Acid Base Imbalances PDF

ACID BASE IMBALANCES By Muhammad Rehan Lecturer Dow Institute of Nursing & Midwifery 1  Objectives At the end of this unit each student will be able to Review the physiological mechanism responsible to regulate acid ba...

ACID BASE IMBALANCES By Muhammad Rehan Lecturer Dow Institute of Nursing & Midwifery 1  Objectives At the end of this unit each student will be able to Review the physiological mechanism responsible to regulate acid base balance in the body i.e. 1. Buffer (phosphate, hemoglobin, carbonate) 2. Renal mechanism 3. Respiratory mechanism Discuss the classification of acid base imbalance in term of:  Respiratory acidosis & alkalosis 2  Metabolic acidosis & alkalosis  Objectives Discuss how to interpret the arterial blood gases (ABGs) to identify four types of acid base imbalances. Discuss the cause, pathophysiology and clinical manifestation of;  Respiratory acidosis and alkalosis  Metabolic acidosis and alkalosis  ACID-BASE BALANCE Acids An acid is a substance that donates hydrogen ions. Release H+ into solution Bases A base is a substance that accepts hydrogen ions. Remove H+ from solution 4  ACID-BASE BALANCE The pH symbol indicates the hydrogen ion concentration of body fluids. Normal blood pH level is 7.35 to 7.45 Acidity increases as the pH decreases. Alkalinity decreases as the pH increases. 5  ACIDOSIS: Process producing acidemia (pH7.45) either too many alkaline substances or not enough acid substances. It can cause : Nervousness muscle spasms or tetany Convulsions Loss of consciousness Death 7 8  ACID-BASE BALANCE BUFFERS Two or more chemical compounds that prevent marked changes in hydrogen ion concentration when either an acid or a base is added to a solution Buffers: Resist changes in pH When H+ added, buffer removes When H+ removed, buffer replaces Types of buffer systems Carbonic acid/bicarbonate Phosphate 10 Protein 11  BICARBONATE BUFFER SYSTEM CO2 + H2O → H2CO3 → H+ + HCO3 (Carbonic Acid) Main extra cellular buffer Also affected by lung and kidneys 12  PHOSPHATE BUFFER SYSTEM Stronger then bicarbonate buffering system More important in buffering ICF and renal tubules than in ECF. H2PO4 → H+ + HPO4 Dihydrogen Phosphate --- weak acid Monohydrogen phosphate weak base. 13  PROTEIN BUFFER SYSTEM Proteins are more concentrated than bicarbonate and phosphate buffers Accounts for 75% of all chemical buffering of body fluids. 14 15  RESPIRATORY REGULATION OF ACID-BASE BALANCE Respiratory regulation of pH is achieved through carbonic acid/bicarbonate buffer system As carbon dioxide levels increase, pH decreases As carbon dioxide levels decrease, pH increases Carbon dioxide levels and pH affect respiratory centers Hypoventilation increases blood carbon dioxide levels Hyperventilation decreases blood carbon dioxide levels 16  REGULATORS OF ACID-BASE BALANCE Increased carbon dioxide levels in extracellular fluid increase rate and depth of respirations so that more carbon dioxide is exhaled. Decreased carbon dioxide levels depress respirations to maintain carbon dioxide. 17  Respiratory Regulation of Acid-Base Balance 18  RENAL REGULATION OF ACID-BASE BALANCE Secretion of H+ into filtrate and reabsorption of HCO3- into ECF cause extracellular pH to increase HCO3- in filtrate reabsorbed Rate of H+ secretion increases as body fluid pH decreases or as aldosterone levels increase Secretion of H+ inhibited when urine pH falls below 4.5 19  REGULATORS OF ACID-BASE BALANCE Renal Control of Hydrogen Ion Concentration The kidneys control extracellular fluid pH by removing hydrogen or bicarbonate ions from body fluids. When the kidneys excrete more bicarbonate ions, the urine becomes more alkaline. When the kidneys excrete more hydrogen ions, the urine becomes more acidic. 20  COMPONENT OF THE ARTERIAL BLOOD GAS: The arterial blood gas provides the following values: PH Measurement of acidity or alkalinity, based on the hydrogen (H+) ions present. The normal range is 7.35 to 7.45. PaO2 The partial pressure of oxygen that is dissolved in arterial blood The normal range is 80 to 100 mm Hg. 21  SaO2 The arterial oxygen saturation The normal range is 95% to 100%. PaCO2 The amount of carbon dioxide dissolved in arterial blood. The normal range is 35 to 45 mm Hg. HCO3 The calculated value of the amount of bicarbonate in the blood stream. The normal range is 22 to 26 mEq/liter 22  DEFINITIONS: Metabolic Acidosis: low pH and low bicarb Metabolic Alkalosis: high pH and high bicarb Respiratory Acidosis: low pH and high PCO2 Respiratory Alkalosis: high pH and low PCO2 23 Imbalance pH PaCO2 HCO3 Respiratory ↓ ↑ Normal acidosis Respiratory ↑ ↓ Normal alkalosis Metabolic ↓ Normal ↓ acidosis Metabolic ↑ Normal ↑ alkalosis 24  Causes of Respiratory acidosis Hypoventilation, possibly related to:  Acute pulmonary edema  Aspiration of a foreign object  Atelectasis  Pneumothorax  Overdose of sedatives  sleep apnea syndrome  Chest trauma  COPD  Neuromuscular disease (muscular dystrophy, myasthenia gravis, and Guillain-Barre syndrome etc……..) 25  Respiratory acidosis Of respiratory origin ~ Shallow breathing ~  CO2 exhaled  CO2 retained Lung diseases blocking gas diffusion e.g. pneumonia, COPD, emphysema,  CO2  H+ pH 7.45 29  Metabolic acidosis Clinical features  Headache  Confusion  Drowsiness,  Increased respiratory rate and depth  Nausea & vomiting  Decreased cardiac output  Decreased blood pressure, cold and clammy skin  Dysrhythmias  Shock Causes:  Diabetic ketoacidosis  Diarrhea  Salicylate overdose  Renal failure 30  Metabolic acidosis Not of respiratory origin ~ Renal disease ~ Diarrhoea ~ Starvation  HCO3  H+  pH < 7.35 31  Metabolic Alkalosis Not of respiratory origin ~ Vomiting ~  Ingestion Bicarb of Soda (NaHCO3)  HCO3  H+  pH > 7.45 32  Metabolic Alkalosis Causes:  Loss of gastric secretions  Overuse of antacids  Potassium-wasting diuretics (thiazides, furosemide)  Excessive adrenocorticoid hormones 33  Metabolic Alkalosis Clinical features Tingling of the fingers and toes Dizziness Hypertonic muscles Tachycardia pH increases above 7.6 Hypokalemia Premature ventricular contractions 34  References:  Norris, T. L. (2019). Porth's Pathophysiology Concepts of Altered Health States (Tenth Edition ed.). Philadelphia: Wolters Kluwer. 35