SaO2 Range Research Articles

Reliability of pulse oximetry at four different attachment sites in immobilized white rhinoceros (Ceratotherium simum)

ObjectivesTo determine the reliability of peripheral oxygen haemoglobin saturation (SpO2), measured by a Nonin PalmSAT 2500A pulse oximeter with 2000T transflectance probes at four attachment sites (third eyelid, cheek, rectum and tail), by comparing these measurements to arterial oxygen haemoglobin saturation (SaO2), measured by an AVOXimeter 4000 co-oximeter reference method in immobilized white rhinoceros (Ceratotherium simum). Study designRandomized crossover study. AnimalsA convenience sample of eight wild-caught male white rhinoceros. MethodsWhite rhinoceros were immobilized with etorphine (0.0026 ± 0.0002 mg kg–1, mean ± standard deviation) intramuscularly, after which the pinna was aseptically prepared for arterial blood sample collection, and four pulse oximeters with transflectance probes were fixed securely to their attachment sites (third eyelid, cheek, rectum and tail). At 30 minutes following recumbency resulting from etorphine administration, the animals were given either butorphanol (0.026 ± 0.0001 mg kg–1) or an equivalent volume of saline intravenously. At 60 minutes following recumbency, insufflated oxygen (15 L minute–1 flow rate) was provided intranasally. In total, the SpO2 paired measurements from the third eyelid (n = 80), cheek (n = 67), rectum (n = 59) and tail (n = 76) were compared with near-simultaneous SaO2 measurements using Bland-Altman to assess bias (accuracy), precision, and the area root mean squares (ARMS) method. ResultsCompared with SaO2, SpO2 measurements from the third eyelid were reliable (i.e., accurate and precise) above an SaO2 range of 70% (bias = 1, precision = 3, ARMS = 3). However, SpO2 measurements from the cheek, rectum and tail were unreliable (i.e., inaccurate or imprecise). Conclusions and clinical relevanceA Nonin PalmSAT pulse oximeter with a transflectance probe inserted into the space between the third eyelid and the sclera provided reliable SpO2 measurements when SaO2 was > 70%, in immobilized white rhinoceros.

Performance of the new SmartCardia wireless, wearable oximeter: a comparison with arterial SaO2 in healthy volunteers

BackgroundOur goal was to evaluate the performance of a new wearable arm located pulse oximeter.MethodsTwelve volunteers were monitored with three pulse oximeters and underwent desaturation to 70% SaO2.We compared the accuracy of SpO2 reading from the SmartCardia system with SpO2 using two well established devices (Masimo and Nellcor) as reference.Oximetry was performed at different level of oxygen saturation varying from 70 to 100%. Bias, ARMS and precision were evaluated using Bland-Altman plots.ResultsThe mean (SD) differences between SaO2 compared to SpO2 and the devices were as follows: SaO2 versus Masimo 2,12 ± 1,01% (95% CI 1,45 to 2,79), SaO2 versus Nellcor 0,78 ± 0,58% (95% CI − 0,29 to 1,65) and SaO2 versus SmartCardia 0,42 ± 0,24% (95% CI − 0,64 to 1,46). The bias between SmartCardia, Masimo, Nellcor devices and SaO2 was 0.16 (95% CI 0.05 to 0.33) and LoA (level of agreements) 2.96 (95% CI − 2,68 to 2,89) for SmartCardia, 2,02 (95% CI 1,49 to 2,54) and LoA − 6 to 11 for Masimo, and 0,76 (95% CI 0,5 to − 1) and LoA − 3,5 to 5,0 for Nellcor. ARMS for the 70–100% SaO2 range was 1,4 for SmartCardia, 5,0 for Masimo and 2,31 for Nellcor.ConclusionsThe new wireless SmartCardia SpO2 measurement system demonstrated in-line results, bias, ARMS and precision in healthy volunteers, when compared with the gold standard SaO2 and with two well established systems, Masimo and Nellcor.Trial registrationThe present trial was prospectively registered at UCSF record (registration number:10–00437), on March 8, 2021.

Use of blood colour for assessment of arterial oxygen saturation in immobilized impala (Aepyceros melampus)

ObjectiveTo determine the relationship between arterial blood colour [as defined by the International Commission on Illumination (CIE) L∗a∗b∗ colour space] and haemoglobin oxygen saturation [functional saturation (SaO2) and fractional saturation (FO2Hb)], and if arterial blood colour can be used to predict arterial haemoglobin oxygen saturation. Study designDescriptive study as an adjunct to two prospective randomized crossover studies. AnimalsA group of 10 wild caught adult female impala (Aepyceros melampus) weighing 34.1 ± 5.2 kg (mean ± standard deviation). MethodsImpala were immobilized with potent opioids (0.09 mg kg–1 of etorphine or thiafentanil). A total of 163 arterial blood samples were collected anaerobically into heparinized syringes from arterial cannulae and analysed immediately using spectrocolourimetry and co-oximetry. Data were analysed by modelling the relationship between predicted arterial blood colour CIE L∗a∗b∗ components and SaO2 and FO2Hb. The models were then used to predict values for L∗, a∗ and b∗ to produce a colour palette for the range of SaO2 and FO2Hb used. The modified version of the Farnsworth-Munsell hue test was used to assess the subjective ordering of the resulting colour palette by 20 observers. ResultsThe second-order polynomial (quadratic) model produced the best fit for all three arterial blood colour CIE L∗a∗b∗ components for both SaO2 and FO2Hb. The regression models were used to generate predicted arterial blood colour CIE L∗a∗b∗ components for the midpoint of each decile over a range of SaO2 and FO2Hb percentages (15% to 95%). The resulting colour palettes were correctly ordered by all observers in the SaO2 range of 45–95% saturation. Conclusions and clinical relevanceAn association between arterial blood colour (as defined by CIE L∗a∗b∗ components) and SaO2 and FO2Hb exists, and arterial blood colour can be used to give a clinically useful estimate of arterial haemoglobin oxygen saturation in impala.

Using near-infrared spectroscopy to measure cerebral metabolic rate of oxygen under multiple levels of arterial oxygenation in piglets

Improving neurological care of neonates has been impeded by the absence of suitable techniques for measuring cerebral hemodynamics and energy metabolism at the bedside. Currently, near-infrared spectroscopy (NIRS) appears to be the technology best suited to fill this gap, and techniques have been proposed to measure both cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2). We have developed a fast and reliable bolus-tracking method of determining CMRO2 that combines measurements of CBF and cerebral venous oxygenation [venous oxygen saturation (CSvO2)]. However, this method has never been validated at different levels of arterial oxygenation [arterial oxygen saturation (SaO2)], which can be highly variable in the clinical setting. In this study, NIRS measurements of CBF, CSvO2, and CMRO2 were obtained over a range of SaO2 in newborn piglets (n=12); CSvO2 values measured directly from sagittal sinus blood samples were collected for validation. Two alternative NIRS methods that measure CSvO2 by manipulating venous oxygenation (i.e., head tilt and partial venous occlusion methods) were also employed for comparison. Statistically significant correlations were found between each NIRS technique and sagittal sinus blood oxygenation (P<0.05). Correlation slopes were 1.03 (r=0.91), 0.73 (r=0.73), and 0.73 (r=0.81) for the bolus-tracking, head tilt, and partial venous occlusion methods, respectively. The bolus-tracking technique displayed the best correlation under hyperoxic (SaO2=99.9±0.03%) and normoxic (SaO2=86.9±6.6%) conditions and was comparable to the other techniques under hypoxic conditions (SaO2=40.7±9.9%). The reduced precision of the bolus-tracking method under hypoxia was attributed to errors in CSvO2 measurement that were magnified at low SaO2 levels. In conclusion, the bolus-tracking technique of measuring CSvO2, and therefore CMRO2, is accurate and robust for an SaO2>50% but provides reduced accuracy under more severe hypoxic levels.

Accuracy of Methemoglobin Detection by Pulse CO-Oximetry During Hypoxia

Methemoglobin in the blood cannot be detected by conventional pulse oximetry, although it can bias the oximeter's estimate (Spo2) of the true arterial functional oxygen saturation (Sao2). A recently introduced "Pulse CO-Oximeter" (Masimo Rainbow SET(R) Radical-7 Pulse CO-Oximeter, Masimo Corp., Irvine, CA) is intended to additionally monitor noninvasively the fractional carboxyhemoglobin and methemoglobin content in blood. The purpose of our study was to determine whether hypoxia affects the new device's estimated methemoglobin reading accuracy, and whether the presence of methemoglobin impairs the ability of the Radical-7 and a conventional pulse oximeter (Nonin 9700, Nonin Medical Inc., Plymouth, MN) to detect decreases in Sao2. Eight and 6 healthy adults were included in 2 study groups, respectively, each fitted with multiple sensors and a radial arterial catheter for blood sampling. In the first group, IV administration of approximately 300 mg sodium nitrite increased subjects' methemoglobin level to a 7% to 8% target and hypoxia was induced to different levels of Sao2 (70%-100%) by varying fractional inspired oxygen. In the second group, 15% methemoglobin at room air and 80% Sao2 were targeted. Pulse CO-oximeter readings were compared with arterial blood values measured using a Radiometer multiwavelength hemoximeter. Pulse CO-oximeter methemoglobin reading performance was analyzed by observing the incidence of meaningful reading errors at the various hypoxia levels. This was used to determine the impact on predictive values for detecting methemoglobinemia. Spo2 reading bias, precision, and root mean square error were evaluated during conditions of elevated methemoglobin. Observations spanned 66.2% to 99% Sao2 and 0.6% to 14.4% methemoglobin over the 2 groups (170 blood draws). Masimo methemoglobin reading bias and precision over the full Sao2 span was 7.7% +/- 13.0%. Best accuracy was found in the 95% to 100% Sao2 range (1.9% +/- 2.5%), progressing to its worst in the 70% to 80% range (24.8% +/- 15.6%). Occurrence of methemoglobin readings in error >5% increased over each 5-point decrease in Sao2 (P < 0.05). Masimo Spo2 readings were biased -6.3% +/- 3.0% in the 95% to 100% Sao2 range with 4% to 8.3% methemoglobin. Both the Radical-7 and Nonin 9700 pulse oximeters accurately detected decreases in Sao(2) <90% with 4% to 15% methemoglobin, despite displaying low Spo2 readings when Sao2 was >95%. The Radical-7's methemoglobin readings become progressively more inaccurate as Sao2 decreases <95%, at times overestimating true values by 10% to 40%. Elevated methemoglobin causes the Spo2 readings to underestimate Sao2 similar to conventional 2-wavelength pulse oximeters at high saturation. Spo2 readings from both types of instruments continue to trend downward during the development of hypoxemia (Sao2 <90%) with methemoglobin levels up to 15%.

Accuracy of a third (Dolphin Voyager) versus first generation pulse oximeter (Nellcor N-180) in predicting arterial oxygen saturation and pulse rate in the anesthetized dog

ObjectiveTo compare the accuracy of a 3rd (Dolphin Voyager) versus 1st generation pulse oximeter (Nellcor N-180). Study designProspective laboratory investigation. AnimalsEight adult dogs. MethodsIn anesthetized dogs, arterial oxygen saturation (SpO2) was recorded simultaneously with each pulse oximeter. The oxygen fraction in inspired gas (FiO2) was successively reduced from 1.00 to 0.09, with re-saturation (FiO2 0.40) after each breathe-down step. After each 3-minute FiO2 plateau, SpO2 and pulse rate (PR) were compared with the fractional arterial saturation (SaO2) and PR determined by co-oximetry and invasive blood pressure monitoring, respectively. Data analysis included Bland-Altman (B–A) plots, Lin's concordance correlation factor (ρc), and linear regression models. ResultsOver a SaO2 range of 33–99%, the overall bias (mean SpO2 − SaO2), precision (SD of bias), and accuracy (Arms) for the Dolphin Voyager and Nellcor N-180 were 4.3%, 4.4%, and 6.1%, and 3.2%, 3.0%, and 4.3%, respectively. Bias increased at SaO2 < 90%, more so with the Dolphin Voyager (from 1.6% to 8.6%) than Nellcor N-180 (from 3.2% to 4.5%). The SpO2 readings correlated significantly with SaO2 for both the Dolphin Voyager (ρc = 0.94) and Nellcor N-180 (ρc = 0.97) (p < 0.001). Regarding PR, bias, precision, and accuracy (Arms) for the Dolphin Voyager and Nellcor N-180 were −0.5, 4.6, and 4.6 and 1.38, 4.3, and 4.5 beats minute−1, respectively. Significant correlation existed between pulse oximeter and directly measured PR (Dolphin Voyager: ρc = 0.98; Nellcor N-180: ρc = 0.99) (p < 0.001). Conclusions and clinical relevanceIn anesthetized dogs with adequate hemodynamic function, both instruments record SaO2 relatively accurately over a wide range of normal saturation values. However, there is an increasing overestimation at SaO2 < 90%, particularly with the Dolphin Voyager, indicating that 3rd generation pulse oximeters may not perform better than older instruments. The 5.4-fold increase in bias with the Dolphin Voyager at SaO2 < 90% stresses the importance of a 93–94% SpO2 threshold to ensure an arterial saturation of ≥90%. In contrast, PR monitoring with both devices is very reliable.

Effect of errors in baseline optical properties on accuracy of transabdominal near-infrared spectroscopy in fetal sheep brain during hypoxic stress

A continuous-wave (cw) near-infrared spectroscopy (NIRS) instrument has been developed to noninvasively quantify fetal cerebral blood oxygen saturation (StO2). A linear Green's function formulism was used to analytically solve the photon diffusion equation and extract the time-varying fetal tissue oxy- and deoxy-hemoglobin concentrations from the NIR measurements. Here we explored the accuracy with which this instrument can be expected to perform over a range of fetal hypoxic states. We investigated the dependence of this accuracy on the accuracy of the reference optical properties chosen based on the literature. The fetal oxygenation of a pregnant ewe model was altered via maternal aortic occlusion. The NIR cw instrument was placed on the maternal abdomen directly above the fetal head, continuously acquiring diffuse optical measurements. Blood was sampled periodically from the fetus to obtain fetal arterial saturation (SaO2) measurements from blood gas analysis. The NIR StO2 values were compared with the fetal SaO2 measurements. Variations in the NIR results due to uncertainty in the reference optical properties were relatively small within the fetal SaO2 range of 30 to 80%. Under hypoxic conditions, however, the variability of the NIR StO2 calculations with changes in the assumed reference properties became more significant.

How safe is intermittent positive pressure ventilation in preterm babies ventilated from delivery to newborn intensive care unit?

Objectives: To examine whether clinically determined ventilator settings will produce acceptable arterial blood gas values on arrival, in preterm infants ventilated from delivery to the newborn intensive care unit (NICU)....

Evaluation of the Nonin 8600V Veterinary Pulse Oximeter in Anesthetized Horses

SummarySpO2 values from the Nonin 8600V veterinary pulse oximeter, using a lingual clip‐type, transmittance sensor applied to the tongue, were compared to directly‐measured SaO2 values from a co‐oximeter, calibrated for equine blood, in 5 halothane‐anesthetized horse. Normocapnia was maintained with controlled ventilartion. The inspired oxygen concentration was varied by mixing nitrogen in oxygen to obtain SpO2 readings of approximately 60, 65, 70, 75, 80, 85, 90, 92, and 100%. At the time of each SpO2 recording, an arterial blood sample was collected for immediate analysis of SaO2. A total of sixty paired measurements were made. The results showed excellent data correlation with a bias (precision) of 0.55 (2.57) and an R‐value of 0.98 over the entire SaO2 range tested. Based on these findings, the Nonin 8600V veterinary pulse oximeter, with the lingual sensor, performed accurately and reliably, and appears to be suitable for clinical use in anesthetized horses. (Vet Emerg &amp; Crit Care, 1999: 13–18)

Validation of reflectance pulse oximetry: an evaluation of a new sensor in piglets.

A new reflectance pulse oximetry sensor, developed for intrapartum estimation of arterial oxygen saturation (SaO2), was calibrated and evaluated. The sensor contains two light emitting diodes of 735 and 890 nm, and a photodetector at a distance of 14 mm from both light emitting diodes. In seven Yorkshire/Hampshire piglets, the reflectance sensor (Nellcor Puritan Bennett Inc.) was calibrated using blood sample SaO2 values. The resulting calibration line was evaluated in four Dutch piglets, by comparing pulse oximetry saturation readings (SpO2) with blood sample and intravascular fiberoptic oximetry SaO2 values. Several reflectance sensors were fixed on each animal. Desaturation levels were obtained by changing the gas mixture of oxygen/ nitrous oxide via a tracheal catheter. In the Yorkshire/ Hampshire piglets, the standard deviation of difference (SpO2-SaO2) was 4.7% (n = 364), over an SaO2 range of 17% to 100%. In the Dutch piglets, the mean difference (SpO2-SaO2) was -1.6% and the standard deviation of difference was 5.4%, over the same SaO2 range (n = 254). Comparisons of continuous recordings of reflectance SpO2 and fiberoptic SaO2 revealed variation in individual regression lines. This new 735/890 nm reflectance sensor demonstrates acceptable accuracy in piglets. A further evaluation during labor should assess its feasibility for fetal surveillance.

Transmission pulse oximetry in the fetal lamb: is there a universal calibration?

Transmission pulse oximetry is widely used for oxygen monitoring. The use of pulse oximeters is steadily expanding toward situations with low arterial oxygen saturation (Sao2) values. Therefore, we evaluated transmission pulse oximetry in the unanesthetized fetal lamb at low Sao2 levels. In seven fetal lambs, fetal hypoxemia was induced by occlusion of the maternal common iliac artery, four days after the instrumentation of the animal. Two Nellcor prototype transmission Y-sensors (light emitting diodes: 660 and 890 nm) were applied, one around a forelimb muscle and one around a skinfold in the neck, and were connected to Nellcor pulse oximeters. The pulse oximeter was calibrated for the skin measurements. Pulse oximeter saturation readings (Spo2) were compared with sample Sao2 values, over an Sao2 range of 13 to 63%. For the neck sensor the SD of the difference was 5.0% (n = 101). For the muscle sensor the mean difference was 19.5% and the SD of the difference was 5.9% (n = 206). Regression analysis showed a different calibration line for the muscle sensor with the equation: Spo2 = 0.92 x Sao2 + 21.90. Continuous recordings were obtained both from the forelimb muscle and from the neck, but the recordings from the neck showed a substantial loss of signal during the hypoxemia period. We conclude that transmission pulse oximetry is less accurate below an Sao2 of 70% in fetal lambs than above 70% Sao2. At these low levels of Sao2, pulse oximeters may need to be constructed with different calibration lines for various application positions of the body.

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%.

The accuracy of a fiberoptic oximeter over a wide range of arterial oxygen saturation values in piglets.

A piglet model was used to evaluate the accuracy of a fiberoptic oximeter over a wide range of arterial oxygen saturation (SaO2) values. In eight anaesthetized piglets, the inspired oxygen concentration was varied from 30% to 6% resulting in a SaO2 range from 100% to 15%. Paired data of the Opticath fiberoptic catheter, which was placed in the descending aorta, and blood sample SaO2 values assessed by a multiwavelength oximeter, were analysed. After in vitro calibration according to the manufacturer's instruction, the fiberoptic catheter started to underestimate the SaO2 below 78%, worsening towards lower SaO2 values. The overall bias was -3.4% and the precision 3.8%. An off-line fit with a non-linear model resulted in a standard deviation of residuals of 2.6%. After several in vivo calibration adjustments when the fiberoptic oximeter deviated more than 4% from the blood sample value, the bias was eliminated over the total SaO2 range and the precision was 3.7%. The Opticath fiberoptic oximeter could have an accuracy for the whole SaO2 range between 15-100% close to the accuracy of the multiwavelength oximeter, when the fiberoptic oximeter is adapted for the underestimation below 78% SaO2.

Evaluation of pulse oximetry in horses surgically treated for colic.

All 43 horses anaesthetised for colic surgery were premedicated with xylazine or diazepam. Anaesthesia was induced with guaifenesin and ketamine, horses were placed in dorsal recumbency and anaesthesia was maintained with isoflurane in oxygen and mechanical ventilation. Haemoglobin saturation readings (SpO2) were taken with a pulse oximeter and compared with computed haemoglobin saturation (SaO2) from arterial blood samples. Readings were taken over a range of SaO2 of 78-100%, mean arterial blood pressure ranged from 24 to 108 mmHg and PaO2 ranged from 53 to 490 mmHg. Analysis of 107 readings showed that SpO2 values predicted SaO2 but time, blood pressure and individual horse did not. Correlation coefficients between SpO2 and SaO2 were 0.85 for all values and 0.88 for values at 30 min. Values for bias and precision were calculated for all SpO2 values and for readings separated into 3 saturation groups: normal, low normal, and abnormal. The pulse oximeter tended to underestimate SaO2 at all times, and was less precise as the saturation decreased.

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.

Augmented hypoxic ventilatory response in men at altitude.

To test the hypothesis that the hypoxic ventilatory response (HVR) of an individual is a constant unaffected by acclimatization, isocapnic 5-min step HVR, as delta VI/delta SaO2 (l.min-1.%-1, where VI is inspired ventilation and SaO2 is arterial O2 saturation), was tested in six normal males at sea level (SL), after 1-5 days at 3,810-m altitude (AL1-3), and three times over 1 wk after altitude exposure (PAL1-3). Equal medullary central ventilatory drive was sought at both altitudes by testing HVR after greater than 15 min of hyperoxia to eliminate possible ambient hypoxic ventilatory depression (HVD), choosing for isocapnia a P'CO2 (end tidal) elevated sufficiently to drive hyperoxic VI to 140 ml.kg-1.min-1. Mean P'CO2 was 45.4 +/- 1.7 Torr at SL and 33.3 +/- 1.8 Torr on AL3, compared with the respective resting control end-tidal PCO2 of 42.3 +/- 2.0 and 30.8 +/- 2.6 Torr. SL HVR of 0.91 +/- 0.38 was unchanged on AL1 (30 +/- 18 h) at 1.04 +/- 0.37 but rose (P less than 0.05) to 1.27 +/- 0.57 on AL2 (3.2 +/- 0.8 days) and 1.46 +/- 0.59 on AL3 (4.8 +/- 0.4 days) and remained high on PAL1 at 1.44 +/- 0.54 and PAL2 at 1.37 +/- 0.78 but not on PAL3 (days 4-7). HVR was independent of test SaO2 (range 60-90%). Hyperoxic HCVR (CO2 response) was increased on AL3 and PAL1. Arterial pH at congruent to 65% SaO2 was 7.378 +/- 0.019 at SL, 7.44 +/- 0.018 on AL2, and 7.412 +/- 0.023 on AL3.(ABSTRACT TRUNCATED AT 250 WORDS)

Repetitive apneas induce periodic hypertension in normal subjects through hypoxia.

Periodic increases in blood pressure (BP) can occur in the sleep apnea syndrome (SAS) during recurrent apneas. To investigate the mechanisms causing this periodic hypertension, we simulated SAS by imposing a matching breathing pattern on seven healthy awake male volunteers. Continuous finger arterial BP, electrocardiogram, arterial O2 saturation (SaO2), end-tidal CO2, and tidal volume were measured. The role of hypoxia was studied by comparing apneas during depletion of O2 in the spirometer with those during 100% O2 breathing. In all subjects, BP periodically reached values greater than 150/95 mmHg in the hypoxic series. During the hyperoxic apnea series, however, BP remained stable. End-apneic mean BP was shown to be inversely correlated to SaO2 in six subjects in the SaO2 range from 60 to 100%. Although the hypoxic BP pattern closely mimicked that in SAS, the heart rate pattern in four of our subjects remained distinct from that in patients. Atropine could not prevent large BP swings in the hypoxic series. We conclude that SaO2 is a major determinant of periodic hypertension in recurrent apneas. Its effect probably results from chemoreflex modulation of peripheral resistance.

Basic studies of pulse oximetry in a rabbit model

We have developed an animal model for the evaluation of pulse oximetry during severe hypoxaemia. Twelve rabbits were anaesthetized and mechanically ventilated via a tracheostomy tube. Increasing fractions of nitrogen were added to the gas mixture they inhaled to obtain severe hypoxaemia (saturation range 26%-100%). On 412 occasions, simultaneous pulse oximeter (SpO2) and invasive haemoximeter (SaO2) measurements were compared. The regression analysis of the data gave the equation: y = 0.7 x + 26.7, r = 0.90. In the SaO2 range less than or equal to 85%, the bias (mean value of SaO2-SpO2) was higher when compared with SaO2 greater than 85%. In an in vitro study the light absorption characteristics of rabbit haemoglobin (Hb) were compared to human Hb. The millimolar extinction coefficients of both reduced and oxygenated Hb from rabbits were found to be similar to human Hb. We consider the animal model (rabbit) suitable for studies of pulse oximetry during physiological and pathophysiological conditions.

Agreement between Noninvasive Oximetric Values for Oxygen Saturation

We made an assessment of five pulse oximeters in regard to their ability to replace the HP ear oximeter as a noninvasive measurement of SaO2. Trials were performed during isocapnic progressive hypoxia (SaO2 range, 99 to 70 percent) in 22 white and six black subjects. Comparisons between values of SaO2 by oximetry were analyzed by comparing the difference of values by the two methods against their mean. The difference between pulse oximeters and the HP was 2.6 +/- 10.3 percent in all subjects. Results in whites were 1.9 +/- 10.2 percent and in blacks were 5.1 +/- 9.2 percent. The distribution of differences between pulse oximeters and the HP were larger below 80 percent than above 85 percent. We conclude that pulse oximeters give higher values than the HP, a tendency which is more pronounced in black than in white subjects. While the limits of agreement are better at saturations above 85 percent, the 95 percent confidence limits of agreement between pulse oximeters and the HP are rather large (+/- 10 percent) and unacceptable for assuming that pulse oximeters will provide the same values as found in clinical studies using the HP.

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)