Effect of flumazenil on ventilatory drive during sedation with midazolam and alfentanil

The Impacts of Some Sedative Drugs on α -Glycosidase, Acetylcholinesterase and Butyrylcholinesterase Enzymes-potential Drugs for Some Metabolic Diseases

Background:

The present paper focuses on the in vitro inhibition of some sedative drugs such as Midazolam, Propofol, Hipnodex, Ketamine, and Pental sodium on acetylcholinesterase (AChE), Butyrylcholinesterase (BChE), and α-glycosidase (α-Gly) enzymes.

Methods:

These drugs were tested in diverse concentrations, which showed positive effects in vitro AChE, BChE, and α-Gly activities. Ki values were 20.14, 94.93, 636.78, 416.42, and 953.75 µM for AChE, 17.52, 32.03, 88.02, 93.48, and 91.84 µM for BChE, and 10.87, 156.68, 48.21, 37.88, 151.01 µM for α-glycosidase, respectively.

Results:

An enhancing number of experiential observations show potentially harmful effects of sedative drugs on the extension of brain.

Conclusion:

Midazolam exhibited effective inhibitory activity compared with the other drugs for these enzymes.

Hypercapnia Caused by a Therapeutic Dosage of Pregabalin in a Tetraplegic Patient With Cervical Spinal Cord Injury

Pregabalin is often used for the treatment of neuropathic pain in patients with spinal cord injury (SCI). We reported a patient with C5 [S(C5/C6)] ASIA Impairment Scale C SCI due to cervical myelopathy who presented CO2 retention when taking a therapeutic dosage of pregabalin. An 88-year-old patient with cervical SCI was transferred to the department of physical medicine and rehabilitation. When he had transferred, his neuropathic pain had been treated with 150-mg pregabalin per day (75 mg twice a day); however, he still exhibited severe neuropathic pain with a Numeric Pain Rating Scale score of 7 to 8. Dosage for the pregabalin increased from 150 mg/d (75 mg twice a day) to 225 mg/d (150 mg at morning and 75 mg at dinner). That afternoon, he presented drowsiness and confusion, and arterial blood gas analysis (ABGA) demonstrated respiratory acidosis with CO2 retention; pH, 7.312; PaCO2, 62.8 mm Hg; PaO2,58.9 mm Hg; HCO3 concentration, 30.8 mmol/L; base excess, 3.2 mmol/L; and oxygen saturation, 90.4%. Finally, he required tracheal intubation and ventilation. After 6 weeks, the patient was transferred to a general ward, and the follow-up ABGA and end-tidal CO2 showed normal range with the discontinuation of pregabalin. We demonstrated CO2 retention via ABGA in a patient with SCI due to cervical myelopathy who developed hypercapnia after taking a therapeutic dose of pregabalin. Physicians should pay particular attention to CO2 retention when prescribing a therapeutic dosage of pregabalin in a patient with cervical SCI.

Noninvasive End Tidal CO2 Is Unhelpful in the Prediction of Complications in Deliberate Drug Poisoning

STUDY OBJECTIVE

We study the performance of capnometry in the detection of early complications after deliberate drug poisoning.

METHODS

This was a prospective cohort study of self-poisoned adult patients who presented at an emergency department (ED) between April 20, 2012, and May 6, 2014. Patients who ingested at least 1 neurologic or respiratory depressant drug were included. The primary outcome was the predictive value of an end tidal CO2 (etco2) measurement greater than or equal to 50 mm Hg for the detection of early complications defined a priori by hypoxia requiring oxygen greater than or equal to 3 L/min, bradypnea less than or equal to 10 breaths/min, or ICU admission after intubation or antidote administration because of unresponsiveness to pain or respiratory arrest. Consciousness scales and clinical data were recorded at admission and every 30 minutes. Noninvasive etco2 was continuously measured for 2 hours after inclusion unless the patient was admitted to the ICU. Patients and physicians were blinded to etco2 values.

RESULTS

Two hundred one patients were included, 35 of whom exhibited at least 1 complication. An etco2 measurement greater than or equal to 50 mm Hg predicted the onset of a complication, with a sensitivity of 46% (95% confidence interval [CI] 29% to 63%) and a specificity of 80% (95% CI 73% to 86%), leading to a positive predictive value of 33% (95% CI 20% to 48%) and a negative predictive value of 88% (95% CI 81% to 92%). etco2 was less able to predict complications than the Glasgow Coma Scale score at inclusion.

CONCLUSION

Capnometry in isolation does not provide adequate prediction of early complications in self-poisoned patients referred to the ED. A dynamic minute-by-minute assessment of etco2 could be more predictive.

Effect of flumazenil on diaphragm electrical activation during weaning from mechanical ventilation after acute respiratory distress syndrome

BACKGROUND

Diaphragm electrical activation (EAdi) and the ratio of tidal volume to EAdi (VT/EAdi) may provide clinical information on neuroventilatory efficiency (NVE) in patients being weaned from mechanical ventilation. We tested the hypothesis that residual sedation could interfere with respiratory recovery, by assessing the effects of flumazenil on EAdi and VT/EAdi ratio.

METHODS

This observational study included 13 patients breathing with pressure-support ventilation (PSV) after a long period of controlled mechanical ventilation (i.e. >4 days) plus midazolam-based sedation for acute respiratory distress syndrome. EAdi and respiratory patterns were compared before and after a bolus of flumazenil, which was given because neurological status needed to be evaluated.

RESULTS

Flumazenil induced a significant increase in EAdi [+71 (41-123)%, P=0.0002] and VT [+17 (8-32)%, P=0.0005], resulting in significantly decreased NVE [-34 (15-43)%]. The increased VT was significantly correlated with the increased EAdi (ρ=0.70, P=0.009).

CONCLUSIONS

During weaning from mechanical ventilation, the diaphragmatic contribution to the breathing process may be reduced by residual midazolam-induced ventilatory depression. The increased EAdi with reversal of residual sedation was associated with a proportional increase in VT. These findings should be considered by the attending physician when interpreting daily EAdi and VT changes during weaning from mechanical ventilation.

Target-controlled infusion of propofol versus intermittent bolus of a sedative cocktail regimen in deep sedation for gastrointestinal endoscopy: comparison of cardiovascular and respiratory parameters

OBJECTIVE

To investigate whether target-controlled infusion (TCI) with propofol, a method that has theoretically better control of drug concentration, produces less cardiovascular and respiratory suppression than an intermittent bolus of a sedative cocktail regimen in deep sedation for gastrointestinal endoscopy.

METHODS

In total 100 participants who had undergone esophagoduodenoscopy (EGD) and 120 who had undergone colonoscopy were prospectively and randomly enrolled to receive TCI with propofol or intermittent bolus of cocktail regimen containing midazolam, alfentanil and propofol until they were unresponsive to verbal commands. The target concentration was adjusted and the bolus of the cocktail regimen was added based on their responses. The nadir values of heart rate, blood pressure and oxygen saturation during and after the procedure were recorded.

RESULTS

The nadir systolic blood pressure during the endoscopy in the cocktail regimen group was significantly lower than that in the TCI with propofol group. In the cocktail regimen group, the incidence of hypotension during colonoscopy and that of bradycardia during EGD were higher than those in the TCI with propofol group. No participants in the TCI with propofol group experienced hypoxia during endoscopy. In the cocktail regimen group, six participants who had undergone EGD and six who had undergone colonoscopy showed transient hypoxic episodes during or after endoscopy.

CONCLUSION

TCI with propofol produced less cardiovascular and respiratory suppression than intermittent bolus of a sedative cocktail regimen in deep sedation for gastrointestinal endoscopy.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Respiratory CO₂ response in acute cervical spinal cord injury (CO₂ response in spinal cord injury)

STUDY DESIGN

Retrospective study.

OBJECTIVES

The objective of this study was to compare the CO₂ response of acute tetraplegic cervical spinal cord injury (SCI) patients undergoing mechanical ventilation with a control group of critically ill patients ready for weaning of mechanical ventilation and successfully extubated.

SETTING

This study was conducted at the intensive care unit of a University Hospital in Mallorca, Spain.

METHODS

CO₂ response was studied in 12 acute tetraplegic cervical SCI patients at the C4-C7 level and 22 control patients. The control group patients were consecutively selected from a database of patients with mechanical ventilation and who were successfully extubated after a CO₂ response test. To increase the CO₂ , we used the method of re-inhalation of expired air, and we evaluated the hypercapnic ventilatory response, the change in minute ventilation induced by the increase of partial pressure of arterial carbon dioxide (PaCO₂ ), which measures the whole respiratory system (metabolic control, neuromuscular or ventilatory apparatus), and the hypercapnic drive response, the change in the airway occlusion pressure at 100 ms induced by the increase in PaCO2, which measures the chemosensitivity of the respiratory center.

RESULTS

Cervical SCI patients were younger than the control group patients (26±7 and 62±12 years, respectively; P<0.001). Mean values of the hypercapnic ventilatory response in cervical SCI and control groups were 0.52±0.31 and 0.64±0.33 l min(-1) per mm Hg (P=0.40), respectively, and the hypercapnic drive response was 0.24±0.16 and 0.48±0.23 cm H₂O per mm Hg (P=0.001), respectively.

CONCLUSION

Acute tetraplegic cervical SCI patients had reduced hypercapnic drive response that may contribute to the difficult weaning, without reduction in hypercapnic ventilatory response.

The Large Role of Prescription Drugs in Accidental Drug Deaths

Drug abuse may involve illicit drugs, prescription drugs, or the combination of illicit and prescription drugs, with or without the use of alcohol. Historically, illicit drugs have been responsible for many of the drug-related deaths investigated by medical examiner and coroner offices. However, in more recent years, deaths resulting from prescription drugs have become increasingly more common. This study reviewed all accidental (unintentional) drug deaths that were investigated at a medical examiner's office over a one-year time frame. The study revealed that prescription drugs made up the largest category of drug deaths, followed by prescription drug/illicit drug combinations, followed by illicit drugs. Drugs capable of causing or contributing to significant respiratory insufficiency such as opioids, benzodiazepines, relaxants (defined as muscle relaxants or sleep medications), and alcohol, or some combination thereof, were detected in 197 out of 256 (77%) of all accidental drug deaths, and were detected in 132 out of 138 (95%) of all prescription drug deaths (cases without any illicit drugs detected). These prescription drugs were most often found in combination, and their similar respiratory depressant effects can be cumulative and deadly.

Daily titration of neurally adjusted ventilatory assist using the diaphragm electrical activity

PURPOSE

To determine the feasibility of daily titration of the neurally adjusted ventilatory assist (NAVA) level in relation to the maximal diaphragmatic electrical activity (EAdi(maxSBT)) measured during a spontaneous breathing trial (SBT) during pressure support ventilation (PSV).

METHODS

The study included 15 consecutive patients in whom mechanical ventilation weaning was initiated with the NAVA mode. EAdi(maxSBT) was determined daily during an SBT using PSV with 7 cmH2O of inspiratory pressure and no positive end-expiratory pressure (PEEP). If the SBT was unsuccessful, NAVA was used and the level was then adjusted to obtain an EAdi of ~60% of the EAdi(maxSBT). Arterial blood gas analyses were performed 20 min after each change in NAVA level.

RESULTS

Three patients were dropped from the study at day 4 because of worsening of their sickness. The median duration of NAVA ventilation was 4.5 days (IQR 3-6.5). From day 1 to extubation, EAdi(maxSBT) and EAdi increased significantly from 16.6 (9.6) to 21.7 (10.3) μV (P = 0.013) and from 10.0 (5.5) to 15.1 (9.2) μV (P = 0.026), respectively. The pressure delivered significantly decreased from 20 (8) to 10 (5) cmH2O (P = 0.003). Conversely, tidal volume, carbon dioxide tension, and pH values remained unchanged during the same period.

CONCLUSION

These results suggest that daily titration of NAVA level with an electrical goal of ~60% EAdi(maxSBT) is feasible and well tolerated. The respiratory mechanics improvement and increase in respiratory drive allowed for a daily reduction of the NAVA level while preserving breathing, oxygenation, and alveolar ventilation until extubation.

Sedation, analgesia, and delirium in the critically ill patient

Most critically ill patients receive a myriad of psychoactive medications during their hospital stay. An understanding of the pharmacology of the more commonly used sedative and analgesic therapies enables the clinician to aptly utilize these medications and limit toxicity. A key to the appropriate provision of sedative and analgesic pharmacotherapy is a thorough patient assessment, use of validated monitoring tools, and defined therapeutic goals. Limiting these therapies while optimizing patient comfort has been shown to reduce the duration of mechanical ventilation and reduce intensive care unit (ICU) and hospital length of stay and should be the aim of the multidisciplinary medical team. This review is intended to provide the reader with a fundamental understanding of how to facilitate comfort of the mechanically ventilated critically ill adult patients and how to minimize medication-related toxicities.

Symptomatic therapy of dyspnea with strong opioids and its effect on ventilation in palliative care patients

This study assessed the effect of opioid treatment on ventilation in dyspneic palliative care patients who received symptomatic treatment with strong opioids. The assessments measured changes in peripheral arterial oxygen saturation (SaO(2)), transcutaneous arterial pressure of carbon dioxide (tcPCO(2)), respiratory rate (f), and pulse rate (PF) during the titration phase with morphine or hydromorphone. The aims of the study were to verify the efficacy of opioids for the management of dyspnea, assess the effect on ventilation, and show whether nasal O(2) insufflation before opioid application leads to a decrease in the intensity of dyspnea. Eleven patients admitted to our palliative care unit were included in this prospective, nonrandomized trial. At admission, all patients suffered from dyspnea. tcPCO(2), SaO(2), and PF were measured transcutaneously by means of a SenTec Digital Monitor (SenTec AG, Switzerland). During O(2) insufflation, the intensity of dyspnea did not change. In contrast, the opioid produced a significant improvement in the intensity of dyspnea (P=0.003). Mean f decreased as early as 30 minutes after the first opioid administration, declining from 41.8+/-4.7 (35.0-50.0) to 35.5+/-4.2 (30.0-40.0), and after 90 minutes, to 25.7+/-4.5 (20.0-32.0) breaths/min. Other monitored respiratory parameters, however, showed no significant changes. There was no opioid-induced respiratory depression.

A novel molecule with peripheral opioid properties: the effects on hypercarbic and hypoxic ventilation at steady-state compared with morphine and placebo

Frakefamide (FF), is a new peripherally acting mu-opioid receptor agonist. The aim of this double-blind, randomized, double-dummy, four-way, crossover study was to investigate FF effects on hypercarbic and hypoxic ventilation at steady-state after a 6-h infusion. We compared the effect with 2 clinical doses of morphine (M-small and M-large) and placebo in 12 healthy men. The subjects received 1.22 mg/kg of FF, 0.44 mg/kg of M-large, and 0.11 mg/kg of M-small. Sodium chloride 9 mg/mL was used as placebo. Ventilation was studied by pneumotachography and in-line capnography. There were no ventilatory effects caused by FF or placebo. As expected, large doses of morphine influenced both hypercarbic and hypoxic ventilatory responses. We conclude that there were no signs of central respiratory depression caused by FF after 6 h of constant infusion, which supports a peripheral action of the compound. However, morphine caused a dose-dependent central depression during the hypercarbic ventilatory response and a mild depression of hypoxic ventilatory response.

Central sleep apnea in stable methadone maintenance treatment patients

STUDY OBJECTIVES

Methadone, a long-acting mu-opioid agonist, is an effective treatment for heroin addiction. Our previous data show that 6 of 10 methadone maintenance treatment (MMT) patients had central sleep apnea (CSA). This study aims to confirm these results and to investigate the pathogenesis of the CSA.

METHODS

Twenty-five male and 25 female MMT patients and 20 age-, sex-, and body mass index (BMI)-matched normal subjects were tested with polysomnography, blood toxicology, and ventilatory responses to hypoxia and hypercapnia. Resting cardiorespiratory tests were performed in the MMT group

RESULTS

MMT patients and normal subjects were 35 +/- 9 years old (mean +/- SD), and BMI values were 27 +/- 6 kg/m2 and 27 +/- 5 kg/m2, respectively. Thirty percent of MMT patients had a central apnea index (CAI) > 5, and 20% had a CAI > 10. All normal subjects had a CAI < 1, and no difference was found in obstructive apnea-hypopnea index between the two groups. Methadone blood concentration was the only significant variable (t = 2.33, p = 0.025) associated with CAI and explains 12% of the variance. Awake Pa(CO2), antidepressant use, reduced ventilatory response to hypercapnia, and widened awake alveolar-arterial oxygen pressure gradient together explain a further 17% of the CAI variance.

CONCLUSIONS

Thirty percent of stable MMT patients have CSA, a minority of which can be explained by blood methadone concentration. Other physiologic variables may also play a role in the pathogenesis of CSA in MMT patients, and further research is indicated in this area.

Ventilatory Responses to Hypoxia and Hypercapnia in Stable Methadone Maintenance Treatment Patients

RATIONALE

Methadone is a long-acting mu-opioid and is an effective treatment for heroin addiction. Opioids depress respiration, and patients receiving methadone maintenance treatment (MMT) have higher mortality than the general population. Few studies have investigated ventilatory responses to both hypercapnia and hypoxia in these patients.

STUDY OBJECTIVES

We measured hypercapnic ventilatory response (HCVR) and hypoxic ventilatory response (HVR) and investigated possible factors associated with both in clinically stable patients receiving MMT.

DESIGN AND SETTING

Patients receiving long-term, stable doses of methadone recruited from a statewide MMT program, and normal, non-opioid-using subjects matched for age, sex, height, and body mass index were studied with HCVR and HVR.

RESULTS

Fifty MMT patients and 20 normal subjects were studied, and significantly decreased HCVR and increased HVR were found in MMT patients compared to normal subjects (HCVR [mean +/- SD], l.27 +/- 0.61 L/min/mm Hg vs 1.64 +/- 0.57 L/min/mm Hg [p = 0.01]; HVR, 2.14 +/- 1.58 L/min/% arterial oxygen saturation measured by pulse oximetry [Sp(O2)] vs 1.12 +/- 0.7 L/min/% Sp(O2) [p = 0.008]). Respiratory rate and not tidal volume changes were the major physiologic responses contributing to both HCVR and HVR differences between the groups. Variables associated with HCVR in the MMT patients are as follows: obstructive sleep apnea/hypopnea index (t = 5.1, p = 0.00001), Pa(CO2) (t = - 3.6, p = 0.001), body height (t = 2.6, p = 0.01) and alveolar-arterial oxygen pressure gradient (t = 2.5, p = 0.02). Variables associated with HVR in MMT patients are body height (t = 3.2, p = 0.002) and Pa(CO2) (t = - 2.8, p = 0.008).

CONCLUSIONS

Stable long-term MMT patients have blunted central and elevated peripheral chemoreceptor responses. The mechanisms and clinical significance of these findings need further investigation.

Flunitrazepam does not alter cerebral distribution of buprenorphine in the rat

Deaths have been reported among heroin addicts related to combined buprenorphine and flunitrazepam use. The aim of this study was to determine the existence of a drug-drug interaction during the distribution phase of buprenorphine. Arterial blood gases were measured after intravenous administration of buprenorphine alone (30 mg/kg), flunitrazepam alone (40 mg/kg) or both drugs in rats. Buprenorphine kinetics was studied in plasma and in striatum using cerebral microdialysis, both alone and after rat pretreatment with flunitrazepam. In contrast to buprenorphine or flunitrazepam alone, buprenorphine in combination with flunitrazepam induced a significant, rapid and sustained respiratory depression. Arterial PCO2 was increased at 1.5 min (6.7+/-0.2 versus 5.4+/-0.3 and 5.5+/-0.3 kPa, respectively, P=0.04) (mean+/-S.E.M.), and arterial pH decreased (7.37+/-0.02 versus 7.45+/-0.02 and 7.45+/-0.01, respectively, P=0.03). Plasma buprenorphine kinetics was well described by a three-compartment linear model, with a distribution half-life of 7.4+/-2.7 min and an elimination half-life of 463.9+/-152.3 min. However, neither plasma nor striatal buprenorphine kinetics were significantly altered by pre-administration of flunitrazepam. The adverse interaction between flunitrazepam and buprenorphine cannot be explained by a pharmacokinetic drug-drug interaction during the distribution phase of buprenorphine.

A comparison of midazolam and diazepam for conscious sedation during colonoscopy in a prospective double-blind study

BACKGROUND

Midazolam and diazepam are commonly used for conscious sedation, but their comparative respiratory depressive effects have not been accurately studied. We used a novel real-time, on-line, computerized data acquisition system to compare the two agents in a randomized double-blind study.

METHODS

One hundred patients undergoing colonoscopy were studied. The maximum end-tidal carbon dioxide tension (PetCO2) and the minimum oxygen saturation by pulse oximetry (SpO 2) were recorded by computer every minute. Patients received meperidine (25 to 50 mg) and incremental doses of either midazolam or diazepam to an identical end point of slurred speech and/or ptosis. Sedation was scored from 1 (unarousable) to 5 (wide awake).

RESULTS

Sedation scores were 3.6 +/- 0.1 (mean +/- standard error) after each agent. The doses of midazolam and diazepam were 0. 031 +/- 0.002 and 0.106 +/- 0.009 mg/kg, respectively. In the first 45 minutes (PetCO2) was significantly higher with midazolam than with diazepam (p < 0.05). SpO2 was significantly depressed for 80 minutes after each agent, and the number of minutes when the minimum Sp O2 was less than 90% did not differ between the two agents.

CONCLUSIONS

Midazolam was 3.4 times more potent than diazepam. The duration of oxygen desaturation emphasizes the importance of monitoring SpO2 until ventilation and oxygenation have recovered. Although the degree of hypoxemia was comparable, midazolam led to higher end-tidal carbon dioxide tensions.

Procedural sedation and analgesia in the emergency department. Canadian Consensus Guidelines

Procedural sedation and analgesia are core skills in emergency medicine. Various specialty societies have developed guidelines for procedural sedation, each reflecting the perspective of the specialty group. Emergency practitioners are most likely to embrace guidelines developed by people who understand emergency department (ED) skills, procedures, conditions, and case mix. Recognizing this, the Canadian Association of Emergency Physicians (CAEP) determined the need to establish guidelines for procedural sedation in the ED. In March, 1996, a national emergency medicine (EM) working committee, representing adult and pediatric emergency physicians, was established. This committee teleconferenced with representatives of the Canadian Anesthetic Society (CAS) to identify problems, perspectives, and controversial issues, and to define a process for guideline development. The EM committee subsequently reviewed existing literature, determined levels of evidence, and developed the document, which evolved based on feedback from the CAS and CAEP Standards Committees. The final version was approved by the CAEP Standards Committee and the CAEP Board of Directors, then submitted for peer review. These guidelines discuss the goals, definitions, and principles of ED sedation, and make recommendations for pre-sedation preparation, patient fasting, physician skills, equipment and monitoring requirements, and post-sedation care. The guidelines are aimed at non-anesthesiologists practicing part-time or full-time emergency medicine. They are applicable to ED patients receiving parenteral analgesia or sedation for painful or anxiety-provoking procedures. They are intended to increase the safety of procedural sedation in the ED.

Synergistic interaction between the effects of propofol and midazolam with fentanyl on phrenic nerve activity in rabbits

BACKGROUND

It has been shown that the depressive effects of both propofol and midazolam on consciousness are synergistic with opioids, but the nature of their interactions on other physiological systems, e.g. respiration, has not been fully investigated. The present study examined the effect of propofol and midazolam alone and in combination with fentanyl on phrenic nerve activity (PNA) and whether such interactions are additive or synergistic.

METHODS

PNA was recorded in 27 anaesthetised and artificially ventilated rabbits. In three groups, propofol, fentanyl and midazolam were administered intravenously in incremental doses to construct dose-response curves for the depressant effects of each one on PNA. In another two groups, the effect of pretreatment with either fentanyl 1 microgram.kg-1 i.v. or midazolam 0.05 mg.kg-1 i.v. on the effects of propofol and fentanyl respectively on PNA were studied.

RESULTS

Propofol and fentanyl caused a dose-dependent depression of PNA with complete abolition at the highest total doses of 16 mg.kg-1 i.v. and 32 micrograms.kg-1 i.v., respectively. In contrast, midazolam in incremental doses to a total of 0.8 mg.kg-1 reduced mean PNA by 63%, but approximately 12% of PNA remained at a total dose as high as 6.4 mg.kg-1. The mean ED50s, calculated from dose-response curves, were 5.4 mg.kg-1, 3.9 micrograms.kg-1 and 0.4 mg.kg-1 for propofol, fentanyl and midazolam, respectively. Initial doses of either fentanyl 1 microgram.kg-1 i.v. or midazolam 0.05 mg.kg-1 i.v. acted synergistically with subsequent doses of either propofol or fentanyl to abolish PNA at total doses of 8 mg.kg-1 and 8 micrograms.kg-1, respectively.

CONCLUSION

Fentanyl has a synergistic interaction with both propofol and midazolam on PNA and hence potentially on respiration.

Complications of sedation with midazolam in the intensive care unit and a comparison with other sedative regimens

OBJECTIVE

To describe the various complications that have been reported with use of midazolam for sedation in the intensive care unit (ICU).

DATA SOURCES

Publications in scientific literature.

DATA EXTRACTION

Computer search of the literature.

SYNTHESIS

Sedation is required in the ICU in order for patients to tolerate noxious stimuli, particularly mechanical ventilation. Under- and oversedation can lead to complications. To sedate patients in the ICU, midazolam is commonly administered via titrated, continuous infusions. Cardiorespiratory effects tend to be minimal; however, hypotension can occur in hypovolemic patients. Prolonged sedation after cessation of the midazolam infusion may be caused by altered kinetics of the drug in critically ill patients or by accumulation of active metabolites. In addition, paradoxical and psychotic reactions have been rarely reported. Tolerance and tachyphylaxis may occur, particularly with longer-term infusions (> or = 3 days). Benzodiazepine withdrawal syndrome has also been associated with high dose/long-term midazolam infusions. Compared with propofol infusions, midazolam infusions have been associated with a decreased occurrence of hypotension but a more variable time course for recovery of function after the cessation of the infusion. Lorazepam is a more cost-effective choice for long-term (> 24 hrs) sedation.

CONCLUSION

Continuous infusion midazolam provides effective sedation in the ICU with few complications overall, especially when the dose is titrated.

Subpectoral implantation of a cardioverter defibrillator under local anaesthesia

OBJECTIVE

To evaluate patient acceptability of submuscular implantation of a cardioverter defibrillator (ICD) under local anaesthesia with conscious sedation.

DESIGN

Retrospective review. Patient acceptability in the second half of the study was routinely assessed within 24 hours.

SETTING

Regional cardiac centre.

PATIENTS

45 consecutive patients with either aborted sudden death or haemodynamically unstable ventricular tachycardia were referred for ICD implantation.

INTERVENTIONS

A subpectoral implantation technique was employed. Twelve procedures were performed under general anaesthesia. Thirty three patients were sedated with midazolam and diamorphine, and local anaesthesia was achieved with bupivicaine. Ventricular fibrillation for defibrillation threshold testing was induced by alternating current, T wave shock, or ultrarapid burst pacing. Patients were contacted after the procedure to assess acceptability.

RESULTS

32 patients having implantation under local anaesthesia did not recall the surgical procedure. One patient described an awareness of "pushing" as the generator was positioned in the pocket. Seven patients said that the procedure was painless but recalled a test shock, four describing it as mildly uncomfortable. All 33 patients stated that they would be willing to have a second implant under local anaesthesia. Twelve patients who had the implant performed under general anaesthesia had no recollection of the procedure. Mean (SD) total procedure duration was significantly longer in those who had general anaesthesia (93 (16) v 67 (17) minutes; p = 0.0009).

CONCLUSIONS

Subpectoral implantation of ICDs may be performed safely with patient acceptability under local anaesthesia with conscious sedation.