Propofol TCI Reductions Do Not Attenuate Significant Falls in Cardiac Output Associated With Anesthesia Induction and Knee-Chest Positioning in Spinal Surgery.

BACKGROUND: Induction of anesthesia and the knee-chest position are associated with hemodynamic changes that may impact patient outcomes. The aim of this study was to assess whether planned reductions in target-controlled infusion propofol concentrations attenuate the hemodynamic changes associated with anesthesia induction and knee-chest position. MATERILAS AND METHODS: A total of 20 patients scheduled for elective lumbar spinal surgery in the knee-chest position were included. In addition to standard anesthesia monitoring, bispectral index and noninvasive cardiac output (CO) monitoring were undertaken. The study was carried out in 2 parts. In phase 1, target-controlled infusion propofol anesthesia was adjusted to maintain BIS 40 to 60. In phase 2, there were 2 planned reductions in propofol target concentration: (1) immediately after loss of consciousness-reduction calculated using a predefined formula, and (2) before positioning-reduction equal to the average percentage decrease in CO after knee-chest position in phase 1. Changes from baseline in CO and other hemodynamic variables following induction of anesthesia and knee-chest positioning were compared. RESULTS: Induction of anesthesia led to decreases of 25.6% and 19.8% in CO from baseline in phases 1 and 2, respectively (P<0.01). Knee-chest positioning resulted in a further decrease such that the total in CO reduction from baseline to 10 minutes after positioning was 38.4% and 46.9% in phases 1 and 2, respectively (P<0.01). There was no difference in CO changes between phases 1 and 2, despite the planned reductions in propofol during phase 2. There was no significant correlation between changes in CO and mean arterial pressure. CONCLUSIONS: Planned reductions in propofol concentration do not attenuate anesthesia induction and knee-chest position-related decreases in CO. The knee-chest position is an independent risk factor for decrease in CO. Minimally invasive CO monitors may aid in the detection of clinically relevant hemodynamic changes and guide management in anesthetized patients in the knee-chest position.

Effect of Hemodynamic Changes in Plasma Propofol Concentrations Associated with Knee-Chest Position in Spinal Surgery: A Prospective Study.

BACKGROUND: Anesthesia induction and maintenance with propofol can be guided by target-controlled infusion (TCI) systems using pharmacokinetic (Pk) models. Physiological variables, such as changes in cardiac output (CO), can influence propofol pharmacokinetics. Knee-chest (KC) surgical positioning can result in CO changes. OBJECTIVES: This study aimed to evaluate the relationship between propofol plasma concentration prediction and CO changes after induction and KC positioning. METHODS: This two-phase prospective cohort study included 20 patients scheduled for spinal surgery. Two different TCI anesthesia protocols were administered after induction. In phase I (n = 9), the loss of consciousness (LOC) concentration was set as the propofol target concentration and CO changes following induction and KC positioning were quantified. In phase II (n = 11), based on data from phase I, two reductions in the propofol target concentration on the pump were applied after LOC and before KC positioning. Propofol plasma concentrations were measured at different moments in both phases: after induction and after KC positioning. RESULTS: Schnider Pk model showed a good performance in predicting propofol concentration after induction; however, after KC positioning, when a significant drop in CO occurred, the measured propofol concentrations were markedly underestimated. Intended reductions in the propofol target concentration did not attenuate HD changes. In the KC position, there was no correlation between the propofol concentration estimated by the Pk model and the measured concentration in plasma, as the latter was much higher (P = 0.013) while CO and BIS decreased significantly (P < 0.001 and P = 0.004, respectively). CONCLUSIONS: Our study showed that the measured propofol plasma concentrations during the KC position were significantly underestimated by the Schnider Pk model and were associated with significant CO decrease. When placing patients in the KC position, anesthesiologists must be aware of pharmacokinetic changes and, in addition to standard monitoring, the use of depth of anesthesia and cardiac output monitors may be considered in high-risk patients.

Total Intravenous Anesthesia for Neurosurgical Procedures in Narcoleptic Patients: Two Case Reports.

INTRODUCTION: Narcoleptic patients may be at increased risk of prolonged emergence, postoperative hypersomnia, apneic episodes, and sleep paralysis after general anesthesia. Modafinil is the first-line treatment, however, the implication it has on general anesthesia is not clear. This report present 2 cases of narcoleptic patients medicated with modafinil that were submitted to total intravenous anesthesia for neurosurgical procedures. CASE PRESENTATION: Informed consent was obtained from both patients. Clinical information was obtained from patients' interviews and medical records. Intraoperative data was collected using Datex Ohmeda, Bispectral index, Entropy, and LiDCO rapid monitors, and exported to excel sheets to allow its analysis. Both patients maintained modafinil on the day of surgery and were not administered sedative premedication. Propofol was administered by bolus during induction of anesthesia. In one of the patients, the predicted cerebral concentration of propofol required for loss of consciousness was high. Anesthesia was maintained with remifentanil and propofol by target controlled infusion and titrated according to bispectral index (BIS), entropy, and analgesia nociception index (ANI). During the surgical procedure, the patients did not require vasopressors. Emergence from anesthesia was very fast and no narcoleptic event occurred postoperatively. CONCLUSIONS: Sedative premedication should be avoided and the use of short-acting anesthetic agents, such as propofol and remifentanil through target-controlled infusion most likely improves titration of anesthesia. The continuation of modafinil preoperatively might have contributed to the rapid emergence, yet, might also have been responsible for the high cerebral concentration of propofol that was required for loss of consciousness in one of the patients.