Descriptor
% of nonadaptation
Face format
30.5
Discomfort
28.8
Air leaking
27.7
Claustrophobia
18.6
Uncooperative patient
10.1
Patient agitation
6.7
Other causes
There are many possible side effects and adverse events. If the mask causes discomfort, it is possible to check the fit, adjust the straps, or choose another mask type. Masks can cause erythema or nasal bridge ulceration and it is appropriate to apply artificial skin (hydrocolloid dressing) to prevent this. In prolonged treatment, nasal or oral dryness may occur and the recommendation is to use nasal saline/emollient. To prevent leaks, an oro-nasal mask is sometimes preferred or pressures can be reduced slightly. Check for air leaks into the eyes (which can lead to conjunctivitis), around the nose, and at the side of the interface.
High-performing ventilators show leaks through a numerical estimate expressed as a percentage and compensate for them. In the first 10–15 min of treatment, the percentage of acceptable leaks is not more than 20 %. A successful patient adaptation and a patient-ventilator interaction should then progress to a reduction in the percentage of leaks from the system.
The effectiveness of treatment is achieved by obtaining the right balance between high leaks and excessive intolerance of the interface device. Remember that when positive pressure (inspiratory positive airway pressure, or IPAP) reaches more than 20 cmH2O, it may cause a marked increase in leaks.
17.2.2.3 Patient-Ventilator Interaction and Pressure-Flow Graph Interpretation
Especially in the first 10–15 min of ventilation, it is crucial to monitor the adaptation of the patient to the ventilator and whether the ventilator is really assisting with the patient’s respiratory efforts. One hand should be positioned on the abdomen of the patient, feeling breaths and then comparing them with those reported in the graphs of flow and pressure (Fig. 17.1). Each inspiration by the patient should match the curve of respiratory support delivered by the ventilator and shown on the graph. The assessment of inspiratory function includes evaluation of synchronization between inspiratory effort and the onset of ventilation assistance and trigger sensitivity. Synchronization is evaluated by assessing the time lag between the onset of effort and the initial delivery of flow.
Fig. 17.1
Matching patient effort and ventilator assistance
In Fig. 17.1, the interval A-B on the x-axis (time) represents the trigger delay, corresponding to trigger sensitivity. Inadequate matching between ventilator and patient could be to the result of a delay of ventilation assistance exceeding 360 ms [9] (too hard a trigger, inadequate circuit connections).
Ineffective efforts (muscle contractions not able to trigger the ventilator) are the most frequent problems in patients with obstruction and ventilated with high inspiratory pressures and high tidal volumes that avoid complete exhalation of the accumulated air. Therefore, the patient tries to start a new breath (Fig. 17.2, part a) when the degree of hyperinflation is too high to allow him or her to return to the equilibrium point of the respiratory system and then to trigger the ventilator. The analysis of the parameters of flow and airway pressure shows a few small “ bumps” that are not followed, or are contemporaneous, to an inspiratory support by the ventilator. The patient is unsuccessfully attempting to trigger the machine.
Fig. 17.2
Ineffective efforts (part a) and “hung up” phenomenon (part b)
An assisted inspiration followed quickly by another one (or three, in “triple triggering”) is another problem. It can be explained by setting a flow too high, or a too sensitive expiratory trigger, that requires a modest flow fall to switch from the inspiratory phase to the expiratory phase. Figure 17.2 part b shows a prolonged inspiratory act, and the graph of flow shows a fall, followed by a plateau; this is the “hung up” phenomenon. The patient does not appear to reach a predetermined dropping flow level to switch to the expiratory phase. The problem is usually caused by circuit or interface device leaks that interfere with the ventilator algorithm, increasing the inspiratory time over the maximum established [9]. If the patient is not able to adapt, it is appropriate to ensure that he or she is not muscularly exhausted, that there is no airway obstruction, and that the circuit does not suffer from leaks or disconnections.
17.2.3 Time: After the First 15 Min – Monitoring Vital Signs and Blood Gas Analysis
17.2.3.1 Vital Signs and Clinical Status
The patient treated with NIV should be located in a special area, with an available cohort of staff with adequate experience, equipped with a multi-parameter monitor and devices for emergency management. Primarily, and in the first minutes, it is necessary to assess the work of breathing through the observation of accessory muscle recruitment (such as sternocleidomastoid muscle activity) and respiratory rate. Lack of reduction in respiratory frequency indicates that alveolar ventilation is not obtained because of a wasted ventilation. Causes include inappropriate ventilation setting leading to patient intolerance, leaks, and missed coordination with the ventilator [3, 10].
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