Ear Oximetry Research Articles

Long-term prospective study in children after respiratory syncytial virus infection

We have prospectively evaluated for the past 8 years 29 children who were hospitalized during infancy with acute lower respiratory tract illness caused by respiratory syncytial virus (RSV). No differences in the prevalence of a family history of atopy or breast-feeding in these infants compared with controls were noted. However, a history of parental smoking was significantly associated with hospital admission for RSV lower respiratory tract disease. Evidence of atopy, as defined by serum IgE levels and radioallergosorbent testing, have developed in only three (10%) of 29 children. Six children (21%) continue to have recurrent lower respiratory tract disease. Fifty-five percent of these children had abnormally low oxyhemoglobin levels (SaO2) measured by ear oximetry for the first 3 to 4 years after the acute illness. Twenty-one percent have persistently low SaO2 levels during the eighth year of follow-up. Spirometric values indicate evidence of peripheral airway obstruction. These studies suggest that an association between RSV lower respiratory tract infections and chronic abnormalities of pulmonary function may be detected sequentially through the first 8 years of life. These abnormalities are not limited to those children developing an atopic state during that same time period.

Oxygen saturation during exercise in cystic fibrosis.

Cystic fibrosis (CF) is often associated with low hemoglobin oxygen saturation and with limited exercise tolerance, yet published reports do not agree on the effect of exercise on oxygenation in CF. We studied oxygen saturation (SaO2) by ear oximetry in 91 patients with CF during progressive exercise to exhaustion. Only 13 of 91 patients changed SaO2 by 5% or more; of these, 4 patients increased SaO2 by 5% or more, whereas 9 decreased by 5% or more. Small changes in SaO2 did not relate to resting pulmonary function, but large decreases in SaO2 were much more likely to be found in patients with forced expiratory volume in one second (FEV1) less than 50% of VC than in those with better pulmonary function (desaturation of 5% or greater was found in only 1 of 62 patients with FEV1 greater than 50% of VC, but in 8 of 29 patients with FEV1 less than or equal to 50% VC). However, even in severely affected patients, modest increases or no change in saturation were more common than large decreases, and 17 of 29 patients with FEV1 less than 50% VC ended exercise with SaO2 greater than 90%, including 3 patients with initial SaO2 below 90%. No single resting pulmonary function test or combination of tests could predict oxygen changes with exercise. Most patients with CF tolerate even maximal exercise without significant desaturation, but patients with FEV1 less than 50% of VC should have supervised exercise testing with ear oximetry before undertaking an exercise program.

NON-INVASIVE MONITORING OF ARTERIAL 02 SATURATION IN NEWBORN INFANTS

Ear oximetry is a simple non-invasive method for measurement of arterial O2 saturation (SaO2) in adults and older children. To evaluate the practicability and accuracy of ear oximetry in newborn infants, we have measured SaO2 in 12 newborns, ages 2.1 days ± 1 (SD) using Biox II-A oximeter and its small ear probe. 15 SaO2 measurements were done during mechanical ventilation (for HMD, diaphragmatic hernia, sepsis) and compared to actual (CO-OX) and calculated SaO2 from simultaneously obtained arterial blood. Blood pressure was in normal range at the time of study. Bilirubin and Hb levels were noted. There was excellent correlation between SaO2 measured by ear oximetry and CO-OX values (n=12; r=0.987) and calculated SaO2 (n=13; r=0.989)(range: 43-99%). SaO2 measured on the scrotum correlated equally well to CO-OX SaO2 (n=6; r=0.979). Bilirubin and Hb levels had no effect on differences between the various SaO2 measurement methods. Ear oximetry is an accurate and practical method for monitoring SaO2 especially in chronic hypoxemia situations during the neonatal period. Transcutaneous PO2 monitoring will be preferred for preterm infants at risk of hyperoxia. However ear oximetry has the advantages of easier application of the probe with less risk of skin burns, and thus longer continuous monitoring of SaO2 in hypoxemic newborn infants.

CHRONIC OBSTRUCTION OF PERIPHERAL AIRWAYS AND HYPOXEMIA IN ASTHMATIC CHILDREN

Both in vivo and in excised lungs, the nitrogen washout alveolar plateau (phase 3 slope) correlates with histopathologically detected obstruction of peripheral airways. We hypothesized that children with abnormally steep phase 3 slopes between episodes of asthma should exhibit both hypoxemia and relatively severe clinical courses because of chronic obstruction of peripheral airways. To test this, we measured phase 3 slope and supine arterial oxygen saturation (SaO2, by ear oximetry) and reviewed the clinical histories of 25 children in stable condition between episodes of wheezing. We found that the 7 children with abnormally steep phase 3 slopes also had the lowest values for SaO2 (mean 93.7±1.4 SD %). Phase 3 slope had a significant negative correlation with SaO2. There was no correlation between SaO2 and expiratory flow rate, density dependence of expiratory flow or the ratio of residual volume to total lung capacity. During the year preceding the study, outpatient visits resulting in injections of adrenaline were significantly more frequent in the 7 children with steep phase 3 slopes than in the 18 with normal phase 3 slopes (P< .05). We conclude 1) groups of asthmatic children with and without persistent obstruction of peripheral airways can be identified by the single breath nitrogen washout and 2) those children with persistent obstruction of peripheral airways tend to be hypoxemic and have a relatively high incidence of status asthmaticus.

Influence of head-dependent positions on lung volume and oxygen saturation in chronic air-flow obstruction.

We investigated the influence of head-dependent positions upon functional residual capacity (FRC) and arterial oxygen saturation in 25 patients with clinically stable chronic air-flow obstruction and 25 normal subjects. Lung volume was measured by gas dilution in normal subjects and by plethysmography in patients with chronic obstructive pulmonary disease (COPD). Arterial oxygen saturation was determined by ear oximetry. In normal subjects, sitting FRC declined by 29.9% when a horizontal-supine posture was assumed, but underwent little further change as the supine subject was tilted head-downward to -25 degrees. Lateral decubitus positions caused declines from sitting FRC of 17.1% at 0 degrees, and 27.4% at -25 degrees. In contrast, patients with COPD experienced negligible changes in lung volume as position was varied. The mean falls from sitting FRC were 3.5% and 1.9% in the 0 degree supine and 0 degree lateral decubitus postures, respectively, and little further volume loss occurred in head-dependency. Eight patients actually increased FRC when recumbent. Positional lung volume changes measured by gas dilution exceeded those measured by plethysmography, suggesting that increased air trapping helped to maintain FRC as position was altered. Patients with COPD did not desaturate in any position tested. We conclude that patients with advanced COPD conserve lung volume and do not desaturate when tipped into head-dependent positions. Reduction of FRC is unlikely to contribute to the hypoxemia or dyspnea previously reported to occur in these patients during chest physiotherapy.

Noninvasive Monitoring of Arterial Blood Gases: A Report of the ACCP Section on Respiratory Pathophysiology

During the past decade, there have been steady advances in the attempt to monitor noninvasively arterial blood gases. This article discusses some of these techniques as well as some older, welldescribed methods of estimating arterial Pco2. The three major areas to be considered are ear oximetry, transcutaneous measurements of gas tension, and derivations of the arterial Pco2 from measurements of the alveolar gases.

Intravenous Naloxone in Acute Respiratory Failure

A 58-year-old man presented with acute on chronic respiratory failure. In the acute stage of his illness an infusion of the opiate antagonist naloxone caused an improvement in oxygen saturation as measured by ear oximetry from 74% to 85%, while a saline infusion resulted in a return of oxygen saturation to the original value. When he had recovered from the acute episode the same dose of naloxone had no effect on oxygen saturation. These findings suggest that in acute respiratory failure there may be overproduction of, or increased sensitivity to, endorphins.

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.

Short-term respiratory effects of 0.12 ppm ozone exposure in volunteers with chronic obstructive pulmonary disease.

Twenty-five volunteers with chronic obstructive pulmonary disease of mild to moderately severe degree underwent 1-h exposures to 0.12 ppm ozone (O2) in purified air with intermittent mild exercise. Their responses were assessed in terms of forced expiratory performance, ear oximetry, and reported symptoms. Control studied consisted of similar exposures to purified air alone. Control studies were separated from O2 exposures by 1 month, and the order was randomized. All studies took place in a controlled-environment chamber, and were preceded by approximately 1 h of rest in a purified-air environment. No significant disturbances in forced expiratory performance or symptoms attributable to O2 exposure were found. A slight but significant tendency to decreased arterial hemoglobin oxygen saturation (SaO2) during exercise in O2 was observed. The decrement in SaO2 with O2 relative to clean air (mean 1.3%) was near the limit of resolution of the ear oximeter test and was detected by signal averaging, thus its physiologic or clinical significance is uncertain.

Lung volume, closing volume, and gas exchange.

The effect of a voluntary reduction in lung volume on arterial O2 saturation (SaO2) was studied in 10 normal subjects aged 19-63 yr. SaO2 was measured by ear oximetry first during tidal breathing at functional residual capacity, and then during tidal breathing at 380 ml above residual volume. Tidal volume and breathing frequency were kept constant, and end-tidal CO2 partial pressure remained stable or fell in 9 out of 10 subjects. When lung volume was reduced, SaO2 fell by a mean of 1.5% (range 0-3%). Closing volume (CV) was measured by the N2-washout method (mean 0.89 liter, range 0.41-1.44). There was a close correlation between CV and the fall in SaO2 (r = 0.867, P = 0.001). Arterial and mixed venous CO2 were measured in one subject; the results indicated some fall in cardiac output following the lung volume change, but this accounted for less than half of the fall in SaO2. The relationship between CV and the lung volume at which tidal breathing occurs is an important determinant of pulmonary gas exchange through its effect on the matching of ventilation to perfusion.

Evaluation of ear oximetry in the measurement of arterial oxygen saturation

Evaluation of ear oximetry in the measurement of arterial oxygen saturation

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.

1626 PHYSIOLOGICAL CORRELATES OF INTERSTITIAL LUNG DISEASE (ILI)) IN CHILDREN: OXYGEN DESATURATION (DeSaO2) DURING EXERCISE

Young children with ILD may be uncooperative or too ill to perform meaningful tests of pulmonary function. We have evaluated children with ILD using pre, during (DUR), and post exercise (EX) stress ear oximetry (SaO2) and other more routine tests of pulmonary function. Responses in children with ILD, healthy children (CON), those with bronchial asthma (BA), and cystic fibrosis (CF) were compared.* all values represent averages ** standard error of the mean Exercise produced significant DeSaO2 (PRE-DUR) in the ILD, CF, and control groups. The control group DeSaO2 response was minimal. The ILD group exhibited the greatest changes. The alterations in the CF subjects were intermediate in degree. Desaturation responses during exercise clearly separated the ILD group from the others and correlated well with low FVC (R2=.60). Post EX SaO2 values promptly returned to near baseline in most children. We have found DeSaO2 during exercise to be a sensitive, and reproducible test of ILD in children.

Arterial blood gas tensions and pH.

1 The definition of PO2 and its relationship to the oxygen saturation (SO2) by the oxygen dissociation curve (ODC) is described with details of the ligands of the ODC and the effects of haemoglobinopathies on P50 (the position of the ODC) and the slope of the ODC (Hill's 'n'). 2 The definition of PCO2 and description of CO2 transport by blood leads to consideration of the basis of acid base balance. 3 Acid base balance is expressed in terms of arterial blood (H+) (or pH) PCO2 relationship using a non-logarithmic diagram. 4 The measurement of arterial blood gas tensions is described with comments on arterial puncture and available modern automated blood gas electrodes and their calibration. 5 Non-invasive indirect measurements of blood gas tensions, by ear oximetry are described, with calibration figures on the Hewlett-Packard 47021A ear oximeter. End-tidal PO2 and PCO2 measurements by mass spectrometer or infra-red CO2 analyser, and of transcutaneous PO2 measurements by a heated polarographic electrode are described. 6 These measurements are necessary to study the effects of pharmacological agents on the chemical control of breathing, on pulmonary gas exchange, and on acid base balance in humans. The measurements are in everyday use in clinical practice, both to aid diagnosis of respiratory diseases, assess their severity, and to quantiate the effects of therapeutic agents.

Effects of sodium nitrate aerosol on cardiopulmonary function of dogs, sheep, and man

Submicronic aerosols of nitrate salts are synthesized in the atmosphere through further oxidation of nitrogen oxides produced during the burning of fossil fuels. This study was conducted to determine whether brief exposure to submicronic aerosol of sodium nitrate in high concentrations adversely affects the cardiopulmonary system. In all studies, submicronic aerosol of sodium chloride was used as a control. Anesthetized dogs breathing up to 10 mg/m 3 of sodium nitrate (NaNO 3) aerosol for 7.5 min showed no significant alterations in respiratory resistance, static lung compliance, and functional residual capacity. A 4-hr exposure to NaNO 3 aerosol (5 mg/m 3) produced neither significant changes in lung mechanics, functional residual capacity, pulmonary and systemic arterial pressures, cardiac output, heart rate, and arterial blood gases in anesthetized dogs nor a change in tracheal mucous velocity in conscious sheep. Both normal and asthmatic adults who breathed submicronic aerosol of NaNO 3 (up to 1 mg/m 3) for 10 min showed no significant changes in lung volumes, distribution of ventilation, ear oximetry, dynamic mechanics of breathing, and oscillation mechanics of the chest-lung system. NaNO 3 aerosol (1000 μg/m 3 for 10 min did not significantly change pulmonary capillary blood flow, diffusing capacity, oxygen consumption, and pulmonary tissue volume as measured by a rebreathing technique. Thus, brief exposure to high concentrations of submicronic aerosol of sodium nitrate does not produce immediate adverse effects on cardiopulmonary function of anesthetized dogs, conscious sheep, and normal and asthmatic adults.

Disordered breathing and oxygen desaturation during sleep in patients with chronic obstructive lung disease (COLD)

Seven patients with chronic obstructive lung disease (COLD) were monitored during their overnight sleep to determine the occurrence of disordered breathing and oxygen desaturation. Nasal and oral airflows were sensed by thermistor probes, chest wall movement by impedance pneumography and arterial oxygen saturation by ear oximetry. These variables were correlated with electroencephalographic and electrooculographic tracings. The subjects had a mean base line oxygen saturation of 89.2 per cent and slept an average of 218 minutes. Six of these seven subjects had one to 30 episodes of oxygen desaturation (decrease more than 4 per cent), 4 seconds to 30 minutes in duration, with declines in saturation as great as 36 per cent. In two subjects, saturation dropped to less than 50 per cent. Breathing was disordered in five of the seven subjects and included apnea and hypopnea. Subjects experienced from nine to 37 episodes of disordered breathing. Disordered breathing caused 42 per cent of the episodes of desaturation, all of which were less than 1 minute in duration. The mean maximum decline in saturation was 7.6 per cent. All episodes of desaturation lasting longer than 5 minutes occurred in rapid eye movement (REM) sleep and were not caused by disordered breathing. The mean maximal decrease in saturation was 22 per cent. This study reveals that disordered breathing is common in subjects with COLD and often causes desaturation but that it cannot explain all episodes of sleep desaturation.

Noninvasive estimation of arterial oxygenation in newborn infants

Two noninvasive methods of estimating arterial oxygenation were compared in a group of 48 infants ranging in birth weight from 870 to 4,000 gm, with diagnoses including apnea of prematurity, hyaline membrane disease, meconium aspiration, and congenital heart disease. Both transcutaneous oxygen measurements and ear oximetry gave reasonably accurate estimations of arterial oxygen levels within commonly used clinical ranges (PO2 50 to 70 mm Hg, arterial saturation 90 to 98%). Infants with shock demonstrated a wide range of values for transcutaneous oxygen levels, suggesting that this method has limited usefulness in this situation. Ear oximetry had limited ability to distinguish high, but safe, levels of arterial oxygen from excessively elevated levels. While neither method can be recommended for replacement of arterial oxygen sampling, both methods may be useful in a clinical setting if care is exercised in interpretation of the results and if the values obtained are checked against those from arterial blood.

The pulmonary hemodynamic effects of aerosols of isoproterenol and ipratropium in normal subjects and patients with reversible airway obstruction.

The hemodynamic effects of isoproterenol sulfate, ipratropium bromide, and Freon® propellant were measured in 8 normal subjects and 10 patients with reversible airway obstruction who were placed in...

COMPARISON OF NON-INVASIVE METHODS OF ESTIMATING OXYGENATION IN INFANTS: TCO2 EAR OXIMETRY

Two non-invasive methods of estimating arterial oxygenation in newborn infants were compared: ear oximetry (Hewlett-Packard 47201A) and transcutaneous oximetry(TCO2) (Roche 5301). 33 infants ranging in weight from 870 to 4000 gm, age from 6 hours to 28 days were studied. In one group of 15 infants, TCO2 was compared with simultaneously determined PaO2 sampled from a temporal or umbilical artery. These values were highly correlated (r=.75, p<.001, Syx=15.5). In a group of 18 infants SaO2, PaO2, and saturation by ear oximetry were determined simultaneously. Correlation between these values was also high (r=.84,p<.001, Syx=8.2). Deviation of non-invasively determined values for oxygenation vs values obtained by direct arterial sampling did not depend on systolic pressure, pH, or length of time the sensor was applied to the subject. Similar results were found in a group of 6 infants where both non-invasive methods were used together. While the ear oximeter gives more precise data and exhibits a less “damped” signal than TCO2, it is more difficult to maintain contact between sensor and subject for long periods of time and is therefore less practical in its present form for use in neonates. Both methods are accurate and practical, and are clinically useful in (1)unstable patients during the onset or recovery from illness, and (2) patients with apnea who lack an umbilical artery catheter.

PATTERNS OF HYPOXEMIA IN INFANTS WITH RESPIRATORY SYNCYTIAL VIRUS(RSV) BRONCHIOLITIS AND PNEUMONIA, MEASURED BY EAR OXIMETRY

The degree and duration of hypoxemia in babies with RSV has not been studied. We used an ear oximeter to measure dally the arterial satuation(% Sat)on 32 infants consecutively admitted with RSV bronchiolitis and pneumonia; median age 2 months. Oximetry readings compared to simultaneous arterial gases gave a correlation coefficient of 0.95, and 0.7 compared to capillary gases. On admission these infants' mean % Sat was 86%(pO2=53 mm Hg), range 75-95%(pO2 41-75). The lowest mean value was not until day 3 and was 85%(pO2 51) with a range of 53-96%(pO2 28-87). The severity of hypoxemia fluctuated in any given day and was prolonged. At discharge the mean % Sat=90%(pO2 60) range 83-98% (pO2 47-113); only 3 infants had values >93%(or >pO2 66). Mean % Sat of 9 infants 3-7 weeks after discharge was 96%(pO2 87), range 93-98%(pO2 66-113). Clinical detection of hypoxemia was difficult. Marked hypoxemia existed without cyanosis. However, severity of hypoxemia correlated with cyanosis, respiratory rate, younger age and % bands. No correlation existed with total WBC, PMNs, nor clinical severity judged by retraction and lethargy. Thus, RSV hypoxemia may be severe, prolonged, and clinically occult. Ear oximetry is a valuable and non-invasive technic in the management of infants with RSV lower respiratory tract disease.