Affiliations: New York, NY
Dr. Shapiro is Assistant Professor of Clinical Medicine, Columbia University, and Director of Medical Intensive Care Unit, St. Luke’s-Roosevelt Hospital.
Correspondence to: Janet M. Shapiro, MD, Division of Pulmonary-Critical Care Medicine, St. Luke’s Hospital MU 316, 1111 Amsterdam Ave, New York, NY 10025
Intensive care management of status asthmaticus has
advanced in recent years. Knowledge of the inflammatory basis of severe
asthma and the pathophysiologic consequences of airway
obstruction1 has translated into improvements in the
medical and ventilatory approaches.
Still, status asthmaticus carries a significant risk of morbidity and
mortality in the ICU. In this issue of CHEST (see page
1616), Afessa and colleagues present an observational study of 132
medical ICU admissions for status asthmaticus in an urban hospital.
There was a notable predominance of African-American patients (67%)
and women (79%). Invasive mechanical ventilation was required in 48
patients (36%), and noninvasive ventilation was initiated in 27
patients (20%), 5 of whom subsequently required intubation.
Eleven patients died, giving a mortality rate of 8.3%. Features
distinguishing nonsurvivors were lower initial arterial pH and higher
Paco2, higher APACHE (acute
physiology and chronic health evaluation) II score, development of
sepsis and organ failures, and need for mechanical ventilation. The
occurrence of pre-ICU cardiopulmonary arrest can explain many of the
findings. Three of four patients suffering pre-ICU cardiopulmonary
arrest and anoxic encephalopathy died. The mean APACHE score of 25
among nonsurvivors is much higher than that among survivors in this
series and in the literature.2 Pre-ICU cardiopulmonary
arrest or tension pneumothorax had occurred in five of the patients
with the highest APACHE II scores. The authors note a higher mortality
rate than predicted based on APACHE II; however, the group includes
patients in whom circulatory arrest may be considered the principal ICU
The mortality rate of 21% among intubated patients is striking.
In contrast to the high mortality of such patients in prior
years,3several series over the past 2 decades report
lower mortality rates of 0 to 6%,4–6 although mortality
was 22% in one study.7Of 75 patients intubated for
status asthmaticus over a 5-year period at my hospital in New York
City, 2 patients (2.6%) died; both had suffered prehospital
cardiorespiratory arrest with resultant anoxic
encephalopathy.8 Most ICU deaths thus appear to be
consequences of pre-ICU cardiopulmonary arrest.5–6,8
The frequency of mechanical ventilation varies in the literature from
30%4 to 100%6–7 and is likely subject to
differences in disease severity in particular
locations,9–10 ICU admission criteria, and clinicians’
decisions to initiate mechanical ventilation. The ventilator management
is guided by the principle of preventing dynamic hyperinflation. Based
on studies1 of trapped gas volume, targeting a minute
ventilation of 115 mL/kg and plateau pressure < 25 cm
H2O will usually prevent severe dynamic
hyperinflation and unnecessary extreme hypercapnia. A low tidal volume
(8 mL/kg) and a slow respiratory rate (10 to 14/min) are set to provide
a prolonged expiratory time, thereby minimizing air trapping and its
consequences of hemodynamic compromise and barotrauma. Measurements of
peak airway pressures and auto-positive end-expiratory pressure have
not been found to correlate with complications. Permissive hypercapnia
(with levels of Paco2 up to 90 mm Hg)
is generally tolerated when adequate oxygenation is achieved; the main
contraindication is intracranial disease.,11 Permissive
hypercapnia is therefore avoided in patients who have already suffered
an anoxic brain injury and cerebral edema following cardiorespiratory
Hypotension is a common complication after initiation of mechanical
ventilation, reported by Williams et al5 in 20 to 41% of
cases. Barotrauma was found to complicate status asthmaticus in 14 to
27% of their patients.5 In the current study, three of
the four cases of pneumothorax developed during bag ventilation after
intubation. The authors raise an excellent point that the approach to
manual bag ventilation in the field is a potential area for education
Noninvasive ventilation was attempted in 20% of patients in the study
by Afessa et al. Although there are no trials comparing noninvasive and
invasive ventilation, noninvasive ventilation may have a role in
selected patients with status asthmaticus.12Most patients
with severe asthma, including many presenting with
hypercapnia,13 improve rapidly with conventional therapy
and do not require intubation, so it may be difficult to prove the
benefit of noninvasive support. The fact that there were two deaths
among the five patients initially treated with noninvasive ventilation
who required intubation raises the possibility that delaying invasive
ventilatory support led to refractory deterioration.
Data concerning the six patients in the current study who developed
neurologic dysfunction are not presented. Major neurologic syndromes
may complicate critical care of status asthmaticus. Myopathy has been
attributed to concomitant neuromuscular blockade and corticosteroid
administration.2,14–15 In one series, myopathy was
detected in 10% of 64 episodes of status asthmaticus, occurring in
30% of those who received neuromuscular blockade.2
Consequences of myopathy include increased duration of mechanical
ventilation and hospital stay, as well as the need for
rehabilitation.2,14 Neuromuscular blocking agents are
therefore avoided in patients with status asthmaticus. Critical illness
polyneuropathy may complicate the course of patients who acquire sepsis
while in the ICU.16 Anoxic encephalopathy is a devastating
consequence of cardiopulmonary arrest; of our six patients who had
suffered pre-ICU cardiopulmonary arrest, two patients died and two
patients remained in a coma and were discharged to nursing
Although the median duration of mechanical ventilation was 3 days in
this series, as in the literature,6 many patients required
assisted ventilation for a longer period, placing them at risk of ICU
complications. Sepsis was reported in 13% of patients and was the
immediate cause of death in three patients. GI bleeding and probable
venous thromboembolism were proximate causes of death in one patient
each in the current study.
ICU survival should be expected for those patients who have not
suffered cardiorespiratory arrest. However, these patients remain at
risk for future asthma death. One study17 of 121 survivors
of status asthmaticus demonstrated a 15% mortality within the next 6
years; cigarette smokers were at especially high risk of death.
Afessa and colleagues provide a complete description of the ICU course
in their patients with status asthmaticus. However, important questions
remain. We lack information on the patients’ asthma histories and
access to appropriate outpatient medical care. The authors describe
many patients who were admitted to the ICU multiple times during the
Black and Hispanic individuals predominate among patients with
severe asthma and fatal asthma in urban areas.10,18–
Cigarette smoking and illicit drug use19present
additional exacerbating factors. A recent study20 reported
that high-risk asthmatic women were hospitalized twice as often as men.
Minority women account for > 70% of ICU patients with status
asthmaticus in the current study and in most series in the
literature.4,7,14 In addition to biological differences,
contributing factors may include poverty, environmental concerns in the
home, and gender differences in the quality of care.21One
study reported poor ability to utilize a metered-dose inhaler among
women22 and raises the additional possibility of
inadequate instruction offered to women.21
Patients may underestimate the degree of worsening airflow obstruction.
Reduced perceptions of dyspnea and hypoxia were found among 11 patients
following respiratory failure due to status asthmaticus.23–
Psychosocial factors, including denial of illness24 and
illicit drug use,19 can impede action in a deteriorating
situation. Survivors of respiratory failure who are noncompliant with
medical visits may be at particular risk of death. In a prospective
study25 in which close outpatient follow-up was offered to
12 such patients, 2 of the 5 patients who declined the protocol died
within the 18-month period.
Afessa and colleagues describe the high mortality and morbidity among
patients admitted to an ICU for status asthmaticus. This examination
reinforces the challenges to the pulmonary-critical care community to
improve the entire spectrum of care—from the outpatient setting to the
ICU—and thus enhance outcome in status asthmaticus.
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