Anesthesiology
-
Editorial Comment Review
Do low-dose inhalational anesthetic agents alter ventilatory control?
-
Normal thermoregulatory function is believed to be modulated by thermosensitive neurons in the preoptic region of the anterior hypothalamus and other sites within the central nervous system including the spinal cord. Previous evidence has demonstrated modulation of segmental spinal cord thermoregulatory mechanisms from more rostral central nervous system sites. The ability of the volatile anesthetics to disrupt normal thermoregulatory function and produce shivering-like activity during emergence is well documented. The purpose of the current investigation was to examine the action purpose of the current investigation was to examine the action of the volatile anesthetics halothane, isoflurane, and enflurane on thermoregulatory responses produced at the preoptic region and spinal cord. ⋯ The ability of preoptic region heating and cooling to modulate postanesthetic shivering implies that while thermoregulatory pathways remain intact, volatile anesthetics produce an imprecision in the control of thermoregulatory responses at the level of the anterior hypothalamus. Attenuation of shivering-like responses generated at spinal cord levels in pontine-transected cats implies a significant blunting action of thermoregulatory response mechanisms at the level of the spinal cord or lower brain stem.
-
Anesthetic doses of dexmedetomidine (DMED), a highly selective alpha 2 agonist, are not well tolerated hemodynamically. The combination of an opioid with DMED might reduce the dosage requirements for each drug and thereby allow the same anesthetic depth to be achieved with lesser degrees of their individual side effects. ⋯ There was a positive interaction, additive or synergistic, between DMED and fentanyl with respect to their enflurane-sparing effects. The interaction allowed the same depth of anesthesia to be achieved by lower doses of all three drugs, potentially limiting the intensity of their individual side effects. However, the presence of fentanyl increased the degree of bradycardia induced by DMED.
-
Combined spinal-epidural anesthesia is a technique growing in popularity. However, there have been no attempts to investigate the risk of epidural drug reaching the subarachnoid space in high concentration by passing through the meningeal hole left by the spinal needle. This study begins to address this question by quantitating the flux of morphine and lidocaine through the spinal meninges of the monkey in vitro after puncture with three different-sized needles. ⋯ Epidural anesthesia after accidental or intentional puncture of the spinal meninges has occasionally resulted in high spinal blocks and total spinal anesthesia. This study suggests that drug movement through the meningeal hole is responsible for this complication and that the risk may be decreased by using the smallest possible needle to puncture the meninges.
-
The peripheral chemoreceptors are responsible for the ventilatory response to hypoxia (acute hypoxic response) and for 30% of the normoxic hypercapnic ventilatory response. To quantify the effects of subanesthetic concentrations of halothane on the respiratory control system, in particular on the peripheral chemoreceptors, we studied the response of humans to carbon dioxide and oxygen at two subanesthetic concentrations of halothane. ⋯ The results show depression of the ventilatory responses to hypoxia and hypercapnia during inhalation of subanesthetic concentrations of halothane. The depression is attributed to a selective effect of halothane on the peripheral chemoreflex loop. The oxygen and carbon dioxide responses mediated by the peripheral chemoreceptors are affected proportionally. It is argued that the decrease in central time constants is caused by an effect of halothane on central neuronal dynamics.