CPAP -vs- BiPAP: What RTs Need to Know

Non-invasive positive pressure ventilation (NIPPV) include machines that allow you to ventilate and oxygenate patients without the need to perform the invasive procedure of intubation. These machines can only be used on a spontaneously breathing patient.

Another acronym commonly used to describe NIPPV is NIV, which essentially stands for Non-Invasive Ventilation. You may actually see other similar acronyms, and they all essentially refer to the same thing.

The two most common forms of NIV are:

1. CPAP 
2. BiPAP 

So, what are they and how might they help your patients?

1. CPAP: This is continuous positive airway pressure. It's a pressure exhale applied during the respiratory cycle that helps keep air passages open so that the next breath comes in easier. Since it keeps the airways patent, it assures adequate oxygenation, and is often prescribed to increase oxygenation.

Indications for CPAP.

• Hypoxemia that is refractory to high concentrations of oxygen by other means. 
• Obstructive Sleep Apnea to prevent the upper airway from collapsing 

Adjusting CPAP settings. CPAP is increased or decreased to maintain a desired SpO2, which is usually greater than 90% SpO2 and 60 PaO2.

BiPAP: This is an acronym for Bi-level (or Biphasic) Positive Airway Pressure. It provides a combination of both IPAP and EPAP.

• IPAP. This is Inspiratory Positive Airway Pressure. It is a pressure during inspiration that assists a patient obtain an adequate tidal volume. Because it provides assistance with inhalation, it therefore decreases the work of breathing required to get air in. Because it assures adequate ventilation, it is often prescribed to blow off carbon dioxide (CO2). 
• EPAP. This is Expiratory Positive Airway Pressure. It is the same thing as CPAP. EPAP is simply used here so you know your talking about CPAP on a BiPAP machine. EPAP is used to improve oxygenation.

Indications for BiPAP.

• Respiratory Failure due to accessory muscles fatigue. It assures adequate ventilation to blow off CO2 and improve oxygenation. 
• COPD to decrease airway resistance, thereby decreasing work of breathing required to take in an adequate tidal volume. By increasing ventilations, it helps to blow off CO2. It also keeps airways patent to improve oxygenation. 
• Pulmonary Edema to help decrease cardiac output which decreases venous return to the right ventricle to reduce blood return to the heart. It also keeps airways patent to help improve oxygenation. It also helps keep alveoli patent to improve oxygenation (prevents alveolar collapse). By keeping alveoli patent, and redistributing alveolar fluid, it helps to reduce pulmonary compliance and reduce work of breathing. 
• Atelectasis to help keep airways patent to improve oxygenation 
• Pulmonary Embolis to improve oxygenation 
• Pneumonia to assure adequate ventilations and oxygenation

Adjusting BiPAP settings. As a rule of thumb, the following rules are true.

IPAP. Increase to blow off CO2. It should not be higher than 20 to prevent pressure from blocking the esophagus. By providing adequate tidal volumes it may also help improve oxygenation.

EPAP. Increase to improve oxygenation.

PS. Pressure Support. This is the gap between IPAP and EPAP. The greater the PS is the more CO2 will be blown off.

Patient Leak. It is important to have a small leak to prevent skin breakdown. Most modern machines will compensate for a small leak.

Alarms. Adjusted as appropriate for each patient.

Contraindications for BiPAP include.

• Inability of patient to protect own airway (decreased level of consciousness). This includes the inability of the patient to pull off the mask if it becomes full of fluid, such as vomit or spit. 
• Increased secretions (i.e. pulmonary edema, increased sputum production) 
• Any patient at risk of vomiting (post stomach surgery, drug overdose). In this case you may be able to use BiPAP if an NG is inserted. Most machines will compensate just fine for the leak around the tube. 
• Bullous lung disease (emphysema) because the high pressure may cause a pneumothorax 
• Pneumothorax may be complication due to increased pressure;;may blow out rest of good lung 
• Hypotension; High pressures decrease cardiac output 
• Non-compliant patient. Surely you cannot force a patient to use this equipment. 

Study Results. Studies show that the use of NIPPV for respiratory failure in COPD patients results in a greater reduction in CO2 and a normalization of pH, compared to those in the control group who did not use NIPPV. A study also showed those receiving conventional therapy were intubated 67% of the time, while those receiving NIPPV were intubated only 9% of the time. This prevents the complications of mechanical ventilation, particularly the difficulty associated with extubating patients with lung disease.

Studies also show that length of stay in a hospital is reduced among the COPD pupulation using NIPPV. NIPPV may also be used on the medical/ surgical floors, reducing cost. However, those in severe respiratory failure may still require a stay in the critical care unit.

Studies also show that most patients, or about 80%, tolerate NIPPV just fine. (see references #3 and 4 below).

Bottom Line. Non-Invasive Positive Pressure Ventilation machines are ideal for many patients to improve oxygenation and ventilation. They have prevented many critical patients from having to go through the invasive procedure of intubation and mechanical ventilation. They are also useful to assure adequate ventilation and oxygenation in the home setting, especially during the nighttime when breathing seems to be more relaxed.

This post was originally published on 8/4/8 on respiratorytherapycave.blogspot.com; it has been edited for accuracy.

Further Reading.

• Good start settings for BiPAP
• My interview with Roxlyn Cole, A COPD patient who uses BiPAP at night
• Study: Non-Invasive Positive Pressure Ventilation For Acute Respiratory Failure
• Barnes, Peter J., et al, editor, "Asthma and COPD: Basic Mechanisms and Clinical Management," 2nd edition, 2009, page 842 
• Non-Invasive Positive Pressure Ventilation (CPAP or BiPAP NPPV) for Cardiogenic Pulmonary Edema
• 17 Biggest Myths of Respiratory Therapy

NIV proven useful for COPD, CHF, yet failure rates still high

Noninvasive ventilation (NIV), either in the form of Noninvasive Positive Pressure Ventilation (NPPV) or Continuous Positive Airway Pressure (CPAP), has been used in the critical care setting since the end of the 1980s, and is now commonly used in both Europe and the United States for the treatment of COPD exacerbatons and heart failure.

Studies also show that NIV may significantly decrease work of breathing, either by improving minute ventilation (COPD) or by decreasing venous return to the heart (CHF), and thereby reducing the need for intubation to 15% (although it is as high as 38% in patients with chronic respiratory disease).

However, despite it being so commonly used, and despite all the advancements in technology and equipment that have improved patient comfort, studies continue to show that anywhere from 20-30% of patients fail.  Of the patients who fail, 30-40% require intubation and mechanical ventilation.

A good indication of failure, or a good predictor of who will fail, is hypercapnia after initiation of NIV.

Contou et al, however, concluded that experienced respiratory therapists may make adjustments at the patient interface (mask) or changes in settings that make the experience more comfortable and more effective, thus resulting in a reduction in NIV failure rates to under 15%, thereby reducing mortality rates to 5%.

Contou et al also showed that, by using an NIV protocol and having the patient closely monitored in by experienced personnel, including a nurse and respiratory therapist, 48% of patients who were semi-comatose responded well to NIV therapy without the need for intubation.

The study shows that trialing patients on NIV in an experienced unit where the patient was closely monitored, even those who would otherwise have been intubated, has proven to be effective, thus further reducing the need for intubation.

Likewise, the researchers reported, "it has been shown that NIV failure was not associated with an increased mortality rate in hypercapnic patients; thus, delayed intubation in some patients likely did not worsen their outcome."

The bottom line here is that NIV protocols that allow the nurse and respiratory therapist to closely monitor and adjust the settings on the NIV "might reduce the intubation rate.

References:

1. Contou, Damien, Chiara Fragnoli, Ana cordoba-Izquierdo, Florence Boissier, Christan Brun-Buisson, and Arnaud W. Thille, "Noninvasive Ventilation for Acute Hypercapnic Respiratory Failure:  Intubation Rate in an Experienced Unit," Respiratory Care, December, 2013, volume 58, number 12, pages 2045-2052

Oxygenating with home BiPAP and CPAP machines

When using a ventilator, either for mechanical ventilation or noninvasive ventilation, a fixed FiO2 is set during ventilatory support. This is the best way of supplying supplemental oxygen to patients, especially because it may be adjusted to maintain a desired saturation.

However, when using a patient's home noninvasive ventilation equipment, either set up for BiPAP or CPAP, oxygen is typically placed directly into the circuit using a constant flow.  When this occurs, the amount of oxygen actually inhaled depends on a variety of factors:

• Oxygen flow
• Leakage
• Circuit
• Interface (face mask, nasal mask, etc.)
• Location of where oxygen is bleed into the system

Studies are still inconclusive as to where the best place to insert the oxygen into the system.  Some therapists place it near the machine, while others place it near the patient interface.  Ideally, the oxygen flow should be adjusted to maintain a desired Spo2.  This may be important for patients who are using their home units in the hospital setting.  

For patients who present in acute respiratory failure, when adequate oxygenation is not obtained with a patient's home unit, a ventilator (which may include a noninvasive ventilation device such as a Vision or V60) should be used in order to deliver a fixed FiO2 that can be easily adjusted to maintain an adequate SpO2.

References:

1. Storre, Jan H, Sophie E. Huttmann, Emelie Ekkernkamp, Stephan Wlterspacher, Claudia Schmoor, Michael Dreher, and Wolfram Windisch, "Oxygen Supplementation in Noninvnasive Home Mechanical Ventilation: The Crucial Roles of CO2 Exhalation Systems and Leakages," Respiratory Care, January, 2014, volume 59, number 1, pages 113-119

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Non-invasive ventilation with humidification: the latest evidence

There continues to be a debate as to the effectiveness of applying humidification to noninvasive ventilation (NIV). Some argue that humidification is not indicated because, regardless of the type of mask used (oronasal, nasal, nasal plugs, face mask), air will be humidified by the patient's natural mechanism.  Yet the crux of the evidence says this is not true, and that supplemental humidification is essential.

The last evidence appears in the January, 2014, issue of Respiratory Care, "Hygrometric properties of inspired gas and oral dryness in patients with acute respiratory failure during noninvasive ventilation."  The authors note the following:

Especially when the NIV ventilator uses unhumidified gas, the upper airway can suffer mucosal dryness and airway dysfunction.  The leak compensation applied by NIV ventilators creates high flow throughout the respiratory cycle, which contributes to loss of heat and moisture. About 40-60% of nasal CPAP users with obstructive sleep apnea report nasal congestion, oral dryness, and throat soreness after breahing dry, cold gases.  

They go on to say:

Lack of humidification during NIV is related to greater mucus viscosity and secretion retention, which increases the risk of upper airway obstruction.  Although there are no general recommendations or guidelines conserning humidification during NIV, humidifying devides are commonly applied when NIV continues for more than 24 hours, if pipeline or cycling gas is in the inspiratory gas, or if the patient frequently experiences difficulty in expelling secretions or reports dryness and discomfort."

The authors note the advantages of adding humidification with NIV is that is that it "adds water vapor to the inspiratory gas during NIV," and this, "ameliorates nasal congestion, and improves satisfaction."

There are presently no guideliness for the use of humidification with NIV, although most hospitals have an unwritten rule to apply it to the unit if a patient requires NIV for greater than 24 hours.  While there is no proven ideal temperature, most experts recommend 31° in the heated humidifier and 34° at the Y-piece.

After performing a study of ICU patients of Tokushima University Hospital to determine the effects of humidification on 16 patients (9 male and 7 female) in acute respiratory failure requiring NIV, the authors concluded:

Clinicians should ensure that proper humidification is supplied when patients complain of oral dryness or when little condensation is observed inside the mask.

Keep in mind here that this is one study with analysis by one group of researchers.  Although other studies have come to similar conclusions.  Consider the following:

1. Holland et all concluded that "NPPV delivers air with a low relative humidity, especially with high inspiratory pressure. Addition of a heated humidifier increases the relative and absolute humidity to levels acceptable for nonintubated patients, with minimal effect on delivered pressure. Consideration should be given to heated humidification during NPPV, especially when airway drying and secretion retention are of concern.
2. Rodriquez et al found that heated humidifiers were more effective than a heat and moisture exhchanger (HME)

So, the evidence is abounding that patients who receive NPPV do benefit from heated humidity.  

References:

1. Oto, Jun, Emiko Nakataki, Nao Okuda, Mutsuo Onodera, Hideaki Imanaka, and Masaji Nishimura, ""Hygrometric properties of inspired gas and oral dryness in patients with acute respiratory failure during noninvasive ventilation." Respiratory Care, January, 2014, volume 59, Number 1, pages 39-45
2. Holland, A.E., L. Denehy, C.A. Buchan, J.W. Wilson, "Efficacy of a heated passover humidifier during noninvasive ventilation: a bench study," Respiratory Care, January, 2007, 52(1), pages 38-44, accessed 5/18/14, http://www.ncbi.nlm.nih.gov/pubmed/17194316
3. Rodrigues, Antonia M., Raffaele Scala, Arie Soroksky, Ahmed BaHammam, Alan de Klerk, Arschang Valipour, Davide Chiumello, Claude Martin, and Anne E. Holland, "
   Clinical review: Humidifiers during non-invasive ventilation - key topics and practical implications," Critical Care, 2011, Volume 16, Issue 1, accessed 4/18/14, http://ccforum.com/content/16/1/203

How does NIV help with CHF?

There have been a few physicians who have explained to me that noninvasive ventilation helps patients with congestive heart failure (CHF), or pulmonary edema, because it forces fluid out of the lungs.  But this is a myth.

The true value of NIV for CHF is best described by Jeffrey Sankoff, MD, from Emergency Physicians: 

Contrary to popular belief, NIMV does NOT push edema fluid out of the lungs. Patients with acute CHF have an imbalance in the CO (cardiac output) of the right and left sides of the heart. With the inciting event (detailed above) the left ventricle becomes compromised but the right ventricle usually does not. So the right ventricle continues to pump forward a normal volume of blood but the left ventricle becomes unable to keep pace. Fluid backs up into the lungs resulting in capillary leak and pulmonary edema. With NIMV, the resultant positive intra-thoracic pressure decreases venous return (blood flowing back to the heart). This reduces right-sided CO to a level that the left heart can equal or even exceed. Fluid ceases to back up and will even begin to be reabsorbed as left ventricular CO improves. Pulmonary edema ceases to worsen and may even diminish, often rapidly.

I think it's essential to understand this, because I have also had physicians place patients on NIV with the hope that it would help with their breathing, but also that it might improve their blood pressure.  The truth is, however, the low blood pressure is a contraindication for NIV, and now you know why.

What are the advantages of NIV?

Sometimes there is confusion regarding the advantages of NIV, otherwise referred to as BiPAP. I have had doctors order it because it "forces fluid out of the lungs" in heart failure, and because it "increases blood pressure." Yet neither of these are actual benefits of NIV. That said, what are the benefits of NIV? The are:

1. IPAP increases ventilation and helps to blow off CO2 
2. CPAP increases FRC and therefore keeps the lungs open so the next breath comes in easier
3. Both IPAP and CPAP help to reduce work of breathing
4. Both the IPAP and CPAP help reduce work of heart

So, how does BiPAP reduce work of heart because the increased intrathoracic pressure decreases preload to the heart, thereby decreasing cardiac output, and thereby decreasing blood pressure.  In this way, it helps to decrease the patients work of heart.  That is how it helps with heart failure.  It does not force fluid out of the lungs. It does not increase blood pressure.

Indications and contraindications for NIV

Noninvasive ventilation (NIV) is commonly ordered, and in many cases allows an opportunity for a patient to recover in lieu of intubation and mechanical ventilation. 

According to the National Institute of Health, the following are the indications:

• Acute respiratory failure 
• Acute or chronic respiratory insufficiency 
• Documented sleep apnea

However nice NIV is, there are times when it is contraindicated.  It is up to the respiratory therapists to remind the attending physicians of these contraindications when they arise.  

Contraindications for NIV are

• Absence of a drive to breathe
• Inability to maintain a patent airway
• Inability to adequately clear secretions 
• Acute sinusitis or otitis media 
• Risk for aspiration of gastric contents 
• Hypotension (NIV may decrease cardiac output, decrease venous return)
• Pre-existing pneumothroax or pneumomediastinum 
• Epistaxis 
• Recent facial, oral or skull surgery or trauma 
• History of allergy or sensitivity to mask materials where the risk from allergic reaction outweighs the benefit of ventilatory assistance