I85PREP
⌘ K
CRT study materials
CRT study resources

CRT (CREST): Patient Data - TMC Detailed Content Outline (2020–2026)

CRT · Work through your exam, one topic at a time.

All guide sections

Patient Data - TMC Detailed Content Outline (2020–2026)

Domain I, Patient Data, covers the interpretive items on the TMC: history, physical findings, vital signs, arterial blood gases, pulmonary function, imaging, hemodynamic and monitor data. The exam asks you to collect the data, decide what it means, and choose the next action - not simply to name a value.

Read the ABG in a fixed order

  • pH first: acidemia < 7.35, alkalemia > 7.45.
  • PaCO2 next: it moves opposite to pH in respiratory disorders (high CO2 with low pH = respiratory acidosis) and in the same direction in metabolic disorders.
  • Compensation: for every 10 mmHg rise in PaCO2, HCO3 rises about 1 mEq/L if acute and 3–4 if chronic; for every 10 mmHg fall, HCO3 falls about 2 (acute) or 4–5 (chronic).
  • Oxygenation: always read PaO2 with its FiO2 attached. PAO2 = FiO2 × (760 − 47) − PaCO2/0.8; the A–a gradient is normally about age/4 + 4. A normal gradient with hypoxemia points to hypoventilation or low inspired oxygen; a widened gradient points to V/Q mismatch, shunt or diffusion defect.

Spirometry and volumes

FEV1/FVC below 0.70 (or below the lower limit of normal) defines obstruction; a rise of ≥12% and ≥200 mL after bronchodilator is significant reversibility. A low FVC with a preserved ratio suggests restriction, confirmed by TLC < 80% predicted. DLCO falls in emphysema, interstitial disease and anemia; it is normal or high in asthma.

Hemodynamics and monitors

CVP 2–6 mmHg, PCWP 6–12 mmHg, cardiac index 2.5–4.0 L/min/m², SvO2 65–75%. High PCWP with low cardiac index suggests cardiogenic causes; low PCWP with low index suggests hypovolemia.

Worked example

pH 7.28, PaCO2 60, HCO3 27, PaO2 55 on room air. Acidemia with elevated CO2 is respiratory acidosis. Expected acute HCO3 is 24 + 2 = 26, so 27 represents acute (or minimally compensated) change. PAO2 = 0.21 × 713 − 75 ≈ 75 mmHg; A–a gradient ≈ 20, only mildly widened, so hypoventilation dominates. Action: support ventilation, titrate oxygen to target, treat the cause - not bicarbonate.

Traps that cost marks

  • Calling hypercapnia "chronic" without checking HCO3 or a baseline value.
  • Reading PaO2 without recording the FiO2 it was drawn on.
  • Using SpO2 to judge ventilation.
  • Accepting compensation that is numerically impossible - that signals a mixed disorder.
  • Labeling restriction from spirometry alone without lung volumes.

Equipment - TMC Detailed Content Outline (2020–2026)

Domain II, Equipment, tests whether you can select a device, set it correctly, verify its performance and troubleshoot it at the bedside. Items cover oxygen delivery, humidification and aerosol devices, ventilators and alarms, artificial airways and monitors.

Oxygen delivery

  • Low-flow systems (nasal cannula 1–6 L/min ≈ 24–44%; simple mask 5–10 L/min ≈ 35–55%) deliver variable FiO2 that falls as inspiratory demand rises.
  • Air-entrainment systems give a fixed FiO2 when the total flow exceeds demand: 24% at 25:1, 28% at 10:1, 35% at 5:1, 40% at 3:1, 50% at about 1.7:1 air:oxygen.
  • Cylinder duration = (gauge pressure × cylinder factor) ÷ flow. E-cylinder factor 0.28 L/psi, H/K 3.14, M 1.56.

Humidification and aerosol

Heated humidifiers target 31–37 °C at the airway; HMEs are for short-term use and are avoided with copious or bloody secretions, hypothermia and very low tidal volumes. Small-volume nebulizers run at 6–8 L/min with 3–5 mL fill; ultrasonic nebulizers are used for continuous bland aerosol.

Ventilator troubleshooting

Compare peak and plateau pressures. A rise in peak only (gradient > 5–10 cm H2O) means a resistance problem - secretions, bronchospasm, biting, kinked tube. A rise in plateau means a compliance problem - pneumothorax, atelectasis, ARDS progression, abdominal distension. A low-pressure or disconnect alarm means circuit leak, cuff leak or patient disconnection.

Monitors

Pulse oximetry is affected by poor perfusion, motion, nail polish and dyshemoglobins (normal in carbon monoxide poisoning, low in methemoglobinemia) and never assesses ventilation. Capnography (PetCO2 35–45 mmHg) reflects ventilation: a sudden drop suggests disconnection, embolism or arrest; a gradual rise suggests hypoventilation or fever.

Worked example

A ventilated patient shows peak 48 cm H2O, plateau 22 cm H2O, with coarse breath sounds. The gradient of 26 cm H2O is a resistance problem, not a compliance problem; the plateau is acceptable, so the lung is not the issue. Action: check for secretions and suction, inspect for biting or a kinked circuit, and auscultate for bronchospasm before touching PEEP or tidal volume.

Traps that cost marks

  • Assuming every high-pressure alarm means pneumothorax.
  • Running a Venturi mask below the patient's inspiratory demand, which lowers the delivered FiO2.
  • Using an HME when secretions are copious or bloody.
  • Trusting SpO2 alone when titrating oxygen in a patient who may be hypercapnic.

Procedures - TMC Detailed Content Outline (2020–2026)

Domain III, Procedures, tests protocol execution and, just as heavily, evaluation of the patient's response. Items cover bronchial hygiene, hyperinflation therapy, aerosol therapy, airway care and suctioning, ventilator initiation and weaning, resuscitation and infection control.

Airway clearance and hyperinflation

Postural drainage positions are chosen by lobe; avoid head-down positioning with elevated intracranial pressure, uncontrolled hypertension or recent hemoptysis. PEP, flutter valves and high-frequency chest wall oscillation are alternatives when positioning is unsafe. Intermittent positive-pressure breathing is contraindicated with untreated pneumothorax, bullous emphysema and active hemoptysis. Incentive spirometry is typically 10 sustained breaths per hour while awake.

Suctioning

Indicate suctioning by visible secretions, coarse crackles, rising peak pressures or desaturation - not by schedule. Preoxygenate 30–60 seconds at FiO2 1.0, use a catheter no larger than half the artificial airway's internal diameter, apply 80–120 mmHg negative pressure for 10–15 seconds, and use sterile technique. Watch for hypoxia, vagal bradycardia and mucosal trauma.

Ventilator initiation and weaning

Initial settings: tidal volume 6–8 mL/kg predicted body weight (4–6 mL/kg in ARDS), rate 12–16, PEEP 5 cm H2O, FiO2 titrated to PaO2 60–80 mmHg or SpO2 88–95%. Weaning readiness requires the cause to be resolved plus objective measures: PaO2/FiO2 above roughly 150–200, PEEP ≤ 5–8, hemodynamic stability, RSBI < 105, negative inspiratory force −20 to −30 cm H2O, vital capacity > 10 mL/kg.

Resuscitation and infection control

CPR at 30:2, 100–120 compressions/min, 5–6 cm depth, with bag-mask ventilation on 100% oxygen and without hyperventilation. Hand hygiene, PPE, closed suction where appropriate and disinfection per manufacturer instructions are standard.

Worked example

A post-operative patient has shallow breathing, basilar crackles and SpO2 91% on 2 L/min nasal cannula, with atelectasis on chest radiograph. First step: coach coughing and deep breathing and start incentive spirometry every hour while awake. Reassess within 30–60 minutes using breath sounds and SpO2. If atelectasis persists, add PEP or positive-pressure hyperinflation; if oxygenation continues to decline, escalate to noninvasive ventilation and notify the physician. Each step is documented and evaluated before moving on.

Traps that cost marks

  • Suctioning on a fixed schedule instead of by indication.
  • Suctioning longer than 15 seconds or without preoxygenation.
  • Weaning without objective criteria.
  • Skipping reassessment after a therapy - the response is part of the procedure.