RTLE key terms

The change in lung volume produced by a given change in transpulmonary pressure, expressed in liters per centimeter of water. Low compliance means the lungs are stiff and require more pressure to inflate.

The opposition to airflow through the bronchial tree, determined mainly by airway caliber and calculated as the pressure gradient between the alveoli and the mouth divided by flow.

A phospholipid mixture secreted by type II alveolar cells that lowers surface tension, stabilizes alveoli of different sizes, and reduces the work of breathing and the tendency for alveolar collapse.

The portion of each breath that reaches the alveoli but does not participate in gas exchange, plus the volume in the conducting airways. It is estimated by the Bohr equation using PaCO2 and mixed expired CO2.

Blood that passes through the pulmonary capillaries without picking up oxygen, so it returns to the left heart with the same oxygen content as mixed venous blood. Causes include atelectasis, consolidation, and ARDS.

A regional imbalance between alveolar ventilation and pulmonary blood flow. It is the most common cause of hypoxemia in lung disease and often responds to supplemental oxygen.

A protective reflex in which small pulmonary arteries constrict when alveolar oxygen tension falls, diverting blood away from poorly ventilated regions. Widespread hypoxic vasoconstriction contributes to pulmonary hypertension.

For a sphere, the pressure needed to keep it inflated is proportional to wall tension and inversely proportional to radius. It explains why small alveoli tend to collapse into larger ones without surfactant.

A fixed-performance oxygen device that uses a jet of oxygen to entrain room air through calibrated ports, delivering a predictable fraction of inspired oxygen, commonly 24% to 50%, regardless of the patient's inspiratory flow.

A system that delivers heated, humidified oxygen blended with air at flows up to about 60 liters per minute, providing a stable FiO2, modest positive pressure, and washout of nasopharyngeal dead space.

A flexible tube passed through the mouth or nose into the trachea to secure the airway, permit positive-pressure ventilation, and allow suctioning. A cuff seals the trachea in adults and older children.

A surgically created opening in the anterior trachea through which a tube is placed to bypass upper airway obstruction, facilitate long-term ventilation, and simplify airway clearance and weaning.

A hand-held self-inflating resuscitation device that delivers positive-pressure breaths when squeezed. Proper mask seal, an oropharyngeal airway, and a two-person technique improve the delivered tidal volume.

The pressure exerted by the inflated balloon of an endotracheal or tracheostomy tube against the tracheal wall. It is typically kept between 20 and 30 cm H2O to prevent aspiration while avoiding mucosal ischemia.

A baseline positive pressure maintained in the airways at end-expiration during mechanical ventilation. It recruits collapsed alveoli, improves oxygenation, and can reduce ventilator-induced lung injury but may lower cardiac output.

The airway pressure measured during an end-inspiratory pause, reflecting the elastic recoil of the lungs and chest wall. It is used to estimate alveolar pressure and guide lung-protective ventilation, with a target usually at or below 30 cm H2O.

Positive alveolar pressure that remains at the end of expiration when the patient does not have enough time to exhale fully. It causes air trapping, increases work of breathing, and can impair venous return and blood pressure.

A spontaneous mode in which each patient-triggered breath is augmented by a set inspiratory pressure, reducing the work of breathing. The patient controls rate, inspiratory time, and, within limits, tidal volume.

A strategy using low tidal volumes of about 4 to 8 mL/kg predicted body weight, limited plateau pressure and driving pressure, and adequate PEEP to reduce ventilator-induced lung injury, especially in ARDS.

A period of minimal or no ventilator support used to assess whether a patient can breathe adequately on their own. It is often combined with a rapid shallow breathing index before extubation.

Ventilatory support delivered through a mask or nasal interface without an artificial airway. It is used mainly for acute hypercapnic exacerbations of COPD and cardiogenic pulmonary edema.

A noninvasive method that estimates arterial hemoglobin oxygen saturation by measuring the absorption of red and infrared light across a pulsatile vascular bed. It does not measure ventilation or directly measure PaO2.

Continuous measurement and display of the carbon dioxide concentration in exhaled gas. The waveform and end-tidal value help confirm endotracheal placement, assess ventilation, and detect apnea or circuit disconnection.

Visible contraction of the sternocleidomastoid, scalene, and abdominal muscles during breathing, indicating increased work of breathing. It is a warning sign of impending respiratory failure.

A palpable vibration felt on the chest wall when the patient speaks certain words. It increases over consolidation and decreases with pleural effusion, pneumothorax, or hyperinflation.

A blood sample analysis that measures pH, PaCO2, PaO2, and bicarbonate, allowing classification of acid-base disorders and assessment of oxygenation and ventilation. It is the reference standard for respiratory failure.

The amount of strong acid or base needed to return a blood sample to normal pH at standard conditions. A positive value suggests metabolic alkalosis; a negative value suggests metabolic acidosis.

The fraction of the forced vital capacity exhaled in the first second of a forced maneuver. A reduced ratio, generally below 0.70, supports airflow obstruction, while a normal or high ratio suggests restriction.

The rate at which carbon monoxide moves from alveolar gas into the blood, reflecting alveolar-capillary membrane integrity and pulmonary capillary blood volume. It is reduced in emphysema, interstitial disease, and anemia.

The average number of apneas and hypopneas per hour of sleep, used to grade sleep-disordered breathing. Values of 5 or more with symptoms, or 15 or more alone, generally define clinically significant obstructive sleep apnea.

A medication that stimulates beta-2 adrenergic receptors on bronchial smooth muscle, producing rapid bronchodilation. Short-acting agents relieve acute symptoms; long-acting agents are maintenance therapy in asthma and COPD.

A pressurized canister that delivers a fixed dose of medication aerosol with each actuation. Correct technique, including shaking and coordinating actuation with inhalation, is essential for lung deposition.

A valved holding chamber attached to a metered-dose inhaler that slows the aerosol, reduces oropharyngeal deposition, and removes the need to coordinate actuation with inhalation.

A device that converts liquid medication into an aerosol using a jet of compressed gas or a vibrating mesh, allowing delivery during tidal breathing. It is useful for patients who cannot coordinate an inhaler.

An inhaled medication such as ipratropium or tiotropium that blocks muscarinic receptors, reducing vagally mediated bronchoconstriction and mucus secretion. It is used in COPD and acute asthma.

A selective pulmonary vasodilator delivered by inhalation that improves oxygenation in persistent pulmonary hypertension of the newborn and some ARDS cases by reducing pulmonary vascular resistance in ventilated lung regions.

A neonatal disorder caused by surfactant deficiency, leading to low lung compliance, atelectasis, and hypoxemia. It occurs mainly in premature infants and is treated with surfactant and nasal CPAP or mechanical ventilation.

Cessation of breathing for 20 seconds or more, or a shorter pause with bradycardia or desaturation, in an infant born before 37 weeks. It reflects immature respiratory control and is treated with caffeine and respiratory support.

Respiratory distress in a newborn who inhaled meconium-stained amniotic fluid, causing airway obstruction, chemical pneumonitis, and sometimes persistent pulmonary hypertension. Management includes suctioning, oxygen, and ventilatory support as needed.

A chronic lung disease of preterm infants characterized by arrested alveolar development and prolonged oxygen or ventilator dependence. It results from injury by mechanical ventilation, oxygen, and infection in an immature lung.