxygen 4:4
• Gaseous oxygen can be condensed to a
pale blue liquid that is strongly
magnetic. Pale blue solid oxygen is
produced by compressing the liquid.
The atomic weight of oxygen is
15.9994; at atmospheric pressure, the
element boils at -182.96° C (-297.33°
F), melts at -218.4° C (-361.1° F), and
has a density of 1.429 g/liter at 0° C
(32° F).
AIR:OXYGEN RATIOs
• AIR
– 0
– 1
– 2
– 3
– 4
– 5
– 6
– 7
– 8
OXYGEN
8
7
6
5
4
3
2
1
0
RATIOFIO2
0:8
1:7
1:3
1:1.67
1:1
1:0.60
1:0.33
1:0.142
8:0
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.21
Normal production of Oxygen is through
the process of Photosynthesis, the
conversion of CO2 into O2.
Manufacturing of Oxygen
• The process of mechanical processing of
Oxygen is a technique known as “Fractional
Distillation.”
• Oxygen is compressed to it’s “Critical
Pressure” which converts O2 in the gaseous
state to it’s liquid state, a pale blue color
with a slight garlic smell.
• Oxygen may be stored as a bulk liquid
agent in “Thermos” type containers or
brought up to just above it’s Critical
Temperature and stored in high pressure gas
cylinders
Oxygen Storage; Gaseous and Liquid
Oxygen is measured as mm. Hg. or Torr.
Given a normal barometric pressure
of 760 mm. Hg. at sea level, zero
percent relative humidity, Oxygen
would exert a partial pressure of
159 Torr [(760) x (20.95/100)]
Normal atmospheric Oxygen, inspired, is heated to 37C @
100% relative hymidity. Relative humidity @ 37C, 100% exerts
a partial pressure of 47 Torr. Thus, the Oxygen tension is
reduced to 149 Torr, PCO2 of 40 reduces O2 tension further to
105 Torr. The diffusion across the Alveolar-Capillary
membrane presents a O2 of 100-104 Torr to the capillary blood.
Blood Gas Electrodes
Oxygen tension is measured by a Clark electrode that measures the
electric charge produced by the oxidative reduction of a chemical
agent when introduced to a sample containing Oxygen.
pH=Glass Electrode
PCO2=Severinghaus Electrode
PO2=Clark Electrode
The Oxyhemoglobin Dissociation Curve is sigmoid shaped
@ 37C, a normal pH, PCO2, 2,3 DPG levels. P50 denotes
the PaO2 @ 50% Saturation and identifies Hb affinity for
O2.
• Of the cells only Erythrocytes contain
Hemoglobin, the element that transports Oxygen
as Oxyghemoglobin.
• Each Gram is capable of carrying 1.34 ml of
combined Oxyhemoglobin, each mm Hg. Of PO2
is capable of carrying 0.0031 ml. Dissolved
Oxygen
Oxygen transport starts from the time of conception
through cellular metabolism then the umbilical cord/
Placenta until birth. The fetus’ blood contains Hemoglobin
F which has a higher hemoglobin and affinity for Oxygen
than adult Hemoglobin; Hb A.
The lungs resume the process of gas exchange at the AlveolarCapillary level after birth until death.
Premature delivery before 28 weeks results in
mechanical ventilation requirements
• HEMOGLOBIN/ HEMATOCRIT
• The hemoglobin in infant and pediatric patient's has been
surveyed and reported between the ranges of 12.5-22 gm./dL
(Hartley-Winkler). Hemodilutional calculations, however, are
predicated on hematocrit values.
• AGE HEMOGLOBIN VALUES
1 Day 18-22 GM/DL
2 Weeks 17 GM/DL
3 Months 10 GM/DL
• 3-5 Years 12.5-13 GM/ DL
The Placenta exchanges Oxygen and Carbon
Dioxide, nutrients from the Mother to the
Fetus’ umbilicus until full term Gestation,
however, the lungs may be developed enough
after 28 weeks to forego artificial mechanical
ventilation
Oxygen is transported through the AlveolarCapillary membrane to the capillaries …arterioles
… arteries
The main objective is cellular oxygen
exchange; conversion of ADP to ATP …
primarily at the Mitochondrial levels
Oxygen deprivation for 3-5 minutes may
lead to irreversible Brain death.
As important, Oxygen deprivation of
myohemoglobin may lead to irreversible
heart damage
Oxygen is a critical component of the Krebs, Citric Acid
Cycle in preventing lactic acidosis
Krebs Cycle; Aerobic Metabolism 2:3
Krebs Cycle 3:3
METABOLIC ACIDOSIS
The aerobic Krebs; Citric Acid cycle
is shut down and replaced by the
anerobic Embden-Meyerhoff cycle
which converts Pyruvic into Lactic
Acid. The increased hydrogen ions
affect the respiratory center of the
Medulla Oblongata affecting
increased ventilation. Venous blood
is presented to the AlveolarCapillary membrane, H + HCO3
associates into H2CO3-, Carbonic
Acid, then dissociates into water and
CO2 gas. The Renal Glomerulus
excretes excess H+.
METABOLIC ACID continued …
Acidemia causes migration of K+
from the interstitum, affecting the
Nervous system’s Na+ pump. The
combination produces Myocardial
depression, decreased CO,
hemostasis, microaggregate
formation, thrombus formation and
possible Myocardial Infarction (MI).
The Renal System attempts to
eliminate H+ via the tubular
Glomerulus.
EXTRACOROREAL MEMBRANE OXYGENATION
is the artificial exchange and delivery of Oxygen.
ECC=artificial oxygen transport
Bubbler Oxygenators
Have a direct gas to
blood interface, thus
causing contact and
complement pathway
activation leading to
activation of C3 and
C5A; pulmonary and
myocardial edema
Membrane Oxygenators eliminate direct gas to blood interfacing and
emulate the O2 and CO2 transfer rates of the lungs via microporus
polypropylene hollow fibers; Carmeda or Trillium bonded
Cardiovascular Perfusionist Calculations
To adequately determine oxygenation delivery
and consumption … several formulas are
deployed • Arterial Oxygen Content, CaO2
•
•
•
•
•
Vol.%
Venous Oxygen Content, CvO2 Vol.%
A-V Content Difference
Oxygen Delivery ml./ min.
Oxygen Extraction %
Oxygen Consumption
– ml./ min.
– ml./ Kg.
– METS
Oxygen Delivery
• CaO2=Arterial Oxygen Content Vol.%
–
–
–
–
Hb x 1.34 x (SaO2/100) + (PaO2 x 0.0031)
CvO2=Venous Oxygen Content Vol.%
Hb x 1.34 x (SvO2/100) + (PvO2 x 0.0031)
Ca-vO2=arterial/ venous Oxygen content
gradient Vol.%=5 Vol.%
• Oxygen consumption is normally derived from the Fick
equation. This method calculates the arterial and venous
oxygen content difference and multiplies that value by the
cardiac output in L/M x 10 (Bolen, Miller).
• VO2 (ml./min.) = (CaO2-CvO2) x CO x 10
• During ECC, if the Hgb, C.O. and A/V venous saturations
are known, oxygen consumption may be calculated
without knowing the PO2 values since dissolved oxygen
normally contributes less than 0.3 Volumes %. of the
arterial O2 content.
• VO2 (ml./min.) = Hb. x 1.34 x [(SaO2-SvO2)/100] x CO
x 10
• The basal oxygen consumption of a neonate may vary due
to a variety of factors. Extracorporeal flowrate
requirements are predicated on the predicted basal and
hypothermic oxygen requirements, level of anesthesia,
degree of hemodilution, oxygen carrying capacity, degree
of hypothermia etc.
Proper Assessment of Oxygen Requirements
• The only proper method to assess Oxygen
consumption is via the Fick Equation.
• Patients in the OR, intubated, “chemically
paralyzed,” artificially ventilated and slightly
hypothermic will have approximately 30%
metabolic reuirements than at a “Steady State,”
thus 250 ml./min Vol.% is reduced to 170 ml./
min.
• 7% additional reduction per degree Celsius
hypothermia
BASAL OXYGEN CONSUMPTION (VO2) vs. BODY WEIGHT
VO2 RANGE
ml./Kg./min
7.5-9.58
7.5-9.00
6.5-8.50
6.0-7.50
5.5-6.50
5.0-6.00
4.5-5.50
4.5-5.00
ADULT 4.0-5.00
AVERAGE
KG.
METS
VO2
ml./min.
5.05
8.25
7.50
6.75
6.00
5.50
5.00
4.75
3.50
05
10
15
20
25
30
35
40
70
2.43
2.36
2.00
1.93
1.71
1.57
1.43
1.36
1.00
42.5
82.5
112.5
135.0
150.0
165.0
175.0
190.0
250.0
Adopted from: Galletti, P.M. and Brecher, G.A.,
Heart- Lung Bypass: Principles and Techniques of Extracorporeal Circulation, Grune &
Stratton, New York; 1962.
•
CARDIOVASCULAR ECC PERFUSION
CALCULATIONS
BSA = Square Root [Ht. (Cm) x Wt. (kg)] / 3600
Blood Volume (BV); Females = Kg. x 55; Males= Kg. x 70
Hemodilutional Hct. = Blood Vol. x (Hct./100) / Blood Vol. + Prime Vol.
Extracorporeal Circulation Blood Flowrates:
37C = 100% x (BSA x CI), V/Q = 1.0 : 1.00 @ Alpha Stat
30C = 75% x (BSA x CI), V/Q = 0.8 : 1.00 @ Alpha Stat
28C = 67% x (BSA x CI), V/Q = 0.6 : 1.00 @ Alpha Stat
25C = 50% x (BSA x CI), V/Q = 0.5 : 1.00 @ Alpha Stat
18C = 25% x (BSA x CI), V/Q = 0.2 : 1.00 @ pH Stat
SUMMARY
• ECC formulas are essential for proper application of ECC
Oxygenation
• It is prudent to maintain normal acceptable clinical Hematology,
Electrolytes and Acid-Base balance for proper Oxygen Transport
• Anemia, Acidosis, Electrolyte Imbalances will impair proper
Oxygenation processes
Okay folks, that’s a “wrap”!