Mahesh P. Mehta

Comparison of Psychologic and Cognitive Functions after General or Regional Anesthesia

The behavior of 105 patients randomly assigned to receive cither general or regional anesthesia and who underwent one of three types of surgery (hysterectomy, prostatectomy, or joint replacement) was assessed before, immediately after, and 3 mo after surgery. Psychologic status was assessed by the Sickness Impact Profile, the SCL-90-R, and a Metamemory Questionnaire. Cognitive functioning was measured by a battery of ten psychomotor, memory, and skilled performance tasks. Physical health was scored by the ASA classification of physical status, a health index, postoperative complications ratings, and a self-rated measure of the patients health. There were cognitive differences across surgery groups due to age and gender variability among the patients; however, the type of anesthesia produced no difference in behavior. Both the physical and mental health indices showed improvement from the preoperativc to the postoperative periods. General anesthesia appears to pose no risk to mental function and recovery beyond that associated with regional anesthesia and surgery.

Spinal cord motoneuron excitability during isoflurane and nitrous oxide anesthesia.

Background Recent evidence suggests that the spinal cord is an important site of anesthesia that is necessary for surgical immobility, but the specific effect of anesthetics within the spinal cord is unclear. This study assessed the effect of isoflurane and nitrous oxide on spinal motoneuron excitability by monitoring the H‐reflex and the F wave. Methods Eight adult patients, categorized as American Society of Anesthesiologists physical status 1 or 2, who were undergoing elective orthopedic surgery were anesthetized with 0.6, 0.8, 1.0, and 1.2 times the estimated minimum alveolar concentration (MAC) of isoflurane. Nitrous oxide was added in graded concentrations of 30%, 50%, and 70%, whereas the isoflurane concentration was decreased to maintain a total MAC of 1. The H‐reflex of the soleus muscle and the F wave of the abductor hallucis muscle were measured before anesthesia and 15 min after each change of anesthetic concentration. Four or more trials of the H‐reflex and 18 trials of the F wave were recorded at each concentration of anesthesia. The effect of the anesthetics on the H‐reflex and F wave was analyzed using Dunnetts test. Results H‐reflex amplitude was decreased to 48.4 +/‐ 18.6% of preanesthesia level at 0.6 MAC isoflurane and to 33.8 +/‐ 19.1% when isoflurane concentration increased from 0.6 MAC to 1.2 MAC. F wave amplitude and persistence decreased to 52.2 +/‐ 33.6% and 44.4 +/‐ 26% of baseline at 0.6 MAC isoflurane, and to 33.8 +/‐ 26% and 21.7 +/‐ 22.8% at 1.2 MAC isoflurane. Isoflurane plus nitrous oxide (total 1 MAC) decreased H‐reflex amplitude to 30.4–33.3% and decreased F wave persistence to 42.8–56.3% of baseline. Conclusions Both isoflurane alone and isoflurane plus nitrous oxide decrease H‐reflex and F‐wave amplitude and F‐wave persistence. These effects suggest that isoflurane and nitrous oxide decrease motoneuronal excitability in the human spinal cord. This may play an important role in producing surgical immobility.

Facilitation of Rapid Endotracheal Intubations with Divided Doses of Nondepolarizing Neuromuscular Blocking Drugs

The authors sought to determine whether prior administration of a small, subparalyzing dose of nondepolarizing muscle relaxant would shorten the onset time of an intubating dose of muscle relaxant. Initially, in 60 anesthetized patients, twitch response of adductor pollicis to ulnar nerve stimulatio

The Additive Contribution of Nitrous Oxide to Isoflurane MAC in Infants and Children

The purpose of this study was to determine the contribution of nitrous oxide to isoflurane MAC in pediatric patients. MAC was determined in 47 infants and small children (mean ages 16.6 +/- 6.7 months) during isoflurane and oxygen anesthesia (n = 11) and isoflurane and nitrous oxide anesthesia (25% nitrous oxide [n = 12], 50% nitrous oxide [n = 12], and 75% nitrous oxide [n = 12]). After assigning patients to one of four groups, anesthesia was induced with increasing inspired concentrations of isoflurane in oxygen. After anesthetic induction and tracheal intubation, ventilation was controlled (carbon dioxide partial pressure = 32 +/- 5 mmHg), and nitrous oxide was added to the inspired gas mixture to achieve end-expired nitrous oxide concentrations of 0, 25, 50, or 75%. Inspired and expired gas samples were obtained from a distal sampling port in the tracheal tube. The response to skin incision in each patient was assessed at a previously selected end-tidal concentration of isoflurane. The MAC of isoflurane was determined in each group using the up-and-down method described for evaluating quantal responses. The mean duration of constant end-tidal concentrations prior to skin incision was 14 +/- 7 min (range 6-46 min). The ratio of expired to inspired nitrous oxide and isoflurane concentrations during the period of constant end-tidal concentrations was 0.96 +/- 0.01 and 0.93 +/- 0.03 respectively. The MAC of isoflurane in oxygen was 1.69 +/- 0.13 vol% (mean +/- standard deviation).(ABSTRACT TRUNCATED AT 250 WORDS)

Additive Contribution of Nitrous Oxide to Halothane Mac in Infants and Children

Fifty-one infants and small children (14.7 ± 7.2 mo) were studied to determine the MAC of halothane in O2 (n = 11) and in the presence of three different nitrous oxide (N2O) concentrations (25% [n = 13], 50% [n = 13], and 75% [n = 14]). In the three N2O groups, after randomly assigning patients to an N2O group, anesthesia was induced with halothane and N2O using a pediatric circle system. After endotracheal intubation, halothane and N2O end-expired concentrations were adjusted to predetermined concentrations. The initial halothane concentrations in each group were based on the assumption that each percent N2O reduced halothane concentrations by 0.01 vol % (assumed halothane MAC = 1.0 vol %). Based on the response of the preceding subject in each group, halothane concentrations were increased or decreased depending on whether the response was to move or not to move, respectively, in response to the surgical incision. The mean duration of constant end-tidal concentrations before skin incision was 10 min. End-tidal gases were sampled and measured from a separate distal sampling port of an endotracheal tube during controlled ventilation (Perkin-Elmer Mass Spectrometer). The MAC value for halothane in O2 was 0.94 ± 0.08 vol % (mean ± SD). The MAC values of halothane in the presence of 25%, 50%, and 75% N2O were 0.78 ± 0.12 vol %, 0.44 ± 0.10 vol %, and 0.29 ± 0.06 vol %, respectively. All concentrations of N2O significantly reduced the MAC of halothane. A regression analysis through all four data points yielded a linear relationship (r2 = 0.87) with a predicted MAC for N2O of 105 vol %. Unlike halothane and isoflurane, the predicted MAC of N2O in infants and children is similar to that reported by others in adults. Similar to the results of clinical studies in adults, the contribution of N2O to halothane MAC in children is additive.

Reliability of capnography in identifying esophageal intubation with carbonated beverage or antacid in the stomach

To evaluate the reliability of capnography in identifying esophageal intubation in the presence of a carbonated beverage in the stomach, we first investigated the amount of CO2 released from different carbonated beverages and antacids in a simulated stomach; next we measured the end-expired CO2 level during esophageal ventilation with a carbonated beverage in the stomachs of six swine. CO2 levels of approximately 20% were consistently observed in all carbonated beverages. The CO2 levels obtained with sodium bicarbonate, Maalox, and sodium citrate were 19.3%, 2.0%, and 0%, respectively. CO2 waveforms were observed during esophageal ventilation in five of six animals after intragastric administration of a carbonated beverage. An end-expired CO2 level of 2.5% or more was observed in two swine. The highest end-expired CO2 level measured was 5.3%. We conclude that although capnography is convenient and effective, it lacks all the attributes of an ideal monitor for detecting esophageal intubation.

The Neuromuscular Blocking and Cardiovascular Effects of Doxacurium Chloride in Patients Receiving Nitrous Oxide Narcotic Anesthesia

The purpose of this study was to evaluate neuromuscular and cardiovascular effects of doxacurium chloride, a new long-acting neuromuscular blocking agent, during a stable state of nitrous oxide and narcotic anesthesia. Ninety-three ASA physical status I or II patients were studied after informed written consent had been obtained. Eighty-one patients (group A) received doxacurium. The 81 patients were divided into nine subgroups according to the dose of doxacurium administered (0.01–0.06 mg·kg-1). Patients in a control group (group B) (n=12) received pancuronium. To assess neuromuscular responses, a force displacement transducer recorded the twitch response of the adductor pollicis muscle following ulnar nerve stimulation. The ED50 and ED95 for doxacurium were estimated to be 0.013 mg·kg-1 and 0.023 mg·kg-1, respectively. The time to maximum twitch suppression following a dose of 1.0 (ED95) and 1.7 (ED95) was 10.3 ± 1.3 min and 7.6 ± 0.8 min, respectively. After an ED95 dose of doxacurium the time to spontaneous recovery to 95% of control twitch height was 73.7 ± 8.7 min. With larger doses of doxacurium, 0.04 mg·kg-1 (1.7 × ED95) and 0.05 mg·kg-1 (2.2 × ED95), the time to spontaneous recovery to 95% of control twitch height was 125.8 ± 24.8 and 204.0 ± 21.2 minutes, respectively. When 25% twitch height recovery or more was present the reversal of doxacurium induced neuromuscular blockade was prompt. After administration of 0.04 mg · kg-1 of doxacurium or 0.08 mg · kg-1 of pancuronium, the time for spontaneous recovery to 25% of control twitch height recovery was 77.4 ± 7.5 min (n = 23) and 71.4 ± 6.7 min (n = 10), respectively. When identical multiple maintenance doses of doxacurium were administered, the subsequent neuromuscular block following each maintenance dose was of similar magnitude and duration. At 1,2, and 5 min following pancuronium, heart rate and mean blood pressure increased. Following doxacurium small decreases in mean blood pressure occurred at 2 and 5 min, while heart rate decreased 5 min following drug injection. Doxacurium is a new, long-acting, nondepolarizing relaxant. Further study is warranted to assess the cardiovascular effects of this neuromuscular blocking drug in patients with cardiovascular disease.

Neuromuscular and cardiovascular effects of mivacurium chloride in surgical patients receiving nitrous oxide-narcotic or nitrous oxide-isoflurane anaesthesia

The neuromuscular and cardiovascular effects of mivacurium chloride were studied during nitrous oxide-oxygen narcotic (fentanyl) (n = 90) and nitrous oxide-oxygen isoflurane (ISO) anaesthesia (n = 45). In addition, a separate group (n = 9) received succinylcholine during fentanyl anaesthesia to compare its neuromuscular effects with mivacurium. Mivacurium was initially administered as a single bolus in doses from 0.03 mg · kg−1 to 0.25 mg · kg−1 to study the dose-response relationships, as well as the cardiovascular effects of mivacurium. Neuromuscular block (NMB) was measured by recording the twitch response of the adductor pollicis muscle following ulnar nerve stimulation (0.15 Hz, 0.2 ms supramaximal voltage). The ED95 values for mivacurium were estimated to be 0.073 mg · kg−1 and 0.053 mg · kg−1 in the fentanyl and ISO groups respectively. The duration of block (time from injection to 95 per cent recovery) for a dose of 0.05 mg · kg− 1 mivacurium was 15.3 ± 1.0 min and 21.5 ± 1.3 min for fentanyl and ISO anaesthesia, respectively. The recovery index (25–75 per cent) between initial bolus dose (6.1 ± 0.5 min), repeat bolus doses (7.6 ± 0.6 min), mivacurium infusion (6.7 ± 0.7 min) and succinylcholine infusion (6.8 ± 1.8 min) were not significantly different. There was minimal change in mean arterial pressure (MAP) or heart rate (HR) following bolus doses of mivacurium up to 0.15 mg · kg−1. Bolus administration of 0.20 mg · kg−1 or 0.25 mg · kg−1 of mivacurium decreased MAP from 78.2 ± 2.5 to 64.0 ± 3.2 mmHg (range 12–59 per cent of control) (P < 0.05). The same doses when administered slowly over 30 sec produced minimal change in MAP or HR.RésuméLes effets cardiovasculaires et neuromusculaires du chlorure de mivacurium ont été étudiés lors d’une anesthésie au narcotique (fentanyl) protoxyde d’azote-oxygène (n = 90) et isoflurane (ISO) protoxyde d’azote-oxygéne (n = 45). En plus, un groupe séparé (n = 9) a reçu du succinylcholine lors d’une anesthésie au fentanvl afin de comparer ces effets neuromusculaires avec le mivacurium. Le mivacurium a été initialement administré comme un bolus unique les doses de 0,03 mg · kg−1 et 0,25 mg · kg−1 afin d’étudier la courbe dose-réponse et les effets cardiovasculaires du mivacurium. Le bloc neuromusculaire (NMB) a été mesuré en enregistrant la réponse au twitch de l’adducteur du pouce après stimulation du nerf cubital (0.15 Hz, 0.2 ms voltage supramaximal). Les valeurs de ED95 du mivacurium ont été estimées à 0,073 mg ·kg−1 et 0,053 mg · kg−1 respectivement pour le groupe fentanyl et ISO. La durée du bloc (temps à partir de l’injection à la recouvrance à 95 pour cent) pour une dose de 0,05 mg · kg−1’ de mivacurium était de 15,3 ± 1,0 min. et 21,5 ± 1,3 min. respectivement pour le groupe fentanyl et le groupe ISO. L’index de recouvrance (25–75 pour cent) entre le bolus initial (6,1 ± 0,7 min) la dose de rajout (7,6 ± 0,6 min) et la perfusion de mivacurium (6,7 ± 0,7 min) et la perfusion de succinycholine (6,8 ± 1,8 min) n’était pas significativement différent. On a observé des changements minimes dans la pression artérielle moyenne (MAP) ou la fréquence cardiaque (HR) après le bolus de mivacurium jusqu’à 0,15 mg · kg−1. Une administration en bolus de 0,20 mg · kg−1 ou 0,25 mg · kg−1 de mivacurium a diminué la pression artérielle moyenne de 78,2 ± 2,5 à 64.0 1 3,2 mmHg (écart de 12–59 pour cent du contrôle) (P < 0.05). Les mêmes doses lorsque administrées lentement au-dessus de 30 secondes ont produit des changements minimes de la pression artérielle moyenne et de la fréquence cardiaque.

A comparative study of methods of detection of esophageal intubation

The trachea and esophagus of 21 patients were simultaneously intubated to comparatively evaluate methods for detecting esophageal intubation. In succession, the trachea and esophagus were ventilated with the same inspiratory volume of 621 +/- 45 mL (mean +/- SD). Carbon dioxide (CO2) levels, volumes, and temperatures of expired gas were measured from the tracheal and esophageal tubes. End-expired CO2 levels of gases from the trachea and esophagus were 4.9 +/- 0.7% and 0.6 +/- 0.6%, respectively, with CO2 waveforms observed in 7 (33%) patients with esophageal intubations. Volumes expired from the tracheal tube averaged 615 +/- 64 mL and from the esophageal tube 35 +/- 16 mL (P less than 0.001). Peak temperatures of expired gas recorded from the tracheal tube (32.0 +/- 0.73 degrees C) were higher than those from the esophageal tube (27.3 +/- 1.2 degrees C) (P less than 0.001). The shape of temperature waveforms with a correctly placed tracheal tube remained constant with each ventilation, contrary to that obtained from an esophageal tube. Although the occasional detected of CO2 waveforms from an esophageal tube might lead to an incorrect assessment of tube placement, this limitation of CO2 analyzer can be offset by measurement of volume and temperature of expired gas in identifying placement of an endotracheal tube.

The Minimum Alveolar Concentration of Isoflurane in Patients Undergoing Bilateral Tubal Ligation in the Postpartum Period

Background The minimum alveolar concentration (MAC) of volatile anesthetics is decreased during pregnancy, but MAC in the early postpartum period has not been reported. The aim of this study was to determine the MAC of isoflurane and to evaluate the relation between MAC and serum progesterone and beta-endorphin in patients after delivery. Methods Eight patients undergoing elective bilateral tubal ligation during general anesthesia in the early postpartum period (< 12 h postpartum) and eight patients undergoing this procedure in the late postpartum period (12-25 h postpartum) were studied. Eight patients undergoing bilateral tubal ligation more than 6 weeks after delivery served as control subjects. Anesthesia was induced with propofol and maintained with isoflurane in oxygen to a steady end-tidal concentration of 0.8-1.0 vol% for 10 min. Reaction to a standardized electric stimulation applied to the forearm was graded as positive (gross or delayed movement) or negative. By using the bracketing technique, the concentration of isoflurane was increased or decreased by 0.1 vol%, depending on the positive or negative responses. Results The MAC (mean plus/minus SD) in patients in the early postpartum period was significantly less (0.75 plus/minus 0.17 vol%) than that in control subjects (1.04 plus/minus 0.12 vol%; P < 0.01) and that in patients in the late postpartum period (0.95 plus/minus 0.2 vol%; P < 0.05). The difference in MAC values between late postpartum and control was not significant (P > 0.05). There was an inverse correlation between progesterone concentration postpartum and time after delivery (r = -0.527; P = 0.036), but no relation between beta-endorphin and time after delivery (r = 0.089; P = 0.744). There was no correlation between plasma progesterone or beta-endorphin and MAC by multiple regression (r = 0.166; P = 0.950). Conclusions Isoflurane MAC remains 28% less than normal within the 1st 12 h postpartum and then returns to normal 12-25 h after delivery.