Esophageal Pressure Measurement: A Primer

Abstract

Over the last decade, the literature exploring clinical applications for esophageal manometry in critically ill patients has increased. New mechanical ventilators and bedside monitors allow measurement of esophageal pressures easily at the bedside. The bedside clinician can now evaluate the magnitude and timing of esophageal pressure swings to evaluate respiratory muscle activity and transpulmonary pressures. The respiratory therapist has all the tools to perform these measurements to optimize mechanical ventilation delivery. However, as with any measurement, technique, fidelity, and accuracy are paramount. This primer highlights key knowledge necessary to perform measurements and highlights areas of both uncertainty and ongoing development.

Keywords: PEEP; esophageal pressure measurement; lung-protective ventilation; mechanical ventilation; respiratory system driving pressure; transpulmonary driving pressure.

Fig. 1.

Relationship of the esophagus with the pleural space and airway. Representative computed tomography of the chest of a patient with an orogastric tube. A and B: upper and mid thorax; note the relationship of the trachea, the esophagus, and the pleural space. C: lower thorax; notice the relationship of the heart with the esophagus. An esophageal catheter placed too high will transmit airway pressures and too low the heart will transmit large cardiac oscillations.

Fig. 2.

Diagram of the respiratory system with one-compartment lung and chest wall. The chest wall is subdivided into rib cage and diaphragmatic and abdominal wall components. The arrows labeled Δ muscle pressure (ΔP_mus) indicate the positive directions of the corresponding P_mus differences. The diagram shows the pressure difference formulas color coded to allow better understanding of the terms transalveolar and transpulmonary pressure difference. From reference 10. ΔP_mus = muscle pressure difference; di = diaphragm; P_aw = pressure at the airway opening; P_A = alveolar pressure; P_pl = pressure in the intrapleural space; RC = rib cage; BS = body surface; ab = abdomen; P_tp = transalveolar pressure; P_tp = transpulmonary pressure.

Fig. 3.

Computed tomography of the chest highlighting the pleural pressure (P_pl) gradient and dependent and non-dependent areas of the lung. Line A demonstrates the P_pl at the non-dependent areas of the lung. Line B demonstrates the mid-lung P_pl; note the yellow circle is the esophagus and is the location where P_pl is being measured. Line C is the pressure at the dependent areas of the lung. The asterisk demonstrates collapse/atelectasis of the injured lung. The P_pl gradient is the difference in pressure from line A to C. The blue line outlines the pleura. The red line outlines the heart.

Fig. 4.

Demonstration of the esophageal pressure waveform during the insertion of an esophageal balloon. P_aw = airway pressure; P_es = esophageal pressure; P_g = gastric pressure; PS = pressure support. From reference 4 with permission.

Fig. 5.

Occlusion test. Panel A demonstrates the pressure at the airway opening (P_aw) (red line) and esophageal pressure (P_es) (blue line) during an end-expiratory (EE) pause maneuver (occlusion) in a patient with inspiratory effort. Notice the overlap of pressures during inspiratory effort. The blue arrow is the ΔP_es and the red arrow the ΔP_aw used to calculate the ratio. Panel B demonstrates the P_aw and P_es in a patient without any effort and on mechanical ventilation. Between the mechanical breaths (*), an EE pause maneuver is performed along with gentle compressions of the chest. The blue arrow is the ΔP_es and the red arrow the ΔP_aw used to calculate the ratio. Adapted with permission from reference 4. P_es = esophageal pressure; P_aw = pressure at the airway opening.

Fig. 6.

Site of measurements to evaluate the transpulmonary pressure (P_tp). Top panel has the pressure at the airway opening (P_aw), the middle panel the esophageal pressure (P_es) as a surrogate for pleural pressure. And the lower panel has the P_tp. Asterisk highlights the cardiac oscillations. A: the end-expiratory (EE) P_aw; B: the EE P_es; C: the EE P_tp; D: the end-inspiratory (EI) P_aw; E: the EI P_es; F: the EI P_tp. Modified from reference 30. Reprinted with permission from reference 30. P_aw = pressure at the airway opening; P_es = esophageal pressure; P_tp = transpulmonary pressure.

Fig. 7.

Esophageal pressure (P_es) measurement using a bedside monitor. The effect of inspiratory and expiratory muscles on P_es measurements. The measurements are done on the pulmonary artery screen to allow freezing the screen. Scale is in mm Hg; to convert to cm H₂O, multiply by 1.36. Bidirectional interrupted white arrow highlights the esophageal swing (ΔP_es). Panel A: vigorous inspiratory and expiratory effort. ΔP_es was 16 cm H₂O; the end-expiratory (EE) P_es was 32.6 cm H₂O. Notice the upslope on the expiratory phase. Panel B: same patient after administration of sedatives in preparation for neuromuscular blockade. The ΔP_es is 3.4 cm H₂O and EE P_es 25 cm H₂O. The asterisk highlights a rise in pressure due to late cycle of the mechanical breath. Panel C demonstrates the patient P_es during neuromuscular blockade. The ΔP_es is absent. The rise in P_es reflects the transmission of the mechanical breath to the pleural space. The EE P_es is now 23 cm H₂O. The circle highlights the EE pressure. PA = pulmonary artery.

Fig. 8.

Graphic depiction of the esophageal pressure (P_es) and the pressure at the airway opening, timing of events, and measurement of the esophageal swing. 1: Start of breath by P_es; 2: start of the mechanical ventilation breath; 3: end of breath by P_es; 4: end of mechanical ventilation breath. A is the end-expiratory P_es. B is the nadir of the P_es. Reprinted with permission from Cleveland Clinic Foundation. P_es = esophageal pressure; P_aw = pressure at the airway opening.