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Diaphragmatic dysfunction and respiratory illness(Review)

Mar

152012

Diaphragmatic dysfunction can result from nerve damage, primary muscle problems, or

problems with the muscle's interaction with the chest wall. The true incidence of

diaphragmatic paralysis is unknown, since many patients are asymptomatic. Treatment for

diaphragmatic dysfunction usually consists of watchful waiting, addressing underlying

causes, with mechanical ventilation if respiratory failure develops.

Causes of Diaphragmatic Weakness or Paralysis

Diaphragmatic paralysis is likely most often idiopathic and unilateral. When a cause for

diaphragmatic paralysis can be identified, it may be due to:

Trauma or surgery causing cervical cord or phrenic nerve damage (high C-spine

injuries involving C3-C5, phrenic nerve injury during cardiac surgery);

Mechanical ventilation;

COPD and other diseases that cause lung hyperinflation;

Myopathies and neuropathies (myasthenia gravis; critical illness neuro/myopathy;

amyotrophic lateral sclerosis, poliomyelitis, with a 35 year delay until diaphragmatic

weakness);

Inflammatory disorders (e.g., sepsis);

Mediastinal masses.

Symptoms of Unilateral & Bilateral Diaphragmatic Paralysis

Unilateral diaphragmatic paralysis or weakness rarely causes symptomatic dyspnea at

rest, but may result in dyspnea on exertion or the patient's voluntary restriction of activity. It

can sometimes cause dyspnea when lying on one's back (supine). Often, unilateral

diaphragmatic paralysis is detected incidentally on a chest X-ray obtained for other

purposes.

Bilateral diaphragmatic paralysis frequently causes dyspnea at rest, with exertion, when

supine (necessitating sleeping in a recliner), bending over, or when swimming with water

above waist level. Sleep disorders are also common in these patients, and symptoms thereof

(fatigue, somnolence, awakening during sleep) may be the first presentation of bilateral

diaphragmatic paralysis. Recurrent pneumonias (possibly due to basilar atelectasis) and

recurrent respiratory failure are also possible.

Rather than causing problematic dyspnea or respiratory insufficiency on its own,

diaphragmatic paralysis likely acts more often as a "co-conspirator" that reduces respiratory

reserve and the threshold for respiratory failure. Many people with diaphragmatic paralysis

are well-compensated when at rest and not acutely ill, but an acute illness such as

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pneumonia or an exacerbation of heart or lung disease may increase respiratory demand

beyond the ability of the paralyzed diaphragm, with resulting severe dyspnea or respiratory

failure. Diaphragmatic dysfunction also likely makes it more difficult to escape from

dependence on mechanical ventilation.

Diagnosis of Diaphragmatic Paralysis

A number of tests can help identify diaphragmatic dysfunction. Tests for diaphragmatic

paralysis include:

Chest X-rays in diaphragm paralysis may show elevated hemidiaphragms and basal

subsegmental atelectasis; insensitive in detecting bilateral paralysis as films may often be

interpreted as "poor effort" or "low lung volumes." Chest X-ray is 90% sensitive for

unilateral paralysis but only 44% specific (high false positive rate).

Fluoroscopy of the diaphragm (sniff test): the patient sniffs energetically during

fluoroscopy; descent of the diaphragm is the normal response. People with unilateral

diaphragmatic paralysis have a paradoxical upward movement of the weak hemidiaphragm,

which gets "sucked up" by the negative pleural pressure created by the working

hemidiaphragm. The sniff test is not considered to be accurate in diagnosing bilateral

diaphragmatic paralysis, with a ~6% false positive rate and a higher false negative

rate.

Pulmonary function tests show restriction, which may be moderate to severe (30-50%

predicted total lung capacity) in bilateral diaphragmatic paralysis. The restriction worsens

when supine, evidenced by a drop in vital capacity of 30 to 50% in bilateral diaphragm

paralysis. This test is sensitive and has a high negative predictive value: if there is no

reduction in FVC when supine, there is probably no significant diaphragmatic paralysis.

Maximal static inspiratory pressure (MIP) and sniff nasal inspiratory pressure are

reduced to ~60% predicted in people with unilateral diaphragmatic paralysis and to ~30%

predicted in bilateral diaphragmatic paralysis. However, these tests are effort-dependent

and less reproducible than lung volumes; with a high false positive rate for respiratory

weakness.

Ultrasound can be extremely useful in measuring diaphragmatic function. The point of

contact between the diaphragm and the rib cage should be viewed. The diaphragm should

thicken with inspiration, indicating shortening; if the diaphragm does not thicken,

paralysis is present. As a fast, inexpensive and noninvasive test, ultrasound offers many

advantages and can also be used serially to assess recovery of a paralyzed diaphragm. A

2011 study among 88 mechanically ventilated patients suggested that diaphragmatic

weakness on ultrasound could help predict extubation failure and inability to wean from

mechanical ventilation.

Electromyography of the diaphragm is technically difficult and its results can therefore

be hard to interpret or rely upon. It can potentially help differentiate between a myopathy

and neuropathy, if one of these is strongly believed to be the cause of diaphragmatic

dysfunction.

Physical Examination Findings in Diaphragmatic Dysfunction

Generally speaking, physical findings are more likely in people with bilateral diaphragmatic

paralysis. Some, all, or none of these physical examination findings may be present in

people with diaphragmatic dysfunction.

Abdominal paradox, with the abdomen moving inward as the thorax expands during

inspiration; this is the "classic" sign of diaphragmatic dysfunction, caused by the accessory

muscles creating negative pleural pressure that "sucks up" the flaccid diaphragm into the

chest during inspiration. Abdominal paradoxical breathing is almost exclusively found in

people with bilateral diaphragmatic paralysis; if present in unilateral paralysis, it means the

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respiratory muscles in general are weak.

Other possible physical examination findings in diaphragmatic paralysis include:

Tachypnea

Use of accessory muscles during quiet breathing; detectable by contraction of the

sternocleidomastoid muscles during neck palpation

Decreased diaphragmatic excursion (percussing the lower rib cage at end

inspiration and end expiration; the change in resonance should span at least 3 - 5 cm )

Treatments for Diaphragmatic Paralysis

Most people with diaphragmatic paralysis do not require treatment, other than watchful

waiting, potentially with serial examinations. Many or most people with diaphragmatic

paralysis have other likely contributing causes for dyspnea (obesity and deconditioning, lung

and heart disease, etc.), making a determination of the contribution of diaphragmatic

paralysis to dyspnea extremely difficult.

A common-sense approach to treatment of diaphragmatic paralysis can include:

Remove/treat any obvious contributing factors (hypokalemia, hypophosphatemia,

high-dose steroids, neurotoxic drugs, neuromuscular blockers).

Nocturnal noninvasive ventilation for people with an awake pCO2 of 45+ mm Hg;

nocturnal hypoxemia (SaO2 < 88% of >5 consecutive min); or progressive

neuromuscular disease and a maximal static inspiratory pressure (MIP) < 60 cm H2O

or forced vital capacity (FVC) < 50% predicted.

Treat sleep-disordered breathing, if present, with continuous positive airway

pressure (CPAP) or nocturnal noninvasive ventilation.

Surgical plication of the hemidiaphragm involves "tightening" the loose, paralyzed

hemidiaphragm by oversewing its center. This therapy improved lung function and dyspnea

in retrospective, uncontrolled trials. It is of no use in bilateral diaphragmatic paralysis, and

is relatively contraindicated in progressive neuromuscular disease and in severely obese

people. Because unilateral paralysis is usually either minimally symptomatic or improves

with time, plication should be considered only after a long period of watchful waiting.

Phrenic pacing is only appropriate for ventilator dependent patients, mainly quadriplegics

with cervical spine injuries at C3-C5 or above ("high quads").

Read more: McCool FD, Tzelepis GE. Dysfunction of the Diaphragm. N Engl J Med

2012;366:932-942.

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Posted by Pulmonary Central

Preventing DVT and PE in hospitalized medical patients

(Guideline, ACCP Recs)

Insurers sound off to NPR against

moneymaking sleep centers

One Response to Diaphragmatic dysfunction and respiratory illness(Review)

Wooley says:

October 16, 2012 at 11:10 pm

Good review

Add new etiology: pulmonary vein ablation therapy for atrial fibrillation. This can occur with

electrical or cryotherapy. I have seen two cases this year.

M. Wooley

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