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(Chest. 2001;120:1616-1621.)
© 2001 American College of Chest Physicians

Clinical Course and Outcome of Patients Admitted to an ICU for Status Asthmaticus*

Bekele Afessa, MD, FCCP; Ian Morales, MD and James D. Cury, MD

* From the Department of Internal Medicine (Dr. Morales) and the Division of Pulmonary and Critical Care (Drs. Cury and Afessa), University of Florida Health Science Center, Jacksonville, FL.

Correspondence to: Bekele Afessa, MD, Division of Pulmonary and Critical Care Medicine and Internal Medicine, Mayo Clinic, 200 First St SW, Rochester, MN 55905


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: To describe the prognostic factors, clinical course, and outcome of patients with status asthmaticus treated in a medical ICU (MICU).

Design: Analysis of prospective data.

Setting: A multidisciplinary MICU of an inner-city university hospital.

Patients: We collected data on 132 hospital admissions of 89 patients with status asthmaticus treated in our MICU from August 1995 through July 1998.

Measurements: APACHE (acute physiology and chronic health evaluation) II scores were among the parameters measured.

Results: Seventy-nine percent of the patients were female, and 67% were African American (mean ± SD age, 42.4 ± 15.1 years). Patients in 48 of the 132 hospital admissions (36%) required invasive mechanical ventilation; sepsis developed in patients during 17 hospital admissions (13%), nonpulmonary organ failure developed during 16 hospital admissions (12%), and ARDS developed during 2 hospital admissions (2%). Pneumothorax developed in four patients and required tube thoracostomy in all four patients. The median APACHE II score was 11. Predicted mortality and actual mortality were 6.7% and 8.3%, respectively. The two most common immediate causes of death were pneumothorax (n = 3) and nosocomial infection (n = 3). All the deaths occurred in female patients. Compared with survivors, nonsurvivors had higher APACHE II scores (median, 26 vs 15; p < 0.0001), PaCO2 (63.8 ± 21.3 mm Hg vs 47.8 ± 19.1 mm Hg, p = 0.0101), and lower arterial pH (7.09 ± 0.12 vs 7.27 ± 0.12, p < 0.0001), respectively. Patients in 10 of 48 hospital admissions (21%) who required mechanical ventilation died.

Conclusions: The hospital mortality of patients admitted to an MICU for status asthmaticus is higher than expected. Higher APACHE II score and PaCO2 and lower arterial pH within 24 h of hospital admission are associated with increased mortality. Sepsis and nonpulmonary organ failure are more likely to develop in nonsurvivors than survivors.

Key Words: asthma • ICUs • mechanical ventilation • mortality • status asthmaticus


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
More than 17 million persons were estimated to have asthma in the United States in 1998.1 Worldwide, the prevalence of asthma in adults varies between 2% and 12%.2 In the last 2 decades, the prevalence and death rates for asthma have increased both nationally and regionally, despite numerous advances in diagnosis and treatment.3 4 5 The increase in prevalence and mortality is more pronounced in the minority, inner-city population.6 This study describes the clinical course, in-hospital complications, mortality, and immediate causes of death of adults treated for status asthmaticus in an ICU of an inner-city, tertiary hospital.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
The study involves prospectively collected data of 132 hospital admissions of 89 patients with status asthmaticus. The data were collected as part of the screening of patients admitted to our medical ICU (MICU) for severe exacerbation of asthma or chronic obstructive airway disease for a prospective, randomized study comparing permissive hypercapnia and conventional ventilation. This study included patients in all 132 hospital admissions who were consecutively treated in our MICU over the 3-year period from August 1995 through July 1998. University Medical Center is a 528-bed, tertiary, urban, university hospital located in Jacksonville, FL. The MICU at the University Medical Center, Jacksonville, FL, is a 16-bed facility providing care to critically ill medical and nontrauma neurosurgical and obstetric patients. The data collected included age, race, sex, use and type of mechanical ventilation, length of MICU and hospital stay, development of ARDS, systemic inflammatory response syndrome, organ failure, mortality, and cause of death.

The definition of ARDS was that of the North American/European conference.7 Sepsis was defined according to guidelines of the American College of Chest Physicians/Society of Critical Care Medicine.8 Cardiovascular, hematologic, renal, and CNS failure were defined according to Knaus et al.9 Liver failure was defined as a bilirubin concentration >= 6 mg/dL and prothrombin time >= 4 s over control value. GI failure was defined as GI bleeding or intestinal obstruction or pancreatitis preventing enteral feeding for at least 24 h or until death. APACHE (acute physiology and chronic health evaluation) II scores and predicted mortality rates were calculated as described in the literature.10 The standardized mortality ratio was determined as the ratio of the actual mortality to the predicted mortality.

The decision when to use invasive or noninvasive ventilation was based on the judgment of the emergency department or ICU attending physicians. In general, there was a preference to use noninvasive ventilation first. However, invasive ventilation (Servo 900C; Siemens; Solna, Sweden) was used from the outset in patients with hemodynamic instability, altered mental status, and life-threatening gas-exchange abnormalities. Although the ventilatory approach had some variations, depending on the intensivist and the patient, a lower tidal volume strategy aimed at minimizing airway pressures was applied in most patients. In patients with suspected cerebral edema, hypercapnea was avoided. Static and dynamic compliance at the initiation of mechanical ventilation in the MICU were calculated from the recorded peak airway pressure, positive end-expiratory pressure (PEEP), plateau pressure, and tidal volume. Auto-PEEP was measured by occluding the airway at end expiration by using the expiratory pause button of the ventilator.

Statistical analysis was performed using software (StatView 5.0; SAS Institute; Cary, NC). All means were expressed with SD. Comparisons between groups were made by using Student’s t test, Mann-Whitney U test, {chi}2 test, and Fisher’s Exact Test. All p values < 0.05 were considered significant.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
The age at first hospital admission, race, and sex of the 89 patients are listed in Table 1 . During the 3-year study period, 1 patient was admitted to the MICU nine times, 1 patient was admitted seven times, 2 patients were admitted five times, 2 patients were admitted four times, 5 patients were admitted three times, 5 patients were admitted twice, and 73 patients were admitted once.


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  		Table 1.. Age, Race, and Sex of 89 Patients With Status Asthmaticus*

 
The age of the patients at admission to the MICU was 41.9 ± 15.0 years. Invasive mechanical ventilation was administered to patients in 48 hospital admissions (36%). Difficult airway led to emergency cricothyroidotomy in one patient who had been intubated endotracheally during a previous hospital admission of the study period. Noninvasive mechanical ventilation was administered to patients in 27 hospital admissions (20%); invasive mechanical ventilation was subsequently required for patients in 5 of the 27 hospital admissions. The APACHE II score was 12.1 ± 7.0, and predicted mortality was 6.7 ± 16.8%. None of the patients with an APACHE II score of <= 10 and six of the seven patients (86%) with an APACHE II score > 25 died (Table 2 ). Five of the patients with an APACHE II score > 25 had had cardiac arrest or tension pneumothorax prior to MICU admission. The median length of MICU stay was 2 days, and the median length of hospital stay was 4 days. Forty-eight of the patients (36%) stayed in the MICU for >= 3 days, and 33 of these 48 patients (69%) required invasive mechanical ventilation. The median duration of invasive mechanical ventilation in patients in the 48 hospital admissions was 3 days.


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  		Table 2.. Categories of APACHE II Score in Survivors and Nonsurvivors of Medical ICU Admissions for Status Asthmaticus

 
Eleven of the 89 patients (12%) died. The in-hospital mortality for patients in the 132 hospital admissions was 8.3%. The immediate causes of death are listed in Table 3 . Ten of the deaths occurred during the first hospital admission, and 1 death occurred during the third hospital admission.


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  		Table 3.. Immediate Causes of Death in 11 Patients Hospitalized for Status Asthmaticus

 
Pneumothorax developed in four patients: during bag ventilation after endotracheal intubation (n = 3) and during invasive positive-pressure mechanical ventilation (n = 1). In four patients, anoxic encephalopathy developed after prehospital cardiac arrest, and three of these patients subsequently died.

Sepsis developed in patients in 17 of the 132 admissions (13%). The identified sources of the sepsis were pneumonia (n = 7), blood stream (n = 4), central vascular line (n = 2), urinary tract (n = 1), bronchitis (n = 1), and gallbladder (n = 1). The pathogens were Enterobacter cloacae (n = 5), Pseudomonas aeruginosa (n = 4), Staphylococcus aureus (n = 2), Morganella morganii (n = 1), Klebsiella pneumoniae (n = 1), Enterococcus spp (n = 1), and Viridans streptococci (n = 1).

The types and number of nonpulmonary organ failures that developed in patients in the 132 hospital admissions are listed in Table 4 . ARDS developed in patients in two hospital admissions (1.5%). The in-hospital mortality rate was 8.3%. The standardized mortality ratio was 1.24. The differences between survivors and nonsurvivors are listed in Tables 5 , 6 .


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  		Table 4.. Type and No. of Nonpulmonary Organ Failures in 132 Medical ICU Admissions for Status Asthmaticus

 

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  		Table 5.. Differences in Baseline Characteristics Between Survivors and Nonsurvivors of 132 Medical ICU Admissions for Status Asthmaticus*

 

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  		Table 6.. Differences in Incidence of Sepsis, No. of Organ Failures, and Need for Mechanical Ventilation Between Survivors and Nonsurvivors of 132 Medical ICU Admissions for Status Asthmaticus*

 
Two of the 5 patients (40%) who required invasive mechanical ventilation after the failure of noninvasive ventilation died, compared with 7 of 43 patients (16%) who received invasive mechanical ventilation from the outset (p = 0.0541). Of the 48 patients who required invasive mechanical ventilation, the differences in the initial inspiratory airway resistance, plateau pressure, auto-PEEP, static compliance, and dynamic compliance levels were not statistically significant between survivors and nonsurvivors (Table 7 ).


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  		Table 7.. Differences in Auto-PEEP, Dynamic Compliance, and Static Compliance Levels Between Survivors and Nonsurvivors Who Required Invasive Mechanical Ventilation*

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
In this study, most of the 89 patients admitted to an MICU of an inner-city hospital for status asthmaticus were African American and female. Nonpulmonary organ failure and sepsis developed in patients in 12% and 13% of the 132 hospital admissions, respectively. The in-hospital mortality rate of 8% was higher than the mortality rate predicted by the APACHE II prognostic system. Although it did not reach statistical significance, none of the male patients died, compared with 11 of the 70 female patients. Pneumothorax and nosocomial infections were the immediate causes in 6 of the 11 deaths. Compared with survivors, nonsurvivors had higher APACHE II scores and PaCO2 and lower arterial pH, but a similar ratio of PaO2 to fraction of inspired oxygen. The incidence of sepsis and the number of organ failures were higher in nonsurvivors than in survivors. Of the 48 patients who required invasive mechanical ventilation, there was no significant difference in the auto-PEEP level, dynamic compliance, and static compliance between survivors and nonsurvivors.

Compared with whites, African Americans with asthma have higher mortality and hospitalization rates.4 5 6 Since our hospital serves an indigent, predominantly inner-city population, most of the patients were of African American origin and were of low socioeconomic status. Consistent with previous findings11 showing that more women die of asthma, in the present study most of the patients were female and all the deaths occurred in female patients.

The lack of appropriate prehospital care, positive-pressure-ventilation management in the prehospital setting and the ICU, and nosocomial infections may have contributed to the high mortality rate in the present study. Unlike some other cities, there was no good network to provide care and medications to the indigent population with asthma in Jacksonville, FL. The lack of access to health care and noncompliance have forced a good number of our patients to use the emergency departments as the only source of medical care. Because of differences in the ICU admission criteria and the approach to institution of mechanical ventilation, the rate of ventilatory support is likely to vary among countries and institutions. Previous studies12 13 14 15 16 17 18 have reported that from 2 to 61% of patients hospitalized for status asthmaticus require mechanical ventilation. Only one of these previous studies16 had a prospective component. In the present prospective, observational study, 36% of the patients required invasive mechanical ventilation. The mortality rate of patients requiring mechanical ventilation for status asthmaticus can be as high as 42%.15 The incidence of pneumothorax in patients with status asthmaticus requiring positive-pressure ventilation varies from study to study,12 13 14 15 19 20 21 22 23 ranging from 0 to 33%. In the present study, patients who required invasive mechanical ventilation in 21% of hospital admissions died, and pneumothorax was the immediate cause of 3 of the 11 deaths. The mortality of asthmatic patients requiring invasive mechanical ventilation in the present study was significantly higher than the 6% mortality rate reported by Zimmerman et al24 in an inner-city patient population similar to ours. This finding highlights the need for improving the way we provide positive-pressure ventilation to patients with status asthmaticus, including the way paramedics provide bag ventilation during prehospital care. Strategies aimed at reducing dynamic hyperinflation are likely to decrease the incidence of hemodynamic compromise and barotrauma in patients with status asthmaticus requiring positive-pressure ventilation.25 Although randomized, controlled trials are not available, observational studies13 26 have shown that permissive hypercapnia reduces mortality in these patients.

The development of sepsis and organ failure in critically ill patients is associated with increased mortality.9 27 The incidence and impact of sepsis and multiple-organ failure in status asthmaticus have not been described. In the present study, sepsis developed in 13% and nonpulmonary organ failure developed in 12% of the patients; the most common nonpulmonary organ failure was cardiovascular, probably reflecting the hemodynamic compromise associated with positive-pressure mechanical ventilation in patients with status asthmaticus. Although the median length of ICU stay was only 2 days, 48 patients, most of whom required invasive mechanical ventilation, stayed in the ICU for >= 3 days, accounting for the higher-than-expected incidence rate of sepsis in the present study.

Measurement of severity is important in describing and comparing treatment regimens and disease outcome. The APACHE II prognostic system has been used to predict the outcome of critically ill patients admitted to ICUs for almost 2 decades. However, we know of no studies addressing the role of APACHE II in predicting the mortality of patients treated in ICUs for status asthmaticus. One study28 found that the acute physiology score of APACHE II correlated with the length of ICU stay in patients with acute asthma. In the present study, we found that the observed hospital mortality rate was higher than the APACHE II-predicted mortality rate. This contrasts with another disease group from our MICU,29 in which the observed mortality is lower than the predicted; this finding highlights the need to improve the care we are providing to inner-city asthmatic patients.

This study has several weaknesses. Although it was based on data collected prospectively, it was not designed to answer most of the questions that can arise regarding status asthmaticus. No data were collected about outpatient long-term care, access to health-care facilities, and compliance of the patients. Knowledge of the patients’ baseline characteristics is important to determine whether our findings can apply to other patient populations. Because of the difficulty in gathering information about the outpatient health care in our patient population, we do not have the data to address this issue satisfactorily. Moreover, since the study was performed in a single, inner-city, tertiary medical center, our findings may not apply to other patient populations.

In conclusion, this study describes the prognostic factors, complications, and outcome of patients with status asthmaticus treated in an inner-city MICU. The hospital mortality was higher than expected. All the deaths occurred in female patients, but this result was not statistically significant. Nonsurvivors had higher APACHE II scores and PaCO2 and lower arterial pH than survivors. Nonsurvivors more often had sepsis and organ failure than did survivors. Barotrauma and nosocomial infection contributed to mortality. In order to improve the outcome of patients hospitalized for status asthmaticus, future endeavors should include prevention of iatrogenic and nosocomial complications.


   Footnotes
 
Abbreviations: APACHE = acute physiology and chronic health evaluation; MICU = medical ICU; PEEP = positive end-expiratory pressure

Received for publication September 26, 2000. Accepted for publication March 20, 2001.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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