Recent developments in cerebral monitoring--near-infrared light spectroscopy. An overview

Monitoring of limb perfusion after vascular surgery in critical limb ischemia using near-infrared spectroscopy: A prospective observational study

Background:

Intra and postoperative perfusion monitoring should be used in critical limb ischemia patients undergoing vascular surgery to improve outcomes and reduce costs. While a pulse oximeter can be applied on the affected limb to monitor the arterial saturation of the limb, thus reflecting flow in that limb, we need to focus on other important parameters like muscle oxygen consumption and regional blood flow for a good outcome. Near-infrared spectroscopy (NIRS) can be used in such patients to monitor regional and tissue oxygenation.

Methodology:

In this prospective observational study, 30 adult patients undergoing infra-inguinal bypass were recruited. All these patients were given combined spinal-epidural anesthesia. In addition to routine monitoring, a pulse oximeter and NIRS electrodes were applied on the affected limb. rsO2, limb spO2, and Doppler signals were noted before the induction of anesthesia (baseline) and postoperatively at 0, 6, and 12 h. Improvement in rsO2 and limb spO2 values after surgery was noted and fall in these values was evaluated. Pearson correlation between rsO2 and limb spO2 was assessed. The data was analyzed using repeated-measures ANOVA.

Results:

Pearson correlation between rsO2 and limb spO2 was r > 0.8. Two patients had a fall in rsO2 in postoperative period, which co-related with a fall in limb spO2 and decreased/absent Doppler signals.

Conclusion:

NIRS represents a noninvasive and reliable means to monitor limb perfusion in patients undergoing vascular surgery for rest pain.

The effect of tourniquet deflation on hemodynamics and regional cerebral oxygen saturation in aged patients undergoing total knee replacement surgery

BACKGROUND

Inflation and deflation of a pneumatic tourniquet used in total knee replacement surgery induces various changes in patient's hemodynamic and metabolic status, which may result in serious complications, especially in aged patients. Near-infrared spectroscopy (NIRS) is a monitoring device designed to estimate the regional cerebral oxygen saturation. We evaluated the effect of tourniquet deflation on hemodynamics and regional cerebral oxygen saturation in aged patients undergoing total knee replacement surgery, using NIRS.

METHODS

Twenty-eight American Society of Anesthesiologists physical status I or II patients, over the age of sixty-five years undergoing total knee replacement surgery, were included. Under general anesthesia, the mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), stroke volume (SV), and regional cerebral oxygen saturation (rSO(2)) were recorded before induction of anesthesia and every 2 min after tourniquet deflation for 20 min. Arterial blood gas analysis was performed 5 min before, in addition to 0, and 10 min after tourniquet deflation.

RESULTS

The decrease of rSO(2) was not significant during 20-min deflation period. MAP, CO and SV showed significant decrease during 2 to 12, 4 to 6 and 2 to 6-min period after tourniquet deflation, respectively (P < 0.05). There was no relationship between a maximal decrease of MAP and rSO(2).

CONCLUSIONS

In aged patients undergoing total knee replacement surgery under general anesthesia, tourniquet deflation caused significant changes in hemodynamic and metabolic status, but not in regional cerebral oxygen saturation. It is recommended to monitor neurologic status, as well as hemodynamic and metabolic status to avoid serious complications, especially in aged patients.

Is Near-Infrared Spectroscopy a Reliable Method to Evaluate Clamping Ischemia during Carotid Surgery?

Guidelines do not include cerebral oximetry among monitoring for carotid endarterectomy (CEA). The purpose of this study was to evaluate the reliability of near-infrared spectroscopy (NIRS) in the detection of clamping ischemia and in the prevention of clamping-related neurologic deficits using, as a cutoff for shunting, a 20% regional cerebral oxygen saturation (rSO(2)) decrease if persistent more than 4 minutes, otherwise a 25% rSO(2) decrease. Bilateral rSO(2) was monitored continuously in patients undergoing CEA under general anesthesia (GA). Data was recorded after clamping, declamping, during shunting and lowest values achieved. Preoperative neurologic, CT-scan, and vascular lesions were recorded. We reviewed 473 cases: 305 males (64.5%) mean age 73.3 ± 7.3. Three patients presented transient ischemic deficits at awakening, no perioperative stroke or death; 41 (8.7%) required shunting: 30 based on the initial rSO(2) value and 11 due to a decrease during surgery. Using the ROC curve analysis we found, for a >25% reduction from baseline value, a sensitivity of 100% and a specificity of 90.6%. Reliability, PPV, and NPV were 95.38%, 9%, and 100%, respectively. In conclusion, this study indicates the potential reliability of NIRS monitoring during CEA under GA, using a cutoff of 25% or a cutoff of 20% for prolonged hypoperfusion.

Detection of cerebral ischemia in neurovascular surgery using quantitative frequency-domain near-infrared spectroscopy

OBJECT

There is great value in monitoring for signs of ischemia during neurovascular procedures. Current intraoperative monitoring techniques provide real-time feedback with limited accuracy. Quantitative frequency-domain near-infrared spectroscopy (Q-NIRS) allows measurement of tissue oxyhemoglobin (HbO2), deoxyhemoglobin (HHb), and total hemoglobin (tHb) concentrations and brain tissue oxygen saturation (SO2), which could be useful when monitoring for evidence of intraoperative ischemia.

METHODS

Using Q-NIRS, the authors monitored 25 neurovascular procedures including aneurysm clip placement, arteriovenous malformation resection, carotid endarterectomy, superficial temporal artery-middle cerebral artery (MCA) bypass surgery, external carotid artery-MCA bypass surgery, encephaloduromyosynangiosis, and balloon occlusion testing. The Q-NIRS technology provides measurable cerebral oxygenation values independent from those of the scalp tissue. Thus, alterations in the variables measured with Q-NIRS quantitatively reflect cerebral tissue perfusion. Bilateral monitoring was performed in all cases. Five of the patients exhibited evidence of clinical ischemic events during the procedures. One patient suffered blood loss with systemic hypotension and developed diffuse brain edema intraoperatively, one patient suffered an ischemic event intraoperatively and developed an occipital stroke postoperatively, and one patient showed slowing on electroencephalography intraoperatively during carotid clamping; in two patients balloon occlusion testing failed. In all cases of ischemic events occurring during the procedure, Q-NIRS monitoring showed a decrease in HbO2, tHb, and SO2, and an increase in HHb.

CONCLUSIONS

. Quantitative frequency-domain near-infrared spectroscopy provides quantifiable and continuous real-time information about brain oxygenation and hemodynamics in a noninvasive manner. This continuous intraoperative oxygenation monitoring is a promising method for detecting ischemic events during neurovascular procedures.

Near-infrared spectroscopy in the routine diagnostic work-up of patients with leg ischaemia

OBJECTIVE

To examine the reproducibility and clinical applicability of near-infrared spectroscopy (NIRS) in patients with leg ischaemia.

DESIGN

Prospective comparative diagnostic study.

MATERIALS AND METHODS

Routinely measured peripheral blood pressure and microcirculatory parameters were compared with tissue oxygen saturation (TsO(2)) measurements using a new NIRS device on the calf muscle and the foot. Healthy subjects (n=20) and patients in different stages of leg ischaemia (n=45) were investigated at rest and after provocation: a treadmill test, arterial occlusion and a change in posture. Healthy volunteers were used as an age-matched reference population.

RESULTS

Reproducibility of the NIRS was excellent (intraclass correlation coefficient at rest was 0.91 (95% confidence interval: 80-99). Resting TsO(2) (65%) in healthy controls did not differ significantly from that in patients (Fontaine 2: 66%; F3/4: 68%). After exercise, a significant reduction in TsO(2) was observed only in patients: Fontaine 1: 60%; Fontaine 2: 21%, Fontaine 3/4: 29%. The ankle/brachial index after exercise showed a good correlation (R=0.73) with TsO(2) at the end of the treadmill test. No correlation between NIRS and other micro- or macrocirculatory parameters was found.

CONCLUSION

NIRS is a very reproducible tool to assess tissue oxygen saturation, but is not useful for the routine work-up of patients with leg ischaemia.

Near-infrared spectroscopy in the assessment of cerebral oxygenation at high altitude

Hypoxia plays a key role in the pathogenesis of acute mountain sickness (AMS), but individual susceptibility is variable and cerebral symptoms do not always correlate with PaO2 measurements. Cerebral hypoxia may be more relevant than PaO2. We studied trends in cerebral regional oxygen saturation by the technique of near-infrared spectroscopy in 20 subjects ascending rapidly to 4680 m. Subjects were enrolled in a placebo-controlled, double-blind trial of medroxyprogesterone for the prevention of AMS. The fall in cerebral oxygen saturation was less than in the periphery. At 4680 m, cerebral oxygenation correlated with peripheral saturation but not with PaCO2 or with cerebral symptoms scores. At 4680 m, subjects on medroxyprogesterone had higher cerebral and peripheral saturation compared with those on a placebo. We conclude that cerebral oxygenation monitored with the Critikon 2020 system provided important information on the complex relationship of hypoxia to AMS and that other factors, such as changes in blood flow or capillary permeability, may be equally important.

Monitors of cerebral oxygenation

None of the monitors of cerebral oxygenation discussed above has proven to be effective enough to have become a standard of care in any given area of medical treatment. As described above, each has specific and well-defined shortcomings that prevent its widespread use. These shortcomings may not be so much a failure of technology as an acknowledgement of the complexity of our goal: a monitor that can divide the entire brain into small, focal, and discrete areas and accurately measure the oxygen tension in each one. Because we are asking for the functional equivalent of 30 or 40 simultaneous PbtO2 probes, it is small wonder that we are not yet satisfied. Of the three monitors discussed here, the greatest potential may lie with the transcranial cerebral oximetry. The cerebral oximeter has the biggest potential for improvement because it holds the most potential for technical advancement. Although, for instance, jugular venous bulb oximetric catheters may become somewhat more accurate, the biggest drawbacks in that monitor's usefulness lie in human anatomy and intracerebral blood mixing, not catheter accuracy. PbtO2 probes, also, have little room for improvement. Although every technology can be refined, the PbtO2 probes are already accurate. The fact that they are an invasive monitor, and a regional one at that, will relegate them to a limited number of cases. Cerebral oximeters hold more potential. Their greatest limitations lie in technical aspects that can be, and hopefully will be, improved upon in terms of computer technology as well as algorithm accuracy. The fact that cerebral oximeters can be used on any patient, at any time, on almost any case, makes it, potentially, truly an ideal monitor for anesthesiologists and intensivists alike. There is no certainty that any of these limitations will be surmounted, at least to the degree necessary to achieve desired accuracy. But there is much to anticipate.

Comparison of near-infrared spectroscopy and somatosensory evoked potentials for the detection of cerebral ischemia during carotid endarterectomy

BACKGROUND AND PURPOSE

We sought to assess the clinical value of regional cerebral saturation (rSO2) obtained by means of the cerebral oximeter INVOS 3100A (Somanetics) in comparison to monitoring of somatosensory evoked potentials (SEP) for the reliable detection of severe cerebral ischemia requiring shunt placement in the individual patient undergoing carotid surgery under general anesthesia.

METHODS

In 317 patients undergoing reconstructive surgery on the internal carotid artery, simultaneous recordings of SEP and rSO2 were obtained throughout the operation.

RESULTS

All 287 patients with preserved cortical SEP remained neurologically intact. Shunt placement was performed in 27 patients (9%) after flattening of cortical SEP during cross-clamping of the internal carotid artery. A stable rSO2 value just before cross-clamping and the lowest value after cross-clamping were registered, and the decrease was calculated. A statistically significant (P<0.01) decrease of rSO2 after cross-clamping could be found in patients without (64.9+/-8.3% to 60.9+/-9.9%) as well as in patients with consecutive loss of cortical SEP (65.8+/-9.1% to 56.1+/-13.4%). The difference of the decrease of rSO2 in both groups was highly significant (6.9+/-9.0% versus 15.6+/-14.0%; P<0.001). However, substantial interindividual variability of rSO2 and derived change of rSO2 did not allow the definition of a threshold value indicating need of shunt placement.

CONCLUSIONS

The reliability of SEP for the detection of clamp-related hypoperfusion has been reaffirmed. As long as rSO2 threshold values indicating critical cerebral ischemia are not defined, therapeutic interventions based on monitoring with the cerebral oximeter INVOS 3100A are not justified.