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Zorluk: Çok zorNephrology

A 68-year-old man with a history of type 2 diabetes mellitus and chronic obstructive pulmonary disease (COPD) is brought to the emergency department by his daughter due to lethargy and confusion. The daughter reports that he has had severe nausea and vomiting for the past 3 days and has been unable to eat or take his usual medications, including insulin. On physical examination, the patient is lethargic and oriented to person only. His temperature is 37.2°C (99.0°F), blood pressure is 90/60 mm Hg, pulse is 115/min, and respiratory rate is 24/min with shallow breaths. Mucous membranes are extremely dry, and skin turgor is decreased. Pulmonary examination reveals prolonged expiration with bilateral wheezes and decreased breath sounds.

Laboratory results are as follows:

Arterial blood gas (room air):
pHpH: 7.25
PaCO2PaCO_2: 50 mm Hg
PaO2PaO_2: 55 mm Hg
HCO3−HCO_3^-: 21 mEq/L

Serum chemistry:
Na+Na^+: 140 mEq/L
K+K^+: 4.8 mEq/L
Cl−Cl^-: 90 mEq/L
HCO3−HCO_3^-: 21 mEq/L
Blood urea nitrogen: 45 mg/dL
Creatinine: 2.2 mg/dL
Glucose: 450 mg/dL
Albumin: 4.0 g/dL

Urinalysis is strongly positive for ketones.

Which of the following best describes this patient's primary acid-base disturbances?

  1. High anion gap metabolic acidosis, metabolic alkalosis, and respiratory acidosisCevap
  2. B
    High anion gap metabolic acidosis and respiratory acidosis
  3. C
    High anion gap metabolic acidosis and metabolic alkalosis
  4. D
    Non-anion gap metabolic acidosis and respiratory acidosis
  5. E
    Respiratory acidosis and metabolic alkalosis

Cevap

High anion gap metabolic acidosis, metabolic alkalosis, and respiratory acidosis
This patient has a triple acid-base disorder. First, the anion gap is significantly elevated at 29 mEq/L (140−(90+21)=29140 - (90 + 21) = 29), confirming a primary high anion gap metabolic acidosis (HAGMA), driven by diabetic ketoacidosis. Second, Winter's formula (1.5×21+8=39.51.5 \times 21 + 8 = 39.5) predicts a PaCO2PaCO_2 of roughly 39.5 mm Hg. The patient's actual PaCO2PaCO_2 is 50 mm Hg; this relative hypercapnia confirms a superimposed primary respiratory acidosis (due to COPD exacerbation and hypoventilation). Finally, analyzing the delta-delta reveals a hidden third disorder. The ΔAG\Delta AG is 17 (29−12=1729 - 12 = 17). Adding this to the measured bicarbonate yields a corrected bicarbonate of 38 mEq/L (21+17=3821 + 17 = 38). Because this value is well above the normal 24-26 mEq/L, there is a concurrent primary metabolic alkalosis, perfectly consistent with his 3-day history of severe vomiting.

Adım Adım Çözüm

1
Assess the primary pH disorder.
The patient has an arterial pHpH of 7.25, indicating acidemia.
Establishing the initial direction of the pH abnormality is the first step in acid-base interpretation.
2
Calculate the serum anion gap (AG).
AG=Na+−(Cl−+HCO3−)=140−(90+21)=29AG = Na^+ - (Cl^- + HCO_3^-) = 140 - (90 + 21) = 29
An AG greater than 12 indicates the presence of a primary high anion gap metabolic acidosis (HAGMA). In this patient, the HAGMA is secondary to diabetic ketoacidosis (hyperglycemia, positive ketones) and potentially lactic acidosis/uremia.
3
Determine if respiratory compensation is appropriate using Winter's formula.
Expected PaCO2=1.5×HCO3−+8±2=1.5(21)+8=39.5±2Expected\ PaCO_2 = 1.5 \times HCO_3^- + 8 \pm 2 = 1.5(21) + 8 = 39.5 \pm 2 (Range: 37.5 to 41.5 mm Hg). The measured PaCO2PaCO_2 is 50 mm Hg.
Because the measured PaCO2PaCO_2 (50 mm Hg) is significantly higher than the expected compensated PaCO2PaCO_2 (39.5 mm Hg), there is a concurrent primary respiratory acidosis. This is clinically consistent with the patient's COPD exacerbation and respiratory fatigue.
4
Calculate the delta gap and corrected bicarbonate to check for a third disorder (Delta-Delta).
ΔAG=Measured AG−Normal AG=29−12=17\Delta AG = Measured\ AG - Normal\ AG = 29 - 12 = 17. Corrected HCO3−=Measured HCO3−+ΔAG=21+17=38mEq/LCorrected\ HCO_3^- = Measured\ HCO_3^- + \Delta AG = 21 + 17 = 38 mEq/L.
The corrected HCO3−HCO_3^- represents what the bicarbonate would be if the anion gap metabolic acidosis were resolved. A corrected HCO3−HCO_3^- > 26 mEq/L indicates a concurrent primary metabolic alkalosis, which is clinically explained by the patient's 3 days of severe vomiting (loss of gastric HClHCl).

Anahtar Kavram

Diagnosis of triple acid-base disorders requires sequential calculation of the anion gap, expected respiratory compensation (Winter's formula), and the delta-delta gap.

Alternatif Yöntem

Instead of the additive Delta-Delta calculation (Measured HCO3−+ΔAGMeasured\ HCO_3^- + \Delta AG), the Delta Ratio (ΔAG/ΔHCO3−\Delta AG / \Delta HCO_3^-) can be used. ΔAG=29−12=17\Delta AG = 29 - 12 = 17. ΔHCO3−=24−21=3\Delta HCO_3^- = 24 - 21 = 3. Delta Ratio = 17/3=5.617 / 3 = 5.6. A Delta Ratio > 2.0 strongly indicates a concurrent metabolic alkalosis.
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