P. A. Dailey

Practice guidelines for obstetric anesthesia: An updated report by the American Society of Anesthesiologists Task Force on obstetric anesthesia

PRACTICE guidelines are systematically developed recommendations that assist the practitioner and patient in making decisions about health care. These recommendations may be adopted, modified, or rejected according to clinical needs and constraints and are not intended to replace local institutional policies. In addition, practice guidelines are not intended as standards or absolute requirements, and their use cannot guarantee any specific outcome. Practice guidelines are subject to revision as warranted by the evolution of medical knowledge, technology, and practice. They provide basic recommendations that are supported by a synthesis and analysis of the current literature, expert opinion, open forum commentary, and clinical feasibility data. This update includes data published since the “Practice Guidelines for Obstetrical Anesthesia” were adopted by the American Society of Anesthesiologists in 1998; it also includes data and recommendations for a wider range of techniques than was previously addressed.

Bupivacaine-induced Cardiac Arrhythmias in Sheep

: Controversy persists about the cardiac toxicity of bupivacaine if accidentally administered intravenously during regional anesthesia. Using awake, unanesthetized sheep, we evaluated the cardiac effects of low and high equivalent doses of lidocaine and bupivacaine given intravenously over 10 s. All animals convulsed within 30 s of injections. Although both drugs significantly increased heart rate and systemic and pulmonary arterial blood pressure for up to 10 min, cardiac output was affected variably. The magnitude of hemodynamic changes that each drug produced did not differ significantly from each other at either dose level. However, of the sheep receiving intravenous lidocaine, none developed arrhythmias other than mild sinus tachycardia and minimal ST-T wave changes (which occurred in 25% of the animals). After intravenous bupivacaine injection, all sheep had transient changes on the EKG and/or arrhythmias (e.g., supraventricular tachycardia; atrioventricular condition blocks; ventricular tachycardia; multiform premature ventricular contractions; wide QRS complexes; ST-T wave changes; and in one animal, fatal ventricular fibrillation). Normal sinus rhythm usually returned within 8-10 min. Arterial blood gas and acid-base values stayed within the normal range during the studies, and serum potassium did not change significantly from control. In conclusion, in conscious adult sheep, equivalent doses of lidocaine or bupivacaine produced similar central nervous system (CNS) toxicity when rapidly injected intravenously. In the absence of marked hypoxia, respiratory or metabolic acidosis, hyperkalemia, or hypotension, serious cardiac arrhythmias occurred after bupivacaine but not lidocaine.

Parturients Infected with Human Immunodeficiency Virus and Regional Anesthesia Clinical and Immunologic Response

Background It is estimated that 1.5 million Americans are infected with the human immunodeficiency virus (HIV‐1), and the consequences of HIV infection are a leading cause of death in women aged 15–44 yr. Thus, HIV‐1 disease, or acquired immunodeficiency syndrome, occurs with increasing frequency in the parturient, and there is little information concerning the risks of regional anesthesia. Fear of spreading infection to the central nervous system or adverse neurologic sequelae have led some clinicians to advise against regional anesthesia. Thus, this study was undertaken to evaluate the possible problems or risks associated with regional anesthesia in parturients infected with HIV‐1 and to determine whether anesthesia affected the clinical course of the disease. Methods The clinical course and immunologic function of 30 parturients infected with HIV‐1 were evaluated prospectively. Extensive medical and laboratory evaluation before delivery and 4–6 months postpartum was undertaken. Medical problems related to HIV‐1 disease and use of antiviral drugs also were monitored. The anesthetic management was dictated by the clinical situation and the patients wishes with careful postpartum follow‐up to evaluate possible neurologic changes or infection. Results Regional anesthesia was administered in 18 parturients, and 12 received small doses of opioids or no analgesia. There were no changes in the immunologic parameters studied (CD4 sup + p24, beta sub 2 microglobulins), and HIV‐1 disease remained stable in the peripartum period. There were no infections, complications, or neurologic changes in the peripartum period. Sixty‐eight percent of the infants were HIV‐l‐negative and, in 21% of infants, the HIV‐1 status was indeterminate (probably negative). Conclusions This prospective study of parturients infected with HIV‐1 demonstrated that regional anesthesia can be performed without adverse sequelae. There were no neurologic or infectious complications related to the obstetric or anesthetic course. The immune function of the parturient was stable in the peripartum period. Although the number of patients studied was small, with careful medical evaluation, regional anesthesia is an acceptable choice in the parturient infected with HIV‐1.

Pharmacokinetics, Placental Transfer, and Neonatal Effects of Vecuronium and Pancuronium Administered during Cesarean Section

Vecuronium and pancuronium were compared for placental transfer, pharmacokinetic variables, and neonatal effects during cesarean section under general anesthesia. Eighteen women underwent rapid-sequence intravenous induction using d-tubocurarine, succinylcholine, thiopental, and oxygen. Immediately after tracheal intubation, an intravenous injection of vecuronium (n = 11) or pancuronium (n = 7), 0.04 mg/kg, was given. Maternal venous blood samples were obtained before induction and at frequent intervals for 4 h after administration of vecuronium or pancuronium. Also, maternal venous and umbilical-cord arterial and venous blood samples were obtained at delivery. To describe placental transfer and maternal pharmacokinetics of the drugs, serum drug concentrations were determined using single-ion-monitoring mass spectrometry. The Apgar score and Neurologic and Adaptive Capacity Score (NACS) were used to evaluate neonatal condition. Both drugs crossed the placenta, as demonstrated by low concentrations of vecuronium (8.5-26.4 ng/ml) or pancuronium (12.2-34.2 ng/ml) found in umbilical venous blood. At delivery, the ratio of the drug concentration in umbilical venous blood to that in maternal venous blood was 0.11 +/- 0.02 for vecuronium and 0.19 +/- 0.03 for pancuronium. Vecuronium had a more rapid clearance (6.4 +/- 0.4 ml X kg-1 X min-1, mean +/- SE) and a shorter elimination half-life (36 +/- 1.8 min) than pancuronium (3.0 +/- 0.1 ml X kg-1 X min-1 and 72 +/- 6 min, respectively). No other pharmacokinetic differences were found between the drugs. Neonatal outcome was not affected adversely by either muscle relaxant, as assessed by Apgar scores and NACSs . The short duration of action, the minimal placental transfer, and the apparent lack of clinical neuromuscular effects on the newborn suggest that vecuronium should be a useful muscle relaxant for cesarean section.

Epidural Morphine for the Relief of Postoperative Pain after Cesarean Delivery

To determine the safety, efficacy, and dose response of epidurally administered morphine for analgesia after cesarean delivery, 40 healthy women who underwent cesarean delivery with epidural anesthesia were randomly assigned to receive one of four regimens for relief of postoperative pain: intramuscular administration of morphine, 7.5 mg (N = 10); or epidural administration of morphine, 2 mg (N = 10), 5 mg (N = 10), or 7.5 mg (N = 10). Evaluations were made of intensity and relief of pain, time to administration of additional analgesic medications, changes in vital signs and blood-gas tensions, and adverse effects. Intramuscular administration of 7.5 mg of morphine effectively relieved pain for only a short time. When morphine was administered epidurally, 2 mg proved ineffective whereas both 5 mg and 7.5 mg provided substantial pain relief for approximately 24 h. There were no significant changes in vital signs or blood-gas tensions. Side effects included pruritus and nausea, which occurred frequently but were usually mild and easily treated. We concluded that either 5 mg or 7.5 mg of morphine epidurally administered was effective and safe in providing prolonged analgesia after cesarean delivery.

Evaluation of Neurotoxicity after Subarachnoid Injection of Large Volumes of Local Anesthetic Solutions

Recent case reports describing prolonged neurologic deficit after accidental spinal anesthesia with large volumes of 2− chloroprocaine have led to the suggestion that chloroprocaine may be more likely to cause such complications than other local anesthetics. We evaluated the neurologic effects of lumbar puncture alone and of large-volume subarachnoid administration of 2-chloroprocaine (3%), bupivacaine (0.75%), lidocaine (2%), Elliotts solution B (which is similar to CSF), or the carrier solution of 2-chloroprocaine (Nesacaine) in 48 sheep and 8 monkeys. Cerebrospinal fluid of sheep was collected on days 1 and 7 for biochemical and biological analyses, and CSF pressures of monkeys were recorded before and after injection. Animals were observed for neurologic deficits for seven days. Twelve sheep were unable to stand. Monkeys, on the other hand, had no apparent neurologic deficits. Autopsies revealed that 5 of the 12 sheep had lumbar subpial demyelination with macro- phage infiltration: two of the five had received lidocaine; two received 2-chloroprocaine; and one had only a lumbar puncture. Two other sheep also had subpial demyelination: one had received lidocaine and one received 2-chloroprocaine. Three of the eight monkeys had lumbar subpial demyelination with macrophage invasion; two had received bupivacaine, and one received 2-chloroprocaine. No solution produced significant abnormalities in sheep CSF composition. We conclude that no local anesthetic or solution was more neurotoxic than another when injected in large volumes into the subarachnoid space of sheep or monkeys.

The effect of nitrous oxide on in vitro fertilization success rate

The authors studied the effect of nitrous oxide on success rates for in vitro fertilization and pregnancy in women undergoing laparoscopy for oocyte retrieval. Ninety-eight patients in an in vitro fertilization program were randomly assigned to an anesthetic regimen including either 0.7% (end-tidal) isoflurane with 60% nitrous oxide in oxygen, or 1.4% (end-tidal) isoflurane in oxygen. Success rates for fertilization and pregnancy in 44 additional patients who declined randomization were also studied. Among the 51 randomized patients who did not receive nitrous oxide, 192 oocytes were obtained and 122 fertilized (63.5%), resulting in eight pregnancies (16.3%). From the 47 randomized patients given nitrous oxide, 168 oocytes were retrieved and 114 fertilized (67.9%), resulting in nine pregnancies (19.1%). No significant differences between rates of fertilization or pregnancy emerged between groups. Such differences would have been found with an 80% probability had nitrous oxide had a 20% effect on oocyte fertilization.

Effect of Halothane on Regional Cerebral Blood Flow and Cerebral Metabolic Oxygen Consumption in the Fetal Lamb In Utero

: The effects of halothane on maternal and fetal hemodynamics, distribution of fetal cardiac output, regional cerebral blood flow, and fetal cerebral oxygen consumption were studied in the ewe (N = 9) using radionuclide-labeled microspheres. An adjustable uterine artery occluder was used to produce a controlled state of fetal asphyxia. Measurements were taken during three periods of study: 1) control, 2) asphyxia, and 3) asphyxia plus 15 min of 1% maternal halothane. The fetal cardiovascular response to asphyxia was acidosis, hypoxia, hypertension, bradycardia, and preservation of vital organ blood flows. There was a significant drop in maternal blood pressure when halothane was administered but uterine blood flow was maintained, 308 ml X min-1 during asphyxia versus 275 ml X min-1 with halothane. Fetal blood pressure during asphyxia plus halothane (54 mmHg) was significantly lower than that during asphyxia alone (59 mmHg), while heart rate was significantly higher: 172 beats per minute (bpm) versus 125 bpm (P less than 0.05). Despite these changes, the administration of halothane during asphyxia did not produce a reduction in vital organ flows. Cerebral blood flow was maintained: 357 +/- 37 ml X 100 g-1 X min-1 during asphyxia alone and 344 +/- 26 ml X 100 g-1 X min-1 after halothane administration (P = NS, mean +/- SEM). Cerebral oxygen delivery also was maintained: 8.3 +/- 0.8 ml X 100 g-1 X min-1 during asphyxia alone versus 9.7 +/- 1.5 ml X 100 g-1 X min-1 after halothane, compared with 11.2 +/- 1.1 ml X 100 g-1 X min-1 during the control period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Halothane on Regional Cerebral Blood Flow and Cerebral Metabolic Oxygen Consumption in the Fetal Lamb in Utero

The effects of halothane on maternal and fetal hemodynamics, distribution of fetal cardiac output, regional cerebral blood flow, and fetal cerebral oxygen consumption were studied in the ewe (N = 9) using radionuclide-labeled microspheres. An adjustable uterine artery occluder was used to produce a controlled state of fetal asphyxia. Measurements were taken during three periods of study: 1) control, 2) asphyxia, and 3) asphyxia plus 15 min of 1% maternal halothane. The fetal cardiovascular response to asphyxia was acidosis, hypoxia, hypertension, bradycardia, and preservation of vital organ blood flows. There was a significant drop in maternal blood pressure when halothane was administered but uterine blood flow was maintained, 308 ml ± min−1 during asphyxia versus 275 ml ± min−1 with halothane. Fetal blood pressure during asphyxia plus halothane (54 mmHg) was significantly lower than that during asphyxia alone (59 mmHg), while heart rate was significantly higher: 172 beats per minute (bpm) versus 125 bpm (P < 0.05). Despite these changes, the administration of halothane during asphyxia did not produce a reduction in vital organ flows. Cerebral blood flow was maintained: 357 ± 37 ml ± 100 g−1 · min−1 during asphyxia alone and 344 ± 26 ml ± 100 g−1 min−1 after halothane administration (P = NS, mean ± SEM). Cerebral oxygen delivery also was maintained: 8.3 ± 0.8 ml ± 100 g−1 during asphyxia alone versus 9.7 ± 1.5 ml ± 100 g−1 · min−1 after halothane, compared with 11.2 ± 1.1 ml ± 100 g−1 · min−1 during the control period. Cerebral oxidative metabolism (CMRO2) decreased significantly from 4.1 ± 0.6 ml ± 100 g−1 · min−1 during control to 2.8 ± 0.4 ml ± 100 g−1 · min−1 during asphyxia alone, but no further significant change occured after halothane (2.0 ± 0.3 ml ± 100 g−1 · min−1). Fetal myocardial blood flow was maintained: 625 ± 93 ml ± 100 g−1 ml−1 during asphyxia alone versus 529 ± 79 ml ± 100 g−1 · min−1 after halothane administration. The authors conclude that the addition of 1% maternal halothane in the briefly asphyxiated fetal lamb does not abolish the protective reflexes of increased coronary and cerebral blood flow and decreased CMRO2.

Epidural Morphine Analgesia After Cesarean Delivery

The effectiveness and safety of 5 mg of epidurally administered morphine for postoperative analgesia was determined in 276 healthy women undergoing cesarean delivery. Overall pain relief, time to administration of additional analgesic medications, and adverse side effects were evaluated. Epidural injection of 5 mg of morphine provided good to excellent pain relief lasting 24 to 36 hours for 83% of patients. Also, review of hospital records for a subset of 34 patients revealed that requirements for additional systemic analgesics were markedly less when postoperative pain relief was provided by epidural administration of morphine than by conventional analgesia therapy. Pruritus, nausea, and vomiting occurred frequently, but were easily treated. Although late respiratory depression did not occur in this group, the authors continue to observe patients closely and monitor respiratory rates for 24 hours.