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).

Comparison of two methods of postoperative respiratory care

After abdominal surgery, 64 patients were managed with one of the following two techniques of respiratory care: (1) deep breathing by way of a new device, an incentive spirometric three-ball, flow-measuring device (Triflo); and (2) standard episodic intermittent positive-pressure breathing (IPPB) every four hours. Both series of patients received therapy with a bronchodilator drug by nebulization. All patients had preoperative spirometric measurements followed by five consecutive days of therapy and spirometry. Chest x-ray films were obtained for all patients. There were no significant differences between the two methods of respiratory care, but 57 percent (17/30) in the group receiving therapy with IPPB developed pneumonia, atelectasis, or bronchitis, while only 29 percent (10/34) did so in the group using the incentive spirometric device (P less than 0.05). Spirometric differences were minimal, although the trend favored the incentive spirometric device. Principal conclusions were as follows: (1) deep breathing under the conditions of this investigation was equal to episodic therapy with IPPB; and (2) from an economic standpoint, IPPB, as it is currently practiced, may be disadvantageous when compared with the incentive spirometric device.