Background and Objectives: Intrathecal (IT) sufentanil is commonly used in
parturients to provide rapid onset of labor analgesia without motor block.
This practice, although widely used, has been associated with severe respir
atory depression in some patients. The mechanism of this respiratory depres
sion is unclear, however, rapid cephalad movement and interaction with pare
nteral opioids are 2 frequently cited explanations for this complication. B
ecause this complication has occurred only in women with heights between 15
0 and 157 cm, we elected to study the effect of the distance from injection
site to the cisterna. magna (CM) on peak brainstem cerebrospinal fluid (CS
F) concentrations.
Methods: Ten adult ewes were injected with IT sufentanil (0.3 mug/kg) at a
mean distance of either 71 cin (65 to 78 cm) from the brainstem. (pelvic gr
oup) or 37 cm (34 to 42 cm)from the brainstem (thoracic group). CSF was the
n sampled at 5-minute intervals from the CM.
Results: Measurable CM concentrations of sufentanil were noted in the brain
stem at 20 and 25 minutes, respectively, for the thoracic and the pelvic gr
oups. Peak sufentanil concentrations from the thoracic group were nearly 10
-fold higher (0.553 +/- 0.43 ng/mL) compared with the pelvic group (0.064 /- 0.002 ng/mL) when measured in the CM (P = .023)
Conclusions: Our results suggest that sufentanil migrates relatively large
distances in the IT space. Injection site (distance from the brainstem) app
ears to be a prominent factor in determining brainstem concentrations and s
ubsequent respiratory depression after spinal administration.