Monitoring Systems in Home Ventilation

Abstract

Non-invasive ventilation (NIV) is commonly used at home for patient with nocturnal hypoventilation caused by a chronic respiratory failure. Monitoring NIV is required to optimize the ventilator settings when the lung condition changes over time, and to detect common problems such as unintentional leaks, upper airway obstructions, and patient-ventilator asynchronies. This review describes the accuracy and limitations of the data recorded by the ventilator. To efficiently interpret this huge amount of data, clinician assess the daily use and regularity of NIV utilization, the unintentional leaks and their repartition along the NIV session, the apnea-hypopnea index and the flow waveform, and the patient-ventilator synchrony. Nocturnal recordings of gas exchanges are also required to detect nocturnal alveolar hypoventilation. This review describes the indication, validity criteria, and interpretation of nocturnal oximetry and transcutaneous capnography. Polygraphy and polysomnography are indicated in specific cases to characterize upper airway obstruction. Telemonitoring of the ventilator is a useful tool that should be integrated in the monitoring strategy. The technical solution, information, and limitations are discussed. In conclusion, a basic monitoring package is recommended for all patients complemented by advanced monitoring for specific cases.

Keywords: chronic respiratory failure; monitoring; noninvasive ventilation; telemonitoring.

Figure 1

Typical profiles of unintentional leaks repartition overnight.

Figure 2

The flow waveform examination may show some respiratory events that are not always detected by the AHI. The shape of the decrease in flow suggests some mechanism and localization of the obstruction. However, a respiratory polygraphy is needed to characterize the mechanism.

Figure 3

The most common patient–ventilator asynchronies can be detected by monitoring detailed pressure and flow waveforms. Red arrows show where is the asynchrony.

Figure 4

Nocturnal pulse oximetry measurement using a stand-alone device in patients using NIV. Typical results in statistics and on visual inspection of the SpO₂ curve for different types of respiratory events. Mechanisms of desaturation may coexist, which affect the SpO₂ curve. SpO₂ m: mean SpO₂; ODI: oxygen desaturation index; V_A/Q: ventilation perfusion ratio; UAO: upper airway obstructions.

Figure 5

Nocturnal pulse oximetry using a sensor connected to the ventilator. Upper panel shows the full night recording of pressure, flow, total leaks, and SpO₂. Two prolonged desaturations marked with the arrow occur due to large increase in leakages. Lower panel show a focus over a 2 min period. A short desaturation marked with the arrow occurs, following a decrease in flow without an increase in leaks, suggesting an upper airway obstruction.

Figure 6

Transcutaneous capnography. Typical results in statistics and on visual inspection of the PtcCO₂ curve for different types of respiratory events. ΔPtcCO₂: difference between the maximum and the baseline PtcCO₂. Green line is raw measurement. Blue line is measurement corrected for drift.

Figure 7

Nocturnal transcutaneous capnography using a device connected to the ventilator. Upper panel shows the full night recording of pressure, flow, total leaks, and raw measurement of PtcCO₂. PtcCO₂ decreases along the night from 40 to 30 mmHg, suggesting hyperventilation. Lower panel shows an increased PtcCO₂ along the night from 40 to 52 mmHg, suggesting alveolar hypoventilation. However, there is a concomitant increase in total leaks, which means that nonintentional leaks are the main cause of PtcCO₂ increase.

Figure 8

Polygraphy combined with the ventilator. Upper panel shows an upper airway obstruction without unintentional leaks. Belts do not move during the event, suggesting a laryngeal obstruction due to a decrease in the respiratory drive. Lower panel also shows an upper airway obstruction without unintentional leaks. Belts show a phase opposition with a negative inflexion on the thoracic belt (pink) and a positive inflexion of the abdominal belt (black) during the event. This feature suggests a pharyngeal airway obstruction with preserved respiratory drive.

Figure 9

Example of respiratory polygraphy when the belts are connected directly to the ventilator. The ventilator built-in software display from top to bottom: breath trigger color code, pressure, flow, total leaks, SpO₂, effort belts (thoracic belt in pink and abdominal belt in black), and transcutaneous capnography measured by an external device connected to the ventilator.

Figure 10

Telemonitoring of NIV. The workflow starts by screening the patients with abnormalities and focuses on trends over one month and one night. Green and red square inform about the daily use above or below 5 h per day, respectively. AHI: Apnea Hypopnea Index.

Figure 11

Strategy to monitor NIV. The basic monitoring package is recommended for all patients while advanced monitoring tools are only required in selected patients.