Cerebral Blood Flow and Exchange of Oxygen, Glucose, Ketone Bodies, Lactate, Pyruvate and Amino Acids in Infants

Abstract

Cerebral blood flow (CBF) and cerebral av-differences of oxygen and circulating substrates were measured in normocapnic infants during general anaesthesia before elective surgery in order to study possible age-dependent variations. CBF was determined by a minor modification of the Kety-Schmidt technique from desaturation curves of nitrous oxide (N2O) in arterial and cerebral venous blood (N2O analysed by gas chromatography on 15 mul blood samples) after reduction of inhaled N2O from 75 to 50%. The reproducibility was +/-4.6%. Lactate, pyruvate and oxygen were determined in whole blood and amino acids in plasma by ion-exchange chromatography. Reliable av-differences of glucose, acetoacetate and D-beta-hydroxybutyrate could be calculated from plasma values and hematocrits. Mean values from 12 infants (age 11 days-12 months) were: CBF 69 ml/100 g0min-1; cerebral uptake (in mumoles/100 g-min-1): oxygen 104, glucose 27, acetoacetate 0.9, D-beta-hydroxybutyrate 2.3; cerebral release: lactate 2.4 and pyruvate 0.8. Significant uptake of amino acids was found only for histidine 0.95 and arginine 0.7. Significant correlations between arterial concentration and cerebral exchange were found for: ornithine, arginine, phenylalanine, aspartic acid, serine, glutamine and acetoacetate. CBF and substrate exchange were unrelated to age within the group. Infants had higher mean CBF and greater uptake of ketone bodies than has been reported in adults.

Cerebral Blood Flow and Autoregulation After Pediatric Traumatic Brain Injury

“…Using modified nitrous oxide method, Kennedy, et al reported higher CMRO 2 and lower cerebrovascular resistance in healthy awake children (3-11 years) compared to young adults; CMRO 2 :5.2 ml (231 μmol)/ 100g/min vs. 4.2 ml (187 μmol)/100g/min, and cerebrovascular resistance:0.8 mmHg/100g/ min vs. 1.4 mmHg/100g/min [22]. Studies of healthy anesthetized children also suggest agerelated increases in CMRO 2 after infancy: 104 μmol/100g/min in infants [34] vs. 135 μmol/ 100g/min in 3 weeks-14 years children [35]. However, one PET study of children <1 year reported lower regional CMRO 2 in young children compared to adults [36].…”

Carbohydrate as nutrient in the infant and child: range of acceptable intake

“…The proposed lower limit assumes that glucose is the only source of energy for the brain. This probably is not true (Denne & Kalhan, 1986;Settergren et al, 1976).…”

“…The average rate of oxygen consumption in children was 235 mmola100 gÁmin. Two studies (Settergren et al, 1976(Settergren et al, , 1980 recorded lower rates of oxygen consumption, 104 and 135 mmola 100 gÁmin. These measurements were done while the children were under general anesthesia in preparation for surgery.…”

“…This is in part the consequence of lack of easy accessibility of this organ for such studies. Previous studies have quanti®ed oxygen and glucose consumption by the brain in anesthetized or unanesthetized children using Fick's principle (Settergren et al, 1976(Settergren et al, , 1980Mehta et al, 1977;Kennedy & Sokoloff, 1957;Kennedy, 1956;Sokoloff et al, 1977). Arterio-venous gradients of glucose, oxygen, lactate, pyruvate and ketones were measured across the brain.…”

“…It should be underscored that such computation assumes that oxidation is the only fate of cerebral glucose uptake, and that glucose is the only oxidative fuel being utilized by the brain. The last two assumptions are appropriate, considering that the contribution of ketones, except in prolonged fasting in adults, is small and that non-oxidative disposal of glucose, that is, release of lactate and pyruvate by the brain, is also small (Settergren et al 1976(Settergren et al , 1980Mehta et al, 1977). Recently, cerebral metabolic rate of glucose has been quanti®ed in children and adults using positron emission tomography (PET).…”