Volume assured versus pressure preset non-invasive ventilation for compensated ventilatory failure in COPD.

BACKGROUND: The addition of domiciliary non-invasive ventilation (NIV) to standard therapy in chronic obstructive pulmonary disease (COPD) patients with compensated ventilatory failure (CVF) is reported to have beneficial effects. Compliance with NIV is an important factor. Volume assured NIV (va-NIV) may improve compliance and ventilation during sleep by automatically titrating ventilatory pressures. METHODS: A prospective single centre, randomised, parallel group trial comparing va-NIV and pressure preset NIV (pp-NIV) in COPD patients with CVF naïve to domiciliary NIV was performed (ISCRTN91892415). The primary outcomes were arterial blood gases, mean overnight oximetry (mSpO2) and compliance after three months. Secondary outcomes included pulmonary function, exercise capacity and health-related quality of life assessment. RESULTS: Forty patients were randomised in a 1:1 ratio. The va-NIV median target minute ventilation was 8.4 L/min and pp-NIV median inspiratory pressure was 28 cmH2O. There were no significant differences between groups in primary or secondary outcomes after three months. Mean (SD) PaO2 8.7 (1.7) versus 7.9 (1.7) kPa (p = 0.19), PaCO2 6.7 (0.5) versus 7.3 (1.1) kPa (p = 0.1), mSpO2 89.7 (4.2) versus 89.8 (3.9) % (p = 0.95), compliance 5.0 (3.1) versus 4.7 (3.2) hours (p = 0.8) in va-NIV versus pp-NIV respectively. Patients allocated va-NIV spent fewer days in hospital initiating therapy 3.3 (1.6) versus 5.2 (2.8) (p = 0.02). Both groups showed significant improvements in PaCO2 and mSpO2 after three months treatment. CONCLUSIONS: Domiciliary va-NIV and pp-NIV have similar effects on physiological outcomes in COPD patients with CVF and both are well tolerated.

Weaning from prolonged invasive ventilation in motor neuron disease: analysis of outcomes and survival.

INTRODUCTION: Non-invasive ventilation (NIV) improves prognosis in patients with motor neuron disease (MND) in the absence of major bulbar involvement. However, some experience a rapid and unexpected decline in respiratory function and may undergo emergency tracheal intubation. Weaning from invasive ventilation can be difficult, and reported independence from invasive ventilation is uncommon with poor prognosis. The outcomes of patients with MND referred to a specialist weaning service following emergency tracheal intubation were examined and compared with MND patients electively initiating NIV. METHODS: A case note review was performed on all patients with MND invasively ventilated and referred to a specialist weaning service between 1992 and 2007. Outcomes were compared with those electively commenced on NIV during the same period. RESULTS: Thirty patients were referred for weaning from invasive ventilation which was started in 17 before MND was diagnosed. Fourteen patients (47%) were weaned from invasive ventilation but still required NIV, 13 failed to wean, and three died. Seventeen were discharged home from hospital. The median survival from tracheal intubation was 13.7 months (95% CI 0 to 30.8) for those previously diagnosed and 7.2 months (95% CI 5.1 to 9.4) for those not previously known to have MND. Comparison with patients initiated electively on NIV demonstrated similar survival estimates to that from emergency intubation (median 9.4 (95% CI 6.9 to 12.0) vs 7.8 (95% CI 2.6 to 12.9) months respectively). CONCLUSION: The prognosis in MND following acute respiratory failure and intubation is not always complete ventilator dependence if patients are offered a comprehensive weaning programme.

Is there an alternative to pre-flight hypoxic challenge testing in scoliotic patients?

INTRODUCTION: Hypoxic challenge testing (HCT) is not readily available in all hospitals. It has recently been shown that resting oximetry does not reliably predict the results of HCT in patients with extrapulmonary restrictive lung disease. We assessed other clinical tests to see if they might be used as an alternative screen for HCT. METHODS: People with primary thoracic scoliosis were recruited. Resting SpO(2), arterial blood gases (ABG's), lung function and shuttle walking test (SWT) were measured. All subjects underwent HCT breathing an inhaled oxygen fraction of 15% for 20 min, or until SpO(2) fell below 85%, when ABG's were taken. RESULTS: Fourteen people (5 male) with thoracic scoliosis, Cobb angle 93 (31) degrees , aged 65 (8.5) years, FEV(1) 0.86 (0.4) L, FVC 1.2 (0.4)L were studied. The resting SpO(2) was 96 (2) %, PaO(2) 9.2 (1) kPa and PaCO(2) 6.1 (0.4) kPa. HCT was positive in 11 subjects (PaO(2) <6.6 kPa). Eight of 11 HCT positive subjects had a resting SpO(2) > 95%. Positive correlation was found between SpO(2) at SWT termination and PaO(2) following HCT (r = 0.56, p = 0.02). Those with saturations of 92% or under at SWT termination had positive HCT. CONCLUSIONS: Despite normal resting SpO(2) subjects with thoracic scoliosis may have positive HCT. Current recommendations for air travel do not accurately identify these people. Desaturation following a SWT may provide a useful screening tool, however a low threshold for performing HCT on people with thoracic scoliosis prior to air travel is warranted.

Long-term non-invasive ventilation to manage persistent ventilatory failure after COPD exacerbation.

BACKGROUND AND OBJECTIVE: Patients with ventilatory failure at discharge from hospital following an exacerbation of COPD (ECOPD) have increased work of breathing and reduced inspiratory muscle strength compared with those with a normal arterial carbon dioxide tension (PaCO(2)). They also have a significantly worse prognosis. Long-term non-invasive positive pressure ventilation (NIPPV) may offer a treatment strategy but benefits have not been established. METHODS: We examined the outcomes of 35 patients, with a PaCO(2) >7.5 kPa and normal pH, following hospital admission with an ECOPD. Patients were initiated on long-term NIPPV. Our aims were to establish if NIPPV was tolerated and to describe the effects on ventilatory parameters. RESULTS: Daytime arterial blood gases and nocturnal ventilatory parameters improved significantly on NIPPV. Diurnal PaO(2), self-ventilating, rose from (mean (SD)) 7.3 (1.8) to 8.1 (0.9) kPa (P = 0.005) and PaCO(2) fell from 8.8 (1.3) to 7.3 (0.8) kPa (P

A bench test to confirm the core features of volume-assured non-invasive ventilation.

UNLABELLED: Volume-assured non-invasive ventilation (NIV) theoretically guarantees minute ventilation with circuit leak compensation unlike other modes of NIV. Bench testing demonstrated that minute ventilation was maintained with varying lung compliance and resistance with minimal effect from circuit leak, confirming for the first time the core features of volume-assured NIV. BACKGROUND AND OBJECTIVE: Volume-assured non-invasive positive pressure ventilation (va-NIPPV) is a novel mode designed to adapt pressure support (PS) to achieve a target minute ventilation (TgV). This may optimize ventilation; however, no data confirm that va-NIPPV compensates appropriately for the changes in pulmonary mechanics and circuit leak seen in clinical practice. Bench testing assessed these principles. METHODS: A ventilator featuring a va-NIPPV mode was studied. A test lung with varying compliance and resistance, and pneumotachograph were used. Eight lung model settings were chosen: (i) low resistance and high compliance; (ii) low resistance and low compliance; (iii) high resistance and high compliance; and (iv) high resistance and low compliance, all with and without additional circuit leak. An expiration valve, respiratory rate of 15, inspiratory time of 1 s and PS between 3 and 21 cm H2O were used. Va-NIPPV was tested with varying TgV after establishing the range of minute ventilation possible in a pressure preset mode. RESULTS: At a TgV of 10 L/min, va-NIPPV delivered minute ventilation of (median (interquartile range) ): 11 (10.9-11, 10.2 (10.2-10.3), 12.4 (12.4-12.4) and 11.2 (10.9-11.2) L/min in test lung settings 1, 2, 3 and 4, respectively. Additional leak between 8-33 L/min had little effect. Similar results were seen at other TgV, within the ventilator's PS capabilities. CONCLUSIONS: These data confirm that va-NIPPV is able to approximate a preset TgV with varying lung compliance and resistance, and that additional circuit leak has little effect on the delivered minute ventilation.