Kenji Yoshitani

A comparison of the INVOS 4100 and the NIRO 300 near-infrared spectrophotometers

We determined whether two different devices for measuring near-infrared spectroscopy (NIRS)—the INVOS 4100 and the NIRO 300—produce similar cerebral oxygenation data during the CO2 challenge test. Nineteen patients anesthetized with sevoflurane, 67% nitrous oxide in oxygen, and fentanyl were studied. A series of measurements of regional cerebral oxygen saturation (rSo2), measured by the INVOS 4100, and tissue oxygen index (TOI), measured by the NIRO 300, were performed in the following conditions: 1) normocapnia (Paco2, 35–45 mm Hg); 2) hypocapnia (Paco2, 25–35 mm Hg); 3) normocapnia; and 4) hypercapnia (Paco2, 45–55 mm Hg). Hemodynamic variables, including arterial blood gases and cerebral blood flow velocity, were measured at the same time with transcranial Doppler. The values and percentage changes of rSo2 and TOI were compared by using regression analysis and Bland and Altman analysis. The rSo2 showed a significant positive correlation with TOI (r = 0.58, P < 0.01). The percentage change of rSo2 also showed a significant positive correlation with the percentage change of TOI during the CO2 challenge (r = 0.85, P < 0.01). Bland and Altman analysis revealed a bias of −0.5% with 2 sd of 15.6% when comparing the rSo2 value with the TOI value, and it showed a bias of −3.4% with 2 sd of 15.2% when comparing the percentage change of rSo2 with the percentage change of TOI, indicating unacceptable disagreement of these data. These results indicate that cerebral oxygen saturation and its relative change during the CO2 challenge may vary depending on the type of NIRS used. Because the measurement technique and algorithm were different in each device, we should carefully consider the clinical application of the values produced by NIRS.

Effects of Hemoglobin Concentration, Skull Thickness, and the Area of the Cerebrospinal Fluid Layer on Near-infrared Spectroscopy Measurements

Background: Previous studies documented that near-infrared spectroscopy values were affected by factors related to optical path length, such as hemoglobin concentration, the differential path length factor, skull thickness (t-skull), and the area of the cerebrospinal fluid layer (a-CSFL). Lately, the NIRO-100 (Hamamatsu Photonics, Hamamatsu, Japan) has provided a tissue oxygen index (TOI) that theoretically is not supposed to be affected by optical path length. Therefore, the authors hypothesized that TOI is not influenced by the above-described individual factors. Methods: Cardiac surgical or neurosurgical 103 patients (65 men and 39 women; aged 63 ± 14 yr) were studied. TOI and regional cerebral oxygen saturation (rSO2) (INVOS 4100; Somanetics, Troy, MI) were measured sequentially on patients in a resting state. The t-skull and a-CSFL were calculated using computed tomographic image slices of the head corresponding with the position of near-infrared spectroscopy sensors. The effects of these two factors, hemoglobin concentration and mean arterial pressure, on TOI and rSO2 values were evaluated by linear regression analysis. Results: Simple linear regression analysis showed that mean arterial pressure (r = 0.27, P = 0.008), t-skull (r = 0.22, P = 0.034), a-CSFL (0.26, P = 0.012), and hemoglobin concentration (r = 0.42, P < 0.0001) were significant determinants of rSO2. Multiple linear regression analysis showed that hemoglobin concentration (r = 0.34, P < 0.001), a-CSFL (r = −0.252, P = 0.012), and t-skull (r = 0.22, P = 0.037) were significant determinants of rSO2. On the other hand, simple and multiple linear regression analysis showed that there was no significant determinant of TOI. Conclusion: rSO2 values were affected by hemoglobin concentration, a-CSFL, and t-skull, but TOI values were not affected by individual factors.

Influence of patient variables and sensor location on regional cerebral oxygen saturation measured by INVOS 4100 near-infrared spectrophotometers.

Cerebral oximeter based on near-infrared spectroscopy has been used as a continuous, noninvasive monitoring of regional cerebral oxygen saturation (rSO2). Although the absolute rSO2 values have a wide range of variability, the factors affecting a variability of rSO2 values have not been extensively investigated. The authors investigated the influence of patient variables and sensor location on rSO2 measured by the cerebral oximeter INVOS 4100 in 111 patients anesthetized with sevoflurane, fentanyl, and nitrous oxide in oxygen. The sensors for rSO2 measurements were applied on the right forehead (R), 1 cm lateral to R (R1), on the left forehead (L), 1 cm lateral to L (L1), and on the center of the forehead (C). The relationship between the rSO2 values and patient variables were also analyzed. Values of rSO2 at R1 and L1 were significantly lower than those at R and L, respectively. Values of rSO2 at C were significantly higher compared with those at other sites. There were no significant correlations between the rSO2 values and values of weight, height, and head size. Values of rSO2 were similar between males and females. A significant negative correlation between the rSO2 values and age and a positive correlation between the rSO2 values and hemoglobin concentration were observed. These data indicate that patient age, hemoglobin concentration at the measurement, and sensor location can affect rSO2 values.

The efficacy of motor-evoked potentials on cerebral aneurysm surgery and new-onset postoperative motor deficits.

Surgical clipping may cause stenosis of parent arteries or occlusion of perforating arteries in cerebral aneurysm surgery. To prevent postoperative motor deficits, motor-evoked potentials (MEPs) have been used. This enables to detect cerebral ischemia. However, the rate of false negatives (motor deficits with preserved MEP) has been relatively higher than in aortic surgery. We hypothesized that postoperative motor deficits with preserved intraoperative MEP do not always represent false negatives. We reviewed medical records of patients for cerebral aneurysms surgery with transcranial MEP monitoring from September 2003 to March 2009. We reviewed aneurysm location and size, abnormal computed tomography findings, and clinical outcome. Motor status was evaluated immediately after extubation and anytime when the symptom of motor deficits was found. One hundred and eleven patients underwent cerebral aneurysm clipping with transcranial MEP. Ninety-eight patients manifested no intraoperative MEP changes and no postoperative motor deficits. Six patients showed intraoperative MEP changes, resulting in no motor deficits in 4 patients with MEP recovery and hemiparesis in 2 without MEP recovery. Four patients of 6 had aneurysm in anterior choroidal artery (AchA). Other 6 patients showed postoperative motor deficits despite preserved intraoperative MEP. Two of 6 patients showed no motor deficits just after extubation, but developed deficits 5 hours after coming out of anesthesia. Only 1 of the 6 patients had aneurysm in AchA. In AchA aneurysm surgery, intraoperative MEP monitoring seems to be useful. False negative in MEP monitoring may include new-onset hemiparesis despite preserved intraoperative MEP.

Risk factors of stroke and delirium after off-pump coronary artery bypass surgery

Off-pump coronary artery bypass surgery (CABG) has not abolished the risk of postoperative stroke and delirium seen for on-pump CABG. Advanced arteriosclerotic changes are common in both on-pump and off-pump CABG. We sought to analyze if advanced arteriosclerotic changes are risk factors of stroke or transient ischemic attack (TIA), and delirium after off-pump CABG. Patients undergoing off-pump CABG between 2001 and 2005 were reviewed using medical records (n=685). Potential risk factors of postoperative stroke and delirium were identified from previous studies. Further, variables retrieved from carotid artery duplex scanning as indices of advanced arteriosclerosis, were examined. The incidences of postoperative stroke/TIA and delirium after off-pump CABG were 2.6% (n=18) and 16.4% (n=112), respectively. Carotid artery stenosis >50% was a significant risk factor of stroke or TIA (P=0.02) as well as delirium (P=0.04) after off-pump CABG. A history of atrial fibrillation (AF) (P=0.037) or diabetes mellitus (P=0.041) was a risk factors of postoperative stroke or TIA. In contrast, age over 75 years (P=0.006), creatinine >1.3 mg/dl (99 μmol/l) (P=0.011), a history of hypertension (P=0.001), past history of AF (P=0.024), and smoking (P=0.048) were significant risk factors of postoperative delirium.

Jugular bulb oxygen saturation under propofol or sevoflurane/nitrous oxide anesthesia during deliberate mild hypothermia in neurosurgical patients.

Sevoflurane and propofol have been widely used as anesthetic agents for neurosurgery. Recent evidence has suggested that the influence of these anesthetics on cerebral oxygenation may differ. In the present study, the authors investigated jugular bulb oxygen saturation (SjO2) during propofol and sevoflurane/nitrous oxide anesthesia under mildly hypothermic conditions. After institutional approval and informed consent, 20 patients undergoing elective craniotomy were studied. Patients were randomly divided to the group S/N2O (sevoflurane/nitrous oxide/fentanyl anesthesia) or the group P (propofol/fentanyl anesthesia). After induction of anesthesia, the catheter was inserted retrograde into the jugular bulb and SjO2 was analyzed. During the operation, patients were cooled and tympanic membrane temperature was maintained at 34.5°C. SjO2 was measured at normocapnia during mild hypothermia and at hypocapnia during mild hypothermia. There were no statistically significant differences in demographic variables between the groups. During mild hypothermia, SjO2 values were significantly lower in group P than in group S/N2O. The incidence of SjO2 less than 50% under mild hypothermic-hypocapnic conditions was significantly higher in group P than in group S/N2O. These results suggest that hyperventilation should be more cautiously applied during mild hypothermia in patients anesthetized with propofol and fentanyl versus sevoflurane/nitrous oxide/fentanyl.

The association of high jugular bulb venous oxygen saturation with cognitive Decline after hypothermic cardiopulmonary bypass

This study was conducted to investigate whether jugular bulb venous oxygen saturation (Sjvo2) predicted cognitive decline after cardiac surgery with hypothermic cardiopulmonary bypass (CPB). We studied 35 patients undergoing cardiac surgery. After the induction of anesthesia, a 5.5F fiberoptic oximetry catheter was retrogradely inserted into the jugular bulb, and Sjvo2 and other cerebral oxygenation variables were analyzed before, during, and after CPB. At each point, an oxyhemoglobin dissociation curve was drawn, and the P50 value of jugular bulb venous blood was calculated by computer analysis. Cognitive function was assessed with the revised version of Hasegawa’s Dementia Scale and the Benton Revised Visual Retention Test before and early after the operation. In 15 patients (the Decline group), cognitive function was declined after surgery, whereas it remained unchanged in 20 patients (the Normal group). Sjvo2 was significantly higher and cerebral oxygen extraction was significantly lower before and during CPB in the Decline group than in the Normal group (P < 0.05). The oxygen pressure at an oxygen saturation of 50% was significantly lower before and after CPB in the Decline group than in the Normal group (P < 0.05). Logistic regression analysis showed that high Sjvo2 was a predictor of cognitive decline after cardiac surgery. We conclude that high Sjvo2 was associated with cognitive decline after cardiac surgery with hypothermic CPB.

Neuroprotection during cardiac surgery

Cerebral injury following cardiac surgery continues to be a significant source of morbidity and mortality after cardiac surgery. A spectrum of injuries ranging from subtle neurocognitive dysfunction to fatal strokes are caused by a complex series of multifactorial mechanisms. Protecting the brain from these injuries has focused on intervening on each of the various etiologic factors. Although numerous studies have focused on a pharmacologic solution, more success has been found with nonpharmacologic strategies, including optimal temperature management and reducing emboli generation.

A novel survival model of cardioplegic arrest and cardiopulmonary bypass in rats: a methodology paper

BackgroundGiven the growing population of cardiac surgery patients with impaired preoperative cardiac function and rapidly expanding surgical techniques, continued efforts to improve myocardial protection strategies are warranted. Prior research is mostly limited to either large animal models or ex vivo preparations. We developed a new in vivo survival model that combines administration of antegrade cardioplegia with endoaortic crossclamping during cardiopulmonary bypass (CPB) in the rat.MethodsSprague-Dawley rats were cannulated for CPB (n = 10). With ultrasound guidance, a 3.5 mm balloon angioplasty catheter was positioned via the right common carotid artery with its tip proximal to the aortic valve. To initiate cardioplegic arrest, the balloon was inflated and cardioplegia solution injected. After 30 min of cardioplegic arrest, the balloon was deflated, ventilation resumed, and rats were weaned from CPB and recovered. To rule out any evidence of cerebral ischemia due to right carotid artery ligation, animals were neurologically tested on postoperative day 14, and their brains histologically assessed.ResultsThirty minutes of cardioplegic arrest was successfully established in all animals. Functional assessment revealed no neurologic deficits, and histology demonstrated no gross neuronal damage.ConclusionThis novel small animal CPB model with cardioplegic arrest allows for both the study of myocardial ischemia-reperfusion injury as well as new cardioprotective strategies. Major advantages of this model include its overall feasibility and cost effectiveness. In future experiments long-term echocardiographic outcomes as well as enzymatic, genetic, and histologic characterization of myocardial injury can be assessed. In the field of myocardial protection, rodent models will be an important avenue of research.

Effect of combined anticoagulation using heparin and bivalirudin on the hemostatic and inflammatory responses to cardiopulmonary bypass in the rat.

Background:Despite high-dose heparin anticoagulation, cardiopulmonary bypass (CPB) is still associated with marked hemostatic activation. The purpose of this study was to determine whether a reduced dose of bivalirudin, added as an adjunct to heparin, would reduce thrombin generation and circulating markers of inflammatory system activation during CPB as effectively as full-dose bivalirudin, without adversely affecting postoperative hemostasis. Methods:Using a model of normothermic CPB in rats, the authors prospectively compared markers of thrombin generation (thrombin–antithrombin complexes) and inflammatory markers (tumor necrosis factor α, interleukin 1β, interleukin 6, and interleukin 10) in three groups: conventional high-dose heparin (H), full-dose bivalirudin (B), and a combined group (standard high-dose heparin with the addition of reduced dose bivalirudin or H&B), at baseline, after 60 min of CPB, and 60 min after CPB. Postoperative hemostasis was also assessed. Results:Groups H&B and B showed reduced thrombin–antithrombin complex formation during CPB compared with group H (P = 0.0003), and this persisted after CPB for group B (P = 0.009). Perioperative increases in interleukin 6 and interleukin 10 showed a trend toward being reduced in animals receiving bivalirudin (P = 0.06). Evidence of residual anticoagulation was found in group H&B as measured by activated clotting time (P = 0.04) and activated partial thromboplastin time (P = 0.02), but no intergroup difference in primary hemostasis was found. Conclusions:Bivalirudin attenuates hemostatic activation during experimental CPB with potential effects on markers of the inflammatory response. However, with this dosing regimen, the combination of heparin and bivalirudin does not seem to confer any measurable advantages over full-dose bivalirudin anticoagulation.