The following article is a collective reflection of advanced NIV Techniques based upon the author’s experiences in working with and learning about titrations and the physiology of pulmonary disease. The article previously ran in the Q4 2022 issue of A2Zzz.
There are a number of reasons a patient may need noninvasive ventilation (NIV). Within the field of sleep medicine, some of those reasons may include obesity hypoventilation syndrome, neuromuscular disease, cardiopulmonary disease or traumatic brain injury (TBI). The way to connect these different afflictions in the context of sleep lies in the fixed and variable settings involved in performing NIV.
Many of the common issues that lead a patient to qualify for an NIV titration may be simplified to a few key factors: poor ventilation, its effect on sleep quality and how sleep quality affects health and recovery. The progression of clinical assessment that leads a patient to NIV in the health care system would first require attempting continuous positive airway pressure (CPAP) therapy. CPAP is not considered ventilation as it is a continuous, unidirectional positive pressure. Therefore, the airway compliance provided by CPAP does not reduce CO2 concentrations in the presence of complex chronic respiratory failure, such as the breathing patterns that lead to increased CO2 levels. Elevated levels of CO2 can occur with decreased ventilation. Decreased ventilatory effort during sleep can also be described as a decreased drive to breathe, as CO2 concentration is the primary instigator of breathing.
NIV can be utilized as a tool to provide support to patients that produce a cyclic negative feedback on CO2 concentrations, referred to as central sleep apnea (CSA). Breathing patterns affected by rising CO2 concentrations are observed in the sleep lab manifested as CSA or complex central sleep apnea, the combination of obstructive sleep apnea (OSA) and CSA. The goal of NIV is to provide proper ventilation by reducing CO2 in the presence of hypercapnia, thus stabilizing breathing patterns. The additional complexities engaged when exchanging CPAP for NIV are both expiratory and inspiratory efforts, timing of breath rate and inspiration and the patients estimated tidal volume.
Further clinical judgments beyond OSA lead to the skilled operation of ventilation settings, which increase patient comfort with treatment, airway compliance and patient treatment compliance. Quality of life is a common measure for patient self-assessment of their personal wellbeing in their current lifestyle; if providers are able to treat the patient’s illness and improve their lifestyle, then one would assume that the patient’s quality of life would improve as well.
Treating patients with sleep-disordered breathing often has a powerful effect. A majority of the population knows the feeling of periods of restlessness and finally falling asleep or recalling the entirety of the evening tossing and turning. This distress before bed, if caused by airway obstruction or insufficiency, can be treated if they were to breathe properly while resting. Those with complex diseases have a more challenging time reaching the night where they reach a deep sleep because CPAP therapy may not be enough. NIV can come to save the day and provide the patient a better daytime and nighttime quality of life.
Benefits of Initiating Bilevel Therapy
In order to address each of the aforementioned disorders, one must first consider the method of approach to a flow channel with a respiratory waveform that appears to be outside of normal parameters. Being able to address the issue in an organized manner aids the patient’s care by properly tackling the challenge presented in a timely fashion. The first approach to sleep disordered breathing is, primarily, to open the airway. Once the airway obstruction is alleviated, the ventilation and respiratory rate can be assessed.
If first approaching ventilation or respiratory rate, the obstruction — which could be the principal element fluctuating the drive to breathe — may elongate the time it takes for the patient to rest and achieve optimal oxygenation and sleep efficiency. Imagine the in-lab scenario of a common occurrence in an evening performing a PAP titration; the patient has been wearing CPAP for a few hours and having severe OSA with some scattered CSA. The technologist is frustrated in the early hours of the morning from being stuck on this patient having repeat desaturations and arousals from each pressure adjustment. In the lab setting, this can be tough, as the technologist must observe the obstruction and judge the presence of central aspects in the breathing pattern. Naturally, the technician behind the titration is likely to first use the tactic of increasing expiratory pressure. By raising the CPAP level, the central characteristic of the breathing pattern is likely to increase. As noted earlier, CPAP does not provide ventilation.
In the presence of a patient with cardiopulmonary disease, such as right-sided heart failure with cor pulmonale, the hypercapnic cycling that this patient is experiencing could be the respiratory drive struggling to stabilize. Breathing instability, initiated by the increased CPAP level, is likely extended due to the high pressure. The phenomena described may be due to the patient’s inability to exhale CO2 effectively, otherwise known as poor ventilation. Titration using a bi-level setting would provide ventilatory support.
Ventilatory support has a few equivalent names in the respiratory field, including expiratory positive airway pressure (EPAP)/inspiratory positive airway pressure (IPAP) delta and pressure support. Increasing the pressure support allows the patient to do what is called “blowing off CO2.” Hence, reducing the elevated CO2 means the patient has improved ventilation. Identifying the underlying problem, before modifying the wrong portion of the breath, can prevent an hour, or more, of tribulation of resolving the pressure-induced CSA or the onset of hypercapnia.
Another patient comorbid condition, obesity hypoventilation, is an instance in which breathing efficiency is achieved with the use of bi-level therapy. Many morbidly obese individuals struggle with PAP therapy, as they often require high pressures to maintain their airway compliance. The application of high pressure CPAP, beyond 15 cm H2O, tends to be difficult for many patients. If the patient’s airway is close to a level of an acceptable titration (according to the American Association of Sleep Medicine [AASM] Gold Standard guidelines where the airway has a maintained patency with fewer than 10 respiratory desaturations per hour) at the high pressure point, they may begin to express CSA. This CSA is possibly an outcome of the patient’s inability to expire CO2. Hypoventilation is common in many patients who have increased weight due to the increased pressure of the weight on their chest, which inhibits appropriate airflow.
Ventilation: Breath Rate
During over-night titration in the lab, the patient’s ventilation can be improved with a few distinctive pressure adjustments. Along with increased pressure support and tidal volume, other important factors to consider are breath rate and inspiration time (I-Time) manipulation.
If the patient has chronic obstructive pulmonary disease (COPD) and has achieved an open airway, but cannot maintain oxygen saturations within normal limits, then the technologist may trial bi-level therapy. The use of expiratory and inspiratory pressures involved in airway mechanics may enhance CO2 exchange to lower CO2 trapping, thereby increasing oxygenation levels.
Patients with comorbid hypoventilatory diseases, COPD and obesity hypoventilation syndrome may come close to achieving an open airway with bi-level therapy. However, often times the increase in CO2 manifests as stubborn CSA. In this case, the technologist must address the remaining, and steadily developing, central aspects of the breathing pattern. Appropriately addressing the central characteristics of respiration involves, first, a trial adjustment of pressure support settings to improve ventilation, reducing CO2 to normal levels. Once the CO2 has been addressed and the CSA remains, the technologist may apply a respiratory rate to combat the ventilatory periodicity. (The respiratory rate setting will improve ventilation with increased respirations and provide a more consistent expiration of CO2, thus allowing the patient to reach a stable breathing pattern.)
The bi-level setting used to address breathing rate, bi-level spontaneous timed (S/T), also allows for the manipulation of the inspiratory time (I-Time) — which is important for patients with obstructive pulmonary disease or neuromuscular disease. The inability to complete an adequate breath, despite the airway being open, means the volume in the chest must be paid extra attention. This can be addressed by ensuring the breath is being timed properly to the patient. Proper timing of the pressure flow creates the airway patency necessary for the breath to reach peak volume. In turn, a successive breath pattern with peak-to-peak volume allows the best chance for optimal gas exchange. The I-Time for COPD patients can be decreased to allow the inhalation to become more powerful in the beginning of the breath and offers the patient the greatest chest volume attainable. In neuromuscular disease, the chest is restricted which impedes ventilation efficiency. For these patients, it is helpful to increase the inspiratory time. The elongation of the breath can aid patients in attaining and managing sufficient chest volume with a longer slow breath. The breath in patients with restrictive diseases is not insufficient in the beginning of the breath, it is the tightening of the airway at the top of the breath. Slowing the breath allows for an expansion in the patient’s sustained tidal volume, optimizing ventilation and oxygenation.
Ventilation: Volumetric Control
As the progression of PAP titration modalities fails to achieve optimal, or short of adequate, levels of ventilation and oxygenation, patients become increasingly discouraged about their treatment options. Every so often, the sleep lab encounters a patient whose previous modes of treatment have been inadequate in treating their respiratory insufficiency. Air flow channels during PAP therapy can show the sinusoidal waveforms that appear when an airway is compliant and unobstructed, however the waveform can also be sinus in shape without the flow being sufficient. The technologist should track the tidal volumes being reached with each breath during the titration. Each breath that misses the tidal volume desired, absent apnea, creates problematic hypercapnic hypoxemia. The more advanced method of volume control provides support for tidal volume inadequacy.
The patients in the above scenario are often on multiple liters of supplemental oxygen during the evening due to difficulty with appropriate ventilation and severe hypercapnia. Tidal volume adjustments are necessary for patients with sensitive O2 and CO2 imbalances. The volume-assured pressure support (VAPS) mode is able to adjust all the settings of bi-level, including bi-level S/T, and includes volume pressure control. As the tidal volume is achieved with a fixed setting, the optimal pressure within the chest cavity peaks.
If the ventilation is insufficient to maintain minute ventilation and airway compliance, the pressure support may be adjusted with additional focus on tidal volume achievement. A timed breath, adjusted tidal volume and variable expiratory pressures all work together to provide the most compliant airway and efficient ventilation. Some of the more moderate to severe COPD patients with extreme hypoventilation can benefit from a VAPS titration. The breath rate and added expiratory control along with variable pressure support for tidal volume optimization can maximize gas exchange. The ultimate goal of VAPS therapy is to provide relief of central apnea and hypoventilation. Utilizing appropriate expiratory pressure settings provides improved ventilation.
It is the technologist's responsibility to apply the skills of clinical judgment and to pay attention to what interruptions and pathology are present in the PSG aside from obstruction. Treatment of the obstruction and the drive to breathe within the context of an individual’s illness are all factors capable of being addressed during an over-night titration with the use of appropriate treatment settings. Taking the patient disease state and the ventilation into consideration provides the patient with the best care, the best outcome and the best chance at a successful recovery.