CH12- Blood Gases.pdf

CH 12 - BLOOD GASES, PH, AND BUFFER SYSTEMS BY: THUY-NHU LE  Acid: donate hydrogen ions (H+) Base: accept hydrogen ions (H+) ACID-BASE pH= -log (H+) BALANCE Eecrease in one pH unit = 10-fold increase in H+ concentration.  ACID-B...

CH 12 - BLOOD GASES, PH, AND BUFFER SYSTEMS BY: THUY-NHU LE  Acid: donate hydrogen ions (H+) Base: accept hydrogen ions (H+) ACID-BASE pH= -log (H+) BALANCE Eecrease in one pH unit = 10-fold increase in H+ concentration.  ACID-BASE BALANCE pH range of 7.35-7.45. Lungs and kidneys → pH homeostasis.  Buffer: weak acid and a salt of its conjugate base. Resist changes in pH. ACID-BASE BALANCE Bicarbonate-carbonic acid system  AC ID-BASE BALANCE Proteins and phosphates: Phosphate buffer system and urine.  CO2 + H2O → H2CO3 REGULATION H2CO3 → H+ and HCO3- OF ACID-BASE HCO3- → plasma BALANCE Chloride shift: electroneutrality  Buffer system with H+ and REGULATION OF ACID- deoxyhemogoblin. BASE BALANCE REGULATION OF O2 from the lungs → blood. AC ID-BASE Oxyhemogoblin (O2Hb). BALANC E: H+ from deoxyhemoglobin + HCO3 → LUNGS H2CO3 → H2O and CO2 → lungs.  REGULATION OF ACID-BASE BALANCE: LUNGS Increased CO2 → increased H+ → decreased pH. Hyperventilation → decreased H+ → increased pH.  Regulate excretion of acid and base. Reabsorption of HCO3- from urine: REGULATION OF H+ → tubule AC ID-BASE H+ and HCO3- → H2CO3 → CO2 and BALANC E: KID NEYS H2O → cell CO2 and H2O → H2CO3 → H+ and HCO3- HCO3- → blood  REGULATION OF ACID-BASE BALANCE: KIDNEYS Excretion of H+ ions through urine: Dihydrogen phosphate (H2PO4-) Ammonium (NH4+) AC ID-BASE D ISORDER S: AC IDOSIS AND ALKAL OSI S Acidemia/acidosis: blood pH is less than the reference range. [H+] increases from increased [pCO2] or decreased [HCO3-]. Alkalemia/alkalosis: blood pH is greater than the reference range. [H+] decreases from decreased [pCO2] or increased [HCO3-]. AC ID-BASE D ISORDER S: AC IDOSIS AND ALKAL OSI S Respiratory acidosis/alkalosis: disorder caused by respiratory dysfunction. Metabolic acidosis/alkalosis: disorder caused by a change in the bicarbonate level. METABOLIC ACIDOSIS Metabolic acidosis: Overdose of acid producing substances (aspirin, ethanol, methanol, ethylene glycol). Excess production of acidic ketone bodies (diabetic ketoacidosis) Reduced excretion of hydrogen ions (renal tubular acidosis) Excessive loss of bicarbonate from diarrhea (hyperchloremic acidosis) METABOLIC ACIDOSIS Hyperventilation → excessive elimination of CO2 → elevate pH Kidneys → H+ and reabsorbing HCO3-  RESPIR ATORY ACI DOSIS Respiratory acidosis: caused by hypoventilation Increased CO2 (hypercapnia) Compensation by increasing H+ excretion and reclamation of HCO3- → increased HCO3-  RESPIR ATORY ACI DOSIS Respiratory acidosis: Ineffective removal of CO2 from the blood (asthma). Airway obstruction (COPD). Overdose of drugs (barbiturates, morphine, alcohol). Decreased cardiac output (congestive heart failure). Metabolic alkalosis: gain in HCO3-. Excessive loss of stomach acid: vomiting, nasogastric suctioning. Prolonged use of diuretics: METABOLIC Increased H+ excretion → acidic urine and alkaline blood. ALKALOSIS Excess ingestion of antacids. Hypokalemia: H+ shift → HCO3- kidney reabsorption.  Compensation: hypoventilation Increases pCO2, lowers pH METABOLIC Primary cause of metabolic alkalosis ALKALOSIS needs to be addressed.  RESPIRATORY ALKALOSIS Respiratory alkalosis: increased rate of alveolar ventilation → excessive CO2 elimination. High altitudes Anxiety induced hyperventilation Aspirin overdose Pulmonary embolism  RESPIRATORY ALKALOSIS Compensation: decreased Na+ - H+ exchange: Kidneys excrete HCO3- in the urine, reclaim H+ to the blood.  O2 transport to tissue: hemoglobin. One hemoglobin molecule can bind with four O2 molecules. Availability of O2 Concentration and types of hemoglobin OXYGEN present Presence of competing molecules such as CO pH Temperature of blood Levels of pCO2 and 2,3 DPG HEMOGLOBIN Four forms: Oxyhemoglobin (O2Hb): Hb reversibly bound to O2 Deoxyhemoglobin (HHb): Hb without O2 Ferrous (2+) state  HEMOGLOBIN Carboxyhemoglobin (COHb): Hb bound to CO Methemoglobin (MetHb): Hb unable to bind O2: Ferric (3+) state  Hypoxia: insufficient oxygen at the tissue level. Hemoglobin: HEMOGLOBIN Transports and releases O2. Transport CO2 from the tissue to the lungs.  Blood gas analysis: blood obtained from artery, vein, or capillary. BLOOD GAS ANALYSIS Arterial blood gas (ABG) Venous blood gas (VBG) Capillary blood gas (CBG) BLOOD GAS ANALYSIS  ABG Parameters: Step 1: Determine if pH demonstrates acidosis or alkalosis. pH = measured acid-base balance of the blood. Normal range: 7.35 – 7.45 pH > 7.45 = alkalosis pH < 7.35 = acidosis BLOOD GAS ANALYSIS Step 2: Determine if PaCO2 demonstrates a respiratory disorder. PaCO2 = measured partial pressure of carbon dioxide in arterial blood. Normal range: 35 – 45 mmHg Increased PaCO2 = respiratory acidosis Decreased PaCO2 = respiratory alkalosis Normal CO2 = suggests a metabolic disorder  ABG Parameters: Step 3: Determine if HCO3- demonstrates a metabolic disorder. HCO3- = calculated concentration of BLOOD GAS bicarbonate in arterial blood. ANALYSIS Normal range: 22-26 mEq/L HCO3- < 22 = metabolic acidosis HCO3- > 26 = metabolic alkalosis Normal HCO3- = suggests a respiratory disorder  ABG Parameters: Base excess/ deficit = calculated relative excess or deficit of base in arterial blood. BLOOD GAS ANALYSIS High base excess (> +2mmol/L): increased amount of HCO3– in the blood. Low base excess (< -2mmol/L): decreased amount of HCO3- in the blood.  ABG Parameters: BLOOD GAS ANALYSIS PaO2 = measured the partial pressure of oxygen in arterial blood.  Additional ABG Parameters: BLOOD GAS Temperature ANALYSIS FiO2: the concentration of oxygen in a gas mixture Air we inhale is 21% O2 BLOOD GAS ANALYSIS BLOOD GAS ANALYSIS  Clarke electrode. Reduction of O2 → current. Directly proportional to sample pO2. Sources of error: Protein buildup on the membrane’s MEASUREMENT- PO2 surface. Exposure to room air → false increase in pO2. Delay in analyzing sample: WBCs use O2 in metabolic processes → false decrease in pO2.  Glass membrane: Potential difference between measuring electrode and reference electrode. MEASUREMENT- PH Sources of error: Protein buildup Temperature Erroneous calibration  Modified glass electrode (Severinghaus electrode) Gas semi-permeable membrane. MEASUREMENT- Sources of error: PCO2 Temperature Protein buildup Erroneous calibration Exposure to air → falsely decreases pCO2 MEASUREMENT- All blood gas analyzers have electrode TEMPERATURE chambers controlled to 37°C + 0.1°C  From measured pH and pCO2 values: HCO3 MEASUREMENT- CALC ULATED Carbonic acid (H2CO3) PARAMETER S Total carbon dioxide content (ctCO2) Base excess  Collection device. Form and concentration of heparin used for anti-coagulation. SOURCES OF ERROR Maintenance of the anaerobic environment- minimize transport and analysis time. Mixing of the sample well. Air bubbles.