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Non Invasive Mechanical Ventilation in Critical Care Units
Positive pressure ventilation that is delivered via endotracheal
tube or tracheotomy is very effective
 "Aggressive
medical treatment directed at cause in impending respiratory failure along
with NIV is a key to success"
- Dr Charu Jani
Chief - Critical Care
Saifee Hospital
Mumbai
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The issue mechanical ventilation with an endotracheal tube
or via tracheostomy has become a major component of intensive care. However,
unavoidable drawbacks related to the invasive character of this treatment have
been observed, including Ventilator-Associated Pneumonia (VAP). Non-Invasive
Ventilator (NIV) refers to provision of ventilation without need for invasive
artificial airway. Invasive mechanical ventilation is highly effective and reliable
in supporting alveolar ventilation. NIV is a technique of augmenting alveolar
ventilation without invasive airways. It is not designated to provide total
ventilatory support. The use of NIV in patients with respiratory failure is
a recent phenomenon, mainly because of advance in non-invasive inter-phases
and ventilator modes.
During polio epidemic of 1952, it was observed that survival rate improved with
respiratory paralysis and treated with invasive mechanical ventilation. After
that invasive positive pressure, mechanical ventilation became preferred means
of treating ARF. Over past decade, NIV has moved from outpatient to indoor patients
and ICUs, where it is used to treat acute respiratory failure and other critical
condition requiring ventilatory assistance. Initially, NIV was used in patients
with chronic hypoventilation syndrome requiring ventilatory support during sleep.
Lately in 1990s, it has been used in the management of acute and chronic respiratory
disorder in ICU. NIV is delivered by nasal or oro-nasal mask connected to machine.
Non-invasive Ventilator
NIV is simple mask (nasal or facial) connected to the ventilator. It is partial
ventilatory support. It cannot replace the invasive mechanical ventilator, but
can be a complement to Mechanical Ventilation (MV). It is useful in a group
of patients who are not too sick to require MV, but at the same time they are
sick enough to leave them alone only on oxygen. These patients have got impending
respiratory failure and need ventilatory assistance. NIV has to be used on a
patient who is conscious who should be able to expectorate.
NIV can be used in following conditions:
- Acute respiratory failure.
- Acute exacerbation of COPD.
- Acute pulmonary edema.
- Terminal end stage disease where patient refuses
intubation.
- Respiratory failure in iImmuno-compromised patient.
- Can be used for early extubation.
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Check list before starting NIPPV
- Is patient fulfilling criteria of respiratory
failure?
- Have conventional medical treatment been
fully explored?
- Ensure that controlled oxygen therapy,
bronchodilators, steroids, antibiotics and diuretics are given as per
condition.
- NIPPV is not universally successful. There
is incidence of 40 per cent failure.
- Make sure that if needed, immediate provision
of incubation is ready.
Guidelines for initiating NIPPV
Patient's selection: Two steps
First Step:Identification of patients needing ventilator assistance.
Clinical sign of respiratory failure.
Moderate to severe dispose, RR >24 /min, use of accessory muscles,
paradoxical abdominal breathing. Blood gas abnormality. PAO2 < 60 mmhg,
PACO2>45mmhg, PH<7.35, PAO2/FIO2 <200.
Second Step: Excluding patients who has relative or absolute contraindication.
Impending respiratory arrest. Haermodynamically unstable, hypo tension,
unresponsive to fluids, ischemia & arrhythmia. Inability to protect
airway, impaired cough or swallowing reflex. Excessive secretion. Facial
trauma. Agitated patients. Gastro - intestinal instability.
Ventilator selection: Usual critical care ventilator commonly used
in ICU can also be used. Main disadvantage is that it does not compensate
for leak. The presently available portable pressure targeted ventilators
known as bi-level ventilators that are blower-driven are commonly used.
They are considered continuous flow ventilators in which flow delivery
is based on set inspiratory and expiatory pressure levels as per patient's
demand.
Select Interface: Two types - Facials or Nasal. Facial masks are
preferred in acutely distressed patients. Mouth breather, large leak with
nasal mask. Nasal mask is referred in chronic respiratory failures. Common
mistake is to fit the mask too tightly which decreases patient's comfort
and compliance. Set the ventilator. Apply mask for few breaths trial.
Mask should be holding on patient's mouth. It allows patient to get used
to feel of facial / nasal pressure and it increases chance of success
of NIPPV.
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Factors vital to success of NIV are:
- Careful selection of patient.
- Properly timed initiation.
- Comfortable well fitting interface.
- Careful monitoring.
- Standby intubation facility should be kept available.
 Available
hi-tech advanced ventilators are very effective in saving lives. Positive pressure
ventilation that is delivered via endotracheal tube or tracheotomy is very effective.
But it has got its own disadvantages. Artificial airway, that is, endotracheal
tube or tracheostomy carry the risk of:
- Complication related to insertion.
- Loss of airway defense namely cough and swallowing
reflex and that leads to risk of nosocomial infection.
- Ventilated related complication namely barotraumas,
volume trauma.
- Needs for sedation/ paralytic agents.
- Late complication like risk of tracheal stenos.
- Complex cardio thoracic haemodynamic effect.
When to not use:
- Facial trauma.
- Recent surgery of the upper airway or upper gastrointestinal
tract.
- Difficulties in protecting the airway, that is,
lowered consciousness.
- Bowel obstruction.
- Copious tracheal secretions.
- Endotracheal intubation should always be preferred
in the case of marked haemodynamic or respiratory instability with life-threatening
hypoxemia.
Please remember that it is not a curative mode of treatment. Aggressive medical
treatment directed at cause in impending respiratory failure along with NIV
is a key to success.
cjani@vsnl.com
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