Acid-Base Balance PDF

 Normal PH values  Explain normal regulation of PH  Differentiate respiratory acid-base imbalance  Differentiate metabolic acid-base imbalance  Known medical management of acid base imbalance  Acids and bases are formed during normal metabolic processes  Acids:  Is...

 Normal PH values  Explain normal regulation of PH  Differentiate respiratory acid-base imbalance  Differentiate metabolic acid-base imbalance  Known medical management of acid base imbalance  Acids and bases are formed during normal metabolic processes  Acids:  Is a proton donor  Hydrogen containing substance which dissociate in a solution to release H⁺ ion  Base :  Is a proton acceptor  A substance accept H⁺ ion often with the release of hydroxyl OH⁻ ions  Buffer:  is a mixture of weak acid and its conjugate base  Has the ability to resist changes in pH when acid or base added to an aqueous solution  Weak acid: a substance that reversibly donates H⁺  Weak base: a substance that reversibly binds H⁺  pH : refers to the concentration of H⁺ in a solution  1pH unit change = 10 fold change in H⁺ ion  Normal pH : 7.35 – 7.45  Acidosis: An increase H⁺ ion concentration decreases the pH < 7.35  Alkalosis: A decrease in H⁺ ion concentration increase in pH >7.45  The maintenance of acid-base status is very important for hemostasis  A slit change in pH below 7.35 or above 7.45 will cause serious threats to many physiological functions (coma and death)  Are formed continuously during metabolic reactions  Can also entered from outsides  May be lost in abnormal pathological conditions  Daily production of H⁺ ion in form of volatile and non volatile acids, if are not removed, pH of body fluids will be seriously disturbed ❑ Volatile acids:  Produced by oxidative metabolism of CHO, fat and protein e.g. carbonic acid  Excreted through lungs as CO2 ❑ Non volatile acids (Fixed acids):  E.g. phosphoric acid, sulfuric acid, lactic acid and organic acids  Acids generated during catabolism of amino acids, phospholipids and nucleic acids  Remain in body fluid until eliminated by kidneys  Acid-base balance is concerned with maintaining a normal hydrogen ion concentration in the body fluid  The body has three different mechanisms to regulate acid-base status: 1. chemical buffer system which binds free H⁺ ions 2. Respiratory mechanism which remove CO2 3. Renal mechanism which excretes H⁺ ions and conserve the bases HCO3⁻  It is the first line of defense against blood pH changes  It acts very rapidly within seconds  It is the least efficient mechanism It includes: A. The bicarbonate buffer system (NaHCO3/H2CO3) B. The phosphate buffer system (Na2HPO4/NaH2PO4) C. The protein buffer system ▪ It is very important in extracellular fluid (ECF), plasma HCO3 acts immediately and interstitial HCO3 acts within minutes ▪ It consist of HCO3 and H2CO3 B. The phosphate buffer system (Na2HPO4/NaH2PO4): ▪ Phosphate buffer formed inorganic phosphate ▪ It is very important in intracellular fluid (ICF) C. Protein buffer system: ▪ It is the most important buffer in the body ▪ It present in: ▪ Intracellular fluid ▪ Plasma proteins ▪ Hemoglobin (Hb) which is the most important metabolic buffer in the blood and ECF ▪ responsible for 60 % of buffering capacity of the blood  It is the second line of defense mechanism against blood pH changes  It acts within minutes to hours  It is a moderate efficient mechanism  It acts by controlling dissolved CO2 level in the blood  How it works:  Decrease arterial blood pH (e.g. metabolic acidosis) causes changes in the CSF pH that stimulate chemoreceptors within the brain stem that in turn stimulate the respiratory center.  This increase in the alveolar ventilation (rate and depth of breathing)  This in turn decreases PaCO2 which restores the arterial pH to normal levels  It is the third line of defense mechanism against blood pH changes  It acts within few hours to days  It is the most powerful and efficient mechanism  It acts by controlling the HCO3⁻ level in the blood to keep HCO3⁻/ CO2 constant at about 20:1  Prevent changes in blood pH by increase reabsorption of filtered HCO3⁻ and excreting H⁺ ion in urine  An acid base disorder is a change in normal value of extracellular pH  Occurs when renal or respiratory function is abnormal  Or when an acid or base load overwhelm excretory capacity  Normal values:  pH 7.35 – 7.45  PCO2 35 – 45 mmHg  HCO3 22 – 26 mEq/L  Acidosis:  process that increases H⁺ by increasing PCO2 or by reducing HCO3⁻  Decrease in blood pH below normal range  Alkalosis:  Process that reduces H⁺ by reducing PCO2 or by increasing HCO3⁻  Increase in blood pH above normal range  Acidosis and alkalosis are not disease but rather are the result of a wide variety of disorders.  Acidosis and alkalosis are categorized as metabolic or respiratory depending on their primary cause. ❑ Metabolic acidosis and metabolic alkalosis are caused by imbalance in the production of acids or bases and their excretion by the kidney. ❑ Respiratory acidosis and respiratory alkalosis are caused by changes in carbon dioxide due to lung or breathing disorder ❑ Major adverse effect of systemic acidosis (pH < 7.2): Acidosis mainly affect cardiovascular system Acidosis decrease myocardial contractility the clinical effect are minimal until pH < 7.2, cardiac response to catecholamine are decreased these effect are accentuated in patients with myocardial ischemia, left ventricular dysfunction, on B-blockers or under general anesthesia ❑ Major adverse effect of severe systemic alkalosis (pH > 7.6):  reflect impairment on cerebral and coronary artery blood flow due to arterial vasoconstriction  Decrease serum ionized calcium concentration (hypocalcemia) which responsible for neurologic abnormalities (seizures)  Predispose patient to ventricular arrhythmias  Hypokalemia  Alkalosis depress ventilation so impair weaning patients from mechanical ventilation ❑ It is due to a decrease in HCO3⁻ ❑ Causes:  Diabetic ketoacidosis ( accumulation of ketone bodies)  Drugs e.g. aspirin intoxication, acetazolamide, alcohol  Shock (lactic acidosis)  Loss of bases (bicarbonate): diarrhea, Colostomy  renal failure, hepatic failure  Renal tubular acidosis  Cyanide or carbon monoxide poisoning ❑ Sign and symptoms:  no symptoms in mild acidosis  nausea, vomiting and fatigue  Hyperventilation (increase rate) and depth of breathing to correct acidosis by washing CO2  Drowsiness and confusion  If not corrected hypotension, shock, coma and death ❑ Treatment: Treatment of metabolic acidosis includes Treatment of the cause e.g.: Insulin and fluids for treatment of diabetic ketoacidosis and fluids for improvement of tissue perfusion in lactic acidosis Remove toxic substance from the blood Bicarbonate given only when pH