3. 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.
4. 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
5. 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
6. 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
7. 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)
8. 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 ---------------)
9. 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---------)
10. IMPORTANT EQUATION
H+ HCO3 H2CO3 CO2 + H2O
HCO3 Handled by the kidney
CO2 Handled by the lungs
11. 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.
12. 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+)
13. SO
PH 7.40 ------------------ ( ? )
PH 7.20 ------------------ ( ? )
PH 7.50 ------------------ ( ? )
( NORMAL IS 7.35 TO 7.45 )
14. IN DISEASE STATES, ACID – BASE BALANCE
GETS DISTURBED, SO ACIDOSIS OR
ALKALOSIS ( OR MIXED DISTURBANCES )
CAN OCCUR.
15. 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
16. SOME NORMAL VALUES
1) Blood pH:
* 7.35 to 7.45
2) Blood pCO2 :
* Also 7.35 mmHg to 7.45mmHg
3) Blood HCO3:
* 22 to 28 meq/L ( slightly different in various
labs)
17. 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
18. 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)
19. 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)
20. 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)
21. 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)
22. 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)
23. 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
24. COMPENSATION
KIDNEYS LOSE MORE HCO3
SO, THERE IS COMPENSATORY FALL IN SERUM HCO3
END RESULT :
* pH : high
* pCO2 : low
* HCO3 : low ( due to compensation)
25. 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
26. RESP. ALKALOSIS S/S
ACUTE RESPIR. ALKALOSIS CAUSES LOW Ca, & K
S/S INCLUDE :
* LIGHTHEADEDNESS
* CONFUSION
* SIEZURES
* HYPERVENTILATION
* TETANY ( DUE TO LOW Ca)
27. TREAT MENT OF
RESPIRATORY ALKALOSIS
TREAT THE MAIN CAUSE
CHANGE THE VENTILATOR SETTINGS
CAN TRY “REBREATHING EXHALED” AIR IN A PAPER
BAG
28.
29. SO REMEMBER THAT:
* IN RESP. ACIDOSIS, CO2 WILL BE HIGH
* IN RESP. ALKALOSIS, CO2 WILL BE LOW
30. 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)
31. 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)
33. 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
34. 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)
35. S/S ( METABOLIC ACIDOSIS)
HEADACHE, MENTAL STATUS CHANGES,
RESTLESSNESS
COMA MAY OCCUR
36. 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
37. 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
38. 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
39. COMPENSATION
LUNGS EXCRETE LESS PCO2 SO,
COMPENSATORY RISE IN PC02
END RESULT :
* pH : high
* HCO3 : high ( main problem)
* pCO2 : high ( due to compensation)
40. 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)
42. 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
43. SO, REMEMBER THAT:
• IN METABOLIC ACIDOSIS, HCO3 IS LOW
• IN METABOLIC ALKALOSIS, HCO3 IS HIGH
