Cerebral oxygen saturation evaluated by near-infrared time-resolved spectroscopy (TRS) in pregnant women during caesarean section - a promising new method of maternal monitoring

Changes of cerebral oxygenation indices measured by near infrared time-resolved spectroscopy during spinal anesthesia for cesarean section: Simultaneous measurement with cerebral blood flow

AIM

To measure the changes in cerebral oxygenation indices by near infrared time-resolved spectroscopy and the cerebral blood flow simultaneously after spinal anesthesia for cesarean section.

METHODS

This prospective observational study was conducted for 25 pregnant women scheduled for elective cesarean section under spinal anesthesia. During a period of 15 min after spinal anesthesia, cerebral oxygenation (ScO₂ ), and the total cerebral hemoglobin concentration (tHb) were measured using near infrared time-resolved spectroscopy and mean cerebral blood flow velocity (Vm) was measured using transcranial Doppler ultrasonography. Next, in the women who had nausea during the observed period, we compared these values when nausea was detected with those when it was not.

RESULTS

Mean arterial pressure (MAP) decreased to around 60 mmHg (by 25% compared to the control) 6 min after spinal anesthesia. Compared to the control, ScO₂ decreased by about 3% after 6 min and then gradually increased. The tHb, which reflects cerebral blood volume started to decrease just after spinal anesthesia and this continued until 12 min (the decrease was about 12%). Vm decreased by about 7%. In the 14 women who had nausea, MAP, Vm, and ScO₂ values when nausea was detected were significantly lower than when it was not.

CONCLUSION

The changes in cerebral hemodynamics may be small after spinal anesthesia in ordinary cesarean section compared to the reduction of systemic arterial blood pressure. There might be greater decreases in cerebral blood flow and oxygenation when nausea occurred in the pregnant women who experienced it after spinal anesthesia.

Changes of Cerebral Blood Volume During Robot-Assisted Laparoscopic Radical Prostatectomy: Observational Prospective Study Using Near-Infrared Time-Resolved Spectroscopy

Purpose: Robot-assisted laparoscopic radical prostatectomy (RARP) requires a steep head-down tilt and pneumoperitoneum, which may cause an increase in cerebral blood volume (CBV). With a new near-infrared time-resolved spectroscopy device, the tNIRS-1, we can measure the absolute value of the cerebral hemoglobin concentration and hence calculate CBV and cerebral oxygen saturation (rSO₂). Using this device, we evaluated the time course of CBV during surgery and also evaluated the changes in rSO₂ simultaneously. Materials and Methods: We performed a prospective observational study of 21 patients scheduled for RARP. We evaluated CBV and rSO₂ by using the tNIRS-1 at 10 time points during surgery. Results: The CBV was 2.92 ± 0.38 mL ·100 g^-1 after the end of anesthetic preparation. It significantly increased to 3.05 ± 0.44 mL ·100 g^-1 after the head-down tilt and was around 3.1 mL ·100 g^-1 until 120 minutes after the head-down tilt. However, just before the return to the horizontal position, it decreased to 2.93 ± 0.46 mL ·100 g^-1 and then decreased more after the return to the horizontal position. Changes in rSO₂ over time were within only 3%, and no significant differences from the control value were observed. Conclusions: The increase in CBV was <10% despite the steep head-down tilt and pneumoperitoneum, and it was compensated for at around the end of surgery. Clinically significant changes in rSO₂ were not observed during the surgery.

Clinical Brain Monitoring with Time Domain NIRS: A Review and Future Perspectives

Near-infrared spectroscopy (NIRS) is an optical technique that can measure brain tissue oxygenation and haemodynamics in real-time and at the patient bedside allowing medical doctors to access important physiological information. However, despite this, the use of NIRS in a clinical environment is hindered due to limitations, such as poor reproducibility, lack of depth sensitivity and poor brain-specificity. Time domain NIRS (or TD-NIRS) can resolve these issues and offer detailed information of the optical properties of the tissue, allowing better physiological information to be retrieved. This is achieved at the cost of increased instrument complexity, operation complexity and price. In this review, we focus on brain monitoring clinical applications of TD-NIRS. A total of 52 publications were identified, spanning the fields of neonatal imaging, stroke assessment, traumatic brain injury (TBI) assessment, brain death assessment, psychiatry, peroperative care, neuronal disorders assessment and communication with patient with locked-in syndrome. In all the publications, the advantages of the TD-NIRS measurement to (1) extract absolute values of haemoglobin concentration and tissue oxygen saturation, (2) assess the reduced scattering coefficient, and (3) separate between extra-cerebral and cerebral tissues, are highlighted; and emphasize the utility of TD-NIRS in a clinical context. In the last sections of this review, we explore the recent developments of TD-NIRS, in terms of instrumentation and methodologies that might impact and broaden its use in the hospital.

Time-Domain Near-Infrared Spectroscopy and Imaging: A Review

This article reviews the past and current statuses of time-domain near-infrared spectroscopy (TD-NIRS) and imaging. Although time-domain technology is not yet widely employed due to its drawbacks of being cumbersome, bulky, and very expensive compared to commercial continuous wave (CW) and frequency-domain (FD) fNIRS systems, TD-NIRS has great advantages over CW and FD systems because time-resolved data measured by TD systems contain the richest information about optical properties inside measured objects. This article focuses on reviewing the theoretical background, advanced theories and methods, instruments, and studies on clinical applications for TD-NIRS including some clinical studies which used TD-NIRS systems. Major events in the development of TD-NIRS and imaging are identified and summarized in chronological tables and figures. Finally, prospects for TD-NIRS in the near future are briefly described.

Stable tissue-simulating phantoms with various water and lipid contents for diffuse optical spectroscopy

We introduced a method for producing solid phantoms with various water-to-lipid ratios that can simulate the absorption, and to some extent the scattering characteristics of human breast tissue. We also achieved phantom stability for a minimum of one month by solidifying the emulsion phantoms. The characteristics of the phantoms were evaluated using the six-wavelength time-domain diffuse optical spectroscopy (TD-DOS) system we developed to measure water and lipid contents and hemoglobin concentration. The TD-DOS measurements were validated with a magnetic resonance imaging system.

Near-infrared spectrometry in pregnancy: progress and perspectives, a review of literature

Near-infrared spectroscopy (NIRS) allows continuous noninvasive monitoring of in vivo oxygenation in selected tissues. It has been used primarily as a research tool for several years, but it is seeing wider application in the clinical arena all over the world. It was recently used to monitor brain circulation in cardiac surgery, carotid endarteriectomy, neurosurgery and robotic surgery. According to the few studies used NIRS in pregnancy, it may be helpful to assess the impact of severe forms of preeclampsia on brain circulation, to evaluate the efficacy of different treatments. It may also be used during cesarean section to detect earlier sudden complications. The evaluation of placental function via abdominal maternal approach to detect fetal growth restriction is a new field of application of NIRS.

Diffuse reflectance spectroscopy for the measurement of tissue oxygen saturation

Tissue oxygen saturation (StO2) is a useful parameter for medical applications. A spectroscopic method has been developed to detect pathologic tissues, due to a lack of normal blood circulation, by measuring StO2. In this study, human blood samples with different levels of oxygen saturation have been prepared and spectra were acquired using an optical fiber probe to investigate the correlation between the oxygen saturation levels and the spectra. A linear correlation between the oxygen saturation and ratio of the intensities (760 nm to 790 nm) of the spectra acquired from blood samples has been found. In a validation study, oxygen saturations of the blood samples were estimated from the spectroscopic measurements with an error of 2.9%. It has also been shown that the linear dependence between the ratio and the oxygen saturation of the blood samples was valid for the blood samples with different hematocrits. Spectra were acquired from the forearms of 30 healthy volunteers to estimate StO2 prior to, at the beginning of, after 2 min, and at the release of total vascular occlusion. The average StO2 of a forearm before and after the two minutes occlusion was significantly different. The results suggested that optical reflectance spectroscopy is a sensitive method to estimate the StO2 levels of human tissue. The technique developed to measure StO2 has potential to detect ischemia in real time.

Cerebral oximetry assessed by near-infrared spectrometry during preeclampsia: an observational study: impact of magnesium sulfate administration

OBJECTIVES

To determine the regional cerebral oxygen saturation of hemoglobin (rcSO2) in severe preeclamptic parturients exhibiting neurologic symptoms compared with healthy pregnant women (control) and to describe the effects of MgSO4 infusion on rcSO2 and cerebral and systemic hemodynamic variables.

DESIGN

Prospective, observational study.

SETTING

Obstetric critical care unit in a university-affiliated hospital.

PATIENTS

Twenty severe preeclamptic parturients presenting with neurologic signs before any administration of MgSO4, and 20 control parturients.

INTERVENTION

Infusion of MgSO4 in severe preeclamptic patients.

MEASUREMENTS AND MAIN RESULTS

We measured rcSO2 using near-infrared spectroscopy, blood flow velocities of the middle cerebral artery, and cardiac output at baseline, 5 minutes, 1 hour, and 6 hours after the MgSO4 bolus (4 g), followed by continuous MgSO4 infusion (1 g/h). These measurements were also obtained in 20 control parturients at baseline and 6 hours. Baseline rcSO2 was significantly lower in the severe preeclamptic group: 61% (56-69) vs 66% (63-71) (p = 0.037). At inclusion, blood pressures were significantly higher in the severe preeclamptic group compared with the control group, whereas cardiac output and transcranial Doppler readings were similar. Five minutes after the MgSO4 bolus infusion, a median increase of 8.6% (3.2-18.1) in rcSO2 was observed (p = 0.007), reaching values of the control group that were maintained up to 6 hours. Blood pressures and systolic velocities of the middle cerebral artery significantly decreased (p < 0.01) after the MgSO4 bolus, whereas cardiac output did not change. The percentage increase in rcSO2 was negatively correlated to the mean blood pressure (r = 0.60, p < 0.0001).

CONCLUSION

Cerebral oxygenation impairment can be detected by near-infrared spectroscopy monitoring in severe preeclamptic parturients. These results suggested the presence of disorders in cerebral microcirculation and/or changes in cerebral oxygenation. MgSO4 infusion in patients with severe preeclampsia restored rcSO2 to control levels with no systemic side effects. Further studies are needed to confirm the usefulness of near-infrared spectroscopy monitoring in patients with preeclampsia and to assess the action of other antihypertensive therapies on rcSO2.

Brain susceptibility weighted imaging signal changes in acute hemorrhagic anemia: an experimental study using a rabbit model

BACKGROUND

The aim of this study was to investigate susceptibility-weighted imaging (SWI) signal changes in different brain regions in a rabbit model of acute hemorrhagic anemia.

MATERIAL/METHODS

Ten New Zealand white rabbits were used for construction of the model of acute hemorrhagic anemia. Signal intensities of SWI images of the bilateral frontal cortex, frontal white matter, temporal lobe, and thalamic nuclei were measured. In addition, the cerebral gray-white contrast and venous structures of the SWI images were evaluated by an experienced physician.

RESULTS

Repeated bloodletting was associated with significant reductions in red blood cell count, hemoglobin concentration, hematocrit, pH, and PaCO2, and elevations of blood lactate and PaO2. In normal status, the SWI signal intensity was significantly higher in the frontal cortex than in the frontal white matter (63.10±22.82 vs. 52.50±20.29; P<0.05). Repeated bloodletting (5 occasions) caused significant (P<0.05) decreases in the SWI signals of the frontal cortex (from 63.10±22.82 to 37.70±4.32), temporal lobe (from 52.50±20.29 to 42.60±5.54), and thalamus (from 60.40±20.29 to 39.40±3.47), but was without effect in the frontal white matter. The cerebral white-gray contrast and venous structures were clearer after bloodletting than before bloodletting.

CONCLUSIONS

The effect of hemorrhage on the brain is reflected by SWI signal changes in the cerebral cortex and gray matter nuclei.