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