Esophageal Manometry

Abstract

The estimation of pleural pressure with esophageal manometry has been used for decades, and it has been a fertile area of physiology research in healthy subject as well as during mechanical ventilation in patients with lung injury. However, its scarce adoption in clinical practice takes its roots from the (false) ideas that it requires expertise with years of training, that the values obtained are not reliable due to technical challenges or discrepant methods of calculation, and that measurement of esophageal pressure has not proved to benefit patient outcomes. Despites these criticisms, esophageal manometry could contribute to better monitoring, optimization, and personalization of mechanical ventilation from the acute initial phase to the weaning period. This review aims to provide a comprehensive but comprehensible guide addressing the technical aspects of esophageal catheter use, its application in different clinical situations and conditions, and an update on the state of the art with recent studies on this topic and on remaining questions and ways for improvement.

Keywords: ARDS; asynchrony; mechanical ventilation; mechanical ventilator weaning; physiologic monitoring; respiratory mechanics.

Fig. 1.

Examples of flow (pink), airway pressure (P_aw blue), esophageal pressure (P_es, green), transpulmonary pressure (P_L, black) in patients with different breathing conditions (passive, active, or partially active). (A) Flow, P_aw, P_es, and P_L waveforms in a passive patient during volume assist control ventilation. Machine inflation creates a positive deflection on the P_es tracing that comes back to baseline during exhalation. (B) Flow, P_aw, P_es, and P_L waveforms in a patient breathing actively and triggering all of the breaths during pressure support ventilation. The patient’s effort creates a negative swing in the P_es tracing, triggering machine inflation. (C) Flow, P_aw, P_es, and P_L waveforms in a patient triggering the machine but not sustaining effort. The patient’s effort creates an initial negative swing in the P_es tracing. When the patient’s effort stops during the second phase of inspiration, the patient is passive and the machine inflation creates a positive pressure transmitted to the P_es, leading to a positive deflection. During exhalation, P_es goes back to baseline.

Fig. 2.

Pressure waveforms during insertion of an esophageal catheter. P_aw = airway pressure; P_es = esophageal pressure; P_g = gastric pressure; PS = pressure support. From Reference 13, with permission.

Fig. 3.

Static esophageal balloon pressure-volume curves showing the relationship between balloon filling volume and static values of esophageal pressure (P_es), both at end-expiration (circles) and at end-inspiration (squares). On the end-expiratory pressure-volume curve, the intermediate linear section was graphically detected and analyzed for its lower and upper limits (V_MIN and V_MAX, respectively). The range between V_MIN and V_MAX was considered to correspond to appropriate balloon filling, with volumes below V_MIN denoting underfilling and volumes above V_MAX denoting overdistention. The elastance of the esophagus (cm H₂O/mL) was considered equivalent to the slope of this section of the end-expiratory pressure-volume curve. Within the appropriate filling range, we identified V_BEST as the filling volume associated with the maximum difference between end-inspiratory P_es and end-expiratory P_es. From Reference 17, with permission.

Fig. 4.

Example of frequent esophageal spasm hampering esophageal pressure (P_es) monitoring. Regular spasm lasting around 4 s occur every 5 s. During spasms, P_es as high as 38 cm H₂O is not representative of pleural pressure anymore and end-expiratory transpulmonary pressure (P_L) falsely reads -20 cm H₂O. P_aw = airway pressure.

Fig. 5.

Examples of ways to assess patient effort with esophageal pressure. (A) Esophageal pressure (P_es) tracings. C_cw, estimated at 4% of vital capacity, has been superimposed on P_es at the onset of the fall in P_es and at the onset of inspiratory flow generation (ie, the first vertical line), together with dynamic C_L. The colored area comprises the total pressure-time product (PTP) of respiratory muscle pressure. The yellow area is the PTP attributed to intrinsic PEEP, the green area represents elastic PTP, and the gray area represents resistive PTP. (B) Pressure-volume curve of P_es and lung volume. The C_cw and C_L intersect at FRC. The yellow area represents work of breathing (WOB) attributed to intrinsic PEEP, the green area represents elastic WOB, and the gray area represents resistive WOB. C_cw = compliance of the chest wall; C_L = compliance of the lung; FRC = functional residual capacity; PEEP = positive end-expiratory pressure; FRC = functional residual capacity; VC = vital capacity; PEEPi = intrinsic PEEP. Redrawn from data in reference .

Fig. 6.

Flow (pink), airway pressure (P_aw, blue), and esophageal pressure (P_es, green) waveforms showing patient-ventilator dyssynchronies. (A) In pressure assist controlled mode, the machine inflation time (Ti-M) lasts longer than the patient’s neural inspiration (Ti-N), creating delayed cycling. This excess assistance causes ineffective effort in the following breath because the patient’s respiratory muscle contraction is not strong enough to trigger an inflation (ie, wasted effort). This is clearly seen on the P_es tracing, which shows a negative deflection failing to trigger a machine inflation. This can also be suggested by the concomitant bump seen on the flow tracing during the expiration phase. (B) In pressure controlled continuous mandatory ventilation mode, the Ti-M is shorter than the patient’s Ti-N, creating premature cycling. The patient’s inspiratory effort continues beyond machine inspiration and prevents the peak expiration flow usually seen when the expiration valve opens and the exhalation is passive (ie, the patient tries to get flow in while the circuit is supposed to let the flow go out). The bump in the early phase of the exhalation is also suggestive of the patient effort continuing during expiration. (C) In volume controlled continuous ventilation mode, the initial inflation is passive in all breaths, and the machine starts the inspiration phase on a time command. At the end of the inspiration phase, the patient’s effort occurs (ie, the negative swing seen on the first breath), and there is a muscle contraction continuing during the expiration. As during ineffective effort or short cycling, this can be suggested by the bump on the flow seen during expiration. This likely creates an eccentric diaphragm contraction that could be injurious. This sequence of passive inflation followed by a muscle contraction is defined as reverse triggering. Of note, the fourth breath shows the same type of asynchrony, but this reverse triggering is strong enough to trigger a second inflation and breath stacking. This type of reverse triggering with breath stacking can injure the lung by providing tidal volume as high as twice the value set on the machine.