Operational evaluation of the earlobe arterialized blood collector in critically ill patients

The results from the present operational evaluation demonstrate that the EABC®?+?i-STAT®
system concept is safe, fast and easy to use. The observed problems/difficulties attributable
to the collector accounted for 10% of the cases and comprised of superficial cut,
blood leak, collector misalignment and operator’s obstructed vision. These would be
easily amendable with certain design modifications.

The results from the analytical performance evaluation have been published elsewhere
15] and showed good precision levels (coefficient of variation??10% in all gasometrical
variables) and enough accuracy to detect extreme gasometrical alterations of the EABC®?+?i-STAT®
system (percentage of error??20% in all gasometrical variables) when compared with
direct arterial reference samples. This new system was also able to correctly classify
ARDS patients according to severity (sensitivity?=?100%, specificity?=?92.3%, kappa
coefficient?=?0.85) 15]. Therefore, the new technique was considered useful in the initial diagnosis and
treatment of medical emergencies and could prove to be valuable if implemented in
a medical protocol as a first evaluation tool of critically ill patients in remote
environments. From an operational point of view, a limited sampling success rate was
observed. The main causes of sampling failure were low-blood flow from the earlobe
and blood coagulation, which had not been evidenced in previous validation studies
using the EABC®?+?i-STAT® system 14],12],13] or when other capillary blood collection methods were used 3]-10]. A separate evaluation was performed to ascertain what factors could influence earlobe
capillary blood flow and affect sampling procedure, results of which have been published
elsewhere 15]. Using a multivariate analysis, which took into consideration several patient demographics
and medical characteristics, the results evidenced that patient age was the only variable
associated with sampling failure. It was hypothesized that microvascular ageing of
the earlobe capillary bed could have influenced blood flow and blood delivery to the
cartridge, leading to the observed low-sampling success ratio in older patients 15]. Nevertheless, success rate was 90% in patients?50 years (n?=?9) and 100% in 40-year-old patients (n?=?4), which would support the use of the EABC®?+?i-STAT® system in a wide range of
patients, especially those in isolated and extreme environments, such as astronauts
in space 17] or explorers of remote locations on Earth.

The training required for learning the procedure of earlobe arterialized capillary
blood sampling with the new EABC®?+?i-STAT® system was short, requiring only two workshops.
Although a learning curve may exist, its interpretation was difficult and unreliable
due to clustered patient distribution and was not used to determine training needs
of the procedure. The two operators involved in the study reported that the sampling
procedures were easy to perform in either of the patient’s earlobes. Furthermore,
the system was found to be portable, manageable and efficient, requiring a reduced
number of cuts and analysis cartridges in most of the cases. These findings confirm
that the new system is easy to use and requires minimum training as reported in previous
studies.

TAT is a key determinant of laboratory performance evaluation from an operational
point of view 18]. In the present study, a practical approach was chosen and TATs were calculated from
the decision to sample until the finalization of post-sampling procedures. This estimation
of TAT was considered to be the best interpretation and information of the real operational
needs of the technique. Results showed that TAT of the whole procedure was 26 min,
lying below current TATs of most tertiary hospitals 18]. These results were considered adequate given the specific characteristics of the
medical situations where the procedure could be used. However, since TAT calculation
can be controversial sometimes 18], direct analysis time (or isolated laboratory TAT) can be evaluated. In this context,
if preparatory procedures are excluded, results from blood gas analysis can be quickly
obtained in 120 s using the i-STAT® portable analyser, which still represents an appropriate
time to results 16]. Furthermore, since earlobe arterialization was achieved in spite of increases in
vasodilation time, further decrease in time expenditure for the whole procedure can
be envisaged and could lead to a theoretical reduction of TAT to 23.5 min. Additionally,
auxiliary procedures were found to require minimum time expenditure.

This study also confirmed the safety of the new system for both the patient and the
operator. There was only one case of suspected infection of the EL, which resolved
spontaneously. No episodes of accidental injury with the cutting blade or contamination
of the operator with patient’s blood occurred. The safe use of the device was possible
due to the containment of both blood and blade within the collector during operation.
These findings are in agreement with previous studies in which no complications were
reported.

The equipment utilized for providing autonomous gasometrical analysis capabilities
was found to require a small storage volume. Furthermore, although the shelf life
of a refrigerated cartridge can be extended to several months, room temperature storage
during a maximum of 2 months is also possible. These findings make this new system
very suitable for environments with limited storage capabilities such as the International
Space Station and other space systems, as well as in extreme and isolated environments
on Earth.

The present study has a number of limitations. First, the evaluation of the usability
of the proposed new technique and collector comes substantially from the subjective
opinion of operators, which could induce a bias in the evaluation. However, both operators
were able to learn the procedure quickly and required only one cut to obtain a valid
blood sample in most of the cases, which supports that sufficient skills on the use
of the technique had been achieved. Second, as previously discussed, the presence
of a learning curve may suggest that 35 sampling attempts are required to learn the
procedure. However, unbalanced distribution of patients makes this assessment unreliable.
There must be a minimum number of test rounds required; however, data are insufficient
to determine such a number with precision. Third, this evaluation focuses on critically
ill patients in the controlled environment of an ICU. While the use of a varied population
of such patients may provide useful information that could be transferrable to other
similar patients in extreme or remote environments, other uncontrolled factors such
as temperature, humidity or atmospheric pressure may influence performance and operational
characteristics of the technique. Therefore, additional field studies are required
to confirm the potential benefits for patient healthcare in remote environments suggested
in the present analysis.