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PubMed2000

Consequences of inspired oxygen fraction manipulation on myocardial oxygen pressure, adenosine and lactate concentrations: a combined myocardial microdialysis and sensitive oxygen electrode study in pigs.

Adenosine is a potent vasodilator whose concentration has been shown to increase in cardiac tissue in response to hypoxia. However, the time-dependent relationship between the levels of myocardial interstitial adenosine and tissue oxygenation has not yet been completely established. Therefore, the purpose of this study was to investigate the complex relationship between tissue myocardial oxygen tension (PtiO(2)) and interstitial myocardial adenosine and lactate concentrations by developing a new technique which combines a cardiac microdialysis probe and a Clark-type P O(2)electrode. The combined and the single microdialysis probes were implanted in the left ventricular myocardium of anesthetized pigs. The consequences of the combined use of microdialysis and P O(2)probes on myocardial PtiO(2)and microdialysis performances against glucose were evaluated. A moderate but significant reduction in the relative recovery against glucose of the combined probe was observed when compared to that of the single microdialysis probe (42+/-2 v 32+/-1%, mean+/-S.E. M.n=5 P<0.05), at 2microl/min microdialysis probe perfusion flow. Similarly, myocardial oxygen enrichment, measured by the P O(2)electrode, was negligible when microdialysis probe perfusion flow was 2microl/min. Systemic hypoxia (FiO(2)=0.08) resulted in a significant decrease in PtiO(2)from 30+/-4 to 11+/-2 mmHg, limited increase in coronary blood flow (CBF), and a significant increase in myocardial adenosine and lactate concentrations from 0.34+/-0.05 to 0.98+/-0.06micromol/l and from 0.45+/-0.05 to 0.97+/-0.06 mmol/l respectively (P<0.05). Increasing the FiO(2)to 0.3 restored the PtiO(2)and hemodynamic parameters to baseline values with no changes in interstitial adenosine and lactate concentrations. Nevertheless, myocardial interstitial adenosine remained significantly higher than baseline values. In conclusion, this study demonstrates the ability of a combined probe to measure simultaneously regional myocardial PtiO(2)and metabolite concentration during hypoxia. The hypoxia-induced increase in myocardial adenosine persists after correction of hypoxia. The physiological significance of this observation requires further studies.

Adenosine↗
PubMed2006

Oxygen alert cards and controlled oxygen: preventing emergency admissions at risk of hypercapnic acidosis receiving high inspired oxygen concentrations in ambulances and A&E departments.

BACKGROUND: Appropriate resuscitation of hypoxic patients is fundamental in emergency admissions. To achieve this, it is standard practice of ambulance staff to administer high concentrations of oxygen to patients who may be in respiratory distress. A proportion of patients with chronic respiratory disease will become hypercapnic on this. OBJECTIVES AND METHODS: A scheme was agreed between the authors' hospital and the local ambulance service, whereby patients with a history of previous hypercapnic acidosis with a Pao2 >10.0 kPa--indicating that oxygen may have worsened the hypercapnia--are issued with "O2 Alert" cards and a 24% Venturi mask. The patients are instructed to show these to ambulance and A&E staff who will then use the mask to avoid excessive oxygenation. The scheme was launched in 2001 and this paper present the results of an audit of the scheme in 2004. RESULTS: A total of 18 patients were issued with cards, and 14 were readmitted on 69 occasions. Sufficient documentation for auditing purposes was available for 52 of the 69 episodes. Of these audited admissions, 63% were managed in the ambulance, in line with card-holder protocol. This figure rose to 94% in the accident and emergency department. CONCLUSION: These data support the usability of such a scheme to prevent iatrogenic hypercapnia in emergency admissions.

Acidosis, Respiratory↗
PubMed1984

Oxygen transport and utilization in hyperoxia and hypoxia: relation of conjunctival and transcutaneous oxygen tensions to hemodynamic and oxygen transport variables.

A device to measure surface oxygen tension of the palpebral conjunctiva (PcjO2) was developed and tested in 12 mongrel dogs subjected to normoxia, hyperoxia, and hypoxia. Intravascular pressure, hemodynamic, and bulk oxygen transport variables were measured simultaneously with PcjO2 and transcutaneous O2 (PtcO2) and CO2 (PtcCO2). PcjO2 closely paralleled PaO2 as the fractional inspired O2 concentration was changed from 0.21 up to 1.0 and down to 0.05; the correlation coefficient, r, was 0.95 for 305 data sets. During hyperoxia there were no significant hemodynamic or bulk O2 transport changes, but during hypoxia, the cardiac output and O2 extraction increased while PaO2, PtcO2 and PcjO2 fell; O2 delivery and O2 consumption were maintained until just before death.

Animals↗
PubMed2005

Fractionation of the three stable oxygen isotopes by oxygen-producing and oxygen-consuming reactions in photosynthetic organisms.

The triple isotope composition (delta17O and delta18O) of dissolved O2 in the ocean and in ice cores was recently used to assess the primary productivity over broad spatial and temporal scales. However, assessment of the productivity with the aid of this method must rely on accurate measurements of the 17O/16O versus 18O/16O relationship in each of the main oxygen-producing and -consuming reactions. Data obtained here showed that cleavage of water in photosystem II did not fractionate oxygen isotopes; the delta18O and delta17O of the O2 evolved were essentially identical to those of the substrate water. The fractionation slopes for the oxygenase reaction of Rubisco and respiration were identical (0.518 +/- 0.001) and that of glycolate oxidation was 0.503 +/- 0.002. There was a considerable difference in the slopes of O2 photoreduction (the Mehler reaction) in the cyanobacterium Synechocystis sp. strain PCC 6803 (0.497 +/- 0.004) and that of pea (Pisum sativum) thylakoids (0.526 +/- 0.001). These values provided clear and independent evidence that the mechanism of O2 photoreduction differs between higher plants and cyanobacteria. We used our method to assess the magnitude of O2 photoreduction in cyanobacterial cells maintained under conditions where photorespiration was negligible. It was found that electron flow to O2 can be as high as 40% that leaving photosystem II, whereas respiratory activity in the light is only 6%. The implications of our findings to the evaluation of specific O2-producing or -consuming reactions, in vivo, are discussed.

Alcohol Oxidoreductases↗
PubMed1983

Local blood flow, oxygen tension, and oxygen consumption in the rat spinal cord. Part 1: Oxygen metabolism and neuronal function.

A reliable and reproducible microelectrode technique provided consistent simultaneous measurements of local spinal cord blood flow (local SCBF), tissue oxygen tension (TO2), and tissue oxygen consumption (TO2C) in the rat. Local SCBF was measured by the hydrogen clearance technique, local TO2 was measured polarographically, and local TO2C was calculated from the declining slope of local TO2 following temporary arrest of local SCBF. Mean local TO2 values varied only slightly between gray and white matter, while local TO2C and SCBF maintained a 3 to 1 ratio between gray and white matter areas. Measurements were also made of these parameters in specific white matter tracts and laminae of Rexed. Local white matter SCBF was relatively homogeneous throughout the ventral, lateral, and dorsal funiculi. Gray matter blood flow was more variable with topography. The highest local SCBF was recorded in areas rich in internuncial neurons. The somatic motor regions had values slightly higher than recorded in sensory regions.

Animals↗
PubMed1988

Extracorporeal membrane oxygenation selection criteria: partial pressure of arterial oxygen versus alveolar-arterial oxygen gradient.

Extracorporeal membrane oxygenation (ECMO) has dramatically increased the survival rate of hypoxemic neonates who are unresponsive to maximum conventional medical therapy. Because ECMO involves multiple risks, including ligation of the right common carotid artery and right internal jugular vein, ECMO candidates should be neurologically intact neonates with a high probability of death despite maximum conventional ventilatory support. Currently, criteria based on the calculated alveolar-arterial oxygen gradient (A-aDO2) have replaced the neonatal pulmonary insufficiency index for predicting mortality and, thus, ECMO eligibility. A retrospective review of death prediction for the 26 months prior to the initiation of an ECMO program revealed a sensitivity of 67% and a specificity of 96% using the criterion of a PaO2 of less than 50 mm Hg for four hours. An equivalent A-aDO2 criterion of greater than or equal to 630 for four hours produced a sensitivity of 61% and a specificity of 96%. Prediction of mortality in neonates with sepsis was poor regardless of the criteria used. Excluding the deaths due to sepsis increased the sensitivity to 86% and 79% using criteria based on PaO2 and A-aDO2, respectively. It is concluded that the use of criteria based on PaO2 is equivalent to criteria based on A-aDO2 for predicting mortality. Criteria based on PaO2 may, however, decrease both the false-negative rate (patients with an elevated PCO2) and the false-positive rate (patients with intentionally induced hypocarbia secondary to hyperventilation alkalosis).

Blood Gas Analysis↗
PubMed2002

Accurate measurement of near-micromolar oxygen concentrations in aqueous solutions based on enzymatic extradiol cleavage of 4-chlorocatechol: applications to improved low-oxygen experimental systems and quantitative assessment of back diffusion of oxygen from the atmosphere.

An enzymatic method for measuring the O(2) concentrations of aqueous solutions was developed by involving 4-chlorocatechol and catechol 2,3-dioxygenase from Pseudomonas putida. With this system, the amount of O(2) in a sample solution can be measured as the amount of 5-chloro-2-hydroxymuconate semialdehyde formed through the enzyme reaction. The product was stable and its anion exhibited strong absorption around 380 nm (molar absorption coefficient of 4.3 x 10(4) M(-1) cm(-1), pK value of 5.4). A sensitive HPLC method involving a BioAssist Q column was developed to individually quantify the products derived from 4-chlorocatechol and catechol. When the O(2) concentration in a sample solution sealed in a vial was lowered from the air-saturation level by means of the amount enzymatically reacted with a known amount of catechol, the concentration of remaining O(2) could be successfully measured by the HPLC method. We developed devices through which reagents could be added to solutions sealed in cuvettes or the vessel of an oxygen electrode system under a flow of argon. By applying these devices, the submicromolar O(2) concentration of an anoxic solution and the back diffusion of O(2) from the atmosphere could be directly determined for the first time. The K(m) values of the dioxygenase and an ascorbate oxidase for oxygen were also determined to be 7.2 (at pH 7.5) and 114 microM (at pH 6.5), respectively, at 25 degrees C.

Anions↗
PubMed1989

Oxygenation during chest physiotherapy of very-low-birth-weight infants: relations among fraction of inspired oxygen levels, number of hand ventilations, and transcutaneous oxygen pressure.

Chest physiotherapy (CPT) to clear the airway of infants requiring assisted ventilation is a routine procedure in neonatal intensive care units. This study was done to describe the relationships between fraction of inspired oxygen (FiO2) levels and the number of hand ventilations (independent variables) and variations of transcutaneous oxygen pressure (TcPO2) from baseline among intubated very-low-birth-weight (VLBW) infants receiving CPT. The study consisted of 30 observations of 13 intubated VLBW infants receiving CPT. Data were obtained by observations during routine CPT procedures performed by the nurses in charge of the infants. Stepwise multiple regression showed that hand ventilations and FiO2 levels significantly accounted for the variability in TcPO2 levels during CPT. Pearson correlation analysis showed that there was a negative correlation between FiO2 and TcPO2 and between the number of hand ventilations and TcPO2.

Blood Gas Monitoring, Transcutaneous↗
PubMed1990

The relationship between oxygen demand, oxygen uptake, and oxygen supply.

Results of the relationships between oxygen supply, demand, and uptake can be used to interpret cardiac output values, identify types of acute circulatory failure, guide attempts to improve cellular function, and thus prevent the development of multiple organ failure and death. Five steps in the interpretation of cardiac output values are recommended: (1) relate cardiac output to the patient's size; (2) determine the presence of anemia or hypoxemia; (3) measure mixed venous O2 saturation and (4) blood lactate levels; and (5) evaluate O2 uptake before and after a transient increase in cardiac output.

Animals↗
PubMed2004

Effect of sepsis on skeletal muscle oxygen consumption and tissue oxygenation: interpreting capillary oxygen transport data using a mathematical model.

Inherent in the inflammatory response to sepsis is abnormal microvascular perfusion. Maldistribution of capillary red blood cell (RBC) flow in rat skeletal muscle has been characterized by increased 1) stopped-flow capillaries, 2) capillary oxygen extraction, and 3) ratio of fast-flow to normal-flow capillaries. On the basis of experimental data for functional capillary density (FCD), RBC velocity, and hemoglobin O2 saturation during sepsis, a mathematical model was used to calculate tissue O2 consumption (Vo2), tissue Po2 (Pt) profiles, and O2 delivery by fast-flow capillaries, which could not be measured experimentally. The model describes coupled capillary and tissue O2 transport using realistic blood and tissue biophysics and three-dimensional arrays of heterogeneously spaced capillaries and was solved numerically using a previously validated scheme. While total blood flow was maintained, capillary flow distribution was varied from 60/30/10% (normal/fast/stopped) in control to 33/33/33% (normal/fast/stopped) in average sepsis (AS) and 25/25/50% (normal/fast/stopped) in extreme sepsis (ES). Simulations found approximately two- and fourfold increases in tissue Vo2 in AS and ES, respectively. Average (minimum) Pt decreased from 43 (40) mmHg in control to 34 (27) and 26 (15) mmHg in AS and ES, respectively, and clustering fast-flow capillaries (increased flow heterogeneity) reduced minimum Pt to 14.5 mmHg. Thus, although fast capillaries prevented tissue dysoxia, they did not prevent increased hypoxia as the degree of microvascular injury increased. The model predicts that decreased FCD, increased fast flow, and increased Vo2 in sepsis expose skeletal muscle to significant regions of hypoxia, which could affect local cellular and organ function.

Animals↗
PubMed2000

Domicilary oxygen for chronic obstructive pulmonary disease.

BACKGROUND: Long-term domiciliary oxygen therapy has become one of the major forms of treatment for hypoxaemic chronic obstructive pulmonary disease (COPD) patients. OBJECTIVES: To determine the effect of domiciliary oxygen therapy on survival and quality of life in patients with COPD. SEARCH STRATEGY: Randomised controlled trials (RCTs) were identified using the Cochrane Airways Group COPD register using the search terms: (home OR domiciliary) AND oxygen. SELECTION CRITERIA: Any RCT in patients with hypoxaemia and COPD that compared long term domiciliary or home oxygen therapy with a control treatment. DATA COLLECTION AND ANALYSIS: Data extraction was performed independently by two reviewers. MAIN RESULTS: Four randomised controlled trials were identified. Data from none of these trials could be aggregated because of differences in trial design and patient selection. NOTT 1980, continuous oxygen therapy versus nocturnal oxygen therapy: there was a significant improvement in mortality after 24 months (Peto odds ratio 0.45, 95% confidence interval 0.25 to 0.81). MRC 1981, domiciliary oxygen therapy versus no oxygen therapy: there was a significant improvement over five years in mortality in the group receiving oxygen therapy (Peto odds ratio 0.42, 95% confidence interval 0.18 to 0.98). Fletcher 1992, nocturnal oxygen versus no oxygen in patients with COPD and arterial desaturation at night: there was no difference in mortality at 36 months. Gorecka 1997, long term oxygen versus no oxygen in moderate hypoxaemia: there was no effect on survival for up to three years of follow up. REVIEWER'S CONCLUSIONS: Long term oxygen therapy improved survival in a selected group of COPD patients with severe hypoxaemia (arterial PO2 less than 8.0 kPa). Long term oxygen did not appear to improve survival in patients with moderate hypoxaemia or in those with only arterial desaturation at night.

Home Care Services↗
PubMed2005

Oxygen concentrations at the rear and front of the bag in bag valve mask devices during oxygenation of neonates.

OBJECTIVE: To study the concentration of oxygen flowing passively from the front and the rear parts of different brands of self-inflating bag valve mask ventilation devices at different oxygen flows and that flowing actively from the front part at different ventilation rates. METHODS: Two devices were tested, the Ambu device in which the added oxygen enters at a right angle to the axis of the bag and the VBM in which the oxygen enters parallel to the axis of the bag and faces either a hole or a ridge in the intake valve. An oxygen analyzer was used to measure the oxygen concentration at different oxygen flow rates (2, 4, 6, 8 and 10 L/min) supplied by a 100% oxygen source. This was measured in both devices from the front and rear parts as step one. With active ventilation compressing the bag, oxygen concentration was measured from the front part. This was done at ventilation rates of 30 and 60 min(-1). RESULTS: Passive flow oxygenation. With the Ambu device, the oxygen concentration measured at the front part of the bag was 21% and that measured from the rear part was 100%, at all oxygen flow rates. With the VBM brand, in the first position with the oxygen source facing a hole (VBM-hole), the oxygen concentration was high at low flow rates and decreased with increased flow. Similar findings happened when measuring oxygen concentration from its rear part. With the oxygen source facing a ridge (VBM-ridge), the oxygen concentration measured from the front was directly proportional to the oxygen flow rate i.e. it increased with increasing flow. From the rear part, the oxygen concentration was near 100% at all flow rates. Active ventilation. Using the Ambu device, the oxygen concentration increased with increasing flow rate and reached 100% at 10 L/min flow. With VBM-hole, the oxygen concentration increased gradually with increasing flow but never reached 100%. With VBM-ridge, the performance was comparable to the Ambu. In all the situations, the oxygen concentration was higher when the ventilation was done at 30 min(-1) than at 60 min(-1). CONCLUSION: The Ambu device can provide 100% oxygen from its rear part even at low flow rates and 100% oxygen during active ventilation provided at least 10 L/min oxygen is used. The VBM is at a disadvantage when the oxygen source faces a hole; as the jet flowing in the bag causes a Venturi effect; which sucks air in from outside and dilutes the oxygen concentration provided. The ridge type does not have this problem. Ventilation at a rate of 30 min(-1) produced a higher oxygen concentration. The operator should be aware of the limitations of the device used.

Equipment Design↗
PubMed2000

Maternal oxygen administration for fetal distress.

BACKGROUND: Maternal oxygen administration has been used in an attempt to lessen fetal distress by increasing the available oxygen from the mother. OBJECTIVES: The objective of this review was to assess the effects of maternal oxygenation for fetal distress during labour and to assess the effects of prophylactic oxygen therapy during the second stage of labour on perinatal outcome. SEARCH STRATEGY: The Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register were searched. Date of last search: December 1997. SELECTION CRITERIA: Randomised trials comparing maternal oxygen therapy for fetal distress during labour and prophylactic oxygen therapy during the second stage of labour with a control group (dummy or no oxygen therapy). DATA COLLECTION AND ANALYSIS: Eligibility and trial quality were assessed by the reviewer. MAIN RESULTS: No trials addressing maternal oxygen therapy for fetal distress could be located. One trial of 85 women which addressed prophylactic oxygen therapy during labour was included. Cord blood pH values of less than 7.2 were more frequently recorded in the oxygenation group than the control group (relative risk 4.83, 95% confidence interval 1.11 to 21.04). There were no other statistically significant differences between the groups. Within the oxygenation group, those receiving oxygenation for less than 10 minutes had higher umbilical artery pH values than those receiving oxygen for longer than 10 minutes. REVIEWER'S CONCLUSIONS: There is not enough evidence to support the use of prophylactic oxygen therapy for women in labour, nor to evaluate its effectiveness for fetal distress.

Female↗
PubMed2005

A linear correlation between energy of LMCT band and oxygenation reaction rate of a series of catecholatoiron(III) complexes: initial oxygen binding during intradiol catechol oxygenation.

The oxygen reactivity of catecholatoiron(III) complexes has been examined using a series of catecholate ligands as the substrate. All the complexes examined here, [Fe(III)(TPA)(R-Cat)]BPh(4) (1-9) (TPA: tris(pyridin-2-ylmethyl)amine; R-Cat: substituted catecholate ligand, R=3,5-(t)Bu(2) (1), 3,6-(t)Bu2 (2), 3,5-Me2 (3), 3,6-Me2 (4), 4-(t)Bu (5), 4-Me (6), H (7), 4-Cl (8) and 3-Cl (9)), exclusively afforded the intradiol cleaving products of the catecholate ligands upon exposure to O2. It was revealed that 1-7 can be categorized into two classes based on their electrochemical properties; i.e., the complexes having the dialkyl-substituted (group A) and the mono- or non-substituted (group B) catecholate ligands. In spite of their classification, these two groups show a linear correlation between the logarithm of the reaction rate constant with O2 and the energy of the catecholate-to-iron(III) LMCT band, although 2 shows a large negative deviation from the correlation line. Based on this LMCT-energy dependent reactivity of 1 and 3-9 as well as the very low reactivity of 2, we have discussed on the mechanisms of the reaction of [Fe(III)(TPA)(R-Cat)]BPh4 with O2.

Catechols↗
PubMed1993

The oxygen consumption/oxygen delivery curve in severe preeclampsia: evidence for a fixed oxygen extraction state.

OBJECTIVE: Increased total body oxygen consumption requirements are usually met by increased oxygen delivery and increased oxygen extraction. In certain conditions (e.g., adult respiratory distress syndrome) the ability to increase oxygen extraction is lost, and any increase in oxygen consumption depends on increased oxygen delivery. The objective of this study was to investigate the oxygen delivery/oxygen consumption relationship in severe preeclampsia. STUDY DESIGN: Thirty-two patients with severe preeclampsia (blood pressure > 160/110 mm Hg; 3 to 4+ proteinuria) were monitored with a pulmonary artery catheter. Baseline oxygen consumption and delivery in a group without volume expansion or pharmacologic vasodilatation were compared with those in a group who had received a magnesium sulfate infusion. RESULTS: Oxygen consumption, oxygen delivery, arterial-venous-oxygen difference, and the oxygen extraction ratio were low when compared to that for normal 32 to 38 week pregnancy. The oxygen extraction ratio, defined as the ratio of oxygen consumption to oxygen delivery, was abnormally low for pregnancy, especially considering the low oxygen delivery levels in these patients. Oxygen consumption was dependent on oxygen delivery over the entire range of values seen. CONCLUSIONS: Severe preeclampsia is associated with an abnormality of tissue oxygen extraction, as evidenced by a low and unresponsive oxygen extraction ratio. Oxygen consumption increases proportionately with increases in oxygen delivery without reaching an oxygen delivery-independent state. Even at high oxygen delivery levels the oxygen consumption in preeclamptic patients is still abnormally low for pregnancy.

Adolescent↗
PubMed1999

Beneficial effects of helium:oxygen versus air:oxygen noninvasive pressure support in patients with decompensated chronic obstructive pulmonary disease.

OBJECTIVE: To test the hypothesis that, in decompensated chronic obstructive pulmonary disease (COPD), noninvasive pressure support ventilation using 70:30 helium:oxygen instead of 70:30 air:oxygen could reduce dyspnea and improve ventilatory variables, gas exchange, and hemodynamic tolerance. DESIGN: Prospective, randomized, crossover study. SETTING: Medical intensive care unit, university tertiary care center. PATIENTS: Nineteen patients with severe COPD (forced 1-sec expiratory volume of 0.83+/-0.3 l) hospitalized in the intensive care unit for noninvasive pressure support ventilation after initial stabilization with noninvasive pressure support for no more than 24 hrs after intensive care unit admission. INTERVENTIONS: Noninvasive pressure support ventilation was administered in the following randomized crossover design: a) 45 min with air:oxygen or helium:oxygen; b) no ventilation for 45 min; and c) 45 min with air:oxygen or helium:oxygen. MEASUREMENTS AND MAIN RESULTS: Air:oxygen and helium:oxygen decreased respiratory rate and increased tidal volume and minute ventilation. Helium:oxygen decreased inspiratory time. Both gases increased total respiratory cycle time and decreased the inspiratory/total time ratio, the reduction in the latter being significantly greater with helium:oxygen. Peak inspiratory flow rate increased more with helium:oxygen. PaO2 increased with both gases, whereas PaCO2 decreased more with helium:oxygen (values shown are mean+/-SD) (52+/-6 torr [6.9+/-0.8 kPa] vs. 55+/-8 torr [7.3+/-1.1 kPa] and 48+/-6 torr [6.4+/-0.8 kPa] vs. 54+/-7 torr [7.2+/-0.9 kPa] for air:oxygen and helium:oxygen, respectively; p<.05). When hypercapnia was severe (PaCO2 >56 torr [7.5 kPa]), PaCO2 decreased by > or =7.5 torr (1 kPa) in six of seven patients with helium:oxygen and in four of seven patients with air:oxygen (p<.01). Dyspnea score (Borg scale) decreased more with helium:oxygen than with air:oxygen (3.7+/-1.6 vs. 4.5+/-1.4 and 2.8+/-1.6 vs. 4.6+/-1.5 for air:oxygen and helium:oxygen, respectively; p<.05). Mean arterial blood pressure decreased with air:oxygen (76+/-12 vs. 82+/-14 mm Hg; p<.05) but remained unchanged with helium:oxygen. CONCLUSION: In decompensated COPD patients, noninvasive pressure support ventilation with helium:oxygen reduced dyspnea and PaCO2 more than air:oxygen, modified respiratory cycle times, and did not modify systemic blood pressure. These effects could prove beneficial in COPD patients with severe acute respiratory failure and might reduce the need for endotracheal intubation.

Adult↗
PubMed2006

Oxygen distribution in the rabbit eye and oxygen consumption by the lens.

PURPOSE: Excessive exposure to oxygen has been proposed to be a risk factor for nuclear cataracts. For a better understanding of the metabolism of oxygen in the eye, oxygen distribution was mapped in the intraocular fluids, and the rate of oxygen consumption by the lens in rabbits breathing different levels of oxygen was calculated. METHODS: Young albino rabbits were anesthetized, intubated, and exposed to normoxic, hypoxic, or hyperoxic conditions. The hemoglobin saturation of the blood was monitored with a pulse oximeter, and arterial oxygen levels were measured with a blood gas analyzer. A fiberoptic optical oxygen sensor (optode) was used to determine oxygen levels in different regions of the eye. Oxygen flux across the posterior of the lens was calculated from the measured oxygen gradients in the vitreous chamber. RESULTS: Oxygen levels in the ocular fluids changed markedly when rabbits breathed air made hypoxic or hyperoxic. Oxygen levels were highest near the retinal vasculature, the iris vasculature, and the inner surface of the central cornea. Compared with nearby regions, oxygen levels were decreased in the aqueous humor closest to the pars plicata of the ciliary body and near the anterior chamber angle. Oxygen levels were generally lower closer to the lens. From the oxygen gradients in the vitreous body, oxygen consumption by the posterior half of the lens was calculated to be 0.2 to 0.4 microL/h under normoxic conditions. Oxygen consumption by the posterior of the lens increased in proportion to the amount of oxygen supplied. CONCLUSIONS: Intraocular oxygen is mostly derived from the retinal and iris vasculature and by diffusion across the cornea. Freshly secreted aqueous humor and the aqueous humor in the anterior chamber angle are relatively depleted of oxygen. The marked increase in oxygen consumption that occurs when the lens is exposed to increased oxygen is likely to result in the production of higher levels of reactive oxygen species and may provide a link between elevated oxygen levels and the risk of nuclear cataracts.

Animals↗
PubMed2000

Restricted versus liberal oxygen exposure for preventing morbidity and mortality in preterm or low birth weight infants.

BACKGROUND: This section is under preparation and will be included in the next issue. OBJECTIVES: In preterm or low birth weight infants, does targeting ambient oxygen concentration to achieve a lower versus higher blood oxygen range, or administering restricted versus liberal supplemental oxygen, influence mortality, retinopathy of prematurity, lung function, growth or development? SEARCH STRATEGY: The standard search strategy of the Neonatal Review Group was used. An additional literature search was conducted of the MEDLINE, EMBASE, and CINAHL databases in order to locate any trials in addition to those provided by the Cochrane Controlled Trials Register (CENTRAL/CCTR). SELECTION CRITERIA: All trials in preterm or low birth weight infants utilising random or quasi-random patient allocation, in which ambient oxygen concentrations were targeted to achieve a lower versus higher blood oxygen range, or restricted versus liberal oxygen was administered, were eligible for inclusion. DATA COLLECTION AND ANALYSIS: The methodological quality of the eligible trials was assessed independently by each author for the degree selection, performance, attrition and detection bias. Data were extracted and reviewed independently by the each author. Data analysis was conducted according to the standards of the Cochrane Neonatal Review Group. MAIN RESULTS: The restriction of oxygen significantly reduced the incidence and severity of retinopathy of prematurity without unduly increasing death rates in the meta-analysis of the five trials included in this review. The one trial that specifically addressed the question of lower versus higher PaO2 found no effect on death, but did not report (in sufficient detail to warrant inclusion) the effect of this intervention on eye or other outcomes. The effects of either of these oxygen administration policies on other clinically meaningful outcomes including chronic lung disease and long term growth, neurodevelopment, lung or visual function were not reported in any of the available trials. REVIEWER'S CONCLUSIONS: The results of this meta-analysis confirm the commonly held view of today's clinicians that a policy of unrestricted, unmonitored oxygen therapy has potential harms, without clear benefits. However, the question of what is the optimal target range for maintaining blood oxygen levels in preterm/LBW infants was not answered by the data available for inclusion in this review.

Humans↗