CRT (CREST) key terms

The volume of gas moved into or out of the lungs during one unforced breath. It is commonly set between 6 and 8 mL/kg of predicted body weight during mechanical ventilation.

A calculated reference weight derived from height and sex, used to set ventilator tidal volumes rather than actual body weight. It protects lungs from overdistention in patients with obesity or edema.

The total volume of gas exhaled per minute, equal to tidal volume multiplied by respiratory rate. It is the primary determinant of carbon dioxide removal and is adjusted to control PaCO2.

The airway pressure measured during an inspiratory hold when airflow has stopped. It reflects alveolar distending pressure and is targeted at or below 30 cm H2O to limit ventilator-induced lung injury.

The highest airway pressure reached during active gas delivery. It reflects both airway resistance and lung compliance, so a rise may signal secretions, bronchospasm, or a kinked circuit rather than stiff lungs.

The difference between plateau pressure and applied positive end-expiratory pressure. It estimates the cyclic stretch applied to alveoli and is associated with mortality when elevated above roughly 15 cm H2O.

Pressure maintained in the airway at the end of exhalation to keep alveoli open. It improves oxygenation and reduces atelectrauma, but excessive levels impair venous return and can cause barotrauma.

Trapped gas pressure remaining in the alveoli at end exhalation because the next breath begins before complete emptying. It causes air stacking, raises intrathoracic pressure, and can precipitate hypotension or patient-ventilator dyssynchrony.

Progressive retention of gas in the lungs when exhalation is incomplete, often from high respiratory rates or airflow obstruction. It raises end-expiratory lung volume and can lead to hyperinflation and hemodynamic compromise.

Increasing end-expiratory lung volume over successive breaths when expiratory time is too short for full emptying. It reduces compliance and increases the work of breathing, requiring treatment of the underlying cause.

A ventilation strategy using low tidal volumes, limited plateau pressures, and adequate PEEP to prevent ventilator-induced lung injury. It is standard care for acute respiratory distress syndrome and reduces mortality.

A brief sustained increase in airway pressure intended to reopen collapsed alveoli. It may transiently improve oxygenation but carries risk of barotrauma and hemodynamic instability, so it is used selectively.

A graphic display of gas flow versus time during the respiratory cycle. Its shape reveals whether the patient triggers breaths, whether expiratory flow returns to baseline, and whether air trapping is present.

A graphic display of airway pressure versus time. It shows peak and plateau pressures, the presence of inspiratory effort, and whether the patient is fighting the ventilator.

Mismatch between the patient's neural respiratory effort and the ventilator's delivered breaths. It increases work of breathing and discomfort and may prolong ventilation, so it warrants prompt waveform assessment.

The threshold of patient effort or flow change required for the ventilator to deliver a breath. Too sensitive a setting causes auto-triggering; too insensitive a setting increases the patient's work of breathing.

A mode in which every breath receives a set tidal volume, whether patient-triggered or machine-timed. It guarantees minute ventilation but can cause respiratory alkalosis or hyperinflation in patients with high respiratory drive.

A spontaneous mode in which the ventilator adds a set pressure to each patient-initiated breath. The patient controls rate and inspiratory time, making it useful for weaning but unsuitable for patients with unreliable respiratory drive.

Continuous positive airway pressure applied throughout the respiratory cycle while the patient breathes spontaneously. It maintains alveolar recruitment and is used for obstructive sleep apnea and mild hypoxemia.

Ventilatory support delivered through a mask or nasal interface rather than an artificial airway. It reduces intubation rates in hypercapnic exacerbations of COPD and acute cardiogenic pulmonary edema.

Ventilatory support delivered through an endotracheal tube or tracheostomy. It secures the airway and permits precise control of ventilation but carries risks of infection, sedation, and ventilator-induced lung injury.

The process of progressively reducing ventilatory support so the patient resumes spontaneous breathing. It includes daily spontaneous breathing trials and assessment of readiness before extubation.

A period of minimal ventilatory support used to assess whether a patient can breathe independently. Passing the trial suggests readiness for extubation, though airway protection must also be evaluated.

Respiratory rate divided by tidal volume in liters, measured during unassisted breathing. Values below about 105 breaths per minute per liter predict successful weaning, though the index is only one predictor.

Removal of an endotracheal tube once the patient can breathe spontaneously and protect the airway. It requires assessment of cough strength, secretions, and risk of post-extubation stridor.

High-pitched inspiratory noise after tube removal caused by laryngeal edema. It may progress to respiratory distress and requires close monitoring, corticosteroids, or occasionally reintubation.

Collapse or incomplete expansion of lung tissue, often from airway obstruction or inadequate inflation. It causes shunt and hypoxemia and is treated with lung expansion techniques and secretion clearance.

Perfusion of lung regions that receive no ventilation, so blood returns to the heart unoxygenated. It causes hypoxemia that responds poorly to supplemental oxygen and requires recruitment or airway clearance.

Ventilation of lung regions that receive no perfusion, so gas is wasted without gas exchange. It increases the work required to clear carbon dioxide and can cause hypercapnia.

Inequality between airflow and blood flow across lung regions, the most common cause of hypoxemia. It ranges from low-ratio regions that behave like shunt to high-ratio regions that behave like dead space.

Abnormally low arterial oxygen tension, generally below 60 mm Hg. It may result from shunt, hypoventilation, diffusion impairment, or low inspired oxygen and is treated according to cause.

Elevated arterial carbon dioxide tension, generally above 45 mm Hg. It results from hypoventilation, increased dead space, or high metabolic demand and may require ventilatory support.

Noninvasive estimation of arterial oxygen saturation using light absorption through a pulsatile vascular bed. It is affected by poor perfusion, motion, and abnormal hemoglobin species such as carboxyhemoglobin.

A blood sample analyzed for pH, carbon dioxide, oxygen, and bicarbonate to assess acid-base status and gas exchange. It is the reference standard for diagnosing respiratory failure.

Laboratory measurement of the relative concentrations of different hemoglobin species, including oxyhemoglobin, carboxyhemoglobin, and methemoglobin. It is used when pulse oximetry readings seem misleading.

The maximum expiratory flow achieved during a forceful cough, used to assess airway clearance capacity. Low values suggest weak cough and higher risk of secretion retention and respiratory complications.

Techniques that mobilize and remove retained secretions, such as percussion, vibration, and assisted cough. Selection depends on the patient's strength, secretion burden, and tolerance.

A therapy using an inflatable vest that rapidly compresses and releases the chest to loosen secretions. It is an alternative to manual techniques for patients who cannot tolerate positioning or manual percussion.

A device-guided slow deep breathing exercise intended to prevent or reverse atelectasis. It encourages sustained maximal inspiration and is used after surgery and in patients at risk of collapse.