Pharmacokinetic Analysis for Epidural Ropivacaine Induced Cardiac Arrest

 

Tomoko Takeda, M.D., Kenichi Masui, M.D., Ryuji Yonamine, M.D., Isao Fukuda, M.D., Takehiko Ikeda, M.D. and Tomiei Kazama, M.D..

Department of Anesthesiology, National Defense Medical College, Tokorozawa, Saitama, Japan.

 

 

Case

The patient was 39-year-old primigravida who complicated with Takayasu disease. She was scheduled for caesarean section with epidural anesthesia. An epidural catheter was inserted at level L3-4. After negative aspiration tests for blood or cerebrospinal fluid, 20ml of ropivacaine 1% was injected. Eight min after injection, upper level of sensory block was Th8. Heart rate was 150/min (sinus rhythm) and electrocardiogram showed slightly ST depression. Then, she was suffering from shortness of breath and garrulous. Because convulsion occurred at 13 min after injection, tracheal intubation was performed followed by thiopental sodium and vecuronium bromide. And then 14 ,17, and 22 min after injection, electrocardiogram showed pulseless ventricular tachycardia, but immediately returned to sinus rhythm by hitting on her sternum or defibrillation. After the end of operation, newborn and she left the operating room without severe side effects.

 

Pharmacokinetic analysis

A compartment model was developed for analyzing the time course of plasma ropivacaine concentration by using nonlinear least-square curve fitting. Model contained epidural space (Cepi) and central compartment (Ccent), absorption half-life from Cepi to Ccent (ka), and elimination half-life of Ccent (kel). Calculated parameters were followings: ka=14min, Kel=13.3min, maximum drug concentration time (Tmax)=13.3min, and maximum drug concentration (Cmax)=3.66mg/l.

 

Discussion

Because of short time onset of local anesthetic toxicty, intravascular injection was suspected. However, pharmacokinetic analysis suggested few ropivacaine was injected directly into the vessels. A previous study reported that it estimated ka=14min, Tmax=21.6min, and Cmax=2.06mg/l in healthy volunteer. In our case, the cause of high plasma concentration of ropivacaine might be that smaller epidural space and overswelling of vessel might shorten absorption half-life of ropivacaine.

 

Conclusions

At the time of epidural drug administration, local anesthetics might be absorbed from epidural space to vessel more rapidly in pregnant than in nonpregnant. Pharmacokinetic analysis suggested that it might increase the risk of local anesthetic toxicity in pregnant patient.