The Pre-brief
Upon responding to a rapid response, you notice your patient is in respiratory failure with an SPO2 in the 70’s. You place them on a non-rebreather mask and prepare for intubation. Once intubated, you transport the patient to the ICU and place them on the ventilator. A tidal volume of 6cc/kg is set along with an FIO2 of 100%. But what is the appropriate PEEP?
What is PEEP?
It is one of the basic settings dialed in when a patient is on the ventilator. Positive end-expiratory pressure (PEEP) is a critical asset used in conjunction with mechanical ventilation. Typically, 5cmH2O is used unless hypoxemia or ARDS is present. PEEP is the pressure maintained in the airways at end-expiration above atmospheric pressure. Extrinsic PEEP can prevent alveolar collapse, thus improving oxygenation and FRC. It also increases the alveolar surface, which will help enhance ventilation-perfusion (VQ) mismatch. Â
Too little or too much?
Ventilating with too little PEEP can result in atelectasis, decreased compliance, and higher driving pressures. On the other hand, too much PEEP can cause alveolar overdistension and increase intrathoracic pressure, ultimately reducing venous return and cardiac output. However, according to ARDSNet, PEEP increments could be protective if a lower driving pressure delivers the same VT with increased PEEP.
What is Optimal PEEP?Â
Optimal PEEP is when oxygenation is maximized, there is minimal end-expiratory atelectasis and minimal end-inspiratory over-distention.Â
But how do you determine optimal PEEP?Â
Many clinicians have difficulty trying to distinguish between overdistention and under-inflation while trying to determine the best method in obtaining optimal PEEP. There are numerous options for obtaining optimal PEEP. However, the method chosen is usually clinician preference.Â
- ARDS Net PEEP/FiO2 table.
- Titrate PEEP according to maximum compliance. PEEP is increased in increments.
- Set PEEP slightly above the lowest inflection point of the pressure-volume curve. The lowest inflection point reflects the pressure at which collapsed alveoli are opening.
- Setting PEEP by best oxygenation using higher than standard settings, which is usually set between 12-15cmH2O.
- SvO2 monitoring, transpulmonary pressure calculated from an oesophageal balloon, electrical impedance tomography, and sequential CT scans are other ways.
Recently we as clinicians hear a lot about driving pressures. I use and obtain driving pressures every morning as a tool to determine optimal PEEP for my patients.Â
So what is Driving Pressure?
Driving pressure is the plateau airway pressure minus the PEEP set. It is determined by the set tidal volume and the static compliance of the lungs. During volume control ventilation, an inspiratory pause greater than or equal to three seconds gives the most accurate plateau pressure. Driving pressure simplifies optimization of mechanical ventilation and PEEP. Safe ventilation occurs with a plateau less than 30cmH2O and a driving pressure under 15cmH2O. Obtain plateau pressures at different levels of PEEP, changing PEEP in increments of two to determine optimal PEEP. Make sure to wait for one to five minutes to recheck plateau pressures after every PEEP change.
- There are numerous methods that clinicians and facilities use to find optimal PEEP, such as the ones we have been practicing, along with some new approaches such as using an esophageal balloon to monitor chest wall pressures. With every method comes its positives and faults, and no one way is the best. How one decides to find optimal PEEP is left up to the provider and the patient’s presentation.
The Debrief
- Finding the correct setting for PEEP can lead to improved outcomes in ventilated patients.Â
- Driving pressures is a simplistic way of finding optimal PEEP.Â
- Check out this post on driving pressures and PEEP titration by Dr. Matt Suiba.Â
References
- Aoyama, H., Yamaha, Y. & Fan, E. The Future of Driving Pressure: A Primary Goal for Mechanical Ventilation?. j intensive care 6, 64 (2018). HTTPS://doi.org/10.1186/s40560-018-0334-4
- NHLBI ARDS Network. Http://www.ardsnet.org/publications.shtml
- Optimal PEEP for Open Lung Ventilation in ARDS.  Deranged Physiology. (2016). https://derangedphysiology.com/main/requiredreading/respiratory-medicine-and-ventilation/chapter%205121/optimal-peep-open-lung. Â
