Pulmonary and Extrapulmonary Effects of Increased Colloid Osmotic Pressure During Endotoxemia in Rats: Materials and Methods

Anesthesia, Surgery, and Fluid, Balance
The experimental protocol for this study was approved by the Institutional Animal Care and Use Committee of the Miami Children’s Hospital, Miami, FL. Young albino Sprague-Dawley rats (weight range, 250 to 350 g) were anesthetized with 50 mg/kg pentobarbital intraperitoneally. In the supine position, a tracheostomy was performed and an endotracheal tube (7F scale; Becton Dickinson; Sparks, MD) was advanced to a position approximately 1 cm above the carina. Subsequently, a femoral vein and a femoral artery were exposed and cannulated. Each rat then was placed over an electric heating blanket, and the rectal temperature (TH-5, Physitemp; Thermalert; Clifton, NJ with a rat size thermal probe), the mean arterial BP (MABP), and heart rate (HR) [model 2001A; Datascope Corp; Paramus, NJ] were continuously monitored. Normothermia (mean ± SD, 38 ± 0.5°C) was established, while anesthesia and fluid balance, respectively, were strictly maintained by the administration of pentobarbital, 15 mg/kg/h, and by saline solution, 7.5 mL/kg/h IV (Medfusion pump 2010; Medex; Duluth, CA).
The dose of 15 mg/kg/h pentobarbital has been shown to maintain a stable anesthesia for > 6 h in male rats. Previously, we have used 5 mL/kg/h saline solution to maintain fluid balance in anesthetized rats that had been subjected to various critical-care conditions in order to maintain hemodynamic stability over a 6-h period. In the present study, anticipating some hemodynamic instability with endotoxemia, we used a higher volume of 7.5 mL/kg/h saline solution. To avoid confounding factors, this volume was given to both control rats and treatment-group rats. During the entire experimental period, all animals were breathing room air spontaneously.
Experimental Groups
Thirty to 45 min after the completion of all invasive procedures, the baseline values for blood COP (Osmometer model 4420; Wesco, Inc; Logan, UT), MABP, HR, gas-exchange variables (ABL-30 Blood Gas Analyzer; Radiometer; Copenhagen, Denmark), hemoglobin (Hb), and Hb-oxygen saturation (HbO2) [model OSM3 hemoxymeter; Radiometer] were determined. The Pao2, Paco2, and pH values were corrected for body temperature. An equivalent volume of saline solution replaced the blood volume that had been removed for various analyses. According to our previous experience with similarly instrumented rat mod-els, a dose of up to 100 U/kg/h heparin is needed to maintain the openness of venous and arterial lines. T