Extracellular matrix and mechanical ventilation in healthy lungs: back to baro/volotrauma?

Effects of mechanical ventilation on the interstitial extracellular matrix in healthy lungs and lungs affected by acute respiratory distress syndrome: a narrative review

BACKGROUND

Mechanical ventilation, a lifesaving intervention in critical care, can lead to damage in the extracellular matrix (ECM), triggering inflammation and ventilator-induced lung injury (VILI), particularly in conditions such as acute respiratory distress syndrome (ARDS). This review discusses the detailed structure of the ECM in healthy and ARDS-affected lungs under mechanical ventilation, aiming to bridge the gap between experimental insights and clinical practice by offering a thorough understanding of lung ECM organization and the dynamics of its alteration during mechanical ventilation.

MAIN TEXT

Focusing on the clinical implications, we explore the potential of precise interventions targeting the ECM and cellular signaling pathways to mitigate lung damage, reduce inflammation, and ultimately improve outcomes for critically ill patients. By analyzing a range of experimental studies and clinical papers, particular attention is paid to the roles of matrix metalloproteinases (MMPs), integrins, and other molecules in ECM damage and VILI. This synthesis not only sheds light on the structural changes induced by mechanical stress but also underscores the importance of cellular responses such as inflammation, fibrosis, and excessive activation of MMPs.

CONCLUSIONS

This review emphasizes the significance of mechanical cues transduced by integrins and their impact on cellular behavior during ventilation, offering insights into the complex interactions between mechanical ventilation, ECM damage, and cellular signaling. By understanding these mechanisms, healthcare professionals in critical care can anticipate the consequences of mechanical ventilation and use targeted strategies to prevent or minimize ECM damage, ultimately leading to better patient management and outcomes in critical care settings.

Effect of a preoperative single-dose steroid on pulmonary function and postoperative symptoms after modified radical mastectomy: results of a randomized clinical trial

Background

Evidence suggests that a preoperative single-dose steroid improves lung function and decreases the incidence of postoperative symptoms; however, this has not been sufficiently proved in modified radical mastectomy for cancer. This study aimed to evaluate the efficacy of preoperative single-dose steroid administration for postoperative lung function and postoperative symptoms in women undergoing modified radical mastectomy for breast cancer.

Methods

In this controlled clinical trial, conducted between June 2014 and October 2018, we examined 81 patients. Patients received a preoperative single dose of 8 mg dexamethasone (n=41; treatment group) or placebo (sterile injectable water; n=40; control group). We obtained data on postoperative nausea and vomiting and pain intensity and performed spirometry 1 h before and 1, 6, 12, and 24 h after surgery. The use of additional analgesic or antiemetic drugs was recorded. We followed up patients 30 days after discharge and recorded any surgical or medical complications.

Results

The age distribution and anthropometric variables of the two groups were similar. Almost 50% of the patients in each group also underwent breast reconstruction. In the treatment group, pain intensity was always lower, the incidence of postoperative nausea and vomiting was lower at 6, 12, and 24 h, and additional analgesics or antiemetics were required less frequently (P<0.05 for all). Both treatment and control groups demonstrated a restrictive ventilatory pattern immediately after surgery, which in the treatment group was reversed after 24 h. However, the reconstructed patients had a more intense and prolonged restrictive pattern (P<0.05). Surgical morbidity included one seroma observed in the control group. No infections occurred at the surgical site or at any other level, and no patient developed any metabolic disorder. No mortality was observed in either group.

Conclusions

This study establishes that a single preoperative dose of dexamethasone markedly decreased the incidence of postoperative nausea and vomiting and pain, improved respiratory parameters, and decreased the need for additional postoperative analgesic or antiemetic drugs.

Clinical Trial Registration

ClinicalTrials.gov (ID NCT02305173).

Gradually Increasing Tidal Volume May Mitigate Experimental Lung Injury in Rats

BACKGROUND

This study hypothesized that, in experimental mild acute respiratory distress syndrome, lung damage caused by high tidal volume (VT) could be attenuated if VT increased slowly enough to progressively reduce mechanical heterogeneity and to allow the epithelial and endothelial cells, as well as the extracellular matrix of the lung to adapt. For this purpose, different strategies of approaching maximal VT were tested.

METHODS

Sixty-four Wistar rats received Escherichia coli lipopolysaccharide intratracheally. After 24 h, animals were randomly assigned to receive mechanical ventilation with VT = 6 ml/kg for 2 h (control); VT = 6 ml/kg during hour 1 followed by an abrupt increase to VT = 22 ml/kg during hour 2 (no adaptation time); VT = 6 ml/kg during the first 30 min followed by a gradual VT increase up to 22 ml/kg for 30 min, then constant VT = 22 ml/kg during hour 2 (shorter adaptation time); and a more gradual VT increase, from 6 to 22 ml/kg during hour 1 followed by VT = 22 ml/kg during hour 2 (longer adaptation time). All animals were ventilated with positive end-expiratory pressure of 3 cm H2O. Nonventilated animals were used for molecular biology analysis.

RESULTS

At 2 h, diffuse alveolar damage score and heterogeneity index were greater in the longer adaptation time group than in the control and shorter adaptation time animals. Gene expression of interleukin-6 favored the shorter (median [interquartile range], 12.4 [9.1-17.8]) adaptation time compared with longer (76.7 [20.8 to 95.4]; P = 0.02) and no adaptation (65.5 [18.1 to 129.4]) time (P = 0.02) strategies. Amphiregulin, metalloproteinase-9, club cell secretory protein-16, and syndecan showed similar behavior.

CONCLUSIONS

In experimental mild acute respiratory distress syndrome, lung damage in the shorter adaptation time group compared with the no adaptation time group was attenuated in a time-dependent fashion by preemptive adaptation of the alveolar epithelial cells and extracellular matrix. Extending the adaptation period increased cumulative power and did not prevent lung damage, because it may have exposed animals to injurious strain earlier and for a longer time, thereby negating any adaptive benefit.

Effects of lung protective ventilation on postoperative pulmonary outcomes for prolonged oral cancer combined with free flap surgery

The intraoperative lung protective ventilation with low tidal volume, positive end expiratory pressure (PEEP) and intermittent lungs recruitment was found to decrease postoperative pulmonary complications. In this retrospective medical records study, we investigated the effects of lung protective ventilation on postoperative pulmonary outcomes among the patients received prolonged oral cancer combined with free flap surgery.We collected the medical records of the patients received oral cancer surgery with the operation time more than 12 hours from January 2011 to December 2015. We recordedFifty nine cases were included. Thirty cases received the lung protective ventilation and 29 cases received conventional ventilation. Compared to the patients received conventional ventilation, the patients received intraoperative lung protective ventilation showedIn conclusion, for the prolonged oral cancer combined with free flap surgery, the intraoperative lung protective ventilation improves postoperative pulmonary outcomes and decreases the duration of ICU stay.

Adaptive Support Ventilation Attenuates Ventilator Induced Lung Injury: Human and Animal Study

Adaptive support ventilation (ASV) is a closed-loop ventilation, which can make automatic adjustments in tidal volume (V_T) and respiratory rate based on the minimal work of breathing. The purpose of this research was to study whether ASV can provide a protective ventilation pattern to decrease the risk of ventilator-induced lung injury in patients of acute respiratory distress syndrome (ARDS). In the clinical study, 15 ARDS patients were randomly allocated to an ASV group or a pressure-control ventilation (PCV) group. There was no significant difference in the mortality rate and respiratory parameters between these two groups, suggesting the feasible use of ASV in ARDS. In animal experiments of 18 piglets, the ASV group had a lower alveolar strain compared with the volume-control ventilation (VCV) group. The ASV group exhibited less lung injury and greater alveolar fluid clearance compared with the VCV group. Tissue analysis showed lower expression of matrix metalloproteinase 9 and higher expression of claudin-4 and occludin in the ASV group than in the VCV group. In conclusion, the ASV mode is capable of providing ventilation pattern fitting into the lung-protecting strategy; this study suggests that ASV mode may effectively reduce the risk or severity of ventilator-associated lung injury in animal models.

Proteomic Lung Analysis of Mice with Ventilator-Induced Lung Injury (VILI) Using iTRAQ-Based Quantitative Proteomics

Ventilator-induced lung injury (VILI) has implications for mortality from acute lung injury (ALI) and for acute respiratory distress syndrome (ARDS) patients; the complicated mechanisms of VILI have not been well defined. To discover new biomarkers and mechanisms of VILI, isobaric Tag for Relative and Absolute Quantitation (iTRAQ)-based quantitative proteomics were applied to identify differentially expressed proteins in mice treated with high tidal volume ventilation (HV), low tidal volume ventilation (LV) and lipopolysaccharide (LPS). A total of 14 dysregulated proteins showed the same change trend both in the LV and HV group and no change in the LPS group, and most importantly, the fold change of these proteins increased with the increase of volume ventilation, which indicates these proteins may be considered as potential markers specific for VILI. Ingenuity pathway analysis (IPA) canonical pathways analysis identified the top 4 canonical pathways, including the extrinsic prothrombin activation pathway, coagulation systems, the intrinsic prothrombin activation pathway and the acute phase response, suggesting that these pathways, as associated with these proteins' expression, may be important therapeutic targets for reducing VILI. These findings will provide a new perspective for understanding the pathogenesis of VILI in the future.

Impact of Different Tidal Volume Levels at Low Mechanical Power on Ventilator-Induced Lung Injury in Rats

Tidal volume (V_T) has been considered the main determinant of ventilator-induced lung injury (VILI). Recently, experimental studies have suggested that mechanical power transferred from the ventilator to the lungs is the promoter of VILI. We hypothesized that, as long as mechanical power is kept below a safe threshold, high V_T should not be injurious. The present study aimed to investigate the impact of different V_T levels and respiratory rates (RR) on lung function, diffuse alveolar damage (DAD), alveolar ultrastructure, and expression of genes related to inflammation [interleukin (IL)-6], alveolar stretch (amphiregulin), epithelial [club cell secretory protein (CC)16] and endothelial [intercellular adhesion molecule (ICAM)-1] cell injury, and extracellular matrix damage [syndecan-1, decorin, and metalloproteinase (MMP)-9] in experimental acute respiratory distress syndrome (ARDS) under low-power mechanical ventilation. Twenty-eight Wistar rats received Escherichia coli lipopolysaccharide intratracheally. After 24 h, 21 animals were randomly assigned to ventilation (2 h) with low mechanical power at three different V_T levels (n = 7/group): (1) V_T = 6 mL/kg and RR adjusted to normocapnia; (2) V_T = 13 mL/kg; and 3) V_T = 22 mL/kg. In the second and third groups, RR was adjusted to yield low mechanical power comparable to that of the first group. Mechanical power was calculated as [(ΔP,L2/Est,_L)/2]× RR (ΔP,_L = transpulmonary driving pressure, Est,_L = static lung elastance). Seven rats were not mechanically ventilated (NV) and were used for molecular biology analysis. Mechanical power was comparable among groups, while V_T gradually increased. ΔP,_L and mechanical energy were higher in V_T = 22 mL/kg than V_T = 6 mL/kg and V_T = 13 mL/kg (p < 0.001 for both). Accordingly, DAD score increased in V_T = 22 mL/kg compared to V_T = 6 mL/kg and V_T = 13 mL/kg [23(18.5–24.75) vs. 16(12–17.75) and 16(13.25–18), p < 0.05, respectively]. V_T = 22 mL/kg was associated with higher IL-6, amphiregulin, CC16, MMP-9, and syndecan-1 mRNA expression and lower decorin expression than V_T = 6 mL/kg. Multiple linear regression analyses indicated that V_T was able to predict changes in IL-6 and CC16, whereas ΔP,_L predicted pHa, oxygenation, amphiregulin, and syndecan-1 expression. In the model of ARDS used herein, even at low mechanical power, high V_T resulted in VILI. V_T control seems to be more important than RR control to mitigate VILI.

Effects of preoperative dexamethasone on postoperative pain, nausea, vomiting and respiratory function in women undergoing conservative breast surgery for cancer: Results of a controlled clinical trial

The objective was to evaluate whether preoperative administration of dexamethasone improved postoperative nausea and vomiting (PONV), pain and respiratory function tests in women undergoing conservative surgery for breast cancer. This was a controlled clinical trial conducted between June 2013 and October 2014. Eighty patients were evaluated. Patients received a preoperative dose of 8 mg of dexamethasone (n = 40) or placebo (n = 40). The data on PONV and pain intensity was obtained and forced spirometry tests were performed, 1 hr before and at 1, 6, 12 and 24 hr after surgery. Any use of additional analgesic/antiemetic drugs was recorded. Patients were followed until 30 days after surgery for any surgical or medical complications. The pain intensity was lower in the treatment group for all periods; PONV was lower at 6, 12 and 24 hr; Additional analgesics/antiemetics were required less frequently (all p < .05). Both groups exhibited a restrictive ventilatory pattern immediately after surgery, which was reversed in the following hours. However, spirometric values were higher in the dexamethasone group. There were no pulmonary or metabolic complications after surgery. Our conclusions were that dexamethasone significantly reduced the incidences of PONV, pain and improved respiratory parameters, and reduced the need for additional postoperative analgesic and antiemetic drugs.

Poor Adherence to Lung-Protective Mechanical Ventilation in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

To determine the frequency of low-tidal volume ventilation in pediatric acute respiratory distress syndrome and assess if any demographic or clinical factors improve low-tidal volume ventilation adherence.

DESIGN

Descriptive post hoc analysis of four multicenter pediatric acute respiratory distress syndrome studies.

SETTING

Twenty-six academic PICU.

PATIENTS

Three hundred fifteen pediatric acute respiratory distress syndrome patients.

MEASUREMENTS AND MAIN RESULTS

All patients who received conventional mechanical ventilation at hours 0 and 24 of pediatric acute respiratory distress syndrome who had data to calculate ideal body weight were included. Two cutoff points for low-tidal volume ventilation were assessed: less than or equal to 6.5 mL/kg of ideal body weight and less than or equal to 8 mL/kg of ideal body weight. Of 555 patients, we excluded 240 for other respiratory support modes or missing data. The remaining 315 patients had a median PaO2-to-FIO2 ratio of 140 (interquartile range, 90-201), and there were no differences in demographics between those who did and did not receive low-tidal volume ventilation. With tidal volume cutoff of less than or equal to 6.5 mL/kg of ideal body weight, the adherence rate was 32% at hour 0 and 33% at hour 24. A low-tidal volume ventilation cutoff of tidal volume less than or equal to 8 mL/kg of ideal body weight resulted in an adherence rate of 58% at hour 0 and 60% at hour 24. Low-tidal volume ventilation use was no different by severity of pediatric acute respiratory distress syndrome nor did adherence improve over time. At hour 0, overweight children were less likely to receive low-tidal volume ventilation less than or equal to 6.5 mL/kg ideal body weight (11% overweight vs 38% nonoverweight; p = 0.02); no difference was noted by hour 24. Furthermore, in the overweight group, using admission weight instead of ideal body weight resulted in misclassification of up to 14% of patients as receiving low-tidal volume ventilation when they actually were not.

CONCLUSIONS

Low-tidal volume ventilation is underused in the first 24 hours of pediatric acute respiratory distress syndrome. Age, Pediatric Risk of Mortality-III, and pediatric acute respiratory distress syndrome severity were not associated with improved low-tidal volume ventilation adherence nor did adherence improve over time. Overweight children were less likely to receive low-tidal volume ventilation strategies in the first day of illness.

Ventilator-Induced Lung Injury (VILI) in Acute Respiratory Distress Syndrome (ARDS): Volutrauma and Molecular Effects

Acute Respiratory Distress Syndrome (ARDS) is a clinical condition secondary to a variety of insults leading to a severe acute respiratory failure and high mortality in critically ill patients. Patients with ARDS generally require mechanical ventilation, which is another important factor that may increase the ALI (acute lung injury) by a series of pathophysiological mechanisms, whose common element is the initial volutrauma in the alveolar units, and forming part of an entity known clinically as ventilator-induced lung injury (VILI).

Injured lungs can be partially protected by optimal settings and ventilation modes, using low tidal volume (VT) values and high positive-end expiratory pressure (PEEP). The benefits in ARDS outcomes caused by these interventions have been confirmed by several prospective randomized controlled trials (RCTs) and are attributed to reduction in volutrauma.

The purpose of this article is to present an approach to VILI pathophysiology focused on the effects of volutrauma that lead to lung injury and the ‘mechanotransduction’ mechanism. A more complete understanding about the molecular effects that physical forces could have, is essential for a better assessment of existing strategies as well as the development of new therapeutic strategies to reduce the damage resulting from VILI, and thereby contribute to reducing mortality in ARDS.

Surfactant

Exogenous pulmonary surfactant, widely used in neonatal care, is one of the best-studied treatments in neonatology, and its introduction in the 1990s led to a significant improvement in neonatal outcomes in preterm infants, including a decrease in mortality. This chapter provides an overview of surfactant composition and function in health and disease and summarizes the evidence for its clinical use.

A complete audit cycle to assess adherence to a lung protective ventilation strategy

There is clear evidence for the use of a protective ventilation protocol in patients with acute respiratory distress syndrome (ARDS). There is evidence to suggest that protective ventilation is beneficial in patients at risk of ARDS. A protective ventilation strategy was implemented on our intensive care unit in critical care patients who required mechanical ventilation for over 48 h, with and at risk for ARDS. A complete audit cycle was performed over 13 months to assess compliance with a safe ventilation protocol in intensive care. The ARDS network mechanical ventilation protocol was used as the standard for our protective ventilation strategy. This recommends ventilation with a tidal volume (V_t) of 6 ml/kg of ideal body weight (IBW) and plateau airway pressure of ≤30 cm H₂O. The initial audit failed to meet this standard with V_t's of 9.5 ml/kg of IBW. Following the implementation of a ventilation strategy and an educational program, we demonstrate a significant improvement in practice with V_t's of 6.6 ml/kg of IBW in the re-audit. This highlights the importance of simple interventions and continuous education in maintaining high standards of care.

Advances in ventilator-associated lung injury: prevention is the target

Mechanical ventilation (MV) is the main supportive treatment in respiratory failure due to different etiologies. However, MV might aggravate ventilator-associated lung injury (VALI). Four main mechanisms leading to VALI are: 1) increased stress and strain, induced by high tidal volume (VT); 2) increased shear stress, i.e. opening and closing, of previously atelectatic alveolar units; 3) distribution of perfusion and 4) biotrauma. In severe acute respiratory distress syndrome patients, low VT, higher levels of positive end expiratory pressure, long duration prone position and neuromuscular blockade within the first 48 hours are associated to a better outcome. VALI can also occur by using high VT in previously non injured lungs. We believe that prevention is the target to minimize injurious effects of MV. This review aims to describe pathophysiology of VALI, the possible prevention and treatment as well as monitoring MV to minimize VALI.

Alveolar overdistension as a cause of lung injury: differences among three animal species

This study analyses characteristics of lung injuries produced by alveolar overdistension in three animal species. Mechanical ventilation at normal tidal volume (10 mL/Kg) and high tidal volume (50 mL/Kg) was applied for 30 min in each species. Data were gathered on wet/dry weight ratio, histological score, and area of alveolar collapse. Five out of six rabbits with high tidal volume developed tension pneumothorax, and the rabbit results were therefore not included in the histological analysis. Lungs from the pigs and rats showed minimal histological lesions. Pigs ventilated with high tidal volume had significantly greater oedema, higher neutrophil infiltration, and higher percentage area of alveolar collapse than rats ventilated with high tidal volume. We conclude that rabbits are not an appropriate species for in vivo studies of alveolar overdistension due to their fragility. Although some histological lesions are observed in pigs and rats, the lesions do not appear to be relevant.

Time course of lung inflammatory and fibrogenic responses during protective mechanical ventilation in healthy rats

This study aimed to assess pulmonary inflammatory and fibrogenic responses and their impact on lung mechanics and histology in healthy rats submitted to protective mechanical ventilation for different experimental periods. Eighteen Wistar rats were randomized to undergo open lung-mechanical ventilation (OL-MV) for 1, 6 or 12 h. Following a recruitment maneuver, a decremental PEEP trial was performed and PEEP set according to the minimal respiratory system static elastance. Respiratory system, lung, and chest-wall elastance and gas-exchange were maintained throughout the 12 h experimental period. Histological lung injury score remained low at 1 and 6 h, but was higher at 12 h due to overinflation. A moderate inflammatory response was observed with a distinct peak at 6h. Compared to unventilated controls, type I procollagen mRNA expression was decreased at 1 and 12h, while type III procollagen expression decreased throughout the 12h experimental period. In conclusion, OL-MV in healthy rats yielded overinflation after 6 h even though respiratory elastance and gas-exchange were preserved for up to 12 h.

Neonatal ventilatory techniques - which are best for infants born at term?

Few studies have examined ventilatory modes exclusively in infants born at term. Synchronous intermittent mandatory ventilation (SIMV) compared to intermittent mandatory ventilation (IMV) is associated with a shorter duration of ventilation. The limited data on pressure support, volume targeted ventilation and neurally adjusted ventilatory assist demonstrate only short term benefits in term born infants. Favourable results of high-frequency oscillatory ventilation (HFOV) in infants with severe respiratory failure were not confirmed in the two randomised trials. Nitric oxide (NO) in term born infants, except in those with congenital diaphragmatic hernia (CDH), reduces the combined outcome of death and requirement for extracorporeal membrane oxygenation (ECMO). In infants with severe refractory hypoxaemic respiratory failure, ECMO, except in infants with CDH, reduced mortality and the combined outcome of death and severe disability at long-term follow-up. Randomised studies with long term outcomes are required to determine the optimum modes of ventilation in term born infants.

Open lung approach associated with high-frequency oscillatory or low tidal volume mechanical ventilation improves respiratory function and minimizes lung injury in healthy and injured rats

INTRODUCTION

To test the hypothesis that open lung (OL) ventilatory strategies using high-frequency oscillatory ventilation (HFOV) or controlled mechanical ventilation (CMV) compared to CMV with lower positive end-expiratory pressure (PEEP) improve respiratory function while minimizing lung injury as well as systemic inflammation, a prospective randomized study was performed at a university animal laboratory using three different lung conditions.

METHODS

Seventy-eight adult male Wistar rats were randomly assigned to three groups: (1) uninjured (UI), (2) saline washout (SW), and (3) intraperitoneal/intravenous Escherichia coli lipopolysaccharide (LPS)-induced lung injury. Within each group, animals were further randomized to (1) OL with HFOV, (2) OL with CMV with "best" PEEP set according to the minimal static elastance of the respiratory system (BP-CMV), and (3) CMV with low PEEP (LP-CMV). They were then ventilated for 6 hours. HFOV was set with mean airway pressure (PmeanHFOV) at 2 cm H2O above the mean airway pressure recorded at BP-CMV (PmeanBP-CMV) following a recruitment manoeuvre. Six animals served as unventilated controls (C). Gas-exchange, respiratory system mechanics, lung histology, plasma cytokines, as well as cytokines and types I and III procollagen (PCI and PCIII) mRNA expression in lung tissue were measured.

RESULTS

We found that (1) in both SW and LPS, HFOV and BP-CMV improved gas exchange and mechanics with lower lung injury compared to LP-CMV, (2) in SW; HFOV yielded better oxygenation than BP-CMV; (3) in SW, interleukin (IL)-6 mRNA expression was lower during BP-CMV and HFOV compared to LP-CMV, while in LPS inflammatory response was independent of the ventilatory mode; and (4) PCIII mRNA expression decreased in all groups and ventilatory modes, with the decrease being highest in LPS.

CONCLUSIONS

Open lung ventilatory strategies associated with HFOV or BP-CMV improved respiratory function and minimized lung injury compared to LP-CMV. Therefore, HFOV with PmeanHFOV set 2 cm H2O above the PmeanBP-CMV following a recruitment manoeuvre is as beneficial as BP-CMV.

Work of breathing and different levels of volume-targeted ventilation

OBJECTIVES

The objectives of this study were to determine the impact of different volume-targeted levels on the work of breathing and to investigate whether a level that reduced the work of breathing below that experienced during ventilatory support without volume targeting could be determined.

METHODS

The transdiaphragmatic pressure-time product, as an estimate of the work of breathing, was measured for 20 infants (median gestational age: 28 weeks) who were being weaned from respiratory support by using patient-triggered ventilation (either assist-control ventilation or synchronous intermittent mandatory ventilation). The transdiaphragmatic pressure-time product was measured first without volume targeting (baseline) and then at volume-targeted levels of 4, 5, and 6 mL/kg, delivered in random order. After each volume-targeted level, the infants were returned to baseline. Each step was maintained for 20 minutes.

RESULTS

The mean transdiaphragmatic pressure-time product was higher with volume targeting at 4 mL/kg in comparison with baseline, regardless of the patient-triggered mode. The transdiaphragmatic pressure-time product was higher at a volume-targeted level of 4 mL/kg in comparison with 5 mL/kg and at 5 mL/kg in comparison with 6 mL/kg. The mean work of breathing was below that at baseline only at a volume-targeted level of 6 mL/kg.

CONCLUSIONS

Low volume-targeted levels increase the work of breathing during volume-targeted ventilation. Our results suggest that, during weaning, a volume-targeted level of 6 mL/kg, rather than a lower level, could be used to avoid an increase in the work of breathing.