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PubMed2000

Gradual versus abrupt discontinuation of oxygen 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 gradual versus abrupt discontinuation of supplemental oxygen influence mortality, retinopathy of prematurity, lung function, growth or development? SEARCH STRATEGY: The standard search strategy of the Cochrane Neonatal Review Group was used. This included searches of the Oxford Database of Perinatal trials, MEDLINE, previous reviews including cross references, abstracts, conferences and symposia proceedings, expert informants, journal handsearching mainly in the English language. An additional literature search of the MEDLINE, EMBASE, and CINAHL databases was conducted in order to locate any trials in addition to those provided by the Cochrane Controlled Trials Register (CENTRAL/CCTR). SELECTION CRITERIA: All trials utilising random or quasi-random patient allocation, in which gradual weaning was compared with abrupt discontinuation of supplemental oxygen in preterm or low birth weight infants, were eligible for inclusion. DATA COLLECTION AND ANALYSIS: The methodological quality of the eligible trial 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. Results were compared and differences resolved as required. Data analysis was conducted according to the standards of the Cochrane Neonatal Review Group. MAIN RESULTS: The results of the one small trial of 51 infants included in this systematic review indicate a significant reduction in vascular retrolental fibroplasia (i.e. severe ROP) for infants weaned gradually from high oxygen concentrations compared with abrupt discontinuation (RR 0.22, 95% CI 0.07-0.68). This finding was independent of the duration of oxygen therapy. REVIEWER'S CONCLUSIONS: The results of this systematic review provide additional evidence linking routine exposure to high ambient oxygen in the early neonatal period to the development of ROP in preterm/LBW infants. However, due to small numbers and historical oxygen monitoring techniques, they provide little assistance to clinicians with regard to the most appropriate method of oxygen weaning, gradual or abrupt, in modern neonatal care settings.

Humans↗
PubMed2000

Early versus late discontinuation of oxygen 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 early versus late weaning from supplementary oxygen influence mortality, retinopathy of prematurity, lung function, growth or development? SEARCH STRATEGY: The standard search strategy of the Neonatal Review Group was used. This included searches of the Oxford Database of Perinatal Trials, MEDLINE, previous reviews including cross references, abstracts, conferences and symposia proceedings, expert informants, journal handsearching mainly in the English language. An additional literature search of the MEDLINE, EMBASE, and CINAHL databases was conducted in order to locate any trials in addition to those provided by the Cochrane Controlled Trials Register (CENTRAL/CCTR). SELECTION CRITERIA: All trials utilising random or quasi-random patient allocation, in which early weaning was compared with late discontinuation of supplemental oxygen in preterm or low birth weight infants, were eligible for inclusion. DATA COLLECTION AND ANALYSIS: The methodological quality of the one eligible trial was assessed independently by each author for the degree of selection, performance, attrition and detection bias. Data regarding clinical outcomes including mortality, retinopathy of prematurity, and long term growth and development were extracted and reviewed independently by each author. Results were compared and differences resolved as required. Data analysis was conducted according to the standards of the Cochrane Neonatal Review Group. MAIN RESULTS: In the single eligible trial of 99 infants with birthweights less than 1650g, there were no significant differences in neonatal death rates or retrolental fibroplasia (any grade or severe) for all infants, or among infants with birth weights of less than 1000g. No other outcome measures specified a priori as clinically meaningful were reported in enough detail or with satisfactory follow-up rates to include in the analysis (early death; chronic lung disease; and long term growth, development, lung or visual function). REVIEWER'S CONCLUSIONS: The results of this systematic review do not provide strong evidence for either the benefits or harms of early oxygen weaning in preterm/LBW infants. Future research should be directed toward addressing the question of what are the most appropriate target levels of oxygenation, in both the early and late neonatal periods, rather than whether oxygen should be weaned early or late.

Humans↗
PubMed1996

Long-term oxygen therapy at home. Compliance with medical prescription and effective use of therapy. ANTADIR Working Group on Oxygen Therapy. Association Nationale de Traitement à Domicile des Insuffisants Respiratories.

STUDY OBJECTIVE: Daily duration of oxygen administration is an important factor in the effectiveness of long-term oxygen therapy (LTOT) for hypoxic chronic pulmonary disease. We have assessed the daily use of oxygen therapy in 930 patients with COPD and examined factors associated with the effective use of this treatment. METHODS: Objective daily duration of oxygen use over a 3-month period was prospectively measured using the counter clock of the oxygen concentrators or by weighing the liquid oxygen container at each delivery. A questionnaire was filled in by an independent investigator asking about home situation, lifestyle, and whether oxygen therapy was used during all domestic and outside activities. In addition, prescribing physicians were asked about the duration and modalities of oxygen prescribed in each case. RESULTS: The patients had been receiving LTOT for 36 +/- 24 months and had hypoxemia (PaO2 = 56 +/- 9 mm Hg), hypercapnia (PaCO2 = 47 +/- 8 mm Hg), and severe airflow obstruction (FEV1/VC = 42 +/- 14%). The mean duration of oxygen treatment prescribed was 16 +/- 3 h/d. The mean duration of oxygen therapy achieved was 14.5 +/- 5 h, but only 45% of the patients achieved oxygen therapy for 15 h or more per day. Patients with effective use of LTOT, ie receiving oxygen therapy for at least 15 h/d, were significantly more hypoxic (PaO2 = 54 +/- 9 vs 57 +/- 9 mm Hg; p < 0.001), more hypercapnic (PaCO2 = 48 +/- 8 vs 46 +/- 7 mm Hg; p < 0.005), and also more obstructed (FEV1/VC = 39.5 +/- 13 vs 45 +/- 14%; p < 0.001) than the rest of the patients under treatment. Other factors associated with effective use of oxygen were (1) initial prescription for 15 h or more per day, (2) supplementary education on oxygen therapy by a nurse or physiotherapist, (3) cessation of smoking, (4) use of oxygen in all domestic situations (toilet, meals, leisure, etc.), and (5) absence of side effects from oxygen treatment. CONCLUSIONS: Attention by the prescribing physicians to such factors could optimize oxygen prescription and constitute goals for education of patients.

Adult↗
PubMed2002

Implementation of an oxygen therapy clinic to manage users of long-term oxygen therapy.

STUDY OBJECTIVES: To evaluate the initial benefits of establishing an oxygen therapy clinic (OTC) to manage users of long-term oxygen therapy (LTOT). DESIGN: Cross-sectional observational study. SETTING: Military-affiliated, tertiary care hospital. PATIENTS OR PARTICIPANTS: Current users of LTOT at our institution and patients with new oxygen prescriptions between June 2000 and May 2001. INTERVENTION: The OTC evaluation consisted of a focused medical interview and physical examination by a respiratory therapist. Demographic data, indications for supplemental oxygen, oxygen-related diagnoses, cardiopulmonary review of systems, pertinent physical examination findings, pulmonary function testing, and oximetry data were recorded. Patients prescribed oxygen during hospitalization were followed up for recertification within 90 days based on the recommendations of the Fifth Oxygen Consensus Conference. Also, patients with existing oxygen prescriptions and new oxygen prescriptions during the study period were evaluated in the OTC. Data are provided for the initial evaluation in this clinic. MEASUREMENTS AND RESULTS: A total of 283 patients were evaluated in the OTC during the study period. Ninety-seven patients with a new oxygen prescription during hospitalization were evaluated, with a mean +/- SE time from discharge to evaluation of 2.6 +/- 0.4 months. At follow-up, 50.5% of these patients no longer met Medicare guidelines for LTOT. A significant change in oxygen prescription was required in 27.9% of these patients. A total of 95 outpatients with existing oxygen prescriptions were contacted for recertification in the OTC. Of these patients, 31.6% no longer met Medicare criteria for LTOT and 26% required a significant change to their oxygen prescription. Oxygen therapy was discontinued in 22% of the 91 patients who were referred from other outpatient clinics, and the oxygen prescription was changed in another 29.7%. CONCLUSIONS: Results of this initial evaluation suggest that the institution of a respiratory therapist-managed OTC to manage home oxygen patients can significantly decrease inappropriate supplemental oxygen use, which can result in significant cost savings while providing improved health-care delivery. Further evaluation is necessary to identify the long-term benefits and cost savings in this population.

Aged↗
PubMed2003

Relationship in simulation between oxygen deficit and oxygen uptake in decrement-load exercise starting from low exercise intensity.

The purpose of the present study was to determine by simulation whether oxygen deficit kinetics in decrement-load exercise (DLE) starting from a low exercise intensity is related to the oxygen uptake (Vo(2)) kinetics. In this simulation, work rate in DLE was separated into steps that were regarded as constant-load exercises (CLEs). It was assumed that Vo(2) kinetics behaved exponentially at the onset and offset of each CLE, respectively. Vo(2) at the onset of CLEs increases at the same time and becomes a recovery phase step-by-step corresponding to the decrement of work rate. The sum of Vo(2) values at the onset of CLEs at a given time (nt-Vo(2)) corresponds to Vo(2) excluding oxygen debt in DLE. The sum of Vo(2) values at the offset of CLEs at a given time (dt-Vo(2)) corresponds to Vo(2) related to oxygen debt in DLE. The total of net- and dt-Vo(2) values is equivalent to Vo(2) actually observed in DLE (gs-Vo(2)). As the oxygen requirement level is a steady-state value of Vo(2) in CLE, the oxygen deficit level can be obtained by subtracting Vo(2) at the onset of CLE from the steady-state value. The oxygen deficit level at a given time was added in all CLEs. This is oxygen deficit per unit time (df-Vo(2)). Oxygen debt and oxygen deficit were calculated by integrating df-Vo(2) and dt-Vo(2) from the start of exercise to a given time, respectively. Gs-Vo(2) increased, reached a peak, and decreased linearly until the end of the DLE. Oxygen deficit increased rapidly and showed a steady state. Oxygen debt increased linearly after a time lapse. The difference between oxygen deficit and oxygen debt changed like gs-Vo(2) kinetics. Therefore, it is concluded that if we consider the repayment of oxygen debt in the oxygen deficit in DLE, the kinetics of the oxygen deficit becomes similar to gs-Vo(2) kinetics in the simulation.

Exercise↗
PubMed2000

Maternal oxygen administration for suspected impaired fetal growth.

BACKGROUND: Fetal hypoxaemia is often a feature of fetal growth impairment. It has been suggested that perinatal outcome after suspected impaired fetal growth might be improved by giving mothers continuous oxygen until delivery. OBJECTIVES: The objective was to assess the effects of maternal oxygen therapy in suspected impaired fetal growth on fetal growth and perinatal outcome. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register. SELECTION CRITERIA: Acceptably controlled trials comparing maternal oxygen therapy with no oxygen therapy in suspected impaired fetal growth. DATA COLLECTION AND ANALYSIS: Eligibility and trial quality was assessed. MAIN RESULTS: Two studies involving 62 women were included. Oxygenation compared with no oxygenation was associated with a lower perinatal mortality rate (relative risk 0.41, 95% confidence interval 0.21 to 0.78). However higher gestational age in the oxygenation groups may have accounted for the difference in mortality rates. REVIEWER'S CONCLUSIONS: There is not enough evidence to evaluate the benefits and risks of maternal oxygen therapy for suspected impaired fetal growth.

Female↗
PubMed1998

Stimulation of oxygen uptake by prostaglandin E2 is oxygen dependent in perfused rat liver.

The aim of this study was to determine if the effect of prostaglandin E2 (PGE2) on hepatic oxygen uptake was affected by oxygen tension. Livers from fed female Sprague-Dawley rats were perfused at normal or high flow rates (4 or 8 ml . g-1 . min-1) to vary local oxygen tension within the liver lobule. During perfusion at normal flow rates, PGE2 (5 microM) infusion increased oxygen uptake by about 50 micromol . g-1 . h-1; however, when livers were perfused at high flow rates, the increase was nearly twice as large. Simultaneously, glucose output was increased rapidly by about 50%, whereas glycolysis was decreased about 60%. When flow rate was held constant, increases in oxygen uptake due to PGE2 were proportional to oxygen delivery. Infusion of PGE2 into livers perfused at normal flow rates increased state 3 rates of oxygen uptake of subsequently isolated mitochondria by about 25%; however, rates were increased 50-75% in mitochondria isolated from livers perfused at high flow rates. Thus it is concluded that PGE2 stimulates oxygen uptake via mechanisms regulated by oxygen tension in perfused rat liver. High flow rates also increased basal rates of oxygen uptake: this increase was prevented by inactivation of Kupffer cells with GdCl3. In addition, conditioned medium from Kupffer cells incubated at high oxygen tension (75% oxygen) stimulated oxygen uptake of isolated parenchymal cells by >30% and elevated PGE2 production about twofold compared with Kupffer cells exposed to normal air-saturated buffer (21% oxygen). These effects were blocked completely by both indomethacin and nisoldipine. These data support the hypothesis that oxygen stimulates Kupffer cells to release mediators such as PGE2 which elevate oxygen consumption in parenchymal cells, possibly by mechanisms involving cyclooxygenase and calcium channels.

Animals↗
PubMed2004

Intraretinal oxygenation and oxygen consumption in the rabbit during systemic hyperoxia.

PURPOSE: To determine the ability of the retina and choroid in the avascular region of the rabbit retina to regulate intraretinal oxygen levels during periods of acute systemic hyperoxia. METHODS: Oxygen-sensitive microelectrodes were used to measure oxygen tension as a function of depth through the retina and choroid in anesthetized rabbits before and after stepwise incremental increases in inspired oxygen level. The extent of any oxygen increases throughout the retina and choroid was determined, and retinal oxygen consumption was determined by analyzing intraretinal oxygen distribution. RESULTS: Increases in systemic arterial oxygen in the rabbit resulted in significant increases in oxygen tension in the choroid and in all retinal layers. There was no apparent regulation of choroidal oxygen tension, as seen in the avascular retina of the guinea pig. Neither was there any increase in oxygen consumption within the retina, which has been shown to dampen the extent of raised oxygen levels in the inner retina in other mammals. Consequently, all retinal layers in the avascular area of the rabbit retina were exposed to high oxygen levels during systemic hyperoxia. The magnitude of the oxygen changes in all retinal layers was consistent with that in the preretinal vitreous. CONCLUSIONS: Unlike other mammals studied to date, the rabbit does not possess any regulatory mechanisms for controlling the intraretinal oxygen environment during acute increases in systemic arterial oxygen levels. This may well account for the reported vulnerability of the rabbit retina to toxic damage during extended periods of systemic hyperoxia.

Animals↗
PubMed2000

A model of stepwise isovolaemic blood exchange in anaesthetised, spontaneously breathing rats to evaluate the oxygen transport efficiency of artificial oxygen carriers.

Our research pursues the production of hypo-oncotic artificial oxygen carriers, based on artificial covalently cross-linked hyperpolymeric mammalian haemoglobins. To evaluate their in vivo efficiency in oxygen delivery to the tissue we developed a small animal model of stepwise isovolaemic blood exchange in anaesthetised, spontaneously breathing rats. With the aid of a two-way respiratory micro valve for small animals the overall oxygen uptake by the tissue of the animal can be determined. Measurements of oxygen contents in arterial and mixed venous blood and of some further blood parameters together with known oxygen-binding characteristics of artificial and native oxygen carriers, permits the determination of the way the two oxygen carriers contribute to the overall oxygen uptake. These so-called partial oxygen net to transport rates (i.e. partial oxygen uptakes), related to the corresponding intravascular mass flow of the transporters, are characteristic measures of the efficiency of the oxygen transporter, the so-called oxygen transport quality. Other biological indicators for an adequate oxygen supply are oxygen-dependent changes of ventilation, cardiac output, heart rate, and systemic vascular resistance. The performance of artificial oxygen carriers is elucidated by a comparison with experimental results from the analogous treatment of rats with non oxygen-transporting plasma expanders.

Anesthesia↗
PubMed1992

[Home oxygen therapy using liquid oxygen system].

Home oxygen therapy (HOT) for patients with chronic respiratory failure has been believed to increase the quality of life and to improve the prognosis of such patients. In Japan, HOT for chronic respiratory failure has been supported by health insurance since March 1985. Since then, patients with HOT have increased progressively, and it has been reported that there are now over 20,000 patients with HOT. The oxygen concentrator which extracts oxygen from atmospheric air has been commonly used as the oxygen delivery system. Recently the liquid oxygen system has provided an attractive, convenient source of oxygen. Since April 1990, HOT using liquid oxygen system has been supported by health insurance, and its use will become widespread in Japan. A major characteristic of this system is that oxygen condensed into a liquid form allows storage of a larger supply. This system consists of two parts: stationary type which stores the liquid oxygen, and a portable type which can easily be refilled with oxygen a larger source. In the present study, we examined the efficacy of portable liquid oxygen in 50 patients with chronic pulmonary diseases including patients with chronic respiratory failure who had PaO2 < 55 mmHg during air breathing. We measured changes of ten minutes walking distance (10 MD) and blood gas analysis with and without portable liquid oxygen. We also performed on estimation of efficacy of liquid oxygen by questionnaires in patients receiving liquid oxygen for HOT. We did not find a significant improvement of 10 MD with portable liquid oxygen, but found a significant improvement of arterial oxygen tension at the end of walking.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon Dioxide↗
PubMed2006

Nocturnal oxygenation using a pulsed-dose oxygen-conserving device compared to continuous flow.

BACKGROUND: The pulsed-dose oxygen-conserving device (PDOCD) has gained wide acceptance as a tool to reduce the cost and inconvenience of portable oxygen delivery. Despite the widespread use of PDOCDs in awake and ambulating patients, few studies report their use during sleep. This study was designed to compare heart rate and oxygen saturation (measured via pulse oximetry [S(pO2)]) of sleeping patients using one brand of PDOCD versus continuous-flow oxygen. METHODS: We studied 10 home-oxygen patients who were using various continuous-flow oxygen systems and prescriptions. Baseline asleep and awake S(pO2) and heart rate were recorded while the patients used their existing home-oxygen systems (liquid oxygen or oxygen concentrator with nasal cannula) and continuous-flow oxygen prescription. Patients were then switched to a nasal cannula connected to a PDOCD. The PDOCD setting was adjusted to produce an S(pO2) equal to the patient's awake baseline on continuous-flow. This setting was then used while the patient subsequently slept. Mean values for S(pO2) and heart rate and hours of sleep were calculated by the software in the oximeter. Mean values for S(pO2) and heart rate were compared with the paired Student's t test. RESULTS: There was a statistically significant but clinically unimportant S(pO2) difference between the patients who used continuous-flow oxygen and those who used the PDOCD (95.7% vs 93.2%, respectively, p = 0.043). There was no difference in heart rate (77.3 beats/min vs 77.9 beats/min, p = 0.70). The sample size was adequate to detect a difference in heart rate of 5 beats/min at a power of 80%. For the subset of patients whose PDOCD triggering sensitivity was set on sensitive (vs the default lower sensitivity) there was a statistically significant but clinically unimportant S(pO2) difference (continuous-flow 95.6% vs PDOCD 93.2%, p = 0.044). All other comparisons showed no differences, but the samples sizes were too small to make any firm conclusions. One patient experienced an 11% S(pO2) drop with the PDOCD because of an inadequate triggering sensitivity setting. CONCLUSIONS: The PDOCD model we studied was able to deliver oxygen therapy (via nasal cannula) comparable to continuous-flow in 9 of 10 patients. The resting daytime S(pO2) on continuous-flow appears to be an appropriate target for setting the PDOCD to ensure adequate oxygenation, even during sleep, with the PDOCD we tested. We conclude that the PDOCD we tested is able to maintain adequate S(pO2) during sleep in selected patients. Because of differences in design, triggering-signal sensitivity, and oxygen-pulse volume, these results cannot be generalized to all patients or all oxygen-conserving devices. Further research is needed to determine the general performance of PDOCDs on larger populations of oxygen-dependent patients and patients with sleep-disordered breathing.

Female↗
PubMed1990

[Comparison of an oxygen-conserving module "Oxytron" and the reservoir cannula "Oxymizer Pendant" with continuous oxygen administration via nasal prong in hypoxemic patients].

High costs involved in administering continuous long-term oxygen therapy to patients with chronic lung diseases and limited portability of oxygen sources stimulated research into and development of oxygen conserving devices. Oxytron (Weinmann, Hamburg) is a new electronic demand oxygen delivery system which limits oxygen flow to the early phase of inspiration. The reservoir cannula Oxymizer Pendant (Chad-Therapeutics Inc.) is a nasal prong system incorporating a pendant reservoir which stores oxygen during expiration and delivers it as a bolus at the onset of inspiration. Ten patients with significant hypoxaemia at rest received oxygen delivered at various breath interval settings with the Oxytron method and at flow rates of 2, 3 and 41/min with the reservoir cannula Oxymizer Pendant and with continuous flow. The results indicate that significantly less oxygen was required to provide equivalent oxygen saturation with Oxytron as compared with steady flow delivery: an oxygen flow reduction of greater than 75% was achieved at all Oxytron settings tested. With the reservoir cannula oxygen saving was most evident at low oxygen flows: 29.3, 19.4 and 4.7% less oxygen was required than with continuous flow at 2, 3 and 41/min. Individual patient acceptance of various drug delivery systems and response to therapy should be considered when prescribing home oxygen therapy. The use of oxygen saving techniques could result in a substantial cost saving and greater mobility may help to improve compliance in patients requiring continuous oxygen therapy.

Adult↗
PubMedDate not supplied

Effect of oxygen treatment and dressing oxygen permeability on wound healing.

Although it has been shown that both the level of tissue oxygen and its gradient are critical factors in the healing process, optimal conditions for oxygen therapy have not been determined. In this study, both the oxygen level and oxygen gradient for a full-thickness defect were modified on the basis of preceding in vitro studies to determine the effect on the healing process. The goal of this study was to help determine the optimal clinical oxygen treatment protocol. Specifically, the healing of full-thickness defects in a rabbit model as determined by histomorphometric analyses (cell and tissue volume fraction, epithelialization, and contraction) under two types of dressings with or without oxygen treatment (70% O(2)) was investigated. One of the dressings was more oxygen permeable than the other. No significant differences were found in the histomorphometric response between the wounds covered with the oxygen-permeable and oxygen-impermeable dressings in the group without supplemental oxygen. Oxygen treatment, however, seemed to enhance the healing response significantly. According to the histomorphometric response, the wounds covered with the oxygen-impermeable dressings were significantly better than those with the oxygen-permeable dressing in the oxygen-treated group after 1 week, but the wounds covered by the oxygen-permeable dressings were better healed at 3 weeks. Therefore, oxygen-impermeable dressings may be useful only in the early stages of healing, before granulation tissue formation.

Journal Article↗
PubMed1991

A theoretical analysis of the effect of placental metabolism on fetal oxygenation under conditions of limited oxygen availability.

The purpose of this theoretical paper is to examine the effects of placental metabolism on fetal oxygenation under conditions of limited oxygen availability. Features of the mathematical model used here include: (1) ordinary non-linear differential equations defining the oxygen partial pressure profiles in the maternal and fetal streams for a concurrent flow pattern; (2) the presence of maternal and fetal blood flow shunts; (3) consumption of oxygen by a metabolically active placenta; and (4) modification of the fetal input to the placenta by changing the rate of fetal oxygen consumption in response to changes in the rate of oxygen delivered to the fetus via the umbilical vein. Model parameters were chosen to be well within the range of values cited in the literature. Based on these calculations, we conclude that: (1) under normal conditions, approximately one-half of the fetal uterine-umbilical venous oxygen partial pressure difference can be attributed to placental oxygen consumption; (2) utilization of fetal oxygen to help maintain the metabolic activities of the placenta does not significantly impair fetal oxygenation under normal conditions; (3) consumption of oxygen by the placenta will have a significant detrimental effect on the rate of oxygen delivered to the fetus if oxygen availability is compromised; and (4) for the same rate of maternal oxygen delivered to the placenta, maternal hypoxemia has a significantly greater adverse effect on fetal oxygenation than does maternal anemia.

Computer Simulation↗
PubMed1999

Relationship between mixed venous oxygen saturation and markers of tissue oxygenation in progressive hypoxic hypoxia and in isovolemic anemic hypoxia in 8- to 12-day-old piglets.

OBJECTIVE: To examine the hypothesis that mixed venous oxygen saturation (SvO2) values, which reflect the residual oxygen after tissue oxygen extraction, would be similar during hypoxic and anemic hypoxia. DESIGN: SvO2 values, oxygen delivery, arterial oxygen content, and fractional oxygen extraction were compared, and critical values were determined based on lactate, the lactate/pyruvate ratio, and oxygen consumption during hypoxic and anemic hypoxia. SETTING: Laboratory of physiology at a university hospital. SUBJECTS: Two groups of eight piglets, 8 to 12 days old. INTERVENTIONS: Piglets were anesthetized, tracheotomized, intubated, and ventilated. A thoracotomy was performed and a fiberoptic catheter was placed in the pulmonary artery to monitor SvO2. A transit time ultrasound flow probe was positioned around the ascending aorta to measure aorta flow. Progressive hypoxic hypoxia was induced by decreasing FI(O2) from baseline (0.30-0.75) to 0.21, 0.15, and 0.10. Progressive anemic hypoxia was induced by a repeated isovolemic exchange transfusion with 50 mL of pasteurized plasma. MEASUREMENTS AND MAIN RESULTS: Fifteen or 30 mins after each intervention, samples were taken from the carotid artery for blood gases, hemoglobin, lactate, and pyruvate and from the pulmonary artery for blood gases and hemoglobin. Hemodynamic, arterial oxygen saturation, and SvO2 measurements were made. The calculated oxygen delivery and oxygen consumption decreased in both hypoxic and anemic hypoxia. At the lowest oxygen delivery level of anemic hypoxia, the decrease in SvO2 was less than that in hypoxic hypoxia (-26% vs. -55%). The range of critical values for SvO2 calculated for each individual piglet below which lactate, the lactate/pyruvate ratio, and oxygen consumption rapidly changed from baseline value was significantly lower in hypoxic hypoxia (11% to 24%) than in anemic hypoxia (26% to 48%). Fractional oxygen extraction increased significantly but not with a change as high as in hypoxic hypoxia 0.31 (range, 0.20-0.41) vs. 0.49 (range, 0.41-0.54). CONCLUSIONS: In comparison with hypoxic hypoxia, critical values of SvO2 are higher in anemic hypoxia, indicating that oxygen unloading from blood to tissues is impaired in anemic hypoxia. These characteristics in oxygen transport and capillary hemodynamics should be taken into consideration when SvO2 is used in clinical critical care.

Anemia↗