Concept: Oxygen sensor
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.
Diagnostic and interventional procedures are often facilitated by moderate procedure-related sedation. Many studies support the overall safety of this sedation; however, adverse cardiovascular and respiratory events are reported in up to 70% of these procedures, more frequently in very young, very old, or sicker patients. Monitoring with pulse oximetry may underreport hypoventilation during sedation, particularly if supplemental oxygen is provided. Capnometry may result in false alarms during sedation when patients mouth breathe or displace sampling devices. Advanced monitor use during sedation may allow event detection before complications develop. This 2-part pilot study used advanced monitors during planned moderate sedation to (1) determine incidences of desaturation, low respiratory rate, and deeper than intended sedation alarm events; and (2) determine whether advanced monitor use is associated with fewer alarm events.
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.
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.
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%.
Cerebral oximetry allows continuous real-time and non-invasive monitoring of cerebral oxygen saturation (cSO(2)), by measuring oxyhaemoglobin and deoxyhaemoglobin near infrared light absorption, similarly to pulse oximetry. cSO(2) measurement predominantly reflects brain venous compartment, and is correlated with jugular venous saturation. As jugular venous saturation, cSO(2) must therefore be interpreted as a measure of balance between transport and consumption of O(2) in the brain. Cerebral oximetry should be used as a trend monitoring, because its accuracy is insufficient to be considered as reliable measure of absolute value of ScO(2). In adult, correction of intraoperative cerebral desaturation reduces hospital stay, heavy morbidity and mortality, and serious postoperative neurocognitive impairment after cardiac and major abdominal surgery. In children, the occurrence of intra- and postoperative cerebral desaturations during congenital heart surgery is associated with increased neurological morbi-mortality. Cerebral oximetry could be a useful monitoring during anaesthesia of (ex) preterm neonates, due to the risk of impaired cerebral blood flow autoregulation in these patients.
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.
Pulse oximetry provides no indication of downward trends in PaO2 until saturation begins to decrease. The Oxygen Reserve Index (ORI) is a novel pulse oximeter-based nondimensional index that ranges from 1 to 0 as PaO2 decreases from about 200 to 80 mmHg and is measured by optically detecting changes in SvO2 after SaO2 saturates to the maximum. The authors tested the hypothesis that the ORI provides a clinically important warning of impending desaturation in pediatric patients during induction of anesthesia.
- Proceedings of the National Academy of Sciences of the United States of America
- Published almost 2 years ago
Directional change in environmental drivers sometimes triggers regime shifts in ecosystems. Theory and experiments suggest that regime shifts can be detected in advance, and perhaps averted, by monitoring resilience indicators such as variance and autocorrelation of key ecosystem variables. However, it is uncertain whether management action prompted by a change in resilience indicators can prevent an impending regime shift. We caused a cyanobacterial bloom by gradually enriching an experimental lake while monitoring an unenriched reference lake and a continuously enriched reference lake. When resilience indicators exceeded preset boundaries, nutrient enrichment was stopped in the experimental lake. Concentrations of algal pigments, dissolved oxygen saturation, and pH rapidly declined following cessation of nutrient enrichment and became similar to the unenriched lake, whereas a large bloom occurred in the continuously enriched lake. This outcome suggests that resilience indicators may be useful in management to prevent unwanted regime shifts, at least in some situations. Nonetheless, a safer approach to ecosystem management would build and maintain the resilience of desirable ecosystem conditions, for example, by preventing excessive nutrient input to lakes and reservoirs.