Endothelium during microarterial graft procurement and transplantation.

Microarterial grafts are prone to mechanical endothelial injury that can have profound effects on the transplanted vessel, a factor neglected in studies on vascular changes post-transplantation. The aim of this study was to document the integrity of the endothelial lining after both procurement and transplantation of rat aortic grafts, using a minimal touch technique with and without the use of topical papaverine. It was found that procurement using a simple minimal touch technique preserved the endothelium and transplantation could be performed without endothelial injury. The appearance of "normal" endothelium varied with the degree of distension of the artery, suggesting a dynamic endothelial architecture to accommodate changes in the surface area of the artery during pulsation. These findings indicate that transplantation of an arterial segment without injury to the intima is possible and stress the importance of technical controls after both procurement and transplantation to prevent the use of injured grafts and misleading results.

Custom cranioplasty using stereolithography and acrylic.

Numerous methods of cranioplasty have been described. Customization and prefabrication have been reported to reduce operating time and improve cosmesis. An original technique for the manufacture of customized cranioplastic implants has been developed and tested in 30 patients.Thirty patients requiring cranioplasties were selected. Data acquired from computed tomography (CT) were used to manufacture exact plastic replicas (biomodels) of craniotomy defects and master cranioplastic implants using the rapid prototyping technology of stereolithography (SL). The three-dimensional (3D) imaging techniques of mirroring and interpolation were used to extrapolate on existing anatomy to design the master implants. The master implants were hand finished to fit the defect in the corresponding cranial biomodel exactly and were then used to create a cavity mould. The mould was used to cast thermally polymerised custom acrylic implants. The surgeons reported that the customized implants reduced operating time, afforded excellent cosmesis and were cost effective. The patients reported that the opportunity to see the biomodel and implant preoperatively improved their understanding of the procedure. Two complications were noted, one infection and one implant required significant trimming. The simultaneous manufacture of the master implant (male) and biomodel (female) components from SL allowed custom accurate implants to be manufactured. Disadvantages identified were the time required for computer manipulations of the CT data (up to 2 h), difficulty in assessing the accuracy of the computer generated master as a 3D rendering, the potential for SL parts to warp, manufacturing time (minimum 2 days) and the cost of approximately $1300 US per case ($1000 for the SL biomodel and $300 for the acrylic casting).

Spinal biomodeling.

STUDY DESIGN: A prospective trial of stereolithographic biomodeling in complex spinal surgery. OBJECTIVES: To investigate the use of stereolithographic biomodeling as an aid to complex spinal surgery. SUMMARY OF BACKGROUND DATA: Of the array of imaging methods available to assist the spinal surgeon, no single method provides a complete overview of the anatomy, although three-dimensional imaging has been shown to have advantages. METHODS: Stereolithographic biomodeling is a new technology that allows data from three-dimensional computed tomographic scans to be used to generate exact plastic replicas of anatomic structures. Five patients with complex deformities were selected: two children with congenital deformities, a patient with an osteoblastoma, a patient with basilar invagination caused by osteogenesis imperfecta, and a patient with a failed lumbar fusion. Computed tomographic scanning was performed and stereolithographic biomodels generated. The stereolithographic biomodels were used for patient education, operative planning, and surgical navigation. RESULTS: The surgeons reported that biomodeling was useful in complex spinal surgery and was an effective technology. Stereolithographic biomodels were found to be particularly useful in morphologic assessment, in the planning and rehearsal of surgery, for intraoperative navigation, and for informing patients about surgical procedures. CONCLUSIONS: Stereolithographic biomodeling allows imaging data to be displayed in a physical form. This intuitive medium may improve data display and allows surgical simulation on a proxy of the surgical site. Draw-backs of the technology were a minimum 24 hours' manufacturing time and the cost.

Stereolithographic biomodelling in cranio-maxillofacial surgery: a prospective trial.

Stereolithographic (SL) biomodelling is a new technology that allows three-dimensional (3-D) computed tomography (CT) data to be used to manufacture solid plastic replicas of anatomical structures (biomodels). A prospective trial with the objective of assessing the utility of biomodelling in complex surgery has been performed. Forty-five patients with craniofacial, maxillofacial, skull base cervical spinal pathology were selected. 3-D CT or MR scanning was performed and the data of interest were edited and converted into a form acceptable to the rapid prototyping technology SL. The data were used to guide a laser to selectively polymerize photosensitive resin to manufacture biomodels. The biomodels were used by surgeons for patient education, diagnosis and operative planning. An assessment protocol was used to test the hypothesis that 'biomodels in addition to standard imaging had greater utility in the surgery performed than the standard imaging alone'. Biomodels significantly improved operative planning (images 44.09%, images with biomodel 82.21%, P < .01) and diagnosis (images 65.63%, images with biomodel 95.23%, P < .01). Biomodels were found to improve measurement accuracy significantly (image measurement error 44.14%, biomodel measurement error 7.91%, P < .05). Surgeons estimated that the use of biomodels reduced operating time by a mean of 17.63% and were cost effective at a mean price of $1031 AUS. Patients found the biomodels to be helpful for informed consent (images 63.53%, biomodels 88.54%, P < .001). Biomodelling is an intuitive, user-friendly technology that facilitated diagnosis and operative planning. Biomodels allowed surgeons to rehearse procedures readily and improved communication between colleagues and patients.

Stereolithographic (SL) biomodelling in craniofacial surgery.

BACKGROUND: Stereolithographic (SL) biomodelling allows 3D CT to be used to generate solid plastic replicas of anatomical structures (biomodels). Case reports in the literature suggest that such biomodels may have a use in craniofacial surgery but no large series or assessment of utility has been reported. A prospective trial to assess the utility of biomodelling in craniofacial surgery has been performed. METHODS: Forty patients with complex craniofacial abnormalities were selected and 3D CT scanning performed. The data of interest was used to guide a laser to selectively polymerise photosensitive resin to manufacture SL biomodels. The biomodels were used for patient education, diagnosis and operative planning. An assessment protocol was designed to test the hypothesis that biomodels in addition to standard imaging had greater utility in the surgery performed than the standard imaging alone. RESULTS: Anecdotally surgeons found biomodelling useful in 40 complex craniofacial operations. The formal assessment of the first 10 cases suggested biomodels improved operative planning (image 76%, image with biomodel 97%, P < 0.01) and diagnosis (image 82.5%, image with biomodel 99.25%, P < 0.01). Surgeons estimated that the use of biomodels had reduced operating time by a mean of 16% and were cost effective at a mean price of $1100 AUS. CONCLUSION: Biomodelling was reported as an intuitive, user-friendly technology that facilitated diagnosis, operative planning and communication between colleagues and patients. Limitations of the technology were manufacturing time and cost.

The stability of facial advancement surgery (in the management of combined mid and lower dento-facial deficiency).

The short-term (6 weeks postoperative) and long-term (12 months postoperative) skeletal stability of combined maxillary and mandibular advancement was evaluated by cephalometric analysis in 15 patients. The mean horizontal advancement of the maxilla was 5.84 mm. 6 weeks later a mean relapse of 0.03 mm (0.5%) was identified. The mean relapse at long-term follow-up was 0.59 mm (10.1%). The mean horizontal advancement of the mandible was 12.35 mm at menton and 12.65 mm at pogonion. At 6 weeks, mean horizontal relapse, respectively at the above landmarks, was 0.11 mm and 0.21 mm (1.3%). The mean relapse at long-term follow-up was respectively 2.19 mm and 1.98 mm (16.9%). Subjectively and objectively improvements were seen in facial aesthetics and dental occlusion. The results indicated that rigid fixation of osteotomies undertaken to correct 'horizontal facial deficiency' is a surgically predictable and relatively stable procedure when reviewed up to 12 months after surgery.

Do medical students remember multiple choice questions?

The values of pre-testing senior medical students at the start of their surgical terms are the perception that they acquire of the scope of the subject and the extra practice they gain in the technique of sitting multiple choice question (MCQ) exams. The purpose of this study was to determine whether MCQ in a pre-test that were repeated in a post-test were answered more accurately than questions that had not been repeated. For the past 3 years at the University of Queensland, fifth year medical students have been voluntarily sitting pre- and post-tests in each of the four surgical terms. Each examination consisted of 60 clinically oriented surgical questions of a difficulty appropriate for senior medical students. A total of 404 students did both the pre- and post-tests during 1990 and 1991. The two examinations were carefully chosen for comparability. Of the 60 questions in each examination, 30 were repeated in the post-test and 30 were fresh questions in the post-test. The pre- and post-tests were reversed for the second of the two years to increase consistency. There was a general improvement in the standard of results from the pre-test to the post-test. There was also a small improvement for the repeated questions compared to the non-repeated questions (P < 0.0001). The authors conclude that the marked improvement of the post-test compared to the pre-test is mostly attributable to the students increasing their knowledge base through learning during their surgical term.(ABSTRACT TRUNCATED AT 250 WORDS)

Retention of surgical knowledge base by senior medical students.

The medical course at the University of Queensland is 6 years in length. After studies in basic sciences, the fourth year consists of systematic pathology, clinico-pathological correlation and the learning of clinical methods. During the fifth year the core surgical knowledge base is taught. The sixth year is spent in clinical ward work aimed at problem-orientated consolidation of knowledge and skills, and the learning of applied therapeutics. We studied whether the surgical knowledge base taught to our fifth year students was retained a year later by the same students in their final year. A standardized post-test examination which had been presented to the students during their fifth year in 1990 was again presented to them during their sixth year in 1991. We found that the surgical knowledge base of this group of students remained the same in their final year as it had been in their penultimate year. We suggest that to continue testing core surgical knowledge once it has proven satisfactory is not productive. These students should progress to further clinical studies aimed at improving their problem solving ability.

Pre- and post-testing of students in surgery: do medical rotations help?

A prospective multiple choice question (MCQ) study developed to pre- and post-test fifth year medical students at the University of Queensland, was undertaken during 1990. We investigated whether there was a significant gain in their surgical knowledge base resulting from non-surgical rotations during the same year. We have previously reported a retrospective study suggesting that there was such a gain. Comparable clinical surgical pre- and post-tests were adapted from a fresh question bank, and were presented prospectively to four groups of fifth year medical students at the beginning and end of each 7 week General Surgical term. In contrast to our retrospective study, we found there was no significant increment in surgical knowledge using non-parametric Notched Box and Whisker Plot analysis of data. We conclude that this is either because students are compartmentalizing their factual knowledge base between one speciality and the next, or that indeed there is no benefit to Surgical knowledge base from prior non-surgical rotations. Assuming the former, a combined Medical and Surgical Objective Structured Clinical Examination (OSCE) at the end of the fourth year could serve to broaden the student's horizons and reduce factual dissociation during the fifth year.

Surgical knowledge base augmentation by medical rotations: does it happen?

A study of 4 groups of fifth year medical students taking Surgery during the 4 terms of 1989 at the University of Queensland was undertaken to determine whether there was assimilation of factual material relevant to the surgical knowledge base from the other specialty rotations done during the same year of the course. The records of multiple choice question (MCQ) examination results for the 210 students were retrieved and reviewed. The performance of the same students during their fourth-year rotation in Surgery was checked to make sure that the 4 groups did not already display unusual surgical aptitude or incompetence. The questions were categorized in order to ascertain that the content of all the examinations was similar. The results of students doing Surgery during the first of the 4 terms in 1989 were compared with subsequent groups. The difference between the groups was that those in the first term had not had the benefit of fifth year rotations through Internal Medicine, Psychiatry, General Practice and electives. Subsequent groups had increasing experience in the other specialties. The fourth and final group in the year had undertaken all four of the other rotations before doing Surgery. Significant improvement was found in the performance of each of the subsequent groups of students compared with the first-term group. This implies that there is an escalating accural of factual knowledge related to surgery from the fifth-year courses in Internal Medicine, Child Health and Psychiatry.

Efficacy of single or repeated hemoperfusion in a canine model of paraquat poisoning.

Although hemoperfusion has been used to treat paraquat poisoning, its efficacy has been widely debated. This study examines the kinetic and pathologic correlates of paraquat toxicity and hemoperfusion and the efficacy of hemoperfusion in four groups of four dogs. This species was chosen because the kinetics and toxicity of paraquat are similar to those in the human. All dogs given a lethal dose of paraquat dichloride producing 100% mortality as a 2-hr infusion (7.48 mg of paraquat ion per kg) developed the typical clinical, laboratory and pathologic features of paraquat toxicity and died within 5 to 7 days. All dogs given paraquat and hemoperfused for 8 hr daily, beginning at 12 hr, died within 3 to 6 days. Two of four dogs which were hemoperfused once, beginning at 2 hr, survived. One dog in the repeated hemoperfusion only group died from blood loss. Negligible amounts of paraquat (0.4-2.0% of the total dose) were adsorbed during repeated hemoperfusion because of extensive excretion of paraquat in urine and sequestration in peripheral tissues from which redistribution was slow. The efficacy in the single early hemoperfusion group can be attributed to removal of 25% of the dose by the procedure in the two survivors. We conclude that single hemoperfusion may have some clinical application in patients who present within a few hours of the ingestion and have not ingested a dose of paraquat that is multiples of the lethal dose producing 100% mortality. It is doubtful if there is any role for repeated hemoperfusion.

Concurrent determination of hepatic bioavailability of salicylamide by three techniques in the dog.

Three methods of measuring hepatic first-pass metabolism of salicylamide in dogs that had undergone portacaval transposition were compared. The drug in both its radiolabeled (0.74 MBq) and unlabeled (20 mg/kg) forms was infused concurrently into forelimb and hindlimb veins, respectively. Because of the transposition, drug from the hindlimb is subject to first-pass metabolism in the liver. Bioavailability is a complementary measure of the extent of this metabolism. The three methods of determining bioavailability were continuous withdrawal of blood to determine the ratio of the areas under the plasma concentration versus time curves, ratio of specific activities in plasma after all the drug had been administered, and the conventional method, measurement of the ratio of areas determined from sequential plasma concentrations. The three techniques were found to give virtually identical values for bioavailability. Each method has its own advantages, limitations, and possible applications. The continuous withdrawal technique is potentially most applicable for drugs with short half-lives. The ratio of specific activities may be the preferred method for drugs with long half-lives. The conventional method is limited by the number of samples needed, but is potentially useful under those conditions in which data following test and intravenous routes of administration are available.

Management of solitary melanoma metastasis of the brain.

A retrospective analysis of 31 patients operated upon for cerebral secondary melanoma was conducted. There was no operative mortality and no operative complications in 76% of cases. Significant and life-threatening complications occurred in five patients (17%). The major benefit from surgical excision is relief of symptoms: 64% had complete remission of symptoms while a further 20% were substantially improved. A few patients' lives were prolonged by surgery and there are a number of long-term survivors. Surgical excision should be performed when a patient has an accessible solitary cerebral secondary without evidence of melanoma elsewhere.

Femoral false aneurysms: a recommendation for the method of repair.

False aneurysm formation is a major complication of vascular surgery. The most frequent site of anastomotic false aneurysm formation is the femoral artery. Between January 1974 and June 1986, 26 patients with 42 femoral false aneurysms were treated at the Princess Alexandra Hospital. Aneurysms developed following Dacron arterial grafting (29 aneurysms), saphenous vein grafting (10 aneurysms), umbilical vein grafting (one aneurysm) and femoral embolectomy (two aneurysms). Arterial wall failure (with intact suture and graft) was the most frequent operative finding. Ten recurrent aneurysms developed. There was a significantly greater number of recurrences when resuture or patch repair was employed than when an interposition graft was used as a repair. The development of a femoral anastomotic false aneurysm should be viewed as a total failure of that anastomosis and repair should be by replacement with an interposition graft rather than repair of the failed anastomosis by suture or patch.

Creation of a carotid-jugular fistula for repeated hemoaccess in a canine model.

We have developed a method to obtain access to the arterial circulation in the dog, which can be used for repeated hemoperfusion, hemodialysis, and for pharmacokinetic studies. Hemoaccess is achieved by the surgical creation of a carotid-jugular fistula. Using the fistula, which is internal and autogenous, has overcome the problems of thrombosis, dislodgement, and infection, which are associated with external shunts. Blood flow rates of between 70 and 100 ml/min in 12-kg dogs were obtained through a hemodialysis pump. The surgical techniques are described in detail so that other investigators can avail themselves of the methodology.

Time-dependent, plasma-sulfate-independent kinetics of salicylamide in dogs.

The mechanisms of the dose-dependent elimination kinetics of salicylamide in dogs were examined. Salicylamide was infused continuously over three consecutive 90-min periods. The rates of infusion during Periods I and III were the same. During Period II the infusion rate was 2.5-fold higher. Plasma concentrations of inorganic sulfate were kept constant by the administration of exogenous sulfate. The plasma concentrations of salicylamide, which reached steady state during Period I but not during II or III, were twice as high at the end of Period III than those at the end of Period I. Typical Michaelis-Menten kinetics do not explain these results. When salicylamide was given as 40 mg/kg single oral dose, clearance of an intravenous tracer dose of radiolabeled salicylamide was greatly reduced within 10 min but returned to baseline values by 240 min after the oral dose, despite persistently low plasma concentrations of inorganic sulfate. Therefore, dose- and time-dependent factors other than Michaelis-Menten kinetics, depletion of inorganic sulfate concentrations, and rate limitation of supply of "active sulfate" from plasma inorganic sulfate stores produce the dose- and time-dependent kinetics of salicylamide in the dog. Product inhibition of salicylamide sulfoconjugation remains a possible explanation.

Non-linear hepatic first-pass metabolism of salicylamide in dogs after portacaval transposition.

The effect of the rate of input of salicylamide into the portal vein of dogs on the clearance and bioavailability of the drug was examined. The four dogs had undergone portacaval transposition so that a hindlimb infusion delivered the drug directly and only into the liver. On separate occasions, salicylamide, 20 mg/kg, was infused into a hindlimb vein at three different rates, the duration of each infusion was 3, 10, and 30 min. Simultaneously, to measure the bioavailability, 14C-salicylamide was infused at the same rate into a forelimb vein. As the duration of the infusion was increased from 3 to 30 min, the clearance of salicylamide increased significantly from 1.05 +/- 0.21 (mean +/- SD) to 1.57 +/- 0.38 L/min and the half-life decreased significantly from 14.66 +/- 3.60 to 9.09 +/- 2.42 min. Bioavailability decreased from 0.84 +/- 0.11 to 0.61 +/- 0.61, but the differences were not statistically significant. As predicted for a drug that has nonlinear clearance and bioavailability, the rate of infusion of salicylamide affects the values of these parameters.