Respiration Noninvasive Ventilation
Abstract
There is increased interest in noninvasive ventilation because it is effective and avoids the complications of invasive ventilation. Noninvasive ventilation keeps the airway defense mechanisms, allows the patient to eat and talk and decreases infective complications. Efficacy of this treatment depends mainly on the proper selection of patients. The aim of this work is to review types, indications and guidelines of noninvasive ventilation.
Introduction
Animal experiments for artificial respiration began at midsixteenth century led by Andreas Vesalius; however, experiments were immature and crude. Alexander Graham Bell, in 1889 designed and built an artificial respirator for use in distressed newly born infants. In 1950, Dr. Alan Bloxsom created the Bloxsom air lock for use in reviving newborn infants (Donald and Young, 1952).
From this time onwards, there is progressive development of iron lung machines, ventilators and, in general, the art of aided ventilation. Aided mechanical respiration can be invasive, bypassing the upper airway through a tracheotomy, an endotracheal tube or a laryngeal mask.
Providing respiratory support through a nasal or a face mask is noninvasive ventilation (Baudouin and other members of the British Thoracic Society, BTS, Standards of Care Committee, 2002). The aim of this work is to review noninvasive ventilation, when to use it and how to monitor patients put on noninvasive ventilation.
Types of noninvasive ventilation
A pressure difference has to develop, phasically, across the lung for ventilation to occur. This can be achieved by creating a negative pressure in the pleural space; or by creating a positive pressure within the upper airway (Corrado and Gorini, 2002).
1- Noninvasive negative pressure ventilation (NPV):
It is aided ventilation by exposing the thoracic cage to negative sub-atmospheric pressure. This creates a pressure gradient for air to flow through the airway into the pulmonary alveoli (inspiratory phase). When the pressure around the thoracic cage turns atmospheric (or higher), the elastic recoil of lung tissues allows expiration to occur passively (Corrado and Gorini, 2002).
NPV is used on short- term or long-term basis in cases of acute respiratory failure secondary to chronic obstructive pulmonary disease or in neuromuscular disorders and chest wall diseases where there is restrictive ventilatory impairment (Corrado and Gorini, 2002). In pediatric cases, NPV is used for children who do not tolerate face or nasal masks, children with facial skeletal abnormalities or those who have excessive pulmonary secretions (Deep, Munter and Desai, 2007).
Corrado and Gorini, 2002, reviewed the short and long-term uses of negative pressure ventilators. They stated the use of iron-lung machine is effective to manage patients with acute respiratory failure or acute exacerbation of chronic obstructive airway disease.
However; they recommended the need to have more studies on combining NPV and mask pressure positive ventilation and the relative role played by NPV. In long-term use for patients with chronic respiratory failure, noninvasive positive pressure ventilation has largely replaced NPV.
The use of negative pressure ventilators is lesser than it was in the late 1950s till mid 1960s, however; they may still be used for patients who fail to adapt to noninvasive positive pressure ventilation (NPPV). The tidal volume produced by NPV ventilators for a given negative pressure is the efficiency of the ventilator. Compliance (pressure volume relationship) of the chest wall and the surface area of the body to which it is applied, decide the efficiency of the ventilator in use.
Therefore; a tank ventilator is the most efficient as it applies negative pressure to a large body surface area. However; it is bulky and heavy and is intolerable to claustrophobic patients. The cuirass NPV ventilators are the least effective because of the small body surface area it covers. The chest wrap and chest shell ventilators are lightweight, with the chest wrap more efficient, but the negative pressure generators are still heavy.
Problems with air leakage compromise their efficiency. Collapse of the chest wrap ventilator jacket onto the chest wall and upper abdomen, decrease its efficiency. The tank and wrap ventilators limit the patient’s supine positioning and often produce musculoskeletal pains. Patients with deformed chest walls can be managed by custom-made cuirass NPV ventilators.
Although the chest shell ventilator can be used in sitting position, yet if it is not perfectly fit, it produces discomfort and pressure sores. These limitations affect patient’s tolerance to the equipment, what is more important, from clinical view, is they induce obstructive sleep apnea in normal individuals. They increase the negative intraluminal pressure of the airway, producing collapse and obstructive apnea spells (Mehta and Hill, 2001).
2- Noninvasive positive pressure ventilation (NPPV):
It is supplying a two-way positive pressure to assist ventilation (an inspiratory and an expiratory positive airway pressures). An inspiratory positive pressure helps to put the tired respiratory muscle to rest and to improve alveolar oxygenation. The pressure is set up to 15-20 cm/H2O. The expiratory positive pressure helps to keep the airway open (splinting action) to flush CO2.
It also helps to reduce atelectasis and increase the end tidal volume. It is usually set at 4-6 cm/H2O. Delivering oxygen occurs via an opening (portal) in the face or nose mask or through a proximal channel in the ventilator (Christie and others, 2006).
Delivery of oxygen and positive pressure from the ventilator to the patient’s upper air way is through nasal masks, face (oro-nasal) masks or mouthpieces. There are three major types of ventilators to develop positive pressure. Pressure cycled ventilators deliver air at a preset pressure level. The air volume varies, in other , they provide pressure support ventilation. Volume cycled ventilators are used mainly for long-term purposes.
They provide greater pressure and volume than pressure cycled ventilators where tidal volume can be adjusted at 10-15 ml/kg. Therefore; they can also be used in patients who need greater pressure as obese patients and those with deformed chest walls. Ventilators which deliver air at variable pressures for inspiration and expiration are the bi-level positive air pressure ventilators.
Equipments that deliver continuous positive airway pressure (CPAP) are not true ventilators as they do not provide active support to respiration. They provide positive pressure to provide a splinting action to the collapsible upper airway (Mehta and Hill, 2001).
Clinical indications for use of NPPV are:
Setting the standards for noninvasive ventilation
Carlucci and the collaborative group on mechanical ventilation, 2001, conducted an epidemiological study to assess the use of invasive and noninvasive ventilation support in 42 intensive care units. Total number of patients received mechanical ventilatory support was 689. Of this group of patients, 581 patients required endotracheal intubations (35% of them were not intubated on admission).
The remaining 108 patient (16%) were on noninvasive ventilatory techniques. Noninvasive technique was never used on patients in coma. The main indications were; hypoxemic acute respiratory failure, hypercapnic acute respiratory failure and acute pulmonary edema of cardiogenic origin. This study raises the question of when to go for noninvasive ventilation.
2- Guidelines for the use of non invasive ventilation (when to go for noninvasive ventilation): Sinuff and others, 2003 set guidelines for the use of NPPV in cases of acute respiratory failure. These guidelines were: patients should fulfill clinical criteria of being able to protect airway, manage secretions with respiratory rate less than 30 per minute. Second, patients should fulfill gas exchange criteria; which are: blood pH less than 7.35, PaCO2 more than 50 mm/Hg, PaO2 less than 60 mm/Hg and FIO2 0.21 or alternatively, PaO2:FIO2 ratio of less than 200.
Criteria for invasive ventilation (endotracheal intubation- ETI) were: Respiratory arrest or respiratory halts with disturbed consciousness. Agitated patients and those with heart rate of less than 50 per minute with systolic blood pressure less than 90 mm/Hg are also considered for ETI. Patients with blood pH equals or less than 7.30 and PaO2 less than 50 mm/Hg are candidates for ETI. Baudouin et al, 2002 summarized the British Thoracic society guidelines for the use of noninvasive ventilation, they were:
1- NIV (noninvasive ventilation) is suitable for:
a- Cases of respiratory failure secondary to chronic obstructive pulmonary disease (COPD).
b- Cases of acute pulmonary edema of cardiogenic origin,
c- cases of obstructive sleep apnea, deformed chest wall and selected cases of neuromuscular disorders.
d- Blood gases criteria: PaO2 less than 60mm/Hg, PaCO2 more than 50 mm/Hg and blood pH less than 7.35.
2- Patients subjected to NIV should be able to protect their airways, conscious and cooperative, with no excessive respiratory secretions and hemodynamically stable. 2- Contraindications of NIV: Patients with pneumothorax or pleural effusion (undrained), patients with facial burns or persistent fixed upper airway obstruction or with severe vomiting are unsuitable for NIV.
In all cases patient and or family counseling is essential (Baudouin et al, 2002). In setting up noninvasive ventilation, the following points are to be considered:
1- Consider what modality to refer to if NIV fails to improve the patient (consultation of a senior medical staff is always useful).
2- Where the trial will take place (ICU, ward or emergency room).
3- Patient and family counseling, in all cases, consider informing ICU.
4- Select the best masks fit and secure it in place.
5- Attach a pulse oximeter and set up the ventilator.
6- Re-assess after few minutes and re-adjust the ventilator, if needed.
7- Add oxygen if PaO2 is less than 85%.
8- Re-asses after 1-2 hours with arterial blood gases.
9- Consider alternative treatment if:
a) PaCO2 and blood pH deteriorated after 1-2 hours despite proper NIV setting.
b- If PaCO2 improves but PaO2 remains low, consider readjusting the ventilator settings or increase Fio2 (Baudouin et al, 2002).
Monitoring of patients on NPPV is on three levels: 1- Subjective or symptom relief as dyspnea in acute cases and sleep disturbances and fatigue in chronic cases. Patient tolerance to the equipment and interface should be asked for repeatedly. 2- Physiologic responses:
Drop in respiratory rate and return of heart rate to normal or near normal in the first one or two hours are important prognostic factors. Signs of increased respiratory effort (abdominal paradox and working sternomastoid muscles) should be improved. Patient-ventilator synchrony should be monitored and corrected by adjusting ventilator settings whenever needed.
3- Gas exchange is monitored by oximetry and measurements of blood gases. In chronic patients, improvement in gas exchange is usually slow, therefore; measuring arterial blood gases can be delayed for a period of 6-24 hours (Mehta and Hill, 2001).
The price for the successful results of noninvasive ventilation includes trained staff, price of equipment and the consumption of additional nursing and registrar’s time. In order to implement NIV in a hospital or a unit, the question of its cost effectiveness rises. Plant and others, 2003, reported a health economic analysis which modeled the costs and effects of providing NIV to a UK hospital.
They concluded that NIV reduced the overall costs of treatment of patients with chronic obstructive lung disease with mild to moderate acidosis. The procedure helped also to reduce the hospital’s mortality rate. Taking in consideration that the main expenses are to providing the equipments and training the needed staff, further annual revenues will be needed for maintenance and providing the equipment’s auxiliaries.
Conclusion
Noninvasive ventilation refers to assisted ventilation without tracheotomy or endotracheal intubation. It showed efficacy in cases of acute and chronic respiratory failure, acute pulmonary edema of cardiogenic origin and assisting ventilation in cases of chest wall and neuromuscular disorders.
Not all patients are suitable for the non invasive technique. Invasive and noninvasive ventilation should be looked upon as a single modality in the armamentarium of clinicians and the decision to use either of them depends on appropriate patient selection.
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