Regional perfusion of carpal tissues by forced intramedullary administration of fluids was evaluated in 10 horses. Results of subtraction radiography after perfusion with a contrast medium demonstrated that perfusate was delivered to the carpal tissues by the venous system. Perfused India ink was distributed uniformly in the antebrachiocarpal and middle carpal synovial membranes. Histologically, the ink was within the venules of the synovial villi. Immediately after perfusion with gentamicin sulfate (1 g), the gentamicin concentrations in the synovial fluid and synovial membrane of the antebrachiocarpal joint were 349 +/- 240 micrograms/mL and 358 +/- 264 micrograms/g, respectively. When gentamicin concentrations in the synovial fluid of the antebrachiocarpal joint and serum were measured 0, 0.5, 1, 4, 8, 12, and 24 hours after carpal perfusion, the mean peak gentamicin concentration in the synovial fluid was 589 +/- 429 micrograms/mL. At hour 24, the mean gentamicin concentration in the synovial fluid was 4.8 +/- 2.0 micrograms/mL. The resulting peak gentamicin concentration in the serum was 23.7 +/- 14.5 micrograms/mL immediately after the perfusion; it decreased below the desired trough level of 1 micrograms/mL between hours 4 and 8.
Septic arthritis was induced in one antebrachiocarpal joint of seven horses by the intra-articular injection of 1 mL Staphylococcus aureus suspension containing a mean of 10(5) colony-forming units. Twenty-four hours after inoculation, four horses were treated by regional perfusion with 1 g of gentamicin sulfate, and three horses received 2.2 mg/kg gentamicin sulfate intravenously (IV) every 6 hours. Synovial fluid was collected for culture and cytology at regular intervals, and the synovial membranes were collected for culture and histologic examination at euthanasia 24 hours after the first treatment. Gentamicin concentration in the septic synovial fluid after three successful perfusions was 221.2 +/- 71.4 (SD) micrograms/mL; after gentamicin IV, it was 7.6 +/- 1.6 (SD) micrograms/mL. The mean leukocyte count in the inoculated joints decreased significantly by hour 24 in the successfully perfused joints. Terminal bacterial cultures of synovial fluid and synovial membranes were negative in two horses with successfully perfused joints. S. aureus was isolated from the infected joints in all three horses treated with gentamicin IV.
Stewart used physicochemical principles of aqueous solutions to develop an understanding of variables that control hydrogen ion concentration (H+) in body fluids. He proposed that H+ concentration in body fluids was determined by PC02, strong ion difference (SID = sum of strong positive ion concentrations minus the sum of the strong anion concentrations) and the total concentration of nonvolatile weak acid (&ot) under normal circumstances. Albumin is the major weak acid in plasma and represents the majority of A , .These 3 variables were defined as independent variables, which determined the values of all other relevant variables (dependent) in plasma, including H' . The major strong ions in plasma are sodium and chloride. The difference between Na+ and CI-may be used as an estimation of SID. A decrease in SID below normal results in acidosis he purpose of this article is to review the basic T principles of Stewart's approach to acid-base chemistry,'-3 to show how these principles can be easily applied clinically, and to show the clinical usefulness of this approach in the evaluation of the acid-base status in a variety of species and disease states in an emergency or critical care setting. Principles of Stewart's Acid-Base ChemistryStewart's quantitative approach to acid-base chemistry provides a mathematical explanation of the relevant variables that control H+ in body fluids and their interactions. The approach treats body fluids as a system that contains multiple interacting constituents. The Henderson-Hasselbalch approach to evaluating acid-base status considers the interactions of only a few variables in the system, such as pH, PC02, and bicarbonate, whereas Stewart considers the interactions among more variables and allows one to identify the variables that control H+. 1-3Stewart uses 3 physical laws of aqueous solutions to write equations that describe the interactions among the variables in the system. These laws are (1) the maintenance of electrical neutrality (positively charged ion concentrations equal the negatively charged ion concentrations), (2) the satisfaction of the dissociation equilibria for weak electrolytes (partially dissociated when dissolved in water), and ( 3 ) the conservation of mass. Strong electrolytes are completely dissociated in water so there is no equilibrium equation to consider. Equations that satisfy the physical (increase in H+) and an increase in SID above normal results in alkalosis (decrease in H+). Unidentified strong anions such as lactate will decrease the SID, if present. Equations developed by Fencl allow Stewart's work to be easily applied clinically for evaluating the metabolic (nonrespiratory) contribution to acid-base balance. This approach separates the net metabolic abnormality into components, and allows one to easily detect mixed metabolic acid-base abnormalities. The Fencl approach provides insight into the nature and severity of the disturbances that exist in the patient. Sodium, chloride, protein, and unidentified anion derangements may contribute to the...
Antibiotics were delivered to chronically infected tissues by regional limb perfusion in three horses with osteomyelitis associated with orthopedic implants. Two infections were resolved with implants in place; in one, a sequestrum was resorbed. In one horse, regional antibiotic perfusion was applied to treat progressively worsening bone infection after initial implants loosened and were removed.
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