Nuttapol Rittayamai

Evolution of Diaphragm Thickness during Mechanical Ventilation. Impact of Inspiratory Effort

RATIONALE Diaphragm atrophy and dysfunction have been reported in humans during mechanical ventilation, but the prevalence, causes, and functional impact of changes in diaphragm thickness during routine mechanical ventilation for critically ill patients are unknown. OBJECTIVES To describe the evolution of diaphragm thickness over time during mechanical ventilation, its impact on diaphragm function, and the influence of inspiratory effort on this phenomenon. METHODS In three academic intensive care units, 107 patients were enrolled shortly after initiating ventilation along with 10 nonventilated intensive care unit patients (control subjects). Diaphragm thickness and contractile activity (quantified by the inspiratory thickening fraction) were measured daily by ultrasound. MEASUREMENTS AND MAIN RESULTS Over the first week of ventilation, diaphragm thickness decreased by more than 10% in 47 (44%), was unchanged in 47 (44%), and increased by more than 10% in 13 (12%). Thickness did not vary over time following extubation or in nonventilated patients. Low diaphragm contractile activity was associated with rapid decreases in diaphragm thickness, whereas high contractile activity was associated with increases in diaphragm thickness (P = 0.002). Contractile activity decreased with increasing ventilator driving pressure (P = 0.01) and controlled ventilator modes (P = 0.02). Maximal thickening fraction (a measure of diaphragm function) was lower in patients with decreased or increased diaphragm thickness (n = 10) compared with patients with unchanged thickness (n = 10; P = 0.05 for comparison). CONCLUSIONS Changes in diaphragm thickness are common during mechanical ventilation and may be associated with diaphragmatic weakness. Titrating ventilatory support to maintain normal levels of inspiratory effort may prevent changes in diaphragm configuration associated with mechanical ventilation.

Esophageal and transpulmonary pressure in the clinical setting: meaning, usefulness and perspectives

PurposeEsophageal pressure (Pes) is a minimally invasive advanced respiratory monitoring method with the potential to guide management of ventilation support and enhance specific diagnoses in acute respiratory failure patients. To date, the use of Pes in the clinical setting is limited, and it is often seen as a research tool only.MethodsThis is a review of the relevant technical, physiological and clinical details that support the clinical utility of Pes.ResultsAfter appropriately positioning of the esophageal balloon, Pes monitoring allows titration of controlled and assisted mechanical ventilation to achieve personalized protective settings and the desired level of patient effort from the acute phase through to weaning. Moreover, Pes monitoring permits accurate measurement of transmural vascular pressure and intrinsic positive end-expiratory pressure and facilitates detection of patient–ventilator asynchrony, thereby supporting specific diagnoses and interventions. Finally, some Pes-derived measures may also be obtained by monitoring electrical activity of the diaphragm.ConclusionsPes monitoring provides unique bedside measures for a better understanding of the pathophysiology of acute respiratory failure patients. Including Pes monitoring in the intensivist’s clinical armamentarium may enhance treatment to improve clinical outcomes.

Pressure-Controlled vs Volume-Controlled Ventilation in Acute Respiratory Failure: A Physiology-Based Narrative and Systematic Review

BACKGROUND Mechanical ventilation is a cornerstone in the management of acute respiratory failure. Both volume-targeted and pressure-targeted ventilations are used, the latter modes being increasingly used. We provide a narrative review of the physiologic principles of these two types of breath delivery, performed a literature search, and analyzed published comparisons between modes. METHODS We performed a systematic review and meta-analysis to determine whether pressure control-continuous mandatory ventilation (PC-CMV) or pressure control-inverse ratio ventilation (PC-IRV) has demonstrated advantages over volume control-continuous mandatory ventilation (VC-CMV). The Cochrane tool for risk of bias was used for methodologic quality. We also introduced physiologic criteria as quality indicators for selecting the studies. Outcomes included compliance, gas exchange, hemodynamics, work of breathing, and clinical outcomes. Analyses were completed with RevMan5 using random effects models. RESULTS Thirty-four studies met inclusion criteria, many being at high risk of bias. Comparisons of PC-CMV/PC-IRV and VC-CMV did not show any difference for compliance or gas exchange, even when looking at PC-IRV. Calculating the oxygenation index suggested a poorer effect for PC-IRV. There was no difference between modes in terms of hemodynamics, work of breathing, or clinical outcomes. CONCLUSIONS The two modes have different working principles but clinical available data do not suggest any difference in the outcomes. We included all identified trials, enhancing generalizability, and attempted to include only sufficient quality physiologic studies. However, included trials were small and varied considerably in quality. These data should help to open the choice of ventilation of patients with acute respiratory failure.

Mechanical Ventilation–induced Diaphragm Atrophy Strongly Impacts Clinical Outcomes

Rationale: Diaphragm dysfunction worsens outcomes in mechanically ventilated patients, but the clinical impact of potentially preventable changes in diaphragm structure and function caused by mechanical ventilation is unknown. Objectives: To determine whether diaphragm atrophy developing during mechanical ventilation leads to prolonged ventilation. Methods: Diaphragm thickness was measured daily by ultrasound in adults requiring invasive mechanical ventilation; inspiratory effort was assessed by thickening fraction. The primary outcome was time to liberation from ventilation. Secondary outcomes included complications (reintubation, tracheostomy, prolonged ventilation, or death). Associations were adjusted for age, severity of illness, sepsis, sedation, neuromuscular blockade, and comorbidity. Measurements and Main Results: Of 211 patients enrolled, 191 had two or more diaphragm thickness measurements. Thickness decreased more than 10% in 78 patients (41%) by median Day 4 (interquartile range, 3‐5). Development of decreased thickness was associated with a lower daily probability of liberation from ventilation (adjusted hazard ratio, 0.69; 95% confidence interval [CI], 0.54‐0.87; per 10% decrease), prolonged ICU admission (adjusted duration ratio, 1.71; 95% CI, 1.29‐2.27), and a higher risk of complications (adjusted odds ratio, 3.00; 95% CI, 1.34‐6.72). Development of increased thickness (n = 47; 24%) also predicted prolonged ventilation (adjusted duration ratio, 1.38; 95% CI, 1.00‐1.90). Decreasing thickness was related to abnormally low inspiratory effort; increasing thickness was related to excessive effort. Patients with thickening fraction between 15% and 30% (similar to breathing at rest) during the first 3 days had the shortest duration of ventilation. Conclusions: Diaphragm atrophy developing during mechanical ventilation strongly impacts clinical outcomes. Targeting an inspiratory effort level similar to that of healthy subjects at rest might accelerate liberation from ventilation.

Recent advances in mechanical ventilation in patients with acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterised by different degrees of severity and different stages. Understanding these differences can help to better adapt the ventilatory settings to protect the lung from ventilator-induced lung injury by reducing hyperinflation or keeping the lung open when it is possible. The same therapies may be useful and beneficial in certain forms of ARDS, and risky or harmful at other stages: this includes high positive end-expiratory pressure, allowance of spontaneous breathing activity or use of noninvasive ventilation. The severity of the disease is the primary indicator to individualise treatment. Monitoring tools such as oesophageal pressure or lung volume measurements may also help to set the ventilator. At an earlier stage, an adequate lung protective strategy may also help to prevent the development of ARDS. The survival of patients on mechanical ventilation for ARDS can be improved by optimising ventilatory management http://ow.ly/Hapm3

Effort To Breathe With Various Spontaneous Breathing Trial Techniques. A Physiological Meta-analysis

Rationale: Spontaneous breathing trials (SBTs) are designed to simulate conditions after extubation, and it is essential to understand the physiologic impact of different methods. Objectives: We conducted a systematic review and pooled measures reflecting patient respiratory effort among studies comparing SBT methods in a meta‐analysis. Methods: We searched Medline, Excerpta Medica Database, and Web of Science from inception to January 2016 to identify randomized and nonrandomized clinical trials reporting physiologic measurements of respiratory effort (pressure‐time product) or work of breathing during at least two SBT techniques. Secondary outcomes included the rapid shallow breathing index (RSBI), and effort measured before and after extubation. The quality of physiologic measurement and research design was appraised for each study. Outcomes were analyzed using ratio of means. Measurements and Main Results: Among 4,138 citations, 16 studies (n = 239) were included. Compared with T‐piece, pressure support ventilation significantly reduced work by 30% (ratio of means [RoM], 0.70; 95% confidence interval [CI], 0.57‐0.86), effort by 30% (RoM, 0.70; 95% CI, 0.60‐0.82), and RSBI by 20% (RoM, 0.80; 95% CI, 0.75‐0.86). Continuous positive airway pressure had significantly lower pressure‐time product by 18% (RoM, 0.82; 95% CI, 0.68‐0.999) compared with T‐piece, and reduced RSBI by 16% (RoM, 0.84; 95% CI, 0.74‐0.95). Studies comparing SBTs with the postextubation period demonstrated that pressure support induced significantly lower effort and RSBI; T‐piece reduced effort, but not the work, compared with postextubation. Work, effort, and RSBI measured while intubated on the ventilator with continuous positive airway pressure of 0 cm H2O were no different than extubation. Conclusions: Pressure support reduces respiratory effort compared with T‐piece. Continuous positive airway pressure of 0 cm H2O and T‐piece more accurately reflect the physiologic conditions after extubation.

Monitoring patient-ventilator asynchrony.

Purpose of reviewThis article describes and discusses the importance of monitoring patient–ventilator asynchrony, and the advantages and limitations of the specific techniques available at the bedside to evaluate it. Recent findingsSignals provided by esophageal catheters (pressure or electromyogram) are the most reliable and accurate instruments to detect asynchronies. Esophageal signals (providing electrical activity of the diaphragm or/and esophageal pressure) have allowed the recent description of reverse triggering, a new kind of asynchrony, in which mechanical insufflation repeatedly triggers diaphragmatic contractions. However, the use of esophageal catheters is not widespread, and data on the prevalence and consequences of asynchronies are still scarce. The development of software solutions that continuously and automatically record breathing waveforms from the ventilator recording is emerging. Using this technology, recent data support the fact that asynchronies are frequent and may be negatively associated with outcome. SummaryThe prevalence and consequences of asynchronies may be largely underestimated because of a frequent lack of monitoring. Dedicated software solutions that continuously and automatically detect asynchronies may allow both clinical research and clinical applications aimed at determining the effects of asynchronies and minimizing their incidence among critically ill patients.

Trials directly comparing alternative spontaneous breathing trial techniques: a systematic review and meta-analysis

BackgroundThe effect of alternative spontaneous breathing trial (SBT) techniques on extubation success and other clinically important outcomes is uncertain.MethodsWe searched MEDLINE, EMBASE, CENTRAL, CINAHL, Evidence-Based Medicine Reviews, Ovid Health Star, proceedings of five conferences (1990–2016), and reference lists for randomized trials comparing SBT techniques in intubated adults or children. Primary outcomes were initial SBT success, extubation success, or reintubation. Two reviewers independently screened citations, assessed trial quality, and abstracted data.ResultsWe identified 31 trials (n = 3541 patients). Moderate-quality evidence showed that patients undergoing pressure support (PS) compared with T-piece SBTs (nine trials, n = 1901) were as likely to pass an initial SBT (risk ratio (RR) 1.00, 95% confidence interval (CI) 0.89–1.11; I2 = 77%) but more likely to be ultimately extubated successfully (RR 1.06, 95% CI 1.02–1.10; 11 trials, n = 1904; I2 = 0%). Exclusion of one trial with inconsistent results for SBT and extubation outcomes suggested that PS (vs T-piece) SBTs also improved initial SBT success (RR 1.06, 95% CI 1.01–1.12; I2 = 0%). Limited data suggest that automatic tube compensation plus continuous positive airway pressure (CPAP) vs CPAP alone or PS increase SBT but not extubation success.ConclusionsPatients undergoing PS (vs T-piece) SBTs appear to be 6% (95% CI 2–10%) more likely to be extubated successfully and, if the results of an outlier trial are excluded, 6% (95% CI 1–12%) more likely to pass an SBT. Future trials should investigate patients for whom SBT and extubation outcomes are uncertain and compare techniques that maximize differences in support.

Positive and negative effects of mechanical ventilation on sleep in the ICU: a review with clinical recommendations

PurposeSleep is an essential physiologic process that helps to restore normal body homeostasis. Sleep disturbances have been shown to be associated with poor clinical outcomes, such as a greater risk of cardiovascular disease and increasing mortality. Critically ill patients, particularly those receiving mechanical ventilation, may be more susceptible to sleep disruption.Methods and ResultsMechanical ventilation is an important factor influencing sleep in critically ill patients as it may have positive or negative effects, depending on patient population, mode, and specific settings. Other causes of sleep disruption include the acute illness itself, the daily routine care, and the effects of medications. Improving sleep in patients admitted to an intensive care unit has the potential to improve both short- and long-term clinical outcomes. In this article we review the specific aspects of sleep in critically ill mechanically ventilated patients, including abnormal sleep patterns and loss of circadian rhythm, as well as the effects of mechanical ventilation and intravenous sedatives on sleep quality and quantity.ConclusionsWe provide recommendations for clinicians regarding optimal ventilatory settings and discuss fields for future research.