[High-flow nasal oxygen therapy and hypercapnic acute respiratory failure]. / Oxygénothérapie nasale à haut débit et insuffisance respiratoire aiguë hypercapnique.

Humidified high-flow nasal oxygen therapy (HFNO) has, in recent years, come to assume a key role in the management of hypoxemic acute respiratory failure (ARF). While non-invasive ventilation (NIV) currently represents the first-line ventilatory strategy in patients exhibiting hypercapnic ARF, the operating principles and physiological effects of HFNO could be interesting and useful in the initial management of hypercapnic ARF and/or after extubation, particularly in acute exacerbations of chronic obstructive pulmonary disease. Under these conditions, HFNO could be used either alone continuously or in combination with NIV during breaks in spontaneous breathing, depending on the severity and etiology of the underlying hypercapnic ARF.

[Ventilatory management of SARS-CoV-2 acute respiratory failure]. / Prise en charge ventilatoire de l'insuffisance respiratoire aiguë à SARS-CoV-2.

COVID-19 pneumonia presents several particularities in its clinical presentation (cytokine storm, silent hypoxemia, thrombo-embolic risk) and may lead to a number of acute respiratory distress syndrome (ARDS) phenotypes. While the optimal oxygenation strategy in cases of hypoxemic acute respiratory failure (ARF) is still under debate, ventilatory management of COVID-19-related ARF has confirmed the efficacy of high-flow oxygen therapy and restored interest in other ventilatory approaches such as continuous positive airway pressure (CPAP) and noninvasive ventilation involving a helmet, which due to patient overflow are sometimes implemented outside of critical care units. However, further studies are still needed to determine which patients should be given which oxygenation technique, and under which conditions they require invasive mechanical ventilation, given that delayed initiation potentially burdens prognosis. During invasive mechanical ventilation, ventral decubitus and extracorporeal membrane oxygenation have become increasingly prevalent. While innovative therapies such as awake prone position or lung transplantation have likewise been developed, their indications, modalities and efficacy remain to be determined.

Dog behaviours in veterinary consultations: Part II. The relationship between the behaviours of dogs and their owners.

Dogs synchronise their behaviour with those of their owners when confronted with an unfamiliar situation and interactions with their owners have been shown to decrease the dog's stress levels in some instances. However, whether owners may help manage dog anxiety during veterinary consultations remains unclear. In Part I, we compared the behaviour of dogs in the presence or absence of their owners during consultations, which consisted in three phases: exploration, examination, and greeting. Our findings suggest that allowing owners to attend consultations may be beneficial for dogs. In Part II, we investigated the direct relationship between owners' actions and their dog's behaviour. Using the videos from Part I, we examined whether: (1) dogs interact more when their owner is more interactive; (2) owners' stress scores are related to canine stress-related behaviour and emotional state; (3) owners' actions influence canine stress-related behaviours, emotional state and tolerance to manipulations; (4) canine stress-related behaviours and emotional state are associated with increased eye contact with their owners. We analysed the recordings of 29 dog-owner dyads submitted to a veterinary consultation in Part I. The behaviours of the dogs and their owners were analysed, and their emotional states were scored. The ease of manipulations was also scored. Despite limitations (e.g. no physical contact during examinations, no invasive procedures, aggressive dogs excluded, no male owners, limited sample size), our study showed a link between dog and owner behaviours: when owners attended an examination, their negative behaviours intensified the signs of anxiety in their dogs. Additionally, visual and verbal attempts to comfort their dog had no significant effect. However, we observed that the more dogs displayed stress-related behaviours, the more they established eye contact with their owners, suggesting that dogs seek information (through social referencing) or reassurance from their owners.

Dog behaviours in veterinary consultations: Part 1. Effect of the owner's presence or absence.

Veterinary practices can be stressful places for dogs. Decreasing stress during veterinary consultations is therefore a major concern, since animal welfare matters both for owners and veterinarians. Stress can be expressed through behaviour modifications; monitoring canine behaviour is thus one way to assess stress levels. We also know that the owner can affect dog behaviour in different ways. The aim of this study was therefore to assess the effect of the presence of owners on the behaviour of their dogs in veterinary consultations. We studied 25 dog-owner dyads at two standardised veterinary consultations, conducted at intervals of 5-7 weeks; the owner was present for the first consultation and absent for the second (O/NoO group, n = 12), or vice versa (NoO/O group, n = 13). A consultation consisted in three phases: exploration, examination, greeting. Dog behaviours were compared between the two conditions using a video recording. Despite some limitations (e.g. no male owners, the exclusion of aggressive dogs, a limited sample size, minimally invasive veterinary examinations, restricted owner-dog interactions), our results showed that the presence or absence of the owner had no significant effect on the stress-related behaviour of the dog or the veterinarian's ability to handle the animal during the examination phase (P > 0.05). Nevertheless, the behaviour of the dogs towards people was affected before, during, and after the veterinary examination. In the presence of their owner, dogs were more willing to enter the consultation room (P < 0.05), and they appeared more relaxed during the exploration phase (P < 0.01). During the examination, dogs looked in direction of their owner in both situations (owner present and behind the door, respectively; P < 0.001). These results suggest that allowing the owner to stay in the room during veterinary consultations is a better option for canine welfare.

[Operating principles, physiological effects and practical issues of high-flow nasal oxygen therapy]. / Principes de fonctionnement, effets physiologiques et aspects pratiques de l'oxygénothérapie à haut débit.

First-line symptomatic treatment of acute respiratory failure (ARF) usually requires standard oxygen therapy, of which the limits have nonetheless led to the development of heated and humidified high-flow nasal oxygen therapy (HFNO). HFNO enables the delivery, through simple nasal cannula, of up to 100% of well-heated and humidified fraction of inspired oxygen (FiO2), at a maximum flow rate of 50 to 70 L/min of gas according to the devices chosen (specific or ventilator). The technical characteristics and operating principles of HFNO (coverage of the patient's spontaneous inspiratory flow, improved conditioning of the inspired gases, comfortable nasal cannula) yield a number of interdependent physiological effects that improve not only oxygenation conditions but also ventilatory mechanics. While it could be indicated in many clinical situations, including first-line hypoxemic ARF, the simplicity of HFNO implementation and the respiratory comfort it procures should in no way minimize the clinical monitoring of patients for whom endotracheal intubation may be required, and should not be unduly delayed.

Covid-19 severe hypoxemic pneumonia: A clinical experience using high-flow nasal oxygen therapy as first-line management.

PURPOSE: To report a French experience in patients admitted to Intensive Care Unit (ICU) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) requiring high fractional concentration of inspired oxygen supported by high flow nasal cannula (HFNC) as first-line therapy. METHODS: Retrospective cohort study conducted in two ICUs of a French university hospital. All consecutive patients admitted during 28-days after the first admission for SARS-CoV-2 pneumonia were screened. Demographic, clinical, respiratory support, specific therapeutics, ICU length-of-stay and survival data were collected. RESULTS: Data of 43 patients were analyzed: mainly men (72%), median age 61 (51-69) years, median body mass index of 28 (25-31) kg/m2, median simplified acute physiology score (SAPS II) of 29 (22-37) and median PaO2/fraction of inspired oxygen (FiO2) (P/F) ratio of 146 (100-189) mmHg. HFNC was initiated at ICU admission in 76% of patients. Median flow was 50 (45-50) L/min and median FiO2 was 0.6 (0.5-0.8). 79% of patients presented at least one comorbidity, mainly hypertension (58%). At day (D) 28, 32% of patients required invasive mechanical ventilation, 3 patients died in ICU. Risk factors for intubation were diabetes (10% vs. 43%, P=0.04) and extensive lesions on chest computed tomography (CT) (P=0.023). Patients with more than 25% of lesions on chest CT were more frequently intubated during ICU stay (P=0.012). At ICU admission (D1), patients with higher SAPS II and Sequential Organ Failure Assessment (SOFA) scores (respectively 39 (28-50) vs. 27 (22-31), P=0.0031 and 5 (2-8) vs. 2 (2-2.2), P=0.0019), and a lower P/F ratio (98 (63-109) vs. 178 (126-206), P=0.0005) were more frequently intubated. Among non-intubated patients, the median lowest P/F was 131 (85-180) mmHg. Four caregivers had to stop working following coronavirus 2 contamination, but did not require hospitalization. CONCLUSION: Our clinical experience supports the use of HFNC as first line-therapy in patients with SARS-COV-2 pneumonia for whom face mask oxygen does not provide adequate respiratory support.

Comparison of high-flow nasal oxygen therapy and non-invasive ventilation in ICU patients with acute respiratory failure and a do-not-intubate orders: a multicentre prospective study OXYPAL.

INTRODUCTION: A palliative approach to intensive care unit (ICU) patients with acute respiratory failure and a do-not-intubate order corresponds to a poorly evaluated target for non-invasive oxygenation treatments. Survival alone should not be the only target; it also matters to avoid discomfort and to restore the patient's quality of life. We aim to conduct a prospective multicentre observational study to analyse clinical practices and their impact on outcomes of palliative high-flow nasal oxygen therapy (HFOT) and non-invasive ventilation (NIV) in ICU patients with do-not-intubate orders. METHODS AND ANALYSIS: This is an investigator-initiated, multicentre prospective observational cohort study comparing the three following strategies of oxygenation: HFOT alone, NIV alternating with HFOT and NIV alternating with standard oxygen in patients admitted in the ICU for acute respiratory failure with a do-not-intubate order. The primary outcome is the hospital survival within 14 days after ICU admission in patients weaned from NIV and HFOT. The sample size was estimated at a minimum of 330 patients divided into three groups according to the oxygenation strategy applied. The analysis takes into account confounding factors by modelling a propensity score. ETHICS AND DISSEMINATION: The study has been approved by the ethics committee and patients will be included after informed consent. The results will be submitted for publication in peer-reviewed journals. TRIAL REGISTRATION NUMBER: NCT03673631.

Management of acute exacerbations of chronic obstructive pulmonary disease (COPD). Guidelines from the Société de pneumologie de langue française (summary).

Chronic obstructive pulmonary disease (COPD) is the chronic respiratory disease with the most important burden on public health in terms of morbidity, mortality and health costs. For patients, COPD is a major source of disability because of dyspnea, restriction in daily activities, exacerbation, risk of chronic respiratory failure and extra-respiratory systemic organ disorders. The previous French Language Respiratory Society (SPLF) guidelines on COPD exacerbations were published in 2003. Using the GRADE methodology, the present document reviews the current knowledge on COPD exacerbation through 4 specific outlines: (1) epidemiology, (2) clinical evaluation, (3) therapeutic management and (4) prevention. Specific aspects of outpatients and inpatients care are discussed, especially regarding assessment of exacerbation severity and pharmacological approach.

Changes in severity and organ failure scores as prognostic factors in onco-hematological malignancy patients admitted to the ICU.

OBJECTIVE: To determine whether severity and organ failure scores over the first 3 days in an ICU predict in-hospital mortality in onco-hematological malignancy patients. DESIGN AND SETTING: Retrospective study in a 22-bed medical ICU. PATIENTS: 92 consecutive patients with onco-hematological malignancies including 20 hematopoietic stem cell transplantation (HSCT) patients (11 with allogenic HSCT). MEASUREMENTS: Simplified Acute Physiology Score (SAPS) II, Organ Dysfunction and/or Infection (ODIN) score, Logistic Organ Dysfunction System (LODS), and Sequential Organ Failure Assessment (SOFA) score were recorded on admission. The change in each score (Delta score) during the first 3 days in the ICU was calculated as follows: severity or organ failure score on day 3 minus severity or organ failure score on day 1, divided by severity or organ failure score on day 1. RESULTS: In-hospital mortality was 58%. Using multivariate analysis in-hospital mortality was predicted by all scores on day 1 and all Delta scores. Areas under the receiver operating characteristics curves were similar for SAPS II (0.78), ODIN (0.78), LODS (0.83), and SOFA (0.78) scores at day 1. They were also similar for DeltaSAPS II, DeltaODIN, DeltaLODS, and DeltaSOFA. Similar results were observed when excluding patients with allogenic HSCT. CONCLUSION: Severity and three organ failure scores on day 1 and Delta scores perform similarly in predicting in-hospital mortality in ICU onco-hematological malignancy patients but do not predict individual outcome. Decision to admit such patients to the ICU or to forgo life-sustaining therapies should not be based on these scores.

[Quality of care assessment and nosocomial pneumonia in the intensive care unit]. / Evaluation des soins et pneumopathies nosocomiales en réanimation.

INTRODUCTION: Nosocomial pneumonia (NP) is a major cause of infection in the intensive care unit and is responsible for a significant increase in morbidity, mortality and healthcare costs. Ventilator-associated pneumonia is the most frequent and severe form of NP. STATE OF ART: Assessment of the quality of care and healthcare practices relating to the prevention and treatment of nosocomial pneumonia represents a potentially vast area but has been little studied in the literature. Difficulties include the lack of either a "gold standard" for diagnosis, or standardization of techniques for microbiological sampling and, therefore, the lack of reliable indicators of performance in the management of NP. Currently, published data mainly involve diagnostic strategies, preventive measures and antibiotic therapy. PERSPECTIVES AND CONCLUSIONS: In line with the latest published recommendations, clinicians should continue their efforts in this field to improve the management and reduce the impact of NP in the intensive care unit.

[Bickerstaff's brainstem encephalitis]. / La rhombencéphalite postinfectieuse: le syndrome de Bickerstaff.

INTRODUCTION: Bickerstaff's brainstem encephalitis represents a differential diagnostic that must be discuss with meningoencephalitis with ophtalmoplegia, ataxia and confusion. EXEGESE: A 26 year-old woman presented a Bickerstaff syndrome. A severe disturbance of consciousness had lead to admission in intensive care unit with mechanical ventilation. Electrophysiological tests and the brain magnetic resonance were normal. We have not observed systemic anti-G1Qb antibody in our patient. Nevertheless, 66% of patients with Bickerstaff syndrome have anti-GQ1b antibody during the acute phase period. We observed a beneficial effect of IV Ig treatment although no significant improvement was observed with corticosteroids. CONCLUSION: Controlled clinical trials are needed to established the efficacy of IV Ig or plasmapheresis as a specific therapy for this pathology.

Survival and long-term follow-up of tracheostomized patients with COPD treated by home mechanical ventilation. A multicenter French study in 259 patients. French Cooperative Study Group.

To define more clearly the value of home mechanical ventilation by tracheostomy (HMVT) in patients with advanced COPD, a retrospective French multicenter study group analyzed the prognostic factors and long-term survival of 259 patients with severe COPD, who were tracheostomized for at least 1 year. Seventy-eight percent of the patients died by the end of the observation period. The actuarial survival rate for the overall study population was, therefore, 70 percent at 2 years, 44 percent at 5 years, and 20 percent at 10 years. These results appear to be better than those of the major published series and compare to the prognosis of COPD patients treated by long-term oxygen therapy (LTO) 15 hr/24 hr. The parameters most closely correlated with a survival for more than 5 years were age < 65 years, use of an uncuffed cannula, and a PaO2 > 55 mm Hg in room air during the 3 months after tracheostomy (p < 0.01). This study, therefore, confirmed the feasibility of HMVT in COPD and should lead to a review of the place of permanent tracheostomy in the long-term prognosis of severe COPD patients.

Nasal mask ventilation in acute respiratory failure. Experience in elderly patients.

Nasal mask ventilation (NMV) has been used successfully in chronic restrictive respiratory failure and more recently in acute exacerbations of chronic obstructive pulmonary disease (COPD). This study aimed to evaluate the possible role of NMV in acute respiratory failure (ARF) episodes when mechanical ventilation with endotracheal intubation is questionable. Thirty patients (age, 76 +/- 8.1 years) were treated by NMV during ARF episodes (COPD, 20; other chronic respiratory failure [CRF], 5; chronic heart failure [CHF], 4). All patients were hypoxemic (PaO2, 5.85 +/- 1.62 kPa) and hypercapnic (PaCO2, 8.63 +/- 1.89 kPa) with respiratory acidosis (pH, 7.29 +/- 0.08). In all cases, clinical or physiologic parameters indicated the need for mechanical ventilation, but endotracheal intubation was either not applied because of the age and the physiologic condition of the patients (17 cases) or was postponed (13 cases). NMV was performed using a volume-cycled ventilator and a customized nasal mask. Ventilation was continuous during the first 12 hours and the following nights and was then intermittent during the day. Twenty-one patients improved clinically, within a few hours. Progressive correction of arterial blood gases was observed: PaO2 increased during the first hour, but PaCO2 decreased more slowly. Eighteen patients were able to be successfully weaned from NMV. Twelve patients failed to improve despite NMV: eight of them died and four required endotracheal intubation. There was no difference in the success rate between patients in whom endotracheal ventilation was contraindicated or postponed. Clinical tolerance was satisfactory in 23 patients and poor in seven patients. A return to the respiratory condition was observed in the surviving patients with subsequent discharge from hospital. NMV therefore successfully treated respiratory distress initially in 60 percent of the 30 patients. These results suggest that NMV could be a possible alternative in the treatment of ARF, even in very ill patients, when endotracheal ventilation is controversial or not immediately required.

Comparative physiologic effects of noninvasive assist-control and pressure support ventilation in acute hypercapnic respiratory failure.

STUDY OBJECTIVE: To compare the effects of noninvasive assist-control ventilation (ACV) and pressure support ventilation (PSV) by nasal mask on respiratory physiologic parameters and comfort in acute hypercapnic respiratory failure (AHRF). DESIGN: A prospective randomized study. SETTING: A medical ICU. PATIENTS AND INTERVENTIONS: Fifteen patients with COPD and AHRF were consecutively and randomly assigned to two noninvasive ventilation (NIV) sequences with ACV and PSV mode, spontaneous breathing (SB) via nasal mask being used as control. ACV and PSV settings were always subsequently adjusted according to patient's tolerance and air leaks. Fraction of inspired oxygen did not change between the sequences. MEASUREMENTS AND RESULTS: ACV and PSV mode strongly decreased the inspiratory effort in comparison with SB. The total inspiratory work of breathing (WOBinsp) expressed as WOBinsp/tidal volume (VT) and WOBinsp/respiratory rate (RR), the pressure time product (PTP), and esophageal pressure variations (deltaPes) were the most discriminant parameters (p<0.001). ACV most reduced WOBinsp/VT (p<0.05), deltaPes (p<0.05), and PTP (0.01) compared with PSV mode. The surface diaphragmatic electromyogram activity was also decreased >32% as compared with control values (p<0.01), with no difference between the two modes. Simultaneously, NIV significantly improved breathing pattern (p<0.01) with no difference between ACV and PSV for VT, RR, minute ventilation, and total cycle duration. As compared to SB, respiratory acidosis was similarly improved by both modes. The respiratory comfort assessed by visual analog scale was less with ACV (57.23+/-30.12 mm) than with SB (75.15+/-18.25 mm) (p<0.05) and PSV mode (81.62+/-25.2 mm) (p<0.01) in our patients. CONCLUSIONS: During NIV for AHRF using settings adapted to patient's clinical tolerance and mask air leaks, both ACV and PSV mode provide respiratory muscle rest and similarly improve breathing pattern and gas exchange. However, these physiologic effects are achieved with a lower inspiratory workload but at the expense of a higher respiratory discomfort with ACV than with PSV mode.

Long-term efficiency of home nasal mask ventilation in patients with diffuse bronchiectasis and severe chronic respiratory failure: a case-control study.

The aim of this study was to evaluate long-term efficacy and tolerance of nasal mask ventilation (NMV) in a comparative case-control study. Fourteen patients with diffuse bronchiectasis and severe chronic respiratory failure (CRF), treated by long-term oxygen-therapy (LTO) and NMV, were case matched with 14 patients with diffuse bronchiectasis and severe CRF treated with only LTO. Patients and control subjects were compared based on the following parameters: blood gases, FEV1, vital capacity, hospitalizations, and survival. Symptoms, Karnofsky function score, and clinical evolution were also monitored in patients. Three subgroups may be identified according to outcome: two early deaths (subgroup 1), six patients with initial improvement and subsequent deterioration (subgroup 2), and six patients whose conditions remained improved for >2 years (subgroup 3). PaO2 decrease slope was slighter in this last subgroup than subgroup 2. The days of hospitalization were significantly reduced after institution of NMV in the patient group. Comparison between patients and control subjects did not show any difference on PaO2 evolution and on the overall median survival (46 and 40 months in NMV and control group, respectively). Long-term tolerance and compliance remained satisfactory for 11 patients. These results suggest that NMV is feasible as a long-term home treatment in patients with diffuse bronchiectasis. Although our results may have failed to prove a long-term efficiency on the course of blood gases and survival, a beneficial effect is observed with reduction of hospitalizations and improvement of functional status. This study warrants further investigation, in a prospective series, with a larger number of patients.

Effects of repeated administration of zolpidem on sleep, diurnal and nocturnal respiratory function, vigilance, and physical performance in patients with COPD.

STUDY OBJECTIVE: To assess the effects of repeated 10-mg oral doses of zolpidem on diurnal and nocturnal respiratory function, as well as on diurnal vigilance and physical performance in COPD patients with disordered sleep. DESIGN: Prospective single-blind placebo-controlled clinical study. SETTING: Outpatients of a respiratory medicine department. PATIENTS AND METHODS: Patients with stable COPD were enrolled for 10 days (D0 to D10), ie, 9 consecutive nights (N1 to N9). They received placebo on N1 and N9 and zolpidem, 10 mg, from N2 to N8. MEASUREMENTS: The following parameters were measured: nocturnal polysomnographic recordings with respiratory signals and arterial blood gas values on retiring and awakening on N0, N1, N2, N8, and N9; subjective evaluation of the quality of sleep and of diurnal vigilance by visual analog scales every day from D0 to D10; pulmonary function test, central control of breathing, and walking test on D0 and D9; biological laboratory tests and theophylline level on D0 and D8. RESULTS: Ten COPD patients (PaO2 = 72.7 +/- 7.6 mm Hg; PaCO2 = 47.7 +/- 5.4 mm Hg; FEV1 = 0.84 +/- 0.3 L; FEV1/vital capacity = 42.5 +/- 12.3%), 56.8 +/- 8.3 years old, were studied. Compared with placebo, no significant change was found for the various sleep architecture parameters, except an increase in the duration of stage 2 during the D8/N8 night (p < 0.05). In contrast, the autoevaluation score for the quality of sleep was significantly improved during the D6/N6 night relative to that with placebo (p < 0.05), with no change in the other subjective criteria. No variable of the nocturnal respiratory parameters, pulmonary function test, central control of breathing, and physical performance was altered by zolpidem. Arterial blood gas values on awakening were not altered. Clinical and biological tolerance of zolpidem was correct with no significant variation of the theophylline level. CONCLUSION: This study shows that repeated 10-mg oral doses of zolpidem during 8 days does not impair nocturnal respiratory and sleep architecture parameters or diurnal pulmonary function tests, central control of breathing, and physical performances in patients with stable COPD.

Toxicological analysis in agitated patients.

OBJECTIVE: To assess the toxicological etiologies in agitated patients and to evaluate their initial clinical diagnosis in the light of toxicological results analysis. DESIGN: Prospective clinical study. SETTING: Emergency Department (ED) in a 2,650-bed University Hospital. PATIENTS: Fifty-eight consecutively enrolled patients admitted to the ED in agitated states over a 6-month period. MEASUREMENTS AND RESULTS: All patients underwent laboratory tests including blood glucose, ethanol and serum drug screening. Toxicology tests were conducted by fluorescence polarization immunoassay and confirmed by high performance liquid chromatography/diode array detector and gas chromatography-mass spectrometry. The physician's initial diagnosis was evaluated in the light of toxicological analysis results. Serum toxicological analysis revealed that 50/58 patients were under the influence of alcohol and/or a drug. Benzodiazepines (22/58), selective serotonin reuptake inhibitors (5/58) and opiates (4/58) were the most frequently observed. The initial clinical diagnosis was alcohol intoxication in 39 patients, although 1 patient was not under the influence of alcohol and 16 also had benzodiazepine in their sera. Moreover, the diagnosis of serotonin syndrome was overlooked in two patients. CONCLUSION: Most agitated patients were under the influence of alcohol and/or a drug. Benzodiazepine alone or in association with alcohol was surprisingly frequent. A serotonin syndrome may explain the agitation state.

Increased initial flow rate reduces inspiratory work of breathing during pressure support ventilation in patients with exacerbation of chronic obstructive pulmonary disease.

OBJECTIVE: To investigate whether the level of initial flow rate alters the work of breathing in chronic obstructive pulmonary disease (COPD) patients ventilated in pressure support ventilation (PSV). DESIGN: Prospective study. SETTINGS: Medical ICU in University hospital. PATIENTS: Eleven intubated COPD patients. METHODS: We modulated the initial flow rate in order to achieve seven different sequences. In each sequence, the plateau pressure was reached within a predetermined time: 0.1, 0.25, 0.50, 0.75, 1, 1.25 or 1.50 s. The more rapidly the pressure plateau was achieved, the higher was the initial flow rate. In each patient, the pressure support level was an invariable parameter. The order of the seven sequences for each patient was determined randomly. MEASUREMENTS AND RESULTS: Ten minutes after application of each initial flow rate, we measured the following parameters: inspiratory work of breathing, electromyogram (EMG) of the diaphragm (EMGdi), breathing pattern, and intrinsic positive end-expiratory pressure (PEEPi). Comparison between the means for each sequence and each variable measured was performed by two-way analysis of variance with internal comparisons between sequences by Duncan's test. The reduction of the initial flow rate induced a progressive increase in the values of the work of breathing, EMGdi, and mouth occlusion pressure (P 0.1). In contrast, the reduction of the initial flow rate did not induce any significant change in tidal volume, respiratory frequency or PEEPi. CONCLUSIONS: As the objective of PSV is to reduce the work of breathing, it seems logical to use the highest initial flow rate to induce the lowest possible work of breathing in COPD ventilated patients.