573 - Cerebral Blood Flow Measured by Diffuse Correlation Spectroscopy for Monitoring Depth of Anesthesia in Piglets

Monitoring depth of anesthesia during surgery is critical. Near Infrared Spectroscopy (NIRS) measures of cerebral blood volume (CBV) and cerebral oxygenation (OXY) have been used during anesthesia. In addition to OXY cerebral blood flow (CBF) measures can provide reliable assessment of different anesthesia states and enhance depth of anesthesia monitoring. CBF can be measured non-invasively via Diffuse Correlation Spectroscopy (DCS) system.

Objective:

This preliminary study investigates if CBF changes correlate with different states of anesthesia, i.e., light versus deep anesthesia.

Design/Methods:

Newborn piglets were ventilated at normal oxygen and administered inhalational anesthetics Isoflurane and/or Nitrous Oxide, and intravenous Ketamine. Deep anesthesia was defined as the period corresponding to the peak-effect of the drug based on pharmacokinetics, with the animal being immobile and nonresponsive to pain, and light anesthesia as the period after washout of the drug based on pharmacokinetics, with the animal either responsive to pain or mobile. Monitoring included: Continuous recording of vital signs; aEEG (Natus CFM 6000); NIRS; and DCS system, placed on the preorbital to temporal regions of the skull, with a single photon counting module collecting backscattered photons, and an autocorrelator that generates temporal correlation functions fit over a correlation diffusion model to calculate Blood Flow Index (BFI; cm²/s).

Results:

This preliminary study reports four epochs of anesthesia from two piglets. Fig. 1 shows a representative measure of CBF, CBV, oxy-hemoglobin and aEEG during deep and light anesthesia in a piglet after Ketamine. Fig. 2 reveals the increase in CBF during light versus deep anesthesia. Fig. 3 displays the changes in heart rate, CBF, CBV and aEEG during deep and light anesthesia for the 4 epochs. The results show an increase in CBF, CBV, and HR during the emergence from deep to light anesthesia. The response in EEG was delayed compared to the other modalities.

Conclusion(s):

CBF measures were consistently matched with awakening from deep anesthesia in piglets with all the anesthetic drugs administered. The changes in CBF and OXY, CBV preceded those observed by the surface aEEG. This observation is consistent with neurovascular coupling where increased neuronal activity in cortical areas during transitioning from deep to light anesthesia leads to rise in oxygenated hemoglobin and CBV. We hypothesize that the use of DCS for monitoring depth of anesthesia can help prevent unintended transition into a lighter state of anesthesia during a maintenance phase in adults and infants.