Expected Normal Ketone Values After Very Low and Bariatric Surgery
Condition: Diabetes Mellitus; Ketoacidosis
MeSH terms: Ketosis
Study type: Observational

Summary: 
      The investigators propose a multicenter prospective study in patients undergoing either an
      elective bariatric procedure or an elective benign procedure, including laparoscopic/open
      cholecystectomy, laparoscopic/open hiatus hernia repair, laparoscopic/open inguinal hernia
      repair, laparoscopic/open umbilical hernia repair or laparoscopic ventral wall hernia repair.
      Perioperative blood ketone and venous blood gas levels will be measured pre-surgery,
      post-surgery and on post-operative days until discharge.

      Our primary research objective is to clarify the expected perioperative ketone and blood gas
      levels in elective bariatric patients who have been on a VLCD and fasting for surgery,
      compared to elective surgical patients who have only been fasting prior to surgery.
    

Detailed description: 
      Bariatric surgery is fast becoming a mainstream option for achieving long-term weight loss in
      the morbidly obese population due to the paucity of other effective alternatives. It is
      indicated in those with a Body Mass Index (BMI) >40, or those with an obesity-related
      comorbidity with a BMI >35. One of the most common of these comorbidities is Type 2 Diabetes
      Mellitus (T2DM).

      In the weeks preceding bariatric surgery, it is routine for patients to be placed on a very
      low calorie diet (VLCD). The aim is to reduce abdominal wall thickness, visceral adiposity
      and hepatomegaly. Overall, this contributes to reduced technical difficulties at operation.

      VLCD achieve rapid weight loss in the short term by inducing ketosis. This is achieved by
      reducing the consumption of carbohydrate and fat, while increasing protein intake. The
      depletion of caloric intake leads to decreased glucose stores. This then leads to a metabolic
      shift towards production of ketone bodies, which are produced by the liver via the oxidation
      of fatty acids. Ketones are then transported to tissue to take over the role of glucose as
      the main energy source for the central nervous system. The objective is to reduce fat mass
      without causing excess loss of muscle mass.

      Overall the VLCD regime, via the induction of ketosis, is very successful in weight
      reduction. However this mechanism of action, and the production of ketone bodies, is now
      being questioned in those prescribed a new class of glucose lowering medication used to treat
      T2DM.

      Sodium-glucose co-transporter-2 (SGLT2) inhibitors, also called gliflozins, are medications
      that reduce absorption of glucose in the kidney thus increasing excretion via urine. Phase 3
      trials have shown them to be safe for treatment of T2DM however; however concern has been
      raised about development of a euglycaemic diabetic ketoacidosis. It is thought to occur when
      stress hormones lead to increased ketosis in patients taking SGLT2 inhibitors, which appear
      to alter insulin production. This situation can occur in the perioperative period if the
      SGLT2 inhibitors have not been correctly withheld pre-operatively.

      Current guidelines from the Australian and New Zealand College of Anaesthetists recommend the
      cessation of SLGT2 inhibitors 3 days prior to surgery. If this has not occurred, they state
      blood ketones should be tested. If the blood ketones are >0.6, it is a strong recommendation
      to postpone non-urgent surgery. Ketone and base excess levels are then used to monitor
      patients in the perioperative period.

      The confounding factor in these patients now presents itself- what are the expected blood
      ketone levels in bariatric patients who have been on two week of pre-operative VLCD and are
      fasting for surgery?
    

Observational model: Other
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        All patients undergoing either elective laparoscopic/open cholecystectomy,
        laparoscopic/open hiatus hernia repair, laparoscopic/open inguinal hernia repair,
        laparoscopic/open umbilical hernia repair or laparoscopic ventral wall hernia repair or
        elective bariatric procedure will be recruited consecutively. Those in the bariatric arm
        must have been on a VLCD pre operatively. Recruitment does not require blinding or
        randomization.

        Patients will be excluded if they are non-English speaking or cannot consent to the
        project, if they are already taking an SLGT2 inhibitor or if their procedure was abandoned.