AcidBase Disorders

1
Acid-Base Disorders

• Stephen W. Smith, M.D.
• Department of Emergency Medicine
• Hennepin County Medical Center

Cartoons Courtesy of Dr. Rock
Resource www.acid-base.com, Tintinalli
2
Acid-Base Tough Stuff?Its all in your mind
You are routinely missing triple acid- base
disorders

• 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

Dr. Smith
Dr. Rock
3
Summary of important points

• Acidosis/Alkalosis are metabolic states ?
  acidemia/alkalemia
• Doubling or halving the pCO2HCO3 ratio changes
  pH by 0.3
• Bicarbonate therapy based on bicarb 6, not pH
• Low pH with bicarb gt 6 needs Rx with ventilation
• Know the anion gap and MUDPILES
• Anion Gap gt 18 is metabolic acidosis
• no matter what the pH, pCO2, or bicarb.
• Normal Na/Cl ratio is 1.33 (140/105)
• Na/Cl ratio gt 1.4 is metabolic alkalosis (e.g.
  140/99)
• (or compensation for respiratory acidosis)
• Na/Cl lt 1.3 is hyperchloremic acidosis (e.g.,
  140/111)
• (or compensation for resp alkalosis)
• Winters formula pCO2 should be 1.5 x HCO3 8

4
Acidemia and Alkalemia
vs. acidosis and alkalosis

• pH lt 7.36 (H gt 44) is acidemia
• pH gt 7.44 (H lt 36) is alkalemia
• mixed disorders of acidosis and alkalosis may be
  neither acidemic nor alkalemic
• e.g. 7.40/25/pO2/15

5
Relationship of H to pH

• remember 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

pCO2 H Ka X
---------
HCO3
HCO3 pH pK
log --------- pCO2
6
Hydrogen Ion Concentration
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

• (24) (pCO2)
• H (nmol/L) ---------------
• HCO3
• (24) (25)
• H (nmol/L) ------------ 50
• (12)

7.30 / 25 / pO2 / 15
Acid-Base Equations
7
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
8
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

9
Bicarbonate-Carbonic Acid Buffer System

• HCO3 24
• pH 6.1 log --------
• CO2 H2CO3 1.2
• pH 6.1 log 20
• pH 6.1 1.3 7.4

.03 x pCO2
Acid-Base Equations
10

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

Acid-Base Equations
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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

12
H-H Clinical Utility

• pH 6.1 1.6 7.7 log 401.6
• pH 6.1 1.3 7.4 log 201.3
• pH 6.1 1.0 7.1 log 101.0
• pH 6.1 0.7 6.8 log 050.7

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
13
Carbon Dioxide Content (BMP)

• 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
14
ABG? VBG? Et CO2?

• To know acid-base balance, must have
• pH, pCO2, and anion gap
• (HCO3 calculated from pH and pCO2)
• pH pretty consistently correlates venous to
  arterial
• But is lower in venous samples
• Not studied in pts. with severe shock
• Good lit on EtCO2 correlation with arterial pCO2
• Anesthesia, mild metabolic acidosis
• Weve seen it work in procedural sedation
• My experience in severe acid base disorders is
  disappointing
• In severe disorders, at least one initial ABG is
  important
• Electrolytes for AG

15
Correlating CO2 Content and Bicarbonate

• Arterial CO2 content
• 1.5-2.0 mEq/L gt arterial HCO3
• Venous CO2 higher because pCO2 higher
• 1.5-2.0 mEq/L gt arterial CO2
• Venous blood CO2
• 3-4 mEq/L gt arterial HCO3
• Dont accept arterial bicarb gt venous CO2

16
Correlating pH and Potassium levels

• Acidemia produces high K
• Alkalemia produces low K
• pH change of 0.1 is associated with 0.5 change
  in serum K
• Serum K gtgt Plasma K
• Prolonged acidosis renal K wasting

7.10
H
H
H
H
H
K
K
5.5 mEq/L
K
K
K
17
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 gt1.4 high if Na/Cl lt 1.27
• Low chloride is synonymous with metabolic
  alkalosis (or compensation for chronic
  respiratory acidosis)
• Even if pH is normal, low chloride means alkalosis

18
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
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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)
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Increased Anion GapNormal 8-15May differ
institutionallyion specific electrodes

• Accumulation of organic acids (ketones, lactate)
• Toxic Ingestions
• methanol, ethylene glycol, salicylates
• Reduced inorganic acid excretion
• phosphates, sulfates
• Decrease in unmeasured cations (unusual)

Increased AG gt 18 acidosis Alkalosis
(especially that induced by high dose
penicillins) can have a modestly increased AG.
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Increased AG Metabolic Acidosis MUDPILES

• Methanol
• Uremia/Renal Failure
• DKA (AKA, SKA)
• 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 (Doans pills)

Levraut J et al. Int Care Med 23417, 1997
Normal AG does not rule out Lactic Acidosis Very
Low AG makes it very unlikely in well-nourished
patient
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Decreased or Negative Anion GapClin J Am Soc
Nephrol 2 162-174, 2007

• 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
  albumin
• 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

23
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

Anion Gap
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Compensation
Respiratory

• Compensation is rarely complete
• Returns pH toward normal
• Compensation is not a secondary acidosis or
  alkalosis
• High altitude and pregnancy may have full
  compensationbut it takes time
• Acetazolamide hastens compensation
• Improves Mountain sickness

Renal
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Respiratory Compensationfor

• Metabolic Acidosis
• Occurs rapidly
• Hyperventilation
• Kussmaul Respirations
• Deep gt rapid (high tidal volume)
• Is not Respiratory Alkalosis

• Metabolic Alkalosis
• Calculation not as accurate
• Hypoventilation
• Not Respiratory Acidosis
• Restricted by hypoxemia
• PCO2 seldom gt 50-55

pCO20.9 x HCO3 15
pCO21.5 x HCO3 8 /- 2 Winters formula
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Metabolic Compensation

• Acute Hypercapnia
• HCO3 increases 1 mmol/L for each 10 mmHg increase
  in PaCO2 gt40
• Chronic Hypercapnia
• HCO3 incr. 3.5 mmol/L for each 10 mmHg increase
  in PaCO2 gt40

• Acute Hypocapnia
• HCO3 decreases 2 mmol/L for every 10 mmHg
  decrease in PaCO2 lt40
• Chronic Hypocapnia
• HCO3 decreases 5 mmol/L for every 10 mmHg
  decrease in PaCO2 lt40

CO2 H2O H2CO3
H HCO3
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Acute respiratory acidosis or alkalosisKassirer-B
leich equation

• When pH is between 7.30-7.50
• pH change of .08 per 10 mmHg pCO2 change
• 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 dont use paper bags
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3 most important equations so far

• Chronic resp. acidosis steady-state pCO2 is
  increased by 10 for every 3.5 increase in HCO3
• Acute metabolic acidosis
• pCO2 1.5 x HCO3 8 (/- 2)
• Acute metabolic alkalosis
• pCO2 0.9 x HCO3 15

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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)
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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 93593, 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 mls normal saline
• like hypertonic saline leads to Hypernatremia
  Fluid overload

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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 bicarb

32
When to give bicarb

• Do NOT base it on pH
• Base it on HCO3 level lt 6
• For low pH
• If bicarb lt 6
• give bicarb 1-2 amps
• Recheck ABG
• If pCO2 gt 1.5 (HCO3) 8
• then ventilate better

33
Lactic Acidosis

• Type A Tissue Hypoxia
• Toxins Iron, Isoniazid, CN, metHgb, 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
34
Ketoacidosis

• Increase in FFA load to liver, or increased
  conversion of FFA to Ketoacids
• B-hydroxybutyric (red) (reduced by NADH) gtgt
  Acetoacetate (ox) (oxidized by NAD)
• Not measured by standard ketone tests
• Measure beta-hydroxybutyrate
• Less apparent AG if good urine output
• Very apparent increased AG if dehydrated

Metabolic Acidosis Increased AG
35
Toxic Ingestions

• Cyanide
• Salicylate
• Methanol
• Ethylene glycol
• Paraldehyde
• Iron
• Isoniazid
• Toluene
• Formaldehyde

• All lead to the formation of acid metabolites
  and/or organic acids which result in an increase
  in the anion gap.

Metabolic Acidosis Increased AG
36
Toxic Ingestions

• Methanol..Formic acid
• Ethylene glycolGlycolic acid Lactic
  acid
• Paraldehyde..Acetic and Chloracetic
  
• Salicylates

Metabolic Acidosis Increased AG
37
Rapid Evaluationof elevated AG

• Urine Ketones and Glucose DKA
• Urine Ketones and No Glucose AKA, SKA
• Alcoholism AKA
• Urine Neg. Ketones, get S. Osm. EG, M
• Calcium Oxalate in Urine EG
• Visual changes M
• Osm. Gap NL, get Urine FC Salicylate

38
Rapid Evaluation

• BUN and CR Renal Failure
• No RF, No drugs Lactate, Keto
• Most common Lactate
• AG gt 30 Lactate, Keto
• AG gt 25 Most Lactate, Keto

39
Metabolic Acidosis Normal AGLoss of
HCO3Failure to excrete HAdministration 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

40
Metabolic Acidosis Example

• 18 y.o. WF presents in DKA
• ABG pH 7.00 pCO2 25 Bicarbonate 6
• If Pure metabolic acidosis, then pCO2(1.5)(6)
  8 17
• metabolic acidosis with respiratory acidosis
• --chronic lung disease
• --fatigue from compensation or hypokalemia or
  hypophosphatemia
• --This patient is at risk for tiring out and
  becoming extremely acidotic.

41
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

42
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
  acidosis?
• AG 14 vs. AG 20
• Chronic Hypocapnia
• HCO3 decreases 5 mmol/L for every 10 mmHg
  decrease in PaCO2 lt40

43
Respiratory Alkalosis Example 2

• 15 y.o. girl who just got dumped by her
  boyfriend
• pH 7.70 pCO2 20 Bicarbonate 24
• Reality 7.65/20/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 change in pCO2
• --when pCO2 is cut in half or doubled with
  constant HCO3, pH changes by 0.3

44
Respiratory Acidosis Etiology

• Inadequate minute ventilation
• Head, Chest, Spinal Cord trauma
• Sedative-Hypnotics
• Neuropathy/Myopathy
• Pulmonary Disorder
• Airway Obstruction
• Sleep Apnea

• Increased dead space ventilation
• COPD
• Increased carbohydrate metabolism
• TPN

45
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
• 35-2411. 11/3.5 3. 3 x 10 30. 40 30 70
• Baseline pCO2 70. Pt. has acute resp acidosis.

46
Acute Respiratory Acidosis Example

• 25 y.o. IVDU s/p heroin OD
• pH 7.10 pCO2 80 Bicarbonate 24

47
Metabolic Alkalosis-etiologies

• Hypochloremia, Chloride responsive
• Met Alk is present if Na/Cl ratio is gt 1.4
• 140/105 1.33 140/99 125/91 lt 1.4 125/85 gt
  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 PRBCs has 5 mEq
  citrate
• Anion gap increases usually not more than 5 mEq/l

Chloride unresponsive uncommon disorders of
renin-aldosterone-angiotensin
48
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

49
Severe Alkalosis/alkalemia

• HCO3 gt 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 ? HCO3 x kg x 0.5 (in mmoles)

50
ABG Examples of AlkalosisMetabolic, Resp., and
Mixed
51
Mixed Respiratory acidosis and metabolic alkalosis
52
Metabolic Alkalosis Example 1 Case 43 yo w f

• Brought by friends from convention. Had been
  staggering, speaking incoherently, swearing,
  yelling. In APS, pt. was confused, agitated,
  speaking jibberish. 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. acidosis

53
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! ---gt torsade again spontan.
  resolved
• Pt. paralyzed, hypoventilated, and put on HCl
  drip
• Etiology was Alcoholic ketoacidosis with severe
  vomiting elicited from later history

54
Metabolic Alkalosis Example 2

• 58 year old man with a history of chronic
  abdominal pain has been vomiting for weeks. Very
  ill.

pH 7.58 pCO2 49 Serum Bicarb 45
Respiratory Compensation? 0.9 x (45) 1555 0.9
x (45) 9 49 (as above)
Dx Gastric Outlet Obstruction
55
Case (cont.)

• IMPORTANT This patient has a SEVERE met.
  alkalosis. 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 pain, anxiety, hypoxia could lead to
  lethal compensations.
• This patient needs immediate HCI, or 500 mg IV
  diamox if HCl unavailable, or both
• Also oxygen and perhaps sedation if
  hyperventilating

56
Mixed Disorders

• Respiratory Acidosis
• metabolic acidosis
• metabolic alkalosis
• metabolic acidosis and alkalosis (triple)
• Respiratory Alkalosis
• metabolic acidosis
• metabolic alkalosis
• metabolic acidosis and alkalosis (triple)

57
General approach to Acid-Base

• Determine the pH and pCO2 from the ABG
• pH gt 7.44, primarily alkalosis
• pH lt 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
  present.

58
First Step-Simple disorders
Metabolic Acidosis pH lt7.36 HCO3 lt22
Respiratory Acidosis pH lt7.36 pCO2 gt44
Respiratory Alkalosis pH gt7.44 pCO2 lt36
Metabolic Alkalosis pH gt7.44 HCO3 gt26
ABG 7.22/20/pO2/8 BMP Na140, Cl105,
CO211, AG 24 ? HCO3 13 ? AG 13
Simple Metabolic Acidosis
59
Mixed Disordersunderlined is answer

• pH lt 7.36, HCO3 gt 28
• High bicarb metabolic alk or comp for resp
  acidosis
• pH gt 7.44, HCO3 lt 22
• Low bicarb met acidosis or comp for resp alk
• pH lt 7.36, pCO2 lt 36
• Low pCO2 comp for met acid or resp alk
• pH gt 7.44, pCO2 gt 44
• High pCO2 resp acidosis or comp for met alk

60
Mixed Disorders

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

61
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
62
Mixed Acid-Base Disorders

• Is the magnitude of the increase in AG equal to
  the magnitude of the decrease in serum bicarb?

AG Change gtgt Bicarb Change (chloride is
relatively low) Superimposed Met. Alkalosis
Vomiting DKA or AKA
63
Mixed Alkalosis and Triple Disorder
64
Mixed Acid-Base Example 1

• 27 y.o man with polyuria and polydipsia for one
  week, and intractable vomiting for 4 days. Today
  he is critically ill with a temp. of 104 F.

pH 7.50 pCO2 26 pO2 100
AG 30
150 100 50 3.8 20 1.8
Bicarb24-20 4
650
AG30-12 18
Na/Cl gt 1.4
65
Mixed Acid-Base Example 1

• Anion Gap Metabolic Acidosis
• Concurrent Metabolic Alkalosis
• Respiratory Alkalosis

Vomiting
DKA
Sepsis
66
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

pH 7.25 pCO2 23
AG 20
Bicarb 24-10 14
140 110
AG 20-12 8
10
67
Mixed Acid-Base Example 2

• Anion Gap Metabolic Acidosis
• Hyperchloremic Metabolic Acidosis

68
Mixed Acid-Base Example 3

• 72 y.o. man with a h/o PUD has been vomiting for
  2 weeks. 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
AG150-110 40
Bicarb24-24 0
AG 40-12 28
69
Mixed Acid-Base Example 3

• Anion Gap Metabolic Acidosis (Shock)
• Metabolic Alkalosis (Vomiting)

Normal ABG does not
equal normal
patient.
Dr. Smith
70
Test Case 1

• An 80 year old man has been confused and c/o SOB
  for one week. He also has a hearing problem 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
Diagnosis?
120
AG 140 - 121 19
71
Test Case 1

• Anion Gap 140-(10813) 19, ? AG 7
• ? Bicarb 24-13 11
• pCO2 1.5 (12) 8 26 (compared/w 15)
• Patient is Alkalemic (pH 7.53) indicating a
  Superimposed Respiratory Alkalosis

Dx Metabolic Acidosis and Respiratory Alkalosis
72
Test Case 2

• 23 year old AIDS patient c/o weakness and
  prolonged severe diarrhea. He appears markedly
  dehydrated.

pH 7.25 pCO2 25 pO2 110 HCO3 11
151 129 60 2.0 12 2.0
Diagnosis?
73
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 Acidosis
74
Test Case 3

• 45 y.o. alcoholic man has been vomiting for 3
  days. Vitals BP 100/70, P 110. Intern
  administered Valium 30 mg for tremulousness.

pH 7.30 pCO2 40
145 96 3.0 19
Serum Ketones
Diagnosis?
75
Test Case 3

• Anion Gap 145- (96 19) 30
• ? Bicarb 24-19 5
• ? AG 30-12 18
• Change in AG gtgt Change in Bicarb
• Superimposed Metabolic Alkalosis
• Respiratory compensation?
• 1.5 x (19) 8 36 (compared with pCO240)

76
Test Case 3

• Anion Gap Metabolic Acidosis (AKA)
• Metabolic Alkalosis (Persistent Vomiting)
• Mild Respiratory Acidosis (Oversedation)

77
Test Case 4

• A 22 y.o. diabetic man has been vomiting for
  several days. He appears ill and dehydrated.
  His ABG reveals 7.40/ 40/ 100 on room air. His
  labs are below. The resident states he does not
  have DKA because the ABG is normal. Is the
  resident correct?

130 76 3.0 24
800
78
Test Case 4

• The resident is NOT correct Sorry admit MICU
• Anion gap 130- (76 24) 30
• ? Bicarb 24-24 0
• ? AG 30-12 18
• Change in AG gtgtgt Change in Bicarb

Dx Anion Gap Metabolic Acidosis
(DKA) Metabolic Alkalosis (Vomiting)
79
Test Case 5

• 33 y.o. woman c/o leg pain and SOB which started
  suddenly yesterday.

pH 7.45 pCO2 20 pO2 80
140 116 4.0 14
Diagnosis?
80
Test Case 5

• Anion gap 140- (116 14) 10

Dx Respiratory Alkalosis (PE) with Compensation
81
Summary of Expected Compensation and Other
Equations

• 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

82
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
• Na/Cl gt 1.4 metabolic alkalosis (hypochloremia)
• Na/Cl lt 1.27 non anion gap acidosis
  (hyperchloremia)
• 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 pCO2
• CO2 H2O lt---gt H2CO3 lt---gt H HCO3-

83
Summary of important points

• Acidosis/Alkalosis are metabolic states ?
  acidemia/alkalemia
• Doubling or halving the pCO2HCO3 ratio changes
  pH by 0.3
• Bicarbonate therapy based on bicarb lt 6, not pH
• Low pH with bicarb 6 needs Rx with ventilation
• Know the anion gap and MUDPILES
• Anion Gap gt 20 is metabolic acidosis
• no matter what the pH, pCO2, or bicarb.
• Normal Na/Cl ratio is 1.33 (140/105)
• Na/Cl ratio gt 1.4 is metabolic alkalosis (e.g.
  140/99)
• (or compensation for respiratory acidosis)
• Na/Cl lt 1.27 is hyperchloremic acidosis (e.g.,
  140/111)
• (or compensation for resp alkalosis)
• Winters formula pCO2 should be 1.5 x HCO3 8

84
The End