Influence of socio-economic status on functional recovery after ARDS caused by SARS-CoV-2: the multicentre, observational RECOVIDS study.

PURPOSE: Survivors after acute respiratory distress syndrome (ARDS) due to coronavirus disease 2019 (COVID-19) are at high risk of developing respiratory sequelae and functional impairment. The healthcare crisis caused by the pandemic hit socially disadvantaged populations. We aimed to evaluate the influence of socio-economic status on respiratory sequelae after COVID-19 ARDS. METHODS: We carried out a prospective multicenter study in 30 French intensive care units (ICUs), where ARDS survivors were pre-enrolled if they fulfilled the Berlin ARDS criteria. For patients receiving high flow oxygen therapy, a flow ≥ 50 l/min and an FiO2 ≥ 50% were required for enrollment. Socio-economic deprivation was defined by an EPICES (Evaluation de la Précarité et des Inégalités de santé dans les Centres d'Examens de Santé - Evaluation of Deprivation and Inequalities in Health Examination Centres) score ≥ 30.17 and patients were included if they performed the 6-month evaluation. The primary outcome was respiratory sequelae 6 months after ICU discharge, defined by at least one of the following criteria: forced vital capacity < 80% of theoretical value, diffusing capacity of the lung for carbon monoxide < 80% of theoretical value, oxygen desaturation during a 6-min walk test and fibrotic-like findings on chest computed tomography. RESULTS: Among 401 analyzable patients, 160 (40%) were socio-economically deprived and 241 (60%) non-deprived; 319 (80%) patients had respiratory sequelae 6 months after ICU discharge (81% vs 78%, deprived vs non-deprived, respectively). No significant effect of socio-economic status was identified on lung sequelae (odds ratio (OR), 1.19 [95% confidence interval (CI), 0.72-1.97]), even after adjustment for age, sex, most invasive respiratory support, obesity, most severe P/F ratio (adjusted OR, 1.02 [95% CI 0.57-1.83]). CONCLUSIONS: In COVID-19 ARDS survivors, socio-economic status had no significant influence on respiratory sequelae 6 months after ICU discharge.

Influence of socioeconomic status on functional recovery after ARDS caused by SARS-CoV-2: a multicentre, observational study.

INTRODUCTION: Prognosis of patients with COVID-19 depends on the severity of the pulmonary affection. The most severe cases may progress to acute respiratory distress syndrome (ARDS), which is associated with a risk of long-term repercussions on respiratory function and neuromuscular outcomes. The functional repercussions of severe forms of COVID-19 may have a major impact on quality of life, and impair the ability to return to work or exercise. Social inequalities in healthcare may influence prognosis, with socially vulnerable individuals more likely to develop severe forms of disease. We describe here the protocol for a prospective, multicentre study that aims to investigate the influence of social vulnerability on functional recovery in patients who were hospitalised in intensive care for ARDS caused by COVID-19. This study will also include an embedded qualitative study that aims to describe facilitators and barriers to compliance with rehabilitation, describe patients' health practices and identify social representations of health, disease and care. METHODS AND ANALYSIS: The "Functional Recovery From Acute Respiratory Distress Syndrome (ARDS) Due to COVID-19: Influence of Socio-Economic Status" (RECOVIDS) study is a mixed-methods, observational, multicentre cohort study performed during the routine follow-up of post-intensive care unit (ICU) functional recovery after ARDS. All patients admitted to a participating ICU for PCR-proven SARS-CoV-2 infection and who underwent chest CT scan at the initial phase AND who received respiratory support (mechanical or not) or high-flow nasal oxygen, AND had ARDS diagnosed by the Berlin criteria will be eligible. The primary outcome is the presence of lung sequelae at 6 months after ICU discharge, defined either by alterations on pulmonary function tests, oxygen desaturation during a standardised 6 min walk test or fibrosis-like pulmonary findings on chest CT. Patients will be considered to be socially disadvantaged if they have an "Evaluation de la Précarité et des Inégalités de santé dans les Centres d'Examen de Santé" (EPICES) score ≥30.17 at inclusion. ETHICS AND DISSEMINATION: The study protocol and the informed consent form were approved by an independent ethics committee (Comité de Protection des Personnes Sud Méditerranée II) on 10 July 2020 (2020-A02014-35). All patients will provide informed consent before participation. Findings will be published in peer-reviewed journals and presented at national and international congresses. TRIAL REGISTRATION NUMBER: NCT04556513.

Role of ICU-acquired weakness on extubation outcome among patients at high risk of reintubation.

BACKGROUND: Whereas ICU-acquired weakness may delay extubation in mechanically ventilated patients, its influence on extubation failure is poorly known. This study aimed at assessing the role of ICU-acquired weakness on extubation failure and the relation between limb weakness and cough strength. METHODS: A secondary analysis of two previous prospective studies including patients at high risk of reintubation after a planned extubation, i.e., age greater than 65 years, with underlying cardiac or respiratory disease, or intubated for more than 7 days prior to extubation. Patients intubated less than 24 h and those with a do-not-reintubate order were not included. Limb and cough strength were assessed by a physiotherapist just before extubation. ICU-acquired weakness was clinically diagnosed as limb weakness defined as Medical Research Council (MRC) score < 48 points and severe weakness as MRC sum-score < 36. Cough strength was assessed using a semi-quantitative 5-Likert scale. Extubation failure was defined as reintubation or death within the first 7 days following extubation. RESULTS: Among 344 patients at high risk of reintubation, 16% experienced extubation failure (56/344). They had greater severity and lower MRC sum-score (41 ± 16 vs. 49 ± 13, p < 0.001) and were more likely to have ineffective cough than the others. The prevalence of ICU-acquired weakness at the time of extubation was 38% (130/244). The extubation failure rate was 12% (25/214) in patients with no limb weakness vs. 18% (12/65) and 29% (19/65) in those with moderate and severe limb weakness, respectively (p < 0.01). MRC sum-score and cough strength were weakly but significantly correlated (rho = 0.28, p < .001). After multivariate logistic regression analyses, the lower the MRC sum-score the greater the risk of reintubation; severe limb weakness was independently associated with extubation failure, even after adjustment on cough strength and severity at admission. CONCLUSION: ICU-acquired weakness was diagnosed in 38% in this population of patients at high risk at the time of extubation and was independently associated with extubation failure in the ICU.

Inability of Diaphragm Ultrasound to Predict Extubation Failure: A Multicenter Study.

BACKGROUND: Diaphragmatic dysfunction may promote weaning difficulties in patients who are mechanically ventilated. OBJECTIVE: The goal of this study was to assess whether diaphragm dysfunction detected by ultrasound prior to extubation could predict extubation failure in the ICU. METHODS: This multicenter prospective study included patients at high risk of reintubation: those aged > 65 years, with underlying cardiac or respiratory disease, or intubated > 7 days. All patients had successfully undergone a spontaneous breathing trial. Diaphragmatic function was assessed by ultrasound prior to extubation while breathing spontaneously on a T-piece. Bilateral diaphragmatic excursion and apposition thickening fraction were measured, and diaphragmatic dysfunction was defined as excursion < 10 mm or thickening < 30%. Cough strength was clinically assessed by physiotherapists. Extubation failure was defined as reintubation or death within the 7 days following extubation. RESULTS: Over a 20-month period, 191 at-risk patients were studied. Among them, 33 (17%) were considered extubation failures. The proportion of patients with diaphragmatic dysfunction was similar between those whose extubation succeeded and those whose extubation failed: 46% vs 51% using excursion (P = .55), and 71% vs 68% using thickening (P = .73), respectively. Values of excursion and thickening did not differ between the success and the failure groups: at right, excursion was 14 ± 7 mm vs 11 ± 8 (P = .13), and thickening was 29 ± 29% vs 38 ± 48% (P = .83), respectively. Extubation failure rates were 7%, 22%, and 46% in patients with effective, moderate, and ineffective cough (P < .01). Ineffective cough was the only variable independently associated with extubation failure. CONCLUSIONS: Diaphragmatic dysfunction assessed by ultrasound was not associated with an increased risk of extubation failure.

Preload dependence indices to titrate volume expansion during septic shock: a randomized controlled trial.

INTRODUCTION: In septic shock, pulse pressure or cardiac output variation during passive leg raising are preload dependence indices reliable at predicting fluid responsiveness. Therefore, they may help to identify those patients who need intravascular volume expansion, while avoiding unnecessary fluid administration in the other patients. However, whether their use improves septic shock prognosis remains unknown. The aim of this study was to assess the clinical benefits of using preload dependence indices to titrate intravascular fluids during septic shock. METHODS: In a single-center randomized controlled trial, 60 septic shock patients were allocated to preload dependence indices-guided (preload dependence group) or central venous pressure-guided (control group) intravascular volume expansion with 30 patients in each group. The primary end point was time to shock resolution, defined by vasopressor weaning. RESULTS: There was no significant difference in time to shock resolution between groups (median (interquartile range) 2.0 (1.2 to 3.1) versus 2.3 (1.4 to 5.6) days in control and preload dependence groups, respectively). The daily amount of fluids administered for intravascular volume expansion was higher in the control than in the preload dependence group (917 (639 to 1,511) versus 383 (211 to 604) mL, P = 0.01), and the same held true for red cell transfusions (178 (82 to 304) versus 103 (0 to 183) mL, P = 0.04). Physiologic variable values did not change over time between groups, except for plasma lactate (time over group interaction, P <0.01). Mortality was not significantly different between groups (23% in the preload dependence group versus 47% in the control group, P = 0.10). Intravascular volume expansion was lower in the preload dependence group for patients with lower simplified acute physiology score II (SAPS II), and the opposite was found for patients in the upper two SAPS II quartiles. The amount of intravascular volume expansion did not change across the quartiles of severity in the control group, but steadily increased with severity in the preload dependence group. CONCLUSIONS: In patients with septic shock, titrating intravascular volume expansion with preload dependence indices did not change time to shock resolution, but resulted in less daily fluids intake, including red blood cells, without worsening patient outcome. TRIAL REGISTRATION: Clinicaltrials.gov NCT01972828. Registered 11 October 2013.

Open lung biopsy in nonresolving ARDS frequently identifies diffuse alveolar damage regardless of the severity stage and may have implications for patient management.

PURPOSE: The aim of the present study was to assess the rate of diffuse alveolar damage (DAD) on open lung biopsy (OLB) performed in the ICU for nonresolving ARDS. METHODS: A single-center retrospective study of patients meeting the Berlin definition criteria for ARDS who had undergone OLB for nonresolving ARDS. Patients were classified into mild, moderate and severe ARDS categories and according to the presence or absence of DAD on the OLB. The ARDS categories were assessed at baseline and at the time of the OLB. The OLBs were reviewed by two pathologists blinded to the ARDS classification. The primary endpoint was the rate of DAD according to the ARDS stage in the patients with nonresolving ARDS who had OLB. The secondary endpoint was the ability of DAD to predict ARDS among all the patients who had OLB. The same clinico-histopathological confrontation was cross validated in another ICU. RESULTS: From January 1998 to August 2013, 113 patients underwent OLB for acute hypoxemic respiratory failure, 83 of whom met the inclusion criteria for ARDS. At the time the OLB was performed, 11 of these patients had mild, 56 moderate, and 16 severe ARDS, respectively. The median (1st-3rd quartiles) time to OLB was 13 (10-18) and 9 (6-14) days from the onset of respiratory symptoms and from ARDS onset, respectively, with no statistical difference between the three ARDS groups. DAD was found in 48 (58 %) patients with ARDS, 4 (36 %) in the mild, 33 (59 %) in the moderate, and 11 (69 %) in the severe stage (P = 0.23). For the 113 patients who underwent OLB, the sensitivity and specificity of DAD to the Berlin definition was 0.58 (0.46-0.69) and 0.73 (0.54-0.88), respectively. Similar results were found in the other ICU. CONCLUSIONS: DAD is present in the majority of patients with nonresolving ARDs and its frequency is no different across the three ARDS stages. On this basis, the systematic use of steroids in nonresolving ARDS is not recommended.

Prone positioning in severe acute respiratory distress syndrome.

BACKGROUND: Previous trials involving patients with the acute respiratory distress syndrome (ARDS) have failed to show a beneficial effect of prone positioning during mechanical ventilatory support on outcomes. We evaluated the effect of early application of prone positioning on outcomes in patients with severe ARDS. METHODS: In this multicenter, prospective, randomized, controlled trial, we randomly assigned 466 patients with severe ARDS to undergo prone-positioning sessions of at least 16 hours or to be left in the supine position. Severe ARDS was defined as a ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (FiO2) of less than 150 mm Hg, with an FiO2 of at least 0.6, a positive end-expiratory pressure of at least 5 cm of water, and a tidal volume close to 6 ml per kilogram of predicted body weight. The primary outcome was the proportion of patients who died from any cause within 28 days after inclusion. RESULTS: A total of 237 patients were assigned to the prone group, and 229 patients were assigned to the supine group. The 28-day mortality was 16.0% in the prone group and 32.8% in the supine group (P<0.001). The hazard ratio for death with prone positioning was 0.39 (95% confidence interval [CI], 0.25 to 0.63). Unadjusted 90-day mortality was 23.6% in the prone group versus 41.0% in the supine group (P<0.001), with a hazard ratio of 0.44 (95% CI, 0.29 to 0.67). The incidence of complications did not differ significantly between the groups, except for the incidence of cardiac arrests, which was higher in the supine group. CONCLUSIONS: In patients with severe ARDS, early application of prolonged prone-positioning sessions significantly decreased 28-day and 90-day mortality. (Funded by the Programme Hospitalier de Recherche Clinique National 2006 and 2010 of the French Ministry of Health; PROSEVA ClinicalTrials.gov number, NCT00527813.).

Evaluation of recruited lung volume at inspiratory plateau pressure with PEEP using bedside digital chest X-ray in patients with acute lung injury/ARDS.

BACKGROUND: We wanted to assess whether there was a significant relationship between recruited lung volume (V(rec)) and change in density on digital processed chest x-ray measured at 2 different levels of inspiratory plateau pressure corresponding to 2 PEEP levels in patients with acute lung injury or ARDS. METHODS: In 14 subjects, PEEP 5 cm H2O and 15 cm H2O were prospectively applied in a random order for 10 min. At the end of each period, chest x-ray was taken using a digital portable device, and a pressure-volume curve of the respiratory system was performed. We also assessed P(aO2), and the static and the dynamic (C(dyn,rs)) compliance of the respiratory system. Change in end-expiratory lung volume between tidal breath and relaxation volume of the respiratory system was determined. Radiological attenuation was measured on chest x-rays in 4 regions of interest in the right lung, and in 3 regions of interest in the left lung, drawn in posterior intercostal spaces from top to bottom, by using dedicated software. The ratio of lung density in each region between PEEP 15 and PEEP 5 (rP15/P5) and their arithmetic mean (µP15/P5) were computed. V(rec) was determined from the pressure-volume curves. RESULTS: The median value of rP15/P5 in the 98 lung levels was 0.91 (0.80-1.01), which was significantly different from 1 (P < .001). The values of rP15/P5 were not significantly different between the lung levels. The median values of V(rec) and µP15/P5 were 288 (173-402) mL and 0.90 (0.80-0.97), respectively. There was a significant negative correlation between V(rec) and µP15/P5 (R = -0.77, P = .01). The reduction in µP15/P5 tended to correlate with the increase in C(dyn,rs) (R = -0.49, P = .077) or in P(aO2) (R = -0.53, P = .05) between PEEP 15 cm H2O and PEEP 5 cm H2O. CONCLUSIONS: Digital chest x-ray done at the bedside in acute lung injury/ARDS subjects was able to detect a reduction in density between PEEP 5 cm H2O and PEEP 15 cm H2O, which correlated with V(rec).

Comparison of Alpha 200 and CoughAssist as intermittent positive pressure breathing devices: a bench study.

BACKGROUND: Intermittent positive pressure breathing (IPPB) is used in non-intubated patients to increase lung volume and to enhance coughing. Alpha 200 (Salvia Lifetec, Kronberg, Germany) is a specific IPPB device. CoughAssist (Respironics France, Carquefou, France) is a mechanical insufflator-exsufflator used to remove secretions in patients with inefficient cough. Both can also be used for intubated or tracheotomized patients. We assessed the impact of various artificial airways on the ability of the Alpha 200 and CoughAssist to generate insufflated volume. METHODS: We measured the insufflated volume and pressure at the airway opening in a lung model under 2 conditions of compliance (30 or 60 mL/cm H(2)O) at single resistance of 5 cm H(2)O/L/s. The devices were used at 2 set pressures: 30 and 40 cm H(2)O. The Alpha 200 was set at 2 inflation flows: 0.5 and 1 L/s, whereas CoughAssist was set at its highest value of 10 L/s. Measurements were done without (control) and with different size endotracheal tubes and tracheostomy cannulae. The relationships between insufflated volume and measured pressure were analyzed using linear regressions. RESULTS: The slopes and intercepts of the control relationship between insufflated volume and pressure were significantly greater with Alpha 200 at each set flow than with CoughAssist. As artificial airways were used, the insufflated volume did not differ from the control with CoughAssist, while with Alpha 200 it increased at each flow setting and for all mechanical conditions. The largest differences in insufflated volume between the 2 devices were observed for the largest endotracheal tubes and tracheostomy cannulas and for the lowest inflation flow setting in Alpha 200. These results can be explained in terms of how the devices function, as CoughAssist adapts by increasing flow, while Alpha 200 adapts by increasing inspiratory time. CONCLUSIONS: This bench study has shown that in the presence of artificial airways the value of the insufflated volume generated by the CoughAssist device was significantly lower than that generated by the Alpha 200 device.

Expiratory flow-volume loop profile and patient outcome in chronic obstructive pulmonary disease in acute respiratory failure: a prospective observational study in a single intensive care unit.

BACKGROUND: Expiratory flow-volume (EFV) loops are continuously displayed on the screen of intensive care unit (ICU) ventilators. OBJECTIVES: It was the aim of this study to investigate the relationships of EFV to chronic obstructive pulmonary disease (COPD) patient outcome. METHODS: This is a prospective study on COPD patients who received invasive mechanical ventilation for acute respiratory failure in the ICU. Within the 24-hour post-intubation period, the angle of the EFV slope during the last 50% of expiration was computed and patients were stratified into 4 quartiles. Resistance, compliance of the respiratory system and change in end-expiratory lung volume above relaxation volume were assessed. Patients were followed up to hospital discharge. The main outcome was hospital mortality. Secondary outcomes were ICU mortality, length of ICU stay, duration of invasive ventilation, number of intubations, oxygen and non-invasive ventilation. RESULTS: Thirty-eight patients were analysed. The first quartile comprised 9 patients (median angle 11°, interquartile range 8-12), the second 10 patients (median angle 26°, range 19-30), the third 10 patients (median angle 42°, range 39-46), and the fourth 9 patients (median angle 53°, range 49-64). Hospital and ICU mortality were not different between groups. Lengths of ICU and hospital stay and length of invasive ventilation were significantly different between groups, with the highest values observed in the first quartile. The rate of oxygen use and non-invasive ventilation in the ICU and at hospital discharge was significantly different between groups, with the highest rate observed in the first quartile. There was a significant negative correlation between angle and resistance, compliance of the respiratory system and change in end-expiratory lung volume above the relaxation volume. CONCLUSION: The slope of the angle during the last 50% of expired volume in the COPD patients was associated with worsened respiratory mechanics and higher morbidity.

Efficacy and safety of recruitment maneuvers in acute respiratory distress syndrome.

Recruitment maneuvers (RM) consist of a ventilatory strategy that increases the transpulmonary pressure transiently to reopen the recruitable lung units in acute respiratory distress syndrome (ARDS). The rationales to use RM in ARDS are that there is a massive loss of aerated lung and that once the end-inspiratory pressure surpasses the regional critical opening pressure of the lung units, those units are likely to reopen. There are different methods to perform RM when using the conventional ICU ventilator. The three RM methods that are mostly used and investigated are sighs, sustained inflation, and extended sigh. There is no standardization of any of the above RM. Meta-analysis recommended not to use RM in routine in stable ARDS patients but to run them in case of life-threatening hypoxemia. There are some concerns regarding the safety of RM in terms of hemodynamics preservation and lung injury as well. The rapid rising in pressure can be a factor that explains the potential harmful effects of the RM. In this review, we describe the balance between the beneficial effects and the harmful consequences of RM. Recent animal studies are discussed.

Performance of the coughassist insufflation-exsufflation device in the presence of an endotracheal tube or tracheostomy tube: a bench study.

BACKGROUND: The CoughAssist is a mechanical insufflator-exsufflator designed to assist airway secretion clearance in patients with ineffective cough. The device may benefit intubated and tracheotomized patients. We assessed the impact of various artificial airways on peak expiratory flow (PEF) with the CoughAssist. METHODS: We measured PEF and pressure at the airway opening in a lung model during insufflation-exsufflation with the CoughAssist, at 3 set pressures: 30/-30, 40/-40, and 50/-50 cm H(2)O, first without (control), and then with different sizes (6.5 to 8.5 mm inner diameter) of endotracheal tube (ETT) and tracheostomy tube (6, 7, and 8 mm inner diameter), compliance settings of 30 and 60 mL/cm H(2)O, and resistance settings of 0 and 5 cm H(2)O/L/s). We analyzed the relationship between PEF and pressure with linear regression. RESULTS: With compliance of 30 mL/cm H(2)O and 0 resistance the slope of the control relationship between PEF and pressure was statistically significantly greater than during any conditions with ETT or tracheostomy tube. Therefore, in comparison to the control, the relationship of PEF to pressure significantly went in the direction from top to bottom as the ETT or tracheostomy tube became narrower. The findings were the same with compliance of 30 mL/cm H(2)O and resistance of 5 cm H(2)O/L/s. With compliance of 60 mL/cm H(2)O the highest set pressure values were not achieved and some relationships departed from linearity. The control slope of the relationship between PEF and pressure with compliance of 60 mL/cm H(2)O and 0 resistance did not significantly differ with any ETT or tracheostomy tube. CONCLUSIONS: The artificial airways significantly reduced PEF during insufflation-exsufflation with CoughAssist; the narrower the inner diameter of the artificial airway, the lower the PEF for a given expiratory pressure.

Management and long-term outcome of patients with chronic neuromuscular disease admitted to the intensive care unit for acute respiratory failure: a single-center retrospective study.

BACKGROUND: Patients with chronic neuromuscular disease represent less than 10% of those receiving mechanical ventilation in the intensive care unit (ICU). Little has been reported regarding either ICU management of acute respiratory failure (ARF) in the era of noninvasive mechanical ventilation (NIV) or long-term outcomes. OBJECTIVE: To describe the respiratory management of patients with chronic neuromuscular diseases admitted to our university hospital ICU for ARF, and the long-term outcomes. METHODS: We retrospectively analyzed patients with chronic neuromuscular diseases admitted to our ICU for a first episode of ARF between January 1, 1996, and February 27, 2007. We assessed severity of illness on ICU admission, respiratory management during ICU stay, and outcomes on June 15, 2008. RESULTS: During the study period, 87 patients (44 with hereditary and 43 with acquired neuromuscular diseases) had their first ARF episode that required ICU admission. In the hereditary-diseases group and the acquired-diseases group, respectively, the rates of NIV use during the ICU stay were 82% and 63% (P = .040), the intubation rates were 30% and 56% (P = .02), and the tracheotomy rates were 9% and 12% (difference not significant). At the final assessment (median 3 years) the mortality rate was 58%, and mortality was not significantly related to the type of neuromuscular disease. At final assessment, 46% of the patients were on NIV and 29% had tracheotomy. CONCLUSIONS: In our ICU, chronic neuromuscular disease is an uncommon cause of ARF, for which we often use NIV. These patients had a low probability of death in the ICU. Long-term outcome was independent of the type of neuromuscular disease.

Quantitative analysis of acid-base disorders in patients with chronic respiratory failure in stable or unstable respiratory condition.

BACKGROUND: The Stewart approach theorizes that plasma pH depends on P(aCO2), the strong ion difference, and the plasma total concentration of non-volatile weak acids (A(tot)). The conventional approach measures standardized base excess, bicarbonate (HCO3⁻), and the anion gap. OBJECTIVE: To describe acid-base disorders with the Stewart approach and the conventional approach in patients with chronic respiratory failure. METHODS: This was an observational prospective study in a medical intensive care unit and a pneumology ward of a university hospital. There were 128 patients included in the study, of which 14 had more than one admission, resulting in 145 admissions. These were allocated to 4 groups: stable respiratory condition and elevated HCO3⁻ (Group 1, n = 23), stable respiratory condition and non-elevated HCO3⁻ (Group 2, n = 41), unstable respiratory condition and elevated HCO3⁻ (Group 3, n = 44), and unstable respiratory condition and non-elevated HCO3⁻ (Group 4, n = 37). Elevated HCO3⁻ was defined as ≥ 3 standard deviations higher than the mean value we found in 8 healthy volunteers. Measurements were taken on admission. RESULTS: In groups 1, 2, 3, and 4, the respective mean ± SD values were: HCO3⁻ 33 ± 3 mM, 26 ± 3 mM, 37 ± 4 mM, and 27 ± 3 mM (P < .001); strong ion difference 45 ± 3 mM, 38 ± 4 mM, 46 ± 4 mM, and 36 ± 4 mM (P < .001); and A(tot) 12 ± 1 mM, 12 ± 1 mM, 10 ± 1 mM, 10 ± 2 mM (P < .001). Non-respiratory disorders related to high strong ion difference were observed in 12% of patients with elevated HCO3⁻, and in none of those with non-elevated HCO3⁻ (P = .003). Non-respiratory disorders related to low strong ion difference were observed in 9% of patients with non-elevated HCO3⁻, and in none of those with elevated HCO3⁻ (P = .02). Hypoalbuminemia was common, especially in unstable patients (group 3, 66%; group 4, 65%). Normal standardized base excess (16%), HCO3⁻ (28%), and anion gap (30%) values were common. The Stewart approach detected high effective strong ion difference in 13% of normal standardized base excess, and in 20% of normal anion gap corrected for albuminemia, and low effective strong ion difference in 22% of non-elevated HCO3⁻. CONCLUSIONS: In patients with chronic respiratory failure the acid-base pattern is complex, metabolic alkalosis is present in some patients with elevated HCO3⁻, and metabolic acidosis is present in some with non-elevated HCO3⁻. The diagnostic performance of the Stewart approach was better than that of the conventional approach, even when corrected anion gap was taken into account.

A case of pneumomediastinum in a patient with acute respiratory distress syndrome on pressure support ventilation.

During mechanical ventilation for acute respiratory distress syndrome, tidal volume (V(T)) must be reduced. Once switched to pressure-support ventilation, there is a risk that uncontrolled large V(T) may be delivered. A 63-year-old man with community-acquired pneumonia required tracheal intubation and mechanical ventilation, with a V(T) of 6 mL/kg predicted body weight, PEEP of 10 cm H2O, a respiratory rate of 30 breaths/min, and F(IO2) of 0.60. Plateau pressure was 22 cm H2O. He improved and received pressure-support. Twelve days later a chest radiograph showed suspected air leaks, confirmed via computed tomogram (CT), which showed anterior pneumomediastinum. V(T) received over the previous 3 days had averaged 14 mL/kg predicted body weight. The patient was put back onto volume-controlled mode, and 2 days later there were no air leaks. In pressure-support ventilation, V(T) must be closely monitored to ensure lung-protective mechanical ventilation.