What are we assessing with esophageal pressure measurement
Esophageal pressure measurement is an advanced form of monitoring for mechanically ventilated patients in order to assess transpulmonary pressure and the risk of ventilator-induced lung injuries (VILI), as well as optimize ventilator settings (1, 2). However, there have been concerns about the validity of esophageal pressure to assess pleural pressure (3).
- Esophageal pressure measurement allows us to assess transpulmonary pressure and the risk of ventilator-induced lung injuries, as well as optimize ventilator settings.
- The validity of esophageal pressure to assess pleural pressure has been the subject of some debate.
- A recent physiological study compared end-inspiratory and end-expiratory esophageal pressures with direct measurements of pleural pressure in dependent and non-dependent lung regions at different levels of PEEP.
- Results confirmed the accuracy of absolute values of esophageal pressure to assess pleural pressure, provided that the correct method of esophageal balloon insertion, inflation, and verification is used.
The first concern is the accuracy of an absolute measurement of esophageal pressure to assess pleural pressure. The second concern relates to which regional pleural pressure is assessed by esophageal pressure, assuming a vertical gradient in pleural pressure. Therefore, some clinicians use absolute measurements of esophageal pressure to calculate end-inspiratory and end-expiratory transpulmonary pressure (PL) (4). Other clinicians only consider the changes in esophageal pressure to assess the changes in pleural pressure during mechanical ventilation, and calculate the elastance of the chest wall and the lung (elastance-derived method). End-inspiratory PL is then calculated as plateau pressure multiplied by the ratio between the lung and respiratory-system elastance (5, 6). The two methods result in different estimates of PL (7). A recent study aimed to determine the accuracy of esophageal pressure to reflect pleural pressure (8).
In this physiological study, end-inspiratory and end-expiratory esophageal pressures were compared with direct measurements of pleural pressure in dependent and non-dependent lung regions at different levels of PEEP. The authors used a model of an anesthetized pig with lung injury, and a human cadaver model. Esophageal pressure was measured using an esophageal balloon (Nutrivent catheter) correctly positioned, inflated, and validated (9). Pleural pressure was measured directly by means of pleural sensors inserted surgically in the dependent and non-dependent pleural space. In the animal model, a large range of PEEP values from 4 to 24 cmH2O was tested, using electrical impedance tomography (EIT) and a CT scan to calculate lung collapse and superimposed pressure, respectively. Measurements were performed before and after lung injury induced by surfactant depletion. In the human cadaver model, lung characteristics were similar to those of a lung-injured patient. The range of PEEP values tested was between 5 and 15 cmH2O.
Results confirmed a vertical decrease in pleural pressure from the non-dependent to the dependent lung region. The gradient magnitude in the pig with lung injury was greater than in the pig with a non-injured lung and was correlated to the superimposed pressure calculated by a CT scan. In the human cadaver ventilated at 10 cmH2O of PEEP, the vertical pleural gradient was 10 cmH2O.
In the human cadaver, the end-inspiratory and end-expiratory esophageal pressures were approximately midway between the measured pleural pressure in the dependent and non-dependent lung regions. This relationship was maintained at all levels of PEEP. Therefore, end-inspiratory and end-expiratory PL assessed with esophageal pressure were approximatively midway between PL calculated from pleural pressure in dependent and non-dependent lung regions.
In pigs with lung injury, the end-expiratory PL needed to prevent atelectasis was 4.6 cmH2O. An end-expiratory PL just above zero was associated with 17±7% atelectasis.
In both pigs and human cadavers, end-inspiratory pleural pressure calculated from the elastance- derived method was very close to pleural pressure measured directly in the non-dependent lung region. Therefore, end-inspiratory PL calculated from the elastance-derived method closely reflected the measured end-inspiratory PL in the non-dependent lung region.
This study confirms the accuracy of absolute values of esophageal pressure to assess pleural pressure, provided that the correct method of esophageal balloon insertion, inflation, and verification is used (9, 10). The main purpose is to optimize ventilator settings in order to prevent lung stress, strain, and atelectrauma. Atelectrauma occurring mainly in the dependent lung can be prevented by adjusting PEEP to reach an end-expiratory PL above zero cmH2O if targeting the mid-lung region, or around 5 cmH2O if targeting the dependent lung region. Lung stress that occurs mainly in the non-dependent lung can be prevented by keeping PL calculated using the elastance-derived method below 15–20 cmH2O. Lung strain occurring in the aerated part of the lung can be prevented by keeping transpulmonary driving pressure (end-inspiratory PL – end-expiratory PL assessed using esophageal pressure) below 10 cmH2O (11).
The HAMILTON-C6*/G5/S1* ventilators offer an auxiliary port for connecting the esophageal catheter pressure line. The clinician can then display the waveform for absolute values of esophageal and transpulmonary pressure.
* Not available in all markets
- Akoumianaki E, Maggiore SM, Valenza F, Bellani G, Jubran A, Loring SH,et al.; PLUG Working Group (Acute Respiratory Failure Section of the European Society of Intensive Care Medicine). The application of esophageal pressure measurement in patients with respiratory failure. Am J Respir Crit Care Med 2014;189:520–531.
- Mauri T, Yoshida T, Bellani G, Goligher EC, Carteaux G, Rittayamai N, et al; PLeUral pressure working Group (PLUG—Acute Respiratory Failure section of the European Society of Intensive Care Medicine). Esophageal and transpulmonary pressure in the clinical setting: meaning, usefulness and perspectives. Intensive Care Med 2016;42(9):1360-73 (abstract only).
- Grieco DL, Chen L, Brochard L. Transpulmonary pressure: importance and limits. Ann Transl Med 2017;5(14):285.
- Talmor D, Sarge T, Malhotra A, O'Donnell CR, Ritz R, Lisbon A, et al. Mechanical ventilation guided by esophageal pressure in acute lung injury. N Engl J Med 2008; 359:2095–2104.
- Staffieri F, Stripoli T, De Monte V, Crovace A, Sacchi M, De Michele M, et al. Physiological effects of an open lung ventilatory strategy titrated on elastance-derived end-inspiratory transpulmonary pressure: study in a pig model. Crit Care Med 2012 ; 40(7):2124-31.
- Chiumello D, Cressoni M, Colombo A, Babini G, Brioni M, Crimella F, et al. The assessment of transpulmonary pressure in mechanically ventilated ARDS patients. Intensive Care Med 2014; 40:1670–1678 (abstract only).
- Gulati G, Novero A, Loring SH, Talmor D. Pleural pressure and optimal positive end-expiratory pressure based on esophageal pressure versus chest wall elastance: incompatible results. Crit Care Med 2013; 41: 1-7 (abstract only).
- Yoshida T, Amato MBP, Grieco DL, Chen L, Lima CAS, Roldan R, et al. Esophageal Manometry and Regional Transpulmonary Pressure in Lung Injury. Am J Respir Crit Care Med 2018;197(8):1018-1026.
- Baydur A, Behrakis PK, Zin WA, Jaeger M, Milic-Emili J. A simple method for assessing the validity of the esophageal balloon technique. Am Rev Respir Dis 1982;126:788–791 (asbtract only).
- Mojoli F, Iotti GA, Torriglia F, Pozzi M, Volta CA, Bianzina S, et al. In vivo calibration of esophageal pressure in the mechanically ventilated patient makes measurements reliable. Crit Care 2016;20:98.
- Baedorf Kassis E, Loring SH, Talmor D. Mortality and pulmonary mechanics in relation to respiratory system and transpulmonary driving pressures in ARDS. Intensive Care Med 2016;42(8):1206-13 (abstract only).
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