Page 88 - Journal of Special Operations Medicine - Spring 2014

repeated after 30 minutes if the patient is still in shock, was induced with ketamine (10mg/kg IM) and inhaled
with no more than 1000mL of the fluid. Hextend is a isoflurane (4%) and oxygen (100% Fio ). Isoflurane was
14
2
plasma volume expander containing 6% hydroxyethyl reduced to 1%–2% following airway instrumentation for
starch (HES) in a physiologically balanced medium of the remainder of the experiment. The animals were venti-
electrolytes, glucose, and lactate (weight average, molec- lated with a tidal volume of 8–10mL/kg and a respiratory
ular weight 670kDa, molar substitution 0.75). The het- rate of 12 breaths per minute using a Narkomed 3A anes-
astarch component of Hextend creates oncotic pressure, thesia machine (Drager Medical Systems, Telford, PA). The
which would normally be provided by blood proteins, left carotid artery was cannulated with a 20-gauge catheter
and permits retention of intravascular fluid. Several used for monitoring. We used a GE Marquette Solar 800
15
studies have demonstrated the benefits of Hextend. 16–21 monitor (GE Healthcare, Pittsburgh, PA) to continuously
For example, Ogilvie et al. demonstrated a reduced monitor HR, SBP, DBP, electrocardiogram, oxygen satura-
number of early deaths and overall mortality when Hex- tion, end-tidal carbon dioxide, and rectal temperature. In
tend was administered. 22 addition, the hemodynamics (SBP, DBP, HR, MAP, CO,
and SV) were continuously monitored using the Vigileo
No study has compared IO and IV routes relative to Monitor (Edwards Lifesciences, Irvine, CA).
time or hemodynamics relative Hextend administration
in a hypovolemic model. The purposes of this study were An 8.5 French × 10cm central venous catheter was in-
to compare the time to administer 500mL of Hextend serted in the right subclavian (Arrow International,
and the hemodynamics of IV and IO routes in a Class II Reading, PA) for the purpose of exsanguination. Fluid
hemorrhage swine model. The hemodynamics included deficit resulting from NPO time would potentially
systolic blood pressure (SBP), diastolic blood pressure change the volume of blood. Data were collected from
(DBP), heart rate (HR), mean arterial pressure (MAP), some subjects as early as 07:00 and some as late as
cardiac output (CO), and stroke volume (SV). The re- 17:00. Hence, we administered a replacement of defi-
search question that guided the study was as follows: cit volume using normal saline so that the deficit would
not be confounding variable. The deficit was calculated
Are there statistically significant differences between IO, using the standard 4-2-1 method, Holiday-Segar for-
IV, and control groups relative to time and hemodynam- mula, before the experiment began. Normothermia was
ics in the administration of Hextend? maintained in each animal by the use of a Bair-Hugger
Model 505 forced air-warming blanket (Arizant Inc.,
Prairie, MN) to sustain body temperature greater than
Procedures
36.0°C. Swine in the IV group had an 18-gauge IV cath-
We used data from a pilot study and calculated a large eter placed in the left ear, and swine in the IO group
effect size (.6). Using an effect size of .6, an α of .05, had a 2.5cm EZ-IO 15-gauge needle (Vidacare Inc., San
and a power of .80, we calculated that we would need Antonio, TX) placed in the humerus. The humerus was
nine subjects per group. This study was a prospective, used because it is one of the recommended sites for IO
experimental mixed (within- and between-) subjects de- administration of fluids and drugs. The IO placement
sign. The research protocol was approved by the local was verified via aspiration of blood and effortless infu-
Institutional Animal Care and Use Committee (IACUC). sion of a 20mL normal saline bolus. In all groups, we
The animals received care in accordance with the Ani- exsanguinated 30% of the swine’s blood volume, which
mal Welfare Act and The Guide for the Care and Use of was calculated based on the weight of each pig. Swine
Laboratory Animals. Twenty-seven Sus scrofa Yorkshire- have the same blood volume as humans (70mL/kg of
cross swine weighing between 67 and 80 kg were equally weight); therefore, a pig that weighs 70 kg has about
assigned by the use of computer-generated random num- 4900mL of blood volume, and 30% exsanguination is
bers to one of three groups: humerus IO (IO group) (n = equal to 1470mL. Thirty percent blood loss represents a
9), IV (IV group) (n = 9), and control group (n = 9). The Class II hemorrhage. The blood was exsanguinated via
rationale for using this weight range is that it represents gravity from the subclavian over 15 to 20 minutes and
the average weight of the U.S. Army Soldier. To avoid was weighed with an electronic scale (Thermal Indus-
23
any variability in subjects, we purchased the pigs from tries of Florida, Owatonna, MN) for calculation of the
the same vendor and used pigs approximately the same 30%. A container was placed on the scale and zeroed to
size and the same gender (male). The swine were fed a account for variations in container weights.
standard diet and were observed for 3 days to ensure a
good state of health. All of the swine were NPO after Data (vital signs and hemodynamics) were collected im-
midnight the day before the experiment. mediately before and after the hemorrhage. After the
hemorrhage, we administered 500mL of Hextend ad-
The swine were sedated with buprenorphine (0.01mg/kg ministered via either the IO or IV route with a pneumatic
IM) 30 minutes before anesthetic induction. Anesthesia pressure bag. One investigator continuously monitored

80 Journal of Special Operations Medicine Volume 14, Edition 1/Spring 2014