title: Effect of hemorrhage rate on early hemodynamic responses in conscious sheep.
abstract: Physiological compensatory mechanisms can mask the extent of hemorrhage in conscious mammals, which can be further complicated by individual tolerance and variations in hemorrhage onset and duration. We assessed the effect of hemorrhage rate on tolerance and early physiologic responses to hemorrhage in conscious sheep. Eight Merino ewes (37.4 ± 1.1 kg) were subjected to fast (1.25 mL/kg/min) and slow (0.25 mL/kg/min) hemorrhages separated by at least 3 days. Blood was withdrawn until a drop in mean arterial pressure (MAP) of >30 mmHg and returned at the end of the experiment. Continuous monitoring includedMAP, central venous pressure, pulmonary artery pressure, pulse oximetry, and tissue oximetry. Cardiac output by thermodilution and arterial blood samples were also measured. The effects of fast versus slow hemorrhage rates were compared for total volume of blood removed and stoppage time (whenMAP < 30 mmHg of baseline) and physiological responses during and after the hemorrhage. Estimated blood volume removed whenMAPdropped 30 mmHg was 27.0 ± 4.2% (mean ± standard error) in the slow and 27.3 ± 3.2% in the fast hemorrhage (P = 0.47, pairedttest between rates). Pressure and tissue oximetry responses were similar between hemorrhage rates. Heart rate increased at earlier levels of blood loss during the fast hemorrhage, but hemorrhage rate was not a significant factor for individual hemorrhage tolerance or hemodynamic responses. In 5/16 hemorrhages MAP stopping criteria was reached with <25% of blood volume removed. This study presents the physiological responses leading up to a significant drop in blood pressure in a large conscious animal model and how they are altered by the rate of hemorrhage.
authors.affiliation: Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, US Food and Drug Administration, Silver Spring, Maryland Christopher.Scully@fda.hhs.gov.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Scully
authors.affiliation: Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, US Food and Drug Administration, Silver Spring, Maryland.
authors.forename: Chathuri
authors.initials: C
authors.lastname: Daluwatte
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: Nicole R
authors.initials: NR
authors.lastname: Marques
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: Muzna
authors.initials: M
authors.lastname: Khan
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: Michael
authors.initials: M
authors.lastname: Salter
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: Jordan
authors.initials: J
authors.lastname: Wolf
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: Christina
authors.initials: C
authors.lastname: Nelson
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: John
authors.initials: J
authors.lastname: Salsbury
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: Perenlei
authors.initials: P
authors.lastname: Enkhbaatar
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: Michael
authors.initials: M
authors.lastname: Kinsky
authors.affiliation: Department of Anesthesiology, The University of Texas Medical Branch, Galveston, Texas.
authors.forename: George C
authors.initials: GC
authors.lastname: Kramer
authors.affiliation: Office of Clinical Pharmacology, Office of Translational Sciences, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, Maryland.
authors.forename: David G
authors.initials: DG
authors.lastname: Strauss
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D062186:Arterial Pressure; D001810:Blood Volume; D002302:Cardiac Output; D003243:Consciousness; D004195:Disease Models, Animal; D005260:Female; D006339:Heart Rate; D006439:Hemodynamics; D006470:Hemorrhage / Q000097:blood / Q000503:physiopathology*; D007022:Hypotension / Q000097:blood / Q000503:physiopathology*; D020896:Hypovolemia / Q000097:blood / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D012756:Sheep; D013997:Time Factors; D014690:Venous Pressure
chemical_list: D010100:Oxygen
keywords: Hemodynamic compensation; hemorrhage; hypovolemia