Feasibility of the mNIHSS in Surgical Patients

Purpose & Justification: Perioperative stroke is a potentially devastating complication that is currently poorly characterized with limited clinical tools available to detect and prevent its occurrence. To date only two stroke assessment scales have been applied to the perioperative setting, though none have been tested in non-cardiac, non-neurologic surgeries. One of those assessments, the National Institutes of Health Stroke Scale (NIHSS), is lengthy and may be impractical in the surgical setting. This is further complicated by several factors potentially existing in surgical patients that may alter the assessment, such as pain and drowsiness from medications. However, there is a modified simpler version of the NIHSS (mNIHSS) that has been shown to have improved reliability than the full version and reduced time requirement, thus making it preferable for perioperative stroke screening. To overcome the current gaps in knowledge and screening for risk of perioperative stroke, this prospective observational study will be assessing the feasibility of applying the mNIHSS in the surgical setting.

Primary Objective: To determine the change in mNIHSS score from baseline to immediately after surgery in the absence of diagnosed stroke in patients after surgery.

Secondary Objectives:

• To determine the components of the mNIHSS most likely to change following surgery;
• To determine the feasibility of administering the mNIHSS in surgical patients (e.g. acceptability, resources, length of time to complete, completeness).
• To determine the relationship between baseline MoCA score and ability to complete the mNIHSS screening after surgery

Research design: This is a prospective observational study involving five testing sessions. A cognitive assessment (MoCA) will be conducted at the time of consent to screen for any cognitive impairment. There will be 4 additional visits during which the mNIHSS will be administered to surgical patients pre and post-operatively.

Statistical Analysis:

Sample Size Calculation There is no specific data available on the application of the mNIHSS in our study population. We estimate that we will require a sample size of 21 patients, assuming a mean difference of 2 (standard deviation 3) points between pre- and post-operatively, an alpha error of 0.05 and power of 80%. Anticipating a 20% drop out rate, we will recruit 25 patients.

Statistical Analysis We will describe the patient population using mean (SD), median (IQR) and percentage as appropriate. The application of the mNIHSS will be described using percent completed for each question, and the time taken to complete the test at each time point (mean, SD).

The change in mNIHSS on postoperative days 0, 1 and 2 will be compared to baseline using a Wilcoxon Signed Ranks test for matched pairs.

All tests will be two-sided with a p-value less than 0.05 considered statistically significant. All statistical analysis will be done using STATA 12.1 (StataCorp, Texas, USA).

Inclusion criteria

We will include older adult patients (65 years or older) presenting for non-cardiac non-neurologic surgery under general anesthesia at Vancouver General Hospital with a minimum two-night stay in hospital.

Exclusion criteria

We will exclude patients undergoing procedures involving the major vasculature of the head and neck, as well as patients who are predicted to require postoperative ventilation or planned tracheostomy. Patients who are not able to read or speak English will be excluded, as well as patients with significant hearing or visual impairment that would make assessment unreliable. In order to complete the mNIHSS accurately, we will exclude patients with significant cognitive impairment suggestive of dementia (MoCA score 17 or less) or a diagnosis of dementia.