Zerebrale Oxymetrie: Klinischer Stellenwert bei kardiochirurgischen Patienten

Cerebral blood flow autoregulation assessment by correlation analysis between mean arterial blood pressure and transcranial doppler sonography or near infrared spectroscopy is different: A pilot study

PURPOSE

Recently, cerebral autoregulation indices based on moving correlation indices between mean arterial pressure (MAP) and cerebral oximetry (NIRS, ORx) or transcranial Doppler (TCD)-derived middle cerebral artery flow velocity (Mx) have been introduced to clinical practice. In a pilot study, we aimed to evaluate the validity of these indices using incremental lower body negative pressure (LBNP) until presyncope representing beginning cerebral hypoperfusion as well as lower body positive pressure (LBPP) with added mild hypoxia to induce cerebral hyperperfusion in healthy subjects.

METHODS

Five male subjects received continuous hemodynamic, TCD and NIRS monitoring. Decreasing levels of LBNP were applied in 5-minute steps until subjects reached presyncope. Increasing levels of LBPP were applied stepwise up to 20 or 25 mmHg. Normobaric hypoxia was added until an oxygen saturation of 84% was reached. This was continued for 10 minutes. ORx and Mx indices were calculated using previously described methods.

RESULTS

Both Indices showed an increase > 0.3 indicating impaired cerebral autoregulation during presyncope. However, there was no significant difference in Mx at presyncope compared to baseline (p = 0.168). Mean arterial pressure and cardiac output decreased only in presyncope, while stroke volume was decreased at the last pressure level. Neither Mx nor ORx showed significant changes during LBPP or hypoxia. Agreement between Mx and ORx was poor during the LBNP and LBPP experiments (R2 = 0.001, p = 0.3339).

CONCLUSION

Mx and ORx represent impaired cerebral autoregulation, but in Mx this may not be distinguished sufficiently from baseline. LBPP and hypoxia are insufficient to reach the upper limit of cerebral autoregulation as indicated by Mx and ORx.

[Significance of patient-specific risk factors for regional cerebral oxygen saturation in beach chair position]

BACKGROUND

Despite numerous studies on the regional cerebral oxygen saturation (rSO₂) measured by near infrared spectroscopy (NIRS) in orthopedic patients in the beach chair position, it is still unclear whether patient-specific factors, such as concomitant cardiovascular diseases, are more frequently associated with the occurrence of cerebral desaturation events (CDE).

OBJECTIVE

The aim of the present study was therefore to identify possible patient-specific risk factors that enable prediction of CDE.

METHODS

Data were collected on 397 orthopedic patients undergoing shoulder surgery in the beach chair position. Routine anesthesia management and standard monitoring was used in all patients. Target value for the inspiratory oxygen concentration (F_IO₂) was set to 50% and for the end-tidal carbon dioxide partial pressure to 35-45 mm Hg. RSO₂ was quantified using NIRS. The responsible anesthesiologist was blinded to the rSO₂ data. A decrease in rSO₂ > 20% or a value < 50% in the beach chair position was defined as CDE. Patients with and without CDE were analyzed with respect to different classifications, American Society of Anesthesiologists (ASA) and Revised Cardiac Risk Index (RCRI) as well as existing arterial hypertension and age. A value of p <0.05 was considered statistically significant.

RESULTS

Patients with CDE (n = 238) were significantly more often classified as ASA > 2 (p = 0.01) and RCRI > 1 (p = 0.01), suffered more often from arterial hypertension (p = 0.01) and were older (median: 60 years compared to 55 years; p = 0.01) than patients without CDE (n = 159) in the beach chair position (Wilcoxon rank sum test). Arterial hypertension remained significant after removing the effect of age (p = 0.03) and RCRI classification (p = 0.04; two-way ANOVA multivariate analysis).

CONCLUSION

On the basis of our study, patient-specific prognosis and risk factors for the occurrence of CDE, such as higher age, ASA > 2 and RCRI > 1 classification as well as pre-existing arterial hypertension could be determined. Arterial hypertension represents the main risk factor for the occurrence of CDE in the beach chair position. RCRI > 1 classification or age, however, only has an effect on the occurrence of pathological rSO₂ values due to the greater probability of simultaneous arterial hypertension.

[Near-infrared spectroscopy : Technique, development, current use and perspectives]

Near-infrared spectroscopy (NIRS) has been available in research and clinical practice for more than four decades. Recently, there have been numerous publications and substantial developments in the field. This article describes the clinical application of NIRS in relation to current guidelines, with a focus on pediatric and cardiac anesthesia. It discusses technical and physiological principles, pitfalls in clinical use and presents (patho)physiological influencing factors and derived variables, such as fractional oxygen extraction (FOE) and the cerebral oxygen index (COx). Recommendations for the interpretation of NIRS values in connection with influencing factors, such as oxygen transport capacity, gas exchange and circulation as well as an algorithm for cardiac anesthesia are presented. Limitations of the method and the lack of comparability of values from different devices as well as generally accepted standard values are explained. Technical differences and advantages compared to pulse oxymetry and transcranial Doppler sonography are illuminated. Finally, the prognostic significance and requirements for future clinical studies are discussed.

[Use of near-infrared spectroscopy for control of limb perfusion during venoarterial ECMO treatment : Application and limitations]

Patients undergoing peripheral venoarterial extracorporeal membrane oxygenation have a high risk of lower limb ischemia. In general, regular controls are carried out based on clinical and laboratory parameters in order to quickly detect and treat complications. These controls are challenging due to states of shock, nonpulsatile flow and vasopressor therapy. As additional monitoring the use of near-infrared spectroscopy (NIRS) is described in the literature as being very successful in detecting ischemia. The present article describes the use and possible limitations of NIRS for the diagnostics of peripheral ischemia.