Controlled oxygen administration in acute respiratory failure in chronic obstructive pulmonary disease: a reappraisal

Oxygen-induced hypercapnia: physiological mechanisms and clinical implications

Oxygen is probably the most commonly prescribed drug in the emergency setting and is a life-saving modality as well. However, like any other drug, oxygen therapy may also lead to various adverse effects. Patients with chronic obstructive pulmonary disease (COPD) may develop hypercapnia during supplemental oxygen therapy, particularly if uncontrolled. The risk of hypercapnia is not restricted to COPD only; it has also been reported in patients with morbid obesity, asthma, cystic fibrosis, chest wall skeletal deformities, bronchiectasis, chest wall deformities, or neuromuscular disorders. However, the risk of hypercapnia should not be a deterrent to oxygen therapy in hypoxemic patients with chronic lung diseases, as hypoxemia may lead to life-threatening cardiovascular complications. Various mechanisms leading to the development of oxygen-induced hypercapnia are the abolition of ‘hypoxic drive’, loss of hypoxic vasoconstriction and absorption atelectasis leading to an increase in dead-space ventilation and Haldane effect. The international guideline recommends a target oxygen saturation of 88% to 92% in patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) and other chronic lung diseases at risk of hypercapnia.  Oxygen should be administered only when oxygen saturation is below 88%. We searched PubMed, EMBASE, and the CINAHL from inception to June 2022. We used the following search terms: “Hypercapnia”, “Oxygen therapy in COPD”, “Oxygen-associated hypercapnia”, “oxygen therapy”, and “Hypoxic drive”. All types of study are selected. This review will focus on the physiological mechanisms of oxygen-induced hypercapnia and its clinical implications.

The effect of 50% oxygen on PtCO2 in patients with stable COPD, bronchiectasis, and neuromuscular disease or kyphoscoliosis: randomised cross-over trials

BACKGROUND

High-concentration oxygen therapy causes increased arterial partial pressure of carbon dioxide (PaCO2) in patients with COPD, asthma, pneumonia, obesity and acute lung injury. The objective of these studies was to investigate whether this physiological response to oxygen therapy occurs in stable patients with neuromuscular disease or kyphoscoliosis, and bronchiectasis.

METHODS

Three randomised cross-over trials recruited stable patients with neuromuscular disease or kyphoscoliosis (n = 20), bronchiectasis (n = 24), and COPD (n = 24). Participants were randomised to receive 50% oxygen and 21% oxygen (air), each for 30 min, in randomly assigned order. The primary outcome was transcutaneous partial pressure of carbon dioxide (PtCO2) at 30 min. The primary analysis was a mixed linear model.

RESULTS

Sixty six of the 68 participants had baseline PtCO2 values < 45 mmHg. The intervention baseline adjusted PtCO2 difference (95% CI) between oxygen and room air after 30 min was 0.2 mmHg (- 0.4 to 0.9), P = 0.40; 0.5 mmHg (- 0.2 to 1.2), P = 0.18; and 1.3 mmHg (0.7 to 1.8), P < 0.001, in the neuromuscular/kyphoscoliosis, bronchiectasis and COPD participants respectively.

CONCLUSIONS

The small increase in PtCO2 in the stable COPD patients with high-concentration oxygen therapy contrasts with the marked increases in PaCO2 seen in the setting of acute exacerbations of COPD. This suggests that the model of studying the effects of high-concentration oxygen therapy in patients with stable respiratory disease is not generalisable to the use of oxygen therapy in the acute clinical setting. Appropriate studies of high-concentration compared to titrated oxygen in acute clinical settings are needed to determine if there is a risk of oxygen-induced hypercapnia in patients with neuromuscular disease, kyphoscoliosis or bronchiectasis.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12615000970549 Registered 16/9/15, ACTRN12615000971538 Registered 16/9/15 and ACTRN12615001056583 Registered 7/10/15.

Extrapulmonary Causes of Respiratory Failure

The causes of respiratory failure can be divided into two main groups: extrapulmonary and pulmonary. Extrapulmonary causes of respiratory failure include conditions that exclusively or primarily cause respiratory failure by their effect on structures other than the lungs (i.e., the extrapulmonary compartment). To place the topic of extrapulmonary respiratory failure into perspective, we briefly review normal and abnormal gas exchange and then examine how one can use this information to suspect or confirm the diagnosis of an extrapulmonary cause of respiratory failure. We then review the individual causes of extrapulmonary respiratory failure. These have been divided into two main functional categories: (1) those that involve a decrease in normal force generation, and (2) those that involve an increase in resistance to (bulk flow) ventilation. We then briefly consider the treatment of these disorders from a respiratory point of view.

Pulmonary hypertension and right heart dysfunction in chronic lung disease

Group 3 pulmonary hypertension (PH) is a common complication of chronic lung disease (CLD), including chronic obstructive pulmonary disease (COPD), interstitial lung disease, and sleep-disordered breathing. Development of PH is associated with poor prognosis and may progress to right heart failure, however, in the majority of the patients with CLD, PH is mild to moderate and only a small number of patients develop severe PH. The pathophysiology of PH in CLD is multifactorial and includes hypoxic pulmonary vasoconstriction, pulmonary vascular remodeling, small vessel destruction, and fibrosis. The effects of PH on the right ventricle (RV) range between early RV remodeling, hypertrophy, dilatation, and eventual failure with associated increased mortality. The golden standard for diagnosis of PH is right heart catheterization, however, evidence of PH can be appreciated on clinical examination, serology, radiological imaging, and Doppler echocardiography. Treatment of PH in CLD focuses on management of the underlying lung disorder and hypoxia. There is, however, limited evidence to suggest that PH-specific vasodilators such as phosphodiesterase-type 5 inhibitors, endothelin receptor antagonists, and prostanoids may have a role in the treatment of patients with CLD and moderate-to-severe PH.

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.

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.

Il percorso diagnostico-assistenziale della broncopneumopatia cronica ostruttiva riacutizzata in Medicina Interna

Introduction

Chronic obstructive pulmonary disease (COPD) is the second leading cause of hospitalization in Internal Medicine departments in Italy and the fourth leading cause of death all over the word. By 2020, COPD will be the third leading cause of death and the fifth leading cause of disability. It is – along with chronic congestive heart failure – one of the most common causes of unscheduled hospital readmissions, and as such it represents a significant economic burden for the health-care system. Exacerbations of COPD are important events in the natural history of this prevalent condition.

Discussion

This review provides a comprehensive state-of-the-art look at prevention and management of COPD exacerbations. Treatment of these episodes has to be tailored to the severity of the clinical presentation. We now have a wide range of therapeutic available options, based on the results of clinical trials. Management of the acute event should include the necessary measures (mainly the administration of inhaled short-acting bronchodilators, inhaled or oral corticosteroids, and antibiotics), with or without oxygen and ventilator support.

Conclusions

To improve the management of COPD exacerbations, the focus of care must be shifted from the episodic acute complications to their systematic prevention. The management of COPD, which is often associated with multiple co-morbidities, is complex and requires a tailored, multifaceted and multidisciplinary approach. Integrated care for COPD also requires that patients be informed about their condition, that they participate actively in their care, and that they have easy access to the necessary health-care services.

Physical diagnosis of chronic obstructive pulmonary disease

Among the various diagnostic strategies of chronic obstructive pulmonary disease (COPD), physical diagnosis is the quickest and requires no extra cost. Rapid physical diagnosis of COPD in primary care practice can lead to earlier actions of preventive measures and counseling for patients. Further, rapid physical diagnosis of COPD in an emergency department is also crucial for timely use of potentially lifesaving therapy specific for COPD patients. In this review, we will present a broad scope of physical findings for rapid physical diagnosis of COPD.

COPD exacerbations.5: management

A review of the most relevant evidence based therapeutic options currently available for the management of exacerbations of COPD.

Adult domiciliary oxygen therapy. Position statement of the Thoracic Society of Australia and New Zealand

Patients with chronic obstructive pulmonary disease and a stable daytime PaO2 of < or = 55 mmHg (7.3 kPa) live longer and have a better quality of life if provided with long-term continuous oxygen therapy. It is reasonable to offer continuous oxygen therapy also to patients with other lung diseases that cause chronic hypoxaemia. Indications for supplemental oxygen therapy during exercise (ambulatory oxygen therapy) and sleep (nocturnal oxygen therapy) are less clear.

Respiratory Failure

Respiratory failure is defined as a failure in gas exchange due to an impaired respiratory system--either pump or lung failure, or both. The hallmark of respiratory failure is impairment in arterial blood gases. This review describes the mechanisms leading to respiratory failure, the indices that can be used to better describe gas exchange abnormalities and the physiologic and clinical consequences of these abnormalities. The possible causes of respiratory failure are then briefly mentioned and a quick reference to the clinical evaluation of such patients is made. Finally treatment options are briefly outlined for both acute and chronic respiratory failure.

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.

Evidence-based approach to acute exacerbations of COPD

Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States, and it accounts for approximately 500,000 hospitalizations for exacerbations each year. New definitions of acute COPD exacerbation have been suggested, but the one used by Anthonisen et al. is still widely accepted. It requires the presence of one or more of the following findings: increase in sputum purulence, increase in sputum volume, and worsening of dyspnea. Patients with COPD typically present with acute decompensation of their disease one to three times a year, and 3% to 16% of these will require hospital admission. Hospital mortality of these admissions ranges from 3% to 10% in severe COPD patients, and it is much higher for patients requiring ICU admission. The etiology of the exacerbations is mainly infectious (up to 80%). Other conditions such as heart failure, pulmonary embolism, nonpulmonary infections, and pneumothorax can mimic an acute exacerbation or possibly act as "triggers." Baseline chest radiography and arterial blood gas analysis during an exacerbation are recommended. Oxygen administration through a venturi mask seems to be appropriate and safe, and the oxygen saturation should be kept just above 90%. Either a short acting beta 2-agonist or an anticholinergic is the preferred bronchodilator agent. The choice between the two depends largely on potential undesirable side effects and the patient's coexistent conditions. Adding a second bronchodilator to the first one does not seem to offer much benefit. The evidence suggests similar benefit of MDIs when compared with nebulized treatment for bronchodilator delivery. If MDIs are to be used, spacer devices are recommended. Steroids do improve several outcomes during an acute COPD exacerbation, and a 10- to 14-day course seems appropriate. Antibiotic use has been shown to be beneficial, especially for patients with severe exacerbation. Changes in bacteria strains have been documented during exacerbations, and newer generations of antibiotics might offer a better response rate. There is no role for mucolytic agents or chest physiotherapy in the acute exacerbation setting. Noninvasive positive pressure ventilation might benefit a group of patients with rapid decline in respiratory function and gas exchange. It has the potential to decrease the need for intubation and invasive mechanical ventilation and possibly decrease in-hospital mortality.

A proposal for a practical treatment guideline designed for the initial two-hours of the management of patients with acute severe asthma and COPD using the principles of evidence-based medicine

We have proposed a clinical treatment guideline for the management of acute, severe asthma and chronic obstructive pulmonarydisease (COPD) using the principles of evidence-based medicine. The content is based upon practical clinical issues in need of consensus. A previous study has shown that this particular area is in serious need of quality control. Based on a strict 2 h time schedule with a unified treatment plan for both asthma and COPD, it is possible to secure for the patients a well-documented medical therapy promoting decision-making and clarification of the patient within this time limit. A summary of the statements is presented in a one-page, user-friendly format in order to cope with the clinician's need of having access to published evidence quickly and easily. A website (www.phanareth.dk or a website provided by Respiratory Medicine) has been established providing regular updates. A strategy for the implementation and the evaluation process has been planned after the publication of this paper. We believe this approach to be an important step towards an increase in the quality of guidelines and also a tool to make "guideline writers" aware of the responsibility of making their recommendations work.

Clinical predictors of acute respiratory acidosis during exacerbation of asthma and chronic obstructive pulmonary disease

Mechanical ventilation (MV) during exacerbation of asthma or chronic obstructive pulmonary disease (COPD) is unequivocally needed when apnoea, cardiorespiratory arrest, coma, hypoxia or treatment failure is present. The need is less clear when the patient can respond, has intact airway reflexes and spontaneous respiration. In this situation, acidosis is an important factor in the decision to institute MV. This study aimed to provide a clinical means of identifying patients with acute respiratory acidosis (ARA) in a setting where blood gas analysis is unavailable. We undertook a prospective, observational study of consecutive patients who presented to two emergency departments with severe and life-threatening exacerbation of asthma or COPD. Each underwent clinical assessment, treatment and blood gas analysis. The outcome measure was ARA or mixed ARA and metabolic acidosis. A total of 127 episodes in patients aged 15-90 years (65.3% males and 34.7% females) were included in the study. Of these, 62.2% had asthma and 37.8% had COPD; 71.7% had life-threatening and 28.3% had severe attacks. Overall, the adjusted odds ratio (and 95% confidence intervals) for predictors of ARA were 7.09 (1.79-28.06) for drowsiness, 4.11 (1.31-12.88) for flushing, 3.34 (1.01-11.02) for having COPD and 2.86 (1.01-8.07) for intercostal retractions. In conclusion, with drowsiness, the likelihood of ARA is about seven times higher. The presence of flushing, COPD and intercostal retractions also increase the risk of ARA.

Prognostic factors, clinical course, and hospital outcome of patients with chronic obstructive pulmonary disease admitted to an intensive care unit for acute respiratory failure

OBJECTIVE

To describe prognostic factors, clinical course, and hospital outcome of patients with chronic obstructive pulmonary disease admitted to an intensive care unit for acute respiratory failure.

DESIGN

Analysis of prospectively collected data.

SETTING

A multidisciplinary intensive care unit of an inner-city university hospital.

PATIENTS

Patients with chronic obstructive pulmonary disease admitted to an intensive care unit for acute respiratory failure from August 1995 through July 1998.

MEASUREMENTS AND MAIN RESULTS

Data were obtained concerning demographics, arterial blood gas, Acute Physiology and Chronic Health Evaluation (APACHE) II score, sepsis, mechanical ventilation, organ failure, complications, and hospital mortality rate. Fifty-nine percent of patients were male, 63% white, and 36% African-American; the mean age was 63.1 +/- 8.9 yrs. Noninvasive mechanical ventilation was tried in 40% of patients and was successful in 54% of them. Invasive mechanical ventilation was required in 61% of the 250 admissions. Sepsis developed in 31% of patients, nonpulmonary organ failure in 20%, pneumothorax in 3%, and acute respiratory distress syndrome in 2%. Multiple organ failure developed in 31% of patients with sepsis compared with 3% without sepsis (p <.0001). Predicted and observed hospital mortality rates were 30% and 15%, respectively. Differences in age and arterial carbon dioxide and oxygen tensions between survivors and nonsurvivors were not significant. Arterial pH was lower in nonsurvivors than in survivors (7.21 vs. 7.25, p =.0408). The APACHE II-predicted mortality rate (p =.0001; odds ratio, 1.046; 95% confidence interval, 1.022-1.070) and number of organ failures (p <.0001; odds ratio, 5.524; 95% confidence interval, 3.041-10.031) were independent predictors of hospital outcome; invasive mechanical ventilation was not an independent predictor.

CONCLUSIONS

Physiologic abnormalities at admission to an intensive care unit and development of nonrespiratory organ failure are important predictors of hospital outcome for critically ill patients with chronic obstructive pulmonary disease who have acute respiratory failure. Improved outcome would require prevention and appropriate treatment of sepsis and multiple organ failure.

Oxygen therapy for hypercapnic patients with chronic obstructive pulmonary disease and acute respiratory failure: a randomized, controlled pilot study

OBJECTIVE

To investigate the effect of oxygen therapy on outcome and on symptomatic hypercapnia.

DESIGN

Randomized, controlled, single-blind study.

SETTING

Multidisciplinary intensive care unit of a university teaching hospital.

PATIENTS

Patients admitted with a clinical diagnosis of an acute exacerbation of chronic obstructive pulmonary disease and a PaO2 <6.6 kPa (50 mm Hg) and PaCO2 >6.6 kPa (50 mm Hg) on air.

INTERVENTIONS

Patients received oxygen therapy titrated to increase arterial oxygen tension to >6.6 kPa (50 mm Hg) or >9 kPa (70 mm Hg). Patients in the low-oxygen tension group also received doxapram if they developed an acidosis with pH <7.2, whereas those in the high-oxygen tension group received doxapram if they developed symptomatic acidosis. Bronchodilator, steroid, and antibiotic therapy was standardized.

MEASUREMENTS AND MAIN RESULTS

Two patients in the low-oxygen tension group (n = 17) required mechanical ventilation and another one died. No patients in the high-oxygen group (n = 17) had a poor outcome, but this difference was not significant. No patient in either group became comatose or developed an acute cardiac arrhythmia.

CONCLUSIONS

Traditional teaching related to oxygen therapy for hypercapnic patients with an acute exacerbation of chronic obstructive pulmonary disease may be incorrect. A large randomized, controlled study is required to confirm this impression.

Predictors of outcome for patients with COPD requiring invasive mechanical ventilation

INTRODUCTION

Accurate outcomes data and predictors of outcomes are fundamental to the effective care of patients with COPD and in guiding them and their families through end-of-life decisions.

DESIGN

We conducted a retrospective cohort study of 166 patients using prospectively gathered data in patients with COPD who required mechanical ventilation for acute respiratory failure of diverse etiologies.

RESULTS

The in-hospital mortality rate for the entire cohort was 28% but fell to 12% for patients with a COPD exacerbation and without a comorbid illness. Univariate analysis showed a higher mortality rate among those patients who required > 72 h of mechanical ventilation (37% vs 16%; p < 0.01), those without previous episodes of mechanical ventilation (33% vs 11%; p < 0.01), and those with a failed extubation attempt (36% vs 7%; p = 0.0001). With multiple logistical regression, higher acute physiology score measured 6 h after the onset of mechanical ventilation, presence of malignancy, presence of APACHE (acute physiology and chronic health evaluation) II-associated comorbidity, and the need for mechanical ventilation > or = 72 h were independent predictors of poor outcome.

CONCLUSIONS

We conclude that among variables available within the first 6 h of mechanical ventilation, the presence of comorbidity and a measure of the severity of the acute illness are predictors of in-hospital mortality among patients with COPD and acute respiratory failure. The occurrence of extubation failure or the need for mechanical ventilation beyond 72 h also portends a worse prognosis.

Management of acute exacerbations of COPD: a summary and appraisal of published evidence

STUDY OBJECTIVES

To critically review the available data on the diagnostic evaluation, risk stratification, and therapeutic management of patients with acute exacerbations of COPD.

DESIGN, SETTING, AND PARTICIPANTS

English-language articles were identified from the following databases: MEDLINE (from 1966 to week 5, 2000), EMBASE (from 1974 to week 18, 2000), HealthStar (from 1975 to June 2000), and the Cochrane Controlled Trials Register (2000, issue 1). The best available evidence on each subtopic then was selected for analysis. Randomized trials, sometimes buttressed by cohort studies, were used to evaluate therapeutic interventions. Cohort studies were used to evaluate diagnostic tests and risk stratification. Study design and results were summarized in evidence tables. Individual studies were rated as to their internal validity, external validity, and quality of study design. Statistical analyses of combined data were not performed.

MEASUREMENT AND RESULTS

Limited data exist regarding the utility of most diagnostic tests. However, chest radiography and arterial blood gas sampling appear to be useful, while short-term spirometry measurements do not. In terms of the risk of relapse and the risk of death after hospitalization for an acute exacerbation, there are identifiable clinical variables that are associated with these outcomes. Therapies for which there is evidence of efficacy include bronchodilators, corticosteroids, and noninvasive positive-pressure ventilation. There is also support for the use of antibiotics in patients with more severe exacerbations. Based on limited data, mucolytics and chest physiotherapy do not appear to be of benefit, and oxygen supplementation appears to increase the risk of respiratory failure in an identifiable subgroup of patients.

CONCLUSIONS

Although suggestions for appropriate management can be made based on available evidence, the supporting literature is spotty. Further high-quality research is needed and will require an improved, generally acceptable, and transportable definition of the syndrome "acute exacerbation of COPD" and improved methods for observing and measuring outcomes.

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.

Hypercapnic respiratory failure in COPD patients: response to therapy

INTRODUCTION

The clinical course of patients with acute exacerbations of underlying COPD presenting with hypercapnic respiratory failure was reviewed.

METHODS

This was a retrospective review of 138 episodes of hypercapnic respiratory failure (PaCO(2) > or = 50 mm Hg and pH < or = 7.35). Patients were admitted to the West Los Angeles VAMC Medical Intensive Care Unit between 1990 and 1994.

RESULTS

Of the 138 hypercapnic episodes, 74 (54%) required intubation. Comparison was made with the 64 cases in which patients responded to medical therapy. Patients requiring intubation had a greater severity of illness, with a higher APACHE II (Acute Physiology and Chronic Health Evaluation II) score (18 +/- 5 vs 16 +/- 4; p < 0.01), higher WBC, higher serum BUN, and greater acidosis (pH, 7.26 +/- 0.07 vs 7.28 +/- 0.06; p = 0.08). Those with the most severe acidosis (pH < 7.20) had the highest intubation rate (70%) and shortest time to intubation (2 +/- 2 h), and they required the longest period of time to respond to medical therapy (69 +/- 60 h). With an initial pH of < 7.25, there was a consistently higher intubation rate. Conversely, those with an initial pH of 7.31 to 7. 35 were less likely to be intubated (45%), had a longer time to intubation (13 +/- 18 h), and had a more rapid response to medical therapy (30 +/- 18 h). Of those patients requiring intubation, most (78%) were intubated within 8 h of presentation, and the vast majority (93%) by 24 h. Of those patients responding to medical therapy, half (52%) recovered within 24 h and the vast majority (92%) recovered within 72 h.

CONCLUSIONS

This study provides a better characterization of the response to therapy of COPD patients with hypercapnic respiratory failure. This should be useful in limiting or omitting medical therapy in high-risk patients, thereby avoiding delays in intubation as well as providing a framework for continued therapy in those more likely to improve.

Comparison of noninvasive positive pressure ventilation with standard medical therapy in hypercapnic acute respiratory failure

STUDY OBJECTIVE

To compare the efficacy of standard medical therapy (ST) and noninvasive mechanical ventilation additional to standard medical therapy in hypercapnic acute respiratory failure (HARF).

DESIGN

Single center, prospective, randomized, controlled study.

SETTING

Pulmonary medicine directed critical care unit in a university hospital.

PATIENTS

Between March 1993 and November 1996, 30 HARF patients were randomized to receive ST or noninvasive positive pressure ventilation (NPPV) in addition to ST.

INTERVENTIONS

NPPV was given with an air-cushioned face via a mechanical ventilator (Puritan Bennett 7200) with initial setting of 5 cm H2O continuous positive airway pressure and 15 cm H2O pressure support.

RESULTS

At the time of randomization, patients in the ST group had (mean+/-SD) PaO2 of 54+/-13 mm Hg, PaCO2 of 67+/-11 mm Hg, pH of 7.28+/-0.02, and respiratory rate of 35.0+/-5.8 breaths/min. Patients in the NPPV group had PaO2 of 55+/-14, PaCO2 of 69+/-15, pH of 7.27+/-0.07, and respiratory rate of 34.0+/-8.1 breaths/min. With ST, there was significant improvement of only respiratory rate (p < 0.05). However, with NPPV, PaO2 (p < 0.001), PaCO2 (p < 0.001), pH (p < 0.001), and respiratory rate (p < 0.001) improved significantly compared with baseline. Six hours after randomization, pH (p < 0.01) and respiratory rate (p < 0.01) in NPPV patients were significantly better than with ST. Hospital stay for NPPV vs ST patients was, respectively, 11.7+/-3.5 and 14.6+/-4.7 days (p < 0.05). One patient in the NPPV group required invasive mechanical ventilation. The conditions of six patients in the ST group deteriorated and they were switched to NPPV; this was successful in four patients, two failures were invasively ventilated.

CONCLUSION

This study suggests that early application of NPPV in HARF patients facilitates improvement, decreases need for invasive mechanical ventilation, and decreases the duration of hospitalization.

Acute exacerbations of chronic obstructive pulmonary disease and mechanical ventilation: a reevaluation

OBJECTIVE

To review the intensive care unit (ICU) experience of patients admitted with acute exacerbations of chronic obstructive pulmonary disease.

DESIGN

Retrospective case series.

SETTING

University teaching hospital.

PATIENTS

We reviewed the records of 100 consecutive ICU admissions of patients with acute exacerbations of chronic obstructive pulmonary disease over a period of 4.25 yrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were characterized using a computerized prospective database and case note review. Multivariate analysis identified variables predicting ICU and hospital length of stay. The Cox proportional hazards model was used to analyze survival after hospital discharge. Seventy-five patients (24 female and 51 male, mean age 68.5 +/- 7 [SD] yrs) with 100 ICU admissions were identified. Premorbid airway obstruction was severe, with forced expiratory volume in 1 sec (FEV1)/forced vital capacity (FVC) of 0.7 +/- 0.34 L and FEV1/FVC of 39 +/- 16%. Thirty-two percent received home-administered oxygen and 42% were housebound. The pre-ICU admission PaCO2 was 86 +/- 28 torr (11.5 +/- 3.7 kPa), with a pH of 7.24 +/- 0.11 and a PaO2/FIO2 of 190 +/- 66. ICU admission Acute Physiology and Chronic Health Evaluation II score was 18 +/- 5. Forty-three patients were mechanically ventilated for a median of 4 days (range 0.08 to 30). Tracheostomy, in seven patients, was maintained for 21 +/- 7 days. Ventilation time and tracheostomy frequency predicted length of ICU stay (median 3 days; range 1 to 40) and hospital stay (17 days; 4 to 97), respectively. ICU and hospital case-fatality rates were 1% and 11%. Out-of-hospital (24-month) probability of survival was predicted by plasma albumin concentration at the time of ICU admission; this probability of survival was .64 at an albumin concentration of 38 g/L.

CONCLUSIONS

ICU admission of severely ill chronic obstructive pulmonary disease patients results in acceptable outcomes. Survival of < or =2 yrs is not affected by mechanical ventilation or tracheostomy requirement.

Influence of the quality of nursing on the duration of weaning from mechanical ventilation in patients with chronic obstructive pulmonary disease

OBJECTIVE

To evaluate the influence of nursing on the duration of weaning from mechanical ventilation in patients with chronic obstructive pulmonary disease.

DESIGN

Data were collected prospectively over a 1-yr period (study year) and compared with previously collected prospective data recorded in our chronic obstructive pulmonary disease database during a 5-yr period.

SETTING

The medical intensive care unit (ICU) of a university hospital.

PATIENTS

Eighty-seven patients with chronic obstructive pulmonary disease. Fifteen patients had chronic obstructive pulmonary disease that required mechanical ventilation for acute exacerbation of their disease (study year), and 72 were patients with chronic obstructive pulmonary disease from the previously collected data.

INTERVENTIONS

The ICU course (duration of mechanical ventilation, mortality) was recorded, as well as several respiratory parameters (pulmonary function tests and arterial blood gases in stable conditions, and nutritional status), and they were compared with an "index of nursing."

MEASUREMENTS AND MAIN RESULTS

We developed an "index of nursing", comparing the effective workforce of the nurses (number and qualifications) with the ideal workforce required by the number of patients and the severity of their diseases. A value of 1.0 represented a perfect match between the needed and the effectively present nurses, whereas a lesser value signified a diminished available workforce. This index was compared with the complications and duration of weaning from mechanical ventilation. During the first 5 yrs, the duration of mechanical ventilation increased progressively from 7.3 +/- 8.0 to 38.2 +/- 25.8 days (p = .006). A significant inverse correlation between the duration of mechanical ventilation and the nursing index (p = .025) was found. In the sixth comparative year, the number of nurses increased (nursing index = 1.05) and the duration of mechanical ventilation decreased to 9.9 +/- 13 days (p < .001, yr 5 vs. yr 6).

CONCLUSIONS

The quality of nursing appears to be a measurable and critical factor in the weaning from mechanical ventilation of patients with chronic obstructive pulmonary disease. Below a threshold in the available workforce of ICU nurses, the weaning duration of patients with chronic obstructive pulmonary disease increases dramatically. Therefore, very close attention should be given to the education and number of ICU nurses.

Pulmonary rehabilitation in chronic respiratory insufficiency. 5. Home mechanical ventilation

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Severe COPD and acute respiratory failure. Correlates for survival at the time of tracheal intubation

The recognition of a reversible cause for acute respiratory failure (ARF) is frequently difficult in patients with severe chronic obstructive pulmonary disease (COPD). We sought to identify clinical findings present at the time of tracheal intubation that were associated with successful weaning and short-term survival among a population of male veterans with severe COPD. Over a 5-year period (1987 to 1991), 39 episodes of ARF requiring mechanical ventilation (MV) were identified in 33 men with severe COPD. All the patients had a baseline FEV1 < 1 L. Univariate analysis suggested a higher serum albumin level and absence of pulmonary infiltrates on chest radiography distinguished survivors (weaned from MV for 72 h) from nonsurvivors (died while undergoing MV or within 72 h of weaning). Multivariate analysis revealed the absence of pulmonary infiltrates on initial chest radiography was the strongest correlate for survival. To examine the significance of these correlates in ARF complicating milder COPD, 19 patients with lesser degrees of chronic airways obstruction and ARF were also studied. Unlike patients with severe COPD, the presence or absence of pulmonary infiltrates on chest radiography was not correlated with survival in patients with milder chronic airways obstruction. Analyzing all COPD patients with ARF, the mortality risk associated with the presence of pulmonary infiltrates on chest radiography increased dramatically with declining baseline lung function. Mortality risk ratio analysis revealed the greatest likelihood for survival was predicted by a higher baseline FEV1 and the absence of pulmonary infiltrates on chest radiography. The extent of baseline airways obstruction alone was not correlated with short-term survival in either group. These observations suggest that in the subset of patients with severe COPD and ARF, the presence of pulmonary infiltrates on chest radiography at the time of tracheal intubation may be associated with less likelihood for survival. An exacerbation of COPD may infrequently be the terminal illness in these patients.

Non-invasive modalities of positive pressure ventilation improve the outcome of acute exacerbations in COLD patients

OBJECTIVE

1) To compare the clinical usefulness of both non-invasive pressure support ventilation (NPSV) and non-invasive intermittent positive pressure ventilation in assist-control (A/C) mode (NIPPV) in chronic obstructive lung disease (COLD) patients with acute hypercapnic respiratory failure: 2) to compare retrospectively the usefulness of non-invasive mechanical ventilation (NMV) with standard medical therapy alone.

DESIGN

Prospective randomized retrospective study.

SETTING

2 Respiratory intermediate intensive units.

PATIENTS

29 COLD patients (age: 62 +/- 8 years) with chronic respiratory failure were hospitalized in a department for rehabilitation during acute relapses of their disease. They were transferred to our intermediate intensive care unit (IICU) and submitted randomly to either NPSV (16 patients) or NIPPV (13 patients).

MEASUREMENTS AND RESULTS

Blood gas analysis, dynamic flows, clinical variables, success rate, time of ventilation, side effects and subjective score of compliance to therapy. Therapy was considered successful when endotracheal intubation was avoided and patients were returned to their condition prior to exacerbation. No statistically significant difference was found between NPSV and NIPPV in success rate (NPSV 87.5%; NIPPV 77%) or in time of ventilation (NPSV: 69 +/- 49; NIPPV: 57 +/- 49 h). A better compliance to non-invasive mechanical ventilation (NMV) was found in NPSV patients than in NIPPV patients; side effects were observed less frequently in the NPSV group. Comparison of the success rate of NMV was retrospectively performed with 35 control COLD patients with chronic respiratory insufficiency who had undergone an acute relapse of their disease in the 2 years preceding the institution of the IICU and had been treated with oxygen and medical therapy alone. Patients submitted to NMV showed a greater success rate than control (82 versus 54%) after a period of ventilation ranging from 4-216 h.

CONCLUSION

Non-invasive mechanical ventilation performed either by NPSV or NIPPV may improve the outcome of acute exacerbations of COLD, as compared to medical therapy alone. NPSV seems to be more acceptable to patients in comparison with NIPPV.

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.

Time course of pulmonary function before admission into ICU. A two-year retrospective study of COLD patients with hypercapnia

Changes in cardiopulmonary function were retrospectively evaluated back to two years before acute exacerbations requiring ICU admission in 16 COLD patients with chronic hypercapnic respiratory insufficiency (age: 61 +/- 6 years, group A). Fifteen hypercapnic COLD patients matched for age, sex, lung function, and blood gas values not requiring an ICU admission in a period of two years, served as control subjects (age: 66 +/- 7, group B). Periodic assessments of spirometry, arterial blood gas values, echocardiography, body weight, and red blood cell count performed in stable state were compared for differences between groups and changes over a period of two years. The results indicated that basal body weight, rate of deterioration over time in FEV1, VC, blood gas values, bicarbonates, and RVD may be related to the necessity of ICU admission in COLD patients with hypercapnic respiratory insufficiency.

Determinants of immediate survival among chronic respiratory insufficiency patients admitted to an intensive care unit for acute respiratory failure. A prospective multicenter study. The French Task Group for Acute Respiratory Failure in Chronic Respiratory insufficiency

In this study, 322 patients were evaluated with two aims: determination of identifiable factors at the time of admission to an ICU that predict short-term survival. Application of the SAPS to this population. Characteristics of patients were as follows: age, 65.5 +/- 14.5 years; COLD, 45 percent; restrictive, 13.4 percent; obstructive and restrictive CRI, 13 percent; asthma progressing to CRI, 11.2 percent; diffuse bronchiectasis, 7.2 percent; neuromuscular diseases, 2.2 percent; others, 8 percent. Cachectic patients, those confined to home, those with initial coma or those who required MV had a higher percentage of M. The SAPS at admission was higher in those patients who died; however, there was no link between the SAPS and M. Prognostic factors in ARF complicating CRI and identifiable at the time of admission to an ICU are few and reflect severity of chronic respiratory disease; SAPS appears to be less useful in ARF complicating CRI.

Acute hypercapnic respiratory failure in patients with chronic obstructive lung disease: risk factors and use of guidelines for management

BACKGROUND

On the basis of a retrospective survey by this unit it was suggested that patients with acute ventilatory failure should be given sufficient controlled oxygen treatment to raise the arterial oxygen tension (PaO2) to above 6.6 kPa, with the addition of a respiratory stimulant if the hydrogen ion concentration ([H+]) rose above 55 nmol/l and assisted ventilation if the patient remained acidotic despite these measures. This study was designed to verify the prognostic factors that determine survival in acute ventilatory failure and determine the outcome when our guidelines were implemented.

METHODS

One hundred and thirty nine episodes of acute hypercapnic (type II) respiratory failure were studied prospectively in 95 patients admitted with acute exacerbations of chronic obstructive lung disease. Patients had to have a PaO2 below 6.6 kPa and an arterial carbon dioxide tension (PaCO2) above 6.6 kPa while breathing air.

RESULTS

The mortality associated with episodes of acute ventilatory failure was 12%. Patients who died tended to be older and were significantly more acidotic, hypotensive, and uraemic on admission than those who survived, but they had similar degrees of hypoxaemia and hypercapnia. Death occurred in 10 of the 39 episodes in which arterial [H+] rose to 55 nmol/l or above, compared with seven of the 100 episodes in which it remained below 55 nmol/l. The respiratory stimulant doxapram was used in 37 episodes and was associated with a reduction in [H+] below 55 nmol/l within 24 hours in 23 episodes. Assisted ventilation was used in only four episodes.

CONCLUSION

Arterial [H+] is an important prognostic factor for survival. Most patients treated according to the guidelines outlined above can be managed successfully without assisted ventilation.

Treatment of acute exacerbations in chronic obstructive pulmonary disease

Therapeutic interventions introduced and refined over the last 10 years, including chronic home oxygen and improved bronchodilators, have resulted in more patients with chronic obstructive pulmonary disease living longer despite more severe functional abnormalities. Episodes of acute respiratory failure in this population remain a major complication requiring rapid assessment and intervention. This article focuses on the diagnostic approach and therapeutic interventions in the patient with obstructive lung disease who presents in acute respiratory distress.

Almitrine bismesylate and oxygen therapy in hypoxic cor pulmonale

The effect of oral treatment with the thiazine derivative almitrine bismesylate was studied in 28 patients with chronic obstructive pulmonary disease and arterial hypoxaemia receiving long term domiciliary oxygen therapy in a placebo controlled, double blind crossover trial. The initial treatment was given for three months and the second for two months. Because almitrine had an unexpectedly prolonged washout effect crossover analysis could not be performed; data from the placebo treatment administered in the second arm of the trial were used to calculate the half life of almitrine. Nine patients were withdrawn from the study (5 almitrine, 4 placebo). Patients' tolerance of the drug was good. The estimated plasma half life of almitrine was 20.5 days, considerably longer than previously reported. Almitrine caused a significant improvement in arterial oxygen tension (PaO2) with a mean maximum increase of 0.7 kPa at a plasma concentration of 500 ng/ml. Higher plasma concentrations were not associated with any further increase in PaO2. There was no significant effect on arterial carbon dioxide tension (PaCO2). In a second, acute study at the end of each arm of the chronic trial nine patients were subjected to increasing oxygen delivery rates (2, 4, and 6 l/min) for 90 minutes or until blood gas concentrations plateaued. Almitrine increased PaO2 in a dose dependent fashion at all delivery rates, but the effect diminished as PaO2 approached normoxic levels. There was no significant effect on PaCO2. Almitrine treatment results in a significant improvement in PaO2 over that achieved by oxygen alone, an effect that diminishes at high flow rates. Whether this is of clinical benefit is not known. In view of the prolonged half life revised dosage schedules are required.