David M. Dewan

Anesthetic and obstetric outcome in morbidly obese parturients

BackgroundLarge studies reporting anesthetic outcome for morbidly obese parturients are lacking. This study compares the anesthetic and obstetric outcome in morbidly obese parturients and matched control parturients. MethodsAnesthesia records were prospectively collected for all patients delivering between September 1978 and November 1989 whose weight exceeded 136.4 kg (300 pounds) at the time of delivery. A retrospective control patient group was collected by matching the first patient weighing less than 136.4 kg, delivered in the same month by the same obstetrician, to the corresponding morbidly obese parturient. Anesthetic and obstetric outcome variables were extracted from medical records and analyzed. ResultsSixty-two percent of 117 morbidly obese women underwent cesarean section, while only 24% of control patients delivered abdominally (P < 0.05). Forty-eight percent of all laboring morbidly obese parturients required emergency cesarean section, compared with 9% of control laboring parturients (P < 0.05). Epidural anesthesia was used successfully for labor and cesarean delivery in 74 of 79 morbidly obese women and 66 of 67 control patients. When compared with control patients, initial epidural anesthesia failure was significantly more likely in morbidly obese women, requiring epidural catheter replacement. Difficult tracheal intubation occurred in 6 of 17 morbidly obese women, compared with 0 of 8 control women (P = 0.06). Morbidly obese women had increased incidences of antepartum medical disease, prolonged cesarean section operation times, serious postoperative complications, and increased hospital stays. ConclusionsThe high incidences of antepartum medical disease and emergency cesarean section complicate anesthetic care in the morbidly obese parturients. Epidural anesthesia is feasible; however, the high initial failure rate necessitates early catheter placement, critical block assessment and catheter replacement when indicated, and provision for alternative airway management.

Epidural Clonidine Produces Antinociception, But Not Hypotension, In Sheep

Intrathecally administered clonidine produces analgesia, but also produces hypotension. To assess the effects of epidural administration, the authors inserted lumbar epidural catheters in seven non-pregnant ewes, and injected, on separate days, clonidine (50–750 mcg), morphine (5–10 mg), and a clonidine-morphine combination (clonidine 150 mcg + morphine 5 mg). Clonidine produced dose-dependent antinociception and sedation, with the lowest maximally effective antinociceptive dose being 300 mcg. Morphine produced less intense antinociception than clonidine, and did not potentiate clonidines effect. Antinociception, but not sedation, following clonidine injection was reversed by epidural injection of the α2-adrenergic antagonist, idazoxan. Epidurally administered naloxone and prazosin did not reverse clonidines antinociceptive effect, nor did intravenously administered idazoxan. Epidurally administered clonidine did not decrease blood pressure or heart rate or affect arterial blood gas tensions or spinal cord histology. These data suggest that epidurally administered clonidine produces analgesia by a local, α2-adrenergic mechanism. In sheep, epidurally administered clonidine does not produce hypotension.

Maternal and fetal effects of epinephrine in gravid ewes

Intravenous cannulation by an epidural catheter may complicate epidural anesthesia. Local anesthetic solutions containing epinephcine produce tachycardia and hypertension when given intravenously and may identify intravenous placement. The authors studied the Maternal and fetal effects of intravenou

Epinephrine enhances analgesia produced by epidural bupivacaine during labor

Reports on the analgesic and hemodynamic effects of epinephrine added to bupivacaine for epidural use in obstetrics are conflicting. In this study, healthy parturients received in a random manner either 10 ml of 0.25% bupivacaine (n = 50) or 10 ml of 0.25% bupivacaine with 1:300,000 epinephrine (n =

Neonatal Neurobehavioral Responses After Epidural Anesthesia for Cesarean Section Using Lidocaine and Bupivacaine

: We compared the early neonatal neurobehavioral responses after lumbar epidural anesthesia for elective cesarean section using 2% lidocaine (n = 10) and 0.5% bupivacaine (n = 21). We tested the infants at 4 and 24 hr after birth and found that the neonates in the lidocaine group scored as well as those in the bupivacaine group on all parameters of the early neonatal neurobehavioral score (ENNS). In fact on one parameter, sucking response at 24 hr, the neonates in the lidocaine group scored significantly higher than those in the bupivacaine group. We concluded that 2% lidocaine does not compromise newborn outcome when compared to 0.5% bupivacaine and that it provides a satisfactory choice for use during elective cesarean section in healthy pregnancies. This conclusion is important in the light of the current concern over the safety of the use of chloroprocaine and bupivacaine in obstetric anesthesia.

Epidural clonidine analgesia in obstetrics: sheep studies

Epidural clonidine administration produces analgesia by a nonopiate, spinal mechanism, and offers advantages over other epidural agents for labor analgesia. To examine clonidines acute maternal and fetal effects, the authors injected clonidine, 300 micrograms, epidurally in seven chronically prepared, near term ewes. Unlike epidural saline injection, clonidine increased maternal and fetal serum glucose (by 178 +/- 30% and 190 +/- 30%, respectively; mean +/- SEM, P less than .01) 1 h following injection. Maternal and fetal serum cortisol and arterial blood gas tensions were unchanged following clonidine. Epidural clonidine injection produced minor decreases (10-15%) in heart rate in ewe and fetus, without altering maternal and fetal blood pressure, intra-uterine pressure, or uterine blood flow. Maternal and fetal serum clonidine concentrations peaked at 58 +/- 8 and 73 +/- 5 min following injection, respectively, and declined with similar half-lives. Heart rate correlated negatively with serum clonidine concentration in both ewe and fetus (P less than .05). Apart from hyperglycemia, which does not occur in humans, these results in sheep suggest that epidurally administered clonidine does not adversely affect the fetus and may be evaluated as an analgesic in obstetrics.

Labor analgesia with epidural bupivacaine plus fentanyl: enhancement with epinephrine and inhibition with 2-chloroprocaine.

Epidural injection of drug combinations may decrease toxicity by decreasing the dose of each component, but may also result in detrimental drug interactions. In this study interactions among bupivaciane, fentanyl, epinephrine, 2-chloroprocaine, and lidocaine for epidural analgesia during labor were examined. In part 1 of the study, healthy parturients received in a random manner either 10 ml of 0.25% bupivacaine with 5 micrograms/ml fentanyl (n = 50), or 10 ml of this combination with 3.33 micrograms/ml freshly added epinephrine (n = 50). Epinephrine prolonged the median duration of pain relief (180 vs. 138 min, P less than 0.05) without affecting duration of first or second stages of labor, or neonatal Apgar scores. Blood pressure decreased slightly more in those receiving epinephrine, although the incidence of hypotension requiring treatment did not differ between groups. Part 2 of the study evaluated the possibility that local anesthetic used for confirming catheter tip location may interfere with the analgesic action of this bupivacaine-fentanyl-epinephrine (BFE) combination. In 50 additional parturients, a test dose of either 2-chloroprocaine (n = 25) or lidocaine (n = 25) was injected through the epidural catheter and was followed by injection of the BFE mixture. The lidocaine test dose group had a greater duration of analgesia than the 2-chloroprocaine test dose group (median duration of 164 vs. 91 min, P less than 0.05). The authors conclude that the addition of epinephrine 3.33 micrograms/ml significantly increases the duration of analgesia obtained from 0.25% bupivacaine with 5 micrograms/ml fentanyl. However, prior injection of 2-chloroprocaine, but not lidocaine, significantly decreases the duration of analgesia achieved with this BFE mixture.

Effect of kappa opioid agonists on visceral nociception induced by uterine cervical distension in rats

&NA; Although uterine distension in rats results in an escape reflex, there exists no model of uterine cervical distension (UCD), the pain stimulus during the first stage of labor. The aims of this study were to develop such a model in virgin rats and to test whether peripherally restricted kappa opioid receptor (KOR) agonists (ADL 10‐0101, ADL 10‐0102, ADL 10‐0116) inhibit responses to UCD. Under intravenous (i.v.) pentobarbital and alpha‐chloralose anesthesia, fine metal rods were inserted in both uterine cervical osses through a small midline laparotomy. UCD was performed by manual separation of the rods (25–100 g). Single‐unit afferent responses in hypogastric nerve or reflex rectus abdominis electromyographic (EMG) activity were determined before and after i.v. KOR agonists. UCD resulted in a stimulus‐dependent increase in single‐unit afferent activity. Units could be characterized as low threshold (mean threshold 6.6±2.7 g), or high threshold (mean threshold 55±8.8 g); all were C fibers, all responded to topical bradykinin. ADL 10‐0116 (10 mg/kg) reduced the afferent response to UCD. Reflex EMG response occurred over a distension force range of 25–100 g, unaffected by i.v. saline. All three KOR agonists produced a dose‐dependent, naloxone‐reversible inhibition of the EMG response with a potency relationship of ADL 10‐0102 (ED50 0.04 mg/kg)>ADL 10‐0101 (ED50 0.65 mg/kg)=ADL 10‐0116 (ED50 0.60 mg/kg). These data support the use of acute UCD as a noxious stimulus, inducing afferent and reflex activity. Like other visceral stimuli, UCD is sensitive to inhibition by KOR agonists.

Sodium Citrate Pretreatment in Elective Cesarean Section Patients

Thirty-two healthy term parturients undergoing elective cesarean section randomly received either no antacid (n = 10), 30 ml of 0.3 molar sodium citrate less than 60 min preoperatively (n = 11), or 30 ml of 0.3 molar sodium citrate longer than 60 min preoperatively (n = 11). Immediately after delivery, the stomach was empatied as completely as possible through a # 18 Salem Sump tube passed orally. Mean gastric pH in the three groups was 1.8 ± 2.7 (SD), 5.0 ± 1.5, and 2.7 ± 1.2, respectively. Gastric pH was significantly higher in the short interval group than in either the control group or in patients receiving their sodium citrate more than 60 min in advance. Gastric volumes were similar. All control patients had a gastric pH less than 2.5. Nine percent of patients receiving sodium citrate less than 60 min in advance arid 50% of patients receiving their sodium citrate longer than 60 min in advance had a pH of less than 2.5. Volumes exceeding 25 ml occurred with equal frequency. No patient in the short interval group had a combination of both pH of less than 2.5 and a volume exceeding 25 ml. This combination occurred with equal frequency in control patients (64%) and in those patients receiving their sodium citrate more than 60 min in advance (50%). We conclude that sodium citrate effectively increases gastric pH when given less than 60 min prior to the induction of anesthesia.

Intrathecal Clonidine in Obstetrics: Sheep Studies

Clonidine may be administered intrathecally as an adjunct to local anesthetics or accidentally during attempted epidural analgesia. To examine clonidines acute maternal and fetal effects, the authors injected clonidine (100, 300, 750, 1500 micrograms cumulative dose at 15-min intervals) intrathecally in nine chronically prepared near-term ewes. Unlike intrathecal saline injection, which did not alter any parameters, clonidine altered maternal blood pressure in a biphasic manner (depression at lower doses and return to baseline after the highest dose). Clonidine produced a dose-dependent decrease in maternal and fetal heart rate. After the highest dose, 1500 micrograms, PO2 decreased in both ewe and fetus, accompanied by fetal hypertension and bradycardia. Clonidine increased maternal and fetal serum glucose, but not cortisol. Although clonidine-induced hypoxemia and hyperglycemia occur only in sheep, fetal bradycardia may limit the usefulness of clonidine in large doses (greater than 10 micrograms/kg) in obstetrics. Lower doses, such as may be used to enhance spinal anesthesia, are well tolerated in sheep.