Profiling multiple provider prescribing of opioids, benzodiazepines, stimulants, and anorectics

BACKGROUND

The main objective of this study was to determine the prevalence of multiple providers for different controlled substances using the largest electronic prescription monitoring program (PMP) in the United States. A secondary objective was to explore patient and medication variables associated with prescriptions involving multiple providers. PMPs monitor the final allocation of controlled substances from pharmacist to patient. The primary purpose of this scrutiny is to diminish the utilization of multiple providers for controlled substances.

METHODS

This is a secondary data analysis of the California PMP, the Controlled Substance Utilization Review and Evaluation System (CURES). The prevalence of multiple provider episodes was determined using data collected during 2007. A series of binomial logistic regressions was used to predict the odds ratio (OR) of multiple prescriber episodes for each generic type of controlled substance (i.e., opioid, benzodiazepine, stimulant, or diet pill (anorectic) using demographic and prescription variables.

RESULTS

Opioid prescriptions (12.8%) were most frequently involved in multiple provider episodes followed by benzodiazepines (4.2%), stimulants (1.4%), and anorectics (0.9%), respectively. The greatest associations with multiple provider episodes were simultaneously receiving prescriptions for different controlled substances.

CONCLUSIONS

Opioids were involved in multiple provider prescribing more frequently than other controlled substances. The likelihood of using multiple providers to obtain one class of medications was substantially elevated as patients received additional categories of controlled substances from the same provider or from multiple practitioners. Polypharmacy represents a signal that requires additional vigilance to detect the potential presence of doctor shopping.

Impact of delayed graft function on renal function and graft survival in deceased kidney transplantation

OBJECTIVES

To define the risk factors for delayed graft function and study the impact of such delays on renal function and long-term allograft survival in renal transplant recipients.

DESIGN

Single-centre retrospective study.

SETTING

Regional hospital, Hong Kong.

PATIENTS

Records of 118 Chinese renal transplant recipients from 1 July 1997 to 31 July 2005 were reviewed, and categorised into delayed and immediate graft function groups.

RESULTS

Delayed graft function was observed in about 19% of patients, for which cold ischaemic time was an important independent predictor. For each additional hour of cold ischaemic time, the odds ratio increased for delayed function by 0.002 (95% confidence interval, 0.001-0.003; P=0.03). Multivariate analysis revealed that neither cold ischaemic time nor delayed graft function was associated with acute rejection. On the other hand, at 1 year both delayed graft function (odds ratio=18.5; 95% confidence interval, 2.6-130.5; P=0.003) and donor age (1.2; 1.1-1.3; P=0.003) were related to a glomerular filtration rate of less than 30 mL/min. When renal function between patients with and without delayed graft function during the first 3 years was compared, it was significantly better in those without delayed graft function. However, there was no significant difference in death-censored graft survival between delayed graft function and immediate graft function groups.

CONCLUSIONS

Delayed graft function has a significant adverse effect on graft function at 1 year. Limiting cold ischaemic time is important as it is an independent predictor of delayed graft function.

A rare cause of nephrotic syndrome: lipoprotein glomerulopathy

Lipoprotein glomerulopathy is a rare kidney disease in which lipoprotein thrombi are seen in the glomerular capillaries. Most of these patients are found in Japan and East Asian countries. The presenting symptoms include proteinuria, an abnormal plasma lipoprotein profile that resembles type III hyperlipoproteinaemia, and a marked increase in serum apolipoprotein E concentration. Previous studies have suggested that lipoprotein glomerulopathy might be related to APOE gene mutation. No effective therapeutic regimen has been established for lipoprotein glomerulopathy. We report the first case of biopsy-proven lipoprotein glomerulopathy in Hong Kong in a patient who presented with nephrotic syndrome and dyslipidaemia. DNA analysis revealed apolipoprotein E Kyoto together with a novel apolipoprotein E mutation, apolipoprotein E (Asp230Tyr) Hong Kong. There was significant improvement in the clinical parameters and resolution of symptoms after the introduction of statins. Further studies will be needed to clarify the role of apolipoprotein E Hong Kong and its interaction with apolipoprotein E Kyoto in the pathogenesis of lipoprotein glomerulopathy.

Prevalence of metabolic syndrome in Chinese renal transplant recipients

OBJECTIVE

To investigate the prevalence of metabolic syndrome in Chinese renal transplant recipients, using two different sets of diagnostic criteria.

DESIGN

Cross-sectional study.

SETTING

Regional hospital, Hong Kong.

PATIENTS

All Chinese patients who received solitary living-related or cadaveric kidney transplantation from 1 July 1997 to 31 December 2005 in our hospital with follow-up of more than 6 months were recruited. The diagnosis of metabolic syndrome was made according to the National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATPIII) criteria and the International Diabetes Federation criteria.

RESULTS

Using the modified (Asian) NCEP-ATPIII criteria, a total of 39 (32%) of 121 patients had metabolic syndrome, which included 20/69 (29%) of the males and 19/52 (37%) of the females. Using the International Diabetes Federation criteria, metabolic syndrome was diagnosed in 26% of the patients, 22% in males and 31% in females. In our patients, the most common component of metabolic syndrome was hypertension and the least common was low high-density-lipoprotein-cholesterol level. Low high-density-lipoprotein-cholesterol levels were significantly more common in female patients.

CONCLUSION

This study shows that there is a high prevalence of metabolic syndrome in our Chinese renal transplant recipients.

Intrasellar germinoma treated with low-dose radiation

A radiation dose lower than what had previously been recommended was given to a case of intrasellar germinoma in a 17-year-old patient who suffered from migraine-like headache for 2 years, amenorrhoea for 3 months and a body-weight loss of 10 kg over 4 months. Baseline assessment of pituitary hormone reserve was within the lower limits of the normal range, except for an elevated serum prolactin level (PRL). Magnetic resonance imaging (MRI) showed an abnormal, slightly enhanced mass in the pituitary fossa, extending along the pituitary stalk and to the hypothalamus. Transsphenoidal removal of the intrasellar part of the tumour was performed and microscopic sections of the surgical specimens revealed a pure germinoma. Adjunctive radiation therapy (RT) was given 3 weeks after surgery. A total dose of only 27 Gy was delivered to this patient. The patient's menstrual cycles resumed in 4 months. Repeated MRI follow-up showed no recurrence of the tumour.

Diffusion tensor imaging of tract involvement in children with pontine tumors

BACKGROUND AND PURPOSE

Conventional MR imaging permits subcategorization of brain stem tumors by location and focality; however, assessment of white matter tract involvement by tumor is limited. Diffusion tensor imaging (DTI) is a promising method for visualizing white matter tract tumor involvement supratentorially. We investigated the ability of DTI to visualize and quantify white matter tract involvement in pontine tumors.

METHODS AND MATERIALS

DTI data (echo-planar, 1.5T) were retrospectively analyzed in 7 patients with pontine tumors (6 diffuse, 1 focal), 4 patient controls, and 5 normal volunteers. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were calculated from the diffusion tensor in 6 regions of interest: bilateral corticospinal tracts, transverse pontine fibers, and medial lemnisci. Relationships between FA and ADC values and results of the neurologic examinations were evaluated.

RESULTS

The corticospinal tracts and transverse pontine fibers were affected more often than the medial lemnisci. The DTI parameters (FA and ADC) were significantly altered in all tracts of patients with pontine tumors (P < .05), compared with those values in the control groups. A marginally significant (P = .057) association was seen between the severity of cranial nerve deficit and decreased FA.

CONCLUSION

DTI provided superior visualization and quantification of tumor involvement in motor, sensory, and transverse pontine tracts, compared with information provided by conventional MR imaging. Thus, DTI may be a sensitive measure of tract invasion. Further prospective studies are warranted to assess the ability of DTI to delineate tumor focality and improve risk stratification in children with pontine tumors.

Varied patterns of postoperative course of disappearance of hemifacial spasm after microvascular decompression

BACKGROUND

The precise course of resolution of postoperative residual HFS after a single MVD has not been well categorised quantitatively in the literature. Not all patients with HFS were cured immediately after a single MVD; some of them exhibited a gradual disappearance of the HFS over a period of time. The time course of the gradual resolution of HFS is categorised and the situation of re-exploration in a few patients whose HFS persisted or recurred is determined.

METHODS

The results of 547 MVDs in 545 Chinese patients were reviewed using the database from the author's personal records between January 1992 and December 2002. Different outcomes were observed and divided into four categories according to the variable convalescent period: type 1, spasm cured immediately; type 2, spasm persisted with milder severity and faded away gradually from 7 days to as long as 2 years; type 3, spasm ceased immediately but recurred after 3 days and ran the same course as in type 2; type 4, failed.

FINDINGS

Four hundred and seventy-nine patients followed a type 1 course, which constituted an 87.9% immediate success rate. Forty-one patients (7.5%) followed a type 2 course, including three whose spasm persisted for more than 2 years. Twenty-three patients (4.2%), including one with venous compression, followed a type 3 course with their spasm ceased within three months. All of them had typical vascular loop compression. Another patient with a venous contact failed to respond positively to the first MVD underwent re-operation within 2 months. Re-operation was also performed in one patient four days after the first MVD due to persisting and even more severe spasm. These two patients were categorized type 4 as they failed the first MVD (0.4%). Late recurrence was noted in five patients from 1 to 2 years after the first MVD, only one of whom underwent re-exploration and was then cured again.

CONCLUSIONS

Approximately 80% of the patients with HFS achieved immediate excellent results after a single MVD, the rest of the patients exhibited residual but usually milder spasms, which resolved gradually over a period of time. According to the patterns of the residual or persisting spasms, the situation and timing of re-exploration can be determined without difficulty. The surgeon should be concerned about missing the responsible vessels in patients with typical HFS who completely failed the first MVD.

Congener-specific polychlorinated biphenyls in cetaceans from Taiwan waters

During 2000 to 2001, a total of 73 blubber samples from 13 species of stranded or accidentally captured cetaceans were collected from Taiwan coastal waters for polychlorinated biphenyl (PCB) analysis. After homogenization, saponification, liquid-liquid extraction, and silica-gel solid-phase extraction, PCB concentrations were determined by gas chromatography/mass spectrometry. Total concentrations of 19 PCB congeners (SigmaPCBs) were between 0.23 microg/g lipid weight of Risso's dolphin to 33.73 microg/g lipid weight of rough-toothed dolphin. Pentachlorobiphenyls, hexachlorobiphenyls and heptachlorobiphenyls were the predominant PCB congeners species. PCB153 was the most abundant congener in all samples. The PCB153/SigmaPCBs consistently comprised between 20% to 30% of all congeners. The toxicity measured as 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) were from 2.7 pg/g lipid weight of finless porpoise to 2,900 pg/g lipid weight of rough-toothed dolphin. PCB 118, a mono-ortho congener, was the largest contributor to TEQs. PCB concentrations and TEQs were higher in mature male than in immature male animals but were inconsistent in female animals because of a possible transferring of PCBs from maternal cetaceans to their offsprings during gestation and lactation. Stranded cetaceans had significantly higher PCB levels than by-catch cetaceans because of their higher lipid consumption during starvation or illness. From the collected samples, we also found that cetaceans from Taiwan waters had relatively lower PCB concentrations and TEQs than those from high-latitude areas.

Corticosteroid therapy in a Chinese patient with nephropathy associated with human immunodeficiency virus infection

A 52-year-old man with 6 years' history of human immunodeficiency virus infection who was receiving highly active antiretroviral therapy presented with acute renal failure and nephrotic syndrome. Renal biopsy revealed features consistent with nephropathy associated with human immunodeficiency virus infection. Treatment consisted of intravenous methylprednisolone followed by oral prednisolone. The patient's renal function improved, although proteinuria persisted. Human immunodeficiency virus-associated nephropathy is very rare in Asian populations and is more common among blacks. To the best of our knowledge, this is the first documented case of nephropathy associated with human immunodeficiency virus infection occurring in Hong Kong.

Polytomous modeling of cognitive errors in computer adaptive testing

In the past two decades of psychometric research, an array of extended item response models has been proposed to capture the complex nature of human cognition. While the literature abounds in model fit analysis, the debate on model selection in different testing conditions continues. This study examines the problems of model selection in computer adaptive testing (CAT) of cognitive errors by comparing the relative measurement efficiency of polytomous modeling over dichotomous modeling under different scoring schemes and termination criteria. Monte Carlo simulation was adopted as the inquiry paradigm to generate 1000 subjects and 100 items in the calibration sample and 200 simulees in the CAT sample. The results suggest that polytomous CAT yields marginal gains over dichotomous CAT when termination criteria are more stringent (shorter test length or smaller standard error of ability estimate). When the conventional dichotomous scoring scheme is adopted, in which all partially correct answers are scored as incorrect, polytomous CAT cannot prevent the non-uniform gain in test information as was observed in paper-and-pencil testing.

Prevention of recurrent central venous stenosis using endovascular irradiation following stent placement in hemodialysis patients

This study was done to evaluate the outcome after brachytherapy (BT) given to prevent restenosis after stent insertion for central venous stenosis in patients with ipsilateral hemodialysis arteriovenous fistulas (AVF). Angioplasty and stenting were performed on 9 primary central venous stenoses in 8 patients with AVF followed by BT, delivering Iridium-192 radiation using an afterloading technique. BT was also administered to three patients with five recurrent stenoses at the stent margins. There was no residual stenosis after angioplasty and stenting. Venographic follow-up (77-644 days, mean 272 days) showed no restenosis in seven primary stenoses. New strictures (45%-100%) developed at the stent margin in six veins (five patients). Angioplasty or stenting was performed for five margin stenoses in three patients, followed by a second BT. Residual stenosis before BT was 0-30%. In our venographic follow-up (140-329 days, mean 215 days), three restenoses occurred (35%-100%). All progressed to complete occlusion on later venographic follow-up irrespective of whether BT was given to the stent margin or not. The mean primary and assisted primary patency of the central veins were 359 days and 639 days, respectively. Endovascular irradiation with a noncentering source does not prolong the patency after angioplasty and stenting of central venous stenosis in hemodialysis patients.

Storage effects on bacterial concentration: determination of impinger and filter samples

Effects of storage on the colony recovery of airborne bacterial samples were evaluated in a laboratory test chamber. Escherichia coli cells and Bacillus subtilis spores were generated by a Collison three-jet nebulizer. Bioaerosol samples were collected by three sampling methods, AGI-30 impingers, Nuclepore filtration and elution methods, and gelatin filters. Effects of storage time was determined by the ratio, Ct/C0, where Ct and C0 were the CFU concentrations of the simultaneously collected samples stored for t and 0 h, respectively. The effect of storage temperature was also studied for AGI-30 samples stored at 25 and 4 degrees C. For impinger samples, it was demonstrated that the bioefficiency of bacterial bioaerosols could survive in the impinger fluid, and even bud more cells at room temperature. In addition, the inhibition effect of refrigerated samples was observed. Therefore, we suggest that samples collected by an impingement method should be refrigerated and processed as soon as possible to avoid the increase of bacterial culturability. Moreover, the effect of storage time on filtration collection for B. subtilis spores was demonstrated to be insignificant. However, E. coli recovery from filters was demonstrated to decrease as storage time increased. It was concluded that the recovery would not decrease during storage if bioefficiencies of the sampling methods were excellent, for example, using filters to collect B. subtilis spores or impingers to collect E. coli cells.

Relationship between adequacy of dialysis and nutritional status, and their impact on patient survival on CAPD in Hong Kong

OBJECTIVE

Superior patient survival on continuous ambulatory peritoneal dialysis (CAPD) with 3 x 2-L exchanges has been reported from Hong Kong. This study examined the relationship between indices of dialysis adequacy and nutrition and patient survival on CAPD in Hong Kong.

DESIGN

A cross-sectional study on prevalent CAPD patients. Patients were assessed for indices of dialysis adequacy and nutritional status with a composite nutritional index (CNI). Patients were then followed for 24 months. Survival data were analyzed according to adequacy indices and nutritional status.

SETTING

All prevalent CAPD patients in nine dialysis centers in Hong Kong as of 1 April 1996.

MAIN OUTCOME MEASURE

Mortality.

RESULTS

937 patients were assessed: 68.2% were using 3 x 2-L exchanges per day; mean age was 54.6 +/- 13 years. Mean total Kt/V was 1.83 +/- 0.42 and total creatinine clearance was 55.6 +/- 19.5 L/week/1.73 m2. 19% of patients were moderately to severely malnourished according to the CNI. There was no significant correlation between indices of adequacy and serum albumin or CNI. The 1- and 2-year patient survival from the time of assessment was 90.9% and 79.8%. There was a trend toward better survival in patients with Kt/V greater than 2.0, but it was not statistically significant. Peritoneal Kt/V did not impact survival in anuric patients. Malnourished patients had poorer survival than patients who were better nourished (p = 0.0259). After adjusting for age and diabetes, CNI was predictive of mortality but Kt/V and creatinine clearance were not.

CONCLUSIONS

This study demonstrates the importance of nutritional status over adequacy indices in predicting patient survival. There was a lack of correlation between nutritional status and conventional indices of dialysis adequacy.

Hypokalemic metabolic acidosis attributed to cough mixture abuse

This report describes a patient with mixed normal anion gap hyperchloremic metabolic and respiratory acidosis associated with hypokalemia attributed to cough mixture abuse. Metabolic acidosis was likely related to an overdose of ammonium chloride, whereas respiratory acidosis was probably related to the effect of hypokalemia on respiratory muscles, causing hypoventilation. Hypokalemia was caused by a transcellular shift of potassium induced by ephedrine and pseudoephedrine. Both ammonium chloride and ephedrine were probably present in the cough mixture obtained by our patient as an over-the-counter medication. Physicians should be aware of the potential for cough mixture abuse to cause major electrolyte disturbances that may carry the risk for major cardiac arrhythmias, particularly in youth.

Cefepime versus vancomycin plus netilmicin therapy for continuous ambulatory peritoneal dialysis-associated peritonitis

Cefepime is a cephalosporin with a broad spectrum of activity against most gram-positive and gram-negative pathogens. In this study, we attempted to compare the safety and efficacy of cefepime monotherapy against the potentially more toxic combination of vancomycin and netilmicin in the treatment of continuous ambulatory peritoneal dialysis (CAPD)-associated bacterial peritonitis. Eighty-one consecutive CAPD patients who presented with peritonitis from January 1, 1998, to June 30, 2000, were recruited for study. Patients were randomized to be administered either intraperitoneal (IP) cefepime, 1 g once daily (group A), or intravenous vancomycin and netilmicin at conventional doses (group B) for 10 days. Bacterial growth was obtained in 52 episodes (66%), and pathogens identified included gram-positive organisms (30 episodes; 38%), gram-negative organisms (14 episodes; 18%), mixed organisms (2 episodes; 2.5%), and fungus (6 episodes; 8%). Eight patients were excluded after randomization for various reasons (6 patients, fungal peritonitis; 2 patients, wrong diagnoses). Because of the relatively low peritonitis rate after the use of a disconnect system, the sample size of this study was relatively small, giving a power of 0.45. There were no significant differences in primary response rates and cure rates (no relapse >28 days after completion of antibiotic therapy) between both groups of patients (group A versus group B, 82% [32 of 39 patients] versus 85% [29 of 34 patients] and 72% [28 of 39 patients] versus 76% [26 of 34 patients], respectively; P = not significant). No significant side effect was encountered in either group. Total peritonitis-related hospitalizations were 84 patient-days (1, 7, 8, 11, 20, and 37 patient-days) and 115 patient-days (3, 6, 9, 14, 21, 21, and 41 patient-days), whereas total costs per patient cure were estimated to be US $1,039 and US $1,371 in groups A and B, respectively. We conclude that once-daily 1-g IP cefepime monotherapy is a simple, safe, and cost-effective alternative to vancomycin and netilmicin therapy in the treatment of CAPD-associated bacterial peritonitis.

Assessing the potential for the stomatal characters of extant and fossil Ginkgo leaves to signal atmospheric CO2 change

The stomatal density and index of fossil Ginkgo leaves (Early Jurassic to Early Cretaceous) have been investigated to test whether these plant fossils provide evidence for CO(2)-rich atmosphere in the Mesozoic. We first assessed five sources of natural variation in the stomatal density and index of extant Gingko biloba leaves: (1) timing of leaf maturation, (2) young vs. fully developed leaves, (3) short shoots vs. long shoots, (4) position in the canopy, and (5) male vs. female trees. Our analysis indicated that some significant differences in leaf stomatal density and index were evident arising from these considerations. However, this variability was considerably less than the difference in leaf stomatal density and index between modern and fossil samples, with the stomatal index of four species of Mesozoic Ginkgo (G. coriacea, G. huttoni, G. yimaensis, and G. obrutschewii) 60-40% lower than the modern values recorded in this study for extant G. biloba. Calculated as stomatal ratios (the stomatal index of the fossil leaves relative to the modern value), the values generally tracked the CO(2) variations predicted by a long-term carbon cycle model confirming the utility of this plant group to provide a reasonable measure of ancient atmospheric CO(2) change.

Neuronal correlates of motor performance and motor learning in the primary motor cortex of monkeys adapting to an external force field

The primary motor cortex (M1) is known to control motor performance. Recent findings have also implicated M1 in motor learning, as neurons in this area show learning-related plasticity. In the present study, we analyzed the neuronal activity recorded in M1 in a force field adaptation task. Our goal was to investigate the neuronal reorganization across behavioral epochs (before, during, and after adaptation). Here we report two main findings. First, memory cells were present in two classes. With respect to the changes of preferred direction (Pd), these two classes complemented each other after readaptation. Second, for the entire neuronal population, the shift of Pd matched the shift observed for muscles. These results provide a framework whereby the activity of distinct neuronal subpopulations combines to subserve both functions of motor performance and motor learning.

Urea reduction ratio that considers effects of ultrafiltration and intradialytic urea generation

We modified the urea reduction ratio (URR) equation to correct the effects of ultrafiltration and intradialytic urea generation on the delivered dose of hemodialysis: mURR = [1 - (R/1 + 2*UF/BW) + 0.01*t] x 100% where mURR is modified URR, R is postdialysis plasma urea nitrogen (PUN) to predialysis PUN ratio, UF is ultrafiltrate volume in liters, BW is postdialysis body weight in kilograms, and t is dialysis session length in hours. The equation was validated against 145 hemodialysis treatments on 33 stable maintenance dialysis patients. The mURR values obtained closely predicted single-pool Kt/V (spKt/V) values. In contrast to conventional URR, the range of spKt/V values at each mURR value is narrow over a wide range of UF, t, and R values. Based on the mURR equation, mURR values of 64%, 70%, and 76% are mathematically equivalent to spKt/V levels of 1.0, 1.2, and 1.4, respectively. This equation can be a useful bedside tool to quantify hemodialysis dose.

Inactivation of macaque lateral intraparietal area delays initiation of the second saccade predominantly from contralesional eye positions in a double-saccade task

Previous studies have shown that, although lateral intraparietal (LIP) area neurons have retinotopic receptive fields, the response strength of these cells is modulated by eye position. This combining of retinal and eye position information can form a distributed coding of target locations in a head-centered coordinate frame. Such an implicit head-centered coding offers one mechanism for maintaining spatial stability across eye movements and can be used to compute new oculomotor error vectors after each eye movement. An alternative mechanism is to use eye displacement signals rather than eye position signals to maintain spatial stability. The aim of this study was to distinguish which of these two extra-retinal signals (or perhaps both signals) are employed in a double saccade task, which required the monkey to use extraretinal information associated with the first saccade to localize a remembered target for a second saccade. By varying the direction and the end point of the first saccade and selectively inactivating area LIP in one hemisphere with muscimol injection, we were able to distinguish between the two mechanisms by observing how the second saccade was impaired in this task. The displacement mechanism predicts that, if the first saccade is in the contralesional direction, the second saccade will be impaired, and the end point of the first saccade would not be important. The eye position mechanism predicts that if the first saccade ended in the contralesional head-centered space, the second saccade will be impaired, no matter in which direction the first saccade is made. Results showed that, after area LIP lesion, when the first saccade stepped into the contralesional field, the error rate of the second saccade became higher and the latency longer. However, when the end point of the first saccade was constant, the direction of the first saccade had much less effect on the second saccade. These results suggest that eye position, and not eye displacement, is the more predominant factor in this task. In a different behavioral paradigm, the monkeys performed single visual and memory saccades from different initial eye positions. It was found that the impairment of either the metrics or dynamics of visual and memory saccades did not significantly vary with the different eye positions. It thus appears that the performance of single visual and memory saccades is best described in an oculocentric coordinate frame that does not rely on extraretinal signals. Altogether these results lend further support to the hypothesis that, by combining retinal and eye position signals, area LIP contains concurrent eye-centered and head-centered representations of the visual space. Depending on the task, either representation can be used.

Stability of urea and creatinine in spent hemodialysate

Urea and creatinine levels in spent hemodialysates showed only small declines in spite of incubation at 37 degrees C for 36 hours. In the determination of dialysate-side solute removal, it would seem prudent to keep spent dialysate cold during collection to retard bacterial breakdown of these waste products.