Survey of pain specialists regarding conversion of high-dose intravenous to neuraxial opioids

Abstract

The conversion of high-dose intravenous (IV) opioids to an equianalgesic epidural (EP) or intrathecal (IT) dose is a common clinical dilemma for which there is little evidence to guide practice. Expert opinion varies, though a 100 IV:10:EP:1 IT conversion ratio is commonly cited in the literature, especially for morphine. In this study, the authors surveyed 724 pain specialists to elucidate the ratios that respondents apply to convert high-dose IV morphine, hydromorphone, and fentanyl to both EP and IT routes. Eighty-three respondents completed the survey. Conversion ratios were calculated and entered into graphical scatter plots. The data suggest that there is wide variation in how pain specialists convert high-dose IV opioids to EP and IT routes. The 100 IV:10 EP:1 IT ratio was the most common answer of survey respondent, especially for morphine, though also for hydromorphone and fentanyl. Furthermore, more respondents applied a more aggressive conversion strategy for hydromorphone and fentanyl, likely reflecting less spinal selectivity of those opioids compared with morphine. The authors conclude that there is little consensus on this issue and suggest that in the absence of better data, a conservative approach to opioid conversion between IV and neuraxial routes is warranted.

Conversion of Intrathecal Opioids to Fentanyl in Chronic Pain Patients With Implantable Pain Pumps: A Retrospective Study

“…This IV:EP:IT ratio of 100:10:1 was supported by Krames et al from experience from their practice . In a survey of pain practitioners, Gorlin et al confirmed the use of this conversion ratio when they reported the majority (68%) used IV:EP ratio of 10:1 and (65%) 100:1 IV:IT for morphine conversion . The same ratio was commonly used for converting fentanyl IV to EP and EP to IT as well (40–42%).…”

Continuous peripheral nerve blocks compared to thoracic epidurals or multimodal analgesia for midline laparotomy: a systematic review and meta-analysis

“…Although there is some uncertainty about equianalgesic dose conversion from IV systemic to epidural opioids, the most commonly cited conversion is 10:1 for both morphine and hydromorphone. [49] Thus, even low dose opioids added to epidural solutions can contribute to a large proportion of the cumulative opioid consumption. Furthermore, the patients would receive this amount of opioid whether they needed it or not.…”

Curing Opioid Toxicity with Intrathecal Targeted Drug Delivery

“…For purposes of this conversation, we will only discuss the conversion of morphine. It is well accepted that oral to parenteral morphine is a conversion factor of three, parenteral to epidural morphine is a conversion factor of ten, and epidural to IT morphine is a conversion factor of ten [29, 30]. Therefore, when calculating an “equianalgesic dose” of oral morphine to IT morphine, it roughly equates to 1 (oral): 3 (parenteral): 10 (epidural): 10 (intrathecal) or 300 times greater.…”