Manual Hyperinflation

Introduction

Manual Resuscitator Bag used for Manual Hyperinflation or "bagging"

Manual hyperinflation also known as manual ventilation or ‘bagging’, is a technique used by respiratory physiotherapists in the management of ventilated patients or patients self-ventilating through a tracheostomy. Manual hyperinflation is used to increase lung volumes and aid secretion clearance when used in conjunction with suctioning. Manual hyperinflation involves the use of a manual resuscitator bag (MRB) connected to oxygen to provide a slow, deep inspiratory breath followed by an inspiratory pause of 1-2 seconds, and a rapid release of the resuscitation bag .

Mechanism of action

To increase volume

Manual hyperinflation is used to manage atelectasis. The mechanism it is thought to work is by increasing alveolar recruitment. The squeezing of the resuscitation bag increases the baseline tidal volumes during inspiration by approximately 1L . This increase in tidal volume plus inspiratory hold allows time for alveoli and collateral airways to open, thereby increasing lung compliance and reducing atelectasis .

For secretion clearance

MH not only increases the tidal volume but the quick release of the resuscitation bag increases the elastic recoil of the lung and therefore increases the expiratory flow rate. The expiratory flow rate is necessary to mobilise secretions.

The mechanism for how this works can be explained by the engineering concept of two-phase gas-liquid flow; moving gas in a tube transfers momentum to the stationary liquid, and occurs when the expiratory flow rate is greater than inspiratory flow rate. A normal cough generates very high expiratory airflow, which creates mist flow of the secretions to enable them to be expelled from the airways. However, the expiratory flow generated with Manual Hyperinflation is still much slower than a normal cough, and so moves secretions using annular flow instead. Manual Hyperinflation may therefore prevent mucus plugging and associated lobar collapse . The use of a pressure manometer is recommended to ensure this expiratory flow bias .

Once the secretions have been mobilised, suctioning is often used to clear them from the patient.

whereby altering the pattern of airflow determines the movement of the liquid (secretions) within the airways (fig 1). A normal cough generates very high expiratory airflow, which creates mist flow of the secretions to enable them to be expelled from the airways. However, the expiratory flow generated with MHI is still much slower than a normal cough, and so moves secretions using annular flow instead. MHI may therefore prevent mucus plugging and associated lobar collapse

Indications

• • Clearance of retained secretions and mucus plugging
  • Recruitment of areas of atelectasis or collapse
  • To improve ventilation/perfusion (V/Q) matching
  • To improve lung compliance
  • To improve regional lung ventilation
  • To improve oxygenation

Absolute Contraindications

• •   Undrained pneumothorax
  • Severe bronchospasm
  •   Head injury with ICP > 25mmHg
  •   Severe arterial hypotension
  • High peak end inspiratory pressure (PEEP) ventilation and PEEP dependency
  •   Nitric Oxide ventilation
  •   High Frequency Oscillation Ventilation

Relative Contraindications

Note: These relative contraindications are for ‘therapeutic’ manual hyperinflation.

·         Cardiovascular (CVS) instability/arrhythmias	Compromised venous return- further increases effort required to maintain adequate tissue perfusion
·         Acute Respiratory Distress Syndrome (ARDS)	Increases risk of pneumothorax/barotrauma NB! This does not preclude the use of the MRB in resuscitation situations in this patient group
·         Severe exacerbation Chronic Obstructive Pulmonary Disease (COPD) / Bronchospasm	Increased airway pressure will increase airway irritation and inflammatory response
·         High PEEP (> 10cmH2O)	The break in the circuit will cause loss of PEEP and can de-recruit lung
·         Raised intracranial pressure (ICP)	Increased intrathoracic pressure reduces mean arterial pressure which can compromise cerebral perfusion pressure
·         Proximal Tumor/obstruction	Risk of dislodging or causing trauma
·         Emphysematous Bullae	Increases risk of pneumothorax
·         Recent lung  surgery e.g. lobectomy/pneumonectomy	High airway pressure may cause trauma/pneumothorax. Check with surgeons regarding stump pressure.
·         Hypotension (Systolic <80)	Increased positive pressure in thoracic cavity compromises venous return – reduces cardiac output
·         Patients dependent on hypoxic drive	High levels of O2 being delivered/increased PaO2 levels may reduce drive to breathe
·         Acute Head Injury	As for raised ICP
·         Unexplained Haemoptysis	May be indicative of acute trauma to the lung parenchyma
·         High respiratory rate	Difficult to co-ordinate the technique
·         Subcutaneous Emphysema	May indicate the presence of a pneumothorax
·         ECMO patients	Should be discussed with on-call ECMO consultant

Technique

Original Editor - Sarah Popperwell Top Contributors - Sarah Popperwell, Kim Jackson, Rachael Lowe, Safiya Naz and Adam Vallely Farrell