Baroreflex control of heart rate during cardiac sympathectomy by epidural anesthesia in lightly anesthetized humans

To evaluate the effects of acute sympathetic denervation on the baroreflex control of heart rate, baroreflex sensitivities were compared in lightly anesthetized humans who had either cervical (N = 20) or lumbar epidural anesthesia (N = 18), or neither (N = 18). Levels of anesthesia during cervical block using 10 ml of 2% mepivacaine without epinephrine were C3-T7 and T7-S1 during lumbar epidural block. Baroreflex sensitivity was assessed with a pressor test using phenylephrine infusion to increase systolic blood pressure by 60 mm Hg within 2 min. There were no statistically significant differences in the baroreflex sensitivities in the absence of epidural block and during lumbar epidural block, the slopes of the regression line (in msec of RR interval change per mm Hg increase in systolic blood pressure, i.e., msec/mm Hg) relating systolic pressure and the succeeding pulse interval being 3.8 +/- 1.4 (mean +/- SD) and 3.7 +/- 1.7, respectively. The mean slope during cervical block, 1.1 +/- 1.2 msec/mm Hg, was significantly different from the slopes observed in the absence of epidural block and during lumbar epidural block (P less than 0.01). The results suggest that cardiac sympathectomy induced by epidural anesthesia can suppress partially baroreceptor function by interrupting sympathetic efferent fibers innervating the heart during high levels of epidural anesthesia, but that lumbar sympathectomy during epidural anesthesia is unlikely to affect baroreceptor activity.

Effects of intravenous or subarachnoid morphine on cerebral and spinal cord hemodynamics and antagonism with naloxone in dogs

In order to elucidate the possible mechanism(s) by which opiates may affect cerebral and spinal circulation, and cerebral metabolism, cerebral blood flow (CBF) and spinal cord blood flow (SCBF) were measured simultaneously following intravenous or subarachnoid administration of morphine in dogs lightly anesthetized with halothane. The mean values of CBF and SCBF, using hydrogen clearance methods, were 52.3 +/- 14.7 ml . 100 g-1 . min-1 (mean +/- 1 SD) and 22.3 +/- 9.0 ml . 100 g-1 . min-1, respectively. Morphine hydrochloride, 1 mg/kg, when given intravenously, reduced both CBF and SCBF to approximately 73% of the control values (P less than 0.01). These changes were accompanied by decreases in the cerebral metabolic rates for oxygen (CMRO2) and glucose (CMRglucose). The circulatory effects and, in part, the metabolic effects, were reversed by naloxone 40 microgram/kg iv. Prior administration of naloxone blocked the morphine effects on CBF and SCBF and suppressed the effects on CMRO2 and CMRglucose. The decreases in blood pressure (MAP) and heart rate (HR) were similar following morphine iv with or without prior administration of naloxone. However, when 0.2 mg morphine was injected into the spinal subarachnoid space, the above variables remained unaffected. Neither naloxone alone, nor its subsequent intravenous administration following spinal morphine, affected cerebral and spinal circulatory or cerebral metabolic indices. These results indicate that intravenous morphine affects both cerebral and spinal cord blood flow via the opiate receptors at supraspinal sites of action.

Plasma concentrations of lidocaine associated with cervical, thoracic, and lumbar epidural anesthesia

We measured arterial plasma concentrations of lidocaine by enzyme immunoassay when 10 ml of 2% lidocaine without epinephrine was injected into the cervical, thoracic, or lumbar epidural spaces in 30 patients. There was no difference in the time courses of plasma levels of lidocaine. Peak concentrations were achieved 10 min after injection and were similar regardless of the site of injection. These results indicate the absence of significant differences in the rate of vascular absorption of lidocaine from different parts of the epidural space.

Postcardiopulmonary resuscitation pulmonary edema

Although severe pulmonary edema is encountered occasionally in patients needing CPR, there has been no definitive description on the mortality and morbidity of pulmonary edema after CPR. The author experienced severe pulmonary edema after standard CPR in 20 of 71 patients who suffered sudden, unexpected cardiac arrest and regained heart function by CPR. The varied onset of pulmonary edema, which may have developed when massive pink frothy secretions exited from the endotracheal tube, ranged from a few minutes to 45 min after the re-establishment of heart beat. These 20 patients showed a significantly higher P(A-a)O2, insignificant lower plasma protein concentrations, and high plasma osmolarities as compared with those who did not develop pulmonary edema. Only 2 patients with pulmonary edema survived. During CPR, many factors could cause pulmonary edema, including external cardiac massage (ECM), administration or release of catecholamines, hypoxia, acidosis, overhydration, etc. This study indicates that patients who need CPR have a high likelihood of developing pulmonary edema.

Hemifacial spasm: a new technique of facial nerve blockade

A new technique of facial nerve blockade using a special needle and a nerve stimulator was introduced. The results in patients suffering from hemifacial spasm are reported. This technique reduced the difficulties in identifying the facial nerve and decreased the suffering associated with the conventional way of creating these blocks. The technique described may also allow titration of neurolytic agent which may produce complete relief from spasm with much less likelihood of facial paralysis after the nerve blockade.

Circulatory responses to airway stimulation and cervical epidural blockade

In order to investigate the effects of acute cardiac sympathectomy, the circulatory responses due to tracheal intubation and broncho-carinal stimulation were compared in lightly anesthetized, paralyzed patients who had either cervical (n = 18) or lumbar epidural blockade (n = 18), or neither (n = 12). The mean analgesic levels obtained using 2% mepivacaine with epinephrine were C4-T8 in the cervical group, and T7-S1 in the lumbar group. Increases in arterial blood pressure (AP) and heart rate (HR) due to laryngoscopy were significant (P less than 0.01) but similar in the three groups of patients. Broncho-carinal stimulation by a suction catheter did not produce noticeable changes in AP and HR in the cervical group; significant increases were observed in the other two groups (P less than 0.01). It was concluded from this study that acute sympathectomy induced in part by cervical or lumbar epidural block does not attentuate circulatory responses due to laryngoscopy and tracheal intubation. The cervical blockade, however, can prevent such responses due to broncho-carinal stimulation without predominant vagotonic reflexes; this may be attributed to the interruption of sympathetic afferents to the spinal cord at the epidural level.

Effects of morphine sulfate on dorsal-horn neuronal responses to graded noxious thermal stimulation in the decerebrate cat

Effects of morphine sulfate upon activity of the neurons of dorsal-horn lamina V as evoked by graded noxious thermal stimuli applied on the receptive field were studied in spinal cord-transected, decerebrate cats utilizing an extracellular microelectrode recording technique. All single units studied (n = 30) responded to noxious thermal as well as to noxious mechanical stimulation. Their spontaneous discharge frequency was 9.7 +/- 1.5 (mean +/- 1 SE) impulses/sec (IPS), the threshold skin temperature was 44.8 +/- 0.2 C, and a linear correlation existed between skin temperature and discharge frequency at 6.7 +/- 0.6 IPS/degree C. Morphine, 1 and 2 mg/kg, iv, suppressed spontaneous activity by 53 +/- 6 and 84 +/- 6 per cent, respectively; increased threshold skin temperature to 46.5 +/- 0.3 and 47.9 +/- 0.5 C, respectively, and maintained the linear correlation between skin temperature and discharge frequency but depressed the mean slope of the regression line to 4.5 +/- 0.7 and to 2.4 +/- 0.4 IPS/degree C, respectively. Naloxone, 0.02--0.04 mg/kg, iv, reversed all of these changes produced by morphine. The results of the present study are, to the authors' knowledge, the first demonstration of the suppressive effect of morphine on the spinal nociceptive neurons in Rexed lamina V as they respond to graded noxious thermal stimuli. These results may explain the analgesic action of morphine at the spinal level.

Effects of ketamine on nociceptive cells in the medial medullary reticular formation of the cat

Anatomic, physiologic and behavioral evidence suggests that the neurons in the nucleus reticularis gigantocellularis of the medial medullary reticular formation may act as a relay station for the transmission of nociceptive information from the spinal cord to higher brain centers. The nucleus reticularis gigantocellularis may also be the site of action of analgesic agents, such as ketamine hydrochloride. Utilizing extracellular microelectrodes in 23 decerebrate cats, the authors measured the effect of ketamine on neurons in the nucleus reticularis gigantocellularis that were excited by electrical stimulation of peripheral nerves. The frequency of spontaneous single-unit firing activity in the nucleus reticularis gigantocellularis was suppressed by 31 +/- 11 (mean +/- 1 SE) and by 62 +/- 7 per cent with ketamine, 1.0 and 2.5 mg/kg, iv, respectively. The frequency of evoked single-unit activity was suppressed by 57 +/- 9 and 79 +/- 5 per cent with ketamine, 1.0 and 2.5 mg/kg, respectively. Ketamine produces significant depression of single-unit activity of the cells in the nucleus reticularis gigantocellularis, suggesting that this may be an important site of its analgesic action.

An analgesic action of intranvenously administered lidocaine on dorsal-horn neurons responding to noxious thermal stimulation

Using extracellular single-unit recording techniques, effects of intravenously administered lidocaine on dorsal-horn nociceptive neurons were studied in cats made decerebrate whose spinal cords had been transected. Thirty-seven neurons in Rexed lamina V responding to high-threshold mechanical and noxious thermal stimuli (radiant heat, using Hardy-Wolff-Goodell dolorimeter) were studied. Lidocaine hydrochloride, 2.5, 5, and 10 mg/kg, iv, produced dose-related suppression of both spontaneous activity and responses of these neurons to noxious thermal stimulation. Spontaneous discharge frequencies at maximum suppression, observed 3--7 min after administration of each of the three doses of lidocaine were 64 +/- 14 (mean +/- 1 SE), 32 +/- 8, and 25 +/- 9 per cent of control values, respectively; responses to noxious thermal stimuli were 83 +/- 5, 52 +/- 8, and 39 +/- 7 per cent of the control values, respectively. Threshold skin temperature to noxious thermal stimulation increased from 44.7 +/- 0.4 C (control) to 46.3 +/- 0.7 C with lidocaine, 5 mg/kg (P less than 0.05), to 47.8 +/- 0.8 C with lidocaine, 10 mg/kg (P less than 0.01). The times necessary for recovery varied in a dose-related fashion. Plasma lidocaine concentrations 5 min after lidocaine, 5 mg/kg, averaged 3.6 +/- 0.7 microgram/ml. These data support the clinical impression that intravenously administered lidocaine produces analgesia at plasma concentrations of 3--10 microgram/ml. It is suggested that lidocaine may block conduction of nociceptive impulses, at least in part, by suppression of spinal-cord nociceptive neurons.

Pulmonary mechanics during general anaesthesia. The influence of mechanical irritation on the airway

The changes in pulmonary resistance (RL) and compliance (CL), following airway irritation and surgical stimulation, were investigated in 19 anaesthetized, paralysed patients. Thirteen were normal, while six had objective evidence of chronic obstructive pulmonary disease (COPD). Broncho-carinal irritation with a suction catheter produced a 27% increase in RL (0.58+/-0.32kPa litre-1 s to 0.74+/-0.40, P less than 0.01) and a 10% decrease in CL (0.87+/-0.19 litre kPa-1 to 0.81+/-0.22, P less than 0.01). These changes were associated with a significant increase in systolic arterial pressure and heart rate during clinical stages of anaesthesia (end-tidal enflurane, 1.3+/-0.4%, PaCO2 5.20+/-0.53 kPa). These changes did not correlate with depth of anaesthesia, but all returned to the pre-irritation value within 5 min. There was no difference in subjects considered normal and those with COPD. Surgical stimulation did not produce significant changes in pulmonary mechanics; however, repeated broncho-carinal irritation during surgery was associated with a transient increase in RL (P less then 0.01).