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Positive Pressure Ventilation: An Explanation

Overview

Positive-Pressure-Ventilation

Positive-Pressure-Ventilation

Positive pressure ventilation is the process of delivering proper breathing either using a mask, that decreases the effort in the breathing of critically ill patients. Positive pressure ventilation is done either with invasive or non-invasive procedures, which requires oxygen delivery via endotracheal or tracheostomy tube. In this article, we will be discussing the physiology, contraindications, and other information regarding pressure ventilation.

 

What is positive pressure ventilation? 

Positive pressure ventilation is the process of providing respiratory therapy by delivering oxygen-enriched air and other necessary gases by positive pressure into the lungs. Then, the air enters the lungs increasing the interalveolar pressure until a change in flow or pressure is detected by the ventilator, or the set volume operations start to signal their end.  

Positive pressure ventilation has two forms either invasive and non-invasive. The non-invasive process is performed through a special face mask that has a rigid seal. While the invasive process involves an endotracheal tube or tracheostomy tube to deliver positive pressure to the lungs. Ventilation whether positive or negative has some benefits, risks and contraindications. The non-invasive process is used in acute hypercapnic respiratory failure till the patient is responsive to this therapy. The conditions which are responsive to non-invasive ventilation include chronic obstructive pulmonary disease and acute cardiogenic pulmonary edema. 

Anatomy and physiology of airways 

To know positive pressure ventilation, a basic understanding of the anatomy of airways is necessary to understand the physiology and the interaction between inspiratory and expiratory forces that together deliver a breath. The upper respiratory part plays an important role in delivering air to the lungs. It starts in the nasal cavity and moves down the nasopharynx, oropharynx, and larynx to the trachea. The quality of air inhaled is affected by the mucosa, cartilage, lymphatic system of the upper airways. Similarly, these parts have an impact on the PPV delivery system. 

Positive pressure ventilation via a mask in patients with congenital face defects, post-traumatic defects, or obese people having very soft tissues and frequently deals with obstructive sleep apnea. The lower airway extends below the vocal folds to the trachea, where it divides into right and left mainstem bronchi, which are further divided into smaller segmental bronchi. These are subdivided into even smaller bronchioles, which finally lead to the airway’s terminal segment, the alveoli, where gas exchange takes place.

During intubation, the endotracheal tube is placed in the trachea with the aerated cuff below the vocal cords. Technically, breathing in positive pressure ventilation can be specified by changes in volume, pressure and flow during inhalation and exhalation.

How to know if someone needs PPV? 

Though, there are many conditions or indications when a patient needs positive pressure ventilation. Here we will see only the major conditions. 

Major indications for PPV:- 

  • Protection of the open airway in people who cannot maintain an open airway such as a change in the levels of consciousness or trauma 
  • Hypercapnic respiratory failure 
  • Circulatory failure 
  • Hypoxemic respiratory failure 

Contraindications 

Contraindications for non-invasive PPV:- 

  • Emergent intuition 
  • An altered mental state(encephalopathy) 
  • Facial defects or facial trauma 
  • An obstruction in the airway
  • Expected requirement for long-term mechanical ventilation 
  • Gastrointestinal bleeding 

Contraindications for invasive PPV:- 

  • The patient doesn’t want ventilatory support 
  • When the NIPPV is an alternative to provide breathing support due to its fewer complications as compared to typical mechanical ventilation such as ventilator-associated pneumonia, excessive sedation and volutrauma. 

Equipment involved in PPV

Non-invasive positive pressure ventilation is mostly administered by a continuous positive airway pressure(CPAP) or bilevel positive airway pressure machine(BiPAP). A CPAP machine is equipped with a pump and a tube joined with a mask that goes on the patient’s face. BiPAP machine is also used for NIPAP and functions similarly to a CPAP machine. The mask on the patient’s face should be sealed properly, so that the pressure cannot escape from around the mask, and not reduce the inspiratory pressure and the effectiveness of the procedure. 

In case of invasive ventilation procedures, a patient has to go through either intubation or tracheostomy. There are about 47 different modes of ventilators and all of them work on the same principle, that is they provide oxygenation and ventilation to the patient.

Medical support 

The administration of positive pressure ventilation requires the assistance of a trained healthcare provider, who has sufficient knowledge and understanding of ventilators and other positive pressure devices. Because of the low therapeutic index of the mechanical ventilation, also, inappropriate changes in tidal volume or pressure could damage the lungs, also called ventilator-induced injury. Thus, a professional healthcare group is required to take care of severely ill patients. So that even a slight change in the settings of a ventilator will not be ignored. 

Procedure 

Every NIPPV machine is distinct in operation settings. Non-invasive positive pressure procedures require a face mask with a tight seal. The positive pressure built through the machine keeps the upper airway by providing a pneumatic splint. On the other hand, IPPV requires an expert medical provider for successful intubation or tracheostomy procedures. In intubation, the patient needs general anaesthesia to make the process painless and successful. 

As soon the endotracheal tube is placed, its cuff gets inflate and seals the tube inside the trachea. The endotracheal tube is then connected to a ventilator and the operations are set accordingly.

Risks involved in PPV(Positive Pressure Ventilation)

There can be many risks or complications involved with positive pressure ventilation that can be serious. Therefore, there is always a need for an expert medical provider. Particularly, the more invasive procedures of mechanical ventilation bring complications. Although, non-invasive procedures also can have complications, however, the chances are rare. 

The complications in PPV are:- 

  • Ventilator-associated lung injury and barotrauma
  • Ventilator-associated pneumonia 
  • Oxygen toxicity 
  • Hemodynamic effects 
  • Neuromuscular complications