ACID/BASE DISORDERS

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ACID/BASE DISORDERS

• Resident Rounds
• Rob Hall PGY3
• April 24, 2003

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Objectives

• Approach to A/B disorders
• Clinical examples of each disorder
• Differential dx of each disorder
• Combined disorders

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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

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How to interpret an ABG

• 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?

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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!!

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Compensationthe clue to mixed disorders

• ACIDOSIS
• Respiratory
• Acute 110
• Chronic 13
• Metabolic 11

• ALKALOSIS
• Respiratory
• Acute 110
• Chronic 12
• Metabolic 0.61

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80 female with suspected ischemic gut

• pH 6.9, PC02 35, HCO3 8
• Why is the acidemia important?

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Consequences of SevereAcid 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

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Case

• 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?

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Respiratory Alkalosis

• Pain
• Anxiety
• Pregnancy
• Pulmonary disease/hypoxia
• CNS disorder
• Thyrotoxicosis
• ASA

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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?

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Chronic Respiratory Acidosis

• You know that the HC03 increases in a 13 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?

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Respiratory Acidosis

• HYPOVENTILATION
• Brain stem
• Spinal Cord
• Motor neuron
• Peripheral nerve
• NMJ
• Muscle
• Chest wall
• Obesity hypoventilation

• IMPAIRED GAS EXCHANGE
• Airway obstruction
• Bronchospasm
• Pneumonia
• Pulmonary edema
• PE
• Aspiration
• COPD

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ANION GAP

• What is the anion gap?
• What is the formula?
• What is a normal anion gap?
• What could cause a LOW anion gap?

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ANION GAP

• Na
• K
• Ca
• Mg

• Cl-
• HCO3-
• P04-
• S04-
• Albumin
• Organic acids

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Low Anion Gap

• Hypoalbuminemia
• Increased Ca, Mg, K
• Lithium intoxication
• Multiple myeloma

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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

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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?

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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?

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Increased AGMAAMUDPILECATO

• A ASA
• M Methanol, Metformin
• U Uremia
• D DKA
• P Paraldehyde, Phenformin
• I Isoniazid, Iron
• L Lactate
• E Ethylene glycol

• C CO, CN
• A AKA, alcohol
• T Toluene, Theophylline
• O Other
• H2S
• Any toxin that leads to lactic acidosis
  (essentially all severe overdoses with
  hypotension, seizures)

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How to narrow the ddx with an increased AGMA

• Normal glucose rules out DKA
• BUN, Creatinine
• ASA level
• ABG for carboxyHb, lactate
• Toxic alcohol level

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Which toxins cause an increased AGMA independent
of lactate?

• Methanol
• Ethylene glycol
• ASA

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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?

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Metabolic Acidosis and bicarbonate therapy

• Complications
• Paradoxical CSF acidosis
• Hypokalemia
• Hypocalcemia
• Hypernatremia
• Volume overload
• Overshoot alkalosis

• Indications for Bicarb
• pH lt 7.10
• ASA
• Methanol
• Ethylene glycol
• NOT DKA (increased rates of cerebral edema)
  Glaver NEJM 2001

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Ddx of Normal AGMA

• Gain acid
• 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

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Ddx of Metabolic Alkalosis

• Chloride Responsive
• Vomiting
• NG drainage
• Diuretics
• Vilous adenoma

• Chloride Resistant
• Primary hyperaldosteronism
• Cushings
• Steroids
• Ectopic ACTH
• Barters syndrome

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A mud pile cat!

• SSSSSuffering ssssssucatash look at the size of
  those