Published ahead of print on June 16, 2005, doi:10.1164/rccm.200406-694OC
© 2005 American Thoracic Society doi: 10.1164/rccm.200406-694OC
Effects of Different Ventilator Settings on Sleep and Inspiratory Effort in Patients with Neuromuscular DiseasePulmonary Division, Istituto Scientifico di Montescano and Pavia, Fondazione S. Maugeri, IRCCS; and Department of Clinical Neurology and Child Psychiatry, IRCCS C. Mondino, Pavia, Italy Correspondence and requests for reprints should be addressed to Francesco Fanfulla, M.D., Sleep Laboratory, Pulmonary Division, Fondazione Salvatore Maugeri IRCCS, Istituto Scientifico di Montescano, Via per Montescano, 27040 Montescano (PV), Italy. E-mail: ffanfulla{at}fsm.it
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.
Key Words: noninvasive mechanical ventilation sleep polysomnography respiratory failure home care Noninvasive mechanical ventilation (NIMV) is being increasingly used as a treatment for chronic hypercapnic respiratory failure. Its use in patients affected by restrictive thoracic disorders, and in particular in patients with neuromuscular disease, suggested that it alleviates symptoms of chronic hypoventilation in the short term and, according to two small studies, may prolong survival (15). Indeed, a recent Cochrane review stated that "long-term mechanical ventilation should be offered as a therapeutic option to patients with chronic hypercapnic respiratory failure due to neuromuscular diseases" (6). Daytime hypercapnia worsens during sleep, so that the major goal to achieve with the ventilatory treatment, in patients with neuromuscular disease, is the correction of nocturnal hypoventilation (69). When the decision to initiate long-term NIMV is made, the ventilatory parameters to use during the nighttime are mainly determined empirically, based on patient's tolerance when awake and diurnal arterial blood gas variations. No study has so far investigated the possible influence of different ventilator settings, decided a priori according to daytime parameters, on sleep architecture and gas exchange. Indeed, in awake patients with COPD, the empirical setting was shown to parallel, at least to a certain extent, the respiratory muscle unloading and gas exchange achieved when the ventilator was physiologically titrated (10), but was also associated with a significantly higher prevalence of ineffective efforts (i.e., patients' inspiratory efforts unable to trigger the ventilator). In patients with severe respiratory muscle weakness, patientventilator dyssynchrony may be a cause of suboptimal ventilation, especially during the nighttime, when profound modifications in the recruitment of the respiratory muscle may occur during the various stages of sleep. The aim of this study was to compare the effects of two ventilation settings on sleep architecture and patientventilator interaction in patients already established on long-term mechanical ventilation for neuromuscular disorders. The ventilation settings were the "usual" (US) clinically determined setting and a "physiological" (PHYS) setting based on the recordings of inspiratory muscle effort. Some of the results of this study have been previously reported in the form of an abstract (11).
Patients We studied nine inpatients affected by chronic respiratory failure or nocturnal hypoventilation due to miscellaneous neuromuscular disorders who were admitted during a period of clinical stability for a follow-up control. All of the patients were already established on long-term NIMV. The local Ethics Committee approved the study and the patients gave written formal consent.
Home Mechanical Ventilation
Measurements
Daytime Measurements
All physiologic signals were recorded in the last 5 minutes of each unassisted or assisted breathing period. This trial was performed using a home care ventilator that allowed us to set the PEEPe at zero (Helia; Saime, Savigny-le Temple, France). All signals were collected using a personal computer equipped with an A/D board, and stored at a sampling rate of 100 Hz. Arterial blood was sampled from the radial artery at the end of the initial unassisted breathing period and at the end of each period of NIMV with the different settings.
Nighttime Measurements Full standard night polysomnography (Sleep Lab 1000e; Jaeger, Hochberg, Germany) was performed using standard procedures and scored manually according to Rechtschaffen and Kales' criteria (16). Arousals were scored according to the criteria of the American Sleep Disorders Association (17). All the patients were acclimatized before to the sleep study setting, because they had performed a baseline sleep study before the enrollment in the home NIMV program.
Statistical Analysis
All the patients tolerated the procedure and completed the study. The patients' characteristics at the time of study, arterial blood gases at enrollment in the home mechanical ventilation program, and the total duration of the program are shown in Table 1.
Daytime Studies Individual differences in inspiratory and expiratory pressures between US and PHYS are shown in Figures 1A and 1B, and in Table E1 in the online supplement. No significant difference was observed for the inspiratory pressure during US and PHYS. In contrast, a statistically significant difference was found between the mean PEEPe during US and PEEPe during PHYS (Table E1). In comparison with the US, the PHYS resulted in a higher inspiratory pressure in three patients (33.3%) and PEEPe was reduced in three patients.
Table 2 reports data on the respiratory pattern, arterial blood gas concentrations, and respiratory mechanics recorded during spontaneous breathing and during both US and PHYS mechanical ventilation. nPSV significantly improved minute ventilation by increasing tidal volume and reducing the respiratory rate, and likewise significantly improved both PaO2 and PaCO2, independently of the settings used. Finally, the two settings of ventilation considered did not produce statistically different daytime patterns of breathing, blood gases, or respiratory mechanics.
Table 2 also illustrates the mean values of diaphragm function and PEEPidyn recorded in the three experimental conditions. Compared with SB, both ventilator settings induced significant reductions in all the variables of diaphragm effort, as assessed by Pditidal, PTPdi/min, PTPdi/b, and PTPdi/VT. During ventilation administered with the US, we observed variable degree of Pdi reduction, but one patient had a higher Pditidal during nPSV than during SB. Interestingly, this patient was ventilated with a PEEPe of 4 cm H2O, in the absence of any PEEPidyn during SB (Figure 2).
All patients but three were ventilated during US with a PEEPe higher than the PEEPidyn. The PHYS significantly reduced the amount of PEEPidyn. While awake, two patients ventilated with the US and one with the PHYS showed ineffective efforts; this difference between treatments was not significant. The prevalence of these efforts in the total respiratory cycles was negligible with both ventilatory settings (8% and 11% with US and PHYS, respectively).
Nighttime Studies
During sleep with US ventilation, all but two patients showed ineffective efforts during non-REM (NREM) sleep (range 36240 events/hour). As shown in Table 3, during PHYS ventilation we observed a statistically significant lower number of ineffective efforts index during NREM sleep as compared with US ventilation; ineffective efforts were completely eliminated in three patients during PHYS ventilation. When we excluded these three patients from the analysis, the remaining six patients still had a statistically significant reduction of ineffective-effort index from 91.7 ± 98 to 31.7 ± 19.6 (p < 0.05). In all patients, the improvement of sleep quality, expressed by increased REM sleep (% of total sleep time), was strongly correlated to the reduction of ineffective efforts (r = 0.82, p = 0.02; Figure 3).
During US ventilation, three patients had episodes of central apnea (central apnea index /> 5 events/hour; range, 533 events/hour), associated with episode of oxygen desaturation, whereas during PHYS ventilation only one patient showed persistence of central apnea (6.3 events/hour). Both during US and PHYS ventilation a negative correlation was found between central apnea index and amount of REM sleep (expressed as % of total sleep time) (r = 0.79, p < 0.05; r = 0.83, p < 0.05, respectively). It is worth noting that the PHYS lowered the nPSV value in patients with central apneas: the difference in nPSV between patients ventilated with the PHYS and US, although not statistically significant, was 2.25 ± 2.9 cm H2O in patients with central apneas and 0.5 ± 4 cm H2O in those without central apneas during US ventilation.
This study shows that, in stable patients with neuromuscular disorders, the settings of NIMV chosen on an empirical basis while the patient is awake do not predict ventilator synchrony while asleep, and that an incorrect titration of inspiratory support or PEEPe may impede the trigger of the mechanical breath. A physiological setting, based on recording the inspiratory efforts, may minimize the rate of ineffective efforts, resulting in improvement of sleep quality and gas exchange. During wakefulness, both settings are effective in improving arterial blood gases and in unloading inspiratory muscles. Our results therefore suggest that when a patient with nocturnal hypoventilation enters a home ventilation program, the efficacy of the nPSV should be tested by polysomnography to verify the effect of the settings defined during daytime.
Daytime Studies In patients with neuromuscular disorders, the titration of PEEPe seems to be more critical than that of the inspiratory pressure, because these patients may have either a negligible levels of PEEPidyn (< 1 cm H2O) or values higher than 2 cm H2O, which may be considered the limit for applying PEEPe in an attempt to minimize the inspiratory load due the presence of PEEPidyn (18). Considering the severe weakness of these patients' respiratory muscles, the lack of compensation of this resistive threshold may contribute to worsening the load/capacity balance per breath (i.e., the amount of Pdi generated per single breath, compared with the maximal Pdi) and, on the other hand, decrease the trigger sensitivity. In this respect, three of our patients had ineffective efforts while awake.
Conversely, the titration of PEEPe is also critical in patients not showing any PEEPidyn. Most of the so-called "bilevel" ventilators designed specifically for home NIMV are provided with a continuous air flow, so that a positive pressure of
Nighttime Studies The effect of NIMV on sleep quality is varied because, although sleep appeared to be improved in different studies, it rarely became normal (4, 2126). The ventilator setting seems to be crucial to improve sleep quality and gas exchange. In fact, in this study we found that two different problems arose during nocturnal mechanical ventilation: a large number of ineffective breathing efforts in several patients and the occurrence of episodes of central apnea. The improvement of sleep quality during PHYS setting was demonstrated by an increased amount of REM sleep and reduced number of arousals. The increasing percentage of REM sleep observed during PHYS ventilation was correlated with the reduction in ineffective efforts. A phenomenon of missing or ineffective efforts (i.e., Pdi swings unable to trigger the ventilator) has been shown to occur quite often in ventilator-dependent patients with COPD (15). High resistance to airflow, PEEPidyn, low elastic recoil, high ventilatory demands, and short expiratory time on the ventilator has been advocated to explain this phenomenon in mechanically ventilated patients. We found that, when awake, patients with neuromuscular disease had a negligible amount of patientventilator mismatching, probably due to the different mechanical properties. However, this scenario changed considerably during sleep, when the prevalence of ineffective efforts became higher, particular when the patients were receiving ventilation set according to the usual clinical parameters. The PHYS settings resulted in a complete disappearance of the dyssinchrony in three patients and in a significant reduction in the remaining ones. This phenomenon has not been previously described, perhaps because of the different type of ventilation used in the past. The type of mechanical ventilation generally chosen in previous studies was the assist-control mode (22, 23, 27, 28) or a pressure control with a back-up respiratory rate so that the patients' respiratory rate during sleep was the same as the back-up rate of the ventilator (29). In our study, patients received bilevel ventilation in a spontaneous mode so that spontaneous respiratory activity was needed to maintain adequate minute ventilation. The potential benefit of timed versus spontaneous modes of ventilation have not been ever assessed in details, as stated by the Consensus Conference on Clinical Indications for Noninvasive Positive Pressure Ventilation in Chronic Respiratory Failure Due to Restrictive Lung Disease, COPD, and Nocturnal Hypoventilation (30). Factors that could contribute to onset of ineffective efforts may differ from patient to patient: reduction in respiratory drive, reduction in respiratory muscle strength, increased inspiratory load due to augmented upper airway resistance, and mouth leaks may all contribute to the inability to trigger the ventilator adequately (7, 24, 31). In particular, the reduced amount of PEEPidyn with PHY settings may have contributed to improving the trigger sensitivity in these patients with severe respiratory muscle weakness unless, as demonstrated by Parthasarathy and coworkers (32), the recruitment of the expiratory muscles interferes with the ability of the next inspiratory effort to trigger the ventilator. Other factors, such as a high level of PEEPe or over-assistance with a higher tidal volume leading to dynamic hyperinflation, may also be implicated in the genesis of ineffective inspiratory efforts (3336). The main clinical goal for long-term NIMV is to reduce PaCO2, and this is usually achieved with "large" tidal volumes, which may result in "over-assistance" in some patients. This leads to the large amount of ineffective efforts and central apneas during sleep, producing sleep disruption, as demonstrated in our study (37, 38). In our study, central apneas occurred in those patients with higher mechanical inspiratory support during US ventilation and were dramatically reduced after the adjustment of the inspiratory support made during the PHYS ventilation. Over-assistance is not easily appreciated from simple clinical observation, sometimes only being apparent from direct observation of the Pdi signal, and it is not necessarily associated with daytime asynchrony (indeed, only three of our patients showed this phenomenon while awake). Our study shows that the "wrong" settings of home ventilation can be more easily picked up from careful reading of sleep studies. Thus, although analysis of respiratory mechanics is limited to a few specialized centers, sleep studies are commonly performed in a typical respiratory unit, so that in clinical practice it may be feasible useful to validate the US settings by performing a sleep study, reserving recordings of respiratory mechanics for very selected patients (e.g., the patient whose data are shown in Figure 2).
Limitations of the Study
Conclusions
This study was supported by a grant from Telethon Italy # 1125 C. This article has an online supplement, which is accessible from this issue's table of contents at www.atsjournals.org Conflict of Interest Statement: None of the authors have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. Received in original form June 1, 2004; accepted in final form May 26, 2005
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