Continuous Oxygen Saturation Research Articles

Clinical Accuracy of Continuous Hemoglobin Oxygen Saturation Monitoring Devices

Three devices used to measure hemoglobin oxygen saturation in the extracorporeal circuit were studied and compared to a control. The Baxter Bentley OxySat, Oximetrix Accusat, and the Radiometer ABIA blood gas monitor were compared to a control, the IL 282 Co-Oximeter. Fifty-one sample points were obtained during all phases of cardiopulmonary bypass with results as follows: Table 1 Comparison of oxygen saturation devices. r DIFF SD p ACCUSAT 0.94 p<.0001 -0.6 3.2 0.1834 NS ABL-4 0.93 p<.0001 -1.7 3.3 0.0008 S OXYSAT 0.87 p<.0001 -6.8 4.4 0.0001 S r = correlation coefficient with corresponding p value, DIFF = difference from IL282, SD = Standard deviation of difference, p = p value for testing the hypothesis of no difference between test device and IL282, NS = no significant difference, S = significant difference. The Accusat was found to be a statistically more accurate means of monitoring hemoglobin oxygen saturations during cardiopulmonary bypass than the ABL4 and the OxySat. All devices had significant correlation with the control and with each other.

Scientific presentation award: Clinical Accuracy of Continuous Hemoglobin Oxygen Saturation Monitoring Devices

Three devices used to measure hemoglobin oxygen saturation in the extracorporeal circuit were studied and compared to a control. The Baxter Bentley OxySat, Oximetrix Accusat, and the Radiometer ABL4 blood gas monitor were compared to a control, the IL 282 CoOximeter. Fifty one sample points were obtained during all phases of cardiopulmonary bypass with results as follows: Table 1 Comparison of Oxygen Saturation Devices r DIFF SD P ACCUSAT 0.94 p<.0001 -0.6 3.2 0.1834 NS ABL4 0.93 p<.0001 -1.7 3.3 0.0008 S OXYSAT 0.87 p<.0001 -6.8 4.4 0.0001 S r = correlation coefficient with corresponding p value, DIFF = difference from control, SD=Standard deviation of difference, P = p value for testing the hypothesis of no difference between test device and control, NS = No significant difference, S = Significant difference The Accusat was found to be a statistically more accurate means of monitoring hemoglobin oxygen saturations during cardiopulmonary bypass than the ABL4 and the OxySat. All devices had significant correlation with the control and with each other.

Continuous Oxygen Saturation Monitoring during Cardiac Catheterization in Adults

Arterial hypoxemia may contribute to morbidity during cardiac catheterization. Therefore, we measured arterial hemoglobin oxygen saturation (SaO2) continuously using pulse oximetry in 29 patients (age range, 21 to 83 years) undergoing cardiac catheterization. Baseline SaO2 was 96 +/- 0.4 percent. All patients had a decrease in SaO2 at some time during the procedure. Eleven patients (38 percent) had episodes of arterial hypoxemia, defined as a decrease in SaO2 below 90 percent. In these 11 patients, the mean number of episodes of hypoxemia was 16 +/- 7, and the mean duration of each episode was 53 +/- 25 seconds. Multiple stepwise regression analysis showed that the minimum SaO2 during catheterization for any patient was significantly associated with the baseline SaO2, duration of the procedure, and end-diastolic volume (EDV) as described by the following regression equation: minimum SaO2 = 46.8 - 0.0580 (duration of procedure in minutes) + 0.5362 (baseline SaO2) - 0.0159 (EDV). Based on our finding of arterial hypoxemia in greater than one third of our patients, we would consider continuous SaO2 monitoring or supplemental oxygen during cardiac catheterization, especially for those patients with poor ventricular function or low resting SaO2 or those expected to have long procedures.

Measurement of right atrial oxygen saturation by fiberoptic oximetry accurately reflects mixed venous oxygen saturation in swine.

Continuous fiberoptic measurement of mixed venous oxygen saturation (SvO2) via a pulmonary artery catheter is a useful, though invasive, monitoring technique. Continuous right atrial venous oxygen saturation measurement by oximetry offers the potential of a significantly less invasive SvO2 measurement. However, catheter motion, character of the vessel, chamber wall reflection, the filtering technique involved in calculating oxygen saturation, and the streaming of venous blood prior to ventricular mixing may influence the feasibility of continuous right atrial (RA) SvO2 measurement. This study investigated the performance of fiberoptically measured RA SvO2, at a position 2 cm from the tricuspid valve, relative to simultaneously measured pulmonary artery (PA) SvO2. Ten pigs were subjected to circulatory shock or chemically induced lung damage. Over a total monitoring period of approximately 40 hours, 464 paired data points were sampled at 5-minute intervals. The difference between the overall means of RA and PA SvO2 was 0.91% with a standard error of the estimate of 4.7%, a regression equation of RA SvO2 = PA SvO2 (0.94 + 2.1) PA So2, and a correlation coefficient of 0.94. Our conclusion, although extrapolated from a pig model, is that fiberoptic SvO2 monitoring may be accomplished less invasively and at a lower cost with a right atrial catheter.

Clinical evaluation of continuous venous oxygen saturation monitoring during anesthesia.

Clinical evaluation of continuous SvO2 monitoring during anesthesia was made in 14 surgical patients utilizing a fiberoptic reflectometry system combined with a pulmonary artery flow-directed balloon catheter. On-line values for SvO2 by the system were closely related to those obtained in vitro from a Radiometer ABL-300. There was a good correlation between changes of in vivo SvO2 and corresponding changes in cardiac index. We also observed that there was a significant correlation between SvO2 and oxygen extraction ratio. Our data indicate that continuous SvO2 monitoring during anesthesia can provide on-line information not only about hemodynamic state but also on oxygen transport.

Sudden infant death syndrome: 1987 perspective

The pathophysiology of SIDS remains unknown. Although a multifactorial cause appears plausible on the basis of available data, new data are needed to determine which components of this multifactorial hypothesis are most important and whether other factors need to be added. We need to better understand control of breathing in the newborn infant and the manner in which maturation of cardiorespiratory control progresses during infancy. The unique period of vulnerability for SIDS, in which risk is less in the neonate than at 2 to 6 months of age, remains unexplained. Is there a worsening in some aspect of cardiorespiratory control in infants destined to die of SIDS? An improved understanding of the increased risk in black infants, preterm infants, and infants with intrauterine drug exposure, although only a small percentage of all SIDS deaths, should contribute substantially to our understanding. Appropriately designed and well-controlled prospective studies are needed in asymptomatic infants at risk, to determine the true contemporary nonintervention rate of SIDS and the extent to which any assessment or intervention lowers this rate. Prospective pneumogram screening studies have demonstrated significant group differences in respiratory patterns in normal infants compared with later SIDS victims, but have failed to achieve sufficient sensitivity and specificity to be useful for populationwide prospective screening. To assess aspects of brainstem cardiorespiratory control in addition to those assessed by a conventional pneumogram, future studies will need to be based on an expanded or modified technology. On the basis of both physiologic considerations and available technology, addition of an oxygen saturation channel offers the most promise for providing a more comprehensive assessment of cardiorespiratory control. If there is an underlying deficiency in asphyxic arousal responsiveness, for example, with or without other respiratory control deficits, continuous monitoring of oxygen saturation as part of a second-generation pneumogram system currently has the greatest promise for providing a modified pneumogram assessment of greater clinical use. The use of continuous oxygen saturation as a home monitoring technique should also be investigated. Power spectrum analysis of cardiorespiratory variability also appears to have potential advantages over conventional pneumogram analyses, and needs to be evaluated in prospective studies. The following statements summarize our current knowledge regarding SIDS, apnea, pneumograms, and home monitors: The cause(s) of SIDS remains unknown.(ABSTRACT TRUNCATED AT 400 WORDS)

Pulse Oximetry in Very Low Birth Weight Infants With Acute and Chronic Lung Disease

With improved survival of very low birth weight infants, the incidence of bronchopulmonary dysplasia has significantly increased. Pulse oximetry appears to be an adequate alternative to transcutaneous PO2, for continuous arterial oxygen saturation (SaO2) monitoring in neonates; however, its usefulness has not been very well documented in very low birth weight infants. We studied 68 patients with birth weight less than 1,250 g; 44 neonates had respiratory distress syndrome and 24 had bronchopulmonary dysplasia. Using a Nellcor N-100 pulse oximeter, we compared transcutaneous oxygen saturation with simultaneous arterial samples analyzed for SaO2 (range 78% to 100%) using an IL 282 co-oximeter. Fetal hemoglobin was measured in 66 patients. We also evaluated the accuracy of transcutaneous PO2 in reflecting arterial PO2 in patients with bronchopulmonary dysplasia. Over a wide range of PO2, PCO2, pH, heart rate, BP, hematocrit, and fetal hemoglobin, linear regression analysis revealed a close correlation between pulse oximeter values and co-oximeter measured SaO2 in patients with acute (r = .88, Y = 19.41 + 0.79X) and chronic (r = .90, Y = 9.72 + 0.92X) disease. Regression analysis of transcutaneous v arterial PO2 in infants with bronchopulmonary dysplasia showed an r value of .78. In addition, in these patients with chronic disease, the mean difference between pulse oximeter SaO2 and co-oximeter measured SaO2 was 2.7 +/- 1.9% (SD); whereas the mean difference between transcutaneous and arterial PO2 was -14 +/- 10.7 mm Hg. Our findings indicate that pulse oximetry can be used reliably in very low birth weight infants with acute and chronic lung disease, for SaO2 values greater than 78%.(ABSTRACT TRUNCATED AT 250 WORDS)

Density of rapid eye movements during active sleep in preterm newborn infants

Rapid eye movement (REM) density has been helpful as a reliable index of phasic eye movements activity during REM (active) sleep in adults. We evaluated this index in 28 newborns, at 34 to 39 weeks of conceptional age (CA). The 5 hours polysomnographic recording during sleep included electroencephalogram, electrooculogram, electrocardiogram, pneumogram, nasal thermistor for detecting airflow, and continuous oxygen saturation (tcPO2) monitoring. REM density was measured by two distinct criteria: REM density as the duration of phasic eye movements in relation to REM periods (REMP). Such index varied from 10.6 to 14.1% and was higher in the 36-37 weeks CA group. REM density was calculated as a percentage of 10-second epochs of REM sleep in which phasic eye movements occurred. This criterion confirmed the narrow range of such index in this age bracket (39.9-44.6%), was higher in the first REMP and in the 36-37 weeks CA group. Our data suggest that REM density is a consistent phasic REM sleep feature in preterm newborns with levels close to the adult population, in spite of the gradual decrease of REM sleep duration with age. Higher indices were also found in the first REMP and in the 36-37 weeks CA group by both methods.

The current status of pulse oximetry. Clinical value of continuous noninvasive oxygen saturation monitoring.

The history of the development of pulse oximetry is outlined and the principle of how the apparatus works is described. The instrument detects hypoxic hypoxia and the shape of the oxygen dissociation curve means that the minimum saturation alarm should be set at 94% in anaesthetic usage. It is accurate to within 2% and is usually unaffected by racial pigmentation, but accuracy can be affected in low perfusion states, hypothermia and in the presence of abnormal forms of haemoglobin and pigments in the blood. Its clinical evaluation in the operating theatre and intensive care unit is reported. It was found to be useful and reliable and would appear to have logistical and other advantages over current methods of detecting hypoxia. Pulse oximetry may make a significant contribution to the safety of anaesthetic practice.

Optimising Cardiopulmonary Bypass Utilizing Continuous Oxygen Saturation Monitoring

Proper management of cardiopulmonary bypass requires the analysis of both arterial and venous blood gases at regular intervals, and is most critical during the rewarming phase. 3,4 In some hospitals blood gas results are received as long as 15 to 30 minutes after the sample is drawn. More frequent blood gas analysis or ideally continuous measurement of oxygen saturation allows the perfusionist to make continuous adjustments as the patient’s oxygen requirements change. Two hundred patients were selected for study. One hundred were perfused using regular periodic blood analyses. A second group of one hundred patients were perfused utilizing an in-line saturation meter. The blood flow rate was 6% lower during hypothermia and 5% lower while warm in the group utilizing the saturation meter. The total gas flow rate was reduced by 20% while cold and 16% while warm in the metered group. The CPB arterial and venous pO2 RANGES were reduced with the use of the oxygen saturation meter. The same make of hybrid oxygenator was utilized on all patients in both study groups. Based on the close correlation of the oxygen saturations afforded by the saturation meter and those measured by the blood gas laboratory, we found the Bentley Oxygen Saturation Meter reliable and accurate. It may help protect the patient from extremes in oxygenation and allows the perfusionist to regulate the oxygenator in the most precise and efficient operation.

Effect of flurazepam on sleep-disordered breathing and nocturnal oxygen desaturation in asymptomatic subjects

We assessed the effect of 30 mg of oral flurazepam on sleep-disordered breathing and nocturnal oxygen desaturation by performing a double-blind, placebo-controlled, randomized study. Asymptomatic subjects, 17 men and three women (mean age 49 years, mean weight 79 kg), were monitored for two consecutive nights. Flurazepam was given to 10 subjects on night 1 and to 10 subjects on night 2. Placebo was ingested on the other nights. Polysomnographic determinations included chest wall movement by impedance pneumography, nasal and oral airflow by thermistor probes, and continuous oxygen saturation by ear oximetry. Flurazepam was associated with significant increases in the number of sleep events (p = 0.01), episodes of apnea (p < 0.01), and total duration of apnea (p < 0.01). The number of episodes of hypopnea of desaturation did not significantly increase, although the degree of desaturation increased after flurazepam ingestion (p = 0.04). Total sleep time significantly increased (p = 0.04), but could not account for the increased number of events. Sleep stage distribution was minimally altered by ingestion of flurazepam.

Cardiac Arrhythmias Frequency During Fiberoptic Bronchoscopy and Correlation With Hypoxemia

To evaluate the occurrence of ECG abnormalities during fiberoptic bronchoscopy in relation to specific stages of the procedure and to hypoxemia, we prospectively studied 50 hospitalized patients aged 53 +/- 18 years (mean +/- SD) who were undergoing bronchoscopy by continuously monitoring cardiac rhythm with a continuous two-channel ECG recorder and oxygen saturation by using ear oximetry. Major disturbances of cardiac rhythm (ie, atrial, ventricular, or both) developed in 20 (40%) patients. Ventricular arrhythmias were recorded in ten patients (20%) and occurred with greatest frequency during passage of the bronchoscope through the vocal cords in five of these patients. Atrial arrhythmias were detected in 16 patients (32%), but their occurrence did not correlate closely with any one stage of the procedure. Arrhythmias were most frequent in association with periods of maximum oxygen desaturation in 12 of these 20 patients. Oxygen desaturation persisted for greater than one hour after bronchoscopy in 34 (68%) of 50 subjects. Notably, no correlation was observed between the frequency of arrhythmias during bronchoscopy and patients' age, sex, prior medications, or preexisting cardiac or pulmonary disorders. In no case was an ECG abnormality associated with adverse clinical sequelae.

Continuous Oxygen Saturation Recording during resuscitation of asphyxiated newborn infants

We measured Oxygen Saturation (SaO2) continuously in 29 severely asphyxiated infants (mean Apgar score 3.5 at 1 min), birthweight 1.05 - 2.7, mean 1.86 Kg. A new dual lumen umbilical arterial catheter containing fiber optics was positioned in the lower aorta. Red light transmitted down one fiber optic is reflected by the blood and the signal converted by the instrument to a digital reading of SaO2. The other lumen is used to sample blood and measure pressure. Electronic calibration is made before insertion. Reliability was shown by comparison with SaO2 measured in a cuvette oximeter (I.L. 182) r = 0.98, S.D. 2.46, n = 139. The time constant is 5 secs. and rapid changes in SaO2 are seen during resuscitation. Immediately after the catheter is inserted changes in SaO2 show the efficiency of assisted ventilation in improving blood oxygenation. Optimal levels of positive end-expiratory pressure and inspired oxygen concentration are quickly determined while blood sampling is reduced. In asphyxia and acidosis SaO2 reflects oxygen content more accurately than PaO2. The relationship between SaO2 and PaO2 for these infants shows that hyperoxia may be avoided if SaO2 is kept below 96%.