Is day surgery safe? A Danish multicentre study of morbidity after 57,709 day surgery procedures.

BACKGROUND: Day surgery is expanding in several countries, and it is important to collect information about quality. The aim of this study was to assess morbidity and unanticipated hospital visits 0-30 days post-operatively in a large cohort. METHODS: We prospectively recorded data from 57,709 day surgery procedures performed in eight day surgery centres over a 3-year period. We cross-checked with the National Patient Registry to identify complications 0-30 days post-operatively, and registrations from The Danish Register of Cause of Death were requested. We retrieved the records of 1174 patients to assign a relation between secondary contact and day surgery. RESULTS: The overall rate of return hospital visits was 1.21% [95% confidence interval (CI): 1.12-1.30%] caused by a wide range of diagnoses. No deaths were definitely related to day surgery. The return hospital visits were due to haemorrhage/haematoma 0.50% (95% CI: 0.44-0.56%), infection 0.44% (95% CI: 0.38-0 49%) and thromboembolic events 0.03%. Major morbidity was rare. The surgical procedures with the highest rate of complication were tonsillectomies 11.4%, surgically induced abortions 3.13% and inguinal hernia repairs 1.23%. CONCLUSION: This large-scale Danish national study confirmed that day surgery is associated with a very low rate of return hospital visits. Despite the rapid expansion of day surgery, safety has been maintained, major morbidity being very rare, and no deaths being definitely related to day surgery.

Comparison between local anaesthesia with remifentanil and total intravenous anaesthesia for operative hysteroscopic procedures in day surgery.

BACKGROUND: This study aimed at comparing total i.v. anaesthesia (TIVA) with monitored anaesthesia care (MAC) during day-surgery operative hysteroscopy regarding: operation time, time to mobilization and discharge, and patient satisfaction. METHODS: Ninety-one healthy women were randomized to MAC with paracervical local anaesthesia and remifentanil or to TIVA with propofol and remifentanil. Time from arrival to leaving the operating theatre, time from arrival in the recovery room to mobilization and discharge readiness, and patient satisfaction with MAC and TIVA were observed. RESULTS: Time from arrival to leaving the operating theatre showed no significant difference between groups (P=0.6). The time to mobilization {MAC: 53 min [inter-quartile range (IQR) 40-83], TIVA: 69 min (IQR 52-96) (P=0.017)} and the total time from arrival to discharge readiness [MAC: 118 min (IQR 95-139), TIVA: 138 (IQR 120-158) (P=0.0009)] were significantly reduced for patients in the MAC group. More patients in the MAC group 45 (91.8%) than in the TIVA group 24 (64.9%) responded positively to the question: would you like to receive the same kind of anaesthesia for a similar procedure in the future? (P=0.003). CONCLUSIONS: Paracervical local anaesthesia combined with remifentanil is suitable for operative hysteroscopy in day surgery.

Return hospital visits and morbidity within 60 days after day surgery: a retrospective study of 18,736 day surgical procedures.

BACKGROUND: As day surgery includes more extensive procedures focus should be put on late outcome. The frequency of day surgery-related return visits and the associated morbidity were examined to identify suitable indicators of quality. METHODS: From two centres, 16,048 patients underwent 18,736 day surgery operations including 4,829 surgical abortions. Patients were retrospectively analysed for contacts to Danish hospitals within 60 post-operative days and the associated morbidity and mortality. Data were obtained from the Danish National Patient Registry and the National Causes of Death Registry. Patient records were studied to validate contacts as being definite, likely, possible or not related. RESULTS: Altogether 113 patients (not including the surgical abortions) were readmitted to hospitals with 117 complications definitely or likely related to day surgery. The most common complications were haematomas or haemorrhage (0.40%) and infections (0.29%). Morbidity after the two most common procedures, hernia repair and knee arthroscopy, was observed in 1:39 patients and 1:220 patients, respectively. More serious complications included four patients with septic arthritis of the knee and six patients with venous thromboembolism. After surgical abortion, pelvic inflammation and bleeding were observed in 3.1% and 2.2%, respectively, with centre differences. Altogether no myocardial infarctions, central nervous system deficits, pneumonias or deaths were recorded that could definitely or likely be related to day surgery. CONCLUSION: Day surgery in Denmark is a safe practice. Readmission rates, haematomas and wound infections are likely future indicators of outcome quality after day surgery.

Intubation conditions after rocuronium or succinylcholine for rapid sequence induction with alfentanil and propofol in the emergency patient.

BACKGROUND AND OBJECTIVE: Previous studies mainly conducted on elective patients recommend doses of 0.9-1.2 mg kg[-1] rocuronium to obtain comparable intubation conditions with succinylcholine 1.0 mg kg[-1] after 60 s during a rapid-sequence induction. We decided to compare the overall intubating conditions of standard doses of rocuronium 0.6 mg kg[-1] and succinylcholine 1.0 mg kg[-1] during a strict rapid-sequence induction regimen including propofol and alfentanil. METHODS: Male and female patients (ASA I-III) older than 17 yr scheduled for emergency abdominal or gynaecological surgery and with increased risk of pulmonary aspiration of gastric content were randomized to a rapid-sequence induction with succinylcholine 1.0 mg kg[-1] or rocuronium 0.6 mg kg[-1]. Patients with a predicted difficult airway were excluded. A senior anaesthesiologist 'blinded' for the randomization performed the intubation 60 s after injection of the neuromuscular blocker. Intubating conditions were evaluated according to an established guideline. Tracheal intubation not completed within 30 s was recorded as failed. RESULTS: 222 patients were randomized. Three patients had their operation cancelled and 10 did not fulfil the inclusion criteria. Clinically acceptable intubation conditions were present in 93.5% and 96.1% of patients in the succinylcholine group (n=107) and the rocuronium group (n=102), respectively (P=0.59). CONCLUSIONS: During a rapid-sequence induction with alfentanil and propofol, both rocuronium 0.6 mg kg[-1] and succinylcholine 1.0 mg kg[-1] provide clinically acceptable intubation conditions in 60 s in patients scheduled for emergency surgery. Under the conditions of this rapid-sequence induction regimen rocuronium may be a substitute for succinylcholine.

Remifentanil vs. alfentanil infusion in non-paralysed patients: a randomized, double-blind study.

BACKGROUND AND OBJECTIVE: Remifentanil has a short duration of action and constant elimination, which allow administration of high doses, without prolonging recovery. Remifentanil has been compared to alfentanil, as part of a total intravenous anaesthetic technique, where remifentanil provided better anaesthetic conditions than alfentanil, without adverse effect on recovery. However, these results were obtained during anaesthesia involving neuromuscular blockade, which may mask both signs of insufficient anaesthesia and side-effects such as muscle rigidity. The aim of this study was to compare remifentanil with alfentanil for anaesthesia without neuromuscular blockade. METHODS: We performed a prospective, randomized, double-blind, four-centre study to compare remifentanil infusion 15 microg kg(-1) h(-1) and alfentanil infusion 60 microg kg(-1) h(-1), using a total intravenous technique for non-paralysed patients, and the laryngeal mask airway for airway management. We enrolled 192 patients, 18-65 yr of age with ASA I-II, undergoing minor surgery. The primary endpoint was the number of patients having pre-defined responses to surgical stimulation. A number of secondary criteria was evaluated to assess undesirable properties of the procedures. RESULTS: In the alfentanil group, 85% of patients responded to surgical stimulation, vs. 35% in the remifentanil group (P < 0.0001). No difference was found in recovery data, or in any other parameter than those related to insufficient anaesthesia. CONCLUSIONS: The remifentanil-based technique provided significantly better anaesthetic conditions than the alfentanil-based technique in the setting of this study, without causing any significant adverse effects.

Acceleromyography of the orbicularis oculi muscle I: significance of the electrode position.

BACKGROUND: This study aimed to establish the best position of the stimulating electrodes for facial nerve stimulation during acceleromyographic monitoring from the orbital part of the orbicularis oculi muscle. METHODS: In 59 anaesthetised patients, an acceleration transducer was positioned over the middle of the eyebrow. In 47 patients, supramaximal train-of-four (TOF) stimulation was established for four electrode pairs with different positions along the facial nerve and behind the ear. The electrode pair with the lowest, the intermediate, and the highest supramaximal stimulating current based on first response (T1) in TOF was found in each patient. A possible response from direct muscle stimulation was evaluated during complete vecuronium block. In 12 patients, supramaximal stimulation was established using a stimulation sequence different from the one used in the first part of the study. RESULTS: The best positions for the stimulating electrodes were either with both electrodes just lateral to the eye, or with one electrode lateral to the eye and one in front of the ear. In most patients, supramaximal stimulation was obtained at these positions at 20-60 mA. However, in 10-21% of the patients, supramaximal stimulation could not be obtained. During complete block, 1-4 responses with a twitch height of 3-11% were recorded in 80% of the patients. CONCLUSION: The best placements of the stimulation electrodes are either just lateral to the eye or along the zygomatic arch. However, supramaximal stimulation may often not be obtainable, and activation of other facial muscles may be a confounding factor that may impede correct evaluation of the degree of neuromuscular block.

Acceleromyography of the orbicularis oculi muscle II: comparing the orbicularis oculi and adductor pollicis muscles.

BACKGROUND: The orbicularis oculi (OO) muscle has been recommended for neuromuscular monitoring when the adductor pollicis (AP) muscle is not available. We investigated whether neuromuscular block could be measured reliably from the orbital part of the OO muscle by the use of acceleromyography. METHODS: During propofol, fentanyl, and alfentanil anaesthesia two TOF-Guards (Organon Teknika NV, Boxtel, the Netherlands) with acceleration transducers placed on the distal phalanx of the thumb and over the middle of the eyebrow, respectively, were used to measure neuromuscular block simultaneously in 23 patients during vecuronium-induced and neostigmine-antagonized neuromuscular block. For both muscles, the simultaneously recorded first response (T1) in the train-of-four (TOF) and TOF-ratio were measured both during onset and recovery of the block. Furthermore, both the AP muscle T1 and TOF-ratio responses were plotted against 10% intervals of the OO muscle responses during onset and recovery, respectively. RESULTS: The orbicularis oculi muscle had a shorter latency and a faster recovery to TOF-ratio 0.80 compared with the AP muscle. During onset and recovery, pronounced variations of the AP muscle T1 and TOF-ratio responses were observed when compared with the OO muscle. CONCLUSION: A significant clinical disagreement exists between the degree of paralysis measured at the OO and the AP muscles. It is impossible to obtain a reasonable estimate of the degree of block at the AP muscle when the block is measured from the OO muscle with acceleromyography. If used, there is substantial risk of overlooking a residual block, and adequate recovery of the block should be confirmed by a final AP muscle measurement.

Rapacuronium 2.0 or 2.5 mg kg-1 for rapid-sequence induction: comparison with succinylcholine 1.0 mg kg-1.

The purpose of this nine-centre study in 602 patients was to show that the frequency of acceptable intubating conditions after rapacuronium 2.0 or 2.5 mg kg-1 is not more than 10% lower than the frequency after succinylcholine 1.0 mg kg-1 during rapid-sequence induction of anaesthesia with fentanyl 1-2 micrograms kg-1 and thiopental 2-7 mg kg-1. Laryngoscopy and intubation were carried out 60 s after administration of muscle relaxant by an anaesthetist blinded to its identity. Intubating conditions were clinically acceptable (excellent or good) in 91.8% of patients given succinylcholine and in 84.1 and 87.6% of patients given rapacuronium 2.0 and 2.5 mg kg-1 respectively. With respect to the percentage of clinically acceptable intubating conditions, the estimated difference (and the upper limit of the one-sided 97.5% confidence interval) between succinylcholine and rapacuronium 2.0 mg kg-1 was 7.8 (14.4)% and between succinylcholine and rapacuronium 2.5 mg kg-1 it was 4.0 (10.2)%. For both comparisons, the upper limit of the one-sided confidence interval exceeded the predefined 10% difference. Hence, it could not be demonstrated that the intubating conditions with either of the two doses of rapacuronium were not inferior to those with succinylcholine 1.0 mg kg-1. The increase in heart rate was significantly greater during the first 5 min in the rapacuronium groups, but the arterial pressure increased significantly only in the succinylcholine group (P < 0.001). Respiratory side-effects were observed in 4.0, 13.5 and 18.5% of patients after succinylcholine and rapacuronium 2.0 and 2.5 mg kg-1 respectively (P < 0.05). As the non-inferiority of intubating conditions after rapacuronium 2.0 and 2.5 mg kg-1 could not be proven, succinylcholine should be considered the neuromuscular blocking agent that provides better intubating conditions for rapid-sequence induction.

Postoperative pain control by epidural analgesia after transabdominal surgery. Efficacy and problems encountered in daily routine.

BACKGROUND: The efficacy of postoperative epidural pain treatment has been well documented in controlled studies. However, the literature concerning results of daily routine use of this method often only emphasises certain aspects of it. METHODS: A prospective study of 168 patients scheduled for major surgery with transabdominal access was performed in order to evaluate efficacy, side effects, complications and rate of acceptance of postoperative epidural pain treatment. The epidural catheter was placed before surgery and the patients received epidural analgesia by a bupivacaine/morphine mixture for 3 days postoperatively, continued by another 3 days with bolus injections of morphine only. RESULTS: Only few complications followed the insertion of the epidural catheter, but in about 16% of the patients the epidural catheter or the drugs administered by it made reinsertion or change in the type of analgesia necessary during the first 3 post-operative days. Despite the possibility for individualising the treatment and p.r.n. analgesics, pain relief when coughing and moving during day 1-3 was insufficient in 30-50% of the patients. Serious side effects were rare, but pruritus was frequent, as were the symptoms of nausea and vomiting. The patients were generally satisfied with the treatment; however, a small group had unacceptable pain when the epidural catheter was inserted. CONCLUSION: Analgesia was insufficient when coughing and moving in an unacceptably large number of the patients. Also the number of epidural catheter related problems was high. In order to make early intervention possible, the patients and epidural catheters should be observed daily and systematically by members of the staff competent to detect possible problems.

[Information, satisfaction and anxiety in connection with anesthesia. A questionnaire study]. / Information, tilfredshed og angst ved anaestesi. En spørgeskemaundersøgelse.

The purpose of the study was to assess the level of information, anxiety and satisfaction with treatment and care among patients undergoing general anaesthesia. A questionnaire was answered by 406 patients. Seventeen criteria comprising various aspects of the total course of anaesthesia were defined to characterise a "satisfactory anaesthetic experience". After the preoperative visit 65% of the nervous patients were less nervous. Only 47% were informed of possible postanaesthetic side effects. Although 86% were "satisfied" with the treatment and care, only 36% met the criteria of satisfaction. The main problems were anxiety (especially fear of not waking up again), nausea and pain after waking up. We conclude that patients are not told enough about anaesthesia and side effects. Many patients, particularly the younger patients and the female patients, are afraid of anaesthesia.

Residual neuromuscular block is a risk factor for postoperative pulmonary complications. A prospective, randomised, and blinded study of postoperative pulmonary complications after atracurium, vecuronium and pancuronium.

BACKGROUND: After anaesthesia involving pancuronium a high incidence of both residual neuromuscular block and postoperative pulmonary complications (POPC) has been reported. The aim of this study was to compare the incidence of POPC following the use of pancuronium, atracurium, and vecuronium, and to examine the effect of residual neuromuscular block on the incidence of POPC. METHODS: A total of 691 adult patients undergoing abdominal, gynaecological, or orthopaedic surgery under general anaesthesia were randomised to receive either pancuronium, atracurium, or vecuronium. Perioperatively, the response to train-of-four (TOF) nerve stimulation was evaluated manually. Postoperatively, the TOF ratios were measured mechanomyographically, and through a 6-day follow-up the patients were examined for pulmonary complications. RESULTS: The incidence of residual block, defined as a TOF ratio < 0.7, was significantly higher in the pancuronium group (59/226: 26%) than in the atracurium/vecuronium groups (24/450: 5.3%). In the pancuronium group, significantly more patients with residual block developed POPC (10/59: 16.9%) as compared to patients without residual block (8/167: 4.8%). In the atracurium/vecuronium groups, the incidence of POPC was not significantly different in patients with (1/24: 4.2%) or without (23/426: 5.4%) residual block. Multiple regression analysis indicated that abdominal surgery, age, long-lasting surgery, and a TOF ratio < 0.7 following the use of pancuronium were potential risk factors for the development of POPC. CONCLUSION: Postoperative residual block caused by pancuronium is a significant risk factor for development of POPC.

The effect of succinylcholine on atracurium-induced neuromuscular block.

BACKGROUND: The interaction between prior succinylcholine and atracurium has been found only after full recovery of succinylcholine block. We investigated whether the effect of succinylcholine on atracurium block may depend on the level of recovery from succinylcholine. METHODS: Fifty patients in 4 groups received atracurium 0.2 mg/kg when first response (T1) in train-of-four (TOF) after succinylcholine 1 mg/kg had recovered to 5%, 25%, 75% or 100%. A control group received only atracurium. The following indices were compared: the time from injection of atracurium to maximum block (onset time) and to return of T1 to 25% (duration 25%), maximal depression of T1, time from 25% to 75% recovery of T1 (interval 25-75%) and time from injection of atracurium to a TOF ratio of 0.75 (duration TOF 0.75). RESULTS: Onset time was shorter, max T1 depression was greater and duration 25% increased the more succinylcholine recovery progressed. Neither interval 25-75% nor duration TOF 0.75 varied with the level of recovery from succinylcholine. The control group showed a shorter latency and onset time compared to the early (5%) recovery group and a longer onset time and less depressed T1 compared to the late (100%) recovery group. There was no difference between the control group and the early or late recovery groups, respectively for duration 25% or duration TOF 0.75. CONCLUSION: The effect of prior administration of succinylcholine on atracurium block depends on the state of recovery from succinylcholine and concerns both its potency, onset and duration characteristics.

Monitoring of neuromuscular transmission by electromyography during anaesthesia. A comparison with mechanomyography in cat and man.

In this study the applicability of the electromyographical method for monitoring neuromuscular transmission during anaesthesia has been investigated. The purpose was to determine the stability and temperature dependence of the EMG and to evaluate and compare EMG area, amplitude and duration during a non-depolarizing neuromuscular block in the tibialis anterior muscle preparation of the cat. Further, in clinical studies the purpose was to investigate differential hand muscle sensitivity to non-depolarizing neuromuscular blocking agents based on the EMG and the standard adductor pollicis mechanomyogram, and to establish the agreement between the electromyographical and the mechanomyographical methods and their relationship to clinical parameters of residual neuromuscular block. For this purpose a new monitoring equipment was developed for simultaneous recording of the evoked mechanomyogram and the surface compound EMG area, amplitude and duration. In the animal studies the EMG was found to be stable with changes less than 10% during 3 hours of stimulation and with a high degree of reproducibility. In contrast, the mechanomyogram proved unstable over time with changes of 35-50% (positive staircase) within minutes after onset of stimulation followed by a slower decline of the response to 70-75% of control. An inverse relationship was found between temperature and both the mechanomyogram and the EMG, the EMG area and duration being more affected (5-7% per degrees C) than EMG amplitude (2-3% per degrees C). During onset and recovery from non-depolarizing neuromuscular block, EMG area and amplitude of the first major negative deflection and of the total compound response both reflected neuromuscular transmission equally. The EMG duration was found to be unsuitable as a predictor of neuromuscular block. In the clinical studies of the hand muscles (adductor pollicis, hypothenar and first dorsal interosseous muscles) small but clinically insignificant differences in EMG-based sensitivity to pancuronium were observed. There was no difference between EMG area and amplitude in the estimated effective doses of pancuronium and roctronium producing 50% and 90% block, respectively (ED50 and ED90), but EMG-based sensitivity of the adductor pollicis muscle was less than when based on mechanomyography. Comparative analysis of first dorsal interosseous EMG and adductor pollicis mechanomyogram during non-depolarizing neuromuscular block was based on the concept of bias (mean difference between the results by the two methods) and limits of agreement (an estimation of how much results obtained with one method are likely to differ from the results of the other method) and evaluated during TOF nerve stimulation. The two methods agreed within acceptable limits during neuromuscular block with estimated bias being less than 2% during onset. A variable bias of 3-7% was observed during recovery, with EMG overestimating block at 25% recovery and underestimating block at 75% and 90% recovery. Limits of agreement were more narrow during onset (+/- 7-8%) than during recovery (+/- 12-17%), EMG area and amplitude equally reflected the degree of neuromascular block. First dorsal interosseous EMG TOF ratio recovered more slowly than TOF ratio of the adductor pollicis mechanomyogram during early recovery. The relationship between the two methods was described as being log-linear, and during late recovery bias between the TOF ratios of the two methods was zero. However, due to the range of deviations between the EMG and the mechanomyogram, EMG TOF ratios down to 0.55 or up to 0.90 in some patients were found to be compatible with adequate recovery of a mechanomyographical TOF ratio of 0.75. Differences between electromyographical and mechanomyographical TOF ratios in their relation to 5 s sustained headlift were only revealed when the TOF ratio was below 0.50-0.60. More patients were then able to perform the test if the TOF ratio was measured from the EMG.(ABSTRACT T

Good clinical research practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents.

Based on an international consensus conference held in Copenhagen in the autumn of 1994, a set of guidelines for Good Clinical Research Practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents are presented. The guidelines are intended to be a help for people working in this research field, and it is hoped that the guidelines will assist researchers, editors, and drug companies to enhance the quality of their pharmacodynamic studies of neuromuscular blocking agents.

The agreement between adductor pollicis mechanomyogram and first dorsal interosseous electromyogram. A pharmacodynamic study of rocuronium and vecuronium.

The agreement between evoked adductor pollicis mechanomyogram and first dorsal interosseous evoked electromyogram (EMG) was evaluated during a pharmacodynamic study of rocuronium and vecuronium. In the first place the effective doses of rocuronium producing 50% and 90% block (ED50 and ED90, respectively) were established in 32 neurolept anaesthetized patients from the adductor pollicis mechanomyogram and the first dorsal interosseous EMG area and amplitude. Secondly, limits of agreement between the two methods were evaluated from the mean difference between methods +/- 2 s.d. in 20 patients during onset of block following 2 x ED90 of rocuronium and vecuronium, and during recovery from the last supplementary dose of 1/2 x ED90. Limits of agreement show how much the EMG may be above or below the mechanomyogram. No differences were found between mechanomyographical and EMG based ED50 (0.20 mg kg-1) and ED90 (0.30-0.32 mg kg-1), respectively. The first EMG train-of-four (TOF) response overestimated block at 25% recovery and underestimated block at 75% and 90% recovery by only 3-7%. Limits of agreement suggested that the EMG may be 7-8% above or below the mechanomyogram during onset compared to 12-17% during recovery. The EMG TOF ratio lagged behind that of the mechanomyogram by 0.05 at TOF ratios below 0.50. No difference was found between methods at a TOF ratio of 0.75. Limits of agreement indicated that the EMG TOF ratio may be 0.12-0.15 above or below that of the mechanomyogram. Agreement between the amplitude and the area of the EMG were better than between the mechanomyogram and the EMG. Evaluation of the time courses of action showed that rocuronium had a faster onset of action than vecuronium (1.8 min compared to 2.8 min) while duration of action and reversal were similar. In conclusion, the first dorsal interosseous EMG amplitude and area can be used to assess rocuronium and vecuronium block.

Monitoring of neuromuscular transmission.

Considerable advances have been achieved in developing new techniques and equipment for the assessment of neuromuscular transmission during anaesthesia. This paper is a review of the methods currently used in research as well as in daily clinical practice. The principles of nerve stimulation and the evoked muscular response, the function of the nerve stimulator, features of the stimulation electrodes, possible stimulation sites, and the various stimulation patterns with their responses are described. The methods for measurement of neuromuscular function with mechanomyography, electromyography and acceleromyography are reviewed, and commercially available equipment for each purpose is described. The clinical evaluation of the responses to nerve stimulation, and which stimulation patterns to prefer during onset, maintenance and recovery of neuromuscular block are dealt with, as well as possible errors to be encountered. Arguments are given for routine use of neuromuscular monitoring in the clinical setting, and situations where monitoring of neuromuscular function are of particular importance are noted.

Monitoring of neuromuscular transmission by electromyography (II). Evoked compound EMG area, amplitude and duration compared to mechanical twitch recording during onset and recovery of pancuronium-induced blockade in the cat.

The feasibility of the compound electromyogram (EMG) was evaluated during onset and recovery from pancuronium block in the tibialis anterior muscle of ten cats. The evoked EMG area, amplitude and duration of the total response and of the major negative deflection were evaluated and compared to the mechanomyogram during 0.1 Hz and train-of-four (TOF) stimulation. EMG areas and amplitudes were found to be linearly and similarly related to the mechanomyogram during onset and recovery. Slopes of the regression lines ranged between 1.00-1.02 and between 1.10-1.22 during onset and recovery, respectively, with high individual correlation coefficients (> 0.95). The TOF ratio of the mechanomyogram was linearly related to the EMG TOF ratio during onset and to the square root of the EMG TOF ratio during recovery, with no differences between EMG areas and amplitudes, suggesting a higher initial recovery of the TOF ratio of the mechanomyogram during recovery. EMG duration increased as the level of block increased but was unsuitable for neuromuscular monitoring. Evaluation of the agreement between the two methods showed that the EMG may be from 15% below to 10% above the mechanomyogram during onset and from 40% below to 45% above the mechanomyogram during recovery, in spite of high correlation coefficients. In contrast, agreement between EMG parameters was found to be high. In conclusion, EMG is more reliable than the mechanomyogram for evaluation of neuromuscular transmission in the cat. EMG amplitudes and areas both reflect the degree of neuromuscular blockade equally well.