Productivity benchmarks for operative service units

BACKGROUND

Easily accessible reliable information is crucial for strategic and tactical decision-making on operative processes. We report development of an analysis tool and resulting metrics for benchmarking purposes at a Finnish university hospital.

METHODS

The analysis tool is based on data collected in a resource management system and an in-house cost-reporting database.

RESULTS

The exercise reports key metrics for four operative service units and six surgical units from 2014 and the change from year 2013. Productivity, measured as total costs per total hours, ranged from 658 to 957 €/h and utilization of the total available resource hours at the service unit level ranged from 66% to 74%. The lowest costs were in a unit running only regular working hour shifts, whereas the highest costs were in a unit operating on 24/7 basis. The tool includes additional metrics on operating room (OR) scheduling and monthly data to support more detailed analysis.

CONCLUSION

This report provides the hospital management with an improved and detailed overview of its operative service units and the surgical process and related costs. The operating costs are associated with on call duties, size of operative service units, and the requirements of the surgeries. This information aids in making mid- to long range decisions on managing OR capacity.

Dexmedetomidine inhibits gastric emptying and oro-caecal transit in healthy volunteers

BACKGROUND

Dexmedetomidine is a potent and selective α2-adrenoceptor agonist used for perioperative and intensive care sedation with certain beneficial qualities. However, based on preclinical observations, it might inhibit gastric emptying and gastrointestinal transit, which could result in unwanted effects in intensive care patients. This study evaluated the effects of dexmedetomidine on gastric emptying and oro-caecal transit time in healthy volunteers.

METHODS

Twelve healthy male subjects were given 1 µg kg(-1) of dexmedetomidine i.v. over 20 min followed by a continuous i.v. infusion of 0.7 µg kg(-1) h(-1) for 190 min. For comparison, subjects were also given 0.10 mg kg(-1) of morphine hydrochloride i.v. over 20 min and a placebo infusion in a randomized order. Gastric emptying was assessed with the paracetamol absorption test and oro-caecal transit time with the hydrogen breath test.

RESULTS

The time to maximum paracetamol concentration in plasma was significantly longer, maximum paracetamol concentration was significantly lower, the area under the plasma paracetamol concentration-time curve was significantly smaller, and oro-caecal transit time was significantly longer during dexmedetomidine infusion compared with morphine or placebo infusion.

CONCLUSIONS

Dexmedetomidine markedly inhibits gastric emptying and gastrointestinal transit in healthy volunteers.

Perioperative use of α2-adrenoceptor agonists and the cardiac patient

The centrally acting alpha2-adrenoceptor agonists clonidine and dexmedetomidine have been used with success to provide haemodynamic stability for patients undergoing surgery. Particularly in the case of patients with overt or underlying cardiac disease the actions of alpha2-adrenoceptor agonists, which include maintenance of stable systemic blood pressure and low heart rate and a reduction in overall oxygen consumption, can be expected to reduce the risk of procedure-related cardiac events. This expectation has been corroborated in clinical trials with clonidine, dexmedetomidine and mivazerol and meta-analyses; additional large controlled trials would be instructive in establishing a robust estimate of the scale of the benefit. In addition, alpha2-adrenoceptor agonists used as premedication have been shown to substantially reduce anaesthetic requirements among surgical patients, and the use of these agents has been associated with a reduced risk of postoperative delirium, which may be expected to improve considerably the postoperative course for at-risk patients. Dexmedetomidine is the only alpha2-adrenoceptor agonist currently approved for use in the intensive care unit. A distinctive feature of dexmedetomidine in that setting is that in addition to haemodynamic stability it confers a distinctive and advantageous quality of sedation: patients are tranquil but responsive to requests from attending staff. This review examines the pharmacological principles underlying the use of alpha2-adrenoceptor agonists as adjuncts to surgery and clinical experience in that indication.

Gene expression of pulmonary cytokines after sevoflurane or thiopentone anaesthesia in pigs

BACKGROUND

Volatile anaesthetics have diverse inflammatory effects on the lungs. They increase gene expression of some pro-inflammatory cytokines in alveolar macrophages whereas in alveolar type II cells they seem to decrease secretion and gene expression of pro-inflammatory cytokines. We have previously detected increased leukotriene C4, nitrate and nitrite concentrations in bronchoalveolar lavage fluid after sevoflurane anaesthesia. In the current study, we measured gene expression of inflammatory cytokines in the lung tissue and plasma concentrations of cytokines in pigs after thiopentone or sevoflurane anaesthesia.

METHODS

Sixteen pigs were randomly selected to receive either a continuous thiopentone infusion (control group, n = 8) or sevoflurane (n = 8) at 4.0% inspiratory concentration (1.5 MAC) in air for 6 h. Tissue samples were collected at the end of the study for measurement of gene expression of inflammatory cytokines. Blood samples were collected during anaesthesia for measurement of plasma cytokine concentrations.

RESULTS

Compared with thiopentone anaesthesia, lower gene expression of tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in lung tissue was observed after sevoflurane anaesthesia. Of measured cytokines IL-1beta, TNF-alpha, IL-6, IL-8 and IL-10 only plasma concentrations of IL-6 could be measured during the study without a difference between the groups.

CONCLUSION

Lower gene expression of TNF-alpha and IL-1beta was found in the intact porcine lung tissue after sevoflurane anaesthesia compared with thiopentone anaesthesia. Clinical significance of this finding is unknown.

Isobaric bupivacaine via spinal catheter for hip replacement surgery: ED50 and ED95 dose determination

BACKGROUND

Continuous spinal anaesthesia with spinal catheters allows incremental dosing of the local anaesthetic and, consequently, less haemodynamic change. However, little is known about the required doses. Therefore, we designed a study to assess the local anaesthetic doses of isobaric bupivacaine which were effective in 50% (ED50) and 95% (ED95) of patients undergoing hip replacement surgery.

METHODS

Forty-eight patients undergoing hip replacement surgery were randomly allocated to one of six possible groups of eight patients to receive 6, 7, 8, 9, 10 or 12 mg of isobaric bupivacaine in a double-blind manner. The ED50 and ED95 values were calculated by a logistic regression model. The position of the spinal catheter tip was confirmed by X-rays.

RESULTS

The ED50 and ED95 values were 7.1 mg (95% confidence interval, 6.0-8.4) and 12.3 mg (95% confidence interval, 8.9-15.7), respectively. The location of the tip of the intrathecal catheter had no effect on local anaesthetic requirements. Eight patients required ephedrine after anaesthesia induction and a further 11 patients required ephedrine for correction of hypotension during surgery.

CONCLUSION

The observed ED50 and ED95 values may guide us to use small doses of isobaric bupivacaine for hip replacement surgery. Hypotension is still possible even if low doses of isobaric bupivacaine are used.

Minimum effective local anaesthetic dose of isobaric levobupivacaine and ropivacaine administered via a spinal catheter for hip replacement surgery

BACKGROUND

Continuous spinal anaesthesia with spinal catheters allows incremental dosing of local anaesthetic and, consequently, less haemodynamic changes. However, little is known about the required doses. Therefore, we designed a study to assess the minimum effective local anaesthetic dose (MLAD) of levobupivacaine and ropivacaine in this context.

METHODS

Forty-one patients undergoing hip replacement surgery were randomly allocated to one of the two local anaesthetic groups in a double-blind manner. The initial dose of local anaesthetic was determined by the response of the previous patient: the effective dose resulted in a 1 mg decrease in the dose of levobupivacaine or ropivacaine, and an ineffective dose resulted in a 1 mg increase. The MLAD was calculated by the Dixon up-and-down method.

RESULTS

The MLAD of levobupivacaine was 11.7 mg (95% CI, 11.1-12.4) and that of ropivacaine 12.8 mg (95% CI, 12.2-13.4).

CONCLUSIONS

These doses are significantly smaller than doses reported before for single-shot spinal anaesthesia. Continuous spinal anaesthesia allows the use of relatively small doses of local anaesthetic.

Surgical closure of patent ductus arteriosus in very-low-birth-weight infants

In many very-low-birth-weight (VLBW) infants the ductus arteriosus fails to close spontaneously, and they subsequently develop signs and symptoms of poor tissue perfusion and heart failure. This study evalutes the results of early surgical closure of patent ductus arteriosus (PDA). We retrospectively reviewed the records of all 101 VLBW infants who weighed 1,500 g or less when their PDA was surgically ligated in Turku University Hospital between 1988 and 1998. The mean gestational age at birth was 27.2 weeks and mean birth weight 963+/-239 g. The operation was performed at 12+/-8 days of age; the infants' weight at operation was 969+/-231 g and they were tracheally extubated 11+/-14 days after the operation. The surgery-related mortality was 3% (3/101) and overall mortality 10% (10/101). We conclude that surgical closure of PDA is safe and effective in VLBW infants.

Sevoflurane EC50 and EC95 values for laryngeal mask insertion and tracheal intubation in children

The laryngeal mask airway (LMA) is a simple, easy to use and safe method for airway control in children. Its insertion needs less anaesthetic, and haemodynamic responses and postoperative sequelae are less than with laryngoscopy and tracheal intubation. This study was designed to determine the end-tidal concentrations of sevoflurane where 50% (EC50) and 95% (EC95) of the attempts to secure the airway would be successful. We randomly assigned 40 children aged 4-12 yr undergoing general surgery to either LMA insertion (n=20) or to laryngoscopy and tracheal intubation (n=20) under sevoflurane anaesthesia. The initial end-tidal concentration of sevoflurane for each child was determined according to the response of the previous child in the same group. Up to three attempts to secure the airway with increasing sevoflurane end-tidal concentrations in 0.3% steps were allowed for each child. The logistic regression model was used to calculate the EC50 and EC95 values. Sevoflurane provided good conditions for both LMA insertion, and laryngoscopy and tracheal intubation without serious adverse effects. The EC50 and the EC95 of sevoflurane were 1.57 (SD 0.33)% and 2.22% for LMA insertion and 2.20 (SD 0.31)% and 2.62% for laryngoscopy and tracheal intubation. Thus, less sevoflurane is required for LMA insertion in children than for laryngoscopy and tracheal intubation.

A comparison of the hemodynamic effects of paracervical block and epidural anesthesia for labor analgesia

BACKGROUND

Both paracervical block (PCB) and epidural analgesia are sometimes associated with hemodynamic effects potentially harmful to the well-being of the fetus. Our study was designed to test the hypothesis that PCB would have a more profound effect on maternal and fetal blood flow than epidural analgesia.

METHODS

Forty-four healthy primiparous parturients were randomized to receive either PCB (n=21) or epidural analgesia (n= 23) with 25 or 30 mg of bupivacaine, respectively, for labor analgesia. Maternal blood pressure and fetal heart rate were recorded. Blood flow was measured using a color Doppler device. The blood flow measurements consisted of assessment of the pulsatility indices (PI) of the right maternal femoral artery and the main branch of the uterine artery (placental side), the umbilical artery and the fetal middle cerebral artery. The measurements were performed before administration of analgesia and approximately 15-20 min later after the onset of analgesia.

RESULTS

Both methods provided in general good analgesia, but rescue medication was required more often after PCB. Epidural analgesia decreased maternal blood pressure more than PCB and the PI of maternal femoral artery decreased after onset of epidural analgesia, indicating epidural-induced vasodilation. The PI of the uterine artery increased after the onset of PCB, indicating vasoconstriction of this artery. No significant adverse effects or differences in the well-being of the newborn were observed, as indicated by similar Apgar scores and pH-status.

CONCLUSION

There were small differences in the effects of PCB and epidural analgesia on uteroplacental circulation as well as on maternal hemodynamics. PCB may have a vasoconstrictive effect on the uterine artery. This and the fact that the parturients required rescue analgesia more frequently after PCB than after epidural block speaks for the feasibility of the latter in obstetrics.

Nursing activities and outcomes of care in the assessment, management, and documentation of children's pain

This study describes how assessment and documentation of children's acute postoperative pain is managed by nurses in university hospitals in Finland. A survey was conducted of 303 nurses working in children's wards of university-affiliated hospitals, and at the same time a retrospective chart review of 50 consecutive cases of operation of acute appendicitis was carried out. Charts were analyzed by content analysis, and the results of the survey are reported with percentage distribution and nonparametric statistical calculations. The results indicate that nurses assess pain mainly by observing the child's behavior and changes in physiology. Pain measurement instruments are rarely used, and nurses do not recognize them. The documentation of pain care is unsystematic and does not support the continuity of care. There is a clear need for development of assessment and documentation practices in the studied hospitals. Future research should look at the postoperative care of pain at home as well as care in non-university-affiliated hospitals.

Management of the paediatric patient

Recent introduction of new fast-onset short-duration anaesthetic drugs and the use of regional anaesthesia techniques in children have resulted in good control of anaesthesia and perioperative pain with few adverse effects. Ambulatory surgery has gained popularity in paediatric practice, particularly as children are often otherwise healthy and usually undergo minor surgery.

Difficult airway in a patient with Marshall-Smith syndrome

Marshall-Smith syndrome is a rare clinical disorder characterized by accelerated bone maturation, dysmorphic facial features, airway abnormalities and death in early infancy because of respiratory complications. Although patients with Marshall-Smith syndrome have several features with potential anaesthetic problems, previous reports about anaesthetic management of these patients do not exist. We present a case, in which severe hypoxia developed rapidly after routine anaesthesia induction in an eight-month-old male infant with this syndrome. After several unsuccessful attempts the airway was finally secured by blind oral intubation. After 2 weeks, laryngeal anatomy was examined with fibreoptic laryngoscopy which revealed significant laryngomalacia. Laryngoscopy was performed without problems with ketamine anaesthesia and spontaneous breathing. The possibility of a compromised airway should always be borne in mind when anaesthetizing patients with Marshall-Smith syndrome. Anaesthesia maintaining spontaneous breathing is safest for children with this syndrome. If tracheal intubation or muscle relaxation is required, precautions are needed to maintain a patent airway. Muscle relaxants should possibly be avoided before intubation.

Reversal of the sedative and sympatholytic effects of dexmedetomidine with a specific alpha2-adrenoceptor antagonist atipamezole: a pharmacodynamic and kinetic study in healthy volunteers

BACKGROUND

Specific and selective alpha2-adrenergic drugs are widely exploited in veterinary anesthesiology. Because alpha2-agonists are also being introduced to human practice, the authors studied reversal of a clinically relevant dexmedetomidine dose with atipamezole, an alpha2-antagonist, in healthy persons.

METHODS

The study consisted of two parts. In an open dose-finding study (part 1), the intravenous dose of atipamezole to reverse the sedative effects of 2.5 microg/kg of dexmedetomidine given intramuscularly was determined (n = 6). Part 2 was a placebo-controlled, double-blinded, randomized cross-over study in which three doses of atipamezole (15, 50, and 150 microg/kg given intravenously in 2 min) or saline were administered 1 h after dexmedetomidine at 1-week intervals (n = 8). Subjective vigilance and anxiety, psychomotor performance, hemodynamics, and saliva secretion were determined, and plasma catecholamines and serum drug concentrations were measured for 7 h.

RESULTS

The mean +/- SD atipamezole dose needed in part 1 was 104+/-44 microg/kg. In part 2, dexmedetomidine induced clear impairments of vigilance and psychomotor performance that were dose dependently reversed by atipamezole (P < 0.001). Complete resolution of sedation was evident after the highest (150 microg/kg) dose, and the degree of vigilance remained high for 7 h. Atipamezole dose dependently reversed the reductions in blood pressure (P < 0.001) and heart rate (P = 0.009). Changes in saliva secretion and plasma catecholamines were similarly biphasic (i.e., they decreased after dexmedetomidine followed by dose-dependent restoration after atipamezole). Plasma norepinephrine levels were, however, increased considerably after the 150 microg/kg dose of atipamezole. The pharmacokinetics of atipamezole were linear, and elimination half-lives for both drugs were approximately 2 h. Atipamezole did not affect the disposition of dexmedetomidine. One person had symptomatic sinus arrest, and another had transient bradycardia approximately 3 h after receiving dexmedetomidine.

CONCLUSIONS

The sedative and sympatholytic effects of intramuscular dexmedetomidine were dose dependently antagonized by intravenous atipamezole. The applied infusion rate (75 microg x kg(-1) x min(-1)) for the highest atipamezole dose was, however, too fast, as evident by transient sympathoactivation. Similar elimination half-lives of these two drugs are a clear advantage considering the possible clinical applications.

Effect of clonidine on changes in plasma catecholamine concentrations and oxygen consumption caused by the cold pressor test

This study was designed to investigate whether clonidine could attenuate the increase in oxygen consumption (VO2), arterial pressure (AP) and plasma catecholamines in response to the cold pressor test (CPT), an intense stimulation of the sympathetic nervous system. Six volunteers were given clonidine (2 micrograms kg-1 and 4 micrograms kg-1) and placebo i.m. in a random, double-blind, cross-over manner. Both clonidine doses decreased plasma catecholamine concentrations (P < 0.01), but only the higher dose of clonidine attenuated the CPT-induced absolute increase in plasma catecholamine concentration compared with the placebo group (P < 0.01). VO2 and AP decreased and were less after clonidine 4 micrograms kg-1 when compared with clonidine 2 micrograms kg-1 and placebo (P < 0.05) throughout the observation period. Thus, although clonidine 4 micrograms kg-1 attenuated the catecholamine response, the increases in VO2 and AP in response to CPT were similar in all groups.

The effect of clonidine or midazolam premedication on perioperative responses during ketamine anesthesia

The use of ketamine as a sole anesthetic induces marked central sympathetic stimulation, causing increased heart rate, blood pressure (BP), and oxygen consumption (VO2). Both alpha 2-agonists and benzodiazepines have been used to attenuate these potentially harmful ketamine-induced responses. This double-blind, randomized, placebo-controlled study was designed to compare the perioperative metabolic, hemodynamic, and sympathoadrenal responses to IM clonidine (2 micrograms/kg) and midazolam (70 micrograms/kg) premedication during ketamine anesthesia. VO2 was measured continuously using indirect calorimetry in 30 ASA physical status I patients. The patients received ketamine, mivacurium, and fentanyl for the induction of anesthesia. Anesthesia was maintained using a ketamine infusion and fentanyl boluses i.v. Preoperatively, both VO2 and BP decreased significantly after the administration clonidine and midazolam compared with placebo (P < 0.01). Intraoperatively, VO2 was higher in the midazolam group than in the placebo and clonidine groups (P < 0.05). Postoperatively, there were no significant differences in BP and VO2, although they stayed at lower level in the clonidine group during the whole postoperative period. Clonidine decreased pre- and postoperative plasma catecholamine concentrations (P < 0.05). Our results indicate that a midazolam-ketamine combination may induce potentially harmful metabolic stimulation, whereas the sympatholytic effects of clonidine on ketamine-anesthetized patients may be beneficial, as perioperative VO2 was decreased.

IMPLICATIONS

Ketamine causes sympathetic stimulation with an ensuing increase in oxygen consumption. Anticipating that clonidine might attenuate this response, we measured oxygen consumption in patients undergoing surgery during ketamine anesthesia. Patients treated with a clonidine-ketamine combination had lower intra- and postoperative oxygen consumption than those treated with a midazolam-ketamine combination.

Nocturnal body movements and hypoxemia in middle-aged females after lower abdominal surgery under general anesthesia: a study with the static-charge-sensitive bed (SCSB)

OBJECTIVE

The aim of this study was to evaluate the feasibility of the static-charge-sensitive-bed (SCSB) combined with pulse oximetry (SpO2) for postoperative monitoring and to determine variables which could be used for evaluating the quality of postoperative sleep and breathing.

METHODS

The frequency of body movements and the perioperative breathing abnormalities were assessed using the SCSB and pulse oximeter in 15 female ASA-class I-II patients undergoing elective lower abdominal surgery under general anesthesia. Anesthesia and control of postoperative pain followed standard practice. The patients were monitored during one preoperative and three consecutive postoperative nights. Movements were analyzed according to their duration and time interval. The effect of opioids was evaluated by measuring arterial oxyhemoglobin saturation (SpO2) with pulse oximetry for one hour before and two hours after administration of standard doses of oxycodone.

RESULTS

The total movement time per hour increased during the first postoperative night (p = 0.003). Conversely, periodic movement activity decreased significantly during the three postoperative nights (p = 0.05, p < 0.001, p = 0.007). The mean SpO2 decreased during the first postoperative night (95.5% vs. 94.2%, p = 0.002), but returned to the preoperative level during the following nights. No episodes of apnea with significant oxygen desaturation (a decrease in SpO2 > 5%) were observed. Opioid administration was associated with decreased mean SpO2 (94.8% vs. 93.6%, p = 0.02), but did not lead to clinically significant hypoxemia (lowest observed SpO2 89.8%).

CONCLUSIONS

Postoperative periodic movement activity was suppressed, but sleep remained fragmented with frequent body movements. In our middle-aged non-obese females (ASA I-II), no severe postoperative hypoxemia was observed during the three-nights postoperative survey. Perioperative movement monitoring with the SCSB was a valuable tool in rejecting movement artefacts of SpO2 and in evaluating general sleep quality.

Lung compliance during laparoscopic surgery in paediatric patients

Insufflation of CO2 and positioning of patients induces changes in cardiovascular and respiratory function during laparoscopic procedures. This study was initiated to assess respiratory mechanics such as lung compliance and peak airway pressure (PIP) during laparoscopic surgery in paediatric patients. Ten consecutive patients (age 1-15 years) scheduled for laparoscopic procedure were included in this open prospective single-group study. Anaesthesia was induced and maintained with intravenous infusions of propofol and alfentanil. Vecuronium was administered to maintain muscle relaxation. Head down tilt induced a mean decrease of 17% in lung compliance, which was further decreased by 27% from the baseline during insufflation of intraabdominal CO2 (intraabdominal pressure 12 mmHg). Coincidently, PIP increased by 19% and 32% from the baseline during Trendelenburg position and peritoneal insufflation. Lung compliance and PIP returned to their respective baseline values after removal of CO2 from the peritoneal cavity. Endtidal CO2 increased from a baseline value of 4.3 kPa to 5.4 kPa (33-42 mmHg) during surgery when ventilator settings were not altered. We conclude that insufflation of CO2 induces significant increases in peak airway pressure with simultaneous decreases in lung compliance.

Reduction of the minimum alveolar concentration of isoflurane by dexmedetomidine

BACKGROUND

alpha 2-Adrenergic agonists have been shown to reduce anesthetic requirements of other anesthetics, and they may even act as complete anesthetics by themselves at high doses in animal models. The present study was designed to define the interaction of intravenous infusion of dexmedetomidine, an alpha 2-adrenergic agonist, and isoflurane in patients having surgery by using the minimum alveolar concentration (MAC) of isoflurane as the measure of anesthetic potency.

METHODS

Forty-nine women scheduled for abdominal hysterectomy were randomly allocated to receive either a placebo infusion (n = 16) or a two-stage infusion of dexmedetomidine with target plasma concentration of 0.3 ng/ml (n = 17) or 0.6 ng/ml (n = 16). The study drug infusion was commenced 15 min before induction of anesthesia with thiopental and alfentanil and was continued until skin incision. The end-tidal concentration of isoflurane for each patient was predetermined according to the "up-down" method of Dixon, and it was maintained for at least 15 min before the patient's response to skin incision was assessed.

RESULTS

The MAC of isoflurane was 0.85% end-tidal in the control group, 0.55% end-tidal with the low dose of dexmedetomidine, and 0.45% end-tidal with the high dose of dexmedetomidine.

CONCLUSIONS

The MAC of isoflurane in the control group was lower than that reported previously in similar patients having surgery, probably due to anesthesia induction with thiopental and alfentanil. Nevertheless, with the high dose of dexmedetomidine, the MAC of isoflurane was still 47% less than that without dexmedetomidine.

Effect of clonidine and dexmedetomidine premedication on perioperative oxygen consumption and haemodynamic state

Premedication has been shown to affect both oxygen consumption and metabolic rate. We have compared the perioperative metabolic and haemodynamic effects of two alpha 2-agonists, clonidine and the more selective dexmedetomidine, in 30 ASA I patients undergoing plastic surgical procedures under general anaesthesia. Patients were premedicated with clonidine 4 micrograms kg-1 (n = 10), dexmedetomidine 2.5 micrograms kg-1 (n = 10) or saline (n = 10) i.m. The doses of clonidine and dexmedetomidine were intended to be equipotent. The maximum decrease in preoperative oxygen consumption was 8% and decreases in systolic and diastolic arterial pressures were 11% from baseline after clonidine and dexmedetomidine. During operation, the maximum reduction in heart rate was 18% in the clonidine and dexmedetomidine groups compared with the placebo group. After operation, the maximum decrease in systolic arterial pressure was 11%, diastolic arterial pressure 15% and oxygen consumption 17% in the clonidine and dexmedetomidine groups compared with placebo. In summary, both clonidine 4 micrograms kg-1 and dexmedetomidine 2.5 micrograms kg-1 decreased perioperative oxygen consumption effectively, with a similar haemodynamic profile.

Cardiovascular and metabolic responses to clonidine and midazolam premedication

In this double-blind placebo controlled study the preoperative cardiovascular and metabolic effects of intramuscular (i.m.) clonidine and midazolam are assessed. Forty-five ASA Grade I patients (n = 15 per group) undergoing plastic surgical procedures were randomly allocated to receive either placebo, clonidine 4 micrograms kg-1 or midazolam 70 micrograms kg-1. Drugs were administered into the deltoid muscle approximately 90 min prior to the scheduled induction of anaesthesia. The metabolic measurements were performed using an indirect calorimetry device. Heart rate and blood pressure were measured noninvasively. Pre-operative subjective anxiety, dryness of mouth and tiredness were assessed using visual analogue scales (VAS). Clonidine increased subjective tiredness significantly more than placebo. Clonidine also induced moderate decreases in blood pressure and heart rate. Oxygen consumption (VO2), CO2 production and energy expenditure (EE) decreased significantly after clonidine and midazolam. The decrease in VO2 and EE was maximally 11-14% on average from the base-lines after clonidine and midazolam. These effects were of longer duration after clonidine and lasted until the end of the 90 min study period. In conclusion, both clonidine and midazolam are effective as a means of decreasing pre-operative VO2 and EE.

Dexmedetomidine as an anesthetic adjunct in coronary artery bypass grafting

BACKGROUND

Alpha 2-adrenergic agonists decrease sympathetic tone with ensuing attenuation of neuroendocrine and hemodynamic responses to anesthesia and surgery. The effects of dexmedetomidine, a highly specific alpha 2-adrenergic agonist, on these responses have not been reported in patients undergoing coronary artery bypass grafting.

METHODS

Eighty patients scheduled for elective coronary artery bypass grafting received, in a double-blind manner, either a saline placebo or a dexmedetomidine infusion, initially 50 ng.kg-1.min-1 for 30 min before induction of anesthesia with fentanyl, and then 7 ng.kg-1.min-1 unit the end of surgery. Filling pressures, blood pressure, and heart rate were controlled by intravenous fluid and by supplemental anesthetics and vasoactive drugs.

RESULTS

Compared with placebo, dexmedetomidine decreased plasma norepinephrine concentrations by 90%, attenuated the increase of blood pressure during anesthesia (3 vs. 24 mmHg) and surgery (2 vs. 14 mmHg), but increased slightly the need for intravenous fluid challenge (29 vs. 20 patients) and induced more hypotension during cardiopulmonary bypass (9 vs. 0 patients). Dexmedetomidine decreased the incidence of intraoperative (2 vs. 13 patients) and postoperative (5 vs. 16 patients) tachycardia. Dexmedetomidine also decreased the need for additional doses of fentanyl (3.1 vs. 5.4), the increments of enflurane (4.4 vs. 5.6), the need for beta blockers (3 vs. 11 patients), and the incidence of fentanyl-induced muscle rigidity (15 vs. 33 patients) and postoperative shivering (13 vs. 23 patients).

CONCLUSIONS

Intraoperative intravenous infusion of dexmedetomidine to patients undergoing coronary artery revascularization decreased intraoperative sympathetic tone and attenuated hyperdynamic responses to anesthesia and surgery but increased the propensity toward hypotension.

Molecular pharmacology of alpha 2-adrenoceptor subtypes

alpha 2-adrenergic receptors mediate many of the physiological actions of the endogenous catecholamines adrenaline and noradrenaline, and are targets of several therapeutic agents. alpha 2-adrenoceptor agonists are currently used as antihypertensives and as veterinary sedative anaesthetics. They are also used in humans as adjuncts to anaesthesia, as spinal analgesics, and to treat opioid, nicotine and alcohol dependence and withdrawal. Three human alpha 2-adrenoceptor subtype genes have been cloned and designated alpha 2-C10, alpha 2-C4, and alpha 2-C2, according to their location on human chromosomes 10, 4 and 2. They correspond to the previously identified pharmacological receptor subtypes alpha 2A, alpha 2C and alpha 2B. The receptor proteins share only about 50% identity in their amino acid sequence, but some structurally and functionally important domains are very well conserved. The most obvious functionally important differences between the receptor subtypes are based on their different tissue distributions; e.g. the alpha 2A subtype appears to be an important modulator of noradrenergic neurotransmission in the brain. The three receptors bind most alpha 2-adrenergic drugs with similar affinities, but some compounds (e.g. oxymetazoline) are capable of discriminating between the subtypes. Clinically useful subtype selectivity cannot be achieved with currently available pharmaceutical agents. The second messenger pathways of the three receptors show many similarities, but small functional differences between the subtypes may turn out to have important pharmacological and clinical consequences. All alpha 2-adrenoceptors couple to the pertussis-toxin sensitive inhibitory G proteins Gi and G(o), but recent evidence indicates that also other G proteins may interact with alpha 2-adrenoceptors, including Gs and Gq/11. Inhibition of adenylyl cyclase activity, which results in decreased formation of cAMP, is an important consequence of alpha 2-adrenoceptor activation. Many of the physiological effects of alpha 2-adrenoceptor activation cannot, however, be explained by decreases in cAMP formation. Therefore, alternative mechanisms have been sought to account for the various effects of alpha 2-adrenoceptor activation on electrophysiologic, secretory and contractile cellular responses. Recent results obtained from studies on ion channel regulation point to the importance of calcium and potassium channels in the molecular pharmacology of alpha 2-adrenoceptors.

The metabolic effects of oral tizanidine in healthy volunteers

This pilot study compared the metabolic effects of placebo and 6 mg and 12 mg of oral tizanidine in random double-blind cross-over fashion in five healthy volunteers. The metabolic measurements were made with a portable metabolic chart (Deltatrac, Datex/Instrumentarium, Helsinki, Finland). Heart rate (HR), systolic (BPS), mean (BPM) and diastolic (BPD) blood pressure were measured noninvasively. Subjective assessment of tiredness and dryness of mouth were measured by using visual analogue scales (VAS). There were no statistically significant differences in tiredness or dryness of mouth between the groups. BPD decreased significantly after both doses of tizanidine when compared to placebo (by an average of 12% after 6 mg of tizanidine and 15% after 12 mg of tizanidine from the baseline). Oxygen consumption and energy expenditure decreased significantly after 6 and 12 mg of tizanidine when compared to placebo. The average decrease in oxygen consumption was 3% after 6 mg of tizanidine and 8% after 12 mg of tizanidine, when compared to the baseline. Energy expenditure decreased by an average of 5% after 6 mg of tizanidine and 9% after 12 mg of tizanidine, when compared to the baseline. There were no other statistically significant differences between the groups. This study indicates that 6 and 12 mg of oral tizanidine can be useful for reducing energy expenditure and oxygen consumption without prominent cardiovascular effects.

Comparison of intramuscular dexmedetomidine and midazolam premedication for elective abdominal hysterectomy

The purpose of this study was to compare the perioperative effects of the intramuscular (i.m.) alpha 2 agonist, dexmedetomidine (DEX), and midazolam (MID) premedication. The study comprised 192 women (64 per group) scheduled for abdominal hysterectomy. The doses of the study drugs were chosen to obtain equal sedative effects. The three groups were: 1) i.m. DEX (2.5 micrograms/kg) and intravenous (i.v.) placebo (DexPla group), 2) i.m. DEX and i.v. fentanyl (FENT) (1.5 micrograms/kg) (DexFent group), and 3) i.m. MID (0.08 mg/kg) and i.v. FENT (MidFent group). I.m. drugs were administered 45-90 min before induction of anesthesia. Preoperative sedation and anxiolysis after DEX was comparable to that after MID. The maximum arterial blood pressure response to endotracheal intubation was blunted in the DexFent group, while in the two other groups blood pressure increased 30-34 mm Hg after endotracheal intubation. The mean isoflurane concentration during surgery was 0.14% in the DexFent group, 0.24% in the DexPla group, and 0.34% in the MidFent group (P < 0.001). During surgery, bradycardia (heart rate < 40 bpm) was observed in 6.2% of DEX patients, and no MID patients, whereas postoperatively 14.1% of DEX patients and 1.6% of MID patients had bradycardia. Fewer patients suffered from postoperative shivering after DEX (10%) than after MID (52%). We conclude that DEX has many desirable effects, but side effects such as bradycardia may limit its routine use in ASA physical status I-II patients.

Metabolic and subjective responses to oral diazepam and midazolam

Diazepam premedication decreases the overall metabolic rate and oxygen consumption. Whether its properties are shared by midazolam is not known. In this study, eight healthy male volunteers were given oral diazepam (10 mg), midazolam (15 mg) and placebo in a random double-blind cross-over fashion. Metabolic responses were measured using an indirect calorimetry device. Subjective responses were measured using a visual analogue scale. Plasma concentrations of diazepam, midazolam and desmethyldiazepam were analysed and correlated to changes in metabolic and subjective responses. When compared to placebo, both diazepam and midazolam significantly decreased oxygen consumption (P < 0.01 in pairwise comparisons) and energy expenditure (P < 0.01 in pairwise comparisons). While there was a significant correlation between the plasma concentrations of diazepam and the changes in metabolic parameters, no such correlation was found with midazolam. Both diazepam and midazolam were subjectively more sedative than placebo (P < 0.05). There was no significant difference between the sedative effects of diazepam and midazolam, but diazepam was subjectively better tolerated than midazolam. These results indicate that both diazepam and midazolam, in addition to their CNS effects, significantly decrease the overall metabolic rate and oxygen consumption in healthy volunteers.

Transarterial brachial plexus anesthesia for hand surgery: a retrospective analysis of 346 cases

STUDY OBJECTIVES

To study the safety and efficacy of the transarterial approach to brachial plexus block with 60 to 70 ml of local anesthetic solution, and to compare the success and complication rates of this block performed by experienced or inexperienced anesthesiologists.

DESIGN

Retrospective analysis of 346 records of ASA physical status I-IV patients who underwent elective unilateral orthopedic upper limb surgery with transarterial plexus anesthesia.

SETTING

University teaching hospital.

MEASUREMENTS AND MAIN RESULTS

Blood pressure (BP) and heart rate were measured at 5-minute intervals. Analgesia was registered as successful, incomplete, or failed. Any patient complaints or adverse reactions were recorded. The first 60 ml of local anesthetic provided surgical analgesia to 64% of patients. With a supplemental 10 ml of anesthetic, the overall success rate was 94%, with only 19 of 346 patients requiring general anesthesia. Experience in performing the block increased the success rate from 90% to 98% (p < 0.001). Six patients experienced either nausea or a transient BP decrease that did not require medication. There was no record of toxic or other serious adverse reaction.

CONCLUSIONS

Transarterial brachial plexus block administered with a 60 to 70 ml dose of local anesthetic provides surgical analgesia for hand surgery with an excellent success rate and without serious adverse effects.

The effects of regional anaesthesia for caesarean section on maternal and fetal blood flow velocities measured by Doppler ultrasound

We studied the effects of spinal anaesthesia (Group S), epidural anaesthesia (Group E), and combined spinal and epidural anaesthesia (Group SE), on maternal and fetal blood flow in 24 healthy parturients (n = 8/group) with uncomplicated singleton pregnancies using Doppler technique. Prior to the induction of anaesthesia, the patients were prehydrated with balanced electrolyte solution 15 ml.kg-1 over a period of 15 min. After the induction of regional anaesthesia, the systolic blood pressure was maintained within 15% limits of the preoperative values using prophylactic etilefrine infusion in Groups S and SE. The flow velocity waveforms of the maternal femoral artery, the main branch of the uterine artery (placental side), the foetal umbilical and middle cerebral arteries were recorded by Doppler technique before and after prehydration as well as after onset of T7 analgesia and the pulsatility indices (PI) were derived. Rapid intravenous prehydration had no effects on uteroplacental or fetal circulation as indicated by unaltered uterine, umbilical, and fetal middle cerebral artery PIs. After the onset of T7 analgesia, the uterine artery PI was increased in Group S indicating increased uterine vascular resistance while no changes occurred in Groups E and SE. No adverse effects were observed on the neonates as indicated by the Apgar score and the umbilical artery and vein acid-base status in any of the groups.

A comparison of dexmedetomidine, and alpha 2-adrenoceptor agonist, and midazolam as i.m. premedication for minor gynaecological surgery

The effects of i.m. dexmedetomidine 1.0 micrograms kg-1, a new alpha 2-adrenoceptor agonist, were compared with those of i.m. midazolam 0.08 mg kg-1 and placebo on vigilance, anaesthetic requirements, haemodynamic state and plasma catecholamine concentrations in a double-blind placebo-controlled study in 107 healthy (ASA physical status I-II) women undergoing cervical dilatation and uterine curettage. The premedicants were administered i.m. 60 min before induction of anaesthesia with thiopentone. Nitrous oxide 70% in oxygen and thiopentone were used for maintenance. Both premedicants were tolerated well and no serious haemodynamic or other adverse events occurred. Dexmedetomidine caused moderate reductions in arterial pressure (maximally by 20%) and heart rate (maximally by 15%). Atropine was administered to two dexmedetomidine-premedicated patients because of bradycardia less than 45 beat min-1. Both premedicants decreased the plasma concentrations of noradrenaline by about 50%, but only dexmedetomidine attenuated the catecholamine response to anaesthesia and surgery. The thiopentone requirements were decreased significantly (P = 0.003) by both dexmedetomidine (17%) and midazolam (19%). Recovery times were 11.3 (SD 4.2) min after midazolam, 8.5 (5.2) min after dexmedetomidine and 5.6 (11.4) min after placebo (P = 0.006 between midazolam and placebo groups, other differences ns).

Assessment of the sedative effects of dexmedetomidine, an alpha 2-adrenoceptor agonist, with analysis of saccadic eye movements

Single intravenous doses (0.5 microgram/kg and 1.0 microgram kg) of dexmedetomidine (4(5)-(1-(2,3-dimethylphenyl)ethyl)imidazole), a selective alpha 2-adrenoceptor agonist, and saline placebo were administered to six healthy volunteers (4 males and 2 females) in a double-blind, placebo-controlled cross-over study. The effects on vigilance were assessed using both subjective estimation (visual analogue scale, VAS) and objective tests (critical flicker fusion frequency, CFF; the Maddox wing; saccadic eye movement analysis). Dose-dependent subjective sedation was seen in VAS measurements, and impairment of vigilance was observed in CFF, Maddox wing and peak saccadic velocity, while saccade latency was not influenced by dexmedetomidine. The changes in vigilance were concurrent with moderate reductions in blood pressure and heart rate. CFF, the Maddox wing and peak saccadic velocity all proved sensitive in the assessment of sedation induced by dexmedetomidine.

Intramuscular dexmedetomidine, a novel alpha 2-adrenoceptor agonist, as premedication for minor gynaecological surgery

The effects of three different doses (0.5, 1.0 and 1.5 micrograms/kg) of dexmedetomidine, a novel alpha 2-adrenoceptor agonist, on vigilance, anaesthetic requirements, haemodynamics, and plasma catecholamine levels were investigated in a double-blind placebo-controlled study in 20 healthy (ASA physical status I-II) women scheduled for uterine dilatation and curettage (UD&C). The drug was administered intramuscularly 60 min before induction of anaesthesia with thiopentone, N2O/O2 (70/30%) and thiopentone was used for maintenance. There were no significant differences between the groups in thiopentone requirements, plasma adrenaline concentrations, or subjective or objective assessment of sedation before anaesthesia and UD&C. Blood pressure, heart rate, and plasma noradrenaline levels were reduced after dexmedetomidine, with three patients receiving atropine for excessive bradycardia (less than 45 beats min-1). The haemodynamic as well as the sedative effects of dexmedetomidine after surgery lasted until the end of the observation period, 4 h after the injection of the drug, indicating that intramuscular administration of this premedication agent may result in a longer than optimal duration of pharmacological actions in connection with short surgical procedures.

Difference in action between oral triazolam and zopiclone

The effects of oral triazolam 0.25 mg and zopiclone 7.5 mg in 7 supine volunteers were compared by means of quantitative measurements of the EEG, saccadic eye movements, visual analogue scale (VAS) for alertness, critical flicker fusion frequency (CFF) and the Maddox wing. Zopiclone reached its maximum effect earlier (62 min) than triazolam (91 min; CFF). On linear regression analysis the average rate constant (regression coefficient) of onset of action of zopiclone was significantly greater than that of triazolam (0.29 vs. 0.17). Triazolam and zopiclone had similar effects, but zopiclone seemed to have a faster onset of action, probably indicating swifter absorption in supine subjects. Quantitative EEG evaluation gave parallel results to the other parameters used, but triazolam and zopiclone showed a dissimilar mechanism of action, as characterized by changes in the alpha frequency.