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 days1.
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 following1:
- 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 LMV3. 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 study4.
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 ways5,6:
- 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 weaned7. 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.
- 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.
- 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.
- 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.
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 opioids9. 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 ventilation10. 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 myofibers11.
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 days12,13. Others introduced daily interruption of sedatives and were able to reduce ventilator days14. 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 Medicine16.