Administration and monitoring of intravenous anesthetics

Anesthesia and intraoperative neurophysiological spinal cord monitoring

PURPOSE OF REVIEW

We will explain the basic principles of intraoperative neurophysiological monitoring (IONM) during spinal surgery. Thereafter we highlight the significant impact that general anesthesia can have on the efficacy of the IONM and provide an overview of the essential pharmacological and physiological factors that need to be optimized to enable IONM. Lastly, we stress the importance of teamwork between the anesthesiologist, the neurophysiologist, and the surgeon to improve clinical outcome after spinal surgery.

RECENT FINDINGS

In recent years, the use of IONM has increased significantly. It has developed into a mature discipline, enabling neurosurgical procedures of ever-increasing complexity. It is thus of growing importance for the anesthesiologist to appreciate the interplay between IONM and anesthesia and to build up experience working in a team with the neurosurgeon and the neurophysiologist.

SUMMARY

Safety measures, cooperation, careful choice of drugs, titration of drugs, and maintenance of physiological homeostasis are essential for effective IONM.

Influence of an "Electroencephalogram-Based" Monitor Choice on the Delay Between the Predicted Propofol Effect-Site Concentration and the Measured Drug Effect

BACKGROUND

Clinicians can optimize propofol titration by using 2 sources of pharmacodynamic (PD) information: the predicted effect-site concentration for propofol (Ceprop) and the electroencephalographically (EEG) measured drug effect. Relation between these sources should be time independent, that is, perfectly synchronized. In reality, various issues corrupt time independency, leading to asynchrony or, in other words, hysteresis. This asynchrony can lead to conflicting information, making effective drug dosing challenging. In this study, we tried to quantify and minimize the hysteresis between the Ceprop (calculated using the Schnider model for propofol) and EEG measured drug effect, using nonlinear mixed-effects modeling (NONMEM). Further, we measured the influence of EEG-based monitor choice, namely Bispectral index (BIS) versus qCON index (qCON) monitor, on propofol PD hysteresis.

METHODS

We analyzed the PD data from 165 patients undergoing propofol-remifentanil anesthesia for outpatient surgery. Drugs were administered using target-controlled infusion (TCI) pumps. Pumps were programmed with Schnider model for propofol and Minto model for remifentanil. We constructed 2 PD models (direct models) relating the Schnider Ceprop to the measured BIS and qCON monitor values. We quantified the models' misspecification due to hysteresis, on an individual level, using the root mean squared errors (RMSEs). Subsequently, we optimized the PD models' predictions by adding a lag term to both models (lag-time PD models) and quantified the optimization using the RMSE.

RESULTS

There is a counterclockwise hysteresis between Ceprop and BIS/qCON values. Not accounting for this hysteresis results in a direct PD model with an effect-site concentration which produces 50% of the maximal drug effect (Ce50) of 6.24 and 8.62 µg/mL and RMSE (median and interquartile range [IQR]) of 9.38 (7.92-11.23) and 8.41(7.04-10.2) for BIS and qCON, respectively. Adding a modeled lag factor of 49 seconds to the BIS model and 53 seconds to the qCON model improved both models' prediction, resulting in similar Ce50 (3.66 and 3.62 µg/mL for BIS and qCON) and lower RMSE (median (IQR) of 7.87 (6.49-9.90) and 6.56 (5.28-8.57) for BIS and qCON.

CONCLUSIONS

There is a significant "Ceprop versus EEG measured drug effect" hysteresis. Not accounting for it leads to conflicting PD information and false high Ce50 for propofol in both monitors. Adding a lag term improved the PD model performance, improved the "pump-monitor" synchrony, and made the estimates of Ce50 for propofol more realistic and less monitor dependent.

Neuroplasticity induced by general anaesthesia: study protocol for a randomised cross-over clinical trial exploring the effects of sevoflurane and propofol on the brain - A 3-T magnetic resonance imaging study of healthy volunteers

BACKGROUND

Although used extensively worldwide, the effects of general anaesthesia on the human brain remain largely elusive. Moreover, general anaesthesia may contribute to serious conditions or adverse events such as postoperative cognitive dysfunction and delirium. To understand the basic mechanisms of general anaesthesia, this project aims to study and compare possible de novo neuroplastic changes induced by two commonly used types of general anaesthesia, i.e. inhalation anaesthesia by sevoflurane and intravenously administered anaesthesia by propofol. In addition, we wish to to explore possible associations between neuroplastic changes, neuropsychological adverse effects and subjective changes in fatigue and well-being.

METHODS

This is a randomised, participant- and assessor-blinded, cross-over clinical trial. Thirty healthy volunteers (male:female ratio 1:1) will be randomised to general anaesthesia by either sevoflurane or propofol. Multimodal magnetic resonance imaging (MRI) of the brain will be performed before and after general anaesthesia and repeated after 1 and 8 days. Each magnetic resonance imaging session will be accompanied by cognitive testing and questionnaires on fatigue and well-being. After a wash-out period of 4 weeks, the volunteers will receive the other type of anaesthetic (sevoflurane or propofol), followed by the same series of tests. Primary outcomes: changes in T1-weighted 3D anatomy and diffusion tensor imaging.

SECONDARY OUTCOMES

changes in resting-state functional magnetic resonance imaging, fatigue, well-being, cognitive function, correlations between magnetic resonance imaging findings and the clinical outcomes (questionnaires and cognitive function). Exploratory outcomes: changes in cerebral perfusion and oxygen metabolism, lactate, and response to visual stimuli.

DISCUSSION

To the best of our knowledge, this is the most extensive and advanced series of studies with head-to-head comparison of two widely used methods for general anaesthesia. Recruitment was initiated in September 2019.

TRIAL REGISTRATION

Approved by the Research Ethics Committee in the Capital Region of Denmark, ref. H-18028925 (6 September 2018). EudraCT and Danish Medicines Agency: 2018-001252-35 (23 March 2018). www.clinicaltrials.gov , ID: NCT04125121 . Retrospectively registered on 10 October 2019.

Operative Gynecological Laparoscopy Under Conscious Sedation

BACKGROUND AND OBJECTIVES

Operative laparoscopy is generally performed under general anesthesia. Local anesthesia and conscious sedation may be useful in select short procedures. In the present study, we evaluated safety and efficacy of operative laparoscopy under conscious sedation.

METHODS

Retrospective observational study evaluating patients undergoing gynecologic laparoscopy. Laparoscopy under conscious sedation was performed for each patient with umbilical direct insertion of a 12-mm port, followed by 2 ancillary ports at 1 cm medially to the anterior superior iliac spine. Conversion to conventional laparoscopy or laparotomy was recorded. Conscious sedation was obtained using Remifentanil and Propofol, administered by an infusion system based on pharmacokinetic and pharmacodynamic models. Local anesthesia was administered at port insertion sites and for paracervical block. Pain intensity was evaluated with the Visual Analog Scale (VAS). Adverse events and drug concentrations throughout the procedure were retrieved.

RESULTS

Our study population included 166 patients. They underwent laparoscopic unilateral versus bilateral salpingo-oophorectomy, ovarian cystectomy, bilateral salpingo-oophorectomy and omentectomy for a borderline ovarian tumor, myomectomy; or underwent surgery for unexplained infertility evaluation, pelvic pain, staging of ovarian cancer. Mean duration of pneumoperitoneum was 22.3 ± 7.2 min. Rate of conversion to laparoscopy under general anesthesia was 17/166 (10.2%) and there were only 3 cases of patients with low tolerability to the procedure. No severe adverse events occurred. Hospital discharge occurred in all unconverted cases after 6 to 18 h.

CONCLUSIONS

Operative laparoscopy under conscious sedation and local anesthesia appears to be a feasible technique in gynecologic surgery with no adverse patient outcomes.

Clinical Pharmacokinetics and Pharmacodynamics of Propofol

Propofol is an intravenous hypnotic drug that is used for induction and maintenance of sedation and general anaesthesia. It exerts its effects through potentiation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) at the GABAA receptor, and has gained widespread use due to its favourable drug effect profile. The main adverse effects are disturbances in cardiopulmonary physiology. Due to its narrow therapeutic margin, propofol should only be administered by practitioners trained and experienced in providing general anaesthesia. Many pharmacokinetic (PK) and pharmacodynamic (PD) models for propofol exist. Some are used to inform drug dosing guidelines, and some are also implemented in so-called target-controlled infusion devices, to calculate the infusion rates required for user-defined target plasma or effect-site concentrations. Most of the models were designed for use in a specific and well-defined patient category. However, models applicable in a more general population have recently been developed and published. The most recent example is the general purpose propofol model developed by Eleveld and colleagues. Retrospective predictive performance evaluations show that this model performs as well as, or even better than, PK models developed for specific populations, such as adults, children or the obese; however, prospective evaluation of the model is still required. Propofol undergoes extensive PK and PD interactions with both other hypnotic drugs and opioids. PD interactions are the most clinically significant, and, with other hypnotics, tend to be additive, whereas interactions with opioids tend to be highly synergistic. Response surface modelling provides a tool to gain understanding and explore these complex interactions. Visual displays illustrating the effect of these interactions in real time can aid clinicians in optimal drug dosing while minimizing adverse effects. In this review, we provide an overview of the PK and PD of propofol in order to refresh readers' knowledge of its clinical applications, while discussing the main avenues of research where significant recent advances have been made.

Pharmacokinetic and pharmacodynamic interactions in anaesthesia. A review of current knowledge and how it can be used to optimize anaesthetic drug administration

This review describes the basics of pharmacokinetic and pharmacodynamic drug interactions and methodological points of particular interest when designing drug interaction studies. It also provides an overview of the available literature concerning interactions, with emphasis on graphic representation of interactions using isoboles and response surface models. It gives examples on how to transform this knowledge into clinically and educationally applicable (bedside) tools.

Adult and pediatric anesthesia/sedation for gastrointestinal procedures outside of the operating room

PURPOSE OF REVIEW

This review presents current trends of safe and efficient anesthesia and sedation for adults and children for gastrointestinal procedures outside of the operating room with a special focus on total intravenous anesthesia (TIVA), target-controlled infusion (TCI), intravenous or topical lidocaine, and the use of the video laryngoscope.

RECENT FINDINGS

The concepts of a well tolerated and adequate anesthesia or sedation for gastrointestinal procedures outside of the operating room have to meet the needs of the adult and pediatric patients and the special requests of the gastroenterologists. Anesthesia and sedation of adults for gastrointestinal procedures with TIVA or TCI and spontaneous breathing is well established. Many institutions perform anesthesia for pediatric patients undergoing gastrointestinal procedures with an inhalational agent, especially in young children and for short procedures. Unlike adults, in young children the airways frequently must be secured with a tracheal tube or laryngeal mask. Respiration may be spontaneous, assisted, or controlled. TIVA and TCI are increasingly chosen for older children and longer procedures. A local anesthetic administered intravenously or topically to the upper airways and the use of the video laryngoscope can facilitate the insertion of the endoscope.

SUMMARY

Both anesthesiologists and nonanesthesiologists have to achieve a consensus and develop quality-improvement strategies to provide safe and efficient anesthesia and sedation for gastrointestinal procedures outside of the operating room for pediatric and adult patients. Techniques using TIVA, TCI, intravenous or topical application of lidocaine, and the video laryngoscope may improve and facilitate gastrointestinal procedures for the patients, the anesthesiologists, and the gastroenterologists.

Laparoscopic Salpingo-oophorectomy in Conscious Sedation

Introduction:

Conscious sedation has traditionally been used for laparoscopic tubal ligation. General anesthesia with endotracheal intubation may be associated with side effects, such as nausea, vomiting, cough, and dizziness, whereas sedation offers the advantage of having the patient awake and breathing spontaneously. Until now, only diagnostic laparoscopy and minor surgical procedures have been performed in patients under conscious sedation.

Case Description:

Our report describes 5 cases of laparoscopic salpingo-oophorectomy successfully performed with the aid of conventional-diameter multifunctional instruments in patients under local anesthesia. Totally intravenous sedation was provided by the continuous infusion of propofol and remifentanil, administered through a workstation that uses pharmacokinetic–pharmacodynamic models to titrate each drug, as well as monitoring tools for levels of conscious sedation and local anesthesia. We have labelled our current procedure with the acronym OLICS (Operative Laparoscopy in Conscious Sedation). Four of the patients had mono- or bilateral ovarian cysts and 1 patient, with the BRCA1 gene mutation and a family history of ovarian cancer, had normal ovaries. Insufflation time ranged from 19 to 25 minutes. All patients maintained spontaneous breathing throughout the surgical procedure, and no episodes of hypotension or bradycardia occurred. Optimal pain control was obtained in all cases. During the hospital stay, the patients did not need further analgesic drugs. All the women reported high or very high satisfaction and were discharged within 18 hours of the procedure.

Discussion and Conclusion:

Salpingo-oophorectomy in conscious sedation is safe and feasible and avoids the complications of general anesthesia. It can be offered to well-motivated patients without a history of pelvic surgery and low to normal body mass index.

Intraoperative target-controlled infusion anesthesia application using remifentanil hydrochloride with etomidate in patients with severe burn as monitored using Narcotrend

OBJECTIVE

This study aims to evaluate the feasibility of intraoperative composite target-controlled infusion (TCI) anesthesia application using remifentanil hydrochloride with etomidate in patients with severe burns, as monitored by Narcotrend.

METHODS

A total of 40 patients with severe burns with eschar excisions and skin grafts were randomly and equally grouped into the etomidate (E) and the propofol groups (P). Anesthesia was induced and maintained by a remifentanil hydrochloride TCI combined with etomidate or propofol. The depth of anesthesia and other relevant indicators were recorded through intraoperative electroencephalogram monitoring using a Narcotrend monitor.

RESULTS

No statistically significant differences were observed between the drug withdrawal times, eye opening requirements, or orientation recoveries of the two groups (P>0.05). The cortisol and aldosterone levels in group E were significantly lower than those in group P 24h post operation (P<0.05). No significant differences between the number of operations, hospitalization duration, mean arterial pressure, heart rate, and postoperative adverse reaction incidence of the two groups were observed at each time point (P>0.05).

CONCLUSION

The application of a composite remifentanil hydrochloride combined with etomidate TCI is feasible for the early eschar excision in patients with severe burns.

Optimizing intravenous drug administration by applying pharmacokinetic/pharmacodynamic concepts

This review discusses the ways in which anaesthetists can optimize anaesthetic-analgesic drug administration by utilizing pharmacokinetic and pharmacodynamic information. We therefore focus on the dose-response relationship and the interactions between i.v. hypnotics and opioids. For i.v. hypnotics and opioids, models that accurately predict the time course of drug disposition and effect can be applied. Various commercial or experimental drug effect measures have been developed and can be implemented to further fine-tune individual patient-drug titration. The development of advisory and closed-loop feedback systems, which combine and integrate all sources of pharmacological and effect monitoring, has taken the existing kinetic-based administration technology forwards closer to total coverage of the dose-response relationship.