RT (CRT/RRT) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Winter's formula

Expected PaCO2 in metabolic acidosis equals (1.5 × HCO3) + 8 ± 2; a measured PaCO2 outside this range indicates a coexisting respiratory disorder.

Alveolar-arterial oxygen gradient

PAO2 minus PaO2; normal is roughly (age ÷ 4) + 4 mmHg on room air, about 5–20 mmHg; widening suggests shunt, V/Q mismatch, or diffusion defect.

Arterial oxygen content formula

CaO2 = (1.34 × hemoglobin × SaO2) + (0.003 × PaO2); normal is about 18–20 mL O2 per 100 mL blood; most oxygen is bound to hemoglobin.

Dead space Bohr equation

Vd/Vt = (PaCO2 − mixed expired PECO2) ÷ PaCO2; normal dead space fraction is about 0.2–0.4; values above 0.6 markedly reduce alveolar ventilation.

Obstructive pattern on spirometry

FEV1/FVC ratio below 0.70 with a reduced FEV1; severity is graded by FEV1 percent predicted, and a bronchodilator response of 12% and 200 mL indicates reversibility.

Cardiac index normal range

Cardiac index equals cardiac output divided by body surface area; normal is 2.5–4.0 L/min/m2; below 2.2 L/min/m2 indicates inadequate tissue perfusion.

Systemic vascular resistance formula

SVR = (mean arterial pressure − central venous pressure) ÷ cardiac output × 80; normal is about 800–1200 dynes·sec·cm−5, and it rises in septic shock.

Cylinder duration calculation

Minutes of oxygen remaining = (gauge pressure in psi × cylinder factor) ÷ flow in L/min; E-cylinder factor is 0.28, H-cylinder 3.14, M-cylinder 1.56.

Venturi mask air-oxygen ratio

Entrainment ratio = (100 − FiO2) ÷ (FiO2 − 21); a 24% Venturi mask uses about 25:1 air-to-oxygen and a 40% mask about 3:1.

Nasal cannula FiO2 estimate

Each liter per minute of nasal cannula flow adds roughly 3–4% FiO2 above room air; 1–6 L/min delivers approximately 24–44%.

Nonrebreather mask FiO2

A nonrebreather with reservoir and one-way valves delivers 60–95% FiO2 at 10–15 L/min; the reservoir must remain inflated and the mask must seal.

COPD oxygen target saturation

In patients at risk for hypercapnia, titrate oxygen to SpO2 88–92%; uncontrolled high FiO2 can worsen V/Q mismatch and cause absorption atelectasis.

Liquid oxygen expansion ratio

One liter of liquid oxygen expands to about 860 liters of gaseous oxygen at room temperature and pressure; this is why small liquid reservoirs last so long.

Oxygen toxicity threshold

Prolonged exposure to FiO2 above 0.60 can cause absorption atelectasis, tracheobronchitis, and pulmonary edema; use the lowest FiO2 that keeps PaO2 55–80 mmHg or SpO2 88–95%.

Postural drainage position duration

Each of the postural drainage positions is typically held 3–5 minutes, with total treatment of 20–30 minutes; treatment is scheduled 1–2 hours after meals.

PEP therapy pressure range

Positive expiratory pressure devices typically apply 10–20 cmH2O during expiration, helping mobilize secretions and maintain airway patency in patients with cystic fibrosis or bronchiectasis.

Suction catheter size rule

Catheter French size should be about twice the endotracheal tube internal diameter in millimeters, and no more than half the tube's internal diameter.

Adult suction negative pressure

Adult suction pressure is typically −80 to −120 mmHg; each pass should last no more than 10–15 seconds and be preceded by hyperoxygenation to prevent hypoxemia.

Incentive spirometry goal

Patients perform about 10 slow, sustained maximal inhalations per hour while awake, holding each breath 3–5 seconds, to prevent or treat atelectasis after surgery.

Aerosol particle deposition size

Particles of 2–5 micrometers deposit in the lower airways and alveoli; larger particles impact in the upper airway, and particles below 1 micrometer are largely exhaled.

Endotracheal tube depth formula

In adults, insertion depth at the incisors in centimeters is roughly three times the tube internal diameter in millimeters; an 8.0 tube is placed about 24 cm.

Endotracheal tube cuff pressure

Cuff pressure should be maintained at 20–30 cmH2O using a manometer; pressures above 30 cmH2O impair tracheal capillary perfusion and risk tracheal stenosis or necrosis.

Confirming endotracheal tube placement

Continuous capnography with an end-tidal CO2 waveform is the gold standard; also check bilateral breath sounds, chest rise, and a chest radiograph showing the tip 3–5 cm above the carina.

Mallampati airway classification

Class I shows soft palate, uvula, and pillars; class IV shows only hard palate. Classes III and IV predict a difficult laryngoscopy and mask ventilation.

Cormack-Lehane laryngoscopy grades

Grade I shows the entire glottis, grade II partial glottis, grade III only the epiglottis, and grade IV only the soft palate; grades III–IV indicate difficult visualization.

Tracheostomy tube placement site

An elective tracheostomy is usually created between the second and fourth tracheal rings, avoiding the first ring and the cricoid cartilage to reduce the risk of stenosis.

Ideal body weight formula

Males: 50 + 2.3 × (height in inches − 60) kg; females: 45.5 + 2.3 × (height in inches − 60) kg; tidal volume of 6–8 mL/kg uses this weight, not actual weight.

Lung-protective tidal volume

Ventilate at 4–6 mL/kg predicted body weight in ARDS, keeping plateau pressure at or below 30 cmH2O and driving pressure at or below 15 cmH2O.

Auto-PEEP detection

Perform an end-expiratory hold; if total PEEP exceeds the set PEEP, auto-PEEP is present. Causes include high rate, short expiratory time, and high tidal volume.

Static compliance calculation

Static compliance = tidal volume ÷ (plateau pressure − PEEP); normal is about 60–100 mL/cmH2O, and values fall with ARDS, pneumothorax, or abdominal distension.

Rapid shallow breathing index

RSBI = respiratory rate ÷ spontaneous tidal volume in liters; a value below 105 predicts successful weaning from mechanical ventilation, and it is measured during a spontaneous breathing trial.

High peak airway pressure causes

When peak pressure rises but plateau is normal, the problem is resistance: secretions, bronchospasm, or a kinked tube; when both rise, suspect decreased compliance.