Concept: Oxygen saturation
Smooth pursuit eye movements (SPEM) are needed to keep the retinal image of slowly moving objects within the fovea. Depending on the task, about 50%-80% of patients with schizophrenia have difficulties in maintaining SPEM. We designed a study that comprised different target velocities as well as testing for internal (extraretinal) guidance of SPEM in the absence of a visual target. We applied event-related fMRI by presenting four velocities (5, 10, 15, 20°/s) both with and without intervals of target blanking. 17 patients and 16 healthy participants were included. Eye movements were registered during scanning sessions. Statistical analysis included mixed ANOVAs and regression analyses of the target velocity on the Blood Oxygen Level Dependency (BOLD) signal. The main effect group and the interaction of velocity×group revealed reduced activation in V5 and putamen but increased activation of cerebellar regions in patients. Regression analysis showed that activation in supplementary eye field, putamen, and cerebellum was not correlated to target velocity in patients in contrast to controls. Furthermore, activation in V5 and in intraparietal sulcus (putative LIP) bilaterally was less strongly correlated to target velocity in patients than controls. Altered correlation of target velocity and neural activation in the cortical network supporting SPEM (V5, SEF, LIP, putamen) implies impaired transformation of the visual motion signal into an adequate motor command in patients. Cerebellar regions seem to be involved in compensatory mechanisms although cerebellar activity in patients was not related to target velocity.
BACKGROUND:: Anesthesiology requires performing visually oriented procedures while monitoring auditory information about a patient’s vital signs. A concern in operating room environments is the amount of competing information and the effects that divided attention has on patient monitoring, such as detecting auditory changes in arterial oxygen saturation via pulse oximetry. METHODS:: The authors measured the impact of visual attentional load and auditory background noise on the ability of anesthesia residents to monitor the pulse oximeter auditory display in a laboratory setting. Accuracies and response times were recorded reflecting anesthesiologists' abilities to detect changes in oxygen saturation across three levels of visual attention in quiet and with noise. RESULTS:: Results show that visual attentional load substantially affects the ability to detect changes in oxygen saturation concentrations conveyed by auditory cues signaling 99 and 98% saturation. These effects are compounded by auditory noise, up to a 17% decline in performance. These deficits are seen in the ability to accurately detect a change in oxygen saturation and in speed of response. CONCLUSIONS:: Most anesthesia accidents are initiated by small errors that cascade into serious events. Lack of monitor vigilance and inattention are two of the more commonly cited factors. Reducing such errors is thus a priority for improving patient safety. Specifically, efforts to reduce distractors and decrease background noise should be considered during induction and emergence, periods of especially high risk, when anesthesiologists has to attend to many tasks and are thus susceptible to error.
Supplemental oxygen is administered in the vast majority of patients in the perioperative setting and in the intensive care unit to prevent the potentially deleterious effects of hypoxia. On the other hand, the administration of high concentrations of oxygen may induce hyperoxia that may also be associated with significant complications. Oxygen therapy should therefore be precisely titrated and accurately monitored. Although pulse oximetry has become an indispensable monitoring technology to detect hypoxemia, its value in assessing the oxygenation status beyond the range of maximal arterial oxygen saturation (SpO2 ≥97%) is very limited. In this hyperoxic range, we need to rely on blood gas analysis, which is intermittent, invasive and sometimes delayed. The oxygen reserve index (ORI) is a new continuous non-invasive variable that is provided by the new generation of pulse oximeters that use multi-wavelength pulse co-oximetry. The ORI is a dimensionless index that reflects oxygenation in the moderate hyperoxic range (PaO2 100-200 mmHg). The ORI may provide an early alarm when oxygenation deteriorates well before any changes in SpO2 occur, may reflect the response to oxygen administration (e.g., pre-oxygenation), and may facilitate oxygen titration and prevent unintended hyperoxia. In this review we describe this new variable, summarize available data and preliminary experience, and discuss its potential clinical utilities in the perioperative and intensive care settings.
Previous results from our trial of early treatment with continuous positive airway pressure (CPAP) versus early surfactant treatment in infants showed no significant difference in the outcome of death or bronchopulmonary dysplasia. A lower (vs. higher) target range of oxygen saturation was associated with a lower rate of severe retinopathy but higher mortality. We now report longer-term results from our prespecified hypotheses.
We present a novel method for estimating respiratory rate in real-time from the photoplethysmogram (PPG) obtained from pulse oximetry. Three respiratory induced variations (frequency, intensity, and amplitude) are extracted from the PPG using the Incremental-Merge Segmentation algorithm. Frequency content of each respiratory induced variation is analyzed using Fast Fourier Transforms. The proposed Smart Fusion method then combines the results of the three respiratory induced variations using a transparent mean calculation. It automatically eliminates estimations considered to be unreliable because of detected presence of artifacts in the PPG or disagreement between the different individual respiratory rate estimations. The algorithm has been tested on data obtained from 29 children and 13 adults. Results show that it is important to combine the three respiratory induced variations for robust estimation of respiratory rate. The Smart Fusion showed trends of improved estimation (mean root mean square error 3.0 breaths/min) compared to the individual estimation methods (5.8, 6.2 and 3.9 breaths/min). The Smart Fusion algorithm is being implemented in a mobile phone pulse oximeter device to facilitate the diagnosis of severe childhood pneumonia in remote areas.
The esophagus is perfused directly by prominent arteries and may provide a more consistent tissue source for pulse oximetry. The goal of this study was to evaluate the sensitivity and accuracy of an esophageal pulse oximetry probe on patients during controlled hypoxemia in comparison to measurements obtained with conventional pulse oximetry (SpulseO(2)). Forty-five ASA I-II adult patients were included in this prospective observational study. Nellcor digital oximetric probes were placed on finger tips for SpulseO(2) before anesthesia. After tracheal intubation, an esophageal probe was placed in the lower segment of the esophagus for esophageal oximetric monitoring (SoesO(2)). All patients were disconnected from the breathing circuit to establish a controlled hypoxemia, and were re-connected to the breathing circuit and ventilated with 100% oxygen immediately when SoesO(2) dropped to 90%. Matched SoesO(2) and SpulseO(2) readings were recorded when SoesO(2) measurements were at 100%, 95%, 90% and the lowest reading. The time for SoesO(2) and SpulseO(2) to drop from 100% to 95%, 90% and return to 100% was recorded. Oxygen saturation from arterial blood samples (SartO(2)) was also measured at each time point respectively. The linear correlation coefficient of the regression analysis between SartO(2) and SoesO(2) was 0.954. The mean ± 2SD of the difference was 0.3% ± 4.3% for SoesO(2) vs. SartO(2) and 6.8% ± 5.6% for SpulseO(2) vs. SartO(2) (P < 0.001). The 95% confidence interval for the absolute difference between SoesO(2) and SartO(2) was 0.3% to 0.7% and 6.2% to 7.4% between SpulseO(2) and SartO(2). The time to reach 90% saturation measured with SoesO(2) was approximately 94 seconds earlier than the SpulseO(2) (P < 0.001). In conclusion, SoesO(2) is more accurate and enables earlier detection of hypoxemia when compared to conventional pulse oximetry during hypoxemia for patients undergoing general anesthesia.
To test the hypothesis that preterm infants randomized to a low vs high O(2) saturation target range have a higher incidence of intermittent hypoxemia.
Pulse oximetry utilizes the technique of photoplethysmography to estimate arterial oxygen saturation (SpO(2)) values. During hypothermia, the amplitude of the photoplethysmograph (PPG) is compromised which can lead to inaccurate estimation of SpO(2). A new mutlimode PPG/pulse oximeter sensor was developed to investigate the behaviour of PPGs during conditions of induced hypothermia (hand immersed in an ice bath). PPG measurements from 20 volunteers were conducted and SpO(2) values were estimated at all stages of the experiment. Good quality PPG signals were observed from the majority of the volunteers at almost all hand temperatures. At low temperature ranges, from 13 to 21 °C, the failure rate to estimate SpO(2) values from the multimode transreflectance PPG sensor was 2.4% as compared to the commercial pulse oximeter with a failure rate of 70%.
Oxygen is necessary for all aerobic life, and nothing is more important in respiratory care than its proper understanding, assessment, and administration. By the early 1970s P(aO(2)) had become the gold standard for clinically assessing oxygenation in the body. Since the 1980s the measurement of arterial oxygen saturation by pulse oximetry has also been increasingly used as an adjunct to (but not a replacement for) P(aO(2)). Despite the desirability of measuring tissue oxygenation directly, no reliable and clinically relevant such measure has emerged. The 2 areas in which oxygen has proven most important in respiratory care are long-term oxygen therapy (LTOT) and the management of potentially life-threatening hypoxemia in acute respiratory failure. That LTOT improves survival in appropriately selected patients with COPD was demonstrated by multicenter studies published more than 30 years ago, and their original selection criteria have so far not been improved upon. Severe hypoxemia in acute lung injury and ARDS can be improved by ventilation with PEEP, and also in many patients by various adjunctive techniques and alternative support strategies. However, the latter measures have not brought clear improvements in survival or other patient-relevant outcomes. In addition, the original goals of “normalizing” arterial oxygenation with high tidal volumes and lung-distending pressures have required modification as appreciation for ventilator-related lung injury has emerged. High concentrations of inspired oxygen may play a role in such injury, but aggressive measures to reduce them in order to avoid oxygen toxicity-which dominated ventilator management in previous decades-have been tempered in the present era of lung-protective ventilation. Although some additions and modifications have emerged, much of what we understand today about oxygen in respiratory care is owed to the pioneering work of Thomas L Petty more than 40 years ago.
We wish to report here a practical approach to an ARDS patient as devised by a group of intensivists with different expertise. The referral scenario is an intensive care unit of a Community Hospital with limited technology, where a young doctor, alone, must deal with this complicate syndrome during the night. The knowledge of pulse oximetry at room air and at 100% oxygen allows to estimate the PaO2 and the cause of hypoxemia, shunt vs. VA/Q maldistribution. The ARDS severity (mild (200