The stability of remifentanil hydrochloride and propofol mixtures in polypropylene syringes and polyvinylchloride bags at 22 degrees-24 degrees C

Propofol-remifentanil patient-controlled sedation for endoscopic procedures: a prospective service audit

PURPOSE

Following demand, we established a patient-controlled propofol-remifentanil sedation service for endoscopy overseen by an anesthesiologist. To assess the effectiveness of the intervention of this service and any complications, we prospectively audited the service. Our primary outcomes of interest were adequacy of sedation and patient satisfaction. Secondary outcomes included any adverse events associated with the sedation.

METHODS

Patients were referred for failure of procedure under endoscopist-administered sedation, refusal of procedure without general anesthesia (GA), or planned complex procedure. We included all 670 procedures performed between 2017 and 2021. We used a mixture of 8.9 mg·mL-1 propofol and 5.4 µg·mL-1 remifentanil with a 1-mL bolus and 20-sec lockout. We assessed the adequacy of sedation using the Modified Gloucester Scale and categorized adverse events according to the Tracking and Reporting Outcomes of Procedural Sedation.

RESULTS

All 670 procedures were accomplished with adequate sedation without the need for ventilation or GA, and all patients were satisfied with the sedation. The complication rate was low, with no sentinel airway or respiratory events. Nineteen out of 670 patients (2.8%) had an incidence of airway obstruction (requiring a simple airway maneuver). The body mass index (BMI) was documented in 18/19 of these patients and the average BMI in this group was 35 kg·m-2. Seven of the 670 patients (1%) had self-terminating apnea, 3/670 patients (0.4%) vomited, no patients aspirated, and 17/665 patients (2.6%) required a vasopressor to maintain blood pressure within 20% of preprocedure values.

CONCLUSION

The results from our prospective service audit indicate that propofol-remifentanil patient-controlled sedation is a safe and reliable technique in patients undergoing endoscopic procedures.

Comparison of Single Target-Controlled Infusion Pump-Delivered Mixed Propofol and Remifentanil with Two Target-Controlled Infusion Pumps-Delivered Propofol and Remifentanil in Patients Undergoing Breast Cancer Surgery-A Prospective Study

Total intravenous anesthesia (TIVA) with remifentanil and propofol (RP) is considered to be an ideal type of general anesthesia (GA) for pediatric and adult patients undergoing medical procedures. However, delivery of an RP mixture by target-controlled infusion (TCI) for GA in surgical procedures has not been described. We investigated the merit of this approach for breast cancer surgery. Eighty-four patients (n = 42 per group) were randomly allocated to propofol and remifentanil either delivered by separate TCI pumps (S group) or in an RP mixture by a single TCI pump (M group). Dosages were adjusted based on the bispectral index (BIS) and the analgesia nociception index (ANI). The primary outcomes were adequate anesthesia (BIS 40-60 and ANI 50-70, respectively), acceptable hemodynamic fluctuations (<30% of baseline) with less frequent TCI pump adjustments, bolus injections of anesthetics, and total consumption of anesthetics during the procedure. The secondary endpoints included time of emergence from anesthesia, patient satisfaction, postoperative pain, rescue with opioids, and adverse events. The characteristics of patients, hemodynamic parameters, BIS and ANI scores, duration of surgery, anesthesia, and emergence were not significantly different between groups. The adjustment frequency of TCI was significantly higher in the S group (3 (range 0-6) vs. 2 (0-6) times; p = 0.005). The total dosage of anesthetics, pain rating, patient satisfaction, need for opioids postoperatively, and incidence of adverse events were not significantly different. We have demonstrated that this RP mixture provided adequate hypnotic and analgesic effects under BIS and ANI monitoring in patients undergoing breast cancer surgery within 1 h.

Plastic particles in medicine: A systematic review of exposure and effects to human health

Single-use plastics (SUPs) have become an essential constituent of our daily life. It is being exploited in numerous pharmaceutical and healthcare applications. Despite their advantages and widespread use in the pharma and medical sectors, the potential clinical problems of plastics, especially the release of micro-nanoplastics (MNPs) and additives from medical plastics (e.g. bags, containers, and administrative sets) and sorption of drugs remain understudied. Certainly, the MNPs are multifaceted stressors that cause detrimental effects to the ecosystem and human health. The origin and persistence of MNPs in pharmaceutical products, their administration to humans, endurance and possible health implication, translocation, and excretion have not been reviewed in detail. The prime focus of this article is to conduct a systematic review on the leaching of MNPs and additives from pharmaceutical containers/administrative sets and their interaction with the pharmaceutical constituents. This review also explores the primary and secondary routes of MNPs entry from healthcare plastic products and their potential health hazards to humans. Furthermore, the fate of plastic waste generated in hospitals, their disposal, and associated MNPs release to the environment, along with preventive, and alternative measures are discussed herein.

Consistency of remifentanil concentrations in propofol-Remifentanil infusions. A laboratory-based study

BACKGROUND

There is increasing interest in two-agent single-pump intravenous infusions for anesthesia and sedation in pediatric patients. Propofol-remifentanil is one such mixture. The poor miscibility of such admixtures when remifentanil is added in very high concentrations and when the admixtures are maintained in static conditions has been demonstrated; however, these physiochemical properties have not been examined in clinically relevant concentrations or settings.

AIM

To examine if propofol-remifentanil admixtures maintain consistent remifentanil delivery when mixed in clinically relevant remifentanil concentrations and subjected to the physical effects of an actively infusing, directly-engaged syringe driver system with an extension line, as occurs when propofol-remifentanil is administered to a patient.

METHODS

A propofol 10 mg.ml^-1 combined with remifentanil 5 mcg.ml^-1 solution was run using a Paedfusor^® propofol target-controlled infusion model for 10 kg and 20 kg children for 57 min at a target plasma concentration of 3 mcg.ml^-1 through a 30 ml syringe, 180 cm minimum volume extension line, lever lock cannula, interlink injection site, and 22 g intravenous cannula into sample pots. Samples were taken at the completion of the loading bolus, 1 and 2 min postcompletion of loading bolus, and every 5 min thereafter. The remifentanil concentration in these samples was then assayed using chromatography.

RESULTS

There was no difference in the concentration of remifentanil in the samples based on the duration of infusion to the endpoint of 1 h, or on the patient weight model used. The concentration remained 5 mcg.ml^-1 +/- 0.5 mcg.ml^-1 per sample. The measurement uncertainty for the assay at 0.5 mcg.ml^-1 is +/- 0.2 mcg.ml^-1 .

CONCLUSION

The concentration of remifentanil was 5 mcg.ml^-1 +/- 0.5 mcg.ml^-1 and was consistent across 57 min of infusion, and two different pediatric weight profiles.

Endo-anesthesia: a primer

Gastrointestinal (GI) endoscopy has witnessed a Cambrian explosion of techniques, indications, and expanding target populations. GI endoscopy encompasses traditional domains that include preventive measures, palliation, as alternative therapies in patients with prohibitive risks of more invasive procedures, and indicated primary treatments. But, it has expanded to include therapeutic and diagnostic interventional endosonography, luminal endoscopic resection, third space endotherapy, endohepatology, and endobariatrics. The lines between surgery and endoscopy are blurred on many occasions within this paradigm. Moreover, patients with high degrees of co-morbidity and complex physiology require more nuanced peri-endoscopic management. The rising demand for endoscopy services has resulted in the development of endoscopy referral centers that offer these invasive procedures as directly booked referrals for regional and rural patients. This further necessitates specialized programs to ensure appropriate evaluation, risk stratification, and optimization for safe sedation and general anesthesia if needed. This landscape is conducive to the organic evolution of endo-anesthesia to meet the needs of these focused and evolving practices. In this primer, we delineate important aspects of endo-anesthesia care and provide relevant clinical and logistical considerations pertaining to the breadth of procedures.

Prospective evaluation of remifentanil-propofol mixture for total intravenous anesthesia: A randomized controlled study

Application of total intravenous anesthesia (TIVA) may be considered as unpractical when compared with inhalational anesthesia. Although it is mostly not recommended, mixing intravenous agents is popular in clinical practice. The aim of the present study was to investigate the suitability of using remifentanil-propofol mixture (MIXTIVA) for TIVA. Adult patients with an American Society of Anesthesiologists grade of I-II scheduled for elective thyroidectomy were randomly allocated to 3 groups (n=32 for each) to receive TIVA with remifentanil and propofol infusions separately (control group, Group I) or with MIXTIVA infusion that contained remifentanil/propofol at a proportion of 2/1,000 or 3/1,000 (remifentanil concentration, 20 or 30 µg/ml in 1% propofol in Group II or Group III, respectively). The extubation time (the primary outcome of the study), the orientation time and number of patients in whom intraoperative hypotension, hypertension or bradycardia episodes were encountered during anesthesia were comparable among the groups. The mean remifentanil infusion rate in Group III was significantly higher than that in the other groups. The mean propofol infusion rates and mean bispectral index (BIS) scores during anesthesia were comparable among groups. Hypotension accompanied with a high BIS was encountered in one patient in Group III. In conclusion, compared to the standard TIVA technique using separate drug infusions, MIXTIVA infusion used for thyroidectomies did not result in any statistically significant difference in recovery and clinical outcomes. This technique may be considered as a practical implementation for busy ambulatory centers performing general anesthesia. The present study was retrospectively registered at clinicaltrials.gov (trial registration no. NCT04394897).

Anesthesia for GI endoscopy in the era of COVID-19

As a result of COVID-19, the last few weeks have necessitated a reevaluation of the sedation paradigm for gastrointestinal (GI) endoscopic procedures. Routine screening and some surveillance procedures have taken a backseat and likely to remain so until a vaccine or effective treatment becomes available. Anesthesia providers and endoscopists are required to adapt to this new reality rapidly. The general aim of sedation remains the same-patient comfort, reduced hypoxia, prevention of aspiration along with rapid recovery, and discharge. The present review focuses on necessary modification to reduce the risk of virus contagion for both patients (from health-care providers) and vice versa. A preprocedure evaluation and consenting should be modified and provided remotely. Unsedated GI endoscopy, sedation with minimal respiratory depression, and modification of general anesthesia are explored. Challenges with supplemental oxygen administration and monitoring are addressed. Guidelines for appropriate use of personal protective equipment are discussed. Measures for limiting aerosolization are deliberated.

De-mystifying the "Mixifusor"

Total intravenous anesthesia (TIVA) using a mixture of propofol and remifentanil in the same syringe has become an accepted technique in Pediatric Anesthesia. A survey by a group of respected UK anesthetists demonstrated a low incidence of serious complications, related to the pharmacology and dose of the drugs. However, a current guideline for the safe use of TIVA recommends against this practice. Pharmaceutical concerns include the physical stability of the emulsion when remifentanil is mixed with propofol; changes in drug concentration over time; nonuniform mixing of propofol and remifentanil; the risk of bacterial contamination; and the potential for drug administration errors. Propofol and remifentanil have markedly different pharmacokinetic profiles. When remifentanil is mixed with propofol and delivered as a target-controlled infusion (TCI) of propofol, remifentanil delivery is not target-controlled but passively follows the variable infusion rates calculated by the syringe driver to deliver predicted plasma or effect-site concentrations of propofol. The pharmacokinetic consequences can be illustrated using pharmacokinetic modeling similar to that used in TCI pumps. The clinical consequences reflect the dose-dependent pharmacodynamics of remifentanil. Increasing the target propofol concentration produces a rapid increase and peak in remifentanil concentration that risks apnea, bradycardia, and hypotension, especially with higher concentrations of remifentanil. The faster decline in remifentanil concentration with falling propofol concentrations risks inadequate narcosis and unwanted responses to surgical stimuli. Remifentanil delivery is inflexible and dosing cannot be adjusted to the clinical need and responses of individual patients. The medicolegal considerations are stark. In UK and EU Law, mixing propofol and remifentanil creates a new, unlicensed drug and the person mixing takes on the responsibilities of manufacturer. If a patient receiving anesthesia in the form of a mixed propofol-remifentanil infusion suffered a critical incident or actual harm, the clinician's practice may come under scrutiny and criticism, potentially involving a legal challenge and the Medical Regulator.

The safety profile and effectiveness of propofol-remifentanil mixtures for total intravenous anesthesia in children

BACKGROUND

Total intravenous anesthesia is used in less than 10% of operations in the UK. Many pediatric anesthetists in the UK and Ireland administer total intravenous anesthesia to children using a mixture of propofol and remifentanil in the same syringe. This unlicensed drug has not been studied clinically, because of lack of Medicines and Healthcare products Regulatory Agency (UK) or Food and Drug Administration (US) approval to undertake such studies.

AIM

The aim of this service evaluation was to assess the safety profile and effectiveness of propofol-remifentanil mixtures in the pediatric population undergoing a variety of surgical procedures.

METHODS

Pediatric Anesthetists in the UK and Ireland who regularly used propofol-remifentanil mixtures for total intravenous anesthesia were invited to submit data. This data were analyzed to assess the effectiveness of anesthesia and the incidence and nature of any complications that occurred.

RESULTS

Usable data were collected from 873 patients. Mixtures were most commonly administered in gastroenterology and ear, nose, and throat procedures. Two-thirds of patients were less than 10 years old, and their mean weight was 28.7 kg. Anesthesia using the mixture alone was successful in all but 3 patients. The commonest nonserious complication was coughing (4.6%), followed by movement (3.3%). The overall incidence of serious, related, unexpected adverse events requiring intervention was 1.7%. These included desaturation (5 patients), apnea (3), abdominal/chest rigidity (2), cough requiring paralysis (2), ventilatory problems (2), and hypotension (1). Most occurred at induction, were attributable to the properties of the drugs being administered and not directly related to the use of the mixture. No life-threatening adverse events were recorded. Complications were less common if a ≤5 μg mL^-1 concentration of remifentanil was used.

CONCLUSION

These data demonstrate that effective anesthesia can be administered to pediatric patients undergoing a wide range of procedures using mixtures of propofol and remifentanil. Serious, related, unexpected adverse events requiring intervention had a low incidence and were largely due to predictable effects of the drugs being administered. A ≤5 μg mL^-1 remifentanil concentration is associated with proportionately less complications.

The effect of concentration, reconstitution solution and pH on the stability of a remifentanil hydrochloride and propofol admixture for simultaneous co-infusion

Background

There are scenarios where pre-mixing and infusing analgesic and anaesthetic agents as a single intravenous (IV) solution is highly desirable; however, it is important to ensure the agents are compatible when mixed. As such, the long-term stability of a remifentanil-propofol mixture, and means of improving this, were assessed across a range of remifentanil concentrations, diluents, and time points.

Methods

Remifentanil was reconstituted with ultrapure water, 0.9% saline, 20% saline, or 8.4% sodium bicarbonate solution (the latter two chosen for their pH characteristics, rather than their use in pharmaceutical reconstitution) and then mixed with propofol (1%) or further diluted with water to derive concentrations of 10–50 μg mL^− 1. Remifentanil and propofol concentrations were determined initially and then periodically for up to 24 h using high performance liquid chromatography (HPLC). Mass spectrometry (MS) was used to detect degradation products in solutions containing 30 μg mL^− 1 of remifentanil. Statistical analysis was performed using ANOVA and Student’s t-test, with a significance value of 0.05.

Results

Isolated remifentanil (pH < 4) and propofol (pH 7.35) did not degrade significantly when reconstituted with water or saline solution over 24 h, while remifentanil reconstituted with sodium bicarbonate degraded significantly (P < 0.001, pH 8.65). Mixing with propofol substantially increased the pH of the mixture and resulted in significant remifentanil degradation for all reconstitution solutions used, while propofol remained stable (pH 6.50). The amount of degradation product detected in samples containing isolated remifentanil and a mixture of the drugs was proportional to the remifentanil degradation observed.

Conclusions

Remifentanil stability is affected by both the reconstitution solution used and when mixed with propofol, with pH appearing to be a contributing factor to degradation. If the pH of the solution and concentration of remifentanil are correctly controlled, e.g. through the use of a more acidic diluent, an admixture of remifentanil and propofol may be useful clinically.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12871-020-01194-5.

Emulsion Stability of Different Intravenous Propofol Formulations in Simulated Co-Administration with Remifentanil Hydrochloride

Background

Propofol and remifentanil often need to be co-administered via the same intravenous catheter line, which predisposes to potential compatibility issues. Our aim was to determine and compare the emulsion stability of three propofol formulations, two with medium chain triglycerides and one with long chain triglycerides, when administered together with remifentanil hydrochloride.

Methods

Remifentanil hydrochloride (Ultiva ® ) 50 µg/mL was mixed with two concentrations (10 and 20 mg/mL) of each propofol formulation in mixing ratios 10+1, 20+1, 1+1 and 1+20. Emulsion stability was assessed immediately after mixing and 4 hours later by measurements of pH, mean droplet diameter, polydispersity index, and calculating percentage of fat residing in globules>5 µm (PFAT5).

Results

High PFAT5 values were observed in certain mixing ratios. The correlation between elevated PFAT5 and high propofol concentration (20 mg/mL), when remifentanil was in abundance and for long contact time indicated that these factors influenced the stability of the propofol emulsions.

Conclusions

Stability differences between the propofol formulations were identified under extreme test conditions. Co-administration of remifentanil and propofol in the same i.v. line is safe when propofol is in abundance. Caution is advised when remifentanil is present in equal parts or in abundance when co-administered with propofol 20 mg/mL.

Practicalities of Total Intravenous Anesthesia and Target-controlled Infusion in Children

Propofol administered in conjunction with an opioid such as remifentanil is used to provide total intravenous anesthesia for children. Drugs can be given as infusion controlled manually by the physician or as automated target-controlled infusion that targets plasma or effect site. Smart pumps programmed with pharmacokinetic parameter estimates administer drugs to a preset plasma concentration. A linking rate constant parameter (keo) allows estimation of effect site concentration. There are two parameter sets, named after the first author describing them, that are commonly used in pediatric target-controlled infusion for propofol (Absalom and Kataria) and one for remifentanil (Minto). Propofol validation studies suggest that these parameter estimates are satisfactory for the majority of children. Recommended target concentrations for both propofol and remifentanil depend on the type of surgery, the degree of surgical stimulation, the use of local anesthetic blocks, and the ventilatory status of the patient. The use of processed electroencephalographic monitoring is helpful in pediatric total intravenous anesthesia and target-controlled infusion anesthesia, particularly in the presence of neuromuscular blockade.

Understanding Infusion Pumps

Infusion systems are complicated electromechanical systems that are used to deliver anesthetic drugs with moderate precision. Four types of systems are described-gravity feed, in-line piston, peristaltic, and syringe. These systems are subject to a number of failure modes-occlusion, disconnection, siphoning, infiltration, and air bubbles. The relative advantages of the various systems and some of the monitoring capabilities are discussed. A brief example of the use of an infusion system during anesthetic induction is presented. With understanding of the functioning of these systems, users may develop greater comfort.

Quality control and stability of ketamine, remifentanil, and sufentanil syringes in a pediatric operating theater

BACKGROUND

Transforming a drug from its commercial form into a ready-to-use drug is common practice, especially in pediatrics. However, the risk of compounding error is real and data on drug stability in practice are not always available.

AIMS

The aim of this study was to assess, in real conditions, both the error rate and stability of three drugs: ketamine, remifentanil, and sufentanil.

METHODS

A new rapid and easy-to-use high-performance liquid chromatography method with a diode array detector has been developed and validated to quantify these drugs and detect their degradation products. Over a 1-month period, 151 syringes were collected in the postanesthesia care unit. Seventy-three were stock solution syringes containing a 10-fold dilution of commercial drugs and 78 were serial dilution syringes made from successive dilutions of stock solutions. A comparison between real and expected concentrations as well as the detection of possible degradation products was carried out on these samples.

RESULTS

All stock solution syringes had good chemical stability throughout the working day. A 4-µg/mL remifentanil serial dilution syringe, however, had to be discarded as a degradation peak was detected. Overall, 15.3% (95% CI, 9.5-21.1%) of syringes had a drug concentration outside the ±10% acceptability range, that is, 11.0% (95% CI, 3.7-18.2%) and 19.5% (95% CI, 10.6%-28.4%) of stock and diluted syringes respectively, with drug amounts ranging from -25.3% to 22.0%. The highest error rates were observed with sufentanil syringes: 20% and 28% for stock solution and serial dilution, respectively.

CONCLUSION

The study shows that stock solution syringes prepared in advance are chemically stable throughout the day, unlike certain serial dilution syringes, indicating that the latter should be prepared just before administration to ensure chemical stability. Our results show that the error rate for serial dilution syringes is twice that of stock solution. Different safety measures are under discussion and have to be further studied.

A follow-up survey of total intravenous anesthesia usage in children in the U.K. and Ireland

BACKGROUND

Total intravenous anesthesia usage in children remains relatively unpopular in the UK and Ireland. A postal survey by Hill et al in 2008 indicated that only 26% of Consultants used a propofol infusion at least once a month.

AIMS

Following an increase in teaching and training opportunities in pediatric total intravenous anesthesia in the UK, we repeated the survey among Consultant members of Association of Paediatric Anaesthetists of Great Britain and Ireland and Society for Intravenous Anaesthesia, to see if this had affected total intravenous anesthesia usage in children and how practice may have changed.

METHODS

We used an anonymous online survey sent to Association of Paediatric Anaesthetists of Great Britain and Ireland and Society for Intravenous Anaesthesia members.

RESULTS

A total of 291 responses were analyzed. Total intravenous anesthesia was the default method of anesthesia in 8% of respondents and a further 46% used total intravenous anesthesia at least monthly. Overall total intravenous anesthesia usage had increased in the past year in 53%. The main indications were malignant hyperthermia susceptibility, and postoperative nausea and vomiting. Ear/nose/throat surgery was the most popular surgical specialty. The main reasons for not using total intravenous anesthesia were that it was too "fiddly" and lack of confidence in the user. Most respondents used propofol in combination with remifentanil. Over 80% used propofol target-controlled infusion. The potential for propofol-related infusion syndrome concerned many, with 74% limiting infusion duration as a result. Bispectral Index was not used routinely by the majority of anesthetists. Even though most anesthetists did not use total intravenous anesthesia routinely, 98% felt they would be confident to anesthetize an malignant hyperpyrexia-positive patient using the technique.

CONCLUSION

This survey has shown that although total intravenous anesthesia is not the default anesthetic technique for most anesthetists, overall usage in children has more than doubled in the past 10 years, with many happy to use it in a wide variety of patients and procedures.

Compatibility of drugs administered as Y-site infusion in intensive care units: A systematic review

OBJECTIVES

To gather all published information about the stability of drugs commonly used in Intensive Care Units (ICU); evaluate the methodology of published data; and generate a compatibility table.

DESIGN

i) A systematic review was conducted searching the following databases: Medline, Stabilis, Handbook of Injectable Drugs and Micromedex. Articles published from 1990 to 2017 in English, Spanish and French were included. ii) Article quality was analyzed according to the stability studies practice guidelines. iii) A compatibility table was produced with data for 44 binary combinations of drugs frequently used in the ICU.

SCOPE

Spanish and international hospital ICU.

RESULTS

The systematic review included 29 studies (27 originals, 2 reviews). None of the included studies followed all the methodological requirements. However, 93% guaranteed correct reproducibility. Accordingly, drug stability knowledge was available for 50.3% of the studied admixtures, in which 77.1% of the binary combinations proved compatible and 16.8% proved incompatible.

CONCLUSIONS

This review provides new reliable evidence about the physicochemical stability of drugs commonly used in the critical care setting. The study contributes to the safe administration of intravenous drugs in critical patients with a view to avoiding adverse events in this frail population.

Adhesion of volatile propofol to breathing circuit tubing

Propofol in exhaled breath can be measured and may provide a real-time estimate of plasma concentration. However, propofol is absorbed in plastic tubing, thus estimates may fail to reflect lung/blood concentration if expired gas is not extracted directly from the endotracheal tube. We evaluated exhaled propofol in five ventilated ICU patients who were sedated with propofol. Exhaled propofol was measured once per minute using ion mobility spectrometry. Exhaled air was sampled directly from the endotracheal tube and at the ventilator end of the expiratory side of the anesthetic circuit. The circuit was disconnected from the patient and propofol was washed out with a separate clean ventilator. Propofol molecules, which discharged from the expiratory portion of the breathing circuit, were measured for up to 60 h. We also determined whether propofol passes through the plastic of breathing circuits. A total of 984 data pairs (presented as median values, with 95% confidence interval), consisting of both concentrations were collected. The concentration of propofol sampled near the patient was always substantially higher, at 10.4 [10.25-10.55] versus 5.73 [5.66-5.88] ppb (p < 0.001). The reduction in concentration over the breathing circuit tubing was 4.58 [4.48-4.68] ppb, 3.46 [3.21-3.73] in the first hour, 4.05 [3.77-4.34] in the second hour, and 4.01 [3.36-4.40] in the third hour. Out-gassing propofol from the breathing circuit remained at 2.8 ppb after 60 h of washing out. Diffusion through the plastic was not observed. Volatile propofol binds or adsorbs to the plastic of a breathing circuit with saturation kinetics. The bond is reversible so propofol can be washed out from the plastic. Our data confirm earlier findings that accurate measurements of volatile propofol require exhaled air to be sampled as close as possible to the patient.

Adherence of volatile propofol to various types of plastic tubing

Propofol is an intravenous anesthetic. Currently, it is not possible to routinely measure blood concentration of the drug in real time. However, multi-capillary column ion-mobility spectrometry of exhaled gas can estimate blood propofol concentration. Unfortunately, adhesion of volatile propofol on plastic materials complicates measurements. Therefore, it is necessary to consider the extent to which volatile propofol adheres to various plastics used in sampling tubing. Perfluoralkoxy (PFA), polytetrafluorethylene (PTFE), polyurethane (PUR), silicone, and Tygon tubing were investigated in an experimental setting using a calibration gas generator (HovaCAL). Propofol gas was measured for one hour at 26 °C, 50 °C, and 90 °C tubing temperature. Test tubing segments were then flushed with N₂ to quantify desorption. PUR and Tygon sample tubing absorbed all volatile propofol. The silicone tubing reached the maximum propofol concentration after 119 min which was 29 min after propofol gas exposure stopped. The use of PFA or PTFE tubing produced comparable and reasonably accurate propofol measurements. The desaturation time for the PFA was 10 min shorter at 26 °C than for PTFE. PFA tubing thus seems most suitable for measurement of volatile propofol, with PTFE as an alternative.

Physicochemical compatibility and emulsion stability of propofol with commonly used analgesics and sedatives in an intensive care unit

Objectives

The purpose of this study was the determination of the physicochemical compatibility and emulsion stability of propofol with other sedatives and analgesics (clonidine hydrochloride, dexmedetomidine, 4-hydroxybutyric acid, (S)-ketamine, lormetazepam, midazolam hydrochloride, piritramide, remifentanil hydrochloride and sufentanil citrate) that are frequently administered together intravenously.

Methods

Drugs were mixed with propofol and stored without light protection at room temperature. Samples were taken at 10 points of time over 7 days. The physical stability and emulsion stability in particular were analysed by visual and microscopical inspection and by measurement of the pH value, zeta potential and globule size distribution. In addition, high-performance liquid chromatography and mass spectrometry were used to identify chemical incompatibilities.

Results

4-Hydroxybutyric acid, midazolam hydrochloride, piritramide and remifentanil hydrochloride are physically incompatible when mixed with propofol. The reason for this is the development of an increased fraction of oil droplets >5 µm leading to a higher risk of emboli. Moreover, propofol is chemically incompatible with remifentanil. The sorption of propofol to the rubber stopper of the syringe was another detectable incompatibility.

Conclusions

Propofol should not be administered with 4-hydroxybutyric acid, remifentanil hydrochloride, midazolam hydrochloride and piritramide through the same intravenous line. Based on the risk of sorption to the rubber material, propofol should be used with caution. A drug loss might occur that leads to an underdosing of the patient requiring a dose adjustment to avoid any adverse consequences. As a result of this study, the drug safety in intensive care units could be optimised.

Remifentanil and propofol undergo separation and layering when mixed in the same syringe for total intravenous anesthesia

BACKGROUND

Propofol and remifentanil can be combined to deliver total intravenous anesthesia (TIVA). Propofol and remifentanil are sometimes mixed in the same syringe. Since remifentanil is a solution and propofol is an emulsion, we hypothesized that they would separate over time when mixed in the same syringe.

METHODS

Nine 60-ml polypropylene syringes were prepared as follows: Group A: 1.25 ml of remifentanil solution (1 mg·ml(-1) ) was added to 48.75 ml of propofol (10 mg·ml(-1) ) in three syringes. Group B: 2.5 ml of remifentanil (1 mg·ml(-1) ) was added to 47.5 ml of propofol (10 mg·ml(-1) ) in three syringes. Group C: 5 ml of remifentanil (1 mg·ml(-1) ) was added to 45 ml of propofol (10 mg·ml(-1) ) in three syringes. The remifentanil lyophilized powder was reconstituted with sterile water and added to the propofol by injection through the port on the bottom of the syringe. The syringe was then inverted five times in succession to mix the drugs. The syringes were mounted in an upright vertical position (plunger on top, port on bottom) with wire on a pegboard. Samples of the mixture were taken from the bottom port (via a 3-way stopcock) and from the top of the syringe (via a stopcock on an 18-gauge needle placed 5 mm through the plunger) at the following time intervals (min) from baseline: T0, T10, T30, T60, T120, T180, T240, T300. Remifentanil and propofol were quantified using specific and validated HPLC/MS/MS assays with automated online sample preparation.

RESULTS

Concentrations of remifentanil were significantly greater at the top than the bottom of the syringes in groups A and B. Concentrations of propofol were significantly greater at the bottom than the top of the syringes in all groups.

CONCLUSION

Our data indicate that remifentanil solution and propofol emulsion are immiscible: remifentanil separates from propofol and rises to the top. Thus, concentrations of remifentanil and propofol delivered to patients from the same syringe during TIVA are not those expected and cannot be reliable. Remifentanil and propofol should be administered in separate syringes when used in combination for TIVA.

Effects of a fentanyl-propofol mixture on propofol injection pain: a randomized clinical trial

BACKGROUND

Propofol injection pain is a common problem that can be very distressing for patients. We compared the effects of injection with saline followed by injection with a fentanyl-propofol mixture, injection with fentanyl followed by a propofol injection, and injection with saline followed by propofol alone on propofol injection pain.

METHODS

The patients were assigned randomly to one of three groups. A rubber tourniquet was placed on the forearm to produce venous occlusion for 1 min. Before anesthesia induction, group C (control, n = 50) and group M (fentanylpropofol mixture, n = 50) received 5 ml of isotonic saline, while group F (fentanyl, n = 50) received 2 µg/kg of fentanyl. After the tourniquet was released, groups C and F received 5 ml of propofol and group M received 5 ml of a mixture containing 20 ml of propofol and 4 ml of fentanyl. At 10 s after the study drugs were given, a standard question about the comfort of the injection was asked of the patient. We used a verbal rating scale to evaluate propofol injection pain. Statistical analyses were performed with Student's t-tests and Fisher's exact tests; P < 0.05 was considered to indicate statistical significance.

RESULTS

The demographic data were similar among the groups. In group M, the number of patients reporting propofol injection pain was significantly lower than in groups F and C (both P < 0.001). No patient in group F or M experienced severe pain, whereas 24 patients (48%) had severe pain in group C (both P < 0.001).

CONCLUSIONS

This study shows that a fentanyl-propofol mixture was more effective than fentanyl pretreatment or a placebo in preventing propofol injection pain.

Significantly reduced hypoxemic events in morbidly obese patients undergoing gastrointestinal endoscopy: Predictors and practice effect

Background:

Providing anesthesia for gastrointestinal (GI) endoscopy procedures in morbidly obese patients is a challenge for a variety of reasons. The negative impact of obesity on the respiratory system combined with a need to share the upper airway and necessity to preserve the spontaneous ventilation, together add to difficulties.

Materials and Methods:

This retrospective cohort study included patients with a body mass index (BMI) >40 kg/m² that underwent out-patient GI endoscopy between September 2010 and February 2011. Patient data was analyzed for procedure, airway management technique as well as hypoxemic and cardiovascular events.

Results:

A total of 119 patients met the inclusion criteria. Our innovative airway management technique resulted in a lower rate of intraoperative hypoxemic events compared with any published data available. Frequency of desaturation episodes showed statistically significant relation to previous history of obstructive sleep apnea (OSA). These desaturation episodes were found to be statistically independent of increasing BMI of patients.

Conclusion:

Pre-operative history of OSA irrespective of associated BMI values can be potentially used as a predictor of intra-procedural desaturation. With suitable modification of anesthesia technique, it is possible to reduce the incidence of adverse respiratory events in morbidly obese patients undergoing GI endoscopy procedures, thereby avoiding the need for endotracheal intubation.

Technical communication: stability of propofol in polystyrene-based tissue culture plates

Propofol has been reported to have high stability in glass and relatively high stability up to 24 hours in polyvinyl chloride-based medical plastics. Recent publications have observed the effects of propofol on cells and tissues grown in culture. Many cell culture plastics are formulated from polystyrene but we could find little information on the stability of propofol exposed to these products. We observed very little change in the concentration of propofol diluted in cell culture medium over 24 hours when exposed to glass, but substantial loss of the drug when exposed to 96-well polystyrene cell culture plates. This decrease was most rapid in the first hour but continued until 24 hours. The type of plastic used in cell and tissue culture experiments with propofol may influence the results by increasing the apparent dose required to see an effect.

Combined propofol and remifentanil intravenous anesthesia for pediatric patients undergoing magnetic resonance imaging

BACKGROUND

A prospective observational case series of children receiving light general anesthesia for magnetic resonance imaging (MRI) was performed. Our purpose was to examine the merit of anesthesia and recovery/discharge times of combined remifentanil and propofol total intravenous anesthesia (TIVA) in spontaneously breathing children.

METHODS

After IRB approval and informed consent, 56 patients receiving Remi/Propofol TIVA (Remifentanil 10 microg.ml(-1) Propofol 10 mg.ml(-1)) were observed. Blood pressure, respiratory rate, endtidal CO(2) (P(E)CO(2)), oxygen saturation and temperature were recorded at the start and finish of anesthesia. In addition, induction and recovery times were noted. Recovery time was from scan completion until discharge from the initial recovery area. Discharge time was from scan completion to discharge home.

RESULTS

Fifty-six patients received Remi/Propofol TIVA. The mean Remi/Propofol recovery and discharge times were 8.9 and 28.2 min, respectively. There was a statistically significant decrease in respiratory rate and increase in CO(2) from the start to the end of the procedure. During the scan, seven patients moved. One patient experienced postprocedure nausea and or vomiting.

CONCLUSIONS

The combination of remifentanil and propofol for TIVA may be an effective method of light general anesthesia in pediatric patients undergoing MRI.

A comparison of patient-controlled sedation using either remifentanil or remifentanil-propofol for shock wave lithotripsy

Patient-controlled sedation (PCS) has been used for extracorporeal shock wave lithotripsy (SWL) because it allows for rapid individualized titration of anesthetics. Because of its sedating effects, the addition of propofol to remifentanil may improve patient tolerance of SWL with PCS. One hundred twenty patients were randomly assigned to receive remifentanil 10 microg or remifentanil 10 microg plus propofol 5 mg for PCS with zero-lockout interval. Nine patients in the Remifentanil group and three patients in the Remifentanil-Propofol group required additional sedatives to complete their SWL (P = 0.128). Compared with the Remifentanil group, the Remifentanil-Propofol group required less remifentanil, had a decreased incidence of postoperative nausea and vomiting, and had a better overall satisfaction level. However, they had an increased incidence of transient apnea and oxygen desaturation. The incidence of apnea was 15% in the Remifentanil group and 52% in the Remifentanil-Propofol group (P < 0.001). All patients were able to move themselves to the stretcher at the end of SWL, and median time to home discharge was <70 min in both groups. Both remifentanil and remifentanil-propofol were useful for PCS during SWL.

IMPLICATIONS

The addition of propofol to remifentanil improves patient satisfaction and decreases postoperative nausea and vomiting. However, it causes more respiratory depression than remifentanil alone. When remifentanil-propofol is used with patient-controlled sedation, appropriate monitoring and a minimum 1-2 min lockout interval is required.