Mechanisms of improvement of respiratory failure in patients with restrictive thoracic disease treated with non-invasive ventilation

Home-based overnight transcutaneous capnography/pulse oximetry for diagnosing nocturnal hypoventilation associated with neuromuscular disorders

OBJECTIVE

To determine the utility of home-based, unsupervised transcutaneous partial pressure of carbon dioxide (tc-Pco(2)) monitoring/oxygen saturation by pulse oximetry (Spo(2)) for detecting nocturnal hypoventilation (NH) in individuals with neuromuscular disorders.

DESIGN

Retrospective case series analyzed consecutively.

SETTING

Multidisciplinary neuromuscular respiratory failure (NMRF) clinic at an academic institution.

PARTICIPANTS

Subjects (N=35, 68.6% men; mean age, 46.9y) with spinal cord injury (45.7%) or other neuromuscular disorders underwent overnight tests with tc-Pco(2)/Spo(2) monitoring. Fifteen (42.9%) were using nocturnal ventilatory support, either bilevel positive airway pressure (BiPAP) or tracheostomy ventilation (TV).

INTERVENTIONS

A respiratory therapist brought a calibrated tc-Pco(2)/Spo(2) monitor to the patient's home and provided instructions for data collection during the subject's normal sleep period. Forced vital capacity (FVC), body mass index (BMI), and exhaled end-tidal Pco(2) (ET-Pco(2)) were recorded at a clinic visit before monitoring.

MAIN OUTCOME MEASURES

Detection of NH (tc-Pco(2) ≥50mmHg for ≥5% of monitoring time). Data were also analyzed to determine whether nocturnal oxygen desaturation (Spo(2) ≤88% for ≥5% of monitoring time), FVC, BMI, or daytime ET-Pco(2) could predict the presence of NH.

RESULTS

NH was detected in 18 subjects (51.4%), including 53.3% of those using BiPAP or TV. NH was detected in 43.8% of ventilator-independent subjects with normal daytime ET-Pco(2) (present for 49.4%±31.5% [mean ± SD] of the study period), and in 75% of subjects with an elevated daytime ET-Pco(2) (present for 92.3%±8.7% of the study period). Oxygen desaturation, BMI, and FVC were poor predictors of NH. Only 3 attempted monitoring studies failed to produce acceptable results.

CONCLUSIONS

Home-based, unsupervised monitoring with tc-Pco(2)/Spo(2) is a useful method for diagnosing NH in NMRF.

Factors associated with noninvasive ventilation response in the first day of therapy in patients with hypercapnic respiratory failure

BACKGROUND AND AIM:

Noninvasive ventilation (NIV) decreases mechanical ventilation indication in the early period of acute hypercapnic respiratory failure (AHcRF) and factors for success have been studied well. But, less is known about the factors influencing the NIV response in the subacute period. This study was aimed to determine the factors influencing the reduction of PaCO₂ levels within first 24 hours of therapy.

METHODS:

NIV response was defined as reduction of PaCO₂ level below 50 mmHg within first 24 hours. Patients with AHcRF, treated with NIV, were divided into 2 groups according to this criterion; group 1 as the nonresponsive, group 2 as the responsive. The differences in NIV methods and characteristics of the two groups were evaluated and compared in this retrospective study.

RESULTS:

A total of 100 patients were included in the study; 66 of them in group 1 and 34 in group 2. No significant differences were identified between the length of NIV application and intensive care unit (ICU) stay, intubation and mortality rates, across the groups. Ninety-one percent of the patients in group 2 had received all night long NIV therapy; this was just 74% in group 1 (P=0.036). Results of multivariate analysis showed that while nocturnal application was significantly associated with better response, prior home ventilation and requirement of higher pressure support (PS) levels significantly and independently associated with poorer response to NIV therapy.

CONCLUSION:

In patients with AHcRF, all night long use of NIV may accelerate healing by improving PaCO₂ reduction within the first 24 hours. A rapid response in PaCO₂ levels should not be expected in patients requiring higher PS levels and using prior home ventilation.

The effect of acute non-invasive ventilation on corticospinal pathways to the respiratory muscles in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease is associated with altered cortical excitability. The relevance of this to the need for non-invasive ventilation is not known. We assessed the diaphragm response to transcranial magnetic stimulation in terms of motor threshold and latency as well as assessing intracortical excitability using paired stimulation in eight long-term users and six non-users of home ventilation with COPD. Overall, intracortical facilitation was strongly correlated with inspiratory muscle strength (r² 0.72, p < 0.001) whereas intracortical inhibition was correlated with PaCO₂ (r² 0.51, p = 0.01). The two groups did not differ in motor evoked potential or latency, nor in the excitability of intracortical inhibitory or facilitatory circuits assessed using paired stimulation. The acute effect of isocapnic non-invasive ventilation was studied in six established ventilator users. Diaphragm motor evoked potential fell but there was no effect on intracortical facilitation or inhibition, implying an effect of neuromechanical feedback at brainstem or spinal level.

Importance of the PaCO(2) from 3 to 6 months after initiation of long-term non-invasive ventilation

BACKGROUND

The level at which arterial carbon dioxide tension (PaCO(2)) a few months after introduction of long-term non-invasive positive pressure ventilation (NPPV) is associated with a favorable prognosis remains uncertain.

METHODS

Data on 184 post-tuberculosis patients with chronic restrictive ventilatory failure who were receiving long-term domiciliary NPPV were examined retrospectively. Average PaCO(2) 3-6 months after NPPV (3- to 6-mo PaCO(2)) and potential confounders were analyzed with discontinuation of long-term NPPV as the primary outcome. The effects of 3- to 6-mo PaCO(2) on annual hospitalization rates due to respiratory deterioration from 1 year before to 3 years after the initiation of NPPV were examined. The effect of the difference between the PaCO(2) value at the start of NPPV (0-mo PaCO(2)) and the PaCO(2) value 3- to 6-mo later (d-PaCO(2)) on continuation rates for NPPV was also assessed in patients who initiated NPPV while in a chronic state.

RESULTS

Patients with relatively low 3- to 6-mo PaCO(2) values maintained a relatively low PaCO(2) 6-36 months after NPPV (p < 0.0001) and had significantly better continuation rates (p < 0.03) and lower hospitalization rates from the 1st to 3rd year of NPPV (p = 0.008, 0.049, 0.009, respectively) than those with higher levels. The 0-mo PaCO(2) (p = 0.26) or d-PaCO(2) (p = 0.86) had no predictive value.

CONCLUSION

A relatively low 3- to 6-mo PaCO(2) value was predictive of long-term use of NPPV. The target values for 3- to 6-mo PaCO(2) may, therefore, be less than 60 mmHg in post-tuberculosis patients, although more studies are needed.

Diurnal hypercapnia in patients with neuromuscular disease

Subjects with progressive neuromuscular diseases undergo a typical sequence of respiratory compromise, leading from normal unassisted gas exchange to nocturnal hypoventilation with normal daytime gas exchange, and eventually to respiratory failure requiring continuous ventilatory support. Several different abnormalities in respiratory pump function have been described to explain the development of respiratory failure in subjects with neuromuscular weakness. Early in the progression of respiratory failure, the use of nocturnal assisted ventilation can reverse both night- and day-time hypercapnia. Eventually, however, diurnal hypercapnia will persist despite correction of nocturnal hypoventilation. The likely beneficial effects of mechanical ventilatory support include resting fatigue-prone respiratory muscles and resetting of the central chemoreceptors to PaCO(2). Recent experience shows that select patients who require daytime ventilation can be supported with non-invasive ventilation continuously to correct gas exchange abnormalities while avoiding detrimental aspects of tracheostomy placement.

Chronic respiratory failure and neuromuscular disease

The outlook for children with respiratory complications of neuromuscular disease has improved significantly in the past 15 years. This has been the result of many advances in clinical care, including improved monitoring of lung function and hypoventilation during sleep; coordinated respiratory care by experienced physicians with access to specialized respiratory services, especially physiotherapy; and, most importantly, the widespread introduction of noninvasive ventilation.

Mechanisms of improvement of respiratory failure in patients with COPD treated with NIV

Background

Noninvasive ventilation (NIV) improves gas-exchange and symptoms in selected chronic obstructive pulmonary disease (COPD) patients with hypercapnic respiratory failure. We hypothesized NIV reverses respiratory failure by one or all of increased ventilatory response to carbon-dioxide, reduced respiratory muscle fatigue, or improved pulmonary mechanics.

Methods

Nineteen stable COPD patients (forced expiratory volume in one second 35% predicted) were studied at baseline (D0), 5–8 days (D5) and 3 months (3M) after starting NIV.

Results

Ventilator use was 6.2 (3.7) hours per night at D5 and 3.4 (1.6) at 3M (p = 0.12). Mean (SD) daytime arterial carbon-dioxide tension (PaCO₂) was reduced from 7.4 (1.2) kPa to 7.0 (1.1) kPa at D5 and 6.5 (1.1) kPa at 3M (p = 0.001). Total lung capacity decreased from 107 (28) % predicted to 103 (28) at D5 and 103 (27) % predicted at 3M (p = 0.035). At D5 there was an increase in the hypercapnic ventilatory response and some volitional measures of inspiratory and expiratory muscle strength, but not isolated diaphragmatic strength whether assessed by volitional or nonvolitional methods.

Conclusion

These findings suggest decreased gas trapping and increased ventilatory sensitivity to CO₂ are the principal mechanism underlying improvements in gas-exchange in patients with COPD following NIV. Changes in some volitional but not nonvolitional muscle strength measures may reflect improved patient effort.

Weaning Strategies in Problem Patients

Weaning usually accounts for approximately 40–50% of the total duration of mechanical ventilation. Approximately two-thirds of patients can tolerate withdrawal of ventilation without the need for more gradual weaning, but there are a significant number of patients for whom weaning is difficult. Weaning failure is defined as the failure of a spontaneous breathing trial, or the need for re-intubation within 48 hours of extubation. This article reviews the causes of failure to wean, and outlines a practical approach to dealing with the difficult-to-wean patient. The key to successful weaning combines an approach which optimises ventilation at night, adopts a stepwise approach to reducing ventilatory dependence during the day, and uses non-invasive ventilation as a ‘bridge’ out of the ICU. Having a weaning protocol and ensuring it is initiated in a timely manner is likely to be as important as what is in the protocol.

Nocturnal noninvasive ventilation

Nocturnal noninvasive ventilation (NNV), the provision of ventilatory assistance via a noninvasive interface mainly during sleep, has assumed an important role in the management of chronic hypoventilatory syndromes. This review focuses on recent developments related to the use of NNV to treat various forms of chronic respiratory failure or insufficiency. In the past, NNV has been used mainly to treat respiratory insufficiency in patients with neuromuscular disease (NMD) or chest wall deformity; it should be instituted when these patients have orthopnea or daytime symptoms associated with nocturnal hypoventilation. An emerging application is to treat obesity-hypoventilation syndrome, particularly in continuous positive airway pressure (CPAP) failures. Additionally, it has a role in managing some patients with obstructive sleep apnea who are hypoventilating or find the lower expiratory pressure with bilevel positive pressure ventilators more tolerable than with CPAP alone. NNV to treat severe, stable COPD remains controversial, although a subgroup of patients with hypercapnea and sleep-disordered breathing (SDB) seems most likely to respond favorably. NNV to treat central SDB in patients with congestive heart failure continues to be investigated. Recent findings from a Canadian CPAP trial were disappointing, but preliminary results on a novel adaptive NNV mode are promising.

Clinical review: long-term noninvasive ventilation

Noninvasive positive ventilation has undergone a remarkable evolution over the past decades and is assuming an important role in the management of both acute and chronic respiratory failure. Long-term ventilatory support should be considered a standard of care to treat selected patients following an intensive care unit (ICU) stay. In this setting, appropriate use of noninvasive ventilation can be expected to improve patient outcomes, reduce ICU admission, enhance patient comfort, and increase the efficiency of health care resource utilization. Current literature indicates that noninvasive ventilation improves and stabilizes the clinical course of many patients with chronic ventilatory failure. Noninvasive ventilation also permits long-term mechanical ventilation to be an acceptable option for patients who otherwise would not have been treated if tracheostomy were the only alternative. Nevertheless, these results appear to be better in patients with neuromuscular/-parietal disorders than in chronic obstructive pulmonary disease. This clinical review will address the use of noninvasive ventilation (not including continuous positive airway pressure) mainly in diseases responsible for chronic hypoventilation (that is, restrictive disorders, including neuromuscular disease and lung disease) and incidentally in others such as obstructive sleep apnea or problems of central drive.

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.

Predictors of long-term survival in patients with restrictive thoracic disorders and chronic respiratory failure undergoing non-invasive home ventilation

BACKGROUND AND OBJECTIVES

Non-invasive positive pressure ventilation (NPPV) is an established treatment in restrictive thoracic disorders (RTD) with chronic hypercapnic respiratory failure. The aim of this study was to identify predictors of long-term survival for patients on NPPV therapy.

METHODS

In a 10-year retrospective cohort of patients with RTD and chronic hypercapnic respiratory failure, survival and the predictive value of nocturnal and daytime blood gases, lung function and laboratory data measured before initiation of NPPV were assessed. The impact of ventilator settings and daily use of NPPV on survival were also evaluated. Patients were re-admitted every 6 months for follow-up assessment.

RESULTS

The study recruited 77 patients; 18 died during the study period and three ceased NPPV. Respiratory failure caused eight of the nine respiratory deaths (88.9%). One-, 2- and 5-year survival rates were 92.5%, 81.0% and 59.0%, respectively. In univariate analyses, higher night-time PaCO(2), base excess (night- and daytime) and lower Hb at baseline were associated with significantly worse survival (P < 0.05). Multivariate Cox regression analysis revealed night-time PaCO(2) as an independent predictor of survival (P = 0.042). The small differences in daily duration of use of NPPV and ventilator settings were not significantly related to survival. At follow up, significant improvements were observed for blood gases, lung and respiratory muscle function, as well as a decrease in Hb level (P < 0.01 each).

CONCLUSIONS

Base excess, Hb and particularly nocturnal PaCO(2) are relevant prognostic factors for survival in RTD and should be considered in assessing patients receiving NPPV.

Neonatal nasal intermittent positive pressure ventilation: what do we know in 2007?

Although neonatal nasal intermittent positive pressure ventilation (NIPPV) is widely used today, its place in neonatal respiratory support is yet to be fully defined. Current evidence indicates that NIPPV after extubation of very premature infants reduces the rate of reintubation. However, much is still not known about NIPPV including its mechanisms of action. It may improve pulmonary mechanisms, tidal volume and minute ventilation but more studies are required to confirm these findings. There is some evidence that NIPPV marginally improves gas exchange. More research is needed to establish which device is best, what settings to use or whether to use synchronised rather than non-synchronised NIPPV, and about the way to wean NIPPV. Future studies should enrol sufficient infants to detect uncommon serious complications and include long-term follow up to determine important neurodevelopment and pulmonary outcomes.

Prognostic value of mouth occlusion pressure in patients with chronic ventilatory failure

BACKGROUND

Mouth occlusion pressure measurement is widely used for assessment of respiratory muscle function, particularly in patients with respiratory failure. However, its predictive value for long-term survival remains largely unexplored.

METHODS

In 464 patients with chronic hypercapnic respiratory failure (CHRF) due to various underlying disorders and receiving non-invasive ventilation (NIV), maximal inspiratory mouth pressure (PI(max)), mouth occlusion pressure at 100 ms during quiet breathing (P(0.1)) and the ratio P(0.1)/PI(max) were assessed prior to and after treatment including NIV. Baseline data and changes at follow-up were used to evaluate their predictive value for long-term survival.

RESULTS

Overall, median (quartiles) P(0.1) was 177.0 (109.2;287.0) %pred, PI(max) 35.0 (24.0;47.0) %pred, and P(0.1)/PI(max) 564.0 (275.7;1082.3) %pred. In multivariate analyses, P(0.1) was related to airflow obstruction, lung hyperinflation, haemoglobin (Hb) and leukocytes, and PI(max) to airflow obstruction and hyperinflation (p<0.05 each). All-cause mortality during follow-up (median 31.6 months) was 31.5%. Survival was associated with age, body-mass index (BMI), lung function, leukocytes, Hb, PI(max), P(0.1) and P(0.1)/PI(max) (p<0.01 each, univariate). Among these multivariate Cox regression identified age, BMI, FEV(1), leukocytes and P(0.1)/PI(max) as independent predictors (p<0.05 each). Furthermore, the decrease of P(0.1)/PI(max) at follow-up was associated with improved survival in patients with high baseline P(0.1)/PI(max) (>50th or 75th percentile; p<0.05).

CONCLUSIONS

In patients with CHRF and current NIV therapy, P(0.1)/PI(max) was an independent predictor of long-term survival, in addition to previously established risk factors. Moreover, a decrease in P(0.1)/PI(max) after treatment including NIV was associated with an improved survival in patients with high baseline P(0.1)/PI(max) values.

Non-invasive positive ventilation in the treatment of sleep-related breathing disorders

This chapter addresses the use of long-term non-invasive positive pressure ventilation (NIPPV) (to the exclusion of continuous positive airway pressure) in the different clinical settings in which it is currently proposed: principally in diseases responsible for hypoventilation characterized by elevated PaCO(2). Nasal masks are predominantly used, followed by nasal pillow and facial masks. Mouthpieces are essentially indicated in case daytime ventilation is needed. Many clinicians currently prefer pressure-preset ventilator in assist mode as the first choice for the majority of the patients with the view of offering better synchronization. Nevertheless, assist-control mode with volume-preset ventilator is also efficient. The settings of the ventilator must insure adequate ventilation assessed by continuous nocturnal records of at least oxygen saturation of haemoglobin-measured by pulse oximetry. The main categories of relevant diseases include different types of neuromuscular disorders, chest-wall deformities and even lung diseases. Depending on the underlying diseases and on individual cases, two schematic situations may be individualized. Either intermittent positive pressure ventilation (IPPV) is continuously mandatory to avoid death in the case of complete or quasi-complete paralysis or is used every day for several hours, typically during sleep, producing enough improvement to allow free time during the daylight in spontaneous breathing while hypoventilation and related symptoms are improved. In case of complete or quasi-complete need of mechanical assistance, a tracheostomy may become an alternative to non-invasive access. In neuromuscular diseases, in kyphosis and in sequela of tuberculosis patients, NIPPV always significantly increases survival. Conversely, no data support a positive effect on survival in chronic obstructive pulmonary disease.

Respiratory muscle training in restrictive thoracic disease: a randomized controlled trial

OBJECTIVE

To investigate the effects of respiratory muscle training (RMT) in patients with restrictive thoracic disorders and intermittent noninvasive positive-pressure ventilation (NPPV).

DESIGN

Prospective randomized controlled trial.

SETTING

Home-based RMT, with assessment in a primary care pulmonary center.

PARTICIPANTS

Thirty patients with restrictive thoracic disorders; 28 patients completed the trial.

INTERVENTION

Three months of RMT by isocapnic hyperpnea or sham training.

MAIN OUTCOME MEASURES

Respiratory muscle strength and endurance, lung function, exercise performance, and health-related quality of life (HRQOL).

RESULTS

After RMT, maximal inspiratory mouth pressure was increased (27.6%+/-36.5%, P=.013). In patients who could perform cycle ergometer testing (n=17), peak oxygen consumption (2.24+/-3.39mLxkg(-1).min(-1) vs -1.71+/-2.54mLxkg(-1).min(-1), P=.014) and maximal work rate (9.4+/-14.8W vs -5.1+/-10.8W, P=.043) increased relative to a control group. Similar differences occurred regarding changes of HRQOL (physical performance, 3.3+/-11.4 score vs -6.6+/-9.0 score; P=.012) and time of ventilator use (-0.6+/-1.2h/d vs 0.4+/-0.5h/d, P=.010). Lung volumes, 12-second maximum voluntary ventilation, 6-minute walking distance, and blood gases were unchanged.

CONCLUSIONS

In patients with restrictive thoracic disorders and NPPV, RMT improved inspiratory muscle strength. Exercise performance and HRQOL were improved when the 2 groups were compared. RMT was practicable and safe despite severe respiratory impairment. Further evaluation, including different training intensities and modalities, seems warranted.

Effect of Home Mechanical Ventilation on Inspiratory Muscle Strength in COPD

BACKGROUND

The mechanism responsible for chronic hypercapnic respiratory failure (HRF) in patients with COPD remains unclear. In this study, we tested the hypothesis that chronic HRF in patients with COPD is associated with low-frequency fatigue (LFF) of the diaphragm.

METHODS

To test this hypothesis, we measured the twitch transdiaphragmatic pressure (Tw Pdi) elicited by stimulation of the phrenic nerves in 25 patients with chronic HRF (mean [+/- SD] Paco(2), 55.2 +/- 5.2 mm Hg) due to COPD before and 2 months after the initiation of noninvasive mechanical ventilation (NIV) [pressure-cycled ventilation with inspiratory positive airway pressure of 19.0 +/- 2.5 cm H(2)O]. We reasoned that had LFF been present, Tw Pdi should rise after effective NIV.

RESULTS

The treatment compliance with NIV was good (median of machine usage was 7.1 h per night). Paco(2) decreased from 55.2 +/- 5.2 to 48.8 +/- 5.9 mm Hg (p < 0.001), and Pao(2) increased from 53.1 +/- 5.9 to 57.7 +/- 7.0 mm Hg (p = 0.007). Mean Tw Pdi at baseline was 11.1 +/- 6.6 cm H(2)O and after treatment was 11.7 +/- 7.2 cm H(2)O (not significant). Also, maximal static inspiratory mouth pressure did not change significantly (44.3 +/- 15.9 cm H(2)O vs 46.5 +/- 19.7 cm H(2)O).

CONCLUSION

LFF of the diaphragm does not accompany chronic HRF in patients with COPD.

Recent Advances in Respiratory Care for Neuromuscular Disease

The impact of ventilatory support on the natural history of neuromuscular disease (NMD) has become clearer over the last 2 decades as techniques have been more widely applied. Noninvasive ventilation (NIV) allows some patients with nonprogressive pathology to live to nearly normal life expectancy, extends survival by many years in patients with other conditions (eg, Duchenne muscular dystrophy), and in those patients with rapidly deteriorating disease (eg, amyotrophic lateral sclerosis) survival may be increased, but symptoms can be palliated even if mortality is not reduced. A growing number of children with NMD are surviving to adulthood with the aid of ventilatory support. The combination of NIV with cough-assist techniques decreases pulmonary morbidity and hospital admissions. Trials have confirmed that NIV works in part by enhancing chemosensitivity, and in patients with many different neuromuscular conditions the most effective time to introduce NIV is when symptomatic sleep-disordered breathing develops.