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Negative Pressure Ventilation: An Explanation

Overview 

Negative-Pressure-Ventilation

Negative-Pressure-Ventilation

Negative pressure ventilation is another type mode of the ventilator. It was the primary method of ventilation for acute respiratory failure before the Copenhagen polio epidemic came in the 1950s. There was insufficient equipment, with a large number of patients needing continuous ventilation through an endotracheal tube. Hence, positive pressure ventilation was in high use. Similarly, negative pressure ventilation has also a big role in saving people’s life dealing with severe respiratory acidosis or a weakened consciousness. 

Also, negative pressure ventilation is used in patients who cannot bear a facial mask because of facial deformity, excessive airway secretion or claustrophobia. 

What is negative pressure ventilation? 

Negative pressure ventilation is a type of ventilation where the surface of the thorax is exposed to subatmospheric pressure or negative pressure during inspiration. This developed negative pressure expands thorax and results in a decrease in the pleural and alveolar pressures. Therefore, creates a pressure gradient causing the air to move from the airway opening to the alveoli. Expiration occurs passively when the pressure near the thorax reaches atmospheric pressure or is greater than that leading to the elastic pullback of the lungs and chest wall. 

Negative pressure ventilation has been successful in small children and has shown effective results on cardiopulmonary circulation that may be an advantage in children receiving complex cardio reconstructive surgery. Negative pressure ventilation is beneficial for both short-term as well as long-term use. Negative pressure ventilation has been a vital procedure in saving people with respiratory failure. However, with the introduction of non-invasive positive pressure ventilation, its use was questioned. 

Nevertheless, it continues to have a very big role in maintaining respiratory control in critically ill patients. Let’s see the clinical applications of the NPV.

Clinical applications of NPV 

Short-term use 

Chronic obstructive pulmonary disease:- Negative pressure ventilation is used as first-line treatment in patients with COPD in ARF(acute respiratory failure). Since negative pressure ventilation is effective as non-invasive positive pressure ventilation intubation can be avoided in the cases where two cases are combined. 

Neuromuscular disorders:- Some reports suggest that negative pressure ventilation provided by an iron lung can be effective in treating ARF patients with neuromuscular diseases. 

Pediatric disease:- in the neonatal care unit, negative pressure ventilation has a big role and it provides an additional facility to neonates. The pressure gradient can either be used continuously or as intermittent negative pressure ventilation. It prevents fragile children from reintubation after extubation. 

Long-term use 

Chronic obstructive pulmonary disease:- there is no evidence that negative pressure ventilation helps improve respiratory muscle function, quality of life and COPD patient’s survival rate. However, no other ventilatory technique including face mask has indeed been shown effective in the long term use for stable COPD patients. 

Neuromuscular disorders:- studies suggests that negative pressure ventilation has been proved successful for long-term mechanical ventilation in patients with neuromuscular disorders. 

At home or in hospital:- There are a group of people and children who needs long-term mechanical ventilation. For instance, for children with a neuromuscular disorder and who requires long-term ventilatory support, negative pressure ventilation can be the best solution. 

Finally, there are groups of people who need long-term ventilatory support includes those having central hyperventilation syndromes(congenital or acquired). 

Advantages of NPV 

Usually, negative pressure ventilation is best for patients who have neuromuscular diseases( but have normal lung compliance). This method of mechanical ventilation is effective in various conditions including neuromuscular and skeletal disorders and specifically for nighttime ventilation. It is highly effective in people with severe respiratory acidosis, impaired consciousness and those who cannot handle facial masks and in children, also, in people having facial deformities, claustrophobia or excess airway secretion. 

Disadvantages of NPV 

Negative pressure ventilation does not work when the patient’s lung compliance is decreased, or the lung resistance is increased. 

Types of negative pressure ventilation

There are many types of NPV:-

  • Iron lung
  • Cuirass ventilator (also called chest shell or tortoise shell)
  • Jacket ventilator ( also called poncho or raincoat ventilator) 

How effective is NPV? 

The effectiveness of NPV depends on the medical assistance followed by well-trained nurses and physiotherapists who holds the knowledge of NPV. During the ventilation period, there can be some issues that may arise and will require medical assistance. 

For instance, in NPV with an iron lung, there might be some issues such as:

  • Transfer from bed inside the tank ventilator’s chamber.
  • Access to nursing procedures during mechanical ventilation 

However, well-trained nurses or medical professionals handle every procedure carefully. 

Conclusion 

There are numerous researches and findings which suggests negative pressure ventilation as an effective method in patients with chronic respiratory failure. However, non-invasive positive pressure ventilation also has similar benefits. Hence, NPPV(non-invasive positive pressure ventilation) has replaced the NPV (negative pressure ventilation). But still, negative pressure ventilation has roles in those patients who cannot handle non-invasive positive pressure ventilation.