• Stress response as measured by levels of circulating epinephrine, norepinephrine, and cortisol. [ Time Frame: Multiple time points ] [ Designated as safety issue: No ]
  
• Inflammatory response as measured by levels of circulating inflammatory mediators (e.g. interleukin-6, interleukin-8, interleukin-10, C-reactive protein, TNF-alpha). [ Time Frame: Multiple time points ] [ Designated as safety issue: No ]
  
• Blood glucose control (amount of insulin required to keep blood glucose 5-8 mmol/L). Renal function as measured by serum creatinine. [ Time Frame: Multiple time points ] [ Designated as safety issue: No ]
  

• Vasopressor requirements to keep mean blood pressure between 60-80 mm Hg. [ Time Frame: Multiple time points ] [ Designated as safety issue: No ]
  
• Left ventricular wall motion score index as measured by TTE and TEE. [ Time Frame: Multiple time points ] [ Designated as safety issue: No ]
  
• Hemodynamics including cardiac output and cardiac index, heart rate, systemic arterial and pulmonary arterial blood pressures, central venous pressure, and systemic and pulmonary vascular resistance. [ Time Frame: Multiple time points ] [ Designated as safety issue: No ]
  
• Time to extubation. [ Time Frame: Time of extubation ] [ Designated as safety issue: No ]
  

It is hypothesized that high spinal anesthesia combined with general anesthesia decreases the intraoperative stress and inflammatory response and improve post-operative pain control and respiratory function in this patient population. It is also hypothesized that the technique will provide stable intraoperative hemodynamics during aortic valve replacement surgery.

Stress response: Levels of hormones such as epinephrine, norepinephrine and cortisol are elevated during cardiac surgery and on the initiation of cardiopulmonary bypass. This stress response has previously been shown to be blunted with the use of high spinal anesthesia when combined with general anesthesia in coronary artery bypass surgery patients (Lee, Grocott, et al).

Inflammatory response: In addition to the stress response there is also an accentuated inflammatory response.

With contact of the patient's blood to the artificial bypass circuit, there is activation of various plasma protease pathways that generate multiple proinflammatory mediators. Complement levels and cytokine levels also rise. Clinical organ dysfunction involving the cardiovascular, pulmonary, renal and neurological systems can ultimately result. The effects of high spinal anesthesia on the inflammatory response that occurs with bypass have not been studied.

Hemodynamics: It has previously been shown that high-spinal anesthesia for coronary artery bypass surgery provides stable intra-operative hemodynamics (Kowalewski, MacAdams, et al; Lee, Grocott, et al.). Although the use of spinal anesthesia in patients with aortic stenosis has been considered to be relatively contra-indicated, total spinal anesthesia may actually improve cardiac function by decreasing systemic afterload and increasing myocardial contractility.

Post-operative analgesia and pulmonary function: The spinal administration of opioids, such as morphine, has been shown to improve post-operative pain management in patients having both cardiac and non-cardiac surgery (Jacobsohn, Lee, et al). Total spinal anesthesia with bupivacaine and spinal morphine combined with general anesthesia may also improve post-operative pain management and facilitate improved post-operative lung function.