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Phương pháp đo áp lực bóng chèn nội khí quản

 

Phương pháp đo áp lực bóng chèn nội khí quản

(mua bán thiết bị y tế)

 

Tracheal Tube Cuff Management

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Tracheal tube cuffs are used in children (> 5-6 years old) and adults to 'seal-off' the lower airway. This seal allows application of positive pressure ventilation to the lungs without extensive gas leaks. The seal provided by the cuff also can help prevent or minimize aspiration of oropharyngeal or supraglottic secretions into the lungs.

Unfortunately, the pressure used to inflate tracheal tube cuffs can cause damage to the surrounding tissues. If the cuff pressure is high enough to blocks off capillary blood flow (ischemia), tissue ulceration and necrosis will occur. Since capillary perfusion pressure range between 20-25 mm Hg, the goal is to keep tracheal tube cuff pressures below these levels whenever possible.

Measuring and Adjusting Cuff Pressures on Ventilator Patients

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Most cuff pressures measurements take place during a regular patient-ventilator system. The procedure described here, the minimal leak technique (MLT), is that used on patients receiving positive pressure ventilation.

Equipment: To measure and adjust tracheal tube cuff pressures on patients receiving positive pressure ventilation, you need a three-way stopcock, a 10 or 20 mL syringe, pressure manometer and stethoscope. Some institutions use bulb devices that combine the functions of the stopcock, syringe and pressure manometer.

Key Elements in Procedure:

1. After preliminary steps (infection control, explaining procedure, etc), attach the syringe and pressure manometer to the stopcock. The stopcock valve indicator should be positioned so that ALL THREE PORTS ARE OPEN.

2. Attach the remaining tapered stopcock port to the cuff's pilot tube valve, being sure that the valve opens and the connection is leak-free. With the stopcock open to the syringe, manometer, and cuff, you can add or remove air while observing the pressure changes on the manometer.

3. Place your stethoscope over the lateral surface of the laryngeal cartilage. If you hear gurgling or airflow during positive pressure breaths, use the syringe to slowly inflate the cuff until the these sounds stop (a leak-free seal). If you hear no sounds during positive pressure breaths, you already have a leak-free seal. Note and record the patient's exhaled volume.

4. Once you obtain a leak-free seal, use the syringe to slowly remove air while you observe the ventilator airway pressure. Stop removing air as soon as the sound of airflow or gurgling can again be heard at the peak inflation pressure (a minimal leak at PIP).

5. Record the cuff pressure and again note and record the patient's exhaled volume. Compute the difference between the current and prior exhaled volume measures (the leak). The goal is a cuff pressure < 20 mm Hg (27 cm H2O) with an acceptable leak (usually < 10% of the delivered volume).

6. Enter/record on the patient record/flowsheet: the method used (MLT), cuff pressure and size of leak.

Volume vs Pressure Measurements

Some clinicians also measure the cuff volume needed to achieve the minimum leak at PIP. This can be useful in detecting trends in cuff inflation over time. For example, the need for increased cuff inflation volumes over time usually indicates tracheal dilation or even tracheomalacia.

In order to measure the MLT cuff inflation volume, you must completely empty the cuff at the start of the procedure and carefully observe the syringe volumes 'injected' during reinflation. Your entry on the patient record/flowsheet would include: the method used (MLT), cuff pressure, cuff volume and the size of the leak. This procedure is more hazardous than the pressure-only method, due to the risk of aspiration when the cuff is deflated.

Take into account the following 'fine points' when making these measurements and adjustments:

  • Simply attaching the measurement system to the pilot tube evacuates some volume from the cuff (and lowers its pressure). For this reason, you should always adjust the pressure to the desired level, never just measure it.
  • Most respiratory care manometers are calibrated in cm H2O, and not mm Hg. Thus the "acceptable range" of 20-25 mm Hg equates to 27- 34 cm H2O. Most hospitals set 25 cm H2O as the "high-end" pressure.
  • The goal is the LOWEST cuff pressure that results in an acceptable leak. If this can be achieved at 8 or 10 cm H2O, all the better.
  • As ventilator pressures rise and fall, the pressure needed to achieve a minimal leak will also rise and fall. Any change in ventilator settings that alters PIP requires a readjustment of the cuff pressure.
  • Achieving a minimal leak in some patients may require cuff pressures exceeding 20-25 mm Hg. This is common at high ventilator pressures (above) or when the tube is too small for the patient's airway. The only reasonable solution in these cases is to use lower pressures and accept larger leaks (which are harmless as long as ventilation is adequate). Seldom will a doctor want to reintubate a patient just to place a larger tube.

Measuring and Adjusting Cuff Pressures on Spontaneously Breathing Patients

The only reason a spontaneously breathing patient with an endotracheal or tracheostomy tube would require a cuff is to protect the lower airway from aspiration. For these patients, cuff inflation pressures should be adjusted to the lowest pressure needed to prevent aspiration.

To determine if aspiration is occurring, you can use the methylene blue test. To perform this test, you add methylene blue to the patient's feedings or have the patient swallow a small amount in water. You then suction the patient's trachea through the artificial airway. If you obtain blue-tinged secretions when performing suctioning, you know that aspiration is occurring.

If aspiration is confirmed, efforts must be made to minimize it. Ideally, the patient should be switched to a system that continually aspirates subglottic secretions. If this is not possible, oropharyngeal suctioning (above the tube cuff) should be performed as needed. In order to decrease the possibility of aspiration with feedings, the head of the bed should be elevated (where possible). Also, the feeding tube can be inserted into the duodenum, with its position confirmed by X-ray. The use of slightly higher cuff pressure during and after feeding may also minimize aspiration.

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Always use the lowest cuff inflation pressures needed to protect the airway and provide for adequate ventilation. How much pressure will be needed will vary according to the patient, tube size, and conditions of treatment (positive pressure ventilation, enteral feeding, etc).

Alternative cuff designs

There are several different cuff designs that can help avoid pressure trauma to the tracheal mucosa. The Lanz tube incorporates an external pressure regulating valve and control reservoir designed to limit the cuff pressure to 16-18 mm Hg. The Kamen-Wilkinson foam cuff provides a tracheal seal at atmospheric pressure. Prior to insertion, you apply negative pressure with a syringe to deflate the foam cuff. Once in position, you open the pilot tube to the atmosphere, and allow the foam to expand against the tracheal wall. The cuff stops expanding when it reaches the inner tracheal wall.

Troubleshooting

The most common cuff problems involve leaks. On ventilator patients, a leak in the cuff itself, the pilot tube, or the one-way valve will result in a potentially large loss of delivered volume and/or inability to maintain the preset pressure limit. With both ventilator and spontaneously breathing patients, cuff leaks also can lead to aspiration.

Small/slow leaks are evident when cuff pressures consistently decrease between readings. With a large cuff leak ('blown cuff'), it will be impossible to maintain any cuff pressure. In addition, a blown cuff results in acute patient changes: decreased breath sounds, significant gurgling or airflow around the tube (as heard over the larynx), large volume loss and/or drop in delivered inspiratory pressure, and inadequate ventilation.

In either case, your first step is to try to re-inflate the cuff, while checking the pilot tube and valve for leaks. If the leak is at the one-way valve, attach a stopcock to its outlet. If the leak is in the pilot tube, place a a needle (with stopcock) in the pilot tube distal to the leak. Usually, one of these methods will allow you to reinflate the cuff and thus avoid reintubation. Unfortunately, a patient with a blown cuff normally requires reintubation.

Because the clinical signs of partial extubation are essentially the same as those observed with a blown cuff, DO NOT recommend extubation/reintubation until you can confirm that a cuff leak is the real problem. Before presuming a cuff leak, you should attempt to advance the tube slightly and reassess the leak and equality of breath sounds in both lung fields. Next, rule out or correct any pilot tube or valve leakage. Last, try to measure the cuff pressure. If you cannot maintain any cuff pressure, a large leak is confirmed and the patient will need to be reintubated.

 

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