Recent advances in pulse oximetry

Ninety years of pulse oximetry: history, current status, and outlook

Significance

This year, 2024, marks the 50th anniversary of the invention of pulse oximetry (PO), which was first presented by Takuo Aoyagi, an engineer from the Nihon Kohden Company, at the 13th Conference of the Japanese Society of Medical Electronics and Biological Engineering in Osaka in 1974. His discovery and the development of PO for the non-invasive measurement of peripheral arterial oxygenation represents one of the most significant chapters in the history of medical technology. It resulted from research and development efforts conducted by biochemists, engineers, physicists, physiologists, and physicians since the 1930s.

Aim

The objective of this work was to provide a narrative review of the history, current status, and future prospects of PO.

Approach

A comprehensive review of the literature on oximetry and PO was conducted.

Results and Conclusions

Our historical review examines the development of oximetry in general and PO in particular, tracing the key stages of a long and fascinating story that has unfolded from the first half of the twentieth century to the present day-an exciting journey in which serendipity has intersected with the hard work of key pioneers. This work has been made possible by the contributions of numerous key pioneers, including Kurt Kramer, Karl Matthes, Glenn Millikan, Evgenii M. Kreps, Earl H. Wood, Robert F. Show, Scott A. Wilber, William New, and, above all, Takuo Aoyagi. PO has become an integral part of modern medical care and has proven to be an important tool for physiological monitoring. The COVID-19 pandemic not only highlighted the clinical utility of PO but also revealed some of the problems with the technology. Current research in biomedical optics should address these issues to make the technology even more reliable and accurate. We discuss the necessary innovations in PO and present our thoughts on what the next generation of PO might look like.

Accuracy of point-of-care testing devices for haemoglobin in the operating room: meta-analysis

BACKGROUND

Point-of-care tests (POCT) for haemoglobin are increasingly used to guide intraoperative transfusion. However, their accuracy compared to central laboratory tests is unknown. The objective was to perform a systematic review and meta-analysis of method comparison studies assessing the accuracy of POCT versus central laboratory haemoglobin tests in patients undergoing surgery.

METHODS

Electronic databases were searched from inception to April 2020 (updated August 2023). Any methodological approach comparing haemoglobin measurements between POCT and central laboratory in patients undergoing surgery under anaesthesia in the operating room were included. Data abstraction was guided by PRISMA and risk of bias was assessed by QUADAS-2. Data were extracted independently and in duplicate by two reviewers. Outcomes included mean differences between POCT and central laboratory haemoglobin with associated standard deviations and 95% limits of agreement (LOA).

RESULTS

Of 3057 citations, 34 studies were included (n = 2427, 6857 paired measurements). Several devices were compared (pulse co-oximetry, n = 25; HemoCue, n = 10; iSTAT, n = 6; blood gas analysers, n = 10; haematology analyser, n = 2). Median sample size was 41 patients, and 11 studies were funded by device manufacturers. Fifteen of 34 studies had low risk of bias. Pooled mean differences (95% LOA) were: pulse co-oximeters 2.3 g/l (-25.2-29.8), HemoCue -0.3 g/l (-11.1-10.5), iSTAT -0.3 g/l (-8.4-7.8) and blood gas analysers -2.6 g/l (-17.8-12.7).

CONCLUSION

All POCT examining intraoperative haemoglobin measurement yielded pooled mean difference LOAs larger than the allowable limit difference of ±4 g/dl. Intraoperative haemoglobin measured by POCT should not be considered interchangeable with central laboratory values and caution is necessary when using these tests to guide intraoperative transfusion.

Respiratory Monitoring During Mechanical Ventilation: The Present and the Future

The increased application of mechanical ventilation, the recognition of its harms and the interest in individualization raised the need for an effective monitoring. An increasing number of monitoring tools and modalities were introduced over the past 2 decades with growing insight into asynchrony, lung and chest wall mechanics, respiratory effort and drive. They should be used in a complementary rather than a standalone way. A sound strategy can guide a reduction in adverse effects like ventilator-induced lung injury, ventilator-induced diaphragm dysfunction, patient-ventilator asynchrony and helps early weaning from the ventilator. However, the diversity, complexity, lack of expertise, and associated cost make formulating the appropriate monitoring strategy a challenge for clinicians. Most often, a big amount of data is fed to the clinicians making interpretation difficult. Therefore, it is fundamental for intensivists to be aware of the principle, advantages, and limits of each tool. This analytic review includes a simplified narrative of the commonly used basic and advanced respiratory monitors along with their limits and future prospective.

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.

Patient monitoring in the nonoperating room anesthesia (NORA) setting: current advances in technology

PURPOSE OF REVIEW

Nonoperating room anesthesia (NORA) procedures continue to increase in type and complexity as procedural medicine makes technical advances. Patients presenting for NORA procedures are also older and sicker than ever. Commensurate with the requirements of procedural medicine, anesthetic monitoring must meet the American Society of Anesthesiologists standards for basic monitoring.

RECENT FINDINGS

There have been improvements in the required monitors that are used for intraoperative patient care. Some of these changes have been with new technologies and others have occurred with software refinements. In addition, specialized monitoring devises have also been introduced into NORA locations (depth of hypnosis, respiratory monitoring, point-of care ultrasound). These additions to the monitoring tools available to the anesthesiologist working in the NORA-environment push the boundaries of procedures which may be accomplished in this setting.

SUMMARY

NORA procedures constitute a growing percentage of total administered anesthetics. There is no difference in the monitoring standard between that of an anesthetic administered in an operating room and a NORA location. Anesthesiologists in the NORA setting must have the same compendium of monitors available as do their colleagues working in the operating suite.

Perfusion index as an objective measure of postoperative pain in children undergoing adenotonsillectomy: a cohort study

Postoperative pain in children is usually undertreated because of their inability to complain. While several pain assessment scales have been developed, they have shortcomings such as subjectivity and being observer-dependent. This study aimed to assess the validity of the perfusion index as an objective measure of postoperative pain in children undergoing adenotonsillectomy. Children aged 3-7 years were enrolled. The Children's Hospital of Eastern Ontario Scale (CHEOPS) was used to assess postoperative pain. The perfusion index was measured at the same time intervals as CHEOPS. The highest CHEOPS before rescue analgesia was administered and CHEOPS when the patients became pain-free were recorded with the corresponding perfusion index. The primary outcome was the correlation between the postoperative CHEOPS and the corresponding postoperative perfusion index. The secondary outcomes were the ability of perfusion index changes to predict the presence of postoperative pain and patients' response to analgesics. The postoperative perfusion index was negatively correlated with CHEOPS at 30 and 90 min postoperatively. The change in the preoperative baseline perfusion index (ΔPI-pre) was moderately correlated with the highest CHEOPS (CHEOPS-1) (r = 0.61, p = 0.001). The change in the postoperative perfusion index (ΔPI-po) was negatively correlated with the change in the CHEOPS (ΔCHEOPS) (r = - 0.53, P = 0.0001). The ΔPI-pre was an excellent predictor of postoperative pain (AUROC 0.83 with 71% sensitivity, 83% specificity, and a cut-off value of ≥ 0.26). The perfusion index is a good objective measure for predicting the presence of postoperative pain in children undergoing adenotonsillectomy under general anesthesia. Trial registration: ClinicalTrials.gov; ID: (NCT03854604) registered on February 2019.

The Use of Pulse Oximetry in the Assessment of Acclimatization to High Altitude

Background: Finger pulse oximeters are widely used to monitor physiological responses to high-altitude exposure, the progress of acclimatization, and/or the potential development of high-altitude related diseases. Although there is increasing evidence for its invaluable support at high altitude, some controversy remains, largely due to differences in individual preconditions, evaluation purposes, measurement methods, the use of different devices, and the lacking ability to interpret data correctly. Therefore, this review is aimed at providing information on the functioning of pulse oximeters, appropriate measurement methods and published time courses of pulse oximetry data (peripheral oxygen saturation, (SpO₂) and heart rate (HR), recorded at rest and submaximal exercise during exposure to various altitudes. Results: The presented findings from the literature review confirm rather large variations of pulse oximetry measures (SpO₂ and HR) during acute exposure and acclimatization to high altitude, related to the varying conditions between studies mentioned above. It turned out that particularly SpO₂ levels decrease with acute altitude/hypoxia exposure and partly recover during acclimatization, with an opposite trend of HR. Moreover, the development of acute mountain sickness (AMS) was consistently associated with lower SpO₂ values compared to individuals free from AMS. Conclusions: The use of finger pulse oximetry at high altitude is considered as a valuable tool in the evaluation of individual acclimatization to high altitude but also to monitor AMS progression and treatment efficacy.

A comparison of finger and forehead pulse oximeters in heart failure patients during maximal exercise

BACKGROUND

Pulse oximeters, clinically used to measure oxygen saturation (SpO₂), rely on adequate perfusion of the tissues over which they are placed. Heart failure (HF) patients can have impaired peripheral perfusion which may compromise the accuracy of a peripherally placed pulse oximeter. This decrease in peripheral perfusion may be especially apparent during exercise. The objective of this study was to determine if pulse oximeter accuracy is dependent on location in heart failure patients during peak exercise.

METHODS

20 participants with HF (7F, age 64.±11 yr) and 9 participants with coronary artery disease as controls (CAD: 3F, age 66±5 yr) performed a maximal exertion treadmill exercise stress test while wearing both finger and forehead pulse oximeters.

RESULTS

At peak exercise, the two pulse oximeters measurements of SpO₂ differed from each other by 3.8 ± 3.3% in the HF group (p<0.01) and 2.0 ± 1.4% in the CAD group (p = 0.065). The difference between the pulse rate from the pulse oximeters and the heart rate from the 12-lead ECG in the HF group was 12±20 BPM (p<0.01) for the finger pulse oximeter, and 2 ± 3 BPM (p = 0.162) for the forehead pulse oximeter.

CONCLUSIONS

Forehead pulse oximeters may be more reliable compared to finger pulse oximeters in obtaining SpO₂ measurements in HF patients during a treadmill maximal exercise test.

Comparison of invasive and noninvasive blood hemoglobin measurement in the operating room: a systematic review and meta-analysis

Noninvasive hemoglobin (Hb)-monitoring devices are new inventions in pulse oximeter systems that show hemoglobin levels continuously. The aim of this systematic review and meta-analysis was to evaluate the accuracy and precision of noninvasive versus standard central laboratory Hb measurements in the operating room. We systematically searched multiple databases. Then, for the quality assessment of studies, we modified QUADAS-2 in the Revman 5.3 software. The GRADE approach was used to measure the quality of evidence (Grading of Recommendations Assessment, Development, and Evaluation). Data were analyzed using the meta-analysis method (random effect model) using STATA 11 software. A total of 28 studies on 2000 participants were included in the meta-analysis. Meta-analysis results of mean differences between noninvasive and the central laboratory Hb measurements in overall pooled random effects were - 0.27 (95% LoA (0.44, - 0.10); P value < 0.05). According to this meta-analysis, noninvasive hemoglobin measurement has acceptable accuracy in comparison with the standard invasive method.

Sleep-disordered breathing in hospitalized patients with congestive heart failure: a concise review and proposed algorithm

Congestive heart failure (CHF) is the most common cause of hospital admission in the USA costing the taxpayers billions of dollars. Sleep-disordered breathing (SDB) is a common co-morbid condition associated with CHF with prevalence estimated to be 60-70%. Despite substantial evidence supporting the negative impact of SDB on CHF, the condition is underrecognized and undertreated. Patients admitted to the hospital with CHF and SDB are prime candidates for intervention with positive airway pressure (PAP) therapy as they form a "captive audience," and timely intervention and education may mitigate sub-optimal outcomes. In conclusion, this review explores emerging data on the cost effectiveness and outcome of early intervention with PAP in hospitalized CHF patients.

Clinical prediction rule to predict pneumonia in adult presented with acute febrile respiratory illness

OBJECTIVE

To derive a clinical prediction rule to predict pneumonia in patients with acute febrile respiratory illness to emergency departments.

METHOD

This was a prospective multicentre study. 537 adults were recruited. Those requiring resuscitation or were hypoxaemic on presentation were excluded. Pneumonia was defined as new onset infiltrates on chest X-ray (CXR), or re-attendance within 7 days and diagnosed clinically as having pneumonia. A predictive model, the Acute Febrile Respiratory Illness (AFRI) rule was derived by logistic regression analysis based on clinical parameters. The AFRI rule was internally validated with bootstrap resampling and was compared with the Diehr and Heckerling rule.

RESULTS

In the 363 patients who underwent CXR, 100 had CXR confirmed pneumonia. There were 7 weighted factors within the ARFI rule, which on summation, gave the AFRI score: age ≥ 65 (1 point), peak temperature within 24 h ≥ 40 °C (2 points), fever duration ≥3 days (2 points), sore throat (-2 points), abnormal breath sounds (1 point), history of pneumonia (1 point) and SpO2 ≤ 96% (1 point). With the bootstrap resampling, the AFRI rule was found to be more accurate than the Diehr and Heckerling rule (area under ROC curve 0.816, 0.721 and 0.566 respectively, p < 0.001). At a cut-off of AFRI≥0, the rule was found to have 95% sensitivity, with a negative predictive value of 97.2%. Using the AFRI score, we found CXR could be avoided for patients having a score of <0.

CONCLUSION

AFRI score could assist emergency physicians in identifying pneumonia patients among all adult patients presented to ED for acute febrile respiratory illness.

Continuous noninvasive monitoring in the neonatal ICU

PURPOSE OF REVIEW

Standard hemodynamic monitoring such as heart rate and systemic blood pressure may only provide a crude estimation of organ perfusion during neonatal intensive care. Pulse oximetry monitoring allows for continuous noninvasive monitoring of hemoglobin oxygenation and thus provides estimation of end-organ oxygenation. This review aims to provide an overview of pulse oximetry and discuss its current and potential clinical use during neonatal intensive care.

RECENT FINDINGS

Technological advances in continuous assessment of dynamic changes in systemic oxygenation with pulse oximetry during transition to extrauterine life and beyond provide additional details about physiological interactions among the key hemodynamic factors regulating systemic blood flow distribution along with the subtle changes that are frequently transient and undetectable with standard monitoring.

SUMMARY

Noninvasive real-time continuous systemic oxygen monitoring has the potential to serve as biomarkers for early-organ dysfunction, to predict adverse short-term and long-term outcomes in critically ill neonates, and to optimize outcomes. Further studies are needed to establish values predicting adverse outcomes and to validate targeted interventions to normalize abnormal values to improve outcomes.

Photoplethysmographic Signal to Screen Sleep-Disordered Breathing in Hospitalized Heart Failure Patients: Feasibility of a Prospective Clinical Pathway

OBJECTIVES

The purpose of this study was to evaluate the plethysmographic signal-derived oxygen desaturation index (ODI) as an inpatient screening strategy to identify sleep-disordered breathing (SDB) in patients with congestive heart failure (CHF).

BACKGROUND

SDB is highly prevalent among patients hospitalized with CHF but is widely underdiagnosed. We evaluated overnight photoplethysmography as a possible screening strategy for hospitalized patients with CHF.

METHODS

Consecutively admitted heart failure patients with high clinical suspicion of SDB and ODI ≥5 were offered outpatient polysomnography (PSG), which was completed within 4 weeks of discharge. PSG was considered positive if the apnea hypoxia index (AHI) was ≥5. A Bland-Altman plot was used to assess agreement between ODI and AHI. Receiver-operator characteristics were determined for ODI ≥5 and AHI ≥5.

RESULTS

A screening questionnaire identified 246 of 282 consecutive patients with positive symptoms for SDB. Of these patients, 105 patients were offered further evaluation and 86 had ODI ≥5 (mean ODI 17 ± 17). Among these 86 patients, 68 underwent outpatient PSG within 4 weeks of discharge. PSG showed that 64 (94%) had SDB, with a mean AHI of 28. Inpatient ODI correlated well with PSG-derived AHI. The area under the curve was 0.82 for AHI ≥5. The Bland-Altman plot revealed no major bias. Matthew's correlation coefficient revealed that the optimal cut-off for ODI is 5.

CONCLUSIONS

Screening hospitalized patients with heart failure using targeted inpatient ODI identifies a cohort of patients with a high prevalence of SDB. Our screening strategy provides a potentially cost-effective method for early detection and treatment of SDB.

Lock-in amplification for implantable multiwavelength pulse oximeters

Standard as well as multiwavelength pulse oximetry as established methods for measuring blood oxygen saturation or fractions of dyshemoglobins suffer from different kinds of interference and noise. Employing lock-in technique as a read-out approach for multiwavelength pulse oximetry is proposed here and strongly decreases such signal disturbance. An analog lock-in amplifier was designed to modulate multiple LEDs simultaneously and to separate the signals detected by a single photodiode. In vivo measurements show an improved signal-to-noise ratio of photoplethysmographic signals and a suppression of interference by means of the lock-in approach. This allows the detection of higher order overtones and, therefore, more detailed data for pulse wave analysis, especially for implantable sensors directly applied at arteries.

Pulse oximetry: fundamentals and technology update

Oxygen saturation in the arterial blood (SaO₂) provides information on the adequacy of respiratory function. SaO₂ can be assessed noninvasively by pulse oximetry, which is based on photoplethysmographic pulses in two wavelengths, generally in the red and infrared regions. The calibration of the measured photoplethysmographic signals is performed empirically for each type of commercial pulse-oximeter sensor, utilizing in vitro measurement of SaO₂ in extracted arterial blood by means of co-oximetry. Due to the discrepancy between the measurement of SaO₂ by pulse oximetry and the invasive technique, the former is denoted as SpO₂. Manufacturers of pulse oximeters generally claim an accuracy of 2%, evaluated by the standard deviation (SD) of the differences between SpO₂ and SaO₂, measured simultaneously in healthy subjects. However, an SD of 2% reflects an expected error of 4% (two SDs) or more in 5% of the examinations, which is in accordance with an error of 3%–4%, reported in clinical studies. This level of accuracy is sufficient for the detection of a significant decline in respiratory function in patients, and pulse oximetry has been accepted as a reliable technique for that purpose. The accuracy of SpO₂ measurement is insufficient in several situations, such as critically ill patients receiving supplemental oxygen, and can be hazardous if it leads to elevated values of oxygen partial pressure in blood. In particular, preterm newborns are vulnerable to retinopathy of prematurity induced by high oxygen concentration in the blood. The low accuracy of SpO₂ measurement in critically ill patients and newborns can be attributed to the empirical calibration process, which is performed on healthy volunteers. Other limitations of pulse oximetry include the presence of dyshemoglobins, which has been addressed by multiwavelength pulse oximetry, as well as low perfusion and motion artifacts that are partially rectified by sophisticated algorithms and also by reflection pulse oximetry.

Noninvasive monitoring by photoplethysmography

The photoplethysmogram (PPG) is a noninvasive circulatory signal related to the pulsatile volume in tissue and is displayed by many pulse oximeters. The PPG is similar in appearance to the invasive arterial waveform, but is noninvasive and ubiquitous in hospitals. There is increasing interest in seeking circulatory information from the PPG and developing techniques for a wide variety of novel applications. This article addresses the basic physics of photoplethysmography, physiologic principles behind pulse oximetry operation, and recent technological advances in the usefulness of the PPG waveform to assess microcirculation and intravascular fluid volume monitoring during intensive care.

Wavelength selection method with standard deviation: application to pulse oximetry

Near-infrared spectroscopy provides useful biological information after the radiation has penetrated through the tissue, within the therapeutic window. One of the significant shortcomings of the current applications of spectroscopic techniques to a live subject is that the subject may be uncooperative and the sample undergoes significant temporal variations, due to his health status that, from radiometric point of view, introduce measurement noise. We describe a novel wavelength selection method for monitoring, based on a standard deviation map, that allows low-noise sensitivity. It may be used with spectral transillumination, transmission, or reflection signals, including those corrupted by noise and unavoidable temporal effects. We apply it to the selection of two wavelengths for the case of pulse oximetry. Using spectroscopic data, we generate a map of standard deviation that we propose as a figure-of-merit in the presence of the noise introduced by the living subject. Even in the presence of diverse sources of noise, we identify four wavelength domains with standard deviation, minimally sensitive to temporal noise, and two wavelengths domains with low sensitivity to temporal noise.