Cerebral Arterial Oxygen Saturation Research Articles

Does glycemic level affect neurologic outcomes during cardiopulmonary bypass?

Perioperative hyperglycaemia, aggravated by cardiopulmonary bypass (CPB), is associated with adverse outcomes. Increased potential for stroke in these patients may be improved by different interventions. Blood glucose level changes as an intrinsic response to both stress and extrinsic sources; might affect early mortality and morbidity. In this study, we tried to identify a relationship existence between cerebral arterial oxygen saturation (rSO2) and blood glucose levels, and thus; evaluate changes in rSO2 caused by changes in blood glucose levels measured at predetermined time points of CPB. Forty six patients with American Society of Anaesthesiologists (ASA) physical status at least III and even IV, undergoing elective open cardiac surgery were prospectively studied. Preparation for surgery, anaesthesia and perioperative vital data monitoring (five-channel) ECG, pulse oximetry, capnography, nasopharynx and rectal temperature, invasive arterial blood pressure, central venous pressure and near-infrared spectroscopy (NIRS) monitoring were done in the same standardised way for each patient. The Mini-Mental State Examination (MMT) questionnaire was used for these patients before and 24 hours after the operation to assess neurologic adverse effects. NIRS values and blood glucose levels were sampled at the following stages of the intervention: the reference level (T0) was obtained immediately after cannulation of the arterial system and before anaesthesia; the second sample (T1) was taken 20 min after anaesthesia was introduced; the third sample (T3) was taken after 20 min of the aortic cross-clamp; the fourth sample (T4) was taken 20 min after the removal of the aortic cross-clamp; and the final sample (T5) was obtained 24 h after the surgery. No statistically signifi;cant relationship was found between changes in rSO2 and changes in blood glucose levels before surgery, after anaesthesia, ischemia, reperfusion, and surgery, in either diabetic or non-diabetic patients. Our findings showed increase in blood glucose levels and decrease in rSO2 as expected in ischemia and reperfusion periods of bypass. There was no significant difference between preoperative and postoperative MMT values of diabetic and non-diabetic patients. Cerebral oxygen saturation measured by NIRS may be a useful monitorization in open cardiac surgery. Our fndings suggests that hyper/hypoglycemia during surgery did not reflect changes in cerebral oxygenation, thus neurologic outcomes when other variables remained constant. Further studies using this approach in different surgeries and patient groups are needed.

Utility of cerebral oxymetry for assessing cerebral arteriolar carbon dioxide reactivity during cardiopulmonary bypass.

Our study evaluated changes in cerebral arterial oxygen saturation (rSO2) during cardiopulmonary bypass (CPB) that were caused by changes in arterial carbon dioxide tension (PaCO2). A group of 126 patients undergoing routine, elective, first-time coronary artery bypass graft surgery (CABG) was entered into a prospective study using bilateral near-infrared spectroscopy (NIRS) before anesthetic induction (T1), after anesthetic induction (T2), and continuing at 5-minute intervals during moderate hypothermic (32°C) CPB. Pump flows were set at 2.5 L/min/m(2) and adjusted to maintain mean arterial pressure (MAP) within 10 mmHg of the MAP recorded at the initial fifth minute of CPB (T3). Thirty-two patients were excluded from data collection because MAP could not be stabilized within the target range of 60-90 mmHg. In the remaining 94 patients, after obtaining steady state flow, MAP, and oxygenation, a trial period of hypocarbia (mean PaCO2 of 30 mmHg) was induced by increasing oxygenator fresh gas flow rate (FGFR) to 2.5 L/min/m(2) (T4). A reciprocal period was then measured at reduced FGFR (0.75 L/min/m(2)) (T5). After 20 minutes of a higher (2.75 L/min/m(2)) (FGFR), mean PaCO2 decreased from a baseline of 38 ± 4 mmHg to 30 ± 2 mmHg. This was associated with a parallel decrease (-10 ± 9%) in mixed cerebral oxygen saturation without alteration of mean arterial oxygen tension (PaO2), lactate, MAP, CPB flow, or other parameters implying increased cerebral oxygen extraction. Parallel changes in PaCO2 and rSO2 occur during CPB when other variables remain constant, and are due to the effects of carbon dioxide on cerebral arterioles. Cerebral oxygen saturation measured by NIRS may be a useful indirect measure of PaCO2 when continuous blood gas analysis is not possible during open-heart surgery. Cerebral oximetry values may be useful measurements for setting an optimum gas flow rate through the oxygenator.

Cerebral Arterial and Venous Contributions to Tissue Oxygenation Index Measured Using Spatially Resolved Spectroscopy in Newborn Lambs

Bedside assessments of cerebral oxygenation are sought to monitor cerebral injury in patients undergoing intensive care. Spatially resolved spectroscopy measures tissue oxygenation index (TOI, %) which reflects mixed cerebral arterial and venous oxygenations. We aimed to evaluate arterial and venous components of TOI (cerebral arterial to venous volume ratio [A:V ratio]) in the newborn lamb brain using cerebral arterial and venous blood samples, and to investigate the impact of acute hypoxemia on the A:V ratio and TOI. Nine lambs were ventilated with varied inspired oxygen to generate arterial oxygen saturations between 25% and 100%. Cerebral arterial and venous oxygen saturations analyzed using cooximeter of arterial and superior sagittal sinus blood were used to estimate TOI (TOIcox), assuming cerebral A:V ratio of 25:75. TOIcox was compared with the TOI measured by spatially resolved spectroscopy (TOIsrs). Actual cerebral arterial and venous volume fractions were reestimated using TOIsrs = cerebral arterial volume fraction cerebral arterial oxygen saturation + cerebral venous volume fraction*cerebral venous oxygen saturation. Median (range) TOIsrs was 48.5% (32.0-64.1%), and TOIcox was 48.4% (13.7-74.4%), and the two were significantly correlated (R = 0.77). The mean difference between TOIsrs and TOIcox was 2.4% (limits of agreement ± 18.1%). The TOIsrs - TOIcox difference varied with oxygen saturations, with TOIsrs higher than TOIcox at low saturations, and lower at high saturations. Cerebral arterial volume fraction was 22.9-27.5% in normoxia and markedly increased in hypoxemia. TOI corresponds with cerebral oxygenation. The variable agreement of TOIsrs with TOIcox may reflect changes in cerebral A:V ratio due to arterial oxygenation-related vasoreactivity.

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.

Continuous noninvasive measurement of cerebral arterial and venous oxygen saturation at the bedside in mechanically ventilated neonates.

To test the practicablity of a new spectrophotometric method using pulse oximetric techniques in combination with special filters for the noninvasive determination of cerebral arterial and venous oxygen saturation and oxygen extraction in neonatal intensive care unit patients. The spectrophotometer used three different wavelengths at a sampling rate of 100 Hz. Clinical evaluation of a new method and comparison with previously published data. Design and construction of the special spectrophotometer at the Biomedical Engineering Laboratory of the Swiss Federal Institute of Technology. Measurements in the neonatal intensive care unit of the University Hospital, Zurich, Switzerland. Convenience sample of 15 clinically stable newborn infants, who were mechanically ventilated and receiving supplemental oxygen. Median gestational age was 29 5/7 wks (range 26 3/ 7 to 36 0/7), median birth weight was 1555 g (720 to 2500), median postnatal age was 4 days (1 to 10). The emitter and receiver were placed on the forehead near the sagittal sinus, between 2 and 2.8 cm apart, and the pulsating light attenuations (arterial and venous pulse waves) were recorded. Arterial and venous pulse waves were satisfactory in 10 of 15 infants. Mean cerebral arterial oxygen saturation was 89.9 +/- 5.4% (SD), mean cerebral venous oxygen saturation was 73.0 +/- 8.9%, and mean cerebral oxygen extraction was 16.9 +/- 11.7%. A linear regression analysis demonstrated a significant correlation between mean PCO2 and venous oxygen saturation (slope 1.0%/torr, p < .05) and between mean PCO2 and cerebral oxygen extraction (slope -1.3%/torr, p < .05). This new method has the potential for monitoring continuously, noninvasively, and simultaneously cerebral arterial and venous oxygen saturation and oxygen extraction in mechanically ventilated preterm infants.