ABG CASE STUDIES & INTERPRETATION It’s not magic understanding ABG’s, it just takes a little practice! Acid base balance- relative constancy of concentration of hydrogen ions in internal environments of an organism that provides high-grade completeness of the metabolic processes proceeding in cells and fabrics. Hydrogen index (pH) - negative decimal logarithm of the activity, or concentration, of hydrogen ions in solution (-lg[H]). Its the main quantitative characteristic of the acidity of aqueous solutions. Hydrogen indicator was introduced S. Serensen (S.Sеrensen) in 1909 He suggested abbreviation "PH" instead - lg[H +]. Indicator value pH depends on the ratio between positively charged ions (forming an acidic environment) and negatively charged ions (forming an alkaline environment). The human body constantly strives to balance this ratio, maintaining a strictly defined level pH. When the balance is disturbed, they can occurmany serious diseases. at pH equal to 7.0 talk about neutral environment. The lower the level pH - the more acidic the environment (from 6.9 to 0). The alkaline environment has a high level pH (from 7.1 to 14.0). 1. Functional systems support acid base balance in the body The acid-base state is maintained by powerful homeostatic mechanisms. They are based on the features of physicochemical properties blood buffer systems and physiological processes, in which the systems participate: external respiration, kidneys, liver, gastrointestinal tract, etc. Buffers systems Role buffer systems is in support normal pH blood. Buffer system represents by itself mixture weak acids and her salt, formed strong basis. Plasma exposure strong acid causes a reaction of buffer systems, as a result of which a strong acid is converted into a weak one. The same exactly happens and when exposed to biological liquid strong basis, which after interaction with buffer systems turns into weak basis. As a result of these processes pH changes either do not occur or are minimal. All these systems are in the blood, where they maintain a pH = 7.4, despite the entry into the blood from the intestines and tissues of significant amounts of acids and small quantity basics. Maintenance of stability of active reaction of blood is provided buffer systems, Which include: 1. Bicarbonate buffer system [carbon acid - H2СО3, bicarbonate sodium - NaHCO3)] - the main buffer of intercellular fluid and blood, is formed in the kidneys and facilitates the excretion of H+. 2. Phosphate buffer system [monobasic (NаН2RO4) and dibasic (Na2NRA4) phosphate sodium] - facilitates breeding H+ in tubules kidney. The main role isregulation CLR inside the cells (especially the kidneys), supports the "regeneration" of the bicarbonate system in the blood. 3. Plasma protein buffer system - the main intracellular buffer. In an acidic environment, it binds hydrogen ions, in an alkaline environment - gives. 4. Hemoglobin buffer system [Hemoglobin - potassium salt of hemoglobin] - plays a major role in the transport of CO2 from tissues to the lungs, begins to act within minutes. 2. Involvement of bodies in regulation of acid base balance Respiratory system.The respiratory system is involved in regulation acid base balance, changing voltage CO2 in the blood. Closely bound to bicarbonate buffer. -at reduction frequencies breath (hypoventilation) increases CO2 concentration in the blood, which leads to an increase in the concentration of H2СО3 and developing acidosis. -at increase frequencies breath (hyperventilation) decreases voltage CO2, decreases number H2СО3 and developing alkalosis. Ren regulate the acid-base state, eliminating or reducing violations by removal protons (H+) and increasing or decreasing [NaCO3ˉ] in liquid media. Secretion H+ is regulated by CO2 content in extracellular fluid: the higher the concentration of CO2 - the more excretion H +, which leads to increased acidity of urine. When increases level H+ in blood, the kidneys produce HCO3ˉ, which helps maintain it in the body correlation acids/basis at the level of 1:20. If the extracellular fluid increases HCO3ˉ or decreases [H+], the kidneys are delayed H+ and remove HCO3-, in this case the urine becomes alkaline. Acidosis increases the synthesis and excretion of ammonia in the kidneys, alkalosis has the return action. Liver. Its cells synthesize proteins of the buffer system; oxidized organic acids to CO2 and water; lactate is converted to glucose and c glycogen, together acidic and alkaline metabolic products are excreted from the body with bile. Gastrointestinal highway. At tinning liquid environments organism selection salt acids in cavity stomach is inhibited, at acidified - intensifies. selection HCO3- in strait pancreatic bets intensifies at tinning liquid environments, at acidified - decreases. Bone cloth. On+, K +, Ca2 +, Mg2 +, what contained in bone fabric,, can exchange on ions hydrogen,, compensatingacidosis. INheavy cases this process maybe cause to decalcification skeleton. 3. Violation acid-base state of the body In terms pathology acid-base balance can change both in the acidic (acidosis) and in the alkaline (alkalosis) side. acidosis - acid-base imbalance, characterized by the appearance in the blood of an absolute or relative excess of acids and an increase in the concentration of hydrogen ions. alkalosis - acid-base imbalance, in which there is an absolute or relative increase quantity basics and reducing the concentration of hydrogen ions. Classification of acid-base disorders 1. For mechanism of development of acidosis and alkalosis are divided into: 1. Respiratory (gas, respiratory) 2. Metabolic (non-gas, exchange) 2. According to the degree of severity distinguish: 1. Compensated acidosis and alkalosis. With compensated acidosis and alkalosis buffer and physiological systems of the body involved in the neutralization and excretion of acidic and alkaline products provide support pH within normal limits. 2. Decompensated acidosis and alkalosis. With decompensated acidosis and alkalosis there is depletion and insufficiency protective mechanisms,, pH shifts beyond the norm. Acid base imbalances • Metabolic acidosis • Metabolic alkalosis • Respiratory acidosis • Respiratory alkalosis CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3 LUNGS REN Metabolic • METABOLIC ACIDOSIS: Decrease the HCO3 - --> the pH goes down. • Compensation: Respiratory Alkalosis (hyperventilation) will bring the pH back near normal. • Causes: Diarrhea, DKA, LA, renal failure. • METABOLIC ALKALOSIS: Increase the HCO3 - --> the pH goes up. • Compensation: Respiratory Acidosis (hypoventilation) can help to bring the pH+ Respiratory • RESPIRATORY ACIDOSIS: Increase the PCO2---> the pH goes down. Hypoventilation. Compensation: Metabolic Alkalosis can help bring the pH back near normal. • Causes: pneumonia, Bronchitis,Asthma • RESPIRATORY ALKALOSIS:Decrease the PCO2-> the pH goes up.Hyperventilation. • Compensation: Metabolic Acidosis can help bring the pH back near normal. METABOLIC ALKALOSIS CAUSES: • Vomiting: Lose enough stomach acid to produce alkalosis. • Diuretics: Loop diuretics and thiazides can lead to hypokalemia ------> secondary metabolic alkalosis. • Transfusion of large quantities of alkaline solutions • Antacids overuse RESPIRATORY ACIDOSIS: causes: CNS DEPRESSION DRUGS:Opiates,sedatives,anaes thetics OBESITY HYPOVENTILATION SYNDROME STROKE NEUROMUSCULAR DISORDERS: NEUROLOGIC: POLIO,GBS,TETANUS,BOTULISM MUSCULAR DYSTROPHY AIRWAY OBSTRUCTION CHEST WALL RESTRICTION ACUTE ASPIRATION, LARYNGOSPASM PLEURAL: Effusions, empyema, pneumothorax,fibrothorax CHEST WALL: Kyphoscoliosis, scleroderma,ankylosing spondylitis,obesity SEVERE PULMONARY RESTRICTIVE DISORDERS PULMONARY FIBROSIS PARENCHYMAL INFILTRATION: Pneumonia, edema RESPIRATORY ALKALOSIS Causes: • High altitude • Psychogenic hyperventilation • Neuromuscular disease • Respiratory center depression • Inadequate mechanical ventilation • Sepsis • Burns Metabolic acidosis Causes: • Metabolic acidosis: Is caused by a decreaseinHCO3-concentration inblood. • Causes: 1.Increased production of acids: Lactate acidosis, ketoacidosis, Salicylate poisoning. 2.Loss of HCO3-: Diarrhea and kidneys renal tubular acidosis 3.Blood profile: pH decreased [HCO3-] decreased, PCO2 decreased Compensation of Metabolic acidosis: • • • Respiratory compensation: decrease in pH stimulates respiratory center causing hyperventilation which produces decrease in PCO2. Renal Compensation: excess H+ is excreted as titratable acid and NH4+. Treatment: lactate containing solution which converts HCO3- ion the liver. Assessment of acid base status • Direct arterial blood measurements: ABG pH NB: use heparinised blood, pCO2 measured within 10 minutes pO2 • Derived measures: Bicarbonate (HCO3-) Normal Values: pH =7.35-7.45 (7.4) HCO3-=22 - 26mEq / L pCO2 = 35 - 45mm Hg (24mEq / L) (40mm Hg ) Metabolic alkalosis Metabolic acidosis Respiratory acidosis Respiratory Alkalosis Metabolic Acidosis pH 7.30 PaCO2 40 HCO3 15 Metabolic Alkalosis pH 7.50 PCO2 40 HCO3 30 Respiratory Acidosis pH 7.30 PaCO2 60 HCO3 26 Respiratory Alkalosis pH 7.50 PaCO2 25 HCO3 23 What are the compensations? Respiratory acidosis --metabolic alkalosis Respiratory alkalosis --metabolic acidosis In respiratory conditions, therefore, the kidneys will attempt to compensate and visa versa. • Buffers kick in within minutes. Respiratory compensation is rapid and starts within minutes and complete within 24 hours. Kidney compensation takes hours and up to 5 days Acid base disorder-worksheet Practice ABG’s 1. Respiratory alkalosis 2. Respiratory acidosis 3. Metabolic acidosis 4.Compensated Respiratory acidosis 5. Metabolic alkalosis 6. Compensated Respiratory acidosis 7. Compensated Metabolic alkalosis 8. Metabolic acidosis 9. Respiratory acidosis 10. Metabolic alkalosis STEPS OF ASSESSING ABG • STEP 1: Diagnose whether it is acidosisor alkalosis- (pH will help) • STEP2:Diagnose whether compensatedor non compensated • STEP3:Diagnosewhetheritis metabolic or respiratory(Look at the value of bicarbonate and pCO2) Work sheet Diarrhea may lead to----------? Acid loss due to vomiting and gastric suction maylead to ______ alkalosis? Overuse of _________may lead to metabolic alkalosis? Problem#1 • • 67 year female known diabetic for past 20years presented with sudden onset of severe chest pain and Shortness of breath. ABG analysis showed: pH 7.36 PCO2 33 mmHg HCO3 18 mmol/L • Discuss the probable diagnosis. • • • Problem #2 A 30-year old man with DM presents with polyuria, polydipsia, fever, cough, and purulent sputum. His ABG shows the following Na+140 / Cl- 104 K+7.0 pH: 6.95 pCO2 : 33 Hco3 : 7.0 Discuss the probable diagnosis. Problem#3 • 45 year old male was admitted to the emergency room with complaints of mild vomiting, associated with disorientation and muscular weakness. His blood investigations showed the following pH =7.20 Na -137meq/l HCO3-=16mEq /L pCO2 = 34mm Hg Glucose=685mg/dl urea49mg/dl Cl-108meq/l K -5.8 Problem #4 • 60 year male presents to the ED from a nursing home. You have no history other than he has been breathing rapidly and is less responsive than usual. • • • Na+ 123 Cl- 99 HCO3 - 5 pH 7.31pCO2 10 Discuss the probablediagnosis. Problem # 5 60year old man was admitted with severe abdominal pain, which started some 2 hours back. Clinically he was in a state of shock with distended abdomen. Femoral pulses could not be palpable His ABG shows the follows pH : 7.05 pCO2: 26.3 mmHg HCO3: 7 mmol/L Discuss the probable diagnosis.
