The Influence of Inspired Oxygen Fraction and End-Tidal Carbon Dioxide on Post–Cross-Clamp Cerebral Oxygenation During Carotid Endarterectomy Under General Anesthesia

Optimization of cerebral oxygenation based on regional cerebral oxygen saturation monitoring during carotid endarterectomy: a Phase III multicenter, double-blind randomized controlled trial

BACKGROUND

Whether the optimization of cerebral oxygenation based on regional cerebral oxygen saturation (rSO2) monitoring reduces the occurrence of cerebral ischemic lesions is unknown.

METHODS

This multicenter, randomized, controlled trial recruited adults admitted for scheduled carotid endarterectomy. Patients were randomized between the standard of care or optimization of cerebral oxygenation based on rSO2 monitoring using near-infrared spectroscopy. In the intervention group, in case of a decrease in rSO2 in the intervention, the following treatments were sequentially recommended: (1) increasing oxygenotherapy, (2) reducing the tidal volume, (3) legs up-raising, (4) performing a fluid challenge and (5) initiating vasopressor support. The primary endpoint was the number of new cerebral ischemic lesions detected using magnetic resonance imaging pre- and postoperatively. Secondary endpoints included new neurological deficits and mortality on day 120 after surgery.

RESULTS

Among the 879 patients who were randomized, 665 (75.7%) were men. There was no statistically significant difference between groups for the mean number of new cerebral ischemic lesions per patient up to 3 days after surgery: 0.35 (±1.05) in the standard group vs. 0.58 (±2.83), in the NIRS group; mean difference, 0.23 [95% CI, -0.06 to 0.52]; estimate, 0.22 [95% CI, -0.06 to 0.50]. New neurological deficits up to day 120 after hospital discharge were not different between the groups: 15 (3,39%) in the standard group vs. 42 (5,49%) in the NIRS group; absolute difference, 2,10 [95% CI, -0,62 to 4,82]. There was no significant difference between groups for the median [IQR] hospital length of stay: 4.0 [4.0-6.0] in the standard group vs. 5.0 [4.0-6.0] in the NIRS group; mean difference, -0.11 [95% CI, -0.65 to 0.44]. The mortality rate on day 120 was not different between the standard group (0.68%) vs. the NIRS group (0.92%); absolute difference = 0.24% [95% CI, -0.94 to 1.41].

CONCLUSIONS

Among patients undergoing carotid endarterectomy, optimization of cerebral oxygenation based on rSO2 did not reduce the occurrence of cerebral ischemic lesions postoperatively compared with controlled hypertensive therapy.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01415648.

Carbon Dioxide, Blood Pressure, and Perioperative Stroke: A Retrospective Case-Control Study

BACKGROUND

The relationship between intraoperative physiology and postoperative stroke is incompletely understood. Preliminary data suggest that either hypo- or hypercapnia coupled with reduced cerebrovascular inflow (e.g., due to hypotension) can lead to ischemia. This study tested the hypothesis that the combination of intraoperative hypotension and either hypo- or hypercarbia is associated with postoperative ischemic stroke.

METHODS

We conducted a retrospective, case-control study via the Multicenter Perioperative Outcomes Group. Noncardiac, nonintracranial, and nonmajor vascular surgical cases (18 yr or older) were extracted from five major academic centers between January 2004 and December 2015. Ischemic stroke cases were identified via manual chart review and matched to controls (1:4). Time and reduction below key mean arterial blood pressure thresholds (less than 55 mmHg, less than 60 mmHg, less than 65 mmHg) and outside of specific end-tidal carbon dioxide thresholds (30 mmHg or less, 35 mmHg or less, 45 mmHg or greater) were calculated based on total area under the curve. The association between stroke and total area under the curve values was then tested while adjusting for relevant confounders.

RESULTS

In total, 1,244,881 cases were analyzed. Among the cases that screened positive for stroke (n = 1,702), 126 were confirmed and successfully matched with 500 corresponding controls. Total area under the curve was significantly associated with stroke for all thresholds tested, with the strongest combination observed with mean arterial pressure less than 55 mmHg (adjusted odds ratio per 10 mmHg-min, 1.17 [95% CI, 1.10 to 1.23], P < 0.0001) and end-tidal carbon dioxide 45 mmHg or greater (adjusted odds ratio per 10 mmHg-min, 1.11 [95% CI, 1.10 to 1.11], P < 0.0001). There was no interaction effect observed between blood pressure and carbon dioxide.

CONCLUSIONS

Intraoperative hypotension and carbon dioxide dysregulation may each independently increase postoperative stroke risk.

EDITOR’S PERSPECTIVE

Correlation between brain tissue oxygen tension and regional cerebral oximetry in uninjured human brain under conditions of changing ventilation strategy

Controversy surrounds regional cerebral oximetry (rSO₂) because extracranial contamination and unmeasured changes in cerebral arterial:venous ratio confound readings. Correlation of rSO₂ with brain tissue oxygen (PbrO₂), a “gold standard” for cerebral oxygenation, could help resolve this controversy but PbrO₂ measurement is highly invasive. This was a prospective cohort study. The primary aim was to evaluate correlation between PbrO₂ and rSO₂ and the secondary aim was to investigate the relationship between changing ventilation regimens and measurement of PbrO₂ and rSO₂. Patients scheduled for elective removal of cerebral metastases were anesthetized with propofol and remifentanil, targeted to a BIS range 40–60. rSO₂ was measured using the INVOS 5100B monitor and PbrO₂ using the Licox brain monitoring system. The Licox probe was placed into an area of normal brain within the tumor excision corridor. FiO₂ and minute ventilation were sequentially adjusted to achieve two set points: (1) FiO₂ 0.3 and paCO₂ 30 mmHg, (2) FiO₂ 1.0 and paCO₂ 40 mmHg. PbrO₂ and rSO₂ were recorded at each. Nine participants were included in the final analysis, which showed a positive Spearman’s correlation (r = 0.50, p = 0.036) between PbrO₂ and rSO₂. From set point 1 to set point 2, PbrO₂ increased from median 6.0, IQR 4.0–11.3 to median 22.5, IQR 9.8–43.6, p = 0.015; rSO₂ increased from median 68.0, IQR 62.5–80.5 to median 83.0, IQR 74.0–90.0, p = 0.047. Correlation between PbrO₂ and rSO₂ is evident. Increasing FiO₂ and PaCO₂ results in significant increases in cerebral oxygenation measured by both monitors.

Association between the reactivity of local cerebral oxygen saturation after hypo-to-hypercapnic tests and delirium after abdominal surgery in older adults: A prospective study

OBJECTIVE

This study aimed to investigate the correlation between changes in regional cerebral oxygen saturation (rSO2) and postoperative delirium in older adults undergoing major abdominal surgery.

MATERIALS AND METHODS

This prospective study enrolled older adults scheduled for elective major abdominal surgery at the Second Affiliated Hospital of Anhui Medical University from August 2021 to January 2022. The change in rSO2 from baseline was determined using the hypo-to-hypercapnic test. The main study outcome was the occurrence of postoperative delirium.

RESULTS

A total of 101 participants were included for analysis, of whom 16 (15.8%) developed postoperative delirium. Compared with non-delirium participants, the mean arterial pressure and heart rate were not significantly different in the postoperative delirium group at T0, T1, T2, T3, T4, and T6 (all P_interaction > 0.05), but the delirium group had lower pH, lower PaO2, and higher lactate levels at T4, T5, and T6 (all P_interaction < 0.05). rSO2 at T0, T1, T2, T3, T4, and T6 was 69.0 (63.2-75.2), 70.7 ± 7.3, 68.2 ± 7.5, 72.1 ± 8.0, 69.9 ± 7.8, 67.4 ± 7.2, and 71.7 ± 8.1, respectively. The postoperative change in rSO2 during the hypercapnia test (TΔrSO2%) was 6.62 (5.31-9.36). Multivariable analysis showed that the Cumulative Illness Rating Scale (odd ratio, OR = 1.89, 95% confidence interval, CI: 1.10-3.25, P = 0.021), preoperative albumin levels (OR = 0.67, 95% CI: 0.48-0.94, P = 0.022), rSO2 at T4 (OR = 0.61, 95% CI: 0.41-0.89, P = 0.010), and postoperative TΔrSO2% (OR = 0.80, 95% CI: 0.66-0.98, P = 0.028) were independently associated with postoperative delirium in older adults undergoing elective abdominal surgery.

CONCLUSION

The rSO2 measured at T4 and postoperative TΔrSO2% were independently associated with postoperative delirium in older adults undergoing elective abdominal surgery.

Effect of hemoglobin content on cerebral oxygen saturation during surgery for scoliosis in pediatric patients

BACKGROUND

Although regional cerebral oxygen saturation (rScO₂) monitoring has been widely used in clinical practice, the relationship between hemoglobin (dHB) content and rScO₂ is incompletely understood. The aim of this study was to analyze the effect of hemoglobin content on rScO₂ in pediatric patients undergoing general anesthesia for correction of scoliosis.

METHODS

Ninety-two pediatric patients aged 3 to 14 years undergoing scoliosis correction surgery were enrolled. Continuous monitoring of bilateral regional cerebral oxygen saturation by near-infrared spectroscopy (NIRS, CASMED, USA) was performed after entering the operation room. rScO₂ was recorded when the patients entered the operating room (T₀, baseline), after anesthesia induced intubation (T₁), and after radial artery puncture (T₂). The lowest value of rScO₂ during surgery was also recorded. The arterial blood pressure (ABP), heart rate (HR), pulse oxygen saturation (SpO₂), end tidal carbon dioxide partial pressure (PetCO₂) were continuously recorded. Patients were classified as low rScO₂ or high rScO₂ group according to whether the lowest intraoperative rScO₂ was 15% lower than the baseline value. An analysis and comparison of differences in hemoglobin content in these two groups was carried out.

RESULTS

The preoperative hemoglobin-postoperative hemoglobin of patients in the high rScO₂ group was significantly lower than that in the low rScO₂ group (t = - 7.86, p < 0.01), the amount of bleeding during the operation was also less than that in the low rScO₂ group (t = - 6.05, p < 0.01), and the systolic pressure of patients was higher than that in the low rScO₂ group (t = 4.27, p < 0.01).

CONCLUSIONS

The decrease in hemoglobin level which occurs during surgery leads to a decrease in cerebral oxygen saturation. In order to ensure patient safety during surgery, it is necessary to carry out volume management and appropriate transfusion and fluid replacement in a timely manner.

TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR1800016359 . Registered 28 May 2018.

Decreased cerebral oxygen saturation levels during direct laryngoscopy with spontaneous ventilation in children

INTRODUCTION

Direct laryngoscopy in children is usually performed with spontaneous ventilation and monitored by pulse oximetry. It is currently unknown if spontaneous ventilation has an effect on cerebral oxygenation. We hypothesized that cerebral oxygenation may be impeded during direct laryngoscopy with spontaneous ventilation in children.

OBJECTIVE

Our objective was to determine if children who undergo direct laryngoscopy under general anesthesia with spontaneous breathing experience significant reductions in cerebral oxygen saturation levels, and whether or not these reductions are accompanied by decreases in peripheral oxygen saturation levels.

METHODS

This pilot study included 16 consecutive children who underwent direct laryngoscopy under general anesthesia and spontaneous ventilation. The INVOS™ system, which is currently used to monitor cerebral oxygen saturation levels during neurosurgery and cardiothoracic surgery, consists of a processing unit and 2 sensors that are applied to the patient's forehead. We used it to record cerebral oxygenation levels throughout the procedure. Peripheral pulse oximetry was recorded simultaneously, and the results were compared to the levels recorded by the INVOS™ system.

RESULTS

Cerebral oxygen saturation levels decreased by more than 20% from baseline in 7/10 children with tracheostomy and in 2/6 children without tracheostomy, while peripheral oxygen saturation levels remained intact in all the children. The mean time from induction of anesthesia to significant decrease in the cerebral oxygenation level (rSO2) was 14 ± 6 min for the tracheostomy group and 14.5 ± 1.5 min for the no tracheostomy group.

CONCLUSIONS

Children who undergo direct laryngoscopy under general anesthesia with spontaneous ventilation may display reductions in brain oxygenation levels that are not detected by standard pulse oximetry, which reflects only peripheral oxygenation levels. Further study is required to explore the possible effect of this phenomenon in children who undergo direct laryngoscopy.

Cerebrovascular Disease and Perioperative Neurologic Vulnerability: A Prospective Cohort Study

Background: Stroke is a devastating perioperative complication without effective methods for prevention or diagnosis. The objective of this study was to analyze evidence-based strategies for detecting cerebrovascular vulnerability and injury in a high-risk cohort of non-cardiac surgery patients.

Methods: This was a single-center, prospective cohort study. Fifty patients undergoing non-cardiac surgery were recruited −25 with known cerebrovascular disease and 25 matched controls. Neurologic vulnerability was measured with intraoperative cerebral oximetry as the primary outcome. Perioperative neurocognitive testing and serum biomarker analysis (S-100β, neuron specific enolase, glial fibrillary acid protein, and matrix metalloproteinase-9) were measured as secondary outcomes.

Results: Cerebral desaturation events (an oximetry decrease ≥20% from baseline or <50% absolute value for ≥3 min) occurred in 7/24 (29%) cerebrovascular disease patients and 2/24 (8.3%) controls (relative risk 3.5, 95% CI 0.81–15.2; P = 0.094). Cognitive function trends were similar in both groups, though overall scores (range: 1,500–7,197) were ~1 standard deviation lower in cerebrovascular patients across the entire perioperative period (−1,049 [95% CI −1,662, −436], P < 0.001). No significant serum biomarker differences were found between groups over time. One control patient experienced intraoperative hypoxic-ischemic injury, but no robust biomarker or oximetry changes were observed.

Conclusions: Cerebrovascular disease patients did not demonstrate dramatic differences in cerebral oximetry, cognitive trajectory, or molecular biomarkers compared to controls. Moreover, a catastrophic hypoxic-ischemic event was neither predicted nor detected by any strategy tested. These findings support the need for novel research into cerebrovascular risk and vulnerability.

Different ventilation techniques and hemodynamic optimization to maintain regional cerebral oxygen saturation (rScO2) during laparoscopic bariatric surgery: a prospective randomized interventional study

PURPOSE

The purpose of this study was to assess the changes in regional cerebral oxygen saturation (rScO₂) in response to different ventilation strategies: inspired oxygen concentration (FiO₂), end-tidal carbon dioxide (EtCO₂), and positive end expiratory pressure (PEEP) in addition to optimizing mean arterial pressure (MAP) in obese patients subjected to laparoscopic bariatric surgery in the reverse trendelenburg position.

METHODS

50 obese patients were randomly assigned into one of two groups. Each group is 25 patients. Control patients subjected to a ventilation strategy aimed to maintain FiO₂ 0.4 and EtCO₂ 30 mmHg without PEEP. Study patients were assigned to specific protocol; T0, baseline rScO₂; T1, 5 min following induction; T2, PP/RTP (10 min after pneumoperitoneum and reverse trendelenburg position); T3, PEEP 10 cmH₂O; T4, FiO₂ 1.0; T5, EtCO₂ 40 mmHg and T6, MAP/BL; MAP back to baseline in both groups.

MAIN RESULTS

10 min after PP/RTP, there was a significant decrease in rScO₂ in both groups. At T4, with FiO₂ 1.0, there was significant improvement in rScO₂ when compared to T2. At T5, with EtCO₂ 40 mmHg, rScO₂ significantly enhanced when compared to EtCO₂ 30 mmHg. At T4 and T5, we observed highly significance difference between both groups. At the end of the procedure and when MAP increased back to baseline (T6) in both groups, rScO₂ statistically increased in both groups when compared to T2.

CONCLUSION

In obese patients, subjected to laparoscopic bariatric surgery in reverse trendelenburg position, adjustment of ventilation strategies and hemodynamic optimization succeeded to improve rScO₂.

Quantitative analysis of the effect of end-tidal carbon dioxide on regional cerebral oxygen saturation in patients undergoing carotid endarterectomy under general anaesthesia

AIMS

Regional cerebral oxygen saturation (rSO₂ ) is currently the most used measure in clinical practice to monitor cerebral ischaemia in patients undergoing carotid endarterectomy (CEA). Although end-tidal carbon dioxide (P_ET CO₂ ) is known as a factor that influences rSO₂ , the relationship between P_ET CO₂ and rSO₂ has not been quantitatively evaluated in patients with severe arteriosclerosis. This study aimed to evaluate the effect of P_ET CO₂ on rSO₂ in patients undergoing CEA under general anaesthesia.

METHODS

The intervention to change P_ET CO₂ was conducted between skin incision and clamping of the carotid artery. The rSO₂ values were observed by changing P_ET CO₂ in the range of 25-45 mmHg. The P_ET CO₂ -rSO₂ relationship was characterized by population analysis using a turnover model.

RESULTS

In total, 1651 rSO₂ data points from 30 patients were used to determine the pharmacodynamic characteristics. Hypertension (HTN) and systolic blood pressure (SBP) were significant covariates on the slope factor in the stimulatory effect of P_ET CO₂ on rSO₂ and fractional turnover rate constant (k_out ), respectively. The estimates of the parameters were k_out (min^-1 ): 3.59 for SBP <90 mmHg and 0.491 for SBP ≥90 mmHg, slope: 0.00321 for patients with HTN and 0.00664 for patients without HTN.

CONCLUSION

The presence of HTNattenuates the response of rSO₂ after a change in P_ET CO₂ . When cerebral blood flow is in a state of decline caused by a decrease in SBP to <90 mmHg, the response of rSO₂ to P_ET CO₂ is increased. It is advisable to maintain SBP >90 mmHg in patients with HTNduring CEA.

A validation method for near-infrared spectroscopy based tissue oximeters for cerebral and somatic tissue oxygen saturation measurements

We describe the validation methodology for the NIRS based FORE-SIGHT ELITE^® (CAS Medical Systems, Inc., Branford, CT, USA) tissue oximeter for cerebral and somatic tissue oxygen saturation (StO₂) measurements for adult subjects submitted to the United States Food and Drug Administration (FDA) to obtain clearance for clinical use. This validation methodology evolved from a history of NIRS validations in the literature and FDA recommended use of Deming regression and bootstrapping statistical validation methods. For cerebral validation, forehead cerebral StO₂ measurements were compared to a weighted 70:30 reference (REF CX_B) of co-oximeter internal jugular venous and arterial blood saturation of healthy adult subjects during a controlled hypoxia sequence, with a sensor placed on the forehead. For somatic validation, somatic StO₂ measurements were compared to a weighted 70:30 reference (REF CX_S) of co-oximetry central venous and arterial saturation values following a similar protocol, with sensors place on the flank, quadriceps muscle, and calf muscle. With informed consent, 25 subjects successfully completed the cerebral validation study. The bias and precision (1 SD) of cerebral StO₂ compared to REF CX_B was −0.14 ± 3.07%. With informed consent, 24 subjects successfully completed the somatic validation study. The bias and precision of somatic StO₂ compared to REF CX_S was 0.04 ± 4.22% from the average of flank, quadriceps, and calf StO₂ measurements to best represent the global whole body REF CX_S. The NIRS validation methods presented potentially provide a reliable means to test NIRS monitors and qualify them for clinical use.

Effect of Mild Hypercapnia on Lung Oxygenation in Sitting Position During Shoulder Arthroscopy Under General Anesthesia

Background

Mild hypercapnia is permitted during surgeries in sitting position under general anesthesia to maintain cerebral regional oxygen saturation (rSO₂). However, since hypoventilation may cause gas exchange impairment, we evaluated effects of mild hypercapnia on lung oxygenation during shoulder arthroscopy in sitting position.

Material/Methods

Forty patients were randomly allocated to a normocapnia group (ETCO₂ 35 mmHg, n=20) or a hypercapnia group (45 mmHg, n=20). The mean arterial pressure (MAP), heart rate (HR), and rSO₂ were measured 5 min after intubation in supine position (T0), and at 2, 4, 6, 8, 10, 20, 30, 40, 50, and 60 min of remaining in sitting position (T1–10). Arterial blood gas was analyzed at T0 and T5. The oxygenation index (PaO₂/FiO₂) and dead-space ventilation ratio (Vd/Vt) were calculated.

Results

There were no differences in PaO₂/FiO₂ at T0 and T5 between the 2 groups. At T5, the Vd/Vt was higher in the normocapnia group than in the hypercapnia group (p=0.04). The Vd/Vt at T5 increased from T0 in the normocapnia group. The incidence of cerebral desaturation in the hypercapnia group (0/20) was lower than in the normocapnia group (5/20) (p=0.047). Among rSO₂, MAP, and HR, only changes in rSO₂ over time between the 2 groups differed significantly (p=0.048).

Conclusions

Mild hypercapnia did not decrease lung oxygenation in sitting position, probably due to attenuation of the increase in dead-space ventilation ratio. Since hypercapnia maintained rSO₂ without changes in oxygenation index and hemodynamic parameters, mild hypercapnia should be maintained during shoulder arthroscopy in sitting position under general anesthesia.

Retrospective evaluation of the effect of carotid artery stenosis on cerebral oxygen saturation during off-pump coronary artery bypasses grafting in adult patients

Background

It is unknown whether cerebral oxygenation in patients with carotid artery stenosis (CAS) undergoing off-pump coronary artery bypass grafting (CABG) differs from that in patients without CAS. Thus, the effect of the presence of CAS ≥ 50 % on cerebral oxygenation during off-pump CABG in adult patients was evaluated retrospectively.

Methods

Eleven patients with CAS ≥ 50 % and 14 patients without CAS ≥ 50 % were enrolled. Regional cerebral tissue oxygen saturation (rSO₂) was quantified using near-infrared spectroscopy. Mean arterial pressure, cardiac index, central venous pressure (CVP), and rSO₂ at specific points were collected, and significant changes in each parameter were detected using repeated analysis of variance. Mean rSO₂ and minimum rSO₂ during anastomosis were analyzed by one-way analysis of variance. Multiple logistic regression analysis was used to estimate the odds ratio (OR) with 95 % confidence interval (CI) for cerebral desaturation (a decrease in rSO₂ ≥ 10 % from preoperative value).

Results

Two patients with CAS ≥ 50 % who received complete carotid artery stenting preoperatively were excluded from the analyses. In both patients with and without CAS, a decrease in rSO₂ and cardiac index and an increase in CVP were observed during anastomosis. Mean (SD) maximum decrease in rSO₂ from preoperative value was 9.2 (12.7) % on the left side and 8.1 (11.7) % on the right side in patients with CAS ≥ 50 %, and 13.5 (11.3) % on the left side and 16.1 (9.8) % on the right side in patients without CAS ≥ 50 % (p = 0.316). Neurological complications were not identified in both patients with and without CAS ≥ 50 %. In multiple logistic regression analysis, CAS ≥ 50 % was not associated with an increased risk of cerebral desaturation (OR 0.160, 95 % CI 0.036–0.707, p = 0.016), and rSO₂ decreased with decreasing cardiac index < 2.0 l/min/m² (OR 3.287, 95 % CI 2.218–5.076, p < 0.001).

Conclusions

CAS ≥ 50 % was not an independent risk factor of cerebral desaturation during off-pump CABG. Our results suggest that maintaining cardiac output can prevent a decrease in cerebral oxygenation in both patients with and without CAS ≥ 50 %.

Influence of Ventilation Strategies and Anesthetic Techniques on Regional Cerebral Oximetry in the Beach Chair Position: A Prospective Interventional Study with a Randomized Comparison of Two Anesthetics

BACKGROUND

Beach chair positioning during general anesthesia is associated with cerebral oxygen desaturation. Changes in cerebral oxygenation resulting from the interaction of inspired oxygen fraction (FIO2), end-tidal carbon dioxide (PETCO2), and anesthetic choice have not been fully evaluated in anesthetized patients in the beach chair position.

METHODS

This is a prospective interventional within-group study of patients undergoing shoulder surgery in the beach chair position that incorporated a randomized comparison between two anesthetics. Fifty-six patients were randomized to receive desflurane or total intravenous anesthesia with propofol. Following induction of anesthesia and positioning, FIO2 and minute ventilation were sequentially adjusted for all patients. Regional cerebral oxygenation (rSO2) was the primary outcome and was recorded at each of five set points.

RESULTS

While maintaining FIO2 at 0.3 and PETCO2 at 30 mmHg, there was a decrease in rSO2 from 68% (SD, 12) to 61% (SD, 12) (P < 0.001) following beach chair positioning. The combined interventions of increasing FIO2 to 1.0 and increasing PETCO2 to 45 mmHg resulted in a 14% point improvement in rSO2 to 75% (SD, 12) (P <0.001) for patients anesthetized in the beach chair position. There was no significant interaction effect of the anesthetic at the study intervention points.

CONCLUSIONS

Increasing FIO2 and PETCO2 resulted in a significant increase in rSO2 that overcomes desaturation in patients anesthetized in the beach chair position and that appears independent of anesthetic choice.

Neurologic Derangement and Regional Cerebral Oxygen Desaturation Associated With Patency of the Circle of Willis During Carotid Endarterectomy

OBJECTIVES

To explore the relationship between the maximal fractional decrease of regional cerebral oxygen saturation (rSO2) in neurologic derangement and the patency of the circle of Willis and contralateral carotid artery stenosis.

DESIGN

A prospective observational study.

SETTINGS

A tertiary-care university hospital

PARTICIPANTS

This study enrolled 307 patients undergoing carotid endarterectomy under regional anesthesia.

INTERVENTIONS

No interventions.

MEASUREMENTS AND MAIN RESULTS

Magnetic resonance angiography and carotid color-duplex ultrasound were performed, and the rSO2 was recorded. The relationship between the maximal fractional decrease of rSO2 from preclamp baseline against shunt insertion and patency of the circle of Willis was analyzed by a 2-way analysis of variance. Receiver operating characteristic analysis of the maximal fractional decrease of rSO2 also was performed to calculate the cut-off value for detecting neurologic derangement. In addition, probability of shunt insertion was estimated by logistic regression. Patency of the circle of Willis did not influence the maximal fractional decrease of rSO2. When both anterior and posterior circulations were nonpatent, the degree of contralateral carotid artery stenosis (Contra) was 54.7%±29.0% versus 40.7%±26.0% in patients with versus without shunting, respectively (p<0.05). The cut-off value of rSO2 for predicting shunt insertion was 25.8%, regardless of the patency of the circle of Willis. Probability of shunt insertion for nonpatent anterior circulation = exp(-2.02+0.02×Contra)/[1+exp(-2.02+0.02×Contra)].

CONCLUSIONS

The rSO2 can be used to predict shunt insertion, regardless of the patency of the circle of Willis. The probability of shunt insertion increased with increasing degree of contralateral carotid artery stenosis in the absence of anterior circulation in the circle of Willis.

Regional anaesthesia for carotid endarterectomy

Summary Regional anaesthesia is a popular choice for patients undergoing carotid endarterectomy (CEA). Neurological function is easily assessed during carotid cross-clamping; haemodynamic control is predictable; and hospital stay is consistently shorter compared with general anaesthesia (GA). Despite these purported benefits, mortality and stroke rates associated with CEA remain around 5% for both regional anaesthesia and GA. Regional anaesthetic techniques for CEA have improved with improved methods of location of peripheral nerves including nerve stimulators and ultrasound together with a modification in the classification of cervical plexus blocks. There have also been improvements in local anaesthetic, sedative, and arterial pressure-controlling drugs in patients undergoing CEA, together with advances in the management of patients who develop neurological deficit after carotid cross-clamping. In the UK, published national guidelines now require the time between the patient's presenting neurological event and definitive treatment to 1 week or less. This has implications for the ability of vascular centres to provide specialized vascular anaesthetists familiar with regional anaesthetic techniques for CEA. Providing effective regional anaesthesia for CEA is an important component in the armamentarium of techniques for the vascular anaesthetist in 2014.

Effect of ventilation on cerebral oxygenation in patients undergoing surgery in the beach chair position: a randomized controlled trial

BACKGROUND

Surgery in the beach chair position (BCP) may reduce cerebral blood flow and oxygenation, resulting in neurological injuries. The authors tested the hypothesis that a ventilation strategy designed to achieve end-tidal carbon dioxide (E'(CO₂)) values of 40-42 mm Hg would increase cerebral oxygenation (Sct(O₂)) during BCP shoulder surgery compared with a ventilation strategy designed to achieve E'(CO₂) values of 30-32 mm Hg.

METHODS

Seventy patients undergoing shoulder surgery in the BCP with general anaesthesia were enrolled in this randomized controlled trial. Mechanical ventilation was adjusted to maintain an E'(CO₂) of 30-32 mm Hg in the control group and an E'(CO₂) of 40-42 mm Hg in the study group. Cerebral oxygenation was monitored continuously in the operating theatre using near-infrared spectroscopy. Baseline haemodynamics and Sct(O₂) were obtained before induction of anaesthesia, and these values were then measured and recorded continuously from induction of anaesthesia until tracheal extubation. The number of cerebral desaturation events (CDEs) (defined as a ≥20% reduction in Sct(O₂) from baseline values) was recorded.

RESULTS

No significant differences between the groups were observed in haemodynamic variables or phenylephrine interventions during the surgical procedure. Sct(O₂) values were significantly higher in the study 40-42 group throughout the intraoperative period (P<0.01). In addition, the incidence of CDEs was lower in the study 40-42 group (8.8%) compared with the control 30-32 group (55.6%, P<0.0001).

CONCLUSIONS

Cerebral oxygenation is significantly improved during BCP surgery when ventilation is adjusted to maintain E'(CO₂) at 40-42 mm Hg compared with 30-32 mm Hg.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT01546636.

Regional anesthesia for vascular surgery

Vascular surgical patients are a diverse group of patients who tend to be elderly, with multiple comorbidities, while vascular procedures may involve significant blood loss and ischemia of tissues beyond the arterial obstruction. Regional anesthesia techniques may offer benefits to patients undergoing vascular surgery because of their cardiorespiratory comorbidities. However, this group of patients is commonly receiving multiple medications, including anticoagulants, so regional techniques are not without risks. This review will discuss this topic based around 3 fundamental revascularization procedures, carotid, abdominal aortic aneurysm repair, and infrainguinal surgery, discussing the clinical applications of regional techniques relevant to each key area.

Review article: cerebral near-infrared spectroscopy in adults: a work in progress

Near-infrared spectroscopy (NIRS) has potential as a noninvasive brain monitor across a spectrum of disorders. In the last decade, there has been a rapid expansion of clinical experience using NIRS to monitor cerebral oxygenation, and there is some evidence that NIRS-guided brain protection protocols might lead to a reduction in perioperative neurologic complications after cardiac surgery. However, there are no data to support the wider application of NIRS during routine surgery under general anesthesia, and its application in brain injury, where it might be expected to have a key monitoring role, is undefined. Although increasingly sophisticated apparatuses, including broadband and time-resolved spectroscopy systems, provide insights into the potential of NIRS to measure regional cerebral oxygenation, hemodynamics, and metabolism in real-time, these innovations have yet to translate into effective monitor-guided brain protection treatment strategies. NIRS has many potential advantages over other neuromonitoring techniques, but further investigation and technological advances are necessary before it can be introduced more widely into clinical practice.

The influence of basic ventilation strategies and anesthetic techniques on cerebral oxygenation in the beach chair position: study protocol

Background

Beach chair positioning during general anesthesia is associated with a high incidence of cerebral desaturation; poor neurological outcome is a growing concern. There are no published data pertaining to changes in cerebral oxygenation seen with increases in the inspired oxygen fraction or end-tidal carbon dioxide in patients anesthetized in the beach chair position. Furthermore, the effect anesthetic agents have has not been thoroughly investigated in this context. We plan to test the hypothesis that changes in inspired oxygen fraction or end-tidal carbon dioxide correlate to a significant change in regional cerebral oxygenation in anesthetized patients in beach chair position. We will also compare the effects that inhaled and intravenous anesthetics have on this process.

Methods/design

This is a prospective within-group study of patients undergoing shoulder arthroscopy in the beach chair position which incorporates a randomized comparison between two anesthetics, approved by the Institutional Review Board of the University of Michigan, Ann Arbor. The primary outcome measure is the change in regional cerebral oxygenation due to sequential changes in oxygenation and ventilation. A sample size of 48 will have greater than 80% power to detect an absolute 4-5% difference in regional cerebral oxygenation caused by changes in ventilation strategy. The secondary outcome is the effect of anesthetic choice on cerebral desaturation in the beach chair position or response to changes in ventilation strategy. Fifty-four patients will be recruited, allowing for drop out, targeting 24 patients in each group randomized to an anesthetic. Regional cerebral oxygenation will be measured using the INVOS 5100C monitor (Covidien, Boulder, CO). Following induction of anesthesia, intubation and positioning, inspired oxygen fraction and minute ventilation will be sequentially adjusted. At each set point, regional cerebral oxygenation will be recorded and venous blood gas analysis performed. The overall statistical analysis will use a repeated measures analysis of variance with Tukey’s HSD procedure for post hoc contrasts.

Discussion

If simple maneuvers of ventilation or anesthetic technique can prevent cerebral hypoxia, patient outcome may be improved. This is the first study to investigate the effects of ventilation strategies on cerebral oxygenation in patients anesthetized in beach chair position.

Trial registration

NCT01535274

The influence of basic ventilation strategies on cerebral oxygenation in anesthetized patients without vascular disease

OBJECTIVES

Optimizing cerebral oxygenation is of paramount importance in certain intraoperative situations. There is, however, a paucity of published data pertaining to changes in cerebral oxygenation seen with increases in the inspired fraction of oxygen (FIO2) or end-tidal carbon dioxide (PETCO2) in anesthetized patients without vascular disease. Here we tested the hypothesis that changes in FIO2 or PETCO2 correlate to a significant change in regional cerebral oxygenation (rSO2) in anesthetized patients without vascular disease.

METHODS

This was a prospective pilot study approved by the IRB. We measured rSO2 using the INVOS 5100B monitor in ten anesthetized patients. Patients were excluded if they had a history of or risk factors for vascular disease, suffered from respiratory failure, or did not speak English. Following induction of anesthesia and intubation, FIO2 and minute ventilation were sequentially adjusted. At each set point, rSO2 was recorded and arterial blood gas analysis was performed. Each patient acted as their own control. A paired-sample t test was used to evaluate the change in rSO2 resultant upon each intervention.

RESULTS

The baseline rSO2 was measured with patients awake, breathing room air and varied between 48 and 72%. While maintaining PETCO2 in the range 30-35 mmHg, rSO2 was 8% higher when 100% oxygen was delivered compared to FIO2 30% (P = 0.021). While maintaining PETCO2 in the range 40-45 mmHg, rSO2 was 7% higher when 100% oxygen is delivered compared to FIO2 30% (P = 0.032). While maintaining FIO2 at 100%, rSO2 was 2% higher when PETCO2 was in the range 40-45 mmHg compared to PETCO2 30-35 mmHg (P = 0.017). While maintaining FIO2 at 30%, rSO2 was not statistically different between PECO2 40-45 mmHg and PETCO2 30-35 mmHg.

CONCLUSIONS

Modulating oxygenation and ventilation in anesthetized patients without vascular disease leads to measurable changes in rSO2.