Ana Córdoba-Izquierdo

Patient-Ventilator Asynchrony During Noninvasive Ventilation: A Bench and Clinical Study

BACKGROUND Different kinds of ventilators are available to perform noninvasive ventilation (NIV) in ICUs. Which type allows the best patient-ventilator synchrony is unknown. The objective was to compare patient-ventilator synchrony during NIV between ICU, transport—both with and without the NIV algorithm engaged—and dedicated NIV ventilators. METHODS First, a bench model simulating spontaneous breathing efforts was used to assess the respective impact of inspiratory and expiratory leaks on cycling and triggering functions in 19 ventilators. Second, a clinical study evaluated the incidence of patient-ventilator asynchronies in 15 patients during three randomized, consecutive, 20-min periods of NIV using an ICU ventilator with and without its NIV algorithm engaged and a dedicated NIV ventilator. Patient-ventilator asynchrony was assessed using flow, airway pressure, and respiratory muscles surface electromyogram recordings. RESULTS On the bench, frequent auto-triggering and delayed cycling occurred in the presence of leaks using ICU and transport ventilators. NIV algorithms unevenly minimized these asynchronies, whereas no asynchrony was observed with the dedicated NIV ventilators in all except one. These results were reproduced during the clinical study: The asynchrony index was significantly lower with a dedicated NIV ventilator than with ICU ventilators without or with their NIV algorithm engaged (0.5% [0.4%-1.2%] vs 3.7% [1.4%-10.3%] and 2.0% [1.5%-6.6%], P < .01), especially because of less auto-triggering. CONCLUSIONS Dedicated NIV ventilators allow better patient-ventilator synchrony than ICU and transport ventilators, even with their NIV algorithm. However, the NIV algorithm improves, at least slightly and with a wide variation among ventilators, triggering and/or cycling off synchronization.

Noninvasive Ventilation for Acute Hypercapnic Respiratory Failure: Intubation Rate in an Experienced Unit

BACKGROUND: Failure of noninvasive ventilation (NIV) is common in patients with COPD admitted to the ICU for acute hypercapnic respiratory failure (AHRF). We aimed to assess the rate of NIV failure and to identify early predictors of intubation under NIV in patients admitted for AHRF of all origins in an experienced unit. METHODS: This was an observational cohort study using data prospectively collected over a 3-year period after the implementation of a nurse-driven NIV protocol in a 24-bed medical ICU of a French university hospital. RESULTS: Among 242 subjects receiving NIV for AHRF (PaCO2 > 45 mm Hg), 67 had cardiogenic pulmonary edema (CPE), 146 had acute-on-chronic respiratory failure (AOCRF) (including 99 subjects with COPD and 47 with other chronic respiratory diseases), and 29 had non-AOCRF (mostly pneumonia). Overall, the rates of intubation and ICU mortality were respectively 15% and 5%. The intubation rates were 4% in CPE, 15% in AOCRF, and 38% in non-AOCRF (P < .001). After adjustment, non-AOCRF was independently associated with NIV failure, as well as acidosis (pH < 7.30) and severe hypoxemia (PaO2/FIO2 ≤ 200 mm Hg) after 1 hour of NIV initiation, whereas altered consciousness on admission and ventilatory settings had no influence on outcome. CONCLUSIONS: With a nurse-driven NIV protocol, the intubation rate was reduced to 15% in patients receiving NIV for AHRF, with a mortality rate of only 5%. Whereas the risk of NIV failure is associated with hypoxemia and acidosis after initiation of NIV, it is also markedly influenced by the presence or absence of an underlying chronic respiratory disease.

Comparison of Sleep Quality With Mechanical Versus Spontaneous Ventilation During Weaning of Critically Ill Tracheostomized Patients

Background:In mechanically ventilated patients under mechanical ventilation in the ICU, ventilatory mode or settings may influence sleep quality. The aim of this study was to evaluate the direct impact of mechanical ventilation per se on sleep quantity and quality in patients who were able to tolerate separation from mechanical ventilation over prolonged periods. Design and Setting:Randomized crossover clinical trial in a medical ICU. Patients:Sixteen conscious patients, free of sedation and tracheostomized because of prolonged weaning from mechanical ventilation, were included in the study when able to tolerate at least 5 hours of spontaneous ventilation. Interventions:Patients were randomized to receive either spontaneous ventilation or mechanical ventilation at low levels of pressure support for two crossover periods of 5-hour duration each, from 22:00 to 08:00. Polysomnography was performed throughout the study. Measurements and Results:Total sleep time was higher during mechanical ventilation than during spontaneous ventilation (183 min vs 132 min, p = 0.04). No significant differences between mechanical ventilation and spontaneous ventilation were observed in slow wave sleep time (45 min vs 28 min), rapid eye movement sleep time (11 min vs 3 min), or the fragmentation index (25 vs 23 arousals and awakenings per hr). In four patients, however, our analysis of patient–ventilator interaction suggested that the ventilatory settings were suboptimal and could have been improved to potentially improve sleep. Conclusions:In difficult-to-wean tracheostomized patients, sleep quality was similar with or without the ventilator. Sleep quantity was higher during mechanical ventilation. Reconnection to the ventilator during the night period may favor sleep efficiency in tracheostomized patients in prolonged weaning.

Sleep in hypercapnic critical care patients under noninvasive ventilation: conventional versus dedicated ventilators.

Objective:To compare sleep quality between two types of ventilators commonly used for noninvasive ventilation: conventional ICU ventilators and dedicated noninvasive ventilators; and to evaluate sleep during and between noninvasive ventilation sessions in critically ill patients. Design:Physiological sleep study with a randomized assessment of the ventilator type. Setting:Medical ICU in a university hospital. Patients:Twenty-four patients admitted for acute hypercapnic respiratory failure requiring noninvasive ventilation. Interventions:Patients were randomly assigned to receive noninvasive ventilation with either an ICU ventilators (n = 12) or a dedicated noninvasive ventilators (n = 12), and their sleep and respiratory parameters were recorded by polysomnography from 4 PM to 9 AM on the second, third, or fourth day after noninvasive ventilation initiation. Measurements and Main Results:Sleep architecture was similar between ventilator groups, including sleep fragmentation (number of arousals and awakenings/hr), but the dedicated noninvasive ventilators group showed a higher patient–ventilator asynchrony-related fragmentation (28% [17–44] vs. 14% [7.0–22]; p = 0.02), whereas the ICU ventilators group exhibited a higher noise-related fragmentation. Ineffective efforts were more frequent in the dedicated noninvasive ventilators group than in the ICU ventilators group (34 ineffective efforts/hr of sleep [15–125] vs. two [0–13]; p < 0.01), possibly as a result of a higher tidal volume (7.2 mL/kg [6.7–8.8] vs. 5.8 [5.1–6.8]; p = 0.04). More sleep time occurred and sleep quality was better during noninvasive ventilation sessions than during spontaneous breathing periods (p < 0.05) as a result of greater slow wave and rapid eye movement sleep and lower fragmentation. Conclusions:There were no observed differences in sleep quality corresponding to the type of ventilator used despite slight differences in patient–ventilator asynchrony. Noninvasive ventilation sessions did not prevent patients from sleeping; on the contrary, they seem to aid sleep when compared with unassisted breathing.

Comparison Between Neurally Adjusted Ventilatory Assist and Pressure Support Ventilation Levels in Terms of Respiratory Effort.

Objectives:To understand the potential equivalence between neurally adjusted ventilatory assist and pressure support ventilation levels in terms of respiratory muscle unloading. To compare the respiratory pattern, variability, synchronization, and neuromuscular coupling within comparable ranges of assistance. Design:Prospective single-center physiologic study. Setting:A 13-bed university medical ICU. Patients:Eleven patients recovering from respiratory failure. Interventions:The following levels of assistance were consecutively applied in a random order: neurally adjusted ventilatory assist levels: 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, and 7 cm H2O/&mgr;volt; pressure support levels: 7, 10, 15, 20, and 25 cm H2O. Measurements and Main Results:Flow, airway pressure, esophageal pressures, and peak electrical activity of the diaphragm were continuously recorded. Breathing effort was calculated. To express the percentage of assist assumed by the ventilator, the total pressure including muscular and ventilator pressure was calculated. The median percentage of assist ranged from 33% (24–47%) to 82% (72–90%) between pressure support 7 and 25 cm H2O. Similar levels of unloading were observed for neurally adjusted ventilatory assist levels from 0.5 cm H2O/&mgr;volt (46% [40–51%]) to 2.5 cm H2O/&mgr;volt (80% [74–84%]). Tidal variability was higher during neurally adjusted ventilatory assist and ineffective efforts appeared only in pressure support. In neurally adjusted ventilatory assist, double triggering occurred sometimes when electrical activity of the diaphragm signal depicted a biphasic aspect, and an abnormal oscillatory pattern was frequently observed from 4 cm H2O/&mgr;volt. For both modes, the relationship between peak electrical activity of the diaphragm and muscle pressure depicted a curvilinear profile. Conclusions:In patients recovering from acute respiratory failure, levels of neurally adjusted ventilatory assist between 0.5 and 2.5 cm H2O/&mgr;volt are comparable to pressure support levels ranging from 7 to 25 cm H2O in terms of respiratory muscle unloading. Neurally adjusted ventilatory assist provides better patient-ventilator interactions but can be sometimes excessively sensitive to electrical activity of the diaphragm in terms of triggering.

Severe but not mild hypercapnia affects the outcome in patients with severe cardiogenic pulmonary edema treated by non-invasive ventilation

BackgroundPatients with severe cardiogenic pulmonary edema (CPE) are frequently hypercapnic, possibly because of associated underlying chronic lung disease (CLD). Since hypercapnia has been associated with outcome, we aimed to identify factors associated to hypercapnia and its role on outcome of patients with CPE and no underlying CLD.MethodsObservational cohort study using data prospectively collected over a 3-year period. After excluding patients with any CLD or obstructive sleep apneas, all patients treated by non-invasive ventilation (NIV) for severe CPE were included. Hypercapnia was defined as PaCO2 >45 mmHg and non-rapid favorable outcome was defined as the need for intubation or continuation of NIV for more than 48 h.ResultsAfter excluding 60 patients with underlying CLD or sleep apneas, 112 patients were studied. The rates of intubation and of prolonged NIV were 6.3 % (n = 7) and 21.4 % (n = 24), respectively. Half of the patients (n = 56) had hypercapnia upon admission. Hypercapnic patients were older, more frequently obese, and were more likely to have a respiratory tract infection than non-hypercapnic patients. Hypercapnia had no influence on intubation rate or the need for prolonged NIV. However, patients with severe hypercapnia (PaCO2 >60 mmHg) needed longer durations of NIV and intensive care unit (ICU) stay than the others.ConclusionsAmong the patients admitted for severe CPE without CLD, half of them had hypercapnia at admission. Hypercapnic patients were older and more frequently obese but their outcome was similar compared to non-hypercapnic patients. Patients with severe hypercapnia needed longer durations of NIV than the others without increase in intubation rate.

Noninvasive ventilation for acute hypercapnic respiratory failure: is it the same as in hypercapnic coma?--reply.

In Reply: We read with a great interest the comments made by Dr Killen H Briones Claudett concerning adjustments of ventilatory settings during noninvasive ventilation (NIV) to treat subjects with hypercapnic coma. In a recent original article published in the December 2013 issue of Respiratory