Learn to meet two common challenges: facilitating rapid weaning and helping patients who are difficult to wean from mechanical ventilation.

PATIENTS RECEIVE mechanical ventilation for many reasons and for varying lengths of time. Some need ventilatory support for only a few hours; others need it for weeks, months, or even years.

In this article, I'll focus on your role in caring for patients at two extremes of the ventilatory support weaning continuum: those who can be considered for rapid weaning and those who are difficult to wean. But before considering these special situations, let's review some basics about mechanical ventilation.

Reviewing ventilatory support

Mechanical ventilation is indicated when the body can't meet its oxygen demand through spontaneous breathing or when the body can't adequately remove carbon dioxide (CO₂). Various conditions can increase the oxygen demand, such as abnormalities in the respiratory system, neuromuscular disease, or cardiovascular system failure.

Mechanical ventilation aims to provide adequate ventilatory support to meet the patient's oxygen demands without harming the patient. Ventilation is delivered via an artificial airway: an oral or nasal endotracheal tube or a surgically placed tracheostomy tube.

Tidal volume and frequency, supplemental oxygen (F_Io₂), mode of ventilation, pressure support, and positive end-expiratory pressure (PEEP) are set on the ventilator. The patient may need a sedative or analgesic to control anxiety or pain and may also receive intravenous fluid and nutritional support. These interventions are designed to let the body recover, heal, and regenerate if possible. If the patient recovers well enough to resume spontaneous breathing, weaning begins.

Some patients, such as those with acute heart failure and chronic obstructive pulmonary disease (COPD), may need just a few hours of mechanical ventilation while being treated for heart failure. For other patients, such as premature babies or burn victims, weaning may not occur until after days or weeks of ventilatory support. A baby's immature lungs need time to develop well enough to support spontaneous ventilation. The burn victim may need time for the airways to heal or require full support while his body recovers from the burn.

Some patients have trouble being weaned from ventilatory support. When weaning is attempted, these patients can't maintain spontaneous breathing and continue to need some degree of ventilatory support. For example, a patient with a neurologic injury and paralysis of the diaphragm may make some progress at weaning, but not enough to be totally free from mechanical support. This patient may require minimal ventilation (or perhaps nighttime only support).

For some patients, weaning isn't an option because the injury, disease, or system failure is too great to overcome. These patients remain mechanically ventilated for the rest of their lives.

When to use rapid weaning

The rapid-wean approach is generally reserved for patients without pulmonary disease who were placed on mechanical ventilation to treat an acute or postoperative condition that's expected to respond quickly to treatment. The formal rapid-wean approach, which has the patient off the ventilator in 6 to 8 hours, is typically used for patients who've had open-heart surgery for coronary artery bypass graft surgery or a valve repair or replacement. Most other postoperative patients are weaned and extubated in the operating room as soon as anesthesia wears off (or is reversed). In essence, these patients undergo a rapid-wean procedure under the care of the anesthesia staff before being moved to the postanesthesia care unit.

For this article, I'll discuss a rapid-wean approach in the setting of an intensive care unit (ICU) with patients who've had open-heart surgery. Keep in mind that this approach relies on the use of a protocol and must be initiated by physician order.

For open-heart-surgery patients, a rapid-wean strategy has several benefits. Early extubation reduces length of stay in the ICU and in the hospital, reduces the risk of ventilator-associated pneumonia (VAP), and lowers the cost of care. Cardiac surgery, an expensive procedure, is performed on more than 500,000 patients each year in the United States. If rapid weaning goes as planned, weaning and extubation is accomplished with few or no problems for most of these patients. But if patients are moved too quickly in being weaned and extubated and have to be reintubated, or suffer from other complications related to early weaning or extubation, they could require a longer length of stay, incur added health care costs, and face a higher risk of VAP or even death.

These three considerations are key to the success of rapid weaning.

1. Choosing appropriate patients to wean quickly. The rapid-weaning protocol should detail which patients are candidates, based on hemodynamic, neurologic, and respiratory parameters. (For details, see Sample rapid-weaning protocol.)A key feature to weaning is the spontaneous breathing trial. A patient who's met all the readiness criteria is placed on a T-piece. A low level of PEEP (for example, 5 cm H₂O) and low levels of pressure support (5 to 7 cm H₂O) may be used during the spontaneous breathing trial.

2. Careful use of analgesia and anesthesia. Once standard, high doses of opioids (for example, more than 20 mcg/kg of fentanyl) are now giving way to low-dose opioids (for example, 20 mcg/kg or less of fentanyl), short-acting opioids, and use of hypnotic agents for anesthesia during cardiac surgery, without significantly increasing the rate of reintubation. Using lower doses and short-acting agents results in fewer problems with depressed respiratory drive.

3. Effective, efficient use of a well-designed protocol. Protocols for patients who've had open-heart surgery should be designed to safely reduce ventilatory support while maintaining stable hemodynamic values, adequate oxygenation and elimination of CO₂, and acceptable or appropriate neurologic status. A multidisciplinary approach involving physicians, nurses, and respiratory therapists is essential when developing, testing, implementing, and evaluating the protocol.

Patients who've been receiving mechanical ventilation for a prolonged time may have many barriers to overcome in order to wean. When going into this process, the health care team must take into consideration the reason mechanical ventilation was initiated and evaluate whether this has been corrected. Then they can address the prolonged effects of mechanical ventilation. Most patients who are difficult to wean have problems in one or more of the following areas.

* Neurologic problems. Ventilator dependence may involve problems in the brainstem from stroke, trauma, or brain tumors; damage from excessive sedation or opioid use; or malfunction in nervous system conduction of impulses to the respiratory muscles due to nerve damage from trauma or disease. In rare cases, these obstacles can be overcome or reversed by medical treatment or by the body's own healing and reprogramming process. Otherwise, these patients will remain on mechanical ventilation for the rest of their lives. Even so, caregivers can work to reduce mechanical support and supplemental oxygen as much as possible while providing the best quality care.

* Inability to carry the respiratory load. This may be related to respiratory muscle fatigue from excessive work of breathing (which may be imposed by the ventilator or by the artificial airway), muscle atrophy from inactivity, or muscle damage from trauma or surgery. Bronchospasm or excessive secretions may also be factors. Patients with hyperinflated lungs due to air trapping, which often occurs with COPD, have flattened diaphragms that compromise the effectiveness of inspiratory efforts.How can the ventilator or artificial airway increase the work of breathing? If the ventilator circuit contains rain out (a collection of water in the low points) or the heat and moisture exchangers (HME) are clogged, the ventilator is less sensitive to the patient's efforts to breathe. If the patient tries to trigger a breath and the machine doesn't respond, the patient's work of breathing increases. Some older ventilators may not respond rapidly to a high respiratory rate, thus missing delivery of a breath.In addition, some ventilators may not end the inspiratory flow at an appropriate point, resulting in a breath that's shorter or longer than the patient's desired inspiration. This may cause the patient to breathe out of synchronization with the ventilator, increasing his work of breathing. Other factors that increase the work of breathing include artificial airways that are too small, too long (which tend to kink), or in a position that allows the patient to bite down and occlude the lumen. Correcting problems like these can relieve muscle fatigue, reduce the work of breathing, and improve the patient's ability to carry the respiratory load.

* Metabolic factors, such as inadequate nutrition and electrolyte imbalances. Patients who have chronic CO₂ retention from COPD have respiratory acidosis compensated by bicarbonate retention. Sometimes these patients are overventilated during mechanical ventilation, which causes excessive bicarbonate excretion as the CO₂ is blown off. The result is a metabolic imbalance that may interfere with weaning. Kidney failure also may contribute to metabolic imbalances that interfere with weaning.

* Inadequate oxygenation. Failure of the lung-to-cell oxygen delivery process may result from low blood oxygen content, inadequate cardiac output, or impaired oxygen uptake in the cell because of sepsis. Physical assessment, lab values, or chest X-rays often reveal causes for oxygenation problems that delay or interfere with weaning. Examples include anemia, ventilation-perfusion abnormalities due to atelectasis, infections such as pneumonia, shock, and pulmonary embolism.

* Cardiovascular limitations. Excessive fluid in the body and ineffective cardiac emptying can result in heart failure, which impedes weaning. Conversely, positive pressures in the thorax generated by the ventilator may reduce venous return to the heart and decrease cardiac output; this also impedes weaning.

* Psychological factors. Patients who've been on prolonged mechanical ventilation are afraid of losing this support. Because psychological barriers can be significant, provide careful, frequent communication and reassurance for the patient and family throughout weaning.

Making weaning work

Multidisciplinary teams play a key role in helping patients who have difficulty weaning succeed. Besides the patient and his family, an effective team may include physicians, nurses, respiratory therapists, occupational and physical therapists, speech therapists, social workers, nutritionists, wound care specialists, and chaplains. This group should interact daily at the bedside, participate in plans for care, and conduct formal weekly discussions of the care plan and the patient's needs.

The patient can benefit from an evidence-based approach to weaning. (See Guidelines for weaning.) Recent studies have shown that a daily "sedation vacation" can reduce the duration of mechanical ventilation, possibly because the "awake" patient is more likely to undergo daily assessment of his readiness to wean and extubate. A daily interruption in sedation also reduces ICU stay. (For more details on sedation vacations, see "Best-Practice Interventions: How Can You Prevent Ventilator-Associated Pneumonia?" in the February issue of Nursing2006.)

To rest patients' respiratory muscles, use assist/control mode with appropriate trigger sensitivity.

The following interventions are appropriate for patients using the rapid-weaning approach and are crucial to weaning success for patients who have difficulty weaning. For patients who've been on long-term ventilation, addressing all aspects of mechanical ventilation and hindrances to spontaneous breathing will maximize weaning success. Try these interventions to help make weaning easier:

* Elevate the head of the bed at least 30 degrees unless contraindicated to help relieve diaphragmatic pressure from abdominal contents and reduce the chance of aspiration pneumonia. Also, you can more easily manage excessive secretions when the patient's head is elevated.

* Kinetic therapy (mechanical rotation of patients with 40-degree turns by a specialized bed) reduces the incidence of VAP and atelectasis.

* Suctioning should be performed as often as indicated to clear secretions. Consider using a closed-system suction catheter so you don't have to open the patient-ventilator circuit.

* Adequate humidification of inspired air helps prevent mucus plugs.

* Prevent bronchospasm with bronchodilator therapy, either through a nebulizer or the equally effective metered-dose inhaler with a spacer device.

* Careful attention to proper infection control practices reduces the risk of VAP and other infections.

* Prophylactic antacids can help reduce the patient's risk of stress ulcers, which occur in 25% of patients receiving mechanical ventilation. Raising the pH of gastric contents also may protect against a greater pulmonary inflammatory response to aspiration of gastrointestinal contents.

* Sleep deprivation in the ICU can impair efforts to wean, so try to minimize noise and avoid unnecessary interruptions when the patient is sleeping.

* Fight depression and motivate the patient to improve by making his daytime environment stimulating. Clocks, calendars, and an outside view help link the patient to time and season. Pictures, music, TV, and visits from friends and family also can help stimulate and motivate. Help him communicate using devices such as writing tablets or picture and alphabet boards. If he has a tracheostomy, he may be able to speak by using a one-way speaking valve on a fenestrated tube. Also include the patient and the family in developing care plans.

The rapid-wean patient and the difficult-to-wean patient represent the two opposite ends of the mechanical ventilation spectrum. But by working with the patient, his family, and other members of the health care team, you can help your patient breathe independently and leave the ventilator behind.

Sample rapid-weaning protocol

1. Initiate postoperative mechanical ventilation using ventilator settings ordered by the anesthesia provider.

2. Obtain arterial blood gas (ABG) analysis 20 minutes after initiation of mechanical ventilation. Correlate ABG results with pulse oximeter and end-tidal carbon dioxide (ETCO₂) values.

3. Nurse or respiratory therapist assesses patient and documents his readiness to begin weaning. Criteria are:

* appropriate level of consciousness (alert, oriented, follows commands)

* hemoglobin level greater than 9 grams/dL, electrolyte levels within normal limits, and temperature of 36[degrees] C to 38[degrees] C (96.8[degrees] F to 100.4[degrees] F)

* key ABG values within normal limits (pH, 7.3 to 7.5; Paco₂, 30 to 50 mm Hg; PaO₂ greater than 70 mm Hg, Sao₂ of 92% or greater)

* ETCO₂ less than 40 mm Hg

* F_Io₂ less than 0.5 and total patient/ventilator respiratory rate (the sum of the mechanical ventilator breaths and spontaneous breaths) less than 30 breaths/minute.

4. Decrease intermittent mandatory ventilation (IMV) rate by 2 breaths/minute when the patient is awake and alert, responding appropriately, and assisting the ventilator and his Spo₂ is greater than 92%, ETCO₂ is less than 40 mm Hg, and hemodynamic values are acceptable. Acceptable hemodynamic values are: heart rate less than 120 beats/minute with no serious arrhythmias, BP greater than 100 mm Hg systolic, pulmonary capillary wedge pressure less than 18 mm Hg, cardiac index greater than 2 liters/minute/m² without intra-aortic balloon pump therapy, and chest tube drainage less than 100 mL/hour.

5. If the patient is stable 15 to 30 minutes after the IMV rate is changed, continue decreasing the IMV rate by 2 breaths/minute every 15 to 30 minutes as long as the patient's Spo₂ stays above 92%, his ETCO₂ is less than 40 mm Hg, and his hemodynamic values are acceptable. Stop when the IMV rate equals 2 breaths/minute.

6. Titrate the F_Io₂ to 0.4 in increments of 0.05 to 0.1 as long as the patient's Spo₂ is above 92%.

7. If the patient is receiving positive end-expiratory pressure (PEEP) of more than 5 cm H₂O, decrease PEEP by 5 cm H₂O every 30 minutes until PEEP is equal to 5 cm H₂O, as long as the patient's Spo₂ is above 92%.

8. Obtain an ABG analysis as needed and notify the physician or anesthesia provider if the patient's Spo₂ falls below 92% or ETCO₂ rises above 40 mm Hg or if he shows any signs of agitation or distress.

9. Discontinue weaning if the patient can't maintain acceptable hemodynamic, neurologic, or respiratory parameters. Return to previous ventilator settings and notify the physician.

10. When the IMV rate equals 2 breaths/minute, obtain an ABG analysis and correlate the results with the patient's Spo₂ and ETCO₂ values. Obtain lung function tests; the patient's tidal volume should be greater than 5 cc/kg, spontaneous respiratory rate between 8 and 30 breaths/minute, vital capacity greater than 15 cc/kg, minute ventilation less than 10 liters/minute, and maximal inspiratory pressure less than -20 cm H₂O. If readiness to wean criteria, hemodynamics, and lung mechanics criteria are met, place the patient on a T-piece at the current F_IO₂ and perform a spontaneous breathing trial.

11. Obtain an ABG analysis if the patient tolerates the spontaneous breathing trial for 30 minutes (as evidenced by his ability to stay on the T-piece with acceptable neurologic, hemodynamic, and respiratory parameters).

12. If the ABG results meet acceptable criteria, the patient will be extubated. Place him on supplemental oxygen at 5 to 6 liters/minute via nasal cannula. Maintain his Spo₂ over 92%. While he's awake, have him use an incentive spirometer every hour.

These guidelines, published in 2001, were developed by a collective task force comprising physicians, nurses, and respiratory therapists.

1. Search for all causes for the patient being ventilator-dependent and correct or reverse them.

2. Perform a formal assessment about readiness to wean if the patient meets the criteria listed below. Some patients may still be considered for weaning even if one of the following criteria isn't met:

* The cause of the respiratory failure has been partially or fully reversed.

* The patient's Pao₂/F_Io₂ is 150 to 200, positive end-expiratory pressure is between 0 and 8 cm H₂O, his F_Io₂ is less than 0.5, and pH is 7.25 or greater.

* The patient's hemodynamic status is stable, with no ischemia and no clinically important hypotension.

* The patient can initiate an inspiratory effort.

3. Perform a formal assessment of readiness to wean. If the patient can tolerate a 30- to 120-minute spontaneous breathing trial, he's ready. Tolerance is based on respiratory pattern (no retractions or obvious signs of distress and respiratory rate less than 30 breaths/minute), adequate gas exchange, hemodynamic stability, and subjective comfort level.

4. Once the patient is discontinued from mechanical ventilation, assess airway patency and his ability to clear secretions. If the airway isn't patent, or if he can't clear secretions, leave the artificial airway in place.

5. If he failed the spontaneous breathing trial, determine and correct the cause. Then evaluate him based on guideline 2. If criteria are met, perform a spontaneous breathing trial every 24 hours.

6. Between breathing trials, use a ventilator mode that provides support that is stable, nonfatiguing, and comfortable. Let the patient rest to avoid overloading the ventilatory muscles.

7. Use proper analgesics and sedatives at the lowest possible dose, to avoid blunting the respiratory drive.

8. Employ properly designed weaning protocols performed by a nurse/therapist team. Use sedation protocols.

9. If the patient will clearly need prolonged mechanical ventilation, he should have a tracheostomy. Early in the course of treatment is better than later.

10. A patient should be classified as permanently ventilator-dependent only after 3 months of failed weaning attempts, unless he clearly has irreversible disease or injury, such as amyotrophic lateral sclerosis or spinal cord injury.

11. If weaning attempts in the ICU have failed, transfer a medically stable patient to a specialized facility that has a good safety and success record in accomplishing ventilator discontinuation.

12. When a patient has been on prolonged mechanical ventilation, go slowly in weaning and gradually increase the time used for spontaneous breathing trials. Respiratory muscles need to be retrained and strengthened for patients who've been ventilator-dependent for prolonged periods.

The author has disclosed that he has no significant relationship with or financial interest in any commercial companies that pertain to this educational activity.

SELECTED REFERENCES

Ely E, et al. Mechanical ventilator weaning protocols driven by nonphysician health-care professionals: Evidence-based clinical practice guidelines. Chest. 120(6, Suppl.):454S-463S, December 2001.

Grap M, et al. Collaborative practice: Development, implementation, and evaluation of a weaning protocol for patients receiving mechanical ventilation. American Journal of Critical Care. 12(5):454-460, September 2003.

MacIntyre NR. Evidence-based ventilator weaning and discontinuation. Respiratory Care. 49(7):830-836, July 2004.

MacIntyre NR, et al. 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-395S, December 2001.

Marelich G, et al. 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):459-467, August 2000.

Sessler C. Wake up and breathe. Critical Care Medicine. 32(6):1413-1414, June 2004.

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