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Zorluk: OrtaNephrology

Emergency medical services bring a 68-year-old man to the hospital after his daughter found him lethargic and struggling to breathe. For the past 48 hours, he has experienced a fever and a worsening productive cough. His medical history is significant for severe chronic obstructive pulmonary disease (COPD), hypertension, and type 2 diabetes mellitus. His daily medications include tiotropium, lisinopril, and empagliflozin.

Vital signs are:
Temperature: 38.2°C (100.8°F)
Blood pressure: 110/65 mm Hg
Pulse: 118/min
Respirations: 26/min
Oxygen saturation: 86% on room air

Physical examination reveals a somnolent but arousable patient. Lung auscultation demonstrates diffuse wheezing and right lower lobe crackles with a prolonged expiratory phase.

Laboratory results are as follows:

ParameterResult
Sodium140 mEq/L
Potassium4.6 mEq/L
Chloride104 mEq/L
Bicarbonate12 mEq/L
Blood urea nitrogen32 mg/dL
Creatinine1.4 mg/dL
Glucose195 mg/dL
Albumin4.0 g/dL

Arterial blood gas analysis on room air reveals:

ParameterResult
pH7.12
pCO2_238 mm Hg
pO2_256 mm Hg

Which of the following best characterizes this patient's acid-base status?

  1. High anion gap metabolic acidosis with concurrent respiratory acidosisCevap
  2. B
    High anion gap metabolic acidosis with appropriate respiratory compensation
  3. C
    High anion gap metabolic acidosis with concurrent respiratory alkalosis
  4. D
    Normal anion gap metabolic acidosis with concurrent respiratory acidosis
  5. E
    Mixed high and normal anion gap metabolic acidosis with appropriate respiratory compensation

Cevap

High anion gap metabolic acidosis with concurrent respiratory acidosis
This patient's acid-base status is evaluated in a stepwise fashion. First, the arterial pH is 7.12, indicating acidemia. The low serum bicarbonate (12 mEq/L) confirms a metabolic acidosis. Second, the anion gap must be calculated: AG=Na+−(Cl−+HCO3−)=140−(104+12)=24AG = Na^+ - (Cl^- + HCO_3^-) = 140 - (104 + 12) = 24 mEq/L. A normal anion gap is 10-14 mEq/L, so the patient has a high anion gap metabolic acidosis (HAGMA), which in this clinical scenario is likely secondary to sepsis or euglycemic diabetic ketoacidosis from empagliflozin use.

Next, to evaluate for mixed acid-base disorders, Winter's formula (pCO2=1.5×[HCO3−]+8±2pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2) is used to determine the expected respiratory compensation. For this patient, the expected pCO2=1.5×12+8=26±2pCO_2 = 1.5 \times 12 + 8 = 26 \pm 2 mm Hg. The patient's actual measured pCO2pCO_2 is 38 mm Hg. Because the actual pCO2pCO_2 is significantly higher than the expected range of 24-28 mm Hg, there is relative CO2CO_2 retention, confirming the presence of a concurrent primary respiratory acidosis. This is clinically consistent with a patient experiencing a COPD exacerbation and pneumonia, leading to respiratory fatigue and hypoventilation.

Adım Adım Çözüm

1
Calculate the anion gap to determine the primary metabolic disturbance.
AG = Na+−(Cl−+HCO3−)=140−(104+12)=24Na^+ - (Cl^- + HCO_3^-) = 140 - (104 + 12) = 24 mEq/L.
An anion gap > 12 mEq/L confirms the presence of a high anion gap metabolic acidosis (HAGMA).
2
Apply Winter's formula to determine if respiratory compensation is appropriate.
Expected pCO2=1.5×[HCO3−]+8±2=1.5×12+8±2=26±2pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2 = 1.5 \times 12 + 8 \pm 2 = 26 \pm 2 mm Hg.
This establishes the target pCO2pCO_2 range (24-28 mm Hg) the lungs should achieve to compensate for the metabolic acidosis.
3
Compare the actual pCO2pCO_2 to the expected pCO2pCO_2 calculated from Winter's formula.
The actual pCO2pCO_2 is 38 mm Hg, which is > 28 mm Hg.
An actual pCO2pCO_2 that is higher than the expected calculated range indicates a concurrent respiratory acidosis (relative CO2CO_2 retention).

Anahtar Kavram

In patients with metabolic acidosis, Winter's formula is essential to determine whether the respiratory response is adequate; an actual pCO2 higher than the expected range indicates a concurrent respiratory acidosis.
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