The air test as a clinically useful indicator of intravenously placed epidural catheters.

The authors performed a clinical trial in 313 patients in labor to determine the safety and efficacy of an air test for unintentional intravenous placement of epidural catheters. Following routine aspiration for blood and cerebrospinal fluid, 1 ml of air was injected through each epidural catheter while heart tones were continually monitored with a Doppler ultrasound probe placed over the maternal precordium. In 281 patients, Doppler heart tones did not change following air injection (negative air test). All but eight of these patients developed an adequate level of analgesia following anesthetic administration, and no patients with negative air tests developed signs or symptoms of local anesthetic toxicity (false-negative rate, 0%; 95% confidence limits, 0.0-1.1%). Doppler heart tone changes followed air injection in 22 cases (positive air test). In 16 of these, intravenous catheter position was subsequently shown by aspiration of blood from the catheter or by the use of test doses consisting of local anesthetics with or without epinephrine. In six cases, adequate levels of analgesia developed despite a positive air test (false-positive rate, 2%; 95% confidence limit, 0.7-4.3%). None of the 303 patients receiving the air test developed any complications attributable to the injection of air (95% confidence limits, 0.0-1.0%). The authors conclude that air, with precordial Doppler detection, is a safe and effective test for identifying intravenously located epidural catheters.

Incidence of electrocardiographic changes during cesarean delivery under regional anesthesia.

Serial electrocardiograms were obtained on 93 healthy ASA physical status I and II term parturients during nonemergent cesarean delivery under regional anesthesia. Electrocardiographic changes occurred in 44 of the 93 patients (47.3%); in 35 of these 44 patients, the changes were characteristic, or suggestive, of myocardial ischemia. Symptoms of chest pain, pressure, and dyspnea occurred in 15 of the 44 patients with electrocardiographic changes; no patient without electrocardiographic change developed symptoms of chest pain, pressure, or dyspnea. Small but statistically significant differences were noted in heart rate, diastolic and systolic arterial pressures, and rate-pressure product between the patients with electrocardiographic changes and those without. The authors speculate that myocardial ischemia is a likely cause of both the electrocardiographic changes seen in these patients and of the symptoms of chest pain and dyspnea that they sometimes experience.

Isoproterenol is an effective marker of intravenous injection in laboring women.

The purpose of this randomized, double-blind study was to determine if isoproterenol 5 micrograms iv produces a consistent, noticeable tachycardia in healthy, laboring women. Maternal heart rate, fetal heart rate, and uterine contractions were continuously recorded and maternal blood pressure was measured every minute for 10 min before and after each patient received either normal saline (NS group; n = 10) or isoproterenol 5 micrograms (ISO group; n = 10) iv. The data-collecting investigator and a nurse palpating the patient's radial artery determined which solution they thought had been administered. The authors analyzed the maternal heart rate tracings using baseline-to-peak (a greater than or equal to 25 beat/min maternal heart rate increase occurring within 120 s of drug injection and lasting greater than or equal to 15 s) and peak-to-peak (a greater than or equal to 10 beat/min increase in the maximum maternal heart rate during the 2-min postinjection over the maximum maternal heart rate during the 2 min preinjection) criteria for detection of an intravascular marker. Mean maternal heart rate in the ISO group was significantly higher than in the NS group 20, 30, 40, 50, and 60 s following the injection (P less than 0.01). The peak-to-peak criterion and the data-collecting investigator correctly classified all patients. Five ISO group patients were not identified by the baseline-to-peak criterion. The nurse palpating the mother's radial artery misidentified two patients. Systolic blood pressure was significantly higher in ISO group than in NS group patients 1 min (P less than 0.05) and 2 min (P less than 0.01) following drug injection. Diastolic and mean blood pressures did not change. No fetal distress occurred. Isoproterenol 5 micrograms is an effective marker of intravascular injection in laboring women; however, the safety and efficacy of epidural isoproterenol must be demonstrated in animals before isoproterenol can be incorporated in an epidural anesthesia test dose.

Evaluation of a continuous noninvasive blood pressure monitor in obstetric patients undergoing spinal anesthesia.

A noninvasive blood pressure monitor (Finapres) that continuously displays the arterial waveform using the Penaz methodology has recently been introduced into clinical practice. We compared this device with an automated oscillometric blood pressure monitor (Dinamap 1846SX) in 20 patients during spinal anesthesia for nonemergency cesarean section according to a procedure suggested by the Association for the Advancement of Medical Instrumentation. After administration of the spinal anesthetic, the Finapres monitor produced systolic, mean, and diastolic pressure measurements greater than those of the Dinamap monitor (6.6 +/- 12.5, 3.3 +/- 10.4, and 7.2 +/- 9.8 mm Hg, respectively). In most patients, the Finapres measurements were similar to those determined by the Dinamap; however, in 4 patients, mean systolic differences were greater than 20 mm Hg. These patients did not differ from the others in age, height, weight, or baseline blood pressure, and the pressure values recorded by the Finapres monitor were substantially higher than those measured by auscultation in the labor room. In 30% of the patients, the offset between Dinamap and Finapres blood pressure measurements changed markedly over the course of the surgical procedure. The Finapres monitor occasionally stopped working and had to be restarted. In 1 patient (not included in this analysis), the Dinamap monitor was unable to determine the blood pressure due to patient shivering; this did not appear to interfere with the Finapres. We conclude that the Finapres monitor does not consistently provide blood pressure information equivalent to that of the Dinamap in obstetric patients undergoing spinal anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Needle bevel direction and headache after inadvertent dural puncture.

To study the effect of needle bevel direction on the incidence and severity of headache following inadvertent dural puncture occurring during the identification of the epidural space, the authors randomly assigned obstetric anesthesia residents to identify epidural space with the bevel of the epidural needle oriented either parallel or perpendicular to the longitudinal dural fibers. If dural puncture occurred, an observer unaware of the needle bevel direction, daily assessed the presence and severity of any subsequent headache. Of the 1,558 women who received epidural analgesia during this study, 41 women suffered dural puncture, 20 with the needle bevel oriented perpendicular to the longitudinal dural fibers and 21 with the needle bevel inserted parallel to the dural fibers (NS). Fourteen of 20 women in the group in which the needle bevel was perpendicular to dural fibers developed a moderate to severe headache, whereas only five of 21 in the group in which the needle bevel was parallel to dural fibers did so (P less than 0.005). Similarly, we administered a therapeutic blood patch to ten of 20 women in the perpendicular group but to only four of 21 in the parallel group (P less than 0.05). Thus, identifying the epidural space with the needle bevel oriented parallel to the longitudinal dural fibers limits the size of the subsequent dural tear and, therefore, lowers the incidence of headache should dural perforation occur.