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PubMed1996

Fetal pulse oximetry and visual on-line signal identification in the second stage of labor.

OBJECTIVE: To determine the accuracy of reflection pulse oximetry and visual on-line signal identification during the second stage of labor. STUDY DESIGN: The reflection pulse oximetry system used allows visual on-line identification of valid signals by showing the original red and infrared signals. With this system oxygen saturation measurements are averaged over nine heartbeats only. An atraumatic suction probe was used. The measurements of the last 10 minutes before delivery were compared with umbilical venous cord blood samples taken soon after delivery. RESULTS: The correlation between reflection pulse oximetry readings during the last 10 minutes before delivery and umbilical vein oxygen saturation was significant (r = 0.45; p < 0.0005). Standard regression analysis showed R2 of 0.45. This did not change if weighted by the rate of valid signals (R2 = 0.42). If the predelivery loss of valid signals was less than 5 minutes, the correlation improved (r = 0.47, p < 0.001). Umbilical vein pH did not correlate with pulse oximetry readings. CONCLUSION: The reflection pulse oximetry system used allows visual on-line identification of even short periods of valid signals and reflects actual oxygen saturation in fetal arterial blood.

Equipment Design↗
PubMedDate not supplied

Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults.

OBJECTIVE: The purposes of the study were to: (1) describe the aggregate strength of the relationship of arterial oxygen saturation as measured by pulse oximetry with the standard of arterial blood gas analysis as measured by co-oximetry, (2) examine how various factors affect this relationship, and (3) describe an aggregate estimate of the bias and precision between oxygen saturation as measured by pulse oximetry and the standard in vitro measures. DESIGN: A meta-analysis was conducted. SAMPLE: Seventy-four studies from 1976 to 1994 met the inclusion criteria of: (1) adult study population, (2) quantitative analysis of empirical data, and (3) bivariate correlations or bias and precision estimates between pulse oximeter and co-oximeter values. RESULTS: There were a total of 169 oximeter trials on 41 oximeter models from 25 different manufacturers. Studies were conducted in various settings with a variety of subjects, with most being healthy adult volunteers. The weighted mean r, based on 39 studies (62 oximeter trials) for which the r statistic and number of data points were available, was 0.895 (var [r] = 0.014). Based on 23 studies (82 oximeter trials) for which bias and precision estimates and number of data points were available, the mean absolute bias and precision were 1.999 and 0.233, respectively. Several factors were found to affect the accuracy of pulse oximetry. CONCLUSION: Pulse oximeters were found to be accurate within 2% (+/- 1 SD) or 5% (+/- 2 SD) of in vitro oximetry in the range of 70% to 100% Sao2. In comparing ear and finger probes, readings from finger probes were more accurate. Pulse oximeters may fail to record accurately the true Sao2 during severe or rapid desaturation, hypotension, hypothermia, dyshemoglobinemia, and low perfusion states.

Adult↗
PubMed1992

Prehospital pulse oximetry: useful or misused?

STUDY OBJECTIVE: This study evaluated the ability of emergency medical technicians (EMT-As) and emergency medical technicians-paramedics (EMT-Ps) to use pulse oximetry measurements in determining patient oxygen requirements. DESIGN: Prospective case series. SETTING: Cleveland emergency medical services (EMS) system. TYPE OF PARTICIPANTS: Five hundred thirty-two consecutive patients transported to Cleveland area hospitals by the Cleveland EMS system; no exclusions. INTERVENTIONS: EMT-Ps and EMT-As predicted patients' supplemental oxygen requirements based on clinical assessment. Pulse oximetry was performed while patients were breathing room air (RA SpO2). Treatment intervention, including oxygen supplementation and medication given, oxygen saturation after intervention, and oxygen saturation on arrival at the hospital, was also recorded. Therapy guided by the patient's initial RA SpO2 was reviewed to determine the appropriateness of oxygen therapy. RESULTS: Data were analyzed using the chi 2 test and correlation analysis. Eleven percent (59) of patients transported by Cleveland EMS had an initial RA SpO2 of less than 91%. Advanced life support units increased oxygen supplementation on all desaturated patients, whereas basic life support units failed to make appropriate increases in FIO2 in 20% (two) of desaturated patients (P less than .0001). Sixty percent (164) of patients transported by EMT-Ps and 62% (162) of patients transported by EMT-As had an initial RA SpO2 of 97% or greater. EMT-Ps gave supplemental oxygen therapy to all but 7% (11) of these already well-saturated patients, and EMT-As gave supplemental oxygen to all but 6% (nine) of these patients. EMT-Ps administered a higher FIO2 than they had predicted clinically necessary to 2% (four) of patients with an initial RA SpO2 of 97% of greater, whereas EMT-As gave a higher FIO2 than initially predicted to 16% (25) of such patients (P less than .0001). CONCLUSION: EMT-Ps were more likely to appropriately base oxygen therapy on oximetry measurements than were EMT-As. Both groups failed to decrease supplemental oxygen in patients with high explicit protocols for EMS systems contemplating the use of oximetry to guide oxygen therapy. Our results further suggest that pulse oximetry could be used to avoid unnecessary oxygen therapy on a significant number of patients transported by EMS systems because they are already well saturated on room air.

Cost Control↗
PubMed1996

Effects of a novel hemoglobin-based oxygen carrier on percent oxygen saturation as determined with arterial blood gas analysis and pulse oximetry.

STUDY OBJECTIVE: Hemoglobin-based oxygen carrier 201 (HBOC-201) is a polymerized hemoglobin of bovine origin being developed for use in hemorrhage during surgery or trauma. Pulse oximetry is commonly used in clinical practice to assess percent saturation of hemoglobin (Spo2). The ability to measure Spo2 in the presence of HBOC-201 will be important for the use of this compound in patient care. METHODS: We carried out a randomized, single-blind, placebo-controlled study at the Upjohn Research Clinics in Kalamazoo, Michigan, with normal, healthy adult men and women as subjects. The members of four groups of adult subjects (N=24) each received 45 g of HBOC-201 (nine each, men and women) or a control solution (Ringer's lactate) (three each, men and women). Each subject underwent phlebotomy (about 15% of estimated blood volume) followed by 3:1 hemodilution with Ringer's lactate and then either HBOC-201 or control solution. An indwelling arterial catheter in the radial artery was used for serial arterial blood gas sampling. Arterial blood gas measurements were made with a cooximeter (Instrumentation Laboratories). Fingertip pulse oximetry was used (Criticare 504-US; Criticare, Incorporated). Paired pulse oximetry and arterial blood gas sampling were made serially (at approximately hourly intervals) over 24 hours. RESULTS: The mean +/- SEM difference for Spo2 for arterial blood gas analysis compared with the pulse oximetry reading in the presence of HBOC-201 was 1.1% +/- 0.75%; in controls it was .1% +/- 0.64% (P<.001) for each) over the 24 hours after dosing. This relationship was constant despite increased concentrations of plasma hemoglobin (between 1 and 2g/dl [10 to 20 g/L]) in the HBOC-201 groups. CONCLUSION: Accurate determinations of Spo2 can be made with pulse oximetry in subjects given HBOC-201 over the normal range of Spo2.

Adolescent↗
PubMed1999

Pulse oximetry with the laryngeal mask airway.

This study evaluated the accuracy of pulse oximetry measured by a modified laryngeal mask airway (LMA). Ten anaesthetized patients (ASA I-II, aged 18-45) undergoing elective knee arthroscopies (mean-duration 40 min) were studied. A transmission pulse oximeter probe/sound OHMEDA was attached on the back of LMA (sizes 4 and 5) in an area in contact with the floor of the laryngeal part of the pharynx. Pharyngeal pulse oximetry as well as LMA cuff pressure were monitored and recorded every 5 min from the time of insertion (T0) to removal (T8) and were compared to simultaneous finger pulse oximeter readings. At T2 the cuff was over-inflated to obtain a 100 cm H2O intracuff pressure. At T3 the cuff pressure was decreased at 60 cm H2O. Pharyngeal pulse oximetry correlated with finger pulse oximetry throughout the study and was not effected by over-inflation of the LMA. This modification of the LMA provides an accurate method of measuring pulse oximetry which may be of use in a variety of circumstances.

Adult↗
PubMed1997

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.

Animals↗
PubMed2002

Enamel nail polish does not interfere with pulse oximetry among normoxic volunteers.

OBJECTIVE: To determine if enamel nail polish interferes with pulse oximetry. DESIGN: Laboratory investigation. PARTICIPANTS: 12 healthy nonsmoking volunteers. METHODS: Spectrophotometry was performed on polystyrene cuvettes painted with 3 uniform layers of nail polish enamel in triplicate. Absorbances were compared at 660 and 940 nm for 10 colors across the visible spectrum and documented by the Institute of Electrical and Electronic Engineers color code against Pantone matches on a color scanner. Colors were then selected that had the greatest A660-A940 difference and pulse oximetry (Nellcor N-209A. Pleasanton , CA) was performed on nails painted with these colors on 12 subjects using an unpainted digit as a control. RESULTS: When tested by the oximeter, there were no SpO2 differences detected between nail polish colors, nor were there any differences between the painted and the unpainted control digits across subjects (F = 0.51, ANOVA; p = 0.67). Blue (B), green (G), and lime green (G') possessed the largest A660-A940 difference and potentially could interfere with pulse oximetry but did not do so in the clinical model. CONCLUSION: Enamel finger nail polish pigments do not interfere with pulse oximetry as previously reported, the A660-A940 difference must be greater than 1.88 +/- 0.23 SD AU in order to affect pulse oximetry.

Adult↗
PubMed2002

The use of pulse oximetry to exclude pneumonia in children.

The objective of this study was to determine whether pulse oximetry alone or in conjunction with the clinical examination is predictive of pneumonia in children who present to the emergency department with respiratory complaints. A retrospective comparison of children with radiographic pneumonia with children with respiratory complaints and negative chest radiography was used. The study took place in an emergency department of a large academic, tertiary care hospital. All children less than 24 months of age who presented with a respiratory complaint and underwent chest radiography during a 1-year period were included. Charts of children with radiographic pneumonia were compared with charts of children without pneumonia, retrospectively. Data abstracted onto data collection forms included: pulse oximetry measurement, vital signs, general appearance, lung examination, and final radiology interpretation of chest radiographs. Pneumonia was defined as a chest radiograph showing any opacity consistent with pneumonia as read by a board-prepared or -certified radiologist. A total of 803 children qualified for the study. Radiograph interpretations were available for 762, and 10.5% were found to have radiographic pneumonia. The median pulse oximetry reading of children with radiographic pneumonia was 97% (interquartile range 95th-98th percentile) compared with 98% (interquartile range 96th-99th percentile) in the control group. Forty-five percent (35 of 78) of the children with radiographic pneumonia showed oxygen saturations of 98% or higher with greater than 10% (8 of 78) displaying oxygen saturations of 100%. By using logistic regression, pulse oximetry was not found to be a statistically significant predictive variable for radiographic pneumonia. Pulse oximetry could not be used to rule out the presence of radiographic pneumonia in children less than 2 years of age who presented with respiratory complaints.

Humans↗
PubMed2002

Utility of pulse oximetry in the detection of arterial hypoxemia in liver transplant candidates.

Hepatopulmonary syndrome, arterial hypoxemia caused by intrapulmonary vasodilatation, occurs in approximately 10% of patients with cirrhosis. The severity of hypoxemia affects liver transplant candidacy and is associated with increased morbidity and mortality posttransplantation. Screening guidelines for detecting the presence of arterial hypoxemia do not exist. The aim of this study is to investigate the accuracy and utility of pulse oximetry in the detection of hypoxemia (PaO(2) < 70 mm Hg) in patients with cirrhosis. Two hundred prospective liver transplant candidates were compared with 94 controls. Arterial oxyhemoglobin saturation was obtained by pulse oximetry (SpO(2)) and compared with simultaneous arterial blood gas (ABG) oxyhemoglobin values (SaO(2); bias = the difference). PaO(2), carboxyhemoglobin, methemoglobin, and routine clinical and biochemical parameters were investigated to account for the bias. SpO(2) overestimated SaO(2) in 98% of patients with cirrhosis (mean bias, 3.37%; range, -1% to 10%). Forty-four percent of patients with cirrhosis and controls had a bias of 4% or greater. No clinical or biochemical parameters of cirrhosis accounted for the overestimation of pulse oximetry. Twenty-five subjects with cirrhosis were hypoxemic, and an SpO(2) of 97% or less showed a sensitivity of 96% and a positive likelihood ratio of 3.9 for detecting hypoxemia. An SpO(2) of 94% or less detected all subjects with an arterial PaO(2) less than 60 mm Hg. Pulse oximetry significantly overestimates arterial oxygenation, and the inaccuracy is not influenced by liver disease. Nevertheless, pulse oximetry can be a useful screening tool to detect arterial hypoxemia in patients with cirrhosis, but a higher threshold for obtaining an ABG must be used.

Adult↗
PubMedDate not supplied

[Fetal pulse oximetry during risk deliveries in German clinics--a representative national survey in 81 obstetric departments].

BACKGROUND: The development of a new technique to evaluate the normal fetal acid-base balance in risk deliveries with pathological fetal heart rate has been seen with great expectations over the last years. The aim of this representative survey was to ask for the actual status of the fetal pulse oximetry in clinical use in German delivery rooms and to analyze hopes, expectations and system errors. PATIENTS RESPECTIVELY AND METHODS: Collecting data were done by a representative, time limited anonymous questionnaire in all German clinics who used Nellcors fetal pulse oximetry N-400 in measuring fetal arterial saturation in the years 1995 - 1999 during risk deliveries with non-reassuring fetal heart rate. RESULTS: With 66,6 % of the departments participating a number of 54 clinics returned the questionnaires. An average of 4.5 times per month fetal pulse oximetry was used per clinic and in over 90 % of all cases the handling and fixation of the sensor was without problems. There is qualified staff in every clinic and regarding the satisfaction with this system an average note of 2.8 was assigned. Fetal pulse oximetry will be established in some years to replace fetal blood analysis and to reduce operative deliveries. Technical problems in cases of insufficient sensor fixation at the fetal head and with the re-sterilization of fetal sensors must be solved in the future. CONCLUSIONS: Fetal pulse oximetry will be incorporated as the third method of monitoring the fetus during labor.

Attitude of Health Personnel↗
PubMed1993

Validation of arterial oxygen saturation measurements in utero using pulse oximetry.

The noninvasive measurement of fetal arterial oxygen saturation using pulse oximetry could be of potential use in assessing fetal well-being in utero during labor. In this study, the accuracy and technical feasibility of reflectance pulse oximetry in utero was evaluated in acutely instrumented fetal sheep using a specially designed sensor. Following recalibration of the analysis algorithms, fetal arterial saturation could be measured by pulse oximetry in utero. Arterial oxygenation measurements obtained using pulse oximetry correlated well with simultaneous in vitro measurements over the range of 6 to 81%. We conclude that in utero pulse oximetry is technically feasible, appears useful and accurate, and merits further evaluation.

Algorithms↗
PubMed1996

[Validity of fiber optic cerebral vein oximetry during extracorporeal circulation].

INTRODUCTION: This study investigates the accuracy of continuous jugular bulb venous oximetry during different conditions of hypothermic cardiopulmonary bypass (CPB) (27 degrees C) for coronary artery bypass graft. METHODS: 38 ASA III patients were studied following Ethical Care Committee approval and informed consent. Patients were anaesthetized with fentanyl, midazolam, continuous infusion of etomidate and pancuronium. Ventilation was performed with oxygen in air. CPB was managed according to alpha-stat conditions under moderate hypothermia (27 degrees C). SjO2 (%) and jugular bulb temperature (degree C) were measured by a fiberoptic thermodilution catheter (Opticath F 5.5, Abbott Critical Care Systems) placed in the jugular bulb via the internal jugular vein. Appropriate catheter position was x-ray controlled prior to the measurements. The fiberoptic data were compared to co-oximetric data of blood samples after induction of anaesthesia, 2 min following start of CPB, during cooling, stable hypothermia and rewarming of CPB. STATISTICS: Assessing of agreement (Bland/Altman and Bartko). RESULTS: Jugular venous oximetry correlated closely with the co-oximeter determinations after induction of anaesthesia. However, following start of CPB accuracy was decreased. During cooling, stable hypothermia and rewarming oximetric data correlated well with co-oximetry, however, over-estimating the SjO2 by 1.4 to 2%. CONCLUSION: The present data show that continuous jugular bulb venous oximetry is accurate and reliable for continuous SjO2 monitoring during hypothermic CPB for cardiac surgery. Induction of CPB and hemodilution affect accuracy slightly, but changes are well detected. Before clinical intervention SjO2 should be confirmed by laboratory co-oximetry.

Adult↗
PubMed2000

Assessment of fetal scalp oxygen saturation determination in the sheep by transmission pulse oximetry.

OBJECTIVE: Electronic fetal heart rate monitoring has an unacceptable false-positive nonreassuring rate, which results in an excess of operative interventions. As a more objective measure of fetal oxygenation, fetal scalp pulse oximetry has been used to assess fetal blood oxygen saturation (SO (2)). The current devices use reflectance oximetry, which has inherent limitations. These include varying depths of signal penetration, variation with position, and potential for optical interference. In this study we evaluated a newly developed transmission pulse oximetry device consisting of transmitter and receiver diodes mounted within the coil of a standard scalp electrode (Spiral O(2)CTG; Respironics Inc, Marietta, Ga). STUDY DESIGN: Six pregnant ewes at 127 to 135 days' gestation (term, 145 days' gestation) were anesthetized, intubated, and prepared with a femoral artery catheter. Fetuses were prepared with brachial artery and jugular vein catheters. Maternal inspired oxygen fraction was titrated from 21% to 3%. Oximetry O(2)CTG devices were positioned on the fetal scalp, and recordings were compared with directly determined fetal arterial pH, PO (2), and SO (2) values. RESULTS: Maternal SaO (2) and PaO (2) ranged from 102% to 16% and 110 to 18 mm Hg, respectively. Fetal SaO (2) and PaO (2) ranged from 76% to 12% and 28 to 8 mm Hg, respectively. There was excellent correlation between direct fetal SaO (2) and scalp SO (2) (r (2) = 0.90; scalp SO (2) = 0.79 SaO (2) + 6.89). With an SaO (2) of <30% as the cutoff point for assessment of fetal compromise, scalp SO (2) measurements had a 94% +/- 10% specificity and a 94% +/- 10% positive predictive value. CONCLUSION: (1) Preliminary studies of the Spiral O(2)CTG sensor demonstrated high correlation of scalp SO (2) with fetal SaO (2). (2) Although potential inaccuracies remain, transmission oximetry may offer potential advantages in consistency, ease of application, and technology with respect to the current reflection oximeter devices.

Animals↗
PubMed2000

A multicenter controlled trial of fetal pulse oximetry in the intrapartum management of nonreassuring fetal heart rate patterns.

OBJECTIVE: Recent developments permit the use of pulse oximetry to evaluate fetal oxygenation in labor. We tested the hypothesis that the addition of fetal pulse oximetry in the evaluation of abnormal fetal heart rate patterns in labor improves the accuracy of fetal assessment and allows safe reduction of cesarean deliveries performed because of nonreassuring fetal status. STUDY DESIGN: A randomized, controlled trial was conducted concurrently in 9 centers. The patients had term pregnancies and were in active labor when abnormal fetal heart rate patterns developed. The patients were randomized to electronic fetal heart rate monitoring alone (control group) or to the combination of electronic fetal monitoring and continuous fetal pulse oximetry (study group). The primary outcome was a reduction in cesarean deliveries for nonreassuring fetal status as a measure of improved accuracy of assessment of fetal oxygenation. RESULTS: A total of 1010 patients were randomized, 502 to the control group and 508 to the study group. There was a reduction of >50% in the number of cesarean deliveries performed because of nonreassuring fetal status in the study group (study, 4. 5%; vs. control, 10.2%; P =.007). However, there was no net difference in overall cesarean delivery rates (study, n = 147 [29%]; vs. control, 130 [26%]; P = .49) because of an increase in cesarean deliveries performed because of dystocia in the study group. In a blinded partogram analysis 89% of the study patients and 91% of the control patients who had a cesarean delivery because of dystocia met defined criteria for actual dystocia. There was no difference between the 2 groups in adverse maternal or neonatal outcomes. In terms of the operative intervention for nonreassuring fetal status, there was an improvement in both the sensitivity and the specificity for the study group compared with the control group for the end points of metabolic acidosis and need for resuscitation. CONCLUSION: The study confirmed its primary hypothesis of a safe reduction in cesarean deliveries performed because of nonreassuring fetal status. However, the addition of fetal pulse oximetry did not result in an overall reduction in cesarean deliveries. The increase in cesarean deliveries because of dystocia in the study group did appear to result from a well-documented arrest of labor. Fetal pulse oximetry improved the obstetrician's ability to more appropriately intervene by cesarean or operative vaginal delivery for fetuses who were actually depressed and acidotic. The unexpected increase in operative delivery for dystocia in the study group is of concern and remains to be explained.

Adult↗
PubMed2003

Evaluation of non-reassuring fetal heart rate patterns with fetal pulse oximetry combined with vibratory acoustic stimulation.

OBJECTIVE: To determine the value of fetal pulse oximetry and vibratory acoustic stimulation in the presence of non-reassuring fetal heart rate patterns during labor. DESIGN: Prospective study in women monitored by cardiotocography and fetal pulse oximetry during labor. MATERIALS AND METHODS: During a period of 18 months, 907 consecutive parturients in labor were monitored by cardiotocography. Out of these women, 63 were selected on the basis of a non-reassuring fetal heart rate tracing during the first stage of labor. In these cases, fetal pulse oximetry was applied. Vibratory acoustic stimulation was applied in fetuses without spontaneous reactivity in order to evaluate the fetal status. RESULTS: Our cases were classified into three groups, according to the lower fetal oxygen saturation levels, from the time of oximetry application until delivery. Group A consisted of 29 cases where fetal oxygen saturation levels were > or = 41%, group B (20 cases) with fetal oxygen saturation of 31-40% and group C (14 cases) with levels of < 30%. Spontaneous reactivity was observed in 15 fetuses of group A and seven of group B, while no case of reactivity was noted in group C. Vibratory acoustic-induced reactivity was associated with low fetal oxygen saturation levels. The mean umbilical artery pH levels were 7.29 +/- 0.051 in group A, 7.21 +/- 0.057 in group B and 7.04 +/- 0.05 in group C. CONCLUSION: Fetal pulse oximetry should be indicated not only in fetuses without any reactivity but also in those with induced reactivity, after the application of vibratory acoustic stimulation.

Acoustic Stimulation↗
PubMed2005

Pulse oximetry in the oesophagus.

Pulse oximetry has been one of the most significant technological advances in clinical monitoring in the last two decades. Pulse oximetry is a non-invasive photometric technique that provides information about the arterial blood oxygen saturation (SpO(2)) and heart rate, and has widespread clinical applications. When peripheral perfusion is poor, as in states of hypovolaemia, hypothermia and vasoconstriction, oxygenation readings become unreliable or cease. The problem arises because conventional pulse oximetry sensors must be attached to the most peripheral parts of the body, such as finger, ear or toe, where pulsatile flow is most easily compromised. Since central blood flow may be preferentially preserved, this review explores a new alternative site, the oesophagus, for monitoring blood oxygen saturation by pulse oximetry. This review article presents the basic physics, technology and applications of pulse oximetry including photoplethysmography. The limitations of this technique are also discussed leading to the proposed development of the oesophageal pulse oximeter. In the majority, the report will be focused on the description of a new oesophageal photoplethysmographic/SpO(2) probe, which was developed to investigate the suitability of the oesophagus as an alternative monitoring site for the continuous measurement of SpO(2) in cases of poor peripheral circulation. The article concludes with a review of reported clinical investigations of the oesophageal pulse oximeter.

Adult↗
PubMed1995

Nocturnal oximetry: is it a screening tool for sleep disorders?

The objective of this study was to examine the usefulness of home oximetry for the screening of sleep disorders presenting with excessive daytime sleepiness (EDS). This was accomplished by blinded comparison of diagnosis by oximetry alone versus polysomnographic diagnosis carried out at a sleep disorders center at a tertiary referral hospital. This study included three hundred patients who had been referred because of EDS and suspected sleep apnea. A number of measurements were made. The arterial oxygen saturation (SaO2) data were sampled at 2 Hz and stored digitally during polysomnography (PSG). From the SaO2 data recorded onto paper six scorers calculated the number of desaturations > 3% per hour (desaturation index: DI) and then made a diagnosis [normal, DI < 5; mild obstructive sleep apnea (OSA), 5 < DI < 20; moderate OSA, 20 < DI < 40; severe OSA, DI > 40]. Upper airway resistance syndrome (UARS) was diagnosed when DI was < 5 but associated with small fluctuations in SaO2. The diagnosis made by each of six scorers was compared to the clinical diagnosis made independently using PSG. Thirty-one (10.3%) of all the records were rejected by scorers because of inadequate SaO2 signals requiring technologist intervention. Sensitivity of screening for sleep-breathing disorders was 90.0% and specificity was 75.0%. All moderate and severe OSA patients were detected by oximetry. However, among the 66 patients who were classified as normal by oximetry, 1 had mild OSA, 20 had UARS, 9 had periodic limb movements in sleep, 4 had narcolepsy and 2 had a parasomnia. In conclusion, home oximetry may not have sufficient sensitivity and specificity to detect breathing disorders reliably during sleep and is useless for other disorders of sleep.

Adult↗
PubMed2000

Arterial and venous contributions to near-infrared cerebral oximetry.

BACKGROUND: Cerebral oximetry is a noninvasive bedside technology using near-infrared light to monitor cerebral oxygen saturation (Sco2) in an uncertain mixture of arteries, capillaries, and veins. The present study used frequency domain near-infrared spectroscopy to determine the ratio of arterial and venous blood monitored by cerebral oximetry during normoxia, hypoxia, and hypocapnia. METHODS: Twenty anesthetized children aged < 8 yr with congenital heart disease of varying arterial oxygen saturation (Sao2) were studied during cardiac catheterization. Sco2, Sao2, and jugular bulb oxygen saturation (Sjo2) were measured by frequency domain near-infrared spectroscopy and blood oximetry at normocapnia room air, normocapnia 100% inspired O2, and hypocapnia room air. RESULTS: Among subject conditions, Sao2 ranged from 68% to 100%, Sjo2 from 27% to 96%, and Sco2 from 29% to 92%. Sco2 was significantly related to Sao2 (y = 0. 85 x -17, r = 0.47), Sjo2 (y = 0.77 x +13, r = 0.70), and the combination (Sco2 = 0.46 Sao2 + 0.56 Sjo2 - 17, R = 0.71). The arterial and venous contribution to cerebral oximetry was 16 +/- 21% and 84 +/- 21%, respectively (where Sco2 = alpha Sao2 + beta Sjo2 with alpha and beta being arterial and venous contributions). The contribution was similar among conditions but differed significantly among subjects (range, approximately 40:60 to approximately 0:100, arterial:venous). CONCLUSIONS: Cerebral oximetry monitors an arterial/venous ratio of 16:84, similar in normoxia, hypoxia, and hypocapnia. Because of biologic variation in cerebral arterial/venous ratios, use of a fixed ratio is not a good method to validate the technology.

Brain↗