present on the Earth as gases (O2, O3, O4); H2O, and in countless chemical formulas
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 1:4
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 2:4
Three structural forms of oxygen are known: ordinary oxygen, containing two atoms per molecule, formula O 2 ; ozone, containing three atoms per molecule, formula O 3 ; and a pale blue, nonmagnetic form, O 4, 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 3:4
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). Oxygen 4:4
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 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 Alveolar- Capillary 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
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 Alveolar- Capillary 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
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 AVERAGE KG. METS VO2 ml./Kg./min ml./min. 7.5-9.585.05052.43 42.5 7.5-9.008.25102.36 82.5 6.5-8.507.50152.00112.5 6.0-7.506.75201.93135.0 5.5-6.506.00251.71150.0 5.0-6.005.50301.57165.0 4.5-5.505.00351.43175.0 4.5-5.004.75401.36190.0 ADULT 4.0-5.003.50701.00250.0 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