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Biomedical subjects

S K Samra

Publications and source records attributed to S K Samra.

At least 19 recordsLinked to original sources
PubMed2001

Remifentanil- and fentanyl-based anesthesia for intraoperative monitoring of somatosensory evoked potentials.

We sought to compare effects of remifentanil- and fentanyl-based anesthesia on the morphology of somatosensory evoked potentials (SSEPs) and speed of recovery from anesthesia. Forty-one patients undergoing spinal surgery and requiring intraoperative monitoring of SSEPs were randomized into two groups. In Group 1, anesthesia was induced with sodium thiopental and maintained with fentanyl, 50% nitrous oxide in oxygen, and 0.5%--0.75% isoflurane. In Group 2, anesthesia was induced with sodium thiopental and maintained with remifentanil, 50% oxygen in air, and 0.5%--0.75% isoflurane. The variables compared included hemodynamic changes during the induction and intubation, the interval from the end of anesthesia to extubation, intraoperative blood loss and fluid administration, and changes in latency and amplitude of the P37--N45 component of posterior tibial nerve somatosensory evoked potentials and the N20--P24 component of median nerve somatosensory evoked potentials. The two groups were matched for demographics, ASA physical status, and duration of surgery. Hemodynamic profiles after the induction and intubation were similar. There were significant differences between groups in time intervals from the end of anesthesia to extubation (15.3 +/- 12.8 vs 5.3 +/- 2.3 min; P = 0.0001) and ability to follow verbal commands (14.6 +/- 11.9 vs 4.5 +/- 2.4 min; P = 0.0001), with the Remifentanil group showing earlier recovery. Variability (coefficient of variation) of P37--N45 latency was greater (0.026 vs 0.014; P = 0.001) in the Fentanyl group.

Adult↗
PubMed2000

Upstream tissue inhibitor of metalloproteinases-1 (TIMP-1) element-1, a novel and essential regulatory DNA motif in the human TIMP-1 gene promoter, directly interacts with a 30-kDa nuclear protein.

Elevated expression of the tissue inhibitor of metalloproteinases-1 (TIMP-1) protein and mRNA has been reported in human diseases including cancers and tissue fibrosis. Regulation of TIMP-1 gene expression is mainly mediated at the level of gene transcription and involves the activation of several well known transcription factors including those belonging to the AP-1, STAT, and Pea3/Ets families. In the current study, we have used DNase-1 footprinting to identify a new regulatory element (5'-TGTGGTTTCCG-3') present in the human TIMP-1 gene promoter. Mutagenesis and transfection studies in culture-activated rat hepatic stellate cells and the human Jurkat T cell line demonstrated that the new element named upstream TIMP-1 element-1 (UTE-1) is essential for transcriptional activity of the human TIMP-1 promoter. Electrophoretic mobility shift assay studies revealed that UTE-1 can form protein-DNA complexes of distinct mobilities with nuclear extracts from a variety of mammalian cell types and showed that induction of a high mobility UTE-1 complex is associated with culture activation of freshly isolated rat hepatic stellate cells. A combination of UV-cross-linking and Southwestern blotting techniques demonstrated that UTE-1 directly interacts with a 30-kDa nuclear protein that appears to be present in all cell types tested. We conclude that UTE-1 is a novel regulatory element that in combination with its cellular binding proteins may be an important component of the mechanisms controlling TIMP-1 expression in normal and pathological states.

Animals↗
PubMed2000

A comparison of remifentanil and fentanyl in patients undergoing surgery for intracranial mass lesions.

UNLABELLED: We compared the effects of remifentanil versus fentanyl during surgery for intracranial space-occupying lesions. Patients were randomly assigned to receive either remifentanil (0.5 microg. kg(-1). min(-1) IV during the induction of anesthesia reduced to 0.25 microg. kg(-1). min(-1) after endotracheal intubation; n = 49) or fentanyl (dose per usual practice of the anesthesiologist; n = 54). Anesthesia maintenance doses of isoflurane, nitrous oxide, and opioid were at the anesthesiologist's discretion for both groups. There were no differences between opioid groups for the frequency of responses (hemodynamic, movement, and tearing) to intubation, pinhead holder placement, skin incision, or closure of the surgical wound. Adverse event frequencies were similar between groups. Times to follow verbal commands (P < 0.001) and tracheal extubation (P = 0. 04) were more rapid for remifentanil. The percentage of patients with a normal recovery score (were alert or arousable to quiet voice, were oriented, were able to follow commands, had motor function unchanged from their preoperative evaluation, were not agitated, and had modified Aldrete Scores of 9-10) at 10 min after surgery was more for remifentanil (45% vs 18%; P = 0.005). By 20 min, no difference between groups existed (P = 0.27). Anesthesiologists used more isoflurane in the fentanyl group (4.22 vs 1.93 minimum alveolar anesthetic concentration hours). Neurosurgeons, blinded to treatment group, favored the use of remifentanil. Similar frequencies of light anesthesia responses and other adverse events suggest that intraoperative depths of anesthesia were similar in the two groups. Under these conditions, emergence was more rapid with remifentanil. This is consistent with the necessity for less isoflurane use in the remifentanil group and the intrinsic rapid clearance of this opioid. IMPLICATIONS: Patients given remifentanil-based anesthesia for craniotomy had faster recovery times from anesthesia than did those given fentanyl-based anesthesia.

Anesthesia Recovery Period↗
PubMed2000

Evaluation of a cerebral oximeter as a monitor of cerebral ischemia during carotid endarterectomy.

BACKGROUND: Stroke is an important contributor to perioperative morbidity and mortality associated with carotid endarterectomy (CEA). This investigation was designed to compare the performance of the INVOS-3100 cerebral oximeter to neurologic function, as a means of detecting cerebral ischemia induced by carotid cross-clamping, in patients undergoing carotid endarterectomy with cervical plexus block. METHODS: Ninety-nine patients undergoing 100 CEAs with regional anesthesia (deep or superficial cervical plexus block) were studied. Bilateral regional cerebrovascular oxygen saturation (rSO2) was monitored using the INVOS-3100 cerebral oximeter. Patients were retrospectively assigned to one of two groups: those in whom a change in mental status or contralateral motor deficit was noted after internal carotid clamping (neurologic symptoms; n = 10) and those who did not show any neurologic change (no neurologic symptoms; n = 90). Data from 94 operations (neurologic symptoms = 10 and no neurologic symptoms = 84) were adequate for statistical analyses for group comparisons. A relative decrease in ipsilateral rSO2 after carotid occlusion (calculated as a percentage of preocclusion value) during all operations (n = 100) was also calculated to determine the critical level of rSO2 decrease associated with a change in neurologic function. RESULTS: The mean (+/- SD) decrease in rSO2 after carotid occlusion in the neurologic symptoms group (from 63.2 +/- 8.4% to 51.0 +/- 11.6%) was significantly greater (P = 0.0002) than in the no neurologic symptoms group (from 65.8 +/- 8.5% to 61.0 +/- 9.3%). Logistic regression analysis used to determine if a change in rSO2, calculated as a percentage of preclamp value, could be used to predict change in neurologic function was highly significant (likelihood ratio chi-square = 13.7; P = 0.0002). A 20% decrease in rSO2 reading from the preclamp baseline, as a predictor of neurologic compromise, resulted in a sensitivity of 80% and specificity of 82.2%. The false-positive rate using this cutoff point was 66.7%, and the false-negative rate was 2.6%, providing a positive predictive value of 33.3% and a negative predictive value of 97.4%. CONCLUSION: Monitoring rSO2 with INVOS-3100 to detect cerebral ischemia during CEA has a high negative predictive value, but the positive predictive value is low.

Adult↗
PubMed1999

An assessment of contributions made by extracranial tissues during cerebral oximetry.

This study was designed to determine the extent of contribution made by extracranial tissues to estimation of regional cerebrovascular saturation (ScO2) during cerebral oximetry. Thirty four patients undergoing carotid endarterectomy under regional anesthesia were studied. Bilateral ScO2 monitoring with two INVOS 3100 A cerebral oximeters was used. Effect of occlusion of external carotid artery (ECA) for five minutes on ScO2 readings followed by occlusion of internal and common carotid arteries was studied. ScO2 readings at 1 minute intervals were stored on computer disks for off-line analysis. Numerical data were subjected to a two way repeated measures analysis of variance to study the effect of side (ipsilateral or contralateral) and phase (pre clamp, ECA clamp, ICA clamp and post clamp) of operation. A value of p<0.05 was considered significant. There was no significant change in ScO2 on the contralateral side. On the ipsilateral hemisphere ScO2 decreased from 67.4+/-8.5 to 65.6+/-8.3 with ECA occlusion and to 61.4+/-9.6 after ICA occlusion returning to 64.8+/-9.8 after all clamps were released. Decrease after ECA occlusion was not significant (p = 0.12) while that after ICA occlusion was significant when compared to pre clamp value (p<0.001). After release of all clamps ipsilateral ScO2 returned toward baseline but remained significantly lower (p<0.05) than pre clamp values. When readings from two hemispheres were compared, a significant difference (p<0.001) was noted during ICA occlusion only. We conclude that the mathematical algorithm used for calculation of ScO2 by INVOS 3100 A cerebral oximeter measures predominantly the intracranial cerebrovascular saturation.

Aged↗
PubMed1997

Cerebral oximetry during circulatory arrest for aneurysm surgery.

A patient underwent surgical clipping of a complex giant intracranial carotid aneurysm with the aid of extracorporeal circulation and complete hypothermic circulatory arrest. During the entire procedure, cerebrovascular oxygen saturation (ScO2) was spectroscopically measured. The patient experienced circulatory arrest for 34 min; for 15 of the 34 min ScO2 was < 34% (minimum 32%). The patient tolerated the procedure without new neurological deficit, thus demonstrating that the previously suggested "critical" level of 35% ScO2 is not absolute.

Adult↗
PubMed1996

Cerebral oximetry in patients undergoing carotid endarterectomy under regional anesthesia.

BACKGROUND AND PURPOSE: Near-infrared spectroscopy is a technique that can potentially monitor changes in cerebral oxygenation. There are at present limited clinical data regarding the value of this technology in relating neurological outcome to cerebrovascular hemoglobin oxygen saturation (ScO2). This investigation reports changes in ScO2 due to carotid cross-clamping during carotid endarterectomy in awake patients. METHODS: ScO2 was monitored in 38 adult patients undergoing 41 carotid endarterectomies under regional anesthesia. Ipsilateral and contralateral hemispheres were monitored simultaneously during 36 operations, with ipsilateral monitoring alone in the remaining 5 operations. RESULTS: No significant difference was detected between ipsilateral and contralateral ScO2 during preclamp or postclamp periods. Carotid cross-clamping caused a statistically significant (P < .01) decrease in the ipsilateral ScO2, which decreased from 71.8 +/- 6.91% to 65.8 +/- 8.2%, while the contralateral ScO2 remained stable at 70.5 +/- 7.5% and 70.3 +/- 7.9%. The change in ipsilateral ScO2 ranged from +2.6% to -28.6% of the preclamp value. The difference between ipsilateral and contralateral ScO2 during cross-clamping was statistically significant (P < .001). The duration of cross-clamping was 39 +/- 11 minutes (range, 18 to 89 minutes). The decrease in ipsilateral ScO2 was highly variable from patient to patient and did not correlate with the duration of cross-clamping. CONCLUSIONS: These results suggest that carotid artery occlusion causes a statistically significant but variable decrease in ScO2 in the majority of patients. Data in this investigation provide a range of ScO2 values that was not associated with a clinically detectable neurological dysfunction.

Adult↗
PubMed1995

Topographic electroencephalogram of propofol-induced conscious sedation.

OBJECTIVES: To determine the effects of increasing doses of propofol that induce conscious sedation on the topographic electroencephalogram (EEG) of human volunteers and to test the hypothesis that more frontal brain areas are affected by low doses of propofol. METHODS: The scalp EEG was recorded monopolarly from 16 different sites based on the 10-20 International System. Microcomputer-based hardware and RHYTHM 7.1 software were used to obtain quantitative power frequency topographic EEG data. A total of 10 normal adult volunteers were given incremental doses of propofol targeted to plasma concentrations of 0 to 1200 ng/ml. RESULTS: Sedative concentrations of propofol produced a dramatic increase in beta 1, an increase in alpha 2 and beta 2, and an increase in delta activity at the largest concentration, with almost no change in theta activity. The increase in beta 1 activity had a linear correlation with plasma propofol levels (r = 0.9). Topographic mapping indicated that beta 1 activation was primarily in the frontal and central regions, with focal changes more in the left hemisphere. CONCLUSIONS: Topographic brain EEG mapping techniques indicate that frontal brain beta 1 EEG activity may be useful as an objective brain index of propofol conscious sedation.

Adult↗
PubMed1995

A study of radiologic imaging techniques and airway grading to predict a difficult endotracheal intubation.

STUDY OBJECTIVES: To study whether a detailed radiographic examination of neck and upper airway can help identify normal looking patients in whom endotracheal intubation may be difficult; determine whether such parameters as identified by magnetic resonance imaging (MRI) can also be identified in a soft tissue radiograph; and to study the correlation between oropharyngeal appearance, based on Mallampati's classification, and laryngoscopic findings in a large number of patients requiring endotracheal intubation. DESIGN: Prospective. SETTING: University medical center. PATIENTS: 20 adult patients in whom an unanticipated difficult endotracheal intubation was encountered, and a control group of 20 patients in whom endotracheal intubation was easily accomplished. INTERVENTIONS: Difficult-to-intubate patients were identified according to prospectively established criteria. Control subjects, in whom the trachea was easily intubated, were matched for age, gender, height, weight, and oropharyngeal appearance. MEASUREMENTS AND MAIN RESULTS: In all 40 study patients, a soft tissue radiograph and an MRI scan of the neck were obtained. We measured 21 parameters from both radiographic studies. There were no significant differences between the two groups in 20 of 21 measured parameters on MRI scans and soft tissue radiographs. Only one measurement--the distance between the uppermost visible part of the airway and the posterior pharyngeal wall (measured from MRI scans only)--between the two groups achieved statistical significance. The values recorded from MRI and soft tissue radiographs were not significantly different. Airway grading system first suggested by Mallampati had a fair correlation with laryngoscopy findings associated with a difficult endotracheal intubation. CONCLUSIONS: No significant difference between the two groups could be identified on soft tissue radiography or MRI scans.

Adult↗
PubMed1995

Effects of propofol sedation on seizures and intracranially recorded epileptiform activity in patients with partial epilepsy.

BACKGROUND: Case reports suggesting both pro- and anticonvulsant effect(s) of propofol have been published in recent years. The effects of sedative doses of propofol on epileptiform activities in patients suffering from intractable partial epilepsy were systematically investigated. METHODS: Fourteen patients suffering from complex partial seizures were studied. Electroencephalogram (EEG) was recorded from intracranial electrodes implanted in the hippocampi and temporal neocortex. Propofol was given as a computer-controlled infusion in four steps to achieve target plasma propofol concentrations of 0.3, 0.6, 0.9, and 1.2 micrograms/ml. Each concentration was maintained for 30 min, and steady-state kinetics were confirmed by blood levels drawn at 10th and 30th min at each level. Between the 15th and 30th min of each concentration of propofol, EEG was analyzed for presence of electroencephalographic seizure activity and/or number of interictal spikes (IIS). Effects of propofol on IIS frequency at different electrode sites were compared using a two-way repeated measures analysis of variance. A value of P < 0.05 was considered significant. RESULTS: None of the patients developed a seizure during the 2 h of propofol infusion. No "false spikes" (spikes developing with propofol infusion in areas where no spikes were seen in baseline EEG) were seen. Although effects of propofol on IIS frequency were highly variable across patients and at different propofol doses in the same patient, there was no statistically significant effect of propofol on any electrode site with any of the doses studied. CONCLUSIONS: We were unable to demonstrate a significant change in epileptiform activity with sedative doses of propofol in patients suffering from complex partial epilepsy.

Adult↗
PubMed1994

Comparison of the effectiveness of bilateral ilioinguinal nerve block and wound infiltration for postoperative analgesia after caesarean section.

We have studied the effects of bilateral ilioinguinal nerve block and wound infiltration with 0.5% bupivacaine on postoperative pain and analgesic requirements in 62 patients undergoing Caesarean section under general anaesthesia. A control group received no local anaesthetic supplementation. Both ilioinguinal block and wound infiltration reduced significantly the pain scores and analgesic requirements in the immediate postoperative period (P < 0.05). The differences in pain scores and analgesic requirements between the study groups were not statistically significant (P > 0.05).

Analgesia, Obstetrical↗
PubMed1994

Electrophysiologic effects of propofol sedation.

The scalp electroencephalogram (EEG), the long latency cognitive P300 auditory evoked response (AER), and reaction times were recorded in 10 volunteers sedated with a computer-controlled infusion of propofol to target plasma concentrations of 0.3, 0.6, 0.9, and 1.2 micrograms/mL. The observed mean +/- SE venous plasma concentrations were 0.152 +/- 0.042, 0.372 +/- 0.078, 0.679 +/- 0.104, and 1.065 +/- 0.112 micrograms/mL, respectively. Scalp EEG topographic mapping revealed that beta 1 activation was primarily frontal and central with relative sparing of the temporal lobes. The P300 response was dramatically reduced by propofol in a concentration-dependent manner, even though the subjects were conscious but clearly sedated. Mean +/- SE reaction times were increased by propofol sedation from 347 +/- 35 ms (control) to 391 +/- 48, 460 +/- 70, 549 +/- 64, and 622 +/- 120 ms at increasing mean venous plasma propofol concentrations. The mean percentage +/- SE of correct responses decreased from 98.1 +/- 2.0 (control) to 99.1 +/- 1.7, 87.4 +/- 9.2, 82.8 +/- 12.9, and 69.8 +/- 20.9 at increasing propofol concentrations. Dramatic alterations in the EEG, P300 response, and reaction times were observed, especially with the higher plasma concentrations which produced conscious sedation.

Adult↗
PubMed1991

Enhancement of somatosensory evoked potentials by etomidate in cats: an investigation of its site of action.

Enhancement of somatosensory evoked potentials by etomidate has been reported in recent clinical studies. This investigation was designed to investigate the central nervous system site of action responsible for this effect. Six adult cats were anesthetized with halothane (0.8-1%) in a mixture of 50% N2O in O2. A recording electrode was placed stereotactically in the ventral posterior lateral nucleus of thalamus (VPL), and a ball electrode was placed over the surface of the hind limb region of primary sensory cortex. Somatosensory evoked potentials in response to stimulation of tibial nerve thus were simultaneously recorded from cerebral cortex and VPL. The effect of two doses (1 and 3 mg.kg-1) of etomidate given 2 h apart on the latency and amplitude of cortical (positive wave at 15 ms) and thalamic (positive deflection at 10 ms, followed by negative deflection at 17 ms) evoked potentials was studied. There was no significant effect of etomidate on either latency or amplitude of early, positive thalamic potentials. Both doses of etomidate caused a significant increase in the latency and amplitude of cortical potentials. The mean latency of cortical potential increased by 1.72 ms (11%) after the 1 mg.kg-1 dose and 2.3 ms (15.9%) after the 3 mg.kg-1 dose. The maximum mean increase in the amplitude of cortical potentials was 14.3 microV (mean increase 78%, range 28-241%) after 1 mg.kg-1 and 19.1 microV (mean increase 112%, range 28-202%) after 3 mg.kg-1. Cortical amplitude remained significantly elevated for 30 min after 1 mg.kg-1 and for the remainder of the study period (60 min) after 3 mg.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Comparative disposition and whole-body autoradiographic distribution of [2-14C]azidothymidine and [2-14C]thymidine in mice.

Azidothymidine (AZT) is the only approved drug for treatment of acquired immunodeficiency syndrome caused by human immunodeficiency virus. The drug is known to be metabolized by mammalian systems. The objectives of this study were: 1) to investigate the biologic fate of AZT using whole-body autoradiography; and 2) to compare the biologic fate of AZT with that of the parent molecule thymidine (dThd). Male Sprague-Dawley mice were given (intravenously) a tracer dose of [2-14C]AZT (273 microCi/kg) or [2-14C]dThd (218 microCi/kg). Treated animals were sacrificed at various time periods (2 min, 5 min, 4 hr and 24 hr) and processed for whole-body autoradiography. Tissue distribution of radioactivity in the autoradiographs was quantitated using computer-aided image analysis. The elimination of AZT and dThd was also examined by radiochemical analyses of urine, feces and expired air of treated animals over a 24-hr period. Twenty-four hr following AZT treatment, the radioactivity excreted in urine, feces and in exhaled air (as 14CO2) accounted for 86, 4.6 and 3.7% of the dose, respectively. Within 2 min after administration of AZT, maximum radioactivity was detected in the kidney. The brain, spinal cord and testes were conspicuous because of virtual lack of radioactivity. All other parenchymatous organs (liver, lung, heart and spleen) had apparent similar levels of radioactivity that were higher than those in the connective tissues. At a later time period (4 hr), the radioactivity in most organs was eliminated except in the renal medulla, contents of gastrointestinal tract, urinary bladder and mouth cavity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Effects of nitrous oxide on global and regional cortical blood flow.

We conducted regional cortical blood flow studies using the xenon-133 clearance technique on 12 volunteers during the administration of 25% and 50% N2O and during baseline conditions (breathing room air or 100% O2). Global cortical blood flow was very highly significantly increased above baseline measures in all subjects by 50% N2O (mean increase 37% above 100% O2 condition). A smaller but still significant increase was observed with 25% N2O. Analysis of regional cortical blood flow revealed heterogeneity in the pattern of changes; that is, the baseline pattern was altered by the inhalation of N2O, most often resulting in an accentuation of relative frontal blood flow. The anterior-posterior gradient in N2O-induced blood flow changes differs from that observed with simple vasodilatory agents, such as CO2, with which the increase is purely systemic and the baseline pattern is preserved. This indicates that N2O has differential effects on cerebral metabolism that may well reflect the typical alterations in experiential state reported by subjects.

Adult↗
PubMed1989

Effect of hypocapnia on local cerebral glucose utilization in rats.

The effect of hypocapnia on regional cerebral glucose utilization (L-CMRg) was studied in 14 Sprague Dawley rats. After cannulation of femoral vessels, halothane was discontinued and anesthesia was maintained with 70% N2O in oxygen. The animals' lungs were mechanically ventilated to achieve normocapnia (PaCO2 = 40 +/- 2 mmHg) in group A or hypocapnia (PaCO2 = 25 +/- 2 mmHg) in group B. L-CMRg was measured by the 14C-2-deoxyglucose autoradiographic method. Twenty-six anatomically discrete structures representing cortical, subcortical, limbic, and brainstem areas were studied. In hypocapnic animals, mean values for L-CMRg were higher in 25 out of 26 structures studied. The increase in L-CMRg was heterogenous. The structures that had higher L-CMRg during normocapnia showed the greatest increase in L-CMRg. When the two groups were compared using a profile analysis, in six regions (lateral and ventral thalamus, inferior colliculus, lateral habenulla, medial geniculate body, and auditory cortex), a value of P less than 0.05 was obtained.

Animals↗