A presentation that describes about acid base disorders

1. Prof. Dr. Dalia Ragab
Ass. Professor of Critical Care Medicine
Cairo University

2. Acid-Base: Tough Stuff?
It’s all in your mind
• 7.53/15/80/12
• 7.25/25/110/10
• 6.88/32/100/7
• 7.58/49/98/45
• 7.30/40/156/19
• 7.10/30/365/9
• 7.72/28/95/37
• 7.45/20/80/14
You are routinely
missing triple acid-
base disorders
Dr. Smith
Dr. Rock

3. Acidemia and Alkalemia vs. acidosis and alkalosis
pH < 7.36 ([H+] > 44) is acidemia
pH > 7.44 ([H+] < 36) is alkalemia
mixed disorders of acidosis and alkalosis may
be neither acidemic nor alkalemic
e.g. 7.40/25/pCO2/15

4. Relationship of [H+] to pH
pH = -(log 10 [H+]) = - log 10 .00000004
=-(log 10 [40 x 10-9])
= - (-7.40) = 7.40 at nl pH
calculator makes east conversion both ways
suppose [H+] doubles to .000000080
then pH = - log 10 (2 x .000000040)
= -(log 10 (2) + log 10 (.00000004)
= - (.3 + (-7.40))
= -(-7.10)
= 7.10
since [H+] is dependant on the ratio of pCO2/HCO3,
then if pCO2 doubles while HCO3 remains constant,
pH will drop by .3 units
HCO3
pH = pK + log ---------
pCO2
pCO2
[H+]= Ka X ---------
HCO3

5. Hydrogen Ion Concentration
(24) (pCO2)
H+ (nmol/L)= ---------------
HCO3
(24) (25)
H+ (nmol/L)= ------------ = 50
(12)
[H+] pH
20 7.7
25 7.6
32 7.5
40 7.4
50 7.3
64 7.2
80 7.1
101 7.0
128 6.9
160 6.8
Acid-Base Equations
7.30 / 25 / pCO2 / 12

6. Henderson-Hasselbalch Equation
Base
HCO3
pH = pK + log --------- = 6.1 + log ---------
Acid H2CO3 + CO2
pK = the pH at which half of the compound is ionized = 6.1
Base= HCO3
Acid= Carbonic Acid= H2CO3 + pure dissolved CO2 = pCO2 (.03)
Acid-Base Equations

7. Bicarbonate-Carbonic Acid Buffer System
CO2 + H2O H2CO3 HCO3 + H
(carbonic anhydrase)
at pH = 7.40 and pCO2 = 40: [HCO3] = 24
Henderson-Hasselbalch Equation:
pH = pK + log 10 [(HCO3)/(H2CO3 + CO2)]
(at normal) = 6.1 + log 10 (24/pCO2 x .03)
= 6.1 + log (24/1.2) = 6.1 + log 20 = 6.1 + 1.3
= 7.40

8. Bicarbonate-Carbonic acid system
HCO3- 24
pH= 6.1 + log ------------- ---- log 20 = 1.3
pCO2 (.03) 1.2
HCO3- 12
pH= 6.1 + log ------------- ---- log 10 = 1.0
pCO2 (.03) 1.2
• The normal ratio of HCO3 to H2CO3 is 20:1
• The log of 20 is 1.3.
• If you cut the HCO3 in half to 12, the ratio is 10:1
• The log of 10 is 1.0
• The pH thus decreased by 0.3
• Whenever the ratio of HCO3 to H2CO3 is reduced by one-half, the pH
falls by 0.3.

9. [HCO3]/pCO2 ratio determines pH
HCO3- 24
pH= 6.1 + log ------------- ---- log 20 = 1.3
40 (.03) 1.2
HCO3- 48
pH= 6.1 + log ------------- ---- log 20 = 1.3
80 (.03) 2.4
HCO3- 12
pH= 6.1 + log ------------- ---- log 20 = 1.3
20 (.03) 0.6
HCO3- 6
pH= 6.1 + log ------------- ---- log 5 = 0.7
pCO2 (.03) 1.2

10. H-H Clinical Utility
pH= 6.1 + 1.6= 7.7 log 40=1.6
pH= 6.1 + 1.3= 7.4 log 20=1.3
pH= 6.1 + 1.0= 7.1 log 10=1.0
pH= 6.1 + 0.7= 6.8 log 05=0.7
If the ratio of bicarbonate to pCO2 is doubled or
reduced by half, the pH changes by 0.3
Likewise, if the ratio of HCO3 and pCO2 does not
change (both up or both down, in equal proportions), there will be no
pH change

11. Carbon Dioxide Content
• Total of all carbon dioxide present in the blood
• Normally 24 to 31 mEq/L
• Includes:
– Carbonic Acid + Pure dissolved CO2 (= .03 x pCO2 )
pCO2 ranges 10-120
= 0.3-3.6 mEq/L
– Bicarbonate 24 mEq/L
– Carbamino Compounds 0.5 to 1.0 mEq/L
Electrolytes

12. Correlating Chloride and Bicarbonate
• Tend to move in opposite directions:
• Metabolic Alkalosis
– High Bicarbonate
– Low Chloride
• Metabolic Acidosis
– Low Bicarbonate
– Chloride Normal (Anion Gap) or High (non-AG)
– Chloride low if Na/Cl >1.4; high if Na/Cl < 1.27
– Low chloride is synonymous with metabolic alkalosis (
or compensation for chronic respiratory acidosis)
– Even if pH is normal, low chloride means alkalosis

13. Anion Gap
• Described by Gamble in 1939
• Electroneutrality
• Na+, Cl-, and HCO3 are measured ions
Na + UC = Cl + HCO3 + UA
UC = Sum of unmeasured cations
UA = Sum of unmeasured anions
Anion Gap

14. Anion Gap
Unmeasured Cations:
• total 11 mEq/L
– Potassium 4
– Calcium 5
– Magnesium 2
Unmeasured Anions:
• total 23 mEq/L
– Sulfates 1
– Phosphates 2
– Albumin 16
– Lactic acid 1
– Org. acids 3
Na + UC = Cl + HCO3 + UA
140 + 11 = 104 + 24 + 23
151 = 151
UA - UC = Na - (Cl + HCO3); Anion Gap = Na - (Cl + HCO3)

15. Increased Anion Gap
Normal = 8-15
• Accumulation of organic acids (ketones, lact
ate)
• Toxic Ingestions
– methanol, ethylene glycol, salicylates
• Reduced inorganic acid excretion
– phosphates, sulfates
• Decrease in unmeasured cations (unusual)

16. Increased AG Metabolic Acidosis:
MUDPILES
• Methanol
• Uremia/Renal Failure
• DKA
• INH, Iron--lactate
• Paraldehyde
• Lactic Acidosis
– Has many etiologies
– Cyanide, CO, Toluene, HS
– Poor perfusion
• Ethylene glycol
• Salicylates
– Methyl salicylate
• (Oil of wintergreen)
– Mg salicylate (Doan’s pills
)
Normal AG does not rule out Lactic Acidosis
Very Low AG makes it very unlikely in well-nourished patient
Levraut J et al. Int Care Med
23:417, 1997

17. Decreased or Negative Anion Gap
• Low protein most important
• Albumin has many unmeasured negative charges
• “Normal” anion gap (12) in cachectic person
–Indicates anion gap metabolic acidosis
• 2-2.5 mEq/liter drop in AG for every 1 g drop in albumi
n
• Other etiologies of low AG:
– Low K, Mg, Ca, increased globulins (Mult. Myeloma), Li, Br
(bromism), I intoxication
• Negative AG
– more unmeasured cations than unmeasured anions
– Bromide, Iodide, Multiple Myeloma

18. Change in Anion Gap vs. HCO3
• In simple AG Metabolic Acidosis
– decrease in plasma bicarbonate = increase in AG
Anion Gap = 1
HCO3
• Helpful in identifying mixed disorders
• Values greater than 1.2 or less than 0.8 suggest t
he presence of a mixed acid-base disorder or an
independent factor affecting the anion gap.
Anion Gap

19. Compensation
• Compensation is rarely complete
• Returns pH toward normal
• Compensation is not a secondary aci
dosis or alkalosis
• High altitude and pregnancy may hav
e full compensation—but it takes tim
e
– Acetazolamide hastens compensation
– Improves Mountain sickness
Respiratory
Renal

20. Respiratory Compensation for
Metabolic Acidosis:
• Occurs rapidly
• Hyperventilation
– “Kussmaul Respirations”
– Deep > rapid (high tidal volu
me)
• Is not Respiratory Alkalosis
Metabolic Alkalosis:
• Calculation not as accur
ate
• Hypoventilation
• Not Respiratory Acidosis
• Restricted by hypoxemia
• PCO2 seldom > 50-55
pCO2=1.5 x HCO3 + 8 +/- 2
Winter’s formula
pCO2=0.9 x HCO3 + 15

21. Metabolic Compensation
Acute Hypercapnia:
HCO3 increases 1 mmol/
L for each 10 mmHg in
crease in PaCO2 >40
Chronic Hypercapnia:
HCO3 incr. 3.5 mmol/L f
or each 10 mmHg incr
ease in PaCO2 >40
Acute Hypocapnia:
HCO3 decreases 2 mmol/L
for every 10 mmHg decr
ease in PaCO2 <40
Chronic Hypocapnia:
HCO3 decreases 5 mmol/L
for every 10 mmHg decr
ease in PaCO2 <40
CO2 + H2O H2CO3 H + HCO3

22. Acute respiratory acidosis or alkalosis
Kassirer-Bleich equation
• When pH is between 7.30-7.50:
– pH change of .08 per 10 mmHg pCO2 cha
nge
–7.32/50/pO2/22
–7.48/30/pO2/25
–7.22/60/pO2/20
–7.58/20/pO2/26
Ionized hypocalcemia, Carpo-pedal spasm, Paresthesias; don’t use paper bags

23. 3 most important equations so far
• Chronic resp. acidosis: steady-state pCO2 is
increased by 10 for every 3.5 increase in HC
O3
• Acute metabolic acidosis:
– pCO2 = 1.5 x HCO3 + 8 (+/- 2)
• Acute metabolic alkalosis:
– pCO2 = 0.9 x HCO3 + 15

24. Metabolic Acidosis--Bad
• Impaired cardiac contractility
• Decreased threshold for v fib
• Decreased Hepatic and Renal perfusion
• Increased Pulm Vasc resistance
• Inability to respond to catecholamines
• Vascular collapse
Increased Anion Gap
Normal Anion Gap (Hyperchloremic)

25. Reasons to Limit Bicarbonate therapy
• Initially injected into 3 liter plasma volume
– (not 5 liter blood volume because does not enter red cells)
• CO2 + H2O H2CO3 H+ + HCO3-
• Theoretical, but probably does not happen:
– Increase intracellular acidosis
• In vitro: small and transient (Goldsmith DJ et al, Clin Sci 93:593, Dec 97)
• Unpublished functional MRI studies show this is limited
• Will increase pCO2 and need for ventilation
• Normal Saline: 150 mEq/l of Na, Bicarb: 1000mEq/l
– As much Na as 350 ml’s normal saline
– like hypertonic saline: leads to Hypernatremia & Fluid ove
rload

26. Base Deficit
volume of distribution, extracellular fluid 0.3 L/kg
• = 0.3 x kg x (24 – HCO3) in mEq/l
– one ampule of bicarb = 50 mEq/50 ml
• E.g.: 70 kg person with bicarb of 3
– 0.3 x 70 x 21 = 441 mEq
– 441mEq ÷ 50 mEq/ml/ampule = 9 Amps of bicarb
• Suppose you want to get the bicarb back to 6
– 0.3 x 70 x (6-3) = 63
– 63 mEq ÷ 50 mEq/ml/ampule = 1.25 Amps of bicar
b

27. When to give bicarb
• Do NOT base it on pH
• Base it on HCO3 level < 6
• For low pH
–If bicarb < 6
• give bicarb 1-2 amps
• Recheck ABG
–If pCO2 > 1.5 (HCO3) + 8
• then ventilate better

28. Lactic Acidosis
Type A: Tissue Hypoxia
Toxins: Iron, Isoniazid, CN, metHg
b, CO, HS
Shock States
Profound Anemia
Massive catecholamines
Hypoxia
Anaerobic exertion
seizures, sprinting
Cyanide, CO, HS
Beriberi
TPN and alcoholics
Type B: Normal tissue O2
--paucity of NAD+
--excess of NADH
Diabetes Mellitus
Liver Failure
Renal Failure
Carcinoma
Hypoglycemia
EtOH ingestion
Many others
Pyruvate (ox) Lactate (red)
NAD NADH
Metabolic Acidosis: Usually Increased AG

29. Toxic Ingestions
• Cyanide
• Salicylate
• Methanol
• Ethylene glycol
• Paraldehyde
• Iron
• Isoniazid
• Toluene
• Formaldehyde
All lead to the formation of aci
d metabolites and/or organic
acids which result in an increa
se in the anion gap.
Metabolic Acidosis: Increased AG

30. Rapid Evaluation
• BUN and CR Renal Failure
• No RF, No drugs Lactate, Keto
• Most common Lactate
• AG > 30 Lactate, Keto
• AG > 25 Most Lactate, Keto

31. Metabolic Acidosis: Normal AG
Loss of HCO3
Failure to excrete [H+]
Administration of [H+]
• Loss of HCO3
– Severe diarrhea
– Post-hypocapnia
– Ureteroileostomy
– Acetazolamide
• Failure to excrete [H+]
– Renal Tubular Acidosis
• Types 1-4
• Toluene
• Administration of [H+]
– Ammonium chloride

32. Metabolic Acidosis: Example
18 y.o. presents in DKA
ABG: pH 7.00 pCO2 25 Bicarbonate 6
If Pure metabolic acidosis, then pCO2=(1.5)(6) + 8= 1
7
metabolic acidosis with respiratory acidosis:
--chronic lung disease
--fatigue from compensation or hypokalemia or h
ypophosphatemia
--This patient is at risk for tiring out and becoming
extremely acidotic.

33. Respiratory Alkalosis: Etiology
• Salicylates
• Increased ICP
• Liver Failure
• Hypoxia
• CHF
• Pericardial effusion
• Pulmonary Embolus
• Hyperthyroidism
• Pregnancy
• Sympathomimetics
– Amphetamines
– Cocaine
– PCP
• Hyperventilation
– Shock
– Sepsis
– Trauma/Pain
– Psychogenic/Anxiety
• CNS disease

34. Respiratory Alkalosis: Example 1
18 y.o. with several days of SOB due to pneumonia
:
pH 7.43 pCO2 25 Bicarbonate 16
Significant Renal Compensation or metabolic acido
sis?
AG = 14 vs. AG = 20
Chronic Hypocapnia:
HCO3 decreases 5 mmol/L for every 10 mmHg decrease in PaCO2 <40

35. Respiratory Alkalosis: Example 2
15 y.o. girl who just got dumped by her boyfri
end:
pH 7.70 pCO2 20 Bicarbonate 20
Reality: 7.70/20/pO2/20, because hypocapnia
leads to lower bicarb as well.
--Too soon for Renal Compensation
--When near normal: pH change of .08 for each 10 mmHg ch
ange in pCO2
--when pCO2 is cut in half or doubled with constant HCO3, p
H changes by 0.3

36. Respiratory Acidosis: Etiology
• Inadequate minute ve
ntilation
– Head, Chest, Spinal
Cord trauma
– Sedative-Hypnotics
– Neuropathy/Myopa
thy
– Pulmonary Disorder
– Airway Obstruction
– Sleep Apnea
• Increased dead space
ventilation
– COPD
• Increased carbohydrat
e metabolism
– TPN

37. Chronic Respiratory Acidosis: Example
65 y.o. WM Veteran with stable COPD:
pH 7.32 pCO2 70 Bicarbonate 35
Significant Renal Compensation
But when he arrives in the ED, this is the only ABG you have:
• 7.23/85/pO2/35
• 35-24=11. 11/3.5 = 3. 3 x 10 =30. 40 + 30 = 70
– Baseline pCO2 = 70. Pt. has acute resp acidosis.

38. Acute Respiratory Acidosis: Example
25 y.o. IVDU s/p heroin OD:
pH 7.10 pCO2 80 Bicarbonate 24

39. Metabolic Alkalosis-etiologies
• Hypochloremia, “Chloride responsive”
– Met Alk is present if Na/Cl ratio is > 1.4
• 140/105 = 1.33; 140/99; 125/91 < 1.4; 125/85 > 1.4
– Chloride and potassium loss (not H+ loss):
• Vomiting, NG suction
• Diuretics
– Post-hypercapnia (i.e. the metabolic compensation for resp.
acidosis lingers after the resp. acidosis is resolved)
– Volume contraction
• including edematous states, esp. liver failure
• Alkali ingestion
• Massive transfusion: 1 u PRBC’s has 5 mEq citrate
• Anion gap increases usually not more than 5 mEq/l
Chloride unresponsive: uncommon disorders of renin-aldosterone-an

40. Beware Severe Alkalemia
due to:
Severe underlying pathology
also:
General and Cerebral vasoconstrictor
Shift of oxyhemoglobin dissociation
Hypokalemia
Increased SVR and decreased CO:
Decreased Contractility
Cardiac arrhythmias refractory
Seizures

41. Severe Alkalosis/alkalemia
• HCO3 > 45
• Be sure oxygenation OK
• Avoid respiratory stimulation
• Acetazolamide, 500 mg IV
– Monitor K, Mg, PO4
• HCl infusion
– 0.1M solution (100 mmol/L, 0.2 mmol/kg/hour
)
– Central line
– Total dose = Δ HCO3 x kg x 0.5 (in mmoles)

42. ABG Examples of Alkalosis
Metabolic, Resp., and Mixed
Normal Simple
Metabolic
Resp. Mixed
Severe
Mixed
Mild
Na 140 139 139 139 139
K 4 3 3.5 2.8 3.0
Cl 105 89 107 92 92
HCO3 24 35 20 32 32
AG 11 15 12 17 8
pCO2 40 47 25 30 39
pH 7.40 7.49 7.54 7.65 7.53

43. Mixed Respiratory acidosis and metabolic alkalosis
Acute resp
acidosis
Simple
acute resp
acidosis
Simple
Chronic
resp
acidosis
Simple
metabolic
alkalosis
Mixed resp
acid and met
alkalosis
Na 140 140 140 140 140
K 4.0 4.5 4.5 3.0 3.5
Cl 105 105 94 92 86
HCO3 25 27 36 36 42
AG 10 8 10 12 12
pCO2 40 70 70 48 70
pH 7.40 7.13 7.33 7.49 7.40

44. Metabolic Alkalosis: Example 1
Case: 43 yo w f
Brought by friends from convention. Had been stag
gering, speaking incoherently, swearing, yelling. I
n APS, pt. was confused, agitated, speaking jibberi
sh. Brought to ED. Friends left.
110/70 128 r 22 t 98
uncooperative, pretending to smoke cigarette
o/w exam negative except for dry MM
Valium, Cogentin, Haldol given
125/65/64/142 AG = 23 7.67/35/78/40
2.1/37/3.9
U/A, Etoh, U tox all neg. lactate 1.5
resp. alk. + met. alk. + (because of large AG) met. aci
dosis

45. Case continued
To MICU
Pt. arrests. Moniter shows torsade. Pt. intubated and
CPR. Spontaneously back to NSR, now intubated,
unconscious, ventilated by bag
Pt. goes back into torsade.
What immediate effective treatment was done?
bagging stopped! ---> torsade again spontan. resolved
Pt. paralyzed, hypoventilated, and put on HCl drip
Etiology was Alcoholic ketoacidosis with severe vomitin
g elicited from later history

46. Metabolic Alkalosis: Example 2
58 year old man with a history of chronic abdomi
nal pain has been vomiting for weeks. Very ill.
pH 7.58 pCO2 49 Serum Bicarb 45
Respiratory Compensation?
0.9 x (45) + 15=55
0.9 x (45) + 9 = 49 (as above)
Dx: Gastric Outlet Obstruction

47. Case (cont.)
• IMPORTANT: This patient has a SEVERE met. alkalosi
s. Were it not for his resp. compensation, he would
die. If pCO2 = 40, pH = 7.75 (very dangerous)
• Anything which could trigger resp. alk., including pai
n, anxiety, hypoxia could lead to lethal compensation
s.
• This patient needs immediate HCI, or 500 mg IV diam
ox if HCl unavailable, or both
• Also: oxygen and perhaps sedation if hyperventilatin
g

48. Mixed Disorders
• Respiratory Acidosis
+ metabolic acidosis
+ metabolic alkalosis
+ metabolic acidosis and alkalosis (triple)
• Respiratory Alkalosis
+ metabolic acidosis
+ metabolic alkalosis
+ metabolic acidosis and alkalosis (triple)

49. General approach to Acid-Base
• Determine the pH and pCO2 from the
ABG
–pH > 7.44, primarily alkalosis
–pH < 7.36, primarily acidosis
• If the Arterial pH is relatively normal and
– One of PCO2 or HCO3 are abnormal
• one can assume that a mixed abnormality is prese
nt.

50. First Step-Simple disorders
Metabolic Acidosis
pH <7.36
HCO3<22
Metabolic Alkalosis
pH >7.44
HCO3>26
Respiratory Acidosis
pH <7.36
pCO2 >44
Respiratory Alkalosis
pH >7.44
pCO2 <36
ABG: 7.22/20/pO2/8; BMP: Na=140, Cl=105, CO2=11, AG = 24
Δ HCO3 = 13; Δ AG = 13 Simple Metabolic Acidosis

51. Mixed Disorders underlined is answer
• pH < 7.36, HCO3 > 28
– High bicarb = metabolic alk or comp for resp acido
sis
• pH > 7.44, HCO3 < 22
– Low bicarb = met acidosis or comp for resp alk
• pH < 7.36, pCO2 < 36
– Low pCO2 = comp for met acid or resp alk
• pH > 7.44, pCO2 > 44
– High pCO2 = resp acidosis or comp for met alk

52. Mixed Disorders
• If the Arterial pH is relatively normal and th
e PCO2 and/or HCO3 are abnormal, one can
assume that a mixed abnormality is present
.

53. Mixed Acid-Base Disorders:
• Is the degree of respiratory compensation for
a metabolic acidosis too much or too little?
pCO2 lower than calculated
Superimposed Resp. Alk.
pCO2 higher than calculated
Superimposed Resp. Acidosis
Salicylate poisoning
Sepsis
Increase ICP + Shock
Sedative OD + Shock
Ventilatory Impairment
Remember: 1.5 x Bicarb + 8

54. Mixed Acid-Base Disorders:
• Is the magnitude of the increase in AG equal t
o the magnitude of the decrease in serum bica
rb?
AG Change >> Bicarb Change (chloride is relatively low)
Superimposed Met. Alkalosis
Vomiting + DKA or AKA

55. Mixed Alkalosis and Triple Disorder
Normal Mixed met.
And resp.
alkalosis
Plus lactic
acidosis (triple
disorder)
Na 140 140 140
K 4 3 3
Cl 105 92 92
HCO3 25 34 29
AG 10 14 19
pCO2 40 30 30
pH 7.40 7.67 7.61

56. Mixed Acid-Base: Example 1
27 y.o man with polyuria and polydipsia for one
week, and intractable vomiting for 4 days. Tod
ay he is critically ill with a temp. of 104 F.
pH 7.50 pCO2 26 pO2 100
150 100 50
3.8 20 1.8
650
AG= 30
Bicarb=24-20= 4
AG=30-12= 18
Na/Cl > 1.4

57. Mixed Acid-Base: Example 1
• Anion Gap Metabolic Acidosis
• Concurrent Metabolic Alkalosis
• Respiratory Alkalosis DKA
Vomiting
Sepsis

58. Mixed Acid-Base: Example 2
25 y.o. woman admitted 6 hours ago with severe
DKA. Her initial pH was 6.9 with a pCO2 of 10,
and serum bicarb of 2.4. After insulin and NS
hydration, her lab values returned as follows…
140 110
10
AG= 20
Bicarb= 24-10= 14
AG= 20-12= 8
pH 7.25 pCO2 23

59. Mixed Acid-Base: Example 2
• Anion Gap Metabolic Acidosis
• Hyperchloremic Metabolic Acidosis.
• Respiratory alkalosis

60. Mixed Acid-Base: Example 3
72 y.o. man with a h/o PUD has been vomiting for 2 w
eeks. Vitals on presentation: P 140, BP 60/P
pH 7.40 pCO2 40 pO2 300 (FiO2 50%), HCO3 = 24
150 86 100
2.6 24 2.5
AG=150-110= 40
Bicarb=24-24= 0
AG= 40-12= 28

61. Mixed Acid-Base: Example 3
• Anion Gap Metabolic Acidosis (Shock)
• Metabolic Alkalosis (Vomiting)
Normal ABG does not
equal normal
patient….
Dr. Smith

62. Test Case #1
An 80 year old man has been confused and c/o S
OB for one week. He also has a hearing proble
m and has seen 3 ENT docs in the past month.
Family denies medications.
pH 7.53 pCO2 15 pO2 80 HCO3 12
140 108
3.0 13
120 Diagnosis?
AG = 140 - 121 = 19

63. Test Case #1
Anion Gap= 140-(108+13)= 19, Δ AG = 7
Δ Bicarb= 24-13= 11
pCO2= 1.5 (12) + 8= 26 (compared/w 15)
Patient is Alkalemic (pH= 7.53) indicating a Su
perimposed Respiratory Alkalosis
Dx: Metabolic Acidosis and Respiratory Alkalosis

64. Test Case # 2
23 year old AIDS patient c/o weakness and pr
olonged severe diarrhea. He appears mark
edly dehydrated.
pH 7.25 pCO2 25 pO2 110 HCO3 11
151 129 60
2.0 12 2.0 Diagnosis?

65. Test Case # 2
• Anion Gap= 151-(129 + 11)= 11 (normal)
• The patient is Acidemic (pH 7.25)
• Respiratory compensation normal?
1.5 (HCO3) + 8 plus or minus 2
1.5 (11) + 8= 24.5 (compare with 25)
Dx: Uncomplicated Non-AG Metabolic Aci
dosis

66. Test Case #3
45 y.o. alcoholic man has been vomiting for 3 da
ys. Vitals: BP 100/70, P 110. Intern administe
red Valium 30 mg for tremulousness.
pH 7.30 pCO2 40
145 96
3.0 19
Serum Ketones +
Diagnosis?

67. Test Case #3
• Anion Gap= 145- (96 + 19)= 30
• Δ Bicarb= 24-19= 5
• Δ AG= 30-12= 18
• Change in AG >> Change in Bicarb
• Superimposed Metabolic Alkalosis
• Respiratory compensation?
1.5 x (19) + 8= 36 (compared with pCO2=40)

68. Test Case #3
• Anion Gap Metabolic Acidosis (AKA)
• Metabolic Alkalosis (Persistent Vomiting)
• Mild Respiratory Acidosis (Oversedation)

69. Test Case #4
A 22 y.o. diabetic man has been vomiting for sev
eral days. He appears ill and dehydrated. His
ABG reveals 7.40/ 40/ 100 on room air. His lab
s are below. The resident states he does not h
ave DKA because the ABG is normal. Is the res
ident correct?
130 76
3.0 24
800

70. Test Case #4
• The resident is NOT correct; Sorry admit MICU
• Anion gap= 130- (76 + 24)= 30
• Δ Bicarb= 24-24= 0
• Δ AG= 30-12= 18
• Change in AG >>> Change in Bicarb
Dx: Anion Gap Metabolic Acidosis (DKA)
Metabolic Alkalosis (Vomiting)

71. Test Case #5
33 y.o. woman c/o leg pain and SOB which sta
rted suddenly yesterday.
pH 7.45 pCO2 20 pO2 80
140 116
4.0 14 Diagnosis?

72. Test Case #5
• Anion gap= 140- (116 + 14)= 10
Dx: Respiratory Alkalosis (PE) with
Metabolic acidosis

73. Summary of Expected Compensation and Other Equa
tions
• pH = pKa + log HCO3/H2CO3
• [H+] = 24 x pCO2/HCO3
• for each doubling of [H+], pH drops by 3
• In acute respiratory alkalosis, if mild, the pH changes by 0.
08 for every 10 mmHg change in pCO2

74. Expected Compensation (cont.)
• pure stable met. acidosis: pCO2 = 1.5 x HCO3 + 8 =-- 2
• pure stable met. alkalosis: pCO2 = .9 (HCO3) + 15
more commonly pCO2 = .9(HCO3) + 9
• acute resp. acidosis:
– HCO3 up by 1/mEg/1 for each 10 mmHg inc. of pCO2.
• Chronic resp. acid:
– HCO3 up 3.5 mEg/1 for each 10 of pCO2
• Acute resp. alk: HCO3 down 2 mEg/1 for each 10 of pCO2
• Chronic resp. alk: HCO3 down 5 mEg/1 for each 10 of pC
O2
• CO2 + H2O <---> H2CO3 <---> H + + HCO3-

75. Summary of important points
• Acidosis/Alkalosis are metabolic states ≠ acidemia/alkalemia
• Doubling or halving the pCO2:HCO3 ratio changes pH by 0.3
• Bicarbonate therapy based on bicarb ≤ 6, not pH
• Low pH with bicarb > 6 needs Rx with ventilation
• Know the anion gap and MUDPILES
• Anion Gap > 18 is metabolic acidosis
– no matter what the pH, pCO2, or bicarb.
• Normal Na/Cl ratio is 1.33 (140/105)
– Na/Cl ratio > 1.4 is metabolic alkalosis (e.g. 140/99)
• (or compensation for respiratory acidosis)
– Na/Cl < 1.3 is hyperchloremic acidosis (e.g., 140/111)
• (or compensation for resp alkalosis)
• Winter’s formula: pCO2 should be = 1.5 x HCO3 + 8