Indices for monitoring nociception during general anesthesia
Regarding diagnostic accuracy and prediction probability for nociceptive response, which is the optimal approach: an analgesic index or clinical parameters? Researchers at the University Medical Center Hamburg-Eppendorf in Germany compared the Analgesia Nociception Index (heart rate variability), Surgical Pleth Index (photoplethysmography) and pupillary dilatation on the one hand to heart rate, mean arterial pressure, and bispectral index on the other hand. The primary endpoint was the correlation between Δ values and the remifentanil dose administered.
38 patients were anesthetized with propofol and increasing doses of remifentanil, and each patient was given standardized tetanic and intracutaneous electrical painful stimulations on each analgesic level.
Under propofol sedation, sensitivity and specificity of the Analgesia Nociception Index, the Surgical Pleth Index and pupillary dilatation were higher for detecting both painful stimulations (PK = 0.98, 0.87 and 0.98, respectively) than heart rate, mean arterial pressure and bispectral index (PK = 0.74, 0.75 and 0.55, respectively). Baseline values had limited prediction probability toward the nociceptive response (Analgesia Nociception Index: PK = 0.7; Surgical Pleth Index: PK = 0.63; pupillary dilatation: PK = 0.67; and bispectral index: PK = 0.67). The remifentanil dose had an effect (P < 0.001) on all parameters except for bispectral index (P = 0.216).
The Analgesia Nociception Index, the Surgical Pleth Index and pupillary dilatation are better suited to detect painful stimulations than heart rate and mean arterial pressure. However, their predictive value was only limited. The results of this study also confirm that bispectral index should not be used as a marker of analgesia.