Anesthesia and analgesia
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Anesthesia and analgesia · Jun 2005
The effect of peripheral resistance on impedance cardiography measurements in the anesthetized dog.
In the vasodilated and septic patient, the impedance method of measuring cardiac output (CO) may underestimate the true value. In this study, we sought to determine whether impedance CO (COIC) measurements are influenced by total peripheral resistance (TPR). In eight anesthetized and ventilated dogs, a high-precision flowprobe was placed on the ascending aorta, and direct CO was measured (CO flowprobe (COFP)). ⋯ Correlation coefficients (r) between the CO bias and TPR ranged from 0.46 to 0.89 (P < 0.0001). The bias changed by 0.62 +/- 1.8 L/min, or by 34%, every time TPR halved or doubled. This finding explains the poor agreement between COIC and other methods of CO measurement found in validation studies involving critically ill patients.
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Anesthesia and analgesia · Jun 2005
The block of total and N-type calcium conductance in mouse sensory neurons by the local anesthetic n-butyl-p-aminobenzoate.
To contribute to the understanding of the mechanism underlying selective analgesia by epidural application of suspensions of the local anesthetic butamben (n-butyl-p-aminobenzoate; BAB), we investigated the effect of dissolved BAB on calcium channels in sensory neurons. Small-diameter dorsal root ganglion neurons from newborn mice were used to measure whole-cell barium or calcium currents through calcium channels upon voltage-clamp stimulation. BAB suppressed the voltage-step-evoked barium current of these cells in a concentration-dependent manner with a 50% inhibitory concentration of 207 +/- 14 microM (n = 40). ⋯ The time constants of inactivation and deactivation of the N-type current became smaller in the presence of BAB, thus suggesting that kinetic changes are involved in the inhibition of this current. BAB caused a similar inhibition of the total calcium current and its N-type component when these currents were evoked by command potentials with the shape of an action potential. This inhibition of calcium currents by BAB should be considered in the search for the mechanism of selective analgesia by epidural suspensions of this local anesthetic.