RT (CRT/RRT) cheat sheet

Normal ABG on room air: pH 7.35–7.45, PaCO2 35–45 mmHg, HCO3− 22–26 mEq/L, PaO2 80–100 mmHg.

Metabolic acidosis: pH < 7.35 with HCO3− < 22; expected PaCO2 = (1.5 × HCO3−) + 8 ± 2 (Winter's formula).

Metabolic alkalosis: pH > 7.45 with HCO3− > 26; expected PaCO2 = (0.7 × HCO3−) + 21 ± 2.

Acute respiratory acidosis raises HCO3− about 1 mEq/L per 10 mmHg rise in PaCO2; chronic compensation raises it 3–4 mEq/L per 10 mmHg.

P/F ratio = PaO2 ÷ FiO2 (as a decimal); normal > 400, < 300 marks impaired oxygenation, < 200 severe impairment.

A–a gradient = PAO2 − PaO2, where PAO2 = (FiO2 × 713) − (PaCO2 ÷ 0.8); normal is roughly (age ÷ 4) + 4 mmHg.

CaO2 = (1.34 × Hb × SaO2) + (0.003 × PaO2); oxygen delivery DO2 = cardiac output × CaO2 × 10.

Vd/Vt = (PaCO2 − PECO2) ÷ PaCO2; normal 0.2–0.4, and a value above 0.6 indicates a large dead-space fraction.

Spirometry: FEV1/FVC < 0.70 indicates obstruction; a reduced FVC with a normal or high ratio suggests restriction.

Cylinder duration (min) = (gauge pressure in psi × cylinder factor) ÷ flow in L/min; factors are E = 0.28, M = 1.56, G = 2.41, H = 3.14.

Liquid oxygen expands 860:1 (1 L liquid ≈ 860 L gas); a bulk system feeds the wall pipeline at approximately 50 psi.

Nasal cannula at 1–6 L/min delivers about 24–44% FiO2; each L/min adds roughly 3–4% above room air.

Venturi mask entrainment ratio = (100 − FiO2) ÷ (FiO2 − 21); a 24% mask is about 25:1 air-to-oxygen, 28% about 10:1, 40% about 3:1.

Simple mask at 5–10 L/min gives 35–55% FiO2; a nonrebreather with reservoir at 10–15 L/min gives 60–95%.

High-flow nasal cannula delivers up to 60 L/min of heated, humidified gas at 21–100% FiO2 and generates roughly 1 cmH2O of positive pressure per 10 L/min.

Target SpO2 is 92–96% for most patients and 88–92% for those at risk of hypercapnia, such as COPD or obesity hypoventilation.

FiO2 above 0.60 for prolonged periods risks absorption atelectasis, tracheobronchitis, and pulmonary oxygen toxicity.

Pulse oximetry reads falsely high with carboxyhemoglobin and falsely low with methemoglobin, poor perfusion, motion artifact, or dark nail polish.

Postural drainage uses up to 12 positions; each is held 3–5 minutes for a total treatment of 20–30 minutes.

Recumbent drainage positions are avoided for 1–2 hours after meals because of vomiting and aspiration risk.

Percussion is applied with cupped hands over the affected lobe for 3–5 minutes per position; vibration is applied during exhalation.

PEP therapy applies 10–20 cmH2O of expiratory resistance; the Flutter and Acapella add oscillating airflow to aid secretion clearance.

Contraindications to postural drainage include raised intracranial pressure, unstable hemodynamics, recent hemoptysis, and untreated pneumothorax.

Suction catheter French size is about twice the ETT internal diameter in millimeters and should not exceed half that internal diameter.

Adult suction pressure is −80 to −120 mmHg; each pass lasts 10–15 seconds or less and is preceded by hyperoxygenation.

Aerosol particles of 2–5 µm deposit in the lower airways, particles above 5 µm impact in the upper airway, and particles below 1 µm are largely exhaled.

Incentive spirometry goal is about 10 sustained maximal inhalations per hour while awake, each held 3–5 seconds, to prevent atelectasis.

Adult ETT internal diameter: men 8.0–8.5 mm, women 7.0–7.5 mm; insertion depth at the incisors is roughly 3 × internal diameter (8.0 mm tube → 24 cm).

On chest radiograph the ETT tip should lie 3–5 cm above the carina with the head in a neutral position.

Continuous waveform capnography is the gold standard for confirming and continuously monitoring ETT placement.

ETT cuff pressure is kept at 20–30 cmH2O with a manometer; tracheal mucosal capillary pressure is about 30 cmH2O.

Mallampati class I shows palate, uvula, and pillars; class II palate and uvula; class III soft palate only; class IV hard palate only; classes III–IV predict difficulty.

Cormack-Lehane grades: I = full glottis, II = partial glottis, III = epiglottis only, IV = soft palate only.

A curved Macintosh blade is placed in the vallecula to indirectly lift the epiglottis; a straight Miller blade directly lifts the epiglottis.

BURP maneuver (backward, upward, rightward pressure) improves the glottic view; the Sellick maneuver is cricoid pressure applied to compress the esophagus.

Emergency cricothyrotomy is the adult rescue airway; it is generally avoided in young children because of the small cricoid cartilage.

Initial tidal volume is 6–8 mL/kg predicted body weight; in ARDS it is 4–6 mL/kg with plateau pressure ≤ 30 cmH2O.

Driving pressure = plateau pressure − PEEP; the ARDS target is ≤ 15 cmH2O.

Static compliance = Vt ÷ (Pplat − PEEP), normally 60–100 mL/cmH2O; dynamic compliance = Vt ÷ (Ppeak − PEEP).

Airway resistance = (Ppeak − Pplat) ÷ flow; a rising peak with stable plateau indicates increased resistance such as secretions or bronchospasm.

Auto-PEEP is measured with an end-expiratory hold; it increases with high respiratory rate, long inspiratory time, and large tidal volume.

RSBI = spontaneous respiratory rate ÷ spontaneous tidal volume in liters; < 105 predicts weaning success, and a spontaneous breathing trial lasts 30–120 minutes.

Permissive hypercapnia accepts PaCO2 of roughly 50–80 mmHg with pH ≥ 7.20–7.25 to limit ventilator-induced lung injury.

Pressure support of 5–8 cmH2O offsets endotracheal tube and circuit resistance; PSV with PEEP is a common weaning mode.

High-pressure alarm = obstruction, secretions, biting, or decreased compliance; low-pressure alarm = disconnection or leak; apnea alarm = no spontaneous effort in a supported mode.