NBRC CRT key terms

Volume of gas moved into or out of the lungs during one breath, usually set at 6 to 8 mL/kg of predicted body weight in adults. It is used to calculate minute ventilation and static compliance.

Total volume of gas entering and leaving the lungs each minute, equal to tidal volume multiplied by respiratory rate. Resting adult values are roughly 5 to 8 L/min and rise with fever, pain, and metabolic acidosis.

Volume of gas left in the lungs at the end of a quiet expiration. It reflects the balance between lung elastic recoil and outward chest wall pull and keeps alveoli open between breaths.

Ratio of the forced expiratory volume in one second to the forced vital capacity. A value below about 70% suggests airflow obstruction, making it a core spirometry measurement.

Change in lung volume per unit change in distending pressure, measured during an inspiratory hold when flow has stopped. It is calculated as tidal volume divided by plateau pressure minus total PEEP.

Pressure difference between the airway opening and the alveoli divided by gas flow. It rises with bronchospasm, retained secretions, and small endotracheal tubes, and shows up as a climbing peak inspiratory pressure.

Airway pressure measured during an end-inspiratory hold with no gas flow. It reflects alveolar distending pressure and lung compliance, and values above 30 cm H2O are linked to lung injury.

Positive alveolar pressure remaining at end-expiration when the next breath begins before exhalation is complete. It is detected with an expiratory hold in a passive patient and is caused by high rates or short expiratory times.

Laboratory analysis of an arterial sample reporting pH, PaCO2, PaO2, and calculated bicarbonate. It is the standard method for judging ventilation, oxygenation, and acid-base status.

PaO2 from an arterial blood gas divided by the fraction of inspired oxygen. It grades the severity of hypoxemia, and a very low value suggests shunt that supplemental oxygen cannot correct.

Continuous graphic display of carbon dioxide in exhaled gas. The end-tidal value approximates alveolar PCO2, confirms endotracheal tube placement, and reveals disconnection or cardiac arrest.

Percentage of cardiac output that passes through the lungs without contacting ventilated alveoli. Hypoxemia caused by shunt responds poorly to higher inspired oxygen and is estimated from the P/F ratio.

Procedure in which the circuit is pressurized with the patient connection occluded to confirm that set volume or pressure is not lost through loose connections, cracked tubing, or a faulty valve.

Adjusting a measuring device against a known reference standard so its readings are accurate. It is done at manufacturer-specified intervals and after sensor replacement, repair, or erratic readings.

Ventilator alarm that sounds when airway pressure exceeds a set limit. Common causes are secretions, bronchospasm, biting, kinked tubing, water in the circuit, and pneumothorax.

Alarm that activates when airway pressure falls below a set threshold, signaling a leak or disconnection. Causes include a disconnected circuit, a deflated cuff, or a chest tube air leak.

Device that mixes compressed air and oxygen in adjustable proportions to deliver a precise oxygen concentration. It needs both gas sources at adequate and roughly equal pressure to hold the set value.

Instrument that measures the oxygen concentration of gas being delivered. It is calibrated to room air and to 100% oxygen and is checked before use with a blender or ventilator.

Device that warms and adds water vapor to inspired gas so it reaches near body temperature and full saturation. It prevents heat loss and thick, dry secretions during invasive ventilation.

Passive device placed in the breathing circuit that traps heat and water from exhaled gas and returns them on the next inspiration. It is avoided with thick secretions, very low tidal volumes, or hypothermia.

Infection control practices used for every patient regardless of diagnosis: hand hygiene plus gloves, gown, and eye or face protection based on the expected contact with blood and body fluids.

Precautions for organisms spread by tiny droplet nuclei that stay suspended in air, such as tuberculosis. They require a negative-pressure room, a fit-tested N95 respirator or better, and a closed door.

Process that destroys all microorganisms except large numbers of bacterial spores. It is used for semi-critical items such as flexible bronchoscopes and reusable airway devices that contact mucous membranes.

Cleaning the hands with soap and water or an alcohol-based rub. It is the single most effective measure for preventing healthcare-associated infection and is done before and after patient contact and after glove removal.

Fraction or percent of oxygen in the gas a patient inspires, ranging from 0.21 in room air to 1.0. It is adjusted to reach a target saturation or PaO2 while staying as low as is effective.

Positive pressure maintained in the airway at the end of expiration. It keeps alveoli open, improves oxygenation, and reduces atelectasis, and it serves as the reference pressure when calculating static compliance.

Ventilator mode in which every breath, machine or patient initiated, receives the set tidal volume or pressure at a set backup rate. The patient can raise the rate but not the depth of each breath.

Spontaneous mode in which each patient-triggered breath is boosted by a set inspiratory pressure. The patient sets rate and inspiratory time, and the mode is often used while weaning.

Mode that delivers a set number of mandatory breaths each minute and allows spontaneous breaths between them, which may be pressure supported. It gradually returns work of breathing to the patient.

Positive pressure delivered through a nasal or full-face mask instead of an artificial airway. It is used for hypercapnic respiratory failure, COPD exacerbation, and some cases of pulmonary edema.

Device that delivers heated, humidified gas at flows of about 30 to 60 L/min through nasal prongs. The high flow meets inspiratory demand, flushes dead space, and provides a small amount of positive pressure.

Strategy using tidal volumes near 6 mL/kg of predicted body weight with plateau pressure kept at or below 30 cm H2O. It reduces ventilator-induced lung injury and is standard care in acute respiratory distress syndrome.

Brief application of higher airway pressure to reopen collapsed alveoli, followed by enough PEEP to keep them open. It is used in hypoxemic respiratory failure and requires watching for hypotension.

Period of minimal ventilator support, such as a T-piece or low level of pressure support, used to judge whether a patient can breathe without the machine before extubation.

Device that uses gas flow to turn a liquid drug into an aerosol inhaled through a mouthpiece or mask. It delivers bronchodilators and other agents, typically with flow set at 6 to 8 L/min.

Pressurized canister that releases a fixed dose of drug, used with a chamber that reduces drug impact in the mouth and throat and improves lung deposition, especially when the patient has poor coordination.

Handheld device that gives visual feedback while the patient takes slow, deep breaths, encouraging lung expansion and helping prevent atelectasis after surgery or during prolonged bed rest.