Effect of external PEEP in patients under controlled mechanical ventilation with an auto-PEEP of 5 cmH2O or higher.
BACKGROUND
In some patients with auto-positive end-expiratory pressure (auto-PEEP), application of PEEP lower than auto-PEEP maintains a constant total PEEP, therefore reducing the inspiratory threshold load without detrimental cardiovascular or respiratory effects. We refer to these patients as "complete PEEP-absorbers." Conversely, adverse effects of PEEP application could occur in patients with auto-PEEP when the total PEEP rises as a consequence. From a pathophysiological perspective, all subjects with flow limitation are expected to be "complete PEEP-absorbers," whereas PEEP should increase total PEEP in all other patients. This study aimed to empirically assess the extent to which flow limitation alone explains a "complete PEEP-absorber" behavior (i.e., absence of further hyperinflation with PEEP), and to identify other factors associated with it.


METHODS
One hundred patients with auto-PEEP of at least 5 cmH2O at zero end-expiratory pressure (ZEEP) during controlled mechanical ventilation were enrolled. Total PEEP (i.e., end-expiratory plateau pressure) was measured both at ZEEP and after applied PEEP equal to 80 % of auto-PEEP measured at ZEEP. All measurements were repeated three times, and the average value was used for analysis.


RESULTS
Forty-seven percent of the patients suffered from chronic pulmonary disease and 52 % from acute pulmonary disease; 61 % showed flow limitation at ZEEP, assessed by manual compression of the abdomen. The mean total PEEP was 7 ± 2 cmH2O at ZEEP and 9 ± 2 cmH2O after the application of PEEP (p < 0.001). Thirty-three percent of the patients were "complete PEEP-absorbers." Multiple logistic regression was used to predict the behavior of "complete PEEP-absorber." The best model included a respiratory rate lower than 20 breaths/min and the presence of flow limitation. The predictive ability of the model was excellent, with an overoptimism-corrected area under the receiver operating characteristics curve of 0.89 (95 % CI 0.80-0.97).


CONCLUSIONS
Expiratory flow limitation was associated with both high and complete "PEEP-absorber" behavior, but setting a relatively high respiratory rate on the ventilator can prevent from observing complete "PEEP-absorption." Therefore, the effect of PEEP application in patients with auto-PEEP can be accurately predicted at the bedside by measuring the respiratory rate and observing the flow-volume loop during manual compression of the abdomen.
Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy. giuseppe.natalini@gmail.com.
Giuseppe
G
Natalini
Department of Anesthesia and Intensive Care, Spedali Civili Hospital, Brescia, Italy.
Daniele
D
Tuzzo
Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy.
Antonio
A
Rosano
Department of Anesthesia and Intensive Care, SS. Annunziata Hospital, Savigliano, Italy.
Marco
M
Testa
Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy.
Michele
M
Grazioli
Department of Anesthesia and Intensive Care, Misericordia Hospital, Grosseto, Italy.
Vincenzo
V
Pennestrì
Department of Anesthesia and Intensive Care, San Giovanni Bosco Hospital, Naples, Italy.
Guido
G
Amodeo
Department of Anesthesia and Intensive Care, Agnelli Hospital, Pinerolo, Italy.
Francesco
F
Berruto
Department of Anesthesia and Intensive Care, Santa Maria degli Angeli Hospital, Pordenone, Italy.
Marialinda
M
Fiorillo
Department of Anesthesia and Intensive Care, Cattinara Hospital, Trieste, Italy.
Alberto
A
Peratoner
Department of Anesthesia and Intensive Care, Mellino Mellini Hospital, Chiari, Italy.
Andrea
A
Tinnirello
Department of Anesthesia, Critical Care Medicine and Emergency, University of Brescia at Spedali Civili, Brescia, Italy.
Matteo
M
Filippini
Department of Anesthesia and Intensive Care, Cardarelli Hospital, Naples, Italy.
Paolo F
PF
Marsilia
Respiratory Epidemiology, Occupational Medicine and Public Health, Imperial College, London, UK.
Cosetta
C
Minelli
Department of Anesthesia and Intensive Care, Fondazione Poliambulanza Hospital, Brescia, Italy.
Achille
A
Bernardini
Auto-positive end-expiratory pressure; Dynamic hyperinflation; Flow limitation; Mechanical ventilation; Positive end-expiratory pressure; Respiratory rate