You are in the ICU as the nocturnal intensivist and a morbidly obese patient with ARDS is transferred to the unit. She is intubated, on the ventilator, with a PEEP setting of 10 cm H2O and FiO2 100% with a PaO2/ FiO2 of 88. You wonder if there is a way to measure the optimal PEEP required for this patient, and you realize one of the ways is an esophageal balloon!
Transpulmonary pressure, or the difference between the airway pressure and pleural pressure, is an important concept to understand when managing patients with Acute Respiratory Distress Syndrome, or ARDS and obese patients. Esophageal pressures have been found to be the best surrogate for pleural pressures, so let’s delve a bit further into this concept.
Why is it important to know the transpulmonary pressure?
Knowing this value in critically ill and obese patients can potentially help avoid lung injury due to the overdistension and/or repetitive opening and closing of the alveoli in the airways. In ARDS and in critically ill obese obese patients, chest wall mechanics are impaired and simply looking at the airway pressures or vent mechanics may not be an accurate enough assessment of what is truly happening at the alveolar level.
How is this maneuver performed?
- The distal end of the balloon is connected to a monitor that examines wave forms or a pressure transducer and the esophageal balloon catheter is inserted into the stomach, just how a nasogastric tube is inserted.
- When the catheter is in the stomach, as evidenced by aspiration of gastric contents, auscultation, or ultrasound visualization of air insufflation, the catheter is inflated about half way and retracted back into the mid lower third of the esophagus, which is usually a marker on the catheter at about 35-45 cm.
- At this point, a negative deflection will appear at the beginning of inspiration in a spontaneously breathing patient. Then, a dynamic occlusion test is done, which measures the ratio of change in the esophageal pressure to the change in the airway opening pressure during 3-5 spontaneous breaths against a closed airway. Readings close to each other indicate a valid measurement.
- The PEEP settings are then increased incrementally until the transpulmonary pressure is around 0-10 cm H2O. A slightly positive transpulmonary pressure keeps the lungs open and expanded. The PEEP settings to achieve this is in the optimal PEEP for the patient.
EPVENT 1 was a single center, randomized control trial that compared mechanical ventilation guided by the esophageal balloon versus mechanical ventilation guided by ARDS network trial. The investigators found that the optimal PEEP in the esophageal balloon group was 18 + 5 cm H2O whereas the ARDS network protocol group was 12 + 5 cm H2O. With these measurements the PaO2/ FiO2 was 280 +– 126 mmhg in the esophageal balloon arm and 191 + 71 in the control arm. The study was terminated early, after 61 patients were enrolled, due to the outstanding improvement PaO2/ FiO2 in the treatment arm. There was no difference in mortality and it was not powered high enough to show differences in ventilator free days, length of stay, or long term clinical outcome.
The EPVENT2 was a multicenter, randomized control trial across 14 hospitals that essentially continued from it’s first phase in EPVENT1. The major difference between these two trials is that EPVENT2 compared it to hhe high PEEP table, thus the set PEEP was higher in this trial than EPVENT1. The authors concluded that in patients with moderate to severe ARDS, PEEP guided by esophageal pressures did not result in difference in death and days free from mechanical ventilation compared with the ARDS network trial PEEP settings. There were a lot of weaknesses to this trial, not to be discussed here but can be found in the discussion portion of the study, and more trials are needed to examine this further. One point to note is that these trials did not include obese patients, which is a population that may benefit from this tool.
The insertion of the esophageal balloon is entirely operator dependent, and if the balloon is malpositioned, the readings will be inaccurate.
If the patient has a large amount of consolidation or fibrotic lung in the dorsal lung regions, it will be difficult to achieve the optimal PEEP based on the fact that the esophageal catheter is in the ventral and middle part of the lung. It is highly unlikely that the transpulmonary pressure is the same throughout and overdistension can occur in the areas that are not affected by the consolidation. In short, the ARDS lung is heterogeneous and the esophageal balloon reflects pressures in the surrounding areas, and it will be closer to the plateau pressures in the dependent regions but overestimate the plateau pressure in the non-dependent regions.
- An esophageal balloon catheter is another tool in the toolkit to examine the optimal PEEP for obese critically ill patients and patients with ARDS.
- It does come with its own caveats, but if the operator is skilled in inserting the catheter and interpreting the data, it can be a great instrument to assess for the ideal PEEP in these specific patient populations.
- Akoumianaki E, Maggiore SM, et al. The application of esophageal pressure measurement in patients with respiratory failure. Am J Respir Crit Care Med. 2014 Mar 1;189(5):520-31.
- Beitler JR, Sarge T, et al.. Effect of Titrating Positive End-Expiratory Pressure (PEEP) With an Esophageal Pressure-Guided Strategy vs an Empirical High PEEP-Fio2 Strategy on Death and Days Free From Mechanical Ventilation Among Patients With Acute Respiratory Distress Syndrome: A Randomized Clinical Trial. JAMA. 2019 Mar 5;321(9):846-857.
- Mojoli F, Torriglia F, et al. Technical aspects of bedside respiratory monitoring of transpulmonary pressure. Ann Transl Med. 2018;6(19):377.
- Piraino T and Cook D. Optimal PEEP Guided by Esophageal Balloon Manometry. Respiratory Care April 2011, 56 (4) 510-513.
- Talmor D, Sarge T, Malhotra A, et al. Mechanical ventilation guided by esophageal pressure in acute lung injury. N Engl J Med. 2008;359(20):2095-2104.