Remifentanil update: clinical science and utility

Analgesia during abdominal aortic aneurysm endovascular repair: remifentanil vs. fentanyl-midazolam--a randomized controlled trial

BACKGROUND AND OBJECTIVE

Endovascular repair offers a less surgically invasive procedure for abdominal aortic aneurysms but nevertheless, still requires analgesic sedative cover to ensure an acceptable level of patient comfort and cardiorespiratory stability. The peculiarity of this kind of operation is that painful stimuli are concentrated in specific moments separated by intervals devoid of pain, so the insurgence of pain can be predicted and prevented with a bolus of analgesic, making a continuous infusion not essential, but potentially useful in achieving a better analgesic stability. The primary objective of the study was pain control measured by Visual Analogue Scale; secondary endpoints were cardiorespiratory stability and an acceptable level of sedation.

METHODS

The sedative analgesic protocols of two groups of randomly allocated patients, undergoing abdominal aortic aneurysm endovascular repair, were compared. The experimental group received remifentanil infusion (0.03-0.1 microg kg min) and the control group received intravenous doses of fentanyl and midazolam (1-3 microg kg and 0.05-0.1 mg kg, respectively).

RESULTS

Fifty patients were investigated out of 60 enrolled. There were no relevant differences concerning cardiorespiratory stability and level of sedation, but pain levels were significantly lower in the experimental group: mean Visual Analogue Scale 0.35+/-0.40 vs. 1.49+/-0.62 (P<0.001) and area under the curve 17.48+/-5.09 vs. 33.05+/-8.19 (P<0.001).

CONCLUSION

Both techniques were shown to be safe and most importantly effective in offering cardiovascular stability and analgesia for American Society of Anaesthesiologists III-IV patients undergoing endovascular abdominal aortic aneurysm repair. However, remifentanil continuous infusion proved to offer significantly more stable pain control compared with the currently used combination fentanyl-midazolam.

The hemodynamic changes during the infusion of remifentanil for patients under sevoflurane anesthesia during arthroscopic shoulder surgery

BACKGROUND

In spite of its minimal invasiveness, hemodynamic instability frequently happens during arthroscopic procedures. This study was performed to investigate the clinical efficacy of remifentanil for controlling the intra-operative hemodynamics during the performance of arthroscopic shoulder surgery.

METHODS

Sixty patients (ASA class 1 and 2) who were scheduled for arthroscopic shoulder surgery were recruited for this study. After the induction and maintenance of anesthesia with thiopental sodium, rocuronium bromide, sevoflurane and nitrous oxide, the patients were randomly allocated to receive either saline or three different doses of remifentanil (0.03, 0.05 or 0.07 microg/kg/min) to assess the hemodynamic changes such as the systolic blood pressure, the diastolic blood pressure and the heart rate.

RESULTS

The hemodynamics in the remifentanil groups were more stable than those in the saline group (P < 0.05), but there were some cardiovascular side effects such as hypertension (remifentanil 0.03 microg/kg/min), hypotension and bradycardia (remifentanil 0.07 microg/kg/min) with using remifentanil.

CONCLUSIONS

Remifentanil 0.05 microg/kg/min under anesthetic maintenance with sevoflurane showed better hemodynamic stability than the other two remifentanil groups during arthroscopic shoulder surgery.

Mini-series: II. clinical aspects. clinically relevant CYP450-mediated drug interactions in the ICU

BACKGROUND

In the critically ill, multiple drug therapies for acute and chronic conditions are often used at the same time and adverse drug events occur frequently. Many pharmacological and disease-related factors, e.g. altered renal and hepatic function, catecholamine-related circulatory changes, altered drug volume of distribution, enteral versus parenteral feeding and morbid obesity, along with concomitant multiple drug regimens may account for the wide inter-individual variability in drug exposure and response in critically ill patients and for the high risk for drug-drug interactions to occur. The practicing intensivist must remain aware of the major mechanisms for drug-drug interactions, among which the drug-metabolizing enzyme inhibitory or induction potential of associated chemical entities are paramount. Metabolism-based drug-drug interactions are largely due to changes in levels of drug-metabolizing enzymes caused by one drug, leading to changes in the systemic exposure clearance of another. Among the numerous drug-metabolizing enzymes identified to date, the activity of cytochrome P450s (CYP450) is a critical determinant of drug clearance and appears to be involved in the mechanism of numerous clinically relevant drug-drug interactions observed in critically ill patients.

DISCUSSION

This manuscript will cover a practical overview of clinically relevant CYP450-mediated drug-drug interactions. Medications frequently used in the intensive care unit such as benzodiazepines, immunosuppressive agents, opioid analgesics, certain anticonvulsants, the azoles and macrolides have the potential to interact with CYP450-mediated metabolism and may lead to toxicity or therapeutic failure.

Remifentanil for postoperative patient-controlled analgesia after laparoscopic-assisted vaginal hysterectomy: dose-finding study

BACKGROUND

This randomized, double-blinded clinical study was designed to compare the efficacy and safety of three regimens of intravenous (IV) patient-controlled analgesia (PCA) with remifentanil for postoperative analgesia after laparoscopic-assisted vaginal hysterectomy during the first 24 postoperative hours.

METHODS

Thirty-four patients were randomly allocated into three groups. The first group received IV remifentanil PCA at a basal rate of 0.02 microgram/kg/min, a bolus of 0.3 microgram/kg, and a lockout time of 15 min. The second group received IV-PCA at a basal rate of 0.025 microgram/kg/min, a bolus of 0.375 microgram/kg, and a lockout time of 15 min. The third group received IV-PCA at a basal rate of 0.03 microgram/kg/min, a bolus of 0.45 microgram/kg, and a lockout time of 15 min. Age, weight, height, and duration of surgery and anesthesia were recorded. Heart rate, systolic and diastolic blood pressure (BP) and oxygen saturation by pulse oxymetry were recorded in the recovery room as a base line after the operation. Heart rate, systolic and diastolic BP, sedation score, visual analogue scale (VAS), and postoperative nausea and vomiting (PONV) scores were recorded at 1 h, 3 h, 6 h, 12 h, and 24 h after the initiation of IV-PCA.

RESULTS

Thirty two patients were evaluated. The VAS in group 1 at 1, 3 and 6 hours after surgery was significantly higher than in other groups (P < 0.05). There were no clinically relevant differences between the groups in PONV, sedation scores, or hemodynamic parameters.

CONCLUSIONS

This study suggests that IV remifentanil PCA with at a basal rate of 0.025 microgramram/kg/min (group 2) provided efficacious analgesia after laparoscopic-assisted vaginal hysterectomy. Special attention must be given to respiratory depression during establishment of PCA with remifentanil.

The effects of age and sex on electroconvulsive therapy using remifentanil as the sole anesthetic agent

OBJECTIVE

This study examines electroencephalographic (EEG) and motor seizure duration and dynamic energy according to age and sex using remifentanil anesthesia in standard electroconvulsive therapy (ECT).

BACKGROUND

In an earlier study, we showed that remifentanil provides superior anesthesia for ECT in terms of providing adequate seizure duration with lower stimulus doses in patients refractory to maximal ECT settings with methohexital.

METHODS

Patients, refractory to maximal ECT settings with methohexital, received remifentanil as the sole anesthetic agent. Stimulus dose was determined by the dose-titration method. Electroencephalographic seizure duration, motor seizure duration, and dynamic energy in joules (j) were compared between male and female subjects and among patients aged 40 years or younger, older than 40 years but aged 65 years or younger, and older than 65 years.

RESULTS

Seventy-two patients were included in the study. There was no significant difference in remifentanil doses between female and male subjects. There was no significant statistical difference between female and male subjects regarding motor seizure duration, EEG seizure duration, or dynamic energy (P > 0.05). There were significant statistical differences among different groups in terms of motor seizure duration, EEG seizure duration, and dynamic energy (P< 0.05). The younger age group had longer motor and EEG seizure durations and required lower dynamic energy.

CONCLUSIONS

There is no significant effect of sex on ECT with remifentanil anesthesia regarding EEG or motor seizure durations or dynamic energy; however, statistically significant differences were observed based upon age. Younger patients had both increased motor and EEG seizure duration compared with older patients who may require higher stimulus doses than younger patients for comparable motor and EEG seizure durations.

Medications for analgesia and sedation in the intensive care unit: an overview

Critically ill patients are often treated with continuous intravenous infusions of sedative drugs. However, this is associated with high risk for over-sedation, which can result in prolonged stay in the intensive care unit. Recently introduced protocols (daily interruption and analgosedation) have proven to reduce the length of intensive care unit stay. To introduce these protocols, new agents or new regimens with the well established agents may be required. In this article we briefly discuss these new regimens and new agents, focusing on the short-acting substances.

Remifentanil-TCI and propofol-TCI for conscious sedation during fibreoptic intubation in the acromegalic patient

BACKGROUND AND OBJECTIVE

To evaluate the use of remifentanil-propofol administered as target-controlled infusion during awake fibreoptic intubation for anticipated difficult tracheal intubation in acromegalic patients.

METHOD

In all, 20 consecutive acromegalic patients underwent elective endonasal endoscopic transsphenoidal pituitary surgery. After premedication with midazolam 0.03 mg kg(-1), initially a target-controlled infusion of remifentanil 1.0 ng mL(-1) and propofol 1.5 microg mL(-1) was started. The fibreoptic intubation was performed by the same physician experienced with the fibreoptic technique. During the fibreoptic procedure the target concentrations of remifentanil and propofol ranged between 1.0 and 5.0 ng mL(-1), and between 1.5 and 3.5 microg mL(-1), respectively. Changes in heart rate and mean arterial pressure were recorded during airway manipulation, during tracheal intubation, and at 1 and 3 min after. On the first postoperative day, patient recall and level of discomfort during fibreoptic intubation were evaluated.

RESULTS

Endotracheal intubation was efficaciously and quickly secured in all patients. A significant increase in mean arterial pressure and heart rate was recorded only during tracheal intubation (P < 0.05). Oxygenation was sufficient and no bradypnea or apnoea was recorded. All patients later described their anaesthetic experience as satisfactory. During fibreoptic intubation, remifentanil (ng mL(-1)) and propofol (microg mL(-1)) mean effect-site concentrations were 3.2 +/- 0.3 and 2.0 +/- 1.0, respectively.

CONCLUSION

Remifentanil and propofol target-controlled infusion provided satisfactory conscious sedation allowing for successful oral fibreoptic intubation in acromegalic patients with no recall.

Emotional perception modulated by an opioid and a cholecystokinin agonist

RATIONALE

The cholecystokinin (CCK) and opioid neuromodulatory systems work in an antagonistic fashion and can modulate emotional states and noxious input in opposite directions. In this behavioral study, we generalize this idea and suggest that CCK and opioids can modulate the processing of other external signals, e.g., visual stimuli rather than only noxious input.

OBJECTIVES

The objective of this study was to determine whether CCK and an opioid agonist could modulate the emotional experience of visual stimuli.

MATERIALS AND METHODS

Thirteen healthy male volunteers viewed standardized pictures with either neutral or unpleasant content. Simultaneously, one of three treatments was administered in a randomized, double-blind crossover design: the CCKb receptor agonist pentagastrin (0.1 microg/kg), the mu-opioid receptor agonist remifentanil (0.0625 microg/kg), or saline. Self-ratings of the emotional experience of pictures and drugs were sampled together with psychological tests and recording of heart rate.

RESULTS

Pentagastrin treatment increased the rating of unpleasantness for both neutral and unpleasant pictures, while it decreased the rating of pleasantness for the neutral pictures. These effects did not correlate with the degree of general unpleasantness induced by the drug. Remifentanil treatment increased the pleasantness for the neutral pictures. While pentagastrin treatment induced a heart rate increase, unpleasant pictures induced a heart rate decrease, and the magnitude of change in heart rate correlated positively for these conditions.

CONCLUSIONS

This study shows that the CCK and the opioid system modulate how external stimuli are emotionally perceived, suggesting a possible involvement in affective disorders.

Remifentanil and etomidate for laryngeal mask airway insertion

Etomidate does not depress the upper airway reflexes, making it difficult to insert a laryngeal mask airway (LMA) when using it for anaesthesia. This study investigated the effect of adding remifentanil to etomidate for LMA insertion. Fifty adult patients, undergoing cystoscopy, were randomized to two groups. The propofol-remifentanil group (n=25) received propofol anaesthesia induction (2.5 mg/kg) and a remifentanil bolus of 0.5 microg/kg, followed by a 2-min remifentanil infusion of 0.05 microg/kg per min. The etomidate-remifentanil group (n=25) received etomidate anaesthesia induction (0.3 mg/kg) and remifentanil as described. The LMA was inserted by a blinded anaesthetist who assessed a number of parameters. Only 13 LMAs were inserted at the first attempt in the etomidate-remifentanil group compared with 23 in the propofol-remifentanil group. Gagging, chest rigidity and myoclonus occurred significantly more frequently in the etomidate-remifentanil group. We conclude that the addition of remifentanil to etomidate anaesthesia induction does not improve LMA insertion.

Early awakening and extubation with remifentanil in ventilated premature neonates

BACKGROUND

Morphine is one of the most commonly used drugs for sedation and analgesia during mechanical ventilation, but its pharmacological profile has limitations, such as prolonged duration of action, especially in premature neonates. Because of its very short context-sensitive half-time, remifentanil has rapid onset and quickly decreases in plasma concentration after interrupting administration. The aim of the present study was to compare a continuous infusion of remifentanil and morphine during mechanical ventilation of premature neonates with respiratory distress syndrome (RDS).

METHODS

Twenty premature neonates (28-34 weeks) with RDS were randomized in a prospective double-blinded study to receive either a continuous infusion of morphine (n = 10) or remifentanil (n = 10) for mechanical ventilation. The length of time to awaken and extubate the neonate after interrupting opioid administration was recorded. We also recorded stress (COMFORT scale), pain response [Neonatal Infant Pain Scale (NIPS)], hemodynamic and ventilatory variables as well as adverse effects secondary to infusion of the specific opioid.

RESULTS

After terminating infusion, the length of time required to awaken and extubate the neonates was 18.9- and 12.1-fold longer, respectively, in the morphine group than in the remifentanil group. Both groups produced good quality sedation and analgesia as evaluated by the NIPS and COMFORT scores. No major side effects were observed.

CONCLUSIONS

Our results show an interesting potential for the use of remifentanil in premature neonates. Remifentanil allowed an adequate level of sedation and analgesia as well as rapid recovery after discontinuation. However, further properly designed clinical trials are needed before it can be generally recommended.

Elektive Kolonresektionen in Deutschland

BACKGROUND

Fast-track rehabilitation after elective colon resection is an interdisciplinary multimodal procedure, which combines surgical and anesthesiological aspects. This leads to an improved and accelerated recovery and avoids perioperative complications. This survey focuses on the extent and use of such concepts in Germany.

METHODS

In January 2006, a questionnaire was sent to 1270 anesthesiology departments in Germany in which they were asked to describe the standard anesthesia procedures based on a conventional sigmoid resection.

RESULTS

The response rate was 385 out of 1270 (30.3%). Preoperative fasting of solid food 12 h before the operation was practiced in 52% and for 6 h in 44% of the clinics. For fluid intake the fasting time was 6 h in 47% and 2 h in 41%. Prophylactic measures for postoperative nausea and vomiting (PONV) were administered in 33% of clinics. Propofol (68%) was the leading narcotic, fentanyl (56%) and sufentanil (48%) were the most commonly used intraoperative analgesics and 75% of clinics used epidural analgesia.

CONCLUSION

In Germany the anesthesiological treatment after elective colon surgery adheres broadly to the evidence-based recommendations for fast-track concepts.

Target-controlled infusion of propofol combined with variable rate infusion of remifentanil for anaesthesia of a dog with patent ductus arteriosus

An 18-month-old Lurcher was anaesthetized for surgical ligation of a patent ductus arteriosus using a target-controlled infusion (TCI) of propofol and a variable rate infusion of remifentanil. Before anaesthesia, radiographic and echocardiographic examination indicated that the dog had left-sided congestive heart failure and impaired left ventricular systolic function. Ramipril and furosemide were administered pre-operatively. Following pre-anaesthetic medication with morphine, 0.5 mg kg(-1), by intramuscular injection, and pre-oxygenation, remifentanil was infused for 5 minutes at 0.2 microg kg(-1) minute(-1), followed by induction of anaesthesia using intravenous propofol administered by TCI, set at a target concentration of 3.5 microg mL(-1) of propofol in blood. Tracheal intubation was performed and 100% oxygen delivered through a non-rebreathing (Bain) system and then a circle system in the operating theatre. Anaesthesia was maintained with propofol and remifentanil, adjusted according to clinical requirements. Peri-operative analgesia consisted of intercostal bupivacaine nerve block, with meloxicam, morphine and remifentanil.

Results of forty years Yellow Card reporting for commonly used perioperative analgesic drugs

BACKGROUND

A variety of analgesics are used perioperatively and associated adverse drug reactions (ADRs) may complicate anaesthesia and recovery.

METHODS

We aimed to measure the demographics of reported suspected ADRs to alfentanil, fentanyl, ketorolac, morphine, nalbuphine, papaveretum, pethidine and remifentanil. We report a retrospective analysis of Yellow Card reports of suspected ADRs from 1965-2004 as classified in the Adverse Drug Reaction On-line Tracking database (ADROIT) of the Medicines and Healthcare products Regulatory Agency (MHRA).

RESULTS

In total, 1312 reactions were retrieved. A single drug was reported in 908, 39 were fatal and 219 categorised as 'allergic'. Allergic phenomenon varied from 2/33 (6%) for remifentanil to 11/53 (21%) for alfentanil. 'Cardiovascular' reactions were reported frequently with remifentanil (18/33, 55%) and alfentanil (19/53, 36%) and these generated a signal for possible hazards from proportional reporting ratios (PRRs). The opioid fentanyl was associated with similar hazard signals for muscular and psychiatric ADRs.

CONCLUSIONS

Perioperative vigilance may reduce morbidity and mortality from preventable ADRs to analgesic drugs. Denominator and diagnostic data are essential for prospective studies.

Anesthesia care for adult live donor hepatectomy: our experiences with 100 cases

A total of 100 patients who underwent elective lobar donor hepatectomy from 2000 to 2002 at the University of Rochester Medical Center were reviewed. Assessed clinical data were estimated blood loss, intraoperative central venous pressure (CVP), blood product and fluid administration, perioperative arterial blood gas tension and acid-base state, metabolic status, perioperative serum levels of aspartate aminotransferase, alanine aminotransferase, prothrombin time, albumin, and lactate, procedure duration, and perioperative complications. All patients survived surgery, and the average duration of surgery (from skin incision to skin closure) was 615 +/- 99.6 minutes. Mean blood loss was 549 +/- 391 mL (range, 80-2,500 mL), and only 4 patients required homologous blood transfusion. The intraoperative blood loss did not correlate with CVP values. A total of 72 patients received isotonic sodium bicarbonate solution, and their metabolic variables were superior to those of normal saline group patients (arterial pH, 7.35 +/- 0.03 vs. 7.29 +/- 0.07; base excess, -4.3 +/- 2.4 vs. 7.3 +/- 3.4; and serum bicarbonate level, 20.6 +/- 2.2 vs. 18.6 +/- 2.9). However, the better control of metabolic acidosis was not associated with serum lactate levels or other outcome measures. Maintaining the CVP < 5 mmHg was not associated with blood loss. Clinically significant anesthetic complications were severe metabolic acidosis, pneumothorax and respiratory insufficiency immediately following extubation in the operating room. In conclusion, placement of a thoracic epidural catheter delivering a local anesthetic in addition to intravenous (IV) patient-controlled analgesia with opiates provided safe and effective pain control in most patients. Further prospective studies should shed a light on the optimal care of patients undergoing liver donor hepatic resection.

Caesarean section using total intravenous anaesthesia in a patient with Ebstein’s anomaly complicated by supraventricular tachycardia

Ebstein's anomaly is a rare congenital cardiac defect associated with both displacement and incompetence of the tricuspid valve. The condition is commonly complicated by supraventricular tachycardias. We describe the management of a patient with this condition undergoing caesarean section. Propofol and remifentanil total intravenous anaesthesia resulted in haemodynamic stability and delivery of a healthy baby who breathed spontaneously after two minutes.

IMPLANTATION OF ELECTRODES FORDEEP BRAIN STIMULATION OF THE SUBTHALAMIC NUCLEUS IN ADVANCED PARKINSON'S DISEASE WITH THE AID OF INTRAOPERATIVE MICRORECORDING UNDERGENERAL ANESTHESIA

OBJECTIVE

Deep brain stimulation (DBS) is widely accepted in the treatment of advanced Parkinson's disease (PD) and other movement disorders. The standard implantation procedure is performed under local anesthesia (LA). Certain groups of patients may not be eligible for surgery under LA because of clinical reasons, such as massive fear, reduced cooperativity, or coughing attacks. Microrecording (MER) has been shown to be helpful in DBS surgery. The purpose of this study was to evaluate the feasibility of MERfor DBS surgery under general anesthesia (GA) and to compare the data of intraoperative MERas well as the clinical data with that of the current literature of patients undergoing operation under LA.

CLINICAL PRESENTATION

The data of nine patients with advanced PD (mean Hoehn and Yahr status, 4.2) who were operated with subthalamic nucleus (STN) DBS under GA, owing to certain clinical circumstances ruling out DBS under LA, were retrospectively analyzed. All operations were performed under analgosedation with propofol or remifentanil and intraoperative MER. For MER, remifentanil was ceased completely and propofol was lowered as far as possible.

INTERVENTION

The STN could be identified intraoperatively in all patients with MER. The typical bursting pattern was identified, whereas a widening of the baseline noise could not be as adequately detected as in patients under LA. The daily off phases of the patients were reduced from 50 to 17%, whereas the Unified Parkinson's Disease Rating Scale III score was reduced from 43 (preoperative, medication off) to 19 (stimulation on, medication off) and 12 (stimulation on, medication on). Two patients showed a transient neuropsychological deterioration after surgery, but both also had preexisting episodes of disorientation. One implantable pulse generator infection was noticed. No further significant clinical complications were observed.

CONCLUSION

STN surgery for advanced PD with MERguidance is possible with good clinical results under GA. Intraoperative MERof the STN region can be performed under GA with a special anesthesiological protocol. In this setting, the typical STN bursting pattern can be identified, whereas the typical widening of the background noise baseline while entering the STN region is obviously absent. This technique may enlarge the group of patients eligible for STN surgery. Although the clinical improvements and parameter settings in this study were within the range of the current literature, further randomized controlled studies are necessary to compare the results of STN DBS under GA and LA, respectively.

Systemic and spinal administration of the mu opioid, remifentanil, produces antinociception in amphibians

Remifentanil is a relatively new opioid analgesic related to the fentanyl family of mu opioid receptor agonists and is used clinically for its unique property of having an ultra-short duration of action. However, there is little preclinical data on the analgesic (antinociceptive) effects of remifentanil and none obtained in non-mammalian animal models. The antinociceptive effects of remifentanil were assessed by using the acetic acid test in amphibians. Systemic and spinal administration of remifentanil was made by subcutaneous and intraspinal injections in the Northern grass frog, Rana pipiens. After administration, remifentanil produced dose-dependent and long-lasting antinociceptive effects which persisted for five hours after systemic administration but gave a shorter duration of action after spinal delivery. The antinociceptive effects of remifentanil were significantly blocked by pretreatment with systemic naltrexone. Systemic and spinal administration of remifentanil produced log dose-response curves which yielded ED50 values of 7.1 nmol/g and 3.2 nmol/animal respectively. The relative antinociceptive potency of remifentanil compared to other opioids administered to amphibians is similar to that found in mammalian models.

An Analysis of Remifentanil in the Pulmonary Vascular Bed of the Cat

In this investigation we sought to identify the role of remifentanil in the feline pulmonary vascular bed. Using adult mongrel cats in separate experiments, the effects of glibenclamide (adenosine triphosphate-sensitive K+ channel blocker), diphenhydramine (histamine H(1)-receptor antagonist), L-N5-(1-Iminoethyl) ornithine hydrochloride (nitric oxide synthase inhibitor), and naloxone (opioid receptor antagonist) were investigated in pulmonary arterial responses to remifentanil (opioid agonist), pinacidil (adenosine triphosphate-sensitive K+ channel activator), and bradykinin (nitric oxide synthase inducer). Under increased tone conditions in the isolated left lower lobe vascular bed of the cat, remifentanil induced a dose-dependent vasodepressor response that was not significantly altered after administration of glibenclamide and L-N5-(1-Iminoethyl) ornithine hydrochloride. Responses to remifentanil were significantly attenuated after administration of diphenhydramine and naloxone. The results suggest that remifentanil has potent vasodepressor activity in the feline pulmonary vascular bed and that these responses are mediated by histamine and opioid receptor sensitive pathways.

Intraoperative Direct Mechanical Stimulation of the Anterior Cruciate Ligament Elicits Short- and Medium-Latency Hamstring Reflexes

The anterior cruciate ligament (ACL) has not only a mechanical but also a sensorimotor function. Patients with injuries of the ACL frequently complain of knee instability despite good mechanical stabilization after surgical reconstruction. Compared with healthy subjects, their latencies of hamstring reflexes after anterior tibia translation are considerably increased. There is evidence for the existence of a reflex arc between the ACL and the hamstrings. The aim of this study was to determine if there is a direct reflex response after an isolated mechanical stimulation of the ACL in humans. In 10 patients who underwent arthroscopy, hamstring electromyographic (EMG) responses were assessed intraoperatively after applying an isolated load on the ACL. Latencies, amplitudes, and integrals of the EMG responses were analyzed. In four patients, the measurements were repeated after injection of local anesthetics into the ACL. In all subjects, responses with mean latencies of 42 ± 4.4 (SD) ms corresponding to a medium latency response (MLR) were found. In seven subjects, they were preceded by responses with a short-latency (SLR) of 24 ± 2.7 ms. The maximum amplitude was 8.6 ± 7 mV, the integral 0.064 ± 0.05 mV*s. The injection of local anesthetics reduced the amplitude by 34 ± 12% and the integral by 50 ± 20%. Direct mechanical stimulation of the ACL evokes considerably smaller SLRs and MLRs than anterior tibia translation during standing. It is argued that latency changes observed in patients with ACL ruptures may be rather due to changes in the sensorimotor integration of the afferent input from the knee joint than to the absence of the direct ACL reflex.

Glycopyrrolate during sevoflurane–remifentanil-based anaesthesia for cardiac catheterization of children with congenital heart disease

BACKGROUND

Remifentanil is recommended for use in procedures with painful intraoperative stimuli but minimal postoperative pain. However, bradycardia and hypotension are known side-effects. We evaluated haemodynamic effects of i.v. glycopyrrolate during remifentanil-sevoflurane anaesthesia for cardiac catheterization of children with congenital heart disease.

METHODS

Forty-five children undergoing general anaesthesia with remifentanil and sevoflurane were randomly allocated to receive either saline, glycopyrrolate 6 microg kg(-1) or glycopyrrolate 12 microg kg(-1). After induction of anaesthesia with sevoflurane, i.v. placebo or glycopyrrolate was administered. An infusion of remifentanil at the rate of 0.15 microg kg(-1) min(-1) was started, sevoflurane continued at 0.6 MAC and cisatracurium 0.2 mg kg(-1) was given. Heart rate (HR) and non-invasive arterial pressures were monitored and noted every minute for the first 10 min and then every 2.5 min for subsequent maximum of 45 min.

RESULTS

Baseline HR [mean (SD)] of 117 (20) beats min(-1) decreased significantly from 12.5 min onwards after starting the remifentanil infusion in the control group [106 (18) at 12.5 min and 99 (16) beats min(-1) at 45 min]. In the groups receiving glycopyrrolate, no significant decrease in HR was noticed. Glycopyrrolate at 12 microg kg(-1) induced tachycardia between 5 and 9 min after administration. Systolic and diastolic arterial pressures decreased gradually, but there were no significant differences in the pressures between groups.

CONCLUSION

I.V. glycopyrrolate 6 microg kg(-1) prevents bradycardia during general anaesthesia with remifentanil and sevoflurane for cardiac catheterization in children with congenital heart disease. Administering 12 microg kg(-1) of glycopyrrolate temporarily induces tachycardia and offers no additional advantage.