The Effects of Remimazolam on Cerebral Blood Flow Following General Anesthesia Induction

The resistance index (RI) of the middle cerebral artery (MCA) is a hemodynamic parameter. It reflects downstream cerebrovascular resistance and is defined by the formula: RI = (Peak Systolic Velocity - End-Diastolic Velocity) / Peak Systolic Velocity.

A normal RI in the MCA for healthy adults typically ranges from 0.50 to 0.70 (or 50-70%). Values are influenced by age, with neonates and infants having higher normal values (often up to 0.80-0.85) which decrease toward adult levels with maturation. In elderly individuals, a slight increase may be observed due to reduced vascular compliance.

An elevated RI (>0.80) generally indicates increased distal vascular resistance, which can be caused by intracranial hypertension, severe microangiopathy, or brain death. A very low RI (<0.50) may suggest a hyperemic state or proximal stenosis.

Mean blood flow velocity (MV), often referred to as Time-Averaged Maximum Velocity (TAMV), is a key hemodynamic parameter measured by Doppler ultrasound. It represents the average speed of the fastest-moving blood cells within a vessel over one complete cardiac cycle.

For the middle cerebral artery (MCA) in healthy adults, the normal MV typically ranges from 40 to 65 cm/s. This value is age-dependent, being higher in children and gradually decreasing with advancing age. A sustained MV outside this range, particularly when asymmetric compared to the contralateral side, can indicate pathological conditions such as stenosis, hyperemia, or impaired autoregulation. Its calculation integrates both systolic and diastolic flow, making it a stable indicator of overall cerebral perfusion.

The Pulsatility Index (PI) is a dimensionless hemodynamic parameter derived from Transcranial Doppler (TCD) ultrasound. It quantifies the pulsatility of the blood flow waveform, reflecting downstream cerebrovascular resistance. It is calculated using the formula: PI = (Peak Systolic Velocity - End-Diastolic Velocity) / Mean Velocity.

For the middle cerebral artery (MCA) in healthy adults, the normal PI typically ranges from 0.70 to 1.10. Age significantly influences this value; neonates have a much higher normal PI (often >1.50), which decreases to adult levels during childhood. An elevated PI (>1.20) generally indicates increased distal resistance, which can be caused by intracranial hypertension or small vessel disease. Conversely, a very low PI (<0.60) may suggest a hyperdynamic state or proximal stenosis.

post-anesthesia care unit (PACU) length of stay. There is no single universal "normal value" for Post-Anesthesia Care Unit (PACU) length of stay, as it is highly dependent on the type of surgery, anesthesia technique, institutional protocols, and patient-specific factors. For straightforward, outpatient, or minor inpatient surgeries, a typical stay often ranges from 30 minutes to 2 hours. The primary discharge criteria are based on standardized scoring systems, most commonly the Aldrete score or its modifications. Patients must achieve a predetermined score (usually ≥9 out of 10) indicating stable vital signs, adequate oxygenation, intact consciousness, and controlled pain and nausea before discharge to a ward or home. Prolonged stays beyond expected benchmarks are used as a quality indicator to identify and address potential complications like postoperative nausea and vomiting, pain, or hemodynamic instability.

Postoperative cognitive score was assessed by the Mini-Mental State Examination, MMSE). MMSE is a standardized, 30-point questionnaire used to screen for cognitive impairment. It assesses five key domains: orientation (to time and place), registration and recall of words, attention and calculation (e.g., serial sevens), language abilities (naming, repetition, comprehension, reading, writing), and visual construction (copying a pentagon).

Administration involves a trained examiner asking the patient specific questions in a quiet setting, typically taking 5-10 minutes. One point is awarded for each correct task, with a maximum total score of 30.

Results are interpreted based on the total score: 27-30 suggests normal cognition, 24-26 indicates mild cognitive impairment, 19-23 signifies moderate impairment, and a score ≤18 points to severe impairment.