Mechanical ventilation for asthma: a 10-year experience

BACKGROUND

Asthmatics requiring admission to the intensive care unit and/or mechanical ventilation have increased morbidity and mortality. The purpose of this study is to examine morbidity and mortality in patients requiring intubation and mechanical ventilation for asthma over a 10-year period. This study also reviews the clinical features and management of these patients.

METHODS

We performed a retrospective review of medical records over a 10-year period of adult patients who required mechanical ventilation for a primary diagnosis of asthma. The study was conducted at a university-affiliated, county hospital.

RESULTS

One hundred twenty-seven patients with 162 episodes of asthma requiring mechanical ventilation were identified. The majority of the patients (64%) were women. The predominant ethnicity was African-American (65%). These patients had multiple risk factors for asthma mortality, including recent hospital admissions, prior episodes of near-fatal asthma, medication non-compliance, and poor outpatient follow-up. Over the 10 years of the study, outpatient management of these patients changed, with the percentage of admissions in which patients had been given inhaled corticosteroids increasing from 18 percent in 1990 to 80 percent in 1998. Management of mechanical ventilation also changed. The average tidal volume settings significantly decreased after 1995. The most common complication was atelectasis, which was seen in 33 cases. Evidence of barotrauma, including pneumothorax, pneumomediastinum, and subcutaneous emphysema, was present in 10 cases. There were four deaths. All four of the patients suffered cardiopulmonary arrest in the field with subsequent anoxic brain injury and withdrawal of care.

CONCLUSIONS

Although these patients had multiple risk factors for mortality from asthma, no deaths in this study were related to complications of mechanical ventilation. This low mortality may be related to changes in management of mechanical ventilation as well as changes in chronic outpatient asthma therapy.

Acute severe asthma: recent advances

PURPOSE OF REVIEW

Acute severe asthma is challenging to the clinician both in terms of recognition and appropriate treatment. About 30% of these episodes need admission to the medical intensive care unit with a mortality of 8%. Relapse rates vary from 7 to 15% depending on how well the patient is managed. The purpose of this review is to discuss recent advances in identification of risk factors, pathophysiology and management of acute severe asthma.

RECENT FINDINGS

Although the exact mechanism for acute severe asthma is unclear, some that are implicated include inflammation, airway remodeling and downregulation of beta-receptors. None of the environmental factors have been clearly related to the development of near fatal attacks. Genetic polymorphisms have been associated with severe asthma. Lack of steroid responsiveness has been linked to severe asthma attacks. Chemokines and basement membrane changes characteristic of severe asthma are reported in a few studies. Lack of symptom perception in a certain group of patients with acute severe asthma leads to delayed interventions. Specific treatment modalities and ventilator management is reviewed.

SUMMARY

Severe asthma is a phenotype of asthma with variable pathology and clinical presentation. Early recognition and timely intervention is needed to prevent significant mortality and morbidity.

Hypotension is a predictor of mortality in acute exacerbations of chronic obstructive pulmonary disease

OBJECTIVES

To identify variables that predict the in-hospital course and prognosis of patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

METHODS

A retrospective analysis of 94 patients (20 females) with AECOPD. Twenty-one variables including arterial blood gas studies were analysed.

RESULTS

The mean age was 61.2 years. The in-hospital mortality rate was 12.8%; 28.6% of patients required invasive mechanical ventilation and 37.2% required ICU care. In univariate analysis, aypotension at presentation (systolic blood-pressure < 90 mmHg) [p = 0.002, odds ratio OR 10.95, 95% confidence interval (CI) 1.90-63.00); central cyanosis (p = 0.007, OR 6.91, 95% CI 1.42-33.59); and cor-pulmonale (p = 0.009, OR 10.46, 95% CI 1.26-86.46) were univariately associated with in-hospital mortality. On multivariate analysis, hypotension (p = 0.049, OR 18.419, 95% CI 1.013-334.752) remained the only independent predictor.

CONCLUSIONS

More than the markers of poor gas exchange, the presence of hypotension indicates a poor in-hospital prognosis in AECOPD.

Review of ventilatory techniques to optimize mechanical ventilation in acute exacerbation of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major global healthcare problem. Studies vary widely in the reported frequency of mechanical ventilation in acute exacerbations of COPD. Invasive intubation and mechanical ventilation may be associated with significant morbidity and mortality. A good understanding of the airway pathophysiology and lung mechanics in COPD is necessary to appropriately manage acute exacerbations and respiratory failure. The basic pathophysiology in COPD exacerbation is the critical expiratory airflow limitation with consequent dynamic hyperinflation. These changes lead to further derangement in ventilatory mechanics, muscle function and gas exchange which may result in respiratory failure. This review discusses the altered respiratory mechanics in COPD, ways to detect these changes in a ventilated patient and formulating ventilatory techniques to optimize management of respiratory failure due to exacerbation of COPD.

Role of vocal cord function and dysfunction in patients presenting with symptoms of acute asthma exacerbation

A total of 48 patients presenting to the emergency department as acute asthma exacerbation were prospectively studied. Rhinolaryngoscopy was conducted with simultaneous flow measurements and spirometry performed before and after the procedure. Measurements of the vocal cord opening during various phases of respiration were analyzed. Only 4 of 48 patients had anterior two-thirds closure of the vocal cords with a diamond-shaped opening posteriorly during expiration. One additional patient had inspiratory and expiratory closure of the vocal cords. The previously unreported high incidence of anterior two-thirds closure (10.4%) of the vocal cords suggests that the upper airway has a role to play in a significant number of patients presenting with symptoms of asthma exacerbation.

Smoking and systemic disease

Cigarette smoking is associated with a number of adverse health effects, including well-established links to cardiopulmonary disease and several cancers. Some of the other important systemic diseases associated with smoking are the subjects of this article, such as diabetes mellitus and insulin resistance, and thyroid diseases. Also reviewed here is the impact of smoking on male and female infertility, on selected dermatologic conditions, and on gastrointestinal diseases including peptic ulcer and inflammatory bowel diseases.

Predictors of development and outcome in patients with acute respiratory distress syndrome due to tuberculosis

OBJECTIVE

To study the predictors of development and determinants of outcome in patients with acute respiratory distress syndrome (ARDS) due to tuberculosis (TB).

METHODS

Retrospective case-control study of demographic, clinical and laboratory data of hospitalised adult patients with active TB.

RESULTS

Of 2733 TB patients treated during 1980-2003, 29 (1.06%; 1.21 patients/year; mean age 31.6 +/- 10.9 years; 16 males) developed ARDS (cases). Seven had pulmonary TB and 22 had miliary TB (MTB); 298 (mean age 32.0 +/- 14.2 years; 110 males) who did not develop ARDS constituted controls. Presence of MTB (OR 4.6, 95%CI 1.2-17.8; P = 0.02), duration of illness beyond 30 days at presentation (OR 177.9, 95%CI 39-811.7; P < 0.001), absolute lymphocyte count < 1625/ mm3 (OR 4.5, 95%CI 1.1-19.3; P = 0.04) and serum ALT > 100 IU (OR 15.7, 95%CI 3.0-81.1, P < 0.001) were independent predictors of ARDS development. Twelve cases died (41.4%). Patients with APACHE II score >18; those with APACHE II score <18 in the presence of hyponatraemia and PaO2/FIO2 ratio <108.5 were likely to die.

CONCLUSIONS

In patients with TB, prolonged illness, MTB, absolute lymphocytopaenia and elevated ALT are independently associated with ARDS development. APACHE II score, serum sodium and PaO2/FIO2 ratio are determinants of outcome.

Neurologic disorders in pregnancy

BACKGROUND

Neurologic dysfunction, coma, and seizures are common in obstetric patients in the intensive care unit.

OBJECTIVE

To review common neurologic disorders resulting in critical illness in pregnancy.

REVIEW

Obstetric disorders causing coma and seizures include eclampsia, acute fatty liver of pregnancy, and amniotic fluid embolism. Preexisting disorders such as epilepsy may worsen in one-third of pregnant patients, and seizures are common during labor. Changes in hemodynamics, blood volume, and hormonal effects on the vessel wall increase risk of bleeding from berry aneurysms and arteriovenous malformations during pregnancy and the postpartum period. Acute intermittent porphyria produces seizures and hypertension, closely mimicking eclampsia. Cerebral venous sinus thrombosis is common in postpartum patients, especially in developing countries. Brain tumors invariably enlarge during pregnancy because of fluid retention and the presence of estrogen and progesterone receptors on tumor cells. Infections such as cerebral malaria and acute viral hepatitis with fulminant hepatic failure are common causes of coma and seizures during pregnancy in tropical regions of Asia, Africa, and Latin America. Patients may be admitted to the intensive care unit with type II respiratory failure due to myasthenic crisis, Guillain-Barre syndrome and spinal cord disease. Relapses of multiple sclerosis are infrequent during pregnancy but increase in the postpartum period.

CONCLUSIONS

In all instances, the effects of the disorders, diagnostic tests, and treatment on the fetus must be carefully weighed. Prompt delivery may be lifesaving for mother and fetus in conditions such as eclampsia and acute fatty liver of pregnancy; expectant treatment may be more appropriate in others.

Localization and upregulation of cysteinyl leukotriene-1 receptor in asthmatic bronchial mucosa

We have tested the hypothesis that the CysLT(1) receptor is expressed by a variety of bronchial mucosal immune cells and that the numbers of these cells increase in asthma, when stable and in exacerbations. We have applied in situ hybridization and immunohistochemistry to endobronchial biopsy tissue to identify and count inflammatory cells expressing CysLT(1) receptor mRNA and protein, respectively, and used double immunohistochemistry to identify the specific cell immunophenotypes expressing the receptor. Double-labeling demonstrated that bronchial mucosal eosinophils, neutrophils, mast cells, macrophages, B-lymphocytes, and plasma cells, but not T-lymphocytes, expressed the CysLT(1) receptor. The numbers of CysLT(1) receptor mRNA and protein positive inflammatory cells in nonsmoking, nonatopic control subjects without asthma were 13 and 16 mm(-2), respectively (median values; n = 15), and were significantly greater in stable asthma (50 and 43 mm(-2), respectively; n = 17; P < 0.001). Compared with stable asthma, there were further significant increases in subjects hospitalized for a severe exacerbation of their asthma (mRNA: median = 113 and protein: 156 mm(-2); n = 15; P < 0.002). For the combined data of both asthma subgroups, there were strong positive correlations between the increased numbers of CD45+ leukocytes and the greater numbers of cells expressing CysLT(1) receptor (mRNA: r = 0.60, P < 0.001; protein: r = 0.73, P < 0.0001). In conclusion, a variety of immunohistologically distinct inflammatory cells express the CysLT(1) receptor in the bronchial mucosa and both these and the total number of leukocytes increase in mild stable disease and increase further when there is a severe exacerbation of asthma.

Critically ill obstetric patients in an American and an Indian public hospital: comparison of case-mix, organ dysfunction, intensive care requirements, and outcomes

OBJECTIVE

To compare case-mix, health care practices, and outcome in obstetric ICU admissions in inner-city teaching hospitals in economically developed and developing countries.

DESIGN

Retrospective study.

SETTING

Ben Taub General Hospital (BTGH), Houston, Texas, and King Edward Memorial Hospital (KEMH), Mumbai, India.

PATIENTS

Women admitted during pregnancy or 6 weeks postpartum between 1992 and 2001.

MEASUREMENTS AND RESULTS

Patients from BTGH (n=174) and KEMH (n=754) had comparable age, number of organs affected, incidence of medical disorders (30%), liver dysfunction, and thrombocytopenia. Fewer KEMH patients received prenatal care (27 vs 86%) and came to hospital within 24 h of onset of symptoms (60 vs 90%). They had higher APACHE II scores (median 16 vs 10), greater incidence of neurological (63 vs 36%), renal (50 vs 37%), and cardiovascular dysfunction (39 vs 29%). Severe malaria, viral hepatitis, cerebral venous thrombosis, and poisoning were common medical disorders. The BTGH group had higher incidence of respiratory dysfunction (59 vs 46%) and disseminated intravascular coagulation (40 vs 23%), placental anomalies, HELLP syndrome, chorioamnionitis, peripartum cardiomyopathy, puerperal sepsis, urinary infection, bacteremia, substance abuse, and asthma. More BTGH patients required mechanical ventilation and blood component therapy, whereas more KEMH patients needed dialysis. Of BTGH patients, 78.2% were delivered by cesarean section (vs 15.4%). Maternal (2.3 vs 25%) and fetal (13 vs 51%) mortality were lower in BTGH patients.

CONCLUSIONS

There were marked differences in medical diseases, organ failure, and intensive care needs. Higher mortality in the Indian ICU may be due to difference in case mix, inadequate prenatal care, delay in reaching hospital, and greater severity of illness.

Effect of airway pressure display on interobserver agreement in the assessment of vascular pressures in patients with acute lung injury and acute respiratory distress syndrome*

BACKGROUND

Previous investigations have identified significant interobserver variability in the measurements of central venous pressure and pulmonary artery occlusion pressure in critically ill patients. Large interobserver variability in the measurement of vascular pressures could potentially lead to inappropriate treatment decisions.

OBJECTIVE

We postulated that adding an airway pressure signal (Paw) to pressure tracings of central venous pressure and pulmonary artery occlusion pressure would improve interobserver agreement by facilitating identification of end-expiration.

DESIGN

To test this hypothesis, six independent experts used a standard protocol to interpret strip-chart recordings of central venous pressure and pulmonary artery occlusion pressure with or without Paw. Two observers were said to agree if their measurements were within 2 mm Hg of each other. SETTING/SUBJECTS/INTERVENTIONS: A total of 459 strip-chart recordings (303 without Paw and 156 with Paw) were obtained from 121 patients enrolled in the ARDSnet Fluids and Catheters Treatment Trial (FACTT) in 16 different hospitals.

RESULTS

Agreement within 2 mm Hg between two measurements was 79% for central venous pressure strips without Paw vs. 86% with Paw. For pulmonary artery occlusion pressure, agreement increased from 71% without Paw to 83% with Paw. The increase in agreement with the addition of Paw was greater for strips demonstrating >8 mm Hg phasic respiratory variation compared with strips demonstrating less phasic respiratory variation.

CONCLUSION

Paw display is a simple, inexpensive method to facilitate the identification of end-expiration that can significantly improve interobserver agreement.

Critical illness and pregnancy: review of a global problem

Obstetric patients are a small but important group of patients in the intensive care unit (ICU). Their problems are unique and need specialized attention. Decision making may be confounded by physiologic changes in pregnancy. In developed countries with good antenatal care, comparatively fewer obstetric patients are admitted to ICUs, but the maternal mortality rate remains high in the developing countries. Medical disorders and organ dysfunction caused by critical illness of pregnancy differ from region to region. With improvement in antenatal care, the number of ICU admissions for obstetric disorders would decline in developing countries; however, this number may increase gradually in developed countries because of increasing maternal age and pregnancies in women with complicated chronic medical disorders.

Smoking and systemic disease

Cigarette smoking is associated with a number of adverse health effects, including well-established links to cardiopulmonary disease and several cancers. Some of the other important systemic diseases associated with smoking are the subjects of this article, such as diabetes mellitus and insulin resistance and thyroid diseases. Also reviewed here is the negative impact of smoking on male and female infertility, on selected dermatologic conditions, and on gastrointestinal diseases including peptic ulcer and inflammatory bowel diseases.

Respiratory failure in interstitial lung disease

PURPOSE OF REVIEW

Respiratory failure associated with interstitial lung disease (ILD) occurs commonly, often as a terminal event after a prolonged course of illness. Diagnosis and management of the underlying ILD and respiratory failure pose great challenges.

RECENT FINDINGS

Respiratory failure in the absence of a clearly identifiable cause has a high mortality and frequent complications. Patients with idiopathic pulmonary fibrosis who are admitted with respiratory failure have a grim prognosis and may not benefit from prolonged aggressive therapy including mechanical ventilation. Presence of diffuse alveolar damage or usual interstitial pneumonia on lung biopsy specimens from patients with respiratory failure may be a marker of poor prognosis. Recently, the importance of the clinical-radiologic-pathologic diagnosis has been emphasized.

SUMMARY

The prognosis and treatment may vary according to the type of ILD and the cause of the respiratory failure, which must therefore be established before treatment is initiated. Prevention of iatrogenesis and timely application of palliation are as important as specific treatment of underlying ILD.

Early thickening of the reticular basement membrane in children with difficult asthma

Remodeling of the airway wall occurs in adults with asthma, and reticular basement membrane (RBM) thickening is pathognomonic of the asthma process. To investigate whether RBM thickening is present in children with difficult asthma and comparable to that seen in adults with asthma, we used light microscopy to measure RBM thickness in plastic-embedded endobronchial biopsy sections from 19 children with difficult asthma who were prescribed 1,600 microg/day or more of inhaled steroids (age range, 6-16 years), 10 children without asthma (7-16 years), and three adult groups: 8 healthy control subjects (21-42 years), 10 mild steroid-naive subjects with asthma (18-41 years), and 6 adults (3 steroid naive and 3 on inhaled steroids) intubated after a life-threatening attack of asthma (20-64 years). RBM thickness in the children with asthma was similar to that in adults with either mild or life-threatening asthma (median 8.2 [range 5.4-11.1] versus 8.1 [5.8-10.0] and 7.2 [2.8-10.0] microm, respectively) and greater than either adult or pediatric control subjects (8.2 [5.4-11.1] versus 4.4 [3.2-6.3] microm, p < 0.01, and 4.9 [3.7-8.3] microm, p < 0.01). We conclude that RBM thickening is already present in children with difficult asthma and to a similar extent to that seen in adults with asthma. In addition, we find no association with age, symptom duration, lung function, or concurrent eosinophilic airway inflammation.

The effect of heliox-driven bronchodilator aerosol therapy on pulmonary function tests in patients with asthma

To compare the effects of heliox-driven (He 80:O2 20) to air-driven (N 79:O2 21) beta2-agonist aerosol therapy on pulmonary function tests (PFTs) in patients with asthma, a prospective randomized crossover study was undertaken in the asthma clinic of the university-affiliated county hospital in Houston, TX. Thirty-one patients (22 female, age range 18-44) with clinically stable asthma consented. All patients were studied on two different days with both heliox and air as driving gas, therefore serving as their own controls. The PFTs including forced expiratory volume in 1 sec (FEV1), forced vital capacity (FVC), maximal mid-expiratory flow rate (FEF(25-75)), and maximal expiratory flow rate (FEFmax) were obtained while breathing ambient air at baseline and 30 min after the bronchodilator treatment. Albuterol sulfate 2.5 mg was nebulized with either heliox or compressed air at 8 L/min for 8 min. When heliox was used as driving agent, additional heliox was delivered via a closed system and no entrainment of external air was allowed. Primary outcome measure was absolute change in FEV1 (deltaFEV1). There were no statistically significant differences in baseline PFTs on the two days of the study. All patients had good bronchodilator response (> or = 12% improvement in FEV1) with either driving gas. The deltaFEV1 after heliox-driven bronchodilator (HDBD) and air-driven bronchodilator (ADBD) were 0.68+/-0.38 L/sec (CI: 0.54-0.82) vs. 0.51+/-0.26 L/sec (CI: 0.42-0.60), respectively (p=0.004). The deltaFEV1 with HDBD was 49+/-90% (range -36% to 433%) more than ADBD. A subgroup analysis showed this was largely due to better response rates in patients with moderate to severe obstruction. There was more improvement in both FVC and FEFmax with HDBD than ADBD (p<0.05). The changes in FEF(25-75) were similar. We conclude that HDBD therapy improves FEV1, FVC, and FEFmax significantly more than ADBD in patients with asthma. Further large randomized studies are needed to better characterize responders and the impact on clinical outcomes.