Table 3.

Methods of positive end-expiratory pressure selection

Method of PEEP titration	Description	Strengths	Limitations	RCTs, n
Compliance	Selection based on highest static or dynamic compliance.26 Assessed by either incremental or decremental stepwise PEEP trial with or without a recruitment maneuver.	Able to be calculated with any ventilator at the bedside. No additional equipment.	Patient must be passive on ventilator. Takes time to do incremental or decremental trials.	2925–41,43–48,82,87,90,91,93,94
PEEP/FIO2 table	Selected via table that assigns a PEEP (or range of PEEPs) for a given FIO2. There are low PEEP and high PEEP/FIO2 tables, as seen in ALVEOLI trial.7	Simple, requires no equipment, can be reassessed regularly, minimal time investment	Does not take into consideration patient’s mechanics	217,9,25–32,49–59
Oxygenation	Selection by change in oxygenation (SpO2 or PaO2) during either a decremental56 or incremental64 stepwise trial, or maximal oxygenation within a defined range65	Able to be calculated with any ventilator at the bedside	Requires arterial blood gas for PaO2. Does not assess mechanics.	1245,47,54–56,62,64–67,84,88
Esophageal probe	Pressure transduced from esophageal balloon as surrogate for pleural pressure50 PEEP is titrated to end-expiratory transpulmonary pressure > 0 cm H2O	Partitioning of lung and chest wall mechanics, measuring true pressures affecting the lungs	Special equipment, ventilators, and education	1130,33,48–50,52,60–63,85
Imaging—EIT	Maps out areas of collapse, normal aeration, and overdistension within the lung.10 PEEP set to minimize both collapse and overdistension51 or to lowest RVDI.68	Noninvasive bedside method of determining degree of collapse and overdistension	Requires special equipment, monitoring supplies, and education	830,43,51,68–71,89
Pressure-volume curves	Curve generated with single breath69 or plotting breaths of varying volumes.72 PEEP set above the lower inflection point72 or at the point of maximal hysteresis.69	Provides information about respiratory system mechanics	Patient must be passive on ventilator. Plotting curve takes time. Few ventilators can do single breath curve.	769,72–76,92
Driving pressure	Difference between plateau pressure and PEEP. PEEP can be set at the level that corresponds to the lowest driving pressure during an incremental trial.42	Able to be calculated with any ventilator at the bedside. No additional equipment.	Patient must be passive on ventilator. Takes time to do incremental trials.	742,57,79,83,86,95,97
Imaging—ultrasound	PEEP adjusted to optimize aeration as assessed by presence or absence of artifact on lung ultrasound. Can be incremental121 or decremental.109	Able to be measured independent of ventilator mode	Requires training in ultrasound and interrater reliability can be an issue	358,59,122
Plateau pressure	For a given tidal volume, PEEP can be increased until a plateau pressure of 28–30 cm H2O is achieved8	Able to be calculated with any ventilator at the bedside. Can be reassessed quickly.	Patient must be passive on ventilator	28,53
Shunt	Shunt fraction (Qs/Qt) can be calculated using blood from an arterial catheter and a PA catheter. PEEP adjusted for reduction in shunt fraction66 or an absolute value.64	Best measure of oxygenation of the lungs overall. Patient does not need to be paralyzed.	Requires PA catheter. Does not take into consideration patient’s mechanics.	264,66
EELV	EELV (absolute or change) is measured by several techniques including plethysmography123 and nitrogen multiple breath washout technique67	Direct measure of recruitment with different levels of PEEP	Requires specialized equipment	167
Computer-based	Certain ventilators have software such as Intellivent-ASV80 that will automatically adjust variables including PEEP based on certain inputs	Automated methods require little workforce and can adjust as conditions change	Modes are proprietary to different ventilators and may not be available for all patients	196
Airway occlusion pressure (P0.1)	P0.1 is pressure measured in first 0.1 sec of inhalation against occluded airway and is surrogate of respiratory drive can be set to keep P0.1 within a range	Useful in patients weaning. Noninvasive. Most modern ventilators can perform.	Not useful in deeply sedated or paralyzed patients	0
AOP	Low-flow inflation maneuver is done with PEEP 0 cm H2O. Inflection in slope of pressure-time curve is noted as AOP. PEEP is set at or above that level.	Can be measured with any ventilator. Assesses lung mechanics.	Patient must be passive on ventilator. Does not consider hysteresis.	0
Auto-PEEP	Calculated by subtracting total PEEP (measured with end-expiratory hold) from applied PEEP. PEEP is set to a percentage of auto-PEEP between 50% and 100%.	Can be measured with any ventilator. Considers mechanics and can aid in work of breathing.	Limited value in patients without airflow obstruction. Must be passive on ventilator to perform.	0
Dead space	Dead space can be calculated using volumetric capnography124–126 and Bohr’s equation. PEEP can be set to reduce or minimize dead space fraction	Continuously monitored. Patient can breathe spontaneously. Measures ventilatory efficiency.	Volumetric capnography requires special equipment. Does not consider mechanics.	0
Imaging—CT	CT is done at a baseline PEEP, after recruitment, and images are taken as PEEP is gradually decreased. PEEP is set above the level at which lung closure occurs.	Accurate way to measure recruitment and visualize overdistension	Patient must be passive on ventilator. Resource intensive and requires transporting patients.	0
IAP	IAP is measured (via bladder pressure) and PEEP is set at a percentage (from 50%127 to 125%128) of IAP	Simple to perform. Can easily trend. Accounts for mechanics.	Limited value in patients with normal IAP. Patient must be passive to measure accurate IAP.	0
NAVA	NAVA is a mode of ventilation that measures the EAdi with an esophageal catheter. PEEP can be set at the level that has optimal EAdi.81	Accurate way to ensure good patient-ventilator synchrony and assist	Requires special equipment and invasive monitors	0
Oxygen delivery	DO2 is calculated with PaO2 and cardiac output using transesophageal doppler129 or echocardiography.130 PEEP is adjusted to maximize DO2.	Considers oxygenation as well as the hemodynamic consequences of PEEP	Requires special equipment and training. Does not consider mechanics.	0
R/I ratio	Recruitment between two levels of PEEP is inferred based on changes in mechanics and change in EELV. PEEP set based on recruiter vs nonrecruiter.	Can be measured with any ventilator	Patient must be passive on ventilator	0
Stress index	Shape of pressure-time waveform. Upslope at end-inspiration indicates overdistension, and downslope indicates recruitment. PEEP is set to target linear or decreasing index.	Can be measured with any ventilator. Can be monitored continuously. Assesses mechanics.	Patient must be passive on ventilator	0
Time constant	Using a constant driving pressure, PEEP is adjusted and set at the level corresponding to the highest time constant	Can be measured with any ventilator	Patient must be passive on ventilator	0
Weight	PEEP set based on BMI. Stratified BMI by < 30 kg·m−2, 30–50 kg·m−2, and > 50 kg·m−2.	Simple method. May compensate for higher pleural pressures in patients with obesity.	BMI does not consider distribution of body mass. Does not measure mechanics or oxygenation.	0

AOP = airway opening pressure; ASV = adaptive supportive ventilation; BMI = body mass index; CT = computed tomography; DO₂ = oxygen delivery; EAdi = electrical activity of the diaphragm; EELV = end-expiratory lung volume; EIT = electrical impedance tomography; F_IO₂ = inspired fraction of oxygen; IAP = intra-abdominal pressure; NAVA = neurally adjusted ventilatory assist; PaO₂ = partial pressure of oxygen in arterial blood; PEEP = positive end-expiratory pressure; PA = pulmonary artery; Qs = pulmonary physiologic shunt (mL·min⁻¹); Qt = cardiac output (mL·min⁻¹); R/I = recruitment to inflation; RCT = randomized controlled trial; Ref = reference; RVDI = regional ventilation delay index; SpO₂ = peripheral oxygen saturation