ACID BASE DISTURBANCES DR WAQAR ( MBBS, MRCP) ASSISTANT PROFESSOR OF MEDICINE MAAREFA MEDICAL COLLEGE

BASIC DEFINITIONS ACID : A compound which releases H+ ( HCL) BASE ( alkali) : A compound which can accept H+ ( Na HCO3) pH : A measure of H+ activity. This number tells us how “acidic” or “alkaline”( or neutral) is the solution.

CO2 ALSO PRODUCES ACID ( CO2 + H2O = H2CO3 ( CARBONIC ACID) ACIDS ARE PRODUCED DAILY IN THE HUMAN BODY ( LACTIC, ACETOACETIC, HYDROXYBUTYRIC ) CO2 ALSO PRODUCES ACID ( CO2 + H2O = H2CO3 ( CARBONIC ACID) ALKALI IS ALSO PRESENT IN THE BODY (HCO3) BUT BLOOD IS NEITHER ACIDIC NOR ALKALOTIC

IN THE BLOOD, ACID & ALKALI ARE BALANCED NORMAL pH OF BLOOD : 7.35 TO 7.45 IN THE BLOOD, ACID & ALKALI ARE BALANCED SO pH IS STABLE A NORMAL BLOOD pH IS IMPORTANT FOR NORMAL CELL FUNCTIONS

Extra acid or alkali in the blood is immediately “bufferred” ( neutralized) by certain substances in the blood and then excreted. These substances are called BUFFERS. ( eg HCO3, organic acids) eg : H + HCO3 H2CO3 H20 + CO2 BUFFERS : Substances which immediately absorb excess acid or alkali , so that the pH does not change

IF EXCESS ACID REMAINS IN THE BLOOD ACIDOSIS IF EXCESS ALKALI REMAINS ALKALOSIS pH CHANGES ACIDOSIS CAUSES LOW pH ( lower than 7.35) ALKALOSIS CAUSES HIGH pH ( higher than 7.45)

WHAT IS ACIDOSIS ? ACIDOSIS : * EXCESS ACID or LESS ALKALI * pH IS LOW ( less than 7.35) ( normal pH is 7.35 to 7.45) acid alkali acid alkali acid alkali ------------------------------------------------------------------------------------------------------ NORMAL ( ---------- A C I D O S I S ---------------)

WHAT IS ALKALOSIS ? EXCESS ALKALI ( BASE) OR LESS ACID pH IS HIGH ( MORE THAN 7.45) (normal pH is 7.35 to 7.45) ACID ALKALI ACID ALKALI ACID ALKALI ------------------------------------------------------------------------------------ NORMAL (------------------ ALKALOSIS---------)

IMPORTANT EQUATION H+ HCO3 H2CO3 CO2 + H2O HCO3 Handled by the kidney CO2 Handled by the lungs

COMPENSATION WHENEVER THE pH CHANGES IN A DISEASE, THE BODY TRIES TO BRING IT BACK TOWARDS NORMAL. THIS IS CALLED COMPENSATION. COMPENSATION IS NOT 100% COMPLETE, SO pH DOES NOT RETURN TO COMPLETE NORMAL, IF THE DISEASE CONTINUES.

3 THINGS WHICH TRY TO COMPENSATE 1) BUFFERS IN THE BLOOD : ACT WITHIN seconds ( HCO3, Organic acids) 2) LUNGS : WITHIN SECONDS TO MINUTES ( BY KEEPING OR REMOVING CO2) 3) KIDNEYS : WITHIN HRS TO DAYS ( BY handling HCO3 and H+)

SO PH 7.40 ------------------ ( ? ) PH 7.20 ------------------ ( ? ) ( NORMAL IS 7.35 TO 7.45 )

IN DISEASE STATES, ACID – BASE BALANCE GETS DISTURBED, SO ACIDOSIS OR ALKALOSIS ( OR MIXED DISTURBANCES ) CAN OCCUR.

Things we need, to understand acid- base balance ABG ( arterial blood gases) SERUM ELECTROLYTES ( NA, K, CL, HCO3) ABG report is written as follows: ABG : pH/ pCO2/ pO2/ HCO3 eg 7.40/ 45 mmHg / 78 mmHg / 25meq For our discussion, forget about O2

SOME NORMAL VALUES Blood pH: * 7.35 to 7.45 Blood pCO2 : * Also 7.35 mmHg to 7.45mmHg 3) Blood HCO3: * 22 to 28 meq/L ( slightly different in various labs)

ACIDOSIS RESPIRATORY ACIDOSIS METABOLIC ACIDOSIS (DUE TO HIGH CO2 ) (DUE TO: a) Excess acid production b) Decreased acid excre- - tion from the kidneys c) Loss of HCO3

RESPIRATORY ACIDOSIS * IT IS DUE TO HYPOVENTILATION * DUE TO HYPOVENT., CO2 CANNOT BE EXCRETED , SO PCO2 RISES ( think of CO2 as an acid) ETIOLOGIES : * RESP. CENTER DEPRESSION ( MORPHINE) * NEUROMUSCULAR PATHOLOGIES ( KYPHOSIS, RESP MUSCLE PARALYSIS ) * LUNG DISEASE ( COPD)

RESPIRATORY ACIDOSIS PH IS LOW ----- < 7.35 PROBLEM IS IN RESP. SYS. OR LUNGS CO2 RETAINED HIGH CO2 ACIDOSIS( CO2 + H2O = H2CO3) Eg PH / PCO2 / HCO3 7.30/ 50mmHg/ 30 ( Norm pCO2 35 to 45, HCO3 22 to 28)

COMPENSATION ( in resp.acidosis) KIDNEYS RETAIN MORE HCO3 SO, THERE IS COMPENSATORY RISE IN HCO3 END RESULT : * pH : low * PCO2 : high * HCO3 : high ( DUE TO COMPENSATION)

S/S OF RESP. ACIDOSIS S/S USUALLY OCCUR IF IT IS ACUTE HEADACHE, RESSTLESSNESS, DYSPNEA PROGRESSES TO HYPER-REFLEXIA, COMA RESP. ACIDOSIS MAY BE SEEN IN LATE STAGES OF ASTHMA EXACERBATION, WHEN THE PATIENT GETS TIRED IT IS SEEN IN COPD PATIENTS EVEN AT BASELINE STATUS (CHRONIC ACIDOSIS)

TREATMENT OF RESP. ACIDOSIS 1) TREAT THE CAUSE 2) DON’T GIVE HCO3. IT WILL COMBINE WITH H+ IN THE BODY AND PRODUCE MORE CO2 WHICH CAN NOT BE ELIMINATED. SO, CONDITION WILL BE WORSE HCO3 + H = H2CO3 H2O + CO2 3) MAY NEED MECHANICAL VENTILATION ( ventilation takes out CO2 from the lungs)

RESPIRATORY ALKALOSIS pH IS HIGH PROBLEM IS WITH RESPIRATORY RATE HYPERVENTILATION EXCESS CO2 IS ELIMINATED LOW CO2 ALKALOSIS Eg : PH / PCO2/ HCO3 7.50 / 28 / 18

COMPENSATION KIDNEYS LOSE MORE HCO3 SO, THERE IS COMPENSATORY FALL IN SERUM HCO3 END RESULT : * pH : high * pCO2 : low * HCO3 : low ( due to compensation)

CAUSES OF RESPIRATORY ALKALOSIS ANXIETY RESPIRATORY CENTER STIMULATION all these HYPOXIA ( LIVING AT HIGH ALTITUDES ) cause PATIENTS ON VENTILATORS MAY DEVELOP hyper- ASPIRIN POISONING -ventilation ABHA IS A HIGH ALTITUDE CITY. LIVING THERE CAN CAUSE: a) Resp. Alkalosis

RESP. ALKALOSIS S/S ACUTE RESPIR. ALKALOSIS CAUSES LOW Ca, & K S/S INCLUDE : * LIGHTHEADEDNESS * CONFUSION * SIEZURES * HYPERVENTILATION * TETANY ( DUE TO LOW Ca)

TREAT MENT OF RESPIRATORY ALKALOSIS TREAT THE MAIN CAUSE CHANGE THE VENTILATOR SETTINGS CAN TRY “REBREATHING EXHALED” AIR IN A PAPER BAG

SO REMEMBER THAT:. IN RESP. ACIDOSIS, CO2 WILL BE HIGH. IN RESP SO REMEMBER THAT: * IN RESP. ACIDOSIS, CO2 WILL BE HIGH * IN RESP. ALKALOSIS, CO2 WILL BE LOW

METABOLIC ACIDOSIS PH IS LOW --------- < 7.35 MAIN PROBLEM NOT IN RESPIRATION PROBLEM : TOO MUCH METABOLIC ACID IS PRODUCED IN THE BODY, OR IT CANNOT BE EXCRETED OR TOO MUCH ALKALI ( HCO3) IS LOST FROM THE BODY LOW HCO3 Eg: PH/ PCO2/HCO3 7.20 / 30 / 18 ( normal is 22 to 26)

COMPENSATION LUNGS EXCRETE MORE CO2 SO, THERE IS COMPENSATORY FALL IN PCO2 END RESULT : * PH : low * HCO3 : low ( main problem) * PCO2 : low ( due to compensation)

TYPES OF METABOLIC ACIDOSIS HIGH ANION GAP NORMAL ANION GAP

WHAT IS ANION GAP ? CATIONS : Na+, K+ / ANIONS : HCO3-, Cl- Normally, the sum of cations should be equal to sum of anions. But Na + K is > HCO3 +Cl This difference is called Anion Gap. It is actually the unmeasured anions in the blood ( albumin, phosphates etc) NORMAL A.G = 8 TO 16 meq ( Na +K) – (Cl + HCO3) IN SOME CONDITIONS, IT GETS HIGH ( SOME TYPES OF METABOLIC ACIDOSIS) & IN OTHERS, IT IS NORMAL

TYPES OF METABOLIC ACIDOSIS HIGH “ ANION GAP” NORMAL “ ANION GAP” ETIOLOGIES ETIOLOGIES M methanol * Diarrhea loss of U uremia * Ileostomy HCO3 D diab.ketoacidosis P paraldehyde * Renal tubular acidosis (RTA) I infection/sepsis ( type 1, 2 &4) L lactic acidosis E ethanol * Acetazolamide ( a diuretic) S salicylate poisoning(aspirin)

S/S ( METABOLIC ACIDOSIS) HEADACHE, MENTAL STATUS CHANGES, RESTLESSNESS COMA MAY OCCUR

TREATMENT OF METABOLIC ACIDOSIS TREAT THE CAUSE * Drug toxicity (aspirin, methanol) * ketoacidosis : treat accordingly * infection/sepsis * Diarrhea * Lactic acidosis : iv fluids, treat the cause * Uremia : NaHCO3 tab / Dialysis ( remember renal failure ?) I.V. HCO3 CAN BE GIVEN IN METABOLIC ACIDOSIS IF NEEDED

RENAL TUBULAR ACIDOSIS A GROUP OF RENAL DISORDERS ( PROBLEM IN TUBULES) FOUR TYPES. OVERALL RARE. TYPE 4 IS THE MOST COMMON METABOLIC ACIDOSIS WITH NORMAL A.G. TYPE 4 RTA SEEN IN DM

METABOLIC ALKALOSIS IT IS ALKALOSIS SO, PH IS HIGH ( > 7.45 ) NO PRIMARY PROBLEM IN RESP. ACCUMULATION OF EXCESS ALKALI IN THE BODY OR LOSS OF ACID Eg : PH / PCO2 /HCO3 7.50 / 48 / 35

COMPENSATION LUNGS EXCRETE LESS PCO2 SO, COMPENSATORY RISE IN PC02 END RESULT : * pH : high * HCO3 : high ( main problem) * pCO2 : high ( due to compensation)

CAUSES OF METABOLIC ALKALOSIS VOMITING, N/G TUBE SUCTION ( loss of acid) EXCESS INTAKE OF NaHCO3 DIURETICS ( thiazides, loop diuretics) ALL DIURETICS CAUSE METABOLIC ALKALOSIS EXCEPT ACETAZOLAMIDE ( DIAMOX) WHICH CAUSES ACIDOSIS)

S/S CEREBRAL DYSFUNCTION * Restlessness * confusion, lethargy * arrhythmias

TREATMENT IF VOMITING OR NG SUCTION GIVE i.v. N/S If DIURETICS ARE THE CAUSE, GIVE i.v. N/S IF HIGH INTAKE OF HCO3, Stop IT. If pH > 7.7, give isotonic HCL thru central vein

SO, REMEMBER THAT: IN METABOLIC ACIDOSIS, HCO3 IS LOW IN METABOLIC ALKALOSIS, HCO3 IS HIGH

THANK YOU HOPE YOU FOUND IT EASY