Michel de Marchie

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.

Inspiratory Muscle Unloading by Neurally Adjusted Ventilatory Assist During Maximal Inspiratory Efforts in Healthy Subjects

BACKGROUND Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation in which the ventilator is controlled by the electrical activity of the diaphragm (EAdi). During maximal inspirations, the pressure delivered can theoretically reach extreme levels that may cause harm to the lungs. The aims of this study were to evaluate whether NAVA could efficiently unload the respiratory muscles during maximal inspiratory efforts, and if a high level of NAVA would suppress EAdi without increasing lung-distending pressures. METHOD In awake healthy subjects (n = 9), NAVA was applied at increasing levels in a stepwise fashion during quiet breathing and maximal inspirations. EAdi and airway pressure (Paw), esophageal pressure (Pes), and gastric pressure, flow, and volume were measured. RESULTS During maximal inspirations with a high NAVA level, peak Paw was 37.1 +/- 11.0 cm H(2)O (mean +/- SD). This reduced Pes deflections from - 14.2 +/- 2.7 to 2.3 +/- 2.3 cm H(2)O (p < 0.001) and EAdi to 43 +/- 7% (p < 0.001), compared to maximal inspirations with no assist. At high NAVA levels, inspiratory capacity showed a modest increase of 11 +/- 11% (p = 0.024). CONCLUSION In healthy subjects, NAVA can safely and efficiently unload the respiratory muscles during maximal inspiratory maneuvers, without failing to cycle-off ventilatory assist and without causing excessive lung distention. Despite maximal unloading of the diaphragm at high levels of NAVA, EAdi is still present and able to control the ventilator.

Factors Discriminating Spontaneous Pursed-Lips Breathing Use in Patients with COPD

ABSTRACT Pursed-lips breathing (PLB) is often spontaneously performed by chronic obstructive pulmonary disease (COPD) patients. The aim of this study was to evaluate spontaneous PLB prevalence and to identify factors discriminating its use. Fifty-seven patients with COPD (FEV1 = 44.3 ± 17.4%pred) underwent pulmonary function testing and two incremental bicycle exercise tests. Peak workload (Wpeak), oxygen uptake (VO2peak), breathing pattern, and dyspnea (Borg scale) were measured in the first exercise test and spontaneous PLB performance in the second. Six patients spontaneously performed pursed-lips breathing during rest (PLBrest), exercise and recovery, 18 during exercise and recovery (PLBex), 7 during recovery only (PLBrec), 20 not at all (PLBno), and 6 performed other expiratory resistive maneuvers. PLBrest and PLBex patients exhibited a lower Wpeak, O2 uptake, and minute ventilation (VE), greater expiratory flow limitation and higher slopes relating dyspnea to VE or W (%predicted). PLBrest patients were more hypercapnic, had a lower exercise tolerance and diffusion capacity, and greater flow limitation and hyperinflation. PLBrec and PLBno patients were indistinguishable with regard to pulmonary function, dyspnea, and exercise performance. The most significant independent predictors of spontaneous PLB use during exercise were FEV1/FVC and the slope relating dyspnea to VE. Spontaneous PLB is most often performed by COPD subjects when ventilation is stimulated by exercise, and during recovery from exercise. Severity of airflow obstruction and the dyspnea experienced during exercise play an important role in determining whether or not PLB is spontaneously performed by COPD patients.

Effect of increased diaphragm activation on diaphragm power spectrum center frequency

Increased transdiaphragmatic pressure, reduced muscle blood flow, and increased duty cycle have all been associated with a reduction in the center frequency (CFdi) of the diaphragms electrical activity (EAdi). However, the specific influence of diaphragm activation on CFdi is unknown. We evaluated whether increased diaphragm activation would result in a greater decline in the CFdi when pressure-time product (PTPdi) was kept constant. Five healthy subjects performed periods of intermittent quasi-static diaphragmatic contractions with a fixed duty cycle. In separate runs, subjects targeted transdiaphragmatic pressures (Pdi) by performing end-inspiratory holds with the glottis open and expulsive maneuvers at end-expiratory lung volume (EELV). Diaphragm activation and pressures were measured with an electrode array and balloons mounted on an esophago-gastric catheter, respectively. The EAdi, which was 25+/-8%(S.D.) of maximum at EELV, increased to 61+/-8% (P<0.001) when an identical Pdi (averaging 31+/-13 cmH2O) was generated at a higher lung volume (77% of inspiratory capacity). The latter was associated with a 17% greater decline in CFdi (P=0.012). In order to reproduce at EELV, the decrease in CFdi observed at the increased lung volume, a two-fold increase in PTPdi was required. We conclude that CFdi responds specifically to increased diaphragm activation when pressure-time product remains constant.

Interprofessional Survey of Perceived Barriers and Facilitators to Early Mobilization of Critically Ill Patients in Montreal, Canada

Objective: Early mobilization is safe, feasible, and associated with better outcomes in patients with critical illness. However, barriers to mobilization in clinical practice still exist. The objective of this study was to assess the knowledge and practice patterns of intensive care unit (ICU) clinicians, as well as the barriers and facilitators to early mobilization. Design: Cross-sectional survey. Setting: Intensive care units of 3 university-affiliated hospitals in Montreal, Canada. Participants: One hundred and thirty-eight ICU clinicians, including nurses, physicians, respiratory therapists, and physiotherapists. Interventions: None. Measurements: Perceived barriers, facilitators, knowledge, and practice patterns of early mobilization were assessed using a previously validated mobility survey tool. Main Results: The overall response rate was 50.0% (138 of 274). Early mobilization was not perceived as a top priority in 49% of respondents. Results showed that clinicians were not fully aware of the benefits of early mobilization as per the current literature. About 58% of clinicians did not feel well trained and informed to mobilize mechanically ventilated patients. Perceptions on patient-level barriers varied with clinicians’ professional training, but there was a high degree of interprofessional and intraprofessional disagreement on the permissible maximal level activity in different scenarios of critically ill patients. Conclusions: Our survey shows limited awareness, among our respondents, of the clinical benefits of early mobilization and high level of disagreement on the permissible maximal level of activity in the critically ill patients. Future studies should evaluate the role of knowledge translation in modifying these barriers and improving early mobilization.

Bi-level Positive Airway Pressure (BiPAP) with Standard Exhalation Valve Does Not Improve Maximum Exercise Capacity in Patients with COPD

Abstract Background: Although BiPAP has been used as an adjunct to exercise, little is know about its effect on exercise in COPD. We aimed to evaluate the acute effect of BiPAP delivered with a standard valve (Vision, Respironics), compared to no assist, on exercise capacity in individuals with COPD. Methods: Peak exercise workload (WLpeak), dyspnea (Borg), end-expiratory lung volume (EELV), tidal volume (VT), minute ventilation (VE), O2 uptake (VO2), and CO2 production (VCO2) were assessed in 10 COPD patients (FEV1 53 ± 22% pred) during three symptom-limited bicycle exercise tests while breathing i) without a ventilator (noPS), ii) with a pressure support (PS) of 0 cm H2O (PS0; IPAP & EPAP 4 cm H2O) and iii) PS of 10 cm H2O (PS10; IPAP 14 & EPAP 4 cm H2O) on separate days using a randomized crossover design. Results: WLpeak was significantly lower with PS10 (33 ± 16) and PS0 (30.5 ± 13) than noPS (43 ± 19) (p < 0.001). Dyspnea at peak exercise was similar with noPS, PS0 and PS10; at isoload it was lower with noPS compared to PS10 and PS0 (p < 0.01). VT and VE were highest with PS10 and lowest with noPS both at peak exercise and isoload (p < 0.001). EELV was similar at peak exercise with all three conditions. VO2 and VCO2 were greater with PS10 and PS0 than noPS (p < 0.001), both at peak exercise and isoload. Conclusion: Use of BiPAP with a standard exhalation valve during exercise increases VT and VE at the expense of augmenting VCO2 and dyspnea, which in turns reduces WLpeak in COPD patients.

Spinal cord injury modulates the lung inflammatory response in mechanically ventilated rats: a comparative animal study

Mechanical ventilation (MV) is widely used in spinal injury patients to compensate for respiratory muscle failure. MV is known to induce lung inflammation, while spinal cord injury (SCI) is known to contribute to local inflammatory response. Interaction between MV and SCI was evaluated in order to assess the impact it may have on the pulmonary inflammatory profile. Sprague Dawley rats were anesthetized for 24 h and randomized to receive either MV or not. The MV group included C4–C5 SCI, T10 SCI and uninjured animals. The nonventilated (NV) group included T10 SCI and uninjured animals. Inflammatory cytokine profile, inflammation related to the SCI level, and oxidative stress mediators were measured in the bronchoalveolar lavage (BAL). The cytokine profile in BAL of MV animals showed increased levels of TNF‐α, IL‐1β, IL‐6 and a decrease in IL‐10 (P = 0.007) compared to the NV group. SCI did not modify IL‐6 and IL‐10 levels either in the MV or the NV groups, but cervical injury induced a decrease in IL‐1β levels in MV animals. Cervical injury also reduced MV‐induced pulmonary oxidative stress responses by decreasing isoprostane levels while increasing heme oxygenase‐1 level. The thoracic SCI in NV animals increased M‐CSF expression and promoted antioxidant pulmonary responses with low isoprostane and high heme oxygenase‐1 levels. SCI shows a positive impact on MV‐induced pulmonary inflammation, modulating specific lung immune and oxidative stress responses. Inflammation induced by MV and SCI interact closely and may have strong clinical implications since effective treatment of ventilated SCI patients may amplify pulmonary biotrauma.

Mechanical ventilation modulates pro-inflammatory cytokine expression in spinal cord tissue after injury in rats

RATIONALE Spinal cord injury (SCI) may induce significant respiratory muscle weakness and paralysis, which in turn may cause a patient to require ventilator support. Central nervous system alterations can also exacerbate local inflammatory responses with immune cell infiltration leading to additional risk of inflammation at the injury site. Although mechanical ventilation is the traditional treatment for respiratory insufficiency, evidence has shown that it may directly affect distant organs through systemic inflammation. OBJECTIVES This study aimed to better understand the impact of invasive mechanical ventilation on local spinal cord inflammatory responses following cervical or thoracic SCI. METHODS Five groups of female Sprague-Dawley rats were anesthetised for 24 h. Three groups received mechanical ventilation: seven rats without SCI, seven rats with cervical injury (C4-C5), and seven rats with thoracic injury (T10); whereas, two groups were non-ventilated: six rats without SCI; and six rats with thoracic injury (T10). Changes in inflammatory responses were determined in the spinal cord tissues collected at the local site of injury. Cytokines were measured using ELISA. MAIN RESULTS SCI induced local pro-inflammatory cytokine IL-6 expression for all groups. Mechanical ventilation also had effects on pro-inflammatory cytokines and independently increased TNF-α and decreased IL-1β levels in the spinal cords of anesthetized rats. CONCLUSION These data provide the first evidence that mechanical ventilation contributes to local inflammation after SCI and in the absence of direct tissue injury.