Abstract: OBJECTIVE: The purpose of lung recruitment manoeuvres is to open collapsed lung regions, improve gas exchange and optimise regional lung mechanics. This study investigates the efficacy of recruitment manoeuvres for improving regional ventilation distribution as characterised using electrical impedance tomography (EIT). DESIGN, SUBJECTS, INTERVENTIONS: A ventilated ovine smoke inhalation lung injury model was used. Respiratory mechanics and regional filling capacity of the lung were measured using EIT pre- and post- recruitment and compared to a control group. MEASUREMENTS: EIT, expressed as the time course relation of the regional versus the global impedance change, measured the regional filling capacities of the lung. MAIN RESULTS: After smoke inhalation injury, the dependent lung showed a significantly larger area of collapse and a reduced filling capacity compared to the non-dependent lung. After recruitment the ventilated volume increased and the dependent lung showed improved respiratory mechanics, whereas the non-dependent lung was more likely to be hyper-inflated during tidal breathing. CONCLUSIONS: Lung recruitment manoeuvres have a significant impact on regional lung mechanics and individual measurement of ventilation distribution using EIT may assist to improve ventilatory management.

Abstract: OBJECTIVE: Changes in cerebral impedance in the newborn piglet are able to discriminate, within 1-2 h of acute hypoxia, between animals which will have a good neurological outcome, and those who have suffered more severe hypoxia resulting in poor outcome. The aim of this study was to determine if cerebral impedance could be used to identify those human infants with an encephalopathy following acute hypoxia who subsequently have a poor neurological outcome. It is these infants who may benefit most from neural rescue treatment. METHODS: Twenty-four newborn term infants with evidence of severe acute intrapartum hypoxia and encephalopathy were studied. Bioimpedance spectroscopy was commenced as soon as possible after birth and repeated every 30 min until the infant was 12 h old. Neurodevelopmental outcome was assessed at 12 months of age. RESULTS: Although cerebral impedance was different to control values, there was no significant difference in cerebral impedance between hypoxic babies with normal and those with abnormal development. CONCLUSION: Cerebral impedance was increased in hypoxic babies, as predicted from animal data, but the method was not suitable for discrimination of outcome. SIGNIFICANCE: Cerebral impedance is not useful for early identification of infants who subsequently have a poor outcome after acute intrapartum hypoxia and who may benefit from neural rescue treatment.

Abstract: BACKGROUND: Respiratory mortality and morbidity remain major consequences of extreme prematurity. Percutaneous transfer of oxygen and carbon dioxide is possible in the newborn human. Perfluorocarbon (PFC) liquids have excellent oxygen and carbon dioxide carrying capacity. Animals can breath immersed in perfluorocarbon liquids and maintain adequate gas exchange. Our hypothesis is that the combination of spontaneous tidal perfluorocarbon breathing and respiration through the skin immersed in perfluorocarbon will allow adequate gas exchange in the preterm newborn. In this pilot study we aimed to observe the effects of immersion in FC-77 perfluorocarbon liquid on the preterm lamb. PILOT DATA: Four preterm lambs at 100-115 days gestation were delivered using a modified EXIT procedure. Immediately after complete delivery, the catheterised lamb was immersed in warm, oxygenated FC-77 perfluorocarbon liquid. Physiological monitoring was done for up to 60 min. All lambs were warmed adequately and seemed to have centrally intact circulation initially. All had little or no respiratory effort and there was no appreciable lung expansion. All had severe respiratory acidosis. DISCUSSION: For the provision of immediate ex utero care to the 'fetus' there are three requirements: adequate gas exchange surfaces and sufficient oxygen and carbon dioxide gradients, a functioning circulation, and an environment capable of keeping the lamb warm (thus minimising metabolic demand, oxygen consumption and carbon dioxide production). In this pilot study the greatest initial problem was the severe and rapidly worsening respiratory acidosis. The major problem was a lack of respiratory drive. No lung expansion from the outset would yield zero contribution to gas exchange from the lungs. An intact central circulation does not necessarily mean that the pulmonary circulation, respiratory drive and/or the skin circulation are adequate. For adequate gas exchange to occur it will require a 'breathing' animal with expanded alveoli. If the transition from the normal in utero state to immersion in PFC was immediate, and lung expansion was achieved, it could still be possible to achieve adequate gas exchange through the skin and lungs of the extremely preterm newborn. HYPOTHESIS: Given the potential for gas exchange across the skin of the extremely preterm infant we hypothesise that the immersion of extremely preterm infants in PFC liquid will allow optimal percutaneous gas exchange to occur. Given some lung gas exchange with less injurious liquid ventilation (spontaneous or mechanical) we hypothesise that the combination of skin and lung gas exchange will provide sufficient gas exchange to support life.

Abstract: OBJECTIVE: To determine the inspired gas temperature at points from the endo-tracheal tube (ETT) circuit manifold to the tip of the ETT in a model neonatal lung. DESIGN: A model lung attached to standard ventilator circuit, autofeed chamber and humidifier was ventilated using typical pressure-limited, time cycled settings. Temperatures were measured at various distances along the ETT using a K-type thermocouple temperature probe. RESULTS: The inspired gas temperature dropped from the circuit temperature probe site (40 degrees C) to the proximal end of the ETT (37 degrees C). The temperature dropped further as it passed through the exposed part of the ETT (34 degrees C) but then warmed again on entering the lung model so that the inspired gas at the distal end of the ETT was 37 degrees C. Statistically significant differences were found with a one-way ANOVA P-value of <0.0001. The differences between each pair of mean temperatures were statistically significant (all P<0.001) except when comparing the proximal end of the ETT with midway down the ETT (Bonferroni's Multiple Comparison Test, P>0.05). CONCLUSIONS: Inspired gas temperature drops as it passes through the circuit temperature probe site, the proximal end of the ETT and the exposed part of the ETT. The inspired gas rewarms on entering the model lung and exits the ETT at the desired temperature. The effect of measuring temperature closer to the patient, setting the circuit temperature higher and/or increasing the ambient temperature through which the circuit passes, need to be evaluated.

Abstract: The objective of this paper is to establish a reference range of central venous pressure (CVP) values during the first 4 days of life in very low birth weight (VLBW) infants. A prospective observational study with continuous monitoring of CVP in VLBW newborns who had an umbilical venous catheter (UVC) positioned in or near the right atrium is conducted. All UVCs were inserted as part of normal care of the infants. The mean CVP (mCVP) was monitored for 72 h from recruitment, or until the UVC was removed. The mean mCVP was calculated for each infant. The median of the mean mCVPs was then calculated. Data were analysed in 17 infants. The median gestational age was 27 weeks and median birth weight was 940 g. Sixteen were mechanically ventilated and of these, six also received continuous positive airway pressure (CPAP) during the study period. One infant received no respiratory support. One infant died during the study period. The lowest mean mCVP was 2.8 mmHg and the highest was 13.9 mmHg. The median mean mCVP was 4.9 mmHg (interquartile range 4.4-6.1). The normal range of CVP in VLBW infants during the first 4 days of life is wider than previously suggested.

Abstract: BACKGROUND: Perfluorocarbon (PFC) vapour in the expired gases during partial liquid ventilation should be prevented from entering the atmosphere and recovered for potential reuse.This study aimed to determine how much PFC liquid could be recovered using a conventional humidified neonatal ventilator with chilled condensers in place of the usual expiratory ventilator circuit and whether PFC liquid could be recovered when using the chilled condensers at the ventilator exhaust outlet. METHODS: Using a model lung, perfluorocarbon vapour loss during humidified partial liquid ventilation of a 3.5 kg infant was approximated. For each test 30 mL of FC-77 was infused into the model lung. Condensers were placed in the expiratory limb of the ventilator circuit and the amounts of PFC (FC-77) and water recovered were measured five times. This was repeated with the condensers placed at the ventilator exhaust outlet. RESULTS: When the condensers were used as the expiratory limb, the mean (+/- SD) volume of FC77 recovered was 16.4 mL (+/- 0.18 mL). When the condensers were connected to the ventilator exhaust outlet the mean (+/- SD) volume of FC-77 recovered was 7.6 mL (+/- 1.14 mL). The volume of FC-77 recovered was significantly higher when the condenser was used as an expiratory limb. CONCLUSION: Using two series connected condensers in the ventilator expiratory line 55% of PFC liquid (FC-77) can be recovered during partial liquid ventilation without altering the function of the of the ventilator circuit. This volume of PFC recovered was just over twice that recovered with the condensers connected to the ventilator exhaust outlet.

Abstract: Functional electrical impedance tomography (EIT) measures relative impedance change that occurs in the chest during a distinct observation period and an EIT image describing regional relative impedance change is generated. Analysis of such an EIT image may be erroneous because it is based on an impedance signal that has several components. Most of the change in relative impedance in the chest is caused by air movement but other physiological events such as cardiac activity change in end expiratory level or pressure swings originating from a ventilator circuit can influence the impedance signal. We obtained EIT images and signals in spontaneously breathing healthy adults, in extremely prematurely born infants on continuous positive airway pressure and in ventilated sheep on conventional mechanical or high frequency oscillatory ventilation (HFOV). Data were analyzed in the frequency domain and results presented after band pass filtering within the frequency range of the physiological event of interest. Band pass filtering of EIT data is necessary in premature infants and on HFOV to differentiate and eliminate relative impedance changes caused by physiological events other than the one of interest.

Abstract: BACKGROUND: Fetal pulse oximetry improves the assessment of fetal well-being during labor. The objective of this study was to evaluate women's satisfaction with their experience with this additional technology. METHODS: We surveyed women participating in the FOREMOST trial, a randomized controlled trial comparing the addition of fetal pulse oximetry (FPO) to conventional cardiotocograph (CTG) monitoring (intervention group), versus CTG-only (control group), in the presence of nonreassuring fetal status during labor. Our survey evaluated 3 aspects of women's experience: labor, fetal monitoring, and participation in the research. The survey was administered within a few days of giving birth and repeated 3 months later. RESULTS: No differences were found between the intervention and control groups for women's evaluations of their labor, fetal monitoring, research, or overall experiences when surveyed on both occasions. Within each study group, a small but statistically significant decline occurred in women's scores for their experience of labor and overall experience from the initial survey close to the time of giving birth, to 3 months later. The magnitude of differences in responses over time was similar for the both groups. Women were more satisfied after a spontaneous or assisted vaginal birth than after cesarean section. Length of time the research midwife was present had a significant positive effect on women's ratings of their experience several days after giving birth (p = 0.006), but no effect at 3 months. CONCLUSIONS: The addition of fetal pulse oximetry for the assessment of fetal well-being during labor did not affect childbearing women's perceptions of fetal monitoring or their labor. Women evaluated their experience in the research process positively overall. Small changes occurred in women's perception of their satisfaction over time.

Abstract: BACKGROUND: The loss of perfluorocarbon (PFC) vapour in the expired gases during partial liquid ventilation should be minimized both to prevent perfluorocarbon vapour entering the atmosphere and to re-use the recovered PFC liquid. Using a substantially modified design of our previously described condenser, we aimed to determine how much perfluorocarbon liquid could be recovered from gases containing PFC and water vapour, at concentrations found during partial liquid ventilation, and to determine if the amount recovered differed with background flow rate (at flow rates suitable for use in neonates). METHODS: The expiratory line of a standard ventilator circuit set-up was mimicked, with the addition of two condensers. Perfluorocarbon (30 mL of FC-77) and water vapour, at concentrations found during partial liquid ventilation, were passed through the circuit at a number of flow rates and the percentage recovery of the liquids measured. RESULTS: From 14.2 mL (47%) to 27.3 mL (91%) of the infused 30 mL of FC-77 was recovered at the flow rates studied. Significantly higher FC-77 recovery was obtained at lower flow rates (ANOVA with Bonferroni's multiple comparison test, p < 0.0001). As a percentage of the theoretical maximum recovery, 64 to 95% of the FC-77 was recovered. Statistically significantly less FC-77 was recovered at 5 Lmin(-1) (ANOVA with Bonferroni's multiple comparison test, p < 0.0001). Amounts of perfluorocarbon vapour recovered were 47%, 50%, 81% and 91% at flow rates of 10, 5, 2 and 1 Lmin(-1), respectively. CONCLUSION: Using two condensers in series 47% to 91% of perfluorocarbon liquid can be recovered, from gases containing perfluorocarbon and water vapour, at concentrations found during partial liquid ventilation.

Abstract: OBJECTIVE: The objective of the study was to compare operative delivery rates for nonreassuring fetal status between 2 groups of laboring women: those having conventional cardiotocograph monitoring and those having cardiotocograph monitoring plus fetal pulse oximetry. STUDY DESIGN: The intrapartum fetal oximetry prospective, multicenter, randomized, controlled trial (the FOREMOST trial) was conducted in 4 Australian maternity hospitals. The primary outcome was operative birth rates for nonreassuring fetal status. RESULTS: There was a statistically significant 23% relative risk reduction in operative delivery for nonreassuring fetal status in the fetal pulse oximetry + cardiotocograph group (n = 75 of 305, 25%), compared with those in the cardiotocograph-only group (n = 95/295, 32%) (relative risk 0.77, 95% confidence interval 0.599, 0.999, P = .048). There were no significant between-group differences in overall operative births (fetal pulse oximetry + cardiotocograph group 73%, cardiotocograph-only group 71%, relative risk 1.04, 95% confidence interval 0.94, 1.15, P = .478) or neonatal outcomes. CONCLUSION: The use of fetal pulse oximetry to augment fetal well-being assessment during labor resulted in a statistically significant reduction in the operative intervention for nonreassuring fetal status, compared with the use of conventional cardiotocograph monitoring alone. This reduction was achieved with no significant difference in neonatal outcomes.

Abstract: Smoke inhalation injuries are the leading cause of mortality from burn injury. Airway obstruction due to mucus plugging and bronchoconstriction can cause severe ventilation inhomogeneity and worsen hypoxia. Studies describing changes of viscoelastic characteristics of the lung after smoke inhalation are missing. We present results of a new smoke inhalation device in sheep and describe pathophysiological changes after smoke exposure. Fifteen female Merino ewes were anesthetized and intubated. Baseline data using electrical impedance tomography and multiple-breath inert-gas washout were obtained by measuring ventilation distribution, functional residual capacity, lung clearance index, dynamic compliance, and stress index. Ten sheep were exposed to standardized cotton smoke insufflations and five sheep to sham smoke insufflations. Measured carboxyhemoglobin before inhalation was 3.87 +/- 0.28% and 5 min after smoke was 61.5 +/- 2.1%, range 50-69.4% ( P < 0.001). Two hours after smoke functional residual capacity decreased from 1,773 +/- 226 to 1,006 +/- 129 ml and lung clearance index increased from 10.4 +/- 0.4 to 14.2 +/- 0.9. Dynamic compliance decreased from 56.6 +/- 5.5 to 32.8 +/- 3.2 ml/ cmH(2)O. Stress index increased from 0.994 +/- 0.009 to 1.081 +/- 0.011 ( P < 0.01) ( all means +/- SE, P < 0.05). Electrical impedance tomography showed a shift of ventilation from the dependent to the independent lung after smoke exposure. No significant change was seen in the sham group. Smoke inhalation caused immediate onset in pulmonary dysfunction and significant ventilation inhomogeneity. The smoke inhalation device as presented may be useful for interventional studies.

Abstract: Bioelectrical impedance measurements are widely used for the study of body composition. Commonly measurements are made at 50 kHz to estimate total body water or at low frequencies (<10 kHz) to estimate extracellular fluid volume. These measurements can be obtained as single measurements at discrete frequencies, or as fitted data interpolated from plots of measurements made at multiple frequencies. This study compared single frequency and multiple frequency (MF) measurements taken in the intensive care environment. MF bioimpedance (4-1000 kHz) was measured on an adult with and without cardiorespiratory monitoring, and on babies in the neonatal intensive care unit. Measurements obtained at individual frequencies were plotted against frequency and examined for the presence of outlying points. Fitted data for measurements obtained at 5 kHz and 50 kHz with and without cardiorespiratory monitoring were compared. Significant artefacts were detected in measurements at approximately 50 kHz and at integral divisions of this frequency as a result of interference from cardiorespiratory monitors. Single frequency measurements taken at these frequencies may be subject to errors that would be difficult to detect without the aid of information obtained from MF measurements.

Abstract: Perinatal asphyxia is an important cause of neonatal morbidity and mortality. There is the potential to halt cerebral damage if neural rescue strategies are applied within a short period of time after an insult. It is therefore important to be able to accurately identify neonates who may benefit from neural rescue therapies. Recent studies in asphyxiated neonates have correlated S100B and NSE with outcome; however, interpretation of these studies were difficult, as the timing of the measurements were not consistent. We measured NSE and S100 in 1-d-old piglets after a mild or severe hypoxic insult. Measurements were performed at 6-72 h after the insult and correlated with histologic outcome. There were no differences of the NSE or S100 concentrations between controls and the mild hypoxia group. After 24 h, there was a significant difference of NSE between the control/mild insult group and severe insult group. After 48 h, the S100 concentrations were significantly different between the control/mild insult group and the severe insult group. Both proteins showed good correlation at these time points with outcome as measured by histology score at 72 h. In conclusion, NSE and S100B measured in the serum of piglets after hypoxia increased significantly and correlated with outcome. This increase occurs too late to be used within the first 24 h but might be helpful for the clinician in determining the timing of an insult.

Abstract: Cerebral electrical impedance is useful for the detection of cerebral edema following hypoxia in newborn infants. Thus it may be useful for determining neurological outcome or monitoring treatment. Hypothermia is a promising new therapy currently undergoing trials, but will alter impedance measurements. This study aimed to define the relationship between temperature and both cerebral and whole body electrical impedance, and to derive correction factors for adjustment of impedance measurements during hypothermia. In eight anaesthetized 1-2 day old piglets rectal, tympanic and scalp temperatures were monitored continuously. Following baseline readings at a rectal temperature of 39 degrees C, piglets were cooled to 32 degrees C. Four piglets were re-warmed. Cerebral and whole body impedance were measured at each 0.5 degrees C as rectal temperature decreased. There was a strong linear relationship between both cerebral and whole body impedance and each of the temperatures measured. There was no difference in the relationship between impedance and rectal, tympanic or scalp temperatures. The relationship for impedance and rectal temperature was the same during cooling and re-warming. Using the correction factors derived it will be possible to accurately monitor cerebral and whole body fluid distribution during hypothermic treatment.

Abstract: The warming and humidification of inspired gases for ventilated neonates are routine. There are no data on the temperature of the gas at the airway opening in ventilated neonates. Is the inspired gas temperature at the airway opening, as expected and set on the humidifier, around 37 degrees C? We aimed to measure temperature at the airway opening and compare this with the circuit temperature. This was an observational study in a neonatal intensive care unit. Twenty-five mechanically ventilated infants were studied. All had humidifiers with chamber temperature set at 36 degrees C and the circuit temperature set at 37 degrees C. Two temperature probes were inserted and rested at the circuit-exit and at the airway opening, and temperatures were measured for 2 min in each infant. At this time, the circuit temperature was also noted. The mean (SD) temperature at the airway opening in infants nursed in incubators was 34.9 (1.2) degrees C, compared with radiant warmers where the mean (SD) was 33.1 (0.5) degrees C. The mean (SD) difference in temperature from the circuit temperature probe to the airway opening was greater under radiant warmers, with a mean (SD) drop of 3.9 (0.6) degrees C compared with a mean (SD) drop of 2.0 (1.3) degrees C in the incubators. In conclusion, the temperature at the circuit temperature probe does not reflect the temperature at the airway opening. Inspired gas temperatures are lower than the expected 37 degrees C with the normal circuits and usual humidifier settings.

Abstract: A simple mount capable of securely holding a variety of intracranial probes to the skull was constructed from commonly available clinical consumables. Using this device the cerebral cortical blood flow of preterm lambs was measured using a laser Doppler flow probe, and cerebral pH and cortical electrical impedance were measured in newborn piglets using pH electrodes and Ag/AgCl wire electrodes. In both studies, the mount held the various probes for periods up to 6 h with no dislodgement or probe failure. The simple mount presented here can be adapted to a wide variety of intracranial probes and will hold them securely to the skull.

Abstract: OBJECTIVE: To determine whether perfluorocarbon liquid can be condensed from gases containing perfluorocarbon vapour and whether the amount recovered varies with background flow rate. DESIGN AND SETTING: Bench-top experimental study in a neonatal laboratory. INTERVENTIONS: The expiratory limb of a standard ventilator circuit set-up was mimicked, with the addition of a chilled water jacket (Liebig) condenser. Perfluorocarbon vapour was passed through the circuit at a number of flow rates. MEASUREMENTS AND RESULTS: Perfluorocarbon vapour was passed through the circuit and the percentage recovery of liquid measured. More than 60% of the perfluorocarbon vapour was recovered at all flow rates (1, 2, 5 and 10 l/min), with significantly higher recovery obtained (up to 74%) at low flow rates (1 l/min). CONCLUSIONS: Using a simple condenser, more than 60% of perfluorocarbon liquid can be recovered without altering the function of an expiratory limb of a ventilator circuit.

Abstract: OBJECTIVE: We believed that intercostal catheters were often inserted too far into the thoracic cavity in neonatal patients. The aim of this study was to determine the average distance from the catheter tip to the midline, of intercostal catheters inserted in our neonatal unit and the incidence of catheters that were inserted too far into the thoracic cavity. METHODS: During a two year period we examined the chest X-rays of all infants who had an intercostal catheter inserted using an Argyle 10 French trocar thoracic catheter for drainage of a pneumothorax. For each initial chest X-ray following the insertion of the intercostal catheter we measured the horizontal distance in mm from catheter tip to the midline. The tip to midline distance was zero if the tip was at the midline and negative if it crossed the midline. To standardise the tip to midline distance for different size infants we measured the distance in 'inter-vertebral' units. RESULTS: During the two year period, 13 of 24 intercostal catheters (54%) crossed the midline (i.e. were inserted too far). The mean (+/- SD) tip to midline distance was -1.29 (+/- 13.9) mm with a range varying between -40 to 34 mm with a calculated 'inter-vertebral' units mean (+/- SD) tip to midline distance of -0.32 (+/- 1.9) range -4.6 to 4.0. CONCLUSIONS: Fifty four percent of the intercostal catheters inserted in our unit were inserted too far. As the distance markings on the Argyle intercostal catheters are marked from the last side-hole rather than from the tip of the catheter, Argyle intercostal catheters may be inadvertently inserted two centimetres further than they should be.

Abstract: Multi-frequency bio-impedance has the potential to identify infants at risk of poor neurodevelopmental outcome following hypoxia by detecting cerebral edema. This study investigated the relationship between the severity of an hypoxic/ischemic episode, neurological outcome following the hypoxia and non-invasively measured cerebral bioelectrical impedance in piglets. One-day-old piglets were anaesthetised and ventilated. Hypoxia was induced by reducing the inspired oxygen concentration to 3-5%. Severe hypoxia was defined as hypoxia resulting in at least 30 min of low amplitude EEG (<5 microV) as well as hypotension and acidosis. Cerebral bio-impedance was measured before, during and for up to 6 h post-hypoxia. Neurological outcome was determined by a neurology score at 24 and 48 h after hypoxia, and by histological examination of the brain at 72 h. There was no increase in cerebral impedance in control animals. Following mild hypoxia cerebral impedance increased transiently. Following severe hypoxia, cerebral impedance increased and remained elevated. Cerebral impedance following severe hypoxia was significantly higher than after mild hypoxia at 10 min and from 2 to 6 h after resuscitation. Cerebral impedance measurements made up to 1 h and between 3 and 6 h after resuscitation were significantly correlated with neurological outcome. Results indicate that non-invasive cerebral impedance measurements are able to discriminate early between those individuals who have suffered a mild, acute hypoxic episode, and those who have suffered a severe hypoxic episode. The technique has the potential to predict which individuals will have a poor neurological outcome.

Abstract: The association of sustained cerebral edema with poor neurological outcome following hypoxia-ischaemia in the neonate suggests that measurement of cerebral edema may allow early prediction of outcome in these infants. Direct measurements of cerebral impedance have been widely used in animal studies to monitor cerebral edema, but such invasive measurements are not possible in the human neonate. This study investigated the ability of noninvasive cerebral impedance measurements to detect cerebral edema following hypoxia-ischaemia. One-day-old piglets were anaesthetized, intubated and ventilated. Hypoxia was induced by reducing the inspired oxygen concentration to 4-6% O(2). Noninvasive cerebral bioimpedance was measured using gel electrodes attached to the scalp. Cerebral bioimpedance was also measured directly by insertion of two silver-silver chloride electrodes subdurally. Noninvasive and invasive measurements were made before, during and after hypoxia. Whole body impedance was measured to assess overall fluid movements. Intracranial pressure was measured continuously via a catheter inserted subdurally, as an index of cerebral edema. There was good agreement between noninvasive and invasive measurements of cerebral impedance although externally obtained responses were attenuated. Noninvasive measurements were also well correlated with intracranial pressure. Whole body impedance changes did not account for increases in noninvasively measured cerebral impedance. Results suggest that noninvasive cerebral impedance measurements do reflect intracranial events, and are able to detect cerebral edema following hypoxia-ischaemia in the neonate.

Abstract: OBJECTIVE: To establish the CO2 dispersion and retention properties of some mattresses and bed coverings commercially available in Australia. METHODS: Five mattresses were studied in (i) an in vivo model in which an infant's head was covered by a headbox, rebreathing was allowed to occur, and the final steady state CO2 concentration was measured; and (ii) an in vitro model in which 5% CO2 in a headbox was allowed to disperse, and the time taken for the concentration to reach 1% was measured. Five types of bedcover were studied in (i) an in vivo model in which an infant's head was covered by a bedcover and the final steady state CO2 concentration was measured; and (ii) an in vitro model in which 5% CO2 under a bedcover was allowed to disperse, and the time taken for the concentration to reach 1% was measured. RESULTS: The steady state CO2 concentrations ranged from 0.6% to 3.0% for the mattresses (P < 0.05). The time for CO2 to disperse ranged from 5.5 min to 30.4 min (P < 0.05). Steady state CO2 concentrations ranged from 2.5% to 3.6% for the bedcoverings (P > 0.05). The time for CO2 to disperse ranged from 5.4 min to 7.7 min (P > 0.05). CONCLUSIONS: Some commercial cot mattresses and bedcoverings allow high concentrations of CO2 to accumulate in rebreathing environments. Some mattress types studied were more diffusive to CO2, whereas there was no difference between the bedcovers studied. This may have implications for vulnerable infants at risk of sudden infant death syndrome.

Abstract: OBJECTIVES: To examine the fate of research presented at the first annual Perinatal Society of Australia and New Zealand (PSANZ) Congress in 1997, by determining: the rate of publication in peer-reviewed biomedical journals; publication rate by discipline; journals in which work was published; concordance for aims, conclusions, authors and number of study subjects; and time from presentation to publication. METHODS: A MEDLINE search was conducted for any publication in a peer-reviewed journal resulting from a publishable abstract from the proceedings of the first annual PSANZ Congress in 1997. Searching was completed 42 months post-congress. The concordance of aims, conclusions, authors and number of subjects between abstract and published paper was determined. RESULTS: There were 172 publishable abstracts in the proceedings of the PSANZ Congress in 1997, and 78 (45%) were published as 83 articles. Basic sciences had the highest publication rate (67%) and midwifery the lowest (20%). Articles were published in 41 journals, with one-third of the articles in three paediatric journals. There was a match with aims in 75%, and with conclusions in 65%. There were 47/77 with the same number of subjects, 20/77 with more and 10/77 with fewer. There were 22 articles with one author added, 12 had more than one author added, 11 had one author removed and five had more than one author removed. Median time-to-publication was 18 months (interquartile range 9-26 months). CONCLUSIONS: A publication rate of 45% is comparable to other conferences. Basic science and neonatology had the highest publication rates. There were considerable differences between abstract and published article in terms of aims, conclusions, number of subjects and authors.

Abstract: OBJECTIVE: To compare measured tidal volumes with and without perfluorocarbon (perfluorooctyl bromide) vapor, by using tidal volumes in the range suitable for neonates ventilated with partial liquid ventilation. We also aimed to determine the correction factor needed to calculate tidal volumes measured in the presence of perfluorooctyl bromide vapor. DESIGN: Prospective, experimental study. SETTING: Neonatal research laboratory. INTERVENTIONS: Reproducible tidal volumes from 5 to 30 mL were produced with a rodent ventilator and drawn from humidifier chambers immersed in a water bath at 37 degrees C. Control tidal volumes were drawn from a chamber containing oxygen and water vapor, and the perfluorocarbon tidal volumes were drawn from a chamber containing oxygen, water vapor, and perfluorooctyl bromide vapor. MEASUREMENTS AND MAIN RESULTS: Tidal volumes were measured by a VenTrak respiratory mechanics monitor with a neonatal flow sensor and a Dräger pneumotachometer attached to a Dräger neonatal ventilator. All tidal volumes measured with perfluorooctyl bromide vapor were increased compared with control. The VenTrak-measured tidal volumes increased by 1.8% to 3.5% (an overall increase of 2.2%). The increase was greater with the Dräger hot-wire anemometer: from 2.4% to 6.1% (an overall increase of 5.9%). Regression equations for mean control tidal volumes (response, Y) vs. mean perfluorooctyl bromide tidal volumes (predictor, X) are as follows: for the VenTrak, Y = -0.026 + (0.978 x X), r =.9999, p <.0001; and for the Dräger, Y = 0.251 + (0.944 x X), r =.9996, p <.0001. CONCLUSIONS: The presence of perfluorooctyl bromide vapor in the gas flowing through pneumotachometers gives falsely high tidal volume measurements. An estimate of the true tidal volume allowing for the presence of perfluorooctyl bromide vapor can be made from regression equations. Any calculation of lung mechanics must take into account the effect of perfluorooctyl bromide vapor on the measurement of tidal volume.

Abstract: The purpose of this study was to develop a newborn piglet model of hypoxia/ischaemia which would better emulate the clinical situation in the asphyxiated human neonate and produce a consistent degree of histopathological injury following the insult. One-day-old piglets (n=18) were anaesthetised with a mixture of propofol (10 mg/kg/h) and alfentinal (55.5 microg/kg/h) i.v. The piglets were intubated and ventilated. Physiological variables were monitored continuously. Hypoxia was induced by decreasing the inspired oxygen (FiO(2)) to 3-4% and adjusting FiO(2) to maintain the cerebral function monitor peak amplitude at < or =5 microV. The duration of the mild insult was 20 min while the severe insult was 30 min which included 10 min where the blood pressure was allowed to fall below 70% of baseline. Control piglets (n=4 of 18) were subjected to the same protocol except for the hypoxic/ischaemic insult. The piglets were allowed to recover from anaesthesia then euthanased 72 h after the insult. The brains were perfusion-fixed, removed and embedded in paraffin. Coronal sections were stained by haematoxylin/eosin. A blinded observer examined the frontal and parietal cortex, hippocampus, basal ganglia, thalamus and cerebellum for the degree of damage. The total mean histology score for the five areas of the brain for the severe insult was 15.6+/-4.4 (mean +/-S.D., n=7), whereas no damage was seen in either the mild insult (n=4) or control groups. This 'severe damage' model produces a consistent level of damage and will prove useful for examining potential neuroprotective therapies in the neonatal brain.

Abstract: Sudden infant death syndrome (SIDS) is more prevalent in infants of smokers and may involve subtle alterations in autonomic control mechanisms. Autonomic function can be assessed using blood pressure responses to a passive head-up tilt and power spectral analysis of heart rate variability. This study aimed to determine if maternal smoking altered infants' responses to head-up tilt. Blood pressure and heart rate responses to a passive 70 degrees head-up tilt were compared in infants of smokers and non-smokers at 2-3 days and 3 months of age. There were no significant differences between groups in power spectral indices. At 2-3 days, the systolic pressure response to tilt was significantly different between groups (P<0.01). In infants of smokers, systolic pressure decreased by a mean (S.E.) of 7.7(1.1) mmHg, whereas in control infants it remained unchanged. At 3 months, systolic pressure in infants of smokers remained unchanged but increased in control infants by 6.2(2.1) mmHg (P<0.05). These results indicate that maternal smoking alters autonomically mediated cardiovascular responses in the infant.

Abstract: OBJECTIVE: To evaluate whether cardiac responses to a level of hypoxic hypercapnia that may be observed in rebreathing studies are altered with infant sleep position. METHODOLOGY: Eighteen healthy term infants (< 5-days-old) were studied. Heart rate (HR) and HR variability were monitored during air breathing and during 3 min exposure to a mixture of 15% O2/3% CO2 in both the prone and supine positions. Power spectral analysis of HR was performed. RESULTS: Heart rate was the only measured variable to be significantly changed in response to 15% O2/3% CO2. Hypoxic hypercapnia elicited no significant responses in power spectral HR variables. There was no effect of sleeping position on any of the measured variables. CONCLUSIONS: There are no significant differences in cardiac responses to mild hypoxic hypercapnia between sleep positions and power spectral indices of the autonomic control of HR are not altered by sleep position in newborn babies.

Abstract: During partial liquid ventilation perfluorocarbon vapour is present in the exhaled gases. The volumes of these gases are measured by pneumotachometers. Error in measuring tidal volumes will give erroneous measurement of lung compliance during partial liquid ventilation. We aim to compare measured tidal volumes with and without perfluorocarbon vapour using tidal volumes suitable for use in neonates. Tidal volumes were produced with a 100 ml calibration syringe from 20 to 100 ml and with a calibrated Harvard rodent ventilator from 2.5 to 20 ml. Control tidal volumes were drawn from a humidifier chamber containing water vapour and the PFC tidal volumes were drawn from a humidifier chamber containing water and perfluorocarbon (FC-77) vapour. Tidal volumes were measured by a fixed orifice, target, differential pressure flowmeter (VenTrak) or a hot-wire anenometer (Bear Cub) placed between the calibration syringe or ventilator and the humidifier chamber. All tidal volumes measured with perfluorocarbon vapour were increased compared with control (ANOVA p < 0.001 and post t-test p < 0.0001). Measured tidal volume increased from 7 to 16% with the fixed orifice type flow-meter, and from 35 to 41% with the hot-wire type. In conclusion, perfluorocarbon vapour flowing through pneumotachometers gives falsely high tidal volume measurements. Calculation of lung compliance must take into account the effect of perfluorocarbon vapour on the measurement of tidal volume.

Abstract: Objective To determine the effects of maternal smoking on the fetal heart rate response to a vibroacoustic stimulus (VAS). Methods A cardiotocograph was used to record fetal heart rate (FHR). A 5-s VAS was administered to 34 fetuses of non-smoking (control) and 25 fetuses of smoking mothers at 37 weeks' gestation. Changes in FHR, fetal heart rate variability (FHRV), low (0.04-0.15 Hz) and high (0.15-0.3 Hz) frequency spectral power, and the low to high frequency power spectral ratio (LF: HF) were determined. Results In response to VAS, FHR increased significantly more in control fetuses (p = 0.007), compared to fetuses of smokers (mean +/- SEM change, 5.1 +/- 1.2 beats/min vs. 0.04 +/- 1.3 beats/min). The stimulus caused a significant increase in long-term variability (LTV) of 8.3 +/- 2.2 ms in control fetuses and 7.1 +/- 2.2 ms in fetuses of smokers, but this response was not significantly different between the groups. There was no statistically significant difference after the VAS or between groups in the short-term variability (STV), in the spectral power in either band or in LF: HF. Conclusion Smoking during pregnancy attenuates the fetal heart rate response to VAS. Power spectral indices of fetal autonomic activity were not significantly altered by maternal smoking.

Abstract: Variability is inherent in all physiologic signals. This variability provides valuable clinical information or may confound physiologic measurements and the interpretation of results. Both physiologic and nonphysiologic factors may affect variability. Clinicians and researchers need to be aware of physiologic variability and its implications.

Abstract: Anetoderma in premature infants is an uncommon lesion that may be associated with the use of various types of monitoring leads. In 2 infants multiple papules of anetoderma occurred on the forehead in association with the use of gel electrocardiographic electrodes. It is postulated that the cause of these papules was a local hypoxemia caused by pressure from the electrodes. Growth-restricted infants may be particularly predisposed to iatrogenic anetoderma.

Abstract: Fetal oxygen saturation (FSpO2) was monitored with the Nellcor Puritan Bennett N400/FS14 system during 16 labors to establish whether FSpO2 was influenced by maternal bearing down efforts in the second stage of labor. Fetal SpO2 is reported for 16 fetuses where neonatal outcome was normal. One hour of continuous data was recorded: 30 min prior to the onset of maternal bearing down efforts and the first 30 min of pushing. The hour was divided into six epochs of 10-min duration. Differences between mean FSpO2 for the two 30 min of monitoring and for each epoch were sought using repeated measures analysis of variance (ANOVA). The mean FSpO2 for the total 30 min prior to the onset of pushing was 49% (95% confidence intervals 46.5-50.6%), compared to a mean of 46% (95% confidence intervals 43.6-48.7%) during the first 30 min of pushing [F (1, 2.25), p = 0.14]. There was no significant decline in mean FSpO2 for each epoch. Apgar scores at 5 min were all > 7 and umbilical arterial pH values were > or = 7.20 (n = 12). We concluded that mean FSpO2 recorded prior to the onset of maternal bearing down efforts was not significantly different to mean FSpO2 during pushing, with normal neonatal outcome.

Abstract:

Abstract: Oxygen availability to the fetus during uterine contractions has not been widely reported. We examined whether fetal oxygen saturation (FSpO2) values and signal quality (SQ) were affected by uterine contractions. An intrauterine pressure catheter and a Nellcor FS14 fetal oxygen saturation sensor (Nellcor Puritan Bennett Inc., Pleasanton, CA) were placed transvaginally during the first stage of 17 labors. Fetal SPO2 and SQ units were recorded on a beat-to-beat basis and 10 sec averages of the data calculated over 25 contractions per patient. Five epochs were determined: (1) 30 sec prior to a contraction; (2) during a contraction; (3) 50 sec following completion of a contraction; (4) noncontraction periods, excluding epochs 1 or 3; and (5) equivocal, that is, overlap of epochs 1-3. Mean FSpO2 was lowest during epoch 3 (45.0) and highest during epoch 2 (47.3%) (p <0.001). This small difference is unlikely to be of any clinical significance, however. Mean signal quality was lowest in epoch 1 (42.8 units) and highest in epoch 4 (48.0 units) (p <0.05), that is, in noncontraction periods. We conclude that FSpO2 and SQ were unaffected by uterine contractions.

Abstract: Fetal oxygen saturation (FSpO2) was recorded during labour to determine the relationship between FSpO2 and indicators of fetal well-being, including umbilical blood gases, xanthine (X), hypoxanthine (Hx) and Apgar scores. This is one of the largest reported series of fetal pulse oximetry, with 118 fetuses monitored for over 329 hours. Mean FSpO2 for all cases was 46.9% (SD = 9.1%). There was no correlation between FSpO2 during the last 10 minutes of monitoring and arterial pH, Hx or X. A mean FSpO2 > or = 30% was associated with a 5 minute Apgar score of > or = 7 in the majority of cases. One fetus had a mean FSpO2 < 30% during the final 10 minutes of monitoring and an umbilical arterial pH < 7.20, while there were 10 fetuses with an umbilical arterial pH < 7.20, and mean FSpO2 > or = 30%. As these numbers are small, a larger series is necessary to further characterize the small number of fetuses who are significantly hypoxic.

Abstract: OBJECTIVE: Our purpose was to assess the level of agreement between oxygen saturation values obtained from two identical sensors used on different sides of the face of the same human fetus during labor. STUDY DESIGN: Two identical fetal pulse oximeter sensors were placed on 12 fetuses during uncomplicated labor at < or = 38 weeks' gestation. Oxygen saturation, fetal heart rate, and uterine activity were recorded. The agreement between synchronous values of oxygen saturation was assessed by calculating the mean difference and SD of the difference. The SD of a single sensor was estimated as the SD of the difference divided by the square root of 2. RESULTS: The mean oxygen saturation value returned from one sensor was 49.2% and from the other 49.9%; the mean difference was -0.7%. The SD of the difference was 7.5%, and the 95% limits (+/- 2 SDs of the difference) were -15.5% to 14.1%. The SD from a single sensor was estimated as 5.3%. CONCLUSIONS: There was no clinically significant difference between the oxygen saturation values returned from two identical sensors on the one fetus. The magnitude of the SD from a single sensor must be taken into account when an arbitrary "cutoff" or "action" oxygen saturation value in a clinical setting or trial is defined.

Abstract: Infusion of fluids and drugs at very low rates may be necessary in neonatal intensive care. Marked haemodynamic fluctuations occurring during the infusion of inotropes have been shown to be due to the sticking of the plunger in the barrel of syringes used in syringe drivers. The Australian Therapeutic Goods Administration has recommended the use of volumetric or peristaltic pumps in these circumstances. We tested a number of infusion systems and found that 1. some syringes give continuous flow at low rates, and would be suitable for the delivery of inotropes, and 2. some infusion pumps provide non-continuous flow at low rates, and would not be satisfactory for the infusion of inotropes.

Abstract: Flow continuity of two brands of syringe pumps and four brands of syringes was studied as a possible cause of hemodynamic fluctuations observed in neonates. Cyclical fluctuations were observed in the blood pressure of 14 neonates receiving dopamine infusions by syringe pump at flow rates from 0.2 to 1 mL/hr. Atom 235 and IVAC 770 pumps and various sizes of Terumo, Becton Dickinson, Omnifix, and IVAC syringes were evaluated. Flow continuity was assessed by using a gravimetric technique. The force needed to initiate and maintain syringe plunger motion was also measured. Noncontinuous flow was encountered most commonly with Terumo syringes, which delivered boluses at regular intervals at flow rates up to 5 mL/hr. The interval was dependent on flow rate and was similar to the time between the blood pressure fluctuations observed clinically. The syringe plunger force exhibited regular fluctuations indicative of the plunger sticking, and simultaneous measurement of flow established a direct temporal relationship with boluses. The other syringes tested did not exhibit such fluctuations. No differences were found between the two syringe pumps. Syringe plunger sticking, resulting in intermittent boluses and potential blood pressure fluctuations, may occur at low flow rates and with certain syringe brands. This appeared to be the cause of hemodynamic fluctuations in neonates receiving dopamine infusions.

Abstract:

Abstract: The stability constants for the 1:1 complexes of zinc, cadmium and mercury with 1,4,7,10-tetraoxa-13-azacyclopentadecane (L1), 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (L2) and 1,4,7-trioxa-10-azacyclododecane (L3) have been determined potentiometrically (0.1 M NEt4ClO4, 95% methanol). Reaction between L1 or L2 and cadmium nitrate tetrahydrate in methanol results in the isolation of colourless crystalline solids. Crystals of [Cd(L1)(NO3)2] are monoclinic, space group P2(1)/c with a = 7.614(2), b = 28.566(2), c = 7.707(l) angstrom, beta = 107.364(9)-degrees; R = 0.025, R(w) = 0.027 for 2195 (I > 3sigma(I)) reflections. The structure of [Cd(L1)(NO3)2] consists of an almost planar macrocyclic ligand enclosing a cadmium ion in its cavity, with a monodentate and a bidentate nitrate ligand coordinating the cadmium ion on opposite sides of the macrocycle. Crystals of [Cd(L2)(NO3)2] are orthorhombic, space group Pca2(1) with a = 8.738(11), b = 14.140(9), c = 15.176(8) angstrom; R = 0.019, R(w) = 0.022 for 3058 (I > 2.5sigma(I)) reflections. The structure of [Cd(L2)(NO3)2] consists of a cadmium atom enclosed in the cavity of the macrocycle, with a monodentate and a bidentate nitrate ligand on opposite sides of the macrocycle. Two of the oxygen atoms of L2 in [Cd(L2)(NO3)2] do not coordinate the cadmium ion, but the remaining donor atoms of the macrocycle form an almost planar assembly around the cadmium.

Abstract: Lead(II) complexes of the 15- and 18-membered ring macrocycles 1,4,7,10-tetraoxa-13-azacyclopentadecane (L1) and 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (L2) have been prepared. The stability constants for the 1 : 1 lead complexes [L1, log beta-6.0(1); L2, log beta-8.4(1)] have been determined potentiometrically (0.1 M NEt4ClO4, 95% methanol). The complexes [Pb(L1)(NO3)2] and [Pb(L2)(NO3)2] have been examined by C-13 NMR spectroscopy and single-crystal X-ray structural analysis. In the molecule [Pb(L1)(NO3)2] the lead(II) cation is situated 1.52 angstrom above the plane of the macrocyclic ring. The Pb-N(1) distance of 2.465(5) angstrom is the shortest bond to lead(II) in the structure which also exhibits two short [2.627(4) and 2.643(4) angstrom] and two long [2.909(4) and 2.992(5) angstrom] Pb-O(macrocycle) distances. The presence of a stereoactive lone pair of electrons on the cation is inferred from this stereochemistry. In [Pb(L2)(NO3)2] the lead(II) cation lies in the macrocyclic cavity. As for [Pb(L1)(NO3)2], the Pb-N(1) distance of 2.539(9) angstrom is the shortest bond to lead in this structure, which has in addition two short [2.694(7) and 2.697(8) angstrom] and three long [2.877(10), 2.951(6) and 2.999(9) angstrom] Pb-O(macrocycle) interactions. There is no evidence for a stereoactive lone pair of electrons in this structure.

Abstract: The mercury(II) complexes of the fifteen- and eighteen-membered ring macrocycles 1,4,7,10,-tetraoxa-13-azacyclopentadecane (L1); 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (L2) and 16-methyl-1,4,7,10,13-pentaoxa-16-azacyclooctadecane (L3) have been prepared. The complexes {[HgCl(mu-Cl)(L1)][Hg(mu-Cl)2]}n, [Hg((L2)Cl2] and [Hg(L3)Cl2] have been characterised by single crystal X-ray structural analysis. {[HgCl(mu-Cl)(L1)][Hg(mu-Cl)2]}n crystallises in the orthorhombic space group Pbca, with a=7.498(1), b=15.201(1), c=32.575(2) angstrom, U=3713(2) angstrom3, Z=8, D(c)=2.727 g cm-3, With R 0.039, R(w) 0.040. The structure consists of a polymeric chain of five-coordinate mercury atoms [Hg(mu-Cl)2] bearing [HgCl(mu-Cl)(L1)] substituents. One mercury atom is located above the plane of the macrocyclic ligand L1; bond lengths Hg-N 2.145(10), Hg-O 2.664(10)-2.806(9) angstrom. Two Cl ligands are located on the same side of the folded macrocyclic ring, Hg(1)-Cl(1) and Hg(1)-Cl(2) 2.291(4) and 3.129(4) angstrom, respectively, Cl(1)-Hg(1)-Cl(2) 102.37(13)-degrees. [Hg(L2)Cl2] crystallises in the monoclinic space group P2(1)/c, with a=7.648(1), b=7.858(1), c=15.366(3) angstrom, beta=92.462(8)-degrees, U=922.6(3) angstrom3, Z=2, D(c)=1.925 g cm-3 with R 0.029, R(w) 0.032. The mercury atom is eight-coordinate and is located at an inversion centre; bond lengths Hg-Cl 2.327(2), Hg-N/O(1) 2.748(8), av. Hg-O distance 2.856 angstrom; the Cl(1)-Hg-Cl(1a) angle was 180-degrees. [Hg(L3)Cl2] crystallises in the monoclinic space group C2/c, with a=11.751(4), b=10.504(3), c=31.38(2) angstrom, beta=91.92-degrees, U=3871(2) angstrom3, Z=8, D(c)=1.884 g cm-3 and R 0.027, R(w) 0.031. The metal ion is eight-coordinate (five oxygen, one tertiary amine and two chloride donors); there are two short (2.767(5), 2.753(6) angstrom), and three longer (2.961(6), 2.968(6), 2.922(6) angstrom) Hg-O bond lengths, with Hg-N 2.739(6) and Hg-Cl 2.327(2) angstrom. The Cl(1)-Hg(1)-Cl(2) angle was 174.07(8)-degrees.