Takesuke Muteki

Local Anesthetics Depress the Calcium Current of Rat Sensory Neurons in Culture

BackgroundLocal anesthetics are known to inhibit the voltage-gated sodium current (INa) of the nerve membrane, but it has not been fully studied whether anesthetic concentrations of local anesthetics depress the voltage-gated calcium current (Ica) of mammalian neurons. The effects of local anesthetics on Ica, evoked in cultured rat dorsal root ganglion cells were studied. MethodsWhole cell patch clamp recordings were made from rat dorsal root ganglion cells cultured for 1–3 weeks. Ica, was recorded using patch electrodes filled with Cs-aspartate in Na+-free external solution containing 5 mM-Ba2+. All drugs, including local anesthetics, were applied by miniperfuslon from micropipettes by pressure ejection. ResultsTetracaine (300 μM) depressed the peak amplitudes of high voltage-activated (HVA)-Ica to 22.6 ± 8.8% of control values (n = 14) without affecting the current-voltage relation. A tetracaine dose-response curve for HVA-ICa Indicated an apparent dissociation constant of 79.5 μM. Tetracaine (30 μM) depressed nicardlpine-sensltive HVA-ICA (L-type) to 14.3 ± 6.7% (n = 6), β-conotoxin-sensitive HVA-Ica, (N-type) to 81.6 ± 9.6% (n = 7), and low voltage-activated (LVA)-Ica, (T-type) to 65.1 ± 11.1% (n = 6) of their respective controls. Local anesthetics other than tetracaine also depressed HVA-Ica but were of different potency; the rank sequence was dibucaine > tetracaine > bupivacaine > procaine = lidocaine. ConclusionsThese results suggest that both HVA-Ica and LVA-Ica, are depressed by tetracaine used at the concentrations required for spinal anesthesia and that the L-type Ca2+ channel among Ca2+ channel subtypes is the most susceptible to tetracaine. A good correlation between local anesthetic potencies to inhibit HVA-Ica, and their anesthetic potencies implies that the inhibition of calcium influx through voltage-gated channels may contribute to spinal anesthetic mechanisms.

Hemodynamic relationship between renal venous pressure and blood flow regulation during positive end-expiratory pressure.

The hemodynamic relationship between renal venous pressure (RVP) and renal blood flow (RBF) during PEEP was investigated using adult mongrel dogs. When continuous mechanical ventilation (CMV) with 10 cm H2O of PEEP was applied to dogs previously on CMV with zero PEEP, RVP increased from 6.6 to 8.7 mm Hg (p less than .01), and left RBF decreased from 66 to 57 ml/min (p less than .05). RBF recovered by 49% of the difference as soon as PEEP was discontinued when the RVP elevation was maintained at the level observed during 10 cm H2O of PEEP. With 20 cm H2O of PEEP, RVP increased further to 10 mm Hg (p less than .01) and left RBF decreased to 48 ml/min (p less than .05). When the left renal vein was occluded and the RVP was maintained at the level seen during 20 cm H2O of PEEP, left RBF recovered only 50% of the difference from the flow during zero PEEP. We conclude that the reduction in RBF with PEEP application is caused by several factors; however, RVP elevation during CMV with PEEP is influential in decreasing RBF.

Fibre-optic ECG monitoring instrument for use in the operating room

When the ESU is activated, the ECG monitor is exposed to interference generated by the ESU. We analysed this situation to find which of the three possible noise path combinations contributes the most to the noise problem. We showed that the monitoring device should be isolated from both the earth and the AC power line at electrosurgical high frequencies to reduce interference. We therefore propose a fibre-optic ECG monitoring instrument which is ideal for the operating room where high noise performance and excellent electrical safety are indispensable.

Effect of conventional mechanical ventilation and jet ventilation on airway pressure in dogs and plastic models with tracheal stenosis.

OBJECTIVE To evaluate the effect of jet ventilation on tracheal stenosis in dogs and plastic models. DESIGN Prospective, randomized trial in dogs, and multitrial tests in tracheal stenosis models. SETTING Animal laboratory in a university setting. INTERVENTIONS Tracheal stenosis was surgically created around the middle of the trachea. Conventional mechanical ventilation and jet ventilation were compared at the same value of Paco2 in dogs and at the same tidal volume in tracheal stenosis models. SUBJECTS Twelve mongrel dogs and four types of plastic models with combinations of short or long stenosis and fluid or nonfluid stenosis. MEASUREMENTS AND MAIN RESULTS Canine Studies. Mean peak peak airway pressure values at the distal and proximal portion of the stenosis, and the end-expiratory pressure at the distal portion of the stenosis, were significantly higher during conventional mechanical ventilation than during jet ventilation. The mean values of arterial pressure, pulmonary arterial pressure, central venous pressure, and cardiac output did not change significantly between conventional mechanical ventilation and jet ventilation, except for the pulmonary artery occlusion pressure valve. Plastic Mold Studies. peak airway pressure and end-expiratory airway pressure at the poststenotic trachea during jet ventilation with the model lung were significantly lower than during conventional mechanical ventilation. The difference in peak airway pressure, and end-expiratory airway pressure values between jet ventilation and conventional mechanical ventilation increased more in short stenosis and nonfluid stenosis. CONCLUSIONS The jet flow that struck the portion of the stenosed wall reversed direction, even during early expiration. Therefore, the expiration during jet ventilation was facilitated more by the reversed flow than by the expiration during conventional mechanical ventilation. This reversed flow may provide lower end-expiratory airway pressure at the poststenotic portion with jet ventilation than with conventional mechanical ventilation. We conclude that jet ventilation was a useful method of ventilation in cases with tracheal stenosis, especially nonfluid and short stenosis.

Clinical significance of mean circulatory filling pressure and cardiac preload under anesthesia

The circulatory effects of a rapid infusion of plasma substitute with intravenous administration of nitroglycerine (TNG) were investigated in low pressure systems of anesthetized patients by measuring various hemodynamic parameters. Measurements were made when the systolic blood pressure reached 70–80% of the control value after intravenous administration of TNG at 1≈2μg/kg/min and a 3.5% modified gelatin solution (Haernaccel®) at a rate of 0.5 ml/kg/min. After the TNG was administered, the mean circulatory filling pressure (Pms) decreased, and the venous to arterial capacitance ratio (Cv/CA) increased; however, they returned to control values after a rapid Haemaccel® infusion. Changes in the pressure gradient between the X and Y valley of the right atrial pressure wave decreased to 70 ± 14% of the control value when TNG was given and recovered to 106 ± 22% by infusion. Pulmonary vascular resistance (PVR) decreased to 70 ± 24% of the control value when TNG was administered and was restored to 96 ± 40% by a rapid infusion. In the left ventricle, the mean velocity of myocardial circumferential fiber shortening (VCF) decreased in all cases when TNG was given and it recovered by a rapid infusion. In the right ventricle, VCF did not always decrease, and in a few case increased, but all cases recovered by a Haemaccel® rapid infusion. We conclude that the augmentation of the right ventricular preload reserve is achieved by administration of TNG and infusion of a plasma substitute.

Dose-response relation and time course of

The dose-response relation of pipecuronium, the time course of its neuromuscular blocking effects, and the reversibility of the residual block by neostigmine have been investigated in patients under sevofluraney N2O Anesthesia using a neuromuscular transmission analyzer (Accelograph®, Biometer, Denmark). After an initial dose of pipecuronium (0.04 mg·kg−1, i.v., the maximum block rate, onset time, the time from administration until 25% recovery and 50% recovery of control twitch height of the first response to train-of-four nerve stimulation and the interval time of administration of maintenance dose (0.005 mg·kg−1, i.v.) were 93.7±7.68%, 5.0±1.84, 55.4 ±23.92,73.0±29.44 and 38.7±15.50 minutes, respectively. The average intubation score (excellent; 0, good; 1 fair; 2, poor; 3) was 0.63±0.56 at the level of 95.88±5.06% block. Neostigmine (1.5 mg) promptly reversed the residual neuromuscular blockade induced by pipecuronium (reversal time: 10.1±2.98 minutes). No side effects attributable to pipecuronium was seen in this study.In conclusion, pipecuronium is a very useful nondepolarizing neuromuscular blocking agent especially for moderately long surgical procedure over 4–5 hours.

Accelerated reversal of pancuronium blockade with divided administration of neostigmine

During the recovery from anesthesia, neostigmine is often administered to reverse the effects of nondepolarizing blocking agents. In our department, it has been a rule to administer the reversal drugs as slowly as p.ossible in order to avoid a vagotonic effect on the cardiovascular systems. According to Payne et aI., the neostigmine itself might have neuromuscular blocking properties depending upon the methods of administration. To date there have been very few studies on such methods and the ideal one has not yet been found. The present study was designed to evaluate the rate of recovery of the Train-of-Four (TOF) ratio after administration of neostigmine by either a one slow bolus injection or a divided injection.

Clinical Assessment of a New Neuromuscular Monitoring System: TOF Guard® — A Comparison with the Conventional Method

TOF Guard® is one of the latest developments in the field of neuromuscular monitoring equipment. This system uses a miniature acceleration transducer (a piezo-electric ceramic wafer is used), simply fastened to the thumb with tape. The rational behind the method is Newton’s second law, stating that the acceleration is directly proportional to the force. This study was designed to the accuracy of this system in clinical use, comparing with the force transducer method (mechanomyograph).

Clinical assessment of oxygen delivery and consumption during hypotensive anaesthesia - A clinical application of The Deep Picture™

Usual evaluation of the relationship between oxygen delivery (DO2) and oxygen uptake (VO2) is based on the arterial oxygen tension (pO2), oxygen saturation (sO2), haemoglobin concentration (ctHb), the same indicators in mixed venous blood and cardiac output, sometimes supplemented by the expiratory carbon dioxide concentration. And, so far, the relationship among DO2, VO2 and the new parameters for an evaluation of oxygen status (oxygen extraction tension: pK, concentration of extractable oxygen: cx, oxygen compensation factor: Qx) (1) has not been discussed enough.

NEW APPROACH TO CENTRAL VENOUS PRESSURE MONITORING

Precise measurement of the CVP waveforms has to provide a more sensitive tool in monitoring central hemodynamic status.