ABG Review PDF

DAY 3: RESPIRATORY THERAPY COMPREHENSIVE LICENSURE EXAMINATION REVIEW BLOOD GAS Blood gas and pH analysis has more immediacy and potential impact on patient care than any other laboratory determination. National Committee for Clinical La...

DAY 3: RESPIRATORY THERAPY COMPREHENSIVE LICENSURE EXAMINATION REVIEW BLOOD GAS Blood gas and pH analysis has more immediacy and potential impact on patient care than any other laboratory determination. National Committee for Clinical Laboratory Standards There is no substitute for PO2, PCO2, and pH when you are really in the dark about oxygenation status, acid-base, or ventilatory status. Woody Kagler, M.D.  The arterial blood gas report is the cornerstone  in the diagnosis and management of clinical  oxygenation and acid-base disturbances. An  abnormal blood gas report may be the first clue  to an acid-base or oxygenation problem: It may  indicate the onset or culmination of cardiopulmonary  crisis and may serve as a gauge with  regard to the appropriateness or effectiveness of  therapy. Thus, the arterial blood gas report  plays a pivotal role in the overall care of cardiopulmonary  disease. Using the arterial blood  gas report as a reference point, this text explores  the diagnosis, assessment, and intervention of  clinical acid-base and oxygenation problems. INTRODUCTION Arterial blood gas (ABG) analysis is an extremely useful diagnostic test for the clinical assessment of ventilation, acid- base status, and oxygenation. WHITE  Collection of an arterial sample may be done quickly, and it provides important information for decision making in the management of the patient requiring oxygen or ventilatory assistance.  DESCRIPTION  Analysis of arterial and/or mixed venous blood provides information concerning the oxygenation, ventilatory, and acid-base status of the subject from whom the specimen was obtained.  Analysis of samples from other sources (ie, capillary, peripheral venous, umbilical venous samples, and pH measured from other body fluids) may provide limited information Either method provides a blood specimen for direct measurement of partial pressures:  carbon dioxide (PaCO2) and oxygen (PaO2),  hydrogen ion activity (pH),  total hemoglobin (Hbtotal),  oxyhemoglobin saturation (HbO2), and the  dyshemoglobins carboxyhemoglobin (COHb)  methemoglobin (MetHb). INDICATIONS  the need to evaluate the adequacy of a patient's ventilatory (PaCO2), -acid-base (pH and PaCO2), -and/or oxygenation (PaO2 and O2Hb) status, the -oxygen-carrying capacity (PaO2, O2Hb, tHb, and dyshemoglobin saturations) -and intrapulmonary shunt (Qsp/Qt); INDICATIONS  the need to quantitate the response to therapeutic intervention (eg, supplemental oxygen administration, mechanical ventilation) and/or diagnostic evaluation (eg, exercise desaturation);  the need to monitor severity and progression of documented disease processes.  Note: USA setting, blood gas being used more? CLINICAL INDICATIONS FOR ARTERIAL BLOOD GAS ANALYSIS CONTRAINDICATIONS 1. Negative results of a modified Allen test (collateral circulation test) are indicative of inadequate blood supply to the hand' and suggest the need to select another extremity as the site for puncture. 2. Arterial puncture should not be performed through a lesion or through or distal to a surgical shunt (eg, as in a dialysis patient). If there is evidence of infection or peripheral vascular disease involving the selected limb, an alternate site should be selected. CONTRAINDICATIONS 3. Agreement is lacking regarding the puncture sites associated with a lesser likelihood of complications; however, because of the need for monitoring the femoral puncture site for an extended period, femoral punctures should not be performed outside the hospital. 4. Coagulopathy or medium-to-high-dose anticoagulation therapy (eg, heparin or coumadin, Thrombolytics eg. streptokinase, and tissue plasminogen activator) SETTING  Analysis should be performed by trained individuals,in a variety of settings including, but not limited to:  hospital laboratories,  hospital emergency areas,  patient-care areas,  clinic laboratories,  laboratories in physicians' offices.  Clinicians have been using blood samples to assess gas exchange parameters for more than 30 years.  Definition of RESPIRATORY FAILURE still is based largely on blood gas measurements.  Results obtained from sampling arterial blood gas (ABG) are the cornerstone in the diagnosis and management of oxygenation and acid-base disturbances.  ABGs are considered the gold standard of gas exchange analysis, against which all other methods are compared. NORMAL BLOOD GAS VALUES O2SAT=100% ??  Units of Measurement  pH - value is dimension-less  SaO2 - measured as a percentage.  HCO3, BE - reported in milliequivalents per liter (mEq/L).  PaO2 and PaCO2 - measured in millimeters of mercury (mm Hg), a unit of pressure.  unit torr is synonymous  ANATOMICAL LOCATIONS FOR ARTERIAL PUNCTURE The collection of arterial blood is not only technically difficult but can be painful and hazardous to the patient. Therefore, it is essential that individuals performing arterial puncture be familiar with the proper techniques, with the dangers of the procedure, and with necessary precautions. National Committee for Clinical Laboratory Standards Compared with the acquisition of venous blood, arterial sampling is technically more difficult and has greater potential for serious complication. The higher arterial pressure can make bleeding complications more profuse. Furthermore, large clot formation or prolonged spasm in an artery could cut off vital supply of O2 to the tissue. Arterial blood gas samples are also very vulnerable to improper handling technique because of their high gas content. Arterial blood is one of the most sensitive specimens sent for clinical laboratory analysis. RADIAL ARTERY The radial artery is the preferred site for arterial blood sampling for the following reasons: It is near the surface and relatively easy to palpate and stabilize. Effective collateral circulation normally exists in the ulnar artery.  The artery is not near any large veins. The procedure is relatively pain-free. (EGANS 1OTH) Anterior (palmar) view Blue – vein Yellow - nerve Superficial dissection of radial area. Actual proximity of radial artery (A) to median nerve (B) in cadaver is shown.  location makes it easily accessible. located in the wrist on the radial side (thumb side),  close to the surface of the skin.  site most commonly used for taking a patient’s pulse. WHITE ADVANTAGE : RADIAL SITE A big advantage of performing arterial puncture at the radial site is the safety afforded by the presence of collateral circulation.  The hand is supplied with blood by both the radial and ulna arteries. Because repeated punctures may result in vessel damage, swelling with partial or complete occlusion of the vessel may occur. If circulation is inadvertently interrupted resulting from radial artery puncture, the ulnar artery will continue to supply the circulatory needs of the hand. WHITE ADVANTAGE : RADIAL SITE  There are no veins or nerves immediately adjacent to the radial artery;  arterial sampling at this site is facilitated by a reduced chance of inadvertent venous puncture or nerve damage. DISADVANTAGE : RADIAL SITE  The disadvantage of radial artery puncture is the small size of this artery.  The radial artery is a small target.  In case of hypotensive and hypovolemic states or low cardiac output, puncture at this site may be particularly difficult. WHITE RECOMMENDED EQUIPMENT FOR PERCUTANEOUS ARTERIAL BLOOD SAMPLING EGANS PROCEDURE FOR RADIAL ARTERY PUNCTURE 1. Check the medical record to (1) confirm the order and indications and (2) determine the patient’s primary diagnosis, history (especially bleeding disorders or blood-borne infections), current status, Respiratory care orders (especially oxygen therapy or mechanical ventilation), and anticoagulant or thrombolytic therapy. 2. Confirm steady-state conditions (20-30 minutes after changes). 3. Obtain and assemble necessary equipment and supplies. BASIC COMPONENTS OF HYPODERMIC NEEDLE AND SYRINGE 4. Wash hands and put on barrier protection (e.g., gloves, eyewear). 5. Identify the patient using current patient safety standards. 6. Explain the procedure to the patient. 7. Position the patient, extending the patient’s wrist to approximately 30 degrees. LEFT OR RIGHT ARM? 8. Perform a modified Allen test, and confirm collateral circulation. ALLENS TEST  A, The hand is clenched into  a tight fist, and pressure is applied to the radial and ulnar arteries.  B, The hand is opened (but not fully extended); the palm and fingers are blanched.  C, Removal of pressure on the ulnar artery should result in flushing of the entire hand (within 5 to 10 seconds) indicative of adequate collateral circulation or a normal modified Allen test. EGANS 9. Clean site thoroughly with 70% isopropyl alcohol or an equivalent antiseptic. 10. Inject a local anesthetic subcutaneously and periarterially (wait 2 minutes for effect).* 11. Use a preheparinized blood gas kit syringe, or heparinize a syringe and expel the excess (fill dead space only). ?  2 uses of liquid heparin  Anticuagulant and lubricant  1st choice – lithium heparin  liquid heparin = sodium heparin (1000 IU/mL).  Heparin salt, formation of small fibrils in the sample  Higher concentrations of heparin (e.g., 10,000 U/mL) may alter pH and ionized calcium of the sample. 12. Palpate and secure the artery with one hand. 13. Insert the needle, bevel up, through the skin at a 45-degree angle until blood pulsates into the syringe. (A) Stabilizing the patient’s hand. (B) Bevel position and needle angle for an arterial puncture. ? FLASH 14. Allow 1 ml of blood to fill syringe (the need to aspirate indicates a venous puncture).  15. Apply firm pressure to puncture site with sterile gauze until the bleeding stops. 16. Expel any air bubbles from the sample, and cap or plug the syringe. 17. Mix the sample by rolling and inverting the syringe. 18. Place the sample in a transport container (ice slush) if specimen is not to be analyzed within 10-30 minutes. 19. Dispose of waste materials and sharps properly. 20. Document the procedure and patient status in the chart and on the specimen label. 21. Check the site after 20 minutes for hematoma and adequacy of distal circulation. BRACHIAL ARTERY BRACHIAL ARTERY  The site where the brachial artery is commonly punctured is at the elbow in the antecubital fossa.  Advantage of the brachial artery puncture site is its  size. It is large and easily palpated.  Disadvantages to using the brachial artery. It is close to both a large vein and a nerve.  Inadvertent venous sampling is common at this site.  Accidental contact with the nerves at this site may cause extreme discomfort.  Does not have the advantage of collateral circulation. Inadvertent injury leading to stoppage of circulation may result in the loss of the limb. WHITE FEMORAL ARTERY  Accessible for arterial sampling in the groin.  It may be palpated laterally from the pubis bone.  The femoral artery is very large. It is easily palpated and presents a large target.  The only site where arterial sampling is possible in cases of hypovolemia or hypotension, during cardiopulmonary resuscitation (CPR), or with low cardiac output. WHITE  Disadvantages to arterial puncture at this site, including the proximity of a major vein and a lack of collateral circulation.  The artery may also be deep and difficult to locate.  Atherosclerotic plaques commonly form in the femoral artery. If a plaque is dislodged as a result of arterial puncture, circulation to the entire leg may be compromised by formation of emboli.  Close proximity of the femoral vein makes the certainty of arterial sampling questionable. Femoral Artery DORSALIS PEDIS ARTERY ALLEN’S TEST – DORSAL ARTERY  Pressure is applied directly over the artery to occlude it, and then pressure is applied to the nail of the big toe, causing it to blanch.  When pressure on the big toe is released, color returns to the toe if collateral circulation is sufficient from the posterior tibial and lateral plantar arteries. RULES FOR CAREFUL HANDLING OF THE NEEDLE HELP AVOID TRANSMISSION OF BLOOD-BORNE DISEASES: Never recap a used needle without a safety device; never handle a used needle using both hands; never point a used needle toward any part of the body. Never bend, break, or remove used needles from syringes by hand. EGANS Always dispose of used syringes, needles, and other sharp items BLOOD GAS SAMPLING ERRORS The reliability of blood gas analysis is very technique dependent. Every step of the process, from preparation of equipment through reporting the data, has potential problems that affect data reliability. That is, knowledge and skill as a respiratory care practitioner will often determine the accuracy of the procedure. Knowledge of the factors that contribute to sampling errors will help to prevent their occurrence in clinical practice. If a sample is questionable, the relevant facts should be noted with the results of analysis. Clinical decisions are frequently based on data assumed to be entirely accurate. WHITE  PREANALYTIC ERRORS  Problems occurring before sample analysis that can alter the accuracy of the blood gas results. BUBBLES  Particularly if the sample is aspirated, air bubbles are often present in the collected blood sample. These bubbles must be expelled immediately upon collection.  Time bracket ?  Room air contains enough oxygen that it can diffuse into the sample, increasing the arterial oxygen tension (PaO2), or if the PaO2 is greater than 160 mm Hg, it can decrease the PaO2.  This diffusion problem is especially true in patients with hypoxemia.  PaO2 less than 158mmHg?  PaO2 more than 158mmHg? WHITE  FROTH  Carbon dioxide is present in the atmosphere in a concentration of only 0.003%, or around 2 mm Hg at sea level. Because arterial blood normally has a carbon dioxide tension (PaCO2) ranging from 35 to 45 mm Hg, CO2 dissolved in blood will tend to diffuse into the bubbles in the sample, lowering the measured value. DELAY IN SAMPLE ANALYSIS  Blood contains living cells with their own metabolism and metabolic needs.  These cells will continue to consume oxygen and nutrients and produce acids and CO2 even after being withdrawn from the body.  15 minutes elapses before the sample is analyzed, the results can change dramatically (American Association for Respiratory Care, 2001).  Immediately after collection, cool the sample in a slush of ice and water. Ice slows the cells’ metabolism, and even a delay of 30 minutes will not significantly affect the analysis results. Best, to analyze the sample as soon after collectionWHITE as possible.  Samples held longer than this may show lower PaO2, higher PaCO2, or a pH less than the patient’s actual pH. USE OF THE PROPER ANTICOAGULANT  Oxalates, ethylenediaminetetra-acetic acid (EDTA), and the citrate anticoagulants available for use will alter the pH of the arterial sample (American Association for Respiratory Care, 2001).  Sodium heparin is the best anticoagulant to use in arterial blood sampling. Even sodium heparin, if too much is used (more than 0.1 mL of heparin per 1 mL of whole blood), will cause acidosis in the blood sample.  safe general rule to follow is to expel all excess heparin. Heparin will be left in the needle and needle hub, occupying a minimal volume. WHITE  The syringes in blood gas sampling kits often contain dry crystalline or lithium heparin.  Lyophilized heparin  No aspiration of additional anticoagulant is necessary. Simply draw the sample, and the anticoagulant will dissolve.  it is important to mix the sample by gently rolling or shaking the syringe after collection. VENOUS SAMPLING  EFFECTS ON PARAMETER WHITE  Nonanalytical Error  Preanalytical Error  Postanalytical Error  Analytical Error Capillary Blood Gases CAPILLARY BLOOD GASES  Capillary blood gas sampling is used as an alternative to direct arterial access in infants and small children.  Properly obtained capillary blood from a well-perfused patient can accurately reflect and provide clinically useful estimates of arterial pH and PCO2 levels. EGANS  Capillary PO2 is of no value in estimating arterial oxygenation, and O2 saturation by pulse oximetry must also be evaluated when a capillary blood gas sample is obtained.  Direct arterial access is still the preferred approach for assessing gas exchange in infants and small children with severe acute respiratory failure.  Capillary blood values are meaningful only if the sample site is properly warmed.  Warming the skin (to approximately 42° C) causes dilation of the underlying blood vessels, which increases capillary flow well above tissue needs.  Blood gas values resemble the values in the arterial circulation; this is why a sample obtained from a warmed capillary site is often referred to as ARTERIALIZED BLOOD. EGANS  The posterior medial or lateral curvature of the heel is the recommended site for capillary puncture specimens in infants less than 1 month old to avoid TECHNIQUE  Capillary samples are usually obtained from the infant’s heel but may also be obtained from the finger.  When capillary blood is drawn from the heel, this sampling technique is sometimes referred to as a heel stick.  Arterialization (warming to maximize blood flow) of the infant’s heel is done before sampling, and then a lancet is used to puncture the skin surface. WHITE EQUIPMENT  Equipment needed for capillary blood  lancet,  preheparinized glass or plastic capillary tubes  small metal stirrer bar (metal flea),  Magnet  clay or wax sealant or caps,  gauze or cotton balls  bandages  ice  Gloves  skin antiseptic  warming pads (42° C)  sharps container, and labeling materials. EGANS CAPILLARY TUBE WITH METAL FLEA AND MAGNET. PROCEDURE FOR CAPILLARY BLOOD SAMPLING Check the chart (as per arterial puncture). Confirm steady-state conditions (20-30 minutes after changes). Obtain and assemble necessary equipment and supplies. Wash hands and put on barrier protection (e.g., gloves, eyewear). Select site (e.g., heel, earlobe, great toe, finger). Warm site to 42° C for 10 minutes using a compress, heat lamp, or commercial hot pack. Clean skin with an antiseptic solution. Puncture the skin ( 3 torr CALIBRATION PO2 ELECTRODE  THREE-POINT CALIBRATION  Done at least once every 6 months on existing equipment  Done whenever a new electrode is put into use  Should be done to confirm linearity whenever the PO2 value could be > 150 torr, assuming the balance point is set at RA content CALIBRATION PO2 ELECTRODE  TWO-POINT CALIBRATION  The electrodes electronic output is adjusted to two known samples.  Performed at least three times daily, usually every 8 hours.  Can be programmed at predetermined interval CALIBRATION PO2 ELECTRODE  THREE-POINT CALIBRATION  Involves adding a third standard that is intermediate to the other standards to ensure linearity of the electrode response.  Performed every six months or whenever an electrode is replaced. TOTAL QUALITY MANAGEMENT Quality methods and techniques are focused on insuring that the quality of tests performed in the laboratory allow our clinicians to practice good medicine. The central role of quality specifications in quality management. QUALITY ASSURANCE Quality assurance is a systematic process used to monitor, document, and regulate the accuracy and reliability of a procedure or laboratory measurement. Errors in blood gases may occur before, during, or after actual analysis of the sample. Error that occurs before or after actual analysis (e.g., an error due to improper sample or data handling) is called a nonanalytical error. Error that occurs during the actual analysis of the sample (e.g., error due to performance of electrode or technician) is called an analytical error.  Preventive Maintenance Proper maintenance and cleaning of blood gas electrodes is essential.  Calibration Calibration is a procedure done on blood gas electrodes before analyzing blood samples to establish the accuracy of readings in the anticipated range. QUALITY CONTROL (QC)  Defined as a system that includes analysis of control samples (with a known pH, PCO₂ and PO₂), assessment of the measurement against defined limits, identification of problems and specification of corrective action.  Internal quality control can be accomplished by periodic analysis of commercial products with known pH, PCO₂ and PO₂ values. Quality control, concerning blood gas electrodes, refers to the periodic checking of an instrument’s performance to ensure calibration, stability, and reliability. Statistical methods are used to evaluate the accuracy and precision of blood gas measurements. Quality control is probably the most controllable aspect of quality assurance. The two major types of quality control systems are internal quality control and external quality control.  Internal Quality Control Internal quality control programs are designed to ensure that the instruments (i.e., electrodes) within a laboratory perform with precision.  External Quality Control External quality control, also known as proficiency testing, is a system by which laboratories can compare the accuracy of their results with the results obtained from other laboratories. External quality control involves the distribution of identical samples from a central distribution site to participating laboratories.  Creating a measurement and documentation system to confirm the accuracy (precision) and reliability of all blood gas measurements CALIBRATION VS. QUALITY CONTROL  Calibration is when the equipment is adjusted or corrected to match the control standards  Quality Control testing must be performed on a regular basis to determine the accuracy and precision of the equipment against a known standard QUALITY CONTROL VS. QUALITY ASSURANCE  Quality Control – unit  Quality assurance – involves testing the proficiency of both personnel and equipment, providing a dynamic process of identification, evaluation, and resolution of problems that affect blood gas measurements. ACCURACY VS. PRECISION Accuracy refers to the mean (average) value of several measurements. How close the measurements is to the corrected value Accuracy is a measure of how closely the measured results reflect the true or actual value. If a PO2 electrode consistently measures PO2 10mmHg lower than PO2 actually is, it is inaccurate. Problems related to accuracy are usually characterized by systematic error.  Precision refers to how consistently the same measurement will produce the same results  Reproducibility of repeat measurements  racy versus precision. Analytical accuracy and precision are illustrated by the t” a known target. ery good accuracy and precision. oor accuracy but good precision. ccasional accuracy but poor precision. The analogy of shooting at a target has been made to compare the difference between accuracy and precision. The closeness of a particular hit to the bull’s-eye represents accuracy, whereas the pattern of hits indicates precision  TONOMETRY  Tonometry is the equilibration of a fluid with gases of known concentration and under controlled conditions, such as constant temperature, BP, and humidification.  Gold standard for quality control of PCO₂ and PO₂ electrodes. LEVY-JENNINGS CHART  AKA – Shewhart/ Levy-jennings or Quality control charts  Type of quality control chart was introduced into clinical chemistry in the 1950s by Levey and Jennings  Most common method of recording quality control data.  Produce Graphic outcomes that may indicate a particular problem or concern.  Used to record results of each calibration procedure. SAMPLE LEVEY- JENNINGS PLOT.  ANALYTE 1SD NORMAL MEAN 2 SD TIME EXPLANATION  Horizontal scale – time  Vertical scale – analyte -central value – normally expected - line both sides, standard deviation points, showing movements away from what is expected EXPLANATION  Analyte within acceptable limit – in control  Analyte within 2 SD of normal value – In control  Out of control situation exist whenever a single calibration value or series of calibration values is outside established limits ERROR PATTERNS  RANDOM ERROR – unpredictable anomaly, irregularity in precision that occurs when the QC material is sampled. Random error is characterized by an isolated result outside of control limits. A single random error has minor significance and should be disregarded. When random error increases in frequency, however, the machine and techniques should be evaluated carefully. RANDOM ERROR Systematic Error - recurrent measurable deviation away from the mean. 1. Trending is an example of systematic error in which progressive controls either increase or decrease. 2. Shifting relatively abrupt change in measurement outcome followed by clustering or plateauing in a particular area. Error patterns in quality control. Examples of three common changes in quality control data. A, Dispersion is seen when there is an increased frequency of both high and low outliers. B, A progressive drift of the reported values from the previous mean value is called a trend. C, A shift occurs when there is an abrupt change from the established  These charts allow the operator to detect trends and shifts associated with reporting of inaccurate data because of analyzer malfunction.  TREND – Associated with protein buildup on an electrode membrane or electrode nearing end of life expectancy  SHIFT – due to a near tear in the electrode membrane or loss of electrolyte that bathes the electrode. -- result from bubbles beneath the membrane, change in temperature, or contamination of calibration standards.  SYSTEMATIC ERROR – accuracy problem, much more serious.  Must be investigated, corrected, and documented. Schematic representation of a quality control plot for PCO2. The horizontal axis depicts time. White circles represent values within 2 standard deviations of the mean; blue circles represent values outside 2 standard deviations of the mean. Point A represents a random error; POINT OF CARE (POC) TESTING POINT OF CARE (POC) TESTING  Testing that is done outside the main hospital laboratory.  POC testing usually involves use of portable devices located at or near the point of patient care.  Battery powered or AC powered  Uses solid state sensors, rely on fluorescence technology or thin film electrodes.  Measures blood samples of less than 1mL in 60 to 120sec.  iStat 6.8 to 8 pH/ 10 to 100 torr PaCO₂ / 5 to 800mmHg PaO₂ Record the type of specimen you used on your lab report. 1. Apply latex or vinyl gloves and other standard precautions and transmission-based isolation procedures as applicable. Gowns and goggles may be worn when dealing with human blood samples. 2. Remove the cartridge from its pouch. Avoid touching the contact pads or exerting pressure over the calibrant pack in the center of the cartridge. 3. After thoroughly mixing the sample, remove the cap from the sample syringe. Eject a small amount of blood into a gauze pad. 4. Verify that the sample is free of air, has not been iced, and has been run within 10 minutes of the ABG procedure. 5. Direct the dispensing tip or capillary tube containing the blood into the sample well until it reaches the fi ll mark on the cartridge and the well is about half full. 6. Close the cover over the sample well until it snaps into place. (Do not press over the sample well.) 7. Insert the cartridge into the cartridge port on the analyzer until it clicks into place. 8. Allow sufficient time for the readings to stabilize. 9. Enter an operator and patient ID number. 10. Select the tests to be reported, if prompted. 11. Enter additional parameters if required: Patient temperature in degrees Centigrade or Fahrenheit Patient Fio2 setting and ventilator settings Sample type being analyzed 12. View the results shown on the analyzer’s display screen. Record the results on your laboratory report. Print out the results if a printer and blood gas recording slips are available. 13. Discard the syringe and cartridge in a sharps container. 14. Clean up any blood spills with a 1:10 solution of sodium hypochlorite (bleach) solution. 15. Remove your gloves and discard them in an infectious waste container. Wash your hands. OXYHEMOGLOBIN DISSOCIATION CURVE STEPS IN OXYGEN DELIVERY EXPLANATION The three steps or phases in oxygen delivery to the tissues include:  oxygen loading into the blood or external respiration (A),  oxygen transport or delivery to the tissues (B)  oxygen unloading from the blood and utilization by the tissues or internal respiration (C). SCHEMATIC DRAWINGS OF GLOBIN AND HEMOGLOBIN EXPLANATION  A and B, Globin is made up of four polypeptide chains (two alpha chains and two beta chains).  C and D, Each of the four polypeptide chains is combined with a heme group.  Oxygen combines with hemoglobin at the Fe site of each heme group. COMPARATIVE SATURATIONS. EXPLANATION  Saturation is equal to the percentage of hemoglobin that is carrying oxygen.  Hemoglobin can be carrying either four molecules of oxygen (oxygenated) or none (deoxygenated). OXYHEMOGLOBIN DISSOCIATION CURVE. EXPLANATION KEY LANDMARKS ON THE OXYHEMOGLOBIN DISSOCIATION CURVE. EXPLANATION Key landmarks on the oxyhemoglobin dissociation curve.  A- In the normal oxyhemoglobin curve, the hemoglobin is 50% saturated at a PO2 of approximately 26 mm Hg. The PO2 necessary to obtain 50% saturation is called the P50.  B- The normal PO2 of mixed venous blood is 40 mm Hg. Therefore, the normal saturation of mixed venous blood is 75%.  C- critical point to remember in clinical practice is that at a PO2 of 60 mm Hg, saturation is still 90%. Saturation falls quickly when PO2 falls below 60 mm Hg. THE OXYHEMOGLOBIN CURVE AS TWO STRAIGHT LINES. EXPLANATION The oxyhemoglobin curve has two distinct portions: a steep lower portion and a flat upper portion.  Because the end of oxygen loading into the blood occurs on the upper portion, it may be called the association portion.  The end of oxygen unloading to the tissues occurs on the steep portion, thus it may be called the dissociation portion. OXYHEMOGLOBIN CURVE AS A BAR GRAPH. EXPLANATION The bar graph shows the large changes in saturation that accompany PO2 changes on the steep lower portion of the curve. On the upper flat portion of the curve, large changes in PO2 only slightly change saturation because it is almost 100%. SIGNIFICANCE OF PO2 CHANGES ON DIFFERENT PORTIONS OF THE CURVE. EXPLANATION Significance of PO2 changes on different portions of the curve. Saturation increases 55% as PO2 increases by 40 mmHg on the steep portion of the curve, whereas saturation increases by only 7% when PO2 increases by 40 mmHg on the flat portion of the curve. OXYHEMOGLOBIN AFFINITY EXPLANATION The affinity of hemoglobin for oxygen is expressed as the P50. Increases in PCO2, temperature, or DPG; and decreases in pH shift the curve to the right (increased P50 = decreased affinity). Opposite changes shift the curve to the left (decreased P50 = increased affinity). EFFECTS OF SHIFTS OF CURVE ON TISSUE OXYGEN DELIVERY. EXPLANATION A, The normal Hb-O2 curve and the amount of oxygen released to the tissues from hemoglobin. B, A left shift tends to decrease tissue oxygen release. C, A shift to the right tends to increase oxygen release to the tissues. THANK YOU FOR YOUR KIND ATTENTION!!!