Examkin

Soru

Zorluk: OrtaPulmonary and Critical Care

A 5858-year-old man is evaluated in the intensive care unit for worsening respiratory distress. He was admitted 2424 hours ago for septic shock secondary to community-acquired pneumonia and was started on broad-spectrum intravenous antibiotics and a norepinephrine infusion. He is currently receiving high-flow nasal cannula oxygen therapy. He appears restless and is using accessory muscles of respiration.

Vital signs:
ParameterValue
Temperature38.6∘C38.6^\circ\text{C} (101.5∘F101.5^\circ\text{F})
Blood pressure95/60 mm Hg95/60\text{ mm Hg}
Pulse122/min122/\text{min}
Respirations34/min34/\text{min}
Pulse oximetry91%91\%
Laboratory results:
TestResult
Sodium139 mEq/L139\text{ mEq/L}
Potassium4.6 mEq/L4.6\text{ mEq/L}
Chloride103 mEq/L103\text{ mEq/L}
Bicarbonate12 mEq/L12\text{ mEq/L}
Blood urea nitrogen42 mg/dL42\text{ mg/dL}
Creatinine2.1 mg/dL2.1\text{ mg/dL}
Lactate5.5 mmol/L5.5\text{ mmol/L}
Arterial blood gas (on high-flow oxygen):
ParameterValue
pH7.187.18
PaCO2\text{PaCO}_234 mm Hg34\text{ mm Hg}
PaO2\text{PaO}_265 mm Hg65\text{ mm Hg}

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

  1. A
    Primary metabolic acidosis with adequate respiratory compensation
  2. Primary metabolic acidosis with a superimposed respiratory acidosisCevap
  3. C
    Primary metabolic acidosis with a superimposed respiratory alkalosis
  4. D
    Primary respiratory acidosis with adequate metabolic compensation
  5. E
    Primary respiratory alkalosis with a superimposed metabolic acidosis

Cevap

Primary metabolic acidosis with a superimposed respiratory acidosis
This patient has severe acidemia (pH 7.187.18) driven by a low serum bicarbonate (12 mEq/L12\text{ mEq/L}), which establishes a primary metabolic acidosis (lactic acidosis due to septic shock). To determine if the respiratory compensation is adequate, Winter's formula must be applied: Expected PaCO2=(1.5×HCO3−)+8±2\text{PaCO}_2 = (1.5 \times \text{HCO}_3^-) + 8 \pm 2. For this patient, the expected PaCO2=(1.5×12)+8=26±2 mm Hg\text{PaCO}_2 = (1.5 \times 12) + 8 = 26 \pm 2\text{ mm Hg} (range 24−28 mm Hg24-28\text{ mm Hg}). The patient's actual PaCO2\text{PaCO}_2 is 34 mm Hg34\text{ mm Hg}. Because the actual PaCO2\text{PaCO}_2 is greater than the expected range, there is a concurrent, superimposed respiratory acidosis. Clinically, despite the patient's tachypnea (respiratory rate of 34/min34/\text{min}), his alveolar ventilation is insufficient to meet his high metabolic demands, indicating respiratory muscle fatigue and impending respiratory failure.

Adım Adım Çözüm

1
Determine the primary acid-base disorder by evaluating the pH and bicarbonate levels.
The patient has a severely low pH of 7.18 (acidemia) and a low serum bicarbonate of 12 mEq/L.
An acidemia driven by a reduced bicarbonate level indicates a primary metabolic acidosis (in this case, secondary to elevated lactate from septic shock).
2
Calculate the expected respiratory compensation using Winter's formula.
Expected PaCO2 = (1.5 × 12) + 8 = 26 ± 2. Therefore, the expected compensatory range is 24 to 28 mm Hg.
Winter's formula determines if the lungs are appropriately compensating for a primary metabolic acidosis by increasing ventilation to blow off CO2.
3
Compare the patient's actual PaCO2 to the expected PaCO2 range.
The actual PaCO2 is 34 mm Hg, which is higher than the maximum expected value of 28 mm Hg.
An actual PaCO2 that exceeds the expected compensatory range indicates a concurrent, superimposed respiratory acidosis.

Anahtar Kavram

Evaluation of complex acid-base disturbances using Winter's formula to identify mixed metabolic and respiratory disorders.
Tahmini Süre:1m 30s
Bu soruyu puanla

Konular

Pulmonary and Critical Care

Bu konudan daha fazla soru