Randomised crossover study of pressure and volume non-invasive ventilation in chest wall deformity

BACKGROUND: Non-invasive ventilation is an established treatment for chronic respiratory failure due to chest wall deformity. There are few data available to inform the choice between volume and pressure ventilators. The aim of this study was to compare pressure and volume targeted ventilation in terms of diurnal arterial blood gas tensions, lung volumes, hypercapnic ventilatory responses, sleep quality, and effect on daytime function and health status when ventilators were carefully set to provide the same minute ventilation. METHODS: Thirteen patients with chest wall deformity underwent a 4 week single blind randomised crossover study using the Breas PV403 ventilator in either pressure or volume mode with assessments made at the end of each 4 week period. RESULTS: Minute ventilation at night was less than that set during the day with greater leakage for both modes of ventilation. There was more leakage with pressure than volume ventilation (13.8 (1.9) v 5.9 (1.0) l/min, p = 0.01). There were no significant differences in sleep quality, daytime arterial blood gas tensions, lung mechanics, ventilatory drive, health status or daytime functioning. CONCLUSIONS: These data suggest that pressure and volume ventilation are equivalent in terms of the effect on nocturnal and daytime physiology, and resulting daytime function and health status.     

Randomised controlled trial of inhaled corticosteroids in patients with chronic obstructive pulmonary disease

BACKGROUND—Inhaled corticosteroids are known to bebeneficial for patients with asthma, but their role in treatingpatients with stable chronic obstructive pulmonary disease (COPD)remains controversial. A study was undertaken to determine whetherinhaled corticosteroids are of functional benefit in patients who didnot show improvement with a trial of oral corticosteroids.
METHODS—In phase I patients with stable COPD weregiven a two week course of oral placebo followed by two weeks ofprednisone 40 mg per day in a single blind manner to distinguishbetween responders and non-responders to oral corticosteroids. In phaseII a double blind, randomised, parallel group trial of inhaledbudesonide 1600 µg per day versus placebo was carried out in 79 non-responders to oral corticosteroids. The primary outcome measure wasforced expiratory volume in one second (FEV₁), andsecondary outcome measures were exercise capacity, dyspnoea withexertion, quality of life, peak expiration flow rate, and respiratory symptoms.
RESULTS—Randomisation allocated 39 subjects toinhaled corticosteroids and 40 to placebo. There was no difference inthe change in FEV₁ from baseline between the treatment andplacebo groups; mean difference -12 ml (95% CI -88 to 63) at threemonths and -4 ml (95% CI -95 to 87) at six months. The proportionof patients with a 15% or greater improvement was no higher amongthose receiving inhaled corticosteroids than in the placebo group atany of the follow up visits. Changes in secondary outcomes were also no different.
CONCLUSIONS—Inhaledcorticosteroids,even at high doses, were of no physiological or functional benefit inthese patients with advanced COPD.

     

Non-invasive ventilation (NIV) in surgical patients with post-operative acute respiratory failure

Non-invasive ventilation (NIV) is a technique developed to assist patients with acute respiratory failure (ARF) of different origins, which avoids endotracheal intubation. NIV has already been demonstrated to be a useful alternative to invasive mechanical ventilation in patients with acute exacerbation of COPD, cardiogenic pulmonary oedema and other causes of hypoxemic ARF, avoiding several complications directly related to the presence of an endotracheal tube, such as the increased risk for nosocomial pneumonia.Few studies have evaluated the possible role for NIV in patients developing post-operative acute respiratory failure: this chapter will review the possible indications and the clinical results obtained by applying NIV in patients developing ARF after thoracic and abdominal surgery. The role of different interfaces is also discussed.     

Effect of non-invasive mechanical ventilation on sleep and nocturnal ventilation in patients with chronic respiratory failure

BACKGROUND: Chronic respiratory failure (CRF) is associated with nocturnal hypoventilation. Due to the interaction of sleep and breathing, sleep quality is reduced during nocturnal hypoventilation. Non-invasive mechanical ventilation (NMV), usually performed overnight, relieves symptoms of hypoventilation and improves daytime blood gas tensions in patients with CRF. The time course of the long term effect of NMV on sleep and breathing during both spontaneous ventilation (withdrawing the intervention) and NMV was investigated in patients with CRF due to thoracic restriction. METHODS: Fifteen consecutive patients (13 women) of mean (SD) age 57.9 (12.0) years with CRF due to thoracic restriction were included in the study. During the one year observation period four polysomnographic studies were performed: three during spontaneous breathing without NMV-before initiation of NMV (T0) and after withdrawing NMV for one night at six months (T6) and 12 months (T12-)-and the fourth during NMV after 12 months (T12+). Daytime blood gas tensions and lung function were also measured. RESULTS: Spontaneous ventilation (in terms of mean oxygen saturation) progressively improved (from T0 to T12-) during both REM sleep (24.8%, 95% CI 12.9 to 36.9) and NREM sleep (21.5%, 95% CI 12.4 to 30.6). Sleep quality during spontaneous ventilation also improved in terms of increased total sleep time (26. 8%, 95% CI 11.6 to 42.0) and sleep efficiency (17.5%, 95% CI 5.4 to 29.6) and decreased awakenings (54.0%, 95% CI 70.3 to 37.7). Accordingly, REM and NREM sleep stages 3 and 4 significantly improved. However, the most significant improvements in both nocturnal ventilation and sleep quality were seen during NMV at 12 months. CONCLUSIONS: After long term NMV both spontaneous ventilation during sleep and sleep quality in patients with CRF due to thoracic restriction showed evidence of progressive improvement compared with baseline after withdrawal of NMV for a single night at six and 12 months. However, the greatest improvements in nocturnal ventilation and sleep were achieved during NMV at 12 months.     

Randomised placebo controlled trial of daytime function after continuous positive airway pressure (CPAP) therapy for the sleep apnoea/hypopnoea syndrome

BACKGROUND—Patients with the sleepapnoea/hypopnoea syndrome (SAHS) report improved sleepiness, cognitivefunction, and psychological well being after continuous positive airwaypressure (CPAP) therapy, and it is for these daytime features that CPAPis usually given. However, few randomised or controlled studies existon the effects of CPAP on daytime function.
METHODS—A prospective, randomised, single blind,placebo controlled, crossover trial of daytime function after CPAP wasconducted in 23 patients with SAHS, all with 15apnoeas+hypopnoeas/hour and 2 symptoms of SAHS. All patients spentfour weeks on CPAP therapy and four weeks on oral placebo treatment,following randomisation to treatment order. With ethics committeeapproval, patients were told the placebo tablet might improve upperairway function. Average effective CPAP use was monitored using hiddentime clocks. Assessments of objective and subjective sleepiness,symptoms, cognitive performance, and psychological well being wereperformed on the last day of each treatment and compared.
RESULTS—Objective sleepiness measured by sleeponset latency on the multiple sleep latency test improved with CPAP(mean difference from placebo +2.4 min, 95% CI 0.8 to 4.0; p<0.001)as did subjective sleepiness on the Epworth scale (mean difference -6,95% CI -3 to -9; p = 0.001). Symptom total score also fell with CPAP(mean difference -1.6, 95% CI -2.2 to -1.0; p<0.001). Nodeterminants of these changes with active treatment were identified,and no significant enhancements to cognitive function or psychosocial well being were found in this small sample.
CONCLUSIONS—These findings provide furtherevidence for clinically significant benefits to daytime function from CPAP.

     

Comparison of proportional assist ventilation and pressure support ventilation in chronic respiratory failure due to neuromuscular and chest wall deformity

BACKGROUND: The physiological and symptomatic effects of proportional assist ventilation (PAV) and pressure support ventilation (PSV) were compared in stable awake patients with neuromuscular and chest wall deformity (NMCWD). METHODS: Oxygen saturation (SaO(2)), transcutaneous carbon dioxide (TcCO(2)), minute ventilation (VE), tidal volume (VT), respiratory rate (RR), and diaphragm electromyography (EMGdi) were measured in 15 patients during both modes. Subjective effort of breathing and synchrony with the ventilator were assessed using visual analogue scales. RESULTS: Three of 15 patients failed to trigger the ventilator in either mode and were excluded. In the 12 remaining patients there were similar improvements in SaO(2), TcCO(2), VE, VT, and RR during both modes. The mean (SD) percentage fall in EMGdi was greater during PSV (-80.5 (10.7)%) than during PAV (-41.3 (35.2)%; p= 0.01). Effort of breathing (p=0.004) and synchrony with the ventilator (p=0.004) were enhanced more with PSV than with PAV. CONCLUSION: Both PSV and PAV produced similar improvements in physiological parameters. However, greater diaphragm unloading was observed with PSV than with PAV, associated with greater symptomatic benefit. These findings suggest that tolerance to PAV may be compromised in patients with NMCWD.     

Randomised controlled trial of weightlifting exercise in patients with chronic airflow limitation.

BACKGROUND PATIENTS: with chronic airflow obstruction are often limited by muscle fatigue and weakness. As exercise rehabilitation programmes have produced modest improvements at best a study was designed to determine whether specific muscle training techniques are helpful. METHODS: Thirty four patients with chronic airflow limitation (forced expiratory volume in one second (FEV1) 38% of predicted values) were stratified for FEV1 to vital capacity (VC) ratio less than 40% and arterial oxygen desaturation during exercise and randomised to a control or weightlifting training group. In the experimental group training was prescribed for upper and lower limb muscles as a percentage of the maximum weight that could be lifted once only. It was carried out three times a week for eight weeks. RESULTS: Three subjects dropped out of each group; results in the remaining 14 patients in each group were analysed. Adherence in the training group was 90%. In the trained subjects muscle strength and endurance time during cycling at 80% of maximum power output increased by 73% from 518 (SE69) to 898 (95) s, with control subjects showing no change (506 (86) s before training and 479 (89) s after training). No significant changes in maximum cycle ergometer exercise capacity or distance walked in six minutes were found in either group. Responses to a chronic respiratory questionnaire showed significant improvements in dyspnoea and mastery of daily living activities in the trained group. CONCLUSIONS: Weightlifting training may be successfully used in patients with chronic airflow limitation, with benefits in muscle strength, exercise endurance, and subjective responses to some of the demands of daily living.     

Survey of non-invasive ventilation (NIPPV) in patients with acute exacerbations of chronic obstructive pulmonary disease (COPD) in the UK

BACKGROUND: Non-invasive positive pressure ventilation (NIPPV) has been shown to be beneficial in the treatment of acute exacerbations of chronic obstructive pulmonary disease (COPD) complicated by respiratory failure. A survey was undertaken to assess the availability of NIPPV for the treatment of acute exacerbations of COPD and to determine how NIPPV is delivered in hospitals in the UK. METHODS: A questionnaire was sent to consultants with an interest in respiratory medicine from 268 of the hospitals found in the BTS directory. The questionnaire enquired about the hospital as well as the availability of NIPPV in the hospital. If NIPPV was available in the hospital, details of implementation, staffing and funding were determined. RESULTS: Replies to the questionnaire were received from 98.5% of consultants. NIPPV was available in 48% of hospitals, these hospitals tending to serve larger populations and to have more respiratory physicians than the hospitals where NIPPV was not available. There was considerable regional variation in the availability of NIPPV. In hospitals where NIPPV was not available the reason(s) were lack of consultant training in 53%, lack of other staff training in 63%, financial in 63%, and doubt about the benefit of NIPPV in 15% of cases. In those hospitals where NIPPV was available, clinical practice varied greatly: 68% of centres treated fewer than 20 patients a year with this form of treatment and 9% treated more than 60 patients a year. Although NIPPV was paid for completely from the trust equipment budget in 46 hospitals (41%), other money such as research or charitable funds were used at least partially in the other hospitals and NIPPV was financed solely from research or charitable funds in 41 hospitals (37%). CONCLUSIONS: Equipment for NIPPV is available in less than half of the acute hospitals in the UK. In those in which it is available it is generally underused. Lack of training and problems with funding are generally given for the failure to introduce NIPPV.     

Randomised controlled trial of transcutaneous electrical muscle stimulation of the lower extremities in patients with chronic obstructive pulmonary disease

BACKGROUND: Although exercise training improves exercise tolerance in most patients with chronic obstructive pulmonary disease (COPD), some patients with severe disease may not be able to tolerate exercise training due to incapacitating breathlessness. Transcutaneous electrical muscle stimulation (TCEMS) has been shown to improve muscle strength, muscle mass, and performance in paraplegics, patients with knee ligament injury, and patients with peripheral vascular disease. We hypothesised that TCEMS of the lower extremities can improve muscle strength and exercise tolerance in patients with moderate to severe COPD. METHODS: A randomised controlled trial of TCEMS of the lower extremities was performed in 18 medically stable patients of mean (SD) age 60.0 (1.5) years with a mean forced expiratory volume in 1 second (FEV(1)) of 1.03 (0.10) l (38% predicted) and residual volume/total lung capacity (RV/TLC) of 59 (2)%. Stimulation of the lower extremities was performed three times a week, 20 minutes each session, for six continuous weeks. Quadriceps and hamstring muscle strength, exercise capacity, and peak oxygen uptake were measured at baseline and after 6 weeks of stimulation. RESULTS: TCEMS improved both the quadriceps strength (by 39.0 (20.4)% v 9.0 (8.1)%, p=0.046) and hamstring muscle strength (by 33.9 (13.0)% v 2.9 (4.7)%, p=0.038) in the treated (n=9) and sham treated (n=9) groups, respectively. The improvement in muscle strength carried over to better performance in the shuttle walk test in the treated group (36.1% v 1.6% in the treated and sham groups respectively, p=0.007, Mann-Whitney U test). There was no significant change in lung function, peak workload, or peak oxygen consumption in either group. Muscle stimulation was well tolerated by the patients with no dropouts and better than 95% compliance with the protocol. CONCLUSIONS: TCEMS of peripheral muscles can be a useful adjunct to the comprehensive pulmonary rehabilitation of patients with COPD.     

Non-invasive ventilation after extubation in patients with chronic obstructive airways disease: a randomised controlled trial

Non-invasive positive pressure ventilation (NPPV) is a well established therapy for acute respiratory failure in patients with chronic obstructive pulmonary disease, however its role in post-extubation period is uncertain. The objective of this study was to find the effect of NPPV on rate of re-intubation, intensive care unit and hospital stay, and physiological parameters in severe chronic obstructive pulmonary disease patients after planned extubation. Forty patients with severe chronic obstructive pulmonary disease were randomised immediately after planned extubation to receive NPPV (n=20) or conventional therapy (n=20). NPPV was delivered with mean levels of inspiratory positive-airway pressure of 12.10 +/- 1.37 cmH2O and expiratory positive-airway pressure of 6.50 +/- 1.00 cmH2O for a mean period of 34.75 +/- 10 hours for 7 to 11 hours/day. Patients in conventional therapy group received usual treatment. Reintubation rate among NPPV (15%) and conventional (25%) were similar (P=0.44). The duration of intensive care unit stay after extubation (2.05 +/- 2.15 vs 1.55 +/- 0.82 days, P=0.34) and hospital stay (16.10 +/- 6.29 vs 18.25 +/- 7.91 days, P=0.34) in both groups were comparable. Given the load of chronic obstructive pulmonary disease patients and wide availability of NPPV it is safe to recommend its use in these patients soon after extubation, although clear benefit is not documented in this study.     

Predictable normocapnia [correction of normocapnoea] in controlled ventilation of infants with Jackson Rees or Bain system

We have devised a formula for ventilator settings which provide normal minute ventilation without rebreathing during controlled ventilation using a Jackson Rees or Bain system. As VT = VS + VF- VL, where VT = delivered tidal volume, VS = set tidal volume, VF = the volume of fresh gas entering during the inspiratory phase and VL = the lost volume due to the compliance of the system, VS was derived: VS = VL + VT x [1-b/(1 + a)] where a = expiratory-to-inspiratory ratio and b = the ratio of fresh gas flow to the minute ventilation. It was evaluated in 62 infants. Arterial partial pressure of carbon dioxide (mean (SD)) was 4.6 (0.5) kPa (35 (4) mmHg) with a range of 3.42-5.78 kPa (26-44 mmHg). The 90th percentile was 5.1 kPa (39 mmHg). It is concluded that predictable normocapnia [corrected] can be conveniently achieved in infants in controlled ventilation with Jackson Rees or Bain system if our formula is applied.     

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

BACKGROUND: Nocturnal non-invasive ventilation (NIV) is an effective treatment for hypercapnic respiratory failure in patients with restrictive thoracic disease. We hypothesised that NIV may reverse respiratory failure by increasing the ventilatory response to carbon dioxide, reducing inspiratory muscle fatigue, or enhancing pulmonary mechanics. METHODS: Twenty patients with restrictive disease were studied at baseline (D0) and at 5-8 days (D5) and 3 months (3M). RESULTS: Mean (SD) daytime arterial carbon dioxide tension (Paco(2)) was reduced from 7.1 (0.9) kPa to 6.6 (0.8) kPa at D5 and 6.3 (0.9) kPa at 3M (p = 0.004), with the mean (SD) hypercapnic ventilatory response increasing from 2.8 (2.3) l/min/kPa to 3.6 (2.4) l/min/kPa at D5 and 4.3 (3.3) l/min/kPa at 3M (p = 0.044). No increase was observed in measures of inspiratory muscle strength including twitch transdiaphragmatic pressure, nor in lung function or respiratory system compliance. CONCLUSIONS: These findings suggest that increased ventilatory response to carbon dioxide is the principal mechanism underlying the long term improvement in gas exchange following NIV in patients with restrictive thoracic disease. Increases in respiratory muscle strength (sniff oesophageal pressure and sniff nasal pressure) correlated with reductions in the Epworth sleepiness score, possibly indicating an increase in the ability of patients to activate inspiratory muscles rather than an improvement in contractility.