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TEST DOSE
36. Prince G and McGregor D. Obstetric test doses. Anaesthesia 1986;41:1240-1249.This review article answers several questions:
Is the test dose necessary? The test dose helps avoid "two potentially lethal complications": total spinal block and intravascular injection. The incidence of each is 3 to 10 per 10,000 epidurals. Three fatal cases of spinal block have been reported in the U.K. since 1984. Twenty-two cases of maternal cardiac arrest following intravascular injection of bupivacaine were reported, of which 15 were fatal and led to the banning of 0.75% bupivacaine. A two-stage safety check-aspiration to check for blood or cerebrospinal fluid and injection of a small test dose - minimizes these risks.
Is the test dose safe? When placental blood flow is inadequate, "even small intravenous injections of adrenaline can be dangerous to the fetus."
Is the test dose effective? The aspiration test can fail if(1) the catheter is blocked;
(2) if aspiration is done through the needle, but then the catheter punctures a blood vessel (occurs ~ 9% of the time) or the dura (occurs "less frequently");
(3) there is an air lock; or
(4) cerebrospinal fluid is misidentified as saline injected during localization of the epidural space.
Intravascular injection can occur if(1) the aspiration test is not done;
(2) an inadequate amount of anesthetic is injected in the test dose or adrenaline is not used;
(3) the test dose is misinterpreted; or
(4) the catheter migrates later in labor.
Failure of the test dose to predict subarachnoid injection can occur if(1) the aspiration test is not done;
(2) the test dose is inadequate;
(3) the test dose is misinterpreted; or
(4) the catheter migrates.
Despite all precautions, intravascular and subarachnoid injection occur. "It is emphasized that these complications should not cause fatalities if trained personnel and adequate resuscitation facilities are available."
37. Leighton BL et al. Limitations of epinephrine as a marker of intravascular injection in laboring women. Anesthesiology 1987;66:688-691.Epinephrine marks accidental intravascular epidural catheter placement by increasing maternal heart rate. In this randomized double-blind study of unanesthetized healthy laboring women, 10 had saline injected intravenously and 10 had 15 Ugm epinephrine. Investigators were able to determine which mothers had received epinephrine but only after careful study of maternal heart tracings, something not feasible under clinical conditions. Identification was difficult because maternal heart rate normally varies in response to contractions. Other precautions also fail. In one study, aspiration failed to detect 65 of 194 intravascularly placed catheters, and fractionating the anesthetic dosage produced no symptoms in 12 of 51 of these patients. Epinephrine also caused two episodes of fetal distress. One woman became hypertensive, then profoundly bradycardic, which raises the question of risk in a hypertensive mother or an already compromised baby.
38. Dam SL, Rolbin SH, and Hew EM. The epidural test dose in obstetrics: is it necessary? Can J Anaesth 1987;34(6):601-605.This article reviews the controversies surrounding test doses and makes practical recommendations. The drawbacks of a test dose for intravenous placement are:
(1) false positives and false negatives and
(2) test dose amounts of epinephrine entering maternal circulation could decrease uterine blood flow and pose a risk to a compromised fetus. The authors recommend fractionating the dose so that each fraction acts as its own test dose. [Abstract 37 mentions that fractionation too has false negatives.]
Injecting fluid prior to catheter insertion is not recommended because it clouds the aspiration test for cerebrospinal fluid. Dry insertion results in "an acceptable incidence of paraesthesia and return of blood in the catheter." The authors also recommend inserting the catheter no more than 3 cm to minimize the risk of perforating a blood vessel or of kinking and knotting. "Until a controlled study is performed, test doses should be done... with the understanding that they are neither 100 per cent sensitive nor specific in preventing complications," and that epinephrine in test doses may be "detrimental to fetal wellbeing."
TECHNIQUE OF ADMINISTRATION
39. Phillips DC and Macdonald R. Epidural migration during labour. Anaesthesia 1987;42:661-663The catheter used in 100 women with epidural anesthesia was marked in centimeters. As usual, the catheter was looped, covered with gauze, and taped to the skin. At the time of removal, the catheter had migrated outward in 18 women and inward [toward the subarachnoid space in 36, more than one third. One woman in whom it migrated inward developed a spinal headache indicative of concealed dural tap and another the "signs and symptoms of an intravenous injection" at the final top-up for episiotomy repair.
40. Rolbin SH and Hew E. A comparison of two types of epidural catheters. Can J Anaesth 1987;35(5):459-461.In a study of catheter type in 150 women with epidurals, one type of catheter had about half the rate of blood vessel injuries and nerve root irritation compared with the other, but the better catheter still had a 24% rate of nerve root irritation and a 6.7% incidence of vascular injury.
41. Rolbin SH et al. Fluid through the epidural needle does not reduce complications of epidural catheter insertion. Can J Anaesth 1990;37(3):337-340.Some anesthesiologists inject fluid through the epidural needle prior to catheter insertion either to separate the epidural tissues and permit easier passage of the catheter or as a test dose. The authors compared inserting the catheter without fluid injection (N = 77) versus injecting a test dose of lidocaine (N = 68) versus injecting saline (N = 55). The incidence of blood vessel trauma ranged from 9% to 10% and paresthesia [abnormal sensation) ranged from 50% to 56%. However, persisting neurologic deficits are very rare. No differences were significant. But when fluid is injected, the significance of clear fluid upon aspiration [normally a sign of dural puncture] becomes difficult to interpret.
42. McLean BY, Rottman RL, and Kotelko DM. Failure of multiple test doses and techniques to detect intravascular migration of an epidural catheter. Anesth Anaig 1992;74(3):454-456. (bolus 0.25%; infusion 0.0625% with 2 Ug/mI fentanyl)A healthy primigravida had a 3-minute episode of fetal bradycardia after a top-up [see Abstracts 26 and 27 for data on the causal relationship between epidurals and bradycardia], at which time the doctor decided to perform a cesarean for fetal distress and macrosomia. Although aspiration and a test dose revealed no problems with the catheter, when lidocaine was administered for the cesarean, the mother had a grand mal seizure and a fetal bradycardia that continued until the infant was delivered by cesarean under general anesthesia eight minutes later. Mother and baby recovered.
REFERENCES
ASA. Anesthesia & You.. . Planning Your Childbirth. 1992.
Bates RG et al. Uterine activity in the second stage of labour and the effect of epidural analgesia. Br J Obstet Gynaecol 1985;92(1 2): 1246-1250.
Brownridge P. Treatment options for the relief of pain during childbirth. Drugs 1991 ;41(ll):69-80.
Clark RB. Fetal and neonatal effects of epidural anesthesia. Obstet Gynecol Ann 1985;14:240-252.
Cohn V. News and numbers. Ames: Iowa State University Press, 1989.
Fuchs AR. Personal communication, 1990.
Gleeson NC and Griffith AP. The management of the second stage of labour in primiparae with epidural analgesia. BrJ Clin Prac 1991;45(2):90-91.
Goodfellow CF et al. Oxytocin deficiency at delivery with epidural analgesia. Br I Obstet Gynaecol 1 983;90(3):214-21 9.
flumenick SS. Mastery: The key to childbirth satisfaction? A review. Birth 1981 ;8(2):79-83.
Humenick SS and Bugen LA. Mastery: The key to childbirth satisfaction? A study. Birth 1981 ;8(2):84-89.
Jimenez S. Supportive pain management strategies. In Childbirth education: practice, research, and theory. FH Nichols and SS Humenick, eds. Philadelphia: Saunders, 1988.
Johnson M and Everitt B. Essential reproduction. 3d ed. Cambridge, MA: Blackwell Scientific Publications, 1988.
Lagercrantz H and Slotkin T. The "stress" of being born. Sci Am 1986;254(4):100-107. Manyonda IT, Shaw DE, and Drife JO. The effect of delayed pushing in the second stage of labor with continuous lumbar epidural analgesia. Acta Obstet Gynecol Scand 1990; 69:291-295.
Oriol NE. "Report of a study on 'walking epidurals." Presented at Innovations in Perinatal Care: Assessing Benefits and Risks, tenth conference presented by Birth, Boston, Oct 31-Nov 1 1992.
Reynolds F. Epidural analgesia in obstetrics. BMJ 1989;299:751-752.
Richardson T. Epidural anaesthesia for obstetrics: where are we? N Z Med I 1988;101(856 Pt 1):657-658.
San Jose Mercury News. The natural pain of giving birth. Aug 25, 1993.
Simkin P. Stress, Pain, and catecholamines in labor: Part 1. A review. Birth 1986; 13(4):227-233.
Simkin P. Just another day in a woman's life? Women's long-term perceptions of their first birth experiences. Part 1. Birth 1991;18(4):203-210.
Simkin P and Dickersin K. Control of pain in labour. In A guide to effective care in pregnancy and childbirth. Enkin M, Keirse MJNC, and Chalmers I, eds. Oxford: Oxford University Press, 1989.
Wuitchik M, Bakal D, and Lipshitz J. Relationships between pain, cognitive activity and epidural analgesia during labor. Pain 1990;41 :125-132.
ORGANIZATION OF ABSTRACTS
Risks and Benefits (Review)
Epidurals - Obstetric Myths VS Research Realities: Page 1 - Introduction
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