Joseph L. Seltzer

Comparison of tracheal intubating conditions and neuromuscular blocking profiles after intubating doses of mivacurium chloride or succinylcholine in surgical outpatients.

Thirty ASA physical status I or II outpatients scheduled to undergo short procedures (<1 hr in duration) requiring tracheal intubation received either 1.0 mg/kg succinylcholine or 0.20 mg/kg (2.5 × ED95) or 0.25 mg/kg (3 × ED95) mivacurium. A N2O/O2/narcotic anesthetic technique was utilized and the ulnar nerve was stimulated with subcutaneous electrodes placed at the wrist. Tracheal intubation was attempted in all patients either 2 min after mivacurium or 1 min after succinylcholine. Intubation conditions were not different between the succinylcholine and mivacurium groups or between the two mivacurium groups. The onset and duration of neuromuscular blockade were shorter with succinylcholine than with mivacurium. Suppression of the T1 response to 90% of baseline occurred in 0.9 min with 1.0 mg/kg succinylcholine and at 2.2 and 1.5 min respectively, with 0.20 mg/kg and 0.25 mg/kg mivacurium. Initial recovery of the T1 response occurred at 6.4 min after 1.0 mg/kg succinylcholine and 12.7 and 13.6 min respectively after 0.20 mg/kg and 0.25 mg/kg mivacurium. Subsequent to initial recovery from the intubating dose of relaxant, infusions of mivacurium or succinylcholine were administered to maintain approximately 95% block. The mean infusion rates were 6.6 μg·kg−1 ·min−1 mivacurium and 41.2 μg·kg−1 min−1 for succinylcholine. Spontaneous recovery from neuromuscular blockade occurred more quickly after succinylcholine than after mivacurium: the time from cessation of infusion to recovery of T1 to 95% of baseline was 6.5 min in patients given succinylcholine and 16.7 min in patients given mivacurium. When reversal was in order, residual mivacurium-induced blockade was readily antagonized by 0.045 mg/kg neostigmine. In a small group (n = 7) of patients given mivacurium in whom neuromuscular function was still 77–99% blocked when neostigmine was given, the average time from administration of neostigmine to recovery of T1 to 95% of baseline was 7.6 min. There were no differences in the duration of recovery room stay for patients receiving succinylcholine or mivacurium.

Prostacyclin Mediation of Vasodilation Following Mesenteric Traction

Eight untreated patients (group I) and four patients who received ibuprofen preoperatively (group II) scheduled for elective abdominal aortic ancurysm repair were studied. Heart rate (HR); systolic, diastolic, and mean arterial pressure (MAP); systolic and diastolic pulmonary artery pressure; pulmonary capillary wedge pressure (PCWP); cardiac output (CO); and central venous pressure (CVP) were recorded pre-induction, before mesenteric traction, and 5, 15, and 30 min post-mesenteric traction. Plasma samples were obtained at these times for analysis of six-keto-prostaglandin Flα (PGF1α) concentration by radioimmunoassay. Group II patients received ibuprofen 12 mg/kg orally 11/2 h before surgery. Plasma samples from six group I patients and all group II patients taken 5 min after mesenteric traction were added to isolated helical strips of cat superior mesenteric arteries precontracted with norepinephrine (200 ng/ml) for analysis of reduction in developed force. In group I, abdominal mesenteric traction resulted in a significant decrease in MAP (P < 0.03) and SVR (P < 0.005) with an increase in CO (P < 0.05) at 5 min post-mesenteric traction. which returned to mean pre-mesenteric traction values by 30 min and a significant increase in PGF,α concentrations. There was a significant positive correlation between PGF,α and CO (P < 0.001) and a significant negative correlation between PGF,α and SVR (P < 0.01) at 5 min post-mesenteric traction. Post-mesenteric traction plasma samples added to the cat mesenteric artery preparation resulted in vasodilation, as demonstrated by a reduction in developed force of 0.563 ± 0.092 grams, as compared to the reduction by pre-mesenteric traction plasma values of 0.12 ± 0.11 grams (P < 0.01). Group II patients did not develop significant increases in PGF,α, and 5-min post-mesenteric traction plasma samples did not significantly relax the cat mesenteric artery preparations. There were no changes in MAP, SVR, and CO in group II patients. Flushing of the head and neck in association with mesenteric traction was noted in group I only.

Preoxygenation in the morbidly obese: a comparison of two techniques

Morbid obesity by increasing acidity and volume of gastric contents, as well as by increasing and intragastric pressure (l), increases the risk of pulmonary aspiration of gastric contents during general anesthesia. Rapid sequence induction of anesthesia with cricoid pressure can prevent this complication. Gold et al. (2) have shown that four vital capacity breaths of 100% 0, within 30 seconds elevates PaO, in non-obese patients as effectively as 5 min of tidal breathing of 100% 0,. Morbidly obese patients with altered lung volumes and diminished compliance, may respond differently to preoxygenation (3). We therefore compared two methods of preoxygenation in morbidly obese patients undergoing rapid sequence induction and intubation.

Relationship between arterial carbon dioxide and end-tidal carbon dioxide when a nasal sampling port is used

End-tidal carbon dioxide (ETCO2) values obtained from awake nonintubated patients may prove to be useful in estimating a patient’s ventilatory status. This study examined the relationship between arterial carbon dioxide tension (PaCO2) and ETCO2 during the preoperative period in 20 premedicated patients undergoing various surgical procedures. ETCO2 was sampled from a 16-gauge intravenous catheter pierced through one of the two nasal oxygen prongs and measured at various oxygen flow rates (2, 4, and 6 L/min) by an on-line ETCO2 monitor with analog display. Both peak and time-averaged values for ETCO2 were recorded. The results showed that the peak ETCO2 values (mean = 38.8 mm Hg) correlated more closely with the PaCO2 values (mean = 38.8 mm Hg; correlation coefficient r = 0.76) than did the average ETCO2 values irrespective of the oxygen flow rates. The time-averaged PaCO2-ETCO2 difference was significantly greater than the PaCO2-peak ETCO2 difference (P < 0.001). Values for subgroups within the patient population were also analyzed, and it was shown that patients with minute respiratory rates greater than 20 but less than 30 and patients age 65 years or older did not differ from the overall studied patient population with regard to PaCO2-ETCO2 difference. A small subset of patients with respiratory rates of 30/ min or greater (n = 30) did show a significant increase in the PaCO2-ETCO2 difference (P < 0.001). It was concluded that under the conditions of this study, peak ETCO2 values did correlate with PaCO2 values and were not significantly affected by oxygen flow rate. However, obtaining peak ETCO2 values is clinically more difficult, especially when partial air-way obstruction is present.

Multicenter study of contaminated percutaneous injuries in anesthesia personnel.

Background Anesthesia personnel are at risk for occupational infection with bloodborne pathogens from contaminated percutaneous injuries (CPIs). Additional information is needed to formulate methods to reduce risk. Methods The authors analyzed CPIs collected during a 2‐yr period at 11 hospitals, assessed CPI underreporting, and estimated risks of infection with human immunodeficiency virus and hepatitis C virus. Results Data regarding 138 CPIs were collected: 74% were associated with blood‐contaminated hollow‐bore needles, 74% were potentially preventable, 30% were considered high‐risk injuries from devices used for intravascular catheter insertion or obtaining blood, and 45% were reported to hospital health services. Corrected for injury underreporting, the CPI rate was 0.27 CPIs per yr per person; per full‐time equivalent worker, there were 0.42 CPIs/yr. The estimated average 30‐yr risks of human immunodeficiency virus or hepatitis C virus infection per full‐time equivalent are 0.049% and 0.45%, respectively. Projecting these findings to all anesthesia personnel in the United States, the authors estimate that there will be 17 human immunodeficiency virus infections and 155 hepatitis C virus infections in 30 yr. Conclusions Performance of anesthesia tasks is associated with CPIs from blood‐contaminated hollow‐bore needles. Thirty percent of all CPIs would have been high‐risk for bloodborne pathogen transmission if the source patients were infected. Most CPIs were potentially preventable, and fewer than half were reported to hospital health services. The results identify devices and mechanisms responsible for CPIs, provide estimates of risk levels, and permit formulation of strategies to reduce risks.

Arterial and venous dilation by nitroprusside and nitroglycerin--is there a difference?

Whole-body arterial and venous dilating properties of nitroprusside and nitroglycerin were compared with each other in 20 adult patients during cardiopulmonary bypass for coronary artery bypass or valvular heart surgery and were compared with simultaneous forearm vascular measurements. Nitroprusside was found to be a more effective whole-body arterial vasodilator and nitroglycerin a better whole-body venous vasodilator when each drug was infused at rates of 1.5 and 2.0 μg/kg/min. No difference in whole-body vasodilation between the two drugs was found at 1.0 μg/kg/min. Forearm plethysmography did not distinguish between the two drugs at any dose level.

Clinical pharmacology of pipecuronium bromide.

The neuromuscular blocking and cardiovascular effects of pipecuronium, in doses ranging 2--3 times its ED95, were evaluated in 46 patients during thiopental, fentanyl, N2O/O2 anesthesia. The neuromuscular blocking effect of pipecuronium was evaluated by recording of the mechanical twitch of the adductor pollicis muscle in response to stimulation of the ulnar nerve at the wrist. Heart rate, systolic and diastolic blood pressures, and cardiac output were noninvasively measured during the onset of the neuromuscular blockade and compared to a saline control group to separate the effect of anesthesia from those of pipecuronium.The mean ± SD time from administration of pipecuronium to 90% suppression of the first twitch (T1) of the tram-of-four was 2.6 ± 0.8, 2.0 ± 0.6, and 2.1 ± 0.6 min following the 70 μg/kg, 85 μg/kg, and 100 μg/kg dose, respectively. There was no significant difference between the different doses of pipecuronium in the time to 90% suppression of T1. In general, all three doses of pipecuronium provided good to excellent intubating conditions within 3 minutes after its administration. The time from the administration of pipecuronium to 5% recovery of T1 was 52.3 ± 18.2 min in the group given 70 μg/kg. This was significantly longer in patients given 85 μg/kg (71.9 ± 15.7 min) or 100 μg/kg (71.8 ± 22.1 min). Times to the start of recovery of T1 and to 25% recovery of T1 showed a similar significant pattern. In 2/3 of the patients, administration of neostigmine (2.5 mg) resulted in adequate recovery of muscle function within 10 minutes. Only patients with T1 recovery to less than 15% of control or a T4/T1 ratio of zero tended to take longer than 10 minutes for full recovery. Heart rate and systolic and diastolic blood pressures decreased significantly after the induction of anesthesia and during the onset of neuromuscular blockade. The hernody-namic variables, however, were similar between the three pipecuronium groups and a control group (N=16) that received only saline. Therefore, no cardiovascular changes could be attributed to pipecuronium when compared to the control group. Cardiac output did not change significantly over the time course of the study.Pipecuronium bromide produces a long-acting, nondepolarizing neuromuscular blockade. A dose of 70 μg/kg can be expected to provide good intubating conditions in 3 minutes with a clinical duration of approximately one hour. Larger doses (85 μg/kg and 100 μg/kg) may shorten the onset time and increase duration on average by 20 minutes. Higher doses are thus best reserved for procedures of long duration. Because no cardiovascular effects were observed with doses ranging from 2--3 times its ED95, pipecuronium can be recommended for patients in whom cardiovascular stability is desired.

Nicardipine versus placebo for the treatment of postoperative hypertension

Postoperative hypertension can cause serious complications, including bleeding from fresh anastomoses, cardiovascular accident, and myocardial ischemia. Therefore rapid control of blood pressure is essential to prevent poor outcome. In this study, 30 American Society of Anesthesiologists class I and II patients who did not have cardiac surgery and subsequently developed postoperative hypertension were randomly assigned to receive either nicardipine, a new dihydropyridine calcium channel blocker, or placebo. Intravenous nicardipine was given as a loading bolus of 10 mg/hr for 5 minutes and was titrated to 15 mg/hr if needed to achieve a therapeutic response. After therapeutic response, intravenous nicardipine was decreased to 3 mg/hr and subsequently titrated in increments of 1.0 to 2.5 mg/hr to maintain blood pressure control. Systolic and diastolic blood pressures during titration and maintenance did not differ significantly from preoperative levels in patients treated with nicardipine. The mean time to therapeutic response for the nicardipine-treated group was 8.67±1.46 minutes, and the median time to offset of action was 15 minutes. Eleven of the 12 patients who received placebo were crossed over to antihypertensive therapy, and of these, 10 received intravenous nicardipine. In this group all achieved therapeutic response in 7.3±1.18 minutes. The usefulness of intravenous nicardipine for postoperative hypertension was demonstrated in this study by: (1) the rapid control of blood pressure, (2) its continued efficacy during maintenance, and (3) little need to adjust dosage to control blood pressure.

The effect of the prone position on venous pressure and blood loss during lumbar laminectomy

STUDY OBJECTIVE To determine the effects of three different prone support systems (Andrews spinal surgery frame, Cloward surgical saddle, and longitudinal bolsters) on inferior vena cava (IVC) and superior vena cava (SVC) pressures; the validity of measuring central venous pressure (CVP) for the determination of ideal positioning of the patient; and the relationship among frame type, blood loss, and hemodynamic measurements. DESIGN Prospective, randomized study of the hemodynamic effects of the prone position. SETTING Inpatient surgery at a university hospital (regional spinal cord injury treatment center). PATIENTS Eighteen patients free of significant coexisting disease (ASA physical status I and II) undergoing elective lumbar laminectomy. INTERVENTIONS Patients were assigned to one of three support frames and measurement of SVC pressure, IVC pressure, and mean arterial pressures (MAP) were obtained supine, prone, and after repositioning. These pressures and measured blood loss were obtained every 15 minutes during the surgical laminectomy portion of the procedure. MEASUREMENTS AND MAIN RESULTS Patients positioned on the Andrews frame had decreased mean SVC and IVC pressures from 8.7 mmHg and 8.4 mmHg in the supine position to 3.3 mmHg and 1.8 mmHg in the prone position, respectively (p less than 0.001). Prone position CVP also was significantly lower in the Andrews group compared with that in the other two groups (p less than 0.001). Repositioning efforts did not significantly decrease CVP. Blood loss was higher in the Cloward group (1,150 +/- 989 ml) than in the Andrews (245 +/- 283 ml) and bolsters (262 +/- 188 ml) groups (p less than 0.02). CONCLUSIONS Increased blood loss was not associated with increased SVC or IVC pressure, nor was there any significant correlation between any demographic or hemodynamic variable and blood loss. There was no evidence that CVP is useful in determining the ideal prone position in patients undergoing lumbar laminectomy.

A risk-specific anesthesia consent form may hinder the informed consent process.

STUDY OBJECTIVE To evaluate the effect of a preprinted, risk-specific consent form on the amount of anesthetic risk information patients retain from the preoperative interview. DESIGN Postoperative survey of consecutive inpatients to determine risk information retained before and after implementation of a preprinted anesthesia consent form, using standard preoperative risk discussions. SETTING Inpatient units of a university medical center. PATIENTS Two groups of patients, both of whom received a standard oral discussion of anesthetic risk information, were compared. Patients in the control group (125 consecutive inpatients) received this information only orally and were interviewed two weeks prior to implementation of a preprinted anesthesia consent form. Patients in the study group (92 consecutive inpatients) received this information orally and via a preprinted consent form and were interviewed between the fourth and sixth weeks after implementation of a preprinted anesthesia consent form. INTERVENTIONS Anesthesia residents discussed five standard anesthetic risks with elective, adult inpatients (n = 233) during a two-week period immediately before and between the fourth and sixth weeks after instituting the mandatory use of a risk-specific anesthesia consent form. These patients were interviewed postoperatively by one of the authors to determine the amount of anesthesia risk information they retained. MEASUREMENTS AND MAIN RESULTS Results of the postoperative survey showed that patients in the control group retained more information concerning anesthetic risks than did those in the study group (33% vs 19%, p less than 0.01). CONCLUSIONS To improve the informed consent process, either a better method of presenting the preprinted, risk-specific consent form or another method of simultaneously conveying and documenting risk information is needed.