M Nakamura1, Y Sanjo, K Ikeda. 1. Department of Anesthesiology and Intensive Care, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Abstract
OBJECTIVE: In order to predict the partial pressure of volatile anesthetics in brain tissue, we developed a pharmacokinetic simulation model suitable for real time application. The accuracy of this model was examined by comparing the predicted values against measured values for blood sampled from the internal jugular vein, which was used as a measure of the partial pressure in the brain. METHODS: Our model consists of six compartments: alveoli, arterial blood, a group of vessel-rich organs (VRG), muscle, fat, and venous blood. A volatile anesthetic, sevoflurane partial pressure in each compartment were calculated using the parameters of volume, blood flow, and solubility for each tissue as reported in previous studies. Simulated sevoflurane partial pressures in VRG were considered to reflect those in the brain. We studied 11 patients undergoing elective abdominal surgery or mastectomy. Sevoflurane was maintained at a concentration of 3% (by vaporizer setting) for 25 min. Sampling points were at 0 min (before sevoflurane administration) and 1, 2, 4, 9, 16, and 25 min after the start of inhalation. We measured the sevoflurane partial pressure in inspiratory gas (PI(S)), in end-expiratory gas (PET(S)), in arterial blood (Pa(S)), and in internal jugular vein blood (Pj(S)). These values were compared against those for the simulated brain (PB(S)sim). RESULTS: The sevoflurane partial pressures increased, in order from least rapid to most rapid, as follows: Pj(S), PB(S)sim, Pa(S), PET(S), and PI(S). The differences between Pj(S) and PB(S)sim were significantly smaller than those between Pj(S) and PET(S) at all sampling points. PB(S)sim did not differ significantly from Pj(S) at any sampling points after 4 min of inhalation, while PET(S) differed significantly from Pj(S) at all sampling points. CONCLUSION: We conclude that our model is clinically useful for predicting sevoflurane partial pressure in the brain, assuming that Pj(S) reflects the sevoflurane partial pressure in the brain.
OBJECTIVE: In order to predict the partial pressure of volatile anesthetics in brain tissue, we developed a pharmacokinetic simulation model suitable for real time application. The accuracy of this model was examined by comparing the predicted values against measured values for blood sampled from the internal jugular vein, which was used as a measure of the partial pressure in the brain. METHODS: Our model consists of six compartments: alveoli, arterial blood, a group of vessel-rich organs (VRG), muscle, fat, and venous blood. A volatile anesthetic, sevoflurane partial pressure in each compartment were calculated using the parameters of volume, blood flow, and solubility for each tissue as reported in previous studies. Simulated sevoflurane partial pressures in VRG were considered to reflect those in the brain. We studied 11 patients undergoing elective abdominal surgery or mastectomy. Sevoflurane was maintained at a concentration of 3% (by vaporizer setting) for 25 min. Sampling points were at 0 min (before sevoflurane administration) and 1, 2, 4, 9, 16, and 25 min after the start of inhalation. We measured the sevoflurane partial pressure in inspiratory gas (PI(S)), in end-expiratory gas (PET(S)), in arterial blood (Pa(S)), and in internal jugular vein blood (Pj(S)). These values were compared against those for the simulated brain (PB(S)sim). RESULTS: The sevoflurane partial pressures increased, in order from least rapid to most rapid, as follows: Pj(S), PB(S)sim, Pa(S), PET(S), and PI(S). The differences between Pj(S) and PB(S)sim were significantly smaller than those between Pj(S) and PET(S) at all sampling points. PB(S)sim did not differ significantly from Pj(S) at any sampling points after 4 min of inhalation, while PET(S) differed significantly from Pj(S) at all sampling points. CONCLUSION: We conclude that our model is clinically useful for predicting sevoflurane partial pressure in the brain, assuming that Pj(S) reflects the sevoflurane partial pressure in the brain.