Near-infrared spectroscopy to measure brain oxygenation: A comparison of measurements on the skin, skull and dura mater.

BACKGROUND: The reliability of near-infrared spectroscopy (NIRS) for measuring cerebral oxygenation (ScO2 ) is controversial due to the possible contamination from extracranial tissues. We compared ScO2 measured with the NIRS optode on the forehead, the skull and the dura mater in anaesthetised patients undergoing craniotomy. We hypothesised that ScO2 measured directly on the skull and the dura mater would differ from ScO2 measured on the skin. METHODS: This prospective observational study included 17 adult patients scheduled for elective craniotomy. After induction of general anaesthesia, ScO2 was measured on the forehead skin, as well as on the skull and on the dura mater in the surgical field. The primary comparison was the difference in ScO2 measured on the dura mater and on ScO2 measured on the skin; secondary comparisons were the differences in ScO2 on the skull and ScO2 on the skin and the dura mater, respectively. Data were described with median (5%-95% range) and analysed with the Wilcoxon signed-rank test. RESULTS: ScO2 values on the dura mater were obtained in 11 patients, and median ScO2 (48%, 29%-95%) did not differ significantly from ScO2 on the skin (73%, 49%-92%; p = .052), median difference -25% (-35.6% to -1.2%). ScO2 on the skull (N = 16) was lower than that on the skin (63% [43%-79%] vs. 75% [61%-94%]; p = .0002), median difference -10% (-20.8 to -3.0). CONCLUSION: In adults undergoing craniotomy, NIRS-based ScO2 measured on the dura mater did not reach statistically significantly lower values than ScO2 measured on the skin, whereas values on the skull were lower than on the skin, indicating a contribution from scalp tissue to the signal.

Impact of hyperoxia and phenylephrine on cerebral oxygenation: An experimental clinical study.

BACKGROUND: Oxygen supply to the brain is of special importance during intracranial surgery because it may be compromised by intracranial pathology. A high arterial blood pressure (mean arterial pressure above 80 mmHg) and a high arterial oxygen tension (PaO2 above 12 kPa) is therefore often targeted in these patients, when for example intracranial pressure is increased or when a mass effect on brain tissue from a tumour is present, and it is pursued by administering vasopressors such as phenylephrine and by increasing inspiratory oxygen fraction (FiO2 ). However, whether these interventions increase cerebral oxygenation remains uncertain. We aimed to investigate the effect of hyperoxia and phenylephrine on brain tissue oxygen tension (PbtO2 ) in patients undergoing craniotomy. METHODS: In this experimental study, we included 17 adult patients scheduled for elective craniotomy. After securing a stable baseline of the oxygen probe, PbtO2 was measured in white matter peripherally in the surgical field during general anaesthesia. Primary comparisons were PbtO2 before versus after an increase in FiO2 from 0.30 to 0.80 as well as before versus after a bolus dose of phenylephrine (0.1-0.2 mg depending on patient haemodynamics). Data were analysed with the Wilcoxon signed rank test. RESULTS: We obtained complete data sets in 11 patients undergoing the FiO2 increase and six patients receiving the phenylephrine bolus. PbtO2 was 22 (median; 5%-95% range, 4.6-54) mmHg during 30% oxygen, 68 (8.4-99) mmHg during 80% oxygen (p = .004 compared to 30% oxygen), 21 (4.5-81) mmHg before phenylephrine, and 19 (4.2-56) mmHg after phenylephrine (p = .56 compared to before phenylephrine). CONCLUSION: In patients undergoing craniotomy under general anaesthesia, brain tissue oxygen tension increased with a high inspiratory oxygen fraction but remained unchanged after a bolus dose of phenylephrine.

Pain treatment after craniotomy: where is the (procedure-specific) evidence? A qualitative systematic review.

CONTEXT AND OBJECTIVE: Pain following craniotomy has been demonstrated to be frequent and moderate-to-severe in nature. In recent years, the focus on the challenges in treatment of postoperative pain following craniotomy has increased. Fear of using opioids because of their wide array of side-effects has led to the search for alternative analgesic options. The objective of this systematic review was to evaluate current evidence about analgesic therapy following craniotomy. DATA SOURCES: PubMed database, Embase, Cochrane library, Google scholar and the Cumulative Index to Nursing and Allied Health Literature. ELIGIBILITY CRITERIA: Randomised double-blinded placebo-controlled trials (RCTs) with pain or supplemental postoperative analgesic consumption as an endpoint were included in the analysis. RESULTS: A total of 34 RCTs were identified, and nine RCTs were included in the final analysis, with a total of 519 patients (251 control vs. 268 active treatment). Four treatment modalities - scalp infiltration (five RCTs), nerve scalp block (two RCTs), parecoxib (one RCT) and patient-controlled analgesia with morphine (one RCT) - were evaluated. Scalp infiltration with local anaesthetic may provide adequate analgesia in the first few postoperative hours, and nerve scalp block may provide longer lasting analgesia for about 6 h. Morphine was found to reduce total analgesic rescue doses with no significant effect on nausea and no other side-effects. No significant evidence was found to support the use of parecoxib in the treatment of postcraniotomy pain. CONCLUSION: No firm recommendations on analgesic therapy following craniotomy can be given because the number of well performed RCTs is limited and the study populations are very small. However, evidence on scalp infiltration suggests an analgesic effect in the first few postoperative hours. There is an urgent need for well performed RCTs on pain therapy following craniotomy.