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PubMed1994

[Noninvasive patient observation in veterinary medicine: pulse oximetry and capnography. I. Pulse oximetry].

Two non-invasive continuous techniques for monitoring the respiratory function during anaesthesia have been established during the last year: pulse oximetry for monitoring the adequate oxygen supply and capnography for measuring the carbon dioxide elimination. In human medicine both are accepted as essential monitors with great reliability. Whether clinical use and interpretation can be transferred to animals without any restrictions will be discussed by looking on the physical and engineering background as well as the physiologic interpretation of the measured variable and their capability to detect critical events during administration of anaesthesia. Part I: Pulse oximetry measures the arterial oxygen saturation continuously and non-invasively. Its application in veterinary medicine must be discussed critically concerning the method as well as the interpretation. The information obtained is very different during injectable and inhalant anaesthesia. Respiratory depression is easy to detect while the animal breathes room air spontaneously. Is the inspired air enriched with oxygen, like during inhalant anaesthesia, normal values of oxygen saturation can mask the respiratory insufficiency and may give a false sense of security.

Anesthesia↗
PubMed1988

Forehead pulse oximetry compared with finger pulse oximetry and arterial blood gas measurement.

Usual monitoring sites for pulse oximetry involve the fingers, toes, ear lobe, and nasal septum. This study examined the performance of a forehead sensor compared with a finger sensor for the pulse oximeter and arterial blood gas (ABG) analysis. Ten healthy adult volunteers and 22 ventilator-dependent patients were studied. The arterial oxygen saturation detected by forehead pulse oximetry (SpO2) correlated well with finger SpO2 and arterial oxygen saturation (SaO2) determined by arterial blood gas analysis in the healthy volunteers. Forehead SpO2 in mechanically ventilated patients correlated well with finger SpO2 and SaO2 when heart rate detected by pulse oximeter differed less than 10% from apical heart rate. Factors that caused a difference in oximeter-detected heart rate and apical heart rate were extensive tissue edema, head movement, and difficulty securing good tape placement. This suggests that when signal strength is weak, causing poor pulse rate detection, there will also be problems associated with accurate SpO2. The forehead pulse oximeter sensor works well on healthy, well-oxygenated volunteers. Difficulty was experienced when applying and using the sensor on critically ill patients. The reliability of the forehead pulse oximeter sensor has not been established at low saturations.

Adolescent↗
PubMed1989

Effects of methemoglobinemia on pulse oximetry and mixed venous oximetry.

The performance of three commercially available pulse oximeters was assessed in five anesthetized dogs in which increasing levels of methemoglobin were induced. Hemoglobin oxygen saturation in each dog was monitored with three pulse oximeters (Nellcor N-100, Ohmeda 3700, and Novametrix 500) and a mixed venous saturation pulmonary artery catheter (Oximetrix Opticath). Arterial and mixed venous blood specimens were analyzed for PaO2, PaCO2, and pHa using standard electrodes. An IL-282 Co-oximeter was used on the same specimens to determine oxyhemoglobin and methemoglobin as percentages of total hemoglobin. Methemoglobin levels of up to 60% were induced by intratracheal benzocaine. As MetHb gradually increased while the dogs were breathing 100% inspired oxygen, the pulse oximeter saturation (SpO2) overestimated the fractional oxygen saturation (SaO2) by an amount proportional to the concentration of methemoglobin until the latter reached approximately 35%. At this level the SpO2 values reached a plateau of 84-86% and did not decrease further. When, at fixed methemoglobin levels, additional hemoglobin desaturation was induced by reducing inspired oxygen fraction, SpO2 changed by much less than did SaO2 (regression slopes from 0.16 to 0.32). Thus, at high methemoglobin levels SpO2 tends to overestimate SaO2 by larger amounts at low hemoglobin saturations. Plots of SpO2 versus functional saturation (oxyhemoglobin/reduced hemoglobin plus oxyhemoglobin) show an improved but still poor relationship (regression slopes from 0.32 to 0.46). The Oximetrix Opticath pulmonary artery catheter behaves similarly but provides somewhat better agreement with functional saturation than do the pulse oximeters in the presence of methemoglobinemia. Pulse oximetry data (SpO2) should be used with caution in patients with methemoglobinemia.

Animals↗
PubMed1989

Pulse oximetry at the roadside: a study of pulse oximetry in immediate care.

The measurement of tissue oxygen saturation with a pulse oximeter is of proved value in the hospital setting. The development of a portable oximeter has allowed this investigation to be performed during the prehospital phase of a patient's care. Pulse oximetry was performed at the roadside in 25 patients with abnormal trauma scores and found to be of benefit in detecting and monitoring hypoxia in patients with airway obstruction, depressed respiration due to head injury, and, in particular, with closed chest injuries. There were no practical difficulties associated with the use of the instrument either at the roadside or in a moving ambulance. The portable pulse oximeter is a valuable aid in the prehospital monitoring of patients with trauma.

Accidents, Traffic↗
PubMed1989

Toward absolute reflectance oximetry: I. Theoretical consideration for noninvasive tissue reflectance oximetry.

The photon diffusion theory can yield quantitative estimation of tissue hemoglobin saturation, provided that the medium is homogeneous and that one calibration data is available. The error in detection of tissue OS of the gut mucosa ranged from 5 to 10% in oxygen saturation. In application to skin, the two-layer tissue model suggests that by properly designing the optical sensor and by appropriately selecting the illumination wavelengths, it is possible to capture mainly the light returning from the specific depth in tissue. Since the skin layer thickness is roughly in the order of 1 mm, the source and detector separation distance of approximately 3 mm or larger would ensure that the measured reflectance is truly returning from the deeper layer. When such reflectances are normalized to the blood-free reflectance obtained by squeezing the blood out of the tissue, the normalized reflectance truly represents the deeper layer characteristics. In application to head, since the skin and skull thickness is considerable large, separation distance of 40 mm or greater is required to ensure the reflectance is actually returning from the brain. Closely spaced optical sensor would measure the scattering and absorption characteristics of the skin and skull of the head. As for directional changes in optical propagation due to tissue inhomogeneities, multiple light sources at the equi-distance around the detector can be placed to average out the effect. The resultant reflectance can be analyzed based on the similar mathematical treatment as presented in this study. However, since the absolute reflectance level calculated by the theory and the actual reflectance for a given transducer geometry have some deviation, again one point calibration is required to close the gap between them. This can be accomplished through arterialization of the tissue and ventilating with pure oxygen to yield reflectance from tissue containing 100% saturated blood. As for hemoglobin content, isosbestic reflectance, for example at 805 nm, can be utilized to estimate tissue hemoglobin content. Once one point calibration is accomplished, reflectance changes thereafter due to changes in HbT and OST can be fairly accurately predicted by the photon diffusion theory in combination with linear analysis. Concerning separation of arterial and venous blood in tissue, the diastolic and systolic phases of the optical plethysmographic signal can be assumed to relate to venous or DC level, and to arterial or AC component. Since the four components, arterial and venous OS and Hb, are unknowns in the system, four equations or four wavelength measurements are required to sort out each effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

[Pulse oximetry in perioperative monitoring].

BACKGROUND: Monitoring with pulse oximetry might improve patient outcome by enabling an early diagnosis and consequently, correction of perioperative events that might cause postoperative complications or even death. Only a few randomised clinical trials of pulse oximetry have been performed during anaesthesia and in the recovery room which describe perioperative hypoxaemic events, postoperative cardiopulmonary complications and cognitive dysfunction. OBJECTIVES: To study the effect of perioperative monitoring with pulse oximetry to clearly identify the adverse outcomes that might be prevented or improved by the use of pulse oximetry. SEARCH STRATEGY: Trials were identified by computerised searches of the Cochrane Library, MEDLINE, EMBASE, and by checking the reference lists of trials and review articles. SELECTION CRITERIA: All controlled trials that randomised patients to either pulse oximetry or no pulse oximetry during the perioperative period, including the operating and recovery room. DATA COLLECTION AND ANALYSIS: We collected data in relation to events detectable by pulse oximetry, any serious complications that occurred during anaesthesia or in the postoperative period, intra- or postoperative mortality, and duration of recovery or intensive care stay. Formal statistical synthesis of individual trials was not performed in view of the variety of outcomes studied. MAIN RESULTS: Searching identified six reports; four studies with data from a total of 21,773 patients were considered eligible for analysis. Only two studies specifically addressed the outcomes in question; both found no effect on the rate of postoperative complications using perioperative pulse oximetry. Two studies used hypoxaemia detectable by pulse oximetry to assess the value of perioperative monitoring, although outcomes were not given. It was found that hypoxaemia was reduced in the pulse oximetry group both in the operating theratre and in the recovery room. During observation in the recovery room, the incidence of hypoxaemia in the pulse oximetry group was 1.5-3 times less. The postoperative cognitive function using the Wechsler memory scale and continuous reaction time was independent of perioperative monitoring with pulse oximetry. The other study showed that postoperative complications occurred in 10% of the patients in the oximetry group and in 9.4% in the control group. The two groups did not differ in cardiovascular, respiratory, neurologic, or infectious complications. The duration of hospital stay was a median of 5 days in both groups, and an equal number of in-hospital deaths was registered in the two groups. REVIEWERS' CONCLUSIONS: The studies confirmed that pulse oximetry can detect hypoxaemia and related events. However, we have found no evidence that pulse oximetry affects the outcome of anaesthesia. The conflicting subjective and objective results of the studies, despite an intense, methodical collection of data from a relatively large population, indicate that the value of perioperative monitoring with pulse oximetry is questionable in relation to improved reliable outcomes, effectiveness and efficiency.

Humans↗
PubMed2000

Nocturnal pulse oximetry as an abbreviated testing modality for pediatric obstructive sleep apnea.

OBJECTIVE: To determine the utility of pulse oximetry for diagnosis of obstructive sleep apnea (OSA) in children. METHODS: We performed a cross-sectional study of 349 patients referred to a pediatric sleep laboratory for possible OSA. A mixed/obstructive apnea/hypopnea index (MOAHI) greater than or equal to 1 on nocturnal polysomnography (PSG) defined OSA. A sleep laboratory physician read nocturnal oximetry trend and event graphs, blinded to clinical and polysomnographic results. Likelihood ratios were used to determine the change in probability of having OSA before and after oximetry results were known. RESULTS: Of 349 patients, 210 (60%) had OSA as defined polysomnographically. Oximetry trend graphs were classified as positive for OSA in 93 and negative or inconclusive in 256 patients. Of the 93 oximetry results read as positive, PSG confirmed OSA in 90 patients. A positive oximetry trend graph had a likelihood ratio of 19.4, increasing the probability of having OSA from 60% to 97%. The median MOAHI of children with a positive oximetry result was 16.4 (7.5, 30.2). The 3 false-positive oximetry results were all in the subgroup of 92 children who had diagnoses other than adenotonsillar hypertrophy that might have affected breathing during sleep. A negative or inconclusive oximetry result had a likelihood ratio of.58, decreasing the probability of having OSA from 60% to 47%. Interobserver reliability for oximetry readings was very good to excellent (kappa =.80). CONCLUSIONS: In the setting of a child suspected of having OSA, a positive nocturnal oximetry trend graph has at least a 97% positive predictive value. Oximetry could: 1) be the definitive diagnostic test for straightforward OSA attributable to adenotonsillar hypertrophy in children older than 12 months of age, or 2) quickly and inexpensively identify children with a history suggesting sleep-disordered breathing who would require PSG to elucidate the type and severity. A negative oximetry result cannot be used to rule out OSA.

Adenoids↗
PubMed1987

Methylene blue and indocyanine green artifactually lower pulse oximetry readings of oxygen saturation. Studies in dogs.

The effects of fluorescein, methylene blue, and indocyanine green on hemodynamic variables and on pulse oximetry and co-oximetry measurements of arterial hemoglobin oxygen saturation (SaO2) and oxyhemoglobin percentage (% HbO2) were evaluated in 16 anesthetized dogs in vitro by co-oximetry (% HbO2) and in vivo by pulse oximetry (SaO2). The light absorbance (optical density) in plasma (range 500 to 800 nm) was measured by a spectrophotometer. Fluorescein did not affect oximetry measurements, plasma light absorbance in the range measured, or hemodynamic variables. Methylene blue caused dose-dependent decreases in measurements made with both forms of oximetry for up to 30 minutes, the decrease being greater and longer lasting with pulse oximetry (P less than 0.05). Hemodynamic measurements in 5 dogs showed that methylene blue (1 to 5 mg/kg) increased arterial pressure transiently, after which cardiac output, stroke index, and left ventricular stroke work index decreased and left ventricular end-diastolic pressure and systemic and pulmonary vascular resistances increased (P less than 0.05 with 5 mg/kg). Methemoglobin concentration measured by co-oximetry increased significantly (to 19.9 +/- 1.4%, P less than 0.05) 1 minute after 5 mg/kg of methylene blue was injected. Methylene blue had a dose- and time-dependent effect on plasma light absorbance, and this effect peaked in the 660- to 670-nm range. The data do not distinguish the relative contributions of physiology (hemodynamic change), chemistry (methemoglobin production), and physics (optical properties) to the decrease in pulse oximetry and co-oximetry measurements that follows injection of methylene blue. Indocyanine green affected neither hemodynamic variables nor co-oximetry readings but decreased pulse oximetry readings for up to 10 minutes dose dependently.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

The pulse oximetry gap in carbon monoxide intoxication.

STUDY OBJECTIVE: Pulse oximetry has been reported to be falsely elevated in the presence of carbon monoxide (CO). However, the degree to which pulse oximetry overestimates measured oxyhemoglobin saturation (O2Hb) has not been investigated in patients with CO exposure. This study quantifies the effect of CO on pulse oximetry and O2Hb in a series of patients with elevated carboxyhemoglobin (COHb) levels. METHODS: A prospective case series of 25 pulse oximetry measurements, with concurrent arterial blood gas sampling, were obtained on 16 adults with CO exposure. RESULTS: COHb levels (mean, 16.1%; SD, 11.6%; range, 2.2% to 44%) did not significantly correlate with pulse oximetry saturation (mean, 97.7%; SD, 1.5%; range 96% to 100%) (r = .45; P = .1 [NS]). Compared with COHb, a pulse oximetry gap (mean, 17.5%; SD, 1.5%; range, 2.3% to 42%), defined as pulse oximetry saturation minus O2Hb, yielded a linear regression model: pulse oximetry gap = 1.82 + 0.94 x COHb (SEM = 0.07; F = 204; R2 = .90; P < .0001). CONCLUSION: Oxygen saturation as measured by pulse oximetry failed to decrease to less than 96% despite COHb levels as high as 44%. Regression between the pulse oximetry gap and COHb suggests that pulse oximetry overestimates O2Hb by the amount of COHb present. Pulse oximetry is unreliable in estimating O2Hb saturation in CO-exposed patients and should be interpreted with caution when used to estimate oxygen saturation in smokers.

Adult↗
PubMed1997

Pulse oximetry in the evaluation of peripheral vascular disease.

The role of pulse oximetry in the evaluation of peripheral vascular disease (PVD) was investigated. In addition, the value of elevating the limb to improve the sensitivity of detection of PVD by the pulse oximeter was also determined. Pulse oximetry reading in the toes were obtained in 40 young, healthy volunteers and in 40 randomly selected patients referred to the vascular investigation laboratory over a period of two months. All 40 healthy volunteers had normal pulse oximetry readings. Normal pulse oximetry reading in the toes was defined as > 95% O2 Sat and +/-2 of finger pulse oximetry reading. In all 40 patients, pulse oximetry readings were either normal or not detected at all. Since there was no gradation in decrease in the pulse oximetry reading with severity of disease or with elevation of the patient's lower extremity, an absent or no reading was considered as an abnormal result from the test. The frequency of abnormal pulse oximetry readings increased significantly in groups with abnormal ankle-brachial pressure index (ABPI) and also varied significantly with elevation of the patients' lower limbs. In patients with no PVD detected by Doppler (ABPI > 0.9), pulse oximetry readings were normal in all. However, in patients with moderate PVD (ABPI, 0.5-0.9), 84% of the patients' lower limbs had normal pulse oximetry readings and 16% had an abnormal reading at baseline level (flat). An additional 12% of the lower limbs in this group had an abnormal reading on elevation of the limb to 12 inches. In patients with severe PVD (ABPI < 0.5), 54% of the patients' lower limbs had an abnormal reading at baseline and an additional 23% had an abnormal reading at elevation of the limb to 12 inches. In conclusion, pulse oximetry was not a sensitive test for detecting early PVD.

Fingers↗
PubMed1999

Determination of hemoglobin saturation in patients with acute sickle chest syndrome: a comparison of arterial blood gases and pulse oximetry.

STUDY OBJECTIVES: To evaluate three different methods of measuring oxygen saturation in patients suffering from acute sickle chest syndrome. DESIGN: A prospective, descriptive study of 9 months' duration. SETTING: A tertiary care university hospital. PATIENTS: Adult patients with acute sickle chest syndrome scheduled to undergo RBC exchange transfusion. INTERVENTIONS: None. MEASUREMENTS: Baseline hemoglobin oxygen saturation was determined simultaneously by (1) calculation based on PaO2 and an oxyhemoglobin dissociation curve algorithm, (2) co-oximetry, and (3) pulse oximetry. These same measures were repeated after exchange transfusion. Baseline and postexchange hemoglobin electrophoresis was performed in all patients. RESULTS: Baseline calculated saturation overestimated true saturation (determined by co-oximetry) with a baseline mean bias (co-oximetry minus calculated saturation) of -6.78 +/- 2.63% (95% confidence interval for bias: -8.37% to -5.19%). Pulse oximetry was not different than co-oximetry at baseline with a baseline bias of +1.86 +/- 3.25% (95% confidence interval: -0.1% to 3.82%). After exchange transfusion, there was no bias between either co-oximetry and calculated saturation (mean difference: -0.17 +/- 1.31% [95% confidence interval: -0.95% to 0.61%]), or co-oximetry and pulse oximetry (mean difference: +0.3 +/- 1.53% [95% confidence interval: -0.62% to 1.22%]). CONCLUSIONS: Calculated saturation overestimates true saturation during acute sickle chest syndrome. This discrepancy abates after exchange transfusion. Pulse oximetry more closely follows co-oximetry than does calculated saturation during acute sickle chest syndrome.

Acute Disease↗
PubMed1999

Utility of home oximetry as a screening test for patients with moderate to severe symptoms of obstructive sleep apnea.

OBJECTIVE: To determine the value of home oximetry as a screening test in patients with moderate to severe symptoms of obstructive sleep apnea (OSA). DESIGN: Retrospective, observational study. SETTING: The Sleep Unit of a tertiary referral, university hospital. PATIENTS: 116 patients referred for evaluation of moderate to severe symptoms of OSA in which both home oximetry and polysomnography (PSG) were performed. INTERVENTIONS: NA. RESULTS: Three numerical oximetry indices were evaluated: average of desaturations > or =4% and average of resaturations > or =3% per hour of analysis time (DI4% and RI3%, respectively); and cumulative percentages of time spent at saturations below 90% (CT90%). A qualitative assessment was also performed. Oximetry indices were compared with apnea/hypopnea index (AHI) by simple linear regression and Bland-Altman analyses. Optimal cut-off points, in terms of sensitivity and specificity, for the oximetry indices were searched using ROC analysis, at an AHI threshold of > or =10. The correlation between AHI and the desaturation indices was r = 0.50 for CT90%, r = 0.60 for DI4%, and r = 0.58 for RI3%. No bias was found between PSG and oximetry indices in Bland-Altman plots. Neither the numerical indices nor the qualitative analysis achieved an adequate (>0.8) area under the ROC curve. A CT90% <0.79 excluded OSA with 84% sensitivity. A DI4% > or =31.4 or a RI3% > or =40.5 diagnosed OSA with 97% specificity. Using these values, 38% of the patients would have been correctly classified by oximetry alone, 10% would have been incorrectly classified, and 50% could not have been classified with certainty. Eleven (15%) OSA patients would have been missed by oximetry. CONCLUSIONS: Correlation between home oximetry and PSG was not high. Oximetry was more useful to confirm than to exclude OSA in our study. Qualitative assessment was not better than numerical analysis. The greatest value of oximetry in this setting seems to be as a tool to rapidly recognize and treat more severe OSA patients in waiting list for PSG.

Electroencephalography↗