Air: an effective indicator of intravenously located epidural catheters

Local anesthetic systemic toxicity

Local anesthetic systemic toxicity (LAST) is a rare yet devastating complication from the administration of local anesthesia. The ability to recognize and treat LAST is critical for clinicians who administer these drugs. The authors reviewed the literature on the mechanism, treatment, and prevention of LAST, with the goal of proposing a practical method for its management.

The Epidural Test Dose: A Review

This review systematically examines the literature on the ability of the classical epidural test dose and other strategies to detect intravascular, intrathecal, or subdural epidural needle/catheter misplacement. For detection of simulated intravascular misplacements, a sensitivity (S) and a positive predictive value (PPV) > or =80 demonstrated by at least two randomized controlled trials coming from two different centers were determined for the following tests and patient populations: Nonpregnant adult patients = increase in systolic blood pressure (SBP) > or =15 mm Hg (S = 80-100 and 93-100; PPV = 80-100 and 83-100) or either an increase in SBP > or =15 mm Hg or an increase in heart rate > or =10 bpm after the injection of 10 (S = 100; PPV = 83-100) or 15 microg of epinephrine (S = 100; PPV = 83-100); pregnant patients = sedation, drowsiness, or dizziness within 5 min after the injection of 100 microg of fentanyl (S = 92-100; PPV = 91-95); and children = increase in SBP > or =15 mm Hg after the injection of 0.5 microg/kg of epinephrine (S = 81-100; PPV = 100). Conversely, more studies are required to determine the best strategies to detect intrathecal and subdural epidural needle/catheter misplacements in these three patient populations.

Are combined spinal-epidural catheters reliable?

The combined spinal-epidural (CSE) technique can rapidly relieve labor pain. However, the location of the epidural catheter is initially uncertain. In an emergency, this untested catheter may fail to provide adequate anesthesia. This study compared the efficacy of catheters placed as a part of an epidural or needle-though-needle CSE technique in laboring women. Patients requesting pain relief received either epidural (n=601) or CSE (n=1061) analgesia. All patients had a 20 gauge, closed tip multi-holed polyamide catheter. (B. Braun Medical, Inc.) inserted 2-8 cm into the epidural space. Catheters were tested to rule out intrathecal and intravascular location. Then, epidural patients received 10-20 ml local anesthetic +/- opioid in divided doses. CSE patients received and infusion of 0.083% bupivacaine with opioid at 10-15 ml/h. Of the 1495 catheters that were adequately tested, those inserted as part of a CSE technique were more likely to produce bilateral sensory change and adequate analgesia than were those inserted without prior spinal analgesia (98.6% vs 98.2%, P<0.02). Stand-alone epidural catheters were more likely to produce neither sensory change nor analgesia than those inserted as part of CSE technique (1.3% vs 0.2%, P<0.02). The only catheters that failed completely and were not intravascular were stand-alone epidural catheters. In this clinical setting, catheters inserted as part of a CSE technique had a high probability of being in the epidural space and functioning appropriately.

Assessing bupivacaine 10mg/fentanyl 20μg as an intrathecal test dose

After ethics committee approval and verbal consent, women undergoing elective caesarean section given spinal anaesthesia with hyperbaric 0.5% bupivacaine 10 mg (2 mL) plus fentanyl 20 microg (spinal group, n = 20) and women requesting epidural analgesia in labour given the same drugs and doses epidurally, either in the same concentration (epidural small volume group, n = 10) or as 10 mL of 0.1% bupivacaine plus fentanyl 20 microg (epidural large volume group, n = 12) were recruited. The temperature of the great toes, sensory block on the outer ankle (S1 dermatome), motor block at the ankle and haemodynamic changes were recorded every 2 min for 10 min. There was a significant rise in foot temperature only in the spinal group. At four minutes a combination of warm toes and motor or sensory block, usually both, were seen only in the spinal groups. Haemodynamic changes were non-specific. We conclude that bupivacaine 10 mg with fentanyl 20 microg is a reliable agent to detect intrathecal placement by 4 min by which time a combination of motor and sensory block at the ankle and toe warming should be present.

The epidural test dose in obstetric anesthesia: it is not obsolete

Many anesthesiologists have called for the abandonment of the epidural test dose in the obstetric patient, citing its lack of sensitivity and specificity. A test dose of lidocaine 1.5% with epinephrine 1:200,000, in combination with aspiration, is highly effective in detecting incorrect placement of an epidural catheter. If the catheter is intrathecal, it requires approximately 2 minutes to obtain a sensory level. For the detection of an intravascular catheter, a positive test dose would result in a sudden increase in the maternal heart rate of 10 beats per minute within 1 minute after injection. It should not be administered during uterine contraction, as labor pain may trigger a tachycardic response. This test dose has been extensively studied and is safe both for both mother and fetus.

Tests to evaluate intravenous placement of epidural catheters in laboring women: a prospective clinical study

We prospectively evaluated the diagnostic accuracy of an epinephrine-containing epidural test dose (EpiTD) as a marker of intravascular injection in 209 unmedicated laboring women. Maternal heart rate (MHR) was continuously monitored and recorded on a strip chart. A tocodynamometer monitored uterine activity. A lumbar epidural catheter was placed and aspirated. If aspiration was positive for blood or cerebrospinal fluid (CSF), the catheter was replaced. In uterine diastole and with stable MHR, 198 patients received an EpiTD (epinephrine 15 microg plus lidocaine 45 mg) via the catheter. MHR and the generated HR strip were observed. 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 tachycardiac response suggested a negative EpiTD. If the tachycardiac response was deemed equivocal or a uterine contraction followed the EpiTD injection within 1 min, the EpiTD was invalidated and repeated. Catheter aspiration was repeated, and the catheter was removed if aspiration was positive. All patients with negative EpiTD and aspiration received 6-12 mL of epidural bupivacaine 0.25% with or without fentanyl 50 microg. 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 presence of tinnitus and/or metallic taste defined a positive Lido100TD. There were 176 true negatives, 0 false negatives, 14 true positives, and 8 false positives. The sensitivity of EpiTD was 100%, the specificity 96%, the negative predictive value 100%, and the positive predictive value 63%. The prevalence of negative tests was 88%, and the prevalence of positive tests was 12%. The overall accuracy of an EpiTD was 95.5%. We conclude that EpiTD is a reliable test to identify i.v. catheters during the performance of lumbar epidural analgesia in laboring patients.

IMPLICATIONS

Catheters inserted for epidural analgesia in laboring patients may accidentally enter a blood vessel. Local anesthetics injected through these catheters may cause seizures and cardiac arrest. In this study, we concluded that injecting a small amount of epinephrine before injecting a local anesthetic frequently helps to identify these misplaced catheters. Few catheters may actually be in the correct place even after responses to epinephrine.

Intra- and early postpartum ultrasonography: a review. Part II

Part II is a continuation of the preceding segment, which appeared in the previous issue (Survey 1998;53:000-000). This part presents data pertaining to ultrasound-guided procedures (invasive and noninvasive), physiology (fetal behavior), intrapartum hemorrhage, the third stage of labor, post-partum hemorrhage, and postcaesarean ultrasonography. In addition, this article includes data regarding nonobstetric ultrasound including anesthesiology, catheter placement, venous air embolism, effect of epidural anesthesia on uterine blood flow, and urinary retention. Finally, this part presents ultrasonographic data of the maternal cerebral circulation in preeclampsia/eclampsia and of the maternal deep venous system.

Maternal and fetal effects of isoproterenol in the gravid ewe

Detection of the intravascular placement of epidural catheters is an important but difficult task. In this study, we evaluated maternal and fetal hemodynamic responses to intravenous (i.v.) and epidural injection of isoproterenol (ISO), a proposed chronotropic test dose, in gravid ewes. Near-term, chronically instrumented, gravid ewes with single fetuses were studied at least 48 h after surgery. We continuously recorded maternal heart rate (MHR), systemic and pulmonary blood pressures, uterine blood flow (UBF), and fetal blood pressure and heart rate. Maternal cardiac output was measured by thermodilution. In random sequence, each ewe (n = 11) received i.v. injections of saline, epinephrine (EPI) 15 microg; ISO 4, 16, and 80 microg; or epidural (n = 9 ewes) injections of saline, ISO 4 microg and ISO 40 microg. All variables returned to baseline between experiments. Sections of lumber spinal cord were harvested from five animals for later histopathological study. I.v. ISO caused a dose-related increase in MHR. Cardiac output also increased transiently after all doses of ISO but not after EPI. Maternal diastolic blood pressure decreased after ISO 16 and 80 microg. UBF decreased significantly for 120 s after EPI 15 microg. Epidural ISO did not significantly change maternal systemic or pulmonary blood pressure, cardiac output, or UBF. The 40-microg dose increased MHR significantly. No histopathological changes were seen in three ISO-exposed and two control spinal cords. I.v. ISO reliably induces maternal tachycardia in nonstressed gravid ewes. Unlike EPI, I.v. ISO lacks a statistically significant effect on UBF. However, ISO seems to be rapidly absorbed from the epidural space. Identifying the source of maternal tachycardia after epidural injection of a large dose of ISO could be difficult. If the absence of histopathological change is confirmed, ISO represents an alternative to EPI as a chronotropic test dose.

Gas Embolism: Part I. Venous Gas Emboli

Gas emboli syndromes occur in many different settings, and their medical significance ranges from being life-threatening emergencies to being totally innocuous. We discuss venous gas embolization in Part I of this review, and it can result from a variety of traumatic, diagnostic, therapeutic, and surgical interventions. The pathophysiological consequences depend on where the gas bubbles impact and obstruct the circulation—by creating an “air lock” in the right ventricle, by obstruction of pulmonary arterioles, and sometimes with passage into the arterial circulation (so called paradoxical emboli). Various monitoring techniques are available and are known to be useful in high-risk patients. Nevertheless, the diagnosis can be difficult to establish. Myriad and generally nonspecific clinical manifestations may be present; the patient may often exhibit signs and symptoms suggestive of other acute cardiopulmonary or central nervous system events. The classically described “mill-wheel murmur” is actually a rare finding, and it is transient at best. There are no specific diagnostic tests available, and clinicians, must depend on a high level of suspicion in the appropriate settings. Rapid identification of the problem, with prevention of further gas entry into the venous circulation, should be a routine measure. The left lateral decubitus position, administration of 100% oxygen, and hyperbaric oxygenation should all be considered, and they have been shown to be effective treatment modalities.

A pharmacokinetic approach to resolving spinal and systemic contributions to epidural alfentanil analgesia and side-effects

A pilot study was conducted in 7 normal volunteers to demonstrate the feasibility of employing pharmacokinetic tailoring to achieve matching plasma opioid concentration-time curves after epidural (e.p.) and intravenous (i.v.) alfentanil administration. Each subject participated in 1 pretest and 2 test sessions. Our pain model was cutaneous electrical stimulation of the finger and toe, adjusted to produce a baseline pain report of 5 (strong pain on a 0-5 scale). On test day 1, subjects received e.p. alfentanil (750 micrograms) and an i.v. saline infusion. Serial measurements of analgesia, end tidal CO2, pupil size, subjective side effects, and plasma alfentanil concentrations were conducted before and at various time intervals over a 4-h period after alfentanil administration. On test day 2, subjects received e.p. saline and a pharmacokinetically tailored i.v. infusion (using individual pharmacokinetics determined on the pretest day) designed to achieve a plasma concentration-time profile identical to that observed on the epidural day. The same battery of effect measurements was administered as on the 1st test day. Plasma alfentanil was measured to verify the accuracy of the tailored infusion. Plasma alfentanil concentration profiles were nearly identical on both test days. Peak plasma alfentanil concentrations were near the reported minimum effective analgesic concentration (MEAC). Overall, analgesia was slightly greater with e.p. administration. Onset of pain relief was rapid, and duration was approximately 1.5 h with e.p. and 1 h with i.v. alfentanil. There were no differences in pupil size, ETCO2, or subjective side effects between e.p. versus i.v. administration. We conclude that systemic redistribution from the epidural space appears to account for most, but not all, of the analgesia.

Efficacy of an epidural test dose in adult patients anesthetized with isoflurane: lidocaine containing 15 micrograms epinephrine reliably increases arterial blood pressure, but not heart rate

When continuous epidural anesthesia is combined with general anesthesia, the only objective sign of intravascular migration of the epidural catheter are the increments of heart rate (HR) or arterial blood pressure after a local anesthetic test dose containing epinephrine. However, the efficacy of a simulated intravenous (IV) test dose in adult patients under general anesthesia has not been determined. Thirty adult patients were randomly assigned to one of two groups, each of which was anesthetized with 1% end-tidal isoflurane and nitrous oxide after endotracheal intubation. The epinephrine group (n = 15) was given 3 mL of 1.5% lidocaine with epinephrine (1:200,000) IV to simulate an IV administered epidural test dose. The saline group (n = 15) was identical to epinephrine group, but received 3 mL of normal saline IV. HR and arterial blood pressure were measured at 20-s intervals for 4 min after IV injection. In the epinephrine group, significant increases in HR compared with the baseline value were observed from 40 to 80 s after the IV test dose with a mean maximum HR increase of 24 +/- 2 bpm (mean +/- SEM) occurring at 48 +/- 3 s. However, 5 of 15 patients in the epinephrine group developed HR increments smaller than 20 bpm (sensitivity 67%). Since HRs were essentially unchanged in the saline group, specificity, positive predictive value (+PV), and negative predictive value (-PV) were 100%, 100%, and 75%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidural test dose: lidocaine 100 mg, not chloroprocaine, is a symptomatic marker of i.v. injection in labouring parturients

The authors studied the sensitivity (SN) and specificity (SP) of an epidural test dose containing either lidocaine 100 mg or 2-chloroprocaine 100 mg as symptomatic markers of intravascular injection in labouring parturients. In a prospective, double-blind and randomized fashion 48 unmedicated and labouring parturients were equally divided into three groups. After placement of a lumbar epidural catheter the normal saline group (NS) received 5 ml normal saline i.v., the lidocaine group (LD) received lidocaine 100 mg i.v., and the 2-chloroprocaine group (CH) received 2-chloroprocaine 100 mg i.v. All injections were given during uterine diastole. Within the next one to two minutes a blinded observer recorded the patient's perception of the presence of metallic or funny taste, dizziness, and tinnitus. We then calculated SN and SP of each symptom (alone and in combination) along with their positive (+) and negative (-) predictive value (PV). In both groups no symptom alone reached clinically acceptable levels of SN (< 87%). Only in the LD group, tinnitus+taste and dizziness+taste reached a SN of 100% with a SP of 81% and 69% respectively. While the -PV was 100% for both groups of symptoms, the +PV reached 42% for tinnitus+taste and 30% for dizziness+taste. We conclude that lidocaine 100 mg is a sensitive marker of intravascular injection in labouring parturients, and that tinnitus+taste is the most reliable indicator of intravenous injection.