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Hemodynamic and metabolic effects of resuscitation in an uncontrolled hemorrhage model of severe rat liver injury1
THE GARY P. WRATTEN SURGICAL SYMPOSIUM Hemodynamic and Metabolic Effects of Resuscitation in an Uncontrolled Hemorrhage Model of Severe Rat Liver Injury J. B. HOLCOMB, MD, A. E. PUSATERI, PhD, T. W. BASKIN, MD, R. W. ELLISON, MD, J. M. MACAITIS, BS, W. W. BRINKLEY, DVM, AND J. L. SONDEEN, PhD Purpose: The benefits of fluid resuscitation have become controversial for noncompressible uncontrolled hemorrhage. The effect of delayed access to definitive care is an additional confounding variable. Rural and military environments often entail delayed access to surgical care, and current recommendations are for ongoing fluid resuscitation to a normal blood pressure during transport. This approach has been proposed to increase survival time, at the expense of increased blood loss. This study was designed to evaluate the hemodynamic and metabolic response to resuscitation in a rat model of severe liver injury and uncontrolled hemorrhage over 4 hours. Methods: All animals (N ⴝ 21, 275 ⴞ 15 g), underwent a reproducible excision of the median hepatic lobe. The animals received either no resuscitation (NR) or 40°C lactated Ringer’s solution at 1 ml/min, starting at 2.5 minutes after the injury (LR). The end point of resuscitation was a return to the immediate preinjury mean arterial pressure (MAP). Total blood loss, MAP, survival time, fluid volume infused, serum lactate, arterial blood gasses, intra-abdominal pressure, and hematocrit were measured preinjury and at 4 hours or death. Results: Blood loss was greater (p < 0.01) in the LR group (37.8 ⴞ 13.5 ml/kg) than in the NR group (15.9 ⴞ 5.9). Final PaO2 was lower (p < 0.01) in the LR group (55.0 ⴞ 21.5 mm Hg) than in the NR group (92.2 ⴞ 17). No differences were noted between groups in the amount of hepatic median lobe excised (60% ⴞ 7%), overall survival time (86.3 ⴞ 66.0 min), MAP nadir (35.2 ⴞ 0.7 mm Hg at 1.9 ⴞ 0.7 min postinjury), final pH (7.04 ⴞ 0.14), final base excess (ⴚ16.5 ⴞ 4.5 mmol/l), final intra-abdominal pressure (2.2 ⴞ 1.4 mm Hg), and final serum lactate (6.8 ⴞ 4.0 mmol/l).
The opinions expressed herein are the private views of the authors and are not to be construed as official or as reflecting the views of the United States Department of the Army or the United States Department of Defense.
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Published 2000 by Elsevier Science Inc.
Conclusions: In this model of uncontrolled hemorrhage from a solid organ, fluid resuscitation provided no survival or metabolic advantage, serving only to increase blood loss and decrease PaO2. Vigorous resuscitation may not provide benefit when significant injury and prolonged transport times are combined. (Curr Surg 2000;56:423– 427.)
INTRODUCTION The treatment of hemorrhagic shock with rapid infusion of crystalloid solution has been universally accepted since the 1960s and is still the current recommendation by the American College of Surgeons’ Advanced Trauma Life Support course for the initial treatment of hemorrhagic shock.1 However, a recent large urban prospective study of patients with penetrating torso injury and hypotension demonstrated improved survival by delaying resuscitation until the time of operative intervention.2 This clinical study, along with a number of animal studies, have challenged the traditional practice of early and large volume resuscitation.2–16 Unquestionably, after hemorrhage is controlled, fluid resuscitation restores tissue perfusion and decreases organ damage. However, in the face of uncontrolled hemorrhage resuscitation may increase blood pressure, dilute clotting factors, and disrupt the newly formed thrombus leading to recurrent hemorrhage. The underlying question then is not the overall value of fluid resuscitation but when it should be started, what fluid should be utilized, how much should be given, to what end point, and what subset of patients will benefit from resuscitation.2,9,17 Fluid restriction for injured soldiers until the time of operative intervention was first practiced during WWI by Cannon, who advocated gentle prolonged resuscitation with a hypertonic colloid solution.18 This concept was extensively utilized and reported by Beecher in WWII in the shock tents during the Cassino and Anzio campaigns: “When profuse internal bleeding is occuring, it is wasteful of time and of blood to attempt to get the patient’s blood pressure up to 0149-7944/99/$20.00 PII S0149-7944(99)00174-9
423
normal.” He established as an endpoint of resuscitation a systolic blood pressure of 80 to 85 mm Hg, a falling pulse rate, and a warm skin of good color, designed to prevent rebleeding from truncal penetrating wounds.19 Unfortunately, until very recently, this practice disappeared from clinical use. Many animal studies have demonstrated decreased blood loss without resuscitation, and increased blood loss with resuscitation after injury. However, it is unclear if animals that are fully and continuously resuscitated will survive longer than those not resuscitated. This method of resuscitation, not limited to a fixed volume or time, replicates the options currently available to the combat medic. Their alternatives are 2-fold: either resuscitate with continuous fluid replacement to a normal blood pressure or give no fluids. There are many animal models of uncontrolled hemorrhage evaluating the effects of different types of fluid resuscitation after injuries to major vessels or solid organs. Most utilize a fixed volume and/or time of resuscitation and demonstrate an increase in bleeding with fluid resuscitation and variable effects upon survival. The effect of continuous resuscitation on mortality is not known. Utilizing a model of severe uncontrolled hepatic hemorrhage, we evaluated the effect of continuous early resuscitation with lactated Ringer’s solution on survival and blood loss over 4 hours compared with no resuscitation. METHODS AND MATERIALS Twenty-one Sprague–Dawley rats (275 ⫾ 15 g [mean ⫾ SD]) were used in this study. Animals were housed in a climate-controlled facility with food and water available ad libitum. All animals were maintained in an Association for Assessment and Accreditation of Laboratory Animal Care International–accredited facility. The protocol was approved by the Animal Care and Use Committee of the United States Army Institute of Surgical Research, Fort Sam Houston, Texas. All animals received care in strict compliance with the Guide for the Care and Use of Laboratory Animals.20 Animals were assigned to treatments in the study according to a random numbers table. Treatment groups were designated as either no resuscitation (NR) or 40°C lactated Ringer’s solution at 1 ml/min, starting 2.5 minutes after the injury (LR). Anesthesia was induced by a combination of ketamine (70 mg/kg) and xylazine (5 mg/kg) administered intramuscularly. Carotid and jugular venous catheters were placed via cervical cutdown. The internal jugular catheter (25 gauge) was connected to a pump for resuscitation. A rectal temperature probe was placed and connected to a digital thermometer. The preinjury temperature was maintained at 38°C with a warming blanket and heat lamp. Mean arterial pressure (MAP) and systolic and diastolic pressures, as well as heart rate, were recorded at 10-second intervals throughout the study period using a continuous data collection system (Micro-Med, Louisville, Ky) connected to the arterial line. The liver injury model developed by Matsuoka et al13 was modified, yielding a simple, reproducible, nonheparinized severe liver injury model of uncontrolled hemorrhage. After adequate anesthesia was induced, a midline laparotomy was performed. Arterial blood gas, hemoglobin, and serum lactates were measured preinjury and at 4 hours or death, whichever came first. A 3Fr solid-state pressure transducer (Millar Mikro-Tip Catheter Transducer, Millar Instruments, Houston) was placed through the ab-
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dominal wall in the left lower quadrant. This transducer was utilized to record continuous changes in intra-abdominal pressure throughout the experiment. The capsule of the hepatic median lobe was scored in three spots (lateral, medial, and in the midline) 1 cm from the suprahepatic vena cava using a small plastic ruler and a hand-held cautery. The abdominal cavity was wiped dry with a 2 ⫻ 2-inch gauze sponge and the portion of the median lobe distal to the previously placed marks was sharply excised with scissors. No manipulation of the rapidly bleeding liver occurred. Removal of this portion of the median lobe resulted in an easily seen, ventrally located, crescent-shaped cut portion of the liver. The abdominal cavity was then closed immediately using staples. Resuscitation of the animals in the LR group was started 2.5 minutes after the injury. The end point of the resuscitation in the LR group was the preinjury MAP. The LR group resuscitation regimen was continued until the goal was reached and reinitiated if the MAP decreased during the 4-hour study period. The infusion was continued if the goal MAP was not obtained. After the liver injury the animals in both groups were monitored for 4 hours or until death, whichever came first. Autoresuscitation in the NR group was defined as a sustained elevation of MAP above the postinjury nadir point. Death prior to 4 hours was defined as a respiratory rate of 0 and absent carotid pulse. After 4 hours, surviving animals were euthanized intravenously with 0.2 ml of Euthasol (390 mg pentobarbital sodium/ml and 50 mg phenytoin sodium/ml). At the end of the study period, shed blood in the abdominal cavity was removed with 2 ⫻ 2-inch sponges. The total blood loss was calculated as the weight of blood-soaked sponges minus the weight of preweighed dry 2 ⫻ 2-inch sponges for each animal. The total resuscitation fluid for the LR group and time of death for both groups were recorded. The weight of the excised median lobe divided by the preinjury total body weight of the rat was utilized to measure the reproducibility of the injury. Experience during model development revealed that results of ⬍0.8% or ⬎1.2% yielded an injury that resulted in insignificant bleeding or an animal that rapidly bled to death, respectively. By calculating this ratio immediately after injury, animals falling outside the established parameters were prospectively excluded from the study. Additionally, the variability of physiologic response was standardized by prospectively excluding animals that died less than 10 minutes after injury or did not drop their MAP below 60 mm Hg in response to injury. Comparisons between treatment groups were made by t test, for continuous variables, and by Fisher’s exact test for categorical data. Data analysis was performed using the SAS statistical program (SAS Institute, Cary, NC). RESULTS The percentage of liver excised did not differ between groups and averaged 59.9% ⫾ 6.8%, when expressed as percentage of the middle lobe, and 1.0% ⫾ 0.1% of total body weight. Starting MAP (85.5 ⫾ 11.8 mm Hg), postinjury nadir MAP (36.2 ⫾ 13.3 mm Hg), and time to postinjury nadir MAP (1.8 ⫾ 1.2 minutes) were similar across treatments. Additionally, the increases in MAP in the LR and NR groups were the same (61 ⫾ 20 and 70 ⫾ 8 mm Hg), as were the times required for this increase (16 ⫾ 7 and 16 ⫾ 5 minutes, respectively; p ⬎ 0.05).
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Figure 1. Mean arterial pressure for no resuscitation (Œ) and lactated Ringer's solution (}) groups plotted in 15-minute intervals. There were no differences between groups at any time point (p ⬎ 0.05).
Blood loss was greater (p ⬍ 0.01) in the LR group, which averaged 37.8 ⫾ 13.5 ml/kg, than in the NR group, which averaged 15.9 ⫾ 5.9 ml/kg. One animal in each group survived the 4-hour study period. Overall survival time was 85.0 ⫾ 68.4 minutes, with no difference between treatment groups. When percent survival was compared at 15-minute intervals, no differences were observed between treatment groups (Fig. 1). Across groups, intra-abdominal pressure increased from 0.04 ⫾ 1.18 mm Hg before injury to 2.24 ⫾ 1.47 mm Hg at the end of the study period (p ⬍ 0.01). There were no differences in intra-abdominal pressure between groups.
There were no differences between groups for any laboratory variable at the preinjury time point. Changes in laboratory variables with time and differences among treatment groups at the final time point are shown in Table 1.
DISCUSSION The treatment of hemorrhagic shock has evolved over the last 81 years and may have come full circle. During WWI Cannon proposed limiting resuscitation until operative intervention to prevent increasing blood loss.18 The medic in WWI did not usually have access to intravenous fluid, and it was not until the casualty arrived in the shock tents that a limited slow resuscitation over 24 to 48 hours utilizing a hypertonic colloid solution was administered.18 During WWII, Beecher reported 2853 patients with penetrating truncal wounds and noted that the injured soldier would rebleed if resuscitated to a systolic pressure above 80 mm Hg.19 During the Vietnam conflict rapid and large volume crystalloid resuscitation was the norm, based largely on controlled hemorrhage studies of resuscitation. Recently, a prospective clinical trial of hypotensive patients with penetrating truncal wounds demonstrated improved survival
Table 1
pH PaCO2 (mm Hg) PaO2 (mm Hg) HCO3 (mmol/l) BE (mmol/l) IAP (mm Hg) Lactate (mmol/l) HCT (ml/dl) Hgb (g/dl)
NR Preinjury
End
LR Preinjury
End
7.35 ⫾ 0.03 47 ⫾ 4 67 ⫾ 10 25 ⫾ 2 ⫺0.6 ⫾ 2.0 0.1 ⫾ 0.2 1⫾1 38 ⫾ 4 14 ⫾ 1
7,13 ⫾ 0.13* 44 ⫾ 20 92 ⫾ 17† 13 ⫾ 2* ⫺15 ⫾ 2* 2.3 ⫾ 1.5* 7⫾4 33 ⫾ 5† 12 ⫾ 3†
7.33 ⫾ 0.04 49 ⫾ 6 69 ⫾ 11 26 ⫾ 4 0.5 ⫾ 4 0.0 ⫾ 0.2 1⫾1 37 ⫾ 5 14 ⫾ 1
6.94 ⫾ 0.15* 55 ⫾ 18 55 ⫾ 21† 12 ⫾ 4* ⫺18 ⫾ 7* 2.2 ⫾ 1.5* 5 ⫾ 4* 17 ⫾ 10*† 4 ⫾ 2*†
BE ⫽ base excess; HCT ⫽ hematocrit; Hgb ⫽ hemoglobin; IAP ⫽ intra-abdominal pressure. *Differences within groups, preinjury vs final (p ⬍ 0.05). †Differences between groups, at corresponding time points (p ⬍ 0.05). CURRENT SURGERY
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and decreased complications without resuscitation until the time of operative intervention.2 This study was conducted in a large urban environment with a mature emergency medical services system. It must be noted that clinical studies in an urban environment with rapid transport times to definitive care may not directly compare with those involving often delayed transport of military and rural patients. Thus, resuscitative strategy for the hypotensive patient seems to be moving back to the practices of the experienced combat surgeons of WWI and WW II.
Not unexpectedly, blood loss was increased in the LR group, as compared with the NR group (p ⬍ 0.05). The combination of rapid early resuscitation prevented clot maturation and resulted in rebleeding and continued blood loss. We believe that starting the resuscitation early prevented the natural hemostatic mechanism from functioning optimally, thereby increasing the total blood loss. The laboratory changes associated with increased blood loss followed, with hemoglobin and hematocrit decreased in the LR group, as compared with the NR group (p ⬍ 0.05).
In a military environment combat medics have multiple confounding variables to consider when formulating a treatment plan. These include the tactical scenario and mission, available medical supplies and personnel, casualty load, triage, and evacuation plan.21 Additionally, no method exists to prevent the ongoing truncal hemorrhage that accounts for 90% of the hemorrhagic deaths on the battlefield.22 Currently the medic’s resuscitative treatment options are limited to continuous isotonic fluid resuscitation to a “normal” blood pressure or no resuscitation. These options have not been evaluated in an animal study of uncontrolled hemorrhage without the limits of a fixed volume or time of resuscitation. Many animal studies of uncontrolled hemorrhage have shown that vigorous resuscitation increases blood loss and may increase mortality. Likewise, there are other animal studies that demonstrate decreased survival with no resuscitation. The difficulty in directly comparing results from these animal studies are that they utilized a variety of animal models and injuries and a wide range of resuscitation times, fluids, volumes, and end points.
The LR group was significantly more hypoxic than the NR group, which may be explained by a shifting of the oxyhemoglobin dissociation curve and decreased affinity for O2 in the NR group and the fluid volume infused in an attempt to maintain pressure in the LR group. Additionally, the intraabdominal pressure did not differ between groups (p ⬎ 0.05). This equal increase in intra-abdominal pressure is difficult to explain, as the resuscitated group received a mean of 195 ⫾ 90 ml/kg of fluid and thus would have been expected to demonstrate a larger increase than the NR group.
The model utilized in this study is a modification of one developed by Matsuoka et al.13 It is simplified by directly measuring and excising only a measured portion of the median lobe, with the percentage of excised liver correlated to the individual body weight of each animal as an anatomic control for variability. Additionally, the variability of physiologic response was standardized by prospectively excluding animals that died less than 10 minutes after injury or did not drop their MAP below 60 mm Hg in response to injury. The severity of injury was documented by a mean MAP nadir of 35.2 ⫾ 0.7 mm Hg at 1.9 ⫾ 0.7 minutes postinjury, pH of 7.04 ⫾ 0.14, base excess of 16.5 ⫾ 4.5 mmol/l in both groups, and serum lactate of 6.8 ⫾ 4.0 mmol/l. These results are different from the preinjury values (p ⬍ 0.05). We feel that the simplicity and reproducibility of this hepatic injury model combined with the metabolic results and 50% survival at 30 minutes will make this model useful for future hemorrhage control and resuscitation studies. In our study resuscitation was started 2.5 minutes after the injury. This time delay allowed the blood pressure to reach a nadir and, although allowing initial clotting to occur, was of short enough duration to allow for rebleeding to occur. Previous rat studies in an aortotomy model have demonstrated that initiation of resuscitation 10 minutes after injury will not allow for rebleeding to occur.11 When one is evaluating a resuscitation regimen (fluid, rate, or end point) in uncontrolled hemorrhage models the study design must allow for rebleeding. Variation in this time factor among models may account for some of the conflicting hemorrhage and survival results in the many animal studies addressing this question. The rat clotting system is relatively more active than that in some other experimental animals, and this may account for the requirement to initiate resuscitation sooner than 10 minutes after injury.
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Five animals in the NR group did not autoresuscitate, whereas only 1 animal in the LR group did not demonstrate an elevation in MAP in response to resuscitation. The maximum MAP reached in the LR group was 61 ⫾ 20 mm Hg, whereas in the NR group it was 70 ⫾ 8 mm Hg (p ⬎ 0.05). Additionally, the time required to reach this level was the same for both groups, 16 ⫾ 6 minutes. This result is somewhat suprising, as it was assumed that the MAP would be lower in the animals without ongoing resuscitation. The MAP response of the NR animals deserves further study to determine long-term survival of this subset of animals. This investigation may direct optimal resuscitation strategies in defined subgroups of hemorrhaging animals. In conclusion, in this liver injury model of uncontrolled hemorrhage, early, large-volume crystalloid resuscitation did not increase survival over a 4-hour study period, as compared with no resuscitation. The only effects were to double blood loss and decrease PaO2 at death. The optimal timing, amount, rate, and duration of resuscitation remain to be identified. This information will be of critical importance to the military or civilian medic caring for an injured patient while far removed from definitive care. J. B. HOLCOMB, MD* A. E. PUSATERI, PhD* T. W. BASKIN, MD† R. W. ELLISON, MD† J. M. MACAITIS, BS* W. W. BRINKLEY, DVM* J. L. SONDEEN, PhD* *United States Army Institute of Surgical Research Fort Sam Houston, Texas †Brooke Army Medical Center Fort Sam Houston, Texas REFERENCES 1. American College of Surgeons Committee on Trauma. Advanced Trauma Life Support course instructor manual. Chicago: American College of Surgeons, 1997. 2. Bickell W, Wall M, Pepe P, et al. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. N Engl J Med 1994;331:1105–1109. 3. Bickell WH, Bruttig SP, Millnamow GA, O’Benar J, Wade CE. The
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5. 6. 7. 8. 9. 10. 11.
detrimental effects of intravenous crystalloid after aortatomy in swine. Surgery 1991;110:529 –536. Bickell WH, Bruttig SP, Millnamow GA, O’Benar J, Wade CE. Use of hypertonic saline/dextran versus lactated Ringer’s solution as a resuscitation fluid after uncontrolled aortic hemorrhage in anesthetized swine. Ann Emerg Med 1992;21:1077–1085. Bruttig SP, O’Benar JD, Bickell WH, Wade CE. Effects of immediate versus delayed fluid resuscitation on hemorrhage volume and mortality in anesthetized pigs (abstract). Circ Shock 1990;31:70 –71. Elgjo GI, Knardahl S. Low-dose hypertonic saline (NaCl 8.0%) treatment of uncontrolled abdominal hemorrhage: effects on arterial versus venous injury. Shock 1996;5:52–58. Gross D, Landau EH, Klin B, Krausz MM. Quantitative measurement of bleeding following hypertonic saline therapy in uncontrolled hemorrhagic shock. J Trauma 1989;29:79 – 83. Gross D, Landau EH, Klin B, Krausz MM. Treatment of uncontrolled hemorrhagic shock with hypertonic saline solution. Surg Gynecol Obstet 1990;170:106 –112. Kowalenko T, Stern S, Dronen S, Wang X. Improved outcome with hypotensive resuscitation of uncontrolled hemorrhagic shock in a swine model. J Trauma 1992;33:349 –362. Krausz MM, Landau EH, Klin B, Gross D. Hypertonic saline treatment of uncontrolled hemorrhagic shock at different periods from bleeding. Arch Surg 1992;127:93–96. Leppaniemi A, Soltero R, Burris D, et al. Fluid resuscitation in a model of uncontrolled hemorrhage: too much too early, or too little too late? J Surg Res 1996;63:413– 418.
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12. Marshall HP Jr, Capone A, Courcoulas AP, et al. Effects of hemodilution on long-term survival in an uncontrolled hemorrhagic shock model in rats. J Trauma 1997;43:673– 679. 13. Matsuoka T, Hildreth J, Wisner DH. Liver injury as a model of uncontrolled hemorrhagic shock: resuscitation with different hypertonic regimens. J Trauma 1995;39:674 – 680. 14. Milles G, Koucky CJ, Zacheis HG. Experimental uncontrolled arterial hemorrhage. Surgery 1966;60:434 – 442. 15. Shaftan GW, Chiu CJ, Dennis C, Harris B. Fundamentals of physiologic control of arterial hemorrhage. Surgery 1965;58:851– 856. 16. Sindlinger JF, Soucy DM, Greene SP, et al. The effects of isotonic saline volume resuscitation in uncontrolled hemorrhage. Surg Gynecol Obstet 1993;177:545–550. 17. Elliott DC. An evaluation of the end points of resuscitation. J Am Coll Surg 1998;187:536 –547. 18. Cannon W, Fraser J, Cowell E. The preventive treatment of wound shock. JAMA 1918;70:618 – 621. 19. Beecher H. Preparation of battle casualties for surgery. Ann Surg 1945;121:769 –792. 20. Institute of Laboratory Animal Resources, National Research Council. Guide for the care and use of laboratory animals. Washington, DC: National Academy Press, 1996. 21. Butler FK Jr, Hagmann J, Butler EG. Tactical combat casualty care in special operations. Mil Med 1996;161:3–16. 22. Bellamy RF. The causes of death in conventional land warfare: implications for combat casualty care research. Mil Med 1984;149: 55– 62.
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The opinions expressed herein are the private views of the authors and are not to be construed as official or as reflecting the views of the United States Department of the Army or the United States Department of Defense.
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Published 2000 by Elsevier Science Inc.
Conclusions: In this model of uncontrolled hemorrhage from a solid organ, fluid resuscitation provided no survival or metabolic advantage, serving only to increase blood loss and decrease PaO2. Vigorous resuscitation may not provide benefit when significant injury and prolonged transport times are combined. (Curr Surg 2000;56:423– 427.)
INTRODUCTION The treatment of hemorrhagic shock with rapid infusion of crystalloid solution has been universally accepted since the 1960s and is still the current recommendation by the American College of Surgeons’ Advanced Trauma Life Support course for the initial treatment of hemorrhagic shock.1 However, a recent large urban prospective study of patients with penetrating torso injury and hypotension demonstrated improved survival by delaying resuscitation until the time of operative intervention.2 This clinical study, along with a number of animal studies, have challenged the traditional practice of early and large volume resuscitation.2–16 Unquestionably, after hemorrhage is controlled, fluid resuscitation restores tissue perfusion and decreases organ damage. However, in the face of uncontrolled hemorrhage resuscitation may increase blood pressure, dilute clotting factors, and disrupt the newly formed thrombus leading to recurrent hemorrhage. The underlying question then is not the overall value of fluid resuscitation but when it should be started, what fluid should be utilized, how much should be given, to what end point, and what subset of patients will benefit from resuscitation.2,9,17 Fluid restriction for injured soldiers until the time of operative intervention was first practiced during WWI by Cannon, who advocated gentle prolonged resuscitation with a hypertonic colloid solution.18 This concept was extensively utilized and reported by Beecher in WWII in the shock tents during the Cassino and Anzio campaigns: “When profuse internal bleeding is occuring, it is wasteful of time and of blood to attempt to get the patient’s blood pressure up to 0149-7944/99/$20.00 PII S0149-7944(99)00174-9
423
normal.” He established as an endpoint of resuscitation a systolic blood pressure of 80 to 85 mm Hg, a falling pulse rate, and a warm skin of good color, designed to prevent rebleeding from truncal penetrating wounds.19 Unfortunately, until very recently, this practice disappeared from clinical use. Many animal studies have demonstrated decreased blood loss without resuscitation, and increased blood loss with resuscitation after injury. However, it is unclear if animals that are fully and continuously resuscitated will survive longer than those not resuscitated. This method of resuscitation, not limited to a fixed volume or time, replicates the options currently available to the combat medic. Their alternatives are 2-fold: either resuscitate with continuous fluid replacement to a normal blood pressure or give no fluids. There are many animal models of uncontrolled hemorrhage evaluating the effects of different types of fluid resuscitation after injuries to major vessels or solid organs. Most utilize a fixed volume and/or time of resuscitation and demonstrate an increase in bleeding with fluid resuscitation and variable effects upon survival. The effect of continuous resuscitation on mortality is not known. Utilizing a model of severe uncontrolled hepatic hemorrhage, we evaluated the effect of continuous early resuscitation with lactated Ringer’s solution on survival and blood loss over 4 hours compared with no resuscitation. METHODS AND MATERIALS Twenty-one Sprague–Dawley rats (275 ⫾ 15 g [mean ⫾ SD]) were used in this study. Animals were housed in a climate-controlled facility with food and water available ad libitum. All animals were maintained in an Association for Assessment and Accreditation of Laboratory Animal Care International–accredited facility. The protocol was approved by the Animal Care and Use Committee of the United States Army Institute of Surgical Research, Fort Sam Houston, Texas. All animals received care in strict compliance with the Guide for the Care and Use of Laboratory Animals.20 Animals were assigned to treatments in the study according to a random numbers table. Treatment groups were designated as either no resuscitation (NR) or 40°C lactated Ringer’s solution at 1 ml/min, starting 2.5 minutes after the injury (LR). Anesthesia was induced by a combination of ketamine (70 mg/kg) and xylazine (5 mg/kg) administered intramuscularly. Carotid and jugular venous catheters were placed via cervical cutdown. The internal jugular catheter (25 gauge) was connected to a pump for resuscitation. A rectal temperature probe was placed and connected to a digital thermometer. The preinjury temperature was maintained at 38°C with a warming blanket and heat lamp. Mean arterial pressure (MAP) and systolic and diastolic pressures, as well as heart rate, were recorded at 10-second intervals throughout the study period using a continuous data collection system (Micro-Med, Louisville, Ky) connected to the arterial line. The liver injury model developed by Matsuoka et al13 was modified, yielding a simple, reproducible, nonheparinized severe liver injury model of uncontrolled hemorrhage. After adequate anesthesia was induced, a midline laparotomy was performed. Arterial blood gas, hemoglobin, and serum lactates were measured preinjury and at 4 hours or death, whichever came first. A 3Fr solid-state pressure transducer (Millar Mikro-Tip Catheter Transducer, Millar Instruments, Houston) was placed through the ab-
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dominal wall in the left lower quadrant. This transducer was utilized to record continuous changes in intra-abdominal pressure throughout the experiment. The capsule of the hepatic median lobe was scored in three spots (lateral, medial, and in the midline) 1 cm from the suprahepatic vena cava using a small plastic ruler and a hand-held cautery. The abdominal cavity was wiped dry with a 2 ⫻ 2-inch gauze sponge and the portion of the median lobe distal to the previously placed marks was sharply excised with scissors. No manipulation of the rapidly bleeding liver occurred. Removal of this portion of the median lobe resulted in an easily seen, ventrally located, crescent-shaped cut portion of the liver. The abdominal cavity was then closed immediately using staples. Resuscitation of the animals in the LR group was started 2.5 minutes after the injury. The end point of the resuscitation in the LR group was the preinjury MAP. The LR group resuscitation regimen was continued until the goal was reached and reinitiated if the MAP decreased during the 4-hour study period. The infusion was continued if the goal MAP was not obtained. After the liver injury the animals in both groups were monitored for 4 hours or until death, whichever came first. Autoresuscitation in the NR group was defined as a sustained elevation of MAP above the postinjury nadir point. Death prior to 4 hours was defined as a respiratory rate of 0 and absent carotid pulse. After 4 hours, surviving animals were euthanized intravenously with 0.2 ml of Euthasol (390 mg pentobarbital sodium/ml and 50 mg phenytoin sodium/ml). At the end of the study period, shed blood in the abdominal cavity was removed with 2 ⫻ 2-inch sponges. The total blood loss was calculated as the weight of blood-soaked sponges minus the weight of preweighed dry 2 ⫻ 2-inch sponges for each animal. The total resuscitation fluid for the LR group and time of death for both groups were recorded. The weight of the excised median lobe divided by the preinjury total body weight of the rat was utilized to measure the reproducibility of the injury. Experience during model development revealed that results of ⬍0.8% or ⬎1.2% yielded an injury that resulted in insignificant bleeding or an animal that rapidly bled to death, respectively. By calculating this ratio immediately after injury, animals falling outside the established parameters were prospectively excluded from the study. Additionally, the variability of physiologic response was standardized by prospectively excluding animals that died less than 10 minutes after injury or did not drop their MAP below 60 mm Hg in response to injury. Comparisons between treatment groups were made by t test, for continuous variables, and by Fisher’s exact test for categorical data. Data analysis was performed using the SAS statistical program (SAS Institute, Cary, NC). RESULTS The percentage of liver excised did not differ between groups and averaged 59.9% ⫾ 6.8%, when expressed as percentage of the middle lobe, and 1.0% ⫾ 0.1% of total body weight. Starting MAP (85.5 ⫾ 11.8 mm Hg), postinjury nadir MAP (36.2 ⫾ 13.3 mm Hg), and time to postinjury nadir MAP (1.8 ⫾ 1.2 minutes) were similar across treatments. Additionally, the increases in MAP in the LR and NR groups were the same (61 ⫾ 20 and 70 ⫾ 8 mm Hg), as were the times required for this increase (16 ⫾ 7 and 16 ⫾ 5 minutes, respectively; p ⬎ 0.05).
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Figure 1. Mean arterial pressure for no resuscitation (Œ) and lactated Ringer's solution (}) groups plotted in 15-minute intervals. There were no differences between groups at any time point (p ⬎ 0.05).
Blood loss was greater (p ⬍ 0.01) in the LR group, which averaged 37.8 ⫾ 13.5 ml/kg, than in the NR group, which averaged 15.9 ⫾ 5.9 ml/kg. One animal in each group survived the 4-hour study period. Overall survival time was 85.0 ⫾ 68.4 minutes, with no difference between treatment groups. When percent survival was compared at 15-minute intervals, no differences were observed between treatment groups (Fig. 1). Across groups, intra-abdominal pressure increased from 0.04 ⫾ 1.18 mm Hg before injury to 2.24 ⫾ 1.47 mm Hg at the end of the study period (p ⬍ 0.01). There were no differences in intra-abdominal pressure between groups.
There were no differences between groups for any laboratory variable at the preinjury time point. Changes in laboratory variables with time and differences among treatment groups at the final time point are shown in Table 1.
DISCUSSION The treatment of hemorrhagic shock has evolved over the last 81 years and may have come full circle. During WWI Cannon proposed limiting resuscitation until operative intervention to prevent increasing blood loss.18 The medic in WWI did not usually have access to intravenous fluid, and it was not until the casualty arrived in the shock tents that a limited slow resuscitation over 24 to 48 hours utilizing a hypertonic colloid solution was administered.18 During WWII, Beecher reported 2853 patients with penetrating truncal wounds and noted that the injured soldier would rebleed if resuscitated to a systolic pressure above 80 mm Hg.19 During the Vietnam conflict rapid and large volume crystalloid resuscitation was the norm, based largely on controlled hemorrhage studies of resuscitation. Recently, a prospective clinical trial of hypotensive patients with penetrating truncal wounds demonstrated improved survival
Table 1
pH PaCO2 (mm Hg) PaO2 (mm Hg) HCO3 (mmol/l) BE (mmol/l) IAP (mm Hg) Lactate (mmol/l) HCT (ml/dl) Hgb (g/dl)
NR Preinjury
End
LR Preinjury
End
7.35 ⫾ 0.03 47 ⫾ 4 67 ⫾ 10 25 ⫾ 2 ⫺0.6 ⫾ 2.0 0.1 ⫾ 0.2 1⫾1 38 ⫾ 4 14 ⫾ 1
7,13 ⫾ 0.13* 44 ⫾ 20 92 ⫾ 17† 13 ⫾ 2* ⫺15 ⫾ 2* 2.3 ⫾ 1.5* 7⫾4 33 ⫾ 5† 12 ⫾ 3†
7.33 ⫾ 0.04 49 ⫾ 6 69 ⫾ 11 26 ⫾ 4 0.5 ⫾ 4 0.0 ⫾ 0.2 1⫾1 37 ⫾ 5 14 ⫾ 1
6.94 ⫾ 0.15* 55 ⫾ 18 55 ⫾ 21† 12 ⫾ 4* ⫺18 ⫾ 7* 2.2 ⫾ 1.5* 5 ⫾ 4* 17 ⫾ 10*† 4 ⫾ 2*†
BE ⫽ base excess; HCT ⫽ hematocrit; Hgb ⫽ hemoglobin; IAP ⫽ intra-abdominal pressure. *Differences within groups, preinjury vs final (p ⬍ 0.05). †Differences between groups, at corresponding time points (p ⬍ 0.05). CURRENT SURGERY
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and decreased complications without resuscitation until the time of operative intervention.2 This study was conducted in a large urban environment with a mature emergency medical services system. It must be noted that clinical studies in an urban environment with rapid transport times to definitive care may not directly compare with those involving often delayed transport of military and rural patients. Thus, resuscitative strategy for the hypotensive patient seems to be moving back to the practices of the experienced combat surgeons of WWI and WW II.
Not unexpectedly, blood loss was increased in the LR group, as compared with the NR group (p ⬍ 0.05). The combination of rapid early resuscitation prevented clot maturation and resulted in rebleeding and continued blood loss. We believe that starting the resuscitation early prevented the natural hemostatic mechanism from functioning optimally, thereby increasing the total blood loss. The laboratory changes associated with increased blood loss followed, with hemoglobin and hematocrit decreased in the LR group, as compared with the NR group (p ⬍ 0.05).
In a military environment combat medics have multiple confounding variables to consider when formulating a treatment plan. These include the tactical scenario and mission, available medical supplies and personnel, casualty load, triage, and evacuation plan.21 Additionally, no method exists to prevent the ongoing truncal hemorrhage that accounts for 90% of the hemorrhagic deaths on the battlefield.22 Currently the medic’s resuscitative treatment options are limited to continuous isotonic fluid resuscitation to a “normal” blood pressure or no resuscitation. These options have not been evaluated in an animal study of uncontrolled hemorrhage without the limits of a fixed volume or time of resuscitation. Many animal studies of uncontrolled hemorrhage have shown that vigorous resuscitation increases blood loss and may increase mortality. Likewise, there are other animal studies that demonstrate decreased survival with no resuscitation. The difficulty in directly comparing results from these animal studies are that they utilized a variety of animal models and injuries and a wide range of resuscitation times, fluids, volumes, and end points.
The LR group was significantly more hypoxic than the NR group, which may be explained by a shifting of the oxyhemoglobin dissociation curve and decreased affinity for O2 in the NR group and the fluid volume infused in an attempt to maintain pressure in the LR group. Additionally, the intraabdominal pressure did not differ between groups (p ⬎ 0.05). This equal increase in intra-abdominal pressure is difficult to explain, as the resuscitated group received a mean of 195 ⫾ 90 ml/kg of fluid and thus would have been expected to demonstrate a larger increase than the NR group.
The model utilized in this study is a modification of one developed by Matsuoka et al.13 It is simplified by directly measuring and excising only a measured portion of the median lobe, with the percentage of excised liver correlated to the individual body weight of each animal as an anatomic control for variability. Additionally, the variability of physiologic response was standardized by prospectively excluding animals that died less than 10 minutes after injury or did not drop their MAP below 60 mm Hg in response to injury. The severity of injury was documented by a mean MAP nadir of 35.2 ⫾ 0.7 mm Hg at 1.9 ⫾ 0.7 minutes postinjury, pH of 7.04 ⫾ 0.14, base excess of 16.5 ⫾ 4.5 mmol/l in both groups, and serum lactate of 6.8 ⫾ 4.0 mmol/l. These results are different from the preinjury values (p ⬍ 0.05). We feel that the simplicity and reproducibility of this hepatic injury model combined with the metabolic results and 50% survival at 30 minutes will make this model useful for future hemorrhage control and resuscitation studies. In our study resuscitation was started 2.5 minutes after the injury. This time delay allowed the blood pressure to reach a nadir and, although allowing initial clotting to occur, was of short enough duration to allow for rebleeding to occur. Previous rat studies in an aortotomy model have demonstrated that initiation of resuscitation 10 minutes after injury will not allow for rebleeding to occur.11 When one is evaluating a resuscitation regimen (fluid, rate, or end point) in uncontrolled hemorrhage models the study design must allow for rebleeding. Variation in this time factor among models may account for some of the conflicting hemorrhage and survival results in the many animal studies addressing this question. The rat clotting system is relatively more active than that in some other experimental animals, and this may account for the requirement to initiate resuscitation sooner than 10 minutes after injury.
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Five animals in the NR group did not autoresuscitate, whereas only 1 animal in the LR group did not demonstrate an elevation in MAP in response to resuscitation. The maximum MAP reached in the LR group was 61 ⫾ 20 mm Hg, whereas in the NR group it was 70 ⫾ 8 mm Hg (p ⬎ 0.05). Additionally, the time required to reach this level was the same for both groups, 16 ⫾ 6 minutes. This result is somewhat suprising, as it was assumed that the MAP would be lower in the animals without ongoing resuscitation. The MAP response of the NR animals deserves further study to determine long-term survival of this subset of animals. This investigation may direct optimal resuscitation strategies in defined subgroups of hemorrhaging animals. In conclusion, in this liver injury model of uncontrolled hemorrhage, early, large-volume crystalloid resuscitation did not increase survival over a 4-hour study period, as compared with no resuscitation. The only effects were to double blood loss and decrease PaO2 at death. The optimal timing, amount, rate, and duration of resuscitation remain to be identified. This information will be of critical importance to the military or civilian medic caring for an injured patient while far removed from definitive care. J. B. HOLCOMB, MD* A. E. PUSATERI, PhD* T. W. BASKIN, MD† R. W. ELLISON, MD† J. M. MACAITIS, BS* W. W. BRINKLEY, DVM* J. L. SONDEEN, PhD* *United States Army Institute of Surgical Research Fort Sam Houston, Texas †Brooke Army Medical Center Fort Sam Houston, Texas REFERENCES 1. American College of Surgeons Committee on Trauma. Advanced Trauma Life Support course instructor manual. Chicago: American College of Surgeons, 1997. 2. Bickell W, Wall M, Pepe P, et al. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. N Engl J Med 1994;331:1105–1109. 3. Bickell WH, Bruttig SP, Millnamow GA, O’Benar J, Wade CE. The
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detrimental effects of intravenous crystalloid after aortatomy in swine. Surgery 1991;110:529 –536. Bickell WH, Bruttig SP, Millnamow GA, O’Benar J, Wade CE. Use of hypertonic saline/dextran versus lactated Ringer’s solution as a resuscitation fluid after uncontrolled aortic hemorrhage in anesthetized swine. Ann Emerg Med 1992;21:1077–1085. Bruttig SP, O’Benar JD, Bickell WH, Wade CE. Effects of immediate versus delayed fluid resuscitation on hemorrhage volume and mortality in anesthetized pigs (abstract). Circ Shock 1990;31:70 –71. Elgjo GI, Knardahl S. Low-dose hypertonic saline (NaCl 8.0%) treatment of uncontrolled abdominal hemorrhage: effects on arterial versus venous injury. Shock 1996;5:52–58. Gross D, Landau EH, Klin B, Krausz MM. Quantitative measurement of bleeding following hypertonic saline therapy in uncontrolled hemorrhagic shock. J Trauma 1989;29:79 – 83. Gross D, Landau EH, Klin B, Krausz MM. Treatment of uncontrolled hemorrhagic shock with hypertonic saline solution. Surg Gynecol Obstet 1990;170:106 –112. Kowalenko T, Stern S, Dronen S, Wang X. Improved outcome with hypotensive resuscitation of uncontrolled hemorrhagic shock in a swine model. J Trauma 1992;33:349 –362. Krausz MM, Landau EH, Klin B, Gross D. Hypertonic saline treatment of uncontrolled hemorrhagic shock at different periods from bleeding. Arch Surg 1992;127:93–96. Leppaniemi A, Soltero R, Burris D, et al. Fluid resuscitation in a model of uncontrolled hemorrhage: too much too early, or too little too late? J Surg Res 1996;63:413– 418.
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12. Marshall HP Jr, Capone A, Courcoulas AP, et al. Effects of hemodilution on long-term survival in an uncontrolled hemorrhagic shock model in rats. J Trauma 1997;43:673– 679. 13. Matsuoka T, Hildreth J, Wisner DH. Liver injury as a model of uncontrolled hemorrhagic shock: resuscitation with different hypertonic regimens. J Trauma 1995;39:674 – 680. 14. Milles G, Koucky CJ, Zacheis HG. Experimental uncontrolled arterial hemorrhage. Surgery 1966;60:434 – 442. 15. Shaftan GW, Chiu CJ, Dennis C, Harris B. Fundamentals of physiologic control of arterial hemorrhage. Surgery 1965;58:851– 856. 16. Sindlinger JF, Soucy DM, Greene SP, et al. The effects of isotonic saline volume resuscitation in uncontrolled hemorrhage. Surg Gynecol Obstet 1993;177:545–550. 17. Elliott DC. An evaluation of the end points of resuscitation. J Am Coll Surg 1998;187:536 –547. 18. Cannon W, Fraser J, Cowell E. The preventive treatment of wound shock. JAMA 1918;70:618 – 621. 19. Beecher H. Preparation of battle casualties for surgery. Ann Surg 1945;121:769 –792. 20. Institute of Laboratory Animal Resources, National Research Council. Guide for the care and use of laboratory animals. Washington, DC: National Academy Press, 1996. 21. Butler FK Jr, Hagmann J, Butler EG. Tactical combat casualty care in special operations. Mil Med 1996;161:3–16. 22. Bellamy RF. The causes of death in conventional land warfare: implications for combat casualty care research. Mil Med 1984;149: 55– 62.
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