Ketamine-induced peripheral analgesia in rats.
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AIM: To examine whether ketamine may directly act at peripheral nociceptors to produce analgesia. METHODS: Wistar rats were anesthetized with urethane. As a nociceptive flexion reflex (FR), C responses from the posterior biceps semitendinosus (PBST) muscle was evoked by electrical stimulation (2 ms, 80 V, 2-3 pulses, 0.5 Hz) via a pair of stainless steel needles inserted subcutaneously applied to the two toes of ipsilateral hindpw. RESULTS: Subcutaneous injection of ketamine (36 mmol.L-1, 5 microL) into the ipsilateral hindpaw produced an inhibition of C responses. At 9 min after application of ketamine, injection of naloxone (1%, 5 microL) into the same area annulled ketamine-induced inhibition. CONCLUSION: Ketamine as a dissociate anesthetic acts on peripheral nociceptors to produce analgesia, which is related to activity of peripheral opioid receptors. (+info)
Mechanisms of bronchoprotection by anesthetic induction agents: propofol versus ketamine.
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BACKGROUND: Propofol and ketamine have been purported to decrease bronchoconstriction during induction of anesthesia and intubation. Whether they act on airway smooth muscle or through neural reflexes has not been determined. We compared propofol and ketamine to attenuate the direct activation of airway smooth muscle by methacholine and limit neurally mediated bronchoconstriction (vagal nerve stimulation). METHODS: After approval from the institutional review board, eight sheep were anesthetized with pentobarbital, paralyzed, and ventilated. After left thoracotomy, the bronchial artery was cannulated and perfused. In random order, 5 mg/ml concentrations of propofol, ketamine, and thiopental were infused into the bronchial artery at rates of 0.06, 0.20, and 0.60 ml/min. After 10 min, airway resistance was measured before and after vagal nerve stimulation and methacholine given via the bronchial artery. Data were expressed as a percent of baseline response before infusion of drug and analyzed by analysis of variance with significance set at P< or =0.05. RESULTS: Systemic blood pressure was not affected by any of the drugs (P>0.46). Baseline airway resistance was not different among the three agents (P = 0.56) or by dose (P = 0.96). Infusion of propofol and ketamine into the bronchial artery caused a dose-dependent attenuation of the vagal nerve stimulation-induced bronchoconstriction to 26+/-11% and 8+/-2% of maximum, respectively (P<0.0001). In addition, propofol caused a significant decrease in the methacholine-induced bronchoconstriction to 43+/-27% of maximum at the highest concentration (P = 0.05) CONCLUSIONS: The local bronchoprotective effects of ketamine and propofol on airways is through neurally mediated mechanisms. Although the direct effects on airway smooth muscle occur at high concentrations, these are unlikely to be of primary clinical relevance. (+info)
Effect of i.v. ketamine in combination with epidural bupivacaine or epidural morphine on postoperative pain and wound tenderness after renal surgery.
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We studied 60 patients undergoing operation on the kidney with combined general and epidural anaesthesia, in a double-blind, randomized, controlled study. Patients were allocated to receive a preoperative bolus dose of ketamine 10 mg i.v., followed by an i.v. infusion of ketamine 10 mg h-1 for 48 h after operation, or placebo. During the first 24 h after surgery, all patients received 4 ml h-1 of epidural bupivacaine 2.5 mg ml-1. From 24 to 48 h after operation, patients received epidural morphine 0.2 mg h-1 preceded by a bolus dose of 2 mg. In addition, patient-controlled analgesia (PCA) with i.v. morphine (2.5 mg, lockout time 15 min) was offered from 0 to 48 h after operation. Patients who received ketamine felt significantly more sedated at 0-24 h, but not at 24-48 h after operation, compared with patients who received placebo (P = 0.002 and P = 0.127, respectively). There were no significant differences in pain (VAS) at rest, during mobilization or cough, PCA morphine consumption, sensory block to pinprick, pressure pain detection threshold assessed with an algometer, touch and pain detection thresholds assessed with von Frey hairs, peak flow or side effects other than sedation. The power of detecting a reduction in VAS scores of 20 mm in our study was 80% at the 5% significance level. We conclude that we were unable to demonstrate an (additive) analgesic or opioid sparing effect of ketamine 10 mg h-1 i.v. combined with epidural bupivacaine at 0-24 h, or epidural morphine at 24-48 h after renal surgery. (+info)
Impact of network activity on the integrative properties of neocortical pyramidal neurons in vivo.
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During wakefulness, neocortical neurons are subjected to an intense synaptic bombardment. To assess the consequences of this background activity for the integrative properties of pyramidal neurons, we constrained biophysical models with in vivo intracellular data obtained in anesthetized cats during periods of intense network activity similar to that observed in the waking state. In pyramidal cells of the parietal cortex (area 5-7), synaptic activity was responsible for an approximately fivefold decrease in input resistance (Rin), a more depolarized membrane potential (Vm), and a marked increase in the amplitude of Vm fluctuations, as determined by comparing the same cells before and after microperfusion of tetrodotoxin (TTX). The model was constrained by measurements of Rin, by the average value and standard deviation of the Vm measured from epochs of intense synaptic activity recorded with KAc or KCl-filled pipettes as well as the values measured in the same cells after TTX. To reproduce all experimental results, the simulated synaptic activity had to be of relatively high frequency (1-5 Hz) at excitatory and inhibitory synapses. In addition, synaptic inputs had to be significantly correlated (correlation coefficient approximately 0.1) to reproduce the amplitude of Vm fluctuations recorded experimentally. The presence of voltage-dependent K+ currents, estimated from current-voltage relations after TTX, affected these parameters by <10%. The model predicts that the conductance due to synaptic activity is 7-30 times larger than the somatic leak conductance to be consistent with the approximately fivefold change in Rin. The impact of this massive increase in conductance on dendritic attenuation was investigated for passive neurons and neurons with voltage-dependent Na+/K+ currents in soma and dendrites. In passive neurons, correlated synaptic bombardment had a major influence on dendritic attenuation. The electrotonic attenuation of simulated synaptic inputs was enhanced greatly in the presence of synaptic bombardment, with distal synapses having minimal effects at the soma. Similarly, in the presence of dendritic voltage-dependent currents, the convergence of hundreds of synaptic inputs was required to evoke action potentials reliably. In this case, however, dendritic voltage-dependent currents minimized the variability due to input location, with distal apical synapses being as effective as synapses on basal dendrites. In conclusion, this combination of intracellular and computational data suggests that, during low-amplitude fast electroencephalographic activity, neocortical neurons are bombarded continuously by correlated synaptic inputs at high frequency, which significantly affect their integrative properties. A series of predictions are suggested to test this model. (+info)
Haemodynamic stability and ketamine-alfentanil anaesthetic induction.
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We have determined if alfentanil could obtund the haemodynamic instability commonly seen at induction of anaesthesia with ketamine. Five groups of ASA I and II patients received ketamine 1 mg kg-1 i.v., preceded by saline (group 1) or alfentanil 10, 20, 30 or 40 micrograms kg-1 (groups 2-5, respectively). Heart rate (HR), mean arterial pressure (AP), postoperative patient complaints and dysphoria were noted. All groups showed increases (P < 0.05) in both HR and AP after administration of ketamine, which were progressively smaller as the dose of alfentanil increased. After tracheal intubation, all groups showed further increases in HR and AP, with groups 3-5 (alfentanil 20-40 micrograms kg-1) showing significant obtundation (P < 0.05) of these increases compared with group 1. No patient in any group reported postoperative dysphoria or dissatisfaction with their anaesthetic. Ketamine 1 mg kg-1 with alfentanil 20-40 micrograms kg-1 provided statistically significant obtundation of the haemodynamic instability that is common with ketamine alone. (+info)
Prolonged analgesic effect of ketamine, an N-methyl-D-aspartate receptor inhibitor, in patients with chronic pain.
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We examined the role of N-methyl-D-aspartate (NMDA) receptors in chronic (pathological) pain in humans by using the NMDA receptor antagonist ketamine as a probe. Thirty patients with neuropathic pain in the trigeminal area were given an i.m. injection of ketamine 0.4 mg/kg combined with midazolam 0.05 mg/kg. Pethidine 1.0 mg/kg served as a control. Three different response patterns were observed. Ketamine caused a long-term (6-24 h) analgesic effect partly dissociated from the mental side effects in 8 of the 26 patients who completed the study; these patients also had a slight analgesic effect of pethidine. In nine patients, ketamine caused a short-lasting (<2 h) analgesic effect closely associated with the mental side effects, whereas pethidine caused little or no analgesia. The remaining nine patients did not experience any reduction of pain after either drug in spite of characteristic side effects. One week after the i.m. challenge the patients received either 4.0 mg/kg ketamine hydrochloride or placebo capsules to be taken orally as a nightly dose for three consecutive nights. Five of the eight patients who had a long-term analgesic effect of the i.m. challenge reported decreased pain on days after ketamine. None of the others reported an analgesic effect. The phenomenon of long-term depression of pain in a subgroup of patients was thus confirmed when ketamine was given p.o. These findings indicate that NMDA receptors are involved in the perception and maintenance of pathological pain in some patients. In others, pain appears to be mediated by NMDA receptor-independent mechanisms. We suggest that NMDA receptor-independent transmission in central pain pathways may contribute to the reduced efficiency of analgesic drugs often seen in chronic pain states. (+info)
Acid-base disturbance during hemorrhage in rats: significant role of strong inorganic ions.
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The present study tests the hypothesis that changes in the strong inorganic ion concentrations contribute significantly to the acid-base disturbance that develops during hemorrhage in the arterial plasma of rats in addition to lactate concentration ([Lac-]) increase. The physicochemical origins for this acid-base disorder were studied during acute, graded hemorrhage (10, 20, and 30% loss of blood volume) in three groups of rats: conscious, anesthetized with ketamine, and anesthetized with urethan. The results support the hypothesis examined: strong-ion difference (SID) decreased in the arterial plasma of all groups studied because of an early imbalance in the main strong inorganic ions during initial hemorrhagic phase. Moreover, changes in plasma [Lac-] contributed to SID decrease in a later hemorrhagic phase (after 10% hemorrhage in urethan-anesthetized, after 20% hemorrhage in ketamine-anesthetized, and after 30% hemorrhage in conscious group). Inorganic ion changes were due to both dilution of the vascular compartment and ion exchange with extravascular space and red blood cells, as compensation for blood volume depletion and hypocapnia. Nevertheless, anesthetized rats were less able than conscious rats to preserve normal arterial pH during hemorrhage, mainly because of an impaired peripheral tissue condition and incomplete ventilatory compensation. (+info)
Actions of ketamine and its isomers on contractility and calcium transients in human myocardium.
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BACKGROUND: Ketamine has a species-dependent inotropic effect on myocardium. The authors' aim was to investigate the direct inotropic effect and the corresponding intracellular Ca2+ transients of ketamine and its isomers on human myocardium. METHODS: Right auricular myocardial strips obtained during open heart surgery were exposed to increasing concentrations (73 microM, 360 microM, and 730 microM) of racemic ketamine (n = 12), S(+)-ketamine (n = 12), or R(-)-ketamine (n = 11). Isometric force, isotonic shortening, contractility, relaxation, and time to maximal isotonic and isometric force were assessed. Ten muscle strips in each group were loaded with the calcium-sensitive fluorescent dye FURA-2/AM for simultaneous measurements of calcium transients. RESULTS: Compared with the initial control maximal isometric developed force, maximal isotonic shortening amplitude, contractility, and relaxation increased by 12.5-22.4% after perfusion with S(+)-ketamine at the concentration of 73 microM (P < 0.05). In contrast, no changes were seen after addition of 73 microM R(-)-ketamine. The effect of racemic ketamine (73 microM) was between that of the two isomers. At the highest concentration (730 microM) ketamine and its isomers decreased maximal isometric developed force, maximal shortening amplitude, contractility, and relaxation by 26.8-57.4% (P < 0.05), accompanied by a significant decrease of the intracellular calcium transient (by 21.0-32.2%, P < 0.05). CONCLUSIONS: In contrast to R(-)-ketamine, S(+)-ketamine increased isometric force, isotonic shortening, contractility, and relaxation at low concentrations (73 microM) compared with the initial control. At higher concentrations (730 microM) a direct negative inotropic action was observed after perfusion with ketamine and its isomers, which was accompanied by a decreased intracellular Ca2+ transient. (+info)