RT-27 · Analysis & Monitoring

Laboratory Data & Microbiology Interpretation

Electrolytes, CBC, coagulation, cardiac and sputum data read the way a respiratory therapist has to read them.

~16 min read3 concept sections·2 questions with rationale

What you'll be able to do

  • Interpret electrolytes that change ventilation and weaning
  • Use the CBC and coagulation panel before procedures
  • Apply cardiac markers to dyspnea differential
  • Read a sputum Gram stain and judge specimen quality
Concept breakdown
01

Electrolytes drive the ventilator

Weaning failures are frequently metabolic, not pulmonary.

  • Potassium 3.5–5.0 mEq/L. Hypokalemia weakens respiratory muscles and causes arrhythmias; beta agonists and diuretics drive it down.
  • Phosphate and magnesium deficiency directly weaken the diaphragm — correct both before blaming the lung for a failed spontaneous breathing trial.
  • Sodium 135–145 mEq/L; chloride 98–106 mEq/L. A low chloride with a high HCO3 points to a contraction alkalosis from diuresis.
  • Anion gap = Na − (Cl + HCO3), normal 8–12. A widened gap with metabolic acidosis means lactate, ketones, renal failure, or toxins.
  • Glucose extremes and overfeeding raise CO2 production and can prevent weaning.
At the bedside

A patient who fails an SBT with a phosphate of 1.2 has a laboratory problem wearing a pulmonary costume.

Practice quiz

Check yourself before you read the rationale.

Question 1 of 1

A ventilated patient repeatedly fails spontaneous breathing trials with rapid shallow breathing. Labs show potassium 3.0 mEq/L, phosphate 1.3 mg/dL, and magnesium 1.2 mg/dL. The best recommendation is:

Practice questions

Answer first, then read why the distractors fail.

Question 1

A ventilated patient repeatedly fails spontaneous breathing trials with rapid shallow breathing. Labs show potassium 3.0 mEq/L, phosphate 1.3 mg/dL, and magnesium 1.2 mg/dL. The best recommendation is:

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