Changes in cerebral oxygenation in children undergoing surgical repair of ventricular septal defects

Abstract

SummaryMathematical 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.Keywords Body surface area. Metabolic rate. Calorimetry. Rubner's Law, published in 1883, crystallised a belief among physiologists in the mid to late 19th century that, regardless of species, the heat production (i.e. metabolic rate) of an individual was proportional to the body surface area (BSA) [1]. This law was very difficult to disprove because BSA could only be measured by very cumbersome means, such as skinning the subject. Measurement of metabolic rate via direct calorimetry was possible but not widely available. Being unable to measure the metabolic rate in a clinical setting, measuring BSA seemed to provide an acceptable alternative to metabolic rate. There was an impetus around the beginning of the 20th century to derive simpler ways of calculating BSA using mathematical manipulations of various body dimensions. Throughout the remainder of the century, investigators attempted to simplify the equations and expand the application of the formulae. Because of the importance and widespread use of BSA formulae in many areas of medicine, we undertook a literature review to determine the source of and evidence for these equations. MethodsComprehensive literature reviews of documents published around 100 years ago are difficult. The electronic database ÔMedlineÕ only includes publications from 1966 onwards, whilst its paper-based predecessor, Index Medicus, extends to only 1960. The Medline database was searched by combining a medical subject heading (MeSH) search for Ôbody surface areaÕ, which prior to 1970 was classified under ÔanthropometryÕ. The following search strategies were used: MeSH search for ÔmathematicsÕ, or keyword searches for Ôcalculat*Õ, ÔformulaÕ or ÔduBoisÕ (duBois being the author of the most widely used BSA formula). Index Medicus was searched using the ÔanthropometryÕ MeSH term. Documents prior to 1960 were found from the references in articles identified by Anaesthesia, 2003, 58, pages 50-83 Ó 2003 Blackwell Publishing LtdMedline and each relevant document prior to 1960 also had its references searched. The development of Ôheight)weightÕ formulaeThe first published equation for estimating B...

The effect of bloodless pump prime on cerebral oxygenation in paediatric patients

“…Table 2 Physiologic data during the study. (11)(12)(13) or jugular venous saturation (18,19) in children (12,13) and adults (11,18,19). Cerebral oxygen metabolism balance is altered at the start of CPB (11,12), recovers during hypothermic CPB (13,18), and is again altered during rewarming (13,18,19).…”

“…The value of NIRS-measured haemoglobin oxygenation parameters during CPB has been proposed by several authors (11)(12)(13)(14). Contamination from skull and skin can be a potential confounding factor (24), but a small head diameter and thinner skull and scalp minimizes this effect in children.…”

“…This study was performed to compare the effect of bloodless CPB prime with that of red blood cell-containing prime, on regional cerebral oxygen saturation (rSO 2 ) value, as measured by near infra-red spectroscopy (NIRS); NIRS has been used for non-invasive and continuous assessment of cerebral oxygenation during cardiac surgery (11)(12)(13)(14). By using two different wave lengths of near-infrared light, NIRS measures the ratio of oxyhaemoglobin to total haemoglobin in the field beneath the sensor, expressed as a percentage value of rSO 2 (15,16).…”

The bypass plan

“…Additionally in support of this, several studies in various models have shown that the use of real-time arteriovenous and near-infrared saturation monitoring and the monitoring of oxygen uptake, venous oxygen tension, and lactic acid production support the safe use of these lower flow rates during bypass [79][80][81][82][83]. The use of real-time NIRS as a trending device is useful in guiding flow rate requirements during bypass and tolerance to temporary low flows required to improve visualization at the surgical field [84][85][86][87][88]. In a practical sense, the perfusionist determines flow rates during cardiopulmonary bypass primarily by patient temperature, anatomic considerations, achievable venous return, and institutional/surgeon preferences, particularly for systemic vascular resistance and mean arterial blood pressure management.…”

Immediate post-operative care following cardiac surgery

“…As alterações neurológicas no pós-operatório de cirurgia cardíaca podem ser causadas por alguns fatores como hipotermia e perfusão cerebral inadequada durante a operação e a CEC, tempo de parada cárdíaca, isquemia e hipóxia por embolias gasosas, edema cerebral secundá-rio à retenção hídrica, distúrbios metabólicos como hipoglicemia, hipocalcemia, hiponatremia, acidose e hipomagnesemia 7,8 . Podem manifestar-se das mais variadas formas, com agitação, convulsões, coreoatetose 29 (devido à CEC) e coma.…”