| A/C | Assist/control |
| AG | Anion gap |
| APRV | Airway pressure release ventilation |
| ARDS | Acute respiratory distress syndrome |
| ARDSnet | ARDS network |
| AVAPS | Average volume assured pressure support |
| BAL | Bronchoalveolar lavage |
| BE | Base excess |
| BEE | Basal energy expenditure |
| BSA | Body surface area |
| CCI | Chronic critical illness |
| Cao2 | Oxygen content of arterial blood |
| Cc′o2 | Pulmonary capillary oxygen content |
| CDC | Centers for Disease Control and Prevention |
| CI | Cardiac index |
| Cl | Lung compliance |
| Cl− | Chloride ion |
| CMV | Continuous mandatory ventilation |
| CO | Carbon monoxide |
| Co2 | Oxygen content of the blood |
| COPD | Chronic obstructive pulmonary disease |
| CPAP | Continuous positive airway pressure |
| CPP | Cerebral perfusion pressure |
| CPR | Cardiopulmonary resuscitation |
| CSV | Continuous spontaneous ventilation |
| CT | Computed tomography |
| Cv̄o2 | Mixed venous oxygen content |
| CVP | Central venous pressure |
| CW | Chest wall compliance |
| Do2 | Oxygen delivery |
| EAdi | Electrical activity of the diaphragm |
| ECLS | Extracorporeal life support |
| ECMO | Extracorporeal membrane oxygenation |
| EELV | End-expiratory lung volume |
| EPAP | Expiratory positive airway pressure |
| fb | Frequency of breathing; respiratory rate |
| fc | Heart rate |
| Fio2 | Fraction of inspired oxygen |
| FRC | Functional residual capacity |
| Hb | Hemoglobin |
| HbCO | Carboxyhemoglobin |
| HCO3− | Bicarbonate concentration |
| HFJV | High frequency jet ventilation |
| HFOV | High frequency oscillatory ventilation |
| HFPPV | High frequency positive pressure ventilation |
| HFV | High frequency ventilation |
| HME | Heat and moisture exchanger |
| Hz | Hertz |
| I:E | Inspiratory time to expiratory time ratio |
| IBW | Ideal body weight (sometimes called predicted body weight) |
| ICP | Intracranial pressure |
| ICU | Intensive care unit |
| IMV | Intermittent mandatory ventilation |
| iNO | Inhaled nitric oxide |
| IPAP | Inspiratory positive airway pressure |
| ISB | Isothermal saturation boundary |
| IVAC | Infection related ventilator associated condition |
| j | Joules |
| LV | Left ventricle |
| LVSWI | Left ventricular stroke work index |
| MAP | Mean arterial pressure |
| MDI | Metered-dose inhaler |
| MIC | Maximum insufflation capacity |
| MIE | Mechanical insufflation–exsufflator |
| MMV | Mandatory minute ventilation |
| MODS | Multiple organ dysfunction syndrome |
| MPAP | Mean pulmonary artery pressure |
| NO | Nitric oxide |
| Na+ | Sodium |
| NAVA | Neurally adjusted ventilatory assist |
| NIV | Noninvasive ventilation |
| NPE | Neurogenic pulmonary edema |
| OI | Oxygenation index |
| ΔPaw | Change in airway pressure |
| ΔPL | Transpulmonary pressure |
| ΔPOP | Plethysmographic waveform amplitude |
| ΔPpl | Change in pleural pressure |
| P(a-et)CO2 | Difference between arterial and end-tidal Pco2 |
| Pao2/Pao2 | Ratio of arterial PO2 to alveolar Po2 |
| Pao2/Fio2 | Ratio of arterial Po2 to Fio2 |
| P(a-a)o2 | Difference between alveolar Po2 and arterial Po2 |
| Paco2 | Partial pressure of carbon dioxide in arterial blood |
| P̄alv | Mean alveolar pressure |
| Palv | Alveolar pressure |
| Pao2 | Partial pressure of oxygen in arterial blood |
| Pao2 | Alveolar Po2 |
| PAP | Pulmonary artery pressure |
| PAV | Proportional-assist ventilation |
| P̄aw | Mean airway pressure |
| Pb | Barometric pressure |
| Pbo2 | Brain Po2 |
| PC-CMV | Continuous mandatory ventilation with pressure control |
| PC-IMV | Pressure-controlled intermittent mandatory ventilation |
| PCIRV | Pressure-controlled inverse ration ventilation |
| Pco2 | Partial pressure of carbon dioxide |
| PCV | Pressure-controlled ventilation |
| PCWP | Pulmonary capillary wedge pressure |
| Pdi | Transdiaphragmatic pressure |
| Pēco2 | Mixed exhaled Pco2 |
| Ph2o | Water vapor pressure |
| PEEP | Positive end-expiratory pressure |
| PEG | Percutaneous endoscopic gastrostomy |
| Peso | Esophageal pressure |
| Petco2 | End-tidal Pco2 |
| Pexhco2 | Measured mixed exhaled Pco2 including gas compressed in the ventilator circuit |
| pH | Negative log of the hydrogen ion concentration |
| PI | Plethysmographic perfusion index |
| Pimax | Maximum inspiratory pressure |
| PImin | Minimal value of the plethysmographic perfusion index |
| PIP | Peak inspiratory pressure |
| Pmus | Pressure generated by the respiratory muscles |
| PMV | Prolonged mechanical ventilation |
| Po2 | Partial pressure of oxygen |
| Pplat | Plateau pressure |
| PPV | Arterial pulse pressure variation |
| PRVC | Pressure-regulated volume control |
| PSV | Pressure support ventilation |
| Ptcco2 | Transcutaneous Pco2 |
| Ptco2 | Transcutaneous Po2 |
| Pv̄co2 | Mixed venous Pco2 |
| Pvent | Pressure-generated by the ventilator |
| PVI | Plethysmographic variability index |
| Pv̄o2 | Mixed venous Po2 |
| PVR | Pulmonary vascular resistance |
| Q̇c | Cardiac output |
| Q̇s/Q̇t | Pulmonary shunt |
| R | Respiratory quotient |
| RE | Expiratory resistance |
| REE | Resting energy expenditure |
| REM | Rapid eye movement |
| Ri | Inspiratory resistance |
| RSBI | Rapid shallow breathing index |
| RVSWI | Right ventricular stroke work index |
| Sao2 | Hemoglobin oxygen saturation of arterial blood |
| SBT | Spontaneous breathing trial |
| Scvo2 | Central venous oxygen saturation |
| SID | Strong ion difference |
| SIMV | Synchronized intermittent mandatory ventilation |
| Sjvo2 | Jugular venous oxygen saturation |
| Spco | Carbon monoxide measured by pulse oximetry |
| SpHb | Hemoglobin measured by pulse oximetry |
| SpMet | Methemoglobin measured by pulse oximetry |
| Spo2 | Hemoglobin oxygen saturation measured by pulse oximetry |
| SVI | Stroke volume index |
| Sv̄o2 | Mixed venous oxygen saturation |
| SVR | Systemic vascular resistance |
| SVRI | Systemic vascular resistance index |
| TE | Expiratory time |
| TI | Inspiratory time |
| TT | Total cycle time |
| UUN | Urine urea nitrogen |
| V̇ | Flow |
| V̇a | Alveolar ventilation |
| V̇/Q̇ | Ratio of ventilation to blood flow |
| VAC | Ventilator-associated condition |
| VAE | Ventilator-associated event |
| VAP | Ventilator-associated pneumonia |
| VC | Vital capacity |
| V̇co2 | Carbon dioxide production |
| V̇d | Dead space ventilation |
| V̇e | Minute ventilation |
| V̇i | Inspiratory flow |
| VCV | Volume-controlled ventilation |
| VC-CMV | Continuous mandatory ventilation with volume control |
| VC-IMV | volume-controlled intermittent mandatory ventilation |
| VD/VT | Dead space to tidal volume ratio |
| VILI | Ventilator-induced lung injury |
| V̇o2 | Oxygen consumption |
| VS | Volume support |
| VT | Tidal volume |
| W | Work |
| τ | Time constant |