Synthesis, structure, and magnetism of bimetallic manganese or nickel complexes of a bridging verdazyl radical.

Two binuclear metal-radical complexes, formed by the reaction of M(hfac)(2) x 2H(2)O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)(2)](2)) crystallizes in the monoclinic space group C2/c: C(30)H(17)N(6)O(9)F(24)Mn(2), a = 29.947(3), b = 17.143(3), c = 16.276(3) A, beta = 123.748(3)*, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = -48 cm(-1)). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm(-1)). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species.

Strong supramolecular-based magnetic exchange in pi-stacked radicals. Structure and magnetism of a hydrogen-bonded verdazyl radical:hydroquinone molecular solid.

The X-ray crystal structure and magnetic properties of a molecular crystal consisting of 1,5-dimethyl-3-(2-pyridyl)-6-oxoverdazyl radical and hydroquinone (pyvd:hq) are presented. The structure contains a two-dimensional network of hydrogen bonds involving the hydroquinones and the pyridine ring of the pyvd radical. The radicals adopt an unusual head-over-tail (antiparallel) pi-stacked array perpendicular to the hydrogen-bonded planes. The variable-temperature magnetic susceptibility data can be modeled using a one-dimensional antiferromagnetic chain model, with J = -58 cm(-1). The strength of the magnetic coupling is very unusual because there are no close intermolecular radical-radical contacts to provide conventional pathways for magnetic interactions. A pathway for coupling is proposed involving the mediation of magnetic exchange interactions between radical centers by the pyridine rings. Density functional calculations on the pyvd radical, as well as aggregates thereof based on the X-ray structure, have been employed in attempts to understand the possible mechanisms by which the strong magnetic interactions are achieved.

Spin distributions, ring conformations, and spiroconjugation in "phosphaverdazyl" radicals.

Reaction of P-dimethylaminophosphonic acid bis(1-methylhydrazide) (6) with trimethyl orthobenzoate gave 1,2,5,6-tetrahydro-1,5-dimethyl-6-(N,N-dimethylamino)-6-phenyl-1,2,4,5,6-tetrazaphosphorine-6-oxide (7), which was subsequently oxidized to the corresponding P-diemthylamino-6-phosphaverdazyl (5) as a persistent radical. Analysis of the electron paramagnetic resonance spectrum of 5 revealed significant spin density on the exocyclic nitrogen but very little spin density on the phosphorus, in contrast to the previously reported P-phenyl-6-phosphaverdazyl (4). Density functional theory calculations on simplified models of 4, 5, and related radicals were performed and revealed that spin polarization effects and the nature of the substituents on phosphorus have significant effects on the structures and spin distributions of these radicals. The spin transfer to the dimethylamino group in 5 was revealed to arise from spiroconjugation-type overlap between the nitrogen 2p orbital with the verdazyl radical singly occupied molecular orbital.

Risk factors for peri-operative stroke complicating carotid endarterectomy: selective analysis of a prospective audit of 1000 consecutive operations.

BACKGROUND: The aim of the present study was to investigate the role of potential clinical risk factors in the causation of peri-operative stroke associated with carotid endarterectomy. With the change in carotid endarterectomy practice from the use of a shunt to high-dose thiopental for cerebral protection (a previously undocumented method), it was essential to identify accurately the causes of all perioperative strokes. METHODS: A prospective audit was undertaken of 1000 carotid endarterectomies in which the causes and pathology of all peri-operative strokes were documented. The roles of advanced age, female gender, hypertension, previous stroke, contralateral carotid stenosis >70%, and contralateral carotid occlusion as potential causes of peri-operative stroke were defined. Results were statistically analysed using odds ratio and Fisher's exact test. RESULTS: None of the potential risk factors was statistically significant for peri-operative stroke. Female gender was associated with a significant risk of peri-operative stroke due to operative site thrombosis. Complications at the endarterectomy site were the commonest cause of stroke. CONCLUSIONS: Prospective audit is a useful tool for identifying causes of peri-operative stroke and indicating the need for modifications to surgical clinical management which might improve outcomes for carotid endarterectomy.

Depression of I waves in corticospinal volleys by sevoflurane, thiopental, and propofol.

UNLABELLED: Isoflurane depresses the number and amplitude of I waves of the motor-evoked potential produced by transcranial electrical stimulation of the motor cortex and thus affects components of the corticospinal volley that are believed to arise from Laminae III and V. This study extends these observations to sevoflurane (9 patients) and the two IV anesthetics, thiopental and propofol (10 sets of observations in 10 and 6 patients, respectively). The patients' ages ranged from 10 to 17 yr. Sevoflurane was administered to achieve end-tidal concentrations of 0.5%-3%. Thiopental and propofol were given as boluses of 5 mg/kg and 2 mg/kg, respectively, to patients anesthetized with nitrous oxide, fentanyl, midazolam, and a muscle relaxant. Sevoflurane had a depressant effect on I waves essentially similar to that of isoflurane; thiopental depressed I wave activity by an average of 33% (95% confidence interval: 20%-46%, P < 0.001) and propofol by 39% (95% confidence interval: 20%-40%, P < 0.001). With all three anesthetics, later I waves showed the most amplitude depression. The three anesthetics had qualitatively similar effects on I waves. IMPLICATIONS: Sevoflurane, thiopental, and propofol depress components of the corticospinal volley produced by transcranial electrical stimulation of motor cortex in a manner qualitatively similar to isoflurane. The findings indicate that anesthetics with primarily hypnotic actions suppress interneuronal activity in cerebral cortex.

Surgical monitoring of motor pathways.

Intraoperative monitoring of corticospinal function is no longer an experimental technique, having been introduced into routine practice in a number of centers, each of which has now accumulated large series of some hundreds of cases. Different techniques have been developed by these centers; each has advantages and disadvantages, and it is clear that no one technique in particular is optimal for all surgical procedures. The corticospinal system can be activated by transcranial stimulation of the motor cortex or by direct stimulation of the spinal cord with electrical or magnetic stimuli delivered singly or as double or multiple pulses. The evoked activity may be recorded directly from the spinal cord using epidural electrode, or as a postsynaptic volley in motor axons ("neurogenic motor evoked potentials," MEP), or as a compound muscle action potential (CMAP) from innervated muscles. For scoliosis surgery, we use transcranial electrical stimulation, recording the evoked volley from the spinal cord using epidural electrodes at two spinal levels. By simultaneously stimulating the tibial nerves in the popliteal fossae, descending corticospinal volleys and ascending somatosensory volleys can be recorded in the same sweep. Accordingly, this technique allows monitoring of two different modalities of function at two separate levels of the nervous system, a goal that is most desirable because it helps identify the earliest evidence of dysfunction and at the same time minimizes false-positive reports to the surgeon. Our technique has the advantage of being relatively immune to the depressant effects of anesthesia, and full muscle relaxation is possible--even desirable. More peripheral recordings of neurogenic MEP or CMAP, are sensitive to the choice of anesthetic, and the latter requires incomplete curarization. However, these techniques may be appropriate when the pathology is in the low spinal cord or nerve roots.

Hemodynamic ischemic stroke during carotid endarterectomy: an appraisal of risk and cerebral protection.

PURPOSE: The purpose of this study was to validate the commonly accepted indicators of risk of ischemic stroke that indicate the necessity for cerebral protection during carotid endarterectomy (CEA), and to examine the efficacy of high-dose thiopentone sodium (thiopental) as a cerebral protection method in patients who are at high risk of intraoperative ischemic stroke. METHOD: In a prospective study of 37 CEAs performed for symptomatic stenosis > 70%, functional and clinical indicators of risk of ischemic stroke during carotid cross-clamping were identified. Functional indicators of risk were the development of ischemic electro-encephalogram (EEG) changes and stump pressure < 25 mm Hg. Clinical indicators of risk were previous ischemic hemispheric stroke and severe bilateral disease. These indicators were correlated in all patients, some of whom had two or three coexisting indicators of risk. The EEG and stump pressure were monitored continuously during carotid occlusion in all operations. Carotid occlusion times were recorded. Intraluminal shunting was eliminated in favor of high-dose thiopental cerebral protection in all patients. Neurologic outcome was deemed to measure the efficacy of thiopental protection in patients who are identified to be at risk and, hence, in need of cerebral protection. The validity of the indicators used to identify risk of ischemic stroke during CEA was assessed. RESULTS: The absolute stroke risk was found to be 29.7% for the whole group (37 patients) and 57.9% in 19 patients who had commonly accepted indications for protective shunting. The correlation of ischemic EEG changes with stump pressure < 25 mm Hg was only 27.3%, whereas the expected correlation based on well-documented reports in the literature was 100%. The lack of correlation may have been related to the prevention of ischemic EEG changes by thiopental. There were no neurologic deficits in the series. CONCLUSIONS: The absence of neurologic deficit in the study indicated that thiopental protection was effective in preventing ischemic stroke in high-risk patients and safely replaced intraluminal shunting.

Cotrel-dubousset instrumentation in children using simultaneous motor and somatosensory evoked potential monitoring.

STUDY DESIGN: To record prospectively combined motor- and somatosensory-evoked potentials in children during scoliosis surgery using Cotrel-Dubousset instrumentation, without using special anesthetic or muscle relaxant regimens. OBJECTIVE: To determine the outcome of scoliosis surgery guided by a new technique of monitoring motor- and somatosensory-evoked potentials simultaneously. SUMMARY OF BACKGROUND DATA: Other techniques used to assess cord function generally are limited by special anesthetic requirements or assess only a limited part of the cord or monitor motor function separately from somatosensory function. METHODS: Spinal cord function was monitored using epidural leads to record simultaneously the descending motor volley (by transcranial electrical stimulation) and the ascending somatosensory volley (by tibial nerve stimulation) at two spinal levels. RESULTS: Combined motor- and sensory-evoked potentials were recorded successfully in 138 of 160 children (81%). Changes in evoked potential waveforms were seen in eight patients (5%), but resolved or lessened in response to appropriate measures. Curve correction was satisfactory, and there were no new postoperative deficits or worsening of preexisting deficits in any patient. CONCLUSION: A spinal cord monitoring system is described that is safe, reliable, accurate, and makes it unnecessary to resort to the "wake-up" test.

Variability of motor-evoked potentials recorded during nitrous oxide anesthesia from the tibialis anterior muscle after transcranial electrical stimulation.

When recorded as a compound muscle action potential (CMAP), the motor-evoked potential (MEP) is affected by volatile anesthetics and nitrous oxide. However, MEPs recorded using epidural electrodes in the presence of nitrous oxide are highly reproducible from trial to trial. We wished to establish the reproducibility over time of the CMAP produced by supramaximal transcranial electrical stimulation of the human motor cortex. Cascades of 100 successive CMAPs were recorded from the tibialis anterior muscles of six anesthetized patients undergoing scoliosis surgery, in response to transcranial electrical stimuli of > 500 V. Satisfactory CMAPs could be recorded in the presence of nitrous oxide, but not isoflurane. Latencies and amplitudes were reproducible in repeated sequences of 100 responses. However, amplitude and, to a lesser extent, latency, were highly variable within a sequence. In addition, occasional individual stimuli, although rarely successive ones, failed to evoke a CMAP. CMAPs have a much higher trial-to-trial variability than corticospinal volleys recorded from the epidural space. Using the present methodology it would be difficult to rely on CMAP recordings as an indicator of corticospinal function in the clinical monitoring situation.

Carotid endarterectomy without a shunt for symptomatic lesions associated with contralateral severe stenosis or occlusion.

PURPOSE: The purpose of this study was to assess the adequacy of thiopental protection against ischemic cerebral damage in patients undergoing carotid endarterectomy for symptomatic stenosis greater than 70% in association with contralateral stenosis greater than 70% or contralateral occlusion. METHODS: All patients (n=259) with severe bilateral carotid disease who underwent carotid endarterectomy for symptomatic stenosis greater than 70% were extracted from the database of an ongoing prospective carotid surgery study. Large-dose thiopental sodium without shunting was used for cerebral protection during endarterectomy. Asymmetric electroencephalogram changes during the operation, carotid occlusion time, stroke onset, and neuropathologic outcomes were analyzed. RESULTS: Three contralateral strokes occurred in the series, producing a cerebral morbidity/mortality rate of 1.2% (major 0.4%, minor 0.8%). Transient morbidity was 1.9% made of two reversible ischemic neurologic deficits and three transient ischemic attacks. New asymmetric electroencephalography changes were seen in 49 (19% patients, one of whom had transient deficit. Average occlusion time was 35 minutes. All strokes occurred within 24 hours of the procedure. Patients with previous stroke and and systemic hypertension seemed at greatest risk, and the contralateral hemisphere was the area at greatest risk. All transient deficits were ipsilateral and related to technical complications rather failed protection. CONCLUSIONS: Thiopental cerebral protection eliminates strokes caused by complications of shunting, prevents ischemic stroke during carotid occlusion for periods up to 67 minutes (average 35 minutes), allows meticulous management of the operative site, may modify or minimize clinical neurologic deficit, and in our experience has rendered intraluminal shunting obsolete.

Thiopental sodium cerebral protection during carotid endarterectomy: perioperative disease and death.

PURPOSE: This study reports our experience with thiopental sodium (Pentothal) cerebral protection, without intraluminal shunting, during carotid endarterectomy. Only those complications that occurred during surgery or within 30 days of operation have been addressed. METHOD: A prospective, unselected, consecutive series of 621 carotid endarterectomies was done during a 7-year period, with electroencephalography-monitored, high-dose Pentothal for cerebral protection. RESULTS: Five ischemic strokes (0.8%), completion of two strokes-in-evolution (0.3%) and four strokes caused by cerebral hemorrhage (0.6%) occurred in 11 patients in the perioperative (30-day) period, for a combined cerebral morbidity-mortality rate of 1.7%. Four reversible ischemic neurologic deficits (0.6%) and two transient ischemic attacks (0.3%) in six patients produced a transient deficit rate of 0.9%. Symptomatic coronary artery disease coexisted in 37% of the patients but resulted in only five acute myocardial infarctions (0.7%), one of which was fatal (0.1%). Other perioperative complications in 10 patients (1.5%) were associated with the operative procedure. There were no complications directly attributable to the high-dose Pentothal. Prospective data collection has allowed definition of the disease and cause of all cerebral complications. CONCLUSION: The complications in this series have been related to surgical and clinical management problems rather than failure of cerebral protection. Cerebral protection with high-dose Pentothal under electroencephalographic control has been effective and complication free.

Laparoscopy explosion hazards with nitrous oxide.

BACKGROUND: During laparoscopic surgery utilizing carbon dioxide as the insufflating agent, nitrous oxide will diffuse into the peritoneal cavity if it is used as part of the anesthetic. Bowel perforation and the subsequent release of volatile bowel gas could create a explosion hazard. METHODS: Two related studies were undertaken. The first quantified the transfer of nitrous oxide, over time, in 19 female patients undergoing laparoscopy. The second established the lower limits of flammability of a range of concentrations of methane and hydrogen diluted with nitrogen (simulated bowel gas) in a range of concentrations of nitrous oxide diluted with carbon dioxide (simulated peritoneal gas). RESULTS: The mean concentrations of N2O at 10, 20, and 30 min from the time of insufflation were 19.9 +/- 4.8%, 30.3 +/- 6.8%, and 36.1 +/- 6.9%, respectively. The maximum reported concentrations of methane and hydrogen in bowel gas are 56% and 69%, respectively. The concentration of nitrous oxide necessary to support combustion of 56% methane is approximately 47%. By contrast, the concentration of nitrous oxide needed to support combustion of 69% hydrogen is approximately 29%. CONCLUSIONS: The authors have shown that it is possible for nitrous oxide to reach concentrations in the peritoneal cavity that can support combustion of bowel gas.

Reoperation for recurrent coronary artery disease--a ten year experience.

The need for reoperation caused by recurrence of coronary artery disease is becoming increasingly common. Although reoperation is more difficult and time-consuming, with careful surgical technique it can be carried out with the same mortality as that described by many units for primary coronary artery bypass grafting (1.2-2.0%). In the 172 patients described here, who had coronary artery reoperations between 1981 and 1990, there were two in-hospital deaths (1.2%). There were three postoperative bleeds which required return to theatre. No patient suffered a postoperative neurological deficit or postoperative myocardial infarction. These reoperations comprised 6.9% of the 2497 coronary artery operations carried out in the same period. Follow-up disclosed eight late deaths, from five-62 months after operation; all survivors claim to be symptomatically improved. Consideration should be given to the potential problems of reoperation when carrying out primary myocardial revascularisation.

Some effects of isoflurane on I waves of the motor evoked potential.

We have investigated the effects of isoflurane anaesthesia on the motor evoked potential recorded in the extradural space during corrective spinal surgery in 15 patients. Isoflurane was added to a nitrous oxide in oxygen mixture supplemented with fentanyl and a neuromuscular blocking agent. Isoflurane was administered to achieve end-tidal concentrations of 2%, 1% and 0% in all patients, and also of 1.5% and 0.5% in nine patients. Transcranial electrical stimulation of the motor cortex was used to elicit descending volleys in corticospinal axons (the motor evoked potential). With stimuli of 450-750 V and no isoflurane, multiple I waves were always seen following the D wave. In all patients the number of I waves decreased and individual I waves became smaller in amplitude the greater the isoflurane concentration, but there were only minor changes in the D wave. The greatest depressant effect on I waves occurred at an end-tidal concentration of 0.5%. Given that I waves are an index of synaptic transmission, anaesthetic-induced changes in I waves may provide a useful model for the neuronal events underlying anaesthesia-induced unconsciousness.

Monitoring spinal cord function during scoliosis surgery with Cotrel-Dubousset instrumentation.

Cotrel-Dubousset instrumentation has been a major advance in spinal surgery but, at least theoretically, it carries a higher risk of spinal cord damage. This paper describes our experience in monitoring the function of either ascending sensory pathways or both ascending sensory and descending motor pathways in the spinal cord during such procedures. Seventy-nine juvenile and adult patients are presented in whom either somatosensory recording (n = 39) or simultaneous corticospinal and somatosensory monitoring (n = 40) was attempted by means of epidural electrodes during corrective surgery with Cotrel-Dubousset instrumentation. Abnormal evoked responses were seen in two cases but these resolved in both before the operation was completed. No new neurological deficits occurred nor were any pre-existing deficits increased.

Corticospinal volleys evoked by anodal and cathodal stimulation of the human motor cortex.

1. In fifteen neurologically normal subjects, corticospinal volleys evoked by transcranial stimulation of the motor cortex were recorded from the spinal cord using epidural electrodes in the high-thoracic and low-thoracic regions during surgery to correct scoliosis. 2. Anodal stimulation at the vertex produced complex corticospinal volleys that could be recorded at both sites, with multiple waves analogous to the D and I waves documented in animal experiments. These volleys were of higher amplitude when the cathode was 7 cm lateral to the vertex rather than 7 cm anterior. There were no differences in conduction time between the two recording sites for D and I waves, when these waves could be identified at the low-thoracic site. 3. Anodal stimuli of 150 V commonly produced a descending volley containing a single peak at both recording sites. Modest increases in stimulus intensity to 225-375 V produced a peak 0.8 ms in advance of the wave of lowest threshold in thirteen subjects and, in seven subjects, further increases produced an additional peak 1.7 ms in advance of the first-recruited wave. The early peaks increased in size with stimulus intensity, replacing the first-recruited wave. These results suggest that the site of impulse initiation with electrical stimulation of the motor cortex shifts from superficial cortex to deep structures, approximately 5 and 10-11 cm below the cortex. These sites are probably the internal capsule and the cerebral peduncle. 4. With cathode at the vertex and anode over the 'hand area' the response of lowest threshold occurred at the latency of the anodal D wave but could not be recorded at the low-thoracic site, suggesting that it was generated by the anode over the 'hand area'. Slightly higher intensities induced a 'cathodal D wave' and still higher intensities produced late peaks at latencies of anodal I waves. These cathodal D and I waves involved axons innervating lumbar segments. There was no evidence that cathodal stimulation preferentially produced I waves. Cathodal stimulation at the vertex with the anode 7 cm anteriorly produced similar results: D waves were produced at relatively low intensities, but I waves appeared at relatively high stimulus intensities if at all.(ABSTRACT TRUNCATED AT 400 WORDS)

Combined carotid and coronary artery surgery: a review of the literature.

This article reviews 41 different reports that describe various means of surgical management of coexistent carotid and coronary artery disease in almost 1,500 patients. Stroke is the major risk for patients undergoing myocardial revascularization in the presence of symptomatic carotid artery disease or an asymptomatic carotid bruit that reflects an ulcerative lesion or stenosis exceeding 75%. However, patients with asymptomatic carotid stenosis should not routinely undergo prophylactic carotid endarterectomy. Myocardial infarction is the major hazard in patients undergoing carotid endarterectomy who have coronary artery disease. This risk is magnified when the disease is silent. A high level of awareness and rigorous screening are essential in all patients suspected of having coexistent disease. Although a protocol for the management of these patients is important, individual assessment is essential.

Coexistent carotid and coronary arterial disease. Outcome in 50 cases and method of management.

The coexistence of coronary and carotid arterial disease in the same patient requires that particular measures be undertaken to avoid the risks of myocardial infarction and stroke. The last 50 patients requiring operations on both subsystems and with no mortality and minimal morbidity are reported. A method for the management is described, to allow discrimination between those patients needing a combined coronary-carotid procedure and those in whom the operations should be staged. The application of this protocol to the last 1732 patients who presented with coronary and/or carotid artery disease has resulted in all overall mortality of 0.63% and morbidity of 0.17%.