Letters to the Editor: In Response
Mechanism of Analgesic Action of Intrathecal Sufentanil
We thank Drs. Ferouz and Norris for their comments regarding our study. We agree that most likely there is an interplay of spinal and supraspinal actions of intrathecal sufentanil that produces analgesia and side effects (nausea/vomiting, pruritus, hypotension, and respiratory depression). In our article, we discuss the compelling evidence for direct cephalad spread of hydrophillic opioids within the cerebrospinal fluid . Although we agree that opioid baricity and patient position affects labor analgesia, the height of the location in the central nervous system wherein dextrose interferes with the effects of intrathecal sufentanil remains unclear. We speculated that intrathecal hyperbaric sufentanil injected with patients in the sitting position restricted cephalad spread such that the decreased sufentanil concentrations achieved in the lower thoracic spinal regions resulted in a decreased duration of analgesia. Similar effects of baricity and patient positioning on local anesthetic drug concentrations have been described. For example, higher lumbosacral concentrations associated with intrathecal injections of isobaric local anesthetic solutions, compared with hyperbaric solutions, result in longer durations of associated dermatomal anesthesia .
The purpose of this clinical study was to determine systematically whether patient position and baricity could be manipulated to enhance intrathecal sufentanil-induced labor analgesia, not to specifically examine the mechanism of dextrose interference with intrathecal sufentanil labor analgesia. We originally hypothesized that hyperbaric preparations of spinal sufentanil would prolong analgesia by concentrating the sufentanil near the site of injection. In contrast, we concluded from this study that dextrose diminished the quality and duration of labor analgesia from that of intrathecal sufentanil injected with patients in the sitting position. Thus, we recommend that dextrose not be added to intrathecal sufentanil when administered to patients in the sitting position ; and, in fact, our clinical practice now parallels this recommendation.
Jennifer C. Gage, MD
Robert D'Angelo, MD
Department of Anesthesiology; Wake Forest University School of Medicine; Winston-Salem, NC 27157-1009
1. Gage JC, D'Angelo R, Miller R, et al. Does dextrose affect analgesia or the side effects of intrathecal sufentanil? Anesth Analg 1997;85:826-30.
© 1998 International Anesthesia Research Society
2. Barash PG, Cullen BF, Stoelting RK. Clinical Anesthesia, 2nd ed. Philadelphia: JB Lippincott, 1992:826-8.