After approval by the animal research committee of the University Hospital Hamburg-Eppendorf, 6 MHN German Landrace pigs weighing 39–48
kg, aged 3–5 months, and 6 MHS Pietrain pigs weighing 26–33
kg, aged 3–5 months, from a special breeding farm (Research Station Thalhausen, Technical University Munich, Germany) were investigated. Prior to the study, in all animals genomic DNA was isolated from blood preserved in ethylenediaminetetraacetic acid to check for the presence of the Arg615-Cys point mutation on chromosome 6, indicating MH susceptibility [12
Swine were fasted overnight with free access to water. General anesthesia was induced by administration of ketamine 10
intramuscularly (Ketavet, Pharmacia & Upjohn, Erlangen, Germany). After insertion of a venous cannula into an ear vein, anesthesia was deepened with propofol 10
(Diprivan 2%, Astra-Zeneca, Plankstadt, Germany) and fentanyl 10μ
(Fentanyl-Janssen, Janssen-Cilag, Neuss, Germany) intravenously (i.v.). After tracheotomy and intubation, the lungs were mechanically ventilated with an air/oxygen mixture (fraction of inspired oxygen (FiO2
) 0.4). Anesthesia was maintained with propofol 10
and fentanyl 50μ
. Neuromuscular blocking drugs were not administered. A multilumen central-venous line was inserted into the right internal-jugular vein. One lumen was used for withdrawal of blood samples and measurement of central-venous pressure (CVP), the second for administration of theophylline and fluid infusion (5–10
Ringer's solution), and the third for administration of anesthetics. Cannulas were inserted into both femoral arteries: one was used for withdrawal of blood samples, the other for continuous measurement of arterial pressure and body core temperature (PiCCO, Pulsion Medical Systems, Munich, Germany). Normothermia was maintained by forced-air warming, and rectal and intravascular body temperatures were measured continuously.
A blood-gas analyzer (ABL625, Radiometer, Copenhagen, Denmark) was used for monitoring arterial and venous oxygen saturation, oxygen partial pressure (pO2
), carbon dioxide partial pressure (pCO2
), pH, and potassium and lactate levels. Mechanical ventilation was adjusted to maintain venous pCO2
at 46 ± 4
mmHg; the body core temperature was adjusted to 37.5 ± 0.2°C before the experiment was started. Once a steady state was achieved for at least 30 minutes, baseline values were recorded for all variables.
Theophylline (Bronchoparat, Klinge Pharma, Munich, Germany) 1.0
was administered as an i.v. bolus. Subsequent doses were given every 10 minutes to reach cumulative doses of 3.5, 8.5, 18.5, 33.5, 53.5, and 93.5
. The clinical occurrence of MH was defined by the development of two of three conditions: central-venous pCO2
mmHg, central-venous pH ≤ 7.20, and an increase of intravascular body core temperature by ≥2.0°C as measured using the PiCCO system.
During the experiments, hemodynamic variables (heart rate (HR), mean arterial pressure (MAP), CVP, cardiac output), end-tidal CO2 concentration (etCO2), rectal and intravascular body temperature (°C), blood-gas concentrations (O2 saturation (SaO2), pCO2, pH), and lactate levels were measured every 5 minutes. Every 10 minutes, blood samples were taken for gas-chromatographic measurement of theophylline concentrations. After all experiments were completed, the pigs were killed using 10% magnesium chloride solution i.v.
Statistical evaluation was performed using a computer-based program (StatView 4.57, Abacus Concepts, Berkeley, CA). All data are presented as median and range. Intergroup variations were calculated with the Mann-Whitney test; intragroup differences were calculated with analysis of variance for repeated measures. If appropriate, subsequent comparisons were performed using Scheffé's posthoc method. Results were considered significant if P values were less than 0.05.