Learn more about NIV & CPAP

Non-invasive positive pressure ventilation (NIPPV) is an alternative to mechanical ventilation for patients with respiratory failure as a method of providing ventilatory support without the need for tracheal intubation. Non-invasive positive pressure ventilation has been used increasingly over the past decade in an effort to both avoid endotracheal intubation and to accelerate weaning from mechanical ventilation.

Principles of NIV
  • Positive pressure is maintained throughout the respiratory cycle, with a higher pressure during inspiration.
  • Bi-level NIV results in reduced work of breathing and an improvement in tidal volume and CO2 removal

Equipment for Non-invasive Ventilation

NIV requires a machine capable of delivering pressurised, oxygenated gas through a mask to the patient. Modern sophisticated intensive care ventilators may be used if they have been loaded with the appropriate software. However, in practice, since they are not usually designed for this purpose, problems with inadequate flows and poor triggering of spontaneous breaths are common. Less expensive, purpose-built machines are much simpler to use and perform better.

Different models of NIV machines of varying complexity are available, although all are capable of providing high gas flows to maintain preset airway pressures, as well as sensing the respiratory effort made by the patient. The more advanced machines can deliver up to 100% oxygen, whereas the simpler machines require oxygen to be added to the distal breathing circuit through a side port. With this latter system the inspired oxygen concentration is variable, depending on flow within the circuit, and it is not possible to provide more than 60% inspired oxygen. This is important to consider when treating hypoxic patients.

The machine is attached to the patient via a breathing circuit. This tube delivers the inspiratory gas and also allows the sensors to detect the patient’s respiratory effort. The circuit is attached to the patient usually via a mask. This may be a full-face mask, a nasal mask or nasal cushions (within the nostrils). The choice depends on the patient’s condition and preference. Patients often prefer nasal masks, but must keep their mouths closed for optimal performance. Full-face masks are more effective for severe respiratory failure. Recently a full head helmet has been developed to overcome the problems of pressure sores and claustrophobia. The helmet sits on the shoulders and does tend to be noisy (patients often request earplugs) but is generally very well tolerated.

If the patient is making some effort to breathe, the machine may be set to assist spontaneous breaths. If this is not possible, the machine can be set to provide controlled ventilation at a rate set by the clinician.

Advantages of NIV compared to conventional ventilation

Compared with conventional ventilation, NIV is a relatively inexpensive and simple technique which prevents the need for conventional ventilation in some patients and improves survival. Major advantages include:

· Avoiding many of the complications associated with conventional ventilation: adverse effects from induction drugs; risk of failed intubation; risk of aspiration of gastric contents; airway trauma; tracheal stenosis; sinusitis; vocal cord damage; risk of ventilator associated pneumonia

· Avoiding the need for sedation

· Easier communication with patient

· Requires less intensive nursing care

Disadvantages of NIV compared to conventional ventilation

Conventional ventilation remains the gold standard for treatment of respiratory failure in the ICU. NIV is not appropriate for all patients; it is contraindicated in some (see below) and ineffective in those who are severely ill. Minor problems are common and include air leaks and skin damage from mask pressure. Major complications such as pneumothorax are very rare. Concerns that NIV increases the risk of aspiration have not been demonstrated studies of comparing NIV to conventional ventilation.

Indications for the use of NIV

NIV is commonly used for the treatment of respiratory failure from:

· Exacerbation of chronic obstructive airways disease (COPD)

· Pulmonary oedema

· Respiratory failure in immunocompromised patients. E.g. AIDS, malignancy

· Weaning from conventional ventilation and prevention of need for reintubation in high risk patients

· Chest trauma

For patients with exacerbations of COPD, NIV results in a significant reduction in mortality and length of hospital stay when compared to conventional ventilation. NIV is now recommended as first line therapy for those requiring ventilatory support.

Immunosuppressed patients with respiratory failure requiring mechanical ventilation are very susceptible to ventilator associated pneumonia and have a mortality rate of over 90 percent. The use of NIV has resulted in significantly improved outcome in these patients.

NIV is also used to wean patients from conventional ventilatory support, resulting in shorter duration of ventilation, reduced complications, reduced hospital stay and reduced mortality.

Relative contraindications
  • Very low level of consciousness that will not be quickly reversed by NIV
  • Inability to clear secretions
  • Claustrophobia - patient can usually be talked through this
  • Severe facial trauma or deformity preventing adequate seal
  • Condition requiring prolonged ventilation or surgery eg pneumonia or CCF in a young person - if there condition is severe enough to require NIV they are either going to be tubed for a long time or may require cardiac surgery.
Adverse effects
  • Hypotension - consider fluid loading, have a pressor ready.
  • Agitation - consider sedation with haloperidol (rather than a benzodiazepine which may reduce respiratory drive)
  • Aspiration - ensure patient at least 45˚ head up and 1:1 nursing
  • Pressure areas

 

Glossary
 
MODES
 
S Spontaneous
S/T Spontaneous Timed; ie BPAP (Bi-level Positive Airway Pressure)

CPAP Continuous Positive Airway Pressure

 

 

PARAMETERS

 

IPAP: Inspiratory Positive Airway Pressure. Sets inspiratory pressure

EPAP: Expiratory Positive Airway Pressure. Sets expiratory Pressure

Rate: Sets the back-up rate; ie the number of breaths per minute the ventilator will deliver if the patient becomes apneic.  For acute patients, set the back-up rate to no more than half the patients measured respiratory rate.  Typical range for setting Rate is 10 to 15 bpm

Ti Insp Time Sec: Sets the duration of the inspiratory phase for back-up breaths.  Should be 1/3 of the back-up breath cycle. Eg 10 bpm, one breath cycle = 6 seconds.  Set Timed Insp to 2 seconds.  Only applied to timed breaths.  Spontaneous patient triggered breaths have inspiratory time determined by the patient.

Rise Time Sec: Sets how quickly the pressure increases from EPAP to IPAP - range is 1 to 6. Each step of one = 0.1 sec.  Acts a “comfort control” for patient.  Set a short (1 or 2) rise time if the patient has a high respiratory rate.

Ramp Time Min & Ramp Start Cm H2O: The Ramp function enables you to begin ventilation at very low pressures – Ramp Start - and over a period of time - Ramp Time – gradually increase the settings to the set EPAP and IPAP.  Ramp Time is set in steps of 5 minutes up to 45 minutes.  The Ramp function is mainly used for patients on nocturnal ventilation and is not normally used for patients in acute respiratory failure in a ward environment

 

 

PATIENT DATA

 

Rate: Measured respiratory rate of the patient

Est. Vt (mls): Exhaled Tidal Volume; ie the amount of air exhaled by the patient each breath. Measured in millilitres(mls).  Pressure support assists patient spontaneous effort, so if pressure support increases, Vt should also increase. Typical Vt target is 7 to 10 ml per Kg ideal body weight. Flashes when peak inspiratory flow for successive breaths varies by more than 15 L/min.

Est. MV (L): Exhaled Minute Ventilation; ie the amount of air exhaled over the last minute.  Measured in Litres (L).  Calculated by Respiratory Rate x Tidal Volume

Leak (Lpm): Amount of leak from around the mask. Breath by breath, Focus measures the total amount of leak.  Pt Leak indicates how good is the mask fit.  For optimal mask fit, adjust the mask to give a Pt Leak of 7 to 25 litres per minute.  This ensures you do not over tighten the mask with consequent increased risk of pressure sores. 

# Apnea: Number of Apnea periods (10 seconds or more with no spontaneous trigger) in last hour. Not really used to evaluate acute patients.

Trigger: Indicates whether breath triggered by the patient or Ventilator (timed breath)