Effect of a change in global metabolic rate on peripheral oxygen consumption in neonates

Abstract

Aim: To evaluate the effect of an induced change in global metabolic rate on peripheral oxygen consumption (VO 2 ) in healthy full term neonates. Subjects and methods: Twenty four healthy full term neonates were studied. Peripheral VO 2 was measured by near infrared spectroscopy (NIRS) using arterial occlusion and measurement of the oxyhaemoglobin (HbO 2 ) decrement slope. Global VO 2 was measured by open circuit calorimetry. Global and peripheral VO 2 were measured in each neonate before and after a routine bath. Abdominal and forearm skin temperatures were also recorded. Results: Nineteen neonates completed the study. Global VO 2 increased by 30.7% (p = 0.001), and peripheral VO 2 by 23.1% (p = 0.001). A correlation between the fractional changes in global and peripheral VO 2 was apparent (r = 0.76, p = 0.001). Abdominal skin temperature decreased by 0.8°C (p = 0.001), and forearm skin temperature by 0.6°C (p = 0.04). Conclusions: Measurement of peripheral VO 2 using NIRS with arterial occlusion is responsive to conditions that increase global metabolic rate. Any change in global VO 2 must be taken into consideration during the interpretation of peripheral VO 2 measurements in neonates. E arly in circulatory compromise, compensatory mechanisms maintain oxygen delivery to vital organs, such as the brain and heart, through redistribution of blood flow away from the periphery. This will give rise to reduced peripheral perfusion, thereby limiting oxygen uptake by these areas. Studies during critical care in adults, using invasive oxygen electrodes, suggest that hypoxic changes in skeletal muscle may be observed before there is a significant change in blood pressure.1 Therefore a method for assessment of peripheral oxygen consumption in neonates may give an early warning of the need for circulatory support during critical care.2 Cerebral ischaemic lesions are still an important cause of neurodevelopmental problems in preterm infants. 3 There is evidence that prevention of hypotension is important in the prevention of these lesions, 4-6 and the British Association of Perinatal Medicine guidelines 7 promote the maintenance of mean arterial pressure above predefined limits. Unfortunately this strategy has not been effective in preventing the development of these lesions. The cause of this white matter damage is almost certainly multifactorial, with contributions from antenatal infection (chorioamnionitis) 8 9 and hypocapnia. 10 11 Nevertheless it is possible that improved management of the circulation, particularly in the first 48 hours of life may improve brain perfusion and lead to improved outcomes for these babies.Previously we reported a non-invasive method for measurement of peripheral oxygen consumption (VO 2 ) in neonates using near infrared spectroscopy (NIRS) with arterial occlusion.12 Before assessing this technique during critical care, it was necessary to understand how changes in the external environment may affect the measurements obtained. Changes in environmental temperature may have a profound effect...

Foot Pulse Oximeter Perfusion Index Correlates with Calf Muscle Perfusion Measured by Near-Infrared Spectroscopy in Healthy Neonates

“…To the best of our knowledge, this is the first time that foot PI, measured by pulse oximetry, is compared with parameters relating to the peripheral perfusion and oxygen consumption measurable by NIRS. [10][11][12]15,16,18,22 Only recent developments of pulse oximetry have enabled foot PI to be calculated. 2,3 Although the mechanisms underlying PI changes remain to be elucidated, local skin vasoconstriction appears to be the most likely reason for significantly lower PI readings in very sick patients.…”

“…Given the lack of other noninvasive methods, NIRS has been the only bedside clinical tool available in the last few years for evaluating muscle circulatory status in healthy and sick neonates and many significant clinical studies have been published. [8][9][10][11][12]16,18,22,25 NIRS was combined in our study with arterial/venous occlusion maneuvers to measure local muscle BF, VO 2 , and SvO 2 . 9,10,22 Using this NIRS approach, FOE proved to be a better indicator of the need for transfusion in anemia than hemoglobin concentration.…”

“…This would explain not only a BF change due to the arterial inflow, but also a BF redistribution from the capillaries to the skeletal muscles 26 according to the energy demands. Neonatal calf and forearm VO 2 were measured by NIRS on both arterial and venous occlusion, but Hassan et al 10 demonstrated that arterial occlusion produces more consistent results; they used arterial occlusion to investigate the effects of a change in global metabolic rate on peripheral oxygen consumption, 12 and the effect of limb cooling on peripheral and global oxygen consumption. 11 As for VO 2 We agree with his results because this method gave us a lower coefficient of variation than venous occlusion, as well as a lower VO 2 value (0.3 mM/100 ml/minute) than the 3.2 mM/100 ml/ minute obtained using venous occlusion.…”

“…(1) mM O 2 /100 ml/minute ¼ 9.3 mM O 2 cm/min; 11,12 (2) mM O 2 /100 ml/minute is comparable with ml O 2 /kg/minute, 19 assuming that a mole of a gas, at body temperature and sea level, corresponds to a 25.4 l (Avogadro's law); and 1 kg corresponds to 1000 ml, assuming a muscle density of 1.06 g/ml. 20 Data Analysis and Statistics All parameters were checked for normal distribution using the Kolmogorov-Smirnov test procedure.…”

“…6 Near-infrared spectroscopy (NIRS) has been used largely in neonates for the noninvasive assessment of brain tissue oxygenation 7 and, less often, to evaluate limb oxygenation. [8][9][10][11][12] Considering that: (1) the spot measurement of BF and VO 2 by NIRS takes at least 20 minutes; and (2) the accuracy of NIRS changes is limited because path length and its changes are not known, 7 the foot PI measured by pulse oximetry seems to be more feasible than indirect NIRS methods for monitoring peripheral perfusion in the neonatal intensive care unit. We hypothesized that foot PI could also adequately evaluate limb perfusion.…”