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PubMed2003

In vivo electron paramagnetic resonance oximetry with particulate materials.

Electron paramagnetic resonance (EPR) methods can be used to study tissue pO(2) (PtO(2)) in anesthetized or awake animals (EPR oximetry). The method takes advantage of the fact that some paramagnetic materials have an EPR linewidth that is sensitive to the pO(2) in which the material is located. This article provides an overview of the method of EPR oximetry using implanted particulate materials as the sensors of pO(2). Characteristics of these materials are described to help the reader understand the factors involved in choosing the optimum particulate material. Examples of biological studies are included that show how EPR oximetry may be used on both awake and anesthetized animals.

Animals↗
PubMed1999

Respiratory monitoring: arterial blood gas analysis, pulse oximetry, and end-tidal carbon dioxide analysis.

The use of arterial blood gas analysis, pulse oximetry, and capnography has become commonplace in the assessment of veterinary patients. Blood gas analysis allows for the qualitative and quantitative assessment of both metabolic and respiratory acid-base problems, including the interrelationships between ventilation, oxygenation, and metabolic conditions. Blood gas analysis is a useful adjunct to clinical patient assessment and other diagnostics in determining appropriate therapy for specific and complex conditions. Both pulse oximetry and capnography are useful monitoring tools. However, they have technical limitations and cannot comprehensively evaluate patient oxygenation and ventilation. Pulse oximetry and capnography are not replacements for arterial blood gas analysis, but rather serve as adjunctive monitoring tools.

Acidosis, Respiratory↗
PubMed2004

Jugular bulb oximetry for prediction of vasospasm following subarachnoid hemorrhage.

BACKGROUND: Cerebral vasospasm adversely impacts the outcome of those suffering aneurysmal subarachnoid hemorrhage (SAH). Prediction of vasospasm could improve outcomes. We hypothesized that preclinical vasospasm would be heralded by an increase in cerebral oxygen extractions (AVDO2) which could be detected by jugular bulb oximetry. A pilot study was conducted to address this hypothesis. METHODS: Fourteen consenting patients with aneurysmal SAH, undergoing early surgery, were entered into the study. Four patients were withdrawn from the study secondary to failure of catheters or religious belief. At the time of craniotomy, a jugular bulb catheter was placed. Post-operatively, arterial and jugular bulb blood samples were taken every 12 hours to calculate AVDO2. As this was an observational study, no change in management occurred based on measurements. RESULTS: Four of 10 patients had clinical vasospasm. These patients had a significant rise in AVDO2 approximately one day prior to the onset of neurologic deficits (P<0.001). Symptoms resolved along with a significant improvement in AVDO2 on instituting hypertensive, hemo-dilutional, and hypervolemic therapy in these patients. The six patients who did not exhibit clinical vasospasm did not demonstrate significant rise in AVDO2. CONCLUSIONS: Jugular bulb oximetry is simple and cost effective. Increases in AVDO2 using this technique were predictive of clinically evident vasospasm in the subsequent hours to days. This investigation supports a larger study to assess the utility of jugular bulb oximetry in predicting vasospasm in aneurysmal SAH.

Adult↗
PubMed1999

A comparison of pulse oximetry and near infrared spectroscopy (NIRS) in the detection of hypoxaemia occurring with pauses in nasal airflow in neonates.

OBJECTIVE: The aim of this study was to compare the ability of NIRS and pulse oximetry to detect changes in cerebral oxygenation occurring in response to a pause in nasal airflow (PNA). METHODS: Twenty-one recordings of cerebral oxygenation index by NIRS together with oxyhemoglobin saturation by pulse oximetry were measured on 17 preterm infants with a history of apnoea. Photoplethysmography was used to confirm the accuracy of the pulse oximetry data. PNA events were defined as pauses of greater than 4 seconds in a thermistor trace measuring nasal air flow. RESULTS: Baseline variability in oxygenation index (Hbdiff) was found to be from -0.12 to +0.13 micromol 100 g brain(-1). A fall in Hbdiff or SpO2 was defined as a decrease of greater magnitude than 2 standard deviations from the baseline, i.e., -0.12 micromol 100 g brain(-1) and 3% respectively. In 68% of 468 PNA events a fall in oxyhemoglobin saturation (SpO2) was detected and in 56% a fall in Hbdiff was detected. In 20% of events there was no fall in cerebral oxygenation despite a fall in SpO2. In 8% of PNA episodes we recorded a fall in cerebral oxygenation but no fall in SpO2. When a fall in cerebral oxygenation was recorded, the fall was greater when the event was also associated with a fall in SpO2 (median (interquartile range (IQR)) 0.32 (0.21-0.69) vs. 0.25 (0.16-0.43) micromol 100 g brain(-1), p < 0.05). When all the PNA episodes were reviewed no close correlation was shown between the magnitude of change in cerebral oxygenation and the change in SpO2 for small changes in both indices. However, large falls (>1.5 micromol 100 g brain(-1)) in cerebral oxygenation were closely associated with large changes in SpO2. CONCLUSIONS: We conclude that both techniques are sensitive to changes in oxygenation during PNA. Small changes in cerebral Hbdiff and arterial SpO2 do not always correlate for physiological reasons. A change in Hbdiff of >0.3 micromol 100 g brain(-1) is likely to be physiologically significant and is associated with a change in SpO2 of 12%.

Air Movements↗
PubMed2000

Estimation of jugular venous O2 saturation from cerebral oximetry or arterial O2 saturation during isocapnic hypoxia.

OBJECTIVE: Near-infrared spectroscopy (NIRS) has the potential for providing valuable information about oxygen delivery to the brain. However, questions have been raised about the accuracy of these measurements. This study was undertaken to compare noninvasive cerebral saturation measurements to jugular venous saturation under conditions of hypoxia and hypercapnia. METHODS: Data was obtain on forty-two subjects. Cerebral oxygenation was measured with a Somanetics INVOS 4100-SSA placed on the forehead of the subjects. PETCO2 was controlled to approximately 2 and 7 mmHg above resting values and PETO2 was controlled to 80, 45, 60 and 41 mmHg consecutively for four of five minutes each. Internal jugular blood gas measurements were made via a retrograde catheter. RESULTS: Both the cerebral oximetry measured saturation (rSO2) and the jugular venous saturation (SjvO2) were significantly increased by increasing the PETCO2 at all levels of hypoxia. The increase in the rSO2 was less than the increase in SjvO2. The rSO2 had a bias of 5.2% and a precision of 10.7% compared to the measured SjvO2. DISCUSSION: Cerebral oxygen saturation measured by cerebral oximetry compares well to the measured SjvO2 in normal subjects, despite multiple physiological reasons for differences. The closer relationship of SjvO2 to rSO2 than SaO2 under the conditions of these experiments indicates that the measurement reflects primarily intracranial saturation. However, outcome studies under clinical conditions are needed to determine the clinical utility of cerebral oximetry.

Adult↗
PubMed1999

Clinical investigation of a new combined pulse oximetry and carbon dioxide tension sensor in adult anaesthesia.

OBJECTIVE: To test the accuracy of a new combined oxygen saturation and cutaneous carbon dioxide tension (SPO2-PCO2) sensor in a routine adult clinical environment. This probe provides a non-invasive and continuous monitoring of the arterial oxyhaemoglobin saturation, arterial carbon dioxide tension and pulse rate at the ear lobe. The sensor is intended to measure both relevant respiration/ventilation parameters in one single probe. METHODS: Ten adult patients were consecutively studied during general anaesthesia. During the first 5 min after sensor placement at the ear lobe, arterial blood samples were drawn each minute. Carbon dioxide tension and oxygen saturation measurements were obtained simultaneously at 1-min intervals. After this period, patients were hyper-, normo- and hypoventilated. After 15 min at each setting, the simultaneously obtained cutaneous and arterial carbon dioxide tension values were compared. RESULTS: A total of 80 comparisons between ear lobe SpO2-PCO2 measurement, finger clip pulse oximetry and arterial blood gas values were analysed. Three minutes after sensor placement, there were no significant differences between ear probe (cutaneous) and arterial carbon dioxide tensions (p = 0.367). Comparison of arterial with cutaneous carbon dioxide values demonstrated an excellent linear correlation (r2 = 0.92), and showed a standard error of estimate (SDEE) of 0.26 kPa (1.95 mmHg) only. The mean difference was -0.08 kPa (-0.60 mmHg) with a limits of agreement range of -0.38 kPa to +0.22 kPa (-2.85 mmHg to +1.65 mmHg). Concerning oxygen saturation measurements, the absolute SpO2 value deviated 1% or less from standard pulse oximetry. CONCLUSIONS: During general anaesthesia, postoperative recovery and critical care treatment, both monitoring of oxygenation and ventilation is important. Since pulse oximetry estimates only arterial oxygen saturation, periodic blood sampling is still necessary to determine the patient's arterial carbon dioxide status. We could demonstrate that the difference between cutaneous and arterial PCO2 was clinically unimportant, and therefore we conclude that the two methods of estimating the patient's carbon dioxide status may be used interchangeably. Our results demonstrated that 3 min after sensor placement, the new SpO2-PCO2 sensor prototype proved to be a reliable tool for continuous non-invasive monitoring of oxygenation and ventilation.

Adult↗
PubMed1999

Inferior mesenteric venous sampling, pulse oximetry, and assessment of colonic perfusion during aortic aneurysm surgery.

Ischemic colitis is a serious complication of aortic surgery. The condition continues to be difficult to diagnose at an early stage. This study monitors the biochemical changes in systemic and selective inferior mesenteric vein (IMV) blood sampling during aortic surgery and compares the reproducibility of this method to intraoperative colonic pulse oximetry in a series of 18 patients undergoing infrarenal aortic aneurysm repair. Base excess, pH, pCO2, and lactate were altered by aortic cross-clamping but returned to normal within 48 hr. IMV inorganic phosphate levels were higher than systemic values, suggesting improved sensitivity with selective sampling. BB isoenzymes of creatine kinase remained normal in all patients. Pulse oximetry signals were inconsistently obtained from the colon. This study establishes the physiological changes in IMV biochemistry during aortic surgery. Unlike intraoperative pulse oximetry, selective IMV sampling provides reproducible measurements of colonic perfusion. This simple and safe technique warrants further assessment of its accuracy at diagnosing ischemic colitis.

Alanine Transaminase↗
PubMed2001

Jugular bulb oximetry during cardiac surgery.

Imbalance between cerebral oxygen supply and demand is thought to play an important role in the development of cerebral injury during cardiac surgery. This article presents an overview of cerebral oxygenation monitored by jugular bulb oximetry during cardiac surgery with cardiopulmonary bypass. The general principles of jugular bulb oximetry including physiology, intermittent and continuous monitoring, technical considerations, limitations and potential complications are discussed. Different applications of jugular bulb oximetry during bypass surgery and the possible therapeutic approaches to impaired cerebral oxygenation are described.

Brain Chemistry↗
PubMed2003

Evaluation of oesophageal pulse oximetry in patients undergoing cardiothoracic surgery.

Pulse oximetry probes placed peripherally may fail to give accurate values of blood oxygen saturation when the peripheral circulation is poor. Because central blood flow may be preferentially preserved, we investigated the oesophagus as an alternative monitoring site. A reflectance blood oxygen saturation probe was developed and evaluated in 49 patients undergoing cardiothoracic surgery. The oesophageal pulse oximeter results were in good agreement with oxygen saturation measurements obtained by a blood gas analyser, a CO-oximeter and a commercial finger pulse oximeter. The median (IQR [range]) difference between the oesophageal oxygen saturation results and those from blood gas analysis were 0.00 (-0.30 to 0.30 [-4.47 to 2.60]), and between the oesophageal oxygen saturation results and those from CO-oximetry were 0.75 (0.30 to 1.20 [-1.80 to 1.80]). Bland-Altman analysis showed that the bias and the limits of agreement between the oesophageal and finger pulse oximeters were -0.3% and -3.3 to 2.7%, respectively. In five (10.2%) patients, the finger pulse oximeter failed for at least 10 min, whereas the oesophageal readings remained reliable. The results suggest that the oesophagus may be used as an alternative monitoring site for pulse oximetry even in patients with compromised peripheral perfusion.

Adult↗
PubMed1999

Awake daytime oximetry measurements in the management of infants with chronic lung disease.

OBJECTIVE: To assess the value of 1-h daytime awake oximetry as a means of weaning oxygen flows in infants with oxygen dependent chronic lung disease. METHODS: A cohort study of oxygen dependent infants enrolled in a 3-month period. One hour of awake oximetry data were compared with equal time periods defined within a polysomnographic study and at the same oxygen flow rate. Sensitivity results were derived from the decision to wean oxygen to a lower flow or air. RESULTS: Twenty-two infants were enrolled and 27 studies were performed. The infants that could be weaned had an awake median of mean oxygen saturations of 97% and spent 14% of the time < or = 95% but only 2% < or = 92%, while for those not weaned, the awake median of mean oxygen saturations was 94% with 43% of their time < or = 95% and 26.8% < or = 92% saturation. CONCLUSIONS: Daytime oximetry can predict the outcome of polysomnography with a sensitivity of 100% and a specificity of 65%, and could be used to wean oxygen or as a screening tool for polysomnographic studies in infants with chronic lung disease provided there are reasonably long periods of monitoring and mean oxygen saturations above 95%.

Bronchopulmonary Dysplasia↗
PubMed2001

Postoperative monitoring of pediatric toe-to-hand transfers with differential pulse oximetry.

Twenty-three toe-to-hand transfers performed in 21 children were monitored after surgery using differential pulse oximetry for 4 to 12 days. Pulse rate recorded by the pulse oximetry monitored the patency of the arterial anastomosis, whereas oxygen saturation (SaO(2)) corresponded to the patency of the venous anastomosis; these were both compared with the systemic pulse rate and oxygen saturation recorded by a second control pulse oximeter probe attached to a contralateral finger or toe. All 23 toe transfers were ultimately successful, but 2 required re-exploration for anastomotic problems detected by the pulse oximeter. Based on this experience, the following criteria have been developed for the nursing and junior medical staff: if the arterial pulse of the toe transfer is lost completely or if the pulse rate differs significantly from the systemic pulse rate, measured by the second control pulse oximeter, thrombosis of the arterial anastomosis should be suspected. If the oxygen saturation of the toe transfer decreases below the oxygen saturation measured by the control pulse oximeter and this differential is sustained over a period of time, thrombosis of the venous anastomosis should be suspected. Differential pulse oximetry appears to be superior to temperature monitoring and percutaneous and laser Doppler monitoring and provides the most simple and continuous technique of noninvasive postoperative monitoring of toe-to-hand transfers in children requiring reconstruction of traumatic or congenital deformities.

Adolescent↗
PubMed2005

[Reliability of fetal pulse oximetry for the detection of fetal acidosis].

Fetal pulse oximetry is a continuous method to exclude the lack of oxygen in cases of non-reassuring fetal heart rate. This study aims at the evaluation of the predictive value of this method concerning the development of fetal acidosis. 136 fetuses with non-reassuring heart rate were monitored by fetal pulse oximetry. In all cases fetal blood pH and base excess were determined repeatedly by fetal blood analysis (FBA). The pH value and base excess in the umbilical artery and scalp blood as well as the changes of pH and base excess were correlated to the duration of low, medium and high fetal oxygen saturation (FSpO (2)). Sensitivity, specificity, positive and negative predictive values were calculated for the assumption that "FSpO (2) < or = 30 % for at least 10 or 15 minutes" predicts a pH or base excess in the umbilical artery and in FBA of < 7.1/7.15/7.2 or < or = -4/8/12 mmol/L and a decline of pH (base excess) by more than 0.05 (0.1) pH units (4 mmol/L). A highly significant negative correlation was found between umbilical artery and FBA pH and base excess as well as the change of both and the duration of low oxygen saturation. Additionally the change of FBA pH depends on the duration of medium FSpO (2). A pH below 7.15 in FBA as well as base excess < or = -12 mmol/L were safely detected by a cut-off of "FSpO (2) < or = 30 % for at least 10 minutes" and pH < 7.1 and base excess < or = -12 mmol/l in FBA in 100 % and 75 %, respectively. A decline of pH by more than 0.1 pH units and of base excess by more than 4 mmol/L were excluded by a negative predictive value of 98 %. In conclusion, medium and progressive acidosis can be reliably excluded by fetal pulse oximetry.

Acidosis↗
PubMed2001

Pulse oximetry saturation levels during routine unsedated diagnostic upper gastrointestinal endoscopy.

BACKGROUND: Diagnostic procedures account for over 90% of all upper gastrointestinal endoscopies. Pulse oximetry saturation (SpO2) levels were assessed in patients attending for routine unsedated diagnostic gastroscopy to identify factors associated with oxygen desaturation. METHODS: Three hundred and thirty unsedated patients were monitored with continuous pulse oximetry. A further 154 patients who requested sedation prior to endoscopy were studied as a positive control group. RESULTS: SpO2 levels were lower in sedated compared to unsedated patients (P < 0.0001). Six unsedated patients (2%) desaturated to 90% or less during endoscopy compared to 32 sedated patients (21%) (P < 0.0001). SpO2 levels in unsedated patients were not related to patient sex, age, cigarette smoking, endoscope diameter, basal SpO2 levels or duration of endoscopy. In contrast, examination of the pharyngeal area and epiglottis (P = 0.0002) and a longer intubation time (P = 0.0002) were associated with lower SpO2 levels. The lowest SpO2 level recorded during unsedated endoscopy was 88%. CONCLUSION: Pulse oximetry is not a prerequisite to performing routine unsedated diagnostic gastroscopy in patients without severe systemic disease.

Case-Control Studies↗
PubMedDate not supplied

Retinal oximetry using intravitreal illumination.

PURPOSE: To demonstrate spectroscopic retinal oximetry measurements on arteries and veins in swine using intravitreal illumination. Retinal arterial and venous saturations are measured for a range of inspired O2 levels after pars plana vitrectomy. METHODS: Pars plana vitrectomy and intravitreal manipulations were performed on two female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiberoptic intraocular illuminator inserted into the vitreous. The retinal vessels were illuminated obliquely, minimizing vessel glints. Multispectral images of the retinal vasculature were obtained as the swine's arterial blood oxygen saturation was decreased from 100% to 67% in decrements of approximately 10%. Retinal vessel spectra were used to calculate oxygen saturation in selected arteries and veins. Arterial oxygen saturations were calibrated using blood gas analysis on blood drawn from a Swan-Ganz catheter placed in the femoral artery. RESULTS: Oblique illumination of retinal vessels using an intravitreal fiberoptic illuminator provided a substantial reduction in the central vessel glint usually seen in fundus images, thus simplifying the analysis of spectral data. The vessel shadows were displaced from the vessel image simplifying the light paths in the eye. Using a full spectral analysis simplified by the light path reductions, we calculated retinal vessel saturations. The reduction of glint allowed for increased accuracy in measuring retinal vessel spectral optical density. Abnormally low retinal venous oxygen saturations were observed shortly after pars plana vitrectomy. CONCLUSIONS: Retinal oximetry using intravitreal illumination has been demonstrated. As a research tool, intravitreal illumination addresses several difficulties encountered when performing retinal oximetry with transcorneal illumination.

Animals↗
PubMed2006

Survival of patients with ALS following institution of enteral feeding is related to pre-procedure oximetry: a retrospective review of 98 patients in a single centre.

A retrospective review was carried out on the influence of pre-procedure respiratory assessment on survival of patients with amyotrophic lateral sclerosis (ALS) requiring nutritional support with either a gastrostomy or a nasogastric feeding tube. Over a five-year period 98 patients (49 male, 49 female; median age 61 years, range 26-86 years) with ALS were referred for enteral feeding with either radiological inserted gastrostomy (RIG), percutaneous endoscopic gastrostomy (PEG) or nasogastric tube (NG). Case notes review was performed to record patient age, sex, pre-procedure respiratory assessment, method of enteral feeding and survival post-procedure. Kaplan-Meier survival curves were constructed for each group, with Cox regression analyses performed in order to establish the effect of each variable on outcome. Median survival (with 95% confidence intervals) following RIG, PEG and NG was 6.31 months (4.58-8.04 months), 7.13 months (4.81-9.45 months) and 0.95 months (0.00-2.77 months), respectively. The survival advantage between RIG and PEG was not statistically significant (p = 0.50), but for NG versus RIG and PEG groups combined, there was a significant difference (p = 0.03). For patients with normal overnight oximetry, median survival was 8.54 months (3.88-13.21 months), compared to 4.80 months (1.20-8.39 months) in the abnormal oximetry group (p = 0.03; relative risk 1.97). It is concluded that RIG and PEG are equivalent in terms of post-procedure survival. Abnormal oximetry prior to the procedure is a significant indicator of post-procedure survival.

Adult↗
PubMed2005

Simultaneous measurement of rat brain cortex PtO2 using EPR oximetry and a fluorescence fiber-optic sensor during normoxia and hyperoxia.

Electron paramagnetic resonance (EPR) oximetry is a promising, relatively non-invasive method of monitoring tissue partial pressure of oxygen (PtO(2)) that has proven useful in following changes in PtO(2) under various physiologic and pathophysiologic conditions. Optimal utilization of the method will be facilitated by systematic comparisons with other available methods. Here, we report on the absolute values and changes of rat brain PtO(2) using EPR oximetry and the OxyLite, an oxygen monitor based on fluorescence quenching, at adjacent locations in the same brain. EPR oximetry utilizes an implanted oxygen-sensitive material and reports tissue PtO(2) at the surface of the material. OxyLite measures PtO(2) using the fluorescence lifetime of a chromophore fixed to the tip of an optical fiber that is inserted into tissue. Measurements were made at a depth of 2-3 mm into the cortex during normoxia and during breathing of carbogen (95% O(2):5% CO(2)) followed by a return to normoxia. We conclude that in this study (1) PtO(2) values reported by the two methods are similar but not exactly the same, (2) both methods can record a baseline and rapid changes in PtO(2), (3) changes in PtO(2) induced by increasing FiO(2) from 0.26 to 0.95 (carbogen) were similar by the two methods and (4) in some rats breathing carbogen, absolute values of PtO(2) were above the sensitive range of the OxyLite method.

Animals↗
PubMed2004

Pulse oximetry in the diagnosis of acute mountain sickness.

Acute mountain sickness (AMS) is a common condition in individuals who travel to altitudes over 2000 m. While AMS is an important public health problem, no measurements can reliably support or predict the diagnosis with any degree of confidence. We therefore set out to study whether pulse oximetry data are associated with AMS. We studied 169 subjects who had recently arrived by foot at 3080 m. Subjects completed a demographic survey, which collected data on ascent profiles and AMS symptoms. Resting arterial oxygen saturation and pulse rate were then measured using finger pulse oximetry. Forty-six subjects (27%) had AMS, using the Lake Louise score. Only pulse rate was significantly associated with the presence of AMS (OR: 1.4; 95% CI, 1.1 to 1.9; p < 0.05, backwards stepwise logistical regression). A trend showed worse AMS diagnoses were associated with higher mean pulse rates (p < 0.05, ANOVA linear weighted analysis). While some previous studies have shown an association between decreased oxygen saturation and acute mountain sickness at altitude, our results did not demonstrate such an association. The utility of pulse oximetry remains limited in the diagnosis of AMS. We recommend further study to determine the possible utility of pulse rate in the diagnosis and prediction of AMS.

Acute Disease↗
PubMed1990

Carboxyhaemoglobin concentrations, pulse oximetry and arterial blood-gas tensions during jet ventilation for Nd-YAG laser bronchoscopy.

Oxygen saturation measured with pulse oximetry (SpO2) is overestimated in the presence of carboxyhaemoglobin (COHb). Smoke produced during laser resection of tracheobronchial malignancies may increase concentrations of COHb. We have measured COHb concentrations in 14 patients undergoing laser resection and compared SpO2 with functional oxygen saturation (SaO2) to ascertain if pulse oximetry is an accurate monitor of oxygen saturation. During the procedure frequent changes occur in ventilatory mechanics. Arterial blood-gas tensions were measured to see if gas exchange was satisfactory. Mean preoperative COHb was 1.4%. There was no significant change in COHb in any patient at any stage during treatment. The highest value was 2.05%. The mean difference between SaO2 and SpO2 was 1.13% (95% confidence interval 0.70-1.56%). Oxygen saturation may therefore safely be monitored by pulse oximetry in patients managed by our technique. Empirical setting of a jet ventilator provided acceptable blood-gas tensions, although sometimes it was necessary to increase the FlO2 to greater than 0.3 to maintain oxygenation.

Adult↗