Comparison of three methods of determining oxygen consumption and resting energy expenditure

Resting energy expenditure (REE) in intensive care unit patients was evaluated by three methods--indirect calorimetry (REE-IC), Fick equation (REE-F), and estimation from the Harris-Benedict equation (REE-HB). The mean REE-IC and REE-F values did not differ significantly. However, both values were significantly higher than the REE-HB. The present study indicates that a reasonably accurate estimate of the REE can be obtained from data available by Swan-Ganz catheterization. The Fick method is technically simpler to perform and less expensive than indirect calorimetry. The invasive nature of Swan-Ganz catheterization is a major disadvantage. However, right-sided heart catheterization frequently is required for the management of intensive care unit patients. For them, REE-F appears to be a reasonable alternative.     

Surface-area-normalized Kt/V: a method of rescaling dialysis dose to body surface area-implications for different-size patients by gender

Dialysis is measured as Kt/V, which scales the dose (Kt) to body water content (V). Scaling dialysis dose to body surface area (S(dub)) has been advocated, but the implications of such rescaling have not been examined. We developed a method of rescaling measured Kt/V to S(dub) and studied the effect of such alternative scaling on the minimum adequacy values that might then be applied in male and female patients of varying body size. We examined anthropometric estimates of V and S (Watson vs. Dubois estimates) in 1765 patients enrolled in the HEMO study after excluding patients with amputations. An S-normalized target stdKt/V was defined, and an adequacy ratio (R) was computed for each patient as R = D/N where D = delivered stdKt/V (calculated using the Gotch-Leypoldt equation for stdKt/V) and N = the S-normalized minimum target value. In the HEMO data set, we determined the extent to which baseline (prerandomization) stdKt/V values would have exceeded such an S-based minimum target stdKt/V. The median V(wat):S(dub) ratios were significantly higher in men (21.34) than in women (18.50). The average of these (20) was used to normalize the current suggested minimally adequate value (stdKt/V > or = 2.0/week) to the S-normalized target value (stdKt/S > or = 40 L/M(2)), assuming that average modeled V = average anthropometric V. To achieve this S-normalized target, the required single-pool (sp) Kt/V was always higher in women than in men at any level of body size. For small patients (V(wat) = 25L), required stdKt/V values were 2.05 and 2.21/week for men and women, respectively, corresponding to spKt/V values of 1.31 and 1.52/session. On the other hand, large (V(wat) = 50L) male patients would need spKt/V values of only 1.0/session. Prerandomization baseline dialysis sessions in the HEMO study were found to meet such a new S-based standard in almost all (766/773) men and in 885/992 women. An analysis of scaling dose to anthropometrically estimated liver size (L) showed similar gender ratios for V(wat):L and V(wat):S(dub), providing a potential physiologic explanation underpinning S-based scaling. S-based scaling of the dialysis dose would require considerably higher doses in small patients and in women, and would allow somewhat lower doses in larger male patients. Current dialysis practice would largely meet such an S-based adequacy standard if the dose were normalized to a V(wat):S(dub) ratio of 20.     

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 oxygen consumption, carbon dioxide production, and resting energy expenditure in premature and full-term infants

A newly developed closed circuit water-sealed infant calorimeter has been used to measure oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory quotient (RQ) and resting energy expenditure (REE) in 31 infants. There were 17 full-term and 14 premature infants. VO2 was measured volumetrically, keeping the inspired oxygen concentration constant. VCO2 was determined by infrared analysis of the mixed expired gases. Values for REE and RQ were calculated from measurements of VO2 and VCO2. All values were normalized for the infants body weight. Our findings demonstrate significant differences in VO2, VCO2, and REE associated with weight, gestational age, postnatal age, activity, feeding, and sex. In addition, VO2, VCO2, and REE were significantly higher for the premature infants. The water-sealed indirect calorimetry system: (a) is safe and noninvasive, (b) does not interfere with infant tube feeding or IV infusion, (c) permits long-term monitoring of metabolic activity, and (d) allows a more exact matching of oral and intravenous feedings to actual energy expenditure. We are finding that indirect calorimetry removes the guess work from writing daily caloric regimens, with potential advantage for the treatment of sick infants.     

Variance inflation in sequential calculations of body surface area, plasma volume, and prostate-specific antigen mass

OBJECTIVE

To assess the magnitude of variability among 11 formulae for human body surface area (BSA) and then among eight for plasma volume (PV), as used to represent physiological indices for body metabolism, drug dosages and body fluid management, and to evaluate the potential cumulative effect of variance inflation with prostate‐specific antigen (PSA) mass as an endpoint.

PATIENTS AND METHODS

In 3020 men undergoing robotic radical prostatectomy (RRP) at the Vattikuti Urology Institute between 2001 and 2008, the variation in BSA and PV formulae was calculated, as well as PSA mass, using analysis of variance (anova ), Bland‐Altman plots, linear regression, and correlation analyses.

RESULTS

For estimating BSA, anova indicated significant variance among the 11 formulae used (P < 0.001) with a between‐groups variance of 5.45. Bland‐Altman plots reported bias when the Dubois formula was compared to other BSA formulae. Furthermore the anova for PV, with BSA as a predictor, indicated significant variance among the eight formulae used (P < 0.001), with a mean between‐group variance of 444.4 and a mean inflation factor of 81.5. Scatter plots between one PV formula (Boer) and others had a good linear fit. For PSA mass, anova indicated significant variance (P < 0.001) using PV as a predictor, with a mean between‐group variance of 16 799.6 and a mean variance inflation factor of 37.8.

CONCLUSIONS

There is significant variation in the BSA calculated by commonly used formulae. This variation is carried over and further magnified in the sequential calculation of PV and PSA mass. Hence arbitrary selection of BSA and PV formulae is likely to affect inferences.     

Measurement of dialyzer clearance, dialysis time, and body size: death risk relationships among patients

BACKGROUND: Urea pharmacokinetic equation systems have contributed to better understanding of treatment dose among hemodialysis patients. The methods are indirect, however, and require the measurement of blood urea nitrogen (BUN) concentration before and after a dialysis session to estimate the total treatment dose that clinicians prescribe [urea clearance x dialysis time (Kt)] indexed to an estimate of body size [the volume of urea distribution in the body (V)] yielding the ratio, Kt/V. New technology permits direct on-line measurement of average small molecule clearance (Kecn) during each dialysis treatment that can be multiplied by time (t) to give a direct measurement of total treatment dose (Kt). This study evaluated the relationship of measured Kt with death risk. It also evaluated the relationship of simple body size measures to risk and also the combination of one such measure [body surface area (BSA)] with Kt to death risk. METHODS: The data were taken from the Fresenius Medical Care (NA) (FMCNA) clinical database that included patients who had outcome data, height and weight measurements, and at least one average Kecn and t measurement during April 2002. Kecn, t, and the body size measures [body weight, body mass index (BMI), and BSA)] were averaged during the month. Those values were used as predictors of survival during the next 1 year in unadjusted and case mix adjusted proportional hazards (Cox) models. RESULTS: Increasing values of Kecn, t, Kt and all of the body size measures were associated with lower death risk. The body size measure most closely associated with risk was the BSA that was used in subsequent models. Kt and BSA were independent risk predictors. There was a significant interaction between Kt and BSA in the case mix but not the unadjusted model indicating that the risk burden of lower total dialysis dose, Kt, may be greater among small than large patients. CONCLUSION: The direct measurement of dialysis dose during each treatment is practical and the values reported by it are clinically relevant. Higher dose was associated with better survival in both small and large patients treated three times weekly. Furthermore, smaller patients may require proportionately greater total dose than larger patients to achieve comparable survival.     

Predicting success of metabolic surgery: age,body mass index,C-peptide,and duration score

BackgroundSurgery is the most effective treatment of morbid obesity and leads to dramatic improvements in type 2 diabetes mellitus (T2DM). Gastrointestinal metabolic surgery has been proposed as a treatment option for T2DM. However, a grading system to categorize and predict the outcome of metabolic surgery is lacking. The study setting was a tertiary referral hospital (Taoyuan City, Taoyuan County, Taiwan).MethodsWe first evaluated 63 patients and identified 4 factors that predicted the success of T2DM remission after bariatric surgery in this cohort: body mass index, C-peptide level, T2DM duration, and patient age. We used these variables to construct the Diabetes Surgery Score, a multidimensional 10-point scale along which greater scores indicate a better chance of T2DM remission. We then validated the index in a prospective collected cohort of 176 patients, using remission of T2DM at 1 year after surgery as the outcome variable.ResultsA total of 48 T2DM remissions occurred among the 63 patients and 115 remissions (65.3%) in the validation cohort. Patients with T2DM remission after surgery had a greater Diabetes Surgery Score than those without (8 ± 4 versus 4 ± 4, P < .05). Patients with a greater Diabetes Surgery Score also had a greater rate of success with T2DM remission (from 33% at score 0 to 100% at score 10); A 1-point increase in the Diabetes Surgery Score translated to an absolute 6.7% in the success rate.ConclusionThe Diabetes Surgery Score is a simple multidimensional grading system that can predict the success of T2DM treatment using bariatric surgery among patients with inadequately controlled T2DM.     

Effects of sex,body mass index,and body size on the outcome of coronary artery bypass surgery: Iranian experience

Objective  

Sex, body mass index, and body surface area have been proposed as important determinants of outcome after coronary artery bypass graft surgery.     

In vivo inflammatory response to polymethylmethacrylate particulate debris: Effect of size,morphology, and surface area

Particulate debris, including that from polymethylmethacrylate (PMMA) cement, is observed commonly in the membrane surrounding loose joint prostheses. Such debris is assumed to cause an inflammatory response and contributes to osteolysis and failure of the implant. A subcutaneous rat air-pouch model was used to assess quantitatively the in vivo effects of the size, morphology, and surface area of PMMA particles on the acute inflammatory response. PMMA particles were divided into three groups. In Group A, mechanical grinding of cured bone cement produced irregularly shaped particles; Group B included spherical particles of PMMA powder (Simplex P); and Group C consisted of commercially prepared spherical latex particles. All three groups had two size distributions: < 20 μm and 50–350 μm. For a given mass or dose, the small, irregularly shaped mechanically produced particles in Group A elicited a significantly greater inflammatory reaction than the large particles in Group A, as expressed by the release of tumor necrosis factor (TNF), neutral metalloprotease (NMP), and prostaglandin E₂ (PGE₂) and the white blood cell (WBC) count within a 24-hour period. Similar findings were seen in Group B. Particles in Group C were used to compare the effect of absolute numbers of large and small particles and surface area. Large (10–126 μm) spherical PMMA particles at a dose of 1.7 × 10⁶ particles/ml caused a significantly higher inflammatory response, as measured by WBC count and production of NMP and PGE₂, than small (1–10 μm) spheres at a dose of 4 × 10⁶ particles/ml. However, the production of TNF in the rats was significantly increased with small particles (p < 0.05) at a concentration 4-fold less than that with the large particles (4 × 10⁵ compared with 1.7 × 10⁶ particles/ml). This finding may reflect a different cellular mechanism for the TNF component of the inflammatory response than is measured by WBC counts or by levels of PGE₂ and NMP. As the calculated surface area of the PMMA particles increased, a threshold level was reached, at which point the inflammatory response increased dramatically. The size of particles has a role in the prolongation and intensity of the release of specific cytokines. The total surface area of the particles appeared to be an important factor in determining the inflammatory response, as measured by WBC count, PGE₂, TNF, and NMP.     

A comparison study of methods for estimation of a burn surface area: Lund and Browder,e-burn and Mersey Burns

IntroductionOne of the greatest challenges in burn care is the estimation of a total burn surface area (TBSA). It is especially challenging and needs to take into account the growing proportions and the age of a paediatric patient. The aims of this study is to: (1) assess the reliability of the three modalities (LB, MB, and EB) in calculating the extent of burn injuries and fluid resuscitation, and (2) compare the features in terms of usability and efficacy.MethodsParticipants were recruited from Women’s and Children’s Hospital (WCH), South Australia’s surgical and emergency department. Participants were introduced to LB, MB and EB, and then commenced calculation of TBSA on two simulated paediatric (patient A: 12 months, patient B: 4 years) burns. The participants were categorized into three groups; (1) Burns-naïve, (2) Burns-experienced, and (3) Burns-expert.ResultsA total of 45 participants took part in this validation study: doctors (49%), nurses (33%), nursing students (11%) and medical students (7%). The burns-naïve group demonstrated higher means in both patients and has greater variance, TBSA mean 28.8%, range 14–40.5% and mean 37.4%, range 20–52.3% in patient A and B respectively. Two-way ANOVA analysis shows a statistically significant interaction between the effects of level of experience and use of applications on estimation of TBSA in larger burns.ConclusionInnovative software and mobile applications demonstrate a high potential as clinical adjuncts in achieving better health outcomes in any health care system. Both Mersey Burns and e-burn reduced the risk of human error particularly from untrained or non-specialised clinicians, however, e-burn proved to be more favourable in our study. Technology-aided models are the future of burns assessment, and further studies are warranted to determine their impact on overall clinical outcome.     

Results of high dose rate brachytherapy, anterior pelvic exenteration and external beam radiotherapy for carcinoma of the female urethra

PURPOSE: We evaluated a multimodality approach to locally advanced urethral carcinoma in women. MATERIALS AND METHODS: Between August 1996 and July 1999, 6 women were treated for locally advanced carcinoma of the urethra with anterior pelvic exenteration followed by high dose 192iridium intraoperative radiation therapy. Four of the 6 patients were also treated with neoadjuvant or concomitant platinum based chemotherapy. RESULTS: Two patients had no evidence of disease, 3 had distant metastasis and 2 had local recurrence at a mean followup of 21 months (range 12 to 47). Radiation was relatively well tolerated with no major adverse events. CONCLUSIONS: High dose intraoperative brachytherapy followed by external beam radiation is relatively well tolerated. Local control seems to have improved. We must evaluate a larger cohort of patients to determine this impact of the combined modality on local control and patient survival.     

Efficacy of an educational program on dialysis, renal transplantation, and organ donation on the opinions of high school students: a randomized controlled trial

AIM: Organ shortage is a rate-limiting factor for transplantation. The aim of this study was to evaluate the impact of an educational program targeted to high school students on opinions concerning organ donation. METHODS: Sixteen public high schools in Torino, Italy, were randomized (2001 to 2002) as interventions (n = 8) or controls (n = 8). Intervention was composed of first questionnaire, first lesson (one to two classes; 2 hours, by a trained nephrology fellow); second lesson (all classes together; coordinated by a nephrologist, with patients and trainees); second questionnaire. Control included questionnaires. Statistical analysis compared the opinions in the questionnaires after stratification for age, sex, and type of school. RESULTS: Fourteen schools completed the program (seven interventions: 937 first and 808 second questionnaires; controls: 739 and 659). Television (82.5%) and newspapers (43.2%) were the main sources of information; knowledge on renal transplantation (grafts feasible per patient, average duration) was low; only 12.2% of the students gave correct answers. The opinions on living donation were highly positive (76.8%) with no difference in control, intervention schools, first and second questionnaires, according to sex, age, or type of school. The opinions on cadaveric transplantation were affected by the educational intervention with a drop in negative answers (from 33.7% to 16%), with an increase in positive (from 31.5% to 42.9%) and in uncertain ones (from 34.8% to 41.1%) among the intervention schools; 98% of the students appreciated the program. CONCLUSION: The positive effect on student opinions suggests the need to develop educational approaches as a part of our routine clinical work.     

Extrapolation of cardiac index from analysis of the left ventricular outflow velocities in children: implication of the relationship between aortic size and body surface area

BACKGROUND: It has recently been reported in critically ill patients that a linear relationship exists between cardiac index (CI) measured with thermodilution and mean aortic blood flow velocity (MAFV). This hypothesis can be validated mathematically only if the aortic area (AA index) indexed to body surface area (BSA) remains constant and if the relationship between aortic diameter (PhiAo) and BSA is nonlinear. However, several other equations have described the relationship between BSA and, respectively, PhiAo and aortic area (AA) in children. The aim of this study was to determine if the relationships calculated between BSA and aortic size in children (without left ventricular outflow tract abnormality) could validate the hypothesis that MAFV and CI are well linked linearly, leading to its use to determine CI. METHODS: Two hundred and thirty-two measurements performed in 126 children and infants were retrospectively analysed. PhiAo was measured in the long axis view at the annulus using two-dimensional mode echocardiography with a 5-MHz transducer. Various linear and nonlinear relationships between BSA and, respectively, PhiAo, PhiAoindex, AA and AAindex were determined based on a nonlinear regression method with a model as follows: y=a(xc) + b. The comparisons between regressions were conducted based on the estimation error. RESULTS: The relationships between PhiAo and BSA appeared nonlinear and was well described by: PhiAo=2.96(BSA1/4) - 1.31 with a non-zero y-intercept and PhiAo=1.64(BSA1/2) with a zero y-intercept. In contrast, the relationships between AA and BSA were linear. The AAindex was not linked to BSA and can be considered as constant. The coefficient a of the equation appeared similar to those obtained mathematically with the relationship previously described between MAFV and CI. CONCLUSIONS: The hypothesis that CI can be extrapolated to the measurement of MAFV appears valid as regards the relationships calculated between aortic size and BSA in children without left ventricular outflow tract abnormality.     

Laser nerve repair by solid protein band technique. I: Identification of optimal laser dose,power, and solder surface area

Thirty-four tibial nerves in 17 adult male wistar rats were repaired by applying protein bands longitudinally across the nerve join. The bands were then irradiated with a fibre-coupled diode laser (λ = 810 nm). The relations among the laser weld breaking force, the power, and the solder surface area were investigated, while maintaining a consistent ratio between the total mass of protein solder in a band and total laser energy delivered (the laser energy dose). When this laser energy dose was held constant, the average breaking force of the laser welds irradiated by 72 mW laser output power was weaker than that reached after 90 mW laser radiation. There is a linear relation between the solder breaking force and the solder surface area when band thickness, laser power, and laser dose are unvaried. © 1998 Wiley-Liss, Inc. MICROSURGERY 18:55–59, 1998.