Reiko Takeshima

Circulatory responses to baroreflexes, Valsalva maneuver, coughing, swallowing, and nasal stimulation during acute cardiac sympathectomy by epidural blockade in awake humans

Reflex circulatory responses are chiefly governed by the integrated functions of both sympathetic and parasympathetic nervous systems at any moment. To examine how sympathetic denervation of the important effector organ, the heart, modifies such reflex responses, the authors compared circulatory responses to arterial baroreflexes, the Valsalva maneuver (VM), coughing (C), swallowing (S), and nasal stimulation (NS) before and after cervical epidural blockade using 10 ml of 1.5% lidocaine in awake, healthy humans.The cervico-thoracic sympathetic denervation (sensory block of C4-T7) caused a slight suppression of the baroreflex sensitivity assessed by increases in RR intervals to increased systolic blood pressure with a pressor test (phenylephrine) in all eight subjects studied; the mean slopes of the regression lines were 29.1 ± 9.8 ms · mmHg−1 before the blockade and 17.2 ± 6.3 ms · mmHg−1 after the blockade (P < 0.05). However, the baroreflex sensitivity to a depressor test (nitroglycerin) remained unchanged following the blockade. Furthermore, the responses in heart rate and blood pressure to VM (Phases II and IV) and the responses in heart rate to C, S, and NS were partially suppressed after the blockade (P < 0.05). Despite these suppressions, the overall responses to VM, C, S, and NS remained unchanged after the blockade. No predominant parasympathetic responses such as profound hypotension and bradycardia were observed during any maneuver after the blockade.Since the vagus nerves were kept intact, these results indicate that acute sympathetic denervation of the central organs appears to preserve reflex circulatory responses to physical maneuvers such as producing high intrathoracic pressure, moderate changes in blood pressure or swallowing, though with some suppression of the cardiac acceleratory response. The results suggest that sympathetic control of heart rate functions as an inhibitor of the vagus rather than an active cardiac accelerator.

Comparison of arterial baroreflex function in humans anesthetized with enflurane or isoflurane.

To compare the depressive effects of isoflurane and enflurane on the arterial baroreflex function, we examined baroreflex control of heart rate during the entire course of clinical anesthesia. Isoflurane and enflurane were found to have similar depressive effects on the baroreflex control of heart rate when used in combination with N2O and O2. Suppression in the baroreflex sensitivity, defined by the slopes of regression line (change in msec of RR interval per mm Hg increase or decrease in systolic blood pressure) was from 7.1 ± 3.9 to 1.8 ± 0.7 msec/mm Hg in patients given isoflurane and from 7.8 ± 4.3 to 3.0 ± 1.9 msec/mm Hg in those given enflurane when evaluated by a pressor test (bolus IV phenylephrine), The slope of the depressor test (bolus IV nitroglycerin) also decreased from 4.7 ± 2.8 to 1.9 ± 1.5 msec/mm Hg with isoflurane and from 5.6 ± 3.2 to 2.3 ± 1.2 msec/mm Hg with enflurane. During surgery in which anesthetic concentration invariably needed to be increased, the suppression of the baroreflex sensitivity remained unchanged in both groups of patients. During recovery, the arterial baroreflex function in patients given isoflurane recovered more rapidly than that in patients given enflurane. This difference may be related to a more minor degree of suppression of isoflurane on the autonomic nervous system compared to enflurane.

The Effects of Subarachnoid Lidocaine and Phenylephrine on Spinal Cord and Cerebral Blood Flow in Dogs

To investigate the central nervous system circulation during spinal anesthesia, local spinal cord blood flow (SCBF) and cerebral blood flow (CBF) were measured simultaneously by the hydrogen clearance technique following subarachnoid lidocaine, phenylephrine, or a combination of both. The mean control values of SCBF and CBF were 22.4 ± 7.9 ml.100 g−1·min−1 and 53.1 ± 12.0 ml·100 g−1·min−1, respectively, in dogs lightly anesthetized with halothane.The subarachnoid administration of lidocaine solutions (1, 2, 3, and 5%), 1 ml, failed to produce statistically significant changes in SCBF (P > 0.05). Whereas, when phenylephrine (0.1, 0.2, 0.3, and 0.5%), 1 ml, was injected into the spinal subarachnoid space, SCBF decreased significantly with concentrations greater than 0.2% (P < 0.05). When a mixture of lidocaine (24 mg) and phenylephrine (1 mg) was administered into the subarachnoid space, SCBF decreased significantly and returned to control within 60–90 min. CBF did not change significantly with any of the injections, remaining within less than ±12% of control. Dextrose solutions in water (5 and 7.5%), which were used for dilution of the drugs, did not affect either SCBF or CBF. These results indicate that local spinal cord blood flow can be affected significantly during spinal anesthesia when phenylephrine is added to the local anesthetic solution. However, the circulatory effects of drugs injected into the spinal subarachnoid space appear to be restricted to the local spinal cord per se and do not involve other parts of the CNS.

Spinal cord blood flow during spinal anesthesia in dogs: the effects of tetracaine, epinephrine, acute blood loss, and hypercapnia

To examine the effects of subarachnoid tetracaine and epinephrine on spinal cord blood flow (SCBF), lumbar SCBF and cerebral blood flow (CBF) were measured simultaneously by the hydrogen clearance technique in dogs (n = 45) anesthetized with halothane. The lumbar subarachnoid administration of tetracaine, 5 mg dissolved in 1 ml of a 7.5% dextrose solution had no significant effect on either SCBF or CBF for 4 hr even though arterial blood pressure and heart rate decreased significantly. After subarachnoid epinephrine alone (100, 300, and 500 micrograms), SCBF varied widely but did not change significantly with any of the injections, nor did CBF. Responses of SCBF to hypercapnia and to acute blood loss during spinal anesthesia with tetracaine were also examined. Increased PaCO2 (from 35 to 57 mm Hg) increased both SCBF and CBF similarly before and after subarachnoid tetracaine; SCBF increased from 26.8 +/- 9.0 ml X 100 g-1 X min-1 (mean +/- SD) before to 34.2 +/- 13.6 ml X 100 g-1 X min-1 during hypercapnia during spinal anesthesia, which was almost identical to the increase (from 31.5 +/- 8.1 ml X 100 g-1 X min-1 to 39.9 +/- 6.0 ml X 100 g-1 X min-1) before spinal anesthesia. Whereas acute blood loss (approximately 20% of estimated blood volume) during spinal anesthesia with tetracaine caused a 23% reduction of SCBF (P less than 0.05), in the absence of tetracaine SCBF remained unchanged during hemorrhagic hypovolemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventilatory and Circulatory Responses to Carbon Dioxide and High Level Sympathectomy Induced by Epidural Blockade in Awake Humans

In order to examine the effects of cervico-thoracic epidural block with 1.5% lidocaine on Ventilatory and circulatory responses to carbon dioxide, the authors studied the CO2-ventilatory response curves and the changes in heart rate (HR) and blood pressure (AP) to rebreathing of exhaled gas before and after the block in healthy volunteers. Neither resting ventilation nor ventilatory response to CO2 was affected by the epidural block (mean analgesic level extended from C4 to T7); the slope of the CO2-ventilatory response curve averaged 2.38 ± 0.81 L·min-1·mm Hg-1 (mean ± SD) before and 2.32 ± 0.82 L·min-1·mm Hg-1 after the block. Resting HR and AP decreased significantly (P < 0.01) after the block, but responses in HR and AP to CO2 rebreathing were not significantly changed by the block. Plasma concentrations of norepinephrine and epinephrine were similar before and after the block both with and without CO2 rebreathing. These results indicate that high levels of sympathetic denervation induced by epidural block do not impair circulatory and ventilatory responses to carbon dioxide in awake, healthy humans.

Determination of the distance between the laryngoscope blade and the upper incisors during direct laryngoscopy : comparisons of a curved, an angulated straight, and two straight blades

We compared visibility and dental complications from a variety of blades during tracheal intubation. Ninety-eight patients who received tracheal intubation were enrolled. They were divided into two groups: Study 1 (n = 50) and Study 2 (n = 48). Four laryngoscopic evaluations were planned for each patient using Miller and Wisconsin straight blades with different heel heights, a Macintosh curved blade, and a Belscope angulated straight blade (Study 1: Miller No. 3, Wisconsin No. 3, Macintosh No. 4, and Belscope medium; and Study 2 Miller No. 2, Wisconsin No. 2, Macintosh No. 3, and Belscope medium, respectively). All laryngoscopies were performed by the same anesthesiologist. The distance between the blade and the upper central incisors was measured when the optimum visibility of the glottis was obtained. The visibility was determined according to the Cormack and Lehane grading. Analysis of the distance between the blade and upper incisors was performed using the results of the 44 patients (166 distances) in Study 1 and the 48 patients (181 distances) in Study 2 who had a visibility of two or better. The Belscope blade provided a significantly greater visual field than the other types of blade. Two patients sustained a fracture of the central incisor and subluxation of the central incisor, respectively, during laryngoscopy in which a Wisconsin blade was used. The average incidence of dental injury was 1/191. The Belscope blade may contribute to a reduced likelihood of upper dental injuries during laryngoscopy.

The effect of age on retrieval of local anesthetic solution from the epidural space.

We conducted this prospective study to determine whether advancing age is correlated with retrieval of local anesthetic solution from the epidural space.Three hundred forty-six patients (ASA physical status I or II, 20-93 yr of age, 177 female and 169 male patients) undergoing epidural anesthesia were enrolled. The epidural space was identified by a loss of resistance technique using air, and a catheter was introduced 3 cm. Three milliliters of 2% lidocaine with epinephrine was injected as a study dose by hand at a rate of 1 mL/s with the patient in the supine position. The syringe was immediately aspirated to retrieve the local anesthetic solution. A retrieved volume of 0.5 mL or more with a glucose concentration less than 6 mg/dL was defined as retrieval positive, and a volume of less than 0.5 mL was defined as retrieval negative. There was a significant correlation between age and retrieval volume among all the patients (Y = 0.008X-0.222, P < 0.0001) with a significant increase in the positive retrieval incidence and volume from the patients in their 50s (11%, 0.6 +/- 0.3 mL) to the patients in their 60s (26%, 1.0 +/- 0.6 mL) (P < 0.05 for both). The incidence of positive retrieval and the retrieval volume were greater in the patients in their 60s and older (30%, 1.1 +/- 0.63 mL) than in the younger than 60 (10%, 0.6 +/- 0.3 mL) (P < 0.0001 and P < 0.001). The glucose concentration was 2.3 +/- 1.2 mg/dL in the positive cases. We conclude that there is a weak positive correlation between age and the local anesthetic solution retrieved from the epidural space. Implications: We conducted a study in 346 patients to determine whether advancing age could be correlated with retrieval of local anesthetic solution from the epidural space. We found a weak positive correlation between advanced age and the amount of solution retrievable from the epidural space. Further studies are required to determine whether this phenomenon may call for dose adjustments in patients aged more than 60 yr. (Anesth Analg 1997;85:1091-6)