Modelling of the Effect of End-Tidal Carbon Dioxide on Cerebral Oxygen Saturation in Beach Chair Position under General Anaesthesia

Impact of mild hypo- and hyperventilation on cerebral oxygen supply during general anesthesia

OBJECTIVE

Cerebral blood flow autoregulation is affected by several physiologic and medical factors. Especially arterial carbon dioxide pressures (PaCO2) impact cerebral blood flow. Only extensive changes in end-tidal CO2 have been studied so far. The aim of this study was to evaluate the impact of mild hypo- and hyperventilation on cerebral blood flow as assessed by regional cerebral red blood cell oxygen saturation (rSO2) in two age groups.

METHODS

Two groups of patients were compared under general anesthesia before the surgical procedure was started: A younger patient group (age < 40 years; YP) and older patients aged > 60 years (OP). Anesthetic management was standardized. In both groups, end-tidal CO2 was adjusted either to a low-normal value of 35-37 mmHg or a high-normal value of 43-45 mmHg for 15 min each. The sequence of these interventions was randomized. rSO2 was estimated by near-infrared spectroscopy (NIRS). The primary outcome was defined as the difference in rSO2 between hypo- and hyperventilation between the two age groups.

RESULTS

A total of 78 patients were included. In both groups, there was a statistically significant difference in rSO2 values after 15 min of hypo- versus hyperventilation. In the YP-group, rSO2 was 74 ± 4% after 15 min of hypoventilation and decreased to 68 ± 6% during hyperventilation (p < 0.001). In the OP-group, rSO2 was 71 ± 5% and 65 ± 6%, respectively (p < 0.001). There was no difference concerning changes in comparison of younger and elder patient groups (in both groups, Δ rSO2 = 6 ± 3%; p = 0.732).

CONCLUSION

Even mild hypoventilation increased rSO2 compared to mild hyperventilation and this difference occurred independent of age.

Evaluation of renal near-infrared spectroscopy for predicting extubation outcomes in the pediatric intensive care setting

Background

In pediatric intensive care units, extubation failure following invasive mechanical ventilation poses significant health risks. Determining readiness for extubation in children can minimize associated morbidity and mortality. This study investigates the potential role of renal near-infrared spectroscopy (RrSO2) in predicting extubation failure in pediatric patients.

Methods

A total of 84 patients aged between 1 month and 18 years, mechanically ventilated for at least 24 h, were included in this prospective study. RrSO2 levels were measured using near-infrared spectroscopy before and during an extubation readiness test (ERT). The primary outcome measure was extubation failure, defined as a need for reintubation within 48 h.

Results

Of the 84 patients, 71 (84.6%) were successfully extubated, while 13 (15.4%) failed extubation. RrSO2 was found to be lower in the failed extubation group, also decrease in RrSO2 values during ERT was significantly greater in patients with extubation failure. ROC analysis indicated a decrease in ΔRrSO2 of more than 6.15% from baseline as a significant predictor of extubation failure, with a sensitivity of 0.984 and a specificity of 0.889.

Conclusion

Monitoring changes in RrSO2 values may serve as a helpful tool to predict extubation failure in pediatric patients. Further multi-center research is warranted to improve the generalizability and reliability of these findings.

Effects of permissive hypercapnia on intraoperative cerebral oxygenation and early postoperative cognitive function in older patients with non-acute fragile brain function undergoing laparoscopic colorectal surgery: protocol study

BACKGROUND

Perioperative brain protection in older patients has been the focus of research recently; meanwhile, exploring the relationship between regional cerebral oxygen saturation (rSO2) and brain function in the perioperative period has been an emerging and challenging area-the difficulties related to the real-time monitoring of rSO2 and the choice of feasible interventions. As an advanced instrument for intraoperative rSO2 monitoring, the clinical application of near-infrared spectrum (NIRS) cerebral oxygen monitoring has gradually increased in popularity and is being recognized for its beneficial clinical outcomes in patients undergoing cardiac and noncardiac surgery. In addition, although sufficient evidence to support this hypothesis is still lacking, the effect of permissive hypercapnia (PHC) on rSO2 has expanded from basic research to clinical exploration. Therefore, monitoring intraoperative rSO2 in older patients with NIRS technology and exploring possible interventions that may change rSO2 and even improve postoperative cognitive performance is significant and clinically valuable.

METHODS

This study is a single-center randomized controlled trial (RCT). 76 older patients are enrolled as subjects. Patients who meet the screening criteria will be randomly assigned 1:1 to the control and intervention groups. PHC-based mechanical ventilation will be regarded as an intervention. The primary outcome is the absolute change in the percent change in rSO2 from baseline to the completion of surgery in the intervention and control groups. Secondary outcomes mainly include observations of intraoperative cerebral oxygenation and metabolism, markers of brain injury, and assessments of patients' cognitive function using scale through postoperative follow-up.

DISCUSSION

The findings of this RCT will reveal the effect of PHC on intraoperative rSO2 in older patients with nonacute fragile brain function (NFBF) and the approximate trends over time, and differences in postoperative cognitive function outcomes. We anticipate that the trial results will inform clinical policy decision-makers in clinical practice, enhance the management of intraoperative cerebral oxygen monitoring in older patients with comorbid NFBF, and provide guidance for clinical brain protection and improved postoperative cognitive function outcomes.

TRIAL REGISTRATION

ChiCTR, ChiCTR2200062093, Registered 9/15/2022.

Near-Infrared Spectroscopy in Neurocritical Care: A Review of Recent Updates

Neurocritical diseases and conditions are common causes of long-term disability and mortality. Early recognition and management of neurocritically ill patients is a significant challenge for neurosurgeons, neurologists, and neurointensivists. Although cerebral angiography, magnetic resonance imaging, computed tomography, and radionuclide imaging are useful in neuromonitoring and neuroimaging, they have several important limitations: they are not readily available, cannot be used for a continuous assessment of cerebral function, and frequently require patient transport to the radiological department. Near-infrared spectroscopy (NIRS) is an inexpensive, portable, noninvasive method that does not require advanced expertise and can be used at the bedside for critically ill patients without moving them to the radiology department. NIRS can detect and monitor multiple critical parameters, including cerebral oximetry, intracranial pressure, temperature, and cerebral blood flow. NIRS can be valuable for a wide variety of neurocritical diseases and conditions, such as ischemic and hemorrhagic strokes, severe traumatic brain injury, brain tumors, and perioperative neurosurgery. Although NIRS has been studied extensively in multiple neurocritical conditions, more evidence on its application is needed.

THE IMPORTANCE OF NON-INVASIVE REGIONAL BRAIN OXIMETRY IN PREVENTING POSTOPERATIVE COGNITIVE DYSFUNCTION DURING LAPAROSCOPIC CHOLECYSTECTOMY IN ELDERLY AND SENILE PATIENTS

The adverse effect of general anesthesia in elderly patients during surgery requires monitoring of functions and processes to identify their dangerous abnormalities to prevent complications. The aim of the study. To establish the effectiveness of non-invasive regional brain oximetry with rSO2 determination during anesthetic support in laparoscopic cholecystectomy (LCE) to prevent postoperative cognitive dysfunction in elderly and senile patients. Material and methods. 84 elderly and senile patients with diagnosed gallstone disease, acute cholecystitis, who underwent LCE with sevofluran inhalational anesthesia and total intravenous anesthesia with propofol were examined. rSO2 was monitored. Cognitive functions were assessed using neuropsychological scales and the MMSE mental state examination scale. Results. rSO2 was found to be significantly decreased during the carbon dioxide insufflation as compared to before premedication: in LH (left hemisphere) – by 7.0 %, in RH (right hemisphere) – by 6.9 % (Group I); in LH – by 7.4 %, in RH – by 7.5 % (Group II). rSO2 was significantly increased during the surgery, particularly in the middle of the operation, as compared to before premedication: in LH – by 14.66 %, in RH – by 13.94 % (Group I); in LH – by 11.60 %, in RH – by 11.53 % (Group II). The day following the surgery, cognitive functions significantly decreased by 8.7 % on the Luria's test, by 6.0 % on the MMSE test (Group I); in Group II – by 10.1 % and 6.3 %, respectively, as compared to before premedication. On Day 5 after the surgery, cognitive functions decreased by 2.7 % on the Luria's test, by 0.35 % on the MMSE test (Group I); in Group II – by 2.7 % and 0.35 %, respectively, as compared to before premedication. Conclusions. A decrease in rSO2 can occur during LCE in the Trendelenburg position, despite the fact that other intraoperative indicators remain stable, which allows it to remain unrecognized. rSO2 monitoring in the perioperative period contributes to alertness and timely measures to prevent postoperative cognitive dysfunction.

A Pilot Randomized Controlled Study of Mild Hypercapnia During Cardiac Surgery With Cardiopulmonary Bypass

OBJECTIVES

To test whether targeted therapeutic mild hypercapnia (TTMH) would attenuate cerebral oxygen desaturation detected using near-infrared spectroscopy during cardiac surgery requiring cardiopulmonary bypass (CPB).

DESIGN

Randomized controlled trials.

SETTING

Operating rooms and intensive care unit of tertiary hospital.

PARTICIPANTS

The study comprised 30 patients undergoing cardiac surgery with CPB.

INTERVENTIONS

Patients were randomly assigned to receive either standard carbon dioxide management (normocapnia) or TTMH (target arterial carbon dioxide partial pressure between 50 and 55 mmHg) throughout the intraoperative period and postoperatively until the onset of spontaneous ventilation.

MEASUREMENTS AND MAIN RESULTS

Relevant biochemical and hemodynamic variables were measured, and cerebral tissue oxygen saturation (SctO₂) was monitored with near-infrared spectroscopy. Patients were followed-up with neuropsychological testing. Patient demographics between groups were compared using the Fisher exact and Mann-Whitney tests, and SctO₂ between groups was compared using repeated measures analysis of variance. The median patient age was 67 years (interquartile range [IQR] 62-72 y), and the median EuroSCORE II was 1.1. The median CPB time was 106 minutes. The mean intraoperative arterial carbon dioxide partial pressure for each patient was significantly higher with TTMH (52.1 mmHg [IQR 49.9-53.9 mmHg] v 40.8 mmHg [IQR 38.7-41.7 mmHg]; p < 0.001) as was pulmonary artery pressure (23.9 mmHg [IQR 22.4-25.3 mmHg] v 18.5 mmHg [IQR 14.8-20.7 mmHg]; p = 0.004). There was no difference in mean percentage change in SctO₂ during CPB in the control group for both hemispheres (left: -6.7% v -2.3%; p = 0.110; right: -7.9% v -1.0%; p = 0.120). Compliance with neuropsychological test protocols was poor. However, the proportion of patients with drops in test score >20% was similar between groups in all tests.

CONCLUSIONS

TTMH did not increase SctO₂ appreciably during CPB but increased pulmonary artery pressures before and after CPB. These findings do not support further investigation of TTMH as a means of improving SctO₂ during and after cardiac surgery requiring CPB.

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.