Long-Term Mechanical Ventilation Equipment for Neuromuscular Patients: Meeting the Expectations of Patients and Prescribers

Knowledge and Patient Comfort

Only 78% of the patients were able to correctly describe their MV mode as volume control, pressure control, or a combined mode, and less than of half of the patients were able to describe their MV mode as assisted, controlled, or both. This shows that most patients have a poor knowledge of their MV and of patient-ventilator synchronization. Interestingly, 92% of the patients who had the possibility to trigger the ventilator insufflations considered that they were able to do it, including all the tracheostomized patients using an assist mode. However, 8% of the non-tracheostomized patients and 18% of the tracheostomized patients considered their ventilator trigger insufficiently sensitive. On the other hand, the ventilator trigger was reported as “too sensitive” by 5% and 3% of the nontracheostomized and tracheostomized patients, respectively. These results reflect the difficulty of finding a trigger sensitivity that is neither too high nor too low. This is particularly difficult for patients whose inspiratory muscle strength may decrease, which should lead to increasing the trigger sensitivity. An alternative could be the use of a new trigger technology, such as the detection of the inspiratory effort by means of inspiratory muscle electromyography, such as with neutrally adjusted ventilator assistance.⁶ For a home ventilator such a trigger would require an implantable device for monitoring inspiratory muscle electromyography. When we asked the patients if they would accept a minor surgical procedure to improve their ventilator synchrony, the majority refused, and only 11% were immediately favorable. Similarly, the majority of the prescribers were not enthusiastic with regard to this possible breakthrough.

Comparison of Patients' and Prescribers' Opinions

Both the patients and prescribers attached considerable importance to patient/ventilator synchrony, patient respiratory comfort during MV, and the option of built-in patient-controlled cough support. However, the demand for these characteristics and options was generally stronger among the prescribers than among the patients.

Cough support by air-stacking, which does not require any modification of a volumetric ventilator, and intermittent inspiratory pressure may be easily integrated into conventional home ventilators. In contrast, percussive and cough-assist methods require additional technology that may increase ventilator weight and size. A review of the literature⁷ suggests that mechanical insufflation-exsufflation can increase the inspired volume at least as well as the other inflation methods, and peak cough flow is as fast as or faster than manual assisted cough associated to an inflation method, and patients seem to prefer mechanical insufflation-exsufflation to the other assisted-cough methods. Finally, the insufflation-exsufflation method seems to be at least among the best methods for improving airway clearance. A cheap alternative technique could be to use the ventilator to increase the inspired volume associated with manual assisted cough, if ventilator manufacturers can integrate an intermittent inspiratory pressure mode. The possibility of built-in patient-controlled cough support was considered important by both the patients and prescribers, but the prescribers ranked it higher than did the patient.

The majority of our patients had no preference for any of the different assisted-cough methods, which may be explained by a lack of knowledge and experience. Curiously, among the patients who preferred a technique, they preferred insufflation-exsufflation, followed by intermittent inspiratory pressure and the percussive device, whereas an intermittent inspiratory pressure device was the most frequent cough support device used by the patients, followed by insufflation-exsufflation and the percussive device. This paradox may be explained by the influence of the prescribers, of whom two thirds preferred insufflation-exsufflation, in agreement with the literature.⁷ Therefore we expect that the number of patients using insufflation-exsufflation will increase in the near future.

Evaluation of the Patients' Equipment Versus the Prescribers' Current Choices

The choice of the MV mode according to the daily duration of MV is one of the most striking observations of this survey. Indeed, a pressure control mode, mostly delivered by a bi-level pressure device or a pressure support device, was preferentially used in patients needing only nocturnal MV, because these modes are more comfortable than volume control modes during non-leak conditions.⁸ Most clinicians prescribe pressure control modes during sleep, as they allow adjustment of inspiratory time, leak compensation, and improved patient comfort. However, a volume control mode predominated in the patients who also needed daytime MV, mainly via mouthpiece. Although pressure control mode may be used with a mouthpiece, volume control ventilators have better performance for mouthpiece ventilation.⁹ Furthermore, mouthpiece ventilation allows the patient to disconnect him or herself from the ventilator, ideally during expiration, for example to allow speech after each insufflation. Pressure control ventilators, in contrast, respond to disconnection by activating the turbine, to attempt to maintain the targeted positive pressure level. In addition, by definition, pressure control modes are not able to generate the high pressures necessary for effective breath-stacking or lung-volume recruitment.^9,10 In contrast, volume control ventilators are able to provide both the tidal volume for sustained ventilation and the pressure and volume required for effective lung-volume recruitment and achievement of a maximal insufflation capacity.^9,10 Nevertheless, another option for improving cough could be an independent cough-assist device. A second option could be to integrate an additional intermittent-positive-pressure mode (see below) into the ventilator.

When we compared the MV modes used by the patients to the current prescriber prescriptions, we observed that PRVC mode was gaining popularity over volume control mode. PRVC ventilation is a new mode that combines volume control and pressure control with an algorithm that estimates the patient's tidal volume over several breaths, enabling the calculation of the pressure change necessary to achieve the target tidal volume. PRVC is designed to adapt the amount of pressure to changes in respiratory impedance. However, theoretically, PRVC ventilation is not able to cope with unintentional leaks, especially when these leaks vary over time,¹¹ as with NIV via mouthpiece or ventilation via uncuffed tracheostomy tube. When unintentional leaks occur during pressure control ventilation, the inspiratory flow delivered by the ventilator increases to reach the target inspiratory airway pressure, whereas the tidal volume decreases.¹² Carlucci et al¹³ recently observed that, depending on the circuit configuration, many MV devices recognize the delivered volume as the tidal volume. Therefore the inspiratory pressure adjustment may paradoxically decrease to a lower level during unintentional leak, which worsens the decrease in tidal volume. In contrast, when the tidal volume is estimated by the expired volume, the tidal volume can be overestimated.^14,15 Finally, the majority of the PRVC ventilation devices are currently not reliable during unintentional leak, underlining the need to check these modes during unintentional leak.

The fitting and comfort of noninvasive interfaces are crucial for the effectiveness of NIV during sleep.¹⁶ All different types of interfaces were used by the patients. However, despite their advantage of a minimal facial contact, which widens the field of vision and allows the use of eyeglasses, few patients used nasal pillows.¹⁷ Until recently, all nasal pillows available in France had intentional leak and therefore could be used only with bi-level ventilators, given that any modification of a medical device (eg, sealing a hole) was prohibited by French law. We encourage manufacturers to develop non-leak nasal pillows, which may be an alternative to mouthpiece MV during daytime.¹⁸ Another solution to reduce the risk of skin damage is to alternate various types of interfaces. If most prescribers are in favor of this solution, it is not the case for the patients.

As reported in the literature,¹⁷ HME was the most commonly used humidification system among the tracheostomized patients, whereas a heated humidification was the most commonly used among the NIV patients. Humidification and warming of the inspired gas may be used to prevent the adverse effects of cool, dry gases on the airway epithelium. The major cause of humidity loss is a unidirectional flow from the ventilator circuit to the patient because of mouth leaks during nasal NIV, and between the tracheal tube and the trachea when using an uncuffed tube during invasive MV. These leaks are extremely common in neuromuscular patients.^19,20 Therefore, although an HME and a heated humidifier showed similar tolerance and side effects during long-term MV,²¹ we prefer a heated humidifier because of its greater efficacy in case of unintentional leak.^22–24 In addition, as compared to a heated humidifier, an HME increases the resistance of the circuit and the dead space, and therefore the work of breathing, during invasive MV.^25,26 However, a tracheostomized patient using a wheelchair represents an exception. In that situation a water tank humidifier built into the circuit and located behind the patient, and often above the tracheostomy tube, exposes the patient to a risk of water inhalation. An HME, in contrast, is safe.