Effect of body mass index on overnight oximetry for the diagnosis of sleep apnea

Overnight oximetry is widely used for screening for the sleep apnea hypopnea syndrome (SAHS). The degree of desaturation at an apnea event is known to be affected by the degree of obesity. We hypothesized that the diagnostic ability of oximetry for SAHS is affected by the degree of obesity. A total of 424 consecutive patients referred for possible SAHS were studied. The subjects were classified into three groups of normal-weight, overweight and obese based on the body mass index (BMI). The apnea-hypopnea index (> or = 15 h(-1)) by polysomnography was used as the diagnostic gold standard. Oximetry data were automatically analyzed to calculate the oxygen desaturation index (ODI2/3/4:at 2%/3%/4% threshold). The diagnostic abilities of the ODI were different in the three BMI-groups at a given cutoff value, e.g. the sensitivity/specificity of ODI4 (cutoff = 15) were 54%/100%, 83%/ 97%, and 98%/78% for the normal-weight, overweight and obese groups, respectively (P < 0.0001). The gender and the age had no significant effect on the ability. We demonstrated the diagnostic sensitivity and specificity of the ODI for SAHS depended on the BMI. Oximetry as a screening tool for SAHS may become more useful by selection of a cutoff value appropriate for the BMI of each subject.     

Home overnight pulse oximetry in patients with COPD: more than one recording may be needed

STUDY OBJECTIVES: Home overnight pulse oximetry (OPO) is used to assess nocturnal desaturation in patients with COPD, but the current practice of relying on one recording has not been studied. We assessed the variability of nocturnal desaturation in patients with COPD between nights, as measured by home OPO. DESIGN: Study subjects attended for clinical evaluation, spirometry, and arterial blood gas analysis. OPO was prospectively completed at home on 2 consecutive nights (study night 1 [N1] and study night 2 [N2]) and repeated at 3 weeks (study night 3 [N3]). SETTING: Respiratory Services, Green Lane Hospital, Auckland, New Zealand. PATIENTS: Twenty-six patients with clinically stable COPD (mean age, 69.3 years [SD, 6.9]; FEV(1), 28.6% predicted [SD, 10.6]; PO(2), 71.3 mm Hg [SD, 9.8]). Patients with asthma or clinical evidence of obstructive sleep apnea were excluded. MEASUREMENTS AND RESULTS: Mean nocturnal saturation (MNS) and time spent with saturation below 90% (TB90%) were calculated for N1, N2, and N3. Group mean recording length, MNS, and TB90% were similar for each night. Little variation in MNS was seen between nights (N1 and N2 mean difference, 1.31%; N2 and N3, 1.26%; N1 and N3, 1.25%). Larger variation was seen between nights for TB90% (N1 and N2 mean difference, 17.46%; N2 and N3, 9.95%; N1 and N3, 14.05%). No factors were identified that predicted increased variability of TB90%. Using the current definition of "significant nocturnal desaturation" (TB90% > or = 30% of the night), 9 of 26 patients (34.6%) changed category between "desaturator" and "nondesaturator" from N1 to N2. CONCLUSION: Nocturnal desaturation in patients with COPD exhibits considerable night-to-night variability when measured by home OPO. A single home OPO recording may be insufficient for accurate assessment of nocturnal desaturation.     

Evaluation of pulse oximetry in anemia from hemoglobin-H disease.

A patient with hemoglobin-H (Hb-H) disease developed an acute hemolytic crisis after treatment with trimethoprim and sulfamethoxazole. Despite her poor clinical condition and profound anemia (Hb, 2.7 g/dL), pulse oximetry continued to demonstrate a high O2 saturation percentage. Manipulation of Beer's law shows that anemia theoretically should not affect pulse oximetry values. The literature describes the effects of dyshemoglobinopathies such as carboxyhemoglobinemia and methemoglobinemia on O2 saturation percentage measured by pulse oximetry, but the effect of genetic hemoglobinopathies on pulse oximetry values is largely unreported. Because most hemoglobinopathies do not significantly change the protein-heme electronic interaction, the values of O2 saturation percentage determined through pulse oximetry should remain clinically valid. Hb-H is an exception to this generalization; as in patients with carboxyhemoglobinemia, pulse oximetry measurements showing high O2 saturation percentage do not correspond to high levels of oxygen available for delivery to tissues.     

Prediction of obstructive sleep apnea: comparative performance of three screening instruments on the apnea-hypopnea index and the oxygen desaturation index

Sleep and Breathing - To evaluate the performance of the NoSAS&nbsp;(neck, obesity, snoring, age, sex) score, the STOP-Bang&nbsp;(snoring, tiredness, observed apneas, blood pressure, body...     

Hemoglobinopathy case finding by pulse oximetry

Pulse oximetry is a widely used, noninvasive instrument for monitoring oxygen saturation. Its use, however, is limited in the setting of dyshemoglobinemias. We report a case of hemoglobin Rothschild in an Asian patient diagnosed as a result of routine pulse oximetry. This case reiterates the limitations of pulse oximetry in patients with dyshemoglobinemias, while introducing its use as a case-finding tool for such conditions.     

Prediction of aortic augmentation index using radial pulse transmission-wave analysis

OBJECTIVE: Current arterial transfer functions have low capability in predicting aortic augmentation index (AIx) from radial pulse contour (RPC), because of the difficulty in accurately identifying the merging point (inflection point) in the derived aortic pulse contour (APC). We hypothesize that the formation time between each characteristic wave in APC is about one-third of ejection duration (ED/3). We sought to assess the accuracy of ED/3 in identifying the merging point in APC as compared to the conventional differential method. In addition, we sought to derive the AIx from RPC based on an arterial transfer function and the ED/3 method. METHODS: APC and RPC sequences were measured digitally and simultaneously in 60 subjects (37 males; aged 60 +/- 10 years). An ensemble-averaged RPC-to-APC transfer function was determined from 30 randomly selected subjects and was used to derive APC sequences in the 30 additional subjects. The accuracy of AIx predicted from RPC was determined. RESULTS: In patients with a clearly identifiable merging point in APC, the ED/3 method identified the merging point of measured APC within 1.97 +/- 0.60 ms of that identified by the conventional differential method, with identical AIx. The AIx and merging point of derived APC using the ED/3 method were also within 0.22 +/- 1.01% and 1.81 +/- 1.64 ms, respectively, of those of the measured APC using the conventional differential method. The accuracy of the predicted AIx was independent of age, sex, body-mass index and presence of hypertension. CONCLUSION: In a quiet resting state, the ED/3 is an alternative method for identifying the merging point in APC. In conjunction with transfer-function technique, AIx can be derived accurately from RPC.     

Choice of oximeter affects apnea-hypopnea index

STUDY OBJECTIVES: Current Medicare guidelines include an apnea-hypopnea index (AHI) > or = 15 events per hour, in which all hypopneas must be associated with 4% desaturation, to qualify for reimbursement for therapy with continuous positive airway pressure (CPAP). The present data demonstrate the effect of pulse oximeter differences on AHI. DESIGN: Prospective study, blinded analysis. SETTING: Academic sleep disorder center. PATIENTS: One hundred thirteen consecutive patients (84 men and 29 women) undergoing diagnostic sleep studies and being evaluated for CPAP based on the Medicare indications for reimbursement. INTERVENTIONS: Patients had two of four commonly used oximeters with signal averaging times of 4 to 6 s placed on different digits of the same hand during nocturnal polysomnography. MEASUREMENTS AND RESULTS: Apneas and candidate hypopneas (amplitude reduction, > 30%) were scored from the nasal cannula airflow signal without reference to oximetry. Candidate hypopneas then were reclassified as hypopneas by each oximeter if they were associated with a 4% desaturation. Although the use of three oximeters resulted in a similar AHI (bias, < 1 event per hour), the fourth oximeter showed an overall increase in AHI of 3.7 events per hour. This caused 7 of 113 patients to have an AHI of > or = 15 events per hour (meeting the Medicare criteria for treatment) by one oximeter but not when a different oximeter was used. More importantly, when our analysis was limited to those patients whose number of candidate hypopneas made them susceptible to the threshold value of 15 events per hour, 7 of 35 patients who did not meet the Medicare AHI standard for treatment by one oximeter were reclassified when a different oximeter was used. CONCLUSION: In the present study, oximeter choice affected whether the AHI reached the critical cutoff of 15 events per hour, particularly in those with disease severity that was neither very mild nor very severe. As oximetry is not a technique that produces a generic result, there are significant limitations to basing the definition of hypopnea on a fixed percentage of desaturation in determining the eligibility for CPAP therapy.     

Accuracy and precision of buccal pulse oximetry

Objective

We sought to describe the accuracy and precision of buccal pulse oximetry (SbpO₂) compared with arterial oxygen saturation (SaO₂) and pulse oximetry (SpO₂) in healthy adults at normoxemia and under 3 induced hypoxemic conditions.

Methods

In this prospective, correlational study, SbpO₂, SaO₂, and SpO₂ values were recorded at normoxemia and at three hypoxemic conditions (SpO₂ = 90%, 80%, and 70%) for 53 healthy, nonsmoking adults who were without cardiac or pulmonary disease, baseline hypoxemia, peripheral edema, dyshemoglobinemia, and fever. Bland-Altman analyses were used to assess agreement and precision between SbpO₂ and SaO₂ measures and between SbpO₂ and SpO₂ measures. Data were adjusted to account for a lag time between buccal and finger sites.

Results

When comparing SbpO₂ and SaO₂ values, mean differences of -1.8%, .3%, 2.4%, and 2.6% were evident at the normoxemia, 90%, 80%, and 70% levels, respectively. When comparing SbpO₂ and SpO₂ values, the mean differences were -1.4%, .1%, 3.3%, and 4.7% at the normoxemia, 90%, 80%, and 70% levels, respectively. The SbpO₂ and SaO₂ values met a priori precision criteria (1.6%; 95% confidence limit, -4.9% to 1.3%) at normoxemia. The SbpO₂ and SpO₂ values met precision criteria at normoxemia (1.5%; 95% confidence limit, -4.4% to 1.5%) and 90% (1.9%; 95% confidence limit, -3.6% to 3.8%) conditions, but exceeded precision criteria at the other tested conditions. On average, SpO₂ lagged 21 seconds behind SbpO₂.

Conclusion

Buccal oximetry is an inaccurate and imprecise method of assessing SpO₂ when oxygen saturation is <90%. The divergence between SbpO₂ and both SaO₂ or SpO₂ values increased as hypoxemia worsened. The buccal method overestimated oxygen saturation in proportion to the degree of hypoxemia. Such overestimates may lead nurses to conclude falsely that a patient's arterial oxygen saturation is acceptable when further assessment or intervention is warranted.     

Use of pulse oximetry in critically ill adults

Pulse oximetry represents a major advance in noninvasive oxygenation monitoring in critically ill adults. Its technology has given practitioners a safe, accurate, and continuous method for assessing arterial oxygen saturation. A comprehensive understanding of the variables of oxygen transport and hypoxemia is essential to ensure correct data interpretation. The accuracy and clinical limitations of pulse oximeters and sensors are presented in this article. The clinical utility of pulse oximetry monitoring in critically ill adults is discussed, with consideration given to patient selection and specific procedures that incur hypoxemic risk. Issues of quality assurance and risk management that surround the use of pulse oximetry are addressed.     

Prehospital pulse oximetry: useful or misused?

STUDY OBJECTIVE: This study evaluated the ability of emergency medical technicians (EMT-As) and emergency medical technicians-paramedics (EMT-Ps) to use pulse oximetry measurements in determining patient oxygen requirements. DESIGN: Prospective case series. SETTING: Cleveland emergency medical services (EMS) system. TYPE OF PARTICIPANTS: Five hundred thirty-two consecutive patients transported to Cleveland area hospitals by the Cleveland EMS system; no exclusions. INTERVENTIONS: EMT-Ps and EMT-As predicted patients' supplemental oxygen requirements based on clinical assessment. Pulse oximetry was performed while patients were breathing room air (RA SpO2). Treatment intervention, including oxygen supplementation and medication given, oxygen saturation after intervention, and oxygen saturation on arrival at the hospital, was also recorded. Therapy guided by the patient's initial RA SpO2 was reviewed to determine the appropriateness of oxygen therapy. RESULTS: Data were analyzed using the chi 2 test and correlation analysis. Eleven percent (59) of patients transported by Cleveland EMS had an initial RA SpO2 of less than 91%. Advanced life support units increased oxygen supplementation on all desaturated patients, whereas basic life support units failed to make appropriate increases in FIO2 in 20% (two) of desaturated patients (P less than .0001). Sixty percent (164) of patients transported by EMT-Ps and 62% (162) of patients transported by EMT-As had an initial RA SpO2 of 97% or greater. EMT-Ps gave supplemental oxygen therapy to all but 7% (11) of these already well-saturated patients, and EMT-As gave supplemental oxygen to all but 6% (nine) of these patients. EMT-Ps administered a higher FIO2 than they had predicted clinically necessary to 2% (four) of patients with an initial RA SpO2 of 97% of greater, whereas EMT-As gave a higher FIO2 than initially predicted to 16% (25) of such patients (P less than .0001). CONCLUSION: EMT-Ps were more likely to appropriately base oxygen therapy on oximetry measurements than were EMT-As. Both groups failed to decrease supplemental oxygen in patients with high explicit protocols for EMS systems contemplating the use of oximetry to guide oxygen therapy. Our results further suggest that pulse oximetry could be used to avoid unnecessary oxygen therapy on a significant number of patients transported by EMS systems because they are already well saturated on room air.     

Supplemental oxygen impairs detection of hypoventilation by pulse oximetry

STUDY OBJECTIVE: This two-part study was designed to determine the effect of supplemental oxygen on the detection of hypoventilation, evidenced by a decline in oxygen saturation (Spo(2)) with pulse oximetry. DESIGN: Phase 1 was a prospective, patient-controlled, clinical trial. Phase 2 was a prospective, randomized, clinical trial. SETTING: Phase 1 took place in the operating room. Phase 2 took place in the postanesthesia care unit (PACU). PATIENTS: In phase 1, 45 patients underwent abdominal, gynecologic, urologic, and lower-extremity vascular operations. In phase 2, 288 patients were recovering from anesthesia. INTERVENTIONS: In phase 1, modeling of deliberate hypoventilation entailed decreasing by 50% the minute ventilation of patients receiving general anesthesia. Patients breathing a fraction of inspired oxygen (Fio(2)) of 0.21 (n = 25) underwent hypoventilation for up to 5 min. Patients with an Fio(2) of 0.25 (n = 10) or 0.30 (n = 10) underwent hypoventilation for 10 min. In phase 2, spontaneously breathing patients were randomized to breathe room air (n = 155) or to receive supplemental oxygen (n = 133) on arrival in the PACU. MEASUREMENTS AND RESULTS: In phase 1, end-tidal carbon dioxide and Spo(2) were measured during deliberate hypoventilation. A decrease in Spo(2) occurred only in patients who breathed room air. No decline occurred in patients with Fio(2) levels of 0.25 and 0.30. In phase 2, Spo(2) was recorded every min for up to 40 min in the PACU. Arterial desaturation (Spo(2) < 90%) was fourfold higher in patients who breathed room air than in patients who breathed supplemental oxygen (9.0% vs 2.3%, p = 0.02). CONCLUSION: Hypoventilation can be detected reliably by pulse oximetry only when patients breathe room air. In patients with spontaneous ventilation, supplemental oxygen often masked the ability to detect abnormalities in respiratory function in the PACU. Without the need for capnography and arterial blood gas analysis, pulse oximetry is a useful tool to assess ventilatory abnormalities, but only in the absence of supplemental inspired oxygen.     

A clinical evaluation of pulse oximetry during thoracic surgery

To evaluate the utility of pulse oximetry for monitoring oxygenation during thoracic surgery, pulse oximeter oxygen saturation (SpO₂) values from the Nellcor N-100 (Nellcor Inc, Haywood, CA) and Novametrix model 500 (Medical Systems Inc, Wallingford, CT) were compared with simultaneous arterial saturation values (SaO₂) in 20 patients. A total of 255 matched observations were recorded, and the data were divided for statistical analysis into preinduction of anesthesia and postinduction groups. The preinduction group showed a good correlation between SpO₂ and (SaO₂) values, with both pulse oximeters consistently overestimating the Sao, However, once anesthesia was induced, there was no longer any correlation for either of the pulse oximeters versus simultaneous (SaO₂) values, although on average, the SpO₂ values were significantly higher than the corresponding SaO₂ values. It was concluded that pulse oximetry is useful in following trends of oxygenation in patients with preexisting lung pathology undergoing thoracic surgery, but it cannot replace arterial blood gas sampling for the intraoperative management of respiratory function.     

An evaluation of pulse oximetry in prehospital care.

STUDY OBJECTIVES: We performed this study to evaluate the accuracy of pulse oximetry oxygen saturation (SpO2) against direct measurements of arterial oxygen saturation (SaO2) in the field. DESIGN: Prospective, cross-sectional, paired measurements of SpO2 against SaO2. SETTING: This evaluation was done in the prehospital setting. INTERVENTIONS: A pulse oximeter with digital probe was used to measure SpO2 in 30 patients. Arterial blood gases were drawn in the field while the pulse oximeter was in use, and oxygen saturation (HbO2) was measured by CO-oximetry. MAIN RESULTS: There was no significant difference between SpO2 (94.6 +/- 5.4%) and HbO2 (94.9 +/- 5.1%) (P = .495, beta less than .2). There was a strong correlation between SpO2 and HbO2 (r = .898). The bias between SpO2 and HbO2 was -0.3, with a precision of 2.4. When SpO2 was 88% or more, HbO2 was 90% or more in every case. Mean carboxyhemoglobin was 1.3 +/- 0.9%, and mean methemoglobin was 0.9 +/- 0.3%. There was no significant difference between the pulse oximeter heart rate and the ECG heart rate (P = .223, beta less than .2). CONCLUSION: We conclude that pulse oximetry is sufficiently accurate to be useful in the field when SpO2 is more than 88%. It is potentially useful in patients with clinical signs of acute hypoxemia and in patients receiving interventions that may produce acute hypoxemia. Further work is needed to evaluate the accuracy of pulse oximetry in the settings of elevated carboxyhemoglobin, methemoglobin, and very low saturations.     

Reliability of pulse oximetry during exercise in pulmonary patients

To evaluate the reliability of pulse oximetry during exercise, we studied 101 patients primarily with chronic pulmonary diseases. Three devices were used on different patients. Radial arterial blood was sampled at rest and maximal exercise simultaneously to pulse oximetric determination. Measured blood oxygen saturation was significantly different from noninvasive saturation at rest and also at exercise for each device. Nevertheless, changes in pulse oximetry from rest to exercise were significantly correlated with measured saturation for all three devices. Direction of changes in saturation from rest to exercise was correctly evaluated by transcutaneous oximetry in all but six instances where changes were less than 4 percent. Although measured and transcutaneous saturations are significantly different, we conclude that pulse oximetry reliably estimates changes in arterial saturation between rest and exercise for a clinical purpose. None of the three tested devices was better compared with the others in estimating saturation changes at exercise.