Biomedical subjects
David G Baer
Publications and source records attributed to David G Baer.
Effect of fluid resuscitation on acute skeletal muscle ischemia-reperfusion injury after hemorrhagic shock in rats.
BACKGROUND: Severe extremity wounds with vascular injury are common in military trauma, and tourniquets are commonly used for hemorrhage control. The complications of tourniquet use in the setting of trauma are not well studied. This study investigated the combined effect of hemorrhagic shock and fluid resuscitation with Hextend (HX; BioTime, Inc) or lactated Ringer's (LR) on skeletal muscle subjected to tourniquet-induced ischemia-reperfusion injury. STUDY DESIGN: Thirty male Sprague-Dawley rats underwent 33% arterial hemorrhage followed by 3 hours of tourniquet application. Before reperfusion, 10 animals each were resuscitated with lactated Ringer's (3 times shed volume) or HX (shed volume). Ten control animals received no resuscitation. Rats were euthanized 2 hours after tourniquet release and the tibialis anterior and medial gastrocnemius muscles were examined for edema (muscle wet weight) and viability (nitroblue tetrazolium reduction). Contralateral muscles served as controls for each animal, with results expressed as the ratio of the tourniquet limb to contralateral limb values. RESULTS: The tibialis anterior and medial gastrocnemius muscles in all groups experienced edema, with all weight ratios greater than one. Resuscitation with HX resulted in significantly (p < 0.05) greater edema than did no resuscitation in both muscles and greater edema than with lactated Ringer's in the medial gastrocnemius. All groups experienced a loss of viability as well, with nitroblue tetrazolium reduction ratios less than one. Resuscitation with HX resulted in significantly less viability loss than did no resuscitation in the medial gastrocnemius. No significant differences in viability were seen in the tibialis anterior. CONCLUSIONS: Resuscitation with HX or lactated Ringer's does not adversely affect muscle viability in ischemia-reperfusion injury. HX may be a better clinical choice when skeletal muscle ischemia-reperfusion injury is a risk, despite greater edema.
A large animal fatal extremity hemorrhage model and evaluation of a polymeric dressing (fatal extremity hemorrhage).
BACKGROUND: Extremity hemorrhage is a contributor to preventable battlefield mortality. The Army has liberalized tourniquet use guidelines in an attempt to prevent these deaths. To evaluate wound hemostatic agents that might allow for early tourniquet removal while maintaining hemorrhage control, a model of lethal extremity hemorrhage in the goat (Capra hircus) was developed and a polymeric dressing agent (BioFoam) tested. METHODS: After administration of a spinal block, animals were placed in lateral recumbancy with a head-up tilt of 6 degrees, 500 mL crystalloid was injected and 600 u/Kg of heparin was administered. After tourniquet application to the thigh, a soft tissue and vascular injury was created by transecting muscles and the femoral artery. The polymeric wound dressing was applied and the tourniquet was released. RESULTS: In testing, the primary endpoint was mortality within the first hour after tourniquet release. None of the control animals survived the full hour. Two out of five (40%) of the treated animals survived. With survivors' survival time calculated as 60 minutes, survival time was found not to differ between treated (34 +/- 19 minutes) and untreated (29 +/- 18 minutes) animals (p = 0.77). CONCLUSION: The physical characteristics of tissue injury, need for anticoagulation, and manipulation of blood pressure are vital factors contributing to the lethality of a large animal fatal extremity hemorrhage model. BioFoam was successful in preventing fatal arterial extremity hemorrhage after the release of an effective tourniquet in some cases. An agent that can reliably allow for safe tourniquet removal and restoration of collateral circulation is a potential solution to tourniquet-associated morbidity in traumatic extremity injury. The model developed will serve as a rigorous test for such agents.
Effectiveness of self-applied tourniquets in human volunteers.
BACKGROUND: Tourniquets are not commonly used in routine extremity trauma, but can be vital for hemorrhage control in austere conditions. OBJECTIVE: To determine the effectiveness in human volunteers of currently available self-applied tourniquets for extremity hemorrhage. METHODS: Seven tourniquets were tested on the thigh for elimination of detectable distal pulse by Doppler auscultation at the popliteal artery (experiment I, n = 18 subjects). The tourniquets that were effective in >or=80% of subjects in experiment I were tested for effectiveness on the upper arm by auscultation at the radial artery (experiment II, n = 12 subjects). RESULTS: Three of the seven tourniquets were effective in all subjects in experiment I; a fourth tourniquet was effective in 88%. Three of the four successful devices were also 100% effective in experiment II; the fourth was effective in 75%. Failure of tourniquets to eliminate distal Doppler pulse signal was due to inadequate mechanical advantage for tightening, device failure (breakage), or intolerable pinching or circumferential pain prior to pulse elimination. The Combat Application Tourniquet (North American Rescue Products, Inc.), the Emergency & Military Tourniquet (Delfi Medical Innovations, Inc.), and the Special Operations Forces Tactical Tourniquet (Tactical Medical Solutions, LLC) were all found to be 100% effective in elimination of distal arterial pulse in both the arm and the leg in all subjects. CONCLUSION: Some commercially available tourniquets do not reliably occlude arterial blood flow and may not be successful in preventing extremity exsanguination in a trauma patient. Potential purchasers of such devices should bear this in mind when selecting a device for clinical use.
Comparison of battlefield-expedient topical antimicrobial agents for the prevention of burn wound sepsis in a rat model.
Topical antimicrobial therapy has the potential to limit the mortality and morbidity of contaminated battlefield injuries. Many agents available are ill-suited for use on the battlefield; however, mafenide acetate solution (MAS) has known efficacy as a burn dressing adjunct, and previous work with mafenide as a direct chemotherapeutic has shown promise. A total of 71 male Sprague-Dawley rats underwent a 20% TBSA full-thickness scald. Wounds were inoculated with a solution containing 1 x 10 colony-forming units per milliliter of Pseudomonas aeruginosa 1244 (ATCC 27317). Treatments with 10% mafenide acetate cream (MAC), 5% MAS, 5% mafenide hydrochloride solution (MHS), and 4% chlorhexidine gluconate solution (CHG) were established. Agents were applied directly to the wound daily for 10 days. Animals were monitored for 21 days and euthanized if they manifested a moribund state as a result of sepsis. Survival to study completion in the negative control group (no treatment) was 25% (3/12). Survival in the positive control group (MAC) was 100%. None of the test agent groups demonstrated significant survival over the untreated controls; MAS resulted in 5/12 (42%) survival (P = .67), CHG in 4/12 (33%) survival (P = 1.0), and MHS resulted in 2/12 (17%) survival (P = 1.0). There were no significant differences in group weights on day 1. By day 6, all test agent groups were significantly underweight compared with the MAC group. This trend resolved as underweight animals died. We did not demonstrate significant prevention of wound sepsis with these agents as we used them. These techniques should not be substituted for established burn care. Aqueous direct topical antimicrobial agents have logistical advantages over creams and dressing soaks for field use, and the search for a battlefield-expedient agent for use at or near the point of wounding should continue.