Liberation from LMV

Long-term mechanical ventilation (LMV), or prolonged mechanical ventilation, is defined as the need for mechanical ventilation for over 6 hours a day for more than 21 days [1].

Most patients using LMV have multiple diseases that complicate treatment and care. A multicenter survey found that on average each LMV patient had 2.6 premorbid diagnoses on admissions to long-term care hospitals (LTCHs) [2]. The causes for LMV often include the following [1]:

  • Systemic disease factors: Approximately 40% of LMV patients have chronic obstructive pulmonary disease (COPD), 50% have cardiac disease (coronary artery disease or congestive heart failure), and 20% have neurologic disease.
  • Respiratory mechanical factors: Respiratory muscle dysfunction, whether due to preexisting diseases or to respiratory load-capacity imbalance, often leads to LMV. Respiratory load-capacity imbalance can be a result of patient-ventilator asynchrony due to inappropriate ventilatory mode selection, inadequate ventilator flow, inappropriate trigger and cycling sensitivity settings, and intrinsic Positive End Expiratory Pressure (PEEP), such as in COPD patients.
  • Iatrogenic factors: Failure by caregivers to appreciate ventilator liberation capabilities by not appropriately assessing the weaning readiness, nosocomial infections, and over-sedation are some iatrogenic factors contributing to LMV.

Of all patients who receive mechanical ventilation, approximately 5% undergo LMV [3]. LMV imposes a heavy burden, both financially and socially, to the healthcare system, patients and their families. Hospitalization costs for the patient with LMV are high, reaching $150,000 per patient in a 2007 study [4].

A Multidisciplinary Approach is Required
Because patients suffering from LMV usually have multiple comorbidities, coordinated treatment and management of these comorbidities is critical in order for them to be liberated from LMV. In addition, most of these patients have problems in their physical muscle strength, nutrition, and psychosocial issues. A multidisciplinary approach including physicians, nurses, respiratory therapists, physical therapists, nutrition experts, psychologists and social workers is necessary. This approach will ensure, besides conventional treatments, the appropriate selection of suitable ventilatory modes, ventilator settings, and physical, nutritional, and psychological therapies.

Caregivers need to change from an ICU mindset to a multidisciplinary, rehabilitative mindset for LMV patients.

Avoid Patient-Ventilator Asynchrony
Mechanical ventilation occurs with two driving forces: patient respiratory muscles generating spontaneous efforts and mechanical ventilators delivering positive pressure to the patients. Unless either force is completely absent, these two forces very often work in an asynchronous manner. Patient-ventilator asynchrony can happen in several ways [5, 6]:

  • Inspiratory trigger asynchrony (ineffective efforts, delayed trigger, auto-trigger, double trigger)
  • Cycling asynchrony (premature cycling, delayed cycling)
  • Flow asynchrony

Patients under mechanical ventilation often suffer from patient-ventilator asynchrony. Chao et al found that 11% of their LMV patients had inspiratory trigger asynchrony. The patients without trigger asynchrony had a 57% chance of being weaned from mechanical ventilation, but the patients with trigger asynchrony had only a 16% chance of being weaned [7]. When Thille et al examined all types of asynchrony, not just inspiratory trigger asynchrony, in another study, they found that 24% of patients had an asynchrony index ≥10%. (Asynchrony index, orAI, refers to the percent of breaths that had any types of patient-ventilator asynchrony as described above.) The medium number of ventilator days for these patients was 25 days, much longer than the 7 days for patients with an AI <10% [8]. Usually, patients with patient-ventilator asynchrony are older and more likely to have COPD. In addition, it is common to find that they are ventilated with a less sensitive inspiratory trigger setting, higher pressure support level, and larger tidal volume. Reported studies have not been designed to assess whether asynchrony is a cause of longer time on ventilation or a marker for it, but mechanisms have been described by which asynchrony could possibly contribute to longer ventilation times.

Recommendations:

  1. Appropriate selection of ventilatory mode is important. Patients with spontaneous efforts but using volume control or pressure control mode often suffer from patient-ventilator asynchrony because of a) the fixed ventilator inspiratory time that most likely does not match the patient neural inspiratory time; b) the set flow rate in volume control mode being unable to satisfy dynamically changing patient flow demands; and c) the set pressure and volume being unable to match the patient needs for variability. In these patients, a spontaneous mode such as Proportional Assist™* Ventilation (PAV) or pressure support ventilation (PSV) usually results in better synchrony.
  2. Ventilators’ graphic waveforms are a great tool to help uncover any type of patient-ventilator asynchrony. Although the technical capabilities of modern mechanical ventilators make them capable of diagnosing patient-ventilator asynchrony, none currently provide this feature. Until such features are available, clinicians need to frequently examine ventilator graphic waveforms, and to correct patient-ventilator asynchrony by adjusting ventilator settings, such as breath mode, inspiratory time, trigger sensitivity, inspiratory slope/flow, cycling-off threshold, PSV level, and PEEP.
  3. Pay special attention to patients with COPD, with weak spontaneous efforts, with higher PSV settings, with volume control mode, and/or with significant intrinsic PEEP. These patients are particularly susceptible to patient ventilator asynchrony.

Avoid Over-Sedation
The appropriate use of sedatives in patients under mechanical ventilation helps to reduce patient distress, discomfort, accidental self-extubation, as well as O2 consumption. However, sedatives are often overused in these patients. A multicenter study found that clinicians assessed only 43% of ventilated patients for the need of sedation but used sedatives in 72% of these patients. Similarly, only 42% of ventilated patients were assessed for the need of analgesia but 90% of these patients were given opioids [9]. 40%-50% of patients who were assessed for the need of sedation and analgesia were actually in a deep state of sedation.

Sedation, especially over-sedation, lowers the patient’s respiratory drive and is predictive of ineffective triggering that is related to increased duration of mechanical ventilation [10]. Over-sedation can cause diaphragmatic inactivity. The combination of diaphragmatic inactivity and mechanical ventilation for 18-69 hours can result in marked atrophy of human diaphragm myofibers [11].

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Avoidance of over-sedation has been proven to be useful in shortening the duration of mechanical ventilation in many studies. Some clinicians have used protocol-based sedation/analgesia management to avoid over-sedation, and found that these patients needed fewer ventilator days [12, 13]. Others introduced daily interruption of sedatives and were able to reduce ventilator days [14]. Some even proposed no sedation for ventilated patients and were able to show shortened ventilator days, but the patients with no sedation had a higher chance of agitated delirium (one in five patients) [15].

Clinicians should not use sedatives as the first choice in managing patient-ventilator asynchrony. Reassess the ventilator settings first. When sedatives and analgesics are needed, attention needs to be paid to avoid over-sedation in order to facilitate a faster weaning from mechanical ventilation. Review Clinical Practice Guidelines for the Sustained Use of Sedatives and Analgesics in the Critically Ill Adult from the Society of Critical Care Medicine [16].

Weaning Methods
Among LMV patients, 54% can be successfully weaned from mechanical ventilation [17]. The weaning methods chosen greatly affect the speed of weaning. Several large sample clinical studies have been conducted to compare various weaning methods (Table 1).


Table 1. Large Sample Clinical Studies to Compare Weaning Speed among Various Weaning Methods

Authors

Number of Patients Studied

Type of Patients Studied

Weaning Methods and Results

Esteban et al [18]

546

ICU patients

SBT weans 2 times faster than PSV and 3 times faster than SIMV.

Kollef et al [19]

357

ICU patients

Protocol-based weaning is faster than non-protocol-based weaning.

Jubran et al [20]

312

Long-term ventilation patients

SBT using tracheostomy collar weans faster than PSV.

Brochard et al[ 21]

109

ICU patients

PSV weans faster than both SBT and SIMV.

Vitacca et al [22]

52

Long-term ventilation patients

There is no difference between SBT and PSV. However, protocol-based weaning is faster than non-protocol-based weaning.

Note: SBT: spontaneous breathing trial; PSV: pressure support ventilation; SIMV: synchronized intermittent mandatory ventilation.

The results of these studies may be confusing, but several conclusions can be drawn:

  1. Protocol-based weaning weans patients faster.
  2. Weaning using SIMV does not provide an advantage and should be avoided.
  3. SBT and PSV are the modes of choice for faster weaning, and SBT seems more likely to offer the fastest weaning.

Proportional Assist™* Ventilation Plus software with automatic measurements of respiratory resistance and compliance has been proven to provide better patient-ventilator synchrony compared with pressure support ventilation [23, 24]. It has been recently used in several facilities in Canada to wean patients from long-term mechanical ventilation. According to St. Mary’s General Hospital in Ontario Canada, their progressive weaning program using PAV+ software has resulted in 82% overall success rate (i.e., the patients were either liberated from mechanical ventilation or successfully discharged home with long-term assisted ventilation). As the result, the hospital estimated an annual saving of $1.35 million in their facility alone [25, 26]. The procedures of the progressive weaning program using PAV+ are as follows.

1. Phase I – Assessment
a) Place the patient on PAV+ 80% support. If not tolerated, return to previous mode of ventilation and reattempt the next day.

b) PAV+ 80% support becomes the patient’s Resting PAV+ Level. Consider reducing the Resting PAV+ Level only if the patient’s tidal volume is too high or respiratory rate is too low. If PAV+ is not tolerated or is contra-indicated, consider other supportive modes before proceeding to controlled modes of ventilation for rest.

c) Place the patient on PAV+ software 35% support for 30 minutes. If tolerated, extend the patient’s trial until the patient develops respiratory fatigue. A PAV of 35% support will then become the patient’s trial PAV level. The length of time for respiratory fatigue to occur will be used to replace the initial “Length of Each Trial” in Table 2. If the patient does not tolerate PAV+ 35% support for 30 minutes, let the patient rest at 80% support until the next day. Re-attempt the PAV+ trial with a level of support 10% higher than the previous day each day until the patient is able to remain on the trial for 30 minutes. The PAV+ support level required becomes the patient’s Trial PAV+ Level.

2. Phase II – PAV+ Weaning
a) Reduce the PAV+ support to the Trial PAV+ Level during the trials of the PAV+ weaning process. PAV+ level during rest remains at 80%.

Table 2. Progressive Weaning Protocol Time Table

Trial Frequency per Day

Length of Each Trial

Rest Between Trials

Rest Overnight

4

30 min

2 hours

22:00-08:00

3

1 hour

2 hours

22:00-08:00

2

2 hours

2 hours

22:00-08:00

2

3 hours

2 hours

22:00-08:00

2

4 hours

2 hours

22:00-08:00

1

8 hours

N/A

22:00-08:00

1

12 hours

N/A

22:00-08:00

1

16 hours

N/A

22:00-06:00

Stop the trial if any of the following conditions occur: RR > 35 for > 5 minutes, SpO2 < 88%, HR increases 20% from baseline for > 5 minutes, BP increases 20% from baseline for > 5 minutes, respiratory distress and/or accessory muscle use, mental status change, acute cardiac arrhythmia, or etCO2 increases > 15 mmHg from baseline.

b) Consider an accelerated wean to the next step if the f/VT ratio remains < 70-80 at the end of each trial.
c) If the Trial PAV+ Level determined is >60%, once 16 hours have been completed, the clinician should begin again at PAV+ 35% support as per step 1. Patient should rest on a full support mode overnight and in between trials.

d) Patient must complete 16 hours of PAV+ 35% support before moving to Phase III.

3. Phase III – Tracheal Mask Weaning
a) Once patient is weaned to 35% PAV, consider tracheal mask trials using the schedule as described in Table 2. Continue to rest patient overnight on PAV+ 80% support. When patient completes 16-hour tracheal mask trial successfully, move on to 24-hour tracheal mask trial.

Carefully choosing a weaning method can result in shorter weaning duration and thus a big saving. SBT- and PSV-based weaning seems to be better than SIMV. Protocol-based weaning provides shorter duration of weaning. Progressive weaning using PAV+ is promising.

In conclusion, long-term mechanical ventilation imposes a great financial and social burden to the healthcare system, the patient and their families. Clinicians have many tools available for liberating patients faster from mechanical ventilation. A multidisciplinary approach, appropriately managing patient ventilator asynchrony, avoiding over-sedation, and carefully choosing a weaning method are some important tools at the clinicians’ disposal.

Hong-Lin Du, MD, PhD, is vice president, Medical Affairs, at Covidien.

References:

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  2. Scheinhorn DJ, Hassenpflug MS, Votto JJ, et al. Post-ICU mechanical ventilation at 23 long-term care hospitals: a multicenter outcomes study. Chest. 2007;131:85-93.
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  26. Waterloo Wellington Local Health Integration Network: Sending more patients home faster and safely from critical care – Waterloo Wellington extends long term ventilator weaning program. http://www.wwlhin.on.ca/. Accessed March 1, 2013.

* Proportional Assist and PAV are registered trademarks of The University of Manitoba, Canada. Used under license.

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