Cognitive Dysfunction in Hypertensive Patients Having Spine Surgery
Condition: Hypertension
MeSH terms: Hypertension; Cognitive Dysfunction
Study type: Observational

Summary: 
      While hypotension during general anesthesia has routinely been considered to be a tolerable
      abnormality with little clinical consequence, the proposed study takes the innovative
      approach of defining hypotensive events within the construct of a patient's own hypertensive
      status, fractional mean arterial blood pressure (fMAP). Because the investigators primary
      variable is within the control of anesthesia personnel, the study portends a potentially
      simple and easy to implement treatment. The introduction of neuropsychometric measures as the
      relevant evaluator of post-operative cognitive dysfunction is innovative, and may be more
      relevant to the average elderly patient than simple mortality.
    

Detailed description: 
      After major non-cardiac and non-cerebral surgery, postoperative cognitive dysfunction (POCD)
      occurs in a significant percentage of patients. The consequences of POCD are profound.
      Elderly patients having POCD at 1 week have an increased risk of disability or voluntary
      early retirement, and patients having POCD at 3 months have increased mortality.

      The effect of low arterial blood pressure, called hypotension, during surgery on the
      incidence of POCD is not obvious. This effect has been obscured in a number of previous
      studies because, it was assumed that hypotension had to persist for minutes to hours to be
      deleterious, when, in fact, the duration is uncertain. In addition, patient outcomes were not
      analyzed as a function of a history of hypertension. In this research application, the
      investigators focus specifically on patients with a history of hypertension because their
      physiology is different than patients with normal arterial blood pressure. These hypertensive
      patients may be unable to compensate for low arterial blood pressure by a process called
      cerebral autoregulation. As a result, patients with a history of hypertension may be at
      greater risk for decreased cerebral perfusion and cerebral ischemia secondary to decreased
      systemic arterial blood pressure even during surgery for procedures not thought to put the
      brain at risk of ischemia.

      In a prior retrospective study, the investigators analyzed hemodynamic data from fifty
      elderly (average age >60 years) patients having simple lumbar spine surgery, which is not
      thought to be associated with cerebral ischemia. These patients were all examined with a
      battery of neuropsychometric tests before and after surgery. Patients with a history of
      hypertension had cognitive changes that are dependent on the lowest fractional mean arterial
      blood pressure (fMAP), where fMAP is mean arterial blood pressure (MAP) divided by baseline
      MAP. Such changes were not found in patients without a history of hypertension. This
      relationship did not depend on the steady state fMAP or the highest fMAP reached in either
      group.

      To confirm and extend these results the investigators therefore propose and hypothesize that:
      In patients with a history of hypertension, compared to patients without this history, low
      fMAPs during induction predict cognitive performance after surgery.

      To evaluate these hypotheses the investigators will determine the incidence of post-operative
      cognitive dysfunction (POCD) as a function of the fMAP in hypertensive and normotensive
      patients undergoing elective simple lumbar spine surgery.

      If the proposed study demonstrates that acute intra-operative episodes of hypotension are
      deleterious to cognitive performance in patients with hypertension, and that there are
      demonstrable consequences in terms of QOL measures, the possibility of a direct and low cost
      intervention will be available that will lead directly to an efficacy trial using
      non-invasive measures of cerebral blood flow algorithms to prevent POCD.

      The investigators plan to conduct a multicenter study in which 200 elderly patients (>60
      years) are tested with a validated battery of 6 neuropsychometric tests before simple
      elective lumbar spine surgery (microdiscectomy or 1-2 level laminectomies without fusions
      lasting <5 hours and not requiring blood transfusions) and two times after surgery, at 24
      hours and at 1 month. Two questionnaires for QOL will be performed before surgery and at 1
      month. Patients will be questioned whether they have a history of hypertension, and, if they
      do, then its duration and treatment.

      Our analysis will be based on comparing the fMAP to the neuropsychometric performance before
      and after surgery. To see if neuropsychometric changes occur as a component of a routine
      anesthetic, anesthesiologists will not be given a specific protocol for intraoperative
      management.

      The primary outcome measure will be changes in test performance between baseline and the
      post-operative period at 1 day and 1 month. This primary measure will be a rating of overall
      change in performance compared to three values of fMAPs: lowest, steady state and highest
      fMAP attained. Our analysis will also include uni- and multi-variate analyses which will
      include and QOL.
    

Intervention name(s): Lumbar spine surgery; Neurologic/neuropsychometric examinations
Intervention type(s): Procedure; Other
Intervention description(s): (non-experimental) we do not intend to change the criteria of selection for simple lumbar spine surgery, anesthesia, or the postoperative management of the patients studied.; To measure postoperative cognitive dysfunction.
Observational model: Case-Control
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Patients >60 years old will be recruited who are scheduled for elective simple spine
        surgery (microdiskectomy or 1-2 level laminectomies without fusion) and lasting <5 hours
        without blood transfusion.
      
Keywords: hypertension; hypotension; cognitive; neurocognitive; cognitive dysfunction; postoperative cognitive dysfunction (POCD); neuropsychometric