Effectiveness of controlled and spontaneous modes in nasal two-level positive pressure ventilation in awake and asleep normal subjects

[Nocturnal monitoring of home non-invasive ventilation: Contribution of simple tools such as pulse-oximetry, capnography, built-in ventilator software and autonomic markers of sleep fragmentation]

Complex respiratory events, which may have a detrimental effect on both quality of sleep and control of nocturnal hypoventilation, occur during sleep in patients treated by non-invasive ventilation (NIV). Among these events are patient-ventilator asynchrony, increases in upper airway resistance with or without increased respiratory drive, and leaks. Detection of these events is important in order to select the most appropriate ventilator settings and interface. Simple tools can provide important information when monitoring NIV. Pulse-oximetry is important to ensure that an adequate SpO2 is provided, and to detect either prolonged or short and recurrent desaturations. However, the specificity of pulse-oximetry tracings under NIV is low. Transcutaneous capnography discriminates between hypoxemia related to V/Q mismatch and hypoventilation, documents correction of nocturnal hypoventilation, and may detect ventilator-induced hyperventilation, a possible cause for central apnea/hypopnea and glottic closure. Data provided by ventilator software helps the clinician by estimating ventilation, tidal volume, leaks, rate of inspiratory or expiratory triggering by the patient, although further validation of these signals by independent studies is indicated. Finally, autonomic markers of sympathetic tone using signals such as pulse wave amplitude of the pulse-oximetry signal can provide reliable information of sleep fragmentation.

Respiratory muscle unloading during auto-adaptive non-invasive ventilation

RATIONALE

Non-invasive ventilation (NIV) has been shown to improve clinical outcomes in acute and chronic hypercapnic respiratory failure. A new timed, automated, auto-adaptive non-invasive ventilatory mode (TA-mode) has been recently introduced.

OBJECTIVE

To investigate the degree of respiratory muscle unloading with this new mode in comparison to assisted (S-mode) NIV in healthy individuals.

METHODS

Work of breathing, pressure time product and transdiaphragmatic pressure time product were measured during unassisted breathing, assisted and TA-mode-NIV in eight healthy, awake volunteers at inspiratory pressures of 20 and expiratory pressures of 4hPa.

RESULTS

Assisted and TA-mode-NIV reduced the work of breathing by 50 and 89.1%, pressure time product by 61.5 and 72.6% and transdiaphragmatic pressure time product by 77 and 88.7%, respectively when compared to unassisted breathing. The degree of respiratory muscle unloading was higher during TA-mode-NIV when compared to assisted non-invasive ventilation (work of breathing p<0.001, pressure time product p=0.04 and transdiaphragmatic pressure time product p=0,01).

CONCLUSION

TA-mode-NIV achieved significant higher levels of respiratory muscle unloading in healthy individuals when compared to assisted non-invasive ventilation.

Mechanical ventilation in Duchenne patients with chronic respiratory insufficiency: clinical implications of 20 years published experience

Chronic respiratory insufficiency is inevitable in the course of disease progression in patients with Duchenne muscular dystrophy (DMD). Without mechanical ventilation (MV), morbidity and mortality are highly likely towards the end of the second decade of life. The present review reports evidence and clinical implications regarding DMD patients treated with MV. There is no doubt that nocturnal hypercapnia precedes daytime hypercapnia. Historical comparisons have provided evidence that non-invasive intermittent positive pressure ventilation (NIPPV) at night is effective and improves quality of life and survival by 5-10 years. By contrast, the optimal criteria and timing for initiation of NIPPV are inconsistent. A recent randomized study however demonstrated the benefits of commencing NIPPV as soon as nocturnal hypoventilation is detected (Ward S, et al., Randomised controlled trial of non-invasive ventilation (NIV) for nocturnal hypoventilation in neuromuscular and chest wall disease patients with daytime normocapnia. Thorax 2005; 60: 1019-24). The respective role of the three hypotheses of the indirect action of nocturnal NIPPV on daytime blood gases may be complimentary; the main improvement may be due to improved ventilatory response to CO2. The ultimate time to offer full time ventilation with the most advantageous interface is lacking in evidence. Full time NIV is possible with a combination of a nasal mask during the night and a mouthpiece during the day, however tracheostomy may be provided when mechanical techniques of cough-assistance are useless to treat chronic cough insufficiency.

Effect of sleep on patient/ventilator asynchrony in patients undergoing chronic non-invasive mechanical ventilation

BACKGROUND

Patients who require home non-invasive ventilation (NIV) during sleep normally have the ventilation settings adjusted empirically during daytime wakefulness. However, patient-ventilator asynchrony may occur during sleep. To detect the incidence of ineffective efforts (IE) during the sleep compared to wakefulness, we studied 48 patients already enrolled in a long-term home NIV programme.

METHODS

We evaluated arterial blood gases, breathing pattern during spontaneous breathing (SB) and ventilation during wakefulness. In addition, we assessed the breathing pattern and oxygen gas exchange during night-time NIV.

RESULTS

Daytime NIV significantly improved blood gases compared to SB (PaO2 NIV 10.2 +/- 1.95 kPa vs PaO2 SB 8 +/- 1.37, p < 0.001; PaCO2 NIV 5.75 +/- 1.08 kPa, vs PaCO2 SB 6.5 +/- 1.25, p < 0.001). The IE index was higher during sleep compared to wakefulness (48 +/- 39.5 events/h versus 0 +/- 0). The IE index was correlated with the time spent with SaO2 < 90% (r = 0.39, p < 0.01), but not with ventilator parameters, underlying disease, ventilation mode or type of mask. Eight patients had an IE index >100 events/h; these patients had a faster respiratory rate, required a higher level of inspiratory assistance and had poor gas exchange during sleep.

CONCLUSIONS

We conclude that IE to breath are common during nocturnal NIV and that they may be associated with desaturations even in patients who are considered compliant and effectively treated.

Laryngeal response to nasal ventilation in nonsedated newborn lambs

Although endoscopic studies in adult humans have suggested that laryngeal closure can limit alveolar ventilation during nasal intermittent positive pressure ventilation (nIPPV), there are no available data regarding glottal muscle activity during nIPPV. In addition, laryngeal behavior during nIPPV has not been investigated in neonates. The aim of the present study was to assess laryngeal muscle response to nIPPV in nonsedated newborn lambs. Nine newborn lambs were instrumented for recording states of alertness, electrical activity [electromyograph (EMG)] of glottal constrictor (thyroarytenoid, TA) and dilator (cricothyroid, CT) muscles, EMG of the diaphragm (Dia), and mask and tracheal pressures. nIPPV in pressure support (PS) and volume control (VC) modes was delivered to the lambs via a nasal mask. Results show that increasing nIPPV during wakefulness and quiet sleep led to a progressive disappearance of Dia and CT EMG and to the appearance and subsequent increase in TA EMG during inspiration, together with an increase in trans-upper airway pressure (TUAP). On rare occasions, transmission of nIPPV through the glottis was prevented by complete, active glottal closure, a phenomenon more frequent during active sleep epochs, when irregular bursts of TA EMG were observed. In conclusion, results of the present study suggest that active glottal closure develops with nIPPV in nonsedated lambs, especially in the VC mode. Our observations further suggest that such closure can limit lung ventilation when raising nIPPV in neonates.

Lung Function Accurately Predicts Hypercapnia in Patients With Duchenne Muscular Dystrophy

BACKGROUND

In patients with Duchenne muscular dystrophy (DMD), implementation of mechanical ventilation depends on sleep investigation and measurement of CO2 tension. The objective of this cross-sectional study was to determine which noninvasive lung function parameter best predicts nocturnal hypercapnia and diurnal hypercapnia in these patients.

METHODS

According to transcutaneous CO2 (TcCO2) measurement, 114 DMD patients were classified into three groups: nocturnal hypercapnia (n = 38) [group N], diurnal hypercapnia (n = 39), despite nocturnal ventilation (group D), and 24-h normocapnia and spontaneous breathing (n = 37) [group S] as control. TcCO2 tension and lung function variables included vital capacity (VC) and maximal inspiratory pressure (MIP), and breathing pattern variables included tidal volume (Vt) and respiratory rate (RR), measured at the time of group inclusion. The rapid and shallow breathing index (RSBI [RR/Vt]) and Vt/VC ratio were calculated. Areas under the curve from the receiver operating characteristic (ROC) were calculated for those parameters.

RESULTS

Compared to group S, lung function was significantly worse in group N and group D. VC, RR, and RSBI distinguished group S from group N by ROC comparison. Cut-off values of VC < or = 680 mL (ROC, 0.968), MIP < or = 22 cm H2O (ROC, 0.928), and Vt/VC > 0.33 (ROC, 0.923) accurately discriminated group D from group N, but RSBI, RR, and Vt did not.

CONCLUSIONS

Lung function is useful to predict nocturnal hypercapnia in patients with DMD. Moreover, VC < 680 mL is very sensitive to predict daytime hypercapnia.

Titration of non-invasive positive pressure ventilation in chronic respiratory failure

Non-invasive ventilation (NIV) is widely used for acute and chronic respiratory failure. If arterial blood gas tensions do not improve, the level of support can be increased. However, there may be a limit above which increasing ventilatory support leads only to greater interface leak with no improvement in ventilation. The aim of this study was to establish whether there is such a limit. During a daytime study in 24 ventilated stable patients (10 with chronic obstructive pulmonary disease (COPD), 14 with chest wall deformity, CWD), inspiratory pressures up to 20 cm H(2)O and set tidal volumes up to 10 ml kg(-1) were associated with mask leak of <5 l min(-1). Although leak increased with higher levels of support, there was still an increase in minute ventilation. The mean (2 sd) tolerated pressure was 24 cm H(2)O (8-40) in both groups, and set tidal volume 12.7 ml kg(-1) (5.0-20.4) in CWD and 9.6 ml kg(-1) (3.9-14.8) in COPD. Measures of respiratory effort were significantly reduced at all levels with both forms of ventilatory support. There is debate about whether the therapeutic aim of NIV should be to reduce respiratory muscle effort, or to reverse nocturnal hypoventilation. We conclude that if the primary aim is to improve arterial blood gas tensions and this is not achieved, higher levels of ventilation can be obtained using greater pressure or volume, despite additional interface leak. If the aim is to abolish muscle effort completely, there is little to be gained by increasing the level of inspiratory pressure above 20 (CWD) or 25 (COPD) cm H(2)O.

Comparative study of two different modes of noninvasive home mechanical ventilation in chronic respiratory failure

STUDY OBJECTIVE

Two modes of noninvasive home mechanical ventilation (NIHMV) with volumetric ventilators were compared in patients with chronic respiratory failure.

DESIGN

Retrospective, parallel-group, comparative study.

SETTING

Third-level teaching Hospital in Barcelona (Spain).

PATIENTS AND METHODS

We studied 110 patients with chronic hypercapnic respiratory failure secondary to neuromuscular disease, kyphoscoliosis or post-tuberculosis sequelae, starting NIHMV with volumetric ventilators. The assist/control (A/C) ventilation mode was used in 45 patients and the control (C) mode in 65 patients. Clinical characteristics, pulmonary function results and arterial blood gas findings were assessed in each patient before establishing ventilation and at 6 and 12 months after. The patient's satisfaction with ventilation, the time required for adaptation, and compliance with the prescription were also assessed.

MEASUREMENTS AND RESULTS

Significant improvements in PaO(2) and PaCO(2) (P<0.001) were found at 6 and 12 months with both modes of mechanical ventilation. There were no significant differences between the two modes for pulmonary function or blood gas parameters with the exception of maximum inspiratory pressure (MIP) in patients receiving the C mode, which was significantly different as compared to the baseline value after 12 months of use (mean+/-sd: 36.6+/-14.8 and 44.7+/-24.2 cmH(2)O, respectively; P=0.010). No significant differences were found in adaptation, compliance with ventilation or patient satisfaction between the two modes studied.

CONCLUSIONS

According to several factors analysed, results with the A/C or C mode used with volumetric ventilators appear to be comparable in patients with chronic respiratory disease receiving NIHMV. Choice of mode will depend on the acquired experience of the prescribing physicians in each centre.

Effects of Different Ventilator Settings on Sleep and Inspiratory Effort in Patients with Neuromuscular Disease

Patients with neuromuscular disease (NMD) who require long-term ventilation normally have the ventilation set using empirical daytime parameters. We evaluated arterial blood gases (ABG), breathing pattern, respiratory muscle function, and sleep architecture during ventilation with two noninvasive Pressure Support Ventilation (nPSV) settings in nine patients with NMD. The two settings were randomly applied: the usual (US), with the nPSV setting titrated on simple clinical parameters, and the physiological (PHYS), tailored to the patient's respiratory effort. During wakefulness, nPSV significantly improved ABG and minute ventilation and reduced the diaphragmatic pressure-time product (PTPdi/breath), independently of the type of setting (PTPdi/breath spontaneous breathing 5.7 +/- 2.4, US 3.2 +/- 2, PHYS 3.6 +/- 1.6 cm H2O . seconds(-1), p < 0.001). However, during sleep, PHY nPSV resulted in a significant improvement of gas exchange, sleep efficiency (71.7% +/- 14 US vs. 80.6% +/- 8.3 PHYS, p < 0.01) and % of REM sleep (9.1% +/- 7 US vs. 17.3% +/- 5.4 PHYS, p < 0.01). This improvement was significantly correlated with the reduction in ineffective efforts. In NMD, nPSV is effective in improving daytime ABG and in unloading inspiratory muscles independently of whether it is set on the basis of the patient's comfort or the patient's respiratory mechanics. However, PHYS was associated with better sleep architecture and nighttime gas exchange.

Comparison of volume- and pressure-limited NPPV at night: a prospective randomized cross-over trial

Both pressure- and volume-limited non-invasive positive pressure ventilation (NPPV) have been used in patients with chronic respiratory failure. The aim of the present study was to compare the efficacy of ventilation during nocturnal volume- and pressure-limited NPPV. Fifteen patients (nine COPD, six non-COPD) were randomly assigned to receive either volume-limited or pressure-limited NPPV and were switched to the complementary mode after 6 weeks. Ten patients (five COPD, five non-COPD) completed the study. PaCO2 during sleep comparably decreased from 54.6+/-8.0 to 46.2+/-6.1 mmHg during volume-limited NPPV (P<0.05), and to 46.5+/-6.4 mmHg during pressure-limited NPPV (P<0.05). Improvements in sleep quality assessed by polysomnography were comparable, but less gastrointestinal side effects were reported for pressure-limited NPPV (P<0.05). Using a pneumotachograph the variance of inspiratory volumes was lower, but the variance of peak inspiratory pressures was higher during volume-limited NPPV compared to pressure-limited NPPV. Substantial leak volumes which accounted for 57% (volume-limited NPPV) and for 58% (pressure-limited NPPV) of the applied inspiratory volume were independent from the mode of ventilation. In conclusion, nocturnal volume- and pressure-limited NPPV have similar effects on gas exchange and sleep quality in patients with hypercapnic chronic respiratory failure, but volume-limited NPPV is associated with more gastrointestinal side effects.

Assistance ventilatoire à domicile : justifications et contraintes physiopathologiques

INTRODUCTION

Domiciliary assisted ventilation (DAV) may be undertaken invasively or non-invasively. Non-invasive DAV is used for patients suffering from alveolar hypoventilation due to restrictive pathology. Invasive DAV is reserved for "indications of necessity" that is when non-invasive ventilation is contraindicated due to the absence of adequate cough and for alveolar hypoventilation leading to hypercapnoea during spontaneous ventilation.

STATE OF THE ART

The main pathophysiological limitation to non-invasive ventilation is the interference of the glottis. In this mode the glottis imposes a variable resistance to the ventilation delivered. Its behaviour is more predictable during Volume controlled than during pressure controlled ventilation. The control parameters of a Volume controlled ventilator are very different from those used in invasive ventilation during which the respiratory system may be regarded as a single compartment (provided a cuffed tube bypasses the upper airway). In non-invasive DAV: mode VCM, tidal volume 13 mls kg(-1), rate 20 cycles min(-1), insp/exp ratio 1/1.2. In invasive DAV: mode VCM, tidal volume 8-10 mls kg(-1), rate 12 cycles min(-1), insp/exp ratio depending on the pathology 1/2.

PERSPECTIVES

As non-invasive DAV is essentially delivered during sleep the parameters for each patient can be optimised during polysomnography because waking, leading to a partial glottic occlusion, interferes with the ventilation delivered.

CONCLUSIONS

Recent understanding of the way the glottis interferes with mechanical ventilation when delivered non-invasively should lead to a revision of earlier practices based on invasive ventilation.

Non-invasive ventilation and sleep

In this paper, we review the effects of nocturnal mechanical ventilation on sleep. Indeed, although non-invasive assisted ventilation during sleep has been applied extensively, the exact effects of this treatment on sleep quality have not been thoroughly studied. In patients with severe chronic obstructive pulmonary disease and severe restrictive ventilatory defects, the resulting respiratory failure is aggravated by the specific effects of sleep on respiration. Non-invasive mechanical ventilation can lead to improvements in both ventilation and sleep quality. However, this is not always the case. Moreover, sleep-related leaks may jeopardize the efficiency of the ventilatory assistance which in turn may result in a deterioration in sleep quality. Non-invasive mechanical ventilation, if applied during sleep, should require a monitoring procedure during sleep with the aim of obtaining the best possible effects both on ventilation and on sleep quality.