Reducing the Number of Test Items of the Action Research Arm Test Poststroke: A Decision Tree Analysis✰.

OBJECTIVE: The present study aimed to create a shorter version of the Action Research Arm Test (ARAT) without compromising its measurement properties. DESIGN: Secondary analysis of stroke recovery cohorts that used the ARAT to measure upper limb impairment. SETTING: Rehabilitation centers. PARTICIPANTS: Patients with stroke from 5 different stroke recovery cohorts (N=1425). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: A decision tree version of the ARAT (ARAT-DT) was developed using chi-square automated interaction detection. In an independent validation subset, criterion validity, agreement of ARAT-DT with original ARAT scores and score categories, and construct validity with the Fugl-Meyer Upper Extremity Scale score were determined. RESULTS: In total, 3738 ARAT measurements were available involving 1425 subjects. Chi-square automated interaction detection analysis in the development subset (n=2803) revealed an optimized decision tree with a maximum of 4 consecutive items. In the validation data set (n=935), the ARAT-DT differed by a mean of 0.19 points (0.3% of the total scale) from the original ARAT scores (limits of agreement=-5.67 to 6.05). The ARAT-DT demonstrated excellent criterion validity with the original ARAT scores (intraclass correlation coefficient=0.99 and ρ=0.99) and scoring categories (κw=0.97). The ARAT-DT showed very good construct validity with the Fugl-Meyer Upper Extremity Scale (ρ=0.92). CONCLUSION: A decision tree version of the ARAT was developed, reducing the maximum number of items necessary for ARAT administration from 19 to 4. The scores produced by the decision tree had excellent criterion validity with original ARAT scores.

An insight into the antibiofilm properties of Costa Rican stingless bee honeys.

OBJECTIVE: There is an increasing search for antibiofilm agents that either have specific activity against biofilms or may act in synergy with antimicrobials. Our objective is to examine the the antibiofilm properties of stingless bee honeys. METHOD: Meliponini honeys from Costa Rica were examined along with Medihoney as a reference. All honeys were submitted to a screening composed of minimum inhibitory concentration, inhibition of biofilm formation and biofilm destruction microplate-based assays against a Staphylococcus aureus biofilm forming strain. Dialysis led to the isolation of an antibiofilm fraction in Tetragonisca angustula honeys. The honey antibiofilm fraction was evaluated for protease activity and for any synergistic effect with antibiotics on a Staphylococcus aureus biofilm. The active fraction was then separated through activity guided isolation techniques involving SDS-PAGEs, anion exchange and size exclusion fast protein liquid chromatographies. The fractions obtained and the isolated antibiofilm constituents were tested for amylase and DNase activity. RESULTS: A total of 57 Meliponini honeys from Costa Rica were studied in this research. The honeys studied belonged to the Tetragonisca angustula (n=36) and Melipona beecheii (n=21) species. Costa Rican Tetragonisca angustula honeys can inhibit the planktonic growth, biofilm formation, and are capable of destroying a Staphylococcus aureus biofilm. The antibiofilm effect was observed in the protein fraction of Tetragonisca angustula honeys. The biofilm destruction proteins allowed ampicillin and vancomycin to recover their antimicrobial activity over a Staphylococcus aureus biofilm. The antibiofilm proteins are of bee origin, and their activity was not due to serine, cysteine or metalloproteases. There were 2 proteins causing the antibiofilm action; these were named the Tetragonisca angustula biofilm destruction factors (TABDFs). TABDF-1 is a monomeric protein of approximately 50kDa that is responsible of the amylase activity of Tetragonisca angustula honeys. TABDF-2 is a protein monomer of approximately 75kDa. CONCLUSION: Tetragonisca angustula honeys from Costa Rica are a promising candidate for research and development of novel wound dressings focused on the treatment of acute and chronic Staphylococcus aureus biofilm wound infections.

Bovine Staphylococcus aureus Secretes the Leukocidin LukMF' To Kill Migrating Neutrophils through CCR1.

UNLABELLED: Although Staphylococcus aureus is best known for infecting humans, bovine-specific strains are a major cause of mastitis in dairy cattle. The bicomponent leukocidin LukMF', exclusively harbored by S. aureus of ruminant origin, is a virulence factor associated with bovine infections. In this study, the molecular basis of the host specificity of LukMF' is elucidated by identification of chemokine receptor CCR1 as its target. Bovine neutrophils, the major effector cells in the defense against staphylococci, express significant cell surface levels of CCR1, whereas human neutrophils do not. This causes the particular susceptibility of bovine neutrophils to pore formation induced by LukMF'. Bovine S. aureus strains produce high levels of LukMF' in vitro. In culture supernatant of the mastitis field isolate S1444, LukMF' was the most important cytotoxic agent for bovine neutrophils. In a fibrin gel matrix, the effects of the in situ secreted toxins on neutrophils migrating toward S. aureus were visualized. Under these physiological ex vivo conditions, bovine S. aureus S1444 efficiently killed approaching neutrophils at a distance through secretion of LukMF'. Altogether, our findings illustrate the coevolution of pathogen and host, provide new targets for therapeutic and vaccine approaches to treat staphylococcal diseases in the cow, and emphasize the importance of staphylococcal toxins in general. IMPORTANCE: This study explains the mechanism of action of LukMF', a bicomponent toxin found in bovine lineages of S. aureus that is associated with mastitis in cattle. At a molecular level, we describe how LukMF' can specifically kill bovine neutrophils. Here, we demonstrate the contribution of toxins in the determination of host specificity and contribute to the understanding of mechanisms of coevolution of pathogen and host. Our study provides new targets that can be used in therapeutic and vaccine approaches to treat staphylococcal diseases in the cow. We also demonstrate the importance of toxins in specific elimination of immune cells, which has broader implications, especially in human infections.

Microbiocidal effects of various taurolidine containing catheter lock solutions.

BACKGROUND & AIMS: We have recently shown that a catheter lock solution containing taurolidine dramatically decreases catheter-related bloodstream infections (CRBSI) in patients on home parenteral nutrition (HPN) when compared to heparin. Since several taurolidine formulations are commercially available, some of which also contain citrate or heparin, we were interested in the effect of these different locks on growth and biofilm formation of fungal, Gram-negative and Gram-positive pathogens that are known to impede HPN treatment. METHODS: Clinical isolates obtained during CRBSI of HPN patients were grown in the presence of catheter locks (2% taurolidine, 1.34% taurolidine-citrate, 1.34% taurolidine-citrate-heparin, citrate and heparin) or phosphate buffered saline diluted in lysogeny broth medium for bacteria and sabouraud liquid medium for yeasts. Biofilm formation, assessed by crystal violet staining, and growth of clinical isolates were determined by optical density measurements. RESULTS: We found that 12.5× diluted solutions of all taurolidine containing formulations completely prevented growth of Escherichia coli, Staphylococcus aureus and Candida glabrata. Growth of these microbes was detected earlier in 1.34% taurolidine-citrate(-heparin) than in 2% taurolidine, while citrate and heparin did not inhibit growth of clinical isolates compared to PBS. No differences in biofilm formation were found between taurolidine containing solutions. CONCLUSION: Taurolidine containing lock solutions prevent growth of fungal, Gram-negative and Gram-positive pathogens. While 2% taurolidine appears to be the most potent in this respect in this in vitro setting, the relevance of the small differences in growth inhibition between the commercially available taurolidine containing lock solutions for clinical practice remains to be established.

Staphylococcal alpha-phenol soluble modulins contribute to neutrophil lysis after phagocytosis.

Staphylococcus aureus community-acquired (CA) MRSA strains are highly virulent and can cause infections in otherwise healthy individuals. The most important mechanism of the host for clearing S. aureus is phagocytosis by neutrophils and subsequent killing of the pathogen. Especially CA-MRSA strains are very efficient in circumventing this neutrophil killing. Interestingly, only a relative small number of virulence factors have been associated with CA-MRSA, one of which are the phenol soluble modulins (PSMs). We have recently shown that the PSMs are functionally inhibited by serum lipoproteins, indicating that PSMs may exert their cytolytic function primarily in the intracellular environment. To further investigate the intracellular role of the PSMs we measured the effect of the α-type and ß-type PSMs on neutrophil killing after phagocytosis. Using fluorescently labelled S. aureus, we measured bacterial survival after phagocytosis in a plate reader, which was employed next to flow cytometry and time-lapse microscopy. Phagocytosis of the CA-MRSA strain MW2 by human neutrophils resulted in rapid host cell death. Using mutant strains of MW2, we demonstrated that in the presence of serum, the intracellular expression of only the psmα operon is both necessary and sufficient for both increased neutrophil cell death and increased survival of S. aureus. Our results identify PSMα peptides as prominent contributors to killing of neutrophils after phagocytosis, a finding with major implications for our understanding of S. aureus pathogenesis and strategies for S. aureus vaccine development.

Metabolic information from the human fetal brain obtained with proton magnetic resonance spectroscopy.

OBJECTIVE: To study the feasibility of proton magnetic resonance spectroscopy for the examination of human fetal brain metabolism. STUDY DESIGN: Proton magnetic resonance spectroscopy was performed from a selected volume of brain tissue of 21 single normal fetuses of 36 to 41 weeks' gestational age. Absolute brain metabolite tissue levels were estimated by using the brain water content as an internal reference. RESULTS: Proton magnetic resonance spectra showed resonances for four dominating brain metabolites. Inositol, choline, creatine, and N-acetylaspartate could be detected with average tissue levels of 7.42 mmol/L, 3.31 mmol/L, 4.16 mmol/L, and 5.03 mmol/L, respectively. The resonance for N-acetylaspartate could not always be resolved from contaminating lipid signals. CONCLUSION: Proton magnetic resonance spectroscopy of the human fetal brain is feasible and can provide useful information about the fetal condition. The metabolite tissue levels for the fetal brain obtained in this study were in the range observed for neonates of similar gestational age.

Hypoxia in fetal lambs: a study with (1)H-MNR spectroscopy of cerebrospinal fluid.

In fetal lambs, severe hypoxia (SH) will lead to brain damage. Mild hypoxia (MH) is thought to be relatively safe for the fetal brain because compensating mechanisms are activated. We questioned whether MH, leading to mild acidosis, induces changes in cerebral metabolism. Metabolites in cerebrospinal fluid (CSF) samples, as analyzed by proton magnetic resonance spectroscopy, were studied in two groups of seven anesthetized near-term fetal lambs. In group I, SH leading to acidosis with an arterial pH <7.1 was achieved. In group II, MH with an intended pH of 7.23--7.27 was reached [start of MH (SMH)], and maintained during 2 h [end of MH (EMH)]. During SH, choline levels in CSF, a possible indicator of cell membrane damage, were increased. Both during SH and at EMH, CSF levels of lactic acid, alanine, phenylalanine, tyrosine, lysine, branched chain amino acids, and hypoxanthine were increased compared with control values and with SMH, respectively. At EMH, the hypoxanthine CSF-to-blood ratio was increased as compared with SMH. These results indicate that prolonged MH leads to energy degradation in the fetal lamb brain and may not be as safe as assumed.

Ins(1,4,5)P3 receptors in cerebral arteries: changes with development and high-altitude hypoxia.

We and others have shown that adrenergic-mediated contractile responses in cerebral vessels in vitro differ with vessel segment, with developmental age, and with high-altitude, long-term hypoxia. This is associated with significant differences in alpha 1-adrenergic receptor density and norepinephrine (NE)-induced response of the second messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. To test the hypothesis that vessel-specific, developmental, and hypoxic-associated contractility changes are mediated, in part, by changes in Ins(1,4,5)P3-receptor [Ins(1,4,5)P3-R] density or affinity, we performed the following study. In common carotid (Com), circle of Willis, and main branch anterior, middle, and posterior cerebral arteries (MBC) from normoxic fetal (approximately 140 days), newborn (3-5 days), and adult sheep and fetal and adult sheep acclimatized to high altitude, we quantified Ins(1,4,5)P3-R with [3H]Ins(1,4,5)P3. In normoxic Com, Ins(1,4,5)P3-R density values (fmol/mg protein) in fetus, newborn, and adult were 8 +/- 53, 150 +/- 18, and 357 +/- 21, respectively (P < 0.05). In normoxic MBC cerebral arteries, the receptor density values in the three age groups were 115 +/- 15, 105 +/- 9, 99 +/- 5 fmol/mg protein, respectively. For fetal and adult Com, high-altitude, long-term hypoxemia was associated with decreases in Ins(1,4,5)P3-R density of 32 (to 58 +/- 5) and 70% (to 109 +/- 12), respectively, from control values (P < 0.01). In MBC cerebral arteries of fetus and adult, hypoxic-associated decreases in Ins(1,4,5)P3-R density from control were 80 (to 23 +/- 3) and 47% (to 53 +/- 7), respectively (P < 0.01). Ins(1,4,5)P3 binding affinity to the receptor averaged 11.8 +/- 0.5 nM and did not vary significantly as a function of vessel type, developmental age, or hypoxia. In Com, but not in MBC, Ins(1,4,5)P3-R density increased dramatically with developmental age. This suggests that differences in Ins(1,4,5)P3-R density values may account, in part, for differences in contractile responses of the two artery types in the several age groups. In response to long-term, high-altitude hypoxia, Ins(1,4,5)P3-R density values in both fetal and adult Com and MBC decreased significantly, as did their NE-induced contraction. This suggests a cellular basis for changes in cerebrovascular contractility in response to long-term hypoxia and that Ins(1,4,5)P3-R may play a role in acclimatization responses to high altitude.

Accuracy of fetal pulse oximetry and pitfalls in measurements.

Pulse oximetry is a technique for estimating arterial oxygen saturation continuously and non-invasively. Reflectance pulse oximetry might become useful for monitoring the fetus during labour but it is much more susceptible to all kinds of physiological variations than the well-established transmission pulse oximetry for neonatal or adult monitoring. This review focuses on the accuracy of reflectance pulse oximetry. Results of human, animal, in vitro and theoretical models indicate that factors such as; blood volume fraction differences, haematocrit, and blood flow differences are major sources for inaccurate pulse oximetry readings in the fetal arterial oxygen saturation range of 10-80%. These factors cannot be overcome by systems using two wavelengths sensors with the 660/890 or 940 nm combination. Reported precision values (S.D. of difference between pulse oximeter and blood sample saturation) range between 2.5 and 12.9% for various 660 nm sensors. Most sensors were tested only once with a limited number of animals. A new 735/890 nm sensor (Nellcor Puritan Bennett) demonstrates a promising accuracy (precision around 5%) in two studies. Various other sensors have also been developed, but are not or scarcely evaluated. Without thorough establishment of the reliability of this technique, clinical fetal oxygen saturation data are still of limited value.

Validation of reflectance pulse oximetry: an evaluation of a new sensor in piglets.

OBJECTIVE: A new reflectance pulse oximetry sensor, developed for intrapartum estimation of arterial oxygen saturation (SaO2), was calibrated and evaluated. The sensor contains two light emitting diodes of 735 and 890 nm, and a photodetector at a distance of 14 mm from both light emitting diodes. METHODS: In seven Yorkshire/Hampshire piglets, the reflectance sensor (Nellcor Puritan Bennett Inc.) was calibrated using blood sample SaO2 values. The resulting calibration line was evaluated in four Dutch piglets, by comparing pulse oximetry saturation readings (SpO2) with blood sample and intravascular fiberoptic oximetry SaO2 values. Several reflectance sensors were fixed on each animal. Desaturation levels were obtained by changing the gas mixture of oxygen/ nitrous oxide via a tracheal catheter. RESULTS: In the Yorkshire/ Hampshire piglets, the standard deviation of difference (SpO2-SaO2) was 4.7% (n = 364), over an SaO2 range of 17% to 100%. In the Dutch piglets, the mean difference (SpO2-SaO2) was -1.6% and the standard deviation of difference was 5.4%, over the same SaO2 range (n = 254). Comparisons of continuous recordings of reflectance SpO2 and fiberoptic SaO2 revealed variation in individual regression lines. CONCLUSIONS: This new 735/890 nm reflectance sensor demonstrates acceptable accuracy in piglets. A further evaluation during labor should assess its feasibility for fetal surveillance.

Neonatal complications in newborns with an umbilical artery pH < 7.00.

OBJECTIVE: Our purpose was to determine the significance of an umbilical artery pH < 7.00 in relation to neonatal morbidity and mortality. STUDY DESIGN: Between 1986 and 1993 acid-base assessment of the umbilical artery was performed routinely in 10,699 deliveries. In a retrospective cohort study 84 nonanomalous neonates with an umbilical artery pH < 7.00 were individually matched with 84 neonates with an umbilical artery pH > 7.24. Matched variables included year of delivery, gender, parity, maternal age, delivery mode, fetal presentation, gestational age, and birth weight. Differences in morbidity between the two groups during the neonatal period (until 28 days after delivery) were investigated. RESULTS: Neonates with an umbilical artery pH < 7.00 versus > 7.24 showed significant differences in the following: neonatal condition directly post partum; neurologic, respiratory, cardiovascular, and gastrointestinal complications; and neonatal intensive care unit admissions. No significance was found in renal dysfunction and mortality rate. The proportion of premature infants (< 37 weeks) was 17% in both groups. In the acidotic group a 1-minute Apgar score < or = 3 and a 5-minute Apgar score < 7 was predictive for neonatal complications. CONCLUSIONS: Severe intrapartum asphyxia, quantified by an umbilical artery pH < 7.00, poses a threat to the neonate's health.

Reflectance pulse oximetry in fetal lambs: subcutaneous vessels and vasoconstriction affect its reliability.

OBJECTIVE: Reflectance pulse oximetry (RPOX) has been introduced for intrapartum fetal surveillance. The purpose of this study was to describe two possible effects on the reliability of RPOX, namely the effect of the presence of a subcutaneous vein and the effect of vasoconstriction by adrenaline, both at fetal SaO2 levels. METHODS: In four anesthetized fetal lambs, a prototype 660/890 nm reflectance sensor (Nellcor Inc.) was placed on the fetal head, with the photodiode of the sensor precisely over a superficial subcutaneous vein. Measurements were made before and after coagulation of the vein. In five anesthetized fetal lambs, one or two reflectance sensors were placed on the fetal head and/or neck and adrenaline was administered in doses of 0.02 to 0.04 mg via a brachial artery. Pulse oximeter saturation readings (SpO2) were compared with continuous arterial oxygen saturation (SaO2) values obtained using a fiberoptic catheter (Opticath, Abbott) in the carotid artery. RESULTS: When the sensor was placed over the vein, the pulse oximeter read 18% to 24% too low at a SaO2 level of 20% to 50%. After coagulation of the vein, SpO2 readings were in agreement with fiberoptic SaO2 values. Administration of adrenaline resulted in a large overestimation of the SaO2 in 6 of the 7 measurements. CONCLUSIONS: Subcutaneous veins and vasoconstriction can affect the reliability of reflectance pulse oximetry. As comparable situations may occur during labor, SpO2 readings should be interpreted with caution when this kind or comparable types of RPOX sensors are used at low SaO2 levels.

Transmission pulse oximetry in the fetal lamb: is there a universal calibration?

Transmission pulse oximetry is widely used for oxygen monitoring. The use of pulse oximeters is steadily expanding toward situations with low arterial oxygen saturation (Sao2) values. Therefore, we evaluated transmission pulse oximetry in the unanesthetized fetal lamb at low Sao2 levels. In seven fetal lambs, fetal hypoxemia was induced by occlusion of the maternal common iliac artery, four days after the instrumentation of the animal. Two Nellcor prototype transmission Y-sensors (light emitting diodes: 660 and 890 nm) were applied, one around a forelimb muscle and one around a skinfold in the neck, and were connected to Nellcor pulse oximeters. The pulse oximeter was calibrated for the skin measurements. Pulse oximeter saturation readings (Spo2) were compared with sample Sao2 values, over an Sao2 range of 13 to 63%. For the neck sensor the SD of the difference was 5.0% (n = 101). For the muscle sensor the mean difference was 19.5% and the SD of the difference was 5.9% (n = 206). Regression analysis showed a different calibration line for the muscle sensor with the equation: Spo2 = 0.92 x Sao2 + 21.90. Continuous recordings were obtained both from the forelimb muscle and from the neck, but the recordings from the neck showed a substantial loss of signal during the hypoxemia period. We conclude that transmission pulse oximetry is less accurate below an Sao2 of 70% in fetal lambs than above 70% Sao2. At these low levels of Sao2, pulse oximeters may need to be constructed with different calibration lines for various application positions of the body.

Arterial oxygen saturation in relation to metabolic acidosis in fetal lambs.

OBJECTIVE: We studied the relationship between preductal arterial oxygen saturation and metabolic acidosis in 18 chronically instrumented fetal lambs (gestational age 119 to 133 days) in two experimental designs. In the first group the onset of metabolic acidosis was determined. In the second group the progression of metabolic acidosis was studied as was the cardiovascular and hormonal changes resulting from hypoxemia. STUDY DESIGN: In nine fetal lambs maternal fraction of inspired oxygen was lowered stepwise by increasing flows of nitrogen delivered into the trachea through a small indwelling catheter (group 1), and in nine fetal lambs maternal blood flow was reduced stepwise by means of a vascular occluder (group 2). RESULTS: Baseline arterial oxygen saturation values ranged from 26% to 67% with normal pH and extracellular fluid base excess values in both groups 1 and 2. In both groups pH and extracellular fluid base excess started to decrease below 30% arterial oxygen saturation, with a progressive decrease below 20% arterial oxygen saturation to an end value for pH of 7.14. In some fetal lambs pH and extracellular fluid base excess decreased initially at 20% to 30% arterial oxygen saturation and then stabilized at the lower level. Fetal heart rate in group 1 increased during hypoxemia from 155 to 179 beats/min. In group 2 baseline fetal heart rate was 153 beats/min and fell with every step change in arterial oxygen saturation but subsequently increased to 172 beats/min by the end of the period of hypoxemia. Baseline values for epinephrine, norepinephrine, dopamine, cortisol, and mean arterial pressure were not related to baseline arterial oxygen saturation levels, and each of these variables was increased at the end of hypoxemia in group 2. CONCLUSION: Preductal arterial oxygen saturation can reach values between 20% and 30% before anaerobic metabolism starts. During the progressive acidosis blood pressure was increased, which can be attributed to a strong rise in catecholamines.

The effect of pulsating arteries on reflectance pulse oximetry: measurements in adults and neonates.

OBJECTIVE: The objective of our study was to describe the results from human experiments during normoxia that demonstrate the effect of pulsating arteries on the measured arterial oxygen saturation (SpO2) using a reflectance pulse oximeter sensor. METHODS: In 6 healthy adults and 7 healthy neonates, a Nellcor reflection sensor (FS-10 oxisensor, Nellcor, Inc., Pleasanton, CA) was placed in three different positions: (1) on the forehead, (2) on the temporal area, with the photodiode placed over the superficial temporal artery, and (3) on the temporal area, with the light-emitting diodes (LEDs) placed over the superficial temporal artery. RESULTS: Placement of the sensor in position 2 resulted in a significantly lower SpO2 reading, compared to sensor position 1: 5.8% (p < 0.01) lower for adults and 7.5% (p < 0.01) lower for neonates. Placement of the sensor in position 3 resulted in significantly larger plethysmographic signals, compared to sensor position 1; but, the Spo2 readings were alike. CONCLUSIONS: Pulsating arteries can affect the reliability of reflection pulse oximetry. Depending on the position of the sensor, a falsely low Spo2 value can be observed.

Notes on the apparent discordance of pulse oximetry and multi-wavelength haemoglobin photometry.

Multi-wavelength photometers, blood gas analysers and pulse oximeters are widely used to measure various oxygen-related quantities. The definitions of these quantities are not always correct. This paper gives insight in the various definitions for oxygen quantities. Furthermore, the possible influences of dyshaemoglobins and fetal haemoglobin on the accuracy of pulse oximetry are discussed. As pulse oximeters are constructed for the determination of arterial oxygen saturation, they should be validated with sample oxygen saturation values and not with the oxyhaemoglobin fraction. The influence of carboxyhaemoglobin is insubstantial over an oxygen saturation range of 0% to 100%. Through the presence of methaemoglobin, pulse oximetry will give an underestimation above 70% and an overestimation below 70% oxygen saturation. The influence of fetal haemoglobin is insignificant in the neonatal use of pulse oximetry, in the range of 75% to 100% arterial oxygen saturation. However, a pulse oximeter underestimates the arterial oxygen saturation at the 25% level with 5%, if the pulse oximeter has been calibrated in human adults. Such a low level of arterial oxygen saturation can be present in the fetus during labor.

The accuracy of a fiberoptic oximeter over a wide range of arterial oxygen saturation values in piglets.

A piglet model was used to evaluate the accuracy of a fiberoptic oximeter over a wide range of arterial oxygen saturation (SaO2) values. In eight anaesthetized piglets, the inspired oxygen concentration was varied from 30% to 6% resulting in a SaO2 range from 100% to 15%. Paired data of the Opticath fiberoptic catheter, which was placed in the descending aorta, and blood sample SaO2 values assessed by a multiwavelength oximeter, were analysed. After in vitro calibration according to the manufacturer's instruction, the fiberoptic catheter started to underestimate the SaO2 below 78%, worsening towards lower SaO2 values. The overall bias was -3.4% and the precision 3.8%. An off-line fit with a non-linear model resulted in a standard deviation of residuals of 2.6%. After several in vivo calibration adjustments when the fiberoptic oximeter deviated more than 4% from the blood sample value, the bias was eliminated over the total SaO2 range and the precision was 3.7%. The Opticath fiberoptic oximeter could have an accuracy for the whole SaO2 range between 15-100% close to the accuracy of the multiwavelength oximeter, when the fiberoptic oximeter is adapted for the underestimation below 78% SaO2.