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Biomedical subjects

A W Gelb

Publications and source records attributed to A W Gelb.

At least 37 records · Page 2Linked to original sources
PubMed1999

Rats show unimpaired learning within minutes after recovery from single bolus propofol anesthesia.

PURPOSE: To examine the learning ability of rats shortly after recovery from a bolus dose of propofol by assessing learning on a swim-to-platform task. Also, muscarinic blockade was used as a pharmacological test of whether learning shortly after propofol anesthesia resembles normal learning. METHODS: Propofol anesthetized rats (15-20 mg x kg(-1) i.v.) were trained on a swim-to-platform task five to seven minutes after recovering from surgical anesthesia and tested two to three hours later In addition, the muscarinic antagonist scopolamine hydrobromide (5 mg x kg(-1) s.c.) was given to a subgroup of rats before testing. During 10 trials, the number of times a given rat took 10 sec or longer to locate and climb onto a visible platform was tabulated and counted as errors. RESULTS: When trained shortly after recovery from the anesthetic, propofol anesthetized rats made 3.2 +/- 0.4 compared with 1.0 +/- 0.1 errors in controls (P < 0.0001). Two to three hours later both groups performed equally well. Rats trained after propofol anesthesia and given scopolamine before testing made 0.7 +/- 0.5 errors and performed as well as normal controls, 1.2 +/- 0.2 errors when subjected to the same procedures without propofol anesthesia, and better than scopolamine-treated untrained rats, 5.5 +/- 0.7 errors, (P < 0.05). CONCLUSION: Training five to seven minutes after recovery from propofol anesthesia resulted in normal retention of the swim- to-platform task. It also produced the same resistance to the disruptive effects of scopolamine as did training in rats that were not anesthetized. Thus, the ability to learn recovers rapidly after propofol anesthesia induced by a single intravenous bolus dose.

Anesthesia Recovery Period↗
PubMed1999

Cerebral blood volume measurements using dynamic contrast-enhanced x-ray computed tomography: application to isoflurane anaesthetic studies.

A convenient and simple method of measuring cerebral blood volume (CBV) will aid in the clinical management of patients with cerebrovascular diseases and head trauma. Using a two-compartment model to characterize the distribution of x-ray contrast agent in the brain, we have developed a non-equilibrium (dynamic) x-ray CT method to measure CBV and have applied this method to study the effects of isoflurane. CBV and cerebral blood flow (CBF, ex vivo) measurements were made in two groups of New Zealand White rabbits at varying (study group) and constant (control group) arterial CO2 concentration. ANOVA for repeated measures was used on the control data to determine the precision of our two-compartment CT-CBV method. The results showed that the precision of our CT-CBV measurement was 9.8%. In addition a paired t-test analysis of the control data revealed that the duration of isoflurane anaesthesia had no effect on the repeated measurements of CBV or CBF. The rate of change in CBV (0.049 ml/100 g/mmHg) and CBF (6.2 ml/min/100 g/mmHg) with respect to changes in arterial CO2 concentration under the influence of isoflurane anaesthesia was similar to those reported in previous studies, thus validating our experimental CT-CBV and CBF measurements. Our CT-CBV method will lead to more information on the relationship between CBV and CBF under different pharmacological interventions in both normal and disease conditions.

Analysis of Variance↗
PubMed1999

Mild hypothermia as a protective therapy during intracranial aneurysm surgery: a randomized prospective pilot trial.

OBJECTIVE: To conduct a pilot trial of mild intraoperative hypothermia during cerebral aneurysm surgery. METHODS: One hundred fourteen patients undergoing cerebral aneurysm clipping with (n = 52) (World Federation of Neurological Surgeons score < or =III) and without (n = 62) acute aneurysmal subarachnoid hemorrhage (SAH) were randomized to normothermic (target esophageal temperature at clip application of 36.5 degrees C) and hypothermic (target temperature of 33.5 degrees C) groups. Neurological status was prospectively evaluated before surgery, 24 and 72 hours postoperatively (National Institutes of Health Stroke Scale), and 3 to 6 months after surgery (Glasgow Outcome Scale). Secondary outcomes included postoperative critical care requirements, respiratory and cardiovascular complications, duration of hospitalization, and discharge disposition. RESULTS: Seven hypothermic patients (12%) could not be cooled to within 1 degrees C of target temperature; three of the seven were obese. Patients randomized to the hypothermic group more frequently required intubation and rewarming for the first 2 hours after surgery. Although not achieving statistical significance, patients with SAH randomized to the hypothermic group, when compared with patients in the normothermic group, had the following: 1) a lower frequency of neurological deterioration at 24 and 72 hours after surgery (21 versus 37-41%), 2) a greater frequency of discharge to home (75 versus 57%), and 3) a greater incidence of good long-term outcomes (71 versus 57%). For patients without acute SAH, there were no outcome differences between the temperature groups. There was no suggestion that hypothermia was associated with excess morbidity or mortality. CONCLUSION: Mild hypothermia during cerebral aneurysm surgery is feasible in nonobese patients and is well tolerated. Our results indicate that a multicenter trial enrolling 300 to 900 patients with acute aneurysmal SAH will be required to demonstrate a statistically significant benefit with mild intraoperative hypothermia.

Acute Disease↗
PubMed1999

CT assessment of cerebral perfusion: experimental validation and initial clinical experience.

PURPOSE: To validate a dynamic single-section computed tomographic (CT) method to measure cerebral blood volume (CBV) and cerebral blood flow (CBF) by using a noncarotid artery as the input and to demonstrate the feasibility of this method in a pilot series of patients. MATERIALS AND METHODS: Twelve dynamic contrast material-enhanced CT studies were performed in beagles. CBV, CBF, and mean transit time (MTT) values were calculated by using an internal carotid artery (ICA) and a noncarotid artery as the input artery to the brain. Patient studies with use of the radial artery as the input were performed (a) repetitively in two patients after subarachnoid hemorrhage, (b) in a patient with a symptomatic ICA occlusion before and after the intravenous injection of 1 g of acetazolamide, and (c) in a patient with a malignant brain tumor. RESULTS: Linear regression analyses revealed highly significant correlations (P < .001) between CBV (r, 0.98; slope, 0.96), CBF (r, 0.89; slope, 0.87), and MTT (r, 0.80; slope, 0.76) values calculated with the ICA and the noncarotid inputs. The CT-derived patient data correlated well with ancillary clinical and neuroradiologic findings. CONCLUSION: Dynamic single-section CT scanning to measure CBV and CBF on the basis of a noncarotid input is a highly accessible and cost-effective blood flow measurement technique.

Animals↗
PubMed1999

Effect of beta-adrenoreceptor blockade with nadolol on the duration of local anesthesia.

BACKGROUND: beta-adrenoreceptor blockers, or beta-blockers, are drugs commonly prescribed for hypertension, angina and migraine headaches. In a patient taking beta-blocker medication, administration of a local anesthetic containing a vasoconstrictor could result in an adverse interaction. METHODS: The authors conducted a double-blind, randomized, crossover, placebo-controlled study to test the hypothesis that a nonselective beta-blocker--nadolol--enhances vasoconstriction induced by the epinephrine contained in local anesthetic, thus resulting in an increased duration of anesthesia. Ten healthy male volunteers were given either a placebo or a single, standard oral dose of nadolol (80 milligrams). The upper lateral incisor teeth were anesthetized using lidocaine with or without epinephrine. RESULTS: The mean duration of pulpal and soft-tissue anesthesia was increased in subjects who took nadolol compared with those who took placebo by 17 minutes (58 percent) and 16.5 minutes (19 percent), respectively, when they received 1 milliliter of lidocaine containing 1:100,000 epinephrine. These differences were both clinically and statistically significant (P = .007). Using lidocaine without epinephrine produced no clinically or statistically significant difference in duration of pulpal or soft-tissue anesthesia in the two groups of subjects. The authors noted no significant changes in blood pressure or pulse rate. CONCLUSIONS: Administration of local anesthetic containing epinephrine to subjects receiving a beta-blocker increased the duration of pulpal and soft-tissue anesthesia. There was no difference in duration of anesthesia between groups when local anesthetic without epinephrine was used. CLINICAL IMPLICATIONS: Use of local anesthetic containing a vasoconstrictor should be avoided in patients taking beta-blocker medication because of a possible adverse drug interaction. However, when a vasoconstrictor is indicated for hemostasis, the local anesthetic should be administered slowly and in small amounts as pulse rate and blood pressure are being monitored. The patient should be informed that the duration of anesthesia might be prolonged.

Adrenergic beta-Antagonists↗
PubMed1999

The effect of sevoflurane and isoflurane anesthesia on interictal spike activity among patients with refractory epilepsy.

UNLABELLED: The electrophysiologic effects of sevoflurane are not well characterized in humans. Among patients with refractory epilepsy, this study compared 1) electroencephalographic (EEG) interictal spike activity during wakefulness and sevoflurane anesthesia, and 2) electrocorticographically (ECoG) recorded interictal spike activity during sevoflurane and isoflurane anesthesia. We studied 12 patients undergoing insertion of subdural electrodes. Before commencing anesthesia, awake (baseline) EEG recordings were obtained. After inhaled induction, EEG interictal spike activity was evaluated during stable, normocapnic, and hypocapnic (Paco2 = 28-30 mm Hg), sevoflurane anesthesia administered at 1.5 times the minimum alveolar anesthetic concentration (1.5 MAC). Immediately after surgery, ECoG recordings were obtained from subdural electrodes during 1) 1.5 MAC isoflurane, 2) 0.3 MAC isoflurane, and 3) 1.5 MAC sevoflurane anesthesia. EEG spike frequency increased in all patients during sevoflurane anesthesia compared with awake recordings (P = 0.002). Compared with 0.3 MAC isoflurane anesthesia, ECoG interictal spike frequency was higher in all patients during 1.5 MAC sevoflurane anesthesia (P = 0.004) and in 8 of 10 patients during 1.5 MAC isoflurane anesthesia (P = 0.016). Under sufficiently rigorous conditions, both sevoflurane and isoflurane can provoke interictal spike activity at near burst-suppression doses. This property is more prominent with sevoflurane than isoflurane. IMPLICATIONS: The results of this study suggest that the capacity to modulate neuroexcitability is a dose-dependent feature of volatile anesthetics that is manifested most prominently at near burst-suppression doses (i.e., 1.5 times the minimum alveolar anesthetic concentration) and is minimal or absent at low doses.

Adolescent↗
PubMed1999

Dynamic CT measurement of cerebral blood flow: a validation study.

BACKGROUND AND PURPOSE: Our objective was to develop a method to correct for the effect of partial volume averaging (PVA) in the CT measurement of contrast enhancement in small arteries, and to validate a dynamic contrast-enhanced CT method for the measurement of regional cerebral blood flow (rCBF). METHODS: Contrast-enhanced CT scans of tubes of known inner diameters were obtained to estimate the size-dependent scaling factors (PVSF) due to PVA. The background-subtracted image profiles of the contrast-filled tubes were fitted to gaussian curves, and the standard deviations (SDs) of these curves were correlated with the PVSF of each tube. In the second part of this investigation, 13 studies were performed in six New Zealand white rabbits under normal conditions. Dynamic CT measurements of rCBF, regional cerebral blood volume (rCBV), and regional mean transit time (rMTT) were calculated in the left and right parietal lobes and the basal ganglia. The CT rCBF values were compared with those obtained by the microsphere method, which is the standard of reference. RESULTS: We found strong correlations for the SDs of the gaussian curves to the known inner diameters of the tubes and to their size-related PVSF. These correlations demonstrated that the error from PVA in the measurement of arterial enhancement can be corrected without knowledge of the actual size of the artery. The animal studies revealed a mean (+/- SD) rCBF of 73.3 +/- 31.5 mL/100 g per minute, a mean rCBV of 1.93 +/- 0.74 mL/100 g, and a mean rMTT of 1.81 +/- 1.02 seconds. A strong correlation was found between rCBF values derived by the CT and the microsphere methods. CONCLUSION: We have validated a new dynamic CT method for measuring rCBF. The accuracy of this technique suggests that it can be used as an alternative diagnostic tool to assess the cerebral hemodynamics in experimental and clinical situations.

Animals↗
PubMed1998

Propofol and hyperventilation for the treatment of increased intracranial pressure in rabbits.

UNLABELLED: Using a rabbit model of intracranial hypertension, we studied (a) the additive effect of propofol and hyperventilation (HV) on increased intracranial pressure (ICP), (b) the ICP-lowering effect of additive therapy (i.e., propofol plus HV versus HV plus propofol), and (c) whether combined therapy induced cerebral ischemia. Twenty-three New Zealand White rabbits were studied, of which seven were control animals. The animals were anesthetized with midazolam and fentanyl. An extradural balloon was used to increase ICP to 26+/-2 mm Hg. Elevation of ICP resulted in a >50% reduction in ipsilateral somatosensory evoked potential (SEP) amplitude. The rabbits were then randomized to be treated with propofol followed by HV (Group 1, n = 8) or HV then propofol (Group 2, n = 8). With HV, PaCO2 was reduced from 41+/-2 mm Hg to 27+/-3 mm Hg. In Group 1 rabbits, the ICP decreased with treatment (from 26+/-2 to 12+/-2 mm Hg). The reduction in ICP was significantly greater (P = 0.008) than that in Group 2 rabbits (from 26+/-2 to 16+/-5 mm Hg). In both groups, propofol and HV had an additive effect in reducing ICP. Further, when propofol was used as the initial treatment, there was a significant increase in SEP amplitude that was not apparent in Group 2 rabbits. In conclusion, we found propofol and HV to be additive in the treatment of increased ICP. In animals treated with propofol followed by HV, there was a greater decrease in ICP than in rabbits treated initially with HV and then propofol. IMPLICATIONS: We have demonstrated that propofol has a greater effect on increased intracranial pressure than hyperventilation when used as the initial treatment and that the two treatments are additive. Should control of intracranial pressure be required after the administration of propofol, then hyperventilation may be added to the treatment.

Anesthesia↗
PubMed1998

Myocardial infarction after noncardiac surgery.

BACKGROUND: In this study, the authors intensively monitored isoenzyme and electric activity of the heart for the first 7 days after noncardiac surgery in a large group of patients at risk for postoperative myocardial infarction (PMI). METHODS: After institutional review board approval and written informed consent were received, 323 patients, aged 50 yr or older, who had ischemic heart disease and presented for noncardiac surgery, were enrolled in this prospective, blinded study. After operation, patients had daily clinical assessments, electrocardiograms, and measurements of creatine kinase (CK), CK-2 (mass and activity), and Troponin-T on the operative night, twice daily on postoperative days 1-4, and then daily on days 5-7. A diagnosis of PMI was made if the total CK was > 174 U/l and in the presence of two of the following: (1) CK-2/CK (mass or activity) > 5%, (2) new Q waves lasting > or = 0.04 s and 1 mm deep in at least two contiguous leads, (3) Troponin-T was > 0.2 microg/l, or (4) a positive result of pyrophosphate scan. RESULTS: Eighteen of the 323 patients (5.6%) had a PMI, of which 3 (17%) were fatal. Only 3 of 18 patients had chest pain, whereas 10 of 18 patients (56%) had other clinical findings. The electrocardiographic classification of the PMI was Q wave in 6, non-Q wave in 10, and indeterminate in 2. The PMIs occurred on the day of operation in 8, on day one in 6, on day two in 3, and on day four in 1 patient. CONCLUSIONS: This study determined that PMI was an early event, only occasionally associated with chest pain, and usually non-Q wave in nature.

Aged↗
PubMed1998

Effect of nitrous oxide on cerebral blood flow velocity after induction of hypocapnia.

Hyperventilation may reverse increases in cerebral blood flow velocity caused by inhalation of nitrous oxide (N2O). This study sought to determine whether inhalation of 50% nitrous oxide after the induction of hyperventilation increases cerebral blood flow velocity as measured by transcranial Doppler ultrasonography. Seven volunteers breathed air/O2 through a modified Circle system at normocapnia followed by air/O2 with hyperventilation, and then N2O/O2 with hyperventilation. Expired gas concentrations were measured in the expiratory limb of the circuit distal to a one-way valve. Hyperventilation reduced end-tidal carbon dioxide from 38+/-1 mmHg to 26+/-1 mmHg. Hypocapnia was maintained during inhalation of N2O (EtCO2=28+/-1 mmHg). Mean cerebral blood flow velocity decreased 34% with hyperventilation (38+/-4 cm/second versus 59+/-9 cm/second, p < 0.05) and returned to baseline with the addition of nitrous oxide (58+/-7 cm/second), despite persistent hypocapnia. The addition of nitrous oxide to the inspired gas mixture after induction of hypocapnia reversed reductions in cerebral blood flow velocity associated with hyperventilation. Potential benefits of induced hypocapnia in patients with intracranial pathology may be offset by the administration of N2O.

Adult↗
PubMed1997

Propofol patient-controlled sedation during hip or knee arthroplasty in elderly patients.

PURPOSE: Little information is available regarding the use of patient-controlled sedation (PCS) among the elderly. This study evaluated the safety and efficacy of propofol PCS among elderly patients undergoing hip or knee arthroplasty. METHODS: Forty patients, aged 65-78 yr, undergoing hip or knee arthroplasty under regional anaesthesia were randomized to receive propofol PCS (dose = 0.3 mg.kg-1, delay = three min; n = 20) or anaesthetist-administered midazolam-fentanyl sedation (n = 20). Sedation, anxiety and discomfort visual analogue scores (VAS) were measured, by an independent observer, preoperatively, immediately at the end of surgery and one hour following admission to the postanaesthetic care unit (PACU). Cognition was evaluated, using an abbreviated Mini Mental Status Examination, preoperatively and in the PACU. Patient satisfaction, based on VAS and a brief questionnaire, was measured in the PACU. The incidence of intraoperative complications was also compared. RESULTS: Patient satisfaction was high in each group. Sedation and anxiety VAS were similar in each group. A high incidence of pain with drug injection was noted among patients receiving propofol (80%). Transient deeper levels of sedation (6 vs 1; P = 0.05) were observed more commonly in the propofol PCS group. CONCLUSION: Propofol PCS provides effective sedation. Using a propofol dose of 0.3 mg.kg-1, transient episodes of deeper sedation were noted more frequently among patients receiving PCS. These episodes did not require intervention but, suggest that this propofol PCS dose approaches the limit of safety and should be further reduced for some elderly patients.

Adjuvants, Anesthesia↗
PubMed1997

Propofol sedation during awake craniotomy for seizures: electrocorticographic and epileptogenic effects.

This prospective study evaluated the effects of propofol sedation on the incidence of intraoperative seizures and the adequacy of electrocorticographic (ECoG) recordings during awake craniotomy performed for the management of refractory epilepsy. Thirty patients scheduled for temporal or frontal lobectomy for epilepsy under bupivacaine scalp block were randomized to receive patient-controlled propofol sedation (PCS) combined with a basal infusion of propofol (n = 15) or neurolept analgesia using an initial bolus dose of fentanyl (0.7 microg/kg) and droperidol (0.04 mg/kg) followed by a fentanyl infusion (n = 15). Propofol administration was suspended 15 min before ECoG recording in the PCS group. The occurrence of inappropriate intraoperative seizures was noted and, based on blind review, the adequacy of ECoG recordings was compared. A higher incidence of intraoperative seizures was noted among the neurolept patients (6 vs 0, P = 0.008). Intraoperatively, ECoG recordings were adequate to proceed with resection in both groups. Evidence of low spike activity on ECoG did not correlate with the type of sedation administered. Higher frequency background ECoG activity was noted among patients who received propofol, but this did not interfere with ECoG interpretation. The use of propofol sedation does not appear to interfere with ECoG during epilepsy surgery, provided administration is suspended at least 15 min before recording.

Adjuvants, Anesthesia↗
PubMed1997

Propofol sedation during awake craniotomy for seizures: patient-controlled administration versus neurolept analgesia.

This prospective study evaluated the safety and efficacy of patient-controlled sedation (PCS) using propofol during awake seizure surgery performed under bupivacaine scalp blocks. Thirty-seven patients were randomized to receive either propofol PCS combined with a basal infusion of propofol (n = 20) or neurolept analgesia using an initial bolus dose of fentanyl and droperidol followed by a fentanyl infusion (n = 17). Both groups received supplemental fentanyl and dimenhydrinate for intraoperative pain and nausea, respectively. Comparisons were made between groups for sedation, memory, and cognitive function, patient satisfaction, and incidence of complications. Levels of intraoperative sedation and patient satisfaction were similar between groups. Memory and cognitive function were well preserved in both groups. The incidence of transient episodes of ventilatory rate depression (<8 bpm) was more frequent among the propofol patients (5 vs 0, P = 0.04), particularly after supplemental doses of opioid. Intraoperative seizures were more common among the neurolept patients (7 vs 0, P = 0.002). PCS using propofol represents an effective alternative to neurolept analgesia during awake seizure surgery performed in a monitored care environment.

Adjuvants, Anesthesia↗
PubMed1997

Comparison of the Bullard and Macintosh laryngoscopes for endotracheal intubation of patients with a potential cervical spine injury.

BACKGROUND: In the emergency trauma situation, in-line stabilization (ILS) of the cervical spine is used to reduce head and neck extension during laryngoscopy. The Bullard laryngoscope may result in less cervical spine movement than the Macintosh laryngoscope. The aim of this study was to compare cervical spine extension (measured radiographically) and time to intubation with the Bullard and Macintosh laryngoscopes during a simulated emergency with cervical spine precautions taken. METHODS: Twenty-nine patients requiring general anesthesia and endotracheal intubation were studied. Patients were placed on a rigid board and anesthesia was induced. Laryngoscopy was performed on four occasions: with the Bullard and Macintosh laryngoscopes both with and without manual ILS. Cricoid pressure was applied with ILS. To determine cervical spine extension, radiographs were exposed before and during laryngoscopy. Times to intubation and grade view of the larynx were also compared. RESULTS: Cervical spine extension (occiput-C5) was greatest with the Macintosh laryngoscope (25.9 degrees +/- 2.8 degrees). Extension was reduced when using the Macintosh laryngoscope with ILS (12.9 +/- 2.1 degrees) and the Bullard laryngoscope without stabilization (12.6 +/- 1.8 degrees; P < 0.05). Times to intubation were similar for the Macintosh laryngoscope with ILS (20.3 +/- 12.8 s) and for the Bullard without ILS (25.6 +/- 10.4 s). Manual ILS with the Bullard laryngoscope results in further reduction in cervical spine extension (5.6 +/- 1.5 degrees) but prolongs time to intubation (40.3 +/- 19.5 s; P < 0.05). CONCLUSIONS: Cervical spine extension and time to intubation are similar for the Macintosh laryngoscope with ILS and the Bullard laryngoscope without ILS. However, time to intubation is significantly prolonged when the Bullard laryngoscope is used in a simulated emergency with cervical spine precautions taken. This suggests that the Bullard laryngoscope may be a useful adjunct to intubation of patients with potential cervical spine injury when time to intubation is not critical.

Adult↗
PubMed1997

Intravenous anaesthetics: some cellular sites of action.

Intravenous anaesthetics have diverse effects on neurones within the central nervous system. Only those that occur at clinical concentrations are likely to be relevant. The dominant effect of many agents is the potentiation of the inhibitory neurotransmitter gamma amino butyric acid (GABA) by various mechanisms while inhibiting the effects of excitatory transmitters seems to be less dominant, except for ketamine.

Anesthetics, Inhalation↗
PubMed1997

Patient-controlled sedation using propofol during interventional neuroradiologic procedures.

Patient-controlled sedation (PCS) using propofol has been reported to provide safe and effective sedation during a variety of procedures performed under regional or local anesthesia. In a prospective, randomized fashion, this study evaluated propofol PCS compared to anesthesiologist-administered midazolam-fentanyl sedation during interventional neuroradiologic (INR) procedures. Nineteen patients undergoing 24 INR procedures received propofol PCS (PCS dose, 0.5 mg/kg; lockout interval, 3 min) or anesthesiologist-administered midazolam-fentanyl sedation. Study parameters included discomfort, sedation and anxiety visual analogue scores (VAS), cognitive function, patient satisfaction, and complications. No difference was found between the two sedation techniques with respect to the levels of sedation and anxiolysis. Cognitive function was well preserved in both groups. Patient satisfaction was similarly high in both groups. Complications were similar between groups. These included ventilatory depression (two patients in each group) and excessive sedation (two patients in each group). Three patients in the propofol group became excessively restless, resulting in brief interruptions during the respective procedures. Propofol PCS offers a safe sedation technique during INR procedures with a sedation and anxiolysis profile that was not distinguishable from anesthesiologist-administered midazolam-fentanyl sedation.

Adolescent↗