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Biomedical subjects

J Butterworth

Publications and source records attributed to J Butterworth.

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

Ulnar nerve pressure: influence of arm position and relationship to somatosensory evoked potentials.

BACKGROUND: Although the ulnar nerve is the most frequent site of perioperative neuropathy, the mechanism remains undefined. The ulnar nerve appears particularly susceptible to external pressure as it courses through the superficial condylar groove at the elbow, rendering it vulnerable to direct compression and ischemia However, there is disagreement among major anesthesia textbooks regarding optimal positioning of the arm during anesthesia. METHODS: To determine which arm position (supination, neutral orientation, or pronation) minimizes external pressure applied to the ulnar nerve, we studied 50 awake, normal volunteers using a computerized pressure sensing mat. An additional group of 15 subjects was tested on an operating table with their arm in 30 degrees, 60 degrees, and 90 degrees of abduction, as well as in supination, neutral orientation, and pronation. To determine the onset of clinical paresthesia compared to the onset and severity of somatosensory evoked potential (SSEP) electrophysiologic changes, we studied a separate group of 16 male volunteers while applying intentional pressure directly to the ulnar nerve. Data are presented as mean (median; range). RESULTS: Supination minimizes direct pressure over the ulnar nerve at the elbow (2 mmHg [0; 0-23]; n = 50), compared with both neutral forearm orientation (69 mmHg [22; 0-220]; P < 0.0001), as well as pronation (95 mmHg [61; 0-220]; P < 0.0001). Neutral forearm orientation also results in significantly less pressure over the ulnar nerve compared to pronation (P < or = 0.04). The estimated contact area of the ulnar nerve with the weight-bearing surface was significantly (P < 0.0001) smaller in the supine position (2.2 cm2 [0.5; 0-9]; n = 50) compared with both neutral orientation (5.5 cm2 [5.0; 0-13]) and pronation (5.8 cm2 [6; 0-12]). With the forearm in neutral orientation, ulnar nerve pressure decreased significantly (P < or = 0.01; n = 15) as the arm was abducted at the shoulder from 0 degrees to 90 degrees. In the 16 male subjects tested, notable alterations in ulnar nerve SSEP signals (decrease > or = 20% in N9-N9' amplitude) were detected in 15 of 16 awake males during application of intentional pressure to the ulnar nerve. However, eight of these subjects did not perceive a paresthesia, even as SSEP waveform amplitudes were decreasing 23-72%. Two of these eight subjects manifested severe decreases in SSEP amplitude (> or = 60%). CONCLUSIONS: Extrapolating these results to the clinical setting, the supinated arm position is likely to minimize pressure over the ulnar nerve. With the forearm in neutral orientation, pressure over the ulnar nerve decreases as the arm is abducted between 30 degrees and 90 degrees. In addition, up to one half of male patients may fail to perceive or experience clinical symptoms of ulnar nerve compression sufficient to elicit SSEP changes.

Adult↗
PubMed1998

Differential onset of median nerve block: randomized, double-blind comparison of mepivacaine and bupivacaine in healthy volunteers.

We have compared the delay in onset of 1% mepivacaine and 0.33% bupivacaine in different nerve fibre types in 10 volunteers undergoing median nerve blocks, in a randomized, double-blind, crossover study. Hot, cold, pinprick and light touch sensations, compound motor action potentials (CMAP), sensory nerve action potentials (SNAP) and skin temperature were recorded at 2-min intervals. Hot, cold, pinprick, light touch sensations, SNAP and CMAP were significantly inhibited, and skin temperature was significantly increased after administration of both agents. The first noticeable reduction in cold sensation was detected later after bupivacaine compared with mepivacaine, but after a delay similar to that of other nerve functions. Bupivacaine and mepivacaine inhibited SNAP and CMAP with a similar time delay to steady-state. Bupivacaine produced steady-state inhibition of hot and cold sensations significantly later than mepivacaine; nevertheless, the sequence that sensory modalities failed, with few exceptions, and the extent of anaesthesia at 40 min were similar for both agents. Our technique provides a novel, multi-modal method of comparing local anaesthetics and related agents over time.

Adult↗
PubMed1998

Do shorter-acting neuromuscular blocking drugs or opioids associate with reduced intensive care unit or hospital lengths of stay after coronary artery bypass grafting? CABG Clinical Benchmarking Data Base Participants.

BACKGROUND: The authors hypothesized that shorter-acting opioid and neuromuscular blocking drugs would be associated with reductions in duration of intubation, length of stay (LOS) in the intensive care unit (ICU) after tracheal extubation, or postoperative (exclusive of ICU) LOS, and that shorter durations of intubation would be associated with reduced ICU LOS after extubation and postoperative (exclusive of ICU) LOS. METHODS: One-thousand ninety-four patients undergoing primary coronary artery bypass graft surgery at 40 academic health centers were studied. Multiple patient-related factors were included in multivariate models for hypothesis testing. RESULTS: The duration of tracheal intubation, ICU LOS after extubation, and postoperative (exclusive of ICU) LOS all varied significantly by site. There was no difference between vecuronium and pancuronium in duration of intubation, ICU LOS after extubation, or postoperative (exclusive of ICU) LOS. Use of sufentanil rather than fentanyl was associated with a significant (P=0.045) reduction of 1.9 h (95% CI, 0.04 to 4.1 h) in duration of tracheal intubation but had no significant effect on ICU LOS after extubation, total ICU LOS, postoperative (exclusive of ICU) LOS, or total postoperative LOS. The authors' best model predicts a complex association between increasing duration of intubation and both ICU LOS after tracheal extubation and postoperative (exclusive of ICU) LOS, which was associated with an increase in those measures when duration of intubation exceeded 7.3 or 3 h, respectively. CONCLUSIONS: The LOS measures varied considerably among the institutions. Use of shorter-acting opioid and neuromuscular blocking drugs had no association with ICU LOS after tracheal extubation or with postoperative (exclusive of ICU) LOS. Only when the duration of intubation exceeded threshold values was it associated with increased LOS measures.

Aged↗
PubMed1997

Protective effect of L-carnitine in ammonia-precipitated encephalopathy in the portacaval shunted rat.

L-carnitine administration prevents the neurological symptoms of acute ammonia toxicity. To further evaluate its efficacy in the prevention of hepatic encephalopathy in hyperammonemic conditions, L-carnitine (16 mmol/kg, intraperitoneally [i.p.] was administered 1 hour before ammonium acetate (NH4OAc) (8.5 mmol/kg, subcutaneously) to portacaval shunted (PCS) rats. Cerebrospinal fluid (CSF) ammonia, lactate, and amino acid levels were measured in relation to deteriorating neurological status in these animals. None of 35 L-carnitine-treated animals showed neurological deterioration after NH4OAC administration compared with saline-treated controls; the latter manifested severe encephalopathy progressing through loss of righting reflex to coma. Survival rate was 100% in the L-carnitine-treated group compared with 5% in saline-treated controls. Following NH4OAC administration to PCS rats, CSF ammonia increased to 0.93 +/- 0.15 mmol/L and 1.24 +/- 0.15 mmol/L at precoma and coma stages of encephalopathy (P < .01) respectively. Treatment with L-carnitine reduced CSF ammonia at both precoma and coma stages; the time-course of this protective effect paralleled blood and CSF L-carnitine accumulation. CSF alanine and lactate increases following NH4OAC administration to PCS rats were significantly attenuated following L-carnitine treatment. However, L-carnitine treatment did not lead to significant reductions in plasma ammonia nor CSF or brain glutamine in these animals. These findings show the therapeutic efficacy of L-carnitine in ammonia-precipitated coma in PCS rats and suggest that this protective effect is centrally mediated involving improved mitochondrial respiration. L-carnitine could be of therapeutic benefit in the prevention of hepatic encephalopathy precipitated by ammoniagenic conditions in humans with chronic liver disease.

Amino Acids↗
PubMed1997

Selective alterations of cerebrospinal fluid amino acids in dogs with congenital portosystemic shunts.

Numerous studies suggest that modifications in concentrations of both excitatory and inhibitory amino acids are implicated in the pathophysiology of portal-systemic encephalopathy (PSE), a neuropsychiatric disorder associated with chronic liver disease in humans. In this study, amino acid levels were measured by High Performance Liquid Chromatography (HPLC) in Cerebrospinal Fluid (CSF) of 10 dogs (age range: 3 mo.- 3 yr 4 mo.) exhibiting a congenital portal-systemic shunt, either intra or extra-hepatic, and 8 age-matched control dogs who showed no signs of hepatic or neurologic disorders. Dogs with congenital shunts manifested signs of encephalopathy such as disorientation, head pressing, vocalization, depression, seizures and coma. CSF from dogs with congenital shunts contained significantly increased amounts of glutamate (2 to 3-fold increase, p<0.01), glutamine (6-fold increase, p<0.05) and aromatic amino acids (phenylalanine, tyrosine and tryptophan) compared to CSF of control dogs. Concentrations of GABA and branched chain amino acids (valine, leucine, isoleucine) were within normal limits. Modifications of brain glutamate (an excitatory amino acid) as well as tryptophan (the precursor of serotonin) could contribute to the neurological syndrome characteristic of congenital PSE in dogs.

Amino Acids↗
PubMed1997

Clinical pathways for the high-risk patient.

The goal of managed health care is to reduce health care costs while maintaining or improving the quality of care given to patients. Clinical pathways, which outline the services and therapies planned for a typical patient admitted with a specific diagnosis, may provide a way to control costs and improve patient outcome. These pathways are under development by medical centers and managed-care organizations nationwide, with the aim of planning, managing, documenting, and evaluating multidisciplinary care. A coordinated care plan can take a number of approaches. Time lines identify predictable clinical landmarks and time intervals for a specific medical episode or illness within a given diagnostic-related group or set of diagnostic-related groups. Case-management plans and case managers coordinate a patient's care throughout an episode, eg, an operation, enabling patients to reach defined time points in the course of their care at the expected time. Critical pathways are the favored method of documenting the patient's progress according to the predicted time schedule. This report discusses ways to successfully implement a care plan, highlighting the commitment and effort needed from a multidisciplinary staff to achieve the goal of optimizing efficiency and quality of patient care.

Case Management↗
PubMed1997

Con: calcium is not routinely indicated during separation from cardiopulmonary bypass.

Severe hypocalcemia is uncommon in adult cardiac surgery patients; the nearly ubiquitous mild hypocalcemia does not impair myocardial performance. Clinicians should recognize that in certain circumstances, calcium may interact negatively with catecholamines such as epinephrine or dobutamine. Lastly, evidence suggests that calcium influx during ischemia-reperfusion contributes to myocardial dysfunction after CPB. Therefore, there appears to be no justification for the practice of routinely administering large doses of calcium salts to adult cardiac surgery patients after CPB.

Calcium↗
PubMed1997

Structure-affinity relationships and stereospecificity of several homologous series of local anesthetics for the beta2-adrenergic receptor.

UNLABELLED: Local anesthetics inhibit binding of ligands to beta2-adrenergic receptors (beta2ARs), and, as a consequence, inhibit intracellular cAMP production. We hypothesized that among homologous local anesthetics, their avidity at inhibiting binding of tritiated dihydroalprenolol (3H-DHA) to beta2ARs would increase with increasing length of alkyl substituents and would demonstrate stereospecificity. Specific binding of 3H-DHA to human beta2ARs was assayed in the presence of six different members of the 1-alkyl-2,6-pipecoloxylidide class of local anesthetics (including mepivacaine, ropivacaine, and bupivacaine), the R(+) and S(-) bupivacaine enantiomers, lidocaine, prilocaine, etidocaine, procaine, and tetracaine. Avidity of binding to beta2ARs increased with increasing length of the alkyl chain (pKi values = 2.4, 3.6, 4.3, 4.1, 4.1, 5.9 for the methyl [mepivacaine], ethyl, S(-)propyl [ropivacaine], butyl [bupivacaine], pentyl, and octyl derivatives, respectively). We found no evidence for bupivacaine stereospecificity (pKi values = 4.3 and 4.9 for the S(-) and R(+) isomers, respectively). Other amide and ester local anesthetics also showed increasing potency with increasing length of alkyl substituents (pKi values = 3.6, 3.8, and 4.3 for lidocaine, prilocaine, and etidocaine; 4.2 and 5.6 for procaine and tetracaine, respectively). The correlation between increased inhibition of beta2AR binding and alkyl chain length resembles the correlation between local anesthetic potency at nerve block and increased alkyl chain length. The lack of clear stereospecificity is consistent with the relatively low potency these agents demonstrate at inhibition of beta2AR binding. Finally, the relatively potent inhibition of beta2ARs by etidocaine, tetracaine, and bupivacaine suggests that their propensity for cardiovascular depression after accidental intravenous overdose could result from beta2AR or beta1AR blockade and inhibition of cAMP production. IMPLICATIONS: Local anesthetics demonstrate a rank order of avidity for displacing ligands from beta2-adrenergic receptors such that larger molecules displace ligands at lower concentrations than smaller local anesthetic molecules. This relationship between molecular size and receptor avidity could explain the greater propensity for cardiovascular toxicity of relatively large local anesthetics such as bupivacaine.

Adrenergic beta-2 Receptor Antagonists↗
PubMed1997

Cerebral emboli during cardiac surgery in children.

BACKGROUND: Microemboli occur commonly during cardiac surgery in adults, and, when present, increase the risk of neuropsychological deficits. Their incidence and significance during correction of congenital heart disease is unknown. The authors hypothesized that microemboli would occur before bypass with right-to-left cardiac shunts and would also occur in large numbers when the aortic crossclamp was released in children during repair of congenital heart defects. METHODS: In 25 children studied with carotid artery Doppler, embolic signals were counted and timed in relation to 13 intraoperative events. Patients were classified as either at high risk (obligate right-to-left shunt or uncorrected transposition of the great arteries) or at low risk (net left-to-right shunt or simple obstructive lesions) for paradoxical (venous to arterial) emboli. RESULTS: The median number of emboli detected was 122 (range, 2-2,664). Forty-two percent of all emboli were detected within 3 min of release of the aortic crossclamp. The high-risk group had significantly more emboli (median, 66; range, 0-116) during the time interval before cardiopulmonary bypass than did the low-risk group (median, 8; range, 0-73), with P < 0.01. There was no significant difference between the high- and low-risk groups in the total number of emboli detected. There was no apparent association between number of emboli and gross neurologic deficits. CONCLUSIONS: Microemboli can be detected in the carotid arteries of children undergoing repair of congenital heart disease and are especially prevalent immediately after release of the aortic crossclamp. The role of emboli in causing neurologic injury in children undergoing repair of congenital heart disease remains to be determined.

Cardiopulmonary Bypass↗
PubMed1996

Neuroactive amino acids and glutamate (NMDA) receptors in frontal cortex of rats with experimental acute liver failure.

It has been proposed that alterations of excitatory and inhibitory amino acids play a role in the pathogenesis of hepatic encephalopathy in acute liver failure. To evaluate this possibility, in vivo cerebral microdialysis was used to sample extracellular concentrations of amino acids in the frontal cortex of unanesthetized rats at various times during the progression of encephalopathy resulting from acute liver failure. Liver failure was induced by portacaval anastomosis followed 24 hours later by hepatic artery ligation. Dialysate concentrations of amino acids were measured by high-performance liquid chromatography (HPLC) with fluorescence detection. Deterioration of neurological status was accompanied by two- to four-fold increases in extracellular glutamate, glutamine, and glycine; concentrations of gamma-aminobutyric acid (GABA) and taurine were unchanged. Densities of binding sites for the glutamate (N-methyl-D-aspartate [NMDA]) receptor ligand 3H-MK801, assessed using quantitative receptor autoradiography, however, were unchanged in the frontal cortex of rats at coma stages of ischemic liver failure. Increased extracellular glutamate concentrations were positively correlated with the severity of encephalopathy and with arterial ammonia concentrations. Such changes may result from an ammonia-induced reduction in the capacity for astrocytes to uptake glutamate. Increased extracellular glutamate in brain, together with increases in concentrations of glycine, a positive allosteric modulator of glutamate (NMDA) receptors, are consistent with increased NMDA-related glutamatergic neurotransmission in this model of acute liver failure. Increased extracellular glutamate, therefore, could contribute to the pathogenesis of hepatic encephalopathy and brain edema in acute liver failure.

Animals↗
PubMed1996

"This is your meeting": a qualitative study of person-centered planning.

Participant observation and in-depth interviews were conducted to determine processes involved in person-centered planning. Initial planning meetings of 6 individuals were studied in connection with a project to assist young adults in transition from school to adult life. The organization and structure, facilitation process, participation of families, professionals, friends, and the focal individual were described. Although the major goal of the project was to assure that this was the individual's own meeting, implementation of this principle was constrained in several ways, including facilitators' tendency to behave according to prior roles and training. Six months following initiation, several positive outcomes could be attributed to the planning process. Further, many unplanned positive outcomes appeared to result from person-centered planning.

Activities of Daily Living↗