Physiologic effects of early administered mask proportional assist ventilation in patients with chronic obstructive pulmonary disease and acute respiratory failure

Noninvasive positive pressure in acute exacerbations of chronic obstructive pulmonary disease

PURPOSE OF REVIEW

Noninvasive positive pressure ventilation (NIV) is standard of care for patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD). We review the most current evidence and highlight areas of uncertainty and ongoing research. We highlight key concepts for the clinician caring for patients with AECOPD which require NIV.

RECENT FINDINGS

Implementation of NIV in AECOPD is not uniform in spite of the evidence and guidelines. Initiation of NIV should be done early and following protocols. Low-intensity NIV remains the standard of care, although research and guidelines are evaluating higher intensity NIV. Scores to predict NIV failure continue to be refined to allow early identification and interventions. Several areas of uncertainty remain, among them are interventions to improve tolerance, length of support and titration and nutritional support during NIV.

SUMMARY

The use of NIV in AECOPD is the standard of care as it has demonstrated benefits in several patient-centered outcomes. Current developments and research is related to the implementation and adjustment of NIV.

Prolonged Weaning: S2k Guideline Published by the German Respiratory Society

Mechanical ventilation (MV) is an essential part of modern intensive care medicine. MV is performed in patients with severe respiratory failure caused by respiratory muscle insufficiency and/or lung parenchymal disease; that is, when other treatments such as medication, oxygen administration, secretion management, continuous positive airway pressure (CPAP), or nasal high-flow therapy have failed. MV is required for maintaining gas exchange and allows more time to curatively treat the underlying cause of respiratory failure. In the majority of ventilated patients, liberation or "weaning" from MV is routine, without the occurrence of any major problems. However, approximately 20% of patients require ongoing MV, despite amelioration of the conditions that precipitated the need for it in the first place. Approximately 40-50% of the time spent on MV is required to liberate the patient from the ventilator, a process called "weaning". In addition to acute respiratory failure, numerous factors can influence the duration and success rate of the weaning process; these include age, comorbidities, and conditions and complications acquired during the ICU stay. According to international consensus, "prolonged weaning" is defined as the weaning process in patients who have failed at least 3 weaning attempts, or require more than 7 days of weaning after the first spontaneous breathing trial (SBT). Given that prolonged weaning is a complex process, an interdisciplinary approach is essential for it to be successful. In specialised weaning centres, approximately 50% of patients with initial weaning failure can be liberated from MV after prolonged weaning. However, the heterogeneity of patients undergoing prolonged weaning precludes the direct comparison of individual centres. Patients with persistent weaning failure either die during the weaning process, or are discharged back to their home or to a long-term care facility with ongoing MV. Urged by the growing importance of prolonged weaning, this Sk2 Guideline was first published in 2014 as an initiative of the German Respiratory Society (DGP), in conjunction with other scientific societies involved in prolonged weaning. The emergence of new research, clinical study findings and registry data, as well as the accumulation of experience in daily practice, have made the revision of this guideline necessary. The following topics are dealt with in the present guideline: Definitions, epidemiology, weaning categories, underlying pathophysiology, prevention of prolonged weaning, treatment strategies in prolonged weaning, the weaning unit, discharge from hospital on MV, and recommendations for end-of-life decisions. Special emphasis was placed on the following themes: (1) A new classification of patient sub-groups in prolonged weaning. (2) Important aspects of pulmonary rehabilitation and neurorehabilitation in prolonged weaning. (3) Infrastructure and process organisation in the care of patients in prolonged weaning based on a continuous treatment concept. (4) Changes in therapeutic goals and communication with relatives. Aspects of paediatric weaning are addressed separately within individual chapters. The main aim of the revised guideline was to summarize both current evidence and expert-based knowledge on the topic of "prolonged weaning", and to use this information as a foundation for formulating recommendations related to "prolonged weaning", not only in acute medicine but also in the field of chronic intensive care medicine. The following professionals served as important addressees for this guideline: intensivists, pulmonary medicine specialists, anaesthesiologists, internists, cardiologists, surgeons, neurologists, paediatricians, geriatricians, palliative care clinicians, rehabilitation physicians, intensive/chronic care nurses, physiotherapists, respiratory therapists, speech therapists, medical service of health insurance, and associated ventilator manufacturers.

Non-invasive ventilation for the management of acute hypercapnic respiratory failure due to exacerbation of chronic obstructive pulmonary disease

BACKGROUND

Non-invasive ventilation (NIV) with bi-level positive airway pressure (BiPAP) is commonly used to treat patients admitted to hospital with acute hypercapnic respiratory failure (AHRF) secondary to an acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

OBJECTIVES

To compare the efficacy of NIV applied in conjunction with usual care versus usual care involving no mechanical ventilation alone in adults with AHRF due to AECOPD. The aim of this review is to update the evidence base with the goals of supporting clinical practice and providing recommendations for future evaluation and research.

SEARCH METHODS

We identified trials from the Cochrane Airways Group Specialised Register of trials (CAGR), which is derived from systematic searches of bibliographic databases including the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), the Allied and Complementary Medicine Database (AMED), and PsycINFO, and through handsearching of respiratory journals and meeting abstracts. This update to the original review incorporates the results of database searches up to January 2017.

SELECTION CRITERIA

All randomised controlled trials that compared usual care plus NIV (BiPAP) versus usual care alone in an acute hospital setting for patients with AECOPD due to AHRF were eligible for inclusion. AHRF was defined by a mean admission pH < 7.35 and mean partial pressure of carbon dioxide (PaCO2) > 45 mmHg (6 kPa). Primary review outcomes were mortality during hospital admission and need for endotracheal intubation. Secondary outcomes included hospital length of stay, treatment intolerance, complications, changes in symptoms, and changes in arterial blood gases.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the selection criteria to determine study eligibility, performed data extraction, and determined risk of bias in accordance with Cochrane guidelines. Review authors undertook meta-analysis for data that were both clinically and statistically homogenous, and analysed data as both one overall pooled sample and according to two predefined subgroups related to exacerbation severity (admission pH between 7.35 and 7.30 vs below 7.30) and NIV treatment setting (intensive care unit-based vs ward-based). We reported results for mortality, need for endotracheal intubation, and hospital length of stay in a 'Summary of findings' table and rated their quality in accordance with GRADE criteria.

MAIN RESULTS

We included in the review 17 randomised controlled trials involving 1264 participants. Available data indicate that mean age at recruitment was 66.8 years (range 57.7 to 70.5 years) and that most participants (65%) were male. Most studies (12/17) were at risk of performance bias, and for most (14/17), the risk of detection bias was uncertain. These risks may have affected subjective patient-reported outcome measures (e.g. dyspnoea) and secondary review outcomes, respectively.Use of NIV decreased the risk of mortality by 46% (risk ratio (RR) 0.54, 95% confidence interval (CI) 0.38 to 0.76; N = 12 studies; number needed to treat for an additional beneficial outcome (NNTB) 12, 95% CI 9 to 23) and decreased the risk of needing endotracheal intubation by 65% (RR 0.36, 95% CI 0.28 to 0.46; N = 17 studies; NNTB 5, 95% CI 5 to 6). We graded both outcomes as 'moderate' quality owing to uncertainty regarding risk of bias for several studies. Inspection of the funnel plot related to need for endotracheal intubation raised the possibility of some publication bias pertaining to this outcome. NIV use was also associated with reduced length of hospital stay (mean difference (MD) -3.39 days, 95% CI -5.93 to -0.85; N = 10 studies), reduced incidence of complications (unrelated to NIV) (RR 0.26, 95% CI 0.13 to 0.53; N = 2 studies), and improvement in pH (MD 0.05, 95% CI 0.02 to 0.07; N = 8 studies) and in partial pressure of oxygen (PaO2) (MD 7.47 mmHg, 95% CI 0.78 to 14.16 mmHg; N = 8 studies) at one hour. A trend towards improvement in PaCO2 was observed, but this finding was not statistically significant (MD -4.62 mmHg, 95% CI -11.05 to 1.80 mmHg; N = 8 studies). Post hoc analysis revealed that this lack of benefit was due to the fact that data from two studies at high risk of bias showed baseline imbalance for this outcome (worse in the NIV group than in the usual care group). Sensitivity analysis revealed that exclusion of these two studies resulted in a statistically significant positive effect of NIV on PaCO2. Treatment intolerance was significantly greater in the NIV group than in the usual care group (risk difference (RD) 0.11, 95% CI 0.04 to 0.17; N = 6 studies). Results of analysis showed a non-significant trend towards reduction in dyspnoea with NIV compared with usual care (standardised mean difference (SMD) -0.16, 95% CI -0.34 to 0.02; N = 4 studies). Subgroup analyses revealed no significant between-group differences.

AUTHORS' CONCLUSIONS

Data from good quality randomised controlled trials show that NIV is beneficial as a first-line intervention in conjunction with usual care for reducing the likelihood of mortality and endotracheal intubation in patients admitted with acute hypercapnic respiratory failure secondary to an acute exacerbation of chronic obstructive pulmonary disease (COPD). The magnitude of benefit for these outcomes appears similar for patients with acidosis of a mild (pH 7.30 to 7.35) versus a more severe nature (pH < 7.30), and when NIV is applied within the intensive care unit (ICU) or ward setting.

Mechanical ventilation in patients with chronic obstructive pulmonary disease and bronchial asthma

Chronic obstructive pulmonary disease (COPD) and bronchial asthma often complicate the surgical patients, leading to post-operative morbidity and mortality. Many authors have tried to predict post-operative pulmonary complications but not specifically in COPD. The aim of this review is to provide recent evidence-based guidelines regarding predictors and ventilatory strategies for mechanical ventilation in COPD and bronchial asthma patients. Using Google search for indexing databases, a search for articles published was performed using various combinations of the following search terms: ‘Predictors’; ‘mechanical ventilation’; COPD’; ‘COPD’; ‘bronchial asthma’; ‘recent strategies’. Additional sources were also identified by exploring the primary reference list.

Chronic Obstructive Pulmonary Disease: Inpatient Management

This article outlines the management of patients with acute exacerbations of chronic obstructive pulmonary disease (COPD), which are common in the course of chronic COPD and are associated with substantial morbidity. There are numerous guidelines, but literature suggests that there is substantial variation in care in patients with acute exacerbations of COPD. Key components of acute therapy for most patients include oral steroids, antibiotics, nebulizers, oxygen, and early consideration of noninvasive ventilation. Adjuvant components of care include venous thromboembolism prophylaxis, appropriate immunizations, counseling for smoking cessation, and consideration of pulmonary rehabilitation.

Use of indigenous bubble CPAP during swine flu pandemic in Pune, India

OBJECTIVE

To assess the effectiveness of an indigenously assembled Nasal Bubble CPAP (NB-CPAP) in children during present swine flu pandemic presenting with acute hypoxemic respiratory failure; in improving gas exchange and vital signs; and assess method safety.

METHODS

Thirty Six children with acute hypoxemic respiratory failure admitted to swine flu ICU during the present H1NI pandemic were included (18 confirmed H1N1 positive and 18 confirmed H1N1 negative). After a baseline Arterial Blood Gas, all children received Oxygen via indigenous NB-CPAP Circuit which gave expiratory positive airway pressure of 5 cm water and delivered an FiO(2) of around 70%. Vital signs, pH, PaO(2), PaCO(2), PO(2)/FiO(2) and O(2) saturation were recorded at start and at 6 h into the study.

RESULTS

Median age of the patients was 18 months (58% males, 42% females). Respiratory rate and heart rate improved significantly with indigenous NB-CPAP after 6 h of treatment compared with admission (p < 0.0001 and p < 0.001), respectively. At the end of 6 h on NB-CPAP,PaO(2) (p < 0.0001), PCO(2) (p < 0.0001), PO(2)/FiO(2) (p < 0.0002) and O(2) saturation (p < 0.001) improved significantly. Median duration of NB-CPAP use was 2 days and none required endotracheal intubation. The median hospital stay was 7 days.

CONCLUSIONS

Indigenous NB-CPAP improves hypoxemia and signs and symptoms in hemodynamically stable children with acute respiratory failure due to influenza like illness. It is a cost-effective, safe, well tolerated circuit in highly demanding pandemic situations and may prevent progression to intubation.

A prospective, randomized, controlled trial of noninvasive ventilation in pediatric acute respiratory failure

OUTCOMES

To compare the benefits of noninvasive ventilation (NIV) plus standard therapy vs. standard therapy alone in children with acute respiratory failure; assess method effectiveness in improving gas exchange and vital signs; and assess method safety.

DESIGN

Prospective, randomized, controlled study. SITE: Two pediatric intensive care units in Santiago, Chile, at Clínica Santa María and Clínica Dávila, respectively.

PATIENTS AND METHODS

Fifty patients with acute respiratory failure admitted to pediatric intensive care units were recruited; 25 patients were randomly allocated to noninvasive inspiratory positive airway pressure and expiratory positive airway pressure plus standard therapy (study group); the remaining 25 were given standard therapy (control group). Both groups were comparable in demographic terms.

INTERVENTIONS AND MEASUREMENTS

The study group received NIV under inspiratory positive airway pressure ranging between 12 cm and 18 cm H2O and expiratory positive airway pressure between 6 cm and 12 cm H2O. Vital signs (cardiac and respiratory frequency), Po2, Pco2, pH, and Po2/Fio2 were recorded at the start and 1, 6, 12, 24, and 48 hrs into the study.

RESULTS

Heart rate and respiratory rate improved significantly with NIV. Heart rate and respiratory rate were significantly lower after 1 hr of treatment compared with admission (p = 0.0009 and p = 0.004, respectively). The trend continued over time, heart rate being significantly lower than control after the first hour and heart rate after 6 hrs. With NIV, Po2/Fio2 improved significantly from the first hour. The endotracheal intubation was significantly lower (28%) in the NIV group than in the control group (60%; p = 0.045).

CONCLUSIONS

NIV improves hypoxemia and the signs and symptoms of acute respiratory failure. NIV seems to afford these patients protection from endotracheal intubation.

Proportional-assist ventilation compared with pressure-support ventilation during exercise in volunteers with external thoracic restriction

OBJECTIVES

Proportional-assist ventilation (PAV) is able to unload respiratory muscles in proportion to the subject's inspiratory effort. However, leak-related alterations in the flow signal, effort-induced modifications in respiratory mechanics, or approximate adjustment of PAV could jeopardize such a theory. The aim of this study was to compare noninvasive PAV and pressure-support ventilation (PSV) in healthy volunteers with external thoracic restriction at rest and during exercise.

DESIGN

Prospective, crossover, randomized study.

SETTING

Investigation unit in a nonteaching hospital.

PATIENTS

Seven volunteers with external thoracic restriction.

INTERVENTION

After external thoracic restriction to increase elastance (9.00 +/- 1.63 cm H2O/L estimated from the level of elastic assistance), PAV and PSV were compared at rest and during exercise (90 W for 10 mins).

MEASUREMENTS AND MAIN RESULTS

Flow, airway pressure, and changes in esophageal pressure were measured, and the tidal volume (Vt) and inspiratory muscle effort indexes were calculated. At rest, all variables were comparable during PSV and PAV. Exercise produced a 200% increased in Vt with no change in the breathing frequency and a 400% increased in inspiratory muscle effort indexes. During exercise, peak inspiratory airway pressure was significantly higher with PAV than with PSV (24 +/- 5 vs. 10 +/- 2 cm H2O, p <.05). The Vt and breathing frequency (23 +/- 4 vs. 24 +/- 3 breaths/min) were similar, but the inspiratory muscle effort indexes were significantly lower with PAV than with PSV. A significant linear correlation was found between changes in esophageal pressure and the peak inspiratory airway pressure during PAV (r =.94, p =.0001), whereas, as expected, it was not the case during PSV (r =.27, p =.34).

CONCLUSION

In volunteers with external thoracic restriction mimicking a patient with increased elastic work of breathing, the breathing pattern at rest and during exercise were comparable with PSV and PAV, whereas inspiratory muscle effort was lower with PAV during exercise because of the significant automatic increase in assistance with PAV.

Effect of different levels of pressure support and proportional assist ventilation on breathing pattern, work of breathing and gas exchange in mechanically ventilated hypercapnic COPD patients with acute respiratory failure

BACKGROUND

Proportional assist ventilation (PAV) has been shown to maintain better patient-ventilator synchrony than pressure support ventilation (PSV); however, its clinical advantage regarding invasive ventilation of COPD patients has not been clarified.

OBJECTIVES

To compare the effect of PAV and PSV on respiratory parameters of hypercapnic COPD patients with acute respiratory failure (ARF).

METHODS

Nine intubated hypercapnic COPD patients were placed on the PAV or PSV mode in random sequence. For each mode, four levels (L1-L4) of support were applied. At each level, blood gases, flow, tidal volume (VT), airway pressure (Paw), esophageal pressure (Pes) (n = 7), patient respiratory rate (fp), ventilator rate (fv), missing efforts (ME = fp - fv) were measured.

RESULTS

We found increases in ME with increasing levels of PSV but not with PAV. PO2 and VT increased whereas PCO2 decreased significantly with increasing levels of PSV (p < 0.05). With PAV, PCO2 decreased and VT increased significantly only at L4 whereas PO2 increased from L1 to L4. Runaways were observed at L3 and L4 of PAV. The pressure-time product (PTP) was determined for effective and missing breaths. The mean total PTP per minute (of effective plus missing breaths) was 160 +/- 57 cm H2O/s.min in PSV and 194 +/- 60 cm H2O/s.min in PAV.

CONCLUSION

We conclude that in COPD patients with hypercapnic ARF, with increasing support, PSV causes the appearance of ME whereas PAV develops runaway phenomena, due to the different patient-ventilator interaction; however, these do not limit the improvement of blood gases with the application of both methods.

Non-invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease

BACKGROUND

Non-invasive positive pressure ventilation (NPPV) is being used increasingly in the management of patients admitted to hospital with acute respiratory failure secondary to an exacerbation of chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To determine the efficacy of NPPV in the management of patients with respiratory failure due to an acute exacerbation of COPD.

SEARCH STRATEGY

An initial search was performed using the Cochrane Airways Group trials register and other relevant electronic databases. An updated search was conducted in September 2003 and another in April 2004.

SELECTION CRITERIA

Randomised controlled trials comparing NPPV plus usual medical care (UMC) versus UMC alone were selected. Trials needed to recruit adult patients admitted to hospital with respiratory failure due to an exacerbation of COPD and with PaCO2 > 6 kPa (45 mmHg).

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected articles for inclusion, evaluated methodological quality of the studies and abstracted the data.

MAIN RESULTS

Fourteen studies were included in the review. NPPV resulted in decreased mortality (Relative Risk 0.52; 95%CI 0.35 to 0.76), decreased need for intubation (RR 0.41; 95%CI 0.33 to 0.53), reduction in treatment failure (RR 0.48; 95%CI 0.37 to 0.63), rapid improvement within the first hour in pH (Weight Mean Difference 0.03; 95%CI 0.02 to 0.04), PaCO2 (WMD -0.40 kPa; 95%CI -0.78 to -0.03) and respiratory rate (WMD -3.08 bpm; 95%CI -4.26 to -1.89). In addition, complications associated with treatment (RR 0.38; 95%CI 0.24 to 0.60) and length of hospital stay (WMD -3.24 days; 95%CI -4.42 to -2.06) was also reduced in the NPPV group.

REVIEWERS' CONCLUSIONS

Data from good quality randomised controlled trials show benefit of NPPV as first line intervention as an adjunct therapy to usual medical care in all suitable patients for the management of respiratory failure secondary to an acute exacerbation of COPD. NPPV should be considered early in the course of respiratory failure and before severe acidosis ensues, as a means of reducing the likelihood of endotracheal intubation, treatment failure and mortality.

Non-invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease

BACKGROUND

Non-invasive positive pressure ventilation (NPPV) is being used increasingly in the management of patients admitted to hospital with acute respiratory failure secondary to an exacerbation of chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To determine the efficacy of NPPV in the management of patients with respiratory failure due to an acute exacerbation of COPD.

SEARCH STRATEGY

An initial search was performed using the Cochrane Airways Group trials register and other relevant electronic databases. An updated search was conducted in September 2003.

SELECTION CRITERIA

Randomised controlled trials comparing NPPV plus usual medical care (UMC) versus UMC alone were selected. Trials needed to recruit adult patients admitted to hospital with respiratory failure due to an exacerbation of COPD and with PaCO(2) > 6 kPa (45 mmHg).

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected articles for inclusion, evaluated methodological quality of the studies and abstracted the data.

MAIN RESULTS

Fourteen studies were included in the review. NPPV resulted in decreased mortality (Relative Risk 0.52; 95%CI 0.35, 0.76), decreased need for intubation (RR 0.41; 95%CI 0.33, 0.53), reduction in treatment failure (RR 0.48; 95%CI 0.37, 0.63), rapid improvement within the first hour in pH (Weight Mean Difference 0.03; 95%CI 0.02, 0.04), PaCO(2) (WMD -0.40 kPa; 95%CI -0.78, -0.03) and respiratory rate (WMD -3.08 bpm; 95%CI -4.26, -1.89). In addition, complications associated with treatment (RR 0.38; 95%CI 0.24, 0.60) and length of hospital stay (WMD -3.24 days; 95%CI -4.42, -2.06) was also reduced in the NPPV group.

REVIEWER'S CONCLUSIONS

Data from good quality randomised controlled trials show benefit of NPPV as first line intervention as an adjunct therapy to usual medical care in all suitable patients for the management of respiratory failure secondary to an acute exacerbation of COPD. NPPV should be considered early in the course of respiratory failure and before severe acidosis ensues, as a means of reducing the likelihood of endotracheal intubation, treatment failure and mortality.

Noninvasive pressure support versus proportional assist ventilation in acute respiratory failure

BACKGROUND

Although conventional pressure ventilation (PSV) decreases the rate of intubation in acute respiratory failure, patient-ventilator dyssynchrony is a frequent cause of failure. In proportional assist ventilation (PAV), pressure is applied by the ventilator in proportion to the patient-generated volume and flow; therefore, there is automatic synchrony between the patient's effort and the ventilatory cycle.

OBJECTIVE

The aim of this study was to compare the effects of PSV and PAV during noninvasive ventilation in the treatment of acute respiratory failure.

DESIGN

Prospective randomised study.

SETTING

A multidisciplinary 24-bed intensive care unit of an acute-care teaching hospital in Alicante, Spain. PATIENTS. This study included 117 consecutive adult patients with acute respiratory failure randomised to noninvasive ventilation delivered by PSV ( n = 59) or PAV ( n = 58).

MEASUREMENTS AND RESULTS

There were no statistically significant differences between patients assigned to each mode of ventilation with regard to baseline parameters and aetiological diagnoses of acute respiratory failure. With regard to outcome data, no significant differences were observed between PSV and PAV in the frequency of intubation (37% vs 34%), mortality rate (29% vs 28%), and mean length of stay. Subjective comfort (0-10 visual analogue scale) was rated higher and intolerance occurred less frequently (3.4% vs 15%, P = 0.03) in the PAV than in the PSV mode.

CONCLUSIONS

Although PAV seems more comfortable and intolerance occurred less frequently, no major differences exist in terms of physiological improvement or in terms of outcomes when comparing PSV and PAV.

Acute exacerbations of chronic obstructive pulmonary disease

This article discusses the definition, pathophysiology, cause, clinical presentation, laboratory work-up, and treatment of chronic obstructive pulmonary disease (COPD) exacerbation. The focus is on the presentation of acute exacerbations of COPD in the emergency department and the available evidence for testing and treatment.

Evaluation and initial management of the patient in respiratory distress

Evaluation of the patient in acute respiratory distress poses a complex problem to the emergency physician. Because of the heterogeneity of the population of patients presenting in acute respiratory distress, there is a paucity of evidence-based medicine recommendations. Practice habit dictates most of our diagnostic and therapeutic approach. It is of paramount importance to understand the limitations of history, physical examination, and diagnostic screening studies in evaluating and treating patients with respiratory distress. The emergency physician should become aware of the benefits of NPPV in the management of respiratory failure. Essential to the management of these patients is the ability to anticipate difficulty in airway management and the formulation of alternative airway strategies.

New modes of mechanical ventilation: proportional assist ventilation, neurally adjusted ventilatory assist, and fractal ventilation

Increased knowledge of the mechanisms that determine respiratory failure has led to the development of new technologies aimed at improving ventilatory treatment. Proportional assist ventilation and neurally adjusted ventilatory assist have been designed with the goal of improving patient-ventilator interaction by matching the ventilator support with the neural output of the respiratory centers. With proportional assist ventilation, the support is continuously readjusted in proportion to the predicted inspiratory effort. Neurally adjusted ventilatory assist is an experimental mode in which the assistance is delivered in proportion to the electrical activity of the diaphragm, assessed by means of an esophageal electrode. Biologically variable (or fractal) ventilation is a new, volume-targeted, controlled ventilation mode aimed at improving oxygenation; it incorporates the breath-to-breath variability that characterizes a natural breathing pattern.

Proportional assist ventilation (PAV): a significant advance or a futile struggle between logic and practice?

Proportional assist ventilation is a promising addition to other more conventional modes of mechanical ventilation with the theoretical advantage of improving patient-ventilator interaction. It may also be of use as a diagnostic tool in the control of breathing in mechanically ventilated patients.

Noninvasive proportional assist ventilation compared with noninvasive pressure support ventilation in hypercapnic acute respiratory failure

OBJECTIVES

To compare short-term administration of noninvasive proportional assist ventilation (NIV-PAV) and pressure support ventilation (NIV-PSV).

DESIGN

Prospective, crossover, randomized study.

SETTING

Medicosurgical intensive care unit in a nonteaching hospital.

PATIENTS

Twelve chronic obstructive pulmonary disease patients admitted for hypercapnic acute respiratory failure.

INTERVENTION

NIV-PSV and NIV-PAV given in a randomized order after baseline evaluation in continuous positive airway pressure. Using a flow-triggering ventilator, NIV-PAV was adjusted using the runaway method and compared with NIV-PSV at similar peak inspiratory airway pressure.

MEASUREMENTS AND MAIN RESULTS

Flow, airway pressure, and changes in esophageal pressure were measured and the tidal volume, the patient's inspiratory work of breathing, and the esophageal pressure--time product were calculated. Arterial pH and PaCO(2) were measured and breathing comfort was assessed using a visual analogic scale. Peak inspiratory airway pressure (17 +/- 3 cm H(2)O) and tidal volume were similarly increased with the two modalities with no change in respiratory rate. The change in esophageal pressure was similarly decreased (from 20 +/- 8 cm H(2)O in continuous positive airway pressure to 12 +/- 7 in NIV-PSV and 10 +/- 5 cm H(2)O in NIV-PAV) as well as inspiratory muscle effort indexes. Arterial pH and PaCO(2) were similarly improved. Breathing comfort was significantly improved in NIV-PAV (+38 +/- 38%) but not in NIV-PSV (+11 +/- 23%). The tidal volume was more variable in NIV-PAV (89 +/- 18%) than in NIV-PSV (15 +/- 8%) and changes in tidal volume variability were significantly correlated (p =.02) with changes in breathing comfort.

CONCLUSIONS

In chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure, NIV-PAV was able to unload inspiratory muscles similarly to NIV-PSV but may be more comfortable than NIV-PSV.

Non-invasive proportional assist and pressure support ventilation in patients with cystic fibrosis and chronic respiratory failure

BACKGROUND

Patients with advanced cystic fibrosis can benefit from non-invasive positive pressure ventilation (NPPV) for the treatment of acute decompensation as well as for the management of chronic respiratory failure. This study was undertaken to compare the physiological effects of non-invasive proportional assist ventilation (PAV) and pressure support ventilation (PSV) on ventilatory pattern, transcutaneous blood gas tensions, and diaphragmatic effort in stable patients with cystic fibrosis and chronic CO2 retention.

METHODS

In 12 patients two periods of spontaneous breathing were followed randomly by PSV (12 (3) cm H2O) and PAV (flow assist 4.9 (1.3) cm H2O/l.s, volume assist 18.9 (5.1) cm H2O/l) set for the patient's comfort and administered for 40 minutes with 2 cm H2O continuous positive airway pressure. Ventilatory pattern, transcutaneous blood gas tensions, and surface diaphragmatic electromyography were measured in the last 10 minutes of each application.

RESULTS

On average, both PSV and PAV improved ventilation (+30%), tidal volume (+30%), and transcutaneous CO2 (-7%) while reducing diaphragmatic activity (-30% with PSV, -20% with PAV). Mean inspiratory airway pressure was lower during PAV than during PSV (9.7 (1.9) and 12.9 (2.7) cm H2O, respectively; p<0.05). The mean coefficient of variation of tidal volume was about 20% (range 11-39%) during spontaneous breathing and did not change with either PAV or PSV.

CONCLUSIONS

These results show that short term administration of nasal PAV and PSV to patients with stable cystic fibrosis with chronic respiratory insufficiency is well tolerated, improves ventilation and blood gas tensions, and unloads the diaphragm.

Noninvasive proportional assist ventilation for acute respiratory insufficiency. Comparison with pressure support ventilation

Noninvasive positive pressure ventilation (NPPV) is usually applied using pressure support ventilation (PSV). Proportional assist ventilation (PAV) is a newer mode that delivers assisted ventilation in proportion to patient effort. We hypothesized that PAV for NPPV would support gas exchange and avoid intubation as well as PSV and be more comfortable and tolerable for patients. Adult patients with acute respiratory insufficiency were randomized to receive NPPV with PAV delivered using the Respironics Vision ventilator or PSV using a Puritan-Bennett 7200ae critical care ventilator. Each mode was adjusted to relieve dyspnea and improve gas exchange until patients met weaning or intubation criteria, died, or refused to continue. Twenty-one and 23 patients were entered into the PAV and PSV groups, respectively, and had similar diagnoses and baseline characteristics, although pH was slightly lower in the PAV group (7.30 versus 7.35, p = 0.02). Mortality and intubation rates were similar, but refusal rate was lower, reduction in respiratory rate was more rapid, and there were fewer complications in the PAV group. We conclude that use of the PAV mode is feasible for noninvasive therapy of acute respiratory insufficiency. Compared with PSV delivered with the Puritan-Bennett 7200ae, PAV is associated with more rapid improvements in some physiologic variables and is better tolerated.

In vivo physiologic comparison of two ventilators used for domiciliary ventilation in children with cystic fibrosis

OBJECTIVE

Home noninvasive mechanical ventilation (NIMV) is used with increasing frequency for the treatment of patients with respiratory failure caused by cystic fibrosis, yet the optimal mode of ventilation in such children is unknown. We compared the physiologic short-term effects of two ventilators with different modes (one pressure support and the other assist control/volume-targeted [AC/VT]) commonly used for domiciliary ventilation.

DESIGN

Prospective, randomized, crossover comparison of two ventilators with different modes.

SETTING

Tertiary pediatric university hospital.

PATIENTS

Eight children with cystic fibrosis (age, 11-17 yrs) and chronic respiratory failure (pH 7.4 +/- 0.0; PaO2, 57.5 +/- 7.5 torr; PaCO2, 46.1 +/- 2.5 torr), naive to NIMV.

INTERVENTIONS

Two 20-min runs of pressure support and AC/VT ventilation were performed in random order, each run being preceded and followed by 20 mins of spontaneous breathing.

MEASUREMENTS

Flow and airway pressure and esophageal and gastric pressures were measured to calculate esophageal (PTPes) and diaphragmatic pressure-time product (PTPdi) and the work of breathing.

RESULTS

The two NIMV sessions significantly improved blood gas variables and increased tidal volume with no change in respiratory rate. Indexes of respiratory effort decreased significantly during the two modes of NIMV compared with spontaneous breathing, with PTPdi/min decreasing from 497.8 +/- 115.4 cm H2O x sec x min(-1) during spontaneous breathing to 127.8 +/- 98.3 cm H2O x sec x min(-1) and 184.3 +/- 79.8 cm H2O x sec x min(-1), during AC/VT and pressure support, respectively (p <.0001), and the work of breathing decreasing from 1.83 +/- 0.12 J.L-1 during spontaneous breathing to 0.48 +/- 0.32 J.L-1 and 0.75 +/- 0.30 J.L-1, during AC/VT and pressure support, respectively (p <.0001). In addition, the effect of AC/VT ventilation was significantly superior to pressure support judged by PTPes and the work of breathing, but this result was explained by three patients who adapted extremely well to the AC/VT ventilation, with the disappearance of ventilator triggering, in effect adopting a controlled mode. There was a correlation between the improvement in PTPdi/min or the work of breathing and patient's subjective impression of comfort during the AC/VT ventilation.

CONCLUSIONS

In awake, stable children with cystic fibrosis, both AC/VT and pressure support unloaded the respiratory muscles. The disappearance of ventilator triggering occurred in a subgroup of patients during AC/VT ventilation, and this explained the good tolerance and the superiority of this mode in the present study.

Oscillatory resistance measured during noninvasive proportional assist ventilation

Setting proportional assist ventilation (PAV) requires the measurement of patient resistance and elastance. To avoid patient sedation/paralysis or the use of an esophageal balloon, noninvasive PAV is indirectly set by the "runaway" method or in accordance with patient comfort. The aim of this study was to ascertain whether the forced oscillation technique (FOT) applied by the ventilator during noninvasive PAV is useful in assessing patient respiratory resistance. Nasal PAV was applied to 14 patients with severe chronic obstructive pulmonary disease. During PAV a modified ventilator applied a 5-Hz pressure oscillation to noninvasively assess FOT resistance (Rrs). Lung resistance (RL) was measured in seven of the patients by using an esophageal balloon. Moreover, measurements were also performed in five of the patients when PAV was applied through the mouth. Rrs was close to RL both during nasal (Rrs = 8.9 +/- 3.1, RL = 9.0 +/- 2.6; cm H(2)O x s/L; n = 7, p > 0.05) and mouth (Rrs = 5.6 +/- 2.1, RL = 5.8 +/- 1.4; cm H(2)O x s/L; n = 5, p > 0.05) breathing. Rrs was slightly greater than the maximum value of flow assistance applied during the setting of PAV (FAmax): 11.1 +/- 5.4 and 9.5 +/- 2.9 cm H(2)O x s/L, respectively (n = 14, p > 0.05), both variables being significantly correlated (r = 0.72, p < 0.05). FOT applied by the PAV ventilator allowed the assessment of patient resistance. These results suggest that FOT could be useful in setting PAV flow assistance and in automatically and continuously updating this setting in accordance with patient resistance.