RTLE cheat sheet

Arterial oxygen content: CaO2 = (1.34 × Hb × SaO2) + (0.003 × PaO2); the first term is hemoglobin-bound oxygen and the second is dissolved oxygen.

Alveolar oxygen equation: PAO2 = FiO2 × (PB − 47) − (PaCO2 / R), where R is the respiratory quotient, usually about 0.8.

Carbon dioxide transport is roughly 70% bicarbonate, 20% to 23% carbamino compounds, and 5% to 10% dissolved CO2.

V/Q mismatch: shunt has V/Q = 0 and hypoxemia that responds poorly to supplemental oxygen; dead space has V/Q approaching infinity and wastes ventilation.

Lung capacities: VC = IRV + ERV + VT; FRC = ERV + RV; IC = IRV + VT; TLC = VC + RV.

Compliance = change in volume / change in pressure; elastance is the reciprocal of compliance; airway resistance = pressure difference / flow.

Type II pneumocytes produce surfactant, which lowers alveolar surface tension, increases compliance, and reduces collapse at end expiration.

Right shift of the oxyhemoglobin curve: increased CO2, H+, temperature, and 2,3-BPG reduce hemoglobin affinity and release more oxygen to tissues.

Cardiogenic pulmonary edema results when increased pulmonary capillary hydrostatic pressure, usually from left heart failure, exceeds oncotic pressure and lymphatic drainage.

Cylinder duration in minutes = gauge pressure in psi × cylinder factor / flow in L/min; the E cylinder factor is approximately 0.28.

Nasal cannula at 1 to 6 L/min provides roughly 24% to 44% FiO2; a simple mask at 5 to 10 L/min provides roughly 35% to 55%; a nonrebreather at 10 to 15 L/min provides roughly 80% to 95%.

Venturi air-to-oxygen ratio = (100 − desired FiO2) / (desired FiO2 − 21); total flow = oxygen flow × (1 + ratio).

High-flow nasal cannula provides heated and humidified gas at 21% to 100% FiO2 with flows up to about 60 L/min in adults, producing variable positive airway pressure.

An oropharyngeal airway is contraindicated in a conscious patient with an intact gag reflex; a nasopharyngeal airway is avoided with basilar skull fracture or severe coagulopathy.

Adult endotracheal tube cuff pressure is kept near 20 to 30 cm H2O; average adult oral tube depth is about 21 to 23 cm at the incisors.

Adult suction negative pressure is commonly 80 to 120 mm Hg, with each suction pass limited to about 10 to 15 seconds to reduce hypoxemia and mucosal injury.

Capnography phases: phase I is anatomic dead space, phase II is dead space and alveolar gas mixing, phase III is the alveolar plateau, and phase IV is the inspiratory downstroke.

Pulse oximetry can be falsely normal in carbon monoxide poisoning and is affected by methemoglobin, poor perfusion, motion, and nail polish.

Volume-control ventilation delivers a set tidal volume and rate while pressure varies; pressure-control ventilation delivers a set pressure and inspiratory time while volume varies.

Initial adult settings often use tidal volume 6 to 8 mL/kg predicted body weight, rate 12 to 16/min, PEEP 5 cm H2O, and FiO2 titrated to the target SpO2.

Predicted body weight: male = 50 + 2.3 × (height in inches − 60); female = 45.5 + 2.3 × (height in inches − 60).

Lung-protective ventilation targets plateau pressure ≤30 cm H2O and driving pressure (plateau − PEEP) ≤15 cm H2O in ARDS.

ARDS Berlin criteria: acute onset, PaO2/FiO2 ≤300 with PEEP ≥5 cm H2O, bilateral opacities not fully explained by effusion, collapse, or nodules, and respiratory failure not primarily cardiogenic.

Auto-PEEP is measured with an end-expiratory hold; it causes gas trapping, hypotension, and barotrauma and is reduced by decreasing rate, lengthening expiratory time, and treating obstruction.

Weaning predictors include RSBI = respiratory rate / tidal volume in liters <105, negative inspiratory force more negative than −20 to −25 cm H2O, and vital capacity >10 to 15 mL/kg.

High peak pressure with normal plateau pressure suggests increased airway resistance; high plateau pressure suggests decreased compliance or overdistention.

Permissive hypercapnia is avoided in severe metabolic acidosis, raised intracranial pressure, and hemodynamic instability; VV ECMO supports respiratory failure and VA ECMO supports cardiac failure.

Stridor suggests upper airway obstruction; wheezing suggests lower airway obstruction; crackles suggest alveolar fluid or opening of collapsed airways; absent unilateral breath sounds suggest pneumothorax or mainstem intubation.

Dull percussion suggests consolidation, effusion, or mass; hyperresonance suggests hyperinflation or pneumothorax.

MAP ≈ diastolic pressure + one third of pulse pressure, or (systolic + 2 × diastolic) / 3; cardiac output = heart rate × stroke volume; cardiac index = cardiac output / body surface area.

Normal central venous pressure is about 2 to 8 mm Hg; trends with fluid responsiveness and cardiac function are more useful than a single value.

Pulsus paradoxus is an inspiratory fall in systolic pressure greater than 10 mm Hg and occurs in severe asthma, COPD, and cardiac tamponade.

Glasgow Coma Scale = eye + verbal + motor scores, range 3 to 15; lower scores indicate greater depression of consciousness.

A sudden fall in ETCO2 suggests disconnection, extubation, esophageal intubation, cardiac arrest, or pulmonary embolism; a sudden rise suggests hypoventilation or increased metabolism.

Signs of increased work of breathing include accessory muscle use, retractions, nasal flaring, tripod positioning, grunting, and paradoxical abdominal motion.

Normal adult ABG: pH 7.35 to 7.45, PaCO2 35 to 45 mm Hg, HCO3− 22 to 26 mEq/L, PaO2 80 to 100 mm Hg, and SaO2 95% to 100%.

Primary respiratory acidosis: low pH with high PaCO2; primary respiratory alkalosis: high pH with low PaCO2; primary metabolic acidosis: low pH with low HCO3−; primary metabolic alkalosis: high pH with high HCO3−.

Metabolic acidosis compensation: expected PaCO2 = 1.5 × HCO3− + 8 ± 2; a measured PaCO2 outside this range suggests an additional respiratory disorder.

Anion gap = Na+ − (Cl− + HCO3−); normal is about 8 to 12 mEq/L, and elevation suggests ketoacidosis, lactic acidosis, renal failure, or toxin ingestion.

Obstructive spirometry: FEV1/FVC <0.70, reduced FEV1, and often increased RV and TLC from air trapping.

Restrictive spirometry: FEV1/FVC normal or increased with reduced TLC below 80% predicted; DLCO is low in emphysema, interstitial lung disease, and anemia.

Positive bronchodilator response: increase in FEV1 or FVC of at least 12% and at least 200 mL from baseline.

Sleep apnea severity by apnea-hypopnea index: 5 to 15 mild, 15 to 30 moderate, and greater than 30 severe; obstructive events result from upper airway collapse.

ABG samples should be heparinized, free of air bubbles, transported on ice if delayed, and analyzed promptly because air bubbles raise PaO2 and lower PaCO2.

Beta2 agonists such as albuterol stimulate beta2 receptors, increase cyclic AMP, and relax bronchial smooth muscle; adverse effects include tachycardia, tremor, and hypokalemia.

Anticholinergics such as ipratropium and tiotropium block muscarinic M3 receptors, reducing vagal bronchomotor tone; adverse effects include dry mouth, urinary retention, and acute angle-closure glaucoma risk.

Inhaled corticosteroids reduce airway inflammation but do not relieve acute bronchospasm; rinsing the mouth after use reduces oropharyngeal candidiasis and dysphonia.

Aerosol particles of about 1 to 5 micrometers deposit most effectively in the lower respiratory tract; larger particles impact in the upper airway and smaller particles are often exhaled.

An MDI with a valved holding chamber improves lung deposition and reduces oropharyngeal impaction; the patient exhales, actuates, inhales slowly, and holds the breath about 10 seconds.

Small-volume nebulizers are commonly driven at 6 to 8 L/min; residual volume and dead volume reduce the delivered dose, and mouthpiece delivery avoids nasal deposition.

Theophylline has a narrow therapeutic range of about 5 to 15 micrograms per milliliter; toxicity can cause arrhythmias, seizures, and persistent vomiting.

Exogenous surfactant is used in neonatal respiratory distress syndrome to reduce surface tension, improve compliance, and decrease the need for high ventilator pressures.

Acetylcysteine can cause bronchospasm in reactive airway disease; dornase alfa reduces mucus viscosity in cystic fibrosis by cleaving extracellular DNA.

Normal newborn respiratory rate is about 30 to 60 breaths per minute; sustained tachypnea above 60 with retractions, grunting, or cyanosis indicates respiratory distress.

Apgar score components: appearance, pulse, grimace, activity, and respiration, each scored 0 to 2 at 1 and 5 minutes after birth.

Neonatal resuscitation begins with warmth, drying, and stimulation; positive-pressure ventilation is indicated for apnea, gasping, or heart rate below 100/min.

Neonatal chest compressions are given at 3 compressions to 1 breath when heart rate remains below 60/min after effective ventilation.

Preterm infants with respiratory distress syndrome often receive CPAP at about 5 to 6 cm H2O and surfactant; target SpO2 is commonly 90% to 95% to limit oxygen toxicity.

Uncuffed pediatric endotracheal tube size for children older than 1 year = age in years / 4 + 4; cuffed tube size = age / 4 + 3.5; oral depth ≈ 3 × tube internal diameter.

Bronchiolitis is usually caused by respiratory syncytial virus and is managed with supportive care, hydration, and oxygen or high-flow nasal cannula; routine bronchodilators and steroids are not recommended.

Pediatric asthma exacerbation treatment includes repeated inhaled short-acting beta2 agonists, ipratropium for severe episodes, and systemic corticosteroids; oxygen targets SpO2 about 94% to 98%.

Apnea of prematurity is treated with caffeine citrate, which stimulates the respiratory center and reduces apnea and the need for mechanical ventilation.