A revision of body surface area estimations

Exposed Body Surface Area-A Determinate for UV Radiant Energy in Human UV Exposure Studies

Solar ultraviolet (UV) exposure of people and related health risk is mainly examined by estimating the received UV radiant exposure. However, for several effects such as DNA damage, vitamin D photosynthesis or the probability of developing skin cancer, UV radiant energy is important and with that the size of exposed skin area. There is also a complex interaction between body shape and behavior like sun exposure habits, so that careful analysis is necessary when estimating health effects from UV exposure. In this paper, knowledge on body shape and methods of calculating the total body surface area (BSA) are summarized. BSA depends mainly on the height and weight of a person as well as on gender, ethnicity and body shape. BSA and body shape differ significantly between different populations and both change during life. This paper proposes formulas for BSA that consider height, weight, gender, ethnicity and body shape. As the exposed BSA depends on clothing, finally an approach is presented which aims to calculate the size of body parts released by real garments. In summary, this paper will enable future researchers to quantify the exposed BSA by best matching their study population and consequently investigate risks caused by solar UV exposure.

Population pharmacokinetic evaluation of cefuroxime in perioperative antibiotic prophylaxis during and after cardiopulmonary bypass

AIMS

The purpose of this study was to explore pharmacokinetic and pharmacodynamic aspects of a contemporary dosing scheme of cefuroxime as perioperative prophylaxis in cardiac surgery using cardiopulmonary bypass (CPB).

METHODS

Cefuroxime plasma concentrations were measured in 23 patients. A 1.5-g dose of cefuroxime was administered at start of surgery and CPB, followed by 3 additional doses every 6 hours postoperative. Drug levels were used to build a population pharmacokinetic model. Target attainment for Staphylococcus aureus (2-8 mg/L) and Escherichia coli (8-32 mg/L) were evaluated and dosing strategies for optimization were investigated.

RESULTS

A dosing scheme of 1.5 g cefuroxime preoperatively with a repetition at start of CPB achieves plasma unbound concentrations of 8 mg/L in almost all patients during surgery. The second administration is critical to provide this level of coverage. Simulations indicate that higher unbound concentrations up to 32 mg/L are reached by a continuous infusion rate of 1 g/h after a bolus of 1 g. In the postoperative phase, most patients do not reach unbound concentrations above 2 mg/L. To improve target attainment up to 8 mg/L, the continuous application of cefuroxime with infusion rates of 0.125-0.25 g/h is simulated and shown to be an alternative to bolus dosing.

CONCLUSION

Dosing recommendations for cefuroxime as perioperative antibiotic prophylaxis in cardiac surgery are sufficient to reach plasma unbound concentration to cover S. aureus during the operation. Target attainment is not achieved in the postoperative period. Continuous infusion of cefuroxime may optimize target attainment.

High-Resolution Three-Dimensional Photonic Scan-Derived Equations Improve Body Surface Area Prediction in Diverse Populations

OBJECTIVE

Equations for predicting body surface area (BSA) produce flawed estimates, especially for individuals with obesity. This study aimed to compare BSA measured by a three-dimensional photonic scanner (3DPS) with BSA predicted by six commonly cited prediction equations and to develop new prediction equations if warranted.

METHODS

The 3DPS was validated against manual measurements by breadth caliper for body thicknesses measured at three anatomical sites on a mannequin. BSA was derived from 3DPS whole-body scans of 67 males and 201 females, aged 18 to 83 years, with BMI between 17.8 and 77.8 kg/m² and varied races/ethnicities.

RESULTS

Width and depth measurements by 3DPS and caliper were within 1%, except for hip, with an error of 1.8%. BSA_3DPS differed from BSA predicted by each equation (P < 0.05), except for males by DuBois and DuBois (P = 0.60), Tikuisis (P = 0.27), and Yu (P = 0.45) and for females by Tikuisis (P = 0.70). The combined and sex-specific equations obtained by regressing ln(BSA) on ln(weight in kilograms [W]) and ln(height in meters [H]) are as follows (R² and SEE correspond to ln[BSA]): combined, BSA_3DPS  = 0.03216 × W^0.4904  × H^0.3769 , R²  = 0.982, SEE = 0.021; males, BSA_3DPS  = 0.01624 × W^0.4725  × H^0.5231 ; and females, BSA_3DPS  = 0.01522 × W^0.4921  × H^0.5231 , R² = 0.986, SEE = 0.019.

CONCLUSIONS

New height and weight BSA equations improve BSA estimation in individuals with BMI ≥ 40 and in African Americans, Hispanic Americans, and Asian Americans.

Physiologically based pharmacokinetic evaluation of cefuroxime in perioperative antibiotic prophylaxis

Aims

Adequate plasma concentrations of antibiotics during surgery are essential for the prevention of surgical site infections. We examined the pharmacokinetics of 1.5 g cefuroxime administered during induction of anaesthesia with follow‐up doses every 2.5 hours until the end of surgery. We built a physiologically based pharmacokinetic model with the aim to ensure adequate antibiotic plasma concentrations in a heterogeneous population.

Methods

A physiologically based pharmacokinetic model (PK‐Sim^®/MoBi^®) was developed to investigate unbound plasma concentrations of cefuroxime. Blood samples from 25 thoracic surgical patients were analysed with high‐performance liquid chromatography. To evaluate optimized dosing regimens, physiologically based pharmacokinetic model simulations were conducted.

Results

Dosing simulations revealed that a standard dosing regimen of 1.5 g every 2.5 hours reached the pharmacokinetic/pharmacodynamic target for Staphylococcus aureus. However, for Escherichia coli, >50% of the study participants did not reach predefined targets. Effectiveness of cefuroxime against E. coli can be improved by administering a 1.5 g bolus immediately followed by a continuous infusion of 3 g cefuroxime over 3 hours.

Conclusion

The use of cefuroxime for perioperative antibiotic prophylaxis to prevent staphylococcal surgical site infections appears to be effective with standard dosing of 1.5 g preoperatively and follow‐up doses every 2.5 hours. In contrast, if E. coli is relevant in surgeries, this dosing regimen appears insufficient. With our derived dose recommendations, we provide a solution for this issue.

Standardization of body surface area calculations

Purpose. Antineoplastic agents have a narrow therapeutic index and therefore require the greatest degree of dose individualization. In choosing a body surface area (BSA) for‘mula, the challenge remains in obtaining consensus among prescribers. The objective of this review is to assess the various formulae available for calculating BSA and to adopt a standard formula within an institution.

Methods. Retrospective review of medication orders containing the patient’s height and weight as well as BSA calculated by the outpatient clinic staff within the Cross Cancer Institute (CCI) from 7 to 15 July 1998. Four BSA calculating devices, in current use by the clinical staff, were also tested to determine the formula currently utilized by prescribers.

Results. Thirty-three orders sent to the pharmacy containing the patient’s height, weight, and BSA were reviewed. Ninety-four per cent of the BSA calculated by the clinic staff differed from pharmacy’s calculations by 0% to 4%. One BSA calculation differed by 8% and another differed by 14%. With respect to the available BSA calculating devices, all appeared to be based on the Du Bois formula.

Conclusion. Of the various formulae available for estimating BSA, we concluded that the Mosteller equation is the most acceptable based on both BSA calculation accuracy and ease of use. Based on this determination, the CCI approved the adoption of the Mosteller equation as the institutional standard. This equation was later standardized throughout the entire Alberta Cancer Board. Other methods of dose determination are emerging, including therapeutic drug monitoring and PMT dosing. Further investigation is required as to whether these methods will lead to better standardization of dose.

Technical note: Criterion validity of whole body surface area equations: a comparison using 3D laser scanning

Measurements of whole body surface area (WBSA) have important applications in numerous fields including biological anthropology, clinical medicine, biomechanics, and sports science. Currently, WBSA is most often estimated using predictive equations due to the complex and time consuming methods required for direct measurement. The main aim of this study was to identify whether there were significant and meaningful differences between WBSA measurements taken using a whole body three-dimensional (3D) scanner (criterion measure) and the estimates derived from each WBSA equation identified from a systematic review. The study also aimed to determine whether differences varied according to body mass index (BMI), sex, or athletic status. Fifteen WBSA equations were compared with direct measurements taken on 1,714 young adult subjects, aged 18-30 years, using the Vitus Smart 3D whole body scanner, including 1,452 subjects (753 males, 699 females) from the general Australian population and 262 rowers (148 males, 114 females). Mixed-design analysis of variances determined significant differences and accuracy was quantified using Bland-Altman analysis and effect sizes. Thirteen of the 15 equations overestimated WBSA. With a few exceptions, equations were accurate with a low-systematic error (bias ≤2%) and low-random error (standard deviation of the differences 1.5-3.0%). However, BMI did have a substantial impact with the accuracy of some WBSA equations varying between the four BMI categories. The Shuter and Aslani: Eur J Appl Physiol 82 (2000) 250-254 equation was identified as the most accurate equation and should be used for Western populations 18-30 years of age. Care must be taken when deciding which equation to use when estimating WBSA.

Predictors of outcome of myocarditis

Heart failure from myocarditis may be transient or may progress to unremitting severe cardiac failure. This study was performed to determine the outcomes and prognostic features of pediatric patients with myocarditis. Patients with the diagnosis of myocarditis between 1990 and 2001 were identified through the coding system of Yale-New Haven Hospital. A total of 28 patients were included, with ages ranging from 1 day to 20 years. Before discharge, 11 patients developed unremitting severe cardiac failure. Of the remaining 17 patients, at the time of discharge 10 had normal systolic function and 7 had decreased systolic function. Unremitting cardiac failure developed in 9 of 14 patients (64%) with an ejection fraction < 30% and in only 2 of 14 (14%) of those with an ejection fraction > or = 30% on admission (p < 0.01). Furthermore, shortening fraction < 15%, left ventricular dilatation, and moderate to severe mitral regurgitation on admission as well as arrhythmia were significantly associated with development of unremitting severe cardiac failure. In this series of patients with myocarditis, by the time of discharge 39% of the patients had developed unremitting severe cardiac failure, 25% had depressed systolic function, and 36% had normal systolic function. Predictive factors at admission for poor outcome were ejection fraction < 30%, shortening fraction < 15%, left ventricular dilatation, and moderate to severe mitral regurgitation.

The importance of metabolic rate and the folly of body surface area calculations

Mathematical formulae to calculate body surface area from measurements of height, weight and other parameters date from the late 19th century. Drug doses, fluid therapy, caloric requirements and physiological parameters such as cardiac output, glomerular filtration rate and a variety of respiratory function parameters are all frequently expressed in terms of a body surface area. Body surface area is often used in preference to body mass (weight). However, the original rationale for using body surface area as an estimate for metabolic rate has never been tested and the algorithms used to approximate body surface area have little evidence to support their use in this role. Recent developments in technology using indirect calorimetry allow easy measurement of metabolic rate in the clinical setting. Such measurements should be used for standardisation when weight alone is considered inadequate.

Comparison of thermoregulatory responses between men and women immersed in cold water

Eleven women (age = 24.4 +/- 6.3 yr, mass = 65.0 +/- 7.8 kg, height = 167 +/- 8 cm, body fatness = 22.4 +/- 5.9%, mean +/- SD) were immersed to neck level in 18 degrees C water for up to 90 min for comparison of their thermal responses with those of men (n = 14) in a previous similarly conducted protocol. Metabolic rate increased about three times resting levels in men and women, whereas the rate of rectal temperature cooling (DeltaT(re)/Deltat) in women (0.47 degrees C/h) was about one-half that in men. With use of all data, DeltaT(re)/Deltat correlates with the ratio of body surface area to size and the metabolic rate of shivering correlates inversely to the square root of body fatness. No significant gender differences in total metabolic heat production normalized for body mass or surface area were found among subjects who completed 90 min of immersion (9 women and 7 men). Nor was there a gender difference in the overall percent contribution ( approximately 60%) of fat oxidation to total heat production. Blood concentrations of free fatty acids, glycerol, beta-hydroxybutyrate, and lactate increased significantly during the 90-min immersion, whereas muscle glycogen sampled from the right quadriceps femoris vastus lateralis decreased (free fatty acids, glycerol, and beta-hydroxybutyrate were higher in women). When the subjects were subgrouped according to similar body fatness and 60 min of immersion (6 women and 5 men), no significant gender differences emerged in DeltaT(re)/Deltat, energy metabolism, and percent fat oxidation. These findings suggest that no gender adjustments are necessary for prediction models of cold response if body fatness and the ratio of body surface area to size are taken into account and that a potential gender advantage with regard to carbohydrate sparing during cold water immersion is not supported.

Areas of fat loss in overweight young females following an 8-week period of energy intake reduction

In order to investigate the main areas of fat loss after an 8-week period of energy intake reduction, the distribution of body fat was assessed on 14 females (BMI 27.3+/-0.83 kgm(-2)) (mean +/- SEM), aged 18-22 years. Total body fat was determined by hydrostatic weighing and subcutaneous fat mass and distribution were assessed using ultrasound and waist-hip circumference ratios prior to, and following, an 8-week period during which subjects attempted to reduce their energy intake by about 4.2 MJ day(-1). Subjects lost an average of 2.99+/-0.34 kg (p < 0.001), with greater loss (p < 0.001) of internal fat (1.5+/-0.2 kg) than of subcutaneous fat (0.7+/-0.1). Subjects reduced their waist-hip ratio from 0.771+/-0.01 to 0.762+/-0.01 (p < 0.01), their waist circumference from 807+/-24 to 790+/-23 mm (p < 0.001) and their hip circumference from 1047+/-29 to 1037+/-29 mm (p < 0.001). Those with an android distribution of fat (n = 5) lost more weight than those with gynoid distribution (n = 9) (3.80+/-0.38 kg vs 2.54+/-0.14 kg, p < 0.05); they also showed a greater decrease in waist circumference (27+/-5 vs 14+/-4 mm, p < 0.05) and a greater loss from internal fat stores (2.1+/-0.3 kg vs 1.1+/-0.2 kg, p < 0.05). The findings suggest that individuals are prone to lose internal fat during a short period of reduced energy intake. As the visceral fat store is the largest internal fat depot in the body, this suggests that individuals are indeed losing fat that could predispose to upper body obesity.