Pulse Oximeter Readings Research Articles

Evaluation of pulse oximetry in anaesthetised foals using multiple combinations of transducer type and transducer attachment site.

A commercially available pulse oximeter was evaluated in anaesthetised foals to determine its accuracy for estimating arterial haemoglobin saturation (SaO2). Five different transducer/transducer attachment site (TTAS) combinations were evaluated; 1-3) a fingertip transmission transducer attached to the foal's ear, lip and tongue, 4) an adhesive transmission transducer positioned on the foal's ear and 5) a forehead reflectance transducer placed on the ventral aspect of the foal's tail-base. Eight normal, Quarter Horse foals (age 5-10 days) were studied while under general anaesthesia. Alterations in arterial carbon dioxide tension (PaCO2) were produced by changing the level of ventilation. At each level of ventilation, alterations of arterial haemoglobin saturation (SaO2) were produced by varying the inspired fraction of oxygen (FIO2). At each level of ventilation and each level of FIO2, arterial blood samples were obtained for blood gas analysis while pulse oximeter readings were recorded simultaneously for each TTAS combination. Arterial blood oxygen saturation (SaO2) was calculated from arterial blood gas values and the equine blood oxygen dissociation curve. Pulse oximeter readings from each TTAS combination were compared with SaO2 values with linear regression analyses. Bias and precision values were determined and the sensitivity and specificity of each TTAS combination for detecting desaturation (SaO2 < 90%) were determined. Linear regression analyses indicated significant (P < 0.05) linear correlation between oxygen saturation determined by pulse oximeter (SpO2) and SaO2 for each of the 5 TTAS combinations. The combinations TTAS-1, TTAS-3 and TTAS-4 tended slightly to underestimate SaO2 at high SaO2 ranges, but overestimated SaO2 at low ranges of SaO2. Combination TTAS-2 overestimated SaO2 over all ranges of SaO2. Combination TTAS-5 consistently underestimated SaO2 at all ranges of SaO2. In general, accuracy and precision of each TTAS combination decreased at lower SaO2 ranges. All TTAS combinations, except TTAS-2 and TTAS-4, had good sensitivity for detecting SaO2 less than 90%. All TTAS combinations except TTAS-5 demonstrated good specificity. We concluded that pulse oximetry appears to be a valuable method for assessing SaO2 and detecting desaturation in anaesthetised foals. Clinicians should be aware that the type of transducer used and the anatomical site to which it is attached can have marked effects on the accuracy of pulse oximetry; and that different TTAS combinations may behave differently over various ranges of SaO2.

Difficulty Using a Laryngeal Mask Airway in a Patient with Lingual Tonsil Hyperplasia

Brent W. Fundingsland, M.D., Clinical Instructor.Jonathan L. Benumof, M.D., Professor, Department of Anesthesiology, University of California San Diego Medical Center, 200 West Arbor Drive, San Diego, California 92103-8770.To the Editor:--The successful use of a laryngeal mask airway (LMA) in three patients with undiagnosed lingual tonsil hyperplasia has been described by Biro and Shahinian. [1]The LMA was used without apparent difficulty to treat a "cannot intubate, cannot ventilate" situation occurring unexpectedly at the time of induction. [1]We cared for a patient who was found to have lingual tonsil hyperplasia at the time of induction but in whom the lungs could be ventilated with only marginal success via an LMA.A 55-yr-old woman scheduled for ankle surgery had normal preoperative airway examination results. After induction with propofol and rocuronium, standard mask ventilation, eventually using both an oral airway and two anesthesiologists, yielded no detectable gas exchange. Multiple attempts at laryngoscopy revealed only an abundance of soft, redundant, almost papillomatous appearing tissue at the base of the tongue. Transtracheal jet ventilation was attempted, but after several seconds, subcutaneous crepitus occurred without evidence of gas exchange. The catheter was removed, and a #4 LMA was inserted easily. Although gas exchange was occurring, the highest pulse oximeter reading attained was 92% with an FIO2of 1. The inadequate gas exchange was confirmed further by a simultaneous blood gas analysis (PaO262 mmHg). Using a fiberoptic bronchoscope through the LMA, only a very small portion of the vocal cords could be seen posteriorly. The anterior aspect of the cords was covered with folds of hyperplastic tissue from the lingual tonsil. The bronchoscope was guided through a tiny opening between the cords, and a normal appearing trachea was identified. We were unable, however, to pass a 6.0 mm-ID endotracheal tube over the bronchoscope through the vocal cords. The SpO2decreased to 30% during this apneic intubation attempt, increasing to 85% over about 1 min after the bronchoscope was removed and ventilation resumed via the LMA. Because of the apparently edematous periglottic tissue and decreasing pulse oximeter readings, it was decided to proceed to a cricothyrotomy. Subsequent biopsy revealed a clear diagnosis of lingual tonsillar hyperplasia.This case illustrates, as has been described previously, that the LMA can be a life-saving tool. It also serves as a reminder that this tool at times may be of only limited efficacy as a superglottic ventilatory conduit in the presence of a significant periglottic obstruction. [2].Brent W. Fundingsland, M.D., Clinical Instructor.Jonathan L. Benumof, M.D., Professor, Department of Anesthesiology, University of California San Diego Medical Center, 200 West Arbor Drive, San Diego, California 92103-8770.

Evaluation of Transmittance and Reflectance Pulse Oximetry in a Canine Model of Hypotension and Desaturation

SummaryTen, anesthetized dogs were instrumented with three pulse oximeter probes; two lingual transmittance probes and one rectal reflective probe. Arterial oxygen desaturation was produced by decreasing the inspired oxygen concentration. Hypotension was produced with an infusion of nitroprusside. Simultaneous pulse oximeter readings (SpO2) were compared to co‐oximeter measured arterial saturation (SaO2) collected over a range of SaO2 (50–100%) and mean arterial pressures (40–100mmHg). Each of the monitors and means of evaluating SpO2 studied provided accurate SpO2 measurements over a range of mean arterial pressure from 40–100mmHg. All of the monitors tested tended to overestimate the SaO2 when the arterial saturation was less than 70%.

Detection of pulpal circulation in vitro by pulse oximetry

Evaluation of pulse oximetry as a potential method of determining pulp vitality was the subject of this research. An in vitro model of pulpal circulation was fabricated to test the design for a dental pulse oximetry sensor. Blood samples equilibrated with hypoxic gas mixtures were circulated through the model by a peristaltic pump. A pulse was simulated by introduction of gas bubbles into the blood circulation. Pulse oximeter readings for saturation were recorded and compared with blood gas analysis results. Statistical analysis revealed no difference between pulse oximetry and blood gas analysis with a highly significant correlation coefficient. Clinical evaluation of this application is currently in progress.

Oxygen Therapy in the Postanesthesia Care Unit

In Response: Pulse oximetry became the standard of care in the postanesthesia care unit (PACU) with the expectation that it would be used to guide patient care decisions related to oxygenation. While health care providers have traditionally placed a great deal of confidence in the use of supplemental oxygen, it is not an adequate safeguard against hypoxemia. Kavanagh et al. [1] noted that although it reduces the incidence of desaturation it does not affect the degree or duration. It also does not affect patient outcomes such as the incidence of myocardial ischemia. Our recommendation to use the objective data supplied by the pulse oximeter as a guide for oxygen use is in line with what others, such as DiBenedetto et al. [2], have recommended. The difference in the recommendations was that we chose a pulse oximeter reading of 92% to indicate those at risk for hypoxemia, while DiBenedetto and colleagues recommended a pulse oxymetry reading below 94%. Their use of a more stringent criterion may be due to the difference in populations. DiBenedetto and colleagues studied all patients admitted to the PACU, which would likely include patients having had thoracic and upper abdominal surgery, a group not included in our study. Unfortunately, there is no description in their research report of the type of surgery performed with their sample. Another difference between the two studies is that their patients were breathing room air while being transported to the PACU, whereas ours received supplemental oxygen during transport. As a result of our study, the policy for oxygen administration in the PACU where the study was done has been changed. Now when patients are admitted to the PACU only those whose preoperative workup would indicate them to be at high risk for hypoxemia are given supplemental oxygen. For most patients, the pulse oximeter reading is used along with other clinical variables, such as vital signs, wakefulness, and the like, to determine the need for oxygen. Oxygen is therefore administered only to those who require it. Over a 9-month period there have not been any untoward incidents attributable to this change in policy. Oxygen has, however, continued to be provided during transport. Prior to the start of our study we noted that many patients objected to the application of the high-flow, high-humidity face tent which at that time was routinely used in the unit. Many of the patients were observed removing the face tent immediately after it was applied, which we considered wasteful. Changing the PACU oxygen administration policy has reserved the use of these high-cost oxygen administration devices to only those patients who require increased humidification, reducing hospital waste and costs. Audrey G. Gift, PhD, RN, FAAN University of Pennsylvania School of Nursing, Philadelphia, PA 19104-6096 Kaye Whitmore, RN University of Maryland Medical System, Baltimore, MD 21201

Epidural Anesthesia Affects Pulse Oximeter Readings and Response Time

We investigated the effects of epidural anesthesia on pulse oximeter readings (Spo2) and response time because this type of anesthesia causes significant changes in microcirculation at measurement sites. Twenty patients were divided into lumbar epidural (L-EPI;n=10) and the cervical epidural (C-EPI;n=10) groups. Spo2 and skin blood flow (SBF) were measured at the finger and toe simultaneously by pulse oximeter and laser Doppler flowmeter, respectively. Data were collected before and after epidural anesthesia for 1 min and the response time was calculated by the difference between the finger and toe using the breath-holding method. Epidural anesthesia increased SBF in the blocked area and decreased it in the nonblocked area in both groups (P<0.01, respectively). In the L-EPI group, Spo2 was increased at the finger (P<0.05) and decreased at the toe (P<0.05). In the C-EPI group, Spo2 at both the finger and toe was decreased by the anesthesia. ΔSpo2 (Spo2 at the finger minus Spo2 at the toe) was increased in the L-EPI group (P<0.05) and decreased in the C-EPI group (P<0.01). The difference in the response time became larger in the C-EPI group and smaller or opposite in the L-EPI group after anesthesia. The difference in response time and SBF were significantly correlated (r=0.71;P<0.05). These results indicated that epidural anesthesia lowerd Spo2 and shortened the response time through vasodilation in the blocked area and caused the opposite reactions in the nonblocked area through compensatory vasoconstriction.

Pulse oximetry in ventilated preterm newborns: reliability of detection of hyperoxaemia and hypoxaemia, and feasibility of alarm settings.

The aim of our study was to evaluate the reliability of pulse oximetry in detecting both hyper- and hypoxaemic states and to create clinically feasible alarm limits. A total of 792 readings of a pulse oximeter and corresponding values of arterial oxygen tension from 146 (79M, 67F) artificially ventilated preterm newborns with indwelling umbilical artery catheters were compared. Predictive value analysis of pulse oximeter readings related to arterial oxygen tension confirmed the ability of the pulse oximeter to identify both hypoxaemia and hyperoxaemia. However, a clinically feasible and safe range of alarm limits for maintenance of arterial oxygen tension of 40-90 mmHg (5.3-12 kPa) could only be established at a sensitivity level less than 0.9. At a level of 0.85, the alarm range on the pulse oximeter was 92.5-95%. Based on these findings, we are concerned about using pulse oximetry as the sole means of oxygen monitoring for preterm infants receiving supplementary oxygen. A combination of the pulse oximetry with other methods of blood-gas monitoring seems mandatory.

Epidural anesthesia affects pulse oximeter readings and response time.

We investigated the effects of epidural anesthesia on pulse oximeter readings (Spo2) and response time because this type of anesthesia causes significant changes in microcirculation at measurement sites. Twenty patients were divided into lumbar epidural (L-EPI;n=10) and the cervical epidural (C-EPI;n=10) groups. Spo2 and skin blood flow (SBF) were measured at the finger and toe simultaneously by pulse oximeter and laser Doppler flowmeter, respectively. Data were collected before and after epidural anesthesia for 1 min and the response time was calculated by the difference between the finger and toe using the breath-holding method. Epidural anesthesia increased SBF in the blocked area and decreased it in the nonblocked area in both groups (P<0.01, respectively). In the L-EPI group, Spo2 was increased at the finger (P<0.05) and decreased at the toe (P<0.05). In the C-EPI group, Spo2 at both the finger and toe was decreased by the anesthesia. ΔSpo2 (Spo2 at the finger minus Spo2 at the toe) was increased in the L-EPI group (P<0.05) and decreased in the C-EPI group (P<0.01). The difference in the response time became larger in the C-EPI group and smaller or opposite in the L-EPI group after anesthesia. The difference in response time and SBF were significantly correlated (r=0.71;P<0.05). These results indicated that epidural anesthesia lowerd Spo2 and shortened the response time through vasodilation in the blocked area and caused the opposite reactions in the nonblocked area through compensatory vasoconstriction.

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.

Epidural anesthesia affects pulse oximeter readings and response time

Epidural anesthesia affects pulse oximeter readings and response time

Unexpectedly Low Pulse Oximeter Readings in a Boy with Unstable Hemoglobin Köln

Unexpectedly Low Pulse Oximeter Readings in a Boy with Unstable Hemoglobin Köln

The effect of dyshemoglobins on pulse oximetry: Part I, Theoretical approach and Part II, Experimental results using an in vitro test system.

Pulse oximeters are known to be inaccurate in the presence of elevated concentrations of carboxyhemoglobin and methemoglobin. This paper attempts to alleviate some of the confusion that exists between fractional and functional saturation, and to clarify the comparison of each with SpO2. A series of theoretical relationships between pulse oximeter reading (SpO2) and actual oxygen saturation (both fractional and functional) is derived using simple absorption theory. The theoretical relationships are checked using an experimental in vitro test system. This consists of a blood circuit containing a model finger, capable of simulating the pulsatile transmission signals through a real finger. Theoretical predictions and experimental results are compared and are found to agree well in the presence of carboxyhemoglobin, but less well with methemoglobin. Possible reasons are discussed.

Pulse oximetry during helicopter transport

The study objective was to determine if pulse oximetry readings obtained during helicopter transport were indicative of subsequent arterial blood-gas measured saturations. A prospective study design was chosen. Data were gathered on a convenience sample of patients 18 years and older not under cardiopulmonary resuscitation; 101 patients were used for the study. Pulse oximeter readings of oxygen saturation and heart rate were recorded along with simultaneous vital signs. Arterial saturation in blood gases drawn in the emergency department were added to the patient record. Improper functioning of the pulse oximeter was recorded on 10 (9.9%) of the patients. No correlation was found between the probe type and the documented problems (PHI = 0.009). The pulse oximeter saturation readings were not significantly different from arterial saturation in blood gases when compared by paired samples t-test (t = 0.880, p = 0.383). There was also no significant difference between the patient's heart rate sensed by the pulse oximeter and the simultaneous palpated pulse rate. Percent saturation readings by repeated measures were statistically different (p < 0.05) showing a minimal improvement in saturation over time. Based on this study's findings, the authors feel the pulse oximeter can be a valuable adjunct to patient care during helicopter transport.

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.

Accuracy of pulse oximetry in children with cyanotic congenital heart disease

The use of a pulse oximeter to monitor arterial oxygen saturation (SaO 2) 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 SaO 2 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 (SaO 2 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 SaO 2 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%.

In vitro performance test system for pulse oximeters.

An in vitro system was developed capable of testing the accuracy and reproducibility of pulse oximeter readings. The pulse oximeter probe receives signals through a pulsating blood cuvette. The development of the design of the cuvette is described. Using the final design (or 'model finger'), a comparison is made between readings from a Datex Satlite pulse oximeter (SpO2) and saturation values obtained by use of a multi-wavelength bench oximeter (SaO2). Linear regression analysis of the data gives SpO2 = 0.88 SaO2 + 11.2 (r = 0.979, p < 0.001).

The author replies…

Thank you for clarifying the information about the presence of audible noise in the nursery interfering with pulse oximeter readings. As I reviewed that section, I realized the distinction between audible noise and electrical current was not stated clearly. Perhaps the distinction of decreasing sensory stimulation in the environment would have clarified my intent.

Do fetal pulse oximetry readings at delivery correlate with cord blood oxygenation and acidaemia?

To assess the accuracy of a pulse oximeter in the fetus. A prospective descriptive study, comparing oxygenation and acidaemia of cord blood with oxygen saturation in the arteries of the fetal scalp measured by a pulse oximeter just before delivery. The data were collected using an experimental pulse oximeter and a sensor specifically adapted to cope with the problems of fetal pulse oximetry. The labour ward in a teaching hospital. Thirty seven Caucasian fetuses presenting by the vertex in normal uncomplicated labour. Fetal pulse oximetry reading shortly before birth, umbilical cord oxygenation and pH, and Apgar scores. Data of sufficient quality were obtained from 28 fetuses. There was a highly significant correlation between pulse oximetry reading and umbilical vein oxygen saturation r = 0.59, P = < 0.001). There was also a significant correlation between the pulse oximeter reading and cord blood pH (vein: r = 0.57, P = 0.002, artery: r = 0.63, P = 0.001). Apgar scores were not related to the oximetry results. Pulse oximetry readings reflect fetal oxygenation at birth.

Portable transcutaneous O 2 and CO 2 monitors and pulse oximeters during transport of critically III newborn infants

The clinical assessment of respiratory status during neonatal interhospital transports is difficult. Three non-invasive transcutaneous O 2 /CO 2 monitors and one pulse oximeter were compared to arterial blood samples obtained simultaneously during air and ground transports. All patients were monitored with a transcutaneous O 2 /CO 2 monitor and a pulse oximeter. Arterial blood (one to four samples) was stored in heparinized glass syringes on ice and later analyzed on both a blood gas analyzer and a hemoximeter. Transcutaneous O 2 /CO 2 monitor and pulse oximeter readings were recorded and compared to simultaneously obtained arterial blood samples for PaO 2 , PaCO 2 , and measured hemoglobin oxygen saturation by linear regression analysis. PtcO 2 (R=O.68 for PaO 2 <80 mm Hg and R=0.89 for PaO 2 >80 mm Hg, P<0.05 for both), PtcCO 2 (R=0.75, P<0.05) and pulse oximeter results (R=0.94, P<0.05) correlated significantly with their respective arterial values. These results indicate that PaO 2 , PaCO 2 , and arterial oxygen saturation can be estimated using non-invasive monitoring during air and ground neonatal transports.

The accuracy of pulse oximetry at two haematocrit levels.

The object of this study was to investigate the influence of haematocrit on the accuracy of pulse oximetry. Seven Swedish land race rabbits were studied. The oxygen saturation of haemoglobin was decreased step-wise using increasing fractions of nitrogen to the inspiratory gas. One pulse oximeter probe was attached on the front leg and another probe directly over the common carotid artery. The pulse oximeter readings (SpO2) were compared with simultaneous oxygen saturation analysis (SaO2) by a haemoximeter. The pulse oximeter measurements were performed at the haematocrit levels of approximately 40% and 11%, respectively. We found a good correlation between SpO2 and SaO2 in a wide range of the oxygen saturation, i.e. SaO2 26-100%. After haemodilution the correlation was improved in the range 86-100%, but not in the range 26-85%. No correlation between SpO2 and SaO2 was found when the sensor was attached directly over the artery during normal haematocrit levels. After haemodilution a better correlation was however obtained. These results indicate that the accuracy of pulse oximetry is dependent on the haematocrit level.