Oxygen-induced hypercarbia in obstructive pulmonary disease

Impact of Using a Non-Rebreathing Mask in Patients With Respiratory Failure

BACKGROUND

Liberal oxygen therapy might increase the mortality rate of patients. Non-rebreathing masks (NRM) are a high-flow, non-invasive oxygen device that can provide oxygen concentration up to 95%. This study aimed to determine the impact of using NRM in patients with respiratory failure.

METHODS

This retrospective cohort study was conducted in four medical institutions in Taiwan from January 2010 to December 2016. The association between mortality and NRM use before receiving ventilator support in patients with respiratory failure in the emergency department was analyzed. Patients were divided into the NRM treatment and no NRM treatment groups. A 1:4 propensity score matching was conducted. Regarding the duration of NRM use, treatments were grouped as 0 h, 0-1 h, 1-2 h, and >2 h.

RESULTS

A total of 18,749 patients were included, with 1074 using NRM. After propensity score matching, 1028 patients using NRM (0-1 h: 508, 1-2 h: 193, and >2 h: 327) and 4112 patients not using NRM were analyzed. The 30-day mortality rates were 29.1%, 28.5%, 27.5%, and 35.5% in the 0 h, 0-1 h, 1-2 h, and >2 h treatment groups, respectively. Patients with respiratory failure due to pulmonary disease using NRM over 2 h had a higher mortality rate than patients not using NRM (hazard ratio: 1.3, 95% CI: 1.01-1.66).

CONCLUSIONS

Prolonged use of NRM in patients with respiratory failure due to pulmonary disease possibly increases mortality.

Evaluation of a Novel Ear Pulse Oximeter: Towards Automated Oxygen Titration in Eyeglass Frames

Current oxygen delivery modes lack monitoring and can be cumbersome for patients with chronic respiratory diseases. Integrating a pulse oximeter and nasal oxygen cannulas into eyeglasses would reduce the burden of current solutions. An ear pulse oximeter (OxyFrame) was evaluated on 16 healthy volunteers and 20 hypoxemic patients with chronic respiratory diseases undergoing a prespecified protocol simulating daily activities. Correlation, error, and accuracy root mean square error (ARMS) were calculated to compare SpO2 measured by OxyFrame, a standard pulse oximeter (MASIMO), and arterial blood gas analysis (aBGA). SpO2 measured by OxyFrame and MASIMO correlated strongly in volunteers, with low error and high accuracy (r = 0.85, error = 0.2 ± 2.9%, ARMS = 2.88%). Performances were similar in patients (r = 0.87, error 0 ± 2.5%, ARMS = 2.49% compared with MASIMO; and r = 0.93, error = 0.4 ± 1.9%, ARMS = 1.94% compared with aBGA). However, the percentage of rejected measurements was high (volunteers 77.2%, patients 46.9%). The OxyFrame cavum conchae pulse oximeter was successfully evaluated, and demonstrated accurate SpO2 measurements, compliant with ISO 80601-2-61:2017. Several reasons for the high rejection rate were identified, and potential solutions were proposed, which might be valuable for optimization of the sensor hardware.

Sleep in chronic respiratory disease: COPD and hypoventilation disorders

COPD and obstructive sleep apnoea (OSA) are highly prevalent and different clinical COPD phenotypes that influence the likelihood of comorbid OSA. The increased lung volumes and low body mass index (BMI) associated with the predominant emphysema phenotype protects against OSA whereas the peripheral oedema and higher BMI often associated with the predominant chronic bronchitis phenotype promote OSA. The diagnosis of OSA in COPD patients requires clinical awareness and screening questionnaires which may help identify patients for overnight study. Management of OSA-COPD overlap patients differs from COPD alone and the survival of overlap patients treated with nocturnal positive airway pressure is superior to those untreated. Sleep-related hypoventilation is common in neuromuscular disease and skeletal disorders because of the effects of normal sleep on ventilation and additional challenges imposed by the underlying disorders. Hypoventilation is first seen during rapid eye movement (REM) sleep before progressing to involve non-REM sleep and wakefulness. Clinical presentation is nonspecific and daytime respiratory function measures poorly predict nocturnal hypoventilation. Monitoring of respiration and carbon dioxide levels during sleep should be incorporated in the evaluation of high-risk patient populations and treatment with noninvasive ventilation improves outcomes.

Automated O2 titration improves exercise capacity in patients with hypercapnic chronic obstructive pulmonary disease: a randomised controlled cross-over trial

Automatically titrated O₂ flows (FreeO₂) was compared with constant O₂ flow on exercise capacity, O₂ saturation and risk of hyperoxia-related hypercapnia in patients with severe COPD with baseline hypercapnia and long-term oxygen therapy (LTOT). Twelve patients were enrolled in a randomised double-blind cross-over study to perform exercise with either FreeO₂ or constant flow. Endurance time (primary outcome) and SpO₂ were both significantly improved with FreeO₂compared with constant flow (p<0.04), although pCO₂ was similar in both conditions. Automated titration of O₂ significantly and clinically improved endurance walking time in patients with severe COPD receiving LTOT, without worsening of pCO₂ TRIAL REGISTRATION NUMBER: Results , NCT01575327.

Ventilatory failure, ventilator support, and ventilator weaning

The development of acute ventilatory failure represents an inability of the respiratory control system to maintain a level of respiratory motor output to cope with the metabolic demands of the body. The level of respiratory motor output is also the main determinant of the degree of respiratory distress experienced by such patients. As ventilatory failure progresses and patient distress increases, mechanical ventilation is instituted to help the respiratory muscles cope with the heightened workload. While a patient is connected to a ventilator, a physician's ability to align the rhythm of the machine with the rhythm of the patient's respiratory centers becomes the primary determinant of the level of rest accorded to the respiratory muscles. Problems of alignment are manifested as failure to trigger, double triggering, an inflationary gas-flow that fails to match inspiratory demands, and an inflation phase that persists after a patient's respiratory centers have switched to expiration. With recovery from disorders that precipitated the initial bout of acute ventilatory failure, attempts are made to discontinue the ventilator (weaning). About 20% of weaning attempts fail, ultimately, because the respiratory controller is unable to sustain ventilation and this failure is signaled by development of rapid shallow breathing. Substantial advances in the medical management of acute ventilatory failure that requires ventilator assistance are most likely to result from research yielding novel insights into the operation of the respiratory control system.

Gas exchange in disease: asthma, chronic obstructive pulmonary disease, cystic fibrosis, and interstitial lung disease

Ventilation-perfusion (VA/Q) inequality is the underlying abnormality determining hypoxemia and hypercapnia in lung diseases. Hypoxemia in asthma is characterized by the presence of low VA/Q units, which persist despite improvement in airway function after an attack. This hypoxemia is generally attenuated by compensatory redistribution of blood flow mediated by hypoxic vasoconstriction and changes in cardiac output, however, mediator release and bronchodilator therapy may cause deterioration. Patients with chronic obstructive pulmonary disease have more complex patterns of VA/Q inequality, which appear more fixed, and changes in blood flow and ventilation have less benefit in improving gas exchange efficiency. The inability of ventilation to match increasing cardiac output limits exercise capacity as the disease progresses. Deteriorating hypoxemia during exacerbations reflects the falling mixed venous oxygen tension from increased respiratory muscle activity, which is not compensated by any redistribution of VA/Q ratios. Shunt is not a feature of any of these diseases. Patients with cystic fibrosis (CF) have no substantial shunt when managed according to modern treatment regimens. Interstitial lung diseases demonstrate impaired oxygen diffusion across the alveolar-capillary barrier, particularly during exercise, although VA/Q inequality still accounts for most of the gas exchange abnormality. Hypoxemia may limit exercise capacity in these diseases and in CF. Persistent hypercapnic respiratory failure is a feature of advancing chronic obstructive pulmonary disease and CF, closely associated with sleep disordered breathing, which is not a prominent feature of the other diseases. Better understanding of the mechanisms of hypercapnic respiratory failure, and of the detailed mechanisms controlling the distribution of ventilation and blood flow in the lung, are high priorities for future research.

Control of ventilation in COPD and lung injury

Breathing occurs in single breaths and in patterns which are altered by the onset, progression and resolution of respiratory diseases. Through modulations of rate, depth, and patterning of breathing, the ventilatory control system maintains numerous critical variables within their homeostatic ranges. A dynamic respiratory control system is critical to successful adaptation in the face of progressive pulmonary pathology. The objective of this review, is to illustrate functional changes and compensatory mechanisms which occur with the onset and progression of acute and chronic lung disease. Chronic obstructive pulmonary disease (COPD) will be considered as a model of a slowly progressive pulmonary process, where destruction of lung parenchyma and airway obstruction leads to hypoxemia and hypercapnia. Over time, adaptations of the respiratory control system to this disease include changes in the intrinsic properties of respiratory muscles, chemoreceptor signaling, and central respiratory drive which increase motor output to the respiratory muscles. In contrast, acute respiratory distress syndrome (ARDS) is an exemplar of an acute pulmonary process. The result of severe lung injury, ARDS is characterized by lung infiltrates, rapidly progressive hypoxemic respiratory failure, and possible progression to pulmonary fibrosis. Changes in breathing patterns result from these functional changes, as well as altered processing of afferent feedback by the central controller, possibly influenced by brainstem inflammation. Taken together, these disease models highlight the plasticity of the respiratory control system in response to the development and progression of lung disease.

Clinical consequences of altered chemoreflex control

Control of ventilation dictates various breathing patterns. The respiratory control system consists of a central pattern generator and several feedback mechanisms that act to maintain ventilation at optimal levels. The concept of loop gain has been employed to describe its stability and variability. Synthesizing all interactions under a general model that could account for every behavior has been challenging. Recent insight into the importance of these feedback systems may unveil therapeutic strategies for common ventilatory disturbances. In this review we will address the major mechanisms that have been proposed as mediators of some of the breathing patterns in health and disease that have raised controversies and discussion on ventilatory control over the years.

Critical care in the ED: potentially fatal asthma and acute lung injury syndrome

Emergency department clinicians are frequently called upon to assess, diagnose, and stabilize patients who present with acute respiratory failure. This review describes a rapid initial approach to acute respiratory failure in adults, illustrated by two common examples: (1) an airway disease - acute potentially fatal asthma, and (2) a pulmonary parenchymal disease - acute lung injury/acute respiratory distress syndrome. As such patients are usually admitted to hospital, discussion will be focused on those initial management aspects most relevant to the emergency department clinician.

Safety of conscious sedation in patients with sleep apnea in a veteran population

OBJECTIVES

Due to the presumed higher risk of cardiopulmonary complications in patients with obstructive sleep apnea (OSA), many endoscopy centers consider OSA a contraindication to using conscious sedation. We evaluated the safety of conscious sedation during endoscopy for patients with OSA in a veteran population, and compared this to patients without OSA.

METHODS

Polysomnography studies were reviewed from 2004 to 2009 to identify 200 patients with OSA who had undergone endoscopy. Controls included the last 200 consecutive endoscopies in this institution for patients without OSA. Sixty-three upper endoscopies, 136 colonoscopies, and one enteroscopy were included in the OSA group. Sixty-five upper endoscopies, 133 colonoscopies, one sigmoidoscopy, and one endoscopic ultrasound comprised the control group. Data obtained included demographics, medications prescribed, and any complication noted in the procedure report.

RESULTS

No complications occurred in the control group. In the OSA group, a patient experienced oxygen desaturation during an upper endoscopy and required oxygen supplementation. The procedure was completed and did not require an extended stay in the endoscopy suite.

CONCLUSION

This study demonstrated that endoscopy can be safely done in OSA patients using conscious sedation, and the complication rate is not significantly different than patients without OSA.

[Increased inspiratory oxygen fractions (FIO2) using a conventional drug delivery nebuliser]

Nebulised drugs are very useful in COPD exacerbations. The most frequently used propellant is compressed air, which is commonly administered together with nasal oxygen in those patients with respiratory failure. The purpose of this approach is to avoid the risks inherent in breathing high inspiratory oxygen fractions (FIO(2)).

AIM

To analyze the actual FIO(2) obtained with such a common method under experimental conditions.

METHODS

Volunteers breathed using different patterns (quiet breathing, panting and deep breathing), through either the nose or the mouth, with oxygen flows of 0 vs. 4l/min. Then, they repeated quiet breathing and panting patterns, with nebulization of saline propelled by compressed air (8l/min) and oxygen flows of 0, 2, 4, 6 and 8l/min. The F(I)O(2) was simultaneously determined both in retronasal (RN) and retropharyngeal (RF) areas.

RESULTS

During breathing without simultaneous nebulization and oxygen flow of 4l/min, FIO(2) reached mean values of 0.42-0.71 (RN) and 0.29-0.38 (RF) for the three ventilatory patterns analyzed. With nebulisations during quiet breathing, mean FIO(2) values were 0.39 (RN) and 0.27 (RF) for 2l/min O(2) flow, 0.47 (RN), 0.34 (RF) for 4l/min, 0.58 (RN), 0.38 (RF) for 6l/min, and 0.68 (RN) and 0.50 (RF) for 8l/min. Similar results were obtained with the panting pattern.

CONCLUSION

The FIO(2) obtained using the conventional nebulization system (propulsion with compressed air and simultaneous nasal oxygen therapy) are relatively high, and therefore, might involve risks for COPD patients during exacerbations.

Update on the pharmacologic therapy for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease is a treatable disease characterized by progressive airflow limitation. Prevention of disease progression; improvement of symptoms, exercise tolerance, and health status; and decrease in exacerbations and mortality are the goals of management. Inhaled short-acting bronchodilators are recommended for symptoms in mild disease, whereas inhaled long-acting bronchodilators are recommended for maintenance therapy of daily symptoms. When symptoms are not controlled using one bronchodilator, combining bronchodilators may be more effective. Combining a long-acting beta-agonist with an inhaled corticosteroid is more effective than either agent alone. Several novel therapies are in different stages of development.

High inspired oxygen in hypercapnic respiratory failure

Mbamalu et al’s study (vol 68(3), 2007, p. 156) showed poor knowledge of oxygen (O2) therapy among senior house officers. Two clinical scenarios involving hypoxic patients were presented; one with uncompensated acute respiratory acidosis and another with hypercapnic (type 2) respiratory failure. Respondents were deemed correct in treating the first patient with a high concentration of O2 (FiO2), but incorrect if they did so for the second. The explanation that in patients with type 2 respiratory failure ‘there is a definite risk of suppression of the hypoxic drive … with the resultant development of carbon dioxide (CO2) narcosis in the presence of higher inspired oxygen concentrations’ is worthy of comment.

The effects of oxygen therapy in patients presenting to an emergency department with exacerbation of chronic obstructive pulmonary disease

OBJECTIVE

To elucidate oxygen administration practices in the setting of acute exacerbations of chronic obstructive pulmonary disease (COPD) and compare these practices with those recommended in internationally accepted guidelines.

DESIGN

Retrospective audit.

PARTICIPANTS AND SETTING

65 patients admitted to a Melbourne university teaching hospital via the emergency department (ED), identified through medical records by a discharge diagnosis (discharged between 1 June and 30 September 2005) of acute exacerbation of COPD (AECOPD). Those included had respiratory function test results consistent with British Thoracic Society guidelines for the diagnosis of COPD.

MAIN OUTCOME MEASURES

Length of stay, need for high dependency unit (HDU) admission, use of non-invasive ventilation (NIV), and use of arterial blood gas (ABG) tests.

RESULTS

Our audit showed that 95% of patients defined as retaining carbon dioxide received oxygen at a flow rate greater than 2 L/min. This process began in the ambulance and continued in the ED, often without monitoring of ABG levels. Length of stay was significantly longer (P = 0.029); need for NIV on admission greater (P = 0.0124); and rate of admission to the HDU higher (P = 0.0124) in patients who achieved a partial pressure of arterial oxygen (PaO(2)) >/= 74.5 mmHg compared with those with a PaO(2) < 74.5 mmHg.

CONCLUSIONS

The vast majority of patients with AECOPD presenting to our university teaching hospital receive oxygen therapy outside of internationally accepted guidelines, often without monitoring of ABG levels. The use of high-flow oxygen may contribute to an increased length of stay, more frequent admission to HDU and greater use of NIV among patients who achieve a higher PaO(2).

Management of Acute Exacerbations of Chronic Obstructive Pulmonary Disease in the Elderly

Chronic obstructive pulmonary disease (COPD) is a debilitating disease with rising worldwide prevalence. Exacerbations of COPD cause significant morbidity and become more common with advancing age. Healthcare providers caring for elderly patients should therefore be familiar with effective treatments for exacerbations of COPD. An extensive body of literature has identified several effective drug therapies for exacerbations. These drugs include inhaled bronchodilators, systemic corticosteroids and antibacterials. The two main classes of inhaled bronchodilators are beta-adrenoceptor agonists and anticholinergics. These drugs optimise lung function during exacerbations, with neither class demonstrating clear superiority over the other. Systemic corticosteroids are effective when used either for inpatient or outpatient treatment of exacerbations. They hasten recovery from exacerbations and reduce relapse rates. Antibacterials decrease morbidity from exacerbations and may decrease mortality in the more severe exacerbations. Other effective therapies for the treatment of acute exacerbations of COPD include oxygen and non-invasive ventilation. Oxygen can be safely administered in acute exacerbations associated with hypoxaemia, with titration of oxygen delivery to a goal oxygen saturation of 90%. Non-invasive ventilation reduces the morbidity and mortality associated with acute exacerbations complicated by hypercapnic respiratory failure. Strategies to prevent COPD exacerbations include smoking cessation, long-acting inhaled beta-adrenoceptor agonists, inhaled long-acting anticholinergics, inhaled corticosteroids and vaccination. Mucolytic agents, pulmonary rehabilitation, and case management programmes may also reduce exacerbation risk, but the current evidence supporting these interventions is weaker.

Acute exacerbation of chronic bronchitis: Need for an evidence-based approach

Acute exacerbations of chronic bronchitis (AECB) can be classified into three levels according to severity: (1) home treatment sufficient; (2) hospitalisation required; (3) hospitalisation in the presence of respiratory failure. This evidence-based classification is useful in ranking the clinical relevance of the episode and its outcome, and makes it possible to define the clinical history, clinical evaluation and diagnostic procedures of an exacerbation. Treatment guidelines vary according to severity, but they are essentially based on appropriate bronchodilator therapy (beta(2) agonists and/or anticholinergics, corticosteroids and antibiotics selected according to the local bacterial resistance pattern). It is important that cases requiring management in an intermediate/special respiratory care unit or intensive care unit (ICU) be identified. This is the stage where oxygen therapy and ventilatory support become particularly important. As first choice, they should be non-invasive, saving intubation and invasive ventilatory support for most severe cases characterised by severe acidemia and hypercapnia. We identify the optimal criteria for hospital discharge and follow-up of patients with AECB. In view of the chronic nature of the underlying disease, a correct follow-up is essential to avoid frequent and repeated relapses.

Treatments for COPD

The multicomponent nature of chronic obstructive pulmonary disease (COPD) has provided a challenging environment in which to develop successful treatments. A combination of pharmacological and non-pharmacological approaches is used to combat this problem, and an overview of these approaches and their possible future direction is given. Bronchodilators are the mainstay of COPD treatment and can be combined with inhaled corticosteroids for greater efficacy and fewer side effects. A new generation of pharmacotherapeutic agents, most notably phosphodiesterase-4 inhibitors, which are already in the advanced stages of clinical development, and leukotriene B4 inhibitors (in early clinical development), may shape future treatment as further insight is gained into the pathological mechanisms underlying COPD. Non-pharmacologic treatments for COPD include long-term oxygen therapy (LTOT), nasal positive pressure ventilation (nPPV), pulmonary rehabilitation and lung-volume-reduction surgery (LVRS). Apart from smoking cessation, LTOT is the only treatment to date which has been shown to modify survival rates in severe cases; thus its role in COPD is well defined. The roles of nPPV and LVRS are less clear, though recent progress is reported here. In the future, it will be important to establish the precise value of the different treatments available for COPD--evaluating both clinical and physiological endpoints and using the data to more accurately define candidate patients accordingly. The challenge will be to develop this base of knowledge in order to shape future research and allow clinicians to deliver tailored COPD management programmes for the growing number of patients afflicted with this disease.

Hypercapnia and oxygen therapy in older asthmatic patients

Excessive oxygen administration in hypercapnic chronic obstructive pulmonary disease predisposes to worsening respiratory failure during intercurrent respiratory illness. Chronic hypercapnia is thought to downregulate carbon dioxide chemoreceptor sensitivity, adversely affecting respiratory function/mechanics and worsening ventilation-perfusion inequality. These patients are dependent on hypoxic drive to maintain adequate spontaneous respiration. Whether an analogous situation occurs in asthma in older adults is unknown. These conditions may be difficult to differentiate clinically, and both may respond adversely to the administration of excessive oxygen in the presence of chronic hypercapnia. Although unrestricted oxygen is beneficial and safe in children and young adults with asthma, it may lead to progressive hypercapnia in older patients with asthma, a potential risk highlighted by this case. To avert progressive hypercapnia, oxygen therapy that is carefully adjusted to achieve adequate, but not maximal, tissue oxygenation may be a safer strategy than unrestricted oxygen use in older asthmatic patients. However, the correction of hypoxia overrides strategies to avert oxygen-related hypercapnia.

Chronic obstructive pulmonary disease * 9: management of ventilatory failure in COPD

The management of respiratory failure during acute exacerbations of COPD and during chronic stable COPD is reviewed and the role of non-invasive and invasive mechanical ventilation is discussed.

Treatment of chronic obstructive pulmonary disease in older patients: a practical guide

Chronic obstructive pulmonary disease (COPD) is a common disability, largely encountered in the elderly population, in whom it causes significant morbidity and mortality. The general perception of health professionals is that COPD is often a self-inflicted disorder affecting the more socio-economically disadvantaged segment of the population with significant comorbidity. COPD is the least funded in terms of research in relation to illness burden compared with other chronic diseases. However, recently published guidelines of both the British Thoracic Society and the Global Initiative for Chronic Obstructive Lung Disease have highlighted best management strategies both of chronic symptoms and acute exacerbations in this patient group. The chronic management of COPD should, like asthma, involve a stepwise approach with smoking cessation being pivotal for all severities of COPD, regardless of patient age. The mainstay of therapeutic treatment remains regular bronchodilators, both beta(2)-adrenoreceptor agonists and anticholinergic agents. Current evidence suggests that long-acting beta(2)-adrenoreceptor agonists such as salmeterol and the new long-acting anticholinergic agent tiotropium bromide are more efficacious than their shorter acting equivalents such as salbutamol and ipratropium bromide in terms of bronchodilation, improved well-being and a reduction in acute exacerbation rates. Additionally since they are taken once or twice daily compliance should be improved. The role of long-term inhaled corticosteroids in the chronic management of COPD is contentious. Only those patients with COPD who have been shown to respond to a formal corticosteroid trial, preferably with a 2-week course of oral corticosteroid, should receive long-term inhaled corticosteroids. In the management of acute exacerbations in acidotic patients nasal ventilation is the treatment of choice in addition to conventional treatment with bronchodilators and oral corticosteroids. Antibacterials need not be prescribed universally in all exacerbations of COPD. Pulmonary rehabilitation classes either individually or in groups have been shown to be beneficial in the management of patients with COPD and their use in secondary care is to be encouraged. Most treatment modalities do not improve pulmonary function in patients with severe COPD. Therefore, pulmonary function including spirometry should be used to make the diagnosis of COPD but not as a monitor of efficacy of treatment. Assessment of severity of COPD and improvement with treatment modalities is best done with dynamic exercise testing such as 6-minute walk tests and incremental shuttle walk tests or with the administration of disease-specific physical disability and quality-of-life questionnaires. Most COPD research does not specifically target the older COPD patients and these patients may merit special consideration for their optimum assessment and management.

Coronary MR angiography: true FISP imaging improved by prolonging breath holds with preoxygenation in healthy volunteers

In 15 healthy volunteers undergoing coronary magnetic resonance (MR) angiography, the breath-hold duration with and without preoxygenation was measured. The effect of preoxygenation on coronary artery imaging was also evaluated. A three-dimensional magnetization-prepared true fast imaging with steady-state precession sequence was employed for coronary MR angiography. All subjects showed an increase in comfortable breath-hold duration with preoxygenation. This extra imaging time allowed coronary artery imaging with increased spatial resolution.

The chronic obstructive pulmonary disease exacerbation

Chronic obstructive pulmonary disease is the only leading cause of death with a rising prevalence. The medical and economic costs arising from acute exacerbations of COPD are therefore expected to increase over the coming years. Although exacerbations may be initiated by multiple factors, the most common identifiable associations are with bacterial and viral infections. These are associated with approximately 50% to 70% and 20% to 30% of COPD exacerbations, respectively. In addition to smoking cessation, annual influenza vaccination is the most important method for preventing exacerbations. Controlled O2 is the most important intervention for patients with acute hypoxic respiratory failure. Evidence from randomized, controlled trials justifies the use of corticosteroids, bronchodilators (but not theophylline), noninvasive positive-pressure ventilation (in selected patients), and antibiotics, particularly for severe exacerbations. Antibiotics should be chosen according to the patient's risk for treatment failure and the potential for antibiotic resistance. In the acute setting, combined treatment with beta-agonist and anticholinergic bronchodilators is reasonable but not supported by randomized controlled studies. Physicians should identify and, when possible, correct malnutrition. Chest physiotherapy has no proven role in the management of acute exacerbations.

The role of hypoventilation and ventilation-perfusion redistribution in oxygen-induced hypercapnia during acute exacerbations of chronic obstructive pulmonary disease

The detailed mechanisms of oxygen-induced hypercapnia were examined in 22 patients during an acute exacerbation of chronic obstructive pulmonary disease. Ventilation, cardiac output, and the distribution of ventilation-perfusion (V A/Q ) ratios were measured using the multiple inert gas elimination technique breathing air and then 100% oxygen through a nose mask. Twelve patients were classified as retainers (R) when Pa(CO(2)) rose by more than 3 mm Hg (8.3 +/- 5.6; mean +/- SD) after breathing 100% oxygen for at least 20 min. The other 10 patients showed a change in Pa(CO(2)) of -1.3 +/- 2.2 mm Hg breathing oxygen and were classified as nonretainers (NR). Ventilation fell significantly from 9.0 +/- 1.5 to 7.2 +/- 1.2 L/min in the R group breathing oxygen (p = 0.007), whereas there was no change in ventilation in the NR group (9.8 +/- 1.8 to 9.9 +/- 1.8 L/min). The dispersion of V A/Q ratios as measured by log SD of blood flow (log SD Q) increased significantly in both R (0.96 +/- 0. 17 to 1.13 +/- 0.17) and NR (0.77 +/- 0.20 to 1.04 +/- 0.23, p < 0.05) groups breathing oxygen, whereas log SD of ventilation (log SD Q ) increased only in the R group (0.97 +/- 0.24 to 1.20 +/- 0.46, p < 0.05). This study suggests that an overall reduction in ventilation characterizes oxygen-induced hypercapnia, as an increased dispersion of blood flow from release of hypoxic vasoconstriction occurred to a significant and similar degree in both groups. The significant increase in wasted ventilation (alveolar dead space) in the R group only may be secondary to the higher carbon dioxide tension, perhaps related to bronchodilatation.

Current thoughts regarding treatment of chronic obstructive pulmonary disease

The available evidence indicates that pulmonary rehabilitation benefits patients with symptomatic COPD. The effect of pulmonary rehabilitation programs on health care use is promising but requires further investigation. In contrast, aerobic lower extremity training is of benefit in several areas of importance to patients with COPD. These areas include exercise endurance, perception of dyspnea, quality of life, and self-efficacy. The exact role of upper extremity exercise training programs requires further studies but should be used in patients who develop symptoms with arm activities. Psychological support improves the awareness of the patient and increases his or her understanding of the disease, but when used alone it is of limited value. Pulmonary rehabilitation when coupled with smoking cessation, optimization of blood gases, and medications offers the best treatment option for patients with symptomatic airflow obstruction.

Pressure support ventilation via face mask in acute respiratory failure in hypercapnic COPD patients

OBJECTIVE

To test whether non-invasive ventilation via facial mask could reduce the need for tracheal intubation when mechanical ventilation must be initiated in COPD patients.

DESIGN

Open prospective interventional study.

SETTING

General Intensive Care Service of a County Hospital.

PATIENTS

We have studied 12 COPD patients during 14 episodes of acute exacerbation of chronic respiratory failure who failed to improve with intensive medical therapy and showed impairments in severe respiratory acidosis and/or hypercapnic encephalopathy leading their attending physicians to order mechanical ventilation.

INTERVENTIONS

In these circumstances, a trial of pressure-support (PS) ventilation (Servo Ventilator 900C) via facial mask Vital Signs Inc.) was performed. The level of pressure support was adjusted to obtain a tidal volume > 400 ml. If the patient deteriorated, tracheal intubation and standard mechanical ventilation were performed.

MEASUREMENTS AND RESULTS

Measurements are presented as means +/- SEM. A pressure-support level of 14 +/- 3 cmH2O was used during a period of 8 +/- 4 h. Low levels of external PEEP were used in 4 patients, while it generated excessive leaks in the others. Significant differences (p < 0.05 ANOVA for repeated measures) in data obtained on admission, when patients deteriorated and after pressure support was administered were only observed in PaCO2 (68 +/- 3 versus 92 +/- 3 versus 67 +/- 3 mmHg), arterial pH (7.27 +/- 0.03 versus 7.19 +/- 0.02 versus 7.31 +/- 0.01). SaO2 (60 +/- 4 versus 86 +/- 3 versus 92 +/- 1%) and respiratory rate (35 +/- 2 versus 32 +/- 2 versus 23 +/- 1 breaths.min-1). Three patients needed intubation and one of them died in the ICU.

CONCLUSION

Non-invasive ventilation (pressure-support) via face mask may reduce the need for tracheal intubation in the severe hypercapnic failure of COPD patients.

Frequency of mechanical ventilation and respiratory activity after double lung transplantation

We investigated the contribution of pulmonary afferent nerve fibers to the control of inspiratory activity in awake humans. Eight double lung transplant outpatients and eight normal subjects were hyperventilated with a mechanical ventilator. Respiratory frequency was increased until no respiratory activity was detectable. Then, by either adding CO2 in the inspired gas or decreasing respiratory frequency, end-tidal PCO2 (PETCO2) was increased until inspiratory activity (i.e. change in inspiratory airway pressure peak and/or time profile) was detected. In normal subjects, PETCO2 threshold for inspiratory muscle recruitment was significantly lower when frequency was decreased than when CO2 was added (31.3 +/- 6.8 Torr vs. 38.2 +/- 8.1 Torr respectively, P < 0.005). This was not the case in the double lung transplant group (31.5 +/- 6.5 Torr vs. 32.9 +/- 5.8 Torr). These findings suggest that pulmonary afferent nerves have an inhibitory effect on inspiratory activity in humans.