Blood Gas analyzer. 4 th year Clinical Chemistry Equipment (MLS-CCHM-421) 26/12/2018

Transcription

1 Blood Gas analyzer 4 th year Clinical Chemistry Equipment (MLS-CCHM-421) 26/12/2018

2 Learning objectives By the end of this lecture you will be able to Define Arterial blood gas Identify different component of ABG discuss blood gas analyser Interpret the ABG result define the disturbance of blood ph and identify its different types of it

3 ABG Arterial blood gas (ABG) is a blood test that is performed specially on blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The test is used to determine the ph of the blood, the partial pressure of carbon dioxide and oxygen, and bicarbonate level. Many blood gas analyzers will also report concentrations of lactate, heamoglobin, several elecrtolyts, oxyheamoglobin, carboxyheamoglobin and methmogobin.

4 Components of BG Blood Gas Oxygenation Ventilation Acid-Base PaO 2 SaO 2 Sa: saturation Pa: partial pressure PCO 2 ph T.Elsarnagawy, MASH210, 311,2010 4

5 ABG sampling is usually performed on the: 1. Radial artery 2. Femoral artery 3. Branchial artery at the lower margin of the tendon For the collection, administrate local anesthesia, and prepare equipment and clean gloves.

6 Insert needle (heparinized) at a degree angle, slowly direct it toward pulse, and stop when a flash of blood appears. Allow syringe to fill to proper level, place quaze, and remove needle. Transport of blood specimen immediatly in the proper manner after collection ensures the quality of the sample.

7 Blood gas analyzer Blood gas analyzer are used to measure combinations of ph, blood gases (pco 2 and po 2 ), electrolytes, and metabolites parameters from whole blood sample. Therefore, a highly accurate blood gas analyzers can streamline work processes and reduce errors with minimum maintenance.

8 Currently, blood gas analyzers have the following capabilities: 1. Accurate measurement of ph, pco 2 and po 2 2. Self calibration 3. Accurate measurement of base excess or defect 4. Accurate measurement of plasma bicarbonate 5. Correction for temperature 6. Self troubleshooting abilities 7. Automated blood gas interpretation

9 Blood gas analyzer elecrtodes Reference electrode The reference electrode is used in the measurement of ph and electrolyte parameters and is located in the ph/blood Gas module. T.Elsarnagawy, MASH210, 311,2010 9

10 ph electrode The ph measurement is performed using two separate electrodes: a ph-measuring electrode and a reference electrode The ph-sensitive glass membrane is located at the tip and seals the inner buffer solution with a constant and known ph. T.Elsarnagawy, MASH210, 311,

11 ph electrode A saturated electrolyte solution (potassium chloride) in the reference electrode and a leaky membrane permit current flow from the reference electrode through the sample in the measurement chamber to the measuring electrode. The potential difference is displayed on a voltmeter calibrated in ph units. 11

12 po2 electrode Oxygen electrode measures the oxygen partial pressure in a blood or gas sample. Cathode: platinum Anode: a silver/silver chloride Electrolyte: sodium chloride solution Cathode and anode are placed in the electrolyte Applied voltage: 700 mv 12

13 pco2 electrode The pco2 electrode is a combined ph and Ag/AgCl reference electrode mounted in a plastic jacket, which is filled with a bicarbonate electrolyte. The PCO2 electrode also contains a spacer (usually a porous membrane of nylon) that acts as a support. As CO2 diffuses through the membrane and into the support, the ph of the electrolyte changes The output of this modified ph electrode is proportional to the PCO2 present in the sample. 13

14 Electrode Cartridges T.Elsarnagawy, MASH210, 311,

15 Electrolyte electrodes The K+ electrode is an ion-selective electrode whose sensing element is a PVC membrane containing a potassium-neutral ion carrier. The Na+ electrode is an ion-selective electrode whose sensing element is a Na+-sensitive ceramic pin contained in the tip of the jacket. The Ca++ electrode is an ion-selective electrode whose sensing element is a PVC membrane containing a calcium-neutral ion carrier. 15

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17 NORMAL A.B.G VALUES HB gm/dl HCT FIO PaO2 80(60)-100mmHg PaCO mmHg ph K mmol/l Na mmol/l HCO3ˉ mmol/l BE -- ±2 mmol SaO 2 -- >90% 17

18 ABG Interpretation First, does the patient have an acidosis or an alkalosis. Second, what is the primary problem metabolic or respiratory. Third, is there any compensation by the patient respiratory compensation is immediate while renal compensation takes time. ynm dduh 18

19 Acidosis and alkalosis Acidosis A condition in which the blood has too much acid (or too little base), frequently resulting in a decrease in blood ph Alkalosis A condition in which the blood has too much base (or too little acid), occasionally resulting in an increase in blood ph

20 Acidosis ACIDOSIS / ALKALOSIS H + OH - Alkalosis H + OH - 20

21 ACIDOSIS / ALKALOSIS Deviations from normal Acid-Base status are divided into four general categories, depending on the source and direction of the abnormal change in H + concentrations Respiratory Acidosis Respiratory Alkalosis Metabolic Acidosis Metabolic Alkalosis 21

22 Respirotry acidisis Caused by hyperkapnia due to hypoventilation Characterized by a ph decrease and an increase in CO 2 CO CO 2 CO 2 2 CO CO CO CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 ph CO 2 ph 22

23 RESPIRATORY ACIDOSIS Decreased CO 2 removal can be the result of: 1) Obstruction of air passages 2) Decreased respiration (depression of respiratory centers) 3) Decreased gas exchange between pulmonary capillaries and air sacs of lungs 4) Collapse of lung 23

24 Respirotry alkalosis Cause is Hyperventilation Leads to eliminating excessive amounts of CO 2 Increased loss of CO 2 from the lungs at a rate faster than it is produced Decrease in H +

25 RESPIRATORY ALKALOSIS Can be the result of: 1) Anxiety (emotional disturbances) 2) Respiratory center lesions 3) Fever 4) Salicylate poisoning (overdose) 5) High altitude (low PO 2 ) 25

26 METABOLIC ACIDOSIS Any acid-base imbalance not attributable to CO 2 is classified as metabolic Metabolic production of Acids Or loss of Bases 26

27 Metabolic acidsois Acidosis results from excessive loss of HCO 3- rich fluids from the body or from an accumulation of acids Accumulation of non-carbonic plasma acids uses HCO 3- as a buffer for the additional H + thus reducing HCO 3- levels Metabolic acidosis is always characterized by a reduction in plasma HCO 3- while CO 2 remains normal

28 The causes of metabolic acidosis can be grouped into five major categories 1) Ingesting an acid or a substance that is metabolized to acid 2) Abnormal Metabolism 3) Kidney Insufficiencies 4) Strenuous Exercise 5) Severe Diarrhea

29 Metabolic alkalosis Elevation of ph due to an increased 20:1 ratio May be caused by: An increase of bicarbonate A decrease in hydrogen ions Imbalance again cannot be due to CO 2 Increase in ph which has a nonrespiratory origin

30 Can be the result of: 1) Ingestion of Alkaline Substances 2) Vomiting ( loss of HCl ) A reduction in H + in the case of metabolic alkalosis can be caused by a deficiency of non-carbonic acids This is associated with an increase in HCO 3 -

31 Acid-Base Fully Compensated: Parameters: ph PaCO 2 HCO 3 - Metabolic Alkalosis Metabolic Acidosis Respiratory Alkalosis Respiratory Acidosis Normal >7.40 Normal <7.40 Normal >7.40 Normal <7.40

32 Acid-Base Partially Compensated: Parameters: ph PaCO 2 HCO - 3 Metabolic Alkalosis Metabolic Acidosis Respiratory Alkalosis Respiratory Acidosis

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