Predict Fluid Responsiveness in Spinal Anesthesia
Condition: Hypotension and Shock; Excessive Amount of Blood / Fluid Infusion
MeSH terms: Hypotension
Study type: Interventional

Summary: 
      Spinal anesthesia is still the regional anesthesia technique most widely employed in everyday
      clinical practice.

      The most feared and common of its well known side effects consist in an abrupt reduction of
      systemic vascular resistances, with consequence risk of systemic hypotension. To prevent this
      potentially severe complication, an adequate correction of patients' volume status through a
      preventive administration of fluids is widely used.

      However this volume repletion is commonly accomplished on an empirical basis, without having
      a real insight of patient hemodynamic status, carrying the risk of possible volume overload.

      Aim of the study is to test the clinical impact of two simple, non-invasive methods to guide
      volemic repletion before spinal anesthesia on the reduction of significant hypotension rate,
      compared to empirical fluid administration.
    

Detailed description: 
      The resulting high density of the anesthetic block and the reproducibility of the technique
      have made of spinal anesthesia the most widely diffused regional anesthesia technique.
      Nevertheless the procedure still remains the regional anesthesia technique burdened by the
      potentially most severe side effects, the most frequent of which being systemic arterial
      hypotension.

      Subarachnoidal administration of local anesthetics in fact is associated not only with both a
      motor and sensory block, but also with a blockade of the autonomic nervous system, which
      controls peripheral vascular tone. Sympathetic block leads to a sudden decrease in peripheral
      resistance, with consequent significant increase in vascular bed and relative hypovolemia.

      Transient hypotensive episodes can be generally well tolerated by healthy patients, however
      they may lead to major complications in patients with increased cardiovascular risk. In the
      common clinical practice, it is usual to administer fluids empirically. An empirical
      preventive fluid repletion however can represent per se a risk in patients with impaired
      cardiac and renal functions, since a volume overload of heart chambers with reduced
      compliance can cause pulmonary edema or congestive heart failure.

      Since about ten years both non-invasive and invasive techniques have been developed, with the
      specific purpose of optimizing fluid status on a rational basis. This methods are based on
      the correlation between the levels of mean arterial pressure (MAP), systemic vascular
      resistance (SVR) and cardiac output (CO), according to the equation: MAP = CO * SVR. The
      latter explains why, in case of vasodilation, unless CO is increased, a lowering of SVR will
      inevitably translate into a decrease of MAP.

      Determinants of blood pressure are:

        1. volemic status;

        2. vascular resistance (determined by the control of the sympathetic system);

        3. cardiac output.

      In case of spinal anesthesia the reduction in SVR determines relative hypovolemia (due to an
      increase in total vascular bed). For this reason after spinal anesthesia appears fundamental
      an optimization of patients' volemic status through administration of fluids (eventually
      associated with the administration of amines, in order to contrast massive vasodilation).

      The use of methods to assess fluid responsiveness has been extensively studied in critical
      patients populations. However these techniques have not been studied yet in non critical
      patients. Spinal anesthesia is a model of pharmacological vasodilation which often generates
      significant hypotension, for which nowadays an evidence-based rational treatment based on a
      guided volemic repletion is still lacking.

      WORKING HYPOTHESIS:

      The use of non-invasive methods that have proven to be accurate for the identification of
      patient fluid-responsiveness is currently not validated in patients undergoing spinal
      anesthesia.

      Ultrasound of inferior vena cava by is an effective method to determine the responsiveness to
      fluids in a patient on mechanical ventilation, however it has been proven to be inaccurate in
      spontaneous ventilating patients in critically ill patients, few data being available in non
      critical patients. The study of the inferior vena cava is based on the size of the inferior
      vena cava in its intra-abdominal portion (approximately 2 cm from emergency right atrium) and
      the pattern of its diameter changes with breathing. This measurement is obtained with M-mode
      ultrasound through subcostal view..

      Passive leg raising test (PLRT) has been proven to be a highly accurate method in predicting
      fluid responsiveness in spontaneously breathing patients, in a population of critically ill
      patients. The method is based on the following assumption: active legs elevation, in addition
      to its effect of venous pool shifting from the lower limbs to the thorax, exerts a
      contemporary effect of stimulation on the peri-arterial sympathetic system at iliac-femoral
      level, this causing an orthosympathetic reflex which can increase cardiac output, possibly
      masking hypovolemia. Passive lower limbs raising instead has the advantage of mobilizing
      lower limbs venous blood (estimated 300-500 ml), without activating the orthosympathetic
      reflex. This allows for a quantification of the clinical response to a bolus of fluids, in
      terms of decrease of blood pressure variations following leg raising.

      The hypothesis that investigators want to test is that the use of inferior vena cava
      ultrasound before spinal anesthesia, compared to the standard method (empirical fluid
      administration) and a non-invasive method (PLRT) can reduce the impact of systemic
      hypotension through an adequate titrated volemic repletion, avoiding both hypotension and
      fluid overload. The final purpose is to ensure spinal anesthesia in the safest possible way.

      OBJECTIVES OF THE STUDY:

      Aim of the study is to determine whether vena cava ultrasound, a bedside, unexpensive, non
      invasive methods, which have been tested as predictors of fluid responsiveness in critical
      patients, is effective in guiding titrated fluid repletion in a non critical population, in
      order both to decrease post procedural significant hypotension rate and unnecessary fluid
      overload in patients undergoing spinal anesthesia for elective surgical procedures.
    

Intervention name(s): Trans-thoracic echocardiography; Passive Leg Raising Test
Intervention type(s): Procedure; Procedure
Intervention description(s): Subcostal evaluation of inferior vena cava dimensions and colorability with cyclic spontaneous breathing in order to determine if the patients will be fluid responsive or not.; Application of this test in a standard manner in order to determine if our spontaneous breathing patients are fluid responsive before spinal anesthesia.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Prevention
Keywords: Fluid therapy; Hypotension; Inferior vein cava; Spinal anesthesia; Ultrasonography