Non-Invasive Mechanical Ventilation
For inpatients with acute respiratory distress, there are alternatives to intubation in certain situations. Non-invasive positive pressure ventilation (NPPV) is a form of mechanical ventilation that does not require the placement of an endotrachial tube. It instead relies on close fitting nasal or face masks, delivering positive-pressure to improve gas exchange and reduce work of breathing, augmenting oxygenation and ventilation.
NPPV typically takes one of two forms: CPAP (Continuous Positive Airway Pressure) or BPAP (Bilevel Positive Airway Pressure). CPAP provides a constant pressure, and BPAP employs different pressures on inspiration and expiration. A brief note on terminology: “BPAP” is often mistakenly referred to as “BiPAP®,” which is the brand name of a line of BPAP machines. Hospitalists may be familiar with CPAP and BPAP in non-acute settings. Some patients with obstructive sleep apnea (OSA) or obesity hypoventilation syndrome (OHS) use nocturnal CPAP or BPAP at home. These patients are often continued on CPAP or BPAP when they are admitted to the hospital for non-respiratory issues. Patients often do not know which type of NPPV they use at home, although roughly speaking CPAP is used to maintain upper airway patency in OSA, and BPAP is used to augment ventilation in OHS.
As above, CPAP provides a constant pressure. This raises functional capacity and opens alveoli filled with fluid in patients with pulmonary edema. In addition, by increasing intrathoracic pressure, CPAP can lessen left ventricular transmural pressure and reduce afterload and increase cardiac output. BPAP employs different pressures on inspiration and expiration; a patient-triggered positive pressure “boost” assists inspiration, and on expiration a lower pressure is employed. In addition to improving oxygenation similar to CPAP, the inspiratory boost provided by BPAP decreases work of breathing and increases ventilation.
There is growing literature about the use of NPPV in acute settings to avoid endotrachial intubation. The best results have been seen in chronic obstructive pulmonary disease (COPD) exacerbations and cardiogenic pulmonary edema. A 2004 Cochrane Database review (meta analysis of 14 studies) compared standard therapy alone to NPPV plus standard therapy in patients having a COPD exacerbation complicated by hypercapnia (PaCO2 >45 mmHg). NPPV resulted in decreased mortality (RR 0.52), decreased need for intubation (RR 0.41), reduction in treatment failure (RR 0.48) as well as rapid improvement within the first hour in pH, PaCO2, and respiratory rate. In addition, the NPPV group had fewer complications associated with treatment and had a shorter length of hospital stay.
A 2008 Cochrane Database review (21 studies) compared standard medical care alone to CPAP and/or BPAP plus standard medical care in adult patients with acute or acute-on-chronic cardiogenic pulmonary edema. Compared to standard medical care, NPPV reduced hospital mortality (RR 0.6) and endotracheal intubation (RR 0.53).
There are fewer studies to support the use of NPPV in other causes of respiratory compromise such as pneumonia, asthma, acute respiratory distress syndrome (ARDS), and in immunocompromised patients with pulmonary infiltrates. Larger studies are needed before recommendations can be made.
II. Identify the Goal Behavior.
The hospitalist should be able to 1) identify patients who may benefit from NPPV, 2) recognize contraindications to use, 3) initiate NPPV quickly and safely in an appropriately monitored unit, 4) effectively monitor the patient to trouble-shoot problems, and 5) recognize when NPPV is failing.
III. Describe a Step-by-Step approach/method to this problem.
Step 1: Recognize patients who may benefit from NPPV
Conditions most commonly encountered by the hospitalist where non-invasive positive pressure ventilation might be appropriate include COPD flare and CHF exacerbation. There may also be a role in managing respiratory distress in immunocompromised patients with pulmonary infiltrates. Use in asthma exacerbation has shown some promise, but has not been well studied. Other potential indications for which evidence is less strong include pneumonia, community acquired pneumonia in COPD patients, use in Do-Not-Intubate patients, and symptom palliation in terminally ill patients. Other indications exist for ICU and surgical patients, which will not be covered here.
A key aspect to the safe employment of non-invasive mechanical ventilation is appropriate patient selection. NPPV is typically employed in patients with COPD flare or CHF exacerbation who are experiencing moderate to severe dyspnea, tachypnea (>24 breaths/m in COPD, >30 breaths/m in CHF), with signs of increased work of breathing (accessory muscle use, etc). Laboratory measures such as ABG can also help identify patients that might benefit. Ventilatory compromise (PaCO2 > 45, resp acidosis and pH <7.35), and hypoxemia can help identify candidate patients.
Step 2: Ensure the patient does not have contraindications to NPPV
Equally important is to identify contraindications to use of NPPV. Absolute contraindications include:
Code situations (including respiratory arrest).
NPPV system failures (inability to deliver adequate positive pressure due a poorly fit mask resulting in persistent mask leak – see “Common Pitfalls” for suggestions about mask fit).
Relative contraindications include:
Patients who are unable to protect their airway. This is often an independent indication for placement of an ET tube given the high risk of aspiration in this population.
Patient with weak cough, impaired swallowing, and/or difficulty clearing their secretions. While not an absolute contraindication, great care should be taken when using NPPV in these patients, as the risk of aspiration can increase in the setting of NPPV (mask and positive pressure makes it more difficult to expel secretions).
Actively vomiting/upper GI bleeding patient. This group is also at high risk for aspiration.
Severe community acquired PNA. Unless secretions are minimal or patients can easily clear their own secretions, care should be taken in this population.
Patients with decreased responsiveness. This group may have difficulty protecting their airway, so caution should be exercised. An exception is the patient suffering from decreased responsiveness in the setting of elevated pCO2, since NPPV can correct the acidosis quickly and improve mental status.
Agitated/uncooperative patients (may not tolerate the mask).
Medically unstable patients (hemodynamically unstable, multiorgan failure). This group may benefit from more secure airway control.
Patients with recent upper airway or upper GI surgery. Positive pressure may compromise surgical sites.
Step 3: Initiate NPPV
If a patient is deemed appropriate for NPPV, it is advisable to begin therapy as soon as possible, since delays in initiation may result in clinical worsening, and a patient who would previously have been a good candidate may no longer be appropriate.
Suggested steps to initiating NPPV are as follows:
Alert the patient to the plan to initiate NPPV.
Discuss the plan with nursing staff (and respiratory staff, if available). Some hospitals are able to provide NPPV on the general medical floors. In other hospitals, patients must be in the ICU where ventilators are kept (many ventilators have an NPPV setting).
Select delivery interface (usually face mask, nasal mask, or nasal prongs). Face masks are often used in the acute setting since they have been shown in some studies to achieve higher minute ventilation and lower PaCO2 than nasal masks (while nasal masks can be more comfortable, the tendency of dyspneic patients to mouth breathe can result in air leak through the mouth, which decreases nasal mask effectiveness).
Select CPAP or BPAP. As above, BPAP is indicated in hypercapnic COPD exacerbation. In CHF exacerbation, CPAP can be used.
Set pressures (start low initially - suggested: pressure support 8 cm H2O and PEEP 4-5 cm H2O).
Place mask over patients face, first holding in place while starting ventilation.
Tighten straps just enough to avoid major leaks, but avoid over tightening.
Adjust oxygen to desired sat goals (88-92% in COPD patients and 90% or higher otherwise).
Adjust pressure support to achieve goal expired tidal volume (6 mL/kg or higher) and raise PEEP to achieve desired oxygen saturation.
Make note of mask fit issues (use dressings or artificial skin to protect sites of mask pressure).
Step 4: Monitor patient
Monitor comfort, respiratory rate, oxygen saturation, and patients' dyspnea symptoms every 30 min for 6 to 12 hours then hourly thereafter. Measure arterial blood gases at baseline and within 1 hour from initiation on NPPV. Weaning from NPPV can occur either through slowly decreasing the positive pressure applied, or by giving “breaks” from NPPV for progressively longer periods.
IV. Common Pitfalls.
Hospitalists should ensure that non-invasive positive pressure ventilation occurs in a unit with adequate staffing and monitoring to ensure that any complications are detected and corrected quickly.
NPPV should not be employed to delay inevitable intubation (unless it provides a bridge to make intubation safer).
One common pitfall is to fail to recognize when NPPV is not working. For hypercapnic respiratory failure, after 1 to 2 hours of NPPV if pH does not change or falls and/or if breathing frequency does not change or rises, then NPPV is unlikely to be successful. For hypoxemic respiratory failure, failure is predicted by minimal or no increase in PaO2 to FiO2 ratio at 1-2 hrs.
A contrasting pitfall is to consider NPPV a failure too early, without attempting maneuvers to correct common problems. Some potential problems and suggested solutions follow:
Patient cannot tolerate mask due to agitation/claustrophobia: Very mild sedation can be attempted, although this should be done cautiously to ensure that somnolence/altered mental status does not become a contraindication to continuing NPPV. Different types of mask interfaces, such as nasal masks, mouthpieces, and nasal pillows are not often practical in the acute setting.
Patient cannot tolerate mask due to mask discomfort:Make sure that the mask is fit correctly. Careful adjustment of the mask straps should use the least amount of tension needed to avoid mask leak. At areas of pressure (often the nasal bridge) foam padding or artificial skin products can be employed to increase comfort.
Gastric insufflation: Gastric insufflation can be uncomfortable for the patient, but is not often so severe to require NPPV termination. Pressures should adjusted to the minimum needed to achieve oxygenation and ventilation goals. Anti-gas medications, such as simethicone, can also help for comfort.
V. National Standards, Core Indicators and Quality Measures.
Core indicators and standards were set by the “International Consensus Conferences in Intensive Care Medicine: non-invasive positive pressure ventilation in acute Respiratory failure.” Organized jointly by the American Thoracic Society, the European Respiratory Society, the European Society of Intensive Care Medicine, and the Société de Réanimation de Langue Française, and approved by ATS Board of Directors, December 2000. Am J Respir Crit Care Med. 2001 Jan;163(1):283-91.
VI. What's the evidence?
Cross, A, Cameron, P, Kierce, M, Ragg, M, Kelly, A. "Non-invasive ventilation in acute respiratory failure: a randomised comparison of continuous positive airway pressure and bi-level positive airway pressure". Emerg Med J. vol. 20. 2003. pp. 531-534.
Evans, T. "International consensus conferences in intensive care medicine: noninvasive positive pressure ventilation in acute respiratory failure". Am J Respir Crit Care Med Vol. vol. 163. 2001. pp. 283-291.
Ferrari, G, Milan, A, Groff, P, Pagnozzi, F, Mazzone, M, Molino, P, Apra, F. "Continuous positive airway pressure vs. pressure support ventilation in acute cardiogenic pulmonary edema: a randomized trial". J Emerg Med. vol. 39. 2010. pp. 676-684.
Keenan, S, Sinuff, T, Burns, K, Muscedere, J, Kutsogiannis, J, Mehta, S. "Clinical practice guidelines for the use of noninvasive positive-pressure ventilationnoninvasive continuous positive airway pressure in the acute care setting". Can Med Assoc J. vol. 183. 2011. pp. E195-E214.
Nava, S, Hill, N. "Non-invasive ventilation in acute respiratory failure". Lancet. vol. 374. 2009. pp. 250-259.
Ram, F, Picot, J, Lightowler, J, Wedzicha, J. "Non-invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease (Review)". Cochrane Database Syst Rev. 2009. pp. 1-72.
Sinuff, T, Cook, D, Randall, J, Allen, C. "Evauation of a practice guideline for noninvasive positive-pressure ventilation for acute respiratory failure". Chest. vol. 123. 2003. pp. 2062-2073.
Vital, F, Saconato, H, Ladeira, M, Sen, A, Hawkes, C, Soares, B, Burns, K, Atallah, Á. "Non-invasive positive pressure ventilation (CPAP or bilevel NPPV) for cardiogenic pulmonary edema (Review)". Cochrane Database Syst Rev:. 2008. pp. 1-113.
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