The use of sevoflurane anesthesia during early pregnancy.

Sevoflurane has favorable pharmacodynamic properties such as a rapid, smooth induction and emergence from anesthesia. However, there is only one report of sevoflurane anesthesia during early pregnancy. We report the use of sevoflurane for maintenance of general anesthesia in a pregnant patient undergoing non-obstetric surgery. A 25-year-old, female patient, at 13 weeks gestation, was diagnosed as having a strangulated ileus. General anesthesia was performed and maintained with oxygen, nitrous oxide, and sevoflurane. Six months later a healthy infant without abnormalities was delivered.

Development of a new catheter-tip pressure transducer.

Two major disadvantages of the conventional catheter-tip transducer have been incapability to calibrate baseline pressure and to adjust sensitivity after insertion. A vast majority of conventional catheter-tip transducers are classified as gauge type. Due to their structure they are inherently incapable of recalibrating after insertion. We have overcome this problem by developing a new differential type catheter-tip transducer equipped with a lumen that connects a small chamber at the backside of the transducer to another external port. This lumen is capable of pressure passage. The output of this type depends on the difference between the two imposed pressures. This passage makes a baseline standard possible, when the end of the lumen is exposed to atmospheric pressure. When pneumatic pressure is imposed to the end of the lumen using a syringe, for example, the transducer output shifts up and down in accordance to that pressure, enabling baseline pressure recalibration and verifying the degree of sensitivity after insertion. By obtaining the following data, we confirmed the stability and availability of this transducer: Baseline drift less than 0.04 mmHg/8 hour, frequency characteristics flat up to 60 Hz, and common mode rejection ratio more than 46 dB.

Respiratory impedance estimated from airway and intrapleural pressure curves.

At the cessation point of inspiratory flow on an airway pressure curve of constant-flow CMV (controlled mechanical ventilation), the pressure falls rapidly at first and then gradually tapers down to an endinspiratory plateau. By fitting these two pressure changes to the voltage changes in the respiratory circuit model, the resistance and compliances in the lung periphery and the resistance in the large airway can be estimated. We designed an algorithm estimating the values of circuit elements using a circuit simulator MicroCap III. The validity of this method was examined on the mechanical lung model. The sensitivity came to within +/- 15%. Further validation was carried out on five Beagles treated with methacholine. The large airway resistance, the small airway resistance and compliance, and alveolar compliance demonstrated a two- to three-fold increase in resistances and a two thirds to one-half decrease in compliances, when compared with the base-line values before administration of methacholine. This method can be applied not only to patients during CMV, but also during surgery.

A pilot/introducer needle for central vein cannulation.

A kit for safe and easy insertion of a central vein cannula was devised. A small gauge (22 gauge) metal pilot needle was equipped with a Y-shaped hub which had a side-port to accept a small gauge (0.46 mm) Seldinger guide wire. Once the needle reached the vein, guidewire was threaded in through the side-port. There was no need to remove the pilot needle and no need to repeat vein puncture with a larger-bore needle. Three puncture methods were used with the kit: (1) the central approach via the internal jugular vein, (2) the supraclavicular approach via the junction of the internal jugular vein and subclavian vein, and (3) the infraclavicular approach via the subclavian vein. Each method was used on 20 patients, for total of 60 patients, with a high success rate. Less than 3 minutes were required from puncture to catheter insertion. No serious complications were encountered.

Use of personal computers for translation and publication of an anesthesia textbook.

We used personal computers extensively for translating and publishing in Japanese an anesthesia textbook originally written in English. The procedure included optical character recognition, scanning of figures, use of computer translation, use of electronic mail and computer type-setting. While these have individually been done previously, this is process of any medical textbook published in Japanese. The advantages of combining these technologies are good exchange of information among individual authors/translators, rapid translation process, preliminary visualization of the final product, and overall high quality of the published book.

Evaluation of dynamic response of catheter-manometer systems for pulmonary arterial pressure.

To quantitatively evaluate the waveform distortions observed through a catheter-manometer system, the tolerance range of amplitude errors and that of phase errors are defined as both within +/- 5%, and the frequency bandwidth was calculated where the frequency characteristics of amplitude and those of phase difference satisfy the two tolerance ranges by use of a second-order kinetic equation. The results were expressed by three variables, composed of the natural frequency (fn), damping coefficient (zeta), and highest frequency (fh) corresponding to the frequency bandwidth; a chart was constructed with fn on the x-axis, zeta on the y-axis, and fh as parameter. Also on the chart, the propagation delay times (td's) determined by fn, zeta, and fh were plotted. We measured the frequency characteristics of two 7-Fr Swan-Ganz catheters with lengths of 75 and 110 cm. fn's and zeta's were found to be 13.9 and 10.1 Hz and 0.23 and 0.32, respectively. Referring to this chart, the maximal fh these catheters would be able to reproduce within the tolerance ranges and the propagation td's can be predicted to be 3.2 and 2.4 Hz and 7 and 12 ms, respectively. Suppression of resonance by use of Accudynamic improved the maximal fh's to 3.9 and 2.9 Hz, respectively, but resulted in the increased td's to 14 and 19 ms due to increased zeta.

Natural frequency/damping coefficient relationship of the catheter-manometer system required for high-fidelity measurement of the pulmonary arterial pressure.

Using a digital simulation method, we analyzed the relationship between natural frequency (fn) and damping coefficient (Zeta) of the catheter-manometer system required for high-fidelity measurement of the pulmonary arterial pressure. The pulmonary artery pressure waveform was obtained with a catheter-tip transducer and it was fed into a dynamic simulator programmed on a computer. The original waveform and the output of the simulator were compared and judged visually for the fidelity. From this analysis, the combination of fn and Zeta was obtained and was plotted on a fn-Zeta diagram. It showed as an area, which was convex on the left side and open on the right side. The left-convex endpoint was located at a damping coefficient of about 0.7. At a lower heart rate, this area was extended to the lower frequency side, while, at a higher heart rate, this area was limited to the higher frequency side. The fn-Zeta diagram was also constructed theoretically by calculating the relations between natural frequencies and damping coefficients of a second order system with the amplitude and phase error tolerance set at +/-5% respectively.

Effects of inhalation anesthetics on airway dynamics determined by phasor analysis of respiratory impedance using the forced oscillation method.

By expressing the respiratory system as a two-compartment model and assigning a phasor in the complex plane to each impedance element in the model, the phasor of the respiratory impedance could be constructed graphically, the frequency characteristics determined from the locus of the latter and the effects of variations in the model elements on the frequency characteristics could also be expressed as the locus of the latter. Conversely, it is possible to detect small changes in mechanical properties on the respiratory system by plotting its frequency characteristics on the complex plane. We studied the effects of typical inhalation anesthetics, halothane, enflurane and isoflurane, on the airway dynamics by this method. The inhalation concentration of 1 MAC of halothane and/or enflurane was found to produce bronchodilation associated with a significant reduction in airway resistance, but isoflurane had no such effects. As the magnitude of changes in the real part at 1 Hz, the estimated airway resistance was -2.1 cmH2O/1/s (-25% of the mean value) for halothane, and -0.8 cmH2O/1/s (-11%) for enflurane.

Intraoperative EEG monitoring: (I). Parametric representation of processed EEG during anesthesia.

One of the most common techniques of EEG monitoring during operations is to produce a three dimensional image by displaying the frequency distributions with respect to time as in compressed spectral array (CSA) and density-modulated spectral array (DSA). In order to characterize these images by numerical parameters, we defined two parameters; the percent spectral edge frequency as the frequency at which the one-sided-power sum reaches the designated percentage of the total; and the mean frequency as the power-weighted mean within the interval that includes a dominant spectrum in the frequency distribution. These parameters were superimposed on displays to characterize EEG changes, and they proved to be a very powerful tool to quantitate variations in data among anesthetic techniques and thus efficiently control the depth and duration of anesthesia. We report a number of actual cases.

Intraoperative EEG monitoring: (II). Similarity analysis using density-modulated t array.

A method of showing the similarity, in other words, defining the difference between a pair of EEG patterns has been developed. By using the student t test on the power spectra at the appropriate frequency intervals, the t values obtained can be used as an indicator of the difference between the spectral patterns with respect to the frequency intervals. This so-called t-profile can be computed on real time basis and the result superimposed in different colors using the apparatus described previously to produce a 3-dimensional picture. We call this picture a density-modulated t array or DTA. Along with CSA and DSA (compressed/density-modulated spectral arrays), it proved to be a very powerful tool in intraoperative EEG monitoring.

Parameter estimation of respiratory impedance measured by forced complex-wave oscillations.

Respiratory impedance data measured using the forced oscillation method were analyzed using an equivalent circuit model and the following conclusions were obtained: 1) Use of the complex wave oscillation method provided a measurement range of over 9 cmH2O/1/s with a resolution of 0.13 cmH2O/1/s. 2) The respiratory system was expressed as a two-compartment model. By expressing the circuit characteristics as phasor loci, a method was shown whereby individual impedance parameter values could be derived from the measured impedance phasor loci. 3) Under enflurane anesthesia, the model parameter values were derived as R1 = 1.2, R2 = 1.6 cmH2O/1/s, C1 = 0.02, C2 = 0.041/cmH2O and L = 0.065 cmH2O/1/s2.