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Taking your patient off a ventilator

Following an established protocol can help you wean your patient from a respirator as soon as possible.


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CE credit is no longer available for this article. (Expired May 2009)


Originally Posted May 2007

By Sonia M. Astle, RN, MS, CCRN, CCNS, and Dwayne Smith, RRT

SONIA ASTLE, a member of the RN editorial board, is a critical care nurse specialist, and DWAYNE SMITH is a respiratory therapist at Inova Fairfax Hospital in Falls Church, VA. The authors have no financial relationships to disclose.

Following an established protocol can help you wean your patient from a respirator as soon as possible.

Although the literature reports that ap proximately 33% of patients in the ICU require mechanical ventilation (MV),1 the figure is closer to 90% for the critically ill patients we treat in our ICU. Ventilation saves lives, but its use for more than 24 hours increases the risk of ventilator-associated pneumonia (VAP) and airway trauma, as well as the need for additional sedation.2-5 Prolonged use also increases the cost of hospitalization: The mean incremental charge for an ICU patient on mechanical ventilation is approximately $1,500 per day.6 The emotional toll on patients is more difficult to calculate, as they grapple with serious illness, breathing difficulty, the uncertainty of not knowing how long they'll remain connected to a machine, and not being able to communicate.

To achieve the ultimate goal of getting patients to breathe on their own, timing is critical. The sooner you liberate patients from the ventilator the better, but premature discontinuation of mechanical ventilation can compromise gas ex change and lead to problems with reintubation.2 In fact, nearly one-third of ICU patients on MV can't be weaned on the first attempt.7

The traditional approach to weaning has been a gradual reduction of ventilatory support—starting with cutting back on supplemental oxygen and eventually ending with extubation or tracheal decanulation—under the direction of a physician. In recent years, however, a protocol-specific approach, implemented by nurses and respiratory therapists, has emerged as a common and effective alternative. Several randomized, controlled trials have found that protocols are more likely to reduce the duration of MV, and the rate of reintubation and VAP, than physician-directed weaning models.2-4 At our large hospital, respiratory therapists (RTs) handle weaning in collaboration with nurses, who perform the bulk of the patient assessment; you may play an even greater role on your unit.

Regardless of your function and whether you use a physician- or protocol-directed approach, you'll need to understand the weaning process so that you can evaluate your patient's readiness for weaning, ease his fears, and monitor his progress every step of the way.

Step one: Determine the patient's readiness

To ascertain if your patient is ready to wean, you'll need to first assess how well he's healing from the underlying disease or condition that originally mandated MV, such as sepsis, pneumonia, or myocardial ischemia. A patient who has pneumonia, for instance, is ready to wean if he's stable on antibiotics, has a normal temp, has vitals within normal limits with minimal or no use of pressors, and he's able to cough up secretions.

Other factors that need to be resolved or controlled before attempting to wean include pain, muscle fatigue, renal insufficiency, and poor nutrition.2,8 Your patient should also be easily arousable and off of any continuous IV sedation.

According to arterial blood gas results, his pH should be 7.25 or greater,2 and the PaO2 (partial pressure of arterial oxygen) should be 60 mm Hg or greater. Your patient ought to be on no more than 50% FiO2 (fraction of inspired oxygen), and 8 cm H2O or less of positive end-expiratory pressure (PEEP).2 The PaO2/FiO2 (P/F) ratio, an excellent predictor of oxygenation status and readiness to wean, should be greater than 150 – 300. This figure is eas ily calculated by dividing the PaO2 by the FiO2. For example, if your patient's PaO2 is 80 mm Hg and his FiO2 is 0.4 (40%), his P/F ratio is 200.

In addition, assess hemoglobin level, which should be at least 8 gm/dL. Also be sure magnesium, potassium, and phosphorus are within normal range, since low levels of electrolytes impair respiratory muscle function. Once your patient meets all of the criteria listed in the box on page 37, he's ready to try breathing on his own.

Step two: Getting ready to fly solo

A spontaneous breathing trial (SBT) is a test whereby patients attempt to breathe independently, while usually still connected to ventilators. It can predict whether they have the ability to successfully wean.2 Postop patients who meet all of the weaning criteria may be extubated after a single trial. Depending on the patient's lungs, trials may be as short as five to 15 minutes, and repeated up to four times a day. There are a number of ways that this can be done, but first, you'll need to help the individual prepare mentally.

Although your patient will be excited about the prospect of coming off the ventilator, he'll naturally be worried about his ability to breathe on his own. To ease his anxiety, explain the weaning plan—which may be a hospital protocol or one developed specifically by his healthcare team—to him and his family. Be sure to document your conversation.

Assure your patient that you'll coach him throughout the SBT. Explain that he may experience some discomfort when he starts breathing without the as sistance of the ventilator, as he would if he were exercising other muscles that he hadn't used in a while.

Explain that you'll continually monitor his vital signs and the amount of air he's breathing. Reassure him that you'll stop the trial if he feels anxious about continuing, he has trouble breathing, or his blood pressure, respiratory rate, pulse, or EKG indicates fatigue.

Most patients sit in a chair or upright in bed for the SBT, but if your patient is obese or has spinal deformities, back pain, or contractures, you will need to help him find a position that's more comfortable. To help him relax and better tolerate the trial, encourage him to listen to music, watch television, or hold the hand of a loved one.

Weaning options are carefully selected

In general, clinicians use one of four techniques for weaning, alone or in combinations with which you may be familiar. They are pressure support ventilation, synchronized intermittent mandatory venti lation, continuous positive airway pressure, and rarely today, the T-piece circuit. Of them, pressure support ventilation is the only mode that enhances endurance. All of the other modes help strengthen respiratory muscles.

Physician preference and, more recently, hospital protocol, generally dictate the choice of weaning, but certain other conditions may come into play as well. For example, patients who are extremely debilitated or have congestive heart failure or severe myopathy may fare better with a combination of synchronized intermittent mandatory ventilation and pressure support ventilation, which is less demanding on respiratory muscles.9 As a result, the increase in metabolic demand and venous blood flow that accompanies the transition from MV to spontaneous breathing is less likely to overwhelm the heart's ability to compensate in these patients.9 Here's a description of each method:

Pressure support ventilation (PSV). With this technique, the ventilator delivers a set amount of positive pressure into the lungs each time the patient initiates a breath. The positive pressure continues throughout inspiration and ends when the expira tory phase of ventilation begins. (The expiratory phase actually starts when the patient's inspiratory flow rate falls to 25% of his peak inspiratory flow rate.10) With PSV, the patient controls the length and depth of each respiration and is able to breathe at his own rate. When the machine is set to deliver the maximal level of PS, the patient should be able to breathe comfortably at a respiratory rate of 20 or less, without using accessory muscles, while achieving a tidal volume of at least 8 – 12 mL/kg.

If a patient is tolerating PSV at our hospital, an RT gradually decreases the amount of PS in 2 – 4 cm H2O increments during the day. However, at night, he rests with ventilator support to prevent muscle fatigue. Each day, the weaning process begins again, with PS levels based on the progress the patient made on the previous day. Although targets vary according to a patient's status, a PS of 5 – 6 cm H2O usually indicates that he's ready for extubation, as long as he maintains a respiratory rate below 35, has a systolic BP between 90 and 180 mm Hg,2 and meets the other clinical criteria described in the section on preparing to wean.7

Synchronized intermittent mandatory ventilation (SIMV). With this mode, the machine is set to give the patient a certain number of breaths per minute at a specific tidal volume. In between machine breaths, he breathes spontaneously. The ventilator senses the beginning of the patient's next spontaneous breath and synchronizes the machine breath with his respiratory pattern. As the patient progressively increases the tidal volume of his spontaneous breaths, the RT gradually decreases the set rate on the ventilator.

This method may be used in combination with PSV. Although a patient on PSV must be able to breathe spontaneously, SIMV can provide backup breaths if the patient becomes apneic.

Continuous positive airway pressure (CPAP). For this method, the RT turns on the ventilator's CPAP setting so that the machine delivers positive pressure throughout the inspiratory and expiratory phases of the respiratory cycle. The constant pressure increases the functional residual capacity (FRC), which is the amount of air remaining in the alveoli following normal expiration. Keeping the alveoli open longer improves gas exchange.

Because the patient remains connected to the ventilator, an additional breathing circuit isn't necessary, and you can assess tidal volume, minute volume, and respiratory rate simply by reading the machine. If he can tolerate CPAP for 30 minutes, but not longer than two hours,2 and meets other clinical criteria, the endotracheal tube can be removed. If not, the patient is returned to full ventilator support.

T-piece circuit. This technique—the oldest—is no longer routinely used, although some physicians find it helpful for patients with chronic obstructive pulmonary disease (COPD). Because of added resistance and lower lung compliance, patients with COPD need more time to terminate the inspiratory phase of ventilation. As a result, their condition makes it difficult for them to use PSV, in which the inspiratory phase terminates when inspiratory flow rate drops to a predesignated value.10

Using the T-piece technique, the nurse or the RT disconnects the ventilator and the patient spon taneously breathes humidified oxygen through the T-piece for increasing periods of time. The first trial may be as short as five minutes, but subsequent trials become progressively longer as his respiratory muscles get stronger and he increasingly tolerates breathing on his own. Following each trial, the patient is reconnected to the ventilator. Once he can breathe spontaneously for two hours without clinical distress, he can be extubated. A disadvantage of the T-piece method is that, with the patient not attached to the machine, the nurse can't check tidal and minute volumes during the trial.

Unlike PSV, CPAP and a T-piece trial increase the patient's work of breathing, which involves three phases of respiratory muscle contraction during inspiration (expiration is a passive process). SIMV may also increase the work of breathing, depending on the level of support. Without ventilatory support, the patient must work harder to expand the lungs, overcome the viscosity of lung tissue, and combat airway resistance during the movement of air into the lungs. Factors that increase airway resistance—and ultimately the patient's work of breathing—include secretions and the size of the tube. Because an endotracheal tube is longer than a tracheostomy tube, for instance, it creates more resistance and increases the work of breathing. To decrease resistance—as well as improve access and reduce the risk of vocal cord damage—a physician may choose a tracheostomy over an endotracheal tube.

Monitor for distress during weaning

Before the trial begins, you may need to adjust your patient's sedative medication based on his score on the Richmond Agitation and Sedation Scale (RASS), or another assessment tool like it that measures alertness in patients on sedative medications. You'll need to suction secretions and administer bronchodilators, as ordered, to treat wheezing.

Depending on the chosen weaning technique, the RT will set the ventilator to the desired mode or place your patient on a T-piece. Once the SBT begins, pay particular attention to oxygenation status. His mental status should not change. For example, if he becomes somnolent or shows signs of agitation, discontinue the trial. Your patient's oxygen saturation should remain above 85% – 90%, PaO2 should be greater than 60 mm Hg, and pH should be in the range of 7.25 – 7.40, according to baseline values.

Also, he should remain hemodynamically stable, with his heart rate less than 140 and systolic BP be tween 90 and 180 mm Hg. Heart rate and BP should not vary by more than 20% from his baseline values. Respiratory rate should be less than 35 and not change by more than 50% from baseline.

Watch for perspiration and muscle strain in the neck and chest, signs that your patient is not toler ating the trial. Paradoxical breathing patterns, including abnormal movement of the thoraco abdominal muscles, inward movement of the abdomen during inspiration, and a different rate of motion between the chest and abdomen, also indicate distress.

A rapid shallow breathing index (RSBI), also referred to as the f/Vt, is another parameter that indicates your patient may be ready for weaning. Based on your observations during the SBT, divide his respiratory rate (frequency) by his tidal volume (Vt). For example, if respiratory rate is 20 and tidal volume averages 400 mL (0.4L), then RSBI is 20/0.4 or 50. If the RSBI is below 105 during the SBT, your patient will most likely tolerate extubation.11

If he can't tolerate the SBT, return him to full ventilator support, monitor his vital signs to make sure they return to baseline, and notify the physician if your patient reports chest pain. Reassure him that setbacks are common, explain that he'll have another breathing trial the next day if he meets the criteria,2 and encourage him to rest. Document the method and length of the SBT and how well he tolerated it.

Get ready to meet the challenge

Weaning critically ill patients from mechanical to spontaneous ventilation is a challenge. You can meet that challenge by closely monitoring patients, providing emotional support, and following an established weaning plan.


REFERENCES

1. Esteban, A., Anzueto, A., et al. (2002). Characteristics and outcomes in adult patients receiving mechanical ventilation. JAMA, 28(3), 345.

2. MacIntyre, N. R., Cook, D. J., et al. (2001). Evidence-based guidelines for weaning and discontinuing ventilatory support. A collective task force facilitated by the American College of Chest Physicians, the American Association for Respiratory Care and the American College of Critical Care Medicine. Chest, 120(6 Suppl), 375S.

3. McLean, S. E., Jensen, L. A., et al. (2006). Improving adherence to a mechanical ventilation weaning protocol for critically ill adults: Outcomes after an implementation program. Am J Crit Care, 15(3), 299.

4. Marelich, G. P., Murin, S., et al. (2000). Protocol weaning of mechanical ventilation in medical and surgical patients by respiratory care practitioners and nurses: Effect on weaning time and incidence of ventilator-associated pneumonia. Chest, 118(2), 459.

5. Kress, J. P., Pohlman, A. S., et al. (2000). Daily interruption of sedative infusions in critically ill patients undergoing mechanical ventilation. N Engl J Med, 342(20), 1471.

6. Dasta. J. F., McLaughlin, T. P., et al. (2005). Daily cost of an intensive care unit day: The contribution of mechanical ventilation. Crit Care Med, 33(6), 1266.

7. Burns, S. (2005). AACN procedure manual for critical care (5th ed.). Philadelphia: Elsevier Saunders.

8. Huang, C. J., & Lin, H. C. (2006). Association between adrenal insufficiency and ventilator weaning. Am J Respir Crit Care Med, 173(3), 276.

9. Chulay, M., & Burns, S. M. (2006). AACN essentials of critical care nursing. New York: McGraw-Hill Companies.

10. Jubran, A., & Tobin, M. J. "Methods of discontinuing mechanical ventilation." UpToDate, 14.2." 2006. www.uptodate.com (1 Oct. 2006).

11. Ingenito, E. P., & Drazen, J. M. (2005). Harrison's principles of internal medicine (16th ed.). New York: McGraw-Hill Companies.


Assessment criteria for readiness to wean

  • Reversal of underlying cause of respiratory failure
  • PaO2 ≥60 mm Hg on FiO2 ≤0.4 – 0.5
  • PEEP ≤5 – 8 cm H2O
  • PaO2/FiO2 >150 – 300
  • HR ≤140 beats per minute
  • Stable BP with no/minimal vasopressors, such as dopamine or norepinephrine ≤5 mcg/kg/min
  • No myocardial ischemia
  • Temperature ≤100.4° F (38° C)
  • Hemoglobin ≥8 – 10 gm/dL
  • pH ≥7.25
  • Acceptable electrolyte values
  • Adequate cough
  • Capability to initiate inspiration
  • Adequate mentation without continuous IV sedation

Source: Maclntyre, N. R., Cook, D. J., et al. (2001). Evidence-based guidelines for weaning and discontinuing ventilatory support. A collective task force facilitated by the American College of Chest Physicians, the American Association for Respiratory Care and the American College of Critical Care Medicine. Chest, 120(6 Suppl), 375S.

 

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