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Evaluation and Long-Term Noninvasive Management:

Older Children and Adults

 

INTRODUCTION

 

Since respiratory complications are by far the predominant cause of morbidity and mortality for anyone with a neuromuscular disorder (NMD) and/or generalized muscle weakness, patients should only see physicians who are equipped with the following:

1. A capnograph or transcutaneous CO2 monitor to determine blood CO2 levels.

2. An oximeter to determine if blood oxygen saturation (O2 sat) levels are normal.

3. A peak flow meter to measure unassisted and assisted cough peak flows (CPF).

4. A non-digital spirometer to measure vital capacity (VC) in various positions and maximum insufflation capacity (MIC).

 

Conventionally speaking, physicians typically send patients for pulmonary function testing and sleep polysomnograms, both of which are unnecessary, almost useless, and typically misdirect physicians in what needs to be done for the patient. This eventually results in the patients going into acute respiratory failure, being intubated, and being told that tracheotomy is necessary to survive (see most common mistakes).

 

 

EVALUATION OF OLDER CHILDREN AND ADULTS

 

On every routine outpatient visit before plateau VC is reached for patients with NMD Types 3 and 4, provided that there is no specific reason to suspect alveolar hypoventilation or acute/chronic lung disease, only VC measurements are needed mainly to establish that the VC is still increasing which it normally does until age 20. Once plateau VC is reached, then capnography for end-tidal CO2, oximetry, spirometry for MIC and VC, and CPF need to be measured on every visit for every patient with respiratory muscle weakness.

 

End-tidal carbon dioxide (EtCO2) (measured with capnography) or transcutaneous CO2 greater than 45 mmHg with the person awake is high and termed "hypercapnia." The hypercapnia is likely to be worse when sleeping. Besides taking end-tidal CO2 measurements during the outpatient visit, both capnography and transcutaneous CO2 can also be comfortably monitored in the home during sleep. Knowing the CO2 level and O2 sat during sleep can be helpful when symptoms are questionable and respiratory function parameters are “borderline”. If the sleep CO2 is over 49 mmHg, then it is high and further justification to introduce sleep noninvasive ventilatory support (NVS).

 

Pulse oximetry should be routinely checked. An O2 sat less than 95% when awake generally indicates hypoventilation, airway secretion congestion, or intrinsic lung disease. The oximetry feedback protocol is critical to use at home during intercurrent respiratory tract infections, to prepare intubated and tracheostomized patients for extubation, and during post-extubation and post-decannulation. Monitoring O2 sat along with end-tidal CO2 during sleep can also be helpful when symptoms are questionable and respiratory function parameters are “borderline”. Frequent but not occasional decreases below 95% are abnormal and signal either hypoventilation or possibly sleep disordered breathing (central and obstructive apneas) when respiratory muscles have normal strength. The treatment for the latter is CPAP or bi-level PAP. The treatment for hypoventilation is NVS.

 

Anyone not feeling better by using sleep NVS can safely discontinue it provided that they are re-evaluated in 6-12 months for most neuromuscular conditions, but in 2-3 months for rapidly progressive conditions such as amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease).

 

Spirometry must be done to measure VC in the sitting position, while supine, and with any body brace on and off. Spirometry is also done to determine MIC after air stacking. A sitting-supine difference of greater than 7% is abnormal. Differences greater than 30% (supine VC lower), which are caused by diaphragm weakness, usually cause “orthopnea” or inability to breathe when lying flat and indicate the need to introduce sleep NVS to breathe when reclining.

 

Both unassisted and assisted CPF are measured on every patient visit via a peak flow meter (Access Peak Flow Meter, Cedar Grove, NJ). Inability to exceed 270 to 300 L/m of flow indicates a high risk of pneumonia and respiratory failure occurring during upper respiratory tract infections and the need for rapid/immediate access to mechanical insufflation-exsufflation (MIE) for the oximetry feedback protocol.

 

 

SYMPTOMS

 

Symptoms of respiratory muscle weakness and under breathing (alveolar hypoventilation) include:

 

Most common

• Shortness of breath when supine (“respiratory orthopnea”)

• Morning headaches

• Fatigue

• Daytime sleepiness.

 

Other symptoms

• Difficulty concentrating

• Depression

• Loss of appetite

• Anxiety

• Sleep dysfunction and arousals

• Nightmares

• Shortness of breath

• Irritability

• Decreased libido

• Urinary frequency

• Weight loss

• Muscle aches

• Memory impairment

• Nausea

• Poor control of airway secretions

• Symptoms of heart failure and leg swelling

• Confusion, obtundation, or coma

• Respiratory arrest.

 

Coma from CO2 narcosis rarely happens before people seek medical attention and are placed on bi-level PAP which is suboptimal but can help. Typically, however, when medical attention is sought but sleep nasal NVS is not introduced in a timely manner. Instead, supplemental O2 therapy is prescribed and CO2 narcosis occurs and many do not survive this mismanagement. Sleep NVS should always and only be introduced to treat these symptoms and not introduced on the basis of any particular respiratory parameter. Respiratory parameters, however, can be especially helpful when symptoms are unclear.

 

Fatigue can be part of the neuromuscular condition and other symptoms may be unclear, so anyone whose EtCO2 is elevated during an outpatient visit likely has higher CO2 levels during sleep. Symptoms almost always accompany CO2 levels of 50 mmHg or higher during sleep, while people with lower sleep CO2 levels can be symptomatic. Sleep EtCO2 and O2 sat can be determined by simply monitoring EtCO2 and O2 sat during sleep at home with a combination unit.

 

Once it is determined that the individual is symptomatic from respiratory muscle weakness rather than from central and obstructive apneas, sleep NVS (rather than CPAP or bi-level PAP) is introduced. A portable ventilator is ordered along with an active ventilator circuit. Initially, only sleep NVS is necessary, usually via nasal interfaces. Occasionally, when people lose weight because they breathe to rapidly to swallow food safely or when higher voice volumes are needed, NVS is begun during meals or daytime hours, in general, via a 15-mm angled mouthpiece (Philips-Respironics Inc., Murrysville, Pa). NVS on portable ventilators with active ventilator circuits (ventilator circuits with exhalation valves) preset to deliver 700 to 1500 mL air volumes with backup rates of 10 to 14 breaths per minute should be prescribed for both daytime and sleep ventilation for adolescents and adults. The users use the maximum preset volume with which they are comfortable.

 

Volume-preset NVS is crucial to permit air stacking anytime day or night so that the user can independently increase lung volumes to increase cough flows without requiring personal assistance. Volume-preset is switched to pressure-preset at about 18 to 24 cm H2O when volume deliveries cause severe abdominal distension. The gastroesophageal sphincter (the valve between the stomach and the esophagus) is usually competent up to a pressure of 25 cm H2O. Sometimes gastrostomy is needed, so that the tube can be kept open during sleep to “burp” out the insufflated air.

 

Bi-level PAP should only be considered for use by patients who can not close their glottises (or air stack) and have severe throat muscle dysfunction with spasticity, stridor, and diminished airway patency (i.e. only for people with amyotrophic lateral sclerosis and those with central nervous system disorders who also require ventilatory support). Bi-level PAP should not be used in place of NVS because the expiratory PAP is counterproductive (positive pressure during expiration inhibits expiratory capability of weakened respiratory muscles). It needlessly increases intrathoracic pressure, does not permit air stacking, is less comfortable, and often can not be operated by external battery. Bi-level PAP that targets the delivery of specific tidal volumes chronically under expands the lungs leading to stiff, hypoinflated, non-compliant lungs. It is not absence of positive end-expiratory pressure that causes atelectasis (collapse of the lung’s air sacks), but failure to do regular lung volume recruitment and expulse airway secretions that does. Although high-span bi-level PAP can be used for ventilatory assistance and support and to fully rest inspiratory muscles, the clinicians who prescribe it usually do so from the point of view of treating central and obstructive apneas (after ordering a polysomnogram) and prescribe it at low-span settings which are inadequate to fully rest muscles or ventilate the lungs.

 

With age and/or advancing muscle weakness, stopping nocturnal nasal NVS in the morning can result in shortness of breath so NVS users continue nasal NVS into daytime hours. At that point they should be offered to switch to mouthpiece NVS as an alternative to nasal NVS. Eventually people extend NVS throughout daytime hours and use the oximetry feedback protocol during intercurrent respiratory tract infections to prevent pneumonia and acute respiratory failure.

 

Often before patients need NVS during daytime hours as well as overnight, their cough flows have decreased such that a simple URI can develop into pneumonia and respiratory failure. If cough flows, unassisted or assisted, do not attain about 300 L/m, MIE is necessary and either someone in the home to help them use it or a robot arm to give the patient access to MIE to expulse airway secretions and prevent pneumonia. If the patient cannot keep O2 sat baseline normal throughout daytime hours during respiratory tract infections by using MIE as needed or if they have to use MIE around-the-clock, then they should be hospitalized, preferable in a center that will guarantee them extubation back to noninvasive management (see centers for noninvasive respiratory management).

 

No patient should be coerced into consenting to tracheotomy since only advanced ALS patients and virtually no one with other neuromuscular disorders nor those with uncomplicated critical care deconditioning ever needs them for ventilatory support. It is strongly recommended that consent for tracheotomy not be given and intubated candidates for noninvasive management be referred to a Center for Noninvasive Respiratory Management for extubation and decannulation to CNVS and MIE.

 

Outcomes By Diagnosis

 

 

HISTORY

 

People with weak respiratory muscles often have a history of frequent pneumonias, respiratory hospitalizations, and intubations or tracheostomy tube placements. This is usually caused by intercurrent upper respiratory tract infections (URI) that develop into pneumonia and acute respiratory failure because of ineffective CPF less than 270 to 300 L/m.

 

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