Halm EA, Fine MJ, Marrie TJ, Coley CM, Kapoor WN, Obrosky DS, Singer DE. Time to Clinical Stability in Patients Hospitalized With Community-Acquired PneumoniaImplications for Practice Guidelines. JAMA. 1998;279(18):1452-1457. doi:10.1001/jama.279.18.1452
From the Departments of Health Policy and Medicine, Mount Sinai School of Medicine, New York, NY (Dr Halm); Division of General Internal Medicine, Department of Medicine, and Center for Research on Health Care, University of Pittsburgh, Pittsburgh, Pa (Drs Fine and Kapoor and Mr Obrosky); Department of Medicine and Microbiology, Victoria General Hospital and Dalhousie University, Halifax, Nova Scotia (Dr Marrie); General Medicine Division, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston (Drs Coley and Singer).
Context.— Many groups have developed guidelines to shorten hospital length of
stay in pneumonia in order to decrease costs, but the length of time until
a patient hospitalized with pneumonia becomes clinically stable has not been
Objective.— To describe the time to resolution of abnormalities in vital signs,
ability to eat, and mental status in patients with community-acquired pneumonia
and assess clinical outcomes after achieving stability.
Design.— Prospective, multicenter, observational cohort study.
Setting.— Three university and 1 community teaching hospital in Boston, Mass,
Pittsburgh, Pa, and Halifax, Nova Scotia.
Patients.— Six hundred eighty-six adults hospitalized with community-acquired pneumonia.
Main Outcome Measures.— Time to resolution of vital signs, ability to eat, mental status, hospital
length of stay, and admission to an intensive care, coronary care, or telemetry
Results.— The median time to stability was 2 days for heart rate (≤100 beats/min)
and systolic blood pressure (≥90 mm Hg), and 3 days for respiratory rate
(≤24 breaths/min), oxygen saturation (≥90%), and temperature (≤37.2°C
[99°F]). The median time to overall clinical stability was 3 days for
the most lenient definition of stability and 7 days for the most conservative
definition. Patients with more severe cases of pneumonia at presentation took
longer to reach stability. Once stability was achieved, clinical deterioration
requiring intensive care, coronary care, or telemetry monitoring occurred
in 1% of cases or fewer. Between 65% to 86% of patients stayed in the hospital
more than 1 day after reaching stability, and fewer than 29% to 46% were converted
to oral antibiotics within 1 day of stability, depending on the definition
Conclusions.— Our estimates of time to stability in pneumonia and explicit criteria
for defining stability can provide an evidence-based estimate of optimal length
of stay, and outline a clinically sensible approach to improving the efficiency
of inpatient management.
COMMUNITY-ACQUIRED pneumonia (CAP) is one of the most common inpatient
medical conditions, accounting for more than 600000 hospital admissions in
the United States each year.1 Substantial variation
in the length of hospital stay for CAP has been well documented within different
regions, different hospitals, and even within hospitals.2- 6
These differences in length of stay persist even after adjusting for disease
severity, comorbid conditions, and hospital characteristics, which suggests
that clinical uncertainty and/or differences in physician practice style may
be important and mutable determinants of management.6- 8
In addition, a physician survey of the discharge decision in CAP indicated
that 22% of pneumonia inpatients remained in the hospital beyond reaching
medical stability, indicating sizable opportunity for improving efficiency.9 For these reasons, providers and payers have been
aggressively developing and implementing practice guidelines and critical
pathways to reduce length of stay in pneumonia to decrease the cost of inpatient
However, these guidelines are often criticized for being evidence-free
because length of stay targets offered by hospitals, managed care plans, and
utilization management firms are often based more on comparisons between institutions
(benchmarking) or group consensus than on epidemiological data. Unfortunately,
there are no studies on the time course of recovery in pneumonia that provide
sufficient clinical details to help define an evidence-based estimate of optimal
length of stay. In particular, not much is known about how long it takes a
patient hospitalized with pneumonia to become medically stable.
While explicit definitions of clinical stability are hard to find, most
textbooks and guidelines base the concept of stability on normalization of
heart rate (HR), systolic blood pressure (SBP), respiratory rate (RR), temperature,
oxygenation status, ability to eat, and mental status.11,12
These clinical features have also been identified as key elements in physicians'
decisions about appropriateness for discharge.9
Therefore, to help facilitate a more evidenced-based approach to the management
of CAP, we sought to answer 3 questions: (1) What is the time course of resolution
of vital signs, ability to eat, and mental status abnormalities in patients
hospitalized with pneumonia? (2) What is the risk of major adverse outcomes
once vital sign stability has been achieved? (3) What are the potential opportunities
to safely shorten length of stay?
This study was part of the Pneumonia Patient Outcomes Research Team
(PORT), a prospective, multicenter, observational study of outcomes in hospitalized
and ambulatory patients with CAP. Complete details about the Pneumonia PORT
study have been described previously.13,14
The participating inpatient sites (and number of patients enrolled) were the
University of Pittsburgh Medical Center (n=217) and St Francis Medical Center
(n=59), both in Pittsburgh, Pa; the Massachusetts General Hospital (n=246),
in Boston; and the Victoria General Hospital (n=164), in Halifax, Nova Scotia.
The study was approved by the institutional review boards of all participating
The Pneumonia PORT study inclusion criteria were (1) age 18 years or
older, (2) symptoms suggestive of acute pneumonia, and (3) radiographic evidence
of pneumonia. Patients positive for the human immunodeficiency virus or who
had been hospitalized within 10 days were excluded. Overall, 2287 of the 4002
eligible ambulatory and hospitalized patients (57%) consented to participate.
Enrolled patients were younger (mean age 56 vs 61 years) and were more often
classified as low risk for short-term mortality (69% vs 58%) than eligible,
As part of a substudy on all hospitalized patients enrolled in the Pneumonia
PORT, detailed, daily inpatient data were collected during 2 consecutive sampling
periods. During period 1 (October 15, 1991, through May 14, 1993), chart review
was done on consecutive low-risk patients (<4% predicted risk of death).
During period 2 (May 15, 1993, through March 31, 1994), chart review was done
on all consecutive hospitalized patients regardless of mortality risk. This
strategy found 686 patients who were discharged from the hospital from the
overall PORT cohort of 1343 patients hospitalized with pneumonia. Because
we oversampled low-risk patients during period 1, the 686 patients in the
detailed daily assessment cohort were younger (mean age, 61 vs 74 years) and
had lower predicted 30-day mortality rates (2% vs 6%) than patients in the
overall PORT study who did not have daily chart review. During this substudy,
84% of eligible patients agreed to participate (73% during period 1, which
involved more detailed patient interviews, and 94% during period 2). The mortality
rates for all inpatients enrolled in the Pneumonia PORT study during periods
1 and 2 (prior to exclusion of high-risk cases in period 1) were the same
(7% vs 6%). There were no differences in the mortality rates for patients
entered in the 2 sampling periods when we stratified by admission-mortality
risk class as defined by the pneumonia severity index ([PSI], a multivariable
logistic model of short-term mortality further described below).
Baseline information on sociodemographic characteristics, initial pneumonia
severity, comorbid conditions, vital signs, mental status, ability to eat,
physical examination findings, laboratory results, and chest radiograph findings
was collected on admission. Pneumonia severity was assessed using the PSI,
a well-validated, disease-severity classification based on age, sex, nursing
home residence, 5 comorbid illnesses, vital signs on admission, mental status,
7 laboratory values, and the findings on chest x-ray films from presentation.14 Class I patients have the least severe disease; class
V patients, the most severe disease.
The highest temperature, HR, and RR, and lowest SBP, oxygen saturation,
and PaO2 of each hospital day were abstracted from the medical
chart. The patient's mental status and ability to eat each day was also recorded.
The time to resolution of individual vital signs and clinical status abnormalities
was defined as the first day that the vital sign or clinical variable was
stable. A variable was considered stable if all measurements in the 24-hour
period met stability criteria—a convention used by other investigators.15,16 Stable values for vital signs were
selected prior to analysis based on the literature and common clinical practice.
The stability cut point for HR was at least 100 beats/min; SBP, more than
90 mm Hg; and RR, 24 breaths/min or less. Oxygenation was considered stable
if the oxygen saturation was 90% or greater or the PaO2 was 60
mm Hg or greater and a patient was not receiving mechanical ventilation or
supplemental oxygen by face mask. Since no consensus criteria exist for stable
temperature, RR, and oxygen saturation, we examined a variety of cut points.
Because data reflect usual care, room air oxygen saturation was not available
on all days for all patients. The time to overall stability was defined as
the first day all 5 vital signs and eating and mental status were stable.
We considered admission to an intensive care unit (ICU), coronary care
unit (CCU), or telemetry monitoring unit (TMU) as an indicator of serious
clinical instability. All admissions and transfers to an ICU, CCU, or TMU
were counted as special care unit (SCU) admissions. For the few patients who
had more than 1 SCU admission, only the first episode was counted. Analyses
that focused on SCU admissions solely for respiratory failure, hemodynamic
compromise, and shock yielded results similar to those for all causes, which
we present here. Length of hospital stay was defined as the date of discharge
minus the date of admission. Microbiologic etiology was assigned according
to a previously described classification based on results of sputum Gram stain,
sputum culture, blood culture, pleural fluid culture, and serologic studies.17 No microbiologic testing was performed in 5% of cases.
Data on antibiotic use and route of administration were collected by chart
Means and SDs are presented for normal data and medians with interquartile
ranges (IQRs) for nonnormal data. We used the Kaplan-Meier product-limit method
(with exact calculation of ties) to characterize the time to individual vital
sign stability, overall stability, and first SCU admission.18,19
Differences among strata of PSI class were examined using log-rank tests.19 Patients were censored at the point of the last recorded
value. Those discharged prior to a particular variable stabilizing were censored
as not stable. The day of admission was counted as day 1. All analyses used
2-tailed test significance levels of P<.05 and
were conducted with SAS statistical software (SAS Institute, Cary, NC). Analyses
of outcomes for patients enrolled in the 2 sampling periods yielded similar
findings after controlling for differences in initial disease severity (PSI
class), so we present the data for the entire cohort.
Clinical features of the study subjects are summarized in Table 1. The mean patient age was 58 years (range, 18-101 years).
Half (352) of the sample (N=686) were women. Three quarters of patients (511)
had 1 or more major comorbid illness. Twenty-nine percent of patients (198)
were classified as moderate- (class IV) or high-risk cases (class V). A definitive
microbiologic etiology was determined for only 27% of patients overall (187),
including 57 (8%) with Streptococcus pneumoniae,
43 (6%) with Haemophilus influenzae, 26 (4%) with
multiple organisms, 21 (3%) with aerobic gram-negative rods, and 16 (2%) with
atypical organisms (Legionella species, Mycoplasma pneumoniae, and Chlamydia pneumoniae).
The average vital signs on admission were temperature of 37.7° ±
1°C; HR, 100 ± 19 beats/min; SBP, 134 ± 29 mm Hg; RR, 24
± 6 breaths/min; and oxygen saturation, 92% ± 6%. Only 7 patients
(1%) had an initial admission temperature 35°C or below, and 9 (1%) had
a temperature of at least 40°C (104°F).
Among the 385 patients with HRs of more than 100 beats/min on admission,
the median time to stabilization (HR ≤100 beats/min) was 2 days. Among
the 7% patients with SBP lower than 90 mm Hg on presentation, the median time
to stablize (SBP ≥90 mm Hg) was also 2 days. Similarly, among patients
admitted with abnormalities in RR, oxygen saturation, and temperature, the
median time to stablize RR (≤24 breaths/min), oxygen saturation (≥90%),
and temperature (≤37.2°C [99°F]) was 3 days (Table 2). By day 4, over 75% of all HR, SBP, and RR abnormalities
had been resolved (Figure 1). The
time course of resolution of fever depended on the criterion for stable temperature
(Figure 2). Over 75% of patients
admitted with a fever had a stable temperature by day 3, when stability was
defined as maximal temperature of the day of 38.3°C or less (101°F).
However, according to the most conservative definition (highest temperature
of the day ≤37.2°C [99°F]), stability was not reached by 75% of
patients until day 6. Among the 8% of patients who were admitted with an acute
change in mental status, the median time to return to baseline mental status
was 3 days. Among patients who were unable to eat on admission (or were ordered
not to eat by their physicians), the median time to being able to eat was
2 days. The time to stability of other functional status measures was also
rapid (stable bladder and bowel function: median, 1 day; abililty to ambulate:
median, 2 days).
The time to overall clinical stability, defined as normalization of
all 5 vital signs, ability to eat, and mental status, also varied depending
on the specific definition considered (Table 3). For the least conservative definition (A: temperature ≤38.3°C
[101°F], HR ≤100 beats/min, SBP ≥90 mm Hg, RR ≤24 breaths/min,
and oxygen saturation ≥90% or PaO2≥60 mm Hg), the median
time to overall stability among all patients was 3 days. Lowering the temperature
threshold to 37.8°C [100°F] yielded a similar estimate of 3 days to
stability. However, definitions based on more conservative criteria for stable
temperature, oxygenation, and RR yielded median estimates of time to clinical
stability of 5 to 7 days.
Patients with more severe pneumonia at presentation (classes IV and
V) took longer to reach overall clinical stability compared with patients
in classes I through III for all definitions of stability (Table 3; P<.001). There were no significant
differences in the time to stability among PSI classes I, II, and III for
all definitions. The differences in time to stability among the lowest- and
highest-risk patients were greatest when stability was defined conservatively
(definitions D and E; P<.001).
The proportion of vital sign abnormalities occurring after the initial
day of stability (eg, a temperature spike) varied depending on the individual
vital sign and specific threshold used. Proportions that relapsed were 4%
for SBP, 12% for HR, 17% for RR (≤24 breaths/min), 9% for oxygen saturation
(≥90%), 1% for ability to eat, and 2% for mental status. Recurrence of
fever occurred in 6% of patients for temperature above 38.3°C (101°F),
12% for temperature above 37.8°C (100°F), and 26% for temperature
above 37.2°C (99°F). Fever (defined as temperature above 38.3°C
[101°F]) developed in 2% of patients the day after stability, and in less
than 1% of subjects on subsequent hospital days. Relapses in overall stability
(a significant change in at least 1 variable) occurred in 25% of patients
according to definition A and 45% of cases for the most conservative definition
E. Small, transient fluctuations in RR were the most common cause of these
changes. Relapses were much less likely to occur 2 and 3 days after stability
(occurring 10%-15% and 4%-6% of the time, respectively).
To evaluate the clinical significance of these relapses and further
validate our model of stability, we examined the risk of major adverse events
before and after stability. We chose SCU admissions as an indicator of serious
medical instability. Ninety-one patients (15%) were admitted to an SCU during
their hospital stay. Forty-five percent of these admissions were to an ICU,
45% to a TMU, and 10% to a CCU. The major reasons for admission were special
care monitoring (55%), respiratory failure (34%), and hemodynamic instability
(6%). Nearly two thirds of SCU admissions occurred on the day of admission
and 15% on the day after admission.
Overall, 14% to 15% of patients were admitted to an SCU prior to stability
(Table 4). As expected, patients
in classes I through III had lower rates of admission to an SCU prior to stability
(10%) than class IV (22%) and class V patients (24%, P<.001).
However, for all risk classes and definitions considered, once a patient had
stabilized, the risk of clinical deterioration serious enough to merit subsequent
ICU, CCU or TMU admission was 1% or less. Even among the sickest subgroup
of patients (class V), the absolute risk of needing an SCU after the day of
stability was only 1%.
The median hospital length of stay for the cohort was 6 days (IQR, 4-10
days; mean, 8.9±12.4 days). Regardless of the definition of stability
used, the majority of patients stayed more than 1 day after reaching stability
(Table 5). According to definitions
A and B, which are modeled on commonly used guidelines, over 83% of patients
stayed more than 1 day beyond clinical stability. These patients stayed in
the hospital a median of 4 additional days after reaching stability. According
to definition A, patients in class IV and class V had even longer hospital
stays beyond stability compared with patients in classes I through III (4
vs 6 days, P<.001).
Overall, 648 patients (94%) were treated with parenteral antibiotic
therapy within 24 hours of admission, most commonly macrolides (43%), second-generation
cephalosporins (40%), aminopenicillins (21%), aminoglycosides (18%), and natural
penicillins (14%). Among these 648 patients, the median day of discontinuing
parenteral therapy was day 6 (IQR, 4-8). The median interval between reaching
stability and discontinuation of parenteral antibiotic therapy (or conversion
from parenteral to oral antibiotics) was 3 days according to definition A
(IQR, 1-5) and 2 days for all other definitions (IQR, 1-4). The median time
from discontinuation of parenteral therapy (or conversion to oral therapy)
to discharge was 1 day (IQR, 1-3). Only 29% to 46% of patients in our study
had parenteral antibiotic therapy discontinued or were converted from parenteral
to oral therapy within 1 day of reaching clinical stability (Table 5).
Abnormalities in vital signs are common in patients with pneumonia and
frequently dictate the hospitalization decision.20
Similarly, resolution of vital sign abnormalities are important determinants
of the discharge decision.9 Yet there are few
studies of the time course of clinical recovery in this disease and no studies
of a broad population of patients hospitalized with pneumonia. We found that
vital signs, when considered individually, tend to stabilize within 2 or 3
days of hospitalization. The median time to stability of all vital signs and
mental status abnormalities and regaining the ability to eat was 3 days according
to most conventional definitions examined. However, when more conservative
thresholds for temperature, RR, and oxygen saturation were used, the median
time to stability lengthened to as many as 7 days. The time to stability was
also significantly influenced by disease severity; patients with the most
severe pneumonia at presentation took the longest to recover.
The risk of clinical deterioration serious enough to merit admission
to an ICU, CCU, or TMU was greatest on the day of admission and dropped off
dramatically thereafter. Ninety-three percent of all SCU admissions occurred
prior to a full day of stability. Once overall stability was achieved, the
risk of subsequent clinical deterioration serious enough to require SCU admission
was 1% or less even among the sickest subgroup of patients.
Since relapses in stability, when they did occur, happened predominantly
on the day after a patient gained stability, it might be reasonable to define
potentially unnecessary hospital days as those more than 1 day beyond stability.
Most of the patients we studied stayed in the hospital 3 to 4 days after reaching
stability, suggesting ample opportunity to safely shorten length of stay.
According to definition A (temperature, ≤38.3°C [101°F]; HR, ≤100
beats/min; SBP, ≥90 mm Hg; RR, ≤24 breaths/min; and oxygen saturation, ≥90%),
which is based on commonly used guidelines, over 60% of total hospital days
would have been considered potentially unnecessary.
Our findings are consistent with previous studies that reported the
duration of fever in patients hospitalized with pneumonia due to S pneumoniae (mean, 2.8 days),21H influenzae (mean, 2.7 days), 21Legionella species (range, 2.2-6 days),22,23
and bacteremic pneumococcal pneumonia (mean, 3.1-6.7 days).24- 26
Our data corroborate the practice guideline developed by Weingarten and colleagues,12,27 which used similar vital sign criteria
and focused on hospital days 3 and 4 as the critical period for identifying
low-risk patients with pneumonia who are stable and ready to be converted
to oral antibiotics and discharged shortly thereafter. A recent report on
79 patients with pneumonia also reported a median 3 days to the resolution
of morbidity (defined as temperature, ≤37.9°C [100.2°F]; RR, ≤24
breaths/min; oxygen saturation, ≥90%, and no worsening results on a chest
For groups developing practice guidelines, critical pathways, or utilization
review rules, our results should provide a more evidence-based estimate of
achievable and appropriate length of stay. Guidelines and critical pathways,
which often prespecify days that certain decisions should occur, have been
criticized for their perceived "cookbook" or "one size fits all" approach.29- 31 We believe the explicit
stability criteria we have developed provide a more clinically sensible way
to define appropriateness for discharge for both individual patients and populations.
However, because different definitions of stability can result in greater
than 2-fold differences in the target length of stay, it is important that
local groups reach consensus about which criteria are consonant with their
own attitudes, beliefs, and risk tolerance.
These stability criteria have other implications for patient care decision
making. Previous studies have suggested that early conversion from intravenous
to oral antibiotics in patients with respiratory infections may be safe, effective,
and shorten hospital length of stay.32- 37
In our cohort, only one third of patients were switched to oral antibiotics
within 1 day of reaching stability. It seems reasonable to expect that once
patients achieve stability they could be converted to oral antibiotics and
discharged shortly thereafter in the absence of other active problems. In
addition, information about the usual clinical course of patients with pneumonia
should help providers identify patients who are not improving as expected,
and thus may have complications (such as an empyema) or other underlying pulmonary
processes that might require a change in management.
Our study has several strengths. Our cohort of patients was large and
not restricted to a specific microbiologic etiology. The detailed, daily clinical
information we collected enabled us to describe the clinical course of pneumonia
in much greater detail than in any previous studies. Our findings are also
less prone to institutional, geographical, or seasonal biases because we studied
4 hospitals in 3 geographical regions over a consecutive 30-month period.
However, there are several limitations worth noting. First, microbiological
testing reflected usual clinical practice. As a result, the causative pathogen
was unknown for most patients, and could not be easily factored into our assessments.
However, even in research studies that aggressively pursue etiology data,
a definitive microbiologic diagnosis is lacking in 30% to 50% of cases.17,38,39 Second, because many
patients stayed in the hospital several days after reaching stability, we
cannot know if they would have had a similarly benign course had they been
discharged soon after becoming stable. Third, our model of stability may not
fully take into account all important clinical factors dictating continued
hospitalization. Active comorbid conditions would be factored into our assessments
only if they affected the vital signs, ability to eat, and mental status.
We found only a few cases in which delayed hospital discharge was due to nonclinical
factors such as patient, family, and/or physician preferences, disagreement
among physicians, delays in transfer to a nursing home or transportation home,
or difficulties due to weekends or holidays.40
Fourth, the relapse rates we present may overestimate the true rate since
sicker patients tend to stay in the hospital longer and have more chances
of having abnormal vital signs detected.6- 8
Finally, 2 issues regarding generalizability deserve comment. The patients
we studied tended to be younger and less severely ill than the overall population
of patients hospitalized with pneumonia. However, our analyses do account
for the full spectrum of disease severity at presentation. Nevertheless, the
extent to which our findings apply to groups that may have been underrepresented,
such as the uninsured, nursing home residents, minorities, and the very old
The median time to stability of vital signs and clinical status abnormalities
in patients hospitalized with pneumonia was 3 days by most conventional definitions.
Most patients appeared to stay several days beyond stability with low rates
of late clinical deterioration, suggesting that average length of stay can
be safely shortened. The use of objective criteria for stability should help
providers and payers realize substantial cost savings by shortening unnecessarily
long hospital stays. However, an explicit, discharge decision rule based on
these models should be tested prospectively to ensure that a streamlined hospital
course does not compromise patient outcomes.30,31,41