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Biomedical subjects

R G Tompkins

Publications and source records attributed to R G Tompkins.

At least 91 records · Page 5Linked to original sources
PubMed1995

Permissive hypercapnia as a ventilatory strategy in burned children: effect on barotrauma, pneumonia, and mortality.

OBJECTIVE: To document the incidence of barotrauma, pneumonia, and respiratory death associated with a mechanical ventilation protocol based on permissive hypercapnia in pediatric burn patients. DESIGN: Retrospective review. MATERIALS AND METHODS: Patients were managed using a mechanical ventilation protocol based on permissive hypercapnia, tolerating moderate (pH > 7.20) respiratory acidosis to keep inflating pressures below 40 cm H2O. MAIN RESULTS: Over a 2.5-year interval, 54 burned children (11% of 495 acute admissions) with an average age of 6.5 years (range 5 weeks to 17 years), average burn size of 44% (range 0 to 98%), and median burn size of 46% required mechanical ventilatory support for an average of 12.5 days (range 1 to 56 days). Inhalation injury was diagnosed in 34 (63%) of the children and 72% percent were admitted within 24 hours of injury. Overt barotrauma occurred in 5.6% of the patients, pneumonia in 32%, and respiratory death in 0%. CONCLUSIONS: A conventional ventilation protocol based on permissive hypercapnia is associated with acceptable rates of barotrauma and pneumonia. The low incidence of respiratory death associated with this strategy suggests that it also minimizes ventilator-induced lung injury.

Acidosis, Respiratory↗
PubMed1995

Genetically modified human epidermis overexpressing PDGF-A directs the development of a cellular and vascular connective tissue stroma when transplanted to athymic mice--implications for the use of genetically modified keratinocytes to modulate dermal regeneration.

We investigated the hypothesis that keratinocyte-produced platelet-derived growth factor-AA (PDGF-AA) is involved in epidermal-dermal interactions and that PDGF-AA is an important mediator of the temporal and spatial events of tissue repair. Retroviral-mediated gene transfer was used to introduce the gene encoding human PDGF-A into cultures of human diploid keratinocytes. Genetic modification boosted the endogenous in vitro level of PDGF-AA secretion by over 300 fold. When PDGF-secreting cells were transplanted as epithelial sheets to athymic mice, modified keratinocytes underwent terminal differentiation and generated a stratified epithelium comparable to unmodified cells. Seven days after grafting the newly synthesized connective tissue layer subjacent to the PDGF-A-modified grafts was significantly thicker, was rich in mononuclear cells and fibroblasts, and had increased numbers of blood vessels when compared to control grafts of unmodified cells. These results suggest that PDGF-AA secreted by the epidermis is an important mediator of epithelial-mesenchymal interactions and helps to promote growth and vascularization of the underlying dermal tissue. Further, these data demonstrate the feasibility of using genetically modified cells to modulate tissue regeneration.

Animals↗
PubMed1995

Retrovirus infection: effect of time and target cell number.

Using a model amphotropic recombinant retrovirus encoding the Escherichia coli lacZ gene and quantitative assays to measure virus infection, we have determined the effects of time and target cell number on infectivity. Infection of various numbers of NIH 3T3 fibroblasts showed that the extent of lacZ virus infection was dependent on virus concentration and independent of target cell number. These results demonstrate that multiplicity of infection is not an accurate predictor of the efficiency of retroviral infection. Varying the time of viral infection revealed that maximal infection occurred after greater than 24 h of exposure of the cells to the lacZ virus. Half-maximal infection occurred after 5 h of exposure. After 2 h of adsorption at 37 degrees C, the majority of infectious virus was not adsorbed to cells but was unbound and able to infect other cells. These results are discussed in terms of both their relevance to the fundamental biology of retrovirus infection and the use of recombinant retroviruses for retrovirus-mediated gene transfer with purposes of gene therapy.

3T3 Cells↗
PubMed1994

Selective adhesion of hepatocytes on patterned surfaces.

Successful development of cell-biased bioartificial liver devices necessitates the establishment of techniques and designs for long-term, stable hepatocellular function and efficient transport of nutrients and wastes within the device. Given the relatively large cell mass that one must consider, one possible solution involves the use of micropatterning technology to sandwich hepatocytes aligned in rows between two micropatterned surfaces. Rows of cells would alternate with hepatocyte-free areas, creating efficient transport channels for fluid flow and nutrient exchange. Ultimately, this type of device could also be used as a three-dimensional construct for investigating a variety of cell-surface, cell-extracellular matrix, and cell-cell interactions. To achieve this goal, one must develop techniques for selectively adhering hepatocytes to solid substrates. In this study, reproducible, selective adhesion of hepatocytes on a glass substrate with large regions of adhesive (AS) and nonadhesive (NAS) surfaces was obtained. The AS had hydrophilic characteristics, enhancing deposition of collagen molecules from an aqueous solution, and subsequent hepatocyte adhesion, whereas the NAS had hydrophobic properties and remained collagen-free and hepatocyte-free. In addition, a reproducible processing technique for obtaining patterns of hepatocytes was developed and optimized, using a surface with a single AS band as a first approximation to a micropatterned device. This was achieved by spincoating an aqueous collagen type I solution (0.1 mg/mL) on a banded surface at 500 rpm for 25 seconds. The morphology and long-term function of the hepatocytes attached to AS in nonbanded and banded surface configurations was assessed by mimicking sandwich culture and was shown to be similar to stable, differentiated sandwich cultures. Mathematical modeling was used to determine critical design criteria for the hypothetical micropatterned device. The oxygen distribution and viscous pressure drop were modeled along a typical microchannel and limited to in vivo values. An optimal channel length of 0.6 cm and a flow rate of 2.0 x 10(-6) mL/s were obtained for a channel of 100 microns in width and 10 microns in height. These values were reasonable in terms of practical implementation.

Albumins↗
PubMed1994

Nitric oxide production is intensely and persistently increased in tissue by thermal injury.

NO is a major messenger molecule which regulates immunity and vascular tone, serves as a neurotransmitter and participates in wound healing. It has also been known to be increased in vivo by thermal injury. Urinary nitrate excretion and tissue levels of NO synthase activity were measured after a non-lethal thermal injury. Urinary nitrate excretion decreased by 90% 24-48 h after injury, but dramatically increased by 10-fold thereafter for 30-40 days after injury and remained elevated until the wound healed. This response was inhibited by a competitive inhibitor of NO synthase. These rates of urinary nitrate excretion suggest that NO production is dramatically affected by injury in a pattern that is distinct from that observed after lipopolysaccharide administration. On the basis of these findings, we suggest that the hyperdynamic cardiovascular and hypermetabolic responses seen to continue weeks after thermal injury could be a result of the autocrine and paracrine effects of NO generated locally within the tissues in addition to that generated by inflammatory cells.

Amino Acid Oxidoreductases↗
PubMed1994

Additive effects of thermal injury and infection on gut permeability.

OBJECTIVE: To determine the effects of burn size and burn wound infection on gut permeability to the macromolecule polyethylene glycol 3350 (PEG 3350; molecular weight, 3350 d). DESIGN: Randomized, controlled study using 36 male Sprague-Dawley rats. SETTING: Hospital research laboratory. INTERVENTIONS: Animals received scald burns to 0%, 20%, or 35% of their total body surface area. Half of the animals in each group were infected with Pseudomonas aeruginosa. MAIN OUTCOME MEASURES: Gut permeability was measured using the intestinal absorption and renal excretion of enterally administered PEG 3350 and mannitol (molecular weight, 182 d). RESULTS: There were dramatic increases in PEG 3350 excretion and in the PEG 3350/mannitol ratios (P = .0001 in both instances) that were seen in relation to burn size. Significant increases in PEG 3350 excretion and in the PEG 3350/mannitol ratios (P = .017 and P = .045, respectively) were also seen in animals in which infection was present. This was in addition to the effects of burn size already noted. CONCLUSIONS: A direct relationship between gut permeability and the extent of burn injury was found, which is consistent with the results from a previous study in humans. In addition, this study found that further separate increases in gut permeability occur in the presence of P aeruginosa in burn wound infections.

Animals↗
PubMed1994

Control of methicillin-resistant Staphylococcus aureus in a pediatric burn unit.

BACKGROUND: Control of methicillin-resistant Staphylococcus aureus (MRSA) is particularly difficult in burn units, which are often cited as sources of hospital-wide MRSA outbreaks. We developed a successful MRSA control program and document here its apparent effectiveness in controlling MRSA transmission in a pediatric burn unit. METHODS: An MRSA control program that included surveillance culturing, clinician feedback, flexible, site-specific isolation, and a list of known carriers was consistently applied in a pediatric burn unit through a 7-year period. Microbiology reports of MRSA isolates from patients and environmental surfaces and records of all patients from whom MRSA was isolated were reviewed. RESULTS: During calendar years 1985 through 1991, a total of 991 acutely burned children were admitted to the Boston unit of the Shriners Burns Institute. Forty MRSA cases (4%) were identified. One patient both had MRSA at admission and met our criteria for nosocomial MRSA. Of the remaining 39 patients, 11 had MRSA at admission and 28 had nosocomial MRSA. There were 17 wound infections, two cases of pneumonia, and two bloodstream infections. No deaths were attributed to MRSA sepsis. CONCLUSION: An MRSA control program including surveillance culturing, clinician feedback, flexible, site-specific isolation, and a list of known carriers is associated with a low rate of nosocomial MRSA in a pediatric burn unit.

Adolescent↗
PubMed1994

Staphylococcal toxic shock syndrome in a paediatric burn unit.

A case of staphylococcal toxic shock syndrome (TSS) in a 15-year-old patient undergoing reconstructive burn surgery is reported. This syndrome, first described in menstruating women using tampons, can also occur as a postsurgical complication. The epidemiology, microbiology, clinical presentation and management of non-menstrual TSS are discussed and correlated with the patient present. We advise caution in the use of occlusive dressings and recommend constant isolation of patients with open wounds colonized with a TSST-1 producing strain of Staph. aureus.

Adolescent↗
PubMed1994

Femoral arterial catheterization in paediatric burn patients.

Despite the obvious drawbacks associated with prolonged arterial cannulation, arterial catheters are frequently required in paediatric burn patients with respiratory failure to facilitate monitoring of oxygenation, ventilation and blood pressure, and to allow for the painless performance of phlebotomy. Burn patients with respiratory failure frequently require prolonged arterial catheterization, often for more than 72 h, and many of their cannulation sites are burned. We report our favourable 3-year experience with 81 femoral arterial catheters in 36 paediatric burn patients. When small diameter pressure monitoring catheters are used, femoral cannulation sites are associated with a low rate of mechanical and infectious complications.

Adolescent↗
PubMed1994

Synthesis of 2-[18F]fluoro-2-deoxy-L-glucose and positron emission tomography studies in monkeys.

2-[18F]Fluoro-2-deoxy-L-glucose was synthesized from its trifluoromethanesulfonyl precursor. The precursor was prepared by selective acetylation and triflation of L-mannose. L-Mannose was first treated with acetic anhydride in the presence of a catalytic amount of perchloric acid and then reacted with phosphorus tribromide followed by aqueous sodium acetate to produce pure 1,3,4,6-tetra-O-acetyl-a-L-mannopyranose in 32% yield. This compound was treated with trifluoromethanesulfonic anhydride and pyridine in methylene chloride to form 1,3,4,6-tetra-O-acetyl-O-tritrifluoromethanesulfonyl-a-L-mannopyra nose in 77% yield. Nucleophilic substitution of the triflate with 18F-in the presence of Kryptofix 2,2,2 followed by acid hydrolysis produced 2-[18F]fluoro-2-deoxy-L-glucose with a radiochemical yield of 20-30% (EOS) within 90 min. Biodistribution studies in rats and PET imaging in Rhesus monkeys demonstrated that this sugar analog distributes in the extracellular space of most organs but is excluded from the CNS.

Animals↗
PubMed1994

The use of pentafluorophenyl derivatives for the 18F labelling of proteins.

A simple, one-step method for the radiolabelling of proteins with 18F is described. A series of pentafluorophenyl derivatives were synthesized and tested for 18F exchange using tetrabutylammonium-[18F]fluoride in DMSO, with microwave heating. A number of the compounds examined incorporated 18F quickly and in high yield. Two compounds, pentafluorobenzaldehyde and 2,3,5,6-tetrafluorophenylpentafluorobenzoate, were used to label HSA in good yield. The methods produce low specific activity labelled proteins, but are fast. The yields are reasonable and the reagents do not require a separate modification or activation step for protein labelling.

Animals↗
PubMed1994

Antibody-targeted photolysis of bacteria in vivo.

We have evaluated the efficacy of antibody-targeted photolysis to kill bacteria in vivo using specific antibacterial photosensitizer (PS) immunconjugates. After infecting the dorsal skin in mice with Pseudomonas aeruginosa, both specific and nonspecific tin (IV) chlorin e6-monoclonal antibody conjugates were injected at the infection site. After a 15 min incubation period, the site was exposed to 630 nm light with a power density of 100 mW/cm2 for 1600 seconds. Irradiation resulted in a greater then 75% decrease in the number of viable bacteria at sites treated with a specific conjugate, whereas normal bacterial growth was observed in animals that were untreated or treated with a nonspecific conjugate. Antibody-targeted photolysis may be a selective and versatile tool for treating a variety of infections.

Animals↗
PubMed1994

Cellular distribution of endotoxin after injection of chemically purified lipopolysaccharide differs from that after injection of live bacteria.

Lipopolysaccharide (LPS) chemically extracted from gram-negative bacteria is often used in animal models to study endotoxemia. Laser confocal microscopy and immunofluorescence staining for comparison of injections of live Escherichia coli O111:B4 bacteria with LPS extracted from the same strain showed that cellular localization and time course in rat organs were markedly different after the two injections. Fluorescent staining and image analysis software allowed quantitative comparison of LPS within tissues at different times and doses. Antigenic LPS was detected in all tissues 1 hour after injection of both bacteria and LPS and was present in liver and spleen over the 28-day study period. Whole bacteria were identified in tissue macrophages for the first 48 h after injection; later, bacterial cell walls were replaced by diffuse antigenic material throughout the cytoplasm. Antigenic LPS was localized within hepatocytes only after injection of chemically purified LPS. Cellular localization of LPS in tissues is dependent on the form injected. Animal models that use purified LPS may not be representative of gram-negative bacteremia.

Animals↗
PubMed1994

Transport of fluorescent dextrans across the rat ileum after cutaneous thermal injury.

OBJECTIVE: To determine the time course and spatial distribution of uptake of macromolecules in the small intestine of rats subjected to cutaneous thermal injury. DESIGN: Prospective, controlled animal study. SUBJECTS: Fifty-five female Sprague-Dawley (CD) rats subjected to scald burn injury covering 20% (small injury; n = 29) and 40% (large injury; n = 6) of the total body surface area between 3 and 72 hrs after injury. Animals subjected to sham injury (n = 20) were used as controls. INTERVENTIONS: The intestine was cannulated near the distal ileum and incised 7 cm upstream. After perfusion with physiologic buffer, this intestinal loop was filled with the same buffer containing fluorescent-labeled dextrans (3 and 70 kilodaltons molecular weight) and ligated 4 cm from the injection point. After a 2-hr incubation period, the tissues were fixed with paraformaldehyde and cryosections were examined by laser confocal microscopy. The mesentery was also observed by laser confocal microscopy during incubation with the permeability probes. The disappearance of fluorescence was studied after washing the dextran probes from the gut lumen. MEASUREMENTS AND MAIN RESULTS: In small injuries, there was a transient uptake of the 3-kilodalton dextran by the epithelium in focal regions of the ileum with the effects seen between 7 and 21 hrs after injury. In large injuries, epithelial staining was visible within 3 hrs, and the marker was seen to translocate both to the lymphatics and the blood vessels of the mesentery. In comparison, the 70-kilodalton dextran was visible within the intercellular spaces. Little or no epithelial staining was seen in sham-injured animals. CONCLUSIONS: These results suggest that a transcellular pathway for the translocation of small macromolecules from the lumen to the mesentery can be activated after burn injury. The novel techniques described here will be useful to examine intestinal transport in various pathologic situations.

Animals↗
PubMed1994

Intracompartmental sepsis in burn patients.

An uncommon cause of sepsis in patients with large burns is occult intracompartmental infection. A multi-institution review of 1171 burn admissions identified 5 patients (0.4%) who developed intracompartmental sepsis presenting with fever and purulent drainage or fever, erythema, and swelling on clinical examination. Contributing factors may have included high-volume resuscitation, delayed escharotomy, extravasated intraosseous infusion, cannulation-related arterial injury, and splinting or positioning difficulties. A high index of suspicion and an aggressive surgical approach facilitate successful management of this unusual problem.

Adult↗