Decreased accuracy of pulse oximetry measurements during low perfusion caused by sepsis: Is the perfusion index of any value?

Randomised crossover study on pulse oximeter readings from different sensors in very preterm infants

OBJECTIVE

In extremely preterm infants, different target ranges for pulse oximeter saturation (SpO2) may affect mortality and morbidity. Thus, the impact of technical changes potentially affecting measurements should be assessed. We studied SpO2 readings from different sensors for systematic deviations.

DESIGN

Single-centre, randomised, triple crossover study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

24 infants, born at <32 weeks' gestation, with current weight <1500 g and without right-to-left shunt via a patent ductus arteriosus.

INTERVENTIONS

Simultaneous readings from three SpO2 sensors (Red Diamond (RD), Photoplethysmography (PPG), Low Noise Cabled Sensors (LNCS)) were logged at 0.5 Hz over 6 hour/infant and compared with LNCS as control using analysis of variance. Sensor position was randomly allocated and rotated every 2 hours. Seven different batches each were used.

OUTCOMES

Primary outcome was the difference in SpO2 readings. Secondary outcomes were differences between sensors in the proportion of time within the SpO2-target range (90-95 (100)%).

RESULTS

Mean gestational age at birth (±SD) was 274/7 (±23/7) weeks, postnatal age 20 (±20) days. 134 hours of recording were analysed. Mean SpO2 (±SD) was 94.0% (±3.8; LNCS) versus 92.2% (±4.0; RD; p<0.0001) and 94.5% (±3.9; PPG; p<0.0001), respectively. Mean SpO2 difference (95% CI) was -1.8% (-1.9 to -1.8; RD) and 0.5% (0.4 to 0.5; PPG). Proportion of time in target was significantly lower with RD sensors (84.8% vs 91.7%; p=0.0001) and similar with PPG sensors (91.1% vs 91.7%; p=0.63).

CONCLUSION

There were systematic differences in SpO2 readings between RD sensors versus LNCS. These findings may impact mortality and morbidity of preterm infants, particularly when aiming for higher SpO2-target ranges (eg, 90-95%).

TRIAL REGISTRATION NUMBER

DRKS00027285.

Reflection-Boosted Wearable Ring-Type Pulse Oximeters for SpO2 Measurement with High Sensitivity and Low Power Consumption

In this study, we demonstrated a Monte Carlo simulation to model a finger structure and to calculate the intensity of photons passing through tissues, in order to determine optimal angular separation between a photodetector (PD) and a light-emitting diode (LED), to detect SpO₂. Furthermore, our model was used to suggest a mirror-coated ring-type pulse oximeter to improve the sensitivity by up to 80% and improve power consumption by up to 65% compared to the mirror-uncoated structure. A ring-type pulse oximeter (RPO) is widely used to detect photoplethysmography (PPG) signals for SpO₂ measurement during sleep and health-status monitoring. Device sensitivity and the power consumption of an RPO, which are key performance indicators, vary greatly with the geometrical arrangement of PD and LED within the inner surface of an RPO. We propose a reflection-boosted design of an RPO to achieve both high sensitivity and low power consumption, and determine an optimal configuration of a PD and LED by performing a 3D Monte Carlo simulation and confirming its agreement with experimental measurement. In order to confirm the reflection-boosted performance in terms of signal-to-noise ratio, R ratio, and perfusion index (PI), RPOs were fabricated with and without a highly reflective coating, and then used for SpO₂ measurement from eight participants. Our simulation allows the numerical calculation of the intensity of photon passing and scattering through finger tissues. The reflection-boosted RPO enables reliable measurement with high sensitivity, resulting in less power consumption for the LED and longer device usage than conventional RPOs without any reflective coating, in order to maintain the same level of SNR and PI. Compared to the non-reflective reference RPO, the reflection-boosted RPO design greatly enhanced both detected light intensity (67% in dc and 322% in ac signals at a wavelength λ₁ = 660 nm, and also 81% and 375% at λ₂ = 940 nm, respectively) and PI (23.3% at λ₁ and 25.5% at λ₂). Thus, the reflection-boosted design not only enhanced measurement reliability but also significantly improved power consumption, i.e., by requiring only 36% and 30% power to drive the LED sources with λ₁ and λ₂, respectively, to produce the device performance of a non-reflective RPO reference. It is expected that our proposed RPO provides long-term monitoring capability with low power consumption and an enhanced PI for SpO₂ measurement.

Oropharyngeal and Tongue Pulse Oximetry in 2 Critically Ill Pediatric Patients: A Case Report

Pulse oximetry has become a standard of care to monitor oxygenation. Absent or inaccurate readings can occur with varied patient states. We present preliminary experience with a modification of a standard pulse oximetry using readily available equipment (oral airway and a tongue blade) to allow for continuous pulse oximetry from the oral cavity and tongue in 2 critically ill pediatric patients when standard application of pulse oximetry was not feasible or nonfunctional. These modifications can assist in the care of critically ill patients, allowing for adaptability in monitoring techniques when other options are unavailable.

Photoplethysmogram Analysis and Applications: An Integrative Review

Beyond its use in a clinical environment, photoplethysmogram (PPG) is increasingly used for measuring the physiological state of an individual in daily life. This review aims to examine existing research on photoplethysmogram concerning its generation mechanisms, measurement principles, clinical applications, noise definition, pre-processing techniques, feature detection techniques, and post-processing techniques for photoplethysmogram processing, especially from an engineering point of view. We performed an extensive search with the PubMed, Google Scholar, Institute of Electrical and Electronics Engineers (IEEE), ScienceDirect, and Web of Science databases. Exclusion conditions did not include the year of publication, but articles not published in English were excluded. Based on 118 articles, we identified four main topics of enabling PPG: (A) PPG waveform, (B) PPG features and clinical applications including basic features based on the original PPG waveform, combined features of PPG, and derivative features of PPG, (C) PPG noise including motion artifact baseline wandering and hypoperfusion, and (D) PPG signal processing including PPG preprocessing, PPG peak detection, and signal quality index. The application field of photoplethysmogram has been extending from the clinical to the mobile environment. Although there is no standardized pre-processing pipeline for PPG signal processing, as PPG data are acquired and accumulated in various ways, the recently proposed machine learning-based method is expected to offer a promising solution.

Monitoring free flaps and replanted digits via perfusion index -A proof of concept study

BACKGROUND

Early detection and treatment of vascular complications in replanted digits is essential for the survival. The perfusion index (PI) represents a marker of peripheral perfusion as it shows the ratio of pulsatile to non-pulsatile blood flow.

OBJECTIVE

To evaluate the feasibility and applicability of the PI as a monitoring tool for free flaps and replanted digits by measuring the inter- and intraindividual changes in PI.

METHODS

Five patients were postoperatively monitored according to intern standards by hourly clinical evaluation. Additionally, a pulse oximeter with SET-technology® (Masimo Radial 7, Masimo Corporation, Irvine, USA) was added with a LNCS® Red TFA-1 SpO2 sensor (Masimo Corporation, Irvine, USA) and respectively a LNCS® Neo-3 neonatal finger clip to evaluate the perfusion via PI and SpO2.

RESULTS

All patients showed sufficient perfusion in clinical controls. There was no detectable vascular complication during follow-up. Mean perfusion index was 0.93 with a median of 0.44. The patients showed a mean SpO2 of 90.59%with a median of 89.21%.

CONCLUSION

Our results show a great intra- and interindividual range of PI and SpO2. SpO2 provided an even greater range than PI. Trends in intraindividual PI changes may be a promising monitoring tool for free flaps and replanted digits.

A Cloud-Based Smartphone Solution for Transmitting Bio-Signals From an Emergency Response Vehicle

Most developing countries are currently unable to provide adequate, let alone advanced healthcare support to rural areas. Telemedicine combines the capability of information technology and dedicated people working towards the common goal of providing good quality healthcare in remote areas. In this article, the authors propose a system that can be used to transmit patient vitals like pulse rate, oxygen saturation, and perfusion index readings to a doctor in a remote area, while a patient is in transit. This system uses a smartphone application, a pulse oximeter, and the real-time data transferring capabilities of Firebase (a cloud database). The application has been tested under various network conditions which includes connection types such as 2G (2nd Generation), 3G (3rd Generation), 4G (4th Generation), and Fiber To The Home (FTTH). The work also discusses the possible reasons for the higher performance found in 4G networks over 3G and 2G cellular connections.

Four Types of Pulse Oximeters Accurately Detect Hypoxia during Low Perfusion and Motion

Background

Pulse oximeter performance is degraded by motion artifacts and low perfusion. Manufacturers developed algorithms to improve instrument performance during these challenges. There have been no independent comparisons of these devices.

Methods

We evaluated the performance of four pulse oximeters (Masimo Radical-7, USA; Nihon Kohden OxyPal Neo, Japan; Nellcor N-600, USA; and Philips Intellivue MP5, USA) in 10 healthy adult volunteers. Three motions were evaluated: tapping, pseudorandom, and volunteer-generated rubbing, adjusted to produce photoplethsmogram disturbance similar to arterial pulsation amplitude. During motion, inspired gases were adjusted to achieve stable target plateaus of arterial oxygen saturation (SaO2) at 75%, 88%, and 100%. Pulse oximeter readings were compared with simultaneous arterial blood samples to calculate bias (oxygen saturation measured by pulse oximetry [SpO2] − SaO2), mean, SD, 95% limits of agreement, and root mean square error. Receiver operating characteristic curves were determined to detect mild (SaO2 &lt; 90%) and severe (SaO2 &lt; 80%) hypoxemia.

Results

Pulse oximeter readings corresponding to 190 blood samples were analyzed. All oximeters detected hypoxia but motion and low perfusion degraded performance. Three of four oximeters (Masimo, Nellcor, and Philips) had root mean square error greater than 3% for SaO2 70 to 100% during any motion, compared to a root mean square error of 1.8% for the stationary control. A low perfusion index increased error.

Conclusions

All oximeters detected hypoxemia during motion and low-perfusion conditions, but motion impaired performance at all ranges, with less accuracy at lower SaO2. Lower perfusion degraded performance in all but the Nihon Kohden instrument. We conclude that different types of pulse oximeters can be similarly effective in preserving sensitivity to clinically relevant hypoxia.

A Retrospective Analysis of Oxygen Desaturation during Acoustic Respiratory Rate Monitoring in Non-ICU Patients following Tracheal Extubation after General Anesthesia

Purpose. Acoustic respiratory rate (RRa) monitoring provides an accurate estimation of the respiratory rate (RR). We investigated the incidence of oxygen desaturation under RRa monitoring in a postoperative setting and identified its related factors. Methods. This study was a retrospective chart review of postoperative patients outside an intensive care unit setting. Using the data collected during the first 8 h postoperatively, patients were divided into oxygen desaturated (SpO₂ < 90% for >10 s) and nondesaturated groups under oxygen administration. Multivariate analysis was used to determine oxygen desaturation-associated explanatory factors. Results. Oxygen desaturation was detected in 102 of 935 patients (10.9%). % vital capacity [odds ratio (OR), 0.885 per 10% increase; 95% confidence interval (CI), 0.790 to 0.992], coexisting chronic obstructive pulmonary disease (OR, 2.195; 95% CI, 1.088 to 4.428), and absence of a critical RRa change (RR > 30 or <8 beats/min for >2 min) (OR, 1.972; 95% CI, 1.226 to 3.172) were independently associated with oxygen desaturation. Conclusion. Postoperative oxygen desaturation was observed in more than 10% of the patients whose RR was monitored by RRa under oxygen therapy. It is more likely to occur in patients with impaired pulmonary function or morbid pulmonary status and can also occur in the absence of abnormal RR.

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.

Perfusion index assessment during transition period of newborns: an observational study

Background

Perfusion index (PI) is becoming a part of clinical practice in neonatology to monitor peripheral perfusion noninvasively. Hemodynamic and respiratory changes occur in newborns during the transition period after birth in which peripheral perfusion may be affected. Tachypnea is a frequent symptom during this period. While some tachypneic newborns get well in less than 6 h and diagnosed as “delayed transition”, others get admitted to intensive care unit which transient tachypnea of newborn (TTN) being the most common diagnosis among them. We aimed to compare PI of neonates with TTN and delayed transition with controls, and assess its value on discrimination of delayed transition and TTN.

Methods

Neonates with gestational age between 37 and 40 weeks who were born with elective caesarian section were included. Eligible neonates were monitored with Masimo Set Radical7 pulse-oximeter (Masimo Corp., Irvine, CA, USA). Postductal PI, oxygen saturation and heart rate were manually recorded every 10 s for 3 min for two defined time periods as 10^th minute and 1^st hour. Axillary temperature were also recorded. Newborn infants were grouped as control, delayed transition, and TTN.

Results

Forty-nine tachypneic (TTN; 21, delayed transition; 28) and 30 healthy neonates completed the study. PI values were similar between three groups at both periods. There were no correlation between PI and respiratory rate, heart rate, and temperature.

Conclusion

PI assessment in maternity unit does not discriminate TTN from delayed transitional period in newborns which may indicate that peripheral perfusion is not severely affected in either condition.

Using skin for drug delivery and diagnosis in the critically ill

Skin offers easy access, convenience and non-invasiveness for drug delivery and diagnosis. In principle, these advantages of skin appear to be attractive for critically ill patients given potential difficulties that may be associated with oral and parenteral access in these patients. However, the profound changes in skin physiology that can be seen in these patients provide a challenge to reliably deliver drugs or provide diagnostic information. Drug delivery through skin may be used to manage burn injury, wounds, infection, trauma and the multisystem complications that rise from these conditions. Local anaesthetics and analgesics can be delivered through skin and may have wide application in critically ill patients. To ensure accurate information, diagnostic tools require validation in the critically ill patient population as information from other patient populations may not be applicable.

Evaluating Innovative In-Ear Pulse Oximetry for Unobtrusive Cardiovascular and Pulmonary Monitoring During Sleep

Homecare is healthcare based on the principle "outpatient before inpatient," with the aim of moving at least some care-delivery to the home. But reliable determination of vital signs at home requires new, smart sensors, which can be used by the patients themselves. We present a novel pulse oximetry sensor worn in the ear channel. It was previously shown that measurement of heart rate, arterial oxygen saturation and related respiratory information can be performed with reliable accuracy under laboratory conditions. The present study explores the clinical feasibility of the sensor system for cardiovascular monitoring during sleep, with the aim to diagnose sleep apnea. For this, human trials were performed in a sleep laboratory including patients with a clinical suspicion of sleep apnea. Besides a general analysis of the sensor's signal quality during sleep, the evaluation focuses on heart rate dynamics and time-variant oxygen saturation. In addition, several methods to derive respiration rate from photoplethysmographic signals are examined and discussed. Results from the in-ear sensor are compared with standard polysomnography monitoring and demonstrate that this novel system allows long-term nocturnal measurement of heart rate, oxygen saturation and respiratory rate with sufficient accuracy.

Perfusion index versus non-invasive hemodynamic parameters during insertion of i-gel, classic laryngeal mask airway and endotracheal tube

Background:

Perfusion index (PI) is a non-invasive numerical value of peripheral perfusion obtained from a pulse oximeter. In this study, we evaluated the efficacy of PI for detecting haemodynamic stress responses to insertion of i-gel, laryngeal mask airway (LMA) and endotracheal tube and compare, its reliability with the conventional haemodynamic criteria in adults during general anaesthesia.

Methods:

Sixty patients scheduled for elective general surgery under general anaesthesia were randomised to three groups. (i-gel, LMA and ET groups (n=20/group). Heart rate (HR) (positive if ≥10 bpm), systolic blood pressure (SBP), diastolic blood pressure (DBP) (positive if ≥15 mm Hg) and PI (positive if ≤10%) were monitored for 5 min after insertion. Main outcome measures: SBP, DBP, HR and PI were measured before induction of anaesthesia and before and after insertion of the airway device.

Results:

Insertion of airway devices produced significant increases in HR, SBP and DBP in LMA and ET groups. Moreover, PI was decreased significantly by 40%, 100% and 100% in the three groups. Using the PI criterion, the sensitivity was 100% (CI 82.4-100.0%). Regarding the SBP and DBP criterions, the sensitivity was 44.4% (CI 24.6-66.3%), 55.6% (CI 33.7-75.4%) respectively. Also, significant change in the mean PI over time (from pre-insertion value to the 1^st min, 3^rd min, until the 4^th min after insertion without regard the device type), (P<0.001).

Conclusion:

PI is a reliable and easier alternative to conventional haemodynamic criteria for detection of stress response to insertion of i-gel, LMA and ET during propofol fentanyl isoflurane anaesthesia in adult patients.

Evaluation of Masimo signal extraction technology pulse oximetry in anaesthetized pregnant sheep

OBJECTIVE

Evaluation of the accuracy of Masimo signal extraction technology (SET) pulse oximetry in anaesthetized late gestational pregnant sheep.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Seventeen pregnant Merino ewes.

METHODS

Animals included in study were late gestation ewes undergoing general anaesthesia for Caesarean delivery or foetal surgery in a medical research laboratory. Masimo Radical-7 pulse oximetry (SpO(2) ) measurements were compared to co-oximetry (SaO(2) ) measurements from arterial blood gas analyses. The failure rate of the pulse oximeter was calculated. Accuracy was assessed by Bland & Altman's (2007) limits of agreement method. The effect of mean arterial blood pressure (MAP), perfusion index (PI) and haemoglobin (Hb) concentration on accuracy were assessed by regression analysis.

RESULTS

Forty arterial blood samples paired with SpO(2) and blood pressure measurements were obtained. SpO(2) ranged from 42 to 99% and SaO(2) from 43.7 to 99.9%. MAP ranged from 24 to 82 mmHg, PI from 0.1 to 1.56 and Hb concentration from 71 to 114 g L(-1) . Masimo pulse oximetry measurements tended to underestimate oxyhaemoglobin saturation compared to co-oximetry with a bias (mean difference) of -2% and precision (standard deviation of the differences) of 6%. Accuracy appeared to decrease when SpO(2) was <75%, however numbers were too small for statistical comparisons. Hb concentration and PI had no significant effect on accuracy, whereas MAP was negatively correlated with SpO(2) bias.

CONCLUSIONS AND CLINICAL RELEVANCE

Masimo SET pulse oximetry can provide reliable and continuous monitoring of arterial oxyhaemoglobin saturation in anaesthetized pregnant sheep during clinically relevant levels of cardiopulmonary dysfunction. Further work is needed to assess pulse oximeter function during extreme hypotension and hypoxaemia.

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.

Comparison of S(+)-ketamine and ketamine, with medetomidine, for field anaesthesia in the European brown hare (Lepus europaeus)

OBJECTIVE

To compare anaesthesia and recovery parameters of racemic ketamine or S(+)-ketamine in combination with medetomidine for intramuscular (IM) field anaesthesia in the European brown hare (EBH) (Lepus europaeus).

STUDY DESIGN

Randomized, prospective, blinded clinical trial.

ANIMALS

20 adult EBH (eight male, 12 female), mean ± SD weight 3360 341).

METHODS

Medetomidine (0.2 mg kg(-1) ) and ketamine (30 mg kg(-1) ) (K-M group) or S(+)-ketamine (15 mg kg(-1) ) (S-M group) were administered by IM injection. Time until first effect and loss of righting reflex were recorded. During sedation and anaesthesia heart rate, saturation of arterial haemoglobin, respiratory rate, side stream end tidal CO(2) (Pe'CO(2) ), non invasive blood pressure, body temperature, cardiorespiratory parameters, palpebral reflex, jaw tone and nociception were recorded every 5 minutes. Medetomidine was antagonized with IM atipamezole (1 mg kg(-1) ) 45 minutes after treatment injection. Time until first head lift, standing and total recovery time (T-Recov) were recorded. Incidences of falling and involuntary movements during recovery were counted. Recovery quality was scored by visual analogue scale. Descriptive statistics were used to visualize maintenance data. All other data were included in multiple linear regression models.

RESULTS

Surgical anesthesia was not produced reliably with either protocol. Hypoxaemia occurred in both groups (SpO(2) < 90%). During recovery, falling was noted significantly less often (p < 0.001) in the S-M group (13 ± 7) versus the K-M group (27 ± 13). T-Recov was long, lasting for more than 3 hours in individuals with no significant differences between groups.

CONCLUSION AND CLINICAL RELEVANCE

S(+)-ketamine showed only minor advantages over racemic ketamine. Surgical anaesthesia was not achieved reliably with either protocol. Oxygen supplementation should be considered to prevent hypoxaemia. Further research is needed to develop an injectable field protocol adequate for surgical procedures, but with a rapid smooth recovery.

Utility of digital pulse oximetry in the screening of lower extremity arterial disease

Purpose

The aim of this study was to evaluate screening methods in the lower extremities by measurement of the digital pulse oximetry (oxygen percent saturation [SpO₂]) of toes for peripheral arterial disease (PAD).

Methods

A prospective study was performed among 49 patients (98 limbs) with lower extremity arterial occlusive disease. We attempted to measure the ankle-brachial index (ABI), digital pulse oximetry (SpO₂), and computerized tomographic angiography (CTA). Patients were divided into three groups by the traditional Fontaine classification system by symptom and CTA criteria: 1) Critical limb ischemia (Fontaine III and IV), 2) Claudication; (Fontaine II), and 3) asymptomatic limbs (Fontaine I).

Results

The sensitivity, specificity, positive and negative predictive values between active treatment groups (group I and II; endovascular and open surgery) and conservative group (group III) are all statistically significant. ABI; 55.09%, 94%, 96.7%, 39.02% (R = 12.54, P < 0.000) SpO₂; 87.06%, 87.8%, 84.3%, 90% (R = 40.11, P < 0.000). Pre-SpO₂ and pre-ABI all show statistically significant correlation in group I vs. group II, symptomatic PAD (group I and II) vs. asymptomatic PAD (group III), and the total PAD comparison. The Pearson's correlation coefficient between SpO₂ and ABI all show significant correlation in group II. Pre-SpO₂ vs. Pre-ABI show strong positive correlation except asymptomatic group (group III).

Conclusion

Digital pulse oximetry can be a useful, simple, noninvasive screening device as well as ABI in PAD.

Pulse oximetry in pediatric practice

The introduction of pulse oximetry in clinical practice has allowed for simple, noninvasive, and reasonably accurate estimation of arterial oxygen saturation. Pulse oximetry is routinely used in the emergency department, the pediatric ward, and in pediatric intensive and perioperative care. However, clinically relevant principles and inherent limitations of the method are not always well understood by health care professionals caring for children. The calculation of the percentage of arterial oxyhemoglobin is based on the distinct characteristics of light absorption in the red and infrared spectra by oxygenated versus deoxygenated hemoglobin and takes advantage of the variation in light absorption caused by the pulsatility of arterial blood. Computation of oxygen saturation is achieved with the use of calibration algorithms. Safe use of pulse oximetry requires knowledge of its limitations, which include motion artifacts, poor perfusion at the site of measurement, irregular rhythms, ambient light or electromagnetic interference, skin pigmentation, nail polish, calibration assumptions, probe positioning, time lag in detecting hypoxic events, venous pulsation, intravenous dyes, and presence of abnormal hemoglobin molecules. In this review we describe the physiologic principles and limitations of pulse oximetry, discuss normal values, and highlight its importance in common pediatric diseases, in which the principle mechanism of hypoxemia is ventilation/perfusion mismatch (eg, asthma exacerbation, acute bronchiolitis, pneumonia) versus hypoventilation (eg, laryngotracheitis, vocal cord dysfunction, foreign-body aspiration in the larynx or trachea). Additional technologic advancements in pulse oximetry and its incorporation into evidence-based clinical algorithms will improve the efficiency of the method in daily pediatric practice.

Recent advances in pulse oximetry

Conventional pulse oximetry uses two wavelengths of light (red and infrared) transmitted through a finger and a photodetector to analyze arterial hemoglobin oxygen saturation and pulse rate. Recent advances in pulse oximetry include: extended analysis of the photo plethysmographic waveform; use of multiple wavelengths of light to quantify methemoglobin, carboxyhemoglobin and total hemoglobin content in blood; and use of electronic processes to improve pulse oximeter signal processing during conditions of low signal-to-noise ratio. These advances have opened new clinical applications for pulse oximeters that will have an impact on patient monitoring and management.

In-ear heart rate monitoring using a micro-optic reflective sensor

Cardiovascular diseases are among the most common causes of death in western industrial nations. It is of great interest of both physician and patient to determine the cardiovascular risk factors early in order to take preventive measures. To assist the recognition of irregularities in a subject's cardiovascular system, we develop an optic 24/7 inear monitoring system (IN-MONIT). The central component is a micro-optic remission/reflection sensor (MORES), which is placed inside the auditory canal. There the pulsation of blood within the capillaries is measured by means of optical absorption. From the resulting photoplethysmographic curves (pulse plethysmogram, PPG), the heart rate, oxygen saturation (SpO2), respiratory rate and higher order moments can be derived. The optical absorption data are processed locally using a microcontroller and the results are transferred wirelessly to a personal digital assistant (PDA) or PC for sophisticated classification. This paper introduces the IN-MONIT system and two algorithms for heart rate determination from ECG or PPG data. The performance of these algorithms was tested using annotated ECG data from the "MIT-BIH Normal Sinus Rhythm Database", synchronously recorded ECG and pulse oximeter data, and data acquired by the MORES sensor.

Maximizing the laboratory setting for testing devices and understanding statistical output in pulse oximetry

Maximizing the laboratory setting for testing baseline pulse oximetry accuracy in an arterial desaturation study requires a study design that considers management of several aspects in the physiology of the test subject, special attention to the device under test, and great care in the preanalytical (sample handling) and analytical (Co-oximeter) phases. Statistics used to describe the resulting SpO2 performance include Precision (size of the data cloud), Bias (offset of the data cloud), and A(rms) (accuracy root mean square), which combines the size and offset of the data cloud in one number. The A(rms) is the primary statistic required by regulatory organizations to describe general performance over the entire saturation range. It does not describe any one point, but is a compilation of all points over the range tested. Most pulse oximeters in use today specify an A(rms) of 2%. To meet this specification, two-thirds of the readings will be within 2% of the Co-oximeter reference; however, some individual readings can be as inaccurate as 6% or more. The A(rms) statistic does not have the capacity to represent all pulse oximeter behavior. Saturation pop-ups, drop-downs, frozen readings, and periods of no reading are not portrayed by the A(rms). The next steps in the advancement of regulatory validation testing would be to develop standards that include an expanded analysis of pulse oximeter performance by assessment of pop-ups, dropouts, frozen readings, and periods of no reading through assessment of sensitivity/specificity and possibly a "Performance Index" similar to the approach taken by Barker.