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N Johnston

Publications and source records attributed to N Johnston.

44 records · Page 3Linked to original sources
PubMedDate not supplied

The hazards of using active clinic patients as a source of subjects for clinical studies.

The authors describe and empirically demonstrate a form of bias that results from deriving subjects for clinical studies from available patients currently being followed in specific disease clinics instead of inception cohorts (patients enrolled at a uniform and early point in their disease). They label this effect "clinic patient bias." It is a variation of prevalence-incidence (Neyman) bias in that it also results from the time gap between the onset of a specific characteristic (a risk factor, exposure or disease) and enrollment in the study, causing selective exclusion of fatal or short episodes, or mild or silent cases. Clinic patient bias may distort an estimate of relative risk in either direction. The empirical example is derived from a study of risk factors for developing complications such as peritonitis among end-stage renal disease patients treated with continuous ambulatory peritoneal dialysis (CAPD). The use of available clinic patients rather than an inception cohort (patients newly beginning CAPD) resulted in the demonstration of false apparent risk relationships for two variables: the calendar date when patients began CAPD (with those enrolled at an earlier time appearing to be at lower risk), and serum albumin level at the start of CAPD (with those having lower albumin levels appearing to be at higher risk). This example demonstrates one of the potential hazards of using active or available clinic patients as a source of subjects for clinical studies.

Cross-Sectional Studies↗
PubMedDate not supplied

What is subjective global assessment of nutritional status?

Presented and described in detail is a clinical technique called subjective global assessment (SGA), which assesses nutritional status based on features of the history and physical examination. Illustrative cases are presented. To clarify further the nature of the SGA, the method was applied before gastrointestinal surgery to 202 hospitalized patients. The primary aim of the study was to determine the extent to which our clinician's SGA ratings were influenced by the individual clinical variables on which the clinicians were taught to base their assessments. Virtually all of these variables were significantly related to SGA class. Multivariate analysis showed that ratings were most affected by loss of subcutaneous tissue, muscle wasting, and weight loss. A high degree of interobserver agreement was found (kappa = 0.78, 95% confidence interval 0.624 to 0.944, p less than 0.001). We conclude that SGA can easily be taught to a variety of clinicians (residents, nurses), and that this technique is reproducible.

Humans↗
PubMedDate not supplied

Predicting nutrition-associated complications for patients undergoing gastrointestinal surgery.

We studied 202 patients admitted to two major teaching hospitals for planned gastrointestinal surgery to assess the ability of several techniques of nutritional assessment to predict major postoperative complications (infection and/or wound problems). Subjective global assessment (SGA) and albumin were both of predictive value, and combinations of these variables were useful in differentiating low-risk from high-risk patients. Transferrin, creatinine-height index, percent ideal weight, percent body fat, and total lymphocyte count were not useful in predicting complications. We conclude that SGA and albumin are useful "nutritional assessment techniques" for patients undergoing major gastrointestinal surgery if the purpose of such an assessment is to predict postoperative "nutrition-associated complications." The second major finding of this study was the unexpectedly low rate of complications (10%) which was found in both hospitals. We suggest that these low complication rates may be more generalizable to patient populations derived from a wide community base, rather than those described in other studies in which veterans or patients of lower socioeconomic status comprised the sample.

Female↗
PubMedDate not supplied

An alternative hypothesis from veterinary science for the pathogenesis of noncarious cervical lesions.

An alternative hypothesis to abrasion and erosion for the pathogenesis of noncarious cervical lesions was put forward in 1984; the so-called occlusal theory suggested that tensile stresses from occlusal overload could be involved in the pathogenesis of noncarious cervical lesions and that bending stresses applied to teeth could cause disruption of the surface enamel, resulting in increased susceptibility to dissolution and abrasion at the affected sites and in the development of wedge-shaped lesions. This theory has gained increased acceptance in recent years, although absolute scientific evidence has been scant. These lesions also occur in animals, in particular, the domestic cat, in which they are called feline odontoclastic resorptive lesions. A variety of theories about pathogenesis of these lesions have been put forward, but there is some evidence that occlusal overload may be a contributory factor in the development of an inflammatory response in the periodontal membrane and the presence of enzymes associated with resorption in the gingival crevice. Further investigation may help define a common etiology between the pathogenesis of feline odontoclastic resorptive lesions and noncarious cervical lesions.

Acid Phosphatase↗
PubMedDate not supplied

Nutritional assessment of continuous ambulatory peritoneal dialysis patients.

This study revealed the following. Malnutrition was frequent (41.6%) in patients on CAPD for less than three months and was present in 18.1% of patients on CAPD for longer than 3 months. Fifty percent of these malnourished patients returned to normal on conventional nutritional management within 2 to 6 months, but 10% remained malnourished throughout the study period. There was increased mortality among malnourished patients, but we were unable to demonstrate that the state of nutrition was an independent risk factor, because of the increased prevalence of other co-morbid risk factors known to influence survival and because of the limitation of a small sample size. The influence, if any, of nutritional state as an independent risk factor on the survival of CAPD patients should be answered, because malnutrition is potentially reversible with aggressive nutritional interventions, such as enteral, parenteral, or intraperitoneal supplementation.

Humans↗