S.A. Spencer

Fatty acid balance studies in preterm infants fed formula milk containing long-chain polyunsaturated fatty acids (LCP) II

A milk formula (Prematil‐LCP) containing long‐chain polyunsaturated fatty acids (LCP) and with a fatty acid profile closely resembling breast milk has recently been introduced for preterm infants. A double‐blind randomized controlled trial was performed comparing fatty acid absorption from Prematil‐LCP (n= 10) and standard Prematil (n= 10). Formula‐fed preterm infants underwent 3 d fat balances (once full enteral feeds were established) along with a parallel human milk fed group (n= 11). Plasma samples were taken on the last day. Median total fat excretion (absorption, %) was 2.34 g kg (82.0), 2.64 g kg (82.9) and 1.65 g kg (87.8) with Prematil, Prematil‐LCP and human milk feeding, respectively. This reflected differences in the excretion and absorption of long‐chain saturated fatty acids. All groups excreted detectable LCP. LCP disappearance was higher in infants fed human milk than in those fed Prematil‐LCP, particularly for n‐6 LCP (p <0:01). Nevertheless, excreted LCP equated to <30% dietary intake, with Prematil‐LCP feeding. Plasma lipid fatty acid composition reflected differences in dietary LCP intake.

A Comparison of Pulse Oximetry and Near Infrared Spectroscopy (NIRS) in the Detection of Hypoxaemia Occurring With Pauses in Nasal Airflow in Neonates

Objective.The aim of this study was to compare the ability of NIRSand pulse oximetry to detect changes in cerebral oxygenation occurring inresponse to a pause in nasal airflow (PNA). Methods.Twenty-onerecordings of cerebral oxygenation index by NIRS together with oxyhemoglobinsaturation by pulse oximetry were measured on 17 preterm infants with ahistory of apnoea. Photoplethysmography was used to confirm the accuracy ofthe pulse oximetry data. PNA events were defined as pauses of greater than 4seconds in a thermistor trace measuring nasal air flow. Results.Baseline variability in oxygenation index (Hbdiff) was found to be from−0.12 to +0.13 µmol 100 g brain−1. A fall in Hbdiff orSpO2 was defined as a decrease of greater magnitude than 2 standarddeviations from the baseline, i.e., −0.12 µmol 100 gbrain−1 and 3% respectively. In 68% of 468 PNA events a fall inoxyhemoglobin saturation (SpO2) was detected and in 56% a fall inHbdiff was detected. In 20% of events there was no fall in cerebraloxygenation despite a fall in SpO2. In 8% of PNA episodes werecorded a fall in cerebral oxygenation but no fall in SpO2. Whena fall in cerebral oxygenation was recorded, the fall was greater when theevent was also associated with a fall in SpO2 (median(interquartile range (IQR)) 0.32 (0.21–0.69) vs. 0.25 (0.16–0.43)µmol 100g brain−1, p < 0.05). When all the PNAepisodes were reviewed no close correlation was shown between the magnitudeof change in cerebral oxygenation and the change in SpO2 for smallchanges in both indices. However, large falls (>1.5 µmol 100 gbrain−1) in cerebral oxygenation were closely associated with largechanges in SpO2. Conclusions.We conclude that bothtechniques are sensitive to changes in oxygenation during PNA. Small changesin cerebral Hbdiff and arterial SpO2 do not always correlate forphysiological reasons. A change in Hbdiff of >0.3 µmol 100 gbrain−1 is likely to be physiologically significant and isassociated with a change in SpO2 of 12%.

Effects of positive and negative pressure ventilation on cerebral blood volume of newborn infants

The effects of intermittent positive airway and continuous negative extrathoracic pressure ventilation on cerebral blood volume in preterm infants were studied using near infrared spectroscopy. In 12 infants continuous negative extrathoracic pressure caused a median decrease in cerebral blood volume of 0.14ml/100ml brain (95% confidence intervals (CI) 0.035–0.280) compared with no respiratory support. Oxygenated and deoxygenated haemoglobin also decreased, implying increased venous drainage as the main effect. In 17 infants intermittent positive pressure ventilation also caused a median reduction in cerebral blood volume of 0.06 ml/100 ml brain (95% CI 0.010–0.115) compared with endotracheal positive airway pressure. Deoxygenated haemoglobin increased by 0.07 ml/100 ml brain (95% CI 0.010–0.100) while oxygenated haemoglobin decreased by O.lOml/lOOml brain (95% CI 0.005–0.175). The increase in deoxygenated haemoglobin implies decreased venous drainage and the decrease in oxygenated haemoglobin implies that other factors may also be significant. Heart rate, blood pressure and oxygen saturation were monitored continuously and remained stable.

Measurement of peripheral oxygen utilisation in neonates using near infrared spectroscopy: comparison between arterial and venous occlusion methods.

The aim of this study was to develop an arterial occlusion method and compare it with the venous occlusion method for measurement of peripheral oxygen utilisation in neonates using near infrared spectroscopy (NIRS). Twenty healthy neonates were studied. Arterial occlusion was produced by inflating a neonatal blood pressure cuff to 100 mmHg for 30-40 s and oxygen utilisation (VO(2)) was calculated using the HbO(2) decrement slope following occlusion. Venous occlusion was produced by inflating the cuff to 30 mmHg for 15-20 s and VO(2) was calculated by: VO(2)=HbTx4x(SaO(2)-SvO(2)), where SaO(2) is the arterial oxygen saturation measured by pulse oximetry and SvO(2) is the venous oxygen saturation measured by NIRS. Each baby had a minimum of three arterial and three venous occlusions. Criteria were developed for acceptance/rejection of an occlusion. Using the arterial method, the mean VO(2) was 1.12 mM cm(-1) O(2)/min (S.D.=0.25), (95% CI=1.00-1.24 mM cm(-1) O(2)/min). The coefficient of variation was 6.6+/-4.1%. Using the venous method, the mean VO(2) was 1.60 mM cm(-1) O(2)/min (S.D.=0.48), (95% CI=1. 38-1.82 mM cm(-1) O(2)/min). The coefficient of variation was 12. 6+/-5.7%. The correlation between the two methods was weak (r=0.28 and r(2) was 0.08). The mean difference between the two methods was 0. 47 mM cm(-1) O(2)/min (S.D.=0.51). The limits of agreement were -0. 53 to 1.47 mM cm(-1) O(2)/min. The arterial method gives more consistent results.

Fetal and neonatal cerebral oxygen monitoring with NIRS: theory and practice

Near infra-red spectroscopy (NIRS) is a comparatively new method for monitoring the oxygenation in blood and tissue in the brain of the fetus and the neonate. Absorption of light in the wavelength range 700-1000 nm through such tissue is measured, which is then used to calculate changes in the concentration of cerebral oxygenated and de-oxygenated haemoglobin (HbO2 and Hb) and hence cerebral blood volume (CBV). Studies carried out on several groups of newborn babies have shown clear changes in HbO, Hb and CBV with hypoxia and bradycardia. These changes may well have implications in the occurrence of hypoxic/ischaemic brain injury. Intra partum NIR measurements on the fetal brain have demonstrated clear changes in HbO2, Hb and CBVm, coinciding with the onset of contractions.

Investigation of neonatal brain cytochrome redox by NIRS

Near Infrared Spectroscopy (NIRS) has been used to detect changes in cerebral blood and tissue oxygenation. Redox state of enzyme cytochrome aa3 (Cyt aa3 is thought to give an indication of tissue oxygenation. This information would be of value in exploring the aetiology of cerebral ischaemic lesions in preterm infants. However we have found that the change in cerebral cytochrome redox in infants following desaturation was inconsistent and insignificant.

Two different low birth weight formulae compared.

The performance of two different, commercially available, low birth weight formulae feeds was compared in preterm infants. The aim of the study was to determine the effect of compositional differences on tolerance, stool frequency and consistency, fat balance and weight gain. Inborn infants with birth weight less than 1500 g were randomised at birth to receive Prematil or Osterprem. Thirty infants received more than 900 ml/kg per week of designated formula alone during a total of 70 weeks of study. Three day fat balance was performed on 23 infants. Osterprem contains 40% more fat than Prematil. The composition of this fat is different in that Osterprem contains no medium chain triglycerides (MCT) compared to 30% in Prematil. Clinical evaluation demonstrated that Osterprem is associated with a significantly higher mean energy intake compared to Prematil (3442 and 3127 kJ/kg per week) but mean weight gain is not significantly different (123 and 112 g/kg per week). Mean stool frequency is higher on Osterprem (20.5 and 14.5 stool/week) and the consistency of stools firmer. This is attributable to a higher mean fat output (2.3 and 0.9 g/kg per day) secondary to the higher fat content of the feed and lower mean absorption (71.6 and 83.5%). Both feeds are well tolerated. The study also confirms that absorption of unsaturated fatty acids is inversely proportional to chain length.

Critical appraisal and further development of the methodology for open circuit calorimetry in neonates

A non-invasive technique for open circuit calorimetry based on a Vickers 79 incubator as the gas collection chamber was developed and evaluated. The technique, which involved drawing air from the incubator hood at 11 1/min for gas analysis, did not have a significant cooling effect on the infant and the noise levels within the incubator did not exceed current safety standards. A new technique for checking the calibration of the whole system was developed as the traditional alcohol burn method proved unsatisfactory. Either pure oxygen or carbon dioxide were fed into the incubator hood at controlled physiological rates using a calibrated throttling valve. Over a number of calibration checks the mean error of the system proved to be +/- 4.3% for oxygen and +/- 4.45% for carbon dioxide. Less than a fifth of this error was attributable to the pump and flow meter. When oxygen is introduced to the system at a constant physiological rate it takes 30 min for a plateau to be reached. Therefore it is recommended that this system is used when readings are to be taken in a steady state situation or data is to be cumulated over a long period of time such as in an energy balance study. A run in period of 30 min before collecting data is essential. It is recommended that a calibration check is performed before each study.

Photoplethysmography: a futuristic view for neonatal care.

Non-invasive monitoring techniques have gained wide application during critical care of the newborn infant. These techniques include transcutaneous PO 2 and PCO2 and arterial oxygen saturation using pulse oximetry. The limitations of pulse oximetry for use in the newborn are well recognized (1) and initially there was a great deal of scepticism from neonatologists because of the risk of failing to detect significant hyperoxia. Despite these limitations, this technology is now used almost universally in this patient group, and certainly much more than the transcutaneous methods (2). This is because pulse oximeters are easy to apply and provide information to the clinician rapidly with minimal discomfort to the baby. Therefore, any improvements in this technology in terms of increased reliability or scope are likely to be welcomed by clinicians. The paper by Olsson et al. (3) features the use of photoplethysmography (PPG) in the determination of heart rate and respiratory rate in the newborn infant.