Echocardiography Based Algorithm for Spinal Anaesthesia

Aims and Objectives:

Primary aim:

To compare an echocardiography based algorithm of hemodynamic management as compared to standard practice in decreasing the incidence of spinal hypotension (number of patients developing a decrease in MAP >20% of baseline or MAP <60 mm Hg).

Secondary aims:

1. To compare the number of episodes, magnitude of hypotension (lowest value of BP) and duration of hypotension in either group.
2. To compare the amount of fluids and vasopressors administered to maintain hemodynamic stability in either group.

MATERIALS AND METHODS:

This study is designed as prospective, randomized intention to treat trial. After obtaining written informed consent, a total of 60 patients, above 40 years of age presenting for elective lower abdominal or lower limb surgery and eligible to receive a subarachnoid block at the Postgraduate Institute of Medical Education and Research, Chandigarh from 1st January 2016 to March 31st 2017 will be enrolled in this study. Patients with contraindications to a central neuraxial block such as pre- existing coagulopathy, local sepsis at site of insertion, ongoing hemodynamic instability (defined as systolic blood pressure< 90 mm Hg or MAP< 65mm Hg), unwillingness to undergo a regional anesthesia, co- existing pregnancy, spinal dysraphism or, previous history of spinal instrumentation or surgery, chest deformity, demonstrated systolic dysfunction on screening echocardiography (defined as left ventricular ejection fraction <50% or, fractional shortening < 25%), valvular heart disease (known or diagnosed on screening echocardiography), chronic renal or liver disease and unwilling to participate in the trial will be excluded.

After standard preoperative fasting of 8hr, all patients will receive intravenous access and non-invasive blood pressure monitor set to be recorded automatically every 2 minutes, five lead continuous electrocardiography, pulse oximetry, and capnography for non-intubated patients inside OR. In addition, a screening echocardiogram for right and/ or left heart dysfunction (fractional shortening< 25% or ejection fraction < 50%/ and tricuspid annular plane systolic excursion < 17 mm) and exclusion of valvular heart disease will be performed. If an abnormality is detected patient will be excluded from the study at this point, enrolment proceeding on an intention to treat basis.

Thereafter the patients will be randomized into either of two groups using computer generated random number and sealed envelope method: Gr (E) echocardiography based fluid and hemodynamic management or, Gr (S) standard anaesthetic management. In group E patients, before administering spinal anesthesia, a transthoracic echocardiography (TTE) will be performed to determine the LVEDA using the mid papillary parasagittal short axis (PSAX) view. The average of at least 3 LVEDA measured on above view by an experienced anesthesiologist in TTE will be used for fluid management, as per the proposed algorithm . If spinal hypotension does occur in patients in group E, it will be managed according to the same proposed algorithm.

THE PROPOSED ECHOCARDIOGRAPHY BASED ALGORITHM :

The left ventricular end diastolic area (LVEDA) will be measured by Transthoracic echocardiography using the parasternal short axis view. If the LVEDA is more than 10 square centimeters, the left ventricular preload status will be deemed adequate and administration of spinal anesthesia will be proceeded as usual. If the LVEDA is less than 10 square cms, a fluid(NS/Balanced salt solution) bolus of 250 ml will be administered and LVEDA reassessed. If more than 10 square cms, spinal anaesthesia will be administered. If less, a second bolus of 250 ml fluid will be given and then LVEDA reassessed. If more than 10 square centimeters, spinal anaesthesia will be administered, if not the patient will be considered fluid unresponsive and spinal anesthesia will be administered after giving a phenylephrine iv bolus of 1-2µg/kg and then spinal anaesthesia administered. In the event of postspinal hypotension within 30 minutes of giving spinal anaesthesia, the LVEDA will be reassessed. If more than 10 square centimeters, volume status will be considered adequate and patient will be given a vasopressor bolus of 1-2µg/kg of phenylephrine. If less than 10 square centimeters, the patient volume status will be considered low and a fluid bolus of 250ml and LVEDA reassessed and managed as in a prespinal LVEDA of less than 10 square centimeters.

The patients in group S will receive fluid and vasopressor therapy (if required) as deemed appropriate by the attending anaesthesiologist. The attending anaesthesiologist will be will target a MAP, such that it does not fall below 60 mm Hg nor below >20% of its baseline value.

The anaesthetic management protocol will be standardized for both the groups namely all patient will receive 3.0ml of local anaesthetic fentanyl mixture [2.5ml of 0.5%bupivacaine + 0.5ml(25µg) of fentanyl], ringer lactate/ any balanced salt solution(BSS) for fluid management and phenylephrine 1-2µg/kg intermittent boluses to treat hypotension. No i.v sedative or analgesic medication will be administered until completion of study. Patient position will be kept supine till end of the study period and surgical incision will be given thereafter. The attending anesthesiologist managing case will be not be involved in the study and will be blinded for the goal and parameters recorded in the study.

The patient demographic data characteristics such as age, sex, height, weight, observed echocardiographic parameters, LVEDA and changes in LVEDA following bolus volume administration will be noted. The echocardiographic parameters will be recorded for later analysis. The hemodynamic parameters will be recorded for every 1 minutes for 1st 10 minutes of spinal drug administration and thereafter at 5 minutes interval till the study period. The number of episodes of hypotension and the total fraction of time spent below target values in the first 30 minutes post spinal block (defined by decrease in MAP exceeded >20% from baseline and absolute value <60 mm Hg), magnitude of hypotension (lowest value of BP), volume of crystalloid / colloid, number of times vasopressors were used and total doses of vasopressors required will be noted. Any side effect like nausea/ vomiting, persistent hypotension defined by decrease in MAP exceeding >20% from baseline for 5 minutes or more will be noted.

The blood pressure values within 30 minutes of administering spinal anesthesia will be considered and analysed for study purposes, to exclude the effect of surgical factors on hemodynamics.