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 X min-1 X mm Hg-1 (mean +/- SD) before and 2.32 +/- 0.82 L X min-1 X mm Hg-1 after the block. Resting HR and AP decreased significantly (P less than 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.

Baroreflex function in a patient with Bartter's syndrome

There is little information regarding circulatory responses in Bartter's syndrome, with the exception of marked resistance to vasopressors. We investigated baroreflex function in a 40-year-old woman with this syndrome. The patient showed oscillation of heart rate even with a small increase in blood pressure after administration of vasopressor agents. Variations in heart rate and blood pressure were exaggerated during halothane, nitrous oxide and oxygen anaesthesia. Although the mechanism of the unstable baroreflex in this syndrome remains to be proved, the instability may be attributable to many factors such as prostaglandins, hypovolemia, hypokalemia, halothane, nitrous oxide and positive pressure ventilation.

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 X mmHg-1 before the blockade and 17.2 +/- 6.3 ms X mmHg-1 after the blockade (P less than 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 less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of ketamine in humans with cervical or lumbar epidural blockade

To examine the effect of sympathectomy induced by epidural blockade on the cardiovascular effects of ketamine anesthesia, the authors compared the changes in arterial blood pressure (AP) and heart rate (HR) following intravenous administration of ketamine in patients who had cervical epidural anesthesia (n = 18), lumbar epidural anesthesia (n = 16), or light general anesthesia alone (n = 16). Ketamine, 2 mg/kg, iv, produced statistically significant increases in both AP and HR in all patients studied. However, the per cent increases in systolic AP in the cervical group were statistically less than those in the lumbar epidural group and control groups (P less than 0.05), which did not significantly differ from each other. The changes in HR following ketamine in the cervical group were significantly less than those in the other two groups (at 3-10 min following ketamine) (P less than 0.05). These results indicate that the cardiovascular stimulatory effects of ketamine are suppressed partially by a high level of epidural anesthesia but not by a low level of epidural blockade. Since patients with cervical epidural anesthesia had an analgesic level extending between C4 and Th8, the above attenuative effects of epidural blockade may be considered to be attributable to cardiac sympathectomy induced by a high level of epidural anesthesia.

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 X 100 g-1 X min-1 and 53.1 +/- 12.0 ml X 100 g-1 X 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 greater than 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 less than 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.

[Mechanism of morphine-induced suppression of central nervous system blood flow]

Narcotic agonists such as morphine are well known to decrease cerebral blood flow and metabolism. To investigate a possible mechanism for this action of narcotics, cerebral blood flow (CBF) and spinal cord blood flow (SCBF) were simultaneously measured by the hydrogen clearance technique following intravenous or subarachnoid administration of morphine and subsequent naloxone in lightly anesthetized dogs. The effects of new opiate agonist + antagonists, cyclazocine and buprenorphine, alone or in a combination with naloxone on those CNS blood flow were also investigated. Morphine, 1 mg/kg iv, produced significant decreases in both CBF and SCBF (p less than 0.01), which were reversed by naloxone, 40 micrograms/kg. Naloxone per se did not produce any change in both. Cyclazocine, 50 micrograms/kg iv, also produced significant decreases in both CBF and SCBF (p less than 0.05), but the decreased CBF was not reversed by naloxone. Buprenorphine, 30 micrograms/kg, showed variable changes in both CBF and SCBF, resulted insignificant reduction. However, spinal subarachnoid administration of morphine, 0.2 mg, with which profound analgesia can be obtained in human adults, did not cause any changes in SCBF as well as CBF. These results suggest that narcotic analgesics affect SCBF similar to CBF and morphine decreases CNS blood flow via the activation of supraspinal opiate receptors.