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Biomedical subjects

J R Hedges

Publications and source records attributed to J R Hedges.

At least 127 records · Page 7Linked to original sources
PubMed1986

Dantrolene sodium for treatment of heatstroke victims: lack of efficacy in a canine model.

Dantrolene sodium, a skeletal-muscle relaxant known to be effective for treatment of malignant hyperthermia, was evaluated for efficacy in treatment of heatstroke. Non-exertional heatstroke was induced in 11 dogs by external heating following barbiturate anesthesia. When core temperature reached 43 degrees C (109.4 degrees F) heating was discontinued and control animals (n = 6) were allowed to cool passively in room air. Treatment animals (n = 5) received 5 mg/kg dantrolene sodium intravenously at the start of room-air cooling. Serial temperatures (pulmonary arterial, rectal, cerebral, and subcutaneous), blood chemistry tests (including electrolytes, liver enzymes, and complete blood count), and hemodynamic parameters (including cardiac output, arterial pressure, and urinary output) were followed for 12 hours after induction of heatstroke. Autopsies, including gross and microscopic examination, were performed on all animals. Dantrolene administration did not significantly affect cooling rates, hemodynamic parameters, pathological changes, or clinical outcome. Statistically significant changes in urinary output and serum creatinine observed in the first hours after dantrolene administration can be attributed to the mannitol vehicle in which the drug was delivered. There were no statistically significant differences in these values at 12 hours. Dantrolene sodium does not appear to enhance passive cooling in treatment of non-exertional canine heatstroke.

Animals↗
PubMed1986

Differences in drug delivery with peripheral and central venous injections: normal perfusion.

The differences between central venous (CV) and peripheral venous (PV) injections with respect to drug delivery times and peak concentrations in the left ventricle are examined. In this drug-delivery model, anesthetized dogs (n = 7) received both PV and CV injections of a radionuclide tracer. Measurements of radioactivity levels were made over each ventricle during normal perfusion. There was no statistically significant difference in left ventricular delivery times or peak radioactivity levels between the two different routes. When delivery time was corrected for variations in flow rate, a small but statistically significant difference was seen, the CV route being faster than the PV route (P less than 0.05). The magnitude of the observed difference for normal perfusion (2 seconds) is unlikely to be of clinical significance.

Animals↗
PubMed1986

Hemodynamics of transcutaneous cardiac pacing.

Transcutaneous cardiac pacing has recently been rediscovered as a rapid means of initiating emergency cardiac pacing. Potential myocardial injury from extended transcutaneous pacing could adversely affect cardiac hemodynamics during pacing. This canine study compares the hemodynamics of transcutaneous and transvenous cardiac pacing in animals with induced chronic heart block. One to two weeks following chemical ablation of the His bundle, hemodynamic measurements were made during 60 minutes of transcutaneous and 5-minute periods of conventional right ventricular endocardial pacing. Cardiac index and output were found to increase significantly (P less than 0.005), and systemic vascular resistance was found to decrease significantly (P less than 0.005) from baseline values with both pacing techniques. A hemodynamic difference between pacing techniques was evident only for mean arterial blood pressure; pressure measurements during transvenous pacing were slightly greater than those during transcutaneous cardiac pacing. The hemodynamic measurements were found to be stable during a 60-minute period of transcutaneous cardiac pacing. This study demonstrates that transcutaneous cardiac pacing is as effective hemodynamically as conventional transvenous pacing in animals with induced chronic heart block.

Animals↗
PubMed1986

Transcutaneous and transvenous cardiac pacing for early bradyasystolic cardiac arrest.

Emergency transcutaneous cardiac pacing was studied prospectively in 19 patients presenting to the emergency department with a bradyasystolic cardiopulmonary arrest of 20 minutes duration or less. Pacing was initiated when conventional advanced cardiac life support (including atropine administration) and a fluid challenge failed to restore a pulse. Seventeen patients also had placement of transvenous pacemaker electrodes for cardiac pacing. Transcutaneous cardiac pacing rapidly established a blood pressure in the two patients who for clinical reasons did not receive a transvenous pacemaker. Five patients were transcutaneously paced within five minutes of cardiac arrest (Group 1) and the remaining 14 were paced between five and 20 minutes following cardiac arrest (Group 2). Two of the Group 1 patients were admitted and subsequently recovered full neurological and prearrest cardiac function. Fewer Group 2 patients developed a blood pressure (P = .04), and there were no patients with full neurologic recovery in this group (P = .06). Similar results were found for transvenous cardiac pacing; there was a greater incidence of a palpable pulse and measurable blood pressure (P = .05 for both) in the Group 1 patients than in the Group 2 patients. No difference in clinical outcome was noted between the two pacing techniques. These results support the concept that cardiac pacing must be initiated early if the outcome of bradyasystolic cardiac arrest is to be altered.

Aged↗
PubMed1986

Radiologic assessment of transvenous pacemaker placement during CPR.

During an 18-month period we prospectively studied 36 emergency department patients who had a transvenous pacing catheter placed without fluoroscopic or ECG guidance during closed-chest massage. Transvenous pacing was instituted at a mean elapsed time of 35 minutes (range, ten to 80 minute) after the onset of cardiac arrest, including prehospital and ED care times. Catheter tip position was assessed using postresuscitation or postmortem chest radiographs. Pacing catheters were fixed in the position of electrical capture prior to radiographs; when capture was never achieved, the catheter was fixed at 35 cm from the point of insertion. Position of the catheter tip on radiographs was as follows: right ventricle, ten of 36 patients; right atrium, 18 of 36; and other location, eight of 36. Ectopic catheter tip positions included inferior vena cava (four), pulmonary artery (one), hepatic vein (two), and internal jugular vein (one). Catheter tip position within the right ventricle correlated with a significantly higher incidence of electrical capture when compared with other catheter tip locations (P less than .004). There was a significantly higher incidence of successful placement into the right ventricle when an internal jugular, rather than a subclavian venous, access route was used (P less than .004). Only one of 36 patients was resuscitated successfully; none lived to be discharged from the hospital. Misplacement of the catheter tip may contribute to the poor success rate of transvenous pacing during CPR. The internal jugular vein may be the access site of choice when transvenous pacing is attempted during chest compressions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

High-frequency jet ventilation cooling in a canine hyperthermia model.

A study was undertaken to evaluate high-frequency jet ventilation (HFJV) as an adjunct for the treatment of heatstroke. Eleven mongrel dogs were anesthetized, shaved, and externally heated until core temperature reached 43 C (109.4 F). Control animals (n = 6) were cooled passively in room air. Treatment animals (n = 5) were cooled with the addition of HFJV using a flow-interrupter, high-frequency jet ventilator with a rate of 200, a driving pressure of 40 psi, and an inspiratory to expiratory ratio of .5 to deliver room air. Temperatures were measured in brain, pulmonary artery, rectum, and subcutaneous tissue of the chest wall. Serial arterial blood gases, cardiac outputs, and mean arterial pressures were measured at baseline, maximal heating, and at .5, 1, 2, and 12 hours after heating. Animals were sacrificed 12 hours after heatstroke induction. Cooling rates for brain, pulmonary artery, and rectum achieved in the HFJV group were 1.7 times faster than those for the control group (P less than .05), although slower than previously reported cooling rates with gastric and peritoneal lavage. A higher PO2, a lower PCO2, and a more physiologic pH was maintained in the HFJV group than in the control group at 30 and 60 minutes after onset of cooling (P less than .05). Gross and histopathologic examination showed characteristic changes of heatstroke in both groups; no deleterious findings could be attributed to the use of HFJV itself. HFJV warrants clinical investigation as an adjunct for treatment of hyperthermia.

Animals↗
PubMed1986

Sore throat: to culture or not to culture.

The traditional use of the throat culture to guide treatment of potential streptococcal pharyngitis recently has been questioned because of the following facts: antibiotic therapy within the first 48 hours of illness reduces the severity and symptoms of streptococcal pharyngitis; more rapid treatment of streptococcal pharyngitis may be more effective in prevention of rheumatic fever; clinical and Gram stain criteria can identify individuals with a high probability of a positive throat culture; new latex agglutination tests can identify within minutes individuals with a high probability of a positive throat culture; the throat culture may be falsely negative in individuals with partially treated pharyngitis, an inadequately swabbed or plated specimen, or an improperly read culture plate; and incomplete patient followup increases the true societal cost of traditional therapy based on throat culture results. These issues suggest that a sufficiently accurate screening test for guiding antibiotic therapy at the initial visit may be more clinically beneficial and cost effective than recalling all positive throat culture patients for antibiotic therapy. Nonetheless, a throat culture remains important when a screening test of a patient with suspected streptococcal pharyngitis is negative. Indications for culturing pharyngitis for other potential pathogens also are discussed.

Adult↗
PubMed1986

Evaluation of venous distension device: potential aid for intravenous cannulation.

A device designed to augment venous filling by applying a vacuum to the upper extremity during tourniquet application was evaluated. Ten healthy adult male volunteers with clinical normovolemia were studied for changes in forearm volume and dorsal hand vein turgor during use of an elastic tubing tourniquet, a blood pressure cuff tourniquet, and a vacuum-assisted cuff tourniquet. Use of the device for 30 seconds was not associated with petechia formation and resulted in a significant increase in venous turgor, as measured by an ophthalmologic tonometer, in comparison to the other tourniquet techniques (P less than .005). Use for 60 seconds was associated with mild to moderate subjective discomfort in all volunteers and petechiae in all nine white volunteers. All petechiae resolved in three days. Venous engorgement as reflected by volume displacement was significantly greater for the vacuum device and blood pressure cuff tourniquet combination than other techniques at 30 and 60 seconds of tourniquet application (P less than .005). Brief application of a vacuum to the arm during tourniquet use increases venous turgor and engorgement in normovolemic volunteers.

Adult↗
PubMed1985

Pathological aspects of transcutaneous cardiac pacing.

Although electrical energy has the potential to produce myocardial injury, the risk of tissue damage from transcutaneous cardiac pacing is largely unknown. This study reports the anatomical findings of a canine transcutaneous stimulation study. Ten dogs had 100-mA, 20-msec (pulse duration), transcutaneous impulses delivered across the thorax for 30 minutes at a rate of 80 stimuli per minute. Seventy-two hours later the animals were sacrificed, and the heart, lungs, and tissues of the chest wall were examined for pathological changes. Gross and microscopic lesions consistent with electrically induced myocardial damage were found in all hearts examined. These lesions included myocardial pallor and focal myofibril coagulation necrosis in the right ventricular outflow tract and perivascular microinfarcts in the posterior left ventricular myocardium. These lesions were not extensive; less than 5% of the right ventricular free wall and less than 1% of the left ventricular posterior wall were involved. Lesions of this extent would not be expected to cause clinically detectable changes in cardiovascular status. Short-term use of transcutaneous pacing appears to be safe. Determination of the potential for clinically significant injury with long-term use requires further study.

Animals↗
PubMed1985

Bicarbonate therapy for the cardiovascular toxicity of amitriptyline in an animal model.

The beneficial hemodynamic effects of sodium bicarbonate as treatment for tricyclic antidepressant poisoning were investigated in an animal model. Seven adult dogs (17.5 to 20 kg) were poisoned by an intravenous infusion of amitriptyline. Toxicity was defined as a doubling of the initial QRS width. A continuous infusion was used to maintain toxicity for 30 minutes after which 44.5 mEq of sodium bicarbonate was administered intravenously. Five of the animals survived to completion of the experiment. Three of the surviving animals developed dysrhythmias. All dysrhythmias ceased within one minute of administration of sodium bicarbonate. An increase in mean blood pressure (P less than .05) and serum pH (P less than .05) and a decrease in mean QRS width (P less than .05) occurred following administration of sodium bicarbonate. The maintenance of toxicity for 30 minutes suggests that this model can be used for future studies of tricyclic antidepressant poisoning.

Amitriptyline↗
PubMed1985

Single-dose ceftriaxone treatment of urinary tract infections.

Single-dose antibiotic therapy for urinary tract infections in which no underlying structural or neurologic lesions are present holds the promise of greater patient compliance and convenience. We present the results of a study comparing a single intramuscular dose of a long-acting, third-generation cephalosporin, ceftriaxone, with a standard, five-day regimen of trimethoprim-sulfamethoxazole (TMS). Fifty-two patients were entered into the study. After randomization, 26 were assigned to the TMS group and 26 were assigned to the ceftriaxone group. Of the patients who completed the study, 13 of the TMS group had positive cultures at the time of initial presentation, and 20 of the ceftriaxone group had positive cultures. There was no statistical difference between the groups in symptoms of dysuria, hematuria, frequency, flank pain, and nocturia (alpha = .05). The physical parameters of age, blood pressure, pulse, and temperature were similar in the two groups (alpha = .05), as were the types of infecting organisms (alpha = .05). When comparing the two regimens, the ceftriaxone group cure rate (18 of 20, 90%) was not found to be significantly different from that of the TMS-treated control group (13 of 13) (alpha = .05).

Administration, Oral↗
PubMed1985

Iced gastric lavage for treatment of heatstroke: efficacy in a canine model.

This study was undertaken to evaluate a central cooling technique for heatstroke, gastric lavage with iced tap water, for speed of cooling and efficacy of treatment in an anesthetized canine heatstroke model. Eleven mongrel dogs were anesthetized, shaved, and externally heated until core temperature reached 43.0 C (109.4 F). Control animals (n = 6) were cooled passively in room air. Treatment animals (n = 5) were cooled with the addition of gastric lavage with iced tap water through a large-bore orogastric tube. Temperatures were monitored using thermocouples in the brain, pulmonary artery, rectum, and subcutaneous tissue of the chest wall. Serial enzymatic and hematologic laboratory studies and hemodynamic parameters were measured prior to heating, at the end of heating, and at 0, 0.5, 1, 2, and 12 hours after heating. Animals were sacrificed 12 hours after heatstroke induction and gross and microscopic pathologic examination was performed. Central cooling rates achieved in the lavage group were five to six times faster than in the control group, (P less than .01) and are comparable with those reported in the literature for external cooling techniques. No significant complications were induced by tap water lavage. Rapid cooling in the lavage group resulted in a statistically significant improvement in serum creatinine and LDH after heatstroke induction (P less than .05). Gastric lavage with iced tap water appears to be an effective alternative or adjunctive cooling technique for heatstroke in the dog.

Animals↗
PubMed1985

A hemodynamic model for anaphylactic shock.

The treatment of cardiovascular collapse and anaphylactic shock is largely empiric. A simple animal model was developed to evaluate the hemodynamic alterations in anaphylaxis. Eight adult New Zealand white rabbits of both sexes were studied. All animals weighed 3.8 kg to 5.3 kg. Sensitization was accomplished with a 2-mL subcutaneous dose of horse serum followed in two days with a 2-mL intravenous (IV) dose. At least 14 days elapsed after the IV dose before a 1-mL challenge dose of horse serum was given. On the day of the challenge dose, a femoral arterial catheter, arterial temperature probe, and right atrial catheter were placed under methoxyflurane anesthesia. The temperature probe was positioned in the aortic arch. The methoxyflurane was discontinued and the only sedation given during the shock phase was IV diazepam (0.1 mg/kg to 0.5 mg/kg). At least 30 minutes after methoxyflurane was discontinued, the challenge dose of horse serum was given through the right atrial catheter. Before and during the shock phase cardiac rhythm, arterial pressure, and intravascular temperature were monitored continuously. Cardiac outputs (CO) were performed by a thermodilution technique using 0.8 mL room temperature saline injectate through the right atrial catheter. Temperature deflection of the aortic probe was recorded and cardiac output was calculated. After giving the challenge dose, CO was measured at three, five, ten, 15, 25, 35, 45, and 60 minutes. All eight animals showed a significant (P less than .0005) fall in CO, cardiac index, and blood pressure within three minutes. The fall in cardiac index was 50% or more in all animals. Two animals died as a result of shock.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaphylaxis↗
PubMed1985

Emergency department use of transcutaneous pacing for cardiac arrests.

Transcutaneous cardiac pacing is a rapid technique for pacing the heart using skin electrodes to pass repetitive electrical impulses through the thorax. This paper reports the results of transcutaneous pacing in a series of 52 emergency department patients. Patients were selected for pacing if they were unconscious and in asystole (30 patients) or unconscious with a pulseless or hemodynamically ineffective bradycardia (22 patients). In all cases, transcutaneous pacing was attempted after initial resuscitative drug therapy failed. Of the 26 patients with successful ECG capture, 14 were initially in asystole, 11 were initially in a pulseless bradycardia, and one had a hemodynamically ineffective bradycardia. Of the eight patients developing a pulse, four developed a measurable BP. The four patients who developed a measurable BP were young (ages 22 to 39 yr) and only one had an underlying cardiac etiology for his cardiac arrest. No patient survived to be discharged from the hospital. Twenty-five of the 52 patients also had a transvenous pacemaker inserted, with successful electrical capture in five of the patients. Only one of the transvenously paced asystolic patients subsequently developed a BP. There were no patients successfully paced transvenously who were not successfully paced transcutaneously.

Adult↗
PubMed1984

Central versus peripheral intravenous routes in cardiopulmonary resuscitation.

The central venous (CV) and peripheral venous (PV) routes of drug administration are generally considered to be equally effective during cardiopulmonary resuscitation (CPR). This canine study compared simulated drug delivery via CV and PV routes during CPR. The CV group dogs had a CV catheter placed via the external jugular vein, and the PV group dogs had a PV catheter placed in the distal forelimb. Thirty seconds after the induction of cardiac arrest with KCl, CPR was begun with a gas-powered chest compressor with ventilations after every fifth compression. Sixty seconds later, a 0.5 ml bolus of technetium 99m-labeled serum albumin was given. Time activity curves were obtained over the right and left ventricles. The mean time for the counts to rise to half the left ventricular peak (T1/2LV) was significantly less for the CV group than for the PV group (P less than 0.05), averaging 11 and 84 seconds, respectively. The time to left ventricular peak (TLV) was also statistically shorter for the CV group than the PV group, averaging 118 versus 258 seconds, respectively. This study demonstrates that central venous administration is more rapid than peripheral venous administration during CPR and supports the preferential use of the central venous route for drug administration clinically.

Animals↗