Paolo Formenti

Diaphragm ultrasound as indicator of respiratory effort in critically ill patients undergoing assisted mechanical ventilation: a pilot clinical study

IntroductionPressure-support ventilation, is widely used in critically ill patients; however, the relative contribution of patient’s effort during assisted breathing is difficult to measure in clinical conditions. Aim of the present study was to evaluate the performance of ultrasonographic indices of diaphragm contractile activity (respiratory excursion and thickening) in comparison to traditional indices of inspiratory muscle effort during assisted mechanical ventilation.MethodConsecutive patients admitted to the ICU after major elective surgery who met criteria for a spontaneous breathing trial with pressure support ventilation were enrolled. Patients with airflow obstruction or after thoracic/gastric/esophageal surgery were excluded. Variable levels of inspiratory muscle effort were achieved by delivery of different levels of ventilatory assistance by random application of pressure support (0, 5 and 15 cmH2O). The right hemidiaphragm was evaluated by B- and M-mode ultrasonography to record respiratory excursion and thickening. Airway, gastric and oesophageal pressures, and airflow were recorded to calculate indices of respiratory effort (diaphragm and esophageal pressure–time product).Results25 patients were enrolled. With increasing levels of pressure support, parallel reductions were found between diaphragm thickening and both diaphragm and esophageal pressure–time product (respectively, R = 0.701, p < 0.001 and R = 0.801, p < 0.001) during tidal breathing. No correlation was found between either diaphragm or esophageal pressure–time product and diaphragm excursion (respectively, R = −0.081, p = 0.506 and R = 0.003, p = 0.981), nor was diaphragm excursion correlated to diaphragm thickening (R = 0.093, p = 0.450) during tidal breathing.ConclusionsIn patients undergoing in assisted mechanical ventilation, diaphragm thickening is a reliable indicator of respiratory effort, whereas diaphragm excursion should not be used to quantitatively assess diaphragm contractile activity.

Pleural effusion complicates monitoring of respiratory mechanics

Objectives:Although pleural effusion reduces respiratory system compliance by restricting the lungs, the effusion volume is partially accommodated by chest wall expansion. The implications for these opposing volume changes on airway pressure monitoring in ventilated patients with pleural effusion are unreported. We investigated the interactions among pleural effusion, positive end-expiratory pressure, and indices of respiratory mechanics in a swine model. Design:Interventional animal model. Setting:Hospital animal research facility. Subjects:Nine deeply anesthetized swine. Interventions:The preparation included tracheostomy, arterial/venous catheter placement, and chest tube insertion. Animals were ventilated throughout the study at 9 mL/kg, and frequency was adjusted to maintain normocapnia (inspiratory:expiratory = 1:2, Fio2 = 0.5) and positive end-expiratory pressure of 1 cm H2O and 10 cm H2O. Fluid was instilled into the right pleural space to simulate effusions of 13 mL/kg (pleural effusion 1) and 26 mL/kg (pleural effusion 2). Measurements and Main Results:Quantitative computerized tomography studies (in five animals) and functional residual capacity volumes (wash-in/wash-out technique) were obtained for each pleural effusion/positive end-expiratory pressure combination. Mean functional residual capacity compared to baseline at positive end-expiratory pressure of 1 cm H2O was decreased by pleural effusion 1 and pleural effusion 2 (−42%, −64%) and restored by positive end-expiratory pressure of 10 cm H2O (moderate) to +23% of baseline for pleural effusion 1 and +1% for pleural effusion 2. Plateau pressure increased and compliance decreased in response to pleural effusion 1 and pleural effusion 2. Moderate positive end-expiratory pressure applied during both pleural effusion quantities restored plateau pressure and tidal compliance to prepleural effusion values. Computed tomography studies revealed lung compression and tidal derecruitment cycles occurring with pleural effusion at positive end-expiratory pressure of 1 cm H2O, whereas a moderate positive end-expiratory pressure restored prepleural effusion functional residual capacity and prevented lung and intratidal derecruitment. Conclusions:When pleural effusion is present, respiratory mechanics must be interpreted cautiously and sufficient positive end-expiratory pressure should be applied to prevent extensive collapse and intratidal cycles of recruitment/derecruitment.

Lung recruitment in acute respiratory distress syndrome: what is the best strategy?

Purpose of reviewSupporting patients with acute respiratory distress syndrome (ARDS) using a low tidal volume strategy is a standard practice in the ICU. Recruitment maneuvers can be used to augment other methods, like positive end-expiratory pressure and positioning, to improve aerated lung volume. Clinical practice varies widely, and optimal method and patient selection for recruitment maneuvers have not been determined. Recent findingsRecent developments include experimental and clinical evidence that a stepwise extended recruitment maneuver may match the improvement in aerated lung volume seen with sustained inflation traditionally used, with less adverse effects. Positioning and other chest wall modifications may be useful adjuncts to recruitment maneuvers. In addition, evidence from clinical studies in the operating room suggests that recruitment maneuvers, as a component of an open lung strategy, may be helpful for mechanically ventilated patients with normal lungs. SummaryAs a component of ventilation strategy for patients with ARDS, the use of recruitment maneuvers, especially a stepwise maneuver, in addition to adequate positive end-expiratory pressure and appropriate positioning, is suggested by currently available data. Until their effect on clinical outcomes is further defined, the use of recruitment maneuvers in ARDS and other settings will continue to be guided by individual clinician experience and patient factors.

Current Concepts of ARDS: A Narrative Review

Acute respiratory distress syndrome (ARDS) is characterized by the acute onset of pulmonary edema of non-cardiogenic origin, along with bilateral pulmonary infiltrates and reduction in respiratory system compliance. The hallmark of the syndrome is refractory hypoxemia. Despite its first description dates back in the late 1970s, a new definition has recently been proposed. However, the definition remains based on clinical characteristic. In the present review, the diagnostic workup and the pathophysiology of the syndrome will be presented. Therapeutic approaches to ARDS, including lung protective ventilation, prone positioning, neuromuscular blockade, inhaled vasodilators, corticosteroids and recruitment manoeuvres will be reviewed. We will underline how a holistic framework of respiratory and hemodynamic support should be provided to patients with ARDS, aiming to ensure adequate gas exchange by promoting lung recruitment while minimizing the risk of ventilator-induced lung injury. To do so, lung recruitability should be considered, as well as the avoidance of lung overstress by monitoring transpulmonary pressure or airway driving pressure. In the most severe cases, neuromuscular blockade, prone positioning, and extra-corporeal life support (alone or in combination) should be taken into account.

Experimental intra-abdominal hypertension attenuates the benefit of positive end-expiratory pressure in ventilating effusion-compressed lungs*.

Objective:To test the ability of positive end-expiratory pressure to offset the reduction of resting lung volume caused by intra abdominal hypertension, unilateral pleural effusion, and their combination. Design:Controlled application of intrapleural fluid, raised abdominal pressure and their combination before and after positive end-expiratory pressure in an anesthetized porcine model of controlled ventilation. Setting:Large animal laboratory of a university-affiliated hospital. Subjects:Fourteen deeply anesthetized swine (weight 30–35 kg). Interventions:Unilateral pleural effusion instillation (13 mL/kg), intra-abdominal hypertension (15 mm Hg), and simultaneous pleural effusion/intra abdominal hypertension. Measurements:Tidal compliance, end-expiratory lung aeration by gas dilution functional residual capacity, and quantitative analyses of computerized tomograms of the lungs at the extremes of the tidal cycle. Main Results:Positive end-expiratory pressure of 10 cm H2O (positive end-expiratory pressure10) increased mean functional residual capacity by 368 mL when pleural effusion was present and by 184 mL when intra-abdominal hypertension was present. When pleural effusion and intra-abdominal hypertension were simultaneously applied, positive end-expiratory pressure 10 failed to improve tidal compliance and increased functional residual capacity by only 77 mL, whereastidal recruitment during ventilation remained substantial. Conclusions:The presence of intra-abdominal hypertension negates most of the positive end-expiratory pressure10 benefit in reversing pleural effusion–induced de-recruitment. Relief of intra-abdominal hypertension may be instrumental to the treatment of pleural effusion-associated lung restriction and cyclical tidal collapse and reopening.

Ultrasonographic Assessment of Diaphragm Function in Critically Ill Subjects

The majority of patients admitted to the ICU require mechanical ventilation as a part of their process of care. However, mechanical ventilation itself or the underlying disease can lead to dysfunction of the diaphragm, a condition that may contribute to the failure of weaning from mechanical ventilation. However, extended time on the ventilator increases health-care costs and greatly increases patient morbidity and mortality. Nevertheless, symptoms and signs of muscle disease in a bedridden (or bed rest-only) ICU patient are often difficult to assess because of concomitant confounding factors. Conventional assessment of diaphragm function lacks specific, noninvasive, time-saving, and easily performed bedside tools or requires patient cooperation. Recently, the use of ultrasound has raised great interest as a simple, noninvasive method of quantification of diaphragm contractile activity. In this review, we discuss the physiology and the relevant pathophysiology of diaphragm function, and we summarize the recent findings concerning the evaluation of its (dys)function in critically ill patients, with a special focus on the role of ultrasounds. We describe how to assess diaphragm excursion and diaphragm thickening during breathing and the meaning of these measurements under spontaneous or mechanical ventilation as well as the reference values in health and disease. The spread of ultrasonographic assessment of diaphragm function may possibly result in timely identification of patients with diaphragm dysfunction and to a potential improvement in the assessment of recovery from diaphragm weakness.

Enteral vs. intravenous ICU sedation management: study protocol for a randomized controlled trial

BackgroundA relevant innovation about sedation of long-term Intensive Care Unit (ICU) patients is the ‘conscious target’: patients should be awake even during the critical phases of illness. Enteral sedative administration is nowadays unusual, even though the gastrointestinal tract works soon after ICU admission. The enteral approach cannot produce deep sedation; however, it is as adequate as the intravenous one, if the target is to keep patients awake and adapted to the environment, and has fewer side effects and lower costs.Methods/DesignA randomized, controlled, multicenter, single-blind trial comparing enteral and intravenous sedative treatments has been done in 12 Italian ICUs. The main objective was to achieve and maintain the desired sedation level: observed RASS = target RASS ± 1. Three hundred high-risk patients were planned to be randomly assigned to receive either intravenous propofol/midazolam or enteral melatonin/hydroxyzine/lorazepam. Group assignment occurred through online minimization process, in order to balance variables potentially influencing the outcomes (age, sex, SAPS II, type of admission, kidney failure, chronic obstructive pulmonary disease, sepsis) between groups. Once per shift, the staff recorded neurological monitoring using validated tools. Three flowcharts for pain, sedation, and delirium have been proposed; they have been designed to treat potentially correctable factors first, and, only once excluded, to administer neuroactive drugs. The study lasted from January 24 to December 31, 2012. A total of 348 patients have been randomized, through a centralized website, using a specific software expressly designed for this study. The created network of ICUs included a mix of both university and non-university hospitals, with different experience in managing enteral sedation. A dedicated free-access website was also created, in both Italian and English, for continuous education of ICU staff through CME courses.DiscussionThis ‘educational research’ project aims both to compare two sedative strategies and to highlight the need for a profound cultural change, improving outcomes by keeping critically-ill patients awake.Trial registration numberClinicaltrials.gov #NCT01360346

Melatonin Pharmacological Blood Levels Increase Total Antioxidant Capacity in Critically Ill Patients

In this study, the aim was to test the biochemical effects of melatonin supplementation in Intensive Care Unit (ICU) patients, since their blood levels are decreased. Sixty-four patients were enrolled in the study. From the evening of the 3rd ICU day, patients were randomized to receive oral melatonin (3 mg, group M) or placebo (group P) twice daily, at 20:00 and 24:00, until discharged. Blood was taken (at 00:00 and 14:00), on the 3rd ICU day to assess basal nocturnal melatonin values, and then during the treatment period on the 4th and 8th ICU days. Melatonin, total antioxidant capacity, and oxidative stress were evaluated in serum. Melatonin circadian rhythm before treatment was similar in the two groups, with a partial preservation of the cycle. Four hours from the 1st administration (4th ICU day, 00:00), melatonin levels increased to 2514 (982.3; 7148) pg·mL−1 in group M vs. 20.3 (14.7; 62.3) pg·mL−1 in group P (p < 0.001). After five treatment days (8th ICU day), melatonin absorption showed a repetitive trend in group M, while in group P nocturnal secretion (00:00) was impaired: 20 (11.5; 34.5) pg·mL−1 vs. 33.8 (25.0; 62.2) on the 3rd day (p = 0.029). Immediately from the beginning of treatment, the total antioxidant capacity was significantly higher in melatonin treated subjects at 00:00; a significant correlation was found between total antioxidant capacity and blood melatonin values (ρ = 0.328; p < 0.001). The proposed enteral administration protocol was adequate, even in the early phase, to enhance melatonin blood levels and to protect the patients from oxidative stress. The antioxidant effect of melatonin could play a meaningful role in the care and well-being of these patients.

Drainage of pleural effusion in mechanically ventilated patients: Time to measure chest wall compliance? ☆ ☆☆ ★ ★★ ☆☆☆

PURPOSE Pleural effusion (PE) is commonly encountered in mechanically ventilated, critically ill patients and is generally addressed with evacuation or by fluid displacement using increased airway pressure (P(AW)). However, except when massive or infected, clear evidence is lacking to guide its management. The aim of this study was to investigate the effect of recruitment maneuvers and drainage of unilateral PE on respiratory mechanics, gas exchange, and lung volume. MATERIALS AND METHODS Fifteen critically ill and mechanically ventilated patients with unilateral PE were enrolled. A 3-step protocol (baseline, recruitment, and effusion drainage) was applied to patients with more than 400 mL of PE, as estimated by chest ultrasound. Predefined subgroup analysis compared patients with normal vs reduced chest wall compliance (C(CW)). Esophageal and P(AW)s, respiratory system, lung and C(CW)s, arterial blood gases, and end-expiratory lung volumes were recorded. RESULTS In the whole case mix, neither recruitment nor drainage improved gas exchange, lung volume, or tidal mechanics. When C(CW) was normal, recruitment improved lung compliance (81.9 [64.8-104.1] vs 103.7 [91.5-111.7] mL/cm H2O, P < .05), whereas drainage had no significant effect on total respiratory system mechanics or gas exchange, although it measurably increased lung volume (1717 vs 2150 mL, P < .05). In the setting of reduced C(CW), however, recruitment had no significant effect on total respiratory system mechanics or gas exchange, whereas pleural drainage improved respiratory system and C(CW)s as well as lung volume (42.7 [38.9-50.0] vs 47.0 [43.8-63.3], P < .05 and 97.4 [89.3-97.9] vs 126.7 [92.3-153.8] mL/cm H2O, P < .05 and 1580 vs 1750 mL, P < .05, respectively). CONCLUSIONS Drainage of a moderate-sized effusion should not be routinely performed in unselected population of critically ill patients. We suggest that measurement of C(CW) may help in the decision-making process.

Noninvasive CPAP With Face Mask: Comparison Among New Air-Entrainment Masks and the Boussignac Valve

BACKGROUND: The performances of 2 noninvasive CPAP systems (high flow and low flow air-entrainment masks) were compared to the Boussignac valve in 3 different scenarios. METHODS: Scenario 1: pneumatic lung simulator with a tachypnea pattern (tidal volume 800 mL at 40 breaths/min). Scenario 2: Ten healthy subjects studied during tidal breaths and tachypnea. Scenario 3: Twenty ICU subjects enrolled for a noninvasive CPAP session. Differences between set and effective CPAP level and FIO2, as well as the lowest airway pressure and the pressure swing around the imposed CPAP level, were analyzed. The lowest airway pressure and swing were correlated to the pressure-time product (area of the airway pressure curve below the CPAP level) measured with the simulator. PaO2 was a subjects further performance index. RESULTS: Lung simulator: Boussignac FIO2 was 0.54, even if supplied with pure oxygen. The air-entrainment masks had higher swing than the Boussignac (P = .007). Pressure-time product correlated better with pressure swing (Spearman correlation coefficient [ρ] = 0.97) than with lowest airway pressure (ρ = 0.92). In healthy subjects, the high-flow air-entrainment mask showed lower difference between set and effective FIO2 (P < .001), and lowest airway pressure (P < .001), compared to the Boussignac valve. In all measurements the Boussignac valve showed higher than imposed CPAP level (P < .001). In ICU subjects the high-flow mask had lower swing than the Boussignac valve (P = .03) with similar PaO2 increase. CONCLUSIONS: High-flow air-entrainment mask showed the best performance in human subjects. During high flow demand, the Boussignac valve delivered lower than expected FIO2 and showed higher dynamic hyper-pressurization than the air-entrainment masks.