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Clinical Meetings at RH Year 2010

2010 Sep/Oct - An Application of PAV in Severe COPD

Dr. Ho Man Ying and Dr. Wong Kam Cheung; TB and Chest Unit, Wong Tai Sin Hospital

Case History
A 59-year-old gentleman had known chronic obstructive pulmonary disease (COPD), hypertension and old pulmonary tuberculosis. He had COPD exacerbations every few months in recent years, which worsened to monthly attacks just before referring to us. His medications had been optimized with Seretide Medium 2 puffs BD, Tiotropium bromide (Spiriva®) 18 micrograms daily, and Theophylline SR 200mg BD, before undertaking pulmonary rehabilitation programme (PRP) in our unit.

He had MRC grade 4 dyspnoea. Arterial blood gas revealed hypoxemia (pO2 9.3 kPa) with normal pH & pCO2 in room air. His spirometry showed a post-bronchodilator FEV1 17.8% of the predicted value (Table 1), compatible to stage IV COPD according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification. CXR showed lung hyperinflation, diminished pulmonary vascularity and fibrocalcified foci in the upper lobes.

His St. George Respiratory Questionnaire (SGRQ) had a total score of 47.2 (symptom score 39.8, activity score 85.9, impact score 27.4). In the six minute walk test, he walked a total distance of 112m with a trough SaO2 of 79% (Table 3). He experienced significant desaturation within 30 seconds after starting the baseline treadmill stress test, which was stopped in stage 1 at 2 min 36 sec for safety concern. There was persistent, severe desaturation despite high flow oxygen (Table 2). The baseline peak exercise capacity was 2.1METs, estimated to be equal to 22W.

His exercise programme comprised of both endurance and resistance training, including treadmill and upper limb ergometry, with intensity 70-100% of peak workload.

Our patient had very poor lung function and exercise tolerance. The baseline stress test was stopped within 3 minutes due to severe desaturation, and his maximal voluntary ventilation was only 15.75L. It was unlikely that he could sustain exercise training of sufficient intensity and duration with supplemental O2 to achieve physiological training benefits, due to severe limitation in ventilation. As such, we tried thrice-weekly proportional assist ventilation (PAV) - assisted lower limb cycle ergometer training to facilitate high intensity exercise. PAV was titrated by small, gradual increments in volume and flow assists in the first training session against patient’s comfort. He underwent 21 training sessions, each lasted for 20 minutes at designated workload. Starting at 10W in the first session, the exercise intensity was gradually increased as tolerated to 30W (since the 19th session), which was 136% of the baseline peak exercise capacity (Figure. 1). Figure 1. PAV-assisted training workload in in-patient exercise sessions.



Long-term oxygen therapy was arranged and he was discharged after 6 weeks of in-patient PRP. Home exercise was advised, and he went through a further 8 week-course of out-patient exercise training. The outcome assessment on completion of the whole PRP revealed a significant increase in 6-minute walk distance of 104m (Tab. 3). He had been free from exacerbations of COPD hitherto for 4 months since discharge from the in-patient PRP. A second outcome assessment on 6MWT and SGRQ would be done at 6 months after commencement of PRP and results were not yet available at the time of writing.



Discussion
Pulmonary rehabilitation is a standard of care in the management of COPD patients, according to various international guidelines.1-3 We would focus on the use of non-invasive ventilation (NIV) as an adjunct for exercise training in PRP.1,2

One important limiting factor for poor exercise tolerance in COPD patients is ventilatory limitation. They have increased airway resistance, poor lung emptying, and hence a high end-expiratory lung volume (EELV). During exercise, the increase in respiratory rate and ventilatory demand result in more air trapping, and consequently further rise in EELV. This dynamic hyperinflation increases the work of breathing and severely compromises the exercise capacity.

Use of NIV can overcome such ventilatory limitation by unloading the respiratory muscles and decreasing the work of breathing. As a result, a patient can tolerate longer durations of exercise and at higher exercise intensity. Previous studies have demonstrated that adjunctive use of NIV during exercise could achieve these effects.4-7 It is hypothesized that if the duration and intensity of each individual exercise session can be increased, the magnitude of training-induced effects would be greater after the rehabilitation programme.8

A recent article 8 in March 2010 had reviewed this area. Six studies were included, in which two used PAV, three used BiPAP, and one used inspiratory pressure support (IPS). All were compared against spontaneous breathing, except Van’t Hul et al. 9 compared IPS 10cmH2O against a sham pressure support of 5cmH2O. Johnson et al 10 compared with heliox breathing in addition. The training comprised of six to eight weeks of twice to thrice weekly exercise programme, with training intensity at 50-70% of peak workload.

All except Bianchi et al 11 suggested some benefit of NIV over the other group. Hawkins et al. 12,Costes et al. 13 and Van't Hul et al.9 showed either larger increase in peak exercise work rate, exercise duration or walking distance post-rehabilitation. Physiological changes in terms of maximal voluntary ventilation or plasma lactate level were also demonstrated in Hawkins and other studies. 8,12

Direct comparison with these studies was difficult due to different ventilator settings and contents of rehabilitation programme. However, there were some postulations8 on why Bianchi et al 11 was the only study concluding no benefit from NIV use. Firstly, the degree of severity of COPD in their patients was lower. As dynamic hyperinflation is more pronounced in severe disease, it is expected that less severe patients would benefit less from NIV use. Secondly, both the volume assist setting and the EPAP were low. The dynamic hyperinflation in COPD patients would result in high elastance of the respiratory system and high intrinsic positive end-expiratory pressure, which might not be overcome by the respective low volume assist and EPAP. Lastly, their patients stopped exercise due to dyspnoea rather than leg fatigue, suggesting that the ventilatory limitations were not overcome by the ventilator.

In conclusion, current evidence suggests that in selected severe COPD patients, use of NIV as an adjunct for exercise training can be beneficial. It appears that higher pressures or larger assists are more effective, provided that they can be tolerated. However, the optimal mode of ventilation is still open to debate.

References
  1. Andrew L Ries et al. Pulmonary Rehabilitation: Joint ACCP/AACVPR Evidence-Based Clinical Practice Guidelines (2007). Chest 2007; 131; 4S-42S
  2. Linda Nici et al. American Thoracic Society/ European Respiratory Society Statement on Pulmonary Rehabilitation (2006). American Journal of Respiratory & Critical Care Medicine Vol 173; p 1390-1413, 2006
  3. Morgan M et al. BTS Statement. Pulmonary Rehabilitation. Thorax 2001; 56: 827-834.
  4. Bianchi L et al. Effects of Proportional Assist Ventilation on Exercise Tolerance in COPD Patients with Chronic Hypercapnia. European Respiratory Journal 1998; 11; 422- 427.
  5. Polese G et al. Nasal PAV unloads the Inspiratory Muscles of stable Patients with Hypercapnia due to COPD. European Respiratory Journal 2000; 16; 491-498
  6. Van’t Hul A et al. Acute Effects of Inspiratory Pressure Support during exercise in Patients with COPD. Eur Respir J 2004; 23; 34-40
  7. Ambrosino N et al. New Strategies to improve exercise tolerance in COPD. Euorpean Respiratory Journal 2004; 24; 313- 322.
  8. Corner E, et al. Does the Addition of Non-Invasive Ventilation during Pulmonary Rehabilitation in Patients with Chronic Obstructive Pulmonary Disease Augment Patient Outcome in Exercise Tolerance? A Literature Review. Physiotherapy Research International 2010; 15: 5-15
  9. Van’t Hul A et al. Training with Inspiratory Pressure Support in Patients with severe COPD. European Respiratory Journal 2006; 27:65-72.
  10. Johnson J et al. Effects of Training with Heliox and NIV on exercise ability in Patients with severe COPD. Chest 2002; 122;464-472
  11. Bianchi L, et al. Lack of additional effect of adjunct of assisted ventilation to Pulmonary Rehabilitation in Mild COPD patients. Resp Med 2002; 96: 359 – 367
  12. Hawkins P et al. Proportional Assist Ventilation as an aid to Exercise training in severe Chronic Obstructive Pulmonary Disease. Thorax 2002; 57: 853 – 859
  13. Costes F et al. Non-invasive Ventilation during Exercise Training improves Exercise Tolerance in Patients with Chronic Obstructive Pulmonary Disease. Journal of Cardiopulmonary Rehabilitation 2003; 23: 307 – 331
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