Journal of Clinical Monitoring and Computing 2019 end of year summary: monitoring tissue oxygenation and perfusion and its autoregulation

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.

A Review of Monitoring Methods for Cerebral Blood Oxygen Saturation

In recent years, cerebral blood oxygen saturation has become a key indicator during the perioperative period. Cerebral blood oxygen saturation monitoring is conducive to the early diagnosis and treatment of cerebral ischemia and hypoxia. The present study discusses the three most extensively used clinical methods for cerebral blood oxygen saturation monitoring from different aspects: working principles, relevant parameters, current situations of research, commonly used equipment, and relative advantages of different methods. Furthermore, through comprehensive comparisons of the methods, we find that near-infrared spectroscopy (NIRS) technology has significant potentials and broad applications prospects in terms of cerebral oxygen saturation monitoring. Despite the current NIRS technology, the only bedside non-invasive cerebral oxygen saturation monitoring technology, still has many defects, it is more in line with the future development trend in the field of medical and health, and will become the main method gradually.