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PubMed2006

Cerebral oximetry improves detection of sickle cell patients at risk for nocturnal cerebral hypoxia.

We previously used cerebral oximetry to identify low cerebral venous oxygen saturation in waking children with sickle cell disease (SCD). Because arterial oxyhemoglobin desaturation is common during sleep in SCD patients, this study compared both waking and sleeping systemic arterial and cerebral venous oxygenation dynamics in children with and without SCD. Seventeen African-American (AA) children with homozygous SCD [8 (4-15) years; 29% male; normal transcranial Doppler velocities] were compared with a control cohort (CON) comprised of six healthy AA children [9 (4-16) years, 33% male]. Standard all-night polysomnographic recordings were performed, including measurement of arterial oxygen saturation by pulse oximetry (SpO(2)). Regional cerebral oxygen saturation (rSO(2)) was measured non-invasively with cerebral oximetry. Intra-cohort comparisons examined the influence of sleep on SpO(2) and rSO(2) in the subjects. Inter-cohort comparisons of SpO(2), rSO(2,) and the rSO(2)/SpO(2) ratio assessed the impact of SCD on systemic and cerebral oxygenation during wakefulness and sleep. Cohort differences in SpO(2) were not statistically significant in either wakefulness or sleep. However, only in the SCD cohort was the magnitude of SpO(2) change statistically significant (P = 0.002). In contrast, both waking and sleep rSO(2) cohort median values did differ significantly [awake: CON 76 (67-86) vs. SCD 62 (58-71), P = 0.01; sleep: CON 65 (60-77) vs. SCD 55 (48-61), P = 0.01)]. The waking rSO(2)/SpO(2) ratio was also significantly lower in the SCD group [CON 0.78 (0.68-0.88) vs. SCD of 0.66 (0.61-0.72); P = 0.015]. During sleep, the ratio was also significantly lower in the SCD group [CON 0.71 (0.66-0.81) vs. SCD 0.59 (0.52-0.65); P = 0.011]. Our findings suggest that SCD patients may be at increased risk of cerebral hypoxia during both wakefulness and sleep.

Adolescent↗
PubMed2003

The effects of anesthesia on cerebral tissue oxygen tension: use of EPR oximetry to make repeated measurements.

While very useful data can be obtained from measurements of pO2 within various compartments of the vascular system, such measurements do not necessarily provide accurate information on the pO2 in the brain. Anesthetics can significantly affect the tissue pO2 in the brain by several mechanisms involving both delivery and utilization. Electron Paramagnetic Resonance (EPR or ESR) oximetry has the potential for non-invasively carrying out repeated direct measurements of pO2 in tissues during the course of anesthesia. In this paper we describe the use of EPR oximetry for studying the influence of anesthesia on tissue pO2, and present illustrative results from experiments with five different anesthetics in rats. The results indicate that the tissue O2 can be measured directly using EPR oximetry, and data can be obtained non-invasively during the course of anesthesia.

Anesthetics↗
PubMed1987

Noninvasive monitoring of oxygenation during one-lung ventilation: a comparison of transcutaneous oxygen tension measurement and pulse oximetry.

Oxygenation was monitored concomitantly by measurement of transcutaneous oxygen tension and by pulse oximetry, and the data were compared with arterial blood oxygen tension and saturation values in 10 patients who became hypoxemic when undergoing thoracotomy and one-lung ventilation. A steep decrease in arterial blood oxygen tension was obvious immediately after the institution of one-lung ventilation, reaching the lowest mean value of 63 +/- 2 mm Hg (+/- SEM) at 12 minutes. Despite significant correlation between transcutaneous oxygen tension and arterial blood oxygen tension during one-lung ventilation (r = 0.75; P less than 0.001), the delay in the transcutaneous oxygen tension response resulted in underestimation of the severity of hypoxemia at the beginning of one-lung ventilation. In contrast, the decrease in arterial blood oxygen saturation from 97.9 +/- 0.3% to 92.2 +/- 0.8% as measured by CO-Oximeter was accurately followed by pulse oximetry with almost beat-to-beat response, bringing about a highly significant linear correlation between the two methods (r = 0.93; P less than 0.001). We conclude that pulse oximetry is a simpler and more rapidly responding method than measurement of transcutaneous oxygen tension for detection of hypoxemia during one-lung ventilation in adults.

Blood Gas Monitoring, Transcutaneous↗
PubMed1995

Limitations of forehead pulse oximetry.

During initial clinical tests to calibrate our reflectance pulse oximetry system, we observed serious physiologic limitations to the use of pulse oximetry in the forehead region. We present a case of simultaneous reflectance and transmission mode pulse oximetry monitoring in a child undergoing cardiac surgery for congenital cyanotic heart disease with a large intracardiac shunt. During general anesthesia, when the patient was endotracheally intubated and mechanically ventilated, the transmission mode saturation agreed well with arterial oxygen saturation measurements; but, our reflectance pulse oximeter, with the sensor applied to the forehead, displayed spuriously lower (-18%) oxygen saturations. Before and after anesthesia and surgery, there was fine agreement between reflectance and transmission mode saturation values. We suggest that the difference was caused by vasodilatation and pooling of venous blood due to compromised venous return to the heart, and a combination of arterial and venous pulsations in the forehead region. This means that the reflectance pulse oximeter measured a mixed arterial-venous oxygen saturation.

Anesthesia, General↗
PubMed1991

A prospective study of intraoperative pulse oximetry failure.

Since pulse oximetry is now an ASA standard for intraoperative monitoring, we sought to determine the intraoperative failure rate for this device. We prospectively evaluated the intraoperative failure rate of our pulse oximeters at the four University of Washington Hospitals (University of Washington Medical Center, Veterans Affairs Medical Center [VAMC], Children's Hospital and Medical Center, and Harborview Medical Center [HMC]) recorded from April 1989 to August 1989. We defined failure as the inability to obtain any oximetry reading for a cumulative period of more than 30 minutes during any anesthetic procedure after all equipment malfunctions had been eliminated. Our puse oximeters failed in 124 of 11,046 cases studied; this is a failure rate of 1.12%, which ranged from 0.56% at HMC to 4.24% at VAMC. The failure rate at VAMC (4.24%) was significantly higher than the other hospitals (p less than 0.001). Those cases associated with the pulse oximeter failure had the following characteristics: (1) an ASA status of 3 or higher, (2) lengthy operations, and (3) elderly patients. When the device did fail in a patient, it did not function for 32% of the mean anesthesia time. We conclude that the intraoperative use of the pulse oximetry can provide information about blood oxygen saturation in most patients. However, in approximately 1% of the patients we studied in the operating room, mechanically functioning pulse oximeters failed to provide readings of blood oxygen saturations during routine operative use.

Equipment Failure↗
PubMed1996

A new system to record reliable pulse oximetry data from the Nellcor N-200 and its applications in studies of variability in infant oxygenation.

We have developed a simple system for internal validation of oximetry data collected over many hours from the Nellcor N-200 pulse oximeter (Nellcor, Inc., Hayward, CA). This system uses signals from the oximeter alone and a validation algorithm that is based in a computer connected to the oximeter. Unlike other validation systems, this system does not require connections to other monitors. The system was tested on 10 acutely ill newborns in an intensive care nursery over 16 hr of continuous recording for each infant (birthweight, 2.50 +/- 0.73 kg; age, 3.4 +/- 3.2 days). Oximetry data were accepted as valid using the new system if they surpassed a minimum level of quality (empirically derived, and equal to a 60% fractional success in pulse detection). The validated oximetry data were compared to data obtained using a conventional "compared to the electrocardiogram (ECG)" algorithm. For the new and the conventional algorithms, the distributions of validated SpO2 percents were nearly identical, with data rejection rates of 28.9% for the new system and 37.3% for the conventional system. In the newborns, the new system was used to demonstrate that as the mean saturations decreased, there were striking increases in variability about the reported mean saturation (p < 0.001). While variability in infant SpO2 is a well-known phenomenon, the amount seen here was unexpected. For example, the range of true saturations frequently recorded was quite wide at a reported mean SpO2 of 90% (from 81 to 94%; but, the range was only from 92 to 98% at a mean SpO2 of 96%). These findings demonstrate the usefulness of the new system and, if substantiated in more detailed studies, have important implications for the use of pulse oximeters to assess oxygenation in newborns.

Algorithms↗
PubMed1990

Pulse oximetry used for documenting oxygen saturation and right-to-left shunting immediately after birth.

The objective of this study was to investigate the clinical applicability of pulse oximetry to measure haemoglobin oxygen saturation and heart rate in the first 20 min of life and to analyse the effect of pre- or post-ductal (hand, respectively, foot) fixation of sensors on oxygen saturation. Measurements were carried out on 53 newborn infants selected at random after delivery by caesarean section. Signal detection occurred significantly faster from the hand (50% after 1.3 min, 90% after 4 min) than from the foot (50% after 3.1 min, 90% after 9 min). Both fixation sites showed equally great sensitivity to motion. The heart rates from pulse oximetry recordings were up to 30% lower than those from ECG recordings. Saturation values from the hand were nearly always higher than those from the foot (median difference in the 5th min was 10%; between the 5th and 10th min it was 7%; no significant difference occurred after the 17th min). We conclude that pulse oximetry can be used for documenting oxygenation and right-to-left shunting in newborn infants during the first minutes of life in spite of limitations due to incomplete pulse wave detection and artifacts.

Foot↗
PubMed1993

Accuracy of pulse oximetry at various haematocrits and during haemolysis in an in vitro model.

In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise damage to red blood cells. The pulse oximeter readings (SpO2) were compared with oxygen saturation analyses by a haemoximeter (SaO2). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO2 range 60-100 per cent. At a haematocrit level of 41-44 per cent, there was no correlation between SaO2 and SpO2 readings. After diluting the blood with normal saline to a haematocrit of 10-11 per cent, a good correlation between SaO2 and SpO2 was found. Following haemolysis, the agreement between SaO2 and SpO2 was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may be dependent on the haematocrit level.

Hematocrit↗
PubMed1986

Pulse oximetry during cardiac catheterization in children with congenital heart disease.

One hundred and five children with congenital heart disease were monitored by pulse oximetry during cardiac catheterization. Excellent correlation (r = 0.95) was found between oxygen saturation values obtained with pulse oximetry and those obtained from arterial blood in 133 data pairs. This correlation was described by the regression equation y = 0.91x + 8.1. The correlation was also excellent in 47 data pairs with saturation values of less than 90% (r = 0.94, y = 0.93x + 6.0) from 36 cyanotic children. The clinical usefulness of pulse oximetry in the early recognition of decreased pulmonary blood flow or partial airway obstruction was demonstrated. Early diagnosis of changes in oxygenation was especially helpful in children with cyanotic congenital heart disease, in whom small changes in arterial oxygen tension may cause large changes in oxygen saturation.

Adolescent↗
PubMed1993

Pulse oximetry, capnography, and blood gas measurements: reducing cost and improving the quality of care with technology.

Pulse oximetry appears to improve quality of care by the early detection of hypoxia noninvasively. We tested the hypothesis that the widespread use of pulse oximetry over a 5-year period in the operating rooms at our institution had resulted in a reduction in blood gas measurements and in departmental operating costs. The total number of blood gas determinations per hour of anesthetic time at our institution decreased by 44%, from 7.64 to 4.26 measurements per 100 operating room hours. The number of capnography units in the operating rooms increased from 8 to 14, the number of pulse oximeters increased from 0 to 22, and oximeter use increased from 0 to 100% for all anesthetics. The total cost to provide oximetry, capnography, and blood gas measurements in 1989-1990 was less than the cost to provide blood gas measurements alone in 1985-1986. The introduction of these technologies was accomplished without an increase in cost: $76,880 in 1985-1986 versus $71,025 in 1989-1990.

Anesthesiology↗
PubMed1994

Congenital methaemoglobinaemia detected by preoperative pulse oximetry.

Methaemoglobinaemia is an unusual cause of cyanosis whether it is congenital or acquired. Hence, the diagnosis may not be immediately obvious and appropriate treatment may be delayed. The case described shows that it should be considered when pulse oximetry and arterial blood gas analysis appear to give conflicting results. A healthy 24-yr-old woman was found to have a pulse oximeter reading of 82% prior to induction of anaesthesia for minor surgery. Clinical examination confirmed cyanosis but no other abnormality was detected. She had no important medical history and was not receiving any medications. Arterial blood gas analysis with the patient breathing air showed PaO2 12.03 kPa (90 mmHg). Co-oximeter analysis of this sample revealed a methaemoglobin content of 13.4% and she was subsequently found to have congenital methaemoglobin reductase deficiency. Anaesthesia was induced and maintained with incremental doses of propofol and fentanyl. A spontaneously breathing technique with oxygen in nitrous oxide was employed uneventfully. No specific treatment for methaemoglobinaemia was given. Perioperative pulse oximetry is one of the major advances in patient monitoring in recent years but unexpected results should not be accepted uncritically. A knowledge of the working principles of oximetry is essential to enable appropriate management in the presence of dyshaemoglobins.

Adult↗
PubMed1997

Effect of local limb temperature on pulse oximetry and the plethysmographic pulse wave.

We attempted to evaluate prospectively local thermoregulatory vasoconstriction and vasodilatation in 15 volunteers by means of pulse oximetry and plethysmography as measured by a finger tip-pulse oximeter. Recent studies [1] concluded that the plethysmo time interval (PTI) between the QRS complex on ECG and the upstroke of the plethysmographic wave of the pulse oximeter is useful in evaluating the peripheral circulatory status. Venous (both Vv cubitae) blood samples for determination of SvO2 were drawn, as well as pulse oximetry SpO2 oxygen saturation measurements and calculation of PTI were performed under conditions of normothermia, hypothermia and hyperthermia, before and after immersing the hands of the volunteers in a cold (15 degrees C) and warm (45 degrees C) waterbath. Two pulse oximeters simultaneously were used, one for each hand, in order to check to which extent SpO2, SvO2 and PTI might be influenced by gross limb temperature changes. Our results show that during local hyperthermia SpO2 significantly decreased and during local hypothermia SpO2 increased after immersing the one hand in a warm waterbath and the other hand in a cold waterbath at the same time. The peripheral SvO2 significantly increased in the warm hand and decreased in the cold hand. PTI remained unchanged after exposure to either a cold or a warm waterbath. The possibility of technical causes for the SpO2 changes were eliminated. Finger-tip pulse oximetry SpO2 readings change with limb temperature. The change in venous oxygen saturation can be explained by temperature dependent arteriovenous shunts in the periphery. The observed change in SpO2 probably reflects altered transmission of arterial pulsations to venous blood in the finger.

Adult↗
PubMed1997

Pulse oximetry: a new way of determining the heart rate in chicken embryos.

With pulse oximetry it is possible to record the pulse-synchronic variation of the oxygen saturation due to variable blood flow during systole and diastole. In the present study on chicken embryos, the pulse rate based on oximetry was compared with the heart rate recorded by means of ECG. We conclude that the pulse curve detected by means of pulse oximetry can be used to determine the heart rate in chicken embryos between day 12 and day 20 of incubation.

Animals↗
PubMed1996

Signal processing methods for pulse oximetry.

Current signal processing technology has driven many advances in almost every aspect of life, including medical applications. It follows that applying signal processing techniques to pulse oximetry could also provide major improvements. This research was designed to identify and implement one or more techniques that could improve pulse oximetry oxygen saturation (SpO2) measurements. The hypothesis was that frequency domain analysis could more easily extract the cardiac rate and amplitude of interest from the time domain signal. The focus was on the digital signal processing algorithms that had potential to improve pulse oximetry readings, and then test those algorithms. This was accomplished using the Fast Fourier Transform (FFT) and the Discrete Cosine Transform (DCT). The results indicate that the FFT and DCT computation of oxygen saturation were as accurate without averaging, as weighted moving average (WMA) algorithms currently being used, and directly indicate when erroneous calculations occur.

Algorithms↗
PubMed1994

Failure of pulse oximetry in the assessment of raised limb intracompartmental pressure.

Pulse oximetry has been proposed as an aid to monitoring raised intracompartmental pressures (ICPs). ICP and percentage haemoglobin oxygen saturation in the affected limb were studied in 10 consecutive patients with raised ICP. Compartment pressures ranged from 28 to 64 mmHg (mean 40.9 mmHg). In two patients with absent pulses, pulse oximetry failed to detect pulsatile flow and recorded 0 per cent saturation. The remaining eight patients, including four with absent peripheral pulses, all had percentage haemoglobin saturations within 2 per cent of the opposite normal limb. Arterial haemoglobin desaturation was not associated with raised ICP. The presence of an oximeter signal and a normal reading does not necessarily imply adequacy of tissue perfusion. Pulse oximetry does not appear to be a reliable aid in the diagnosis or monitoring of impaired perfusion due to raised ICP.

Adolescent↗
PubMed1990

Pulse oximetry as a means of assessing bowel viability.

Utilizing a pulse oximeter, oxygen saturation was determined in the periphery (tongue) and compared to the intestinal wall in a canine model. Segmental intestinal ischemia was then produced and the last obtainable pulse oximetry reading was marked with a suture on either end of the ischemic segment. Reexploration was performed within 48 hr and full thickness biopsies were taken in normal intestine and at various distances into the ischemic segment. Blinded evaluation of the biopsies showed that all biopsies taken within 1 cm of a normal pulse oximetry reading were normal, whereas at 3 cm into the ischemic segment 7 of 15 biopsies showed partial necrosis and 5 of 15 showed full thickness necrosis. We conclude that pulse oximetry of the intestinal wall is a valuable method of assessing intestinal viability in this model.

Animals↗
PubMed1994

Clinical experience with transcranial cerebral oximetry.

Transcranial cerebral oximetry based on the principle of near-infrared spectroscopy has been successfully used in a variety of neurosurgical conditions, primarily those associated with disturbed cerebral circulation. The non-invasive technique of cerebral oximetry provides valuable information about brain oxygenation in patients with cerebral ischemia (due to occlusion or stenosis of the internal carotid artery). It is also used in intraoperative monitoring of carotid endarterectomy and surgical procedures performed under deep hypothermia and circulatory arrest, during neuroendovascular procedures, and in critical care settings (in patients with arterial vasospasm and during the terminal period). This article describes our preliminary clinical experience with the use of this new technique and summarizes the current literature on clinical and experimental use of transcranial cerebral oximetry.

Algorithms↗
PubMed1993

Accuracy of pulse oximetry in children with cyanotic congenital heart disease.

The use of a pulse oximeter to monitor arterial oxygen saturation (SaO2) is considered accurate and reliable in the range of 90% to 100%. However, differing reports exist about the accuracy with desaturation. Thus, the suitability of pulse oximetry in desaturated patients was evaluated using a Nellcor N-100 oximeter. In 56 children with cyanotic congenital heart disease, the pulse oximeter reading was compared with the direct measurement of SaO2 by a CO-oximeter OSM 3. The influence of high hematocrit values on the accuracy at low saturation was also investigated. All oxygen saturation measurements (two per child) were carried out after induction of anesthesia (ketamine, fentanyl, pancuronium) during a "steady state" before the surgical procedure. The results indicate that at low levels of saturation (SaO2 below 80%), pulse oximetry is not as accurate as at higher saturations, and overestimates the true value. Bias and precision between saturations measured by the pulse oximeter and the CO-oximeter were 5.8 and 4.8 in the group with a saturation below 80%, and 0.5 and 2.5 in the group with a saturation over 90%, respectively. Because the margin of safety for a patient is small when arterial saturation levels are under 80%, it is advisable under this condition to check the SaO2 measurements by a CO-oximeter. High hematocrit levels did not seem to be responsible for impaired accuracy of pulse oximetry at saturation values below 80%.

Adolescent↗