Negative Pressure Ventilation

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Linda Melchor
Linda Melchor

I have been in the respiratory therapy field for over 30 years. I have worked as a staff therapist, clinical educator, and manager. I worked in all aspects of respiratory therapy from critical care staff therapist, nicu transport team, to air ambulance. My passion is teaching and organizing lecture series. In my off hours, you can find me at comic-con.

The Pre-brief

The Iron Lung saved a great number of lives of those stricken with polio. The technology was then applied to the cuirass ventilator. This shell allowed for access to patients’ bodies for daily care and gave patients more mobility. The cuirass-style ventilator has had waxing and waning in popularity since the days of polio. Case report based evidence is promising and may cause a resurgence of this therapy in our hospitals. Below is an overview of the history and potential new uses of Negative Pressure Ventilation (NPV)

What is Negative Pressure Ventilation?

Let’s think about how we breathe.  Do we breathe by negative pressure or positive pressure? Well, if you said negative pressure, then you are correct.  Every time we take a breath in, we create negative pressure in our thoracic cavity by having our diaphragm drop and allowing air into our lungs. During the Polio epidemic, Philip Drinker and Louis Agassiz Shaw invented the first Iron Lung (1927). Four years later, John Emerson designed a more cost-effective device. 

From the 1930’s to the 1950’s the Iron Lung helped to save many lives. With the Iron Lung, the patient would be placed inside a cylindrical device with only their head exposed. This made it difficult to examine the patient since they had to remain inside the Iron Lung. It works by mimicking how we normally breathe by causing the diaphragm to assist with moving air into the lungs.  This was primarily used for those patients with neuromuscular diseases. The Iron lung can still be found in use on a small group of patients with Polio. 

From the invention of the Iron Lung came the invention of Emerson Chest Respiratory and the Thompson Ventilator, also known as the Cuirass.  The Cuirass, modeled after a medieval knight;’s cuirass, is non-invasive and allows ease to assess the patient from head to toe.  The Cuirass is different from the Iron Lung in the sense that a shell-like device is strapped onto the patients‘ thorax. This allows the patient to sit, stand, and lie down.  The Cuirass is biphasic ventilation, actively controlling both the inspiratory and expiratory phases.  During inspiration, the Cuirass will expand the lungs while lowering chest cavity pressure creating a negative pressure breath.

cuirass of French dragoon (front side). France. 19 century. Period of napoleonic-wars

Negative pressure ventilation still has a role in today’s world. It can be used in various ways. The first one being able to ventilate those patients with disease processes such as ALS, Muscular Dystrophy, and Polio. Secondly, the chest Cuirass can work in conjunction with positive pressure ventilation to assist with weaning. The patient would be placed on CPAP via conventional ventilation and then ventilate with the chest cuirass. This usage of NPV may decrease hospital invasive ventilator days. Using CPAP on conventional and ventilating with NPV allows patients to use respiratory muscles that otherwise could be damaged with positive pressure ventilation, along with eliminating Barotrauma/Volutrauma to the lungs. 

Clinicians can use NPV for weaning when you have difficulty weaning a patient. Place the Cuirass on the patient. Then, on the Cuirass, set a rate, followed by an inspiratory pressure at the same time setting pressure support and PEEP on your conventional. Your patient will still be able to breathe, however, they will start using their muscles. This muscle use could improve lung function. 

Types of patients that can potentially use NPV are as follows:

  • Chronic respiratory failure
  • Neuromuscular disease
  • Cystic Fibrosis
  • Asthma
  • COPD
  • Head and spinal Injuries

Other problems that will potentially respond are small airway disease, when there’s a need to decrease RV workload and improve function, CO2 retention, low or absent respiratory drive, and/or recurrent atelectasis. 

However, not all patients qualify for NPV. This population includes those with impaired swallowing and cough,  uncooperative patients /combative patients, patients who have had a respiratory arrest, and/or unstable cardiorespiratory status arrest.

As the use of the chest cuirass has increased, it has been used on patients with Cystic Fibrosis and COPD exacerbations as a first-line treatment.  The newer version of the cuirass can also do oscillatory therapy for secretion mobilization, which helps those patients who have difficulty moving their secretions.  The Hayek Cuirass has also been used for resuscitation purposes.  It is being used in-home care as well. 

The evolution of the NPV has greatly benefited patients with respiratory problems. It continues to find new areas where it can be of benefit and promote improved quality of life. With time, it will be interesting to see where it features next.

The Debrief

  • Negative pressure ventilation was widely used before 1960, but it is still used in some departments. 
  • The more natural physiologic nature of negative pressure has promising potential for may disease processes. 
  • Negative Pressure Ventilation is contraindicated in patients with impaired airway protection, uncooperative patients, and unstable patients.

References
Linton DM. Cuirass ventilation: a review and update. Crit Care Resusc. 2005 Mar;7(1):22-8. PMID: 16548815.

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