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Healthcare
Outcome of critically ill patients undergoing interhospital
transfer
Graeme J Duke and John V Green
MJA 2001; 174: 122-125
Abstract -
Methods -
Results -
Discussion -
Acknowledgement -
References -
Authors' details
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Abstract |
Objective: To quantify the morbidity and mortality
associated with acute interhospital transfer of critically ill
patients requiring intensive care (ICU) services.
Design: Three-year (1 July 1996 - 30 June 1999)
retrospective case-control study based on review of patients'
medical records.
Setting: Metropolitan hospitals in Melbourne,
Victoria.
Participants: 73 (of 75) consecutive, critically ill
patients from one metropolitan teaching hospital who were
transferred to other hospitals because ICU services were not
available.
Outcome measures: Primary endpoints included
inhospital mortality and length of stay in ICU and hospital.
Secondary endpoints included time from study entry to ICU admission
and the change in predicted mortality risk after resuscitation and
transfer to ICU (inter- or intrahospital transfer).
Results: The Transfer Group experienced a significant
delay in admission to ICU (5.0 [4.0-6.0] v 3.0 [2.0-5.5] hours;
P = 0.001), and a longer stay in ICU (48 [33-111] v 44 [25-78]
hours; P = 0.04), and hospital (10 [3-14] v 6 [3-13] days;
P = 0.02). Hospital mortality in the Transfer Group (24.7%)
was not statistically different from that in the Control Group
(17.8%; P = 0.41; OR, 1.5; 95% CI, 0.68-3.4).
Conclusion: Acute interhospital transfer is associated with
a delay in ICU admission and a longer stay in ICU and hospital, but no
statistically significant difference in mortality. A study of over
300 patient transfers would be required to clarify the morbidity and
mortality risk of acute interhospital transfer.
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Acute interhospital transfer of critically ill patients carries
potential risks, including complications during transfer and delay
in providing definitive care. There are two categories of acute
interhospital transfer.
Category A: The primary (sending) hospital is unable to provide the
expertise, diagnostic services or therapeutic procedures required
by a patient (eg, transfer of a patient with extensive burns to a
hospital with specialised treatment facilities for burns); and
Category B: The primary hospital is temporarily unable to provide
intensive care unit (ICU) services for a patient because of resource
limitations (eg, lack of ICU beds).
Measuring the impact of transfer risk on patient outcomes is complex.
Reports without control data suggest that acute interhospital
transfer increases both morbidity1,2 and
mortality,3 but there are many
confounding variables that influence outcome (eg, severity of
illness, extent of resuscitation, and the expertise available
before and during transfer). To our knowledge, no comparative
outcome study of critically ill patients undergoing acute
interhospital transfer has been published.
A randomised trial of Category A transfer would be complicated by the
difficulty of finding a clinically and ethically appropriate
control group. An alternative is to compare outcomes of patients
undergoing Category B transfer with outcomes of matched patients not
transferred. Both these groups of patients are resuscitated and
managed with similar expertise and support. It is therefore possible
to reduce bias from some of the confounding variables, and to identify
a suitable control group.
We performed a retrospective case-control comparison of
outcomes in critically ill adult patients undergoing Category B
transfer. We hypothesised that acute interhospital transfer
increases morbidity and mortality and sought to answer four
questions: Does acute interhospital transfer of critically ill
patients
- delay admission to an ICU;
- increase severity of illness before admission;
- increase ICU and hospital length of stay; and
- increase mortality?
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The primary hospital was the Northern Hospital, a Melbourne
metropolitan teaching hospital providing all acute-care health
services (except cardiac surgery and organ transplantation).*
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Transfer Group |
All adult patients requiring intensive care services between 1 July
1996 and 30 June 1999 were entered in the study if they
- were deemed by the intensivist on-duty to require intensive care
services;
- were transferred to a (public or private) metropolitan hospital for
those services; and
- received diagnostic and therapeutic interventions that could
otherwise have been provided at the primary hospital.
All patients were transferred by road ambulance with an experienced
medical escort from the primary hospital.
Patients were excluded if they were transferred with the intention of
receiving services not available at the primary hospital (Category A
transfer), or if insufficient data were available.
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Control Group | |
Control patients were selected from patients admitted to the ICU of
the primary hospital, who did not undergo acute interhospital
transfer at any time during the study period. Matching of Control
Group patients with patients in the Transfer Group was undertaken
according to a hierarchy of criteria deemed most likely to influence
patient outcome (Box 1). Due to difficulties matching for all
criteria, priority was placed on the first four. Matching was
undertaken by one author (J V G), who was blinded to the identity and
outcome of the patients.
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Endpoints |
These included inhospital mortality, time from study entry to ICU
admission, length of stay in ICU and hospital, and the change in
predicted mortality risk after resuscitation and transfer to ICU
(Box 2).
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Patient data (Box 2) | |
Patients' data recorded prospectively in the medical records at all
the hospitals involved were reviewed retrospecively by one
investigator (G J D). Physiological and laboratory data were used to
calculate predicted mortality risk (pm) at three time
points (t1, t2 and t3; Box 2), as
an index of illness severity, using the Acute Physiology and Chronic
Health Evaluation (APACHE) II method.4 Length of stay and
pm were chosen as surrogate markers of patient
morbidity.
Because of the broad range of pm within the Transfer Group
(0.01-0.86), we also undertook a post-hoc analysis of the change in
pm ( pm) during each interval as a measure of
the change in physiological status. Since pm is an
indicator of illness severity, and since calculations were
performed before and after resuscitation and transfer, the
physiological impact of resuscitation ([pm at
t2] - [pm at t1]) and of transfer
([pm at t3] - [pm at
t2]) was quantified.
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Statistical analysis | |
Graph-Pad PRISM statistical package was used for data
analysis.5 We used Fisher's exact test
to compare group mortality. Non-parametric tests were used to
compare length of stay in ICU and in hospital, and for intergroup
comparison of pm and m (Mann-Whitney;
P < 0.05). Wilcoxon signed rank test was used for post-hoc
intragroup comparisons of m (P < 0.01).
Data are presented as median (interquartile range) unless otherwise
indicated.
Based on studies without control data,3,6 which showed a doubling of
mortality after acute interhospital transfer and a Control Group
mortality of 18%, we calculated that a sample size of at least 50
patients would be required ( = 0.05,  = 0.80.)
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Ethical approval | |
Ethics committee approval was obtained from each of the 14 hospitals
involved.
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Results |
During the 36 months, 1470 patients required intensive care services
at the primary hospital. Of these, 1338 (91%) were admitted and were
the source of the Control Group patients. Of the 132 (9%) patients not
admitted to the primary hospital ICU, 75 consecutive patients (5.1%)
underwent a Category B transfer (Transfer Group), 35 (2.4%) were
managed elsewhere within the same hospital (eg, general ward) and 22
(1.5%) were transferred for services not available at the primary
hospital (Category A transfers). The last two groups were excluded
from the study. Two eligible patients in the Transfer Group were
excluded because insufficient data were available from the
receiving hospitals, leaving 73 patients.
The destinations of the transferred patients were determined by the
proximity of the other hospitals and the bed availability.
Sixty-four patients were transferred to nine public hospitals, and
11 patients were transferred to five private hospitals (eight of
these patients had no private health insurance, but no public
hospital ICU bed was available within the metropolitan region at that
time). The reasons for transfer were closure of beds in 61 patients
(84%), and equipment problems, all beds occupied and patient request
in six, five and one patient, respectively.
Demographic and other data for the Transfer and Control group
patients, as well as the accuracy of case-control matching, are
summarised in Box 3, and the diagnostic categories of the patients are
shown in Box 4.
Both groups had a high mortality risk at the time of study entry
(commencement of resuscitation -- pm at t1)
and immediately before transfer (pm at t2)
(Box 5). Post-hoc analysis of pm revealed a
significantly greater fall in pm during resuscitation
and during transfer to ICU in the Control Group patients (P
< 0.01). Thirty-seven patients (51%) undergoing acute
interhospital transfer experienced a rise in pm
(t3), compared with only 20 (27%) of the control group
(P = 0.006).
No deaths occurred during transfer. The higher observed mortality in
the Transfer Group (Box 4) was not statistically different from that
in the Control Group (odds ratio [OR], 1.5; 95% CI,
0.68-3.4). The diagnostic group (Box 4) and severity of illness
(pm) were the most important univariate factors
associated with outcome.
Acute interhospital transfer was associated with a significant
delay in ICU admission (Box 5), although some of the control patients
also experienced admission delays (range, 0.5-9.5 hours). The
Transfer Group was also found to have a significantly prolonged
length of stay in ICU and hospital when compared with the Control
Group. These length-of-stay increases were independent of outcome,
diagnosis, age and hospital destination.
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Discussion |
We found that critically ill patients undergoing acute
interhospital transfer experience a delay in admission to ICU, and a
longer length of stay in ICU and hospital. However, there was no
significant difference in hospital mortality between the two
groups, and there were no deaths during transfer.
As indicated by their primary diagnoses, need for life-support and
high mortality risk, all patients in our study were critically ill at
the time of study entry. The apparent safety of acute interhospital
transfer is likely to be the combined result of factors such as
resuscitation and stabilisation before transfer; the use of staffed
and equipped ambulance vehicles; the provision of intensive care
medical expertise and monitoring before, during and after transfer;
and triage to appropriate hospitals.7
Why did the Transfer Group have an increased length of stay? The rise in
pm after acute interhospital transfer in 37 patients
(51%) suggests that it may increase morbidity in some patients. Other
researchers have also reported adverse physiological effects
during transfer of critically ill patients,1,2 and a higher mortality in
patients admitted after interhospital transfer.3,6
Delay in ICU admission inevitably delays diagnostic and therapeutic
procedures. The increased sedation and analgesia to ensure patient
safety and comfort during interhospital transfer may prolong
recovery time. The slower rate of fall of pm in the
Transfer Group is consistent with this premise. Patient management
and discharge practices may vary between institutions and thus
increase length of stay independent of diagnosis and patient origin.
Our study has several important limitations. Retrospective chart
analysis carries potential for observer bias and systematic error.
We attempted to minimise this by sampling data at predetermined fixed
time points and using the same data collector. Patient selection was
unavoidably biased because the Transfer Group constituted a
heterogeneous and non-randomised group of critically ill patients.
Because of the small number of subjects in some diagnostic
categories, the matching of Control Group patients with patients in
the Transfer Group was not perfect, but we attempted to optimise
matching by using a criteria hierarchy. The Control Group patients
had a greater median pm at study entry, and some
experienced a clinically significant delay in ICU admission, both
factors which may have reduced the outcome difference between the
groups.
Although the APACHE-II scoring system4 has been used in the
prehospital setting,3,8 it assumes patients are in
an intensive care environment receiving optimal therapy, and
therefore it may not be a valid tool for use outside an ICU. However,
this potential systematic error applied equally to both groups.
The study size had insufficient power to establish a difference in
mortality. If the observed difference in outcome is clinically
significant it would require a sample size of over 300 transfers to
exclude a type II statistical error. A trial of sufficient power could
be achieved with a 12-month multicentre study of all Category B
transfers within metropolitan Melbourne. During 1998-1999, 369
critically ill adults (3.5% of metropolitan adult intensive care
admissions) underwent a Category B transfer (Department of Human
Services, Critical Care Inter-Hospital Transfer Monitoring and
Advisory Group, personal communication).
At best, our results indicate that acute interhospital transfer does
not affect hospital outcome; at worst, they suggest that it may
adversely affect the outcome of one in every 25 critically ill
patients transferred. Extrapolating our results to the
metropolitan region, acute interhospital transfer may adversely
affect the outcome of 15 patients (95% CI, 0-48) per annum, and
require an additional 1100 hospital bed-days (95% CI,
960-1266 days) per annum -- half in ICU, where the primary
resource limitation exists.9,10
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We would like to thank Professor B Jackson and Dr P Cranswick for their
constructive criticism of the manuscript.
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References |
- Waddell G, Scott PDR, Lees NW, Ledingham IM. Effects of ambulance
transport in critically ill patients. BMJ 1975; 1: 386-389.
-
Karipis H, Scheinkestel CD, Tuxen DV, et al. Safety of
transportation of critically ill patients. Anaesth Intensive
Care 1993; 21: A7111.
-
Bristow P, Brown D, Lee A, Buist M. Transfer of severely ill
patients. Anaesth Intensive Care 1995; 23: A399.
-
Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity
of disease classification system. Crit Care Med 1985; 13:
818-829.
-
GraphPad PRISM, version 1. San Diego: GraphPad Software Inc, 1998.
-
Metcalf A, McPherson K. Study of provision of intensive care in
England, 1993. London: School of Hygiene and Tropical Medicine,
1995.
-
Faculty of Intensive Care, Australian and New Zealand College of
Anaesthetists and Australasian College of Emergency Medicine.
Minimum standards for transport of the critically ill (IC-10).
Melbourne: Australian and New Zealand College of Anaesthetists and
Australasian College of Emergency Medicine, 1996.
-
Bion JF, Edlin SA, Ramsay G, et al. Validation of a prognostic score
in critically ill patients undergoing transport. BMJ 1985;
291: 432-434.
-
Acute Health Services Branch, Department of Health and Community
Services Review of emergency and critical care services in Victoria.
Melbourne: Department of Health and Community Services, 1994.
-
Acute Health Division, Department of Human Services. Review of
intensive care in Victoria [Phase 1 report]. Melbourne: Department
of Human Services, 1997.
(Received 3 Apr, accepted 15 Sep, 2000)
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Intensive Care Department, The Northern Hospital, Melbourne, VIC.
Graeme J Duke, MB BS, FFICANZCA, Director;
John V
Green, MB BS, FFICANZCA, Staff Specialist.
Reprints will not be available from the authors.
Correspondence: Dr G
J Duke, Intensive Care Department, The Northern Hospital, 185 Cooper
Street, Epping, VIC 3076.
graeme.dukeATnh.org.au
©MJA 2001
Readers may print a single copy for personal use. No further
reproduction or distribution of the articles
should proceed without the permission of the publisher. For
permission, contact the
Australasian Medical Publishing Company.
Journalists are welcome to write news stories based on what they read here, but should acknowledge their source as "an article published on the Internet by The Medical Journal of Australia <http://www.mja.com.au>".
<URL: http://www.mja.com.au/>
© 2001 Medical Journal of Australia.
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| 1: Criteria for matching Control Group patients with
Transfer Group patients |
- Discharge diagnosis (APACHE-III diagnostic code)
- Need for mechanical ventilation on admission to Intensive
Care Unit
- Glasgow coma score (GCS) at t1 - within 2 points
- Predicted mortality (pm; APACHE-II methodology4) at
t1 - within 10%
- Age - within 10 years
- Sex
- Source of initial referral (emergency ward, inpatient
ward, operating theatre)
- Date of admission - within 12 months
- Time (t1): day (8:00 to 18:00) or night
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| APACHE=Acute Physiology and Chronic Health Evaluation.
Time, t1=study entry at commencement of resuscitation. |
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| Back to text |
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2: Patient dataset
- Demographic information,
including age, sex, and postcode of residence
- Relevant medical data, including
past history and final diagnosis
- Dates and times of primary
admission, initial referral, interhospital transfer, ICU discharge and
hospital discharge
- Referral source
- Treatment and personnel required
during transfer
- Interventions required (at
both hospitals)
- Data for APACHE II predicted
mortality (pm) score4*
Physiological data: blood pressure, heart rate, respiratory
rate, Glasgow coma score, urine output
Pathological data: haematocrit and total white cell count; serum levels
of sodium, potassium, creatinine, urea, albumin, and glucose; and arterial
pH and blood gas analysis
Clinical data: age, diagnosis,
use of mechanical ventilation, presence of acute renal failure, chronic
health status
- Time of APACHE II predicted mortality (pm) calculations
(see time line)
t1= study entry at commencement of resuscitation.
t2= before transfer to ICU, after initial resuscitation.
t3= on arrival in ICU after transfer.
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APACHE=Acute Physiology and Chronic Health Evaluation.
*Formula for pm score:
logn(pm/12pm)=-3.517+0.146 (k1+k2+k3)+k4+k5, where
k1=a variable score based on physiological and pathological data;
k2=a variable weighting for age;
k3=a variable weighting for chronic health status;
k4=a constant weighting for emergency surgical patients; and
k5=a variable weighting for principal diagnostic category. |
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| 3: Comparison of patient data (Transfer
Group v Control Group - data are median and interquartile range unless indicated
otherwise) and percentage matching between the two groups |
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| Criterion |
Transfer Group |
Control Group |
Percentage matching* |
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| Diagnostic group |
(see Box 4) |
(see Box 4) |
100% |
| Need for mechanical ventilation |
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| (no [%] of patients) |
51 (73%) |
51 (73%) |
100% |
| Predicted mortality at start |
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| of resuscitation (pm at
t1) |
0.30 (0.09-0.62) |
0.37 (0.09-0.60) |
69% |
| GCS: patients with neurological |
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| problems (n=39) |
7 (6-9) |
7 (6-8) |
100% |
| GCS: all patients (n=73) |
9 (6-14) |
8 (6-12) |
96% |
| Age (years) |
54.8 (36.4-67.2) |
57.4 (38.0-70.4) |
67% |
Source of referral (no [%] of
patients) |
61 (83%) from ED |
59 (81%) from ED |
79% |
| Sex ratio (no. of men:women) |
39:34 |
46:27 |
78% |
| Date of admission |
(baseline) |
3 (1-15) months |
75% |
| Time (t1) (8:00-18:00) |
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| (no. [%] of patients) |
28 (38%) |
36 (49%) |
60% |
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| *Percentage of Control Group patients matched
according to criteria given in Box 1. GCS=Glasgow Coma Score. ED=emergency
department. |
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| 4: Diagnostic categories and inhospital
mortality |
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Deaths |
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| Discharge diagnosis |
No. (%) patients |
Transfer Group |
Control Group |
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Trauma
Drug overdose
Cardiac arrest
Cardiogenic shock
Exacerbation of COPD
Status asthmaticus
Pneumonia
Cerebrovascular coma
Metabolic coma
Neurological conditions
Gastrointestinal conditions
Septicaemia
Malignancy
Aortic aneurysm
Total |
12 (16%)
11 (15%)
8 (11%)
7 (10%)
5 (7%)
3 (4%)
4 (5%)
4 (5%)
4 (5%)
4 (5%)
4 (5%)
4 (5%)
2 (3%)
1 (1%)
73 (100%) |
0
0
6
0
0
0
2
2
1
1
2
3
1
0
18 (24.7%) |
0
0
5
1
0
0
1
1
2
1
1
1
0
0
13 (17.8%) |
| 95% CI |
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11-25 |
7-20 |
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| COPD=Chronic obstructive pulmonary
disease. |
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