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At least 613 records · Page 34Linked to original sources
PubMed2002

Diuretic response to acute hypertension is blunted during angiotensin II clamp.

Acute hypertension inhibits proximal tubule (PT) fluid reabsorption. The resultant increase in end proximal flow rate provides the error signal to mediate tubuloglomerular feedback autoregulation of renal blood flow and glomerular filtration rate and suppresses renal renin secretion. To test whether the suppression of the renin-angiotensin system during acute hypertension affects the magnitude of the inhibition of PT fluid and sodium reabsorption, plasma ANG II levels were clamped by infusion of the angiotensin-converting enzyme (ACE) inhibitor captopril (12 microg/min) and ANG II after pretreatment with the bradykinin B(2) receptor blocker HOE-140 (100 microg/kg bolus). Because ACE also degrades bradykinin, HOE-140 was included to block effect of accumulating vasodilatory bradykinins during captopril infusion. HOE-140 increased the sensitivity of arterial blood pressure to ANG II: after captopril infusion without HOE-140, 20 ng x kg(-1) x min(-1) ANG II had no pressor effect, whereas with HOE-140, 20 ng x kg(-1) x min(-1) ANG II increased blood pressure from 104 +/- 4 to 140 +/- 6 mmHg. ANG II infused at 2 ng x kg(-1) x min(-1) had no pressor effect after captopril and HOE-140 infusion ("ANG II clamp"). When blood pressure was acutely increased 50-60 mmHg by arterial constriction without ANG II clamp, urine output and endogenous lithium clearance increased 4.0- and 6.7-fold, respectively. With ANG II clamp, the effects of acute hypertension were reduced 50%: urine output and endogenous lithium clearance increased two- and threefold, respectively. We conclude that HOE-140, an inhibitor of the B(2) receptor, potentiates the sensitivity of arterial pressure to ANG II and that clamping systemic ANG II levels during acute hypertension blunts the magnitude of the pressure diuretic response.

Acute Disease↗
PubMed2002

Angiotensin II clamp prevents the second step in renal apical NHE3 internalization during acute hypertension.

Acute hypertension inhibits proximal tubule (PT) sodium reabsorption. The resultant increase in NaCl delivery to the macula densa suppresses renin release. We tested whether the sustained pressure-induced inhibition of PT sodium reabsorption requires a renin-mediated decrease in ANG II levels. Plasma ANG II concentration of anesthesized Sprague-Dawley rats was clamped by simultaneous infusion of the ANG I-converting enzyme inhibitor captopril (12 microg/min) and ANG II (20 ng. kg(-1). min(-1)). Blood pressure was increased 50 mmHg for 20 min by arterial constriction +/- ANG II clamp or by sham operation. This acute hypertension increased urine output and endogenous Li(+) clearance, and these responses were blunted 40-50% in ANG II clamped rats. Acute hypertension provoked a rapid redistribution of Na(+)/H(+) exchanger isoform 3 (NHE3) out of apical brush-border membranes (21 +/- 4% decrease of total NHE3 abundance) to endosomal/lysosomal membranes (16 +/- 6% increase of total). In ANG II-clamped rats, acute hypertension also provoked disappearance of NHE3 from the apical membranes (27 +/- 2% decrease of total), but NHE3 was shifted to membranes enriched in intermicrovillar cleft and dense apical tubules (step 1) rather than endosomal/lysosomal membranes (step 2). This difference was independently confirmed by confocal analysis. In contrast, the pressure-induced redistribution of Na(+)-P(i) cotransporter type 2 was not altered by ANG II clamp. We conclude that the responses to acute hypertension, including diuresis and redistribution of PT NHE3 into intracellular membranes, require a responsive renin-angiotensin system and that the responses may be induced by the sustained increase in NaCl delivery to the macula densa during acute hypertension.

Acute Disease↗
PubMed1993

Voltage- and space-clamp errors associated with the measurement of electrotonically remote synaptic events.

1. The voltage- and space-clamp errors associated with the use of a somatic electrode to measure current from dendritic synapses are evaluated using both equivalent-cylinder and morphologically realistic models of neuronal dendritic trees. 2. As a first step toward understanding the properties of synaptic current distortion under voltage-clamp conditions, the attenuation of step and sinusoidal voltage changes are evaluated in equivalent cylinder models. Demonstration of the frequency-dependent attenuation of voltage in the cable is then used as a framework for understanding the distortion of synaptic currents generated at sites remote from the somatic recording electrode and measured in the voltage-clamp recording configuration. 3. Increases in specific membrane resistivity (Rm) are shown to reduce steady-state voltage attenuation, while producing only minimal reduction in attenuation of transient voltage changes. Experimental manipulations that increase Rm therefore improve the accuracy of estimates of reversal potential for electrotonically remote synapses, but do not significantly reduce the attenuation of peak current. In addition, increases in Rm have the effect of slowing the kinetics of poorly clamped synaptic currents. 4. The effects of the magnitude of the synaptic conductance and its kinetics on the measured synaptic currents are also examined and discussed. The error in estimating parameters from measured synaptic currents is greatest for synapses with fast kinetics and large conductances. 5. A morphologically realistic model of a CA3 pyramidal neuron is used to demonstrate the generality of the conclusions derived from equivalent cylinder models. The realistic model is also used to fit synaptic currents generated by stimulation of mossy fiber (MF) and commissural/associational (C/A) inputs to CA3 neurons and to estimate the amount of distortion of these measured currents. 6. Anatomic data from the CA3 pyramidal neuron model are used to construct a simplified two-cylinder CA3 model. This model is used to estimate the electrotonic distances of MF synapses (which are located proximal to the soma) and perforant path (PP) synapses (which are located at the distal ends of the apical dendrites) and the distortion of synaptic current parameters measured for these synapses. 7. Results from the equivalent-cylinder models, the morphological CA3 model, and the simplified CA3 model all indicate that the amount of distortion of synaptic currents increases steeply as a function of distance from the soma. MF synapses close to the soma are likely to be subject only to small space-clamp errors, whereas MF synapses farther from the soma are likely to be substantially attenuated.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Hyperpolarization-activated cation current (Ih) in neurons of the medial nucleus of the trapezoid body: voltage-clamp analysis and enhancement by norepinephrine and cAMP suggest a modulatory mechanism in the auditory brain stem.

1. Principal cells in the medial nucleus of the trapezoid body (MNTB) are part of a circuit in the superior olivary complex (SOC) that processes binaural information important for sound localization. MNTB cells have two voltage-dependent currents active near rest that contribute to these cells' highly nonlinear membrane properties and shape their responses to synaptic input. One of these currents, a low-threshold, 4-aminopyridine (4-AP)-sensitive K+ current, has been studied previously under current clamp. Using the single-electrode voltage-clamp technique, we have investigated the other of these currents, a hyperpolarization-activated, mixed cation current (Ih), in brain slices of the rat SOC. 2. Ih is responsible for a prominent "sag" in the voltage response to a steady hyperpolarizing current recorded under current clamp in MNTB cells. In voltage-clamp recordings, hyperpolarizing voltage steps from the resting potential elicited a large inward current that activated and deactivated with biexponential kinetics. Activation time constants were voltage dependent, with tau 1 and tau 2 = 246 and 1620 ms at -75 mV and 107 and 560 ms at -100 mV. 3. Ih was blocked by 1-5 mM cesium and had a reversal potential of -43 mV. Steady-state activation curves derived from tail currents yielded a half-activation voltage of -75.7 mV and slope factor of 5.7 mV, corresponding to < 10% activation of Ih at rest. 4. Application of norepinephrine (15-20 microM) or 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) (1 mM) caused a depolarizing shift in the steady-state activation curve and decreased the activation time constants. The shift in the activation curve resulted in a large increase in the activation of Ih at rest, an inward shift in the holding current, and an increase in the resting membrane conductance. In current-clamp recordings, this increase in the resting activation level of Ih resulted in membrane depolarization of 2-3 mV in the absence of 4-AP, and 5-10 mV in the presence of 4-AP, an increase in the input conductance, and a reduction in the voltage sag in response to hyperpolarizing currents. 5. The resulting change in the resting point of MNTB cells exposed to norepinephrine or 8-Br-cAMP is likely to alter the responses of these cells to synaptic input, both via the direct effect on the resting membrane conductance and by changing the activation of the low-threshold, 4-AP-sensitive potassium current.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Aminopyridine↗
PubMed1994

Depressed skull fractures in children secondary to skull clamp fixation devices.

The use of external skull fixation devices (skull clamps) is a common practice in neurosurgery. The insertion of pins into the skull is usually routine and uneventful in adult patients. However, the safety of skull clamp fixation devices in children is not reported. We have examined our complications over the past 6 years, and have encountered 5 children with depressed skull fractures secondary to application of a skull clamp fixation device. There were 3 boys and 2 girls with ages ranging from 3 to 8 years (mean 5.8 years). Two patients had brainstem gliomas, 2 patients had hypothalamic gliomas and 1 patient had a medulloblastoma. Four of the children required separate cranial procedures for exploration and elevation of the depressed fractures. There were no sequelae associated with the depressed fractures. We conclude that skull clamp fixation devices are safe, but should be used with caution in the pediatric patient. In addition, we present several modifications of existing skull clamps which may decrease the risk of depressed skull fractures.

Brain↗
PubMed1978

Hemodynamic and metabolic changes induced by temporary clamping of the thoracic aorta.

Numerous authors reported a significant deterioration of heart function induced by aortic cross-clamping. Nevertheless, the aorta has been clamped during various surgical procedures without any complication. We studied the hemodynamic and metabolic variations induced by 20 min thoracic aorta cross-clamping in 6 open-chest dogs. During clamping the most striking modifications were an increase in coronary blood flow of over 65%, an increase in cardiac work of over 77% and an increase in total peripheral resistances of over 68% compared to base values. No significant variations were found in the heart rate and cardiac index. Metabolic parameters, such as O2 consumption and lactate consumption increased significantly during the clamping period. The increase in lactate consumption and the progressive and continuous improvement in oxygenation indexes (lactate/pyruvate, redox potential, excess of lactate) proved the absence of any myocardial anoxia during this period. Within 15--30 min after declamping all hemodynamic and metabolic parameters reverted to values close to basal values. These data strongly suggest that the mammalian heart can tolerate this procedure satisfactorily for a limited period of time. In clinical settings, one should consider the base conditions of the cardiovascular system before transposing these conclusions.

Animals↗
PubMed1993

Biological role for the endothelin-A receptor in aortic cross-clamping.

The current study was undertaken to define a biological role for the endothelin-A receptor in a clinically relevant model of altered systemic and renal function produced by suprarenal aortic cross-clamping. This model is associated with profound systemic and renal vasoconstriction, acute renal failure, and a significant increase in circulating endothelin. Studies were performed in three groups of anesthetized mongrel dogs. Group 1 (n = 5) underwent aortic cross-clamping for 1 hour; group 2 (n = 5) underwent aortic cross-clamping for 1 hour in the presence of BQ-123, a specific antagonist of the endothelin-A receptor; group 3 (n = 4) received BQ-123 alone. The marked systemic and renal vasoconstriction associated with aortic cross-clamping in group 1 was markedly attenuated in group 2 in the presence of BQ-123. Unlike the vasoconstrictor response, BQ-123 did not attenuate the decrease in glomerular filtration rate associated with this model. Under unstimulated conditions in group 3, BQ-123 had no actions on systemic or renal hemodynamics. In conclusion, the current study demonstrates that the systemic and renal vasoconstriction associated with aortic cross-clamping are in part mediated through the interaction of endothelin and the endothelin-A receptor. This study demonstrates the functional importance of increased endogenous endothelin in the regulation of vascular tone in this pathophysiological state.

Animals↗
PubMed2006

Design of a subcutaneous vascular access device using Ni-Ti SMA clamps for hemodialysis.

A subcutaneous vascular access device which utilizes an Ni-Ti shape memory alloy (Ni-Ti SMA) spring, has been developed as a new method for subcutaneous vascular access in the treatment of hemodialysis patients. Until now, the connection between the SVAD and needle cannot be externally monitored, and the clamp must be opened and closed with a percutaneous needle by a nephrologist. The SMA-SVAD accomplishes the opening and closing of its clamp using two Ni-Ti SMA springs, and a transcutaneous energy transmission system (TET) transmits energy to the Ni-Ti SMA springs without the need for percutaneous wires. Two SMA springs open and close the clamp of the SMA-SVAD, without affecting any of the other parts of the system. Wasted thermal energy is reduced to minimal values via electrical regional heating methods. The state of the SMA-SVAD can be monitored according to the amount of power consumed by the external energy transmitter. In in-vitro experiments, when the clamp was opened and the pressure difference in the hemodialysis machine was set to 50 mmHg, water flow through SMA-SVAD reached 500 ml/min. The maximal surface temperatures of the SVAD and catheter were successfully maintained at proper levels (approximately 38-39 degrees C), approximately 2-3 degrees higher than the temperature of the surrounding tissues. The time elapsed from the initiation of energy transmission until the opening of the SMA clamp was 5 seconds.

Catheters, Indwelling↗
PubMed2001

The ring-type polymerase sliding clamp family.

Ring-type polymerases consist of a DNA polymerase, a ring-shaped sliding clamp protein and a clamp-loading complex. Sliding clamp proteins are found in all organisms and are called proliferating cell nuclear antigen (PCNA) in eukaryotes and the beta clamp in prokaryotes. Both PCNA and beta form a ring around DNA, which is made up of two subunits of three domains each in beta but three subunits of two domains each in PCNA. Despite this difference and a lack of detectable sequence homology, the structures of the two rings are very similar. The sliding clamp slides along DNA and tethers the polymerase to the DNA, enabling rapid and processive DNA replication.

Animals↗
PubMed1995

Clamping the small intestine during surgery: predicted and measured sealing forces.

During bowel surgery it is often necessary to occlude the bowel using clamps. Occlusion occurs in two stages: approximation of bowel internal surfaces followed by sealing which is necessary to prevent seepage. The occlusive force at both stages depends on the luminal pressure, the latter stage requiring greater force than the former. The difference in luminal pressure across the sealing line results in a slipping force which is resisted by friction between the bowel and the clamp jaw surfaces. A theoretical model was developed to describe these forces and the predicted values obtained from this model were compared with direct measurements carried out on porcine bowel samples in a test rig. It was found that the measured approximation force was between 25 and 50 per cent of the maximum theoretical values and that sealing without seepage requires a clamp force of about ten times the approximation force. Using these results and known intraluminal pressures in the human gastrointestinal tract, a bowel clamp must apply around 7 N to prevent seepage and the coefficient of friction between clamp and bowel should be between 0.6 and 0.9.

Animals↗
PubMed2004

Early experience with a new aortic clamping system designed for port access cardiac surgery: the PortaClamp.

BACKGROUND: We report a clinical study to demonstrate the feasibility and safety of a new aortic crossclamping concept for use in port-access cardiac surgery. The limited access to the aorta in minimally invasive cardiac surgery mandates specific clamping modalities, which entail specific limitations, drawbacks, and costs. Therefore a new autoguided, extravascular, and atraumatic clamping system (PortaClamp) was developed to facilitate port-access surgery while potentially avoiding the complications and costs inherent to endoluminal clamping or "blind" crossclamping. METHODS: Twenty patients underwent various cardiac operations under cardiopulmonary bypass and aortic crossclamping with the PortaClamp between February and September 2003. The method of aortic clamping is described and the operative course and clinical outcome of the patients are reported as surrogates of feasibility and safety. RESULTS: The average time to position the clamp was 196 +/- 75 seconds. Crossclamping through a 10-mm port or incision was achieved successfully, enabling cardiac arrest throughout the procedure in every patient. No patient presented with cardiovascular accident or transient ischemic attack, aortic dissection, or hematoma. Intensive care unit times were 12 +/- 3 hours; length of stay was 7.2 +/- 1.1 days. CONCLUSION: From this early experience we conclude that the PortaClamp system is safe and can effectively be used to crossclamp the aorta inexpensively to facilitate port-access cardiac surgery. Further comparative studies with the existing systems are warranted to confirm that the atraumatic design provides further benefit.

Aged↗
PubMed2006

The effect of timing of cord clamping on neonatal venous hematocrit values and clinical outcome at term: a randomized, controlled trial.

BACKGROUND: The umbilical cord is usually clamped immediately after birth. There is no sound evidence to support this approach, which might deprive the newborn of some benefits such as an increase in iron storage. OBJECTIVES: We sought to determine the effect of timing of cord clamping on neonatal venous hematocrit and clinical outcome in term newborns and maternal postpartum hemorrhage. METHODS: This was a randomized, controlled trial performed in 2 obstetrical units in Argentina on neonates born at term without complications to mothers with uneventful pregnancies. After written parental consents were obtained, newborns were randomly assigned to cord clamping within the first 15 seconds (group 1), at 1 minute (group 2), or at 3 minutes (group 3) after birth. The infants' venous hematocrit value was measured 6 hours after birth. RESULTS: Two hundred seventy-six newborns were recruited. Mean venous hematocrit values at 6 hours of life were 53.5% (group 1), 57.0% (group 2), and 59.4% (group 3). Statistical analyses were performed, and results were equivalent among groups because the hematocrit increase in neonates with late clamping was within the prespecified physiologic range. The prevalence of hematocrit at <45% (anemia) was significantly lower in groups 2 and 3 than in group 1. The prevalence of hematocrit at >65% was similar in groups 1 and 2 (4.4% and 5.9%, respectively) but significantly higher in group 3 (14.1%) versus group 1 (4.4%). There were no significant differences in other neonatal outcomes and in maternal postpartum hemorrhage. CONCLUSIONS: Delayed cord clamping at birth increases neonatal mean venous hematocrit within a physiologic range. Neither significant differences nor harmful effects were observed among groups. Furthermore, this intervention seems to reduce the rate of neonatal anemia. This practice has been shown to be safe and should be implemented to increase neonatal iron storage at birth.

Adult↗
PubMed1997

Renal protection by a dual ETA/ETB endothelin antagonist, L-754,142, after aortic cross-clamping in the dog.

Renal insufficiency is a significant complication that occurs after surgical procedures, requiring cross-clamping of the aorta. The mechanism for this renal dysfunction is currently not known, but studies suggest a potential role of endothelin in mediating the insufficiency. Accordingly, the role of endothelin was assessed using the nonpeptidyl, dual ETA/ETB endothelin antagonist L-754,142 in a model of renal insufficiency in the anesthetized dog induced by cross-clamping the suprarenal aorta for 60 min, followed by 2 h of reperfusion. In vehicle-treated animals (saline, n = 8) after 2 h of reperfusion, plasma [ET-1] increased 66% and renal blood flow (RBF) was reduced by 38% compared with baseline. This decline was associated with an 84% increase in renal vascular resistance and a 54% reduction in GFR (baseline, 46 +/- 5 ml/min; 21 +/- 3 ml/min at 2 h; P < 0.01) and sodium reabsorption (baseline, 6.7 +/- 0.7 microEq/min; 3.0 +/- 0.5 microEq/min at 2 h, P < 0.01). After baseline measurements, pretreatment with L-754,142 at 0.3 mg/kg bolus + 0.1 mg/kg per h continuous infusion (low dose; n = 8) or 3.0 mg/kg bolus + 1 mg/kg per h infusion (high dose; n = 8) initiated 45 min before aortic cross-clamp led to a dose-dependent normalization of RBF and renal vascular resistance within 2 h of cross-clamp removal. GFR was also improved and returned to within 75% of baseline (P < 0.01 versus vehicle) by 2 h of reperfusion with L-754,142 (baseline, 55 +/- 5 ml/min; 42 +/- 5 ml/min at 2 h with the high dose). The improvement of GFR with L-754,142 treatment was associated with a preservation of sodium reabsorption compared with vehicle-treated animals. This study supports a role of endothelin in the pathogenesis of renal insufficiency after aortic cross-clamping and demonstrates that pretreatment with the dual ETA/ETB endothelin antagonist L-754,142 preserves RBF and sodium reabsorption, leading to a significant improvement in GFR.

Acetamides↗
PubMed1993

Spinal epidural oxygen partial pressure and evoked spinal cord potential in relation to the severity of spinal ischemia during cross-clamping of the thoracic aorta.

Experiments were undertaken to determine the relationship between evoked spinal cord potential (ESP) and the partial pressure of oxygen in tissue in the epidural space (E-pO2) during aortic clamping. Eighteen adult mongrel dogs were studied as follows. In group I (n = 6), the descending thoracic aorta was clamped partially at the proximal site for 15 min to maintain the distal arterial pressure at 60, 40, and 20 mmHg consecutively at 15 min intervals. In group II (n = 6), the descending thoracic aorta was clamped proximally for 30 min. In group III (n = 6), the descending thoracic aorta was cross-clamped at proximal and distal sites for 30 min. Postoperative complete paraplegia was observed in 4 of 6 dogs in group III, but none in group II. The change in ESP with aorta cross-clamping was very mild in groups I and II. Transient increases and decreases in the ESP amplitude were observed in group III. The decrease of E-pO2 correlated well with the distal arterial pressure, and a rapid return to baseline of the E-pO2 was observed after declamping. The E-pO2 changed in response to spinal ischemia more rapidly than did ESP in all groups. The critical level of E-pO2 was 50 mmHg or a 40% decrease from baseline. Because the ESP reflects spinal function and the E-pO2 reflects spinal blood pressure, we propose that combined recording of ESP and E-pO2 would improve spinal monitoring during thoracic aortic surgery.

Animals↗
PubMed1985

In vivo hepatic and peripheral insulin sensitivity in rats with non-insulin-dependent diabetes induced by streptozocin. Assessment with the insulin-glucose clamp technique.

Non-insulin-dependent diabetes mellitus (NIDDM) was obtained in adult female rats by neonatal administration of streptozocin (STZ). At 2 mo of age, the basal plasma glucose values in the postabsorptive state were elevated, the glucose disappearance rate measured after intravenous (i.v.) glucose load was significantly lower in the diabetic than in control rats, and in vivo glucose-induced insulin release was drastically reduced. To quantify and characterize the in vivo insulin sensitivity in rats with NIDDM, we have used the insulin-glucose clamp technique. The effects of different concentrations of insulin on glucose production, glucose utilization, and glucose clearance (measured by using 3-3H-glucose) were studied in anesthetized diabetic or control rats while in the postabsorptive state. An inherent condition to set up a valid experimental design was to take into consideration, in the diabetics, the influence of the high blood glucose concentration on glucose uptake and glucose production, since the blood glucose concentration by itself affects these two parameters by a mass action effect independent of insulin. The issue was addressed by evaluating glucose production and utilization in three experimental groups: diabetics clamped at their basal blood glucose level (170 mg/dl), controls clamped at their basal blood glucose level (110 mg/dl), and controls clamped at high blood glucose level (170 mg/dl). In the basal state, glucose production was significantly higher in the diabetics than in controls. When plasma insulin was clamped at submaximal levels (300 microU/ml), the suppression of glucose production was significantly more important in the diabetics than in the two control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Use of GC clamps in DHPLC mutation scanning.

OBJECTIVE: Development of a systematic mutation detection assay strategy for denaturing high performance liquid chromatography (DHPLC). DESIGN: Adaptation of Guanine and Cytosine (GC)-clamping from denaturing gradient gel electrophoresis (DGGE) to DHPLC. METHODS: Three target sequences harboring known allelic variants were studied to develop a general DHPLC assay design strategy. These were exon 10 of the human RET (REarranged during Transfection) gene, exon 52 of the mouse Col1a2 gene, and exon 9 of the human FAS (APO-1, CD-95) gene. Available software was used to analyze melting curves and determine assay conditions. GC clamps of 20 bp or 36 bp were added to polymerase chain reaction (PCR) primers to introduce a high melting temperature (T(m)) domain to each of the target molecules. DHPLC was performed under partially denaturing conditions. RESULTS: DHPLC assays of PCR-amplified sequences can be developed using a personal computer. The following three steps allowed for mutation detection in all three targets. The target sequence should have a uniform T(m)GC clamps of length sufficient to introduce a second melting domain with a T(m) > or = 8 degrees above that of the target sequence should be appended to one of the primers. The DHPLC assay should be performed at the highest temperature at which the target sequence is predicted to be > or = 90% double stranded CONCLUSION: Addition of GC-clamps to primers facilitates mutation detection by DHPLC. The theoretical basis for this observation is identical to that underlying the utility of GC-clamps in DGGE.

Animals↗
PubMed1986

Role of EEG monitoring and cross-clamping duration in carotid endarterectomy.

The usefulness of electroencephalographic (EEG) monitoring as well as the significance of the period of cross clamping in carotid endarterectomy have not been completely defined. In particular, the clinical importance of major EEG changes has not been fully investigated and some recent studies seem to indicate that the method has little value. As to the duration of cross clamping, there is strong evidence that occlusion times of about 15 minutes are tolerated under general anesthesia, but no information is available regarding longer periods of occlusion. The authors describe a consecutive series of 141 carotid endarterectomies in which the patients with EEG changes were shunted only when occlusion was anticipated to last longer than 30 minutes. Early major EEG changes (during the first 4 minutes) occurred in 14% of the cases. In the absence of EEG changes, long occlusion periods of 40 to 50 minutes were well tolerated. In contrast, the 20 patients with major persistent EEG changes did not tolerate protracted occlusion and three of them had immediate postoperative neurological complications. It seems that, in these circumstances, the incidence of neurological deficit is a function of the duration of cross clamping: these three patients had undergone occlusion for 15 to 30 minutes. Their deficits partially resolved. On the basis of these results it is concluded that: EEG recording is a reliable monitoring system in carotid artery cross clamping. No major strokes due to temporary carotid artery occurred in the series. The clinical significance of major persistent EEG changes is not negligible. Cross clamping for longer than 15 minutes in the presence of significant EEG alterations is potentially dangerous.

Aged↗
PubMed1991

Use of MR imaging-compatible Halifax interlaminar clamps for posterior cervical fusion.

Twenty-one patients requiring posterior cervical fusion were treated with magnetic resonance (MR) imaging-compatible Halifax interlaminar clamps for internal fixation. Various levels were involved: the C1-2 level in eight cases, the C4-5 level in four, the C5-6 level in three, the C6-7 level in three, the C4-6 level in two, and the C5-7 level in one. Bilateral clamps were used in 18 cases and unilateral clamps in three. Autogenous iliac bone grafting was performed in all cases but one. Follow-up periods ranged from 1 to 18 months (average 9.2 months), with no complications or mechanical failures occurring thus far. Follow-up diagnostic studies revealed rigid fixation and fusion in all cases. The MR imaging-compatibility of the clamps allowed excellent follow-up studies with minimal artifact. Because of their ease of use, rigid stabilization, good results, lack of complications, and compatibility with MR imaging, the Halifax interlaminar clamp with bone grafting provides an ideal method for posterior cervical stabilization.

Adolescent↗