Transcript ACID/BASE DISORDERS

ACID/BASE DISORDERS
Resident Rounds
Rob Hall PGY3
April 24, 2003
Objectives
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Approach to A/B disorders
Clinical examples of each disorder
Differential dx of each disorder
Combined disorders
Should we even do ABGs?
• MANY studies showing that venous gases
have similar pH and pC02 to ABGs
• MANY studies show that ABGs rarely
change management
How to interpret an ABG
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What is the pH?
Is there an acidemia or alkalemia?
Is it respiratory or metabolic?
Is there any compensation?
Is the compensation appropriate?
What is the anion gap?
Took some pills
• ABG
– pH 7.25
– PC02 22
– HC03 15
• Interpretation?
• Is there a second acid base disorder?
• Metabolic acidosis + respiratory alkalosis
– Think ASA!!
Compensation:
the clue to mixed disorders
• ACIDOSIS
– Respiratory
• Acute 1:10
• Chronic 1:3
– Metabolic 1:1
• ALKALOSIS
– Respiratory
• Acute 1:10
• Chronic 1:2
– Metabolic 0.6:1
80 female with suspected
ischemic gut……
pH 6.9, PC02 35, HCO3 8
Why is the acidemia important?
Consequences of Severe
Acid Base Disorders
• Severe Acidemia
– Negative ionotropy
– Arrythmias
– Reduced response to
catecholamines
– Hyperkalemia
– Muscle weakness
– Altered LOC and
seizures
– Poor enzyme function
• Severe Alkalemia
– Reduced coronary
blood flow
– Arrythmias
– Hypokalemia
– Altered LOC and
seizures
– Poor enzyme function
Case
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75 yo female
Altered LOC
Fever
Sinus tachycardia
Tachypnea
ABG: pH 7.50, pC02
30, HC03 23
• Interpretation?
• Diagnosis?
• Differential dx of the
acid/base disorder?
Respiratory Alkalosis
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Pain
Anxiety
Pregnancy
Pulmonary disease/hypoxia
CNS disorder
Thyrotoxicosis
ASA
Cases
• 70yo smoker since birth
• COPD exacerbation
• pH 7.15, pC02 60, HC03 26
– Is he a chronic CO2 retainer?
• pH 7.35, pC02 60, HC03 32
– Interpretation?
• pH 7.05, pC02 100, HC03 32
– What is his “normal” pC02?
Chronic Respiratory Acidosis
• You know that the HC03 increases in a 1:3
ratio to the increase in pC02
• If the HC03 is up by 7, the pC02 is
chronically up by about 20
• What is the differential dx of respiratory
acidosis?
Respiratory Acidosis
• HYPOVENTILATION
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Brain stem
Spinal Cord
Motor neuron
Peripheral nerve
NMJ
Muscle
Chest wall
Obesity hypoventilation
• IMPAIRED GAS
EXCHANGE
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Airway obstruction
Bronchospasm
Pneumonia
Pulmonary edema
PE
Aspiration
COPD
ANION GAP
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What is the anion gap?
What is the formula?
What is a “normal” anion gap?
What could cause a LOW anion gap?
ANION GAP
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Na+
K+
Ca++
Mg++
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ClHCO3P04S04Albumin
Organic acids
Low Anion Gap
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Hypoalbuminemia
Increased Ca, Mg, K
Lithium intoxication
Multiple myeloma
What is the Delta Gap?
• Delta Gap
– Change in AG – change in HC03
– (AG – 12) – (24 – HC03)
– Essentially looks for similar changes in anion
and drop in bicarb as a marker for additional
acid base disorders
– Questionable validity
Case
• 55yo male, street person, found lying in snow by
CPS, confused, no history, denies ingestions, no
PMHx or meds
• Temp 33, HR 72, BP 120/60, RR 28, sats 98%,
GCS 13
• Exam unremarkable except shivering
• ABG: pH 7.26, pC02 13, HC03 5
• Na 129, K 4.7, Cl 88, C02 7
• What is the A/B disorder?
• What other labs do you want?
Case
BUN 15, Cr 136
ASA –ve
Lactate 1.2
CarboxyHb 0.8%
EtOH –ve
Toxic alcohols –ve
Glucose 2
Urine ketone +ve
• What is the dx?
• What is the ddx of an
increased AGMA?
Increased AGMA:
AMUDPILECATO
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A
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ASA
Methanol, Metformin
Uremia
DKA
Paraldehyde,
Phenformin
Isoniazid, Iron
Lactate
Ethylene glycol
• C
• A
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CO, CN
AKA, alcohol
Toluene,
Theophylline
Other
– H2S
– Any toxin that leads to
lactic acidosis (essentially
all severe overdoses with
hypotension, seizures)
How to narrow the ddx with an
increased AGMA
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Normal glucose rules out DKA
BUN, Creatinine
ASA level
ABG for carboxyHb, lactate
Toxic alcohol level
Which toxins cause an increased
AGMA independent of lactate?
Methanol
Ethylene glycol
ASA
10yo girl, DKA, pH is 6.9
• Would you give bicarb?
• What is the theoretical reason to give bicarb
for acidemia?
• What are the complications?
• What are indications for bicarb?
• Is there any evidence for or against bicarb?
Metabolic Acidosis and
bicarbonate therapy:
• Complications
– Paradoxical CSF
acidosis
– Hypokalemia
– Hypocalcemia
– Hypernatremia
– Volume overload
– Overshoot alkalosis
• Indications for Bicarb
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pH < 7.10
ASA
Methanol
Ethylene glycol
NOT DKA (increased
rates of cerebral
edema): Glaver NEJM
2001
Ddx of Normal AGMA
• Gain acid
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Acid ingestion
Obstructive uropathy
Pyelonephritis
Distal renal tubular
acidosis
• Bicarb loss
– GI
• Diarrhea
• Bowel fistual
• Pancreatic, biliary, or
intestinal drains
• Ureteroenterostomy
– Renal
• Proximal RTA
• Acetazolamide
Ddx of Metabolic Alkalosis
• Chloride Responsive
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Vomiting
NG drainage
Diuretics
Vilous adenoma
• Chloride Resistant
– Primary
hyperaldosteronism
– Cushing’s
– Steroids
– Ectopic ACTH
– Barter’s syndrome
A mud pile cat!
SSSSSuffering ssssssucatash: look at the size of those………