Michael G. Richardson

Densities of dextrose-free intrathecal local anesthetics, opioids, and combinations measured at 37 degrees C.

Dextrose-free anesthetic medications are commonly used to provide subarachnoid anesthesia and analgesia. Hypobaricity has been proposed as a mechanism to explain postural effects on the extent of sensory block produced by these drugs. Densities of dextrose-free solutions of local anesthetics and opioids, and commonly used anesthetic/opioid mixtures were determined at 37.00 degrees C for comparison with the density of human cerebrospinal fluid (CSF). Measurements accurate to 0.00001 g/mL were performed using a mechanical oscillation resonance frequency density meter. All undiluted solutions tested are hypobaric relative to human lumbar CSF with the exception of lidocaine 1.5% and 2.0% with epinephrine 1:200,000. All mixtures of local anesthetics and opioids tested are hypobaric. We observed good agreement between measured densities and calculated weighted average densities of anesthetic mixtures. While the influence of baricity on the clinical effects of dextrose-free intrathecal anesthetics remains controversial, attempts to attribute postural effects to the baricity of these drugs requires establishment of accurate density values. These density data may facilitate elucidation of the mechanisms underlying the behavior of dextrose-free intrathecal anesthetics. (Anesth Analg 1997;84:95-9)

Midazolam Premedication Increases Sedation but Does Not Prolong Discharge Times After Brief Outpatient General Anesthesia for Laparoscopic Tubal Sterilization

Preoperatively administered midazolam may contribute to postoperative sedation and delayed recovery from brief outpatient general anesthesia, particularly in patients who receive significant postoperative opioid analgesics.We evaluated the effects of midazolam premedication (0.04 mg/kg) on postoperative sedation and recovery times after laparoscopic tubal sterilization (Falope rings) in 30 healthy women in a randomized, double-blind, placebo-controlled study. Patients received midazolam or saline-placebo intravenously 10 min before anesthesia. General anesthesia was induced with fentanyl, propofol, and mivacurium and was maintained with N2 O and isoflurane. Sedation was quantified before and after premedication and 15, 30, and 60 min after emergence from anesthesia, using the digit-symbol substitution (DSST) and Trieger dot (TDT) tests. Management of postoperative pain and nausea and discharge criteria were standardized. Groups were similar with respect to age, weight, and duration of surgery and anesthesia. Midazolam was associated with impairment of performance on the TDT and DSST after premedication administration and 15 (TDT and DSST) and 30 (DSST) min after postanesthesia care unit (PACU) arrival. There were no differences in PACU time and time to discharge-readiness. In conclusion, midazolam premedication augments postoperative sedation in this population but does not prolong recovery times. (Anesth Analg 1997;85:301-5)

Intrathecal Hypobaric Versus Hyperbaric Bupivacaine with Morphine for Cesarean Section

Both hyper-and hypobaric solutions of bupivacaine are often combined with morphine to provide subarachnoid anesthesia for cesarean section. Differences in the baricity of subarachnoid solutions influence the intrathecal distribution of anesthetic drugs and would be expected to influence measurable clinical variables. We compared the effects of hyper- and hypobaric subarachnoid bupivacaine with morphine to determine whether one has significant advantages with regard to intraoperative anesthesia and postoperative analgesia in term parturients undergoing elective cesarean section. Thirty parturients were randomized to receive either hyper- or hypobaric bupivacaine (15 mg) with morphine sulfate (0.2 mg). Intraoperative outcomes compared included extent of sensory block, quality of anesthesia, and side effects. Postoperative outcomes, including pain visual analog scale scores, systemic analgesic requirements, and side effects, were monitored for 48 h. Sedation effects were quantified and compared using Trieger and digit-symbol substitution tests. We detected no differences in sensory or motor block, quality of anesthesia, quality of postoperative analgesia, incidence of side effects, or psychometric scores. Both preparations provide highly satisfactory anesthesia for cesarean section and effective postoperative analgesia. Implications: Dextrose alters the density of intrathecal bupivacaine solutions and is thought to influence subarachnoid distribution of the drug. We randomized parturients undergoing cesarean section to one of two often used spinal bupivacaine preparations, hypobaric and hyperbaric. We detected no differences in clinical outcomes between groups. (Anesth Analg 1998;87:336-40)

General anesthesia with remifentanil for Cesarean section in a parturient with an acoustic neuroma.

PurposeTo describe the anesthetic management of a parturient with a large acoustic neuroma undergoing general anesthesia with remifentanil for Cesarean section.Clinical featuresA near-term parturient presented with a large intracranial mass. Cesarean section under general anesthesia was elected one week prior to craniotomy for tumour resection. Remifentanil infusion, 0.2–1.0 μg · kg−1 · min−1, was used from induction to emergence of general anesthesia. The neonate was born seven minutes after the remifentanil infusion was started. She had normal umbilical cord pH and her Apgar scores were 7 and 8, at one and five minutes respectively. Although the neonate received supplemental oxygen, she did not require naloxone. Both mother and neonate made an uneventful recovery.ConclusionRemifentanil was effective in producing stable hemodynamic conditions, without severe neonatal respiratory depression, during induction and maintenance of general anesthesia for a Cesarean delivery in a parturient with a large intracranial tumour.AbstractObjectifDécrire la conduite de l’anesthésie générale avec le rémifentanil pour une césarienne chez une patiente enceinte ayant un neurinome acoustique.Aspects cliniquesUne femme enceinte s’est présentée avec une volumineuse masse intracrânienne quelques semaines avant terme. Une césarienne sous anesthésie générale a été planifiée une semaine avant de procéder à la résection de la tumeur intracrânienne. Le rémifentanil en perfusion intraveineuse a été utilisé de l’induction à l’émergence, à des doses variant de 0.2–1.0 μg · kg−1 · min−1. L’enfant est né après sept minutes de perfusion de rémifentanil. Les gaz du cordon étaient normaux et les Apgar à une et cinq minutes étaient respectivement 7 et 8. Malgré l’apport temporaire d’oxygène, le nouveau-né n’a pas eu besoin de naloxone. La mère et l’enfant ont eu une convalescence sans complication.ConclusionLe rémifentanil a permis des conditions hémodynamiques stables, sans produire de dépression respiratoire significative chez le nouveau-né, pendant l’induction et la maintenance de l’anesthésie générale pour une césarienne chez une patiente avec une volumineuse tumeur intracrânienne.

Maternal posture influences the extent of sensory block produced by intrathecal dextrose-free bupivacaine with fentanyl for labor analgesia

The cephalad extent of sensory block produced by intrathecal (IT) dextrose-free local anesthetics and opioids has been reported to be quite variable. Most reports describing the effects of IT analgesics do not control for patient posture. Because these medications are hypobaric relative to cerebrospinal fluid (CSF), parturients in a sitting position may develop greater cephalad extents of sensory block than those in a lateral position during IT injection. Parturients in labor were randomized to sitting or lateral position during IT administration of dextrose-free bupivacaine 0.25% with fentanyl 0.005%. Extent of sensory block was evaluated at intervals thereafter. Free flow of CSF was obtained in 20 parturients. Those in a sitting position during IT injection had significantly higher maximal cephalad extent of block than those in a lateral position (mean +/- SD, T-3.1 +/- 2.9 vs T-6.3 +/- 3.4, P = 0.036). Mean cephalad extent of block was greater in the sitting group at 20 and 30 min. When sensory block asymmetry was observed, the extent of block was greater on the nondependent side. Posture during IT injection of this dextrose-free analgesic combination affects extent of sensory block in laboring parturients. (Anesth Analg 1996;83:1229-33)

The effects of general versus epidural anesthesia for outpatient extracorporeal shock wave lithotripsy

UNLABELLED Although many anesthetic techniques are described for immersion extracorporeal shock wave lithotripsy (ESWL), regional and i.v. techniques are the most commonly reported. This randomized, prospective study compared general anesthesia (GA) and epidural anesthesia (EPID) with regard to effectiveness, side effects, induction time, and recovery in patients undergoing ESWL using an unmodified Dornier HM-3 lithotriptor. Twenty-six healthy outpatients were randomized to GA (propofol, N2O, laryngeal mask airway) or EPID (lidocaine 1.5% with epinephrine). Intraoperative and postoperative supplemental medications, side effects, and complications were noted. Induction times and times required to meet standard recovery criteria were compared between groups. Patients were surveyed regarding their satisfaction with anesthesia. All patients in the EPID group had effective blocks with a single catheter insertion and local anesthetic injection. In the GA group, the LMA was inserted successfully in all patients. Time from room entry to procedure start was significantly less in the GA group (23 +/- 11 vs 34 +/- 9 min; P < 0.05). Patients in the GA group were ready for discharge home earlier (127 +/- 59 vs 178 +/- 49 min; P < 0.05). Only three patients experienced nausea (one in the GA group, two in the EPID group). There were no differences in patient or urologist satisfaction with anesthesia. We conclude that GA is associated with a rapid recovery compared with EPID. IMPLICATIONS General anesthesia with propofol, nitrous oxide, and a laryngeal mask airway is comparable to epidural anesthesia with lidocaine for outpatient extracorporeal shock wave lithotripsy procedures. However, early recovery is more rapid after general anesthesia compared with epidural anesthesia.

The effects of needle bevel orientation during epidural catheter insertion in laboring parturients.

UNLABELLED Lateral needle bevel orientation during identification of the epidural space has been recommended to reduce the risk of postdural puncture headache (PDPH). Rotation to cephalad or caudad orientation before catheter insertion is assumed necessary for analgesic success. We prospectively compared the effects of catheter insertion through lateral- and cephalad-oriented Tuohy needle bevels in laboring parturients. Anesthesiology residents were randomized to identify the epidural space with bevels oriented cephalad or lateral. Catheters were inserted without needle rotation. Outcomes compared included ease of insertion, analgesic effectiveness, and complications. We evaluated 534 catheter insertions in 500 parturients. Initial catheter insertion produced satisfactory analgesia in 80.2% of the lateral group versus 91.1% of the cephalad group (P < 0.001). Resistance preventing catheter insertion accounted for the difference. There were no differences in i.v. cannulation (5.8% vs 5.1%), dural puncture (3.8% vs 2.0%), PDPH (0.4% vs 0.7%), or asymmetric block (31% vs 27%). There was a slightly higher rate of paresthesias in the lateral group (31% vs 23%; P = 0.048). In 78% of parturients experiencing both paresthesias and asymmetric block, the side of the paresthesia and greater extent of block were the same. Analgesic effectiveness, as measured by using a visual analog scale, was not different between the groups. IMPLICATIONS Two methods of epidural catheter insertion were compared in laboring parturients. Catheter insertion with the needle orifice oriented cephalad was associated with the greatest initial success and the fewest complications.

Nitrous Oxide During Labor: Maternal Satisfaction Does Not Depend Exclusively on Analgesic Effectiveness.

BACKGROUND: Evidence on the analgesic effectiveness of nitrous oxide for labor pain is limited. Even fewer studies have looked at patient satisfaction. Although nitrous oxide appears less effective than neuraxial analgesia, it is unclear whether labor analgesic effectiveness is the most important factor in patient satisfaction. We sought to compare the relationship between analgesic effectiveness and patient satisfaction with analgesia in women who delivered vaginally using nitrous oxide, neuraxial analgesia (epidural or combined spinal-epidural [CSE]), or both (neuraxial after a trial of nitrous oxide). METHODS: A standardized survey was recorded on the first postpartum day for all women who received anesthetic care for labor and delivery. Data were queried for women who delivered vaginally with nitrous oxide and/or neuraxial labor analgesia over a 34-month period in 2011 to 2014. Parturients with complete data for analgesia quality and patient satisfaction were included. Analgesia and satisfaction scores were grouped into 8 to 10 high, 5 to 7 intermediate, and 0 to 4 low. These scores were compared with the use of ordinal logistic regression across 3 groups: nitrous oxide alone, epidural or CSE alone, or nitrous oxide followed by neuraxial (epidural or CSE) analgesia. RESULTS: A total of 6507 women received anesthesia care and delivered vaginally. Complete data were available for 6242 (96%) women; 5261 (81%) chose neuraxial analgesia and 1246 (19%) chose nitrous oxide. Of the latter, 753 (60%) went on to deliver with nitrous oxide alone, and 493 (40%) switched to neuraxial analgesia. Most parturients who received neuraxial analgesia (>90%) reported high analgesic effectiveness. Those who used nitrous oxide alone experienced variable analgesic effectiveness, with only one-half reporting high effectiveness. Among all women who reported poor analgesia effectiveness (0−4; n = 257), those who received nitrous oxide alone were more likely to report high satisfaction (8−10) than women who received epidural analgesia alone (OR 2.5; 95% CI 1.4–4.5; P = .002). Women who reported moderate analgesia (5−7) and received nitrous oxide only were more likely to report high satisfaction compared with the other groups. Among women who reported a high level of analgesic effectiveness, satisfaction with anesthesia was high and not different among groups. CONCLUSIONS: Patients who received nitrous oxide alone were as likely to express satisfaction with anesthesia care as those who received neuraxial analgesia, even though they were less likely to report excellent analgesia. Although pain relief contributes to the satisfaction with labor analgesia care, our results suggest that analgesia is not the only contributor to maternal satisfaction.

Responses to nondepolarizing neuromuscular blockers and succinylcholine in von Recklinghausen neurofibromatosis

Patients with type 1 neurofibromatosis (NF-1) have been reported to have prolonged responses to nondepolarizing (ND) neuromuscular blockers (NMBs). Responses to succinylcholine (SCh) have been described as increased, decreased, or normal. The purpose of this study was to assess responses to NMBs in NF-1 patients in order to determine the clinical significance of abnormal responses. We retrospectively identified all NF-1 patients who received anesthetics at Strong Memorial Hospital between January 1, 1984 and December 31, 1994. We then reviewed all anesthetic records to classify responses to NMBs as normal, abnormal, or indeterminate. Records of 114 anesthetics provided to 44 NF-1 patients were reviewed. Nondepolarizing NMBs were used during 73 anesthetic cases in 38 patients. Responses were normal in 69 cases and indeterminate in 4 (3 in patients with normal responses during other anesthetics). SCh was used during 42 anesthetic cases in 23 patients. Responses were normal in all but one case (indeterminate) in a patient who had had other documented normal responses. Standard milligram per kilogram doses of NMBs were used in all cases, and in none was there evidence of abnormal response. The risk of abnormal response to NMBs in individuals with NF-1 appears to be minimal. We recommend no alteration in dosing of either SCh or ND NMBs in patients with NF-1. (Anesth Analg 1996;82:382-5)

Acute facial, cervical, and thoracic subcutaneous emphysema : A complication of fiberoptic laryngoscopy

and insertion of a 7.0 nasal airway. Obstruction was relieved by positive end-tidal pressure from a mask. Nasal fiberoptic examination using the same model fiberscope as previously described revealed no trauma, but with each inspiration, the hypopharyngeal soft tissue collapsed inward and the epiglottis fell posteriorly, obstructing the glottis and hindering fiberscope passage. After several attempts through both nares, a second anesthesiologist attempted fiberoptic tracheal intubation through the right naris. Oxygen delivered from the wall pipeline supply (50 psi) with a flow of 5 L/min (flow meter regulator) via oxygen tubing was insufflated by intermittent thumb occlusion of the fiberscope channel post. During oxygen insufflation with the fiberscope tip in the nasopharynx, the patient’s right face, neck, thorax, and proximal right upper extremity abruptly developed massive swelling. Palpation revealed crepitus suggestive of acute subcutaneous emphysema. The patient’s oxygen saturation decreased to 77%, but increased to 95% with positive endtidal pressure from a mask using 100% oxygen. The trachea was then intubated with a 6.5 ETT via retrograde wire technique. Chest radiograph revealed bilateral thoracocervical subcutaneous emphysema (Fig. 2). Otolaryngology consultation was obtained in the intensive care unit. Ceftriaxone was administered prophylactically, and her trachea was extubated 10 h later. Fiberoptic examination by the otolaryngologist revealed a puncture laceration of the posterior nasopharyngeal wall. She had diffuse hypopharyngeal swelling and poor hypopharyngeal tone with partial collapse, yet was judged to have an adequate airway. A day later, she developed acute airway obstruction during feeding tube placement and required tracheal reintubation. The patient subsequently underwent tracheostomy and was recovering well until she died on postoperative day 21 from a massive cerebrovascular accident.