Two Mathematical Methods to Estimate Arterial Occlusion Pressure and Tourniquet Effectiveness in Lower Limb Surgery
Condition: Vascular Diseases
MeSH terms: Vascular Diseases; Arterial Occlusive Diseases
Study type: Interventional

Summary: 
      Pneumatic tourniquets are widely used not only to reduce blood loss and to ensure optimal
      operating conditions during extremity surgery, but also in regional anesthesia (local
      intravenous) vein puncture and to control life or limb threatening conditions. However,
      compression of the tissues under a tourniquet is associated with soft tissue damage involving
      the skin, vessels, muscles, and most importantly, nerves, and are commonly pressure related
      and can be affected by tourniquet time as well. Therefore, the "minimal tourniquet inflation
      pressure" necessary to provide a bloodless field has been suggested to minimize the risk of
      complications from excessive inflation pressure. Arterial occlusion pressure (AOP) is the
      lowest pneumatic tourniquet inflation pressure required to stop the arterial blood flow into
      the limb, and its usage has been shown to be useful in optimizing tourniquet cuff pressures.
      The pressure to which a pneumatic tourniquet cuff should be inflated depends on a number of
      variables, including the patient's age, skin, blood pressure and the shape and size of the
      extremity in question, as well as the dimensions of the cuff. One of the estimation method
      for AOP is based on systolic blood pressure (SBP) and tissue padding coefficient (KTP) values
      (AOP=[SBP+10]/KTP) according to extremity circumferences. Unver B. et al., used this method
      to estimate effective tourniquet pressure in total knee replacement under hypotensive general
      anesthesia tourniquet pressure achieved was 169.7±7.9 mmHg, while Tuncali et al., tested it
      again in different lower limb surgeries under general or neuraxial anesthesia with
      normotensive techniques and the achieved maximal tourniquet pressures used was 173.3±15.6
      mmHg. Hong-yun Liu et al., established a new occlusion pressure mathematical model for the
      upper limb based on the correlation analysis between several possible influencing parameters
      and the minimal pneumatic tourniquet pressure.
    

Detailed description: 
      After ethical committee approval and informed consent from the patients, 80 adult patients
      18-40 years old, (ASA I-II), scheduled for knee arthroscopy under general anesthesia with
      pneumatic tourniquet around the thigh, will be randomly allocated (using closed opaque
      envelop) into one of two groups:

        -  Group (A): where the pneumatic tourniquet inflated 20 mmHg above the arterial occlusion
           pressure which will be estimated using the equation of Unver B. et al., [1]:
           (AOP=[SBP+10]/KTP)

        -  Group (B): where the pneumatic tourniquet inflated 20 mmHg above the arterial occlusion
           pressure which will be estimated using the equation of Hong-yun Liu et al., [2]: (AOP =
           17.986 + 3.158X1 + 0.408X2) Patients will be excluded from the study if they are outside
           the age range, hypertensive, diabetic, complaining of any lower limb claudications, any
           vascular disease, hemolytic blood disorders or hypercoagulability.

      Upon arrival to the operating room, standard monitoring will be attached (5 lead ECG, pulse
      oximeter and non-invasive blood pressure) followed by a wide-bore canula will be inserted a
      big vein in the upper limb. General anesthesia will be induced using fentanyl 1 mcg/kg and
      propofol 2-3 mg/kg laryngeal mask airway device will be inserted after atracurium 0.5 mg/kg
      and lungs will be mechanically ventilated to maintain end-tidal CO2 at 36-40 mmHg and
      maintenance of anesthesia will be achieved using isoflurane 1-2 volume %. Hemodynamic
      stabilization will be assured and systolic blood pressure will be maintained within the
      pre-induction values ± 20% using intravenous fluid infusion and titration of inhalational
      anesthetics.

      In all patients, the thigh circumference will be measured 20 cm proximal to the superior pole
      of the patella then, pneumatic the tourniquet cuff will be placed (deflated) around the thigh
      with the distal edge 15 cm proximal to the proximal pole of the patella. The tissue padding
      coefficients based on limb circumferences will be calculated in all patients of group (A)
      according to table (1) [3].

      After three successive stable systolic blood pressure reading (5 minutes apart), an initial
      systolic blood pressure [initial SBP] reading will take and estimated arterial occlusion
      pressure (AOP) will be quickly calculated according to one of the previously mentioned
      equation followed limb exsanguination using an Esmarch bandage, then the tourniquet cuff will
      be inflated to a safety margin pressure 20 mmHg above the calculated (AOP) [3] which will be
      the [initial tourniquet pressure]. The time between the initial SBP taking and tourniquet
      inflation will be measured [initial SBP-to- tourniquet inflation time]. The absence of
      arterial flow in the lower limb is assured using Doppler probe (HD, Philips) positioned, by
      an independent anesthetist, at either the dorsalis pedis artery or the posterior tibial
      artery on the foot to monitor arterial flow distal to the tourniquet. If any arterial flow
      sound will be heard, the estimated tourniquet pressure will be considered insufficient and
      the patient will excluded from the study. When no arterial blood flow is secured, the surgeon
      (blinded to the groups) will allowed to start and will be asked to rate the bloodless
      surgical field using a 4-point scale [1 (Excellent) = No blood in the surgical field, 2
      (Good) = Some blood in the surgical field but no interference with surgery, 3 (Fair) = Blood
      in the surgical field but no significant interference with surgery, 4 (Poor) = Blood in the
      surgical field obscures the view] [3] at the beginning, in the middle, and at the end of the
      surgical procedure.

      During the surgery, systolic blood pressure will be measured every 5 minutes and the
      tourniquet inflation pressure will be always kept 20 mmHg above the SBP.

      Surgical procedure and anesthetic management were performed by the same surgical and
      anesthesia teams respectively. The attending anesthesiologist was aware of the allocated
      group, but the data analyst, surgeon and the patients were blinded to group allocation.

      All the patients will be examined one day after surgery for any complications associated with
      the tourniquet, (e.g. tissue damage, nerve palsy, lower limb blood flow).

      The following will be measured:

        -  Patient's age, weight and gender and lower limb circumference?

        -  Operative duration and tourniquet time.

        -  Initial SBP-to- tourniquet inflation time

        -  Primary outcome: initial and maximal SBP, initial and maximum tourniquet inflation
           pressure.

        -  Secondary outcome: surgeon rating of the bloodlessness of the surgical field.

        -  Any tourniquet associated complications.
    

Intervention name(s): Pneumatic tourniquet inflation pressure
Intervention type(s): Procedure
Intervention description(s): Pneumatic tourniquet inflation pressure estimation using two different mathematical equations
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Treatment