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Biomedical subjects

C R Baxter

Publications and source records attributed to C R Baxter.

At least 19 recordsLinked to original sources

Prophylactic hemodialysis in the treatment of acute renal failure. Annals of Internal Medicine, 53:992-1016, 1960.

Prophylactic hemodialysis has been employed in the treatment of 15 patients with acute renal failure due to acute tubular necrosis (12), bilateral renal cortical necrosis (two), and poststreptococcal glomerulonephritis (one). Dialyses, usually lasting six hours each, were begun before clinical evidence of uremia developed in each patient and/or before the nonprotein nitrogen reached 200 mg.%, and were repeated daily or often enough to maintain the nonprotein nitrogen below 150 mg.%. The hypothesis underlying this technic postulates (1) that wasting, sepsis and impaired wound healing in these patients may reflect tissue injury by the same dialyzable toxic agents which produce the uremic symptoms that are readily reversible by dialysis, and (2) that repeated dialyses should therefore prevent both clinical uremia and the later, often lethal sequelae. The results contrast dramatically with our own past experience in treating patients with acute renal failure with a carefully executed medical regimen together with hemodialysis on conventional indications. Except in one instance of crush injury with progressive intracerebral damage, and one brief occasion in another individual, these patients experienced a stable, convalescent clinical course, remained free of uremic symptoms or chemical imbalances, ate at least three meals daily which were unrestricted in amount and composition, and were ambulatory between dialyses unless confined to bed by associated disease. Wounds healed well. Infection either did not occur, or subsided after appropriate therapy. Fluid restriction was liberalized by means of ultrafiltration with dialysis. Regional heparinization of only the extracorporeal circuit eliminated actual or impending bleeding as a contraindication to dialysis. Chronic vessel cannulation made the frequent dialyses possible, but may have provided the route for repeated, transient bacterial contamination of the blood stream in the first hour of many dialyses. Marked anemia, despite reticulocytosis, moderate to mild weight loss and some mental deficit persisted in spite of the general clinical improvement and well-being. Three patients with tubular necrosis died after seven, 11 and 26 days of oliguria; both patients with bilateral renal cortical necrosis also succumbed, on the seventy-third and ninety-second days of renal failure, and after 29 and 40 dialyses, respectively. At autopsy, evidence of sepsis was conspicuously absent. The remaining 10 patients survived. Thus some, but not all, clinical manifestations of acute renal failure appear to be favorably influenced by prophylactic dialysis treatment. Our initial experience in this group of 15 patients does not of course prove that freedom from complications and a significantly better outlook for survival can be assured to patients with acute renal failure by these methods. However, it seems to offer a reasonable hope of this possibility which we cannot attach to management by medical measures alone, or by dialysis on conventional indications. If this hope is realized in greatly extended, subsequent series, then it seems inevitable that some form of prophylactic dialysis, or some equally effective alternative, should be adopted in treating the majority of patients with acute renal failure.

Acute Kidney Injury↗

Skin burn injury and oxidative stress in liver and lung tissues of rabbit models.

The effects of burn injury (30% of total body surface area) on the levels of oxidized and reduced glutathione, malondialdehyde, and on the activities of certain glutathione-dependent enzymes, have been determined in tissues of rabbit models. Thus, the malondialdehyde, glutathione (GSH), glutathione disulfide (GSSG) concentrations and the specific activities of glutathione peroxidase, glutathione S-transferase, and glutathione reductase were measured in liver and lung of 24-h burn rabbit models and compared to the corresponding values in 24-h sham burn (medicated, anesthetic/analgesic) rabbit models. It was found that the concentrations of malondialdehyde in liver and lung of burn models were increased by 17% and 29% respectively. Glutathione concentrations were decreased by 29% in liver and 13% in lung, and glutathione disulfide concentrations were increased by 35% in liver and 33% in lung, in burn versus sham burn models. It was also found that the specific activities of glutathione peroxidase decreased significantly, resultant to burn injury, by an average of 35% and 27% in liver and lung, respectively. Burn injury also decreased glutathione S-transferase specific activities by 14% in liver and 23% in lung tissues. In contrast, glutathione reductase specific activity was increased in liver tissues (22%), but was decreased (19%), as with the other enzymes studied, in lung tissues of burn models. Control model studies (no medication, no sham burn) show that these effects of burn injury are additional to effects elicited by medication associated with sham burn models. The data of this study are indicative of a major oxidative stress in liver and lung tissues due to burn injury at a remote site.

Animals↗

Immunologic reactions in chronic wounds.

Although, healing is initiated by local inflammation, excessive or prolonged inflammation may delay healing and increase scar potential. Inflammatory cascades in the wound's microenvironment are triggered by complement degradation products; polymorphonuclear leukocyte products; oxygen free radicals; enzymes, particularly proteinases; and microbial products. Infection, ischemia, necrotic or severely damaged tissue, or foreign matter propel and prolong inflammation and challenge host defenses, leaving the patient susceptible to further microbial invasion. Occlusion dressings can minimize necrotic tissue by preventing desiccation, aiding debridement, and providing a barrier against exogenous pathogenic organisms, thus limiting the resulting inflammatory cascade.

Chronic Disease↗

Guidelines for preventing "dilution false negatives" in in vitro laboratory testing of the donor population.

In this article we develop a calculation or formula for use in determining the potential dilution effect of fluids administered during patient treatment on serologic testing parameters. The formula uses basic principles of (a) fluid distribution over time from administration; (b) ratios of plasma and extravascular fluid volumes to body weight; and (c) common practices of fluid resuscitation. A dilution threshold of 50% was set using data from enzyme-linked immunosorbent assay human immunodeficiency virus antibody determinations performed on in vitro diluted seropositive serum samples. These data respond to issues raised by guidelines from the Centers for Disease Control and the U.S. Food and Drug Administration to achieve recipient safety without unnecessarily restricting the potential donor pool.

Blood Transfusion↗

Dipeptidyl peptidase IV and aminopeptidase in burn wound exudates: implications for wound healing.

Two catalytically active proteases, dipeptidyl peptidase IV (DP IV) and aminopeptidase (AP), not previously reported as present in burn wound exudates, have been identified by substrate specificity and susceptibility to known enzyme inhibitors. The ratio of the two enzymes in exudates is significantly different from the ratio in plasma collected from the same patient during the same time interval, suggesting that measurement of exudate components may be more significant than plasma activities in evaluating local conditions in the wound. A number of biologically significant substances are DP IV substrates, and the list can be considerably extended by the sequential action of AP and DP IV. Some polypeptides are converted to their biologically active form by DP IV action, while others are degraded to inactive forms. Either action generates X-Pro dipeptides, which have a demonstrably beneficial effect on wound healing. Although not resolved by molecular sizing or anion exchange chromatography, DP IV and AP in a burn wound exudate were purified by affinity chromatography.

Adult↗

Liposome encapsulation: a method for enhancing the effectiveness of local antibiotics.

BACKGROUND: Treatment of contaminated surgical wounds is often complicated by the failure of local or systemic antibiotic treatment and prophylaxis. Locally administered liposome-encapsulated antimicrobials may offer advantages over free antibiotics, including an increase in efficacy, ease of administration, and safety. The therapeutic advantages, as well as the absorption and distribution of locally administered liposome-encapsulated antibiotics, were compared with those of locally applied unencapsulated antibiotics in a contaminated wound model. METHODS: Anesthetized rats had a 1 cm incision over the midback that was inoculated with 10(8) colony-forming units Pseudomonas aeruginosa (group 1; n = 102) or left uninfected (group 2; n = 35). Before wound closure, infected animals were treated with a local application of 0.3 ml saline solution (untreated; n = 30), 5.5 mg tobramycin in 0.3 ml saline solution (free tobramycin; n = 30), or 0.3 ml liposome-encapsulated tobramycin (LET; n = 42). Animals were killed 24, 48, and 72 hours after operation; serum and tissue tobramycin concentrations and tissue quantitative cultures were studied. Liposomes were radiolabeled to examine organ distribution. RESULTS: The data show that LET produced sustained local concentrations of antibiotic compared with free drug; sustained concentration prolonged the antimicrobial effect despite a single dose of antibiotic. LET reduced tissue bacterial counts to a greater extent and for a longer period of time than free tobramycin. The presence of infection further reduced clearance of LET from the infected site. CONCLUSIONS: The liposomal delivery of local antibiotics in this model of surgical wound infection reduced the number of organisms more effectively than locally applied free drug. Animals treated with LET had consistently less than the 10(5) organisms per gm tissue considered critical for invasive infection, suggesting that liposomal antibiotics may be clinically useful in surgical wound prophylaxis.

Animals↗

Detection of the actin scavenger system in burn wound fluid.

The intravascular actin scavenger system depolymerizes and sequesters actin released after tissue injury. Studies were carried out to determine if this system is active in the extracellular space during wound repair. Using burn wound fluid as a noninvasive means for analyzing the wound environment, we measured actin accumulation and actin complex formation with the plasma proteins responsible for scavenger function. Actin at concentrations as high as 0.25 mg/ml ( approximately 5 micromol/L) was found in burn wound fluid samples from 9 of 11 patients. Wound fluid also contained the two plasma proteins that bind actin-gelsolin (both plasma and cytoplasmic forms) and Gc protein. Because actin in wound fluid was complexed with gelsolin and Gc protein, we conclude that the components of the actin scavenger system are functional in wound tissue. In addition, proteolysis of gelsolin, but not actin or Gc protein, appeared to occur at the wound site. Gelsolin proteolysis was accompanied by the appearance of 49 kd gelsolin fragments, and wound fluid samples lacking intact gelsolin also contained high metalloproteinase levels.

Journal Article↗

Management of burn wounds.

The pathophysiology of thermal injury is described and applied to the clinical diagnosis of the depth of the injury. The basis of the selection of the type of nonoperative therapy for moderate depth second-degree burns is outlined for optimizing healing time. The importance of early tangential (sequential) excision of deep second-degree burns and third-degree burns in reducing functional and cosmetic residual is emphasized.

Burns↗

Liposome delivery of aminoglycosides in burn wounds.

The current study evaluated the pharmacodynamics of topically applied antimicrobials incorporated into radiolabeled liposomes. Radiolabeled 125I-phenyldecanoic acid was used in the formulation of small unilamellar liposomes. Sephadex (cross-linked dextran beads) G-50 columns were run to determine the per cent of radioactivity incorporated into liposomes and persistence of radioactive tag on the liposome after two weeks (greater than 95 per cent) remained incorporated. On the day of the experiment, 31 adult Sprague Dawley rats were subjected to a 10 per cent total body surface area full thickness burn (Walker burn model). All rats were treated with topical application of 0.3 milliliters of tobramycin entrapped in 125I-liposomes, and burn wounds were covered with Opsite (Winfield Laboratories). This formulation resulted in each rat receiving 14 milligrams per kilogram of tobramycin with a specific activity of 10.41 microcuries. Rats were sacrificed at several time periods after burn injury (nine after 24 hours, 12 after 48 hours, 11 after 72 hours). At these time intervals, serum and tissue tobramycin levels were measured, burn dressing, burn tissue and splanchnic organs were harvested and radioactivity was assessed with a gamma scintillation counter to determine tissue concentration of 125I-liposome tobramycin. Concentration of tobramycin in the serum was negligible at 24, 48 and 72 hours postburn, but was significant in the burn tissues at these times. The radioactive recovery data demonstrated that the majority (greater than 90 per cent) of the recovered liposomes remained at the site of application (the burn wound). No splanchnic organs had greater than 2 per cent of the recovered 125I-liposomes at any time period. These data suggest that, in burn wounds, tobramycin incorporated into liposomes remain at the site of initial application, resulting in high local concentrations with little systemic absorption and confirm that liposomes provide an effective vehicle for delivery of antimicrobials at the site of the burn injury.

Animals↗

Nutrition for adult burn patients: a review.

Adequate nutritional support is an important aspect of burn therapy. To accomplish this goal, nutrition assessment must be conducted, with particular attention given to the determination of energy and macronutrient needs. Providing these nutrients by the enteral route is recommended.

Adult↗

Topical liposomal delivery of antibiotics in soft tissue infection.

A new drug delivery system (lipid microcarriers) was studied in an experimental model of infected soft tissue wounds. Superficial, nonlethal infection was produced in the adult rat by injecting 1 ml containing 10(8) colony-forming units (CFU) of Pseudomonas aeruginosa under the superficial fascia of the paraspinus muscle of a 2-cm2 excised wound. All wounds were dressed with N-Terface, a nonadherent wound material, and covered with Kontor sponge, an open-cell polyurethane sponge containing either normal saline (group I), free tobramycin (groups III and V), liposome-entrapped tobramycin (groups II and IV), silver sulfadiazene (group VI), or liposome-entrapped silver sulfadiazene (group VII). At 24, 48, and 72 hr postinjection, animals were sacrificed and colony-forming units of P. aeruginosa per gram of muscle tissue were determined. Group I had significantly higher colony-forming units of P. aeruginosa per gram than groups II and III at 48 and 72 hr and than groups IV and V at all times. One single dose of liposome-encapsulated silver sulfadiazine significantly decreased bacterial counts compared to untreated controls and, to a similar extent, compared to multiple applications of free drug. Colony-forming units in all treatment groups (II and III, IV and V, VI and VII) were similar at all time periods within equivalent dosages. The ability of one application of liposomal-entrapped antibiotics to result in a therapeutic effect that requires multiple applications of topically applied free antibiotics offers potential clinical advantages.

Administration, Topical↗

Hypertonic saline dextran resuscitation of thermal injury.

Burn treatment requires large volumes of crystalloid, which may exacerbate burn-induced cardiopulmonary dysfunction. Small-volume hypertonic saline dextran (HSD) resuscitation has been used for effective treatment of several types of shock. In this study isolated coronary perfused guinea pig hearts were used to determine if HSD improved left ventricular contractile response to burn injuries. Parameters measured included left ventricular pressure (LVP) and maximal rate of LVP rise (+dP/dt max) and fall (-dP/dt max) at a constant preload. Third-degree scald burns comprising 45% of total body surface area (burn groups, N = 75), or 0% for controls (group 1, N = 25) were produced using a template device. In group 2, 25 burned guinea pigs were not fluid resuscitated and served as untreated burns; 20 burns were resuscitated with 4 mL lactated Ringer's (LR) solution/kg/% burn for 24 hours (group 3); additional burn groups were treated with an initial bolus of HSD (4 mL/kg, 2400 mOsm, sodium chloride, 6% dextran 70) followed by either 1, 2, or 4 mL LR/kg/% burn over 24 hours (groups 4, 5, and 6, respectively). Untreated burn injury significantly impaired cardiac function, as indicated by a fall in LVP (from 88 +/- 3 to 68 +/- 4 mmHg; p = 0.01) and +/- dP/dt max (from 1352 +/- 50 to 1261 +/- 90 and from 1150 +/- 35 to 993 +/- 59; p = 0.01, respectively) and a downward shift of LV function curves from those obtained from control hearts. Compared to untreated burns, hearts from burned animals treated with LR alone showed no significant improvement in cardiac function. However hearts from burned animals treated with HSD + 1 mL LR/kg/% burn had significantly higher LVP (79 +/- 4 vs. 68 +/- 4 mmHg, p = 0.01) and +/- dP/dt max (+dP/dt: 1387 +/- 60 vs. 1261 +/- 90 mmHg/sc, p = 0.01; -dP/dt: 1079 +/- 50 vs. 993 +/- 59 mmHg/sc, p = 0.01) than hearts from untreated burned animals and generated left ventricular function curves comparable to those calculated for hearts from control animals. Mortality 24 hours after burn was 29% for untreated burns was 0% for control animals, as well as for groups treated with the Parkland formula or HSD plus 1 or 2 mL/kg/% burn lactated Ringer's. The only deaths after treatment occurred in those animals given HSD plus 4 mL/kg/% burn, Parkland formula (17% mortality).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Oxidative activity of polymorphonuclear leukocytes after thermal injury.

Since defects in polymorphonuclear neutrophil (PMN) function are associated with an increased risk of infection, we measured the metabolic response of neutrophils from 23 burn patients with a mean burn size of 52%. Neutrophils from burn patients had a different pattern of oxygen consumption than control cells; the rate of QO2 at rest was higher, while the magnitude of the respiratory burst was lower in patient than in control PMNs, depending on whether the cells were incubated in media or normal serum. The burn-induced changes in patient PMN metabolism seem to be due to circulating factors, at least in part, since the pattern of increased resting and decreased stimulated QO2 could be transferred to control cells by incubating them in burn serum. Thus, a thermal injury alters neutrophil metabolism as well as systemic metabolism.

Adult↗

Enhanced effectiveness of intraperitoneal antibiotics administered via liposomal carrier.

The local application of antibiotics to treat intraperitoneal contamination has been used with variable results. Liposomes are not rapidly absorbed from the peritoneal cavity, offering a potential delivery system for intraperitoneal antibiotics. The effects of liposome-incorporated antibiotic administration in a fecal peritonitis model were compared with the effects of conventional intraperitoneal and intramuscular antibiotics. Rats were divided into four groups: untreated, intramuscular cefoxitin, intraperitoneal cefoxitin, and intraperitoneal liposome-incorporated cefoxitin. Quantitative blood cultures were drawn at 4 and 24 hours. Liposome delivery of cefoxitin significantly reduced mortality and bacteremia at 4 and 24 hours compared with control subjects and conventional antibiotic groups. Peritoneal abscess formation tended to decrease in the liposome antibiotic group (mean +/- SEM, 6.86 +/- 0.79) compared with the group receiving free intraperitoneal administration of antibiotics (10.33 +/- 1.63). We conclude that liposomal delivery significantly enhances the effectiveness of cefoxitin in this model of peritonitis.

Animals↗

Fluorescence digital microscopy of interstitial macromolecular diffusion in burn injury.

Computer vision techniques implemented on an IBM PC/AT have been applied to the study of microvascular permeability and interstitial diffusion in dorsal skin flap chamber preparations of hamsters. Experimental data was obtained for the leakage of fluorescent labelled dextran (70,000 daltons) after a precisely controlled mild degree of localized thermal trauma and compared with control data acquired prior to burn injury. Computer vision analysis techniques were applied to convert the fluorescent images into two-dimensional concentration maps. Interstitial diffusion coefficient values were computed from measured extravascular concentration profiles around a vessel of interest, assuming cylindrical or rectangular geometry, and optimally fitting a diffusion model to the data. An increase in the apparent diffusivity after mild thermal trauma was observed. Novel techniques were applied to solve hardware problems related to data acquisition and analysis, and a new library of software was developed to handle specific image processing requirements.

Animals↗

Differences in cardiac responses to resuscitation from burn shock.

Isolated coronary perfused hearts from guinea pigs were used to determine if aging alters left ventricular (LV) intrinsic contractile response to resuscitated burn shock. Parameters measured included LV pressure (LVP) and maximal rate of LVP rise (+dP/dt max) and fall (-dP/dt max) at a constant preload (LV enddiastolic pressure [LVEDP]). Compared with young controls (ten), aged control hearts (ten) showed significantly lower LVP (87.4 +/- 2.53 versus 76.0 +/- 1.5, p,0.001), +dP/dt max (1,351 +/- 51 versus 1,048 +/- 49, p,0.001), and -dP/dt max (1,154 +/- 34 versus 916 +/- 27, p,0.001), at an LVEDP of 10 millimeters of mercury. A 43 +/- 2 per cent third-degree burn (Walker model) was studied in ten young and ten aged guinea pigs. Burned aged hearts showed significantly lower LVP (57.1 +/- 2.1 versus 67.5 +/- 3.7, p,0.01) and -dP/dt max (707 +/- 33 versus 993 +/- 59, p,0.001) at an LVEDP of 10 millimeters of mercury. In addition, LV function curves for burned aged hearts were shifted downward and to the right of curves obtained from young burned hearts (p,0.05). Contractile defects in the aged group were not overcome by altered beating frequency, increased extracellular calcium concentration, nor maximally effective increases in diastolic stretch. Finally, we examined the effects of fluid resuscitation (4 milliliters per kilogram per percentage of burns) on contractile function in an additional ten young and ten aged burned guinea pigs. Contractile deficits persisted in both age groups despite adequate fluid resuscitation. Peak LVP and maximal rate of relaxation (-dP/dt) were uniformly depressed in aged as compared with young burned hearts (52.4 +/- 1.5 versus 63.2 +/- 2.7 and 715 +/- 42 versus 909 +/- 52, p,0.01, respectively). These data suggest that severe myocardial contractile change resulting from a major thermal insult in subjects with already compromised hearts is likely a significant limiting factor in the response to burn shock and adequate fluid resuscitation.

Age Factors↗