Short-term effects of positive end-expiratory pressure on breathing pattern: an interventional study in adult intensive care patients

Abstract

Introduction: Positive end-expiratory pressure (PEEP) is used in mechanically ventilated patients to increase pulmonary volume and improve gas exchange. However, in clinical practice and with respect to adult, ventilator-dependent patients, little is known about the short-term effects of PEEP on breathing patterns.

Methods: In 30 tracheally intubated, spontaneously breathing patients, we sequentially applied PEEP to the trachea at 0, 5 and 10 cmH2O, and then again at 5 cmH2O for 30 s each, using the automatic tube compensation mode.

Results: Increases in PEEP were strongly associated with drops in minute ventilation (P < 0.0001) and respiratory rate (P < 0.0001). For respiratory rate, a 1 cmH2O change in PEEP in either direction resulted in a change in rate of 0.4 breaths/min. The effects were exclusively due to changes in expiratory time. Effects began to manifest during the first breath and became fully established in the second breath for each PEEP level. Identical responses were found when PEEP levels were applied for 10 or 60 s. Post hoc analysis revealed a similar but stronger response in patients with impaired respiratory system compliance.

Conclusion: In tracheally intubated, spontaneously breathing adult patients, the level of PEEP significantly influences the resting short-term breathing pattern by selectively affecting expiratory time. These findings are best explained by the Hering-Breuer inflation/deflation reflex.

Figure 1

Time course of tracheal pressure during steps in PEEP. The examination was performed while the patient was breathing spontaneously at (tracheal) continuous positive airway pressure by means of the automatic tube compensation mode. Starting from 5 cmH₂O, the level of PEEP was changed to 0, 5, 10 and (again) 5 cmH₂O for durations of 30 s each for five consecutive runs. Note that the changes in PEEP level were in synchrony with the patient's breathing pattern (i.e. upward steps during inspiration and downward steps during expiration). PEEP, positive end-expiratory pressure; P_trach, tracheal pressure.

Figure 2

Short-term effects of PEEP on breathing pattern. The increase in PEEP is paralleled by an increase in expiratory time with a concomitant fall in both respiratory rate and minute ventilation. The decrease in PEEP has an opposite effect. Tidal volume and inspiratory time were not significantly affected by changes in PEEP in either direction. Results are outlined as averaged percentage changes from zero PEEP and are expressed as mean ± 1 standard error of the mean (SEM). *P < 0.025, versus zero PEEP. PEEP, positive end-expiratory pressure.

Figure 3

Short-term effects of PEEP on V_E in the individual patient. Results are from the investigation with PEEP steps of 30 s duration, and each coloured line shows findings for a different patient. Although V_E is dispersed over a wide range, its behaviour was similar between patients (i.e. V_E decreased with increasing levels of PEEP, and vice versa). PEEP, positive end-expiratory pressure; V_E, minute ventilation.

Figure 4

Short-term effects of PEEP on expiratory time in the individual patient. Results are from the investigation with PEEP steps of 30 s duration, and each coloured line shows findings for a different patient. Although T_ex is dispersed over a wide range, its behaviour was similar between patients (i.e. T_ex increased with the increasing levels of PEEP, and vice versa). PEEP, positive end-expiratory pressure; T_ex, expiratory time.

Figure 5

Effects on breathing pattern brought on by steps in PEEP of different duration. Effects are shown on V_E, which behaved similarly whether the PEEP steps were applied for 10, 30, or 60 s. *P < 0.025, versus zero PEEP. PEEP, positive end-expiratory pressure; V_E, minute ventilation.

Figure 6

Changes of breathing pattern in the first, second and third breath after steps of PEEP. Results are from the investigation with PEEP steps of 30 s duration. The shaded areas represent averaged values of all breath for the corresponding PEEP level; open bars indicate the first, second, and third breath after changes of PEEP. Values are expressed as means ± 1 standard error of the mean (SEM). Note that changes of breathing pattern were beginning to manifest within the first breath and became fully established in the second breath after both upward and downward steps in PEEP. *P < 0.025, versus mean values within the corresponding PEEP level. BTPS, body temperature pressure, (water damp) saturated; PEEP, positive end-expiratory pressure; rr, respiratory rate; T_ex, expiratory time; T_in, inspiratory time; V_E, minute ventilation.