Laser balloon angioplasty: clinical, angiographic and histologic results.

Laser balloon angioplasty combines conventional coronary angioplasty with laser energy to transiently heat vascular tissue. Laser balloon angioplasty, was performed in 21 patients (aged 56 +/- 13 years), including 10 patients treated urgently after acute failure of conventional angioplasty and 11 patients treated with elective laser balloon angioplasty. Immediately after conventional angioplasty, laser doses (1 to 10 doses of 205 to 380 J each) were delivered during inflation of the laser balloon to a pressure of 4 atm. Seven (70%) of 10 patients with acute failure of conventional angioplasty were successfully treated with laser balloon angioplasty, but 3 (30%) were unsuccessfully treated with the laser procedure and required emergency coronary artery bypass surgery. In all three failures, the 3 mm laser balloon angioplasty catheter was not the optimal size for the vessel. In the 11 patients treated with elective laser balloon angioplasty (reference diameter 2.94 +/- 0.22 mm), the minimal luminal diameter increased from 0.45 +/- 0.25 to 1.85 +/- 0.46 mm after conventional angioplasty and to 2.44 +/- 0.29 mm after laser balloon angioplasty (p less than 0.001). This corresponded to a decrease in diameter stenosis from 84 +/- 9% before to 35 +/- 16% after conventional angioplasty and to 15 +/- 10% after laser balloon angioplasty (p less than 0.001). There were no instances of myocardial infarction, emergency coronary artery bypass surgery or death and no acute complications related to delivery of laser energy in this group. Follow-up coronary angiography was performed 5.5 +/- 1.1 months after laser balloon angioplasty in 18 patients discharged from the hospital after a successful procedure. Ten patients (56%) had angiographic restenosis, defined as recurrent diameter stenosis greater than 50%. Six patients were subsequently treated by directional coronary atherectomy, which revealed intimal proliferation indistinguishable from that in patients with restenosis after conventional angioplasty. In conclusion, laser balloon angioplasty may be effective in sealing severe coronary dissections and reversing abrupt closure associated with failed conventional angioplasty. After uncomplicated conventional angioplasty, laser balloon angioplasty improves immediate luminal dimensions, but restenosis appears to be mediated by intimal hyperplasia, similar to that seen after conventional angioplasty.

Recurrent left ventricular false aneurysm.

A recurrent left ventricular false aneurysm 5 years after patch repair and causing progressive congestive heart failure was readily diagnosed by echocardiography and heart catheterization. Its substrate was suture dehiscence of undetermined origin. Urgent repair was successful. The long-term prognosis is guarded.

Management of a child on CAPD with a ventriculoperitoneal shunt.

Long term dialysis in children with multiple handicaps has become easier with the advent of CAPD. In December 1986, an 11 year old with myelomeningocele in end stage renal disease secondary to chronic pyelonephritis required dialysis. Placement of a right ventriculoperitoneal shunt had been done at 4 months of age. Poor family compliance required placement in medical foster care. The peritoneal catheter was replaced three times. Leakage and infection were the major complications resulting in catheter replacement. In March 1988 the child required shunt extension due to accelerated growth after which she developed relapsing peritonitis requiring removal of the peritoneal catheter and externalization of the ventriculoperitoneal shunt. A proximal tap of the ventriculoperitoneal shunt prior to revision had a negative culture but glucose of 471 when serum glucose was 91. Six days after externalization of the shunt and catheter removal, the shunt was converted to ventriculoatrial and the PD catheter replaced. Nasogastic feedings and cycler dialysis became necessary due to worsening nutritional status and hyperabsorption. Successful transplantation occurred 28 months after initial dialysis.

Medical resources on the Internet: searching and appraising.

Finding useful medical information on the Internet depends on searching effectively and critically appraising the resources when they are found. This article offers practical advice for those interested in using the internet for education and training.

Laser balloon angioplasty. A new approach to abrupt coronary occlusion and chronic restenosis.

Abrupt coronary occlusion and long-term restenosis continue to be the major problems associated with percutaneous transluminal coronary angioplasty (PTCA). Laser balloon angioplasty (LBA) is a technique designed to potentially alleviate these problems by sealing arterial dissections, smoothing the luminal surfaces, dehydrating thrombi, and reducing the elastic properties that tend to recoil the stretched artery to its original state. During LBA, laser energy is delivered circumferentially by a 100-microns optical fiber that terminates in a central diffusing tip within an angioplasty balloon. LBA is performed for 20 seconds during the final inflation of the angioplasty balloon. Achieved with decremental ramped laser dosimetry, Nd:YAG laser energy has been shown to be effective in welding experimental arterial dissections over a therapeutic temperature range of 95 degrees-120 degrees C. LBA treatment of rabbit iliac arteries has been superior to balloon angioplasty in inhibiting elastic recoil and causing acute and long-term luminal increment. LBA has also been effective for sealing acute dissections in atherosclerotic rabbit iliac arteries. Additionally, in a canine model, safety in the coronary circulation has been shown, that is, even at 1 month after LBA, angiography demonstrated a cast of the LBA balloon without luminal compromise. Since March 1988, more than 250 patients with symptomatic coronary artery disease have been treated with LBA with nearly uniform clinical success, including frequent reversal of abrupt closure. LBA seems to be a safe modality that may decrease the need for emergency operative procedures and late coronary revascularization after PTCA.

Rapid semiautomated screening and processing of urine specimens.

A rapid urine culture procedure was evaluated in which positive urines were detected by using light-scatter photometry (Autobac). Specimens were analyzed at 3, 5, and 6 h. Specimens detected as positive at 3 h were then further evaluated by a direct 3-h susceptibility procedure (Autobac) and by a 4-h identification procedure (Micro-ID). Of 949 specimens, 175 had >10(5) colony-forming units per ml by colony count. Of these latter specimens, 75.4% had been detected by 3 h, and 95.4% were detected by 6 h. Of specimens positive by Autobac at 3 h, 96% (95.7%) had >10(5) colony-forming units per ml. If pure by Gram stain, those positive specimens were inoculated to direct susceptibility and identification systems. When direct Autobac susceptibilities were compared with the standard Autobac method done from the plate the following day, discrepancy rates were 1.3% very major, 2.1% major, and 7.4% total. The direct identifications were 94% (94.2%) correct when using the Micro-ID manual and a collection of octal patterns unique to this system, in which urine/broth culture inoculum was employed instead of the usual organism colony suspension. Those urine specimens negative after screening at 3 h were evaluated at 5 and 6 h, and an additional 126 specimens were detected as positive. These were then processed by routine plate inoculation, due to the limitations of the work day. By 6 h, 95.4% of specimens with >10(5) colony-forming units per ml were detected. The 4.6% false-negative results consisted of patients on antibiotics, or slowly growing bacteria suspected of being distal urethral contaminants. Thus, 83.5% of the urine cultures received by 9:00 a.m. (10.6% 3-h positives and 72.9% negative at 6 h) could be evaluated and reported within one 8-h work day.

Clinical implications of catheter variability on neonatal continuous arteriovenous hemofiltration.

The clinical impact of catheter diameter variability on performance of neonatal continuous arteriovenous hemofiltration (CAVH) systems was shown by demonstration of the effect of catheter inner diameter on catheter and CAVH system blood flow. Diameter of 3.5 Fr and 5 Fr catheters was determined by experimental measurement of catheter flow-pressure drop relationship with known equations for fluid flow. Physical measurements verified the accuracy of the calculated diameters. These diameters were then used in a mathematical simulation to describe blood flow through an entire neonatal CAVH system and predict clinical performance. Catheters of 5 Fr caliber had a 39% variation in diameter among manufacturers, resulting in a 370% variation in blood flows; 3.5 Fr catheters had a 29% variation in internal diameter with a corresponding blood flow variation of 290%. Computer simulation of a neonatal CAVH system revealed a maximum blood flow of 0.8-3.0 ml/min with available 5 Fr catheters. This wide variation is probably responsible for the lack of consistent results in neonatal CAVH systems to date.

Permeability decay in CAVH hemofilters.

Change in hydraulic permeability over time was measured in four types of continuous arteriovenous hemofiltration (CAVH) hemofilters in order to characterize permeability decay and demonstrate that permeability decay occurs without membrane protein exposure. Polyamide, polysulfone, and polyacrylonitrile membrane hemofilters were placed in a gravity-driven in vitro CAVH apparatus. Distilled and deionized water or saline was used to perfuse the hemofilters. A biphasic pattern of permeability decay was seen in all hemofilter types. A large exponential decline in permeability occurred over the first 1 to 6 hours, with a more gradual decay thereafter. Of all membranes studied, polysulfone hemofilters were the most permeable upon initiation of use but showed the most pronounced early and late permeability decay. Both polyamide and polyacrylonitrile hemofilters showed little permeability decay after a brief exponential decay. These data suggest that early membrane hydraulic permeability decay may not be primarily due to membrane protein coating. Initial high permeability may place some CAVH systems at risk for hemofilter plugging.

Review of urine microscopy for bacteriuria.

Urine microscopy for bacteriuria remains a useful and valid technique for the evaluation of urinary tract infection; however, established interpretive criteria are not agreed on. Our own data and a review of the literature demonstrate that reliable data can be obtained by enumerating the organisms observed in stained or unstained centrifuged and stained uncentrifuged urine specimens. Criteria are given for the interpretation of urine microscopy for maximum sensitivity and specificity for each method reviewed. For clinicians desiring to perform urine microscopy, we recommend the use of oil-immersion microscopy of Gram-stained centrifuged urine sediment and suggest that observing at least one organism per oil-immersion field corresponds with 95% sensitivity and that observing more than five organisms corresponds with 95% specificity for bacteriuria at a level of 10(5) or more colony-forming units per milliliter. Further testing will be required on any negative specimen from a symptomatic patient.

Benefit of bicarbonate dialysis during CAVHD.

The effect of bicarbonate dialysate (BD) on acid-base status in six pediatric CAVHD patients was examined during seven episodes of metabolic acidosis. When metabolic acidosis was not corrected with CAVHD, a sterile BD was substituted for either acetate- or lactate-based dialysate. Pre- and post-BD substitution levels of lactate, HCO3, PCO2, anion gap, and pH were recorded, as well as dose of intravenous (i.v.) bicarbonate. Improvements in pH and serum HCO3 were seen in all seven cases. Anion gap decreased in all but one of the patients who were switched from lactate to bicarbonate dialysate, with improvement most marked in those patients with marked elevation of the anion gap. No adverse effect on PCO2 was noted. Lactate dialysate may be less effective when serum lactate levels are high, and may contribute to further elevation of lactate levels and anion gap. These data suggest that bicarbonate dialysate may be preferable to lactate or acetate dialysate in CAVHD patients with persistent metabolic acidosis.

Early experience with continuous arteriovenous hemofiltration in critically ill pediatric patients.

The applicability of continuous arteriovenous hemofiltration (CAVH) for renal replacement therapy was evaluated in three infants and two young children with catastrophic medical and surgical illnesses. In the first four patients, CAVH was used in conjunction with either peritoneal or hemodialysis. In the fifth patient, CAVH was the sole renal replacement therapy employed; in this critically ill anuric infant, we were best able to evaluate the ability of CAVH to continuously control fluid, electrolyte, and acid-base balance, and allow the administration of adequate parenteral nutrition. The difficulties encountered were related to anticoagulation, establishment of adequate vascular access, and selection of an appropriate hemofilter for the performance of the technique. Despite the application of suction-assistance, we were unable to effectively employ a prototype pediatric hemofilter to attain a level of plasma ultrafiltration consistent with the objectives of therapy. However, we were able to effectively and safely employ an adult hemofilter for these purposes; modifications were made in the adult hemofilter system before its application in the smallest pediatric patients. Our experience suggests that, even in critically ill infants, CAVH can be successfully applied as an effective renal replacement therapy. However, further experience is required before its potential impact on patient survival can be assessed.

Laser balloon angioplasty: effect of tissue temperature on weld strength of human postmortem intima-media separations.

Dehiscence of portions of atheromatous plaques fractured during percutaneous transluminal coronary angioplasty may contribute to both abrupt reclosure and gradual restenosis. Laser balloon angioplasty has been shown to be effective in welding human plaque-arterial wall separations in vitro by heating tissues with a Nd:YAG laser during balloon inflation. To define the potentially useful therapeutic range of tissue temperature required to achieve thermal welds, 220 1-cm diameter discs of human postmortem atheromatous aortic tissue, the intimal plaque of which had been separated from the media, were exposed to 3-25 watts of Nd:YAG laser radiation delivered over a 12-mm2 nominal spot size for 20 seconds via a 400-micron core optical fiber. As measured with a thermistor, adventitial temperature reflected the temperature at the plaque-media junction to within 10 degrees C. The degree of tissue temperature elevation was related to delivered energy, while effective tissue penetration increased to maximum depth of 3 mm at the highest power density. Strength of tissue welds was defined as the force required to shear opposing layers of welded segments. Adventitial tissue temperatures below 80 degrees C were not associated with appreciable welds, while equilibrium temperatures between 95 degrees C and 140 degrees C were consistently associated with effective mean weld strengths, which increased linearly from 25 to 110 g, respectively. Temperatures greater than 150 degrees C were associated with rapid tissue dehydration and charring. These data suggest that the therapeutic range of tissue temperature that provides effective thermal fusion of intima-media separations is broad and that the depth and degree of thermal coagulation can be controlled by manipulation of laser energy delivery.

Laser balloon angioplasty: effect of constant temperature versus constant power on tissue weld strength.

Thermal fusion of intimal plaque with the arterial wall during coronary balloon angioplasty may significantly reduce the incidence of abrupt closure and may reduce the occurrence of delayed restenosis by improvement of luminal size and shape. Although Nd:YAG laser energy has been shown to be effective in the thermal fusion of plaque-arterial wall separations in vitro, the most efficient manner of energy delivery for rapid achievement of therapeutically useful equilibrium tissue temperature during laser exposure has not been defined. A comparison of weld strength achieved was therefore made between two formats of laser delivery: constant power vs. decremental power with an initial high dose followed by the minimal serial decrements necessary to maintain tissue temperature constant for 15 seconds. One hundred sixty-six tissue discs of human postmortem aorta of 11 mm diameter were studied. Intimal plaque was separated from the media, the two layers were juxtaposed, a force of 4 pounds was applied, and a fiberoptic-delivered laser beam was directed perpendicular to the tissue over a 3-mm-diameter nominal spot size. Weld strength was measured as the shear force required to separate completely the two tissue layers. The mean weld strength (75 g) achieved by use of the decremental power format was significantly higher (P less than .01) than the mean strength (32 g and 56 g) achieved by using constant power for 20 and 30 seconds, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

False susceptibility of enterococci to aminoglycosides with blood-enriched Mueller-Hinton agar for disk susceptibility testing.

Disk diffusion susceptibility tests for enterococci are frequently modified by adding 5% sheep blood (SB) to Mueller-Hinton agar; the performance standards from the National Committee for Clinical Laboratory Standards sanction this addition. Susceptibility testing of aminoglycoside antibiotics is not recommended for enterococci; in actual practice, however, some laboratories do include aminoglycoside antibiotics routinely, and others may test upon request or in selected situations. In examining 50 clinical isolates of enterococci, SB-enriched Mueller-Hinton agar frequently gave enlarged zone sizes that falsely indicated susceptibility (72% for gentamicin and tobramycin), with the average increase in zone size being 6.3 and 7.6 mm, respectively. Comparison agar dilution MICs demonstrated uniform resistance, with or without added SB. The effect was shown to be caused by heme in concentrations as low as 0.03 micrograms/ml, which, when combined with aminoglycoside antibiotics, caused a synergistic growth inhibition of the enterococci, resulting in larger aminoglycoside antibiotic zones. We postulate that the heme effect is related to a catalytic cleavage of intracellular H2O2 and resultant lipid peroxidation. No other organism or antimicrobial agent tested demonstrated a similar effect, although other investigators have shown a similar phenomenon with the broad-spectrum cephalosporins. Because enterococci grow well and give accurate susceptibility results on Mueller-Hinton agar without SB supplementation and because of the spectrum of definable problems with a number of antimicrobial agents, we recommend that enterococci routinely be tested without SB.

The effect of activated charcoal on N-acetylcysteine absorption in normal subjects.

The discovery of the effectiveness of oral antidotes such as N-acetylcysteine (NAC) for acetaminophen poisonings has raised questions about the appropriateness of concomitant administration with activated charcoal. A number of studies have attempted to clarify this question without complete success. This study was designed to evaluate the difference in serum levels of NAC when given with activated charcoal. Nineteen patients completed a two-phase cross-over study in which they served as their own controls. Each subject in phase 1 received 140 mg/kg of diluted, chilled NAC orally, and venous blood samples were drawn for analysis. Phase 2 consisted of a 100-g dose of activated charcoal followed by NAC. Samples were transported immediately and assayed using spectrophotometry. A reduction in peak NAC level of 29% (P less than .02) and a reduction of total area under the curve (AUC) of 39% (P less than .001) was noted. Although it may be preferable to avoid completely the use of activated charcoal when using NAC to treat overdoses of acetaminophen, we recommend that if these agents are used together, doses of NAC be increased by 40% to compensate for the decreased oral absorption of NAC.

Laser balloon angioplasty: effect of exposure duration on shear strength of welded layers of postmortem human aorta.

Laser Balloon Angioplasty (LBA) is a technique that may improve the results of balloon angioplasty by thermally sealing arterial dissections and reducing elastic recoil. To define the relationship between laser-exposure duration and the strength of thermal welds made between separated layers of arterial wall, 360 1-cm discs of human postmortem aorta were lased for six different exposure intervals at three different temperature ranges, comparing shear strength of thermal welds in the different groups. Twenty discs were lased to achieve plateau adventitial temperatures of 95 degrees C-104 degrees C (group A), 105 degrees C-114 degrees C (group B), or 115 degrees C-124 degrees C (group C) at each of the exposure periods (5, 10, 15, 20, 25, and 30 sec). A 400-micron fiberoptic coupled to a 1.06 micron continuous wave neodymium:YAG laser was placed perpendicularly 8 mm above the luminal surface of each disc, which had been split midway between the intimal and adventitial surface and reapposed. Mean laser energy ranged 78-378 J delivered in a decremental stepwise fashion to achieve quickly and maintain the target plateau tissue temperature. Mean weld strength increased in relation to both achieved tissue temperature and laser-exposure duration, with at least 10 sec necessary, at temperatures greater than 95 degrees C, for reliable thermal welding. Laser exposure for greater than 20 sec provided no statistical increment in weld strength. In the anticipated clinical performance of LBA, these data suggest that when thermal fusion of disrupted arterial tissues is desired, a laser-exposure duration of 10-20 sec is optimal.