Preoxygenation and pulse oximetry may delay detection of esophageal intubation

A case of delayed detection of esophageal intubation is described. Preoxygenation and pulse oximetry were used, and the first indication of tube misplacement was arterial desaturation indicated by the pulse oximeter. The combination of preoxygenation and pulse oximetry may contribute to delays in early detection of endotracheal tube misplacement for the following reasons: (1) preoxygenation results in a pulmonary reservoir of oxygen sufficient to maintain arterial hemoglobin saturation for an extended period of time; and (2) the maintenance of normal arterial saturations for an extended period after inadvertent esophageal tube placement may lead the practitioner to initially seek other causes of declining oxygen saturations. Although pulse oximetry is an acknowledged advance in patient monitoring, it must not be utilized as an early indication of correct endotracheal tube placement.     

Pulse oximetry in the pulmonary tissue for the non-invasive measurement of mixed venous oxygen saturation

The oxygen saturation of the systemic arterial blood is associated with the adequacy of respiration, and can be measured non-invasively by pulse oximetry in the systemic tissue. The oxygen saturation of the blood in the pulmonary artery, the mixed venous blood, reflects the balance between oxygen supply to the systemic tissues and their oxygen demand. The mixed venous oxygen saturation has also clinical significance because it is used in Fick equation for the quantitative measurement of cardiac output. At present the measurement of the mixed venous oxygen saturation is invasive and requires insertion of a Swan-Ganz catheter into the pulmonary artery. We suggest a noninvasive method for the measurement of the mixed venous oxygen saturation in infants, pulmonary pulse oximetry. The method is similar to the systemic pulse oximetry, which is based on the different light absorption curves of oxygenated and deoxygenated hemoglobin and on the analysis of photoplethysmographic curves in two wavelengths.     

Trans-abdominal monitoring of fetal arterial blood oxygenation using pulse oximetry

Pulse oximetry (oxygen saturation monitoring) has markedly improved medical care in many fields, including anesthesiology, intensive care, and newborn intensive care. In obstetrics, fetal heart rate monitoring remains the standard for intrapartum assessment of fetal well being. Fetal oxygen saturation monitoring is a new technique currently under development. It is potentially superior to electronic fetal heart rate monitoring (cardiotocography) because it allows direct assessment of both the fetal oxygen status and fetal tissue perfusion. Here we present the analysis for determining the most optimal wavelength selection for pulse oximetry. The wavelengths we chose as the most optimal are the first in the range of 670-720 nm and the second in the range of 825-925 nm. Further, we discuss the possible systematic errors during our measurements and their contribution to the obtained saturation results. We present feasibility studies for fetal pulse oximetry, monitored noninvasively through the maternal abdomen. Our preliminary experiments show that the fetal pulse can be discriminated from the maternal pulse and thus, in principle, the fetal arterial oxygen saturation can be obtained. We present the methodology for obtaining these data, and discuss the dependence of our measurements on the fetal position with respect to the optode assembly.     

Investigation of photoplethysmographic signals and blood oxygen saturation values on healthy volunteers during cuff-induced hypoperfusion using a multimode PPG/SpO2 sensor

Photoplethysmography (PPG) is a technique widely used to monitor volumetric blood changes induced by cardiac pulsations. Pulse oximetry uses the technique of PPG to estimate arterial oxygen saturation values (SpO?). In poorly perfused tissues, SpO? readings may be compromised due to the poor quality of the PPG signals. A multimode finger PPG probe that operates simultaneously in reflectance, transmittance and a combined mode called "transreflectance" was developed, in an effort to improve the quality of the PPG signals in states of hypoperfusion. Experiments on 20 volunteers were conducted to evaluate the performance of the multimode PPG sensor and compare the results with a commercial transmittance pulse oximeter. A brachial blood pressure cuff was used to induce artificial hypoperfusion. Results showed that the amplitude of the transreflectance AC PPG signals were significantly different (p < 0.05) than the AC PPG signals obtained from the other two conventional PPG sensors (reflectance and transmittance). At induced brachial pressures between 90 and 135 mmHg, the reflectance finger pulse oximeter failed 25 times (failure rate 42.2 %) to estimate SpO? values, whereas the transmittance pulse oximeter failed 8 times (failure rate 15.5 %). The transreflectance pulse oximeter failed only 3 times (failure rate 6.8 %) and the commercial pulse oximeter failed 17 times (failure rate 29.4 %).     

A system for investigating oesophageal photoplethysmographic signals in anaesthetised patients

The monitoring of arterial blood oxygen saturation in patients with compromised peripheral perfusion is often difficult, because conventional non-invasive techniques such as pulse oximetry (SpO2) can fail. Poor peripheral circulation commonly occurs after major surgery including cardiopulmonary bypass. The difficulties in these clinical situations might be overcome if the sensor were to monitor a better perfused central part of the body such as the oesophagus. A new oesophageal photoplethysmographic (PPG) probe and an isolated processing system have been developed to investigate the pulsatile signals of anaesthetised adult patients undergoing routine surgery. Measurements were made in the middle third of the oesophagus, 25 cm to 30 cm from the upper incisors. The AC PPG signals are sampled by a data acquisition system connected to a laptop computer. The signals recorded correspond to infrared and red AC PPGs from the middle third oesophagus and the finger. Preliminary results from 20 patients show that good quality AC PPG signals can be measured in the human oesophagus. The ratio of the oesophageal to finger AC PPG amplitudes was calculated for the infrared and red wavelengths for each patient. The mean (+/- standard deviation) of this ratio was 2.9 +/- 2.1 (n = 19) for the infrared wavelength and 3.1 +/- 2.4 (n = 16) for the red wavelength. The red and infrared wavelengths used are appropriate for pulse oximetry and this investigation indicates that the mid-oesophagus may be a suitable site for the reliable monitoring of SpO2 in patients with poor peripheral perfusion.     

A system for investigating oesophageal photoplethysmographic signals in anaesthetised patients

The monitoring of arterial blood oxygen saturation in patients with compromised peripheral perfusion is often difficult, because conventional noninvasive techniques such as pulse oximetry (SpO₂) can fail. Poor peripheral circulation commonly occurs after major surgery including cardiopulmonary bypass. The difficulties in these clinical situations might be overcome if the sensor were to monitor a better perfused central part of the body such as the oesophagus. A new oesophageal photoplethysmographic (PPG) probe and an isolated processing system have been developed to investigate the pulsatile signals of anaesthetised adult patients undergoing routine surgery. Measurements were made in the middle third of the oesophagus, 25 cm to 30 cm from the upper incisors. The AC PPG signals are sampled by a data acquisition system connected to a laptop computer. The signals recorded correspond to infrared and red AC PPGs from the middle third oesophagus and the finger. Preliminary results from 20 patients show that good quality AC PPG signals can be measured in the human oesophagus. The ratio of the oesophageal to finger AC PPG amplitudes was calculated for the infrared and red wavelengths for each patient. The mean (±standard deviation) of this ratio was 2.9±2.1 (n=19) for the infrared wavelength and 3.1±2.4 (n=16) for the red wavelength. The red and infrared wavelengths used are appropriate for pulse oximetry and this investigation indicates that the mid-oesophagus may be a suitable site for the reliable monitoring of SpO₂ in patients with poor peripheral perfusion.     

Photoplethysmographic measurements from the esophagus using a new fiber-optic reflectance sensor

A prototype fiber-optic reflectance-mode pulse oximetry sensor and measurement system is developed for the purposes of estimating arterial oxygen saturation in the esophagus. A dedicated probe containing miniature right-angled glass prisms coupled to light sources and a photodetector by means of optical fibers is designed and used to record photoplethysmographic (PPG) signals from the esophageal epithelium in anesthetized patients. The probe is inserted simply by an anesthesiologist in all cases, and signals are recorded successfully in all but one of 20 subjects, demonstrating that esophageal PPG signals can be reliably obtained. The mean value of the oxygen saturation recorded from the esophagus for all subjects is 94.0 ± 4.0%. These results demonstrate that SpO(2) may be estimated in the esophagus using a fiber-optic probe.     

Evaluation of a new reflectance pulse oximeter for clinical applications

The design of a noninvasive reflectance pulse oximeter that uses the same principle of transmittance pulse oximeter and analyses the oxygen saturation of arterial blood was described. Four sets of red and infra-red LEDs were used as light sources. The respective reflectance photoelectric outputs were used to make an internal calibration curve of the instrument relative to the arterial oxygen saturation values measured with a Co-Oximeter (OSM-3) in five healthy nonsmoking subjects during steady-state hypoxaemia. The accuracy of the present instrument was studied in six patients with respiratory failure. From 22 samples, a good correlation coefficient (0.98) with a standard deviation of 1.42 was obtained in the range between 73 and 100 per cent between the arterial oxygen saturation measured with the present instrument and that with the Co-Oximeter. The result strongly suggests the usefulness of this oximeter in monitoring patients with hypoxaemia.     

Dynamic in vivo response characteristics of three oximeters: Hewlett-Packard 47201A, Biox III, and Nellcor N-100

Pulse oximeters (Biox III, Nellcor N-100) and a transmittance oximeter [Hewlett-Packard 47201A (HP)] were compared for SaO2 measurement and responsiveness during dynamic changes in arterial oxygen saturation and heart rate. Five sleep apnea syndrome patients were studied because they had large oscillations in SaO2 and heart rate in sleep. During sleep, each patient exhibited a series of rapid (18.0 +/- 8.3 s, mean +/- SD) oscillations in oxygen saturation (92.1 +/- 2.6% to 74.2 +/- 7.7%). Oxygen saturation measurements were sampled simultaneously from each oximeter by computer (at 2 Hz). Accuracy was assessed by comparing pulse and transmittance oxygen saturation measurements at the peak and trough of each apnea-related oscillation. Oximeter response was defined in terms of the "delay" or absolute time difference between the pulse oximeters and the transmittance oximeter for the determination of the peak and trough saturations. Linear regression analysis was used to establish accuracy and response relationships between pulse oximeter sensors (reusable ear, reusable digit, disposable digit, and disposable nasal sensors) and the transmittance oximeter sensor (reusable ear sensor). Pulse oximeter response delay was highly correlated with heart rate. Pulse oximeter SaO2 measurement and response characteristics varied considerably with sensor type (disposable, reusable) and sensor location (ear, nose, and digit). One must be aware of these differences in clinical and research application.     

Design of a visible-light spectroscopy clinical tissue oximeter

We develop a clinical visible-light spectroscopy (VLS) tissue oximeter. Unlike currently approved near-infrared spectroscopy (NIRS) or pulse oximetry (SpO2%), VLS relies on locally absorbed, shallow-penetrating visible light (475 to 625 nm) for the monitoring of microvascular hemoglobin oxygen saturation (StO2%), allowing incorporation into therapeutic catheters and probes. A range of probes is developed, including noncontact wands, invasive catheters, and penetrating needles with injection ports. Data are collected from: 1. probes, standards, and reference solutions to optimize each component; 2. ex vivo hemoglobin solutions analyzed for StO2% and pO2 during deoxygenation; and 3. human subject skin and mucosal tissue surfaces. Results show that differential VLS allows extraction of features and minimization of scattering effects, in vitro VLS oximetry reproduces the expected sigmoid hemoglobin binding curve, and in vivo VLS spectroscopy of human tissue allows for real-time monitoring (e.g., gastrointestinal mucosal saturation 69+/-4%, n=804; gastrointestinal tumor saturation 45+/-23%, n=14; and p<0.0001), with reproducible values and small standard deviations (SDs) in normal tissues. FDA approved VLS systems began shipping earlier this year. We conclude that VLS is suitable for the real-time collection of spectroscopic and oximetric data from human tissues, and that a VLS oximeter has application to the monitoring of localized subsurface hemoglobin oxygen saturation in the microvascular tissue spaces of human subjects.     

Measuring brain hemodynamic changes in a songbird: responses to hypercapnia measured with functional MRI and near-infrared spectroscopy

Songbirds have been evolved into models of choice for the study of the cerebral underpinnings of vocal communication. Nevertheless, there is still a need for in vivo methods allowing the real-time monitoring of brain activity. Functional Magnetic Resonance Imaging (fMRI) has been applied in anesthetized intact songbirds. It relies on blood oxygen level-dependent (BOLD) contrast revealing hemodynamic changes. Non-invasive near-infrared spectroscopy (NIRS) is based on the weak absorption of near-infrared light by biological tissues. Time-resolved femtosecond white laser NIRS is a new probing method using real-time spectral measurements which give access to the local variation of absorbing chromophores such as hemoglobins. In this study, we test the efficiency of our time-resolved NIRS device in monitoring physiological hemodynamic brain responses in a songbird, the zebra finch (Taeniopygia guttata), using a hypercapnia event (7% inhaled CO(2)). The results are compared to those obtained using BOLD fMRI. The NIRS measurements clearly demonstrate that during hypercapnia the blood oxygen saturation level increases (increase in local concentration of oxyhemoglobin, decrease in deoxyhemoglobin concentration and total hemoglobin concentration). Our results provide the first correlation in songbirds of the variations in total hemoglobin and oxygen saturation level obtained from NIRS with local BOLD signal variations.     

Validation of pulse oximetry during progressive normobaric hypoxia utilizing a portable chamber.

Validation of pulse oximetry in commercially available normobaric hypoxic chambers (NHC) has not been previously reported. The present study examined the validity of pulse oximetry (SpO2) against direct measurements of arterial oxygen saturation (SaO2) via co-oximetry (AVOXimeter 4000) in 13 young adults age 21.3 +/- 0.6 years. Over a period of 2.5 hrs, the inspired fraction of oxygen inside a NHC (Hypoxico, Inc.) was progressively reduced from 20.9% to 11.5%. Measurements of SaO2 at baseline and at 15, 30, 60, 90, 120, and 150 min during the hypoxic exposures were compared with SpO2 estimates of oxygen saturation (Nellcor 295) using reflectance (RS-10, temporal) and transmission (D-25, finger) sensors. Regression analysis and methods for assessing agreement (bias, b; precision, p) of SaO2 with SpO2 were similar (R2 = 0.92, 0.89; b = 0.016, -0.47; p = 2.47, 3.03; RS-10 and D-25, respectively). When SaO2 < 85%, RS-10 had greater validity than D-25 (R2 = 0.73, 0.56; b = 1.38, 1.13; p = 2.72, 4.34; RS-10 and D-25, respectively). In light of these findings, caution should be exercised when monitoring individuals with pulse oximetry during desaturation episodes below 85%. When employing frequent NHC exposures, a priori validation of SpO2 utilized to assess blood oxygen status appears warranted.     

无线传输在脉搏血氧饱和度无创监测中的应用

随着光电子技术的快速发展,基于光电检测原理的血氧饱和度在线测量方法得到了广泛研究。本文对传统双波长透射式血氧饱和度测量方法进行了改进,并在系统中应用了无线数字信号传输和数据小波处理方法。经实验验证,基于以上原理提出的脉搏血氧饱和度检测方法和无线数字信号传输方法,有效地消除了非血氧成分与其他干扰因素对测量结果的影响,并且突破了测量的空间限制。     

Non-invasive respiratory monitoring in paediatric intensive care unit

Monitoring respiratory function is important in a Paediatrics Intensive Care Unit (PICU), as majority of patients have cardio-respiratory problems. Non-invasive monitoring is convenient, accurate, and has minimal complications. Along with clinical monitoring, oxygen saturation using pulse oximetry, transcutaneous oxygenation (PtcO2) and transcutaneous PCO2 (PtcCO2) using transcutaneous monitors and end-tidal CO2 using capnography are important and routine measurements done in most PICUs. Considering the financial and maintenance constraints pulse oximetry with end tidal CO2 monitoring can be considered as most feasible.     

Computer analysis system of blood oxygen saturation in an animal hypoxia model

An experimental animal hypoxia model has been developed. It consists of two sensors (an in vitro and in vivo model), an experimental device and a computer signal processing system. This method can easily be applied to determine and analyse blood oxygen saturation at various hypoxia levels. It can also be used to evaluate the accuracy of pulse oximetry over a wide range of oxyhemoglobin desaturation levels. The DC and AC components of recorded red and infra-red signals, the dual-wavelength ratio R₁₂ and the reading of a pulse oximeter (SpO₂) can be automatically calculated and displayed on a computer screen. Preliminary results of the animal hypoxia test indicate that the measurements made by the instrument correlate well with the oxygen saturation readings of the automatic blood gas analyser AVL945. The computer analysis system is suitable for repeated estimations in the animal model.     

Developments in quantitative oxygen-saturation imaging of breast tissue in vivo using multispectral near-infrared tomography

Imaging of oxygen saturation provides a spatial map of the tissue metabolic activity and has potential in diagnosis and treatment monitoring of breast cancer. Oxygen-saturation imaging is possible through near-infrared (NIR) tomography, but has low signal-to-noise ratio (SNR). This can be augmented by using NIR tomography as an add-on to MRI. Presented are results from a free-standing NIR system and a hybrid MR-guided system for breast imaging. In results from imaging 60 healthy volunteers in the initial NIR system, oxygen saturation was a significant discriminator between the BIRADS classifications of adipose tissue, heterogeneously dense, and extremely dense tissue. By using the MR-guided NIR system, more accurate tissue-specific data were obtained on adipose and fibroglandular volumes, with 11 healthy volunteers. In these data, oxygen saturation in the adipose tissue correlated with percentage of adipose tissue. In two case studies of infiltrating ductal carcinomas, oxygen saturation was reduced at the site of the tumor, as compared with the surrounding healthy tissue, agreeing with conventional thought that hypoxia exists in larger solid tumors. The MRI-guided NIR images of oxygen saturation provide higher resolution and superior SNR and will likely be used in the future to study and characterize specific tissue volumes.     

自适应脉搏氧系统设计与实现

介绍一种自适应脉搏氧测量系统,使用模拟开关切换反馈电阻阻值,粗调系统增益;通过前级反馈调节MCU的DA输出,改变恒流驱动大小,微调系统增益。在两种机制协调下,实现系统增益精确控制,实现信号的宽范围测量,满足在低灌注指数下对弱脉搏的信号采集,并实现脉率、灌注指数、血氧饱和度的精确计算。     

Accuracy of pulse oximetry at various haematocrits and during haemolysis in anin vitro model

In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise damage to red blood cells. The pulse oximeter readings (SpO₂) were compared with oxygen saturation analyses by a haemoximeter (SaO₂). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO₂ range 60–100 per cent. At a haematocrit level of 41–44 per cent, there was no correlation between SaO₂ and SpO₂ readings. After diluting the blood with normal saline to a haematocrit of 10–11 per cent, a good correlation between SaO₂ and SpO₂ was found. Following haemolysis, the agreement between SaO₂ and SpO₂ was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may be dependent on the haematocrit level.     

经食管血氧饱和度监测对食管黏膜安全性影响的实验研究

为研究经食管连续监测动脉血氧饱和度(SteO2)的安全性,将家兔20只,随机分为对照组和高频电刀组,麻醉后将带有2个发光二极管(LED)的氧饱和度检测探头置入食管下段,连接脉搏血氧仪,分别监测2h和6h。监测完毕取2个LED处食管全层组织、探头尖端1cm的近胃端食管全层组织(自身对照)行病理组织学检查。结果显示:两组LED-1、LED-2处食管黏膜切片与自身对照切片的病理检查结果均为黏膜完整,黏膜下层轻度水肿、充血,少量淋巴细胞、单核细胞浸润,病理组织学评分均为2分。结果表明,采用相互匹配的氧饱和度传感器和脉搏血氧仪监测SteO26h是安全的。