Search

Acute renal failure (ARF) is an abrupt decline in or cessation of renal function. It is characterized by the inability to excrete waste products and maintain volume, acid—base, and electrolyte homeostasis. From a biochemical perspective untreated ARF is associated classically with azotemia, metabolic acidosis, hyperkalemia, hyperphosphatemia, and hypocalcemia. In conjunction with a constellation of symptoms and signs, including anorexia, nausea, vomiting, and various neuropsychiatric findings, these biochemical findings comprise the clinical syndrome of uremia.

Dialysis forms the cornerstone of therapy for most patients with end-stage renal disease (ESRD) and many patients with acute renal failure (ARF). Consequently, it is imperative that clinicians managing these patients understand the fundamental principles of dialytic therapies, especially those having a biologic basis. In this chapter, many of these principles are reviewed. The topic of uremic toxicity is first addressed, with emphasis on the classification of uremic toxins based on molecular weight. After a frame of reference is established with a discussion of toxin elimination mechanisms for the native kidney, the dialytic solute removal mechanisms (diffusion, convection, and adsorption) broadly applicable to all renal replacement therapies are reviewed. The relative importance of these mechanisms in the different therapies used in both the ESRD and ARF settings will then be discussed. As the major determinant of overall efficiency of hemodialysis (HD), the most commonly applied renal replacement therapy, diffusive solute removal will be rigorously assessed by applying a “resistance-in-series” model to a dialyser. In much the same way, fluid and mass transfer in peritoneal dialysis will be assessed by examining the elements of the system: peritoneal microcirculation, peritoneal membrane, and the dialysate compartment. Finally, from a kinetic perspective, the differences between intermittent, continuous, and semicontinuous therapies will be discussed, with emphasis on quantification of solute removal.

For the past several years, the topic of hemodialysis (HD) adequacy has been one of the most widely discussed and investigated subjects in all of ESRD therapy. However, considerable disagreement on several fundamental issues in HD adequacy, including the defining criteria, persist. Although this topic has been reviewed extensively in the literature [1-5], this vitally important aspect of the care of the chronic HD patient has not been critically assessed from a quality assurance perspective. The purpose of this chapter is first to provide a clinical overview, including a brief review of landmark studies that provide the basis for current HD adequacy recommendations. The remainder of the chapter deals with implementation of these current recommendations and the quality assurance issues the chronic dialysis unit must consider.

The term “furbearer” is loosely applied to mammals that are, or have been, harvested primarily for their pelts. Furbearers typically include species ranging from 1–20 kg mass in the orders Marsupialia, Rodentia, and Carnivora. Studies of demography and regulation of populations have important implications to furbearer management and conservation, as well as to population ecology generally. Reproductive potential varies considerably among species, although most species attain sexual maturity within 1 year and have high fertility rates. There is solid evidence for inverse density-dependence in fertility and/or recruitment in muskrats. In longer-lived omnivores and carnivores, variation in reproduction is most often related to changes in pregnancy rates, and/or survival of young. Generalization about density-dependent reproduction among these groups is not warranted from the evidence. For many North American furbearers, the largest fraction of mortality is human-related, primarily from legal harvest, but also vehicle collisions and accidents in some areas. Shorter-lived species respond to increased harvest mortality in a compensatory fashion. However there is evidence that increased harvest may be more additive than compensatory among longer-lived carnivores. Disease may periodically affect annual losses, but evidence that harvest reduces disease outbreaks is equivocal. Dispersal is a prominent behavior among most species and, along with other social behaviors, may influence population regulation. Density-dependent effects in reproduction, mortality, and dispersal often limit effectiveness of controlling population levels of many furbearers. Where lightly-harvested populations are dependent on a single prey species, food supply may regulate carnivore populations — a situation especially apparent in northern landscapes. Simulation has been used effectively to study disease, exploitation, and other aspects of population dynamics. We need a quantitative, theoretical framework to more completely understand how competing sources of mortality interact, particularly the effects of time-lagged responses. Managers need efficient methods to assess population density and rates of change. Population genetics of species of special concern are poorly known and potentially significant to conservation efforts. Although we recognize that habitat heterogeneity and fragmentation influence population dynamics, we are only beginning to quantify the consequences at the metapopulation level. There is need for manipulative, replicated, long-term field experiments to study all aspects of population dynamics.

The Pacific greater white-fronted goose (Anser albifrons) population has declined precipitously over the past 20 years. Loss of wetland habitat in California wintering areas has had a significant effect on the population, so recovery of the population may depend on innovative management of the few remaining wetlands. A computer simulation model, REFMOD, was applied to greater white-fronted geese in the Klamath Basin, northern California, to investigate the importance of food availability and hunting disturbance to migrating and wintering populations. Time spent flying and feeding was simulated during fall and early winter, and the resulting energy expenditure was compared with energy consumed to calculate an overall energy balance. This energy balance and the ease with which waterfowl acquired needed food affected emigration rate, and thus, the waterfowl population level was directly tied to availability and distribution of food. The model validly described distances moved by geese from their Tule Lake Refuge roosting site (core) to feeding sites within the surrounding Klamath Basin arena, and exhibited a capability to simulate observed time spent feeding. Based on 25 stochastic simulations, greater white-fronted goose population dynamics were validly simulated over the fall and early-winter (P≥0.8). When food was removed from the Tule Lake Refuge, simulated geese had to fly farther ( 0.05). The elimination did cause an increase in the distance traveled to feed (P 0.05) on the distance traveled to feed or on goose numbers. A 10-fold increase in disturbance hastened emigration and reduced population levels (P