Meta-analysis of arterial oxygen saturation monitoring by pulse oximetry in adults

Validation of Polar Elixir™ Pulse Oximeter against Arterial Blood Gases during Stepwise Steady-State Inspired Hypoxia

PURPOSE

The purpose of this study was to evaluate the accuracy of peripheral oxygen saturation (SpO 2 ) measurements from Polar Elixir™ pulse oximetry technology compared with arterial oxygen saturation (SaO 2 ) measurements during acute stepwise steady-state inspired hypoxia at rest. A post hoc objective was to determine if SpO 2 measurements could be improved by recalibrating the Polar Elixir™ algorithm with SaO 2 values from a random subset of participants.

METHODS

The International Organization for Standardization (ISO) protocol (ISO 80601-2-61:2017) for evaluating the SpO 2 accuracy of pulse oximeter equipment was followed whereby five plateaus of SaO 2 between 70% and 100% were achieved using stepwise reductions in inspired O 2 during supine rest. Blood samples drawn through a radial arterial catheter from 25 participants were first used to compare SaO 2 with SpO 2 measurements from Polar Elixir™. Then the Polar Elixir™ algorithm was recalibrated using SaO 2 data from 13 random participants, and SpO 2 estimates were recalculated for the other 12 participants. For SaO 2 values between 70% and 100%, root mean square error, intraclass correlation coefficients (ICC), Pearson correlations, and Bland-Altman plots were used to assess the accuracy, agreement, and strength of relationship between SaO 2 values and SpO 2 values from Polar Elixir™.

RESULTS

The initial root mean square error for Polar Elixir™ was 4.13%. After recalibrating the algorithm, the RMSE was improved to 2.67%. The ICC revealed excellent levels of agreement between SaO 2 and Polar Elixir™ SpO 2 values both before (ICC(1,3) = 0.837, df = 574, P < 0.001) and after (ICC(1,3) = 0.942, df = 287, P < 0.001) recalibration.

CONCLUSIONS

Relative to ISO standards, Polar Elixir™ yielded accurate SpO 2 measurements during stepwise inspired hypoxia at rest when compared with SaO 2 values, which were improved by recalibrating the algorithm using a subset of the SaO 2 data.

Chinese Society of Cardiology guidelines on the diagnosis and treatment of adult fulminant myocarditis

Fulminant myocarditis is an acute diffuse inflammatory disease of myocardium. It is characterized by acute onset, rapid progress and high risk of death. Its pathogenesis involves excessive immune activation of the innate immune system and formation of inflammatory storm. According to China's practical experience, the adoption of the "life support-based comprehensive treatment regimen" (with mechanical circulation support and immunomodulation therapy as the core) can significantly improve the survival rate and long-term prognosis. Special emphasis is placed on very early identification,very early diagnosis,very early prediction and very early treatment.

Characteristics of pulse oximetry and arterial blood gas in patients with fibrotic interstitial lung disease

BACKGROUND

Fibrotic interstitial lung disease (ILD) is frequently associated with abnormal oxygenation; however, little is known about the accuracy of oxygen saturation by pulse oximetry (SpO2) compared with arterial blood gas (ABG) saturation (SaO2), the factors that influence the partial pressure of carbon dioxide (PaCO2) and the impact of PaCO2 on outcomes in patients with fibrotic ILD.

STUDY DESIGN AND METHODS

Patients with fibrotic ILD enrolled in a large prospective registry with a room air ABG were included. Prespecified analyses included testing the correlation between SaO2 and SpO2, the difference between SaO2 and SpO2, the association of baseline characteristics with both the difference between SaO2 and SpO2 and the PaCO2, the association of baseline characteristics with acid-base category, and the association of PaCO2 and acid-base category with time to death or transplant.

RESULTS

A total of 532 patients with fibrotic ILD were included. Mean resting SaO2 was 92±4% and SpO2 was 95±3%. Mean PaCO2 was 38±6 mmHg, with 135 patients having PaCO2 <35 mmHg and 62 having PaCO2 >45 mmHg. Correlation between SaO2 and SpO2 was mild to moderate (r=0.39), with SpO2 on average 3.0% higher than SaO2. No baseline characteristics were associated with the difference in SaO2 and SpO2. Variables associated with either elevated or abnormal (elevated or low) PaCO2 included higher smoking pack-years and lower baseline forced vital capacity (FVC). Lower baseline lung function was associated with an increased risk of chronic respiratory acidosis. PaCO2 and acid-base status were not associated with time to death or transplant.

INTERPRETATION

SaO2 and SpO2 are weakly-to-moderately correlated in fibrotic ILD, with limited ability to accurately predict this difference. Abnormal PaCO2 was associated with baseline FVC but was not associated with outcomes.

Excessive Oxygen Administration in High-Risk Patients Admitted to Medical and Surgical Wards Monitored by Wireless Pulse Oximeter

The monitoring of oxygen therapy when patients are admitted to medical and surgical wards could be important because exposure to excessive oxygen administration (EOA) may have fatal consequences. We aimed to investigate the association between EOA, monitored by wireless pulse oximeter, and nonfatal serious adverse events (SAEs) and mortality within 30 days. We included patients in the Capital Region of Copenhagen between 2017 and 2018. Patients were hospitalized due to acute exacerbation of chronic obstructive pulmonary disease (AECOPD) or after major elective abdominal cancer surgery, and all were treated with oxygen supply. Patients were divided into groups by their exposure to EOA: no exposure, exposure for 1-59 min or exposure over 60 min. The primary outcome was SAEs or mortality within 30 days. We retrieved data from 567 patients for a total of 43,833 h, of whom, 63% were not exposed to EOA, 26% had EOA for 1-59 min and 11% had EOA for ≥60 min. Nonfatal SAEs or mortality within 30 days developed in 24%, 12% and 22%, respectively, and the adjusted odds ratio for this was 0.98 (95% CI, 0.96-1.01) for every 10 min. increase in EOA, without any subgroup effects. In conclusion, we did not observe higher frequencies of nonfatal SAEs or mortality within 30 days in patients exposed to excessive oxygen administration.

Results of phase 2 randomized multi-center study to evaluate the safety and efficacy of infusion of memory T cells as adoptive therapy in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia and/or lymphopenia (RELEASE NCT04578210)

BACKGROUND AIMS

There are currently no effective anti-viral treatments for coronavirus disease 2019 (COVID-19)-hospitalized patients with hypoxemia. Lymphopenia is a biomarker of disease severity usually present in patients who are hospitalized. Approaches to increasing lymphocytes exerting an anti-viral effect must be considered to treat these patients. Following our phase 1 study, we performed a phase 2 randomized multicenter clinical trial in which we evaluated the efficacy of the infusion of allogeneic off-the-shelf CD45RA- memory T cells containing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells from convalescent donors plus the standard of care (SoC) versus just the SoC treatment.

METHODS

Eighty-four patients were enrolled in three Spanish centers. The patients were randomized into the infusion of 1 × 106/kg CD45RA- memory T cells or the SoC. We selected four unvaccinated donors based on the expression of interferon gamma SARS-CoV-2-specific response within the CD45RA- memory T cells and the most frequent human leukocyte antigen typing in the Spanish population.

RESULTS

We analyzed data from 81 patients. The primary outcome for recovery, defined as the proportion of participants in each group with normalization of fever, oxygen saturation sustained for at least 24 hours and lymphopenia recovery through day 14 or at discharge, was met for the experimental arm. We also observed faster lymphocyte recovery in the experimental group. We did not observe any treatment-related adverse events.

CONCLUSIONS

Adoptive cell therapy with off-the-shelf CD45RA- memory T cells containing SAR-CoV-2-specific T cells is safe, effective and accelerates lymphocyte recovery of patients with COVID-19 pneumonia and/or lymphopenia.

TRIAL REGISTRATION

NCT04578210.

Accuracy of Pulse Oximetry for Long-Term Oxygen Therapy Assessment in Chronic Obstructive Pulmonary Disease

Rationale: Landmark studies of long-term oxygen therapy (LTOT) in patients with chronic obstructive pulmonary disease (COPD) used arterial oxygen pressure (PaO2) to define severe hypoxemia; however, oxygen saturation as measured by pulse oximetry (SpO2) is commonly used instead. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines recommend evaluation with arterial blood gas (ABG) analysis if SpO2 is ⩽92%. This recommendation has not been evaluated in stable outpatients with COPD undergoing testing for LTOT. Objectives: To evaluate the performance of SpO2 compared with ABG analysis of PaO2 and arterial oxygen saturation (SaO2) to detect severe resting hypoxemia in patients with COPD. Methods: Retrospective analysis of paired SpO2 and ABG values from stable outpatients with COPD who underwent LTOT assessment in a single center. We calculated false negatives (FNs) as an SpO2 >88% or >89% in the presence of pulmonary hypertension with a PaO2 ⩽55 mm Hg or ⩽59 mm Hg in the presence of pulmonary hypertension. Test performance was assessed using receiver operating characteristic (ROC) analysis, intraclass correlation coefficient (ICC), test bias, precision, and accuracy root-mean-square (Arms). An adjusted multivariate analysis was used to evaluate factors affecting SpO2 bias. Results: Of 518 patients, the prevalence of severe resting hypoxemia was 74 (14.3%), with 52 missed by SpO2 (FN, 10%), including 13 (2.5%) with an SpO2 > 92% (occult hypoxemia). FNs and occult hypoxemia in Black patients were 9% and 1.5%, respectively, and were 13% and 5%, respectively, among active smokers. The correlation between SpO2 and SaO2 was acceptable (ICC = 0.78; 95% confidence interval, 0.74-0.81); and the bias of SpO2 was 0.45%, with a precision of 2.6 (-4.65 to +5.55%) and Arms of 2.59. These measurements were similar in Black patients, but in active smokers, correlation was lower and bias showed greater overestimation of SpO2. ROC analysis suggests that the optimal SpO2 cutoff to warrant LTOT evaluation by ABG analysis is ⩽94%. Conclusions: SpO2 as the only measure of oxygenation carries a high FN rate in detecting severe resting hypoxemia in patients with COPD undergoing evaluation for LTOT. Reflex measurement of PaO2 by ABG analysis should be used as recommended by GOLD, ideally at a cutoff higher than an SpO2 ⩽92%, especially in active smokers.

Comparative Analysis of Oxygen Saturation by Pulse Oximetry and Arterial Blood Gas in Hypoxemic Patients in a Tertiary Care Hospital

INTRODUCTION

 Oxygen saturation is essential for medical care and is closely regulated within the body. Arterial blood gas (ABG) analysis is used to evaluate critically ill individuals' ventilation, oxygenation, acid-base status, and metabolic condition. Pulse oximetry is an easy and non-invasive way to measure the status of oxygen saturation non-invasively in clinical settings and provides a quick and precise assessment of oxygenation and reduces medical errors. SpO2 may not always be a reliable predictor of arterial oxygen saturation (SaO2), and hypoxemic, hemodynamically compromised, and critically ill patients may have lower SpO2 accuracy. A study is needed to assess and compare various oxygen saturation methods.

AIMS AND OBJECTIVES

 The study aimed to compare the oxygen saturation levels measured by pulse oximetry and ABG analysis in hypoxemic patients. The objectives were to compare the values between SaO2, PaO2, and SpO2 values obtained from the patients, and correlate the study parameters among both techniques.

MATERIALS AND METHODS

The study was conducted from February 2021 to June 2022 among the 102 hypoxemic patients who were admitted to the emergency and surgical intensive care unit (ICU) of Sree Balaji Medical College and Hospital in Chennai. Primary data on ABG analysis and pulse oximetry readings were collected from the study subjects. The patient and their past medical records, physical exam, chest x-ray findings, pulse oximetry, and ABG results were all reviewed. Each patient had their ABG, and pulse oximetry measured simultaneously. A comparison was made between SpO2 and partial pressure of oxygen (PaO2) and arterial oxygen saturation (SaO2) parameters using a paired t-test. The correlation was done against the SpO2 and ABG parameters and assessed for association using the correlation coefficient value; gender was also considered while correlating.

RESULTS AND DISCUSSION

An observational study was done among 102 study samples to comparatively analyze the oxygen saturation by two methods, namely pulse oximetry and ABG, in hypoxemic patients. While comparing the mean values of SaO2 and SpO2, they were 84.41 ± 4.24 and 80.58 ± 5.77, respectively, and this difference was statistically very significant (p < 0.001). While comparing the mean values of PaO2 and SaO2, they were 61.02 ± 5.01 and 84.41 ± 4.24, respectively, and this difference was statistically significant (p = 0.043). While comparing the mean values of PaO2 and SpO2, they were 61.02 ± 5.01 and 80.58 ± 5.77, respectively, and this difference was statistically significant (p = 0.054). Among the study population, with regard to the correlation factor, there is notably a very high and strong positive correlation between SaO2 and SpO2 and between SpO2 and PaO2. There was a negative correlation between SpO2 and finger abnormalities and between SpO2 and blood pressure.

CONCLUSION

 The ABG method is considered the gold standard. When SpO2 levels fall below 90%, pulse oximetry may not be accurate enough to reliably assess oxygenation. In such cases, where alveolar hypoventilation is suspected, it is recommended to complement pulse oximetry with ABG studies. This is because ABG analysis provides a more comprehensive assessment of oxygenation and acid-base status, which can aid in the diagnosis and management of respiratory conditions.

Non-contact oxygen saturation monitoring for wound healing process using dual-wavelength simultaneous acquisition imaging system

Here we report the fabrication of a noncontact pulse oximeter system based on a dual-wavelength imaging system and its oxygen saturation monitoring performance during wound healing. The dual-wavelength imaging system consists of 660 nm and 940 nm light-emitting diodes and a multi-spectral camera that simultaneously accepts visible and near-infrared images. Using the proposed system, images were acquired at 30 fps at both wavelengths, and photoplethysmography signals were extracted by specifying a specific region in the images. We removed the signals caused by small movements and smoothed them using the discrete wavelet transform and moving average filter. To confirm the feasibility of the proposed noncontact oxygen saturation system, a wound model was created using a hairless mouse and oxygen saturation was measured during wound healing. The measured values were compared and analyzed using a reflective animal pulse oximeter. Through a comparative analysis of these two devices, the error of the proposed system was evaluated and the possibility of its clinical application and wound healing monitoring through oxygen saturation measurement confirmed.

Correctly Establishing and Interpreting Oxygenation Status in Sickle Cell Disease

BACKGROUND

As hypoxemia and hypoxia are central elements of disease pathophysiology and disease-related morbidity and mortality in individuals affected by sickle cell disease (SCD), clinical management aims to optimize oxygenation.

CONTENT

Hypoxemia is primarily screened for with pulse oximetry. However, in SCD pulse oximetry can inaccurately reflect arterial saturation, posing the risk of undetected (occult) hypoxemia. Solely relying on pulse oximetry might therefore lead to misdiagnosis or mismanagement, with devastating effects on tissue oxygenation. The interpretation of oxygenation status is multifaceted, and "oxygen saturation" is often used as an umbrella term to refer to distinctly different measured quantities-estimated oxygen saturation (O2Sat), hemoglobin oxygen saturation (SO2) by either pulse oximetry or co-oximetry, and fractional oxyhemoglobin (FO2Hb). While in many clinical situations this ambiguous use is of little consequence, O2Sat, SO2, and FO2Hb cannot be used interchangeably in the setting of SCD, as dyshemoglobins, anemia, cardiopulmonary comorbidities, concomitant medications, and frequent transfusions need to be accounted for. This article describes the parameters that determine blood and tissue oxygen concentration, discusses laboratory method performance characteristics and the correct interpretation of currently available clinical laboratory testing, and reviews the literature on noninvasive vs invasive oxygenation measurements in SCD.

SUMMARY

By correctly establishing and interpreting oxygenation parameters, clinical and laboratory teams can ensure high-quality, equitable healthcare, counteracting systemic exacerbations of health disparities frequently experienced by individuals with SCD.

Design and Application of a Flexible Blood Oxygen Sensing Array for Wearable Devices

The performance of portable or wearable oximeters is affected by improper movement or wear, which causes an error in the blood oxygen concentration calculation. The error comes from external incident stray light or light leakage caused by the improper fit of the sensor to the skin. This study aimed to develop a flexible blood oxygen sensing system with a 3 × 3 array that uses a reflective-type blood oxygen sensing chip to sequentially measure the blood oxygen levels at nine locations through a time division pulse modulation method. Each sensing chip has light transmission and receiving parts. A flip chip package was used to integrate the sensing chip, and a flexible parylene substrate that could fit the curvature of the wrist and locate the array of photo diodes around the radial artery of the wrist was used. By scanning the sensor array in dynamic behavior, the correct light intensity can be extracted to obtain the blood oxygen concentration and prevent errors due to improper fit or sensor movement during exercise.

Correlation of SpO2/FiO2 and PaO2/FiO2 in patients with symptomatic COVID-19: An observational, retrospective study

Some patients affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) experience acute hypoxemic respiratory failure progressing toward atypical acute respiratory distress syndrome (ARDS). The aim of the study is to evaluate whether a correlation between ratio of peripheral saturation of oxygen (SpO₂) and fraction of inspired oxygen (S/F) and ratio of arterial partial pressure of oxygen and fraction of inspired oxygen (P/F) exists in COVID-19-related ARDS as already known in classical ARDS. In this multicenter, retrospective, observational study, consecutive, adult (≥ 18 years) patients with symptomatic coronavirus disease 2019 (COVID-19) admitted to different COVID-19 divisions in Italy between March and December 2020 were included. Patients with SpO₂ > 97% or missing information were excluded. We included 1,028 patients (median age 72 years, prevalence of males [62.2%]). A positive correlation was found between P/F and S/F (r = 0.938, p < 0.0001). A receiver operating characteristic (ROC) curve analysis showed that S/F accurately recognizes the presence of ARDS (P/F ≤ 300 mmHg) in COVID-19 patients, with a cut-off of ≤ 433% showing good sensitivity and specificity. S/F was also tested against P/F values ≤ 200 and ≤ 100 mmHg (suggestive for moderate and severe ARDS, respectively), the latter showing great accuracy for S/F ≤ 178%. S/F was accurate in predicting ARDS for SpO₂ ≥ 92%. In conclusion, our findings support the routine use of S/F as a reliable surrogate of P/F in patients with COVID-19-related ARDS.

The accuracy of pulse oximetry in measuring oxygen saturation by levels of skin pigmentation: a systematic review and meta-analysis

BACKGROUND

During the COVID-19 pandemic, there have been concerns regarding potential bias in pulse oximetry measurements for people with high levels of skin pigmentation. We systematically reviewed the effects of skin pigmentation on the accuracy of oxygen saturation measurement by pulse oximetry (SpO2) compared with the gold standard SaO2 measured by CO-oximetry.

METHODS

We searched Ovid MEDLINE, Ovid Embase, EBSCO CINAHL, ClinicalTrials.gov, and WHO International Clinical Trials Registry Platform (up to December 2021) for studies with SpO2-SaO2 comparisons and measuring the impact of skin pigmentation or ethnicity on pulse oximetry accuracy. We performed meta-analyses for mean bias (the primary outcome in this review) and its standard deviations (SDs) across studies included for each subgroup of skin pigmentation and ethnicity and used these pooled mean biases and SDs to calculate accuracy root-mean-square (Arms) and 95% limits of agreement. The review was registered with the Open Science Framework ( https://osf.io/gm7ty ).

RESULTS

We included 32 studies (6505 participants): 15 measured skin pigmentation and 22 referred to ethnicity. Compared with standard SaO2 measurement, pulse oximetry probably overestimates oxygen saturation in people with the high level of skin pigmentation (pooled mean bias 1.11%; 95% confidence interval 0.29 to 1.93%) and people described as Black/African American (1.52%; 0.95 to 2.09%) (moderate- and low-certainty evidence). The bias of pulse oximetry measurements for people with other levels of skin pigmentation or those from other ethnic groups is either more uncertain or suggests no overestimation. Whilst the extent of mean bias is small or negligible for all subgroups evaluated, the associated imprecision is unacceptably large (pooled SDs > 1%). When the extent of measurement bias and precision is considered jointly, pulse oximetry measurements for all the subgroups appear acceptably accurate (with Arms < 4%).

CONCLUSIONS

Pulse oximetry may overestimate oxygen saturation in people with high levels of skin pigmentation and people whose ethnicity is reported as Black/African American, compared with SaO2. The extent of overestimation may be small in hospital settings but unknown in community settings. REVIEW PROTOCOL REGISTRATION: https://osf.io/gm7ty.

Fraction of Expired Oxygen as a Measure of Preoxygenation Prior to Rapid Sequence Intubation in the Pediatric Emergency Department

BACKGROUND

Pulse oximetry (SpO₂) is a flawed measure of adequacy of preoxygenation prior to intubation. The fraction of expired oxygen (FeO₂) is a promising but understudied alternative.

OBJECTIVE

To investigate FeO₂ as a measure of preoxygenation prior to intubation in a pediatric emergency department.

METHODS

We conducted a prospective, observational study of patients 18 and younger. We collected data using video review, and FeO₂ was measured via inline sampling. The main outcomes were FeO₂ and SpO₂ at the start of preoxygenation, end of preoxygenation/start of intubation attempt, and the end of intubation attempt. We compared FeO₂ and SpO₂ at the end of preoxygenation for patients with and without oxyhemoglobin desaturation.

RESULTS

We enrolled 85 of 88 eligible patients during the 14-month study period. FeO₂ data were available at the start of preoxygenation for 53 of 85 patients (62%), and for the end of preoxygenation for 59 of 85 patients (69%). Median FeO₂ at the start and end of preoxygenation was 90% (interquartile range [IQR] 88, 92) and 90% (IQR 88, 92). Median SpO₂ at the start and end of preoxygenation was 100% (IQR 100, 100). There were 11 episodes of desaturation, with median FeO₂ at the start of intubation attempt of 89.5 (IQR 54.5, 91.5) and median SpO₂ of 100 (IQR 99, 100). Patients who did not have a desaturation event had a median FeO₂ of 90.0 (IQR 88.0, 92.0).

CONCLUSIONS

Measuring FeO₂ during rapid sequence intubation is challenging with feasibility limitations, but may be a more discriminatory metric of adequate preoxygenation.

Pulse Oximeter Performance during Rapid Desaturation

The reliability of pulse oximetry is crucial, especially in cases of rapid changes in body oxygenation. In order to evaluate the performance of pulse oximeters during rapidly developing short periods of concurrent hypoxemia and hypercapnia, 13 healthy volunteers underwent 3 breathing phases during outdoor experiments (39 phases in total), monitored simultaneously by five different pulse oximeters. A significant incongruity in values displayed by the tested pulse oximeters was observed, even when the accuracy declared by the manufacturers were considered. In 28.2% of breathing phases, the five used devices did not show any congruent values. The longest uninterrupted congruent period formed 74.4% of total recorded time. Moreover, the congruent periods were rarely observed during the critical desaturation phase of the experiment. The time difference between the moments when the first and the last pulse oximeter showed the typical study endpoint values of SpO₂ 85% and 75% was 32.1 ± 23.6 s and 24.7 ± 19.3 s, respectively. These results suggest that SpO₂ might not be a reliable parameter as a study endpoint, or more importantly as a safety limit in outdoor experiments. In the design of future studies, more parameters and continuous clinical assessment should be included.

Acute oxygen desaturation characterizes pulmonary aspiration in patients with gastroesophageal reflux disease and laryngopharyngeal reflux

The aim of this study was to characterise pulmonary aspiration of refluxate in patients with gastroesophageal reflux disease (GORD) and laryngopharyngeal reflux (LPR) by continuous pulse oximetry (SpO2) during the supine phase of a scintigraphic reflux study. Variables assessed for significance included age, hiatus hernia, frequency, amplitude of reflux and clearance of reflux from the oesophagus/pharynx. The patients included in this study had established GORD and LPR by clinical history. All patients underwent fused three- dimensional scintigraphic/ X-ray computed tomography (CT) and simultaneous continuous pulse oximetry when supine for 30 minutes. A total of 265 patients (40.4% M, 59.6% F) were studied. Mean age of aspirators was 57.0 years and non-aspirators was 53.5 years. Seven patients had baseline oxygen saturation <95%, with 6/7 showing aspiration by scintigraphy. The remainder had mean baseline saturation of 97.7%. Continuous SpO2 monitoring showed a significant fall in pulmonary aspirators after 20 min of supine acquisition with significant variability. Analysis revealed a cyclic event every 1.5 min in aspirators only. Panel regression analysis showed a significant effect of age, hiatus hernia, pulse rate and reflux frequency on the fall in SpO2. Pulmonary aspiration in patients with LPR and GORD is characterised by acute oxygen desaturation. Variables affecting oxygen desaturation were age, hiatus hernia, pulse rate and reflux frequency. A cyclic event was observed every 1.5 min in aspirators and may be due to reflex homeostatic mechanism attempting to correct perceived hypoxia.

Clinical guide to perioperative management for videothoracoscopy lung resection (Section of Cardiac, Vascular and Thoracic Anesthesia, SEDAR; Spanish Society of Thoracic Surgery, SECT; Spanish Society of Physiotherapy)

The introduction of video-assisted thoracoscopic (VATS) techniques has led to a new approach in thoracic surgery. VATS is performed by inserting a thoracoscope through a small incisions in the chest wall, thus maximizing the preservation of muscle and tissue. Because of its low rate of morbidity and mortality, VATS is currently the technique of choice in most thoracic procedures. Lung resection by VATS reduces prolonged air leaks, arrhythmia, pneumonia, postoperative pain and inflammatory markers. This reduction in postoperative complications shortens hospital length of stay, and is particularly beneficial in high-risk patients with low tolerance to thoracotomy. Compared with conventional thoracotomy, the oncological results of VATS surgery are similar or even superior to those of open surgery. This aim of this multidisciplinary position statement produced by the thoracic surgery working group of the Spanish Society of Anesthesiology and Reanimation (SEDAR), the Spanish Society of Thoracic Surgery (SECT), and the Spanish Association of Physiotherapy (AEF) is to standardize and disseminate a series of perioperative anaesthesia management guidelines for patients undergoing VATS lung resection surgery. Each recommendation is based on an in-depth review of the available literature by the authors. In this document, the care of patients undergoing VATS surgery is organized in sections, starting with the surgical approach, and followed by the three pillars of anaesthesia management: preoperative, intraoperative, and postoperative anaesthesia.

Accuracy of pulse oximeters in measuring oxygen saturation in patients with poor peripheral perfusion: a systematic review

One of the most significant limitations of oximeters is their performance under poor perfusion conditions. This systematic review examines pulse oximeter model accuracy in adults under poor perfusion conditions. A multiple database search was conducted from inception to December 2020. The inclusion criteria were as follows: (1) adult participants (> 18 years) with explicitly stated conditions that cause poor peripheral perfusion (conditions localized at the oximeter placement site; or systemic conditions, including critical conditions such as hypothermia, hypotension, hypovolemia, and vasoconstricting agents use; or experimental conditions) (2) a comparison of arterial oxygen saturation and arterial blood gas values. A total of 22 studies were included and assessed for reliability and agreement using a modified Guidelines for Reporting Reliability and Agreement Studies tool. We calculated the accuracy root mean square error from bias and precision we extracted from the studies. Most oximeters (75%) were deemed accurate in patients with poor perfusion. Modern oximeters utilizing more complex algorithms were more likely to be accurate than older models. Earlobe placement of oximeters seemed more sensitive, with greater measurement accuracy, than on fingertip placement. Only one study controlled for skin pigmentation, and none strictly followed Food and Drug Association recommendations for experiments to determine oximeter accuracy. Oximeters are accurate in poorly perfused patients, especially newer oximeter models and those placed on earlobes. Further studies are needed that examine multiple oximeter models used on a diverse selection of patients while following FDA recommendations to examine oximeter accuracy.

Impact of skin tone on photoacoustic oximetry and tools to minimize bias

The major optical absorbers in tissue are melanin and oxy/deoxy-hemoglobin, but the impact of skin tone and pigmentation on biomedical optics is still not completely understood or adequately addressed. Melanin largely governs skin tone with higher melanin concentration in subjects with darker skin tones. Recently, there has been extensive debate on the bias of pulse oximeters when used with darker subjects. Photoacoustic (PA) imaging can measure oxygen saturation similarly as pulse oximeters and could have value in studying this bias. More importantly, it can deconvolute the signal from the skin and underlying tissue. Here, we studied the impact of skin tone on PA signal generation, depth penetration, and oximetry. Our results show that subjects with darker skin tones exhibit significantly higher PA signal at the skin surface, reduced penetration depth, and lower oxygen saturation compared to subjects with lighter skin tones. We then suggest a simple way to compensate for these signal differences.

Association of ROX Index with Mechanical Ventilator Use in Sepsis Patients in the Emergency Department

Detecting sepsis patients who are at a high-risk of mechanical ventilation is important in emergency departments (ED). The respiratory rate oxygenation (ROX) index is the ratio of tissue oxygen saturation/fraction of inspired oxygen to the respiratory rate. This study aimed to investigate whether the ROX index could predict mechanical ventilator use in sepsis patients in an ED. This retrospective observational study included quick sequential organ failure assessment (qSOFA) ≥ 2 sepsis patients that presented to the ED between September 2019 and April 2020. The ROX and ROX-heart rate (HR) indices were significantly lower in patients with mechanical ventilator use within 24 h than in those without the use of a mechanical ventilator (4.0 [3.2–5.4] vs. 10.0 [5.9–15.2], p < 0.001 and 3.9 [2.7–5.8] vs. 10.1 [5.4–16.3], p < 0.001, respectively). The area under the receiver operating characteristic (ROC) curve of the ROX and ROX-HR indices were 0.854 and 0.816 (both p < 0.001). The ROX and ROX-HR indices were independently associated with mechanical ventilator use within 24 h (adjusted hazard ratio = 0.78, 95% CI: 0.68–0.90, p < 0.001 and adjusted hazard ratio = 0.87, 95% CI 0.79–0.96, p = 0.004, respectively). The 28-day mortality was higher in the low ROX and low ROX-HR groups. The ROX and ROX-HR indices were associated with mechanical ventilator use within 24 h in qSOFA ≥ 2 patients in the ED.

Coronavirus Disease (COVID-19) Control between Drug Repurposing and Vaccination: A Comprehensive Overview

Respiratory viruses represent a major public health concern, as they are highly mutated, resulting in new strains emerging with high pathogenicity. Currently, the world is suffering from the newly evolving severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This virus is the cause of coronavirus disease 2019 (COVID-19), a mild-to-severe respiratory tract infection with frequent ability to give rise to fatal pneumonia in humans. The overwhelming outbreak of SARS-CoV-2 continues to unfold all over the world, urging scientists to put an end to this global pandemic through biological and pharmaceutical interventions. Currently, there is no specific treatment option that is capable of COVID-19 pandemic eradication, so several repurposed drugs and newly conditionally approved vaccines are in use and heavily applied to control the COVID-19 pandemic. The emergence of new variants of the virus that partially or totally escape from the immune response elicited by the approved vaccines requires continuous monitoring of the emerging variants to update the content of the developed vaccines or modify them totally to match the new variants. Herein, we discuss the potential therapeutic and prophylactic interventions including repurposed drugs and the newly developed/approved vaccines, highlighting the impact of virus evolution on the immune evasion of the virus from currently licensed vaccines for COVID-19.

Oximetry neither to prescribe long-term oxygen therapy nor to screen for severe hypoxaemia

BACKGROUND AND OBJECTIVE

Transcutaneous pulse oximetry saturation (S pO2 ) is widely used to diagnose severe hypoxaemia and to prescribe long-term oxygen therapy (LTOT) in COPD. This practice is not based on evidence. The primary objective of this study was to determine the accuracy (false positive and false negative rates) of oximetry for prescribing LTOT or for screening for severe hypoxaemia in patients with COPD.

METHODS

In a cross-sectional study, we correlated arterial oxygen saturation (S aO2 ) and S pO2 in patients with COPD and moderate hypoxaemia (n=240) and calculated the false positive and false negative rates of S aO2 at the threshold of ≤88% to identify severe hypoxaemia (arterial oxygen tension (P aO2 ) ≤55 mmHg or P aO2 <60 mmHg) in 452 patients with COPD with moderate or severe hypoxaemia.

RESULTS

The correlation between S aO2 and S pO2 was only moderate (intra-class coefficient of correlation: 0.43; 95% confidence interval: 0.32-0.53). LTOT would be denied in 40% of truly hypoxaemic patients on the basis of a S aO2 >88% (i.e., false negative result). Conversely, LTOT would be prescribed on the basis of a S aO2 ≤88% in 2% of patients who would not qualify for LTOT (i.e., false positive result). Using a screening threshold of ≤92%, 5% of severely hypoxaemic patients would not be referred for further evaluation.

CONCLUSIONS

Several patients who qualify for LTOT would be denied treatment using a prescription threshold of saturation ≤88% or a screening threshold of ≤92%. Prescription of LTOT should be based on P aO2 measurement.

Clinical guide to perioperative management for videothoracoscopy lung resection (Section of Cardiac, Vascular and Thoracic Anesthesia, SEDAR; Spanish Society of Thoracic Surgery, SECT; Spanish Society of Physiotherapy)

The introduction of video-assisted thoracoscopic (VATS) techniques has led to a new approach in thoracic surgery. VATS is performed by inserting a thoracoscope through a small incisions in the chest wall, thus maximizing the preservation of muscle and tissue. Because of its low rate of morbidity and mortality, VATS is currently the technique of choice in most thoracic procedures. Lung resection by VATS reduces prolonged air leaks, arrhythmia, pneumonia, postoperative pain and inflammatory markers. This reduction in postoperative complications shortens hospital length of stay, and is particularly beneficial in high-risk patients with low tolerance to thoracotomy. Compared with conventional thoracotomy, the oncological results of VATS surgery are similar or even superior to those of open surgery. This aim of this multidisciplinary position statement produced by the thoracic surgery working group of the Spanish Society of Anesthesiology and Reanimation (SEDAR), the Spanish Society of Thoracic Surgery (SECT), and the Spanish Association of Physiotherapy (AEF) is to standardize and disseminate a series of perioperative anaesthesia management guidelines for patients undergoing VATS lung resection surgery. Each recommendation is based on an in-depth review of the available literature by the authors. In this document, the care of patients undergoing VATS surgery is organized in sections, starting with the surgical approach, and followed by the three pillars of anaesthesia management: preoperative, intraoperative, and postoperative anaesthesia.

Personal Protective Equipment Alters Leg Muscle Fatigability Independent of Transcranial Direct Current Stimulation: A Comparison with Pre-COVID-19 Pandemic Results

In response to the COVID-19 pandemic, the use of personal protective equipment (PPE; e.g., face mask) has increased. Mandating subjects to wear PPE during vigorous exercise might affect the fatigue outcomes of transcranial direct current stimulation (tDCS) studies. The purpose of this study was to investigate whether the use of PPE affected the performance of a tDCS-influenced fatigue task in healthy adults. A total of 16 young and healthy subjects were recruited and wore PPE during an isokinetic fatigue task in conjunction with sham, 2 mA, and 4 mA tDCS conditions. Subjects were matched to subjects who did not wear PPE during our previous pre-pandemic study in which right knee extensor fatigability increased under these same conditions. The results show that right knee extensor fatigability, derived from torque and work (FI-T and FI-W, respectively), was higher in the PPE study compared to the No PPE study in the sham condition. Additionally, there were no differences in knee extensor fatigability or muscle activity between sham, 2 mA, and 4 mA tDCS in the present study, which contrasts with our previous results. Thus, PPE worn by subjects and researchers might have a detrimental effect on fatigue outcomes in tDCS studies irrespective of the stimulation intervention.

Impact of RBC Transfusion on Peripheral Capillary Oxygen Saturation and Partial Pressure of Arterial Oxygen

OBJECTIVES

RBCs are known to undergo deleterious changes during storage, known as storage lesions, which have been shown to result in decreased oxygen-carrying capacity. However, there is inadequate literature describing the effects of stored RBC allogeneic transfusion on oxygen parameters in vivo. The oxygen standard parameters were retrospectively assessed before and after RBC transfusion.

METHODS

Patients who received 1 RBC transfusion were assessed for hemoglobin (Hb) levels, peripheral capillary oxygen saturation (Spo2), and partial pressure of arterial oxygen (Pao2) from 12 hours before and 24 hours after transfusion.

RESULTS

In total, 78 patients who were monitored by Spo2 and 28 patients monitored by Pao2 were included in this analysis. Following RBC transfusion, Hb levels increased significantly (P < .001); however, there was a significant decrease in both Spo2 and Pao2 within 24 hours after transfusion (P = .04 and P = .003, respectively), indicating lower tissue oxygenation and lower soluble oxygen level.

CONCLUSIONS

This single-center, retrospective study revealed evidence of significantly decreased oxygenation and tissue perfusion after single-unit RBC transfusion, despite corrected Hb levels.

Determining a target SpO2 to maintain PaO2 within a physiological range

OBJECTIVE

In the context of an ongoing debate on the potential risks of hypoxemia and hyperoxemia, it seems prudent to maintain the partial arterial oxygen pressure (PaO2) in a physiological range during administration of supplemental oxygen. The PaO2 and peripheral oxygen saturation (SpO2) are closely related and both are used to monitor oxygenation status. However, SpO2 values cannot be used as an exact substitute for PaO2. The aim of this study in acutely ill and stable patients was to determine at which SpO2 level PaO2 is more or less certain to be in the physiological range.

METHODS

This is an observational study prospectively collecting data pairs of PaO2 and SpO2 values in patients admitted to the emergency room or intensive care unit (Prospective Inpatient Acutely ill cohort; PIA cohort). A second cohort of retrospective data of patients who underwent pulmonary function testing was also included (Retrospective Outpatient Pulmonary cohort; ROP cohort). Arterial hypoxemia was defined as PaO2 < 60 mmHg and hyperoxemia as PaO2 > 125 mmHg. The SpO2 cut-off values with the lowest risk of hypoxemia and hyperoxemia were determined as the 95th percentile of the observed SpO2 values corresponding with the observed hypoxemic and hyperoxemic PaO2 values.

RESULTS

220 data pairs were collected in the PIA cohort. 95% of hypoxemic PaO2 measurements occurred in patients with an SpO2 below 94%, and 95% of hyperoxemic PaO2 measurements occurred in patients with an SpO2 above 96%. Additionally in the 1379 data pairs of the ROP cohort, 95% of hypoxemic PaO2 measurements occurred in patients with an SpO2 below 93%.

CONCLUSION

The SpO2 level marking an increased risk of arterial hypoxemia is not substantially different in acutely ill versus stable patients. In acutely ill patients receiving supplemental oxygen an SpO2 target of 95% maximizes the likelihood of maintaining PaO2 in the physiological range.

Comparing Central Venous Blood Gas to Arterial Blood Gas and Determining Its Utility in Critically Ill Patients: Narrative Review

Arterial blood gas (ABG) analysis is used in critical care units to determine the degree of oxygenation, adequacy of ventilation, and the presence and severity of acid-base disturbances in the body. However, arterial puncture may result in complications, and the difficulty in acquiring arterial blood may delay care. Central venous blood gas (VBG) is a potentially more accessible alternative to ABG sampling. Current evidence suggests that pH and Pco2 obtained via peripheral VBG correlate well with ABG measurement. Nevertheless, the value of using central VBG to guide clinical decisions or as a surrogate for ABG is unclear. The purpose of this review is to explore the relationship between ABGs and central VBGs in critically ill patients. We performed a MEDLINE search using the following search terms: venous blood gas, arterial blood gas, and central venous blood gas. We excluded studies that did not involve human subjects, and only pH and Pco2 values were reviewed and examined from the studies included. All cited references from included studies were also reviewed to identify relevant literature. We identified 7 studies that met our criteria. In studies of hemodynamically stable patients, the mean difference between arterial and central venous pH and Pco2 was 0.03 units and 4-6.5 mm Hg, respectively. However, in patients with circulatory failure, the difference between central venous and arterial pH/Pco2 was 4-fold greater. We concluded that central VBG parameters of pH and Pco2 are potentially good surrogates for determining arterial pH and Pco2 in a stable patient without severe acid-base disturbances. Furthermore, central VBG can be used as a useful screening tool for arterial hypercapnia. In addition, we derived an adjustment formula for ABG conversion from central VBG: (1) arterial pH = venous pH + 0.05 units and (2) arterial Pco2 = venous Pco2 - 5 mm Hg.

[The MCR: A music therapy technique to support the hospitalization of depression]

INTRODUCTION

The Receptive Composite Montage (RCM) is a musical induction technique designed to cause a positive state to in-patients diagnosed with depression in a psychiatric institution. This research aims at proving that the RCM brings patients into a relaxation state and a positive mood within 20min.

METHOD

Thirty-seven in-patients with depression took part in this study. The average age of the sample was slightly under 49 years old (48.73±12.41). The relaxing aspect of the RCM was monitored thanks to data given by an oximeter, which measures the heartbeats and the oxygen saturation level in the in-patient's bloodstream. In order to complete these data, a focal-sampling observation was carried out. Positive mood induction was estimated based on interviews. The data have been processed through analytical statistics.

RESULTS

Heartbeats and oxygen saturation in the bloodstream during the relaxing phase of the montage (P<.001 and z=.018 respectively) tended to increase during the wake-up phase (P<.001) as was anticipated. In-patients who had felt a negative mood before listening to the RCM reported feeling a significant positive mood once they had listened to the RCM (z=.017).

CONCLUSION

The results obtained show that the RCM does induce a relaxation state by decreasing heartbeats and breathing cycles. Moreover, the qualitative data show that when in-patients listen to the RCM, their mood becomes positive through an emotional exercise causing their mood to shift from negative to positive.

Effect of the novel dual orexin receptor antagonist daridorexant on night-time respiratory function and sleep in patients with moderate chronic obstructive pulmonary disease

In patients with chronic obstructive pulmonary disease (COPD), sleep is often fragmented while, conversely, the use of sleep medications is of concern in these patients due to potential impairment of nocturnal breathing. This randomised, double-blind, placebo-controlled, two-period crossover study was conducted to evaluate the effect of the new dual orexin receptor antagonist daridorexant on night-time respiratory function and sleep in patients with moderate COPD. In each period, the highest Phase-III dose of 50 mg daridorexant or placebo was administered once daily in the evening for 5 consecutive days. The primary endpoint was peripheral oxygen saturation (SpO₂ ) during total sleep time (TST) after last dosing. Night-time respiratory function and sleep were further evaluated based on the apnea-hypopnea index (AHI), sleep duration, and objective sleep parameters. Pharmacokinetics, safety, and tolerability were also assessed. Primary endpoint analysis revealed no significant mean treatment difference (i.e. daridorexant - placebo) for SpO₂ during TST as it was 0.18% (90% confidence interval: -0.21 to 0.57). There was also no difference from placebo for SpO₂ during non-rapid eye movement (REM) and REM sleep at Night 5 and after first dosing. The AHI was slightly increased compared to placebo, but not to a clinically meaningful extent. In addition, daridorexant improved objective sleep parameters (i.e. prolonged TST, increased sleep efficiency, and decreased wake after sleep onset), reached expected plasma concentrations, and was safe and well tolerated. In conclusion, single and multiple doses of 50 mg daridorexant do not impair night-time respiratory function and improves sleep in patients with moderate COPD.

Study of Oxygen Saturation by Pulse Oximetry and Arterial Blood Gas in ICU Patients: A Descriptive Cross-sectional Study

Introduction:

Pulse oximetery is expected to be an indirect estimation of arterial oxygen saturation. However, there often are gaps between SpO2 and SaO2. This study aims to study on arterial oxygen saturation measured by pulse oximetry and arterial blood gas among patients admitted in intensive care unit.

Methods:

It was a hospital-based descriptive cross-sectional study in which 101 patients meeting inclusion criteria were studied. SpO2 and SaO2 were measured simultaneously. Mean±SD of SpO2 and SaO2 with accuracy, sensitivity and specificity were measured.

Results:

According to SpO2 values, out of 101 patients, 26 (25.7%) were hypoxemic and 75 (74.25%) were non-hypoxemic. The mean±SD of SaO2 and SpO2 were 93.22±7.84% and 92.85±6.33% respectively. In 21 patients with SpO2<90%, the mean±SD SaO2 and SpO2 were 91.63±4.92 and 87.42±2.29 respectively. In 5 patients with SpO2 < 80%, the mean ± SD of SaO2 and SpO2 were: 63.40 ± 3.43 and 71.80±4.28, respectively. In non-hypoxemic group based on SpO2 values, the mean±SD of SpO2 and SaO2 were 95.773±2.19% and 95.654±3.01%, respectively. The agreement rate of SpO2 and SaO2 was 83.2%, and sensitivity and specificity of PO were 84.6% and 83%, respectively.

Conclusions:

Pulse Oximetry has high accuracy in estimating oxygen saturation with sp02>90% and can be used instead of arterial blood gas.

Investigating the origin of photoplethysmography using a multiwavelength Monte Carlo model

Photoplethysmography (PPG) is a photometric technique used for the measurement of volumetric changes in the blood. The recent interest in new applications of PPG has invigorated more fundamental research regarding the origin of the PPG waveform, which since its discovery in 1937, remains inconclusive. A handful of studies in the recent past have explored various hypotheses for the origin of PPG. These studies relate PPG to mechanical movement, red blood cell orientation or blood volume variations.

OBJECTIVE

Recognising the significance and need to corroborate a theory behind PPG formation, the present work rigorously investigates the origin of PPG based on a realistic model of light-tissue interactions.

APPROACH

A three-dimensional comprehensive Monte Carlo model of finger-PPG was developed and explored to quantify the optical entities pertinent to PPG (e.g. absorbance, reflectance, and penetration depth) as the functions of multiple wavelengths and source-detector separations. Complementary to the simulations, a pilot in vivo investigation was conducted on eight healthy volunteers. PPG signals were recorded using a custom-made multiwavelength sensor with an adjustable source-detector separation.

MAIN RESULTS

Simulated results illustrate the distribution of photon-tissue interactions in the reflectance PPG geometry. The depth-selective analysis quantifies the contributions of the dermal and subdermal tissue layers in the PPG wave formation. A strong negative correlation (r = -0.96) is found between the ratios of the simulated absorbances and measured PPG amplitudes.

SIGNIFICANCE

This work quantified for the first time the contributions of different tissue layers and sublayers in the formation of the PPG signal.

Lung function and oxygen saturation after participation in Norseman Xtreme Triathlon

OBJECTIVES

To examine evidence of exercise-induced bronchoconstriction (EIB) defined as ≥10% reduction in forced expiratory volume in one second (FEV₁ ) and exercise-induced arterial hypoxemia (EIAH) defined as ≥4% reduction in oxygen saturation (SpO₂ ) from before to after participation in the Norseman Xtreme Triathlon. Secondarily, to assess whether changes in FEV₁ and SpO₂ are related to respiratory symptoms, training volume, and race time.

METHODS

In this quasi-experimental non-controlled study, we included 63 triathletes (50♂/13♀) aged 40.3 (±9.0) years (mean ± SD). Fifty-seven (46♂/11♀) measured lung function and 54 (44♂/10♀) measured SpO₂ before the race, 8-10 minutes after the race (post-test 1) and the day after the race (post-test 2). Respiratory symptoms and training volume were recorded with modified AQUA questionnaire. ANOVA for repeated measures was used to detect differences in lung function and SpO₂ . Statistical significance was accepted at 0.05 level.

RESULTS

Twenty-six participants (46%) presented with EIB at post-test 1 and 16 (28%) at post-test 2. Lung function variables were significantly reduced from baseline to post-test 1 and 2. Thirty-five participants (65%) showed evidence of mild to moderate EIAH. No significant correlations were observed except a weak correlation between maximal reduction in FEV₁ and respiratory symptoms (r = 0.35, P = .016).

CONCLUSION

Our results demonstrated that 46% of the participants presented with EIB and 65% showed evidence of EIAH after the Norseman Xtreme Triathlon. Changes in FEV₁ and SpO₂ were not correlated to weekly training hours or race time. We observed a weak correlation between maximal reduction in FEV₁ and respiratory symptoms.

A comparison of respiratory function in pigs anaesthetised by propofol or alfaxalone in combination with dexmedetomidine and ketamine

BACKGROUND

General anaesthesia in pigs maintained with intravenous drugs such as propofol may cause respiratory depression. Alfaxalone gives less respiratory depression than propofol in some species. The aim of the investigation was to compare respiratory effects of propofol-ketamine-dexmedetomidine and alfaxalone-ketamine-dexmedetomidine in pigs. Sixteen pigs premedicated with ketamine 15 mg/kg and midazolam 1 mg/kg intramuscularly were anaesthetised with propofol or alfaxalone to allow endotracheal intubation, followed by propofol 8 mg/kg/h or alfaxalone 5 mg/kg/h in combination with ketamine 5 mg/kg/h and dexmedetomidine 4 µg/kg/h given as a continuous infusion for 60 min. The pigs breathed spontaneously with an FIO₂ of 0.21. Oxygen saturation (SpO₂), end-tidal CO₂ concentration (PE'CO₂), respiratory rate (f_R) and inspired tidal volume (V_T) were measured, and statistically compared between treatments. If the SpO₂ dropped below 80% or if PE'CO₂ increased above 10.0 kPa, the pigs were recorded as failing to complete the study, and time to failure was statistically compared between treatments.

RESULTS

Alfaxalone treated pigs had significantly higher respiratory rates and lower PE'CO₂ than propofol treated pigs, with a f_R being 7.3 /min higher (P = 0.01) and PE'CO₂ 0.8 kPa lower (P = 0.05). SpO₂ decreased by 0.6% and f_R by 1.0 /min per kg increase in body weight in both treatment groups. Three of eight propofol treated and two of eight alfaxalone treated pigs failed to complete the study, and times to failure were not significantly different between treatments (P = 0.75).

CONCLUSIONS

No major differences in respiratory variables were found when comparing treatments. Respiratory supportive measures must be available when using both protocols.

Variability in the use of pulse oximeters with children in Kenyan hospitals: A mixed-methods analysis

BACKGROUND

Pulse oximetry, a relatively inexpensive technology, has the potential to improve health outcomes by reducing incorrect diagnoses and supporting appropriate treatment decisions. There is evidence that in low- and middle-income countries, even when available, widespread uptake of pulse oximeters has not occurred, and little research has examined why. We sought to determine when and with which children pulse oximeters are used in Kenyan hospitals, how pulse oximeter use impacts treatment provision, and the barriers to pulse oximeter use.

METHODS AND FINDINGS

We analyzed admissions data recorded through Kenya's Clinical Information Network (CIN) between September 2013 and February 2016. We carried out multiple imputation and generated multivariable regression models in R. We also conducted interviews with 30 healthcare workers and staff from 14 Kenyan hospitals to examine pulse oximetry adoption. We adapted the Integrative Model of Behavioural Prediction to link the results from the multivariable regression analyses to the qualitative findings. We included 27,906 child admissions from 7 hospitals in the quantitative analyses. The median age of the children was 1 year, and 55% were male. Three-quarters had a fever, over half had a cough; other symptoms/signs were difficulty breathing (34%), difficulty feeding (34%), and indrawing (32%). The most common diagnoses were pneumonia, diarrhea, and malaria: 45%, 35%, and 28% of children, respectively, had these diagnoses. Half of the children obtained a pulse oximeter reading, and of these, 10% had an oxygen saturation level below 90%. Children were more likely to receive a pulse oximeter reading if they were not alert (odds ratio [OR]: 1.30, 95% confidence interval (CI): 1.09, 1.55, p = 0.003), had chest indrawing (OR: 1.28, 95% CI: 1.17, 1.40, p < 0.001), or a very high respiratory rate (OR: 1.27, 95% CI: 1.13, 1.43, p < 0.001), as were children admitted to certain hospitals, at later time periods, and when a Paediatric Admission Record (PAR) was used (OR PAR used compared with PAR not present: 2.41, 95% CI: 1.98, 2.94, p < 0.001). Children were more likely to be prescribed oxygen if a pulse oximeter reading was obtained (OR: 1.42, 95% CI:1.25, 1.62, p < 0.001) and if this reading was below 90% (OR: 3.29, 95% CI: 2.82, 3.84, p < 0.001). The interviews indicated that the main barriers to pulse oximeter use are inadequate supply, broken pulse oximeters, and insufficient training on how, when, and why to use pulse oximeters and interpret their results. According to the interviews, variation in pulse oximeter use between hospitals is because of differences in pulse oximeter availability and the leadership of senior doctors in advocating for pulse oximeter use, whereas variation within hospitals over time is due to repair delays. Pulse oximeter use increased over time, likely because of the CIN's feedback to hospitals. When pulse oximeters are used, they are sometimes used incorrectly and some healthcare workers lack confidence in readings that contradict clinical signs. The main limitations of the study are that children with high levels of missing data were not excluded, interview participants might not have been representative, and the interviews did not enable a detailed exploration of differences between counties or across senior management groups.

CONCLUSIONS

There remain major challenges to implementing pulse oximetry-a cheap, decades old technology-into routine care in Kenya. Implementation requires efficient and transparent procurement and repair systems to ensure adequate availability. Periodic training, structured clinical records that include prompts, the promotion of pulse oximetry by senior doctors, and monitoring and feedback might also support pulse oximeter use. Our findings can inform strategies to support the use of pulse oximeters to guide prompt and effective treatment, in line with the Sustainable Development Goals. Without effective implementation, the potential benefits of pulse oximeters and possible hospital cost-savings by targeting oxygen therapy might not be realized.

Evaluation of pulse oximetry as a surrogate for PaO2 in awake dogs breathing room air and anesthetized dogs on mechanical ventilation

OBJECTIVE

To evaluate the ability of arterial hemoglobin oxygen saturation measurement via pulse oximetry (SpO2 ) to serve as a surrogate for PaO2 in dogs.

DESIGN

Two-part study: prospective observational and retrospective components.

SETTING

University teaching hospital.

ANIMALS

Ninety-two dogs breathing room air prospectively enrolled on a convenience basis. Retrospective evaluation of 1,033 paired SpO2 and PaO2 measurements from 62 dogs on mechanical ventilation.

INTERVENTIONS

Dogs with concurrent SpO2 and PaO2 measured on room air had a data sheet completed with blood gas analysis. SpO2 , PaO2 , and FiO2 values were collected from medical records of dogs on mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Predicted PaO2 was calculated from SpO2 using the dog oxyhemoglobin dissociation curve. The correlation coefficient between measured and predicted PaO2 was 0.49 (P < 0.0001) in room air dogs and 0.74 (P < 0.0001) in ventilated dogs. In room air dogs, Bland-Altman analysis between measured minus predicted PaO2 versus the average showed a mean bias of -6.0 mm Hg (95% limit of agreement, -35 to 23 mm Hg). The correlation coefficient between PaO2 /FiO2 and SpO2 /FiO2 ratios was 0.76 (P < 0.0001). After combining data sets, receiver operating characteristic curve analysis showed the optimal cutoff value for detecting hypoxemia (PaO2  < 80 mm Hg) was an SpO2 of 95%, with sensitivity and specificity of 77.8% and 89.5%, respectively. Using this cutoff, 6.9% of SpO2 readings failed to detect hypoxemia, whereas 7.2% predicted hypoxemia that was not present.

CONCLUSIONS

The SpO2 was not clinically suitable as a surrogate for PaO2 , though it performed better in mechanically ventilated dogs. As sensitivity for the detection of hypoxemia was poor, pulse oximetry does not appear to be an acceptable screening test. The SpO2 /FiO2 ratio may have value for evaluation of anesthetized dogs on supplemental oxygen. Arterial blood gas analysis remains ideal for assessment of oxygenation.

Deriving the arterial Po2 and oxygen deficit from expired gas and pulse oximetry

The efficiency of pulmonary gas exchange is often assessed by the ideal alveolar-arterial partial pressure difference (A-aDO₂). Through a combination of pulse oximetry and rapidly responding gas analyzers to measure the partial pressures of O₂ and CO₂ in expired gas, one can measure the oxygen deficit. Defined as the difference between the measured alveolar Po₂ and the arterial Po₂ calculated from SpO2, the oxygen deficit is a substitute for the alveolar-arterial Po₂ difference. The oxygen deficit is physiologically reasonable in that it increases with age in healthy subjects and is well correlated with the A-aDO₂. To calculate arterial Po₂ from saturation, the saturation should be below the very flat upper part of the O₂-Hb dissociation curve; good estimates can be made provided the arterial O₂ saturation is below ~95%. Since saturations at or above 95% imply reasonably well-maintained gas exchange efficiency, this limitation is of only minor concern. Calculations show that it is necessary to take into account the change in Po₂ at a saturation of 50% of the O₂-Hb dissociation curve based on the measured alveolar Pco₂. As the measurement is designed to be noninvasive, determination of any base excess is not practical, but calculations show that the effect of assuming a zero base excess is modest, with a similar small effect from an abnormal body temperature. Taken together, these results show that a noninvasive assessment of pulmonary gas exchange efficiency can be obtained from subjects with below-normal arterial O₂ saturations through a combination of expired O₂ and CO₂ measurements and SpO2 made during quiet breathing.NEW & NOTEWORTHY The details and limitations of a noninvasive measurement of pulmonary gas exchange efficiency, the oxygen deficit, are described. The oxygen deficit, calculated from expired gas measurements made during quiet breathing coupled with pulse oximetry, is a good surrogate measurement of the ideal alveolar-arterial Po₂ difference and does not require arterial blood gas sampling.

Facing SpO2 and SaO2 discrepancies in ICU patients: is the perfusion index helpful?

Peripheral oxygen saturation (SpO₂) measured by pulse oximetry is an unreliable surrogate marker for arterial oxygenation (SaO₂) in critically ill patients. We hypothesized that a higher perfusion index (PFI) would be associated with better accuracy of SpO₂ measurement. We retrospectively collected SaO₂, SpO₂, and PFI data for each arterial blood gas (ABG) analysis in a cohort of intensive care unit patients. PFI was categorised as low (PFI < 1.0), intermediate (1.0 ≤ PFI  ≤ 2.5), or high (PFI > 2.5). The correlation between SpO₂ and SaO₂ was studied using Pearson’s correlation. The Bland–Altman plot was used to analyse the agreement between SpO₂ and SaO₂. Furthermore, the correlation between the (SpO₂–SaO₂) difference and PFI was assessed. The level of (dis)agreement was calculated for the three PFI categories separately. Overall, 281 patients and 1281 data points were analysed. There was a significant correlation between SaO₂ and SpO₂ (r = 0.69, p < 0.01). The Bland–Altman analysis revealed a mean difference between SaO₂ and SpO₂ of 0.2% with limits of agreement of ± 6% (SD ± 2%). The correlation between the PFI and the (SpO₂–SaO₂) difference was low; the (SpO₂–SaO₂) difference improved only marginally with higher PFI values. The accuracy of pulse oximetry for estimating arterial oxygenation was moderate and improved little with increasing PFI values. Thus, the additive value of PFI in clinical decision making is limited. Therefore, we advise performing an ABG before adjusting fraction of inspired oxygen (FiO₂) settings.

Accuracy of pulse oximeters at low oxygen saturations in children with congenital cyanotic heart disease: An observational study

BACKGROUND

Pulse oximetry overestimates arterial oxygen saturation (SaO₂ ) at less than 90% saturation in cyanotic children. The Masimo Blue sensor (Masimo Corp., Irvine, CA) is a pulse oximetry sensor developed for use in children with cyanosis. However, there remains a lack of research in actual clinical practice.

AIMS

We evaluated the intraoperative performance of three different pulse oximeters to measure oxyhemoglobin saturation (SpO₂ ) at low saturations in pediatric patients with cyanotic heart disease and the influence of clinical variables (SaO₂ , hemoglobin concentration, perfusion index, and weight) on the accuracy of the sensors.

METHODS

This prospective observational study compared SpO₂ measured using three pulse oximeters (Masimo Blue [Masimo Corp., Irvine, CA]; Masimo LNCS, and Nellcor [Medtronic, Dublin, Ireland]) at selected SaO₂ ranges (≥85%, 75%-84%, 60%-74%, and < 60%). Accuracy was evaluated according to bias and Bland-Altman analysis with appropriate correction for multiple measurements. Relationships between bias and clinical variables were assessed using a generalized estimating equation.

RESULTS

Two hundred and fifty-eight samples were analyzed. The mean overall bias (limits of agreement) of Masimo Blue, Masimo LNCS, and Nellcor sensor was -5.3 (-20.9 to 10.3%), -7.4 (-21.9 to 7.1%), and -7.4 (-22.5 to 15.1%), respectively. However, there was no difference in bias among the three sensors at SaO₂ <60%. Generalized estimating equation showed that SaO₂ value was associated with bias of all sensors. Perfusion index affected the bias of Blue sensor and LNCS sensor, and patients' weight was associated with bias of Nellcor sensor.

CONCLUSION

Masimo blue sensor demonstrated overall lower bias compared to the other two sensors. However, the accuracy of all sensors was similarly poor at SaO₂ less than 60%. Bias was influenced by SaO₂ , perfusion index, and body weight.

Identifying Patients Experiencing Opioid-Induced Respiratory Depression During Recovery From Anesthesia: The Application of Electronic Monitoring Devices

BACKGROUND

Postsurgical patients experiencing opioid-related adverse drug events have 55% longer hospital stays, 47% higher costs associated with their care, 36% increased risk of 30-day readmission, and 3.4 times higher risk of inpatient mortality compared to those with no opioid-related adverse drug events. Most of the adverse events are preventable.

GENERAL AIM

This study explored three types of electronic monitoring devices (pulse oximetry, capnography, and minute ventilation [MV]) to determine which were more effective at identifying the patient experiencing respiratory compromise and, further, to determine whether algorithms could be developed from the electronic monitoring data to aid in earlier detection of respiratory depression.

MATERIALS AND METHODS

A study was performed in the postanesthesia care unit (PACU) in an inner city. Sixty patients were recruited in the preoperative admissions department on the day of their surgery. Forty-eight of the 60 patients wore three types of electronic monitoring devices while they were recovering from back, neck, hip, or knee surgery. Machine learning models were used for the analysis.

RESULTS

Twenty-four of the 48 patients exhibited sustained signs of opioid-induced respiratory depression (OIRD). Although the SpO₂ values did not change, end-tidal CO₂ levels increased, and MV decreased, representing hypoventilation. A machine learning model was able to predict an OIRD event 10 min before the actual event occurred with 80% accuracy.

LINKING EVIDENCE TO ACTION

Electronic monitoring devices are currently used as a tool to assess respiratory status using thresholds to distinguish when respiratory depression has occurred. This study introduces a potential paradigm shift from a reactive approach to a proactive approach that would identify a patient at high risk for OIRD. Capnography and MV were found to be effective tools in detecting respiratory compromise in the PACU.

Comparison of non-invasive to invasive oxygenation ratios for diagnosing acute respiratory distress syndrome following coronary artery bypass graft surgery: a prospective derivation-validation cohort study

Objective

To determine if non-invasive oxygenation indices, namely peripheral capillary oxygen saturation (S_pO₂)/fraction of inspired oxygen (F_iO₂) and partial pressure of alveolar oxygen (P_AO₂)/F_iO₂ may be used as effective surrogates for the partial pressure of arterial oxygen (P_aO₂)/F_iO₂. Also, to determine the S_pO₂/F_iO₂ and P_AO₂/F_iO₂ values that correspond to P_aO₂/F_iO₂ thresholds for identifying acute respiratory distress syndrome (ARDS) in patients following coronary artery bypass graft (CABG) surgery.

Methods

A prospective derivation-validation cohort study in the Open-Heart ICU of an academic teaching hospital. Recorded variables included patient demographics, ventilator settings, chest radiograph results, and S_PO₂, P_aO₂, P_AO_2, S_aO₂, and F_iO₂. Linear regression modeling was used to quantify the relationship between indices. Receiver operating characteristic (ROC) curves were used to determine the sensitivity and specificity of the threshold values.

Results

One-hundred seventy-five patients were enrolled in the derivation cohort, and 358 in the validation cohort. The S_PO₂/F_iO₂ and P_AO₂/F_iO₂ ratios could be predicted well from P_aO₂/F_iO₂, described by the linear regression models S_PO₂/F_iO₂ = 71.149 + 0.8PF and P_AO₂/F_iO₂ = 38.098 + 2.312PF, respectively. According to the linear regression equation, a P_aO₂/F_iO₂ ratio of 300 equaled an S_PO₂/F_iO₂ ratio of 311 (R² 0.857, F 1035.742, < 0.0001) and a P_AO₂/F_iO₂ ratio of 732 (R² 0.576, F 234.887, < 0.0001). The S_PO₂/F_iO₂ threshold of 311 had 90% sensitivity, 80% specificity, LR+ 4.50, LR- 0.13, PPV 98, and NPV 42.1 for the diagnosis of mild ARDS. The P_AO₂/F_iO₂ threshold of 732 had 86% sensitivity, 90% specificity, LR+ 8.45, LR- 0.16, PPV 98.9, and NPV 36 for the diagnosis of mild ARDS. S_PO₂/F_iO₂ had excellent discrimination ability for mild ARDS (AUC ± SE = 0.92 ± 0.017; 95% CI 0.889 to 0.947) as did P_AO₂/F_iO₂ (AUC ± SE = 0.915 ± 0.018; 95% CI 0.881 to0.942).

Conclusions

P_aO₂ and S_aO₂ correlated in the diagnosis of ARDS, with a P_aO₂/F_iO₂ of 300 correlating to an S_PO₂/ F_iO₂ of 311 (Sensitivity 90%, Specificity 80%). The S_PO₂/ F_iO₂ ratio may allow for early real-time rapid identification of ARDS, while decreasing the cost, phlebotomy, blood loss, pain, skin breaks, and vascular punctures associated with serial arterial blood gas measurements.

Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus

Objective

The main objective is to determine if digital pulse oximetry is an acceptable screening tool to detect hemodynamically significant lower extremity peripheral artery disease (PAD) in patients 50 years old and above with type 2 diabetes mellitus (T2DM) seen at the University of Santo Tomas Hospital (USTH).

Methodology

A total of 78 subjects (155 limbs) were included. Using duplex ultrasonography as the reference standard for the presence of hemodynamically significant lower extremity PAD, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were obtained for abnormal percent oxygen saturation (SpO₂) gradients and for ankle-brachial index (ABI).

Results

Of the 155 limbs, 38.7% had hemodynamically significant stenosis. Pulse oximetry had 76.7% sensitivity (95% CI, 65.2% to 88.1%), 85.3% specificity (95% CI, 78.0% to 92.6%), 76.7% PPV (95% CI, 66.5% to 84.4%) and 85.3% NPV (95% CI, 78.4% to 90.2%). ABI had 40.7% sensitivity (95% CI, 30.1% to 51.3%), 88.2% specificity (95% CI, 80.0% to 96.3%), 68.6% PPV (95% CI, 53.6% to 80.4%) and 70.1% NPV (95% CI, 65.1% to 74.5%). Combining both produces 88.1% sensitivity (95% CI, 78.5% to 97.8%), 74.2% specificity (95% CI, 65-83.4%), 68.4 PPV (95% CI, 60.3% to 75.6%) and 90.8% NPV (95% CI, 83.0% to 95.2%).

Conclusion

The results of this study suggest that pulse oximetry has a higher sensitivity than ABI as a screening tool for hemodynamically significant lower extremity PAD in T2DM patients 50 years old and above. Combining these two tests may be done to achieve a higher sensitivity.

Accuracy of pulse oximetry in detection of oxygen saturation in patients admitted to the intensive care unit of heart surgery: comparison of finger, toe, forehead and earlobe probes

Background

Heart surgery patients are more at risk of poor peripheral perfusion, and peripheral capillary oxygen saturation (SpO2) measurement is regular care for continuous analysis of blood oxygen saturation in these patients. With regard to controversial studies on accuracy of the current pulse oximetry probes and lack of data related to patients undergoing heart surgery, the present study was conducted to determine accuracy of pulse oximetry probes of finger, toe, forehead and earlobe in detection of oxygen saturation in patients admitted to intensive care units for coronary artery bypass surgery.

Methods

In this clinical trial, 67 patients were recruited based on convenience sampling method among those admitted to intensive care units for coronary artery bypass surgery. The SpO2 value was measured using finger, toe, forehead and earlobe probes and then compared with the standard value of arterial oxygen saturation (SaO2). Data were entered into STATA-11 software and analyzed using descriptive, inferential and Bland-Altman statistical analyses.

Results

Highest and lowest correlational mean values of SpO2 and SaO2 were related to finger and earlobe probes, respectively. The highest and lowest agreement of SpO2 and SaO2 were related to forehead and earlobe probes.

Conclusion

The SpO2 of earlobe probes due to lesser mean difference, more limited confidence level and higher agreement ration with SaO2 resulted by arterial blood gas (ABG) analysis had higher accuracy. Thus, it is suggested to use earlobe probes in patients admitted to the intensive care unit for coronary artery bypass surgery.

Trial registration

Registration of this trial protocol has been approved in Iranian Registry of Clinical Trials at 2018–03-19 with reference IRCT20100913004736N22. “Retrospectively registered.”

Pulse Oximetry: A Survey of Knowledge among Staff of an Emergency Department

Introduction

Pulse oximetry measures arterial oxygen saturation and was introduced into the clinical field since the 1980s. It provides a simple, portable, non-invasive and inexpensive way for monitoring blood oxygen saturation. Previous studies demonstrated that most hospital staff had limited knowledge on the correct use of pulse oximetry and what might affect the readings. This study aimed at evaluating the extent of knowledge in pulse oximetry among the clinical staff of an emergency department.

Method

A 25-item multiple-choice type questionnaire was given to the medical and nursing staff of the Accident and Emergency Department (AED) of the Alice Ho Miu Ling Nethersole Hospital. In addition to demographic information, respondents were required to answer questions relating to the basic principles of pulse oximetry, recognition of physiological factors limiting its accuracy and management regarding hypothetical scenarios. The scores were expressed and analysed on a scale of 0–100.

Results

A total of 44 questionnaires were completed by 27 nurses and 17 doctors with their test scores ranging from 20 to 72 (median=46). Doctors (median=56) did better than nurses (median=44) in general (P=0.036) but this advantage, however, did not apply to questions on hypothetical scenarios where nurses performed better on the contrary. Correlation analysis proved that there was no linear relationship between respondents' test scores and their years of clinical experience (r=0.051, Spearman). This absence of linear relationship also applied to individual doctors (r=0.244, Spearman) and nurses groups (r=0.162, Spearman).

Conclusion

There was insufficient knowledge on the use of pulse oximetry among staff of the AED. The level of understanding did not correlate with their clinical experience. Training programs targeting both the fresh and the experienced staff are recommended.

Comparison of the peripheral blood eosinophil count using near-patient testing and standard automated laboratory measurement in healthy, asthmatic and COPD subjects

Near-patient testing (NPT) allows clinical decisions to be made in a rapid and convenient manner and is often cost effective. In COPD the peripheral blood eosinophil count has been demonstrated to have utility in providing prognostic information and predicting response to treatment during an acute exacerbation. For this potential to be achieved having a reliable NPT of blood eosinophil count would be extremely useful. Therefore, we investigated the use of the HemoCue^® WBC Diff System and evaluated its sensitivity and specificity in healthy, asthmatic and COPD subjects. This method requires a simple skin prick of blood and was compared to standard venepuncture laboratory analysis. The HemoCue^® WBC Diff System measured the peripheral blood eosinophil count in healthy, asthma and COPD subjects with very close correlation to the eosinophil count as measured by standard venepuncture. The correlations were unaffected by disease status. This method for the measurement of the peripheral blood eosinophil count has the potential to provide rapid near-patient results and thus influence the speed of management decisions in the treatment of airway diseases.

The Accuracy of Noninvasive Peripheral Pulse Oximetry After Palliative Cardiac Surgery in Patients With Cyanotic Congenital Heart Disease

BACKGROUND

Children with cyanotic congenital heart disease (CCHD) live with oxyhemoglobin saturations that are typically expressed as percentages in the range of 70s and 80s. Peripheral pulse oximetry (measurement of SpO₂) performs poorly in this range and yet is widely used to inform clinical decisions in these patients. The reference standard is co-oximetry of arterial samples (SaO₂).

METHODS

In this study, 515 paired measurements of SpO₂ and SaO₂ were taken from 19 children who had undergone palliative cardiac surgery.

RESULTS

SpO₂ (Masimo SET LNCS Neo pulse oximeter) overestimated oxyhemoglobin saturation in 82% of measurements (mean 4.6% ± 6.6%). There was a strong negative correlation between mean bias and SaO₂ ( r = -.96, P = .002, 95% confidence interval: -0.99 to -0.68).

CONCLUSION

The results raise a concern that critical hypoxemia may go undetected and untreated if pulse oximetry is relied upon as the primary means of assessing oxyhemoglobin saturation in children with CCHD. Strong preference must be given to co-oximetry of arterial samples.

A framework for the meta-analysis of Bland-Altman studies based on a limits of agreement approach

Bland-Altman method comparison studies are common in the medical sciences and are used to compare a new measure to a gold-standard (often costlier or more invasive) measure. The distribution of these differences is summarized by two statistics, the 'bias' and standard deviation, and these measures are combined to provide estimates of the limits of agreement (LoA). When these LoA are within the bounds of clinically insignificant differences, the new non-invasive measure is preferred. Very often, multiple Bland-Altman studies have been conducted comparing the same two measures, and random-effects meta-analysis provides a means to pool these estimates. We provide a framework for the meta-analysis of Bland-Altman studies, including methods for estimating the LoA and measures of uncertainty (i.e., confidence intervals). Importantly, these LoA are likely to be wider than those typically reported in Bland-Altman meta-analyses. Frequently, Bland-Altman studies report results based on repeated measures designs but do not properly adjust for this design in the analysis. Meta-analyses of Bland-Altman studies frequently exclude these studies for this reason. We provide a meta-analytic approach that allows inclusion of estimates from these studies. This includes adjustments to the estimate of the standard deviation and a method for pooling the estimates based upon robust variance estimation. An example is included based on a previously published meta-analysis. Copyright © 2017 John Wiley & Sons, Ltd.

Comparative Evaluation of Accuracy of Pulse Oximeters and Factors Affecting Their Performance in a Tertiary Intensive Care Unit

INTRODUCTION

Pulse oximetry is a widely used tool, unfortunately there is a paucity of data investigating its accuracy in Intensive Care Units (ICU) and if they are able to meet mandated FDA criteria as claimed by them in critically ill patients.

AIM

To assess bias, precision and accuracy of pulse oximeters used in ICU and factors affecting them.

MATERIALS AND METHODS

A prospective cohort study, including 129 patients admitted to the ICU of a tertiary referral centre. Pulse oximetry and blood gas were done simultaneously. Pulse oximetry was done using two pulse oximetres: Nonin and Philips. All physiological variables like haemoglobin, lactate, use of vasopressors and blood pressure were recorded. Bland Altman curves were constructed to determine bias and limits of agreement. Effect of physiological variables on bias and difference between performance characteristics of bias was determined using SPSS.

RESULTS

Pulse oximetry overestimated arterial oxygen saturation (SaO₂) by 1.44%. There was negative correlation between bias and SaO₂ (r=-0.32) and positive correlation with lactate (r=0.16). The Philips pulse oximeter had significant higher bias and variability than Nonin pulse oximeter. (2.49±2.99 versus 0.46±1.68, mean difference = 1.98, 95% C.I. = 1.53 - 2.43, p-value <0.001).

CONCLUSION

Pulse oximetry overestimates SaO₂. Bias tends to increase with rising lactate and hypoxia. There is heterogeneity in performance of various pulse oximetry devices in ICU.