A Clinical Trial of Intravenous Lidocaine After Spinal Surgery to Prevent Delirium and Reduce Pain

Postoperative delirium is one of the most frequent adverse events following elective non-cardiac surgery and is associated with cognitive impairment at discharge, as well as in-hospital and long-term mortality, however, despite being a well-recognized problem there is a dearth of effective interventions for prevention and management. A modifiable risk factor associated with postoperative delirium is poor postoperative pain control, and by improving the pain regimen the investigators may be able to decrease the incidence and/or severity of postoperative delirium. In this study, the investigators seek to study whether a postoperative intravenous infusion of lidocaine, known to improve pain control in other contexts, can decrease the risk of postoperative delirium and other opioid-related side effects, following major reconstructive spinal surgery.

Methods:

The investigators will perform a pilot prospective randomized double-blinded placebo-controlled trial of 60 patients undergoing major elective reconstructive spinal surgery to investigate the effect of a postoperative lidocaine infusion on the incidence and severity of postoperative delirium. Major spine surgery is defined as posterior spine fusions >3 levels of instrumentation and fusion, which allows standardization of the level of surgical insult and postoperative analgesic requirements. The intraoperative anesthetic regimen will be standardized to consist of total intravenous anesthesia using sevoflurane, propofol, lidocaine and magnesium (institutional protocol), and fentanyl with boluses allowed per provider discretion.

Patient recruitment, inclusion and exclusion criteria: All surgeons will be contacted before the start of the study to obtain their consent to allow their patients to be studied. The research team has successfully completed multiple National Institutes of Health (NIH) funded cohort and clinical trials at our institution with no surgeon refusing to participate. Eligible patients will be screened from the operating room roster to determine their eligibility. Patients will be contacted by phone or in person for preoperative evaluation. Please see the other section for inclusion and exclusion criteria.

Sample Size Calculation:

The recruitment will be consecutive patients meeting inclusion criteria. Reductions in opioid consumption by ~25% using intravenous lidocaine infusions have been shown to decrease opioid related side effects, but there is essentially no data linking a specific degree of opioid reduction to effects on delirium (46, 47). The most comparable published study to the investigators' proposal is work done by Kaba (2009) studying a lidocaine infusion for abdominal surgery where the average opioid reduction was ~50% (24mg +/-16.3 of piritramide in the placebo vs. 10.33mg +/- 10.33 in the treatment group). Assuming similar reduction in opioids of 50% and similar variance, the proposed sample size, 60 (30 per group), provides a power of 0.8 (alpha = 0.05) to detect a 25% decrease in the use of postoperative opioids.

Randomization: Patients will be randomized utilizing block randomization by a random number generator into either placebo or treatment groups by the research pharmacist. The randomization scheme will be blinded to the researchers and patients.

Anesthetic Management: The anesthetic management will be standardized. All patients will receive a general anesthetic to consisting of 50% oxygen and total intravenous anesthetics consisting of infusions of propofol (60-150 mcg/kg/min), lidocaine (1 mg/kg bolus, then 1.5 mg/kg/hr infusion), magnesium (30 mg/kg bolus, then 6 mg/kg/hr infusion), fentanyl (1 mcg/kg bolus, then 1 mcg/kg/hr infusion, prn boluses), and 0.3 Minimum Alveolar Concentration (MAC) of sevoflurane. Anesthesiologists will be requested to maintain the patient's arterial blood pressure to within 20% of their preoperative baseline using vasoactive agents. Patients will receive mechanical ventilation to maintain normocarbia. Intraoperative warming devices will be used to keep body temperature between 36-37˚C. Oxygen saturation will be maintained >95%. Muscle relaxants will be used during tracheal intubation and only as clinically indicated at other time periods. All patients will be continuously monitored before the induction of anesthesia and during surgery with SEDline Brain Function Monitor (Masimo, Inc., Irvine CA), a standard monitor at our institution. Anesthesiologists will be asked to minimize electroencephalogram (EEG) burst suppression by adjusting the doses of anesthetic drugs since prior studies have suggested a relationship between burst suppression and postoperative delirium (48, 49). Postoperatively, but before discharge from the post anesthetic care unit or upon arrival to the intensive care unit, patients will be randomized to receive either placebo or a lidocaine infusion.

Please see the other sections for a list of primary and secondary outcomes. Briefly the primary outcome is the effect of an intravenous lidocaine infusion on the incidence and severity of postoperative delirium. Secondary outcomes include intravenous lidocaine safety and tolerability, the effect of a lidocaine infusion on opioid usage, pain scores, analgesic satisfaction, opioid related side effects, and functional benefits.

Statistical Analysis The investigators will use descriptive statistics to summarize the characteristics of the study population by treatment groups. The investigators will use an intention to treat paradigm in assessing the effect of the intervention on the outcomes of interest.

Aim 1: To evaluate the safety of a continuous infusion of lidocaine in the first two days after surgery. The investigators will compare the proportion of patients that experienced at least one of the adverse events between the two groups using either the Fisher Exact Test or Chi Square Test as appropriate.

Aim 2: To compare postoperative pain, and opioid usage between patients who receive placebo infusions vs. lidocaine infusions. All opioid doses will be converted to oral morphine equivalents. Specifically, hydromorphone and fentanyl doses will be converted to morphine equivalents using the conversion formula: 1.5 mg of hydromorphone = 10 mg of morphine equivalents, 0.1mg of fentanyl = 10 mg of morphine equivalents (56,57). The investigators will compare the average pain scores and opioids doses between the two treatment groups using two-sample t-tests or Mann-Whitney nonparametric tests if the data are not normally distributed.

Aim 3: To compare the incidence of postoperative delirium between patients who receive placebo infusions vs. lidocaine infusions. Chi-square tests will be conducted to determine the association between lidocaine infusions and incident delirium.

Aim 4: To compare the functional recovery of patients between patients who receive placebo infusions vs. lidocaine infusions. The investigators will compare the results of the 36-Item Short Form Health Survey (SF-36), Oswestry Disability Index (ODI), time to discharge, and ability to participate in physical therapy, using the two sample t-test or Mann-Whitney nonparametric test for continuous outcomes, and Fisher exact Test or Chi Square test for binary outcomes.

Relevant biologic variables - All analyzes will include sex and ethnicity as covariates.

Missing Data - Sensitivity Analyses to Assess the Effects of Missing Data: The investigators will use model-based methods, such as Heckman and Predicted mean matching models to determine the effect of missing observations for each of these reasons on the estimates. The investigators will track the number of missing responses for delirium, and upwardly adjust the sample size accordingly. This strategy may result in having to recruit and follow an additional subject per week in the second year of data collection, which is feasible. The investigators will conduct sensitivity analyses to determine the effect of missing data on the outcomes of interest.