Examkin

Soru

Zorluk: ZorNephrology

A 62-year-old man is brought to the emergency department by emergency medical services due to severe confusion and lethargy. His family reports that he has been increasingly difficult to arouse since yesterday morning. The patient has end-stage renal disease secondary to hypertensive nephrosclerosis and normally receives hemodialysis three days a week. However, he missed his last two scheduled treatments due to transportation issues. His past medical history is also significant for severe chronic obstructive pulmonary disease, for which he requires continuous home oxygen therapy.

Upon arrival, his temperature is 36.8∘C36.8^\circ C (98.2∘F98.2^\circ F), blood pressure is 158/92158/92 mm Hg, heart rate is 105105/min, and respiratory rate is 1212/min and shallow. He is somnolent and oriented only to person. Pulmonary examination reveals a prolonged expiratory phase with diffuse expiratory wheezing.

Arterial blood gas and serum laboratory analysis reveal the following:

ParameterResultReference Range
Arterial Blood Gas (on 2L O₂)
pH7.147.147.35−7.457.35 - 7.45
PaCO₂4242 mm Hg35−4535 - 45 mm Hg
PaO₂6868 mm Hg75−10575 - 105 mm Hg
Serum Chemistry
Sodium136136 mEq/L136−145136 - 145 mEq/L
Potassium6.46.4 mEq/L3.5−5.03.5 - 5.0 mEq/L
Chloride9898 mEq/L95−10595 - 105 mEq/L
Bicarbonate1414 mEq/L22−2822 - 28 mEq/L
Blood urea nitrogen112112 mg/dL8−208 - 20 mg/dL
Creatinine8.88.8 mg/dL0.7−1.30.7 - 1.3 mg/dL

Based on these laboratory findings, which of the following best describes this patient's primary acid-base abnormalities?

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

Cevap

The patient has a mixed acid-base disorder characterized by a high anion gap metabolic acidosis and a concurrent respiratory acidosis.
The correct diagnosis is a mixed disorder consisting of a high anion gap metabolic acidosis and a concurrent respiratory acidosis. The patient's missed hemodialysis sessions have led to uremia, resulting in a primary metabolic acidosis with a calculated anion gap of 24 mEq/L (136−[98+14]136 - [98 + 14]). To determine if respiratory compensation is adequate, Winter's formula is applied: Expected PaCO2 = (1.5×14)+8=29±2(1.5 \times 14) + 8 = 29 \pm 2 mm Hg. The patient's actual measured PaCO2 is 42 mm Hg. Because the actual PaCO2 is substantially higher than the expected compensated value, there is a coexisting primary respiratory acidosis, caused by his severe COPD and respiratory muscle fatigue.

Adım Adım Çözüm

1
Assess the primary acid-base disturbance by looking at the pH and bicarbonate.
The pH is acidemic (7.147.14) and the serum bicarbonate is low (1414 mEq/L), establishing a primary metabolic acidosis.
Identifying the primary direction of the pH and the primary driver (HCO3- vs PaCO2) is the first step in acid-base interpretation.
2
Calculate the serum anion gap (AG) to classify the metabolic acidosis.
AG=Sodium−(Chloride+Bicarbonate)=136−(98+14)=24AG = Sodium - (Chloride + Bicarbonate) = 136 - (98 + 14) = 24 mEq/L. This indicates a high anion gap metabolic acidosis (HAGMA).
An elevated anion gap (>12> 12 mEq/L) reveals the presence of unmeasured anions, which in this case are uremic toxins due to missed hemodialysis.
3
Apply Winter's formula to calculate the expected respiratory compensation (expected PaCO2) for the metabolic acidosis.
ExpectedPaCO2=(1.5×HCO3−)+8±2Expected PaCO_2 = (1.5 \times HCO_3^-) + 8 \pm 2. Therefore, (1.5×14)+8=21+8=29±2(1.5 \times 14) + 8 = 21 + 8 = 29 \pm 2 mm Hg (range 27−3127-31 mm Hg).
Winter's formula determines how much the lungs should physiologically hyperventilate to compensate for the metabolic acid load.
4
Compare the actual measured PaCO2 to the expected PaCO2 calculated in Step 3.
The actual PaCO2 is 4242 mm Hg, which is significantly greater than the expected range of 27−3127-31 mm Hg.
Because the actual PaCO2 is higher than what is required for adequate compensation, the patient is hypoventilating relative to their metabolic state, indicating a superimposed primary respiratory acidosis (due to COPD).

Anahtar Kavram

Mixed Acid-Base Disorders: Utilizing Winter's Formula
Bu soruyu puanla

Konular

Nephrology

Bu konudan daha fazla soru