TESTS TO EVALUATE INTRAVENOUS PLACEMENT OF EPIDURAL CATHETERS IN LABORING WOMEN - A PROSPECTIVE CLINICAL-STUDY

We prospectively evaluated the diagnostic accuracy of an epinephrine-c ontaining epidural test dose (EpiTD) as a marker of intravascular inje ction in 209 unmedicated laboring women. Maternal heart rate (MHR) was continuously monitored and recorded on a strip chart. A tocodynamomet er monitored uterine activity. A lumbar epidural catheter was placed a nd aspirated. If aspiration was positive for blood or cerebrospinal fl uid (CSF), the catheter was replaced. In uterine diastole and with sta ble MHR, 198 patients received an EpiTD (epinephrine 15 mu g plus lido caine 45 mg) via the catheter. MHR and the generated HR strip were obs erved. A positive EpiTD was defined as a sudden increase in MHR of 10 bpm more than the resting MHR, within one minute after the injection, with a fast acceleratory phase of more than 1 bpm. Absence of a tachyc ardiac response suggested a negative EpiTD. If the tachycardiac respon se was deemed equivocal or a uterine contraction followed the EpiTD in jection within 1 min, the EpiTD was invalidated and repeated. Catheter aspiration was repeated, and the catheter was removed if aspiration w as positive. All patients with negative EpiTD and aspiration received 6-12 mL of epidural bupivacaine 0.25% with or without fentanyl 50 mu g . Absence of analgesia without signs or symptoms of systemic toxicity after a maximum of bupivacaine 30 mg defined failed epidural analgesia . All patients with positive EpiTD and negative aspiration received 5 mL of lidocaine 2% epidurally as a second test dose (Lido100TD). The p resence of tinnitus and/or metallic taste defined a positive Lido100TD . There were 176 true negatives, 0 false neg atives, 14 true positives , and 8 false positives. The sensitivity of EpiTD was 100%, the specif icity 96%, the neg ative predictive value 100%, and the positive predi ctive value 63%. The prevalence of negative tests was 88%, and the pre valence of positive tests was 12%. The overall accuracy of an EpiTD wa s 95.5%. We conclude that EpiTD is a reliable test to identify iv cath eters during the performance of lumbar epidural analgesia in laboring patients. Implications: Catheters inserted for epidural analgesia in l aboring patients may accidentally enter a blood vessel. Local anesthet ics injected through these catheters may cause seizures and cardiac ar rest. In this study, we concluded that injecting a small amount of epi nephrine before injecting a local anesthetic frequently helps to ident ify these misplaced catheters. Few catheters may actually be in the co rrect place even after responses to epinephrine.