1 Acid and Base Disturbance

2 pH Review H + is a proton pH Range is from If [H + ] is high, the solution is acidic; pH < 7 If [H + ] is low, the solution is basic or alkaline ; pH > 7

3 The Body and pH Homeostasis of pH is tightly controlled Extracellular fluid = 7.4 Blood = 7.35 – 7.45 (7.40) 8.0 death occurs Acidosis (acidemia) below 7.35 Alkalosis (alkalemia) above 7.45 Normal Serum HCO3- is mmol/L

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5 Small changes in pH can produce major disturbances Most enzymes function only with narrow pH ranges Acid-base balance can also affect electrolytes (Na +, K +, Cl - )

6 The body produces more acids than bases Acids take in with foods Cellular metabolism produces CO 2. CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - Slightly Alkaline plasma of 7.40(H+ : 40 nmol/L) is maintained by kidney capacity to produce an Acidic Urine(PH typically 5- 6)in which the excess of metabolic acid can be excreted.

7 Renal Control of Acid-Base balance Kidneys are Most effective regulator of pH If kidneys fail, pH balance fails Collecting ducts cells, Can eliminate large amounts of acid (Acid is secreted into the lumen by H+_ATPas ) Can also excrete base Can conserve and produce bicarb ions Renal compensatory mechanisms may take hours to days OR EVEN WEEKS

8 Respiratory mechanisms Exhalation of carbon dioxide CO 2 CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - Body pH can be adjusted by changing rate and depth of breathing Respiratory mechanisms (hypo or hyperventilation) take several minutes to hours

9 Urinary Buffers Bicarbonate: some 85% of the filtered Bicarbonate reabsorbed in the Proximal tubule phosphate: Maintain a 20:1 ratio HCO 3 - : H 2 CO Ammonia : Major intracellular buffer H + + HPO 4 2- ↔ H 2 PO4 -

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12 Compensation to Acid-Base Imbalances If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation. If problem is respiratory, renal mechanisms can bring about metabolic compensation.

13 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

14 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

Simple Acid-Base Disorders Primary Compensatory Disorder pH H + Disorder Response Metabolic acidosis    HCO 3 _  pCO 2 Metabolic alkalosis      HCO 3 _  pCO 2 Respiratory acidosis      pCO 2  HCO 3 _ Respiratory alkalosis      pCO 2  HCO 3 _

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17 Respiratory Acidosis Carbonic acid excess caused by blood levels of CO 2 above 45 mm Hg(= PCO kpa). Hypercapnia – high levels of CO 2 in blood causes Chronic conditions: –Depression of respiratory center in brain that controls breathing rateby drugs or head trauma –Paralysis of respiratory or chest muscles _Emphysema Acute conditons: –Adult Respiratory Distress Syndrome –Pulmonary edema –Pneumothorax * Compensation: Kidneys eliminate hydrogen ion and retain bicarbonate ion

18 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 CO 2 Treatment Restore ventilation Treat underlying dysfunction or disease

19 Respiratory Alkalosis cause is sustained hyperventilation Carbonic acid deficit..washing of CO 2 pCO 2 less than 35 mm Hg (hypocapnea),Most common acid-base imbalance causes high altitudes (Oxygen deficiency) Hyperventilation Pul embolisim,Acute anxiety….HYS,Fever, anemia Early salicylate intoxication..stim brain stem resp.center &Cirrhosis chronic liver disease Cl/p : perioaral & digital tingling,Tetany (due to decrease ionised Ca++ caused by increase binding of Ca++ to Albumen in Alkalosis Treatment :Treat underlying cause rebreathe into a paper bag

20 Metabolic Acidosis characterized HCO3- less than 24,Caused by: –Loss of bicarbonate through diarrhea or renal dysfunction –Accumulation of acids (lactic acid or ketones) –Failure of kidneys to excrete H+

Causes of Normal AG (Hyperchloremic) Metabolic Acidosis High K + Low K + Adrenal insufficiencyDiarrhea Interstitial nephritisRTA proximal,Distal Ureteral diversion AG = (Na + + K+) - (Cl - + HCO 3 - ) = 15

Metabolic Acidosis: Elevated Anion Gap AG = (Na + + K+) - (Cl - + HCO 3 - ) = 15 [Note: Diagnostic utility is best when AG > 25] Causes Ketoacidosis Lactic acidosis Intoxications (salicylate,Methanol poisoning) Renal failure Rhabdomyolysis

23 Compensation for Metabolic Acidosis Increased ventilation Renal excretion of hydrogen ions if possible K + exchanges with excess H + in ECF ( H + into cells, K + out of cells)

24 Metabolic Alkalosis Bicarbonate excess - concentration in blood is greater than 24 mmol/L compensation…hypoventilation..ie PCO2 will be more than 5.33 kpa Causes: –Excess vomiting = loss of stomach acid –Loop &Thiazide Diuretics (loss of H+ in urine) –Cushing synd,,primary hyperaldoteronism(corticosteroid excess) –Heavy ingestion of antacids –Severe dehydration

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