Acid-Base Disturbances PDF

Acid –base disturbances Acid-Base Balance Electrolytes that ionize in water and release hydrogen ions are acids; those that combine with hydrogen ions are bases. Sources of Hydrogen Ions – Most hydrogen ions originate as by-products of metabolic processes, including: the aerobic and anaerobic respir...

Acid –base disturbances Acid-Base Balance Electrolytes that ionize in water and release hydrogen ions are acids; those that combine with hydrogen ions are bases. Sources of Hydrogen Ions – Most hydrogen ions originate as by-products of metabolic processes, including: the aerobic and anaerobic respiration of glucose, incomplete oxidation of fatty acids, oxidation of amino acids containing sulfur, and the breakdown of phosphoproteins and nucleic acids. 2 For optimal functioning of cells.. Acids and bases in the body must be in balance. We all consume every day food and drinks which contain acids, metabolism produces also acids... pH Review pH = - log [H+] H+ is really a proton Range is from 0 - 14 If [H+] is high, the solution is acidic; pH < 7 If [H+] is low, the solution is basic or alkaline ; pH > 7 4 Acids are H+ donors. Bases are H+ acceptors, or give up OH- in solution. Acids and bases can be: – Strong – dissociate completely in solution HCl, NaOH – Weak – dissociate only partially in solution Lactic acid, carbonic acid 5 Buffer systems Buffer – Substance that opposes changes to pH by removing or adding H+ – Generally consists of: Weak acid (HY) Anion released by its dissociation (Y–) HY  H+ + Y– and H+ + Y–  HY buffers maintain blood PH within normal limits(7.357.45). Major body buffer systems Three major body buffer systems 1. Phosphate buffer system 2. Buffers pH of ICF and urine Carbonic acid–bicarbonate buffer system Most important in ECF 3.Protein buffer systems (in ICF and ECF) Examples: – – – Hemoglobin buffer system » CO2 + H2O  H2CO3  HCO3– + Hb-H+ » Only intracellular system with immediate effects Amino acid buffers (all proteins) Plasma proteins Regulation of Hydrogen Ion Concentration: 1/Acid-base buffer systems 2/ the respiratory center in the brain stem, 3/ kidneys all help to regulate pH of body fluids – The Respiratory Center The respiratory center in the brain stem helps to regulate hydrogen ion concentration by controlling the rate and depth of breathing. – During exercise, the carbon dioxide, and thus the carbonic acid, levels in the blood increase. – In response, the respiratory center increases the rate and depth of breathing, so the lungs excrete more carbon dioxide. –The Kidneys Nephrons secrete excess hydrogen ions in the urine. 11 Acid-Base Imbalances pH< 7.35 acidosis pH > 7.45 alkalosis The body response to acid-base imbalance is called compensation May be complete if brought back within normal limits Partial compensation if range is still outside norms. 12 Two major types of acidosis are respiratory and metabolic acidosis. Alkalosis also has respiratory and metabolic causes Compensation If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation. If problem is respiratory, renal mechanisms can bring about metabolic compensation. 14 Compensatory Responses Primary Compensation Respiratory: Acidosis pCO2 HCO3 Alkalosis pCO2 HCO3 Metabolic: Acidosis Alkalosis HCO3 HCO3 pCO2 pCO2 Acidosis Principal effect of acidosis is depression of the CNS through ↓ in synaptic transmission. Generalized weakness Deranged CNS function the greatest threat Severe acidosis causes – Disorientation – coma – death 16 Alkalosis Alkalosis causes over excitability of the central and peripheral nervous systems. Numbness Lightheadedness It can cause : – Nervousness – muscle spasms or tetany – Convulsions – Loss of consciousness – Death 17 Metabolic Acidosis Bicarbonate deficit - blood concentrations of bicarb drop below 22mEq/L Causes: – Loss of bicarbonate through diarrhea or renal dysfunction – Accumulation of acids (lactic acid or ketones) – Failure of kidneys to excrete H+ 18 Symptoms of Metabolic Acidosis Headache, lethargy Nausea, vomiting, diarrhea Coma Death 19 Metabolic Alkalosis Bicarbonate excess - concentration in blood is greater than 26 mEq/L Causes: – Excess vomiting = loss of stomach acid – Excessive use of alkaline drugs – Certain diuretics(eg:thiazide diueretic) – Endocrine disorders – Heavy ingestion of antacids – Severe dehydration 20 Compensation for metabolic alkalosis Occurs mainly in the lung(respiratory cmpensation)which retain carbon dioxide(CO2) through slower breathing(hypoventilation) Renal compensation:less effective than respiratory compensation consists of increased excretion of bicarbonate Symptoms of Metabolic Alkalosis Respiration slow and shallow Hyperactive reflexes ; tetany Often related to depletion of electrolytes Atrial tachycardia Dysrhythmias 22 Treatment of Metabolic Alkalosis Electrolytes to replace those lost IV chloride containing solution Treat underlying disorder 23 Respiratory Acidosis Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg. Hypercapnia – high levels of CO2 in blood Chronic conditions: – Depression of respiratory center in brain that controls breathing rate ( drugs or head trauma) – Paralysis of respiratory or chest muscles – Asthma and COPD. 24 Respiratory Acidosis Acute conditons: – Adult Respiratory Distress Syndrome – Pulmonary edema – Pneumothorax 25 Compensation for Respiratory Acidosis Kidneys eliminate hydrogen ion and retain bicarbonate ion 26 Compensation for Respiratory Acidosis Kidneys eliminate hydrogen ion and retain bicarbonate ion 27 Signs and Symptoms of Respiratory Acidosis Breathlessness Restlessness Lethargy and disorientation Tremors, convulsions, coma Respiratory rate rapid, then gradually depressed Skin warm and flushed due to vasodilation caused by excess CO2 28 Treatment of Respiratory Acidosis Restore ventilation Treat underlying dysfunction or disease 29 Respiratory Alkalosis Carbonic acid deficit pCO2 less than 35 mm Hg (hypocapnea) Most common acid-base imbalance Primary cause is hyperventilation 30 Signs and symptoms of respiratory alkalosis Palpitation Tetany Convulsion Sweating Respiratory Alkalosis Conditions that stimulate respiratory center: – Oxygen deficiency at high altitudes – Pulmonary disease and Congestive heart failure – caused by hypoxia – Acute anxiety – Fever, anemia – salicylate poisoning(aspirin overdose) – Cirrhosis – Gram-negative sepsis 32 Compensation of Respiratory Alkalosis Kidneys conserve hydrogen ion Excrete bicarbonate ion 33 Treatment of Respiratory Alkalosis Treat underlying cause IV Chloride containing solution – Cl- ions replace lost bicarbonate ions 34 Diagnosis of Acid-Base Imbalances 1. Note whether the pH is low (acidosis) or high (alkalosis) 2. Decide which value, pCO2 or HCO3- , is outside the normal range and could be the cause of the problem. If the cause is a change in pCO2, the problem is respiratory. If the cause is HCO3- the problem is metabolic. 35 3. Look at the value that doesn't correspond to the observed pH change. If it is inside the normal range, there is no compensation occurring. If it is outside the normal range, the body is partially compensating for the problem. 36 Example A patient is in intensive care because he suffered a severe myocardial infarction 3 days ago. The lab reports the following values from an arterial blood sample: – pH 7.3 – HCO3- = 20 mEq / L ( 22 - 26) – pCO2 = 32 mm Hg (35 - 45) 37 Diagnosis Metabolic acidosis With compensation 38