Comparison of neuromuscular blockade in upper facial and hypothenar muscles

Facial and hand muscles are used frequently for monitoring neuromuscular blockade. Therefore, we compared changes in electrically evoked muscle potential magnitude in upper facial and hypothenar muscles after fixed doses of neuromuscular blockers (succinylcholine, 750 µg/kg; pancuronium, 70 µg/kg; vecuronium, 50 µg/kg; and atracurium, 300 µg/kg). Face-hand comparisons were made in both anesthetized (nitrous oxide/narcotic, n=51) and comatose (closed-head injuries, n=5) patients. In 24 anesthetized patients, complete blockade of the hypothenar muscles prevented quantitative comparison. In the remaining 27 patients, the relaxant effect (as determined by the percentage change from prerelaxant baseline muscle potentials) was significantly smaller (P<0.0001) in the upper facial muscles (65±24% versus 92±8%, mean ±SD). All four evoked muscle responses to train-of-four stimulation were detectable in upper facial muscles of the 19 patients receiving non-depolarizing neuromuscular blocking drugs; this pattern was seen in hand muscles of only 7 patients (P<0.001). The neuromuscular blockade in both the hand (49±54%) and the upper facial area (68±28%,P>0.05) of comatose patients was smaller and more variable than that seen during anesthesia. These results illustrate the valuc of quantitative monitoring of neuromuscular function, especially during highly variable and unpredictable drug-induced blockade in the comatose state. We conclude that during narcotic-based anesthesia the upper facial and hand muscles are differentially sensitive to commonly used neuromuscular blockers.     

Monitoring technique affects measurement of recovery from succinylcholine

To compare recovery time from neuromuscular blockade after the administration of a single intravenous bolus of succinylcholine (1 mg/kg), we measured, both mechanically and electromyographically, the evoked twitch responses in the hand muscles of 10 patients. Electromyographic data were obtained, electronically integrated, and recorded by a newly available clinical monitoring device. Using both the mechanical and the electromyographic devices, we recorded the times for first return of twitch, as well as for 25% and 75% recovery of twitch height compared with prerelaxant twitch baseline values and compared the values by calculating least-squares regression lines. Times given by the electromyographic device for these measures of returning neuromuscular function were notably longer than those given by the mechanical evoked force monitor. No such findings have been reported in previous studies that compared these two techniques for monitoring of muscle recovery from nondepolarizing relaxants. The specific reasons for the differences found in this study are unknown.Presented in part at the annual meeting of the American Society of Anesthesiologists, Oct 12–16, 1985, San Francisco, CA. The authors thank Danae Powers, MD, for providing statistical advice.     

Posttetanic Count Revisited: Are Measurements More Reliable Using the TOF-Watch Accelerographic Peripheral Nerve Stimulator?

OBJECTIVE: Measurement of profound neuromuscular block using posttetanic count is among the most subjective measurements made in clinical anesthesia. The TOF-Watch accelerographic peripheral nerve stimulator provides objective measurements of neuromuscular block that may improve our ability to quantitate intense blockade. METHODS: The TOF-Watch and Digi Stim III peripheral nerve stimulators were used to monitor onset and early recovery of neuromuscular response induced by rocuronium 0.6 mg/kg i.v. in 30 patients anesthetized with general anesthesia. After induction, train-of-four count (when present) was measured at one-min intervals. Subsequently, posttetanic count was measured at three-min intervals until the first response to train-of-four stimulation reappeared. RESULTS: Posttetanic count and train-of-four count measurements were determined to be consistently unreliable throughout the study in seven (23%) patients with the TOF-Watch stimulator and three (10%) patients with the Digi Stim III stimulator (p = NS). Among stimulators yielding reliable measurements, decreases in train-of-four count to 0/4 were noted earlier with the Digi Stim III monitor (median = 2 min) as compared with the TOF-Watch device (median = 4 min) (p < 0.05). Also, posttetanic count decreased to zero in only 35% of patients with the TOF-Watch stimulator versus 67% of patients with the Digi Stim III stimulator (p < 0.05). CONCLUSIONS: Both monitors were similar in their ability to predict return to TOFC = 1 as a function of PTC measurements. The TOF-Watch monitor is easy to apply even in inexperienced hands. However, the device yielded erroneous data in 23% of patients.     

Hand grip force as an assessment of recovery from neuromuscular block

A simple hydraulic hand dynamometer was used to assess the hand grip force before and after general anesthesia. Eight patients received a general anesthetic of nitrous oxide and oxygen and an inhalational agent without relaxants (nonrelaxant group). Ten patients received a similar anesthetic of nitrous oxide and oxygen and an inhalational agent with nondepolarizing relaxants (relaxant group). The patients in the nonrelaxant group showed a mild depression to 77% of initial hand grip force by the time they could hold up their heads for 5 seconds. Patients in the relaxant group had a mean of only 29% of initial hand grip force when they could lift their heads. One hour later, hand grip force increased to 76% of preoperative force in the relaxant group. Hand grip force appears to be a sensitive measurement of residual relaxant effect.     

The effect of muscle movement on the electroencephalogram during anesthesia with alfentanil

Using aperiodic analysis, we examined the impact on the electroencephalogram (EEG) of muscle activity from opiate-induced rigidity with alfentanil. We compared two groups of patients, one receiving alfentanil with neuromuscular blocking agents and the other group receiving no relaxants. The alfentanil-induced muscle rigidity exerted a noticeable effect on the EEG, with a moderate effect on total power at 1 Hz; a marked effect on the total number of waves, cumulative percent power at 3 Hz, and average power at 17 to 19 Hz; and a striking effect on F90, the frequency below which 90% of the power resides. The presence of electromyographic (EMG) noise in the EEG consistently altered the variables derived from the EEG, so that anesthetic depth appeared less than it actually was. This was true in spite of the fact that we gave slightly more alfentanil in the group not receiving a relaxant. Although the observed muscle activity was greater than that usually seen clinically, and may have differed qualitatively, the results do serve as a warning that muscle noise can interfere with the EEG. Currently, there is no computerized technique that will reject or account for this noise, and we must depend on observation to recognize the EMG patterns within the EEG, either with the raw recording or with a detailed analysis (such as aperiodic analysis), and to compensate for this noise if possible. Techniques that average the EEG or that present a single number have difficulty providing this information. These results do not detract from the usefulness of the EMG contained in EEG recordings as a supplementary or complementary indicator of anesthetic lightness.     

A simulation of neuromuscular function and heart rate during induction,maintenance, and reversal of neuromuscular blockade

We developed a two-compartment model to simulate neuromuscular function and heart rate following the administration of four nondepolarizing neuromuscular blocking agents (atracurium, vecuronium, pancuronium, and d-tubocurarine), three neuromuscular block reversal agents (edrophonium, neostigmine, and pyridostigmine), and two anticholinergic agents (atropine and glycopyrrolate). Twitch depression, train-of-four ratio, and heart rate were modeled during fentanyl, halothane, enflurane, or isoflurane anesthesia, optionally supplemented with nitrous oxide. Simulation results, compared with published values for each drug, fell within the clinical accuracy range (onset time 6.1 ± 3.9% [mean ±SEM]; duration, 1.7 ±3.5%, 50% effective dose, 0.5 ±5.7%; and 95% effective dose, 2.1 ±1.1%). The simulation graphically demonstrates the pharmacokinetics, pharmacodynamics, and interactions between neuromuscular blocking agents, reversal agents, and anticholinergic agents. During a simulation, the need for frequent monitoring and repeated delivery of a neuromuscular blocking agent to keep neuromuscular blockade stable becomes apparent, especially with the intermediate-acting neuromuscular blocking agents. When inhalational agents are given concomitantly, the task becomes even more difficult, since potentiation changes with anesthetic uptake. Recurarization, tachycardia, or bradycardia may be seen with the simulation if an improper drug regimen is followed. Concurrent simulation of two identical patients allows comparison of different modes of administration, choice of anesthetic agents, and drug doses.     

Selective versus non-selective neural stimulation in the monitoring of muscular relaxation during general anesthesia

Aim. The depth of muscular relaxation during general anesthesia is monitored through the analysis of the contraction evoked by selective electrical stimulation of a peripheral nerve. The aim of this study was to compare the method of selective stimulation (SS) to a new method based on non-selective electrical stimulation (NSS) delivered over the muscle. Method. Electrical stimuli were delivered as train-of-four impulses to the ulnar nerve (SS) and to the ventral aspect of the contralateral forearm (NSS). The muscular responses of the adductor pollicis brevis (SS) and the forearm supinator longus (NSS) were studied at 30–60 s intervals with piezoelectric transducers before and after the administration of atracurium bolus doses of 0.5 mg/kg to patients under general anesthesia. SS and NSS evoked muscular responses were quantitized as percentages of the control response and compared with linear correlation and concordance analysis. Results. Twenty patients were studied. Basal and post-atracurium muscular responses were similar for the SS and the NSS methods. Precision between SS and NSS was > 85% and accuracy > 92%. Concordance was: basal < 15%, relaxation < 5%, recovery < 10%. Conclusion. NSS is equivalent to SS for muscular relaxation monitoring during general anesthesia. This has important implications to simplify muscular relaxation monitor design.     

Stabilization of the neuromuscular response when switching between different modes of nerve stimulation at surgical degrees of neuromuscular blockade

During general anesthesia, different modes of nerve stimulation are used for estimation of the degree of neuromuscular blockade. When switching between the different modes, it is important to know whether the preceding mode influences the responses to the succeeding mode, and, if so, for how long.The object of our study was to determine the number of stimulations required for stabilization of the muscular response when switching between double-burst stimulation (DBS) applied every 20 sec, train-of-four (TOF) applied every 12 sec, and posttetanic count (PTC) at surgical degrees of neuromuscular blockade.A total of 33 women were anesthetized with fentanyl, thiopental, halothane, and nitrous oxide. A constant degree of neuromuscular blockade was maintained at a twitch height of 4 to 11% of the control twitch height using a continuous infusion of atracurium.The ulnar nerve was stimulated supramaximally at the wrist, and the contraction in the adductor pollicis was measured mechanomyographically. At surgical degrees of neuromuscular blockade, only the first twitch response to TOF stimulation (T1) and the first twitch response to DBS stimulation (D1) are consistently present.When switching from DBS to TOF, 4 to 7 stimulations (56 to 92 sec) were required for stabilization of the T1 response. When switching from TOF to DBS, 3 stimulations (36 to 52 sec) were required for stabilization of the D1 response, and, finally, when switching from PTC to DBS, 5 to 11 stimulations (81 to 201 sec) were required for stabilization of the D1 response. Stabilization of D1 was faster following TOF than following PTC (p<0.01).We conclude that, when switching between different modes of nerve stimulation, the number of stimulations required for stabilization of the responses to the succeeding mode of stimulation depends on the preceding mode.     

An anesthesia information system for monitoring and record keeping during surgical anesthesia

We have developed an anesthesia information system (AIS) that supports the anesthesiologist in monitoring and recording during a surgical operation. In development of the system, emphasis was placed on providing an anesthesiologist-computer interface that can be adapted to typical situations during anesthesia and to individual user behavior. One main feature of this interface is the integration of the input and output of information. The only device for interaction between the anesthesiologist and the AIS is a touch-sensitive, high-resolution color display screen. The anesthesiologist enters information by touching virtual function keys displayed on the screen. A data window displays all data generated over time, such as automatically recorded vital signs, including blood pressure, heart rate, and rectal and esophageal temperatures, and manually entered variables, such as administered drugs, and ventilator settings. The information gathered by the AIS is presented on the cathode ray tube in several pages. A main distributor page gives an overall view of the content of every work page. A one-page record of the anesthesia is automatically plotted on a multicolor digital plotter during the operation. An example of the use of the AIS is presented from a field test of the system during which it was evaluated in the operating room without interfering with the ongoing operation. Medical staff who used the AIS imitated the anesthesiologist’s recording and information search behavior but did not have responsibility for the conduct of the anesthetic.     

New Equipment for Neuromuscular Transmission Monitoring: A Comparison of the TOF-Guard with the Myograph 2000

Objective. The present study is to clarify whether the bias and limits of agreement of the TOF-Guard and the mechanomyograph differ from those of two mechanomyographs on contra lateral arms. Previous studies of the bias and limits of agreement between acceleromyographical (TOF-Guard®) and mechanomyographical measurements of neuromuscular transmission did not take the error introduced by using contra lateral arms into consideration. Methods. Fifty-two women undergoing gynecological surgery were anesthetized with midazolam, fentanyl, thiopental, halothane and nitrous oxide. Neuromuscular blockade was induced and maintained with atracurium. In 32 patients, neuromuscular monitoring was performed with a Myograph 2000® on one hand and a TOF-Guard® at the other (M/T group). In 20 patients, monitoring was performed with a Myograph 2000® at both hands (M/M group). Train-of-four stimulations were applied to the ulnar nerve at the wrist in both groups. Bias and limits of agreement between the contra lateral hands in each group were calculated as proposed by Bland and Altman. Results. When the TOF ratio was 0.25, TOF ratio bias and limits of agreement in the M/T group were 0.86 and 17.58 to –15.85, respectively. Corresponding values in the M/M group were –1.75 and 12.3 to –8.8. Bias in the M/T group decreased significantly to –8.1 when TOF ratio increased to 0.70, resulting in limits of agreement of 12.1 to –28.4. The corresponding values in the M/M group were bias 2.0 and limits of agreement 10.7 to –6.7. TOF-Guard® bias for onset time and time to 5% recovery of T1 (first twitch in TOF) were –19 s and –1.5 min, respectively; both values differed significantly from zero (P < 0.05). Taken together with the changing TOF-ratio bias during recovery in the M/T group, these results indicate different onset and recovery curves for the two monitoring devices. Conclusions. Due to wide limits of agreement and different recovery courses, acceleromyographic and mechanomyographic recordings of neuromuscular transmission cannot be used interchangeably. The substantial variation between simultaneous mechanomyographical recordings of neuromuscular transmission obtained in contra lateral arms suggests that this factor should be taken into account when studying new neuromuscular monitoring techniques using the two-arm technique.     

Sampling intervals for clinical monitoring of variables during anesthesia

Although five minutes is the sampling interval mentioned by the American Society of Anesthesiologists for monitoring blood pressure and heart rate during anesthesia, most patients are monitored more closely by continuous auscultation and with the help of automated instruments. Yet this difference between the interval recommended and that actually used indicates that sampling intervals are not defined clearly enough. Therefore, we present three methods with which to determine sampling intervals during monitoring. To explore the feasibility of these methods we examined data gathered every 7.5 seconds during three typical, noncatastrophic physiologic perturbations induced in an anesthetized dog. We chose hypercapnia secondary to rebreathing, hypotension secondary to deep anesthesia, and hypoxemia secondary to a low concentration of inspired oxygen as realistic examples of what can occur during operation and anesthesia. We studied three variables: respired carbon dioxide, femoral arterial blood pressure, and oxygen saturation of hemoglobin (pulse oximeter). The data obtained during monitoring were subjected to three methods of analysis: (1) recording of sets of data, with various starting times, at five-minute intervals only (moving grid); (2) Fourier analysis; and (3) analysis of slopes. For the data of the experiment, the Fourier analysis yielded, on average, longer sampling intervals than did the analysis of slopes.     

A bolus plus continuous infusion protocol for controlling neuromuscular blockade during anesthesia

Neuromuscular blockade is controlled during anesthesia by administering either bolus doses or a continuous infusion of a blocking agent. To test whether a constant infusion technique requires less attention and provides better control we used a computer to simulate neuromuscular blockade. Using the model we maintained 95% blockade with mivacurium, atracurium, and vecuronium. It required 1.2 changes per hour to maintain the blockade by continuous infusion; an average of 4.5 bolus per hour were required to maintain blockade by the bolus technique. When the bolus and continuous infusion techniques were combined, only 0.16 changes per hour were required. Atracurium was then given to ten patients during anesthesia, following the bolus plus continuous infusion protocol. After a bolus was given to obtain 100% twitch depression, for tracheal intubation, neuromuscular function was assessed by train-of-four stimulation of the ulnar or facial nerves by observing the resultant muscle movement. When the first twitch of the train-of-four returned, relaxation was maintained by continuous infusion. A bolus was given and the drug infusion rate was changed whenever the level of relaxation changed from the desired one twitch of the train-of-four. The infusion rate was adjusted only 1.12±0.79 times per hour. The desired level of muscle relaxation was easily controlled using the bolus plus continuous infusion protocol. The infusion scheme might be implemented in future drug infusion pumps.     

Frequently repeated fick cardiac output measurements during anesthesia

A computer-based system was developed for monitoring cardiac output using the Fick principle during general anesthesia. The variables of the oxygen-consumption Fick equation were measured using the following system: oxygen uptake by an originally developed respiratory gas monitoring system, arteriovenous oxygen saturation difference by pulse and fiberoptic oximetry, and hemoglobin concentration by an in vitro oximeter. Fick cardiac output and systemic vascular resistance were calculated every 30 seconds. Fick cardiac output was compared with thermodilution cardiac output in 11 anesthetized patients. A total of 208 corresponding cardiac output measurements showed a range of 2 to 9 L · min^-1. The correlation coefficient between the thermodilution and Fick cardiac outputs was 0.961, with a regression equation of Fick cardiac output = 1.058 thermodilution cardiac output 0.359. The difference between the thermodilution and Fick cardiac outputs was 0.103 ± 0.395. The Fick cardiac output was significantly lower than the thermodilution cardiac output, especially in the low flow range. We demonstrated that this new monitoring system was clinically feasible and sufficiently accurate, under the limited circumstances of our study. The integration of routinely used equipment has made possible a frequently repcatable method for estimating cardiac output in patients.     

Effects of pulse duration on neuromuscular blockade monitoring: Implications for supramaximal stimulation

Questions have been raised concerning the reliability of surface electrodes in achieving supramaximal stimulation during the monitoring of neuromuscular blockade; needle electrodes are considered reliable in this respect. This study compares interelectrode impedances of needle and surface electrodes during neuromuscular blockade monitoring and suggests those characteristics of the stimulation pulse that can ensure reliable supramaximal stimulation with either type of electrode. Interelectrode voltage and current for surface and needle electrodes were measured by using 1.0-ms pulses at low, medium, and high stimulation levels on 22 surgical patients during anesthesia. Data were collected immediately after electrode application, and again at 10 minutes after application. Stimulation with surface electrodes produced an initial, transient surge of current, followed by a lower steady-state value. At high stimulation levels, the peak transient current was 87% higher than the steady-state current. Needle electrodes produced a constant high-current response. At high stimulation levels the transient impedance of the surface electrode and the impedance of the needle electrode were essentially equal (0.7 k and 0.75 k, respectively). The transient impedance was significantly lower (P<0.001) and was associated with less interpatient variation (P<0.001) and less sensitivity to the duration of electrode application than was the steady-state impedance of the surface electrode. These data suggest that high-current pulses with widths of less than 0.2 ms could provide reliable supramaximal stimulation with either type of electrode.     

Brief wakeful response to command indicates wakefulness with suppression of memory formation during surgical anesthesia

Objective. In a previous study of patients emerging from anesthesia following surgery, we found that a brief wakeful response to command of an eye opening or single hand squeeze or count was not associated with memory formation, while the response of four hand squeezes or counts was associated with memory. We wanted to determine the anesthetic requirements for obtaining this brief wakeful response endpoint during surgery and to determine if memory occurred at this endpoint during surgical anesthesia.Methods. Six different combinations of isoflurane, 70% N₂O, and fentanyl were administered to 326 patients undergoing pelvic laparoscopy. After insertion of the trocar, anesthesia was reduced while patients were given verbal commands, and they were observed for movement responses to surgery and to command. Patients were classified as either not arousing, arousing with a movement response to surgery, or arousing with a wakeful response to command. For the patients who aroused, we calculated the percentage of arousal responses that were wakeful responses to command. The effect of fentanyl dosage upon the percentage of arousal responses that were wakeful responses to command was determined by using a Mann-Whitney test to compare a group of patients receiving fentanyl 2 µg/kg or less, with a group receiving fentanyl 4 µg/kg. In a subset of 39 patients, the potential for memory formation was evaluated by presenting a target sound to 29 patients during a period of either no arousal, movement response to surgery, or wakeful response to command; for a control group of 10 patients, no target sound was presented. All 39 patients were tested for memory of the target sound; the results from each group receiving a target sound were compared with the results of the control group, using a Mann-Whitney test.Main Results. A total of 68 patients aroused with either a movement response or a wakeful response to command. Wakeful responses occurred with only 1 of 39 patients (3%) receiving fentanyl 2 µg/kg or less; but, wakeful responses occurred with 17 of 29 patients (59%) receiving fentanyl 4 µg/kg. The difference between the groups was significant atp=0.01. None of the 68 patients had recall of intraoperative events or unpleasant dreams. None of these patients who were in the multiple-choice memory subset recalled the target sound. There were no statistically significant differences on the multiple-choice memory test between the groups presented with the target sound and the control group. Patient anecdotes suggested that some patients may have had memory of the target sound; but, memory was no more likely in patients with a brief wakeful response to command than in those who responded with a movement to surgical stimulation or those who did not have an arousal response.Conclusions. A brief wakeful response to a command of opening the eyes or squeezing the hand was not associated with increased memory formation during surgery. A brief wakeful response to command was found during surgery when patients received fentanyl 4 µg/kg; but it was rarely found at fentanyl dosages of 2 µg/kg or less.     

Electroencephalographic mapping during isoflurane anesthesia for treatment of mental depression

Seven patients undergoing isoflurane anesthesia were studied using electroencephalographic (EEG) mapping, a computer-assisted technique of EEG processing that permits the analysis of the spatial distribution of frequency components of the human EEG. After induction with thiopental, the patients were hyperventilated (carbon dioxide tension, 25 to 28 mm Hg) with 4% isoflurane in oxygen until a burst-suppression EEG appeared. Brain electrical activity was compared before anesthesia, at 0.5 to 0.8% and 1.8 to 2.1% isoflurane, during bursts, and after anesthesia. Starting from an alpha EEG with occipital predominance, a distinct alpha activation appeared over the whole cortex during 0.5 to 0.8% isoflurane. Decreased alpha amplitude with a maximum over the frontotemporal regions was observed during 1.8 to 2.1% isoflurane. Bursts consisted of high amplitude in all frequency bands. In the delta and the theta bands, voltage was very low before isoflurane administration, and increased in relation to depth of anesthesia. A minimum in delta and theta amplitudes occurred over both central regions. The dominant frequency, defined as the frequency component with the highest amplitude in the frequency spectrum, decreased from 8 to 4 and finally to 1 Hz, while its amplitude increased from 3 to 13 µV. As anesthesia deepened, the dominant frequency shifted from the occiput to the frontal cortex.Brain mapping transfers an immense amount of electroencephalographic (EEG) data into a comprehensive, earsily readable image of brain function during anesthesia for therapy of mental depression. To make use of this technique in the operating room, further investigation and development toward on-line mapping are necessary.     

Placement of the pulmonary arterial catheter before anesthesia for cardiac surgery: Safe,intelligent, and appropriate use of invasive hemodynamic monitoring

Should one catheterize the pulmonary artery (PA) for cardiac surgery before or after induction of anesthesia? Issues of central importance to this question include (1) the patient’s preexisting hemodynamic abnormalities, (2) cardiovascular effects of anesthetic induction drugs, and (3) hemodynamic stress caused by laryngoscopy, cndotrachcal intubation, and PA catheter insertion. Some clinicians use the PA catheter immediately before anesthetic induction to detect and correct acute abnormalities in preload and ventricular function. This approach has been described as being partially responsible for decreased morbidity and mortality m patients with cardiovascular disease. Hemodynamic instability during induction has been reported with many of the common anesthetic induction agents, especially in patients with poor ventricular function. Since blood pressure is the product of cardiac output and systemic vascular resistance, accurate interpretation and treatment of hypotension are possible only when these variables are provided by vigorous use of the PA catheter. Early detection of myocardial ischemia is possible with examination of acute changes in the pulmonary capillary wedge pressure tracing. However, the lack of such information can restrict even the best anesthetist. Insertion of the PA catheter in the awake patient can be accomplished effectively and with minimal risk, so long as good patient rapport, adequate premedication, and continuation of antiangmal medication until the time of surgery are assured. Preinduction placement of the PA catheter provides valuable, objective information for the cardiac anesthesiologist without incurring significant risk to the patient.     

Double burst monitoring during surgical degrees of neuromuscular blockade: A comparison with train-of-four

With double burst stimulation (DBS) it is possible to monitor more profound degrees of neuromuscular blockade than with train-of-four stimulation (TOF). It may therefore be indicated to change between DBS and TOF stimulation during moderate to profound degrees of neuromuscular blockade. Consequently, the aim of the study was to evaluate and compare the twitch height of the first twitch (D1) in DBS and the twitch height of the first twitch (T1) in TOF stimulation during moderate to profound degrees of neuromuscular blockade. Thirty-three patients scheduled for gynaecological laparotomy under general anaesthesia were studied. Mechanomyography was used for neuromuscular monitoring. The T1 twitch height before atracurium was administered served as the control twitch height (T1 control). T1 control was considered as 100%. A constant degree of neuromuscular blockade was maintained at a T1 twitch height at a point between 4 and 11% of T1 control, using a continuous infusion of atracurium. Sequences of 16 DBS and 16 TOF stimulations were given. Two different DBS patterns were examined: DBS_3,350/50, (3 stimuli at 50 Hz followed 0.75 sec later by 3 stimuli at 50 Hz), and DBS_3,380/40, (3 stimuli at 80 Hz followed 0.75 sec later by 3 stimuli at 40 Hz). The data were analysed by the method described by Bland and Altman (1). The D1 repeatability coefficients of 1.72% for DBS_3,350/50 and 1.20% for DBS_3,380/40 were significantly greater than the repeatability coefficient of 1.02% for T1 (p<0.05). The D1 bias of 16.7% for DBS_3,350/50 was significantly less than the D1 bias of 25.7% for DBS_3,380/40 (p<0.05). The limits of agreement between D1 and T1 were 0.1 to 33.3% for DBS_3,350/50 and 2.9 to 48.5% for DBS_3,380/40. In conclusion: The repeatability of responses to DBS and TOF stimulations during moderate to profound degrees of neuromuscular blockade where only one twitch is consistently present is satisfactory. The responses to DBS were greater than responses to TOF as indicated by a positive bias of DBS. The limits of agreement between DBS and TOF responses were so wide that they cannot be used interchangeably.     

The microbiological risk of invasive hemodynamic monitoring in adults undergoing cardiac valve replacement

The microbiological risk of invasive hemodynamic monitoring was studied prospectively in 230 consecutive patients undergoing cardiac valve replacement during prophylactic therapy with cephalothin. A total of 923 catheter tips were cultured, and 1.6% yielded positive cultures. The rate of positive cultures did not differ significantly between catheters inserted percutaneously (1.9% positive) and those inserted surgically (0.5% positive).The incidence of positive catheter tip cultures for intravenous, central venous, arterial, and pulmonary arterial catheters was 0, 1.5, 2.6, and 2.9%, respectively, whereas the surgically inserted right and left atrial catheters yielded 0.6 and 0% positive tip cultures, respectively. One patient developed septicemia related to a right atrial catheter. There was no correlation between the incidence of positive catheter tip cultures and the length of time that the catheters remained in situ. No patient developed early or late endocarditis. Invasive hemodynamic monitoring seems to be microbiologically safe, even in patients undergoing cardiac valve replacement.     

Usefulness of epidurally evoked cortical potential monitoring during cervicomedullary glioma surgery

This report describes a patient with an intramedullary ependymoma at the region of the cervicomedullary junction in whom there was an abolition of somatosensory evoked potentials following median nerve stimulation. During intraoperative monitoring of cortical potentials elicited by epidural cervical cord stimulation, the tumor was removed. Posterior epidural stimulation appeared to depolarize more ascending fibers than did stimulation of a single peripheral nerve. We recommend that, in cases of operations in this vital area, epidurally evoked cortical potentials be monitored intraoperatively.