1 Acid –Base Imbalance Dr. Eman EL Eter

Acid-Base Imbalances 2 pH< 7.35 acidosis pH > 7.45 alkalosis PCO2= mmHg HCO3- = mEq/L 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.

Compensation 3 If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation +buffer system. If problem is respiratory, renal mechanisms can bring about metabolic compensation.

Acidosis 4 Principal effect of acidosis is depression of the CNS through ↓ of synaptic transmission. Generalized weakness Deranged CNS function the greatest threat Severe acidosis causes Disorientation coma death

Causes of acidosis 5 A. Respiratory causes: - CNS depression (anaesthesia). - Resp. muscle paralysis/ diaphragm paralysis, - Rib fractures, etc.. - Obstructive lung diseases e.g. Emphysema Pulmonary edema. A. Metabolic causes: - Diabetic ketoacidosis. -Severe diarrehea. -Hypoaldosteronism -Acute renal failure

Alkalosis 6 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

Causes of alkalosis 7 A- Respiratory: Hyperventilation: - High altitude. - Hysterical. - B. Metabolic: - -Severe vomiting. - Excess antacids. - Hyperaldosteronism.

Respiratory Acidosis 8 Carbonic acid excess caused by blood levels of CO 2 above 45 mm Hg.

Compensation for Respiratory Acidosis 9 Kidneys eliminate hydrogen ion and retain bicarbonate ion. Kidney also generates new bicarbonate.

10

Respiratory Alkalosis 11 Carbonic acid deficit pCO 2 less than 35 mm Hg (hypocapnea) Most common acid-base imbalance Primary cause is hyperventilation

Respiratory Alkalosis 12 Conditions that stimulate respiratory center and wash out CO2 (Hyperventilation): Oxygen deficiency at high altitudes. Anorexia nervosa. Early salicylate intoxication

Compensation of Respiratory Alkalosis 13 Kidneys conserve hydrogen ion Excrete bicarbonate ion

14

Metabolic Acidosis 15 Bicarbonate deficit - blood concentrations of HCO3- drops 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+

Compensation for Metabolic Acidosis 16 Increased ventilation Renal excretion of hydrogen ions if possible K + exchanges with excess H + in ECF ( H + into cells, K + out of cells)

17

Metabolic Alkalosis 18 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 Endocrine disorders: Hyperaldosteronism. Heavy ingestion of antacids Severe dehydration

Compensation for Metabolic Alkalosis 19 Kidney excretes alkaline urine and retain H+ Respiratory compensation difficult – hypoventilation limited by hypoxia.

20

Diagnosis of Acid-Base Imbalances Note whether the pH is low (acidosis) or high (alkalosis) 2. Decide which value, pCO 2 or HCO 3 -, is outside the normal range and could be the cause of the problem. If the cause is a change in pCO 2, the problem is respiratory. If the cause is HCO 3 - the problem is metabolic.

22 Compensated or uncompensated? If pH is normal (between )….Compenstaed If pH is abnormal ( 7.45)….uncompenstated. Respiratory or metabolic? If PCO2>45 = Respiratory acidosis If PCO2<35= Respiratory alkalosis If HCO3-< 22= Metabolic acidosis. If HCO3-> 26 = metabolic alkalosis.

Example: 23 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 =7.21, PCO2= 42, HCO3- = 12: List the condition: acidosis or alkalosis, metabolic or respiratory, compensated or uncompensated? Answer: Metabolic acidosis, uncompensated

Practice 24 pHPaCO2PaHCO3Com/unResp/metabAcid/alka losis uncompensatedmetabolicacidosis uncompensatedrespiratoryalkalosis compensatedrespiratoryacidosis Normal compensatedrespiratoryalkalosis uncompensatedmetabolicalkalosis compensatedrespiratoryacidosis uncompensatedRespiratoryacidosis