Oxygen Saturation Limits Research Articles

Variability in Practice and Implementation of Oxygen Target Saturation Policies in United States' Neonatal Intensive Care Units.

This study aimed to describe target oxygen saturation (SpO2) ranges used for premature infants in United States' neonatal intensive care units (NICUs) and to describe if these target SpO2 ranges have changed in recent years. A 29-question survey focused on target SpO2 practices and policies was distributed via the NICU medical directors listservs for the American Academy of Pediatrics Section of Neonatal-Perinatal Medicine and Pediatrix Medical Group between August and October of 2021. Results were collected via Research Electronic Data Capture (REDCap). We received responses representing 170 unique, levels 2, 3, and 4 NICUs from 36 states. Most NICUs (130, 78%) have recently changed their SpO2 targets in response to target SpO2 clinical trials. Over time, the most commonly reported target SpO2 range has shifted from 88-92% to 90-95. Of NICUs that changed limits, the most common lower SpO2 limits increased from 88 to 90% and the upper SpO2 limits changed from 92 to 95%. The interquartile range for lower SpO2 limit shifted from 85-88% to 88-90% and the IQR for upper SpO2 limit decreased from 92-95 to 94-95%. Most NICUs had designated conditions that would allow for deviations from standard target SpO2 ranges. These most commonly include pulmonary hypertension (152, 95%), severe bronchopulmonary dysplasia (81, 51%), and retinopathy of prematurity (51, 32%). Oxygen saturation limits have changed over time with an overall increase in targeted SpO2. However, there remains considerable interunit variation in SpO2 policies. There is a need to achieve consensus to optimize clinical outcomes. · What are the SpO2 ranges in United States' NICUs?. · There is a shift in SpO2 ranges for preterm infants in NICUs across United States.. · Variability still persists in SpO2 ranges for preterm infants in United States' NICUs..

Supplemental oxygen strategies in infants with bronchopulmonary dysplasia after the neonatal intensive care unit period: study protocol for a randomised controlled trial (SOS BPD study)

IntroductionSupplemental oxygen is the most important treatment for preterm born infants with established bronchopulmonary dysplasia (BPD). However, it is unknown what oxygen saturation levels are optimal to improve outcomes in...

Availability and use of continuous positive airway pressure (CPAP) for neonatal care in public health facilities in India: a cross-sectional cluster survey

ObjectivesTo determine the availability of continuous positive airway pressure (CPAP) and to provide an overview of its use in neonatal units in government hospitals across India.SettingCross-sectional cluster survey of a...

The Availability and Quality of Continuous Positive Airway Pressure (CPAP) for Neonatal Care in Public Health Facilities in India: A Cross- Sectional Cluster Survey

Background: Continuous Positive Airway Pressure (CPAP) is increasingly used in low- and middle-income setting to manage respiratory distress in neonates. Methods: National cross-sectional cluster survey of neonatal care units (SNCU) in 79 medical colleges (MC) and 63 district hospitals (DH) to assess availability, use, and, outcomes of CPAP. Findings: 68·3% of MC and 36·6% of DH used CPAP. Basic infrastructure was widely available. Air-oxygen blenders were available in 50·7% (95%CI 41·4,60·9) of hospitals. Equipment needed for monitoring and/or the detection and management of complications was not always in place; screening for retinopathy in 89·9%(77·2,95·9) MC and 60·3%(44·0,75·6) DH, treatment for retinopathy in 44·3%(30·9,58·5) MC and 7·9%(2·9,20·0) DH, screening for bronchopulmonary dysplasia in 62·0%(49·0,73·5) MC and 22·2%(12·5,36·3) DH, management of pneumothorax in 63·3%(49·8,74·9) of MC and 20·6%(9·8,38·3) of DH. Medical staff trained in the use of CPAP was available in 56·0%(45·8,65·8) of hospitals. The nurse:patient ratio was 7·3(95% CI 6·4-8·5) in MC and 6·6 (5·5-8·3) in DH. 72% MC and 59·3% DH used an upper oxygen saturation limit of above 94%. Respiratory circuits were reused in 52·8% of hospitals. Case Fatality Rates for neonates admitted to a SNCU were 11·5%(9·7,13·3) [13·2%(10·7,15·7) at MC and 7·4%(5·7,9·1) at DC] and 21·4%(16·6,26·2) for neonates receiving CPAP [19·8%(14·6,24·9) MC; 26·3%(15·7,37·0) DH]. Complication rates ranged from 27·9%(21·2,34·5) for rescue mechanical ventilation and 0·7%(0·2,1·2) for pneumothorax. Interpretation: Further support to infrastructure, training, and revision of current guidelines is urgently needed to improve the quality of care and ensure successful scale up of CPAP. Funding Statement: World Health Organization (Reference:2016/613341-0) Declaration of Interests: The authors have no competing interests to declare. Ethics Approval Statement: The study was approved by the Ministry of Health and Family Welfare of India (Child Health Division) and by the Liverpool School of Tropical Medicine’s Research and Ethics Committee (Research protocol 15·032).

Abstract P-419: THE UPPER SATURATION LIMIT IN PAEDIATRIC INTENSIVE CARE PATIENTS: A ZOMBIE PROBLEM

Aims & Objectives: Excessive oxygen can be detrimental to children requiring intensive care. However, reducing the oxygen saturation goal is not part of standard PIC culture. Oxygen is felt to be a therapy which does little harm and is beneficial for most pathologies, however evidence is mounting that excess oxygen is harmful. We investigated the set oxygen saturation limits on our patients and intervened to set them lower. Methods For one week, all monitored patients on the Critical Care unit requiring additional oxygen were analysed. Their monitor saturation limits were noted. Without informing the bedside team, the upper saturation limits were set to 98% (or 90% for a complex cardiac patient), unless the saturation limit was already below this. The following day, the same procedure was performed. Results Of 49 measurements, 38 had the upper limit set to “off” or 100%. 16/17 first measurements in an individual patient were at 100% of “off”. After setting the limit to the patient’s target, only 10/32 had an upper limit at target or less the next morning, 1/32 had an upper limit of 99%, and the 21/32 had been reset to “off” or 100%. Reasons given by the bedside nurses included alarm fatigue and a lack of medical directives.Conclusions In the complex Paediatric Intensive Care environment, there are significant behavioural drivers towards keeping the upper saturation limit off. Alarm fatigue is a real and dangerous problem, leading to substandard care if it is nor addressed. More education is necessary for teams to prioritise the correct oxygen saturations limits.

Gill structural change in response to turbidity has no effect on the oxygen uptake of a juvenile sparid fish.

Turbidity as a result of increased suspended sediments in coastal waters is an environmental stress of worldwide concern. Recent research on fish suggests that detrimental changes to gill structure can occur in turbid waters, with speculation that these alterations diminish fitness variables, such as growth and development, by negatively impacting the O2 uptake capacity (respiration) of fish. Specifically to address this unknown, the impact of turbid water on the gill structure, somatic growth rate and O2 uptake rates of a juvenile sparid species (Pagrus auratus) was addressed following exposure to five different turbidity treatments (<10, 20, 40, 60 or 80 nephelometric turbidity units) for 30 days. Significant gill structural change was apparent with a progressive increase in turbidity and was quantified as a reduction in lamellar density, as well as an increase in basal hyperplasia, epithelial lifting and increased oxygen diffusion distance across the lamellae. The weight of control fish did not change throughout the experiment, but all fish exposed to turbid waters lost weight, and weight loss increased with nephelometric turbidity units, confirming that long-term turbidity exposure is detrimental to growth productivity. The growth of fish could be impacted in a variety of ways, but the specific hypothesis that structural alteration of the gills impairs O2 uptake across the gills and limits growth fitness was not supported because there was no measurable difference in the standard metabolic rate, maximal metabolic rate, aerobic metabolic scope or critical oxygen saturation limit of fish measured in clear water after 30 days of exposure. Although impaired O2 uptake as a result of structurally adjusted gills is unlikely to be the cause of poor fish growth, the exact mechanism by which growth productivity is affected in turbid conditions remains unclear and warrants further investigation.

G530(P) To give oxygen or not? are we adhering to local guidelines on administering targeted oxygen therapy to our neonatal population?

Context This “spot audit” was carried out in a level 3 neonatal unit. Problem Supplementary oxygen therapy is a vitial to the vulnerable neonate. We know that in excess, oxygen can be toxic, contributing to retinopathy of prematurity (ROP). The recent BOOST 2 study has made clinicians rethink what our oxygen saturation limits should be. However, given the increased mortality in those with lower saturation limits, the exact limit remains controversial. The aim of this “spot audit” was simply to determine whether we were adhering to our local guidelines regarding oxygen saturation targeting. Assessment of problem and analysis of its causes This audit was carried out on a weekly basis. The initial few weeks, before any change, ensured that we obtained baseline numbers. The staff were aware that the audit project was being carried out. We quickly identified that there was a need to intervene and a discussion was had with ward sisters. We identified that nurses were key to ensuring that the limits on the saturation monitors were set correctly. Intervention We realised that verbal communication/education alone would be insufficient to increase our compliance. A visual aid, or quick reference card, was developed. This briefly summarised our protocol, i.e. what the saturation limits should be for neonates, based on their risk of ROP. This was produced in a size which ensured that it could be attached to the saturation monitors. Study design A initial prospective audit was carried out over a period of 8 weeks. information regarding risk of ROP and whether or not stauration limits were achieved was collected on a proforma. When possible, I would then refer to the neonates case notes and/or speak to nursing staff caring for them to determine why the monitors may have been set differently to protocol, i.e. medical decision or in error. 2 years after the initial audit, we’ve reaudited the same thing to determine if compliance has been maintained. Strategy for change Initially discussions were had with the ward sister regarding the audit project, but it became apparent that there was a lack of awareness of our local protocol. The quick reference card was produced on a home computer. Medical physics (who ensure up keep of our saturation monitors) were given additional copies of the visual aid. I presented the inital results at a local quality improvement evening. Measurement of improvement Percentages were used to demonstrate compliance. This ensured that all staff could easily interpret the results obtained. During the initial four weeks of the audit, our compliance with our local guideline, regarding oxygen saturation targets within the neonatal population, ranged from 43–70%. After the introduction of the quick reference card, our compliance was 79–94%. We re-audited this recently and our compliance is sustained at 92%. In the majority of cases, the reasons for non compliance included no quick reference card on the saturation monitor! Effects of changes Our change has increased compliance with local guidelines and ensures that oxygen therapy is being targeted appropriately in the majority of cases. It has also increased staffs awareness of the importance of targeted oxygen therapy. Lessons learnt This simple regular audit process can be applied within any healthcare setting. The simplicity of the concept makes it easily reproducibile. Furthermore, it helped identify a key, often overlooked, problem within our unit, and attempted to address it. Message for others We have demonstrated how simple auditing can result in sustained improvement in neonatal care by targeting our oxygen saturations more effectively in compliance with our local guideline.

An objective algorithm for estimating maximum oceanic mixed layer depth using seasonality indices derived from Argo temperature/salinity profiles

AbstractIn this study, we propose a new algorithm for estimating the annual maximum mixed layer depth (M2LD) analogous to a full range of local “ventilation” depth, and corresponding to the deepest surface to which atmospheric influence can be “felt.” Two “seasonality indices” are defined, respectively, for temperature and salinity through Fourier analysis of their time series using Argo data, on the basis of which a significant local minimum of the index corresponding to a maximum penetration depth can be identified. A final M2LD is then determined by maximizing the thermal and haline effects. Unlike most of the previous schemes which use arbitrary thresholds or subjective criteria, the new algorithm is objective, robust, and property adaptive provided a significant periodic geophysical forcing such as annual cycle is available. The validity of our methodology is confirmed by the spatial correlation of the tropical dominance of saline effect (mainly related to rainfall cycle) and the extratropical dominance of thermal effect (mainly related to solar cycle). It is also recognized that the M2LD distribution is characterized by the coexistence of basin‐scale zonal structures and eddy‐scale local patches. In addition to the fundamental buoyancy forcing caused mainly by latitude‐dependent solar radiation, the impressive two‐scale pattern is found to be primarily attributable to (1) large‐wave climate due to extreme winds (large scale) and (2) systematic eddy shedding as a result of persistent winds (mesoscale). Moreover, a general geographical consistency and a good quantitative agreement are found between the new algorithm and those published in the literature. However, a major discrepancy in our result is the existence of a constantly deeper M2LD band compared with other results in the midlatitude oceans of both hemispheres. Given the better correspondence of our M2LDs with the depth of the oxygen saturation limit, it is argued that there might be a systematic underestimation with existing criteria in these regions. Our results demonstrate that the M2LD may serve as an integrated proxy for studying the coherent multidisciplinary variabilities of the coupled ocean–atmosphere system.

Oxygen saturation limits and evidence supporting the targets.

Supplemental oxygen use in the preterm infant is required for survival. Evidence supports a narrow therapeutic window between the helpful and harmful effects of supplemental oxygen in this vulnerable population. The clinical question was-what are the recommended oxygen saturation targets for the preterm infant and the preterm infant corrected to term? Multiple databases were searched for published research in English from 2008 to 2014 using key search terms. A total of 18 articles met inclusion criteria. Early neonatal research linked high levels of supplemental oxygen with retinopathy of prematurity and blindness. Years later, correlations between high arterial oxygen levels and oxidative stress leading to pulmonary and/or neurologic insults were established. Three large multicentered, international studies have recently been published (BOOST II, COT, and SUPPORT), which support oxygen saturation target ranges of 87% to 94% until vascular maturation of the retina is achieved. Two of the 3 studies reported a significant correlation between low saturation limits (85%-89%) and death in the extremely preterm population. Identified best care strategies to prevent states of hypoxia and/or hyperoxia include establishing clear target saturation limits according to recommendations, which are supported by the multidisciplinary team, adequate nurse to patient ratio, improve knowledge deficits, improve bedside compliance, and finally visual cues to remind caregivers of target saturation ranges.

PO-0441 Oxygen Reduction Initiative That Decreased Incidence And Severity Of Retinopathy Of Prematurity Results In Favourable Neuropsychological Outcomes At Age Three

Background and aims High oxygen exposure has adverse long-term medical consequences in premature infants. We hypothesised that a quality improvement initiative decreasing oxygen saturation limits in NICU-admitted infants would affect neuropsychological outcomes at age 3. Methods We studied 83 NICU-admitted participants born at 23–27 weeks; n = 37 (b.2009–2010) with targeted supplemental oxygen rates of 83–93% until 32 weeks, 85–95% until 35 weeks, and >95% after 35 weeks (O 2 Reduced); 8% laser eye surgery; 65% ROP compared with n = 46 (b.2007–2008) with higher target rates (89–100%; O 2 Higher); 28% laser eye surgery; 83% ROP. Group mortality rates ( 2 (n = 83, df=1)= 0.16, p = 0.900. ANCOVAs and regressions were conducted for 19 neuropsychological outcomes. Results O 2 Reduced performed significantly better than O 2 Higher in visual attention, controlling GA (p = 0.042; d= .47); O 2 Reduced was significantly correlated with visual attention (r = 0.288, p 5); ROP was not (r=-0.183, p > 0.05). 18/19 outcome scores favoured O 2 Reduced, low-to-moderate effect sizes ( d range:12–0.47). GA was positively related to all outcomes. A meaningful interaction effect between GA and O 2 Reduced for auditory attention and manual dexterity explained 3%-4% unique variance, respectively. Interaction showed O 2 Reduced’s effect on attention was greatest at 23–24 weeks, and at 27 weeks for manual dexterity. Conclusions Systematic reduction of saturation parameters that decreased retinopathy and laser surgery rates in infancy resulted in favourable three-year-old outcomes suggesting cognitive as well as medical advantages for O 2 Reduced. Moderate effect sizes demonstrated important associations between reduced oxygen saturation rates and 18/19 sensitive performance-based measures. Lowered targeted oxygen saturation rate had favourable yet differential effects across GA in extremely premature survivors.

Current practice of pulse oxygen saturation targets and limits in neonatal intensive care units in Australia and New Zealand

Current practice of pulse oxygen saturation targets and limits in neonatal intensive care units in Australia and New Zealand

Patent ductus arteriosus and effects of low oxygen saturation limits

Patent ductus arteriosus and effects of low oxygen saturation limits

Effects of low oxygen saturation limits on the ductus arteriosus in extremely low birth weight infants

Postnatal increase in oxygen promotes constriction of the patent ductus arteriosus (PDA). According to the findings of prospective observational studies, the clinical practice of targeting lower fractional oxygen saturation between 70 and 90% has been associated with a reduced incidence of severe retinopathy of prematurity (ROP) without affecting survival or neurodevelopmental disability at 1 year of age. Our objective was to investigate the impact of the use of a lower oxygen saturation target range on the incidence of early hemodynamically significant PDA (hsPDA) and the need for ductal ligation in extremely low birth weight (ELBW, <1000 g) infants. In this retrospective study, we analyzed data from 263 ELBW infants managed 4 years before (episode I: target oxygen saturation 89 to 94%) and after (episode II: target oxygen saturation 83 to 89%) implementation of the use of lower oxygen saturation limits in two neonatal intensive care units. Infants with a birth weight of 1000 to 1500 g were managed with the same oxygen saturation target range (89 to 94%) during both episodes, and they served as controls. Parametric and nonparametric tests were used as appropriate and multivariate logistic regression models were used to correct for confounders. There was an increase in the incidence of hsPDA (63.2 vs 74.8%, P=0.043), without an increase in the need for surgical ligation (24.2 vs 29.9%, P=0.3) after implementation of the lower oxygen saturation target range policy. After adjusting for confounders, there was an increase in the odds of having an hsPDA (odds ratio (OR) 1.77, 95% confidence interval (CI) (1.03 to 3.06), P=0.04) but the odds for ductal ligation did not change in episode II (OR 1.25, 95% CI (0.70 to 2.25), P=0.4). The incidence of ROP > or = stage III (50.7 vs 15.7%; P<0.0001) and the need for laser ablation (33.8% vs 8.7%; P<0.0001) were significantly reduced. There was no change in the incidence of hsPDA or ductal ligation in the control group. Targeting lower oxygen saturation limits to minimize periods of hyperoxemia in ELBW infants reduced the incidence of severe ROP and the need for laser ablation. The incidence of early hsPDA was increased; however, final closure rate and the incidence of surgical ligation of the ductus arteriosus were not affected.

Human Milk Intake and Retinopathy of Prematurity in Extremely Low Birth Weight Infants

OBJECTIVES. Our goal was to analyze the association between human milk intake and severe retinopathy of prematurity in extremely low birth weight infants. PATIENTS AND METHODS. This study is a secondary analysis of data collected for a trial of glutamine supplementation in extremely low birth weight infants (birth weight <1000 g). Among the 1433 participants in that trial, data are available regarding human milk intake and the occurrence of severe retinopathy of prematurity (defined in this study as retinopathy of prematurity treated surgically) for 1057 infants. The volume of human milk intake was expressed as the mean volume (milliliters per kilogram per day) and the mean proportional volume (proportion of total nutritional intake) from birth to discharge or transfer. Using logistic regression, we estimated odds ratios and 95% confidence intervals for any human milk intake and, among infants who received human milk, for each 10 mL/kg per day and each 10% increase in volume. RESULTS. Of the 1057 infants included in this cohort, 788 infants (75%) received at least some human milk. Among these milk-fed infants, the median volume of human milk intake was 30 mL/kg per day (interquartile range: 6-83 mL/kg per day), and the median proportional volume of human milk intake was 0.18 (interquartile range: 0.03-0.66). One hundred sixty-three infants (15%) developed severe retinopathy of prematurity. CONCLUSIONS. In extremely low birth weight infants, human milk intake was not associated with a decreased risk of severe retinopathy of prematurity.

EFFECTS OF LOW OXYGEN SATURATION LIMITS ON CLOSURE OF DUCTUS ARTERIOSUS IN EXTREMELY LOW BIRTH WEIGHT INFANTS.

Background Extremely low birth weight (ELBW) infants are at increased risk for developing retinopathy of prematurity (ROP) and lower oxygen saturation limits have decreased the incidence of severe ROP. Although oxygen is known to constrict the ductus arteriosus (DA), a localized ductal wall tissue hypoxia is required for permanent closure of the DA. Objective To compare the incidence of patent ductus arteriosus (PDA) and the need for ductal ligation in ELBW infants before and after implementation of lower oxygen saturation limits. Methods Retrospective data analyses of prospectively collected data on ELBW infants admitted to one of our neonatal intensive care units 4 years before and after the implementation of a new oxygen saturation limit for prevention of ROP were included in the study. Patients with a gestational age of less than 23 weeks were excluded. During the period prior to the implementation of the lower saturation limits (83-89%), ELBW infants requiring oxygen were maintained at oxygen saturations of 89 to 94%. Results A total of 186 ELBW infants comprised our study population. There were 108 patients (birth weight [BW] 744 ± 125 g, gestational age [GA] 25.8 ± 1.6 weeks) before and 78 patients (BW 777 ± 128 g, GA 25.9 ± 1.7 weeks) after the implementation of the lower oxygen saturation limit protocol. There was a significant reduction in the incidence of stage III or greater ROP (26% vs 11%, p = .015). However, the incidence of PDA (52% vs 55%) and ductal ligation (41% vs 42%) was unchanged. Conclusions The use of the lower oxygen saturation limits in ELBW infants resulted in a significant reduction in severe ROP without significantly impacting the incidence of PDA or the need for DA ligation.

Characterization of Fe17R2 phases (R=Pr and Sm) oxidized at 200 °C

The results of oxygen absorption in temperatures ranging from 200 to 500 °C are reported for the phases Fe17R2, R=Pr and Sm. It was observed that the oxygen saturation limit is temperature dependent, being of 3 at/fu at 200 °C, 12.8 at/fu at 300 °C, 20.3 at/fu at 400 °C, and 28.5 at/fu at 500 °C. This implies that above 200 °C the phase is deeply altered by oxygen absorption. Samples with absorption at 200 °C were studied as prepared and heat treated at 500 °C/40 h. The results show that the heat-treated samples consist of Fe17R2, Fe, and R2O3. Metallographic examination, susceptibility, and Mössbauer spectroscopy data support the hypothesis that the as-prepared samples consist of a mixture of Fe17R2 and ordered interstitial Fe17R2Ox.

Oxygen absorption by the Fe/sub 17/Sm/sub 2/ phase

The results of oxygen absorption in temperatures ranging from 200 to 500/spl deg/C are reported. It was observed that the oxygen saturation limit is temperature dependent, being of 3 atoms per formula unit (at/fu) at 200/spl deg/C, 12.8 at/fu at 300/spl deg/C, 20.3 at/fu at 400/spl deg/C and 28.5 at/fu at 500/spl deg/C. This implies that above 200/spl deg/C the phase is deeply altered by oxygen absorption. Samples with absorption at 200/spl deg/C were studied as prepared and heat treated at 500/spl deg/C/40 h. The results show that the heat treated samples consist of Fe/sub 17/Sm/sub 2/, Fe and Sm/sub 2/O/sub 3/. Metallographic examination and susceptibility data support the hypothesis that the as prepared samples consist of a mixture of Fe/sub 17/Sm/sub 2/ and interstitial Fe/sub 17/Sm/sub 2/O/sub 3/.

Superconductivity in Y(Ba 1− yLa y) 2Cu 3O 9−δ

The superconducting properties of the Y(Ba 1− y La y ) 2Cu 3O 9−δ phase (note La solely substituting Ba) are studied over the entire homogeneity range, viz., 0.00 < y < 0.36(2) and 1.69(2) < δ < 3.00(2) for well-defined samples prepared by the citrate gel method and annealed at controlled partial pressures of O 2. Superconductivity (for T c > 5 K, by ac susceptibility) is observed over a large range of compositions. In terms of oxygen content, the lower limit for superconductivity varies from 9 − δ ≈ 6.3 for y = 0.00 to 9 − δ ≈ 7.05 for y = 0.20. T c increases with increasing oxygen content (referring to the oxygen saturation limit 9 − δ = 6.95(1) + y for 320°C at P O 2 = 100 kPa), irrespective of the linkage of the copper-oxygen square chains when 9 − δ exceeds 7. For y = const., T c is hence correlated with the overall hole concentration p = (5 − 2δ − 2y) 3 per (CuO) p− , and these correlations are in turn related to deformation of the structure. For p = const., T c decreases with increasing y, and a hole transfer from the Cu(2) to Cu(1) coordination sphere appears to be composed of: (i) a large contribution due to an increased number of oxygens bonded to Cu(1), (ii) a smaller contribution associated with a decrease in orthorhombic deformation, and (iii) an even smaller contribution [about half and of opposite sign to (ii)] attached to decreased tetragonal deformation. The direction of the hole transfer upon a change in the tetragonal deformation depends on the ratio of the partial deformations of the Cu(1) and Cu(2) coordination polyhedra in the crystallographic c direction, the condition of no hole transfer being established when the Cu(2) pyramid deforms about 7 times faster than the Cu(1) square. On the other hand, an increase in the orthorhombic deformation always causes a Cu(1) to Cu(2) charge transfer. All these effects are overshadowed when p changes with the oxygen content. The effects of La substitution are compared with those of Sr substitution, application of external pressure, and change in oxygen content. The occurrence of superconductivity is correlated with fractional occupancy of a single, non-bonding orbital leading to a metallic state, and this picture is discussed for various oxide systems.

Invertebrate Movements and Some Diel and Seasonal Changes in a Sierra Nevada Peatland

The objectives of this study were to measure diel and seasonal changes in oxygen saturation, water temperature, water level, and aerobic limit in a Sierra Nevada peatland, and to study invertebrate migration in response to the diel changes. 02 saturation, determined with an oxygen electrode at 2 cm, varied from a mid-afternoon minimum (35-44 per cent) to a maximum before sunrise (83-96 per cent), especially in July and August. This finding has not been previously reported for peatlands. Aerobic limit was determined from redwood stakes that are stained when 02 is absent. Minimum aerobic limit occurred in July (4.8 cm ? 0.43 cm) and maximum (18.8 cm ? 1.48 cm) occurred in November. The seasonal change in aerobic limit was not related to water levels since the water table was at the surface each day. Dipterans (Chironomidae and Heleidae) extracted from the peat showed no change in vertical distribution over a 24-hr period. But oligochaetes appeared to have a diel migration. Oligochaete vertical distribution was negatively correlated with surface water temperature (r = 0.90).