Do you have litterature on this? i've looked and didn't find anything convincing.
So, I think its fair to say there isn't a slam dunk answer, but if you really pick apart the studies you have to consider a couple of things. First, potency. There is a reasonable body of literature to suggest that ropi is not as potent as advertised. I put one reference in below. If you accept that then start comparing the toxicity studies, many compare "equipotent" doses. But, if you accept that as suspect and take the study I listed below, it took double the dose of ropi to get equal anesthesia. So, now turn to a toxicity study. I listed one below, in rats. The conclusion, lower cumulative doses of bupi produce cardiac toxicity compared to ropi. But lets look at some of the numbers.
"The cumulative dose of local anesthetic required to produce ASYS was also larger in the Levobupivacaine (57.4 +/- 7.8 mg/kg) and Ropivacaine (107.8 +/-26.8 mg/kg) groups than in the Bupivacaine group (39.6 +/- 9.0 mg/kg) (Fig. 1). Compared with the Levobupivacaine group, the dose that produced ASYS was significantly larger in the Ropivacaine group"
So, Ropi 107.8 vs. Bupi 39.6. So, if you believe our potency study then you need to double up your ropi dose to be equal to bupi. Now this difference in toxicity isn't that big any more.
Personally, I think its a false hope to believe that ropi is that much safer than bupi. It might be a bit safer, but I don't know if that really means that much. Just use lower doses of bupi, if you reduce the dose you will lower risk of cardiac toxicity. And, its cheaper.
In my academic center, on our OB service, we use 1/16% (0.0625%) bupi with 2 mcg/ml of fentanyl in PCEA. It works great in 90%+ of our patients. The rest we occasionally bolus with 0.25% bupi. Unfortunately we can't crank up the concentration. Additionally, we rarely have problems with excessive motor block.
To be fair, my personal experience with ropi in labor epidurals is limited, but I have used some 1/8% ropi (with 2 mcg/ml of fentanyl) and anecdotally I would say I was called with unsatisfied patients at a pretty similar frequency.
My limited list of references
1. Ropi less potent than bupi
Anesthesiology. 1999 Apr;90(4):944-50.
Relative analgesic potencies of ropivacaine and bupivacaine for epidural analgesia in labor: implications for therapeutic indexes.
Polley LS, Columb MO, Naughton NN, Wagner DS, van de Ven CJ.
Department of Anesthesiology, Women's Hospital, University of Michigan Health System, Ann Arbor, USA.
[email protected]
BACKGROUND: The minimum local analgesic concentration (MLAC) has been defined as the median effective local analgesic concentration in a 20-ml volume for epidural analgesia in the first stage of labor. The aim of this study was to assess the relative analgesic potencies of epidural bupivacaine and ropivacaine by determining their respective minimum local analgesic concentrations. METHODS: Seventy-three parturients at < or = 7 cm cervical dilation who requested epidural analgesia were allocated to one of two groups in this double-blinded, randomized, prospective study. After a lumbar epidural catheter was placed, 20 ml of the test solution was given, either ropivacaine (n = 34) or bupivacaine (n = 39). The concentration of local anesthetic was determined by the response of the previous patient in that group to a higher or lower concentration using up-down sequential allocation. Analgesic efficacy was assessed using 100-mm visual analog pain scores with < or = 10 mm within 30 min defined as effective. An effective result directed a 0.01% wt/vol decrement for the next patient. An ineffective result directed a 0.01% wt/vol increment. RESULTS: The
minimum local analgesic concentration of ropivacaine was 0.111% wt/vol (95% confidence interval, 0.100-0.122), and the
minimum local analgesic concentration of bupivacaine was 0.067% wt/vol (95% confidence interval, 0.052-0.082). Ropivacaine was significantly less potent than bupivacaine, with a potency ratio of 0.6 (95% confidence interval, 0.49-0.74). No difference in motor effects was observed. CONCLUSION: Ropivacaine was significantly less potent than bupivacaine for epidural analgesia in the first stage of labor.
2. Toxicity in Rats
Anesth Analg. 2001 Sep;93(3):743-8.
Systemic toxicity and resuscitation in bupivacaine-, levobupivacaine-, or ropivacaine-infused rats.
Ohmura S, Kawada M, Ohta T, Yamamoto K, Kobayashi T.
Department of Anesthesiology and Intensive Care Medicine, School of Medicine, Kanazawa University, Kanazawa, Japan.
[email protected]
We compared the systemic toxicity of bupivacaine, levobupivacaine, and ropivacaine in anesthetized rats. We also compared the ability to resuscitate rats after lethal doses of these local anesthetics. Bupivacaine, levobupivacaine, or ropivacaine was infused at a rate of 2 mg. kg(-1). min(-1) while electrocardiogram, electroencephalogram, and arterial pressure were continuously monitored. When asystole was recorded, drug infusion was stopped and a resuscitation sequence was begun. Epinephrine 0.01 mg/kg was administered at 1-min intervals while external cardiac compressions were applied. Resuscitation was considered successful when a systolic arterial pressure > or =100 mm Hg was achieved within 5 min. The cumulative doses of levobupivacaine and ropivacaine that produced seizures were similar and were larger than those of bupivacaine. The cumulative doses of levobupivacaine that produced dysrhythmias and asystole were smaller than the corresponding doses of ropivacaine, but they were larger than those of bupivacaine. The number of successful resuscitations did not differ among groups. However, a smaller dose of epinephrine was required in the Ropivacaine group than in the other groups. We conclude that the systemic toxicity of levobupivacaine is intermediate between that of ropivacaine and bupivacaine when administered at the same rate and that ropivacaine-induced cardiac arrest appears to be more susceptible to treatment than that induced by bupivacaine or levobupivacaine.
