Stéphane Delisle

Patient-ventilator interaction during pressure support ventilation and neurally adjusted ventilatory assist.

Objective: To compare the effect of pressure support ventilation and neurally adjusted ventilatory assist on breathing pattern, patient-ventilator synchrony, diaphragm unloading, and gas exchange. Increasing the level of pressure support ventilation can increase tidal volume, reduce respiratory rate, and lead to delayed ventilator triggering and cycling. Neurally adjusted ventilatory assist uses diaphragm electrical activity to control the timing and pressure of assist delivery and is expected to enhance patient-ventilator synchrony. Design: Prospective, comparative, crossover study. Setting: Adult critical care unit in a tertiary university hospital. Patients: Fourteen nonsedated mechanically ventilated patients (n = 12 with chronic obstructive pulmonary disease). Interventions: Patients were ventilated for 10-min periods, using two pressure support ventilation levels (lowest tolerable and +7 cm H2O higher) and two neurally adjusted ventilatory assist levels (same peak pressures and external positive end-expiratory pressure as with pressure support ventilation), delivered in a randomized order. Measurements and Main Results: Diaphragm electrical activity, respiratory pressures, air flow, volume, neural and ventilator respiratory rates, and arterial blood gases were measured. Peak pressures were 17 ± 6 cm H2O and 24 ± 6 cm H2O and 19 ± 5 cm H2O and 24 ± 6 cm H2O with high and low pressure support ventilation and neurally adjusted ventilatory assist, respectively. The breathing pattern was comparable with pressure support ventilation and neurally adjusted ventilatory assist during low assist; during higher assist, larger tidal volumes (p = .003) and lower breathing frequencies (p = .008) were observed with pressure support ventilation. Increasing the assist increased cycling delays only with pressure support ventilation (p = .003). Compared with pressure support ventilation, neurally adjusted ventilatory assist reduced delays of ventilator triggering (p < .001 for low and high assist) and cycling (high assist: p = .004; low assist: p = .04), and abolished wasted inspiratory efforts observed with pressure support ventilation in six subjects. The diaphragm electrical activity and pressure-time product for ventilator triggering were lower with neurally adjusted ventilatory assist (p = .005 and p = .02, respectively; analysis of variance). Arterial blood gases were similar with both modes. Conclusions: Neurally adjusted ventilatory assist can improve patient-ventilator synchrony by reducing the triggering and cycling delays, especially at higher levels of assist, at the same time preserving breathing and maintaining blood gases.

Diaphragmatic electromyography during cryoballoon ablation: a novel concept in the prevention of phrenic nerve palsy

BACKGROUND Hemidiaphragmatic paralysis is the most frequent complication associated with cryoballoon ablation for atrial fibrillation. To date, no preventive strategy has proved effective. OBJECTIVE We sought to assess the feasibility of diaphragmatic electromyography during cryoballoon ablation, explore the relationship between altered signals and phrenic nerve palsy, and define characteristic changes that herald hemidiaphragmatic paralysis. METHODS Cryoballoon ablation was performed in the right superior pulmonary vein or superior vena cava in 16 mongrel dogs weighing 37.7 ± 2.4 kg, at sites determined by phrenic nerve capture. During ablation, the phrenic nerve was paced at 60 bpm from the superior vena cava while recording diaphragmatic compound motor action potentials (CMAPs) by esophageal decapolar catheters. Diaphragmatic excursion was monitored by fluoroscopy and abdominal palpation. RESULTS Before ablation, the CMAP amplitude was 592 (interquartile range 504, 566) μV, initial latency 21.5 ± 4.2 ms, peak latency 64.7 ± 21.1 ms, and duration 101.7 ± 13.3 ms. Hemidiaphragmatic paralysis was obtained in all dogs 62 ± 34 seconds into the cryoapplication. The CMAP amplitude decreased exponentially, with no patterned changes in latencies and duration. Discriminatory analyses by receiver-operating curve characteristics identified a 30% reduction in CMAP amplitude as the most predictive cutoff value for hemidiaphragmatic paralysis (c-statistic 0.965; P<.0001). This criterion presaged diaphragmatic paralysis, as detected by abdominal palpation, by 31 ± 23 seconds. CONCLUSION Diaphragmatic electromyographic signals could be reliably recorded during cryoballoon ablation. An exponential decrease in CMAP amplitude precedes diaphragmatic paralysis, with a 30% reduction yielding the best discriminatory potential. A promising safety margin was detected, which merits prospective validation.

Sleep quality in mechanically ventilated patients: comparison between NAVA and PSV modes

BackgroundMechanical ventilation seems to occupy a major source in alteration in the quality and quantity of sleep among patients in intensive care. Quality of sleep is negatively affected with frequent patient-ventilator asynchronies and more specifically with modes of ventilation. The quality of sleep among ventilated patients seems to be related in part to the alteration between the capacities of the ventilator to meet patient demand. The objective of this study was to compare the impact of two modes of ventilation and patient-ventilator interaction on sleep architecture.MethodsProspective, comparative crossover study in 14 conscious, nonsedated, mechanically ventilated adults, during weaning in a university hospital medical intensive care unit. Patients were successively ventilated in a random ordered cross-over sequence with neurally adjusted ventilatory assist (NAVA) and pressure support ventilation (PSV). Sleep polysomnography was performed during four 4-hour periods, two with each mode in random order.ResultsThe tracings of the flow, airway pressure, and electrical activity of the diaphragm were used to diagnose central apneas and ineffective efforts. The main abnormalities were a low percentage of rapid eye movement (REM) sleep, for a median (25th-75th percentiles) of 11.5% (range, 8-20%) of total sleep, and a highly fragmented sleep with 25 arousals and awakenings per hour of sleep. Proportions of REM sleep duration were different in the two ventilatory modes (4.5% (range, 3-11%) in PSV and 16.5% (range, 13-29%) during NAVA (p = 0.001)), as well as the fragmentation index, with 40 ± 20 arousals and awakenings per hour in PSV and 16 ± 9 during NAVA (p = 0.001). There were large differences in ineffective efforts (24 ± 23 per hour of sleep in PSV, and 0 during NAVA) and episodes of central apnea (10.5 ± 11 in PSV vs. 0 during NAVA). Minute ventilation was similar in both modes.ConclusionsNAVA improves the quality of sleep over PSV in terms of REM sleep, fragmentation index, and ineffective efforts in a nonsedated adult population.

Preliminary Evaluation of a New Index to Predict the Outcome of a Spontaneous Breathing Trial

BACKGROUND: The available predictors of spontaneous-breathing-trial (SBT) success/failure lack accuracy. We devised a new index, the CORE index (compliance, oxygenation, respiration, and effort). OBJECTIVE: To compare the CORE index to the CROP index (compliance, rate, oxygenation, and pressure), airway-occlusion pressure 0.1 s after the start of inspiratory flow (P0.1), and rapid shallow breathing index (RSBI) for predicting SBT success/failure in a critical care environment. METHODS: With 47 mechanically ventilated patients recovering from respiratory failure, of various causes, we prospectively examined the SBT success/failure prediction accuracy and calculated receiver operating characteristic curves, sensitivity, specificity, and likelihood ratios of CORE, CROP, P0.1, and RSBI. RESULTS: The specificities were CORE 0.95, P0.1 0.70, CROP 0.70, and RSBI 0.65. The sensitivities were CORE 1.00, CROP 1.00, P0.1 0.93, and RSBI 0.89. The areas under the receiver operating characteristic curve were CORE 1.00 (95% CI 0.92–1.00), CROP 0.91 (95% CI 0.79–0.97), P0.1 0.81 (95% CI 0.67–0.91), and RSBI 0.77 (95% CI 0.62–0.88). The positive likelihood ratios were CORE 20.0, CROP 3.3, P0.1 3.1, and RSBI 2.5. The negative likelihood ratios were CORE 0.0, CROP 0.0, P0.1 0.1, and RSBI 0.2. CONCLUSIONS: The CORE index was the most accurate predictor of SBT success/failure.

Capnographic waveforms obtained in experimental Thiel cadaver model after intubation

We read with interest the study of Silvestri et al. [1] describing apnographic waveforms obtained in two frozen cadavers, after ntubation. These observations highlight the possibilities of realstic simulation, but might present limitations in reproducibility 2]. Here, we report our experience of a more physiologic scenario ased on an experimental Thiel cadaver model where we directly dministrated CO2 in the lung. These observations interestingly omplete those reported by Silvestri et al. particularly given the ossibility of extending this model to CO2 simulation during Cariopulmonary Resuscitation (CPR). Methods. Thiel cadavers were harvested from a specific donation program t the anatomy laboratory of Université du Québec à Troisivières (UQTR). The experiment was conducted in accordance ith Canadian regulations following ethic committee approval CER-14-201-08-03.17). Two cadavers were intubated via direct aryngoscopy. After placement verification by chest auscultation nd chest X-ray, the endotracheal tube (ET) was connected to a onnal T60 ventilator (ALMS, Antony France). The absence of CO2 as confirmed via two different CO2 sensors (mean stream and ide stream), immediately after intubation. Then, CO2 was insufated at low flow (2/min of 10% CO2) through a catheter positioned nto the proximal bronchial tree. The typical End Tidal CO2 (ETCO2) aveform was recorded at the airways opening during ventilation, llustrating the CO2 and alveolar gas mixture in the lung (Fig. 1A). he ET was removed and the cadavers were stored at room temerature (20 ◦C) overnight.

A new physiological model for studying the effect of chest compression and ventilation during cardiopulmonary resuscitation: The Thiel cadaver

BACKGROUND Studying ventilation and intrathoracic pressure (ITP) induced by chest compressions (CC) during Cardio Pulmonary Resuscitation is challenging and important aspects such as airway closure have been mostly ignored. We hypothesized that Thiel Embalmed Cadavers could constitute an appropriate model. METHODS We assessed respiratory mechanics and ITP during CC in 11 cadavers, and we compared it to measurements obtained in 9 out-of-hospital cardiac arrest patients and to predicted values from a bench model. An oesophageal catheter was inserted to assess chest wall compliance, and ITP variation (ΔITP). Airway pressure variation (ΔPaw) at airway opening and ΔITP generated by CC were measured at decremental positive end expiratory pressure (PEEP) to test its impact on flow and ΔPaw. The patients data were derived from flow and airway pressure captured via the ventilator during resuscitation. RESULTS Resistance and Compliance of the respiratory system were comparable to those of the out-of-hospital cardiac arrest patients (CRSTEC 42 ± 12 vs CRSPAT 37.3 ± 10.9 mL/cmH2O and ResTEC 17.5 ± 7.5 vs ResPAT 20.2 ± 5.3 cmH2O/L/sec), and remained stable over time. During CC, ΔITP varied from 32 ± 12 cmH2O to 69 ± 14 cmH2O with manual and automatic CC respectively. Transmission of ΔITP at the airway opening was significantly affected by PEEP, suggesting dynamic small airway closure at low lung volumes. This phenomenon was similarly observed in patients. CONCLUSION Respiratory mechanics and dynamic pressures during CC of cadavers behave as predicted by a theoretical model and similarly to patients. The Thiel model is a suitable to assess ITP variations induced by ventilation during CC.

How Ventilation Is Delivered During Cardiopulmonary Resuscitation: An International Survey

BACKGROUND: Recommendations regarding ventilation during cardiopulmonary resuscitation (CPR) are based on a low level of scientific evidence. We hypothesized that practices about ventilation during CPR might be heterogeneous and may differ worldwide. To address this question, we surveyed physicians from several countries on their practices during CPR. METHODS: We used a Web-based opinion survey. Links to the survey were sent by e-mail newsletters and displayed on the Web sites of medical societies involved in CPR practice from December 2013 to March 2014. RESULTS: 1,328 surveys were opened, and 548 were completed (41%). Responses came from 54 countries, but 64% came from 6 countries. Responders were mostly physicians (89%). From this group, 97% declared following specific CPR guidelines. Regarding practices, 28% declared always or frequently adopting only continuous chest compressions without additional ventilation. With regard to mechanical chest compression devices, 38% responded that such devices were available to them; when used, 28% declared always or frequently experiencing problems with ventilation such as frequent alarms. During bag-mask ventilation in intubated patients, 18% declared stopping chest compression during insufflation, and 39% applied > 10 breaths/min, which conflicts with international CPR guidelines. When a ventilator was used, the volume controlled mode was the most common strategy cited, but there was heterogeneity regarding ventilator settings for PEEP, trigger, FIO2, and breathing frequency. SpO2 and end-tidal CO2 were the 2 most monitored variables cited. CONCLUSIONS: Physicians indicated heterogeneous practices that often differ significantly from international CPR guidelines. This may reflect the low level of evidence and a lack of detailed recommendations concerning ventilation during CPR.

Comparison of inhaled milrinone, nitric oxide and prostacyclin in acute respiratory distress syndrome

AIM To evaluate the safety and efficacy of inhaled milrinone in acute respiratory distress syndrome (ARDS). METHODS Open-label prospective cross-over pilot study where fifteen adult patients with hypoxemic failure meeting standard ARDS criteria and monitored with a pulmonary artery catheter were recruited in an academic 24-bed medico-surgical intensive care unit. Random sequential administration of iNO (20 ppm) or nebulized epoprostenol (10 μg/mL) was done in all patients. Thereafter, inhaled milrinone (1 mg/mL) alone followed by inhaled milrinone in association with inhaled nitric oxide (iNO) was administered. A jet nebulization device synchronized with the mechanical ventilation was use to administrate the epoprostenol and the milrinone. Hemodynamic measurements and partial pressure of arterial oxygen (PaO2) were recorded before and after each inhaled therapy administration. RESULTS The majority of ARDS were of pulmonary cause (n = 13) and pneumonia (n = 7) was the leading underlying initial disease. Other pulmonary causes of ARDS were: Post cardiopulmonary bypass (n = 2), smoke inhalation injury (n = 1), thoracic trauma and pulmonary contusions (n = 2) and aspiration (n = 1). Two patients had an extra pulmonary cause of ARDS: A polytrauma patient and an intra-abdominal abscess Inhaled nitric oxide, epoprostenol, inhaled milrinone and the combination of inhaled milrinone and iNO had no impact on systemic hemodynamics. No significant adverse events related to study medications were observed. The median increase of PaO2 from baseline was 8.8 mmHg [interquartile range (IQR) = 16.3], 6.0 mmHg (IQR = 18.4), 6 mmHg (IQR = 15.8) and 9.2 mmHg (IQR = 20.2) respectively with iNO, epoprostenol, inhaled milrinone, and iNO added to milrinone. Only iNO and the combination of inhaled milrinone and iNO had a statistically significant effect on PaO2. CONCLUSION When comparing the effects of inhaled NO, milrinone and epoprostenol, only NO significantly improved oxygenation. Inhaled milrinone appeared safe but failed to improve oxygenation in ARDS.