[Total intravenous anaesthesia in geriatrics: the example of propofol]

Technical and clinical evaluation of a closed loop TIVA system with SEDLineTM spectral density monitoring: Multicentric prospective cohort study

Introduction

Closed loop total intravenous anesthesia is a technique in which the patient’s hemodynamic and anesthetic depth variables are monitored, and based on this information, a computer controls the infusion rate of drugs to keep them within pre-established clinical parameters.

Objective

To describe the technical and clinical performance of a closed loop system for total intravenous anesthesia with propofol and remifentanil, using the SEDLine^TM monitor

Design

Multicentric prospective cohort study

Setting

Surgery room

Patients

ASA I-II undergoing elective surgery

Measurements

The authors designed a closed loop system that implements a control algorithm based on anesthetic depth monitoring and the Patient State Index (PSI^TM) of the SEDLine monitor for propofol, and on hemodynamic variables for remifentanil. The measurement of clinical performance was made based on the percentage of PSI^TM maintenance time in the range 20–50. Precision analysis was evaluated by measuring median performance error (MDPE) can be defined as the median difference between actual and desired values, which refers to the degree of precision in which the controller is able to maintain the control variable within the objective set by the anesthesiologist; it represents the direction (over-prediction or under-prediction) of performance error (PE) rather than size of errors, which is represented by MDAPE, median absolute percentage error, Wobble index, which is used for measuring the intrasubject variability in performance error.

Results

Data were obtained from 93 patients in three healthcare centers. The percentage of PSI^TM maintenance time in the 20–50 range was 92% (80.7–97.0). MDPE was 10.7 (− 11.0–18.0), MDAPE 21.0 (14.2–26.8) and wobble 10.7 (7.0–16.9). No adverse surgical or anesthetic events were found.

Conclusions

The closed loop total intravenous anesthesia system with SEDLine developed by the authors was used without major complication and appear to be feasible its use in clinical performance.

Critical view of the effect site modelling of propofol

Target controlled infusion (TCI) of Propofol has been the subject of discussion during its 20 years of use, including the validity of the models that represent the course of the effect, such as: Are the different EEG indexes representative of the effect? Is the reactivity of the EEG index used to build models comparable to each other? What is the real reacting time of each monitor? Is the ke0 influenced by the infusion speed? Is the ke0 or the time to peak effect affected by age? How valid are the current Emax models? Are the induction and wakening simple mirror phenomenon as they are represented in the E max models? This review discusses issues related to the complexity and difficulty in obtaining a representation of the effect, and the lack of agreed definitions to be able to construct representative models of the temporary installation of the effect of Propofol for its use in TCI.

Significant and safe reduction of propofol sedation dose for geriatric population undergoing pacemaker implantation: randomized clinical trial

OBJECTIVE

A previous multidisciplinary pilot study based on computer simulations for the geriatric population showed that a dose of 0.5 mg/kg/h of propofol could sedate patients older than 65 for pacemaker implantation. The present study validates that the pacemaker implantation can be done in the elderly using 0.5-1 mg/kg/h of propofol with hemodynamic stability.

METHODS

66 patients from 65 to 88 years old scheduled for pacemaker implantation were randomly assigned one of three doses of propofol. The first group received 2 mg/kg/h of propofol (P2) that is within normal range of the sedation dose. The second group received 1 mg/kg/h (P1) dose and the third group received the dose of 0.5 mg/kg/h (P0.5) according to the simulation-predicted dose for geriatric populations.

RESULTS

All patients kept MAP between 76 and 85 mmHg, with no hypotension episodes in any of the groups; therefore, they were all hemodynamically stable during the procedure. BIS was between 80 and 65 during the pacemaker implantation for the three groups, BIS of group P2 was significantly lower than the other groups. BIS in groups P1 and P0.5 was within the appropriated range for moderate sedation. Brice was positive for auditory recalls only when there was arousing noise in the operating room.

CONCLUSIONS

Moderate sedation, adequate for pacemaker implantation, can be achieved infusing 0.5-1 mg/kg/h of propofol in elderly patients when the patient has proper analgesia management at the device implantation site. The second important condition is to avoid unnecessary and alerting auditory and mechanical stimuli in the operating room, so that the patient will remain calm.

Clinical testing of propofol geriatic dose for sedation designed via in silico trial

The geriatric population shows significant physiological changes due to aging and the multiple co-morbidities that they often present. Conventionally the propofol sedation dose for patients older than 65 years is 80% of the adult dose. We performed an in silico trial for elderly population and the results showed that the necessary simulated dose of propofol was lower than the conventional dose; therefore, a clinical trial was implemented to test three different propofol doses, two of them lower than the conventional dose, during a pacemaker implantation. The clinical trial showed that there was no clinical difference between the effects of the doses. A BIS monitor was used to measure the level of sedation, which proved to be adequate and well maintained by all patients. All the patients maintained an acceptable level of sedation, measured by a BIS monitor. Since propofol has some dose-dependent secondary effects, the use of lower doses, especially the ones designed for this age group, helps to avoid them.