APPROPRIATENESS OF ARTERIAL BLOOD GAS MEASUREMENTS
IN ACUTE CARE GENERAL WARDS
Mohamed Al-Moamary, MD; Diane Daniel, RRT; Faisal Battwa, MB;
Hamdan Al-Jahdali, MD; Abdullah Al-Shimemeri, MD
The measurement of arterial blood gases (ABG) has
assumed an increasingly important role in the process of
clinical evaluation, and has been widely used during the
past three decades. The number of ABG measurements has
increased in different medical conditions due to greater
availability.1 Though ABG measurement indications are
clear, they are occasionally misused.2 The test has some
risks, consumes a considerable amount of physician and
respiratory therapist time, and results in increased cost to
the health care system.3
Pulse oximetry, a noninvasive method that measures
arterial hemoglobin oxygen saturation (SaO2), can play a
major role in reducing the need for ABG measurements.4
This transdigital technique has been shown in normal
healthy volunteers to be easily used, safe, accurate, and
reliable. It is also sensitive in detecting arterial
desaturation.5,6 However, this method is underutilized, even
in situations where it has major benefits, such as tapering
oxygen for hospitalized patients and in intensive care
settings.2,7
We observed overutilization of ABG measurements in
our hospital, where proper use of pulse oximetry could have
reduced the number of requested ABG. To justify the
development and implementation of guidelines for ABG
measurements, we conducted a prospective study to observe
their appropriateness and the frequency of pulse oximetry
usage in acute care general wards. This study did not
interfere with the process of ongoing pulse oximetry usage
or requests for ABG.
Accepted for publication 21 November 1998. Received 19 April
1998.
therapists, with the result filed in the patient’s medical
record for interpretation by the requesting physician. The
respiratory therapists were given orientation on the pulse
oximetry and aims of the study. The study form included
information on diagnosis, indication for ABG measurement,
urgency of requisition, usage of pulse oximetry, measured
SaO2, and route and amount of oxygen.
All ABG requested were reviewed daily by a
pulmonologist (MA) and a senior medical resident (FB)
who determined the appropriateness of each requisition.
ABG requests were considered inappropriate under the
following criteria: 1) when ABG was measured only to
check SaO2 in a stable patient with no known
cardiopulmonary distress or acid-base disturbance; 2) when
ABG measurement could have been avoided in retrospect
by using pulse oximetry prior to ABG; 3) when ABG was
measured without an attempt to achieve adequate SaO2 by
using oxygen; and 4) when ABG measurement was used as
a tool to titer oxygen up or down or to titer it down in
patients with CO2 retention. The patients’ medical records
were reviewed whenever necessary. Pulse oximetry was
measured noninvasively by BCI International 3302
oximeter (Wisconsin, USA) and Ohmeda Biox 3700E
(Ohio, USA).
Data were summarized using simple descriptive
statistics. Chi-squared test was used to check the association
between categorical variables.
Materials and Methods
Results
This was a prospective observational study conducted in
a 550-bed tertiary care teaching hospital over a two-week
period in October 1997. The study involved all ABG
measurements from adult acute care general wards of
approximately 330 beds belonging to different specialties.
All ABG requested were performed by respiratory
During the study period of two weeks, 98 ABG were
requested on 64 patients from adult acute care general
wards. On average, there were seven ABG requests per day
and 1.5 ABG requests per patient. Medical wards were the
most frequent areas requesting ABG (48%) (Table 1). The
total number of ABG requested from all medical wards was
59 (60.2%). Acute and chronic respiratory diseases were
the most frequent diagnoses (34.6%) requiring ABG
measurements (Table 2), followed by 17 measurements
(17.4%) for chronic airway obstruction, five for asthma
(5.1%), three for pulmonary fibrosis (3.1%), three for sleep
apnea (3.1%), three for pulmonary embolism (3.1%), and
three for pneumonia (3.1%). Other disease categories that
From the Pulmonary Section, Department of Medicine and
Cardiopulmonary Services, King Fahad National Guard Hospital, Riyadh,
Saudi Arabia.
Address reprint requests and correspondence to Dr. Al-Moamary:
P.O. Box 84252, Riyadh 11671, Saudi Arabia.
Annals of Saudi Medicine, Vol 19, No 2, 1999
153
AL-MOAMARY
ET AL
TABLE 1. Location of requisition for measurement of arterial blood
gases (ABG).
Ward
Number (%)
General Medicine
47 (48)
Surgery
13 (13.3)
Obstetrics and Gynecology
6 (6.1)
Cardiology
5 (5.1)
Gastroenterology and Liver Transplant
5 (5.1)
Other
22 (22.4)
Total
98 (100)
Wards are not strictly defined, as overflow is allowed between wards,
depending on bed situation.
TABLE
2.
Reasons for 45 inappropriate ABG measurements.
Reason
Number (%)
ABG measured only to check SaO2 in the absence of
cardiopulmonary distress or acid-base disturbance
15 (32.6)
ABG measured without an attempt to achieve
adequate SaO2 by oxygen
12 (26.1)
ABG measured to titer oxygen
9 (19. 6)
ABG measurement could have been avoided in
retrospect by using PO
9 (19.6)
Total
45 (100)
required ABG were 13 patients with liver and
gastrointestinal diseases (13.1%), 10 with motor vehicle
accident and trauma (10.2%), seven with diabetes mellitus,
and 34 for miscellaneous indications (34.7%). Though 13
ABG measurements (13.3%) were done for patients with
liver or gastrointestinal disease, most were part of routine
pre-liver transplant work-up.
Indications for ABG measurements included 37 for
patients with dyspnea (37.8%), 11 to monitor PaO 2
(11.2%), 10 to check saturation (10.2%), nine baseline
ABG (9.2%), six during cardiac arrest (6.1%), five for
patients with chest pain (5.1%), and 20 for other reasons
(20.4%). Fifty-three patients (54.1%) were considered
appropriate by reviewers and 45 (45.9%) were not. Arterial
oxygen saturation by pulse oximetry was checked
concomitantly with 68 ABG measurements (69.5%). Of
these measurements, 31 (45.6%) could have been avoided
by proper utilization of the pulse oximetry.
Fifty-five ABG measurements (56.1%) were urgent
orders, 36 (36.7%) were routine orders, while the status of
the remaining 7 (7.1%) could not be determined. Thirty of
the 55 urgently requested ABG and 17 (47.2%) of the 36
routinely ordered ABG were appropriate (47.2%) (P=0.7).
Discussion
Clinical analyses of blood gases have been made
possible in the past three decades due to several important
advances.7 Due to the important information gained by
ABG measurements, it has become the most frequently
ordered test in intensive care areas.8 Guidelines for the
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Annals of Saudi Medicine, Vol 19, No 2, 1999
usage of ABG measurements have significantly reduced the
number and increased the appropriateness of their use.2,9 On
the other hand, the recent widespread usage of pulse
oximetry to analyze SaO2 has significantly reduced the
number of required ABG.3-6
The development and application of guidelines have
become common practice in many Western countries,
where most of the health care costs are paid for either by
the patient, third-party payers, or to a lesser extent, the
government. In an era of increasing health care costs,9 this
is a financial burden for most patients. In Saudi Arabia, the
cost of ABG measurements is included in the budget of
governmental hospitals, with the result that many physicians
do not appreciate the costs of frequent measurements.
However, the charge of this measurement in the private
sector is 100–200 Saudi riyals (USD27–54). In the absence
of guidelines, there will be no control on the number of
unnecessary ABG measurements.
Our study concentrated specifically on the
appropriateness of measured ABG in a tertiary-care
teaching hospital. The criteria that we used to determine
such appropriateness were extrapolated from different
sources.2,3,6,7,10 Forty-six percent of ABG were
inappropriately ordered, which is compatible with the
experience of others.2,3 The number of ABG measured was
1.5 per patient, the proper timing of ABG requests or
utilization of pulse oximetry theoretically could have
reduced this to 0.8. However, Browning et al. found that
even after the application of ABG guidelines in ICU
settings, 30% of ABG analyses did not meet their
appropriateness criteria.3 By taking this observation into
consideration, the number of ABG in our study could have
been reduced from 1.5 to 1 ABG per patient. Thus, we
believe that the implementation of guidelines for ABG
measurements could have reduced 30 ABG measurements
during the study period, which would be an approximate
reduction from 2496 to 1664 measurements annually, i.e.,
832 fewer ABG measurements. If requested ABG from the
Emergency Department had been included in our study, it is
our assumption that the number of unnecessary ABG
measurements would have been much greater.
Pulse oximetry has added a significant dimension to the
monitoring of arterial oxygen status and deserves
widespread application and use.11 The measurement of
SaO2 by pulse oximetry is clinically accurate to ±4%, and is
a sensitive indicator of relative hypoxemia.12 A pulse
oximetry reading of less than 95% of SaO2 has 100%
sensitivity in identifying hypoxemia. Nevertheless, it tends
to overestimate the lower levels of SaO2, and does not
correlate well with PaO2 during profound hypoxemia with
SaO2 of less than 70%.5,11,12 Pulse oximetry reading can
give erroneous measurements in the presence of
carboxyhemoglobin, methemoglobin, jaundice, strong
ambient light, and black henna stain.13 Though reduction is
available on all acute care wards in our hospital, 31.5% of
measured ABG did not have their SaO2 checked by the
pulse oximetry concomitantly. In 45% of these occasions,
BRIEF REPORT: ARTERIAL BLOOD GAS MEASUREMENTS
ABG measurements could have been avoided if pulse
oximetry had been done. Wider and proper utilization of
this tool would be reflected in decreasing numbers of
unnecessary ABG measurements.
In summary, ABG measurements from acute care wards
in a tertiary-care teaching hospital were found to be
overutilized, a fact that is consistent with data in the
literature. The development and implementation of
guidelines or an algorithm for requested ABG requisition
may significantly reduce the number of requested ABG and
increase their appropriateness.
Acknowledgements
The authors would like to thank Prof. LeRoy Heffernan
and Prof. Sameer Bin Huraib for reviewing the manuscript
and providing valuable comments, and to Mr. Richard
Kellie and the members of the Cardiopulmonary
Department for their assistance and support.
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