Incorporating LOP into Clinical Workflow

A patient’s Limb Occlusion Pressure can be measured automatically using dual-purpose tourniquet cuff technology, automatically using a distal photoplethysmographic sensor accessory, or manually by Doppler Ultrasound [1]. The tourniquet instrument technology available for use will determine which LOP measurement method can be utilized. LOP should be measured just before tourniquet inflation, when possible [2].

Once the patient’s LOP has been determined, a personalized tourniquet pressure can be recommended by adding a safety margin to the LOP value to account for intraoperative changes and limb manipulations [2, 3, 4]. Safety margins can be added based upon the measured LOP, or set to a custom value. Factors that may impact what safety margin to select may include:

• Anesthetic management
• Limb manipulation
• Anticipated intraoperative changes

Always refer to the tourniquet manufacturer’s Instructions for Use for specific details on how to operate the tourniquet instrument and measure Limb Occlusion pressure.

EZ method to measure LOP

User notes for the EZ Method

• Confirm tourniquet instrument has EZ Method capabilities for the intended use case.
• Prepare the patient in accordance with your established procedures and cuff instructions.
• LOP measurement can be completed at anytime prior to tourniquet cuff inflation, for example after sterile solution applied to the limb, or after the final sterile draping is complete.
• The EZ method to measure LOP will typically take between 30-45 seconds to complete.
• The tourniquet will briefly inflate the cuff during the measurement. The cuff will fully deflate once the LOP is determined.
• The limb must not be disturbed during the measurement, as movement could introduce a noisy signal which can cause the measurement to fail.

Example EZ method clinical workflow

1. Bring patient to the OR and administer anesthesia
2. Apply tourniquet cuff and limb protection to the limb*
3. Apply sterile prep solution to the limb
4. While the surgical team is gowning, initiate LOP measurement to determine the personalized tourniquet pressure
5. After measurement is complete, to set the tourniquet pressure accept the LOP and recommended personalized tourniquet pressure
6. Surgical team to complete sterile field preparation
7. Inflate tourniquet to the personalized tourniquet pressure at the request of the surgeon

*Note: if a sterile tourniquet cuff is used, complete the sterile field preparation, apply the sterile tourniquet cuff, and then perform the EZ method LOP measurement.

Distal method to measure LOP

User notes for the distal method

• Confirm the tourniquet instrument comes equipped with a distal sensor accessory.
• The distal sensor is a non-sterile, reusable device. Measure the LOP prior to completing any sterile field preparation.
• The Distal method to measure LOP will typically take between 20 – 40 seconds to complete.
• Adequate signal quality must be achieved to perform a successful measurement. Factors which impact signal quality include: sensor placement, cold digits, and ambient light leakage.

Example distal method clinical workflow

1. Bring patient to the OR and administer anesthesia
2. Apply a clean, non-sterile tourniquet cuff and limb protection to the limb
3. Attach the distal sensor to the digit of the same limb as the tourniquet cuff
4. Achieve adequate signal quality
5. Initiate LOP measurement to determine the personalized tourniquet pressure
6. After measurement is complete, to set the tourniquet pressure accept the LOP and recommended personalized tourniquet pressure
7. Remove the distal sensor from the patient’s digit
8. Complete sterile field preparation
9. Inflate tourniquet to the personalized tourniquet pressure at the request of the surgeon

Manual doppler method to measure LOP

User notes for the doppler method

• Employing Doppler ultrasound to determine a patient’s LOP is more difficult, time consuming and error prone than the automatic methods. Only personnel experienced with Doppler ultrasound use should perform this method.
• The manual Doppler ultrasound method requires two operators. One person to operate the ultrasound device, and the other to operate the tourniquet instrument.
• Unless both the Doppler ultrasound device and its operator are sterile, the LOP measurement must be performed prior to sterile field preparation.
• Due to the audible determination of this method, a quiet environment in the OR is required.
• The pressure of the ultrasound probe can influence results. Pressing too hard on top of the artery can compress the artery and can result in an erroneous LOP determination.

Example manual doppler ultrasound clinical workflow

1. Bring patient to the OR and administer anesthesia
2. Apply non-sterile tourniquet cuff and limb protection to the limb
3. The ultrasound operator finds a distal artery with good audio signal and holds the ultrasound probe steady, without pressing hard, at the determined location
4. The tourniquet instrument operator inflates the tourniquet to a very low set pressure initially (around 50 mmHg)
5. Once the set pressure has stabilized, the tourniquet operator slowly increases the tourniquet set pressure, operating in increments of 5 – 10 mmHg
6. At each increment wait until the pressure has stabilized. The ultrasound operator confirms whether they can still hear a distal pulse
7. Once the distal pulse starts to become quieter, the tourniquet operator should only increment the set pressure by 1 – 2mmHg at each increment
8. The tourniquet pressure at which the distal pulse has entirely disappeared for longer than 5 continuous seconds is the Limb Occlusion Pressure
9. The tourniquet operator deflates the tourniquet. The ultrasound operator should confirm that they hear the return of the distal pulse to ensure that the ultrasound probe did not drift over the course of the measurement
10. The tourniquet operator manually sets the tourniquet pressure to the personalized tourniquet pressure (LOP + safety margin)
11. Complete the sterile field preparation
12. Inflate the tourniquet to the personalized tourniquet pressure at the request of the surgeon

Sources

1. Hughes L, McEwen J. Investigation of clinically acceptable agreement between two methods of automatic measurement of limb occlusion pressure: a randomised trial. BMC Biomedical Engineering. 2021 Dec;3(1):1-8.
2. Recommended practices for care of patients undergoing pneumatic tourniquet-assisted procedures. In: Perioperative Standards and Recommended Practices. AORN, Inc.; 2015.
3. Olivecrona C, Ponzer S, Hamberg P, Blomfeldt R. Lower tourniquet cuff pressure reduces postoperative wound complications after total knee arthroplasty. J Bone Joint Surg Am. 2012 Dec 19;94(24):2216-21.
4. Younger AS, McEwen JA, Inkpen K. Wide contoured thigh cuffs and automated limb occlusion measurement allow lower tourniquet pressures. Clinical orthopaedics and related research. 2004 Nov 1;428:286-93.