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Comparison of Treatment Modalities for

Hemorrhagic Shock

Anthony T. W. Cheung, Patricia L. (Duong) To, Danielle M. Chan,

Sahana Ramanujam, and Michelle A. Barbosa

Department of Medical Pathology and Laboratory Medicine,University of California, Davis School of Medicine,Sacramento, CA, USA

Peter C. Y. Chen

Department of Bioengineering, University of California,San Diego, La Jolla, CA, USA

Bernd Driessen

Department of Clinical Studies, University of Pennsylvania

School of Veterinary Medicine, Kennett Square,PA, USA

The research was partially funded by NIH grant (HL67432) awarded toATWC, a UC Davis Professional Development Award to ATWC, a UC DavisSchool of Medicine Faculty Research Award to ATWC, a UC Davis School ofMedicine Robert Stowell (MD=PhD) Scholarship Award to PLDT, a UC Davis

Hugh Edmondson Summer Research Fellowship to PLDT, and a HowardHughes Medical Institute (S.H.A.R.P.) Research Fellowship to PLDT.The subject materials in this manuscript have been presented, in parts, in a

poster=discussion session in a workshop session lecture at the 9th InternationalSymposium on Blood Substitutes (Tokyo, Japan), a lecture at the 23rd Meetingof the European Society for Microcirculation (Lisbon, Portugal), a lecture atthe 05 Asian Conference on the Microcirculation (Tokyo, Japan), and a lectureat the 10th International Symposium on Blood Substitutes (Providence, RI,USA). In addition, parts of this article have been published in the symposiumproceedings of these international meetings.

The assistance of Cindy Her and Erin Lee, in the preparation of this manu-script, is very much appreciated.Address correspondence to Dr Anthony T W Cheung Professor and Vice

Artificial Cells, Blood Substitutes, and Biotechnology, 35: 173190, 2007

CopyrightQ Informa Healthcare

ISSN: 1073-1199 print/1532-4184 online

DOI: 10.1080/10731190601188257

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Jonathan S. Jahr

Department of Anesthesiology, University of California,

Los Angeles David Geffen School of Medicine, Los Angeles,

CA, and Department of Anesthesiology, Charles Drew

University of Medicine and Science, Los Angeles, CA, USA

Robert A. Gunther

Department of Surgery, University of California,

Davis School of Medicine, Sacramento, CA, USA

Abstract: Allogeneic blood resuscitation is the treatment of choice for hemor-rhagic shock. When blood is unavailable, plasma expanders, including crystal-

loids, colloids, and blood substitutes, may be used. Another treatment modality

is vasopressin, a vasoconstrictor administered to redistribute blood flow, increase

venous return, and maintain adequate cardiac output. While much information

exists on systemic function and oxygenation characteristics following treatment

with these resuscitants, data on their effects on the microcirculation and corre-

lation of real-time microvascular changes with changes in systemic function

and oxygenation in the same animal are lacking. In this study, real-time microvas-

cular changes during hemorrhagic shock treatment were correlated with systemic

function and oxygenation changes in a canine hemorrhagic shock model (5055%

total blood loss with a MAP of 4550 mmHg as a clinical criterion). Following

splenectomy and hemorrhage, the dogs were assigned to five resuscitation groups:

autologous=shed blood, hemoglobin-based oxygen carrier=Oxyglobin1, crystalloid=saline, colloid=Hespan1 (6% hetastarch), and vasopressin. Systemic functionand oxygenation changes were continuously monitored and periodically mea-

sured (during various phases of the study) using standard operating room proto-

cols. Computer-assisted intravital video-microscopy was used to objectively

analyze and quantify real-time microvascular changes (diameter, red-cell velocity)

in the conjunctival microcirculation. Measurements were made during pre-hemor-

rhagic (baseline), post-hemorrhagic (pre-resuscitation), and post-resuscitation

phases of the study. Pre-hemorrhagic microvascular variables were similar in all

dogs (venular diameter 42 4 mm, red-cell velocity 0.55 0.5 mm=sec). Alldogs showed significant (P< 0.05) post-hemorrhagic microvascular changes:20% decrease in venular diameter and 30% increase in red-cell velocity,

indicative of sympathetic effects arising from substantial blood loss. Microvascu-

lar changes correlated with post-hemorrhagic systemic function and oxygenation

changes. All resuscitation modalities except vasopressin restored microvascularand systemic function changes close to pre-hemorrhagic values. However,

only autologous blood restored oxygenation changes to pre-hemorrhagic levels

174 A. T. W. Cheung et al.

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an important role in pre-hospital=en route treatment for hemorrhagic shock.Vasopressin treatment resulted in inadvertent detrimental outcome without the

intended benefit.

Keywords: Blood substitutes; Hemorrhagic shock; Oxygenation; Real-timemicrocirculation; Systemic function

INTRODUCTION

Hemorrhagic shock, when not properly managed or treated in a timelymanner, can lead to irreversible damage and fatality. Therefore, appropriatemanagement and treatment of hemorrhagic shock are crucial modalities thatcan serve to prevent deleterious outcomes. Pre-hospitalen routetreat-ment, which on the average is conducted within 12 hours after blood loss,normally consists of resuscitations using non-oxygen carrying plasma expan-ders (crystalloid or colloid solution) or catecholamines, including epineph-rine and norepinephrine [15]. These treatments are designed to increasecardiac output so as to maintain mean arterial pressure (MAP), by redistri-buting blood flow and increasing venous return, until arrival at the hospitalfor allogeneic blood resuscitation or other definitive intervention.

In the past few years, hemoglobin-based oxygen carriers (HBOC)have been used as resuscitants in experimental trials to treat hemorrhagicshock [1,68]. The HBOC were designed to be very similar to allogeneicblood in oxygen-carrying and hemodynamic properties, with the intentthat they could serve literally as oxygen-carrying blood substitutes. Afew HBOC have been tested in animal models and are now in clinicaltrials in South Africa and Europe. One of the HBOC, Oxyglobin1, hasbeen approved by the Food and Drug Administration (FDA) for canine

use in the United States.Recently, it has been suggested that treatment using vasopressinthe

most potent naturally occurring vasoconstrictor knowncould ade-quately and alternatively serve to redistribute blood flow and, therefore,may be a more effective treatment modality than conventional plasmaexpanders or catecholamines [35,9]. Clinical reports have indicated thatin cases where fluid (plasma expander) or catecholamine resuscitationswere futile, alternative treatment with vasopressin led to successful out-comes [1012]. Several animal studies have shown that vasopressin treat-

ment provided hemodynamic stabilization (monitored via MAP) duringthe pre-hospital phase of shock studies, while fluid- or catecholamine-

Comparison of Treatment Modalities 175

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critical pre-hospital phase of hemorrhagic shock treatment by redistribut-ing blood flow to improve cardiac output and maintain MAP.

HBOC and vasopressin resuscitations, therefore, are modalitiesthat have great potential to manage and treat hemorrhagic shock in apre-hospital setting, in addition to the availability of crystalloid(s) and col-loid(s), which have been used for decades, albeit with variable outcomes.

The goal of this study was to compare the different treatment modal-ities available for pre-hospital use, including an oxygen-carrying blood sub-stitute=HBOC (Oxyglobin1), a non-oxygen-carrying crystalloid (saline), anon-oxygen-carrying colloid (Hespan1), and a potent vasoconstrictor(vasopressin), using autologous=shed bloodthe gold standard for thetreatment of hemorrhagic shockas positive control. The experimentalprotocol was designed to longitudinally and simultaneously measure sys-temic functions, oxygenation characteristics, and microvascular activitiesin pre-hemorrhagic (baseline), post-hemorrhagic (pre-resuscitation) andpost-resuscitation phases of the study for data correlation (in the sameanimal), efficacy comparison, and critical outcome evaluation.

MATERIALS AND METHODS

Animals

Fifteen dogs (healthy adult, male or female, 3035 kg) were studied in a12-month period. They were prepared, instrumented, splenectomized,hemorrhaged (to attain a MAP of 4550 mmHg as a clinical criterion;equivalent to 5055% blood loss), and resuscitated as performed inpreviously reported studies [1315]. The dogs were randomly assigned tofive resuscitation groups (autologous=shed blood, n3; Oxyglobin1,

n3; saline, n3; Hespan1, n3; vasopressin, n3) as briefly describedin Methods. A schematic flow-chart of the study is shown in Figure 1.

Resuscitants

Autologous=shed blood was anti-coagulated blood from the same dogcollected during hemorrhaging for use as positive resuscitation control.

Oxyglobin1 (Hemoglobin Glutamer-200 [Bovine]; Biopure Corpor-

ation, Cambridge, MA) was an oxygen-carrying blood substitute thathas been approved by the FDA for canine use in the United States.


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Hespan1 (6% hetastarch; Abbott Laboratories, Chicago, IL) was anon-oxygen-carrying colloid solution that has been commonly used asa plasma expander.

Arginine Vasopressin (Vasopressin injection USP; AVP; AmericanRegent Laboratories, Shirley, NY) was a potent vasoconstrictor com-monly used in the hospital with the intent to redistribute blood flow.

Animal Preparation and Instrumentation

A total of 15 healthy, adult mongrel dogs were used within a 12-monthperiod. Approval (Animal Welfare Assurance #A-343301) by the Uni-versity of California, Davis Animal Care and Use Committee wasobtained for this study. The experimental protocol used in this studywas in compliance with the Guide for the Care of Laboratory Animals

(National Institutes of Health Publication #8623, revised 1985).Each dog was premedicated with IM oxymorphone (0.02 mg=kg) and

Figure 1. Schematic flow-chart of the study.


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instrumentation period and during the administration of drugs. Anesthe-sia was induced with IV propofol (24 mg=kg) and diazepam (0.5 mg=kg),followed by orotracheal intubation. Anesthesia was maintained followinga balanced protocol, using isoflurane and fentanyl to minimize potentialconfounding hemodynamic effects [16,17]. During animal preparationand instrumentation, isoflurane in oxygen was delivered at an end-tidalconcentration of 0.81.2%, and fentanyl infused at a rate of 0.7 mg=kg=minfollowing an initial bolus of fentanyl (10 mg=kg). The dog was mechani-cally ventilated with an anesthesia ventilator (Model 2000; HallowellEMC, Pittsfield, MA) using tidal volumes (VT) of 1520 mL=kg and a res-piratory rate of 912 breaths per minute to ensure an arterial partial pres-sure of carbon dioxide (PaCO2) in the range of 3545 torr (4.66.0 kPa).End-tidal partial pressure of CO2 (PETCO2), end-tidal concentration ofisoflurane (ISOET), and inspired O2 concentration (FiO2) were continu-ously monitored using a Datex airway gas monitor (Datex 254; Helsinki,Finland).

Each dog was instrumented initially in dorsal recumbency and thenplaced on its side. Further monitoring included continuous recordingof the electrocardiogram (ECG; Monitor Model 78353B, Hewlett Pack-ard, Andover, MA) and arterial O2saturation (SaO2; Model N-180 pulseoximeter, Nellcor Inc., Hayward, CA). Further instrumentation includedplacement of catheters into the dogs femoral artery for arterial bloodwithdrawal, and determinations of systemic arterial pressures using mem-brane transducers (Model 1290A, Hewlett Packard, Watham, MA). An8-fr balloon-tipped flow-directed thermodilution pulmonary arterialcatheter (OptiQ2, Abbott Laboratories, Chicago, IL) was also insertedvia the jugular vein and floated into the pulmonary artery under directmonitoring of pressure traces for measurements of central venous pres-sure (CVP), pulmonary occlusion pressure (POP), mean arterial pressure

(MAP), systolic arterial pressure (SAP), diastolic arterial pressure (DAP),mean pulmonary arterial pressure (MPAP), core body temperature andcardiac output (CO). The pulmonary arterial catheter was connected to acardiac output computer (Critical Care System QVUE, Oximetrix 3,Abbott Laboratories, Chicago, IL) for continuous CO monitoring.Cardiac output was also assessed by thermodilution in triplicate using10 mL of saline at room temperature. Body temperature was maintainedbetween 3839C by means of a heating pad and circulating warm airblanket (Bair Hugger1 Model 505, Augustine Medical Inc., Eden, MN).

After preparation and instrumentation, the dog was splenectomizedfollowing a midline laparotomy to prevent release of sequestered blood


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Measurement of Systemic Variables

A bioengineering station, which was designed to monitor and studyhemorrhagic shock and treatment modalities in large animals in an oper-ation room setting, was established for this study in our laboratory at UCDavis. The bioengineering station was capable of measuring numeroussystemic function and oxygenation variables. Of interest to this study,the measured variables included ECG, MAP, SAP, DAP, MPAP, POP,CVP, heart rate (HR), stroke volume index (SVI), and CO. Arterialand mixed-venous heparinized blood samples were collected intermit-tently (whenever appropriate) from the femoral artery and the rightatrium, respectively. Immediately after collection, blood samples weresealed and stored on ice. Subsequently, arterial and mixed-venous totalhemoglobin (aHbtotal; vHbtotal), arterial plasma hemoglobin (aHbplasma)and methemoglobin (Met-Hb) concentrations, and arterial and mixed-venous O2 saturation (SaO2; SvO2) were measured, using a co-oximeter(Model 482, Instrumentation Laboratories, Lexington, MA). Arterialand mixed-venous O2 content (CaO2; CvO2) were directly measured intriplicate, using an oxygen-specific electrode (LEXO2CON-K, HospexFiberoptics, Chestnut Hill, MA). Mean tissue oxygenation (MtO2) wasmeasured by an oxygen-measuring microprobe inserted percutaneouslyinto the quadriceps femoris muscle of the thigh, using the OxyFloTM=OxyLite2 microprobe technology (Oxford Instruments; Oxford, UK).Arterial and mixed-venous lactate (lactatea; lactatev) concentrations weredetermined in duplicate by means of a lactate analyzer (Model 1500, YSIInc., Yellow Springs, OH). Arterial and mixed-venous pH (pHa; pHv) andpartial pressures of O2(PaO2; PvO2) and CO2(PaCO2; PvCO2) were ana-lyzed with a blood gas analyzer (Rapidlab Model 248, Bayer CorporationDiagnostics Division, Norwood, MA). Blood gas values were corrected

for the body temperature of the animal at the time of sampling. Arterialand mixed venous standard base excesses (SBEa; SBEv) and bicarbonatelevels (aHCO3; vHCO3) were computed by the blood gas analyzer. Othervariables, including body surface area (BSA in m2), systemic vascularresistance (SVR), etc., were calculated using standard equations.

Computer-Assisted Intravital Microscope (CAIM)

The CAIM system was anchored along the front edge of the operatingtable for non-invasive videotaping of the real-time conjunctival microcir-


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the bioengineering station, it has been substantially redesigned and modi-fied to study the microcirculation in the bulbar conjunctiva of the dog sothat real-time microvascular changes in the conjunctival microcirculationcould be videotaped simultaneously with the measurements of systemicfunctions and oxygenation in the same animal for critical correlation(see Figure 2). CAIM was macro-optic based and has an opticalmagnification of 4.5 and an on-screen magnification of 125. The


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optical magnification of CAIM was fixed because of its macro design;this non-changeable magnification was important as it assured that allmicrovascular measurements made in various phases of the experimen-tation were quantified on the same basis without a magnification vari-able. An anti-red (#58 Wratten green filter) fiber-optic light sourcewas used to illuminate the conjunctival microcirculation and to enhancevessel visualization. The angle and level of the front element of CAIMwere adjusted to provide the flattest possible surface for focusing.A COHU video camera (Model 2622-100; 1/2-inch monochrome CCD-format, San Diego, CA) was used to non-invasively videotape the real-time conjunctival microcirculation via a high-resolution video-recorder.Focus of CAIM was centered on the microcirculation in the bulbar con-

junctiva of the left eye of the dog. The microvascular activities werevideotaped and subsequently analyzed via computer-assisted imageanalysis for microvascular morphometry and dynamics using in-housedeveloped imaging software VASCAN and VASVEL [1315,1822].The imaging software can objectively quantify over 20 parameters ofmicrovascular characteristics. However, only venular diameter (morpho-metric) and red-cell velocity (dynamic) characteristics, which we considerrelevant based on previous investigations, were objectively quantified andreported in this study [1315]. Most conjunctival vessels have uniqueshapes and forms and were easily recognizable. In this study, the vesselsof interest were identified and relocated for time-dependent videotaping.During various phases of the experimentation, the same vessels were relo-cated and restudied so that relevant measurements (e.g., vessel diameterand red-cell velocity) were made for longitudinal comparison, with eachvessel serving as its own reference control (see Figures 3 and 4).

Figure 3. A series of three images showing the same location in the conjunctival

microcirculation of a dog during pre-hemorrhagic (basline), post-hemorrhagicand post-resuscitation phases of the experiment in the autologous=shed bloodstudy Because of the unique shape and form of the vessels under observation


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Canine Hemorrhagic Shock Model

Each dog was allowed to stabilize after the splenectomy. The amount ofsequestered blood in the spleen from each dog was measured andincluded in the computation of total blood loss (5055%). At the endof a 60-min stabilization period, pre-hemorrhagic (baseline) measure-ments on systemic function and oxygenation were made (pre-hemorrha-gic phase). In addition, videotape sequences were made via CAIM onthe conjunctival microcirculation simultaneously. Immediately after thebaseline measurements were made, 5055% of the blood volume ofthe dog (based on body weight and the amount of sequestered bloodin the spleen measured after splenectomy) was withdrawn from the lateralsaphenous and femoral veinsat an overall hemorrhage rate of 3236mL=kg=hruntil a MAP of 4550 mmHg was achieved (normally45 min). The method of attaining a MAP of 4550 mmHg as a clinical

criterion was used to ensure the induction of acute but non-lethalhypovolemia and hemorrhagic shock. Within the post-hemorrhagic1-hr acclimatization period to induce hemorrhagic shock, small amountsof blood were withdrawn if needed (whenever MAP increased to over50 mmHg) to maintain a MAP of 50 mmHg (within a 4550 mmHgrange). Shed blood was collected, anticoagulated and used in autologousblood resuscitation to serve as control. In similar manner to pre-hemorrhagic (baseline) measurements, post-hemorrhagic measurementsand videotape sequences were made (post-hemorrhagic phase). At the

end of post-hemorrhagic measurements, the dogs were randomly assignedto one of the five resuscitation groups: autologous=shed blood (resusci-

Figure 4. A series of three images showing the same location in the conjunctivalmicrocirculation of a dog during pre-hemorrhagic (basline), post-hemorrhagicand post-resuscitation phases of the experiment in the crystalloid=saline study.

Again, the same vessels were identified and relocated for longitudinal evaluations.Magnification 125on-screen.


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vasopressin (resuscitated at a loading bolus dose of 0.4 IU=kg followedby 4.8 IU=kg=hr for one hour). Systemic function and oxygenationmeasurements were again made at the completion of the resuscitationprocess (post-resuscitation phase). Videotape sequences were also madesimultaneously.

Statistics

All results were averaged and reported as mean SD. Analysis of vari-ance, students t-test and post hoc Bonferroni corrections were usedwhenever appropriate. A 0.05 significance level was used in this study.P values smaller than 0.01 (e.g., P 0.000045 or P 5.793 104) werepresented as P

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different extents and did not return to pre-hemorrhagic values, withHespan1 being most effective and Oxyglobin1 being least effective.

Shed blood resuscitation restored post-hemorrhagic microvascularchanges to pre-hemorrhagic values. Oxyglobin1, saline, and Hespan1

Figure 5. Post-hemorrhagic and post-resuscitation changes in venular diametersinduced by the five resuscitation treatment modalities.


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resuscitations, similar to the effect of shed blood, also restored post-hemorrhagic microvascular changes close to pre-hemorrhagic values(see Figures 5 and 6). However, vasopressin treatment resulted in furtherdecreases in venular diameter (50%) as well as red-cell velocity (70%)(see Figures 57).

Shed blood resuscitation restored post-hemorrhagic oxygenation(CaO2 and CvO2) changes to pre-hemorrhagic (baseline) values. How-ever, Oxyglobin1, saline, Hespan1, and vasopressin resuscitations did

Figure 7. A series of two images showing the same location in the conjunctivalmicrocirculation of a dog during post-hemorrhagic and post-resuscitation phasesof the experiment in the vasopressin study. Again, the same vessels were identifiedand relocated for longitudinal evaluations. Note the extensive vasoconstrictionarising from the vasopressin infusion. Magnification 125on-screen.


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not have any effect in restoring these post-hemorrhagic oxygenationchanges (see Figures 8 and 9). The unexpected result that Oxyglobin1,an oxygen carrier, did not restore oxygenation changes led to the sus-picion that standard blood sample based oxygenation measurementsmay not adequately measure tissue oxygenation levels. To investigate this

Figure 9. Post-hemorrhagic and post-resuscitation changes in venous oxygencontent (CvO2).


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possibility, the OxyfloTM=OxyliteTM microprobe technology was used tomeasure tissue level oxygenation levels in the same animals. The resultsconfirmed that, of all the resuscitants used in this study, only shed bloodrestored oxygenation at the tissue level to pre-hemorrhagic values. Inaddition, it was also shown that vasopressin resuscitation led to a furtherdecrease in tissue oxygenation (see Figure 10).

DISCUSSION

Allogeneic blood resuscitation is the treatment of choice for hemorrhagicshock. However, in situations when blood is not available (e.g., battle-field or rural area injury), crystalloids, colloids, artificial blood substi-tutes, or vasoactive agents have been used. The goal of this study wasto evaluate the efficacy of these resuscitants in the pre-hospital treatmentof hemorrhagic shock, with special emphasis on studying their effects onthe microcirculation, the raison detre of the vasculature [1]. Few studieshave focused on the real-time microcirculation in large animals due to alack of relevant technologies and appropriate non-invasive research sites.In addition, rarely have real-time microvascular changes been simul-taneously studied and correlated with systemic function and oxygenationchanges in the same animal. The availability of CAIM provided a meansfor non-invasive evaluation of the effects of different resuscitants on thereal-time microcirculation. In addition, the large size of the dog allowedfor extensive measurements of systemic function, blood chemistry, andoxygenation changes to correlate with changes in microvascular para-meters. This study represents the first of its kind in which systemic func-tions, oxygenation, blood chemistry, and microvascular characteristicswere measured in the same animal simultaneously. In addition, the results

can serve as a benchmark for testing treatment modalities for hemorrha-gic shock, and in the future development of artificial blood substitutes.

In order to adequately evaluate the efficacy of different resuscitants,a suitable hemorrhagic shock model (substantially modified from theWiggers model [23]) was adapted in our laboratory in which the dogswere maintained for a 1-hr acclimatization period following hemorrha-ging to ensure the development of hemorrhagic shock for this study. Thismodel may serve as a testing platform for future hemorrhagic shock andresuscitation studies.

In this study, only shed blood resuscitation restored post-hemorrhagicsystemic function and oxygenation changes to pre-hemorrhagic levels.


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at a rate of 30mL=kg=hr. However, Oxyglobin1 was administered at aslower rate (10 mL=kg=hr) as recommended by the manufacturer to pre-vent excessive circulatory hemoglobin overload. This significantly slowerrate of administration, which replenished less blood volume comparedwith the standard protocol, may account for the failure of Oxyglobin1

to restore CO and HR to baseline values. While it was expected that saline,Hespan1, and vasopressin resuscitations would not restore oxygenationcharacteristics due to their non-oxygen carrying capability, it was surpris-ing that oxygen-carrying Oxyglobin1 did not restore oxygenation (CaO2and CvO2) characteristics. To address the possibility that blood-samplebased measurements of oxygenation characteristics may not be reflectiveof tissue level oxygenation, the OxyFloTM=OxyLiteTM microprobe tech-nology was used to obtain measurements of oxygenation at the tissue level.The results indicated that only shed blood resuscitation restored tissueoxygenation to pre-hemorrhagic values and that, indeed, the oxygen-carrying Oxyglobin1 was not effective in improving blood oxygenation.In addition, it was also convincingly shown that vasopressin treatmentresulted in a further decrease in tissue oxygenation (see Figure 10).

In this longitudinal study when efficacy studies were made to mimicpre-hospital treatment of hemorrhagic shock, autologous=shed blood,Oxyglobin1, crystalloid (saline), and colloid (Hespan1) resuscitations wereeffective in restoring MAP from a post-hemorrhagic value of 4550 mmHgto a close-to-baseline (pre-hemorrhagic) level of 95100 mmHg immedi-ately after completion of resuscitation. However, follow-up studies toevaluate the effects of these resuscitants 34 hrs after resuscitation areneeded to show their long-term efficacies in the treatment of hemorrhagicshock.

Vasopressin treatment, instead of achieving the intended goal ofredistributing blood flow to improve CO and maintain MAP, resulted

in detrimental effects, including extensive peripheral vasoconstriction,which led to a cessation of blood flow, significant reduction in red-cellvelocity, significant disappearance of capillaries and arterioles, andsignificant decreases in tissue oxygenation. These results indicate thatvasopressin may not be an appropriate choice as a resuscitant for thetreatment of hemorrhagic shock.

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