Predict Fluid Responsiveness in Spinal Anesthesia (CERU-1401)

Can Non Invasive Methods for Fluid Responsive Assessment Optimize Preventive Volemic Repletion in Order to Prevent Significant Hypotension After Spinal Anesthesia? A Randomized Trial

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.

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: volemic status; vascular resistance (determined by the control of the sympathetic system); 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.

This arm is considered the current clinical standard for spinal anesthesia; its used as a control sample and statistical reference. During the induction phase the patient is fitted with a non-invasive blood pressure monitoring, three-lead ECG, pulse oximetry and peripheral intravenous device. The pressure control is set as the standard every 5 minutes until the procedure under spinal anesthesia, the cuff pressure is placed on the arm that is going to be on top during spinal anesthesia. Data is recorded and vital signs of the patient and is put an infusion of crystalloid (0.9% NaCl or Ringer's acetate) with administration of 500 ml during the entire procedure until the beginning of the operation.

In addition to the current clinical standard (arm A of the study) a trans-thoracic echocardiography is performed with the aim of assessing patient's volume status, identifying if he is responsive to fluid and could benefit from their administration. The echocardiography is performed with the subcostal projection to assess the size of the abdominal inferior vena cava and its collapsing during breathing. According to different pre-established parameters, the patient is defined as unresponsive to fluids or responsive. If it's not responsive, he proceed to spinal anesthesia. Otherwise investigators proceed to the administration of crystalloid (NaCl 0.9% or Hartmann's solution second clinical evaluation) and at the end he's rerun an echocardiographic assessment.

In addition to the arm A of the study, is performed a measurement of end-tidal CO2 (EtCO2) by trans-nasal canula with a patient positioned in semi-recumbent position. After, investigators run the Passive Leg Raising Test (PLRT): the position of the bed is changed in such manner to bring the trunk from 45° to 0° and accordingly the legs from 0° to 45°. Measurements are performed before and during the maneuver : an etCO2 increasing more than 12% from baseline was interpreted as fluid-responsive. If the patient is not responsive to fluids, the patient is moving to the spinal anesthesia. If the patient is responsive investigators proceed to bolus administration, the patient returns to the initial PLRT position and is run again the PLRT until the patient is no longer responsive to fluids.

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.

Primary objective is to quantify significant hypotension rate after spinal anesthesia in patients brought to euvolemia according to the Trans-Thoracic Echocardiography and PLRT (Passive Leg Raising Test), compared to patients treated with the current standard. For arterial hypotension, in accordance with the international standard definitions, now define a drop in systolic blood pressure over 50 mmHg from baseline, an absolute value of systolic blood pressure less than 80 mm Hg, a mean arterial pressure below 60 mmHg or hypotension clinically symptomatic (dizziness, pallor, sweating, nausea).

A secondary objective is to quantify the water administration among the three comparison groups before spinal anesthesia, using the patients in the control group as a reference, in order to assess whether these techniques are associated with more fluid administration.

Another secondary objective is to quantify the water administration among the three comparison groups after spinal anesthesia, using the patients in the control group as a reference, in order to assess whether the techniques of filling, titrate echocardiographic evaluations and/or response to the mobilization of internal liquids are associated with lower dose, does not require more liquid.

Inclusion Criteria: all adult non critical patients requiring elective spinal anesthesia both sex patients with American Society of Anesthesiology class level I, II and III according to international standards spontaneously breathing patients Exclusion Criteria: patients already equipped or requiring invasive blood pressure monitoring (arterial catheter, pulmonary catheter, thermodilution catheter) patients with pre-procedural hypotension, defined as a response in two consecutive measurements of systolic arterial pressure (SAP) less than 80 mmHg or mean arterial pressure (MAP) less of 60 mmHg. patients unable to give informed consent to communication difficulties to language barriers or processes congenital/acquired determinants of mental retard, or any reduction in their ability to understand or want to be able to give their informed consent to the study patients where it is not then possible to perform spinal anesthesia for the patient's refusal to technical difficulties in sampling, clinical pathological conditions for determining a high risk of peri- procedural complications. patients with International Normalized Ratio > 1.5 and/or activated partial thromboplastin time in therapeutic range (defined as a value more than 1.5-2 times the normal values of the patient), anti-Xa activity in the therapeutic range . patients with severe thrombocytopenia (<50 G/l)

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