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Biomedical subjects

H T Benzon

Publications and source records attributed to H T Benzon.

At least 19 recordsLinked to original sources
PubMed1997

Correlation between evoked motor response of the sciatic nerve and sensory blockade.

BACKGROUND: Incomplete sensory blockade of the foot after sciatic nerve block in the popliteal fossa may be related to the motor response that was elicited when the block was performed. We investigated the appropriate motor response when a nerve stimulator is used in sciatic nerve block at the popliteal fossa. METHODS: Six volunteers classified as American Society of Anesthesiologists' physical status I underwent 24 sciatic nerve blocks. Each volunteer had four sciatic nerve blocks. During each block, the needle was placed to evoke one of the following motor responses of the foot: eversion, inversion, plantar flexion, or dorsiflexion. Forty milliliters 1.5% lidocaine was injected after the motor response was elicited at < 1 mA intensity. Sensory blockade of the areas of the foot innervated by the posterior tibial, deep peroneal, superficial peroneal, and sural nerves was checked in a blinded manner. Motor blockade was graded on a three-point scale. The width of the sciatic nerve and the orientation of the tibial and common peroneal nerves were also examined in 10 cadavers. RESULTS: A significantly greater number of posterior tibial, deep peroneal, superficial peroneal, and sural nerves were blocked when inversion or dorsiflexion was seen before injection than after eversion or plantar flexion (P < 0.05). Motor blockade of the foot was significantly greater after inversion. Anatomically, the tibial and common peroneal nerves may be separate from each other throughout their course. The sciatic nerve ranged from 0.9-1.5 cm in width and was divided into the tibial and common peroneal nerves at 8 +/- 3 (range, 4-13) cm above the popliteal crease. CONCLUSIONS: Inversion is the motor response that best predicts complete sensory blockade of the foot. Incomplete blockade of the sciatic nerve may be a result of the size of the sciatic nerve, to separate fascial coverings of the tibial and common peroneal nerves, or to blockade of either the tibial or common peroneal nerves after branching from the sciatic nerve.

Adult↗
PubMed1994

The effect of low-dose bupivacaine on postoperative epidural fentanyl analgesia and thrombelastography.

We performed a prospective, randomized, double-blind study to determine the effect of bupivacaine on postoperative epidural fentanyl analgesia and thrombelastography in 120 patients who underwent extensive gastrointestinal or genitourinary surgery. The patients were randomized into four groups, 30 patients per group: Group I = epidural fentanyl (EF), 10 micrograms/mL in saline; Group II = EF with 0.1% bupivacaine; Group III = EF with 0.15% bupivacaine; and Group IV = EF with 0.2% bupivacaine. Pain relief was evaluated by a visual analog scale (VAS), both at rest and during coughing, and by a visual rating scale (VRS). The VAS, VRS, degree of sedation, and side effects (nausea, vomiting, and pruritus) were evaluated every 2 h from 8:00 AM to 6:00 PM, for 24 h after surgery. Forced vital capacities (FVCs) were determined before surgery and at 24 h after surgery. Blood was withdrawn for thrombelastography (TEG) measurements preoperatively, in the recovery room (PARR), and 24 h postoperatively. The VAS, VRS, sedation scores, changes in postoperative FVCs, and the incidence of side effects were not statistically different among the four groups. The 24-h total volumes of infusion in the four groups (146 +/- 40 mL, 140 +/- 38 mL, 142 +/- 40 mL, 124 +/- 21 mL, respectively) were not statistically different from each other. There were no significant differences in the TEG values [reaction time (R), coagulation time (K), angle (alpha), and maximum amplitude (mA)] among the four groups at anytime nor was there any difference between the baseline, PARR, and 24-h TEG values within any group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

A randomized double-blind comparison of epidural fentanyl infusion versus patient-controlled analgesia with morphine for postthoracotomy pain.

The authors conducted a prospective, randomized, double-blind comparison of an epidural fentanyl infusion versus patient-controlled analgesia (PCA) with morphine in the management of postthoracotomy pain. Thirty-six patients were randomized into one of two groups. The epidural group received an epidural fentanyl infusion, 10 micrograms/mL, and saline through their PCA machine. The PCA group received an epidural saline infusion and morphine, 1.0 mg/mL, through their PCA device. The infusions were escalated according to a study protocol when pain relief was deemed inadequate by the patients. Pain relief was evaluated by a visual analog pain scale (VAS), both at rest and during coughing, and by verbal rating scores (VRS) of pain relief. Degree of sedation and the frequency of nausea, vomiting, and pruritus were also noted. The VAS, VRS, degree of sedation, and side effects were evaluated every 2 h from 7 AM to 7 PM, for 72 h after surgery. Forced vital capacities were determined before surgery and at 24, 48, and 72 h after surgery. The VAS were significantly lower (P = 0.001), and the Total Pain Relief scores higher (P < 0.02) in the epidural group, signifying better analgesia. There were no differences in postoperative forced vital capacity between the two groups. More patients in the PCA group had greater degrees of sedation on postoperative day 1 (P = 0.005), whereas pruritus was more frequent (P < 0.02) in the epidural group. We conclude that an epidural fentanyl infusion is superior to that of PCA with morphine in the management of pain after thoracotomy.

Aged↗
PubMed1993

Onset, intensity of blockade and somatosensory evoked potential changes of the lumbosacral dermatomes after epidural anesthesia with alkalinized lidocaine.

The onset and intensity of blockade of the lumbosacral dermatomes after epidural anesthesia with alkalinized lidocaine were investigated in a randomized, double-blind study in 26 patients. Control subjects (n = 13) received 20 mL of 1.37% lidocaine (1.5% lidocaine plus 1 mL saline per 10 mL lidocaine) with added 1:200,000 epinephrine; the solution pH was 6.20 +/- 0.08. Patients in the alkalinized lidocaine group (n = 13) were given 20 mL of 1.37% lidocaine plus added bicarbonate (1 mL sodium bicarbonate per 10 mL 1.5% lidocaine) and 1:200,000 epinephrine; the solution pH was 7.18 +/- 0.10. Posterior tibial nerve (PTN) somatosensory evoked potentials (SSEPs) and L5 and S1 dermatomal SSEPs of both lower extremities were done before and after the epidural. Alkalinization of lidocaine resulted in a significantly shorter time to block the L2, L4, L5, and S1 dermatomes. Motor blockade was significantly more profound in the alkalinized lidocaine group. Thirteen of 78 PTN and L5 and S1 dermatomal SSEPs were abolished in the alkalinized lidocaine group compared to 4 of 78 SSEPs in the nonalkalinized group. Alkalinization of lidocaine is recommended to shorten the time to block the L5-S1 dermatomes when epidural anesthesia is planned for lower extremity surgery.

Adult↗
PubMed1988

Developmental neurophysiology of mammalian peripheral nerves and age-related differential sensitivity to local anaesthetic.

Using an in vitro nerve preparation, we have studied the relative electrophysiological properties of myelinated and unmyelinated nerve fibres in the vagus nerve of 1-, 9- and 36-month-old rabbits and their sensitivity to local anaesthetic. The baseline (values before infusion of local anaesthetic) mean amplitude and conduction velocity (CV) of the compound action potential (APc) were recorded and the nerve was exposed to a range of concentrations (0.5-4.0 mmol litre-1) of lignocaine for periods sufficient to attain equilibrium block. There was an increase in the amplitude of the A fibre elevation from the 1-month to the 9- and 36-month-old rabbits. The CV of the A and B fibres increased significantly with age, while the CV of the C fibres did not change. The ED50 values of lignocaine for reduction of the A fibre elevation in the 1-, 9- and 36-month-old rabbits were 0.66, 0.94 and 0.85 mmol litre-1, respectively. The respective values for the B fibres were 0.74, 1.21 and 0.82 mmol litre-1, while those of the C fibres were 1.50, 2.44 and 2.07 mmol litre-1. In general, nerves from young and old rabbits were more sensitive to local anaesthetic-induced conduction blockade, suggesting that smaller doses of local anaesthetic are required clinically for anaesthesia in paediatric and older age groups.

Action Potentials↗
PubMed1988

Changes in venous blood lactate, venous blood gases, and somatosensory evoked potentials after tourniquet application.

The effects of inflation of a 7-cm tourniquet applied to the upper arm of eight volunteers on venous lactate, venous blood gases, and ulnar nerve somatosensory evoked potentials (SSEPs) were investigated. The inflation pressure was 100 mmHg over the systolic pressure. Venous blood samples for lactate and blood gas determinations were withdrawn before tourniquet inflation; immediately and at 2, 5, 10, 15 min after tourniquet deflation; and additionally at 30, 45, and 60 min after deflation in the last four volunteers. SSEP stimulating surface electrodes were placed over the ulnar nerve at the wrist. Recording electrodes were placed over the ipsilateral ulnar groove of the elbow, Erb's point, and on the contralateral cortex. Averaged responses were acquired before inflation of the tourniquet, every 5-10 min during tourniquet inflation, and every 5-10 min for 45-60 min after tourniquet deflation. The tourniquet was inflated for 36 +/- 11 min. After deflation of the tourniquet, postdeflation pain and paresthesias were felt by five volunteers; these occurred at 30-120 s after deflation and lasted for 75-120 s. The postdeflation pains were characterized as burning, cramping, paresthesias, buzzing, or severe expansion of the hand. The venous blood lactate levels were significantly elevated for 10 min, and the time course of its change did not correlate with reperfusion pain. The PO2 and O2Hb saturation in venous blood were significantly elevated for 10-15 min after deflation. The elevated lactate and PO2 levels in the presence of a restored blood flow probably result from continued anaerobic muscle metabolism secondary to capillary closure from the tourniquet-induced ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

The effect of polyethylene glycol on mammalian nerve impulses.

Polyethylene glycol (PEG) is a polymeric compound used as a vehicle for depot steroid preparations such as methylprednisolone acetate and triamcinolone diacetate injected into the epidural or intrathecal space to relieve low back pain. There have been reports of neurodysfunction associated with these injections, and it has been postulated that the PEG vehicle is the offending agent. Studies supporting such a possibility have, however, relied upon concentrations of PEG higher than those used clinically (3%) or have used PEG in combination with other drugs. Using an in vitro rabbit sheathed-nerve preparation, we investigated the effects of a 1-hr exposure to different concentrations (3-40%) of PEG in Liley solution on the transmission of impulses of the A, B, and C nerve fibers. The 3% and 10% PEG had no effect on mean amplitudes of the compound action potentials (CAPs) nor did they significantly decrease conduction velocity. Twenty percent PEG slightly depressed and 30% markedly decreased CAPs. Both 20% and 30% PEG significantly slowed the conduction velocities of A, B, and C nerve fibers. Forty percent PEG abolished CAPs. With washout CAPs recovered to at least 80% of their baseline levels, and conduction velocities returned toward baseline levels. The pH of the Liley solution decreased with an increasing concentration of PEG, from 7.4 in the control Liley solution to 6.45 in the solution of 40% PEG.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1986

Somatosensory evoked potential quantification of ulnar nerve blockade.

We investigated the appropriateness of the somatosensory evoked potentials (SSEPs) as an objective monitor of sensory blockade of the ulnar nerve by comparing the effects of saline and lidocaine infiltration of the ulnar nerve at the elbow, with and without epinephrine. The four treatments were administered in random order to each of eight volunteers who were asked to assess the intensity of sensory blockade on a 10-cm visual analogue scale (SVAS). Concomitantly, ulnar nerve SSEPs were recorded at the Erb's point, over the posterior spine at or rostral to C-7, and over the sensory cortex. All 16 of the saline and saline with epinephrine infiltrations resulted in SVAS scores of 1 or less. In contrast, all the lidocaine and lidocaine with epinephrine injections were associated with SVAS scores in excess of 8. With lidocaine this lasted 83 +/- 22 min, and the duration of lidocaine with epinephrine was 248 +/- 82 min. SSEP responses were considered abnormal when there were 15 min or more of a decrease in amplitude by 50% or more and an increase in latency by 15% or more. After plain lidocaine injection, all the amplitude measurements showed depression over 50%, with the exception of cortical measurements in one subject. Similarly, there were increased latencies at Erb's point and C-7 with lidocaine blocks. In contrast, change in cortical latency was seldom seen. Variable selection by multiple linear regression analysis of the six SSEP measurements gave a statistical model that sensory block duration (SVAS greater than or equal to 8) could be specified by the duration of the reduced C-7 amplitude (r = 0.96).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Sign of complete sympathetic blockade: sweat test or sympathogalvanic response?

The sensitivity, specificity, and accuracy of the cobalt blue and ninhydrin sweat tests were compared with the sympathogalvanic response (SGR) in assessment of complete sympathetic blockade. Patients were randomly assigned to receive epidural administration of either preservative-free physiologic saline solution and 80 mg methylprednisolone (group I, control group, 9 patients) or 1.5% lidocaine with 80 mg methylprednisolone (group II, sympathetic blocked group, 10 patients). In group I, there was one false positive SGR (absence of SGR) before the block and there were four false positive SGRs after the block. In comparison, there were no false positive sweat tests (absence of sweating) before and after injection in group I. In group II, there were three false positive SGRs and no false positive sweat test before injection. After injection, one patient with an upper level of sensory blockade at T5 had persistent SGRs and positive sweat tests (false negative results). The study showed the sensitivity of the SGR and the sweat tests to be 90%. The specificity of the SGR was 56% compared to 100% for the sweat tests. The accuracy of the SGR was 74% compared to 95% for the sweat tests.

Adult↗