Inforesp

   

   

   

   

   

   
About ventilation Print the page 


Ventilation
Purpose of ventilation is to maintain the right exchange of gases in the body. This occurs by supplying tissues with oxygen (O2), a gas needed for metabolic processes, and eliminating carbon dioxide (CO2) which accumulates as a result of processes generating energy.

Inspirations (the inhaling of air) and expirations (the exhaling of air) are phases of ventilation and are in the number of 15/16 per minute for an adult at rest.


Respiratory system

To semplify, we can consider the respiratory system formed of:

  1. two lungs (exchangers of gases) having the task to help the exchange of gases between the alveoli (small air cells) and the blood flowing in the small vases (capillary bed) of the lungs
  2. the thorax wall (mechanic pump) which allows the passage of air from the outside to the lungs and viceversa. The thoracic cage, the abdomen-diaphragm and its contents are part of the thorax wall.

The diaphragm is the major inspiratory muscle. The diaphragmatic contractions allows a changement of the volume of air to the lower side of the thorax and at the sime time determines the expansion of the wipes in which the diaphragm is inserted.

Respiratory insufficiency

Respiratory insufficiency may be caused by one or more defaults of the respiratory system (respiratory muscles, thoracic cage, pleura, bronchi or bronchioles, lung tissue).

The mechanic function (mechanic pump) may be altered by pathologies affecting the thoracic cage, the respiratory muscles, the pleura.

The ventilatory function (circulation of air in the lungs) may be compromised by pathologies affecting the bronchi and the bronchioles.

The exchange of gases may be altered by pathologies affecting the lung tissue (lobes and alveoli).

All the respiratory functions are strictly connected: a failure of one of these functions may affect the others and alter the entire mechanism. For instance: if the mechanic function is damaged, the inhaling of air will be affected as well, the circulation of air in bronchi and bronchioles will not be adequate and the exchange of gases will be damaged as a consequence.

Pathologies which may cause respiratory insufficiency

AFFECTED FUNCTIONS PATHOLOGIES
Mechanic function (mechanic pump)

Problems may affect:
motor neuron, thoracic cage, respiratory muscles, pleura
Kyphoscoliosis
Neuromuscular Disorders (Myopathies)
Post-polio Syndrome
A.L.S. (Amyotrophic Lateral Sclerosis)
Ventilatory function (circulation of air)

Bronchi and bronchioles affected

Collapse of upper airways
C.O.P.D. (Chronic Obstructive Pulmonary Disease)
Asthma
Cystic Fibrosis
O.S.A.S. (Obstructive Sleep Apnea Syndrome)
Exchange of gases (supply of oxygen, elimination of carbon dioxide)

Lung tissue (lobes) and alveoli affected
Emphysema
Fibrosis
Silicosis
Tubercolosis sequelae

Symptoms of respiratory insufficiency in Neuromuscular Disorders

Respiratory failure in persons having Neuromuscular Disorders is mainly due to the progressive insufficiency of the mechanic function (mechanic pump) as a consequence of the general weakness of the respiratory muscles.

In Neuromuscular Disorders often the first signs of respiratory insufficiency go unnoticed because the weakening process is slow and difficult to be detected. Shortness of breath, the best-known symptom of too little oxygen, may not occur, especially when weakness prevents persons from exercising.

Symptoms of chronic hypoventilation (underventilation) might be:

. sleep disturbances
. fatigue
. morning headaches
. nightmares, night terrors
. confusion, disorientation, anxiety
. poor appetite, weight loss
. weakened or soft voice
. unproductive cough

If shortness of breath may not be present, fatigue, sleep disturbances, morning headaches especially right after waking are the most common symptoms. Underventilation at night is often the first problem because the needs to breath is lower during sleep and because the abdomen pushes up against the diaphragm when a person lies down.

Mechanical ventilation

Mechanical ventilation in persons having Neuromuscular Disorders helps to improve alveolar ventilation. This is done by ventilators which replace the mechanic pump deteriorated by the progressive weakness of respiratory muscles.

Control ventilation is a mode of setting ventilators. With control ventilation the ventilator simply delivers the set volume of air at the set rate and the user must adjust his or her breathing rate to that of the machine. Control ventilation may be either pressure or volume ventilation.

Pressure ventilation: in this case the pressure that the machine should deliver is set according to prescription. The machine will deliver a volume of air until it senses that the set pressure has been attained, signaling the end of the assisted inspiration.

Volume ventilation: here the volume to be delivered is set and the machine delivers the set volume regardless of the pressures generated in the lungs.

Limits of control ventilation are the setting of pre-determined rates of volume of air regardless of the users requests which may vary during ventilation.

Assist ventilation

To overcome the limits of control ventilation – not adequate to adapt to the users’ needs – triggers are nowadays being used. The trigger is a sensitive mechanism able to start the inspirator act of the ventilator according to the inspiratory/expiratory time ratio previously set.


Ventilators

According to the way of functioning, ventilators may be classified into devices which act on the body (negative pressure body ventilators and other body ventilators) and devices which forces intermittent pressure to the airways (volume-cycled and pressure-cycled ventilators).

Body ventilators include (i) devices which assist inspiratory muscles by intermittently lowering pressure around the chest and abdomen so that air enters the nose and mouth and (ii) devices which apply forces directly to the body to displace respiratory muscles mechanically. Iron lung, chest shell-style ventilators, wrap-style ventilators, oscillator, rocking-bed, exsufflation belt are some type of body vetilators.

Volume-cycled ventilators: are very reliable devices. For this reason they are used in severe respiratory insufficiency which leads often to tracheostomy. It is advisable to choose portable ventilators – easy to fit to the wheelchair – with back-up battery and alarm for possible defaults of the machine.

Pressure-cycled ventilators: these devices deliver either a continuos flow of air into the airways via the nose (CPAP) or one can adjust the positive pressure delivered during inspiration separately from those delivered during expiration, the flow of air being still continuos (BiPAP).

In comparison with volume-cycled ventilators pressure-cycled ventilators are cheaper, are easier to use and are lighter. Do not fit hower to tracheostomy, do not have a battery, do not have an alarm, are noisier.

VOLUME-CYCLED VENTILATORS

(some models)

PRESSURE-CYCLED VENTILATORS

(some models)

Monnal D, Neftis, LTV900, 950, 1000, PLV100, PLV102, PLV102b, PV501, PV 501-2, Bear 33, Eole 3, EV801, iVent201, LP6 Plus, LP10, Achieva PS, Achieva PSO2, Airox Home 2,

BiPAP S, BiPAP S/T, Eclipse Delta, Horizon Bilevel, KnightStar 335, 320, LTV900, LTV950, LTV1000, Nippy, Nippy 2, Nippaed, PV101, PV102, O’Nyx Plus, Rem+Duo, RespiCare S, SC, Helia, Quantum PSV

From

"BREATHE EASY – Respiratory Care for Children With Muscular Dystrophy"
by Sheila Horan, B.S., R.R.T., Robert Warren, M.D., Vikki Stefan, M.D.
team that works closely with the MDA clinic at Arkansas Children’s Hospital in Little Rock
MDA Muscular Dystrophy Association,
Jerry Lewis National Chairman
3300 East Sunrise Drive
Tucson, AZ 85718
(520) 529-2000 www.mdausa.org

Pulmonary monitoring and treatment plan

The following is a respiratory care plan that we recommend for children with neuromuscular diseases seen in our clinic. It does not necessarily represent the views of the Muscular Dystrophy Association (MDA). You may wish to share this page with your MDA clinic physician and the pulmonary medicine team and discuss with them its application to your child’s care.

The forced vital capacity (FVC) will be used to drive this care plan, and management will be determined based on changes in FVC. Aerosol and chest physical therapy for acute upper or low respiratory tract infections may be introduced as symptoms indicate at any point in the plan.

At the time of MD diagnosis:
introduce respiratory care handbook
begin annual pulmonary function testing (PFT)
watch spinal growth by physical examination
 
When FVC is between 75 percent and 61 percent of normal ("predicted"):
give PFT two times per year
follow any spinal curve by physical/radiological exam
instruct in deep breathing with incentive spirometer
 

When FVC is less than 60 percent of normal ("predicted"):
give PFT three times per year
follow any spinal curve by physical/radiological exam
continue deep breathing with incentive spirometer
evaluate for spinal stabilization surgery
 

When FVC is less than 40 percent of normal ("predicted"):
give PFT four times per year
follow spinal curve by physical/radiological exam
give chest X-ray as necessary (actelectasis and/or pneumonias)
test for capillary blood gases
conduct overnight pulse oximetry study
introduce mechanical volume ventilation by nasal or face mask during hours of sleep as required
evaluate for spinal stabilization surgery
 

When FVC is less than 30 percent of normal ("predicted") – lungs at risk for infection and atelectasis:
give PFT six times per year
take chest X-ray as necessary
test for capillary blood gases
conduct overnight pulse oximetry study
increase mechanical volume ventilation to include day and nighttime assistance
tracheostomy may be considered.

 

"Reprinted with permission of the Muscular Dystrophy Association of the United States".
 
 
References:
J.R. Bach – Guide to the Evaluation and Management of Neuromuscular Disease – 1999 Hanley & Belfus, Inc.
J.R. Bach – Pulmonary Rehabilitation: The Obstructive and Paralytic Conditions – 1996 Hanley & Belfus, Inc.
E.A. Oppenheimer – Which ventilator to use? – IVUN News, Summer 1998, Vol. 12, No. 2
S. Horan, R. Warren, V. Stefans – Breathe Easy Respiratory Care for Children With Muscular Dystrophy – MDA, P-160 25M 12/98
G.Carbone, A. Corrado, C. Gregoretti – Ventilazione non invasiva – 1997 ARCHIMEDICA
L’Auxiliare de vie face a l’insuffisant respiratoire – CEFIDEX MAIN TENIR – Juin 1996
F.Mangiola – Apparecchi attinenti la funzione respiratoria – D.M. 110, maggio 1993
www.graylab.ac.uk/cgi-bin/omd?action=Home&Query



Via Lampedusa 11/a 20141 MILANO  Italy fax +39 02 2360084  e-mail: info@inforesp.org - editorial: Liana Garini - web by: ICON
Last update 26/04/2013