Showing the advantages and disadvantages of NIV use in intensive care unit.
Non-invasive Ventilation (NIV) has emerged as an useful aid for management of pulmonary diseases specifically in cases of respiratory failure. NIV provides respiratory support without the need of an endotracheal tube, helping in avoiding the complications associated with intubation such as tracheal trauma, infection, bleeding, injury to the lung tissues and aspiration. NIV has turned out to provide substantial benefit in the management of chronic obstructive pulmonary disease, acute respiratory distress syndrome, cardiogenic pulmonary edema and in cases of neuromuscular disorders. It has now become an integral tool in the management of respiratory failure, both at home as well as hospital settings including critical care units. All patients of respiratory failure irrespective of causes likeAcute exacerbations of COPD, Acute pulmonary edema, Exacerbations of cystic fibrosis, asthma, or restrictive lung disease and Pneumonia admitted in intensive care unit/high dependent units are suitable for NIV. Noninvasive ventilation is standard of care in chronic respiratory failure and has replaced invasive ventilation in such settings. Its flexibility in use and ease of administration allows it to be acceptable by patients as well as caregivers.
- non-invasive ventilation
- acute hypoxic respiratory failure
- Bilevel positive airway pressure
- portable ventilator
- negative pressure ventilation
Brief History: Till mid-20th century Non-invasive Ventilation (NIV) was the mainstay of mechanical ventilatory assistance and it was delivered by negative pressure devices such as the “iron lung” that was used predominantly for poliomyelitis patients with respiratory paralysis. Ironically when its demand and supply suffered during the polio epidemic in Denmark in 1952, there was a transition to positive pressure mechanical ventilation via translaryngeal cuffed endotracheal tubes.
Curiass/shell is a shell or a cage which surrounds the chest and is then connected to a portable ventilator. Raincoat or Poncho is a tight fitting suit which is connected through the means of hoses to a portable ventilator. Rocking bed is another method for providing negative pressure ventilation which induces diaphragmatic motion by placement of the patient on a bed which rocks rapidly flat to upright while the contents of abdomen shift. A pneumobelt is a belt with a bladder which can inflate and deflate with air in a cyclic pattern. The diaphgram moves in response to changes in the intraabdominal pressure. Another form of negative pressure ventilation is a pneumowrap.
It was not until the 1980s with the development of nasal masks for continuous positive airway pressure, used for the treatment of obstructive sleep apnea, that there was a renewed interest in NIV and specifically non-invasive positive pressure ventilation.
Principles of NIV: Non-invasive ventilation (NIV) refers to the use of ventilatory methods without the use of an endotracheal tube or a tracheostomy tube which are artificial invasive methods. NIV provides ventilation through the use of a mask of similar device to the patient’s upper airway (Figure 1). This technique is significantly different from the invasive ones which bypass the upper airway of the patient through the use of a laryngeal mask, tracheal tube or tracheostomy. Initially non-invasive ventilation through the use of masks was used in neuromuscular disorders to provide ventilatory support in the night in view of hypoventilation. This was followed by use of non-invasive ventilation used nocturnally in cases of chronic obstructive pulmonary disease leading to an improvement in the muscle strength of respiratory muscles . Ultimately, NIV delivered through masks turned out to be of utmost benefit and was used as a method of standard ventilation in cases of chronic hypercapnic respiratory failure which could be due to deformities of the chest, neuromuscular disorder or impaired central respiratory drive. Few years later NIV was started to be used in respiratory failure due to lung pathologies rather than respiratory pump failures. Since then, NIV has evolved immensely with a widespread application in the Intensive Care Units.
Currently NIV is also being used in about 20 to 30 percent of acute hypoxic respiratory failure. NIV has even been used in cases of acute respiratory distress syndrome with an alarming success rate of more than 50 percent with improvement being more predominant in the patients whose oxygenation had improved promptly. The advantages and disadvantages of NIV use in intensive care unit have been shown in Table 1.
|Airway defense mechanism is well preserved||Claustrophobic mask|
|Intermittent use of ventilation||Cannot be used in uncooperative patients|
|Patient is able to eat food (Less chances of hypoglycemia) and communicate properly||Time consuming for the health care staff as gas exchange correction requires time in NIV|
|Physiotherapy can be given easily||No protection of airway|
|Comfortable for the patient when compared to invasive ventilation||Difficult to provide suction as direct access to the bronchial tree is not present|
|Reduced requirement for sedation||Irritation to the eye|
|Avoidance of chances of intubation||Needs to be constantly checked for air leaks|
1.1 Interface used in NIV
For the effectiveness of NIV a proper interface is very important, which include variety of masks. These masks include the
Oronasal or full-face mask,
Nasal “pillows” consisting of soft pledgets inserted directly into the nostrils,
Mouthpieces held in place by lip seals resembling a snorkel,
Total face mask resembling a plastic hockey goalie’s mask, and
The helmet (fits over the entire head).
Advantages and disadvantages of interface -
Some degree of air leak either through the mouth or around the mask is common however it can be minimized with proper education and cooperation from the.
The full-face mask interferes with speech, expectoration, and eating and it carries the risks of claustrophobia, aspiration, and rebreathing when compared to the nasal mask.
Dentures should be left in place to optimize the fitting of the mask.
The nasal mask requires patent nasal passages and mouth closure to minimize air leaks.
2. Modes of noninvasive ventilation
2.1 Positive pressure ventilation
Positive pressure ventilation delivers either a tidal volume which is either at a supra-atmospheric pressure or at a preset volume which leads to the inflation of the lungs. Exhalation is itself a passive event; it relies on the elastic recoil of the lungs for the deflation of the lung until equilibrium is attained with the pressure of atmosphere or PEEP.
It is the most commonly utilized mode of NIV in the present time, where the interface with the patient can be in the form of a full face mask, a nasal mask or a nasal pillow.
Benefits of positive pressure ventilation are as follows includes avoidance of intubation and other risks as well as complications which are associated with it. There is also preservation of swallowing along with speech and cough reflex which is beneficial for the patient. There is improvement in the exchange of gas and reduction in the word of breathing through resting of the muscles of respiration.
Candidates for positive pressure ventilation are all the patients with respiratory failure irrespective of the type of respiratory failure and it’s type. Patients with acute exacerbation of chronic obstructive pulmonary disease, acute pulmonary edema, pneumonia and exacerbation of bronchial asthma, cystic fibrosis or intrinsic lung disease can be managed with positive pressure ventilation.
Portable ventilators are utilized in order to provide continuous positive airway pressure (CPAP) or BIPAP. CPAP is used to deliver a pressure which is constantly set during inspiration as well as expiration which leads to an increase in the functional residual capacity resulting in improvement of oxygenation, however, it is not strictly a form of ventilatory assistance. Contraindication for the use of positive pressure ventilation is uncooperative patient, patient having a copious amount of secretions where airway protection is not possible, patient with unstable hemodynamics and patients with decreased mental state.
BIPAP is used to provide positive airway pressure in a manner which is biphasic. There is an inspiratory positive airway pressure (IPAP) which is set for inspiration and a lower expiratory positive airway pressure (EPAP) which is set for expiration. Difference obtained from subtracting EPAP from IPAP yields the degree of ventilatory assistance.
EPAP provides a dual benefit by ensuring proper flow in order to flush carbon dioxide from the single tube of ventilator and avoiding rebreathing along with increasing functional residual capacity and opening up the upper airway to prevent apnea as well as hypopnea. It also counterbalances the intrinsic positive end expiratory pressure in patients suffering from chronic obstructive pulmonary disease.
2.2 Initiation of NIPPV
A portable ventilator can be used to initiate NIPPV. First, there needs to be setting up of volume targeted strategy and the tidal volumes need to be higher than in invasive ventilation. A tidal volume of 10 to 15 cc/kg is used. This can compensate for the leak of air through the mouth as well as around the mask. Respiratory rate can be decided and chosen as in standard ventilation. Adequacy of ventilation/oxygenation should be checked through the means of arterial blood gas. Tidal volume or respiratory rate can be increased if the minute ventilation needs to be increased. Similarly, in an over ventilated lung, respiratory rate or tidal volume may be decreased. Oxygen supplementation is provided in line with the circuit.
BiPAP uses a pressure targeted strategy for ventilation. Inspiratory pressure or IPAP can be chosen from 8 to 20 cm H2O pressure. It can be thought of as pressure support. As the pressure increases it will be more uncomfortable for the patient. Generally, BiPAP is started between a range of 8 to 11 cm H2O.Expiratory pressure or EPAP is set at 3 to 5 cm H2O.It can be thought of as PEEP. Difference obtained from subtracting EPAP from IPAP is the amount of support being provided to the patient. In case the patient required further ventilation, IPAP level can be increased gradually. A back up rate can be set by the ventilator rate which can be chosen as a value below the patient’s spontaneous rate to assure that the patient does not develop apnea. A higher ventilator rate may be chosen in order to prevent periods of prolonged apnea and in order to allow resting of the respiratory muscles. If there needs to be improvement in oxygenation, amount of oxygen can be increased in the circuit or EPAP level may be increased. An Increase in EPAP level leads to decrease in tidal volume. To counter this, IPAP level can be increased in the same increment as the increase in EPAP.
Before Weaning one must consider to check if the patient has improved oxygen saturation at low flow oxygen rate, respiratory rate of below twenty four breaths per minute and ensure that there is interruption of positive pressure ventilation for short duration of time to ensure talking, eating, drinking and assess tolerance and gradually increase these pauses.
Drawbacks in the use of positive pressure ventilation are difficulties arising from the discomfort of the mask, headgear or straps and air leaks. Patients also complain of nasal pain, erythema or breakdown of skin due to use of mask. There can also be nasal congestion or dryness as well as ulceration of the nasal bridge with long duration of mask usage. Eye irritation due to air leak blowing into the eyes, gastric distention and aspiration are other few problems encountered in the use of positive pressure ventilation.
It is important to remember that NIPPV when initiated can induce anxiety in the patients making them uncomfortable. In order to make the patients acclimatized to the technique of NIPPV the patients require a 1:1 assistance by respiratory therapist who also makes fine adjustments in the flow rates and pressures depending on the requirement of the patient. On an average it may take about an hour for patient to become comfortable with NIPPV. IT is crucial to monitor the respiratory rate, heart rate as well as arterial blood gas to detect the effectiveness of NIPPV in correcting acute respiratory failure. At any point, if the patient deteriorated on NIPPV, conversion to endotracheal tube in order to ensure proper oxygenation should be considered.
3. Negative pressure
Negative pressure ventilation works of the mechanism of delivering pressure which is sub-atmospheric resulting in the expansion of the chest and air being drawn into the lungs through the nose and mouth. When the pressure which is around the chest wall returns to normal pressure of the atmosphere there shall be passive expiration. Negative pressure ventilation endeavors to mimic normal breathing mechanics.
Methods for providing negative pressure ventilation include iron lung which was used primarily in the epidemic of polio in the era of 1950’s.Curiass/shell is a shell or a cage which surrounds the chest and is then connected to a portable ventilator. Raincoat or Poncho is a tight fitting suit which is connected through the means of hoses to a portable ventilator. Rocking bed is another method for providing negative pressure ventilation which induces diaphragmatic motion by placement of the patient on a bed which rocks rapidly flat to upright while the contents of abdomen shift. A pneumobelt is a belt with a bladder which can inflate and deflate with air in a cyclic pattern. The diaphgram moves in response to changes in the intraabdominal pressure. Another form of negative pressure ventilation is a pneumowrap.
Indications for negative pressure ventilation include chronic respiratory failure secondary to neuromuscular disease- polio, muscular dystrophy. Generally used for nocturnal ventilatory support, with the patient breathing spontaneously during the day. Negative pressure ventilation has also been used in acute respiratory failure, there are 2 different studies which examined the use of the iron lung and poncho wrap (respectively) in COPD patients with acute respiratory failure. Both studies demonstrated the effectiveness of negative pressure ventilation to correct CO2 retention.
Drawbacks encountered with negative pressure ventilation are worsening of obstructive sleep apnea, problems with correct fitting as well as portability issues. Attendants are often required for the application and removal of the device making the process troublesome for the patients. For the use of negative pressure ventilation the patients must sleep in supine position only making it difficult to use.
4. NIV in acute hypoxemic respiratory failure
Respiratory failure is one of the most common cause leading to admission in intensive care unit and is the concluding pathway of a wide range of diseases with differing pathophysiologies.
A mechanism-based approach enables the clinician to identify the most likely cause for the respiratory failure and to treat appropriately.
4.1 Types of respiratory failure
Hypercapnic respiratory failure - Ventilatory failure and is recognized by an elevated PaCO2 above normal. Patient usually have respiratory pump failure with lungs which are normal or ventilatory failure as a consequence of airway disease or extremely severe lung parenchymal disease with normal lungs or as a consequence of airways disease or very severe parenchymal lung disease.
Hypoxemic respiratory failure - Failure of gas exchange is characterized as hypoxemia (PaO2 less than 60 mm Hg), with or without the widening of gradient between the alveoli and artery. Most of the patients suffering from this type of respiratory failure have a shunt physiology or mismatch of ventilation-perfusion (V/Q) as the primary mechanisms of hypoxemia. Most of these patients have abnormalities detected on chest x-ray.
Mixed respiratory failure with multiple components of various pathophysiologies which can result in hypoxemia as well as hypercarbia.
Type 4 respiratory failure occurs in patients who are postoperative having normal lungs with normal respiratory pump who are either sedated or paralyzed or have metabolic demands which exceed the patient’s ability to compensate. This is seen commonly in patients suffering from intensive metabolic abnormalities such as metabolic acidosis or sepsis.
4.1.1 Acute hypoxemic respiratory failure
Main component is The alveolar–arterial oxygen gradient = PAO2 – PaO2. The normal value is between 10 and 15 mm Hg and is influenced by age, i.e. increases by approximately 3 mm Hg every decade after the age of 30 years. For an FiO2 = 21%, it should be 5 to 25 mm Hg and for an FiO2 = 100%, it should be <150 mm Hg. Hypoxemic respiratory failure with a widened alveolar–arterial oxygen gradient is caused by V/Q mismatching or shunt pathophysiology. Hypoxemia due to V/Q mismatch improves with supplemental oxygen, while no improvement in cases with shunt.
Disease which result in the flooding of airspace, complete or partial collapse of the lung, pulmonary vascular abnormalities or airway disease are the common source of hypoxemic respiratory failure.
Principles for managing the patients suffering from hypoxemic respiratory failure mainly include:-
Rapid re-establishing of optimal arterial saturation which commonly necessitates the need of intubation and mechanical ventilation.
By and large, the patients having infiltrates in the lungs respond less well to non-invasive ventilation.
Using optimal amount of positive end-expiratory pressure ensures the reduction of FiO2 levels to non-toxic levels (FiO2 less than 60 percent).
Using a strategy with low tidal volume along with permissive hypercapnia in patients suffering from acute respiratory distress syndrome or acute lung injury.
Providing general supportive care to the patient in the intensive care unit while there is resolution of patient’s pulmonary pathology.
Due to increased alveolar arterial gradient with V/Q mismatch
Airway disease- Chronic Obstructive Pulmonary Disease, Asthma, Cystic Fibrosis, Bronchiolitis Obliterans Syndrome
Interstitial lung disease- Interstitial Pulmonary Fibrosis, Sarcoidosis, Interstitial pneumonia e.g. Covid 19 pneumonia
Alveolar filling – Pulmonary Edema, Left heart failure, Acute Lung Injury/Acute Respiratory Distress Syndrome, Pneumonia, Trauma, Contusion, Alveolar hemorrhage/proteinosis, Transfusion Related Acute Lung Injury, Acute interstitial pneumonitis, Acute eosinophilic pneumonia, Bronchiolitis Obliterans Organizing Pneumonia/Cryptogenic Organizing Pneumonia, Aspiration, Upper airway obstruction, Near drowning
Pulmonary vascular disease – Thromboembolism, Fat embolism
Due to increased alveolar arterial gradient with Shunt
Same as causes of alveolar filling
Atelactesis – Post operative, Immobility
Intra pulmonary vascular shunt- Pulmonary arteriovenous malformation, Hepatopulmonary syndrome
Intracardiac shunt – Patent foramen ovale, Atrial septal defect, Ventricular septal defect
4.1.3 Evidences of NIV in acute hypoxemic respiratory failure
Oxygen to improve hypoxia in acute hypoxic failure appears to be standard of care and in 2005 it was shown that NIV is better than oxygen in improving PaO2/FiO2 by unloading of respiratory muscles . In Earlier studies it was shown when used appropriately NIV is as effective as invasive mechanical ventilation in improving PaO2/FiO2 by Antonellii et al. thereby avoiding all complications related to endotracheal intubation and related ventilation . But the most important aspect of success versus failure of NIV in acute hypoxic respiratory failure is ‘Timing of initiation vis a vis progression of inciting disease as well as severity of respiratory failure” . In Acute Hypoxic Respiratory Failure, NIV needs to be initiated for mild to moderate hypoxia and before the disease has progressed (a) as window of opportunity to use NIV is narrow (b) as once disease has progressed IMV is indicated.
Failure of NIV in acute hypoxic respiratory failure needs to be identified early to prevent higher mortality. Meta-analysis of NIV use in ALI/ARDS showed intubation rate of 46% (30–86%) and mortality of 35% (19–69%) and these widely variable results indicate that different diseases states causing hypoxic respiratory failure as well as baseline characteristics of individual patients along with threshold of intubation of the centre contribute to success or failure of NIV . But studies are clear that milder is the hypoxia, lesser are the chances of failure indicating baseline PaO2 is one of the determinant of NIV outcome . Further studies also showed earlier is the better as disease has potential for reversibility. Immunosuppressed patients also showed good success rates with use of NIV in acute hypoxic respiratory failure . Hence, use of NIV in acute hypoxic respiratory failure is indicated as follows :
Level 1: in acute cardiogenic pulmonary edema as well as immunocompromised patients with acute hypoxic respiratory failure.
Level 2: evidence is to use in post-operative hypoxic respiratory failure, COPD with community acquired pneumonia as well as to prevent hypoxic failure in acute severe asthma. However NIV in severe community acquired pneumonia without any underlying comorbidity to support use of NIV needs to be used with caution as in to prevent Extubation failure. Also in patients with do not intubate or resuscitate orders.
Level 3: in patients with thoracic trauma, upper respiratory tract obstruction, partial upper airway obstruction as well as treatment in acute severe asthma but with caution to use in severe ARDS.
Level 4: In very elderly (>75 years), obesity hypoventilation syndrome and in IPF with caution.
Rationale of using NIV in acute hypoxic respiratory failure is that the primary or secondary lung failure, both lead to acute hypoxia which can be either due to abnormality in the exchange of gas or failure of the respiratory pump which leads to increase in minute ventilation, this is reversed by the use of NIV (Figure 2).
Modes of bi-level NIV used in hypoxic respiratory failure are defined by triggering: S-Spontaneous (a. patients efforts only triggering NIV), S/T- Spontaneous timed (b. patient’s own as well as timed triggering to give back up RR in case patient has irregular and slow breathing pattern to safe guard adequate ventilation, misses a breath (Figure 3).
Helmet ventilation is the most secure form of NIV in severely hypoxic patients but claustrophobia may prohibit its use. It can be used in severe hypoxic respiratory failure and it’s use in Covid 19 pneumonia and ARDS showed favorable results vis a vis oxygen therapy. However, cardiac instability is contraindication.
NIV is also used to support interventional procedures in patients with hypoxia while doing bronchoscopy or transesophageal Echocardiography.
However, in contrast to use of NIV in hypercapnic respiratory failure in hypoxic respiratory failure one needs to look beyond lungs into systemic component of disease process e.g. shock, acidosis, multi organ failure, etc. as these situations will favor invasive mechanical ventilation.
70% of failures of NIV occur within 48 hours, indicating need for intensive monitoring and identifying features of early failure proactively (Figure 4).
It has been shown that delaying intubation in such cases increases mortality and adds no benefit. Most common cause of failure is inability to correct hypoxia in 2/3rd of failed NIV’s followed by intolerance, progression of disease with hemodynamic instability. Changing NIV machine to guaranteed volume mode (AVAP’s or iVAP) can help to improve tidal volume and hypoxia. Hence all such cases should be managed in ICU settings only. Intolerance can be managed by using different types of masks or correcting into leaks. Use of sedation is strictly under observation with full facility and readiness to intubate.
NIV has penetrated deeply into the roots of medical management even in rural health facilities of India where a study conducted in rural India concluded that :
NIV is able to reduce the mortality and endotracheal intubation through the improvement of the outcome of patients.
NIV in selected group of patients is the modality of treatment of acute hypoxemic respiratory failure.
Close monitoring should be ensured to depict the patient’s response in order to take the decision of intubation on time.
Early introduction of NIV can help in the reduction of intubation rates and the subsequent complications as well as nosocomial infections associated with intubation.
5. NIV in COVID-19 pneumonia
Covid 19 pandemic caused devastation across the world with hospitalization in 5–15% and 5% requiring ICU due to severe and critical hypoxic failure. Secondary to severe covid pneumonia and ARDS. NIV has been used from the beginning of pandemic with China reporting NIV works well and results were similar to that of HFNC in Covid 19. They also reported no nosocomial outbreaks of Covid 19 infection in health cares in ICU units which used NIV. Europe started using CPAP with variable success rates as well as concerns. Initial reports of NIV use in Covid 19 showed that CPAP trial succeed in 40% when used in those requiring >15 L/min of O2 by non-rebreathing mask with baseline SpO2/FiO2(SFR) of >110, RR > 30/min and NLR > 8. Repeat SFR at 30–120 min improved in all patients but cut off of SFR 180 was the best predictor of success or failure of CPAP trial but patients who failed had high mortality (38%) . Intubation rates and mortality in Covid 19 patients who received NIV was similar to the group which received HFNC. European Respiratory Society Living Guideline for management of Covid 19 has recommended use of NIV with helmet or full face mask to treat acute hypoxic respiratory failure secondary to coronavirus infection provided there is no immediate indication for IMV . But caution must be exercised in close monitoring to identify signs of NIV failure in Covid pneumonia. There have been reports of full recovery in COVID-19 patients even after extensive lung involvement by judicious noninvasive ventilation strategies linked with prone ventilation [12, 13, 14].
6. High flow nasal cannula
Keeping in mind the human factors of comfort, humidification and warming of inspired air are essential in creating an effective oxygenation system (Figure 5). Basic components of high flow nasal cannula (HFNC) include a flow generator providing gas flow rates up to 60 liters per minute, an air-oxygen blender that achieves escalation of FIO2 from 21–100% irrespective of flow rates, and a humidifier that saturates the gas mixture at a temperature of 31 to 37 C . To minimize condensation, the heated humidified gas is delivered via heated tubings through a wide-bore nasal prong. In this system all settings are controlled independently, so maximum delivery of oxygen thence better outcome.
Mechanism responsible for high efficacy includes Physiological dead space (which accounts for approximately one-third of the tidal volume of breathing) washout of waste gasses including carbon dioxide (CO2), Decreased respiratory rate, Positive end-expiratory pressure, Increased tidal volume and Increased end-expiratory volume.
It creates a positive end-expiratory pressure to the lower airways in addition to providing positive pressure support to the nasopharynx.
It applies a splinting force to keep alveolar airways from collapsing under increased surface tensile stresses during exhalation.
This allows for improved alveolar recruitment, increasing the effective available surface area within the lungs for gaseous diffusion both to and from the blood.
It has taken over low-flow nasal cannula as later blows cool, dry air directly into the nasal passages which leads to drying of the mucosa, irritation, epistaxis, and cracking of the tissue barriers. This causes, uncomforted and restlessness in the patients thence poor adherence to therapy.
Now a days high-flow nasal cannula systems are having inbuilt warming and humidification systems which provides humidified and body temperature air that is non-irritating to the mucosa, increasing patient comfort.
There is increasing evidence of clinical application of HFNC in Acute hypoxemic respiratory failure, Post-surgical respiratory failure, Acute heart failure/pulmonary edema, Hypercapnic respiratory failure, COPD, Pre and post-extubation oxygenation, Obstructive sleep apnea, Do not intubate the patient and so on.
Hence, Non-Invasive Ventilation (NIV) is a useful tool for pulmonary diseases including acute hypoxic respiratory failure which has penetrated deeply into the routes of India with a vast scope of usage and advantages. A proper monitoring while the patient is on NIV ensures early pick up of NIV failure helping in the proceeding of appropriate corrective steps.
Conflict of interest
“The authors declare no conflict of interest.”
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