2. Indications for ABG
(1) Severe respiratory or metabolic disorders.
(2) Clinical features of hypoxia or hypercarbia
(3) Shock.
(4) Sepsis.
(5) Decreased cardiac output.
(6) Renal failure.
(7) Ideally any patient on oxygen therapy.
(9) ventilated patients.
3. ī PaO2; the partial pressure of oxygen in arterial blood
ī normal range breathing air > 75 mmHg on air (increases with FiO2)
ī pH; the acidity or alkalinity of the blood, determined by the
concentration of hydrogen ions [H+]
ī normal range 7.35 â 7.45
ī PaCO2; the partial pressure of carbon dioxide in arterial blood
ī normal range 35 â 45 mmHg
ī Bicarbonate; a buffer, neutralises the effects of excess acid
ī normal range 22 â 26 mmol L-1
ī Base excess; a measure of the degree of excess acid or alkali
(base) in the blood
īŧ normal range +2 to -2 mmol L-1
Terms used in arterial blood gas analysis
4. ABG: values
ī pH 7.35-7.45
ī PaCO2 35-45 mm Hg
ī PaO2 80-100 mmHg**
ī SaO2 93-98%
ī HCO3
- 22-26 mEq/L
ī Base excess -2.0 to 2.0 mEq/L
ī %MetHb <2.0%
ī %COHb <3.0%
ī CaO2 16-22 ml O2/dl
* At sea level, breathing ambient air
** Age-dependent
âNormal rangesâ difference between Labs
5.
6. CENTRAL EQUATION OF ACID-BASE
PHYSIOLOGY
ī Henderson Hasselbach Equation:
īŧ where [ H+] is related to pH by
īŧ To maintain a constant pH, PCO2/HCO3- ratio should
be constant.
īŧ When one component of the PCO2/ [HCO3-] ratio is
altered, the compensatory response alters the other
component in the same direction to keep the
PCO2/[HCO3- ] ratio constant.
īŧ [H+] in nEq/L = 24 x (PCO2 / [HCO3 -]
īŧ [ H+] in nEq/L = 10 (9-pH)
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
9. 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
ī The normal ratio of HCO3 to H2CO3 is 20:1.
ī The log of 20 is 1.3.
ī If you cut the HCO3 in half to 12, the ratio is 10:1.
ī The log of 10 is 1.0 .
ī The pH thus decreased by 0.3.
ī Whenever the ratio of HCO3 to H2CO3 is reduced by one-half,
the pH falls by 0.3.
13. Compensatory response or regulation
of pH
By 3 mechanisms:
1. Chemical buffers:
īŧ React instantly to compensate for the addition or
subtraction of H+ ions.
2. CO2 elimination:
īŧ Controlled by the respiratory system.
īŧ Change in pH result in change in PCO2 within minutes.
3. HCO3- elimination:
īŧ Controlled by the kidneys.
īŧ Change in pH result in change in HCO3.
īŧ It takes hours to days and full compensation occurs in
2-5 days.
17. Correlating Chloride and Bicarbonate
ī Tend to move in opposite directions.
ī Metabolic Alkalosis:
īŧ High Bicarbonate.
īŧ Low Chloride.
ī Metabolic Acidosis:
īŧ Low Bicarbonate.
īŧ Chloride Normal (Anion Gap) or High (non-AG).
īŧ Chloride low if Na/Cl >1.4; high if Na/Cl < 1.27.
īąLow chloride is synonymous with metabolic alkalosis
(or compensation for chronic respiratory acidosis).
īļEven if pH is normal, low chloride means
alkalosis.
18. The Central Role of the Carbonic Acid-
Bicarbonate Buffer System in the Regulation
of Plasma pH
19. The Central Role of the Carbonic Acid-
Bicarbonate Buffer System in the Regulation
of Plasma pH
20.
21. Compensation
ī Compensation is rarely
complete Returns pH toward
normal.
ī Compensation is not a secondary
acidosis or alkalosis.
ī High altitude and pregnancy may
have full compensationâbut it
takes time
īŧ Acetazolamide hastens
compensation.
īŧ Improves Mountain sickness.
Respiratory
Renal
22.
23.
24.
25. īMajor causes are:
īŧDepletion of bicarbonate reserve.
īŧInability to excrete hydrogen ions at
kidneys.
īŧProduction of large numbers of fixed /
organic acids.
īŧBicarbonate loss due to chronic diarrhea.
Metabolic acidosis
29. Acid-Base: Tough Stuff?
Itâs all in your mind
ī 7.53/15/80/12
ī 7.25/25/110/10
ī 6.88/32/100/7
ī 7.58/49/98/45
ī 7.30/40/156/19
ī 7.10/30/365/9
ī 7.72/28/95/37
ī 7.45/20/80/14
You are routinely
missing triple acid-
base disorders
Dr. Smith
Dr. Rock
30. Six step method
1) Identify any abnormality (is there acidemia or
alkalemia?).
2) Is the primary process metabolic or respiratory?
3) If the primary process is respiratory, is it acute
or chronic?
4) Is the compensation adequate?
5) Is there an AG?
6) Is there a mixed disorder?
31. Step 1 Identify the disorder
ī Take a look at the pH, as it directs towards the
principal disorder.
< 7.35 Acidemia
>7.45 Alkalemia
7.35-
7.45
Normal
Mixed
disorder
32. Acidemia and Alkalemia vs.
acidosis and alkalosis
pH < 7.36 ([H+] > 44) is acidemia.
pH > 7.44 ([H+] < 36) is alkalemia.
īmixed disorders of acidosis and
alkalosis may be neither acidemic
nor alkalemic.
e.g. 7.40/ 25/ pCO2/ 15
33. Step 2 RESPIRATORY or METABOLIC?
ī IS PRIMARY DISTURBANCE RESPIRATORY OR
METABOLIC?
pH PCO2 or pH PCO2 METABOLIC
pH PCO2 or pH PCO2 RESPIRATORY
īļRULE- If either the pH or PCO2 is Normal, there is a
mixed metabolic and respiratory acid base disorder.
34. Step 4 Respiratory
Compensation
Metabolic Acidosis:
ī Occurs rapidly.
ī Hyperventilation.
īŧ âKussmaul Respirationsâ
īŧ Deep > rapid (high tidal
volume).
ī Is not Respiratory
Alkalosis.
Metabolic Alkalosis:
ī Calculation not as
accurate
ī Hypoventilation.
ī Not Respiratory
Acidosis.
ī Restricted by
hypoxemia.
ī PCO2 seldom > 50-55.
pCO2=1.5 x HCO3 + 8 +/- 2
Winterâs formula
pCO2=0.9 x HCO3 + 15
35. Step 4 Metabolic
Compensation
Acute Hypercapnia:
HCO3 increases 1
mmol/L for each 10
mmHg increase in
PaCO2 >40
Chronic Hypercapnia:
HCO3 incr. 3.5 mmol/L
for each 10 mmHg
increase in PaCO2
>40
Acute Hypocapnia:
HCO3 decreases 2
mmol/L for every 10
mmHg decrease in
PaCO2 <40
Chronic Hypocapnia:
HCO3 decreases 5
mmol/L for every 10
mmHg decrease in
PaCO2 <40
CO2 + H2O H2CO3 H + HCO3
36. 3 most important equations
so far
ī Chronic resp. acidosis:
īŧsteady-state pCO2 is increased by 10 for
every 3.5 increase in HCO3.
ī Acute metabolic acidosis:
īŧ pCO2 = 1.5 x HCO3 + 8 (+/- 2)
ī Acute metabolic alkalosis:
īŧ pCO2 = 0.9 x HCO3 + 15
37. Step 5 Anion Gap
ī Described by Gamble in 1939.
ī Electroneutrality.
ī Na+, Cl-, and HCO3 are measured ions
Na + UC = Cl + HCO3 + UA
UC = Sum of unmeasured cations
UA = Sum of unmeasured anions
Anion Gap
38. Anion Gap
Unmeasured Cations:
ī Total 11 mEq/L
īŧPotassium 4
īŧCalcium 5
īŧMagnesium 2
Unmeasured Anions:
ī Total 23 mEq/L
īŧSulfates 1
īŧPhosphates 2
īŧAlbumin 16
īŧLactic acid 1
īŧOrg. acids 3
Na + UC = Cl + HCO3 + UA
140 + 11 = 104 + 24 + 23
151 = 151
Anion Gap = Na - (Cl + HCO3)
39.
40. Acid Base disorders
ī Anion Gap: represent the unmeasured anions normally
present in plasma ( po4, SO4, Creatinine and proteins).
AG = (Na +k) - (CL+HCO3) = 16 Âą 4 mEq/L
if K+ is not calculated= 12 mEq/L
Metabolic acidosis is conveniently divided into:
1. High anionâgap metabolic acidosis: ī unmeasured anions ī
ī HCO3 lactic acidosis; ketoacidosis; drug poisonings (e.g., aspirin,
ethyelene glycol, methanol)
2. Normal anionâgap metabolic acidosis (hyperchloremic
metabolic acidosis)
ī HCO3 ī compensatory ī CL by the kidney.
Diarrhea; some kidney problems e.g., renal tubular
acidosis, interstitial nephritis, small bowel or pancreatic
drainage & fistula or Ureterosigmoidostomy.
41. Acid Base disorders
METABOLIC ALKALOSIS
ī Chloride responsive (responds to NaCl or KCl therapy): diuretics;
Corticosteroids; gastric suctioning; vomiting.
ī Chloride resistant: any hyperaldosterone state, e.g., Cushing's
syndrome; severe K+ depletion.
RESPIRATORY ACIDOSIS
ī Central nervous system depression (e.g., drug overdose).
ī Chest bellows dysfunction (e.g., Guillain-BarrÊ syndrome, myasthenia
gravis).
ī Disease of lungs and/or upper airway (e.g., chronic obstructive lung
disease, severe asthma attack, severe pulmonary edema).
RESPIRATORY ALKALOSIS
ī Hypoxemia (includes altitude), Anxiety, Sepsis, Any acute
pulmonary insult e.g., pneumonia, mild asthma attack, early pulmonary
edema, pulmonary embolism.
42.
43. Causes High AG Metabolic
Acidosis
ī Methanol
ī Uremia/Renal
Failure
ī DKA
ī Paraldehyde
ī INH, Iron-lactate
ī Lactic Acidosis:
īŧ Has many etiologies.
īŧ Cyanide, CO, Toluene, HS.
īŧ Poor perfusion.
ī Ethylene glycol.
ī Salicylates:
īŧ Methyl salicylate
o (Oil of wintergreen)
īŧ Mg salicylate (Doanâs pills)
Levraut J et al. Int Care Med
23:417, 1997
MUDPILES
44.
45. Metabolic Acidosis: Normal
AG
ī Loss of HCO3:
īŧSevere diarrhea.
īŧPost-hypocapnia.
īŧUreteroileostomy.
īŧAcetazolamide.
ī Failure to excrete [H+]
īŧRenal Tubular Acidosis
â Types 1-4.
â Toluene.
ī Administration of [H+]
īŧAmmonium chloride.
1. Loss of HCO3
2. Failure to excrete [H+]
3. Administration of [H+]
46.
47. Decreased or Negative Anion
Gap
ī Low protein most important:
īŧAlbumin has many unmeasured negative charges.
īŧâNormalâ anion gap (12) in cachectic person.
o Indicates anion gap metabolic acidosis.
īŧ2-2.5 mEq/liter drop in AG for every 1 g drop in
albumin.
ī Other etiologies of low AG:
īŧLow K, Mg, Ca, increased globulins (Mult. Myeloma),
Li, Br (bromism), I intoxication.
ī Negative AG:
īŧmore unmeasured anions than unmeasured cations.
īŧBromide, Iodide, Multiple Myeloma.
49. Metabolic Acidosisâ
Bad??
ī Impaired cardiac contractility.
ī Decreased threshold for VF.
ī Decreased Hepatic and Renal perfusion.
ī Increased Pulmonary Vasc resistance.
ī Inability to respond to catecholamines.
ī Vascular collapse.
ī Increased Anion Gap.
ī Normal Anion Gap (Hyperchloremic).
50. Reasons to Limit Bicarbonate
therapy
ī Initially injected into 3 liter plasma volume.
īŧ (not 5 liter blood volume because does not enter red cells).
ī Theoretical, but probably does not happen:
īŧ Increase intracellular acidosis.
īŧ Will increase pCO2 and need for ventilation.
ī N.S: 150mEq/l of Na, Bicarb: 1000mEq/l of Na.
īŧ As much Na as 350 mlâs normal saline.
īŧ like hypertonic saline: leads to Hypernatremia & Fluid overload.
ī Extra bicarbonate can increase potassium
requirements, may increase hepatic production of
ketones, and may delay resolution of cerebral acidosis.
51.
52. Base Deficit
Volume of distribution, extracellular fluid 0.3
L/kg
ī = 0.3 x kg x (24 â HCO3) in mEq/l
īŧone ampule of bicarb = 50 mEq/50 ml
ī E.g.: 70 kg person with bicarb of 3
īŧ0.3 x 70 x 21 = 441 mEq
īŧ441mEq Ãˇ 50 mEq/ml/ampule = 9 Amps of bicarb
ī Suppose you want to get the bicarb back to 6
īŧ0.3 x 70 x (6-3) = 63
īŧ63 mEq Ãˇ 50 mEq/ml/ampule = 1.25 Amps of
bicarb.
53. When to give
bicarbonate
īDo NOT base it on pH.
īBase it on HCO3 level < 6.
īFor low pH:
īIf bicarbonate < 6:
īŧgive bicarb 1-2 amps.
īŧRecheck ABG.
īIf pCO2 > 1.5 (HCO3) + 8:
īŧthen ventilate better.
54.
55.
56. Step 6: Calculate Delta Gap
īą Used only if there is Anion
Gap.
Delta gap = (actual AG â 12) + HCO3
īŊ Adjusted HCO3 should be 24 (+_ 6) {18-30}
īŊ If delta gap > 30 additional metabolic
alkalosis.
īŊ If delta gap < 18 additional non-gap
metabolic acidosis.
īŊ If delta gap 18 â 30 no additional
metabolic disorders.
57. Change in Anion Gap vs. HCO3
ī In simple AG Metabolic Acidosis
īŧdecrease in plasma bicarbonate = increase in AG
Anion Gap
HCO3
īŧ <1 = High anion gap & normal AG acidosis.
īŧ 1-2 = Pure anion gap metabolic acidosis.
īŧ >2 = High anion gap acidosis with concurrent
metabolic alkalosis.
= 1
58. Six step method
1) Identify any abnormality (is there acidemia or
alkalemia?).
2) Is the primary process metabolic or respiratory.
3) If the primary process is respiratory, is it acute
or chronic?
4) Is the compensation adequate?
5) Is there an AG?
6) Is there a mixed disorder?
60. Problem #1
ī 60 ys male presents to the ED from a nursing
home. You have no history other than he has
been breathing rapidly and is less responsive
than usual.
Na+ 123 Cl- 99 HCO3
- 5
pH 7.31 pCO2 10
61. Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Acidemia
62. Six Steps for Acid-Base Analysis
Step 2. Is the primary process metabolic
or respiratory?
pCO2 = 10 should drive pH â
HCO3
- = 5 should drive pH â
63. Six Steps for Acid-Base Analysis
Step 3:
If the primary process is respiratory, is it
acute or chronic?
Skip this step as primary process is metabolic!
64. Six Steps for Acid-Base Analysis
Step 4:
Is there an anion gap?
Na+ - Cl- - HCO3
- > 12?
123 - 99 - 5 = 19
Anion Gap Metabolic Acidosis
65. Six Steps for Acid-Base Analysis
Step 5:
Is the respiratory compensation adequate?
ī Expected pCO2 range =
[1.5(measured HCO3
-)]+8+/- 2
[1.5 (5) +8] +/- 2 = [13.5 â 17.5]
pCO2 = 10
ī Therefore it IS a respiratory alkalosis.
66. Six Steps for Acid-Base Analysis
Step 6:
Are there any other metabolic disturbances?
ī Corrected HCO3
- =
(Measured HCO3
-) + (AG-12)
(5) + (19-12) = 12
ī Since this does not correct bicarbonate back to
normal, there is a non anion gap acidosis.
1.Anion Gap Metabolic Acidosis.
2.Concurrent Respiratory Alkalosis.
3.non - anion gap met. acidosis.
67. Problem #2
ī 42 ys female has the flu for four days with
incessant vomiting. She presents to the ED
two days after stopping insulin due to no food
intake.
Na+ 130 Cl- 80 HCO3
- 10
pH 7.21 pCO2 25
68. Six Steps for Acid-Base Analysis
Step 1.
Is there an acidemia or alkalemia?
Acidemia
69. Six Steps for Acid-Base Analysis
Step 2.
Is the primary process metabolic or
respiratory?
pCO2 = 25 should drive pH â
HCO3
- = 10 should drive pH â
70. Six Steps for Acid-Base Analysis
Step 3:
If the primary process is respiratory, is
it acute or chronic?
Skip this step as primary process is metabolic!
71. Six Steps for Acid-Base Analysis
Step 4:
Is there an anion gap?
AG= Na+ - Cl- - HCO3
- > 12?
130 - 80 - 10 = 40!!
Anion Gap Metabolic Acidosis
72. Six Steps for Acid-Base Analysis
Step 5:
Is the respiratory compensation
adequate?
Expected pCO2 range =
[1.5(measured HCO3
-)]+8+/- 2
[1.5 (10) +8] +/- 2 = [21 - 25]
E.pCO2 = 25, therefore this is normal
respiratory compensation
73. Six Steps for Acid-Base Analysis
Step 6:
Are there any other metabolic disturbances?
ī Corrected HCO3
- =
(Measured HCO3
-) + (AG-12)
(10) + (40-12) = 38
ī Since this over corrects bicarbonate
there is a metabolic ALKALOSIS!!
1.Anion Gap Metabolic Acidosis.
2.Metabolic Alkalosis.
74. Problem #3
30 year old female BMT patient with neutropenic
fever has been receiving multiple antibiotics
including amphotericin B. You are called to the
bedside for her fevers, rigors, and dyspnea.
ī Na+ 125 Cl- 100 HCO3
- 8
ī pH 7.07 pCO2 28 K+ 2.5
75. Six Steps for Acid-Base Analysis
Step 1.
ī Is there an acidemia or alkalemia?
Acidemia
76. Six Steps for Acid-Base Analysis
Step2:
ī Is the primary process metabolic or
respiratory?
PCO2 = 28 should drive pH â
HCO3
- = 8 should drive pH â
77. Six Steps for Acid-Base Analysis
Step 3:
ī If the primary process is respiratory, is it
acute or chronic?
Skip this step as primary process is metabolic!
78. Six Steps for Acid-Base Analysis
Step 4:
ī Is there an anion gap?
Na+ - Cl- - HCO3
- > 12?
125 - 100 - 8 = 17
Anion Gap Metabolic Acidosis
79. Six Steps for Acid-Base Analysis
Step 5:
ī Is the respiratory compensation adequate?
Expected pCO2 range =
[1.5(measured HCO3-)]+8+/- 2
[1.5 (8) +8] +/- 2 = [18-22]
pCO2 = 28, therefore this is a respiratory acidosis
even though the value is below 40!!
80. Six Steps for Acid-Base Analysis
Step 6:
īAre there any other metabolic
disturbances?
īCorrected HCO3
- =
(Measured HCO3
-) + (AG-12)
(8) + (17-12) = 13
ī Since this is below the normal range after
correction,there is a non anion gap acidosis.
1.Anion Gap Metabolic Acidosis.
2.Concurrent Respiratory Acidosis.
3.non - anion gap met. acidosis.
81. Example 4
Case: 43 yo w f Brought by friends from convention.
Had been staggering, speaking incoherently,
swearing, yelling. Pt. was confused, agitated,
speaking jibberish. Brought to ED. Friends left.
110/70 128 R22 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
82. Case continued
To MICU
Pt. arrests. Monitor 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
vomiting elicited from later history.
83. Beware Severe Alkalemia
īdue to:
īŧ Severe underlying pathology.
īalso:
īŧGeneral and Cerebral vasoconstrictor.
īŧShift of oxyhemoglobin dissociation.
īŧHypokalemia.
īŧIncreased SVR and decreased CO: Decreased
Contractility .
īŧCardiac arrhythmias refractory.
īŧSeizures.
84. Severe Alkalosis/alkalemia
ī HCO3 > 45.
ī Be sure oxygenation OK.
ī Avoid respiratory stimulation.
ī Acetazolamide, 500 mg IV
īŧMonitor K, Mg, PO4
ī HCl infusion:
īŧ0.1M solution (100 mmol/L, 0.2 mmol/
kg/hour).
īŧCentral line.
īŧTotal dose = Î HCO3 x kg x 0.5 (in mmoles).
85. Example 4
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
150 100 50
3.8 20 1.8
650
AG= 30
Bicarb=24-20= 4
AG=30-12= 18
Na/Cl > 1.4
86. Mixed Acid-Base: Example
4
ī Anion Gap Metabolic Acidosis.
ī Concurrent Metabolic Alkalosis.
ī Respiratory Alkalosis.
DKA
Vomiting
Sepsis
87. Example 5
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 followsâĻ
140 110
10
AG= 20
Bicarb= 24-10= 14
AG= 20-12= 8
pH 7.25 pCO2 23
88. Mixed Acid-Base: Example 5
īAnion Gap Metabolic Acidosis
īHyperchloremic Metabolic Acidosis.
īRespiratory alkalosis
89. Mixed Acid-Base: Example 6
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
AG=150-110= 40
Bicarb=24-24= 0
AG= 40-12= 28
90. Mixed Acid-Base: Example 6
ī Anion Gap Metabolic Acidosis (Shock)
ī Metabolic Alkalosis (Vomiting)
Normal ABG does not
equal normal
patientâĻ.
Dr. Smith
91. 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
120 Diagnosis?
AG = 140 - 121 = 19
92. Test Case #1
īAnion Gap= 140-(108+13)= 19,
ī Î AG = 7
ī Î Bicarb= 24-13= 11
E.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
93. 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?
94. Test Case # 2
ī Anion Gap= 151-(129 + 11)= 11 (normal)
ī The patient is Acidemic (pH 7.25)
ī 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
95. 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?
96. Test Case #3
ī Anion Gap= 145- (96 + 19)= 30
ī Î Bicarb= 24-19= 5
ī Î AG= 30-12= 18
ī Change in AG >> Change in Bicarb
ī Superimposed Metabolic Alkalosis
ī Respiratory compensation?
1.5 x (19) + 8= 36 (compared with pCO2=40)
97. Test Case #3
ī Anion Gap Metabolic Acidosis (AKA)
ī Metabolic Alkalosis (Persistent Vomiting)
ī Mild Respiratory Acidosis (Oversedation)
98. 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
99. Test Case #4
ī The resident is NOT correct; Sorry admit
MICU
ī Anion gap= 130- (76 + 24)= 30
ī Î Bicarb= 24-24= 0
ī Î AG= 30-12= 18
ī Change in AG >>> Change in Bicarb
Dx: Anion Gap Metabolic Acidosis (DKA)
Metabolic Alkalosis (Vomiting)
100. 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?
101. Test Case #5
ī Anion gap=
140- (116 + 14)= 10
Dx: Respiratory Alkalosis (PE) with
Compensation
102. Absolute
contraindications
1. An abnormal modified Allen's test.
2. Local infection, thrombus, or distorted anatomy at
the puncture site (eg, previous surgical
interventions, congenital or acquired
malformations, burns, aneurysm, stent,
arteriovenous fistula, vascular graft)
3. Severe peripheral vascular disease of the artery
selected for sampling
4. Active Raynaud syndrome (particularly sampling
at the radial site)
103. Relative Contraindications
ī Supra therapeutic coagulopathy and infusion of
thrombolytic agents (eg, during streptokinase or
tissue plasminogen activator infusion) are relative
contraindications to arterial needle stick.
we suggest avoiding repeated arterial needle
sticks when the international normalized ratio is
âĨ3 and/or the activated partial thromboplastin
time is âĨ100 seconds
104. Relative Contraindications
ī Similarly, arterial needle stick and catheterization
can be performed in patients with
thrombocytopenia a platelet count >50 x 109/L,
but is generally avoided in those whose count is
â¤30 x 109/L. For those with counts between 30
and 50 x 109/L limited needle stick sampling is
sometimes performed, when necessary, with
increased compression time.
ī A platelet count <50 x 109/L is generally a
contraindication to arterial catheter insertion.
105. How are ABG done?
ī Site: Radial artery (Brachial, femoral arteries)
īŧ non-dominant hand / good Ulnar artery blood flow/ adequate
pressure following sampling.
ī Positioning of wrist: hyperextended + good support
under wrist.
ī Syringe & Needles: low resistance / heparinized /
small/ blood âpulseâ / īą Arterial cannula.
ī Lignocaine 1% ? Repeated sampling / pain induced
hyperventilation.
ī Complications: Pain, hematoma, air/blood emboli,
infection, vascular trauma/occlusion, arterial spasm.
106.
107. Delayed Analysis
Consumption of O2 & Production of CO2
continues after blood drawn.
īŧ Iced Sample maintains values for 1-2 hours.
īŧ Uniced sample quickly becomes invalid within 15
-20 minutes.
ī PaCO2 ī 3-10 mmHg/hour.
ī Pao2 ī¯
ī pH ī¯ d/t lactic acidosis generated by glycolysis
in R.B.C.
108. FEVER OR HYPOTHERMIA
1. Most ABG analyzers report data at N body temp.
2. If severe hyper/hypothermia, values of pH &
PCO2 at 37 C can be significantly differ from ptâs
actual values.
3. Changes in PO2 values with temp also
predictable.
Hansen JE, Clinics in Chest Med 10(2), 1989 227-237
īą If Pt.âs temp < 37C
Substract 5 mmHg Po2, 2 mmHg Pco2 and Add
0.012 pH per 1C decrease of temperature.
109. AIR BUBBLES:
1. PO2 īž150 mmHg & PCO2 īž0 mm Hg in air bubble(R.A).
2. Mixing with sample, lead to ī PaO2 & ī¯ PaCO2.
ī To avoid air bubble, sample drawn very slowly and
preferabily in glass syringe.
Steady State:
īSampling should done during steady state after change
in oxygen therapy or ventilator parameter.
īSteady state is achieved usually within 3-10 minutes.
110. Leucocytosis :
ī ī¯ pH and Po2 ; and ī Pco2.
ī 0.1 ml of O2 consumed/dL of blood in 10 min in pts with
N TLC.
ī Marked increase in pts with very high TLC/plt counts â
hence imm chilling/analysis essential.
EXCESSIVE HEPARIN:
ī Dilutional effect on results ī¯ HCO3
- & PaCO2
ī Only .05 ml heperin required for 1 ml blood.
īŧ So syringe be emptied of heparin after flushing or only
dead space volume is sufficient or dry heperin should
be used.
111. Summary of important points
ī Acidosis/Alkalosis are metabolic states â acidemia/alkalemia.
ī Doubling or halving the pCO2:HCO3 ratio changes pH by 0.3.
ī Bicarbonate therapy based on bicarb ⤠6, not Ph.
ī Low pH with bicarb > 6 needs Rx with ventilation.
ī Know the anion gap and MUDPILES.
ī Anion Gap > 18 is metabolic acidosis.
īŧ no matter what the pH, pCO2, or bicarb.
ī Normal Na/Cl ratio is 1.33 (140/105)
īŧ Na/Cl ratio > 1.4 is metabolic alkalosis (e.g. 140/99)
â (or compensation for respiratory acidosis)
īŧ Na/Cl < 1.3 is hyperchloremic acidosis (e.g., 140/111)
â (or compensation for resp alkalosis)
ī Winterâs formula: pCO2 should be = 1.5 x HCO3 + 8