Pressure Measurement

In patients without a clear need for surgical consultation, measuring the compartment pressures in the ED assures safe patient disposition and management. Compartment pressure can be quickly and easily measured using a commercially available battery-powered monitor [Stryker STIC Monitor (Stryker Instruments, Kalamazoo, MI) or Ace Intracompartmental Pressure Monitor (Ace Medical Company, Los Angeles, CA)] that has a self-contained pressure transducer and readout. Compartment pressure is measured after careful aseptic preparation, insertion of the side-ported 18-guage needle into the compartment, and injection of a small volume of sterile saline while keeping the apparatus level. There is a brief overshoot as resistance to flow and inertia is overcome, but within a second of time a plateau of pressure will be reached that is the compartment pressure in mmHg. Always check the accuracy of the transducer by filling the needle and transducer with saline and holding it level and open to the atmosphere. It should read zero. Measure the pressure twice, whether normal or high, to assure that the needle had not become lodged in fibrous tissue.

When an electronic pressure transducer and monitor, as is used for vascular pressure measurement, are available, they can be used as follows: (1) Attach a short length of intravenous (IV) extension tubing to a stopcock and then to a pressure transducer. (2) Fill the transducer and tubing with sterile saline. Adjust the height of the transducer to the level of the compartment in question. Zero the transducer with the tubing open to the atmosphere at the level of the compartment. (3) After antiseptic skin preparation, fill a 16-gauge catheter over needle with sterile saline. Insert it into the compartment and remove the metallic needle. Attach the IV tubing to the catheter. (4) Inject a small quantity (less than 1 mL) of saline through the transducer and into the compartment while observing the monitor. A small overshoot will be seen and then the pressure will plateau at true compartment pressure. Wilson and colleagues 2 found this system as accurate as the Stryker device. Uppal and coworkers3 describe a system that uses the Intravenous Alarm Control (IVAC) pump as a monitor. EDs that use the IVAC pump may wish to study his report.

The technique of Whitesides and colleagues4 for compartment pressure measurement had the advantage of requiring only basic materials available in every ED. Unfortunately, the required three-way stopcock is now hard to find, having been replaced by two-way stopcocks for most applications. Electronic pressure transducers have become standard pieces of equipment in the ED and are easier to use. However, those anticipating situations lacking electronic monitoring should obtain the supplies and be familiar with the Whitesides method. This requires a 20-mL syringe, a three-way stopcock, two IV extension tubes, a Luer male blood pressure cuff adaptor, a bedside mercury manometer, a small bottle of sterile saline, and an 18-gauge needle. Assemble the apparatus as shown in Fig,.„270,-5. The bottle of saline is vented with an 18-gauge needle, and the needle on the apparatus is then inserted into the saline and saline withdrawn until the IV extension is half-filled. When removing the needle from the saline bottle, it is important to avoid getting any air in the needle. The needle is then placed in the compartment and the apparatus kept at the level of the needle and the stopcock turned so that it is open in all three directions. Two people are required for this test. One watches the manometer while the other slowly and gently depresses the plunger in the syringe while watching the saline meniscus. When the meniscus moves toward the patient, the operator notifies the manometer watcher, who notes the reading at that instant. In this way, only a minute amount of saline is injected into the compartment. As with the other methods, measure the pressure twice.

FIG. 270-5. The Whitesides method. Tissue pressure is measured by determining the amount of pressure with this closed system that is required to overcome the pressure within the closed compartment while injecting only a minute quantity of saline.

Measure the patient's systolic and diastolic systemic pressure during the time that compartment pressure is measured, as some surgeons use the mean arterial pressure5 or diastolic pressure4 in combination with compartment pressure to decide when emergency fasciotomy is needed. Other surgeons prefer to operate on clinical grounds only. In general, a compartment pressure of 35 to 40 mmHg is considered grounds for emergency fasciotomy.

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