Acid-Base Made Easy - Gathering of Eagles

Acid-Base Made Easy - Gathering of Eagles

10/11/2013
Acidosis
Acid-Base Made Easy
VanderbiltEM.com
Corey M. Slovis, M.D.
Vanderbilt University School of Medicine
Metro Nashville Fire Department
Nashville International Airport
The 3 BMP Rules
1)
Check the Numbers
Check the Numbers
What lab values are abnormal
2)
Calculate the Anion Gap
• Look at BMP for abnormalities
Na+ - (HCO-3 + Cl-)
3)
Apply the Rule of 15
• Hyponatremia, Hyperkalemia, Acidosis?
HCO3 + 15 should equal the:
- pCO2
- last two numbers of pH
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10/11/2013
Anion Gap
Anion Gap
• The gap is the Positives minus the Negatives
• An elevated gap = MUDPILES
• The gap is Na+- [Cl- + HCO3-]
• WNL Gap but HCO3  = HARDUP
• The gap should be about 8-12 (± 2)
• The gap should always be less than 15
Elevated Anion Gap
(Na+-[Cl- + HCO3-]  15)
M
U
D
P
I
L
E
S
Methanol
Uremia
DKA and AKA
Phenformin/Paracetamol
Paraldehyde
INH and Iron
Lactic Acidosis
Ethylene Glycol
Salicylates, Solvents
Normal Gap Acidosis
(Low Bicarb but A.G. is NOT Elevated)
H
Hyperventilation (compensation)
A
R
Acids, Addison’s, Carbonic Anhydrase
Inhibitors
RTA
D
Diarrhea
U
Ureteral Diversion, Ureterosigmoidostomy
P
Pancreatic Fistula, Pancreatic Drainage
Metabolic Acidosis
Always check the Anion Gap
HCO3
pH
Even if the BMP looks normal!!
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Respiratory Alkalosis
pCO2
Experts in Acid-base can tell if
there is Compensation vs. a
Second Primary Process
pH
Compensation is
Always the Opposite
Respiratory Compensation in
Metabolic Acidosis
HCO3
Acidosis
Alkalosis
Metabolic
Respiratory
pH
pCO2
pH
Henderson-Hasselbalch Equation
[H+]
[pCO2]
= 24
[HCO3-]
Ann Intern Med 1968;66:312
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10/11/2013
Rule of 15
Rule of 15
HCO3 + 15 = pCO2  2 and last 2 digits of pH
As HCO3 falls
pCO2
HCO3 + 15
HCO3
Rule of 15
+15
Should equal
new pCO2
Rule of 15
HCO3 + 15 = pCO2
HCO3 + 15 = pCO2  2
• Establishes a new set point
HCO3 + 15 = pH  .02
• Tells you what pCO2 value is compensatory
• If followed = Pure Compensation
If Rule of 15 satisfied, you have a:
Metabolic Acidosis plus a
2 Respiratory Alkalosis
The Rule of 15 is also called the
should be rule because it tells what
the pCO2 and pH should be
if there is appropriate respiratory
compensation.
• If followed = No Second Process
If NOT followed = Another Primary process
TheRule
Rule of
of 15 tells
tell you
The
youthe
thepCO2
pH if a pure wide gap
pCOand
2 and pH if
metabolic acidosis with secondary
respiratory compensation exists
(a 2o Respiratory Alkalosis)
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10/11/2013
Respiratory Compensation in
Metabolic Acidosis
HCO3
pH
pCO2
Rule of 15
HCO3 + 15 = pCO2  2 and last 2 digits of pH
As HCO3 falls
pH
Example: Rule of 15
HCO3 + 15 = pCO2
HCO3
pCO2
Should equal
new pCO2
+15
HCO3
pCO2
Too
high 1 Respiratory Acidosis
If Rule of 15 is followed you have:
+ 15
A Metabolic Acidosis (wide or normal
gap) with an appropriate …
2 Respiratory
Alkalosis only
Too 1 Respiratory Alkalosis
Low
Secondary Respiratory Alkalosis
Rule of 15 Followed
Rule of 15 Not Followed
HCO3 + 15 = pCO2
HCO3 + 15 = pCO2
pCO2 “too high”
1 Respiratory Acidosis
HCO3
HCO3
Secondary Respiratory Alkalosis
plus 15
pCO2
pCO2 “too high”
1 Respiratory Acidosis
Secondary Respiratory Alkalosis
plus 15
pCO2 “too low”
1 Respiratory Alkalosis
pCO2 “too low”
1 Respiratory Alkalosis
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Rule of 15 Not Followed
HCO3 + 15 = pCO2
HCO3
pCO2
pCO2 “too high”
1 Respiratory Acidosis
Secondary Respiratory Alkalosis
If you don’t have an arterial blood gas (ABG)
you can use just the venous pH (VBG)
plus 15
pCO2 “too low”
1 Respiratory Alkalosis
Venous pH
Venous pH
• Very close to Arterial unless in Shock
• 0.02 – 0.03 in 99% of patients
• 7.40 vs 7.37 – 7.38
VpH = 0.01 – 0.03 of Art pH
• Great in DKA and AKA
• ABGs only needed for Arterial pCO2
ABGs
Venous pH
• Very close to Arterial unless in Shock
• On Ventilator
• 0.02 – 0.03 in 99% of patients
• Seriously Ill
• 7.40 vs 7.37 – 7.38
• In Shock
• Great in DKA and AKA
• Severe Lung Disease
• ABGs only needed for Arterial pCO2
• Cardiac Arrest
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Case #2
Case #2
140 100
5.0 10
pH =
140 100
5.0 10
pH = ?
pCO2 = ?
 What are the 3 BMP Rules
pCO2 =
Check the numbers.
Calculate the A.G.
(
37
) = 30 = ↑ = WGMA
+
Case #2
HCO3 = 10
Case #3
pH = 7.25
pCO2 = 25
pCO2
40
HCO3
24
Too
high
25
10
140 100
5.0 20
?
pH = 7.35
pCO2 = 35
?
+ 15 = 35
2 Respiratory
Alkalosis only
Too
Low
+15
VpH = 7.33
40
Case #4
135 100
6.0 15
Case #4
BUN = 30
pH = 7.30
GLU = 600
pCO2 = 30
135 100
6.0 15
BUN = 30
pH = 7.30
GLU = 600
pCO2 = 30
pO2 = 100
pO2 = 100
 Is this pure DKA?
 Is this “just a WGMA + a 2 Respiratory Alkalosis?”
 Is this patient septic also?
Check the numbers.
Calculate the A.G.
 Or could this patient be tiring?
(V pH 7.28)
(
+
) = 20 = ↑ = MUDPILES
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10/11/2013
Rule of 15
HCO3 + 15 = pCO2  2 and last 2 digits of pH
TheRule
Ruleof
of 15
15 tells
tell you
The
youthe
thepCO2
pH if a pure wide gap
pCOand
2 and pH if
metabolic acidosis with secondary
respiratory compensation exists
As HCO3 falls
pCO2
o
(a 2 Respiratory Alkalosis)
Should equal
new pCO2
+15
HCO3
Case #4
HCO3
pCO2
Too
high 1 Respiratory Acidosis
+ 15
HCO3 = 15
pH = 7.30
pCO2
40
HCO3
24
Too
high
2 Respiratory
Alkalosis only
Too 1 Respiratory Alkalosis
Low
30
15
Case #5
Case #4
BUN = 30
pH = 7.30
GLU = 600
pCO2 = 30
pO2 = 100
2 Respiratory
Alkalosis only
Too
Low
+15
135 100
6.0 15
pCO2 = 30
130 105
4.8 15
BUN = 40
pH = 7.30
GLU = 600
pCO2 = 30
pO2 = 100
Wide Gap Metabolic Acidosis
Secondary Respiratory Alkalosis
No Tiring or sepsis causing additional hyperventilation.
Is this mild DKA?
(V pH 7.28)
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Case #5
130 105
4.8 15
Normal Gap Acidosis
(Low Bicarb but A.G. is NOT Elevated)
BUN = 40
pH = 7.30
GLU = 600
pCO2 = 30
H
Hyperventilation (compensation)
pO2 = 100
A
R
Acids, Addison’s, Carbonic Anhydrase
Inhibitors
RTA
D
Diarrhea
U
Ureteral Diversion, Ureterosigmoidostomy
P
Pancreatic Fistula, Pancreatic Drainage
Check the numbers.
Calculate the A.G.
(
+
) = 10 = No A.G. = HARDUP
Case #5
HCO3 = 15
Case #5
pH = 7.30
pCO2 = 30
pCO2
40
HCO3
24
Too
high
30
15
2 Respiratory
Alkalosis only
Too
Low
+15
130
105 BUN = 40
4.8
15
GLU = 600
pH = 7.30
pCO2 = 30
pO2 = 100
Normal Gap Acidosis
(Hyperchloremic)
Secondary Respiratory Alkalosis
Can’t be mild DKA, no A.G. = no Ketoacidosis
52
Case #6
An alcoholic comes in with altered
mental status and very ill appearing.
Someone says he was drinking
“windex for car windshields”.
Toxic Alcohols
• Ethanol  Acetaldehyde
• Isopropyl  Acetone
• Methanol  Formic Acid
Is this methanol?
• Ethylene Glycol  Oxalic Acid
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The most common errors in
alcoholics are made by doctors
and nurses who assume
"He's just drunk."
Ann Emerg Med 1991;20:1146-1147
Ten Commandments of
Emergency Medicine
Methanol
Ann Emerg Med 1991;20:1146-1147
• CH3-OH; MW 32; 3.2 mg% of methanol = 1 mosm
• Assume the Worst
• Always err in a way the patient will
suffer the least
• Formic acid and formaldehyde once metabolized
• Methanol is non-toxic; breakdown products are not
• Diagnosis: Profound acidosis, blindness, retinal
edema, pancreatitis
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Ethylene Glycol
HO-CH2-CH2-OH MW 62 each 6.2 mg% = 1 mosm
• Becomes oxalic acid once metabolized
• An antifreeze agent
• A sweetener for wine
• 40 - 60 deaths a year in USA
• Has no odor
• Profound acidosis from oxalic acid
• Renal failure from oxalate crystals in kidney
Isopropyl Alcohol
CH3-CHOH-CH3 MW 60 each 6.0 mg = 1 mosm
• Becomes acetone once metabolized
Am J Med 1983;75:680-685
• Usually benign
• Twice as drunk, twice as sick, twice as long
• Usually very benign
• Ketosis without acidosis
• Most patients appear just drunk
• No anion gap
• Death possible but requires either a massive
ingestion or use by a young child
• Hemorrhagic gastritis, hypotension
Case #6
130 90
5.5 5
Case #6
BUN = 20
pH = 7.00
GLU = 100
pCO2 = 20
130 90
5.5 5
BUN = 20
pH = 7.00
GLU = 100
pCO2 = 20
pO2 = 110
 Acid Base Diagnosis
pO2 = 110
Check the numbers.
 Is this methanol?
 Is bicarbonate indicated?
Calculate the A.G.
(V pH 6.98)
(
+
) = 35 = ↑ = WGMA
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Case #6
HCO3 = 5
pH = 7.00
pCO2 = 20
pCO2
40
HCO3
24
Too
high
20
5
Corollary to the Rule of 15
2 Respiratory
Alkalosis only
Too
Low
+15
Corollary to the Rule of 15
HCO3
PCO2
pH
As the Bicarbonate falls below 10 and
approaches 5 the expected pCO2
24
40
7.40
20
35
7.35
is not HCO3 + 15.
15
30
7.30
It is:
10
25
7.25
5
15
7.12
2.5
15
6.88
HCO3
= 15
(12-15)
Corollary to the Rule of 15
Corollary to the Rule of 15
HCO3
1 Respiratory Acidosis
As the HCO3 falls below 10 and approaches 5:
HCO3
=
+
15 = pCO2
5=
15
2 Respiratory Alkalosis
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10/11/2013
To check for Methanol
and Ethylene Glycol:
Case #6
130 90
5.5 5
BUN = 20
pH = 7.00
GLU = 100
pCO2 = 20
1)
Get levels
PO2 = 110
2)
Check osmolar gap
3)
Treat based on history and/or physical
and/or lab NOT just levels and/or gap
Wide Gap Metabolic Acidosis
Respiratory Acidosis
If they have already metabolized the toxin,
they can be acidotic with low or no detectable
serum levels or osmolar gap!
Osmolar Gap
Treatment of Methanol and
Ethylene Glycol
For Unexplained Wide Gap Acidosis or
History of Ingestion of Toxic Alcohol
• Calculate Osmolarity
•
Secure ABCs
• (Na x 2 + GLU
+ BUN
+ ETOH
)
20
3
4
•
Consider NGT
• Get measured osmolarity from lab
•
Reverse Acidosis
•
Block Metabolism
•
Enhance Elimination
• Measured – Calculated should = 10
• Elevated Osmolal Gap = Metahnol or E.G.
Treatment of Methanol and
Ethylene Gylcol
Treatment of Methanol and
Ethylene Glycol
• Reverse Acidosis
• Secure ABCs
– Hydrate as needed
• Consider NGT
– Provide glucose and usually start ETOH
cocktail
– Always give thiamine
– 1 amp of bicarbonate for each 0.1 pH unit below 7.35
– 1 meq/kg over 5-10 min will raise pH by 0.1-0.15
– Get pH to 7.35-7.40
• Block Metabolism
– Block Alcohol Dehydrogenes
– Begin Fomepizole (4-MP)
• 15 mg/kg IV then 10 mg/kg IV Q 12 H
– Block Creation of Formic or Oxalic Acid
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10/11/2013
Treatment of Methanol and
Ethylene Gylcol
• Enhance Elimination
– Hemodialysis for Symptomatic, acidotic patients or
those with levels > 25-50 mg%
Is Bicarbonate Indicated?
– HD until levels below 25 mg%
– May delay HD once patient stable and Fomipazole on
board
– HD emergently for:
• visual changes, severe acidosis, coma
Bicarbonate: Yes and No
Using Bicarbonate
Yes: in bicarbonate consuming overdoses
like ASA, Methanol, Ethylene Glycol
Replenish the consumed bicarbonate
Each amp raises pH by 0.1 if given in
under 3-5 minutes
No: for diseases that cause acidosis like
DKA, Sepsis and Lactic Acidosis
Correct the underlying disease
Case #7
1 meq/kg raises pH by 0.1 – 0.15
Status Seizures
AMS
A 23 yo man presents with altered mental status.
He is agitated, febrile and hyperventilating.
140 100
3.8 10
BUN = 20
pH = 7.32
GLU = 70
pCO2 = 20
pO2 = 80
 What is the differential of AMS?
 Acid Base Diagnosis?
 Immediate Rule Out?
• Vital Signs
• Vital Signs
• Toxic–Metabolic
• Toxic–Metabolic
• Structural
• Structural
• Infectious
• Infectious
• Epilepsy
• Psychiatric
(V pH 7.30)
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Case #7
Case #7
HCO3 = 10
140 100
3.8 10
BUN = 20
pH = 7.32
GLU = 70
pCO2 = 20
pH = 7.32
pCO2
40
HCO3
24
Primary Respiratory
Alkalosis
pO2 = 80
10
(
+
) = 30 =
↑
2 Respiratory
Alkalosis only
20
Too
Low
+15
= MUDPILES
Too
high
25
Check the numbers.
Calculate the A.G.
pCO2 = 20
Case #7
If the patient’s pCO2 is lower than it
“should be” via the Rule of 15, or V pH is
higher than it should be,
then the patient is hyperventilating
more than expected from compensation.
140 100
3.8 10
BUN = 20
pH = 7.32
GLU = 70
pCO2 = 20
pO2 = 80
Wide Gap Metabolic Acidosis
This is also a
Primary Respiratory Alkalosis.
Primary Respiratory Alkalosis
Aspirin
Whenever you have a WGMA and a
1o Respiratory Alkalosis always
immediately consider and rule out:
ASPIRIN
SEPSIS
•
•
•
•
•
•
The great imitator
AMS, Seizures
Anxiety, Tachypnea, Tachycardia
Hypoglycemia
Febrile, Meningitis
DIC, MOSF
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10/11/2013
Aspirin Kills
• Acidosis
• Hypoglycemia
• Hypokalemia
• Dehydration – Fever
• Edema: Pulmonary and CNS
Treating Aspirin
• Acidosis
• Hypoglycemia
• Hypokalemia
• Dehydration
• Edema
Bicarbonate
Glucose
KCL
Volume
Judious Volume
X 100,100
Treating Aspirin
Very Acidotic Aspirin Overdoses
D5 + 3 Amps HCO3 + 40 KCL
200cc/hr
If you intubate an Aspirin Overdose
they will get a respiratory acidosis if
you do not ventilate at very high rates
and volumes
• Keep urine non acidotic at 100 cc +/hr
• If not: - more volume if flow too low
- more bicarb if pH too low
• ETT = DOA if not careful
• Call Tox, Use Bicarb, Dialyze
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10/11/2013
Case #8
Case #8
pH = 7.30
140 100
4.0 15
pCO2 = 30
pO2 = 98
pH = 7.30
140 100
4.0 15
pCO2 = 30
pO2 = 98
O2 sat = 100%
 A 19 yo Jeet Kun Do Sensei is found
down in his dojo.
PE
O2 sat = 100%
Decorticate, Papilledema
ECG
Diffuse ST and T waves changes
 Is there pure wide gap metabolic acidosis?
 Any new Rule of 5 to use here?
Case #8
pH = 7.30
140 100
4.0 15
pCO2 = 30
pO2 = 98
O2 sat = 100%
Check the numbers.
Calculate the A.G.
(
+
) = 25 =
↑=
MUDPILES
Case #8
HCO3 = 15
HCO3
24
pH = 7.30
pCO2 = 30
pCO2
40
O2 Sat = 100%
pCO2 = 30
Too
high
15
+15
30
pH = 7.30
2 Respiratory
Alkalosis only
Too
Low
pO2 = 98
O2 Sat = 100%
Trust No One
Believe Nothing
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10/11/2013
Pulse Oximetry Basics
• Pulses light at about 400 cycles/sec
• Can compare arterial to venous saturation
• Accuracy is  2% when sats above 70 - 80%
• Accurate to levels of pO2 of 50 (80% sat)
• Compares arterial and venous absorbance at
both wavelengths
103
J Respir Dis 2001;22:289-296
104
Carbon Monoxide but
100% Saturated, 75% O2, 25% CO
J Respir Dis 2001;22:289-296
105
106
Co-Oximetry
• Measures true saturation's
• Measures at 4 wavelengths
• Specifically evaluates
–Saturated Hgb (O2)
–Desaturated Hgb (CO2)
–Carbon Monoxide (CO)
–Methemoglobin (Me)
107
Ann EM 1997
108
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AMS of Unknown Cause
5 ABG Values
J Respir Dis 2008;29:74-82
•
pO2
•
pCO2
•
pH
•
Measured O2 Sat
•
CO Level
109
O2 Saturation
ABG, O2 Sat, pO2, % Sat
• O2 Sat Monitor
Calculated
• O2 Sat by ABG
Calculated
• O2 Sat by Co Oximetry
Direct Measure
The Only True Measurement
of O2 Saturation
is via Co Oximetry.
112
Case # 9
Case # 9
A German Shepard Activates 911
due to her masters AMS.
140 100
3.2 10
 Diagnosis?
pH = 7.20
pCO2 = 30
pO2 = 80
pH = 7.20
140 100
3.2 10
pCO2 = 30
pO2 = 80
Check the numbers.
Calculate the A.G.
(
+
) = 30 =
↑=
MUDPILES
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Case # 9
HCO3 = 10
HCO3
24
pH = 7.20
1o Respiratory
Acidosis
Case # 9
pCO2 = 30
140 100
3.2 10
pCO2
40
30
pH = 7.20
pCO2 = 30
PO2 = 80
Wide Gap Metabolic Acidosis
Primary Respiratory Acidosis
Too
high
25
X
10
+15
Name That Acidosis
• Blindness
• Methanol
• Urine Findings
• Ethylene Glycol, DKA, RF
• Abdominal Pain
• Methanol, Iron, DKA, Sepsis, ASA
• Funny Breath
• Uremia, DKA, Aspirin (Methyl Salycilate)
• Hypoglycemia
• ASA, Sepsis, Methanol, E.G.
• Status Seizures
• INH, Lactic Acidosis
Name That Acidosis
• Hypoxia
• Lactic Acidosis
• Hypocalcemia
• Ethylene Glycol
• Papilledema
• Methanol
• “In a snow storm”
• Methanol
• pH < 6.8
• INH, ME, EG
The 3 BMP Rules
1)
Check the Numbers
What lab values are abnormal
SUMMARY
2)
Calculate the Anion Gap
Na+ - (HCO-3 + Cl-)
3)
Apply the Rule of 15
HCO3 + 15 should equal the:
- pCO2
- last two numbers of pH
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10/11/2013
Elevated Anion Gap
(Na+-[Cl- + HCO3-]  15)
Methanol
Uremia
M
U
D
DKA and AKA
Phenformin/Paracetamol
Paraldehyde
INH and Iron
Lactic Acidosis
Ethylene Glycol
Salicylates, Solvents
P
I
L
E
S
Always check the Anion Gap
Even if the BMP looks normal!!
Rule of 15
HCO3 + 15 = pCO2  2 and last 2 digits of pH
As HCO3 falls
HCO3
Too
high 1 Respiratory Acidosis
pCO2
+ 15
HCO3
+15
Should equal
new pCO2
pCO2
2 Respiratory
Alkalosis only
Too 1 Respiratory Alkalosis
Low
Corollary to the Rule of 15
As the Bicarbonate falls below 10 and
approaches 5 the expected pCO2
is not HCO3 + 15.
It is:
HCO3
= 15
(12-15)
Whenever you have a WGMA and a
1o Respiratory Alkalosis always
immediately consider and rule out:
ASPIRIN
SEPSIS
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10/11/2013
The Delta Gap
VanderbiltEM.com
• The Rule of 15 looks for “hidden”
respiratory processes
• The Delta Gap looks for “hidden”
metabolic processes in wide gap acidosis.
• Is there a metabolic alkalosis or a second
acidosis (hyperchloremic metabolic
acidosis) in addition to elevated gap
acidosis ?
HCO3
•
•
Anion Gap
The Delta Gap (1:1)
The bicarbonate should go down
by the same amount ( 4)
As the anion
gap goes up
The fall in HCO3- ( HCO3-) should
mirror the rise in AG ( AG)
AG HCO3
AG HCO3
AG HCO3
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10/11/2013
HCO3 20 A.G. 30
Wide Gap Metabolic Acidosis Plus
a Concomitant Metabolic Alkalosis
30
HCO3 10 A.G. 20
Wide Gap Metabolic Acidosis Plus a
Second Metabolic Acidosis (non-gap acidosis)
HCO3
HCO3
24
(+15)
24
20
(- 14)
(- 5)
(+ 5)
19
15
15
AG
10
AG
There are 3 possibilities
with the Delta Gap:
Should be
1) The  HCO3 = the  AG (4) :
thus: no hidden process
vs
2) The HCO3 is higher than it “should be”:
= Metabolic Alkalosis
It is
3) The HCO3 is lower than it “should be”:
= Metabolic Acidosis
(1° Hyperchloremic Metabolic Acidosis)
Case #11
142 92
5.0 20
pH = 7.38
pCO2 = 30
Case #11
pH = 7.38
142 92
5.0 20
pCO2 = 30
pO2 = 60
pO2 = 60
Check the numbers.
 Diagnosis?
Calculate the A.G.
(
+
) = 30 =
↑=
MUDPILES
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10/11/2013
Case #11
HCO3 = 20
HCO3
24
20
Case #11
pH = 7.38
pCO2 = 30
24
30
pCO2
40
o
20 (only by -4)
1 Respiratory
Alkalosis
(-15)
(+15)
35
X
+15
30
2 Respiratory
Alkalosis only
Too
Low
15
9
AG
HCO3
The HCO3 should fall by -15 but it hasn’t.
HCO3 is higher than it “should be.”
Metabolic Alkalosis
Case #11
142 92
5.0 20
pH = 7.38
pCO2 = 30
VanderbiltEM.com
pO2 = 60
Wide Gap Metabolic Acidosis
Primary Respiratory Alkalosis
Metabolic Alkalosis
24