Simultaneous Pulse Oximetry Research Articles

Characterizing systemic physiological effects on the blood oxygen level dependent signal of resting-state fMRI in time-frequency space using wavelets.

Systemic physiological dynamics, such as heart rate variability (HRV) and respiration volume per time (RVT), are known to account for significant variance in the blood oxygen level dependent (BOLD) signal of resting-state functional magnetic resonance imaging (rsfMRI). However, synchrony between these cardiorespiratory changes and the BOLD signal could be due to neuronal (i.e., autonomic activity inducing changes in heart rate and respiration) or vascular (i.e., cardiorespiratory activity facilitating hemodynamic changes and thus the BOLD signal) effects and the contributions of these effects may differ spatially, temporally, and spectrally. In this study, we characterize these brain-body dynamics using a wavelet analysis in rapidly sampled rsfMRI data with simultaneous pulse oximetry and respiratory monitoring of the Human Connectome Project. Our time-frequency analysis across resting-state networks (RSNs) revealed differences in the coherence of the BOLD signal and heartbeat interval (HBI)/RVT dynamics across frequencies, with unique profiles per network. Somatomotor (SMN), visual (VN), and salience (VAN) networks demonstrated the greatest synchrony with both systemic physiological signals when compared to other networks; however, significant coherence was observed in all RSNs regardless of direct autonomic involvement. Our phase analysis revealed distinct frequency profiles of percentage of time with significant coherence between BOLD and systemic physiological signals for different phase offsets across RSNs, suggesting that the phase offset and temporal order of signals varies by frequency. Lastly, our analysis of temporal variability of coherence provides insight on potential influence of autonomic state on brain-body communication. Overall, the novel wavelet analysis enables an efficient characterization of the dynamic relationship between cardiorespiratory activity and the BOLD signal in spatial, temporal, and spectral dimensions to inform our understanding of autonomic states and improve our interpretation of the BOLD signal.

An observational study of simultaneous pulse oximetry and arterial oxygen saturation readings in intensive care unit/high dependency unit in COVID-19 patients

Background: The coronavirus-2019 (COVID-19) pandemic has increased the use of pulse oximeters worldwide. It has become an inevitable tool in the monitoring of the disease. However, the accuracy of pulse oximeters in COVID-19 has not been established. Aims and Objectives: The aims of the study were to examine the relationship between oxygen saturation as measured by pulse oximeter (SpO2) and oxygen saturation measured by arterial blood gas analysis (SaO2) measurements in COVID-19 patients admitted to the intensive care unit (ICU)/high dependency unit (HDU) and to assess the ability of SpO2 readings to detect low SaO2 and low oxygen tension in COVID-19 patients. Materials and Methods: This prospective observational study was conducted in the COVID-19 ICU and high dependency unit of a tertiary care hospital in Bengaluru, India. All patients admitted with confirmed COVID-19, meeting the eligibility criteria, were included in the study. We assessed bias and limits of agreement between paired samples of oxygen saturation from pulse oximetry (SpO2) and arterial oxygen saturation from blood gas analysis (SaO2). Results: The sample mean difference SpO2-SaO2 is −0.86% (bias) and the 95% confidence interval for the mean difference was −1.67 and −0.04. The lower limit of agreement was −7.32 with a 95% confidence interval (−8.74, −5.91). The upper limit of agreement was 5.61 with a 95% confidence interval of 4.19 and 7.02. Conclusion: SpO2 values are not completely dependable in estimating SaO2 in COVID-19 patients in ICU/HDU; therefore, arterial blood gas analysis measurement of oxygen saturation has to be done depending on the clinical scenario CTRI (CTRI/2020/11/029035).

Contributions of Parasympathetic Arousal–Related Activity to Cognitive Performance in Patients With First-Episode Psychosis and Control Subjects

BackgroundCognitive impairment is integral to the pathophysiology of psychosis. Recent findings implicate autonomic arousal–related activity in both momentary fluctuations and individual differences in cognitive performance. Although altered autonomic arousal is common in patients with first-episode psychosis (FEP), its contribution to cognitive performance is unknown. MethodsA total of 24 patients with FEP (46% male, age = 24.31 [SD 4.27] years) and 24 control subjects (42% male, age = 27.06 [3.44] years) performed the Multi-Source Interference Task in-scanner with simultaneous pulse oximetry. First-level models included the cardiac-blood oxygen level–dependent regressor, in addition to task (congruent, interference, and error) and nuisance (motion and CompCor physiology) regressors. The cardiac-blood oxygen level–dependent regressor reflected parasympathetic arousal–related activity and was created by convolving the interbeat interval at each heartbeat with the hemodynamic response function. Group models examined the effect of group or cognitive performance (reaction times × error rate) on arousal-related and task activity, while controlling for sex, age, and framewise displacement. ResultsParasympathetic arousal–related activity was robust in both groups but localized to different regions for patients with FEP and healthy control subjects. Within both groups, arousal-related activity was significantly associated with cognitive performance across occipital and temporal cortical regions. Greater arousal-related activity in the bilateral prefrontal cortex (Brodmann area 9) was related to better performance in healthy control subjects but not patients with FEP. ConclusionsAutonomic arousal circuits contribute to cognitive performance and the pathophysiology of FEP. Arousal-related functional activity is a novel indicator of cognitive ability and should be incorporated into neurobiological models of cognition in psychosis.

The Roth score as a triage tool for detecting hypoxaemia in general practice: a diagnostic validation study in patients with possible COVID-19.

To validate the Roth score as a triage tool for detecting hypoxaemia. The virtual assessment of patients has become increasingly important during the corona virus disease (COVID-19) pandemic, but has limitations as to the evaluation of deteriorating respiratory function. This study presents data on the validity of the Roth score as a triage tool for detecting hypoxaemia remotely in potential COVID-19 patients in general practice. This cross-sectional validation study was conducted in Dutch general practice. Patients aged ≥18 with suspected or confirmed COVID-19 were asked to rapidly count from 1 to 30 in a single breath. The Roth score involves the highest number counted during exhalation (counting number) and the time taken to reach the maximal count (counting time).Outcome measures were (1) the correlation between both Roth score measurements and simultaneous pulse oximetry (SpO2) on room air and (2) discrimination (c-statistic), sensitivity, specificity and predictive values of the Roth score for detecting hypoxaemia (SpO2 < 95%). A total of 33 physicians enrolled 105 patients (52.4% female, mean age of 52.6±20.4 years). A positive correlation was found between counting number and SpO2 (rs = 0.44, P < 0.001), whereas only a weak correlation was found between counting time and SpO2 (rs = 0.15, P = 0.14). Discrimination for hypoxaemia was higher for counting number [c-statistic 0.91 (95% CI: 0.85-0.96)] than for counting time [c-statistic 0.77 (95% CI: 0.62-0.93)]. Optimal diagnostic performance was found at a counting number of 20, with a sensitivity of 93.3% (95% CI: 68.1-99.8) and a specificity of 77.8% (95% CI: 67.8-85.9). A counting time of 7s showed the best sensitivity of 85.7% (95% CI: 57.2-98.2) and specificity of 81.1% (95% CI: 71.5-88.6). A Roth score, with an optimal counting number cut-off value of 20, maybe of added value for signalling hypoxaemia in general practice. Further external validation is warranted before recommending integration in telephone triage.

Parasympathetic arousal-related cortical activity is associated with attention during cognitive task performance

Parasympathetic arousal is associated with states of heightened attention and well-being. Arousal may affect widespread cortical and subcortical systems across the brain, however, little is known about its influence on cognitive task processing and performance. In the current study, healthy adult participants (n ​= ​20) underwent multi-band echo-planar imaging (TR ​= ​0.72 ​s) with simultaneous pulse oximetry recordings during performance of the Multi Source Interference Task (MSIT), the Oddball Task (OBT), and during rest. Processing speed on both tasks was robustly related to heart rate (HR). Participants with slower HR responded faster on both the MSIT (33% variance explained) and the OBT (25% variance explained). Within all participants, trial-to-trial fluctuations in processing speed were robustly related to the heartbeat-stimulus interval, a metric that is dependent both on the concurrent HR and the stimulus timing with respect to the heartbeat. Models examining the cardiac-BOLD response revealed that a distributed set of regions showed arousal-related activity that was distinct for different task conditions. Across these cortical regions, activity increased with slower HR. Arousal-related activity was distinct from task-evoked activity and it was robust to the inclusion of additional physiological nuisance regressors into the models. For the MSIT, such arousal-related activity occurred across visual and dorsal attention network regions. For the OBT, this activity occurred within fronto-parietal regions. For rest, arousal-related activity also occurred, but was confined to visual regions. The pulvinar nucleus of the thalamus showed arousal-related activity during all three task conditions. Widespread cortical activity, associated with increased parasympathetic arousal, may be propagated by thalamic circuits and contributes to improved attention. This activity is distinct from task-evoked activity, but affects cognitive performance and therefore should be incorporated into neurobiological models of cognition and clinical disorders.

A two centre observational study of simultaneous pulse oximetry and arterial oxygen saturation recordings in intensive care unit patients.

The influence of variables that might affect the accuracy of pulse oximetry (SpO2) recordings in critically ill patients is not well established. We sought to describe the relationship between paired SpO2/SaO2 (oxygen saturation via arterial blood gas analysis) in adult intensive care unit (ICU) patients and to describe the diagnostic performance of SpO2 in detecting low SaO2 and PaO2. A paired SpO2/SaO2 measurement was obtained from 404 adults in ICU. Measurements were used to calculate bias, precision, and limits of agreement. Associations between bias and variables including vasopressor and inotrope use, capillary refill time, hand temperature, pulse pressure, body temperature, oximeter model, and skin colour were estimated. There was no overall statistically significant bias in paired SpO2/SaO2 measurements; observed limits of agreement were +/-4.4%. However, body temperature, oximeter model, and skin colour, were statistically significantly associated with the degree of bias. SpO2 <89% had a sensitivity of 3/7 (42.9%; 95% confidence intervals, CI, 9.9% to 81.6%) and a specificity of 344/384 (89.6%; 95% CI 86.1% to 92.5%) for detecting SaO2 <89%. The absence of statistically significant bias in paired SpO2/SaO2 in adult ICU patients provides support for the use of pulse oximetry to titrate oxygen therapy. However, SpO2 recordings alone should be used cautiously when SaO2 recordings of 4.4% higher or lower than the observed SpO2 would be of concern. A range of variables relevant to the critically ill had little or no effect on bias.

Changes in Cerebral Oxygenation in Preterm Infants With Progressive Posthemorrhagic Ventricular Dilatation

BackgroundOptimal timing of intervention in neonatal progressive posthemorrhagic hydrocephalus is often a difficult decision. Unchecked hydrocephalus can lead to irreversible brain injury through impaired perfusion, while placement of a shunt is not without long-term morbidity. The purpose of this study was to assess the use of near-infrared spectroscopy to measure changes in regional cerebral oxygen saturation as an indicator of cerebral perfusion in infants with progressive posthemorrhagic ventricular dilatation. MethodsNear-infrared spectroscopy was used to measure regional cerebral oxygen saturation for more than a one-hour period in infants within 24 hours of cranial ultrasound. Simultaneous pulse oximetry was recorded and oxygen extraction was calculated. Ventricular size was measured by ultrasound using the frontal-occipital horn ratio and compared with average oxygen saturation and oxygen extraction. Statistical analysis was done using the Spearman rank test and analysis of variance. ResultsVentricular measurements were made in 20 very low birth weight premature infants with periventricular-intraventricular hemorrhage and 12 infants with normal ultrasound scans. Ventricular dilatation was associated with lower cerebral oxygen saturation and higher oxygen extraction (P < 0.001). Progressive ventricular dilatation was inversely related to changes in cerebral oxygen saturation (P < 0.001). ConclusionsProgressive posthemorrhagic ventricular dilatation is associated with a significant decrease in cerebral oxygenation and increase in oxygen extraction suggesting a decrease in cerebral perfusion. Near-infrared spectroscopy could potentially provide additional clinical information to assist in determining optimal timing of surgical intervention in preterm infants with progressive ventricular enlargement.

Two methods to adapt the human haemoglobin–oxygen dissociation algorithm to the blood of white rhinoceros (Ceratotherium simum) and to determine the accuracy of pulse oximetry

ObjectivesTo adapt the algorithm for the calculation of oxygen saturation to the blood characteristics of the white rhinoceros by two different methods and to determine the accuracy of conventional pulse oximetry measurements. Study designAdaptation of two mathematical models of the oxygen dissociation curve (ODC). AnimalsTwenty-five captive white rhinoceros (Ceratotherium simum), including 12 males and 13 females, aged 6–32 years. MethodsDuring 33 anaesthetic events, 94 arterial blood gas samples with 72 simultaneous pulse oximetry measurements were analysed. The calculation of oxygen saturation was adapted to the characteristics of rhinoceros blood using two different methods. Firstly, a mathematical model developed in 1984 and, secondly, an oxygen status algorithm (OSA) produced by the same developer in 2005 were tested for their applicability for clinical use. ResultsWhen arterial partial pressure of oxygen is >7.98 kPa (60 mmHg), oxygen saturation exceeds 95%. At partial pressures of 6.12–6.52 kPa (46–49 mmHg) Method 1 determined oxygen saturations of 92.5–95.3% and Method 2 oxygen saturations of 90.2–91.6%. Both methods resulted in similar ODCs and accounted for the low p50 value of rhinoceros blood. Method 1 provided better adaptation in respect to the physiological parameters of the rhinoceros, especially with regard to the Bohr effect, than Method 2. Pulse oximetry was an unreliable method of monitoring arterial oxygen saturation during general anaesthesia in this species. ConclusionAdapting the oxygen saturation algorithm to consider the left shift of the ODC provides a useful tool for monitoring oxygen status, especially as pulse oximetry is insufficiently accurate. Experimental determination of the complete Hill curve is required to further validate and optimize the algorithm for use in the white rhinoceros. Clinical relevanceThe method will facilitate the accurate interpretation of oxygen saturation calculated by blood gas analysis in white rhinoceros.

Early hyperoxia burden detected by cerebral near-infrared spectroscopy is superior to pulse oximetry for prediction of severe retinopathy of prematurity.

ObjectiveFractional tissue oxygen extraction (FTOE) is a measure derived from cerebral near-infrared spectroscopy and simultaneous pulse oximetry (SpO2), capturing the proportion of oxygen delivered in arterial blood that is used by the target tissue. FTOE may provide a better proxy measurement of retinal hyperoxia than pulse oximetry alone and could provide insight into the risk for retinopathy of prematurity (ROP). In this study, we directly compared hyperoxia burden calculated from FTOE with hyperoxia burden calculated from SpO2 alone in order to assess the strength of association between hyperoxia and severe ROP.Study designInfants born before <30 weeks and weighing <1500g underwent synchronized SpO2 and FTOE recording over the first four days following birth. After error correction of the raw recording, hyperoxia burden was calculated as the percentage of the total SpO2 or FTOE recording with measurements exceeding defined thresholds (90/93/95% and 20/15/10%, respectively) and was compared to the outcome of severe ROP, defined as ROP requiring laser therapy, after controlling for important covariates.Result63 infants were included with a mean ± SD gestational age of 25.8 ± 1.5 weeks and birth weight of 898.5 ± 206.9g; 13/63 (20%) had severe ROP. SpO2 hyperoxia burden was not associated with severe ROP at any threshold. FTOE hyperoxia burden was associated with severe ROP at the 15% (p=0.04) and 10% (p=0.03) thresholds. Infants with severe ROP spent 20 and 50% more time exceeding the 15 and 10% thresholds, respectively, as compared to those without severe ROP.ConclusionIn the first 96h of life, FTOE, but not SpO2 hyperoxia burden is associated with severe ROP. These preliminary results suggest that NIRS may be a viable alternative technology for targeted oxygen saturation guidelines.

Exaggerated blood pressure variability in patients with pneumoconiosis: a pilot study.

Chronic hypoxia is a risk factor for cardiovascular disease, but its association with blood pressure (BP) remains unclear. We performed this study to clarify the hypothesis that chronic hypoxia is associated with abnormal BP variability in patients with pneumoconiosis. We recruited 19 patients with pneumoconiosis and 30 age- and BP level-matched control subjects. We used simultaneous pulse oximetry and ambulatory BP monitoring for all subjects. We evaluated their BP levels and variability by determining the SD and coefficient of variation (CV) of the BP data. The dipper pattern was defined as nocturnal BP fall ≥10%; the nondipper pattern was defined as nocturnal BP fall ≥0% but <10%; the riser pattern was defined as nocturnal BP fall <0%. Pearson and Spearman correlation coefficients were used to calculate the correlations between parameters. In patients with pneumoconiosis, the daytime systolic BP (SBP) level was lower, the CV in 24-hour SBP (P < 0.05) and diastolic BP (P < 0.001) were higher than that in control subjects. And although not statistically significant (P = 0.13), the odds ratio of riser pattern was 3.73 in patients with pneumoconiosis, and their nighttime pulse rate was significantly higher (P < 0.05) than that in control subjects. The median daytime pulse oximetry oxygen saturation was inversely associated with mean (r = -0.30; P < 0.01) and SD (r = -0.38; P < 0.001) in daytime SBP. The median nighttime pulse oximetry oxygen saturation was inversely associated (r = -0.55; P < 0.001) and the mean nighttime pulse rate was associated (r = 0.51; P < 0.001) with CV in nighttime SBP. Partial pressure of oxygen was inversely associated with CV in daytime SBP (r = -0.24; P < 0.05). Exaggerated BP variability was seen in patients with pneumoconiosis, and the measures of hypoxia were associated with large fluctuations in ambulatory BP. Chronic and intermittent hypoxia could be the contributing factors of these findings. Clinical Trial Number UMIN000000894 (University Hospital Medical Information Network Clinical Trials Registry website).

Cerebral Arterial Oxygen Saturation Measurements Using a Fiber-Optic Pulse Oximeter

A pilot investigation was undertaken to assess the performance of a novel fiber-optic cerebral pulse oximetry system. A fiber-optic probe designed to pass through the lumen of a cranial bolt of the type used to make intracranial pressure measurements was used to obtain optical reflectance signals directly from brain tissue. Short-duration measurements were made in six patients undergoing neurosurgery. These were followed by a longer duration measurement in a patient recovering from an intracerebral hematoma. Estimations of cerebral arterial oxygen saturation derived from a frequency domain-based algorithm are compared with simultaneous pulse oximetry (SpO2) and hemoximeter (SaO2) blood samples. The short-duration measurements showed that reliable photoplethysmographic signals could be obtained from the brain tissue. In the long-duration study, the mean (±SD) difference between cerebral oxygen saturation (ScaO2) and finger SpO2 (in saturation units) was -7.47(±3.4)%. The mean (±SD) difference between ScaO2 and blood SaO2 was -7.37(±2.8)%. This pilot study demonstrated that arterial oxygen saturation may be estimated from brain tissue via a fiber-optic pulse oximeter used in conjunction with a cranial bolt. Further studies are needed to confirm the clinical utility of the technique.

Can Pulse Oximetry or a Bedside Swallowing Assessment Be Used to Detect Aspiration After Stroke?

Desaturation during swallowing may help to identify aspiration in stroke patients. This study investigated pulse oximetry, bedside swallowing assessment (BSA), and videofluoroscopy as tests for detecting aspiration after stroke. Swallowing was assessed in 189 stroke patients (mean+/-SD age, 70.9+/-12.3 years) within 5 days of symptom onset with a modified BSA (water replaced by radio-opaque contrast agent, followed by chest radiography to detect aspiration). Simultaneous pulse oximetry recorded the greatest desaturation from baseline for 10 minutes from modified BSA onset. Videofluoroscopy was undertaken in 54 (28%) patients. Modified BSA showed a safe swallow in 98 (51.9%), unsafe swallow in 85 (45.0%), and silent aspiration in 6 (3.2%) patients. During swallowing, desaturation by >2% occurred in 27 (27.6%) and by >5% in 3 (3.1%) of the 98 safe-swallow patients on modified BSA. Of the 85 unsafe-swallow patients, only 28 (32.9%) desaturated by >2% and 6 (7.1%) by >5%. Desaturation did not occur in any of the 6 silent aspirators. With the modified BSA to detect aspiration, sensitivity and specificity, respectively, were 0.31 and 0.72 for desaturation >2% and 0.07 and 0.97 for desaturation >5%. By videofluoroscopy, sensitivity and specificity for detecting aspiration were 0.47 and 0.72 for modified BSA, 0.33 and 0.62 for desaturation >2%, and 0.13 and 0.95 for desaturation >5%. Combining a failed modified BSA with desaturation >2% or >5% did not significantly improve predictive values. Modified BSA and pulse oximetry during swallowing, whether alone or in combination, showed inadequate sensitivity, specificity, and predictive values for detection of aspiration compared with videofluoroscopy in stroke patients.

Improving the sampling technique of arterialized capillary samples to obtain more accurate PaO2 measurements

Arterialized earlobe capillary blood samples (ELCS) have been used as a measurement of blood gas status for over 20 years. There is general acceptance that there is a strong correlation and limits of agreement between arterial and arterialized blood samples with respect to pH and PaCO2. Although the correlation between the arterial and arterialized PaO2 is good, the limits of agreement poor. Our aim was to improve the accuracy of this technique in the measurement of PaO2 by simultaneously monitoring the oxygen saturation by pulse oximetry whilst taking an ELCS. We hypothesize that significant discrepancies between the SaO2 and SpO2 highlight either a poorly arterialized sample or an over aerated sample from air bubbles. We compared the SpO2 with the SaO2 of an arterial sample from 27 inpatients. We used the limits of agreement between these samples to define the degree of discordance we would accept between SaO2 and SpO2 before repeat ELCS. Subsequently, 252 consecutive patients attending our respiratory physiology unit over a six-month period had an ELCS and simultaneous SpO2. If there was a discrepancy between SaO2 and SpO2 of > 2% the ELCS was repeated. There was a good correlation and limits of agreement between the SpO2 and arterial SaO2 (r = 0.97, mean difference +/- 95% limits of agreement: 0.34 +/- 2.68). A difference of more than 2% between arterialized SaO2 and SpO2 was identified in 21 patients out of 252 (8.3%) with SaO2 higher in two and lower in 19 (r = 0.96, mean difference +/- 95% limits of agreement: 0.66 +/- 3.1). Repeat ELCS of these 21 samples reduced this discrepancy improving the concordance of the measurements (r = 0.98, mean difference +/- 95% limits of agreement: 0.47 +/- 1.0). In one case a difference of 3% remained between the saturations. We conclude that the addition of simultaneous pulse oximetry with ELCS will identify rogue measurements in about 8% of cases highlighting the need for repeat samples and thus increasing the accuracy of the measurement of PaO2 by ELCS.

Factitious Oxygen Desaturation after Isosulfan Blue Injection

Profound pulse oximetery desaturations are observed following isosulfan blue dye injection during breast sentinel node biopsy. The objective of this study was to examine the effect isosulfan dye has on oxygenation status and the reliability of pulse oximetery in evaluating this parameter. After study design, institutional review board approval was obtained. A prospective 5-month study was performed between January and April 2002. Twenty-one women with invasive breast cancer were monitored during breast sentinel node biopsies. Twenty-two operative cases were analyzed by pulse oximetry and arterial catheterization to record oxygen saturation. Time intervals of analysis were 0, 5, 10, 20, 30, and 40 minutes following injection of isosulfan blue dye. Simultaneous pulse oximetry and arterial blood gas analysis allowed comparison of indirect oximetry oxygen saturation (SpO2) to actual arterial oxygen saturation (SaO2). SpO2 values were decreased from baseline values at 10, 20, and 30 minutes without decrease in SaO2 saturation (P < 0.001). The mean oximetry SpO2 desaturation was 5.6 per cent, with a range to 9 per cent. After injection with isosulfan blue dye, a significant SpO2 desaturation occurs. Clinicians must be aware of the factitious effect isosulfan blue dye has on SpO2 monitoring, to assess accurately the oxygenation status of the anesthetized patient.

Methemoglobin levels during prolonged combined nitroglycerin and sodium nitroprusside infusions in infants after cardiac surgery

Nitroglycerin (NTG) and sodium nitroprusside (SNP) are routinely used perioperatively in infants with congenital heart defects. In this study, NTG and SNP were infused in the operating room to increase venous capacitance, reduce systemic and pulmonary afterload, facilitate weaning off cardiopulmonary bypass, stabilize hemodynamics for transport to the intensive care unit (ICU), and reduce the fluid resuscitation needed upon arrival in the ICU. Because of the risk for accumulation of methemoglobin (MetHb) and cyanmethemoglobin (cyan-MetHb) during prolonged continuous infusion of NTG and SNP, it was decided to (1) quantify ICU use, (2) measure % MetHb at 12-hour intervals, and (3) look indirectly for the accumulation of cyan-MetHb by comparing simultaneous pulse oximetry (SP0 2) (Nellcor N-100 [Nellcor, Haywood, CO]) and CO-oximetry (SaO 2) (Corning 270 [Corning, Medfield, MA]). A total of 69 arterial samples were obtained from 16 infants (median age 4.4 months) following cardiac surgery with bypass. Median doses of NTG, 6.0 mg/ kg (range 0.7 to 27.5), and SNP, 3.3 mg/kg (range 0.6 to 33.4), were infused over a median of 64.5 hours (range 12 to 183) (N = 16 patients). The median MetHb was 0.6% (range 0.0 to 1.5) after infusions of NTG, 1.8 μg/kg/min (range 0.5 to 4), and SNP, 1.3 μg/kg/min (range 0.3 to 8.4) (N = 69 measurements). Regression analysis of oximetry data yielded the equation: SPO 2 = 1.04 SaO 2 - 3.7%, r = 0.97. The mean difference between SPO 2 and SaO 2 data pairs was 0.0% (bias) with a SD (precision) of ±2.3%. Because it was not possible to demonstrate either methemoglobinemia or a differential effect of cyan-MetHb on pulse oximetry and CO-oximetry, the use of NTG and SNP in this population is believed to be relatively safe. However, present clinical laboratory monitoring is inadequate to assess the presence of cyan-MetHb or its contribution to the total percentage of dyshemoglobins.

Comparison of oxygenation measurements in pediatric patients during sickle cell crises

Measurements of the saturation of arterial blood with oxygen (Sa o 2) were compared in 24 children during sickle cell crises. Simultaneous pulse oximetry (Nellcor N-100 pulse oximeter) and arterial blood analysis showed that Sa o 2 measured by pulse oximetry overestimated cooximeter-measured Sa o 2 (mean bias, 6.9%; p < 0.001). The blood gas machine–calculated Sa o 2 also overestimated cooximeter-measured Sa o 2 ( p < 0.001). The bias increased with increasing age ( p = 0.002) and carboxyhemoglobin level ( p = 0.005) but was not related to methemoglobin, total hemoglobin, percentage of hemoglobin S, or percentage of hemoglobin F. (J P EDIATR 1994;124:93-5)

Gastroesophageal Reflux—Induced Hypoxemia in Infants With Apparent Life-Threatening Events(s)

To evaluate relationships between gastroesophageal reflux (GER) and the development and onset of apparent life-threatening event(s) (ALTE), 16 infants presenting with ALTE and 6 control subjects manifesting clinical GER alone were studied using prolonged, esophageal pH monitoring in conjunction with simultaneous pulse oximetry and transthoracic impedance pneumocardiography. Despite the absence of a clinical vomiting history in 14 of 16 patients with ALTE, the incidence of GER was similar in both groups (patients with ALTE vs control subjects, 95% vs 100%). Significant arterial oxygen desaturation (less than 90% for greater than 3 minutes) was monitored during 60 episodes in 14 of 16 infants with ALTE, compared with no episodes of reduced arterial oxygen saturation in control subjects. Fifty-four of 60 of these desaturation events commenced within 3.9 +/- 0.4 minutes (mean +/- SD) of onset of a drop in esophageal pH to less than 4.0. Linear regression analysis indicates a significant correlation between duration of esophageal acidification and length of individual hypoxemic episodes (r = .39). Pneumocardiograms were normal in all patients. These data suggest that unsuspected GER is common in infants presenting with ALTE and, in these patients, GER may be directly associated with reflex hypoxemic episodes. Prolonged intraesophageal pH monitoring, performed simultaneously with evaluation for apnea, should be considered in all infants presenting with ALTE.

Cardiac output in severe anaemia: Sharpey-Schafer, E. P.: Clin. Sc. 5: 125, 1944

Optimal timing of intervention in neonatal progressive posthemorrhagic hydrocephalus is often a difficult decision. Unchecked hydrocephalus can lead to irreversible brain injury through impaired perfusion, while placement of a shunt is not without long-term morbidity. The purpose of this study was to assess the use of near-infrared spectroscopy to measure changes in regional cerebral oxygen saturation as an indicator of cerebral perfusion in infants with progressive posthemorrhagic ventricular dilatation.Near-infrared spectroscopy was used to measure regional cerebral oxygen saturation for more than a one-hour period in infants within 24 hours of cranial ultrasound. Simultaneous pulse oximetry was recorded and oxygen extraction was calculated. Ventricular size was measured by ultrasound using the frontal-occipital horn ratio and compared with average oxygen saturation and oxygen extraction. Statistical analysis was done using the Spearman rank test and analysis of variance.Ventricular measurements were made in 20 very low birth weight premature infants with periventricular-intraventricular hemorrhage and 12 infants with normal ultrasound scans. Ventricular dilatation was associated with lower cerebral oxygen saturation and higher oxygen extraction (P < 0.001). Progressive ventricular dilatation was inversely related to changes in cerebral oxygen saturation (P < 0.001).Progressive posthemorrhagic ventricular dilatation is associated with a significant decrease in cerebral oxygenation and increase in oxygen extraction suggesting a decrease in cerebral perfusion. Near-infrared spectroscopy could potentially provide additional clinical information to assist in determining optimal timing of surgical intervention in preterm infants with progressive ventricular enlargement.