Noncontusive segmental spinal cord injury using radiofrequency current

OBJECTIVE

To develop a nondisruptive model for the study of spinal cord injury.

METHODS

A 2-MHz radiofrequency heating chamber was mounted over the rat T13-L1 vertebral column via a short dorsal incision. Epidural temperature at chamber level was monitored via a small proximal laminotomy. Forty-three rats were studied using time-temperature heating regimens from 45 to 48.5 degrees C and 4 to 15 minutes. A blinded numerical hind limb impairment score (Neurologic Impairment Score) was determined at intervals up to 2 weeks after injury. Segmental spinal cord blood flow was measured using [14C]butanol tissue uptake in injured and control rats.

RESULTS

Above the injury threshold, increasing the time-temperature regimens was associated with a progressively worse Neurologic Impairment Score (r = 0.73-0.87 up to 24 hours after injury). Cord blood flow was unchanged at 2 hours but was 44% depressed at the injury level 6 hours after injury (p < 0.01). Histologically, injury extended minimally beyond the injured segment. Vascular thrombosis was not seen.

CONCLUSION

This comparatively noninvasive model does not mechanically disrupt cord components and results in progressive neurologic impairment that correlates with the time-temperature regimen used for injury. It should be useful in identifying secondary phenomena that worsen functional status after cord trauma.

Diabetes impairs sciatic nerve hyperemia induced by surgical trauma: implications for diabetic neuropathy

The most widely used methods to assess nerve blood flow in diabetics rats are hydrogen clearance polarography and laser Doppler flowmetry, techniques requiring surgical exposure of the nerve. In these experiments, we examined the hypothesis that the trauma of surgical exposure introduces an important and hitherto largely unrecognized variable that could account for discordant reports on nerve blood flow changes induced by diabetes. We used the noninvasive (for sciatic nerve) reference sample microsphere method to quantify sciatic nerve blood flow in unexposed va. surgically exposed nerves in rats with streptozotocin-induced diabetes (at different temperatures and after curarization) and in unexposed vs. surgically exposed nerves in galactose-fed rats. Baseline resting blood flow in unexposed nerves in both animal models of diabetes was either normal or increased (but was decreased in diabetic rats given d-tubocurarine). Furthermore, the normal brisk hyperemic nerve blood flow response to the minimal trauma associated with surgical exposure of the nerve was markedly impaired in diabetic and in galactose-fed rats. Normalization of the blood flow response to trauma in galactose-fed rats by an aldose reductase inhibitor suggests that the impairment is linked to increased polyol pathway metabolism. These findings 1) confirm our previous findings that sciatic nerve blood flow in diabetic rats is increased or unchanged in unexposed nerves, while also confirming reports that in surgically exposed nerves blood flow is higher in control than in diabetic rats, and 2) indicate that blood flows in surgically exposed nerves are largely a measure of vascular responses to injury rather than (patho)physiological blood flow in undisturbed nerves.

Surgical management of calcinosis cutis universalis in systemic lupus erythematosus

Calcinosis cutis is common in several connective tissue diseases but rare in systemic lupus erythematosus (SLE). A 43-year-old woman with a 12-year history of SLE who presented with calcinosis cutis at the time of SLE diagnosis developed a large, ulcerated, draining mass on her left hip. The lesion was excised and skin was grafted, with an excellent early result. The clinical variants and mechanisms of ectopic calcification are discussed, as well as the proposed medical therapies for calcinosis cutis.

Effect of norepinephrine on regional sciatic nerve blood flow

The purpose of this study was to explore further adrenergic regulation of peripheral nerve blood flow (NBF) before and after surgical stress. We applied norepinephrine (NE) to one sciatic nerve of rats either immediately after the nerve had been exposed or 2 hr later. Regional NBF was then measured using [14C]butanol distribution. Biceps femoris muscle flow (MBF) was measured simultaneously. The effect of NE on endoneurial NBF was also measured. Contralateral limbs were controls. Control NBF was 11.9 +/- 1.9 total, 9.1 +/- 1.5 endoneurial (units: ml min-1 100 g-1). If 10(-5) M NE was applied immediately postexposure, neither total nor endoneurial NBF was affected. If 10(-5) M NE was applied 2 hr postexposure, however, total NBF on the control side was 21 +/- 2.3 vs 8.3 +/- 1.2 on the NE side (P < 0.001). In all surgically exposed limbs, MBF was elevated and fell sharply in response to 10(-5) M NE. We conclude that under basal conditions, neither total nor endoneurial NBF is affected by topical NE. When NBF is already elevated from surgical trauma, however, NE reduces it.

Nerve and muscle blood flow during hindlimb ischemia and reperfusion in rats

Animal models of peripheral nerve ischemia have yielded variable results. The question of whether post-ischemia re-establishment of blood flow to the nerves augments injury has not been examined. To study this question, the ipsilateral common iliac and femoral arteries were occluded with arterial snares for 3 hours in rats; 14C-butanol tissue distribution was then used to measure blood flow in both sciatic and posterior tibial nerve trunks and in both biceps femoris muscles during occlusion and reperfusion. Clinical limb function was graded serially, with the undisturbed contralateral limb serving as the study control. Nerve blood flow was reduced throughout the ischemic period and was only 20% of the control value in the posterior tibial nerve. Muscle blood flow was unchanged. All rats had functional impairment, with an average limb function score of 7.5 (normal score < 2). During reperfusion, blood flow in the distal sciatic and posterior tibial nerves was approximately double that of control nerves at 2 hours, and muscle blood flow was also elevated. At 21 hours, tibial nerve blood flow was still twice that of the control nerve, but flows in the distal sciatic nerve and muscle were unchanged from control levels. Clinically, limb function improved progressively after reperfusion. It was concluded that nerve ischemia is attended by a relatively prolonged hyperemic flow response during reperfusion.

Limb ischemia and reperfusion: relationship of functional recovery to nerve and muscle blood flow

The relative importance of nerve versus muscle injury in limb ischemia-reperfusion is poorly understood. We used 14C-butanol tissue distribution to measure regional blood flow simultaneously in the proximal and distal sciatic, the posterior tibial nerve trunk (NBF), and biceps femoris muscle (MBF) of rats during 3 hours of occlusion of the ipsilateral iliac and femoral arteries and subsequently for up to 9 days of reperfusion. Limb motor function was also serially assessed. The contralateral limbs served as controls. Experimental groups were untreated control (n = 16); methylprednisolone, 30 mg/kg (n = 13); the lazaroid U74389F, 3 mg/kg (n = 13); and lazaroid vehicle (n = 13), i.v. 15 minutes before occlusion and 15 minutes after reperfusion.

RESULTS

One hour after occlusion, NBF was -77% of the control value (p < 0.02) but MBF was unchanged (control NBF 15.2 +/- 3.3, control MBF 6.3 +/- 0.9, units mL.min-1 x 100 g-1). At both 2 and 21 hours of reperfusion, NBF was double that of control in all groups (p < 0.01); but MBF, which had been modestly elevated to 10.5 +/- 0.5 at 2 hours (p < 0.01), was already normal at 21 hours in all groups. During days 5 to 9 of reperfusion, NBF was still numerically elevated (NS); MBF remained at control. Functionally, test. limb scores were always grossly abnormal during occlusion (range: 7.1-8.5, normal = < 2). After 1 hour of reperfusion, all test limb scores were improved versus occlusion (p < 0.001, Wilcoxon rank-sum). Subsequently, there was gradual improvement in all groups, scores at 6 days ranging from 1.9 to 2.5.

CONCLUSION

NBF is rapidly and severely reduced during ischemia. During reperfusion, the hyperemic flow response in nerve is more prolonged than in muscle. Limb dysfunction during ischemia and reperfusion may be largely the result of axonal or neuromuscular junction injury or both. Neither of the two treatments had effects on blood flow or limb function.

Effect of surgical trauma on regional blood flow in rat sciatic nerve

The factors affecting peripheral nerve blood flow (NBF) are not well defined. We used [14C]butanol distribution to quantitate NBF in rat sciatic nerve following either (1) simple surgical exposure (EXP) or (2) EXP plus nerve mobilization and isolation (ISOL). Undisturbed contralateral nerves were controls. The epineurial contribution to NBF after EXP was also assessed. Results (units: ml.min-1 x 100 g-1): Within 1 to 6 h after EXP (N = 7), NBF was 22.1 +/- 2.7 vs 11.9 +/- 1.5 control (P < 0.01). Seven to 24 h after EXP (N = 6), NBF was unchanged from control. Two hours following EXP, both endoneurial NBF and total (epineurial plus endoneurial) NBF were elevated (P < 0.05, P < 0.02, respectively). Within 48 h after ISOL (N = 6) NBF was 30.3 +/- 3.9 vs 13.2 +/- 2.1 control (P < 0.005). Three to seven days after ISOL (N = 8), NBF was unchanged from control.

CONCLUSION

Surgical trauma induces a brisk flow response in peripheral nerve that is proportionate in duration to the trauma severity. Measurements of NBF after EXP or ISOL are therefore potentially misleading if the changes in NBF due to the trauma are not accounted for.

Guanethidine chemical sympathectomy: spinal cord and sciatic nerve blood flow

The spinal cord vasculature is innervated by noradrenergic nerve fibers, the role of which in the regulation of regional spinal cord blood flow (RSCBF) is presently unclear. We used the distribution of [14C]butanol to simultaneously measure RSCBF at seven cord levels and the regional blood flow in sciatic nerve (NBF), truncal skin, and biceps femoris muscle. The subjects were control rats and rats that had been given parenteral guanethidine sulfate for 5 wk to induce selective postganglionic "chemical sympathectomy." Flows were measured under basal conditions (group I) and immediately after an arterial hemorrhage (group II). The results indicate that RSCBF was unchanged from control after guanethidine administration in both groups; however, NBF was elevated after guanethidine by 47% in group I and by 41% in group II. We conclude that in the spinal cord as in the brain, sympathetic inflow does not appear to have an important role in the regulation of regional blood flow. Sympathetic inflow appears to partly regulate NBF, however, probably by varying vascular tone.

Methylprednisolone treatment of experimental spinal cord injury

Lipid peroxidation has been identified as a deleterious consequence of contusive spinal cord trauma and of thermal injury. The L3-L6 spinal cord segment was thermally injured using a radiofrequency heating chamber mounted on the vertebral column of anesthetized rats. Hind limb function was assessed 2 hours later. A bolus of methylprednisolone (MP, 30 mg/kg) was then given intravenously, followed by 5.4 mg/kg/hr MP for 6 or 24 hours. Cord water content and regional spinal cord blood flow (RSCBF, 14C-butanol distribution) were measured at seven cord levels after function had been reassessed following treatment. Untreated rats were given vehicle. The study was randomized and blinded.

RESULTS

Edema in heated segments was progressive over 24 hours, but was the same in treated vs untreated rats. RSCBF in heated segments was the same in treated vs uninjured controls at 6 and 24 hours. In untreated rats, RSCBF in the heated segment was elevated by 30% at 6 hours, but was the same as uninjured control by 24 hours. In the unheated segments of untreated rats, RSCBF was elevated at 24 hours. At 24 hours, RSCBF was lower in treated vs untreated rats at all levels, including the heated one. Limb function deteriorated equivalently in both groups.

CONCLUSION

MP obviated the early rise in RSCBF in heated segments and the elevations in RSCBF in uninjured segments, but had no effect on cord edema or on limb function.

Role of extended resection in the initial treatment of locally advanced colorectal carcinoma

The focus of this review is the role of extended resection in the initial treatment of primary colorectal carcinoma. About 10% of patients with newly diagnosed colorectal cancer will have locally advanced disease without evident distant or discontiguous intraabdominal metastases. En bloc resection of such tumors, including attached tissues or organs, provides a 5-year survival rate of about 40%, if the microscopic margins are tumor free. As many as 60% of these large tumors are node negative; in this circumstance the 5-year survival rate approaches 70%. These results are achievable when there is a meticulous preoperative and intraoperative search for metastases, a wide anatomic resection, including en bloc lymphadenectomy, is performed, and tumor manipulation is minimized. Blunt separation of structures adherent to the primary tumor should be avoided because adhesions will be neoplastic in about 50% of cases, and cancer recurrence is virtually certain when tumor is transected. The mortality from multivisceral resection, including total pelvic exenteration, should be 10% or less. We emphasize the importance of including these patients in prospective trials to define their optimal adjuvant therapy. There is a disturbing recurring theme in published series, failure to extend the scope of resection in potentially curable patients. The management of these locally advanced lesions typically receives but cursory notice in otherwise highly detailed reviews or textbook chapters. In the present era of emerging multimodality treatment for colorectal cancer, the adequacy of the one most important treatment component--surgical resection--is seldom emphasized. Furthermore, our perusal of the recent literature disclosed no diminution in the incidence of inadequate resection, suggesting that this subject requires more emphasis in postgraduate surgical education.

The effects of lumbar sympathectomy on regional spinal cord blood flow in rats during acute hemorrhagic hypotension

It has not previously been determined whether the sympathetic nervous system has a role in the regulation of regional blood flow in the spinal cord. The authors used 14C-butanol distribution to measure regional spinal cord blood flow at seven cord levels, in the sciatic nerve, and in the biceps femoris muscle in 36 rats, 18 of which had undergone excision of both lumbar sympathetic chains at least 6 days previously. Blood flows were measured during pentobarbital anesthesia. Mean arterial blood pressure (MABP) was monitored and arterial pO2, pCO2, and pH were determined prior to flow measurement. Anesthetic dose and duration were controlled. Measurements were made in normotensive rats and in rats with MABP maintained at either 69 +/- 3 mm Hg or 48 +/- 3 mm Hg for 1 hour by the withdrawal of arterial blood. One-half of the rats in each group had undergone sympathectomy. The resting cord blood flow was lower than control values following sympathectomy only at the S1-4 cord level (p less than 0.01) and cauda equina (p less than 0.01), and was marginally lower at the L1-2 and L3-6 levels (p less than 0.1). Cord blood flow was unaffected by sympathectomy during moderate hypotension. During severe hypotension, cord blood flow was less than control at the C3-5 level (p less than 0.05), but did not differ from control at the other six levels. Flows in nerve and muscle were consistent with known effects of sympathectomy on peripheral tissues. It is concluded that, at most, sympathectomy may moderately decrease resting blood flow in the cord levels caudal to L-1. Sympathectomy has no major effect on regional spinal cord blood flow in rats stressed by either moderate or severe arterial hemorrhage.

Benefits and limitations of burn wound excision

This review is intended to provide a balanced view of the role of surgical burn wound excision and closure within the larger context of the total care and rehabilitation of patients with burn injury. The historical background leading to present practice is outlined. The salient technical and logistical problems associated with the performance of wound excision are discussed, with emphasis on the necessity for expeditiously completing these procedures which are associated with major blood loss. A realistic analysis of the results of excisional therapy in patients with burns of varying severity is presented. Benefits attributable to the surgical phase of therapy become progressively more difficult to identify as the size of deep burns increases beyond 20% of total body surface area.

Squamous cell carcinoma of the anal canal

Between 1979 and 1988, 33 patients with squamous cell carcinoma of the anal canal were treated with chemoradiation. There were 24 women and 9 men, from 37 to 90 years of age (median: 63 years). Complete tumor regression occurred in 29 of the 33 patients (88%), only one of whom later developed recurrence. In the other four patients, there was persistent tumor after 3 months; three of these patients died within 2 years; and one is alive with distant metastases 2 years later. During the first 5 years of the study, seven patients with complete tumor regression underwent planned abdominoperineal resection following chemoradiation. Four of the abdominoperineal resection specimens were free of tumor, but three were not. These three patients, who had abdominoperineal resection within 3 months of chemoradiation, are disease-free. Ten of the 29 patients who had complete tumor regression had biopsies of the primary site 3 months after treatment. All biopsies were negative for residual carcinoma. At present, 26 patients (79%) are alive and disease-free from 2 to 10 years post-treatment (median: 4 years). Two patients died of unrelated causes, four of cancer, and one is alive with cancer. Complications of the chemoradiation required surgical intervention in two patients, and two others developed severe hematologic toxicity, for a complication rate of 12% (4 of 33 patients). There was no treatment-related mortality. These results support the efficacy of chemoradiation treatment for carcinoma of the anal canal. They suggest that abdominoperineal resection no longer need be part of the planned initial management, and that posttreatment biopsy of the primary site is unnecessary, unless palpable or visible abnormalities are present 3 months after treatment.

Effects of 4-aminopyridine on protein phosphorylation in heat-blocked peripheral nerve

The topical application of 4-aminopyridine (4-AP) reverses within 1-3 min the partial conduction block that results from heating 5-mm segments of rat posterior tibial, peroneal and sural nerves to 45 degrees C for several minutes. Nerves previously blocked in vitro or in vivo were incubated in vitro in the presence of [gamma-32P]ATP. The rate of phosphorylation of soluble nerve proteins that had entered the media was determined. Labeled proteins were separated electrophoretically and autoradiograms prepared. We found that 5 mM 4-AP increases the phosphorylation rate in heat-blocked nerve by approximately 50-fold. The process is calcium-dependent and is heat-labile. Soluble proteins with a molecular weight in the 53-55 kDa range are preferentially but not exclusively phosphorylated in the presence of 4-AP at levels effective in restoring conduction. The results suggest that the potassium channel blocker 4-AP may restore conduction by inducing changes in channel proteins.

Topical silicone gel for the prevention and treatment of hypertrophic scar

We studied the effects of a silicone gel bandage that was worn for at least 12 hours daily on the resolution of hypertrophic burn scar. In a second cohort, the prevention of hypertrophic scar formation in fresh surgical incisions by this bandage was also evaluated. In 19 patients with hypertrophic burn scars, elasticity of the scars was quantitated serially with the use of an elastometer. An adjacent or mirror-image hypertrophic burn scar served as a control. Scar elasticity was increased after both 1 and 2 months compared with that in controls. There was corresponding improvement clinically that persisted for at least 6 months. In the other cohort, scar volume changes in 21 surgical incisions were measured before and after 1 and 2 months. Gel-treated incisions gained less volume than control incisions after both intervals. Clinical assessment corroborated this quantitative demonstration of a decrement in scar volume. We concluded that topical silicone gel is efficacious, both in the prevention and in the treatment of hypertrophic scar.

Effect of adrenalectomy or sympathectomy on spinal cord blood flow in hypothermic rats

We used [14C]butanol distribution to measure regional spinal cord blood flow (RSCBF) in three groups of pentobarbital-anesthetized rats: 1) normals (n = 16); 2) after bilateral adrenalectomy (n = 18); and 3) after excision of the abdominal sympathetic chains (n = 12). Half of the rats in each group were maintained near normothermia; the remainder were colled to a rectal temperature of 25-27 degrees C. In intact rats, there was a 24-37% increase in RSCBF during hypothermia in the cord region C3-L6 inclusive. Neither operative procedure altered RSCBF during normothermia. In hypothermic adrenalectomized rats, RSCBF was elevated only in the C3-C5 cord segment. After sympathectomy, RSCBF was unchanged during hypothermia. In the cauda equina, flow fell in all hypothermic rats. The hypothermia-associated increases in RSCBF were not related to changes in mean arterial blood pressure. We conclude that adrenalectomy near-totally ablates the hypothermia-associated increase in RSCBF measured in intact rats and that abdominal sympathectomy totally ablates it. This evidence complements morphological evidence for adrenergic innervation of the spinal cord vasculature.

Regional blood flow in transected rat spinal cord during hypothermia

Regional blood flow (RBF) increases in the spinal cord and sciatic nerve of acutely hypothermic rats. To determine whether cord transection affects this response, we measured RBF in rat spinal cord and sciatic nerve 2 h after cord transection at vertebrae T8 (n = 18 rats) and T11 (n = 18 rats) using [14C]butanol distribution. Nine in each group were normothermic controls. In T11 transection-hypothermia (25-27 degrees C rectal temperature), RBF increased in the three rostral cord segments by 28-40% (P less than 0.05); caudally, cord RBF was depressed in two segments (P less than 0.05), unchanged in the other; RBF fell in nerve (P less than 0.05). In T8 transection-hypothermia, RBF was unchanged in the two rostral cord segments; caudally, RBF was depressed in one cord segment (P less than 0.05) and unchanged in the others; RBF was unchanged in nerve. We conclude that RBF does not rise in caudal spinal cord segments or in sciatic nerve during hypothermia in rats with prior spinal cord transection.

Current treatment recommendations for topical burn therapy

Infections in burn patients continue to be the primary source of morbidity and mortality. Topical antimicrobial therapy remains the single most important component of wound care in hospitalised burn patients. The goal of prophylactic topical antimicrobial therapy is to control microbial colonisation and prevent burn wound infection. In selected clinical circumstances topical agents may be used to treat incipient or early burn wound infections. At the present time silver sulfadiazine is the most frequently used topical prophylactic agent; it is relatively inexpensive, easy to apply, well tolerated by patients, and has good activity against most burn pathogens. In patients with large burns the addition of cerium nitrate to silver sulfadiazine may improve bacterial control. Mafenide acetate has superior eschar-penetrating characteristics, making it the agent of choice for early treatment of burn wound sepsis. However, the duration and area of mafenide application must be limited because of systemic toxicity associated with prolonged or extensive use. Other agents, such as nitrofurazone or chlorhexidine preparations, may be useful in isolated clinical situations. The undesirable side effects of silver nitrate solution limit its use by most clinicians at the present time.

Regional spinal cord blood flow during local cooling

We used the tissue distribution of [14C]butanol to quantitate regional blood flow in the spinal cord (RSCBF) of pentobarbital-anesthetized, normothermic rats in which segmental local cooling pentobarbital-anesthetized, normothermic rats in which segmental local cooling of the spinal cord (to 25-28 degrees C) at vertebral levels C4-C6 (n = 6) or T13-L1 (n = 6) was induced. Thirty minutes later, blood flow measurements were made at seven levels of the spinal cord and in the sciatic nerve trunks and biceps femoris muscles. Sham-cooled rats served as controls (n = 12). In control rats, RSCBF varied between 41.5 +/- 2.4 and 65.1 +/- 3.2 ml.min-1.100 g-1. Local cooling of the C4-C6 cord segment reduced RSCBF by 32%, from 65.1 +/- 3.2 to 44.4 +/- 3.5 ml.min-1.100 g-1 (P less than 0.01). Tissue vascular resistance (R) in the cooled C4-C6 segment was elevated versus control. There were no other changes in RSCBF at the other cord levels or in the cauda equina. Similarly, local cooling of the T13-L1 segment resulted in a 40% fall in RSCBF in that segment, from 57.1 +/- 2.4 to 34.1 +/- 4.3 ml.min-1.100 g-1 (P less than 0.001). R in the cooled T13-L1 segment was elevated versus control. RSCBF was reduced by 30% in the adjacent proximal T12 segment (P less than 0.001) and by 21% in the adjacent distal L2-L3 segment (P less than 0.05). R was increased in both of these adjacent segments. RSCBF was not altered elsewhere in the cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Patient tolerance study of topical chlorhexidine diphosphanilate: a new topical agent for burns

Effective topical antimicrobial agents decrease infection and mortality in burn patients. Chlorhexidine phosphanilate (CHP), a new broad-spectrum antimicrobial agent, has been evaluated as a topical burn wound dressing in cream form, but preliminary clinical trials reported that it was painful upon application. This study compared various concentrations of CHP to determine if a tolerable concentration could be identified with retention of antimicrobial efficacy. Twenty-nine burn patients, each with two similar burns which could be separately treated, were given pairs of treatments at successive 12-h intervals over a 3-day period. One burn site was treated with each of four different CHP concentrations, from 0.25 per cent to 2 per cent, their vehicle, and 1 per cent silver sulphadiazine (AgSD) cream, an antimicrobial agent frequently used for topical treatment of burn wounds. The other site was always treated with AgSD cream. There was a direct relationship between CHP concentration and patients' ratings of pain on an analogue scale. The 0.25 per cent CHP cream was closest to AgSD in pain tolerance; however, none of the treatments differed statistically from AgSD or from each other. In addition, ease of application of CHP creams was less satisfactory than that of AgSD. It was concluded that formulations at or below 0.5 per cent CHP may prove acceptable for wound care, but the vehicle system needs pharmaceutical improvement to render it more tolerable and easier to use.

4-aminopyridine restores conduction in heat-blocked sciatic branches

We induced partial conduction block in rat sural and posterior tibial nerves by heating a short (5 mm) segment of the midportions of these branches to 45 degrees C until the amplitude of the elicited compound action potential was reduced by at least 50%, an effect that appeared to be irreversible without specific treatment. Excised branches studied in vitro were compared with branches heated in situ with an intact blood supply. The potassium channel blocker 4-aminopyridine (4-AP, 5 mM) was applied topically to the heated segments at intervals after injury. The amplitude of the compound action potential was restored to the control level in all preparations treated within 10 minutes after the induction of conduction block. The reversal appeared to be more rapid in the in vivo preparations, and it persisted for at least 60 minutes. The data suggest that paranodal potassium channel exposure may accompany direct thermal injury to the peripheral nerve.

Topical silicone gel: a new treatment for hypertrophic scars

A prospective, controlled clinical trial was designed to assess the efficacy of a new treatment of hypertrophic scars. Silicone gel sheeting was applied to 14 hypertrophic scars in 10 adults for 8 weeks. The treated scars and untreated, mirror-image or adjacent control scars were photographed, biopsy specimens were taken, and they were measured elastometrically before and after treatment. Photography and elastometry were repeated 4 weeks after treatment was discontinued. All the scars that had been treated for at least 12 hours a day were improved clinically after 4 weeks. There was further clinical improvement during the second 4 weeks of treatment. Elastometrically, the treated scars were improved significantly at 4, 8, and 12 weeks, compared with both their own treatment value and the control scars (p less than 0.05). Control scars were unchanged elastometrically. Clinical improvement persisted for at least 4 weeks after treatment was discontinued. The silicone gel sheeting was well tolerated, except for occasional transient rashes or superficial maceration--both of which resolved promptly when treatment was withdrawn. There was no histologic evidence of inflammation or foreign body reaction suggesting that silicone had entered the treated tissues. We conclude that this simple method of treating hypertrophic scar is efficacious, even in relatively chronic cases. The mechanism of action of silicone gel, which is apparently not related to compression, remains to be determined.

Regional blood flow in the brain and spinal cord of hypothermic rats

[14C]butanol tissue uptake was used to measure simultaneously regional blood flow in three regions of the brain (cerebral and cerebellar hemispheres and brain stem) and in five levels of the spinal cord in 10 normothermic rats (group A) and in 10 rats in which rectal temperature had been lowered to 27.7 +/- 0.3 degrees C by applying ice to the torso (group B). Pentobarbital sodium anesthesia was used. Mean arterial blood pressure varied minimally between groups as did arterial pH, PO2, and PCO2. In group A, regional spinal cord blood flow (rSCBF) varied from 49.7 +/- 1.6 to 62.6 +/- 2.1 ml.min-1.100 g-1; in brain, regional blood flow (rBBF) averaged 74.4 +/- 2.3 ml.min-1.100 g-1 in the whole brain and was highest in the brain stem. rSCBF in group B was elevated in all levels of the cord by 21-34% (P less than 0.05). rBBF, however, was lowered by 21% in the cerebral hemispheres (P less than 0.001) and by 14% in the brain as a whole (P less than 0.05). The changes in calculated vascular resistance tended to be inversely related to blood flow in all tissues. We conclude that rBBF is depressed in acutely hypothermic pentobarbital sodium-anesthetized rats, as has been noted before, but that rSCBF rises under these experimental conditions. The elevation of rSCBF in hypothermic rats confirms our previous observations.

The effect of hypothermia on regional spinal cord blood flow in rats

Spinal cord ischemia may accompany surgical procedures on the aorta or vertebral column. Regional spinal cord blood flow (SCBF) was measured at five vertebral levels in the spinal cords of pentobarbital-anesthetized rats based on the distribution of intravenously injected carbon-14-labeled butanol. In seven normal rats, mean SCBF (+/- standard error of the mean) ranged from 52.7 +/- 5.4 to 68.5 +/- 4.9 ml.min-1.100 gm-1 (depending on the level, being lowest at the thoracic levels) and mean arterial blood pressure (MABP) was 126 mm Hg. Corporal hypothermia (mean rectal temperature 28.1 degrees +/- 0.6 degrees C) was induced by cold exposure in seven other rats, and SCBF, measured immediately thereafter, was significantly elevated at all five levels by 52% to 69% compared to the normal group. However, MABP was elevated in the hypothermic group to 165 +/- 4 mm Hg (p less than 0.0001). Therefore, in seven additional hypothermic rats, MABP was maintained at the control level by withdrawal of arterial blood as necessary. In these animals, SCBF at all levels was still significantly elevated compared with the normal group and the values were nearly identical to those measured in the hypertensive hypothermic rats. It was concluded that hemodynamic autoregulation of SCBF is impaired in the presence of moderate systemic hypothermia in pentobarbital-anesthetized rats.

An outreach burn prevention program for home care patients

Residential fires are the major cause of death from fires and burns in the United States, accounting for nearly two-thirds of annual fatalities. High-risk groups are more accessible now to burn prevention programs because of increasing home health care. Our burn prevention program, directed at homebound patients cared for by our hospital-based home care staff, combines fire safety education and smoke detector installation for this designated high-risk population. The combining of home health care with burn prevention activities has proven to be an effective means of reaching thousands of high-risk homes per year. We believe this approach would be equally effective in other areas.

A new instrument for serial measurements of elasticity in hypertrophic scar

The "elastometer," a hand-held device, was designed and constructed to permit noninvasive quantification of the elastic properties of normal skin or hypertrophic scar. The instrument utilizes a constant-tension spring and a sensitive strain gauge to distract two loci of skin. Normal skin from 15 dogs was measured in vivo with the elastometer and in vitro using standard tensometry. The results correlated significantly by regression analysis (r = .87, p less than .01, 1/Young's Modulus of Elasticity v percent stretch in vivo). Normal dorsal hand skin was tested elastometrically in six volunteers of both sexes. Values (units: percent stretch) ranged from 29 to 43 with a small standard error (+/- 4%). In nine patients with hypertrophic burn scars, the mean percent stretch was 16.2 +/- 1.8 v 37.9 +/- 6.5 in the mirror-image normal skin. There was no overlap between the two groups. There was a trend towards higher values in older scars. Elastometric measurements have increased appreciably in some burn scars undergoing treatment. The elastometer should be useful in documenting objectively the spontaneous maturation of burn scars and/or their response to treatment.

[14C]butanol distribution: a new method for measurement of spinal cord blood flow

[14C]butanol distribution was used to quantitate regional blood flow (SCBF) in the spinal cord (levels T3-5, T7-9, L1-2, L3-S) and in the sciatic nerves (NBF) of control pentobarbital sodium-anesthetized rats (group A), after 1 h of hemorrhagic hypotension (group B), after 15 min of stimulation of one sciatic nerve (group C-1), and after stimulation of one sciatic nerve plus hemorrhage, which maintained mean arterial pressure (MAP) at control (130 mmHg). Group A SCBF ranged from 52.3 +/- 3.5 (L3-S) to 67.4 +/- 2.7 (L1-2) ml.min-1.100 g-1. NBF was 8.0 +/- 0.9 ml.min-1.100 g-1. Group B SCBF was unchanged. NBF fell to 4.0 +/- 0.4 ml.min-1.100 g-1. Group C-1 SCBF was markedly elevated (range 122 +/- 23.1 to 150.1 +/- 18.7 ml.min-1.100 g-1). NBF was 33.5 +/- 4.1 ml.min-1.100 g-1 (stimulated side) and 14.7 +/- 1.4 ml.min-1.100 g-1 (nonstimulated). MAP was elevated (163 +/- 6 mmHg). In group C-2 (MAP was 130 +/- 4 mmHg), SCBF was still elevated at T3-5, L3-S, and marginally elevated at L1-2. NBF was 22.6 +/- 4.7 ml.min-1.100 g-1 (stimulated) but unchanged contralaterally. [14C]butanol distribution provides a sensitive reproducible measure of SCBF and NBF. Autoregulation of SCBF (but not of NBF) occurred in the range 60-160 mmHg MAP. Spinal cord stimulation via the sciatic nerve increased SCBF two- to threefold, but when hypertension was avoided by blood withdrawal, a modest (38%) increase in SCBF still occurred.

Regional blood flow in resting and stimulated sciatic nerve of diabetic rats

The role of ischemia in the pathogenesis of diabetic peripheral neuropathy remains uncertain. We used the distribution of [14C]butanol to measure resting regional sciatic nerve blood flow in normal, anesthetized rats and in rats with acute experimental diabetes from streptozotocin administration. Regional flows in hind limb biceps femoris muscle and skin were simultaneously measured. In additional diabetic rats, these blood flows were compared in both limbs after proximal electrical stimulation of one sciatic trunk (10 shocks/s) for 15 min. One month after streptozotocin administration, 8 of 11 test rats were hyperglycemic. Resting nerve blood flow in the hyperglycemic rats--5.6 +/- 3.07 ml.min-1.100 g-1--was significantly less than that in the controls (9.4 +/- 3.9 ml.min-1.100 g-1, P = 0.002). Muscle blood flow was normal and skin blood flow decreased in these rats. Calculated tissue vascular resistances were elevated in all three tissues. Stimulation of one sciatic trunk in five other diabetic rats resulted in a stimulated nerve blood flow of 15.7 +/- 7.7 ml.min-1.100 g-1, and nerve blood flow in the resting control limb was 7.7 +/- 4.3 ml.min-1.100 g-1 (P = 0.009). Muscle blood flow increased approximately fourfold on the stimulated side but skin blood flow did not increase. Resting sciatic nerve blood flow is modestly decreased in acute streptozotocin-induced diabetes, but the neural blood vessels are still responsive to the increase in nerve metabolic activity associated with nerve stimulation.

Sciatic nerve function following hindlimb thermal injury

Peripheral neuropathy occurs in approximately 20% of patients with major burns and seriously impairs rehabilitation. We describe an experimental model which permits elevation of the tissue temperature in the region of the distal sciatic nerve trunk of rats at a reproducible rate to a predetermined level without inflicting concomitant major cutaneous injury. Radiofrequency current is delivered through parallel copper electrodes mounted in a chamber into which the limb has been inserted. In the present experiments, tissue temperature was arbitrarily elevated to 47 degrees C for 30 sec in 62 rats. There were 43 normal controls. The posterior tibial branch was the most intensively studied, as some of its conduction characteristics can be serially assessed percutaneously. Conduction block, which was apparently irreversible, was present in 67% of posterior tibials by 24 hr postinjury. In branches which were still excitable, prolongation of the absolute refractory period was the most consistent abnormality noted. Slowing of conduction, as evidenced by prolongation of inflection velocity or peak velocity, was never observed. However, this injury resulted in selective conduction failure of sural--but not of peroneal--fibers which conducted at 40 m/sec or greater. Fiber modality is an important determinant of the vulnerability to direct thermal injury of peripheral nerve in vivo.

Regional blood flow in sciatic nerve, biceps femoris muscle, and truncal skin in response to hemorrhagic hypotension

Regional blood flow was measured simultaneously in rat sciatic nerves (NBF), truncal skin (SBF), and biceps femoris muscles (MBF) after graded hemorrhages. A modified 14C-butanol "indicator-fractionation" technique was used. In controls NBF was 11.4 +/- 1.38 ml X min-1 X 100 gm-1 and did not differ significantly between limbs. After hypotension, NBF was: 101 mm Hg, 7.7 +/- 1.3; 83 mm Hg, 5.3 +/- 0.6; 62 mm Hg, 4.1 +/- 0.6; 38 mm Hg, 3.1 +/- 0.3. The relationship between NBF and MAP was linear: (r = 0.56; p less than 0.001). SBF also declined linearly in hypotension (r = 0.54; p less than 0.01), but MBF did not change significantly. No significant change in nerve vascular resistance occurred with hypotension but muscle vascular resistance declined progressively. The data indicate a striking absence of autoregulation of NBF, but MBF, as expected, displayed close autoregulation. The vascular mechanisms which regulate resting NBF following hemorrhage differ from those in both muscle and skin: during hypotension, the calculated neurovascular resistance was unchanged, while the resistance in muscle fell and that in the skin increased.

Elevated regional sciatic nerve blood flow in hypothermic anesthetized rats

The effect of corporal hypothermia on regional blood flow in peripheral nerve is unknown. We compared blood flow in resting sciatic nerves of anesthetized, normothermic rats with that of rats whose rectal temperatures had been acutely lowered to 28 to 30 degrees C. Peripheral nerve regional blood flow in normothermic rats in which one hind limb was cooled was also measured, as were simultaneous flow changes in biceps femoris muscle and thigh skin. Flows were quantitated by the fractional distribution of [14C]butanol. Hypothermia was associated with increased peripheral nerve blood flow and a simultaneous decrease in muscle and skin blood flow. Nerve vascular resistance was not consistently altered in hypothermia, but muscle and skin vascular resistances were elevated. Topical cooling of one limb did not affect the tissue blood flows in either limb. The regulation of resting nerve blood flow in hypothermic rats differs appreciably from that in biceps femoris muscle and skin. Nerve blood flow did not increase with local cooling in normothermic rats. Central, neurally mediated mechanisms may be responsible for the increased regional nerve blood flow in hypothermic rats.

Topical therapy for burns

Topical antimicrobial agents can prevent or minimize burn infections and should be used from the outset in all patients who are at significant risk from sepsis--either because of their wound severity or associated comorbid factors. All of the currently available topical agents have shortcomings; some of them have appreciable toxicity. The recent shift in emphasis toward early surgical closure of extensive deep burns in great part has resulted from appreciation of the inadequacies of currently available topical agents. Topical agents cannot substitute for timely and comprehensive physiologic support of burned patients.

Regional sciatic nerve blood flow response to limb movement

The regional blood flow in the sciatic nerves (NBF), biceps femoris muscles (MBF), and hind limb skin (SBF) was measured simultaneously in anesthetized, normal rats, in other rats immediately after 15 min of electrical stimulation of one sciatic trunk (10 shocks/s), and in a group of similarly stimulated but previously curarized rats. These experiments were done to quantitate NBF during direct nerve stimulation in both the presence and absence of associated vigorous limb twitching, as these relationships have not previously been examined. Tissue blood flows were measured by an "indicator-fractionation" technic, using the distribution of [14C]butanol. NBF in normal controls was 11.1 +/- 1.4 ml X min-1 X 100 g-1; MBF was 6.8 +/- 0.6 ml X min-1 X 100 g-1. In the stimulated limb of noncurarized rats, NBF rose to 19.8 +/- 3.5 ml X min-1 X 100 g-1. MBF was elevated approximately tenfold. SBF also rose. In stimulated limbs of curarized rats, NBF was also approximately double the resting normal value, 23.2 +/- 4.8 ml X min-1 X 100 g-1, but MBF was then only slightly increased. We conclude that sciatic NBF increases appreciably when this nerve is stimulated, irrespective, for the most part, of whether limb motor activity is increased. The vascular mechanisms which regulate NBF differ from and are largely independent of those regulating MBF.

Regional sciatic nerve and muscle blood flow in conscious and anesthetized rats

The regulation of peripheral nerve blood flow is incompletely understood. Regional blood flow in the rat sciatic nerve (NBF) and hamstring muscle (MBF) was measured in both conscious and anesthetized normal rats and in rats that had undergone surgical exposure of one sciatic nerve just prior to measurement. The distribution of [14C]butanol following its bolus intravenous injection was used to determine the flows in a modification of the "indicator fractionation" technique. NBF in normal rats was similar in limb pairs and was unaffected by pentobarbital sodium anesthesia. The pooled value was 12.5 +/- 1.1 ml X min-1 X 100 g-1. NBF was unaffected by sham operation in the conscious rats but was doubled in operated limbs of anesthetized rats (P less than 0.001). MBF in conscious normal rats was five times that measured during anesthesia. As in NBF, sham operation significantly increased MBF only in anesthetized rats (P less than 0.01). [14C]butanol distribution is a sensitive indicator of NBF and MBF. Mere surgical exposure of the nerve significantly increases NBF and MBF in anesthetized, but not in conscious rats.

An effective burn prevention program initiated by a recovered burn patient group

The US death rate from house fires has remained constant during the past 50 years despite a sharp decline in mortality from other fires and causes of burns. The concensus is that smoke alarms can effectively decrease the incidence of this lethal type of burn injury. Our organization of recovered burn patients has focused its efforts around procuring and installing smoke alarms in areas of substandard housing, which predominantly account for house fire deaths and injuries in St. Louis. This effort has resulted in an effective burn prevention program ("Alarms for Life"), which also serves as a model for other communities.

Differential effects of in vitro heating on rat sciatic nerve branches and spinal nerve roots

Locally applied heat induces nerve conduction block. Conflicting observations have been made regarding the relation of fiber conduction velocity to heat sensitivity. This study utilized sciatic nerve branches and spinal nerve roots which were heated until a substantial conduction block occurred. The results indicated that sensory fibers conducting at greater than 40 m/s are more heat-sensitive than motor fibers of the same conduction velocity.

Potassium ion channel blockade restores conduction in heat-injured nerve and spinal nerve roots

Compound action potentials were recorded in vitro from rat peroneal and sural nerves and from dorsal and ventral roots of the cauda equina before and after radiofrequency heating of 5-mm-length segments of these nerves to 41 to 45 degrees C. The heating was continued for intervals sufficient to reduce response amplitude by 50%. Inflection velocity, potential duration at 1/2 peak height, and the proportion of conducting A alpha fibers were also measured. The topical application of 4-aminopyridine (4-AP) and tetraethylammonium chloride (TEA) to the previously heated segments immediately following the radiofrequency injury completely or near-completely restored amplitude height to the preheat value in all experiments. A alpha sensory fibers were the most susceptible to the conduction block. Conduction in these fibers was also the most readily restored by the application of 4-AP or TEA. The effects of TEA, but not of 4-AP, could be reversed by saline or buffer washing. Topical application of verapamil and of magnesium or calcium ions had no discernible effect on heated nerves. We suggest that the mechanism of heat-induced conduction block may be similar to that from early demyelination or stretch injury. Further, motor and sensory A alpha fibers differ both in their vulnerability to heat and in their subsequent response to the application of potassium channel blockers.

Protein dynamics in skeletal muscle after trauma: local and systemic effects

Injury is attended by accelerated skeletal muscle proteolysis. Accurate definition of this hypercatabolic response and its mediation is requisite for specific therapy. We measured protein dynamics in the incubated and intact epitrochlearis and soleus muscles excised from both forelimbs and both hindlimbs of rats 4 days after injury by either a single hind limb scald (90 degrees C water for 3 seconds; metabolic rate (MR) + 15%, urinary urea nitrogen (UUN) + 10%) or a 5% excision (dorsal skin removed to fascia; MR + 40%, UUN + 90%). Protein synthesis (3H phenylalanine incorporation) increased only in the injured soleus from the scalded hind limb (+100%). Actin and myosin breakdown (3-methylhistidine release) increased in all muscles tested and was consistently larger in epitrochlearis than in soleus muscles. Breakdown of the mixed protein pool (tyrosine release) increased but less so than 3-methylhistidine and did not reach significance in the uninjured soleus muscle of scalded rats. With respect to fiber type, white fiber epitrochlearis muscle demonstrated a more pronounced elevation of both measures of breakdown but at a lower metabolic rate than did red fiber soleus muscle. Increasing MR was associated with a linear increase in soleus proteolysis but no further change in epitrochlearis breakdown. We conclude that protein breakdown is increased in skeletal muscle distant from injury; however, even when metabolic stress is severe, synthesis is unchanged. Muscles of different fiber composition are not equally labile. Furthermore, myofibrillar protein is more labile than the mixed protein pool.

A prospective double-blind comparison of piperacillin, cephalothin and cefoxitin in the prevention of postoperative infections in patients undergoing intra-abdominal operations

Piperacillin has been shown to be as safe and effective an agent as cephalothin and cefoxitin when used in patients undergoing elective intra-abdominal surgical procedures. Enterococcus species have been shown in other studies to be susceptible to piperacillin, perhaps making it the preferred antibiotic for prophylaxis in clinical settings when enteric flora will be encountered.

Plasma palmitate turnover in subjects with thermal injury

Using a continuous infusion of [1-13C] palmitic acid tracer, plasma palmitate turnover was measured 14 times in nine bandaged, thermally injured adults. Plasma glucose (102 +/- 4 mg/dl), insulin (21 +/- 4 microU/ml), and glucagon (296 +/- 34 pg/ml) levels were significantly elevated compared with values in uninjured controls. Circulating plasma epinephrine (67 +/- 11 pg/ml) and norepinephrine (219 +/- 57 pg/ml) levels were more than twofold their respective control values of 261 +/- 4 pg/ml and 211 +/- 7 pg/ml but less than the previously defined plasma threshold levels for lipolytic effects of these catecholamines as circulating hormones. Plasma palmitate and free fatty acid concentrations, 113 +/- 8 and 452 +/- 38 microM, respectively, were not different from control values but palmitate flux (2.66 +/- 0.28 mumol kg-1 min-1) and free fatty acid turnover calculated therefrom (10.53 +/- 1.13 mumol kg-1 min-1) were significantly elevated compared to the control rates. While palmitate turnover significantly correlated with plasma palmitate concentration and with per cent body surface area burned, there was no relationship between palmitate flux and circulating epinephrine or norepinephrine levels. These data raise new questions about the relative catabolic roles of catecholamines in bandaged, thermally-injured patients.

The role of concentrated sodium solutions in the resuscitation of patients with severe burns

Seventy-four severely burned patients were resuscitated with intravenous crystalloid solutions that varied in their average sodium concentration. No colloid solution was used. During the first 24 hours, when requirements were greatest, 21 patients received fluids containing less than 150 mEq sodium/L, nearly all of which was lactated Ringer's solution, while for 31 patients the fluids contained more than 199 mEq sodium/L; the remaining 22 patients were treated with fluids of intermediate sodium content (150 to 199 mEq/L). Detailed, computer-assisted analysis of the data was performed. There were no significant intergroup differences in mean hourly urine output, which was in the targeted range of 0.5 to 1 ml/kg, or in urinary sodium excretion. Both the sodium and water loads administered were significantly larger in patients who died than in survivors (P less than 0.0025). This observation is new. The use of concentrated sodium solutions did not increase the sodium requirement, but water loads were significantly lower in patients who received the most concentrated sodium solutions compared to those resuscitated with the least concentrated sodium solutions (P less than 0.014). The data suggest that minimizing the water loads during resuscitation by increasing the sodium content of the administered fluid might improve the chance for survival of severely burned patients.

Fibrinogen catabolism in burned patients

Plasma fibrinogen chromatography and other relevant determinations of factors of known importance in thrombus production and dissolution were done serially in 19 hospitalized burned patients. The findings indicate that the coagulation mechanism was chronically activated and that, judging from the observed, sustained elevation of circulating high molecular weight fibrin (ogen) complexes, intravascular clotting was occurring at a pathological, if variable, rate. In patients older than 50 years of age, a relatively impaired thrombolytic response was also found; the latter finding is of special interest, as it provides biochemical substantiation for the well-recognized clinical proclivity of elderly burn patients to thromboembolic complications.