Expiratory flow limitation in intensive care: prevalence and risk factors

Carlo Alberto Volta,Savino Spadaro,Gaetano Scaramuzzo,Elisabetta Marangoni,Domenico Luca Grieco,Valentina Alvisi,Francesca Dalla Corte,Alberto Fogagnolo,Riccardo Ragazzi,Chiara Rizzuto

doi:10.1186/s13054-019-2682-4

Abstract

BackgroundExpiratory flow limitation (EFL) is characterised by a markedly reduced expiratory flow insensitive to the expiratory driving pressure. The presence of EFL can influence the respiratory and cardiovascular function and damage the small airways; its occurrence has been demonstrated in different diseases, such as COPD, asthma, obesity, cardiac failure, ARDS, and cystic fibrosis. Our aim was to evaluate the prevalence of EFL in patients requiring mechanical ventilation for acute respiratory failure and to determine the main clinical characteristics, the risk factors and clinical outcome associated with the presence of EFL.MethodsPatients admitted to the intensive care unit (ICU) with an expected length of mechanical ventilation of 72 h were enrolled in this prospective, observational study. Patients were evaluated, within 24 h from ICU admission and for at least 72 h, in terms of respiratory mechanics, presence of EFL through the PEEP test, daily fluid balance and followed for outcome measurements.ResultsAmong the 121 patients enrolled, 37 (31%) exhibited EFL upon admission. Flow-limited patients had higher BMI, history of pulmonary or heart disease, worse respiratory dyspnoea score, higher intrinsic positive end-expiratory pressure, flow and additional resistance. Over the course of the initial 72 h of mechanical ventilation, additional 21 patients (17%) developed EFL. New onset EFL was associated with a more positive cumulative fluid balance at day 3 (103.3 ml/kg) compared to that of patients without EFL (65.8 ml/kg). Flow-limited patients had longer duration of mechanical ventilation, longer ICU length of stay and higher in-ICU mortality.ConclusionsEFL is common among ICU patients and correlates with adverse outcomes. The major determinant for developing EFL in patients during the first 3 days of their ICU stay is a positive fluid balance. Further studies are needed to assess if a restrictive fluid therapy might be associated with a lower incidence of EFL.

Highlights

Expiratory flow limitation (EFL) is characterised by a markedly reduced expiratory flow insensitive to the expiratory driving pressure
The primary aim of the present study is to evaluate the prevalence of EFL in intensive care unit (ICU) patients requiring mechanical ventilation for acute respiratory failure, and to determine the main clinical characteristics and risk factors associated with the presence of EFL
The main factors independently related to EFL at ICU admission were a body mass index (BMI) ≥ 30 kg/m2, a mMRC score ≥ 3, a Sequential Organ Failure Assessment (SOFA) score ≥ 6 and a medical history of chronic obstructive pulmonary disease (COPD) (Table 2)

Summary

Introduction

Expiratory flow limitation (EFL) is characterised by a markedly reduced expiratory flow insensitive to the expiratory driving pressure. Incomplete lung emptying is frequently associated with dynamic lung hyperinflation with the generation of intrinsic positive end-expiratory pressure (PEEPi) [18] The latter can have several adverse effects on haemodynamic (i.e. cardiac output depression, increased pulmonary vessel resistance), respiratory muscle function (i.e. altered length-tension characteristics of the diaphragm, increased work of breathing) and patient-ventilator interaction (i.e. patient-ventilator asynchrony). The ensuing inspiration re-open those airways, and repetitive opening and closure of small airways has been shown to induce histological damage of small airways probably due to the development of high shear forces [21, 22] This should elicit an inflammatory response and increase the risk of low lung volume injury [23, 24]

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