Noninvasive Methods of Ventilator Support Case File
Eugene C. Toy, MD, Manuel Suarez, MD, FACCP, Terrence H. Liu, MD, MPH
Case 12:
A 75-year-old man is admitted to the ICU for exacerbation of chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF). The patient experienced retrosternal chest pain lasting 4 minutes, which was relieved by 1 sublingual nitroglycerin tablet 1/150 mg. On initial physical examination, the respiratory rate is 35 breaths/minute, heart rate 123 beats/minute with a regular rhythm, and blood pressure 189/98 mm Hg. Rales and scattered wheezing are heard in the bilateral lung bases. There is a fixed split second heart sound (S2) and a third heart sound (S3) gallop present. The lower extremities show 2+ pitting edema. A chest x-ray (CXR) reveals a CHF pattern and cardiomegaly as well as hyperinflation and COPD changes, without acute infiltrates. Arterial blood gas (ABG) shows a pH of 7.45, PACO2 of 35 mm Hg, and PAO2 of 100 mm Hg on 100% F1O2. The β natriuretic peptide (BNP) level is 1000 pg/mL (normal <100) and troponin I cardiac enzyme level is 5 ng/mL (normal <0.5).
⯈What is the next best step in managing this patient's respiratory status?
⯈What other treatment options should also be considered concurrently?
ANSWER TO CASE 12:
Noninvasive Methods of Ventilator Support
Summary: This 75 -year-old man is in obvious respiratory distress from pulmonary edema after an acute myocardial infarction.
- Next step in management: This patient is in need of ventilatory support, and bi-level positive airway (BiPAP) is an ideal choice since the patient has COPD, acute cardiogenic pulmonary edema (ACPE), and CHF. BiPAP can be started at 10 cm H2O of inspiratory positive airway pressure (IPAP) and 5 cm H2O of expiratory positive airway pressure (EPAP)/PEEP with 100% FIO2.
- Other considerations: Other interventions should be directed at improving cardiac perfusion and improving cardiac output: intravenous angiotensin converting enzyme inhibitors (ACE), IV nitrate therapy for coronary vasodilation relief of chest pain and as preload-reducing agent all improve CO. Diuresis with loop diuretics like furosemide, inhaled β2 agonists, and ipratropium bromide plus IV corticosteroids are also indicated.
ANALYSIS
Objectives
- To be familiar with noninvasive methods of ventilatory support (NIV) .
- To learn the indications for the use o f noninvasive methods o f ventilatory support.
- To understand and know the settings for noninvasive methods of ventilatory support.
- To understand how to wean the patient from noninvasive methods of ventilatory support.
Considerations
This is a 75 -year-old patient with COPD and acute pulmonary edema due to myocardial infarction. The best approach to this awake and cooperative patient is to initially use NIV to relieve the respiratory failure caused by the pulmonary edema. Respiratory failure increases the work of breathing; accordingly, the respiratory related cardiac output needs is increased from 1 % to > 20% of the total cardiac output. If not treated quickly, RSI and MV may be required. NIV is indicated in this patient to alleviate the increased work of breathing; give O2 and bronchodilators. If improvement is not rapidly seen after NIV use, intubation and mechanical ventilation should not be delayed. BiPAP NIV serves to decrease the work of breathing, decrease anxiety, and improve the status of the pulmonary edema by decreasing cardiac and pulmonary preload and venous return to the right ventricle. NIV can avoid the need for invasive rapid-sequence intubation. NIV decreases both preload and afterload, thereby improving cardiac output.
Approach To:
Noninvasive Ventilatory Support
INTRODUCTION
NIV is an effective treatment for 2 main diseases: (1) exacerbations of COPD and (2) exacerbations of CHF. Successful use of NIV avoids the higher risk of ETI and MV. Positive pressure increases intrathoracic pressure and decreases venous return, causing a decreasing preload and acting as immediate treatment of the CHF. The application of pressure support ventilation (PSV) in an NIV delivers relief from respiratory distress by improving ventilation and oxygenation. Oxygenation occurs by diffusion while the exchange of CO2 requires changes in ventilation. NIV use may also reduce mortality in these diseases. BiPAP is the most common mode of NIV. It delivers a preset amount of IPAP and EPAP. The difference between the IPAP and EPAP is the actual PSV provided to the patient.
INITIAL INTERVENTIONS
Supplemental oxygen is used to deliver the desired FIO2 with PSY via a tight-fitting facemask. This has become the predominant method of providing NIV. Successful NIV support leads to a decrease in respiratory rate (RR) , increase in tidal volume (Vt) , and decrease in dyspnea. Other improved measures include decreased diaphragmatic electromyography (EMG) , transdiaphragmatic pressures, hypercapnia, and work of breathing. NIV is achieved through a variety of interfaces such as mouthpieces, nasal masks, facemasks, even a helmet mask, with the facemask being the most common. These aids are used with a variety of NIV modes such as volume ventilation (VV), pressure support (PS) , BiPAP, proportional assist ventilation (PAV), continuous positive airway pressure (CPAP) either with ventilators dedicated to NIV or standard mechanical ventilators fitted to these masks.
NIV support has markedly increased over the past 2 decades, and has become an integral tool in the management of both acute and chronic respiratory failure in the acute care, critical care, and chronic care settings. NIV has been used as a replacement for invasive ventilation.
INDICATIONS FOR NIV
Selection of patients for NIV must be considered carefully. Respiratory failure due to acute cardiogenic pulmonary edema (ACPE) CHF and COPD are the principal indications, since respiratory failure in these settings is rapidly reversible. NIV is an ideal adjunct in the management of the respiratory distress in these conditions.
Patient Inclusion Criteria
- Spontaneously breathing cooperative patient
- Dyspnea is moderate to severe, but short of respiratory failure
- Tachypnea ( >24 breaths/minute)
- Increased work of breathing ( accessory muscle use, pursed-lips breathing)
- Hypercapnic respiratory acidosis (pH range 7.10-7.35 ) ( PACO2 >42 mm Hg)
- Hypoxemia (PAO2/FIO2 < 200 mm Hg, PAO2 < 60 mm Hg on room air)
The 2 most suitable clinical conditions for NIV are chronic obstructive pulmonary disease and cardiogenic pulmonary edema. Some other conditions that also respond to noninvasive ventilation are noted in Table 12-1. Patient exclusion criteria are principally mild disease or very severe distress.
Application of Noninvasive Ventilation
The experience and expertise of health-care providers, specifically nursing and respiratory therapy staff, cannot be underestimated. NIV implementation is dependent on the staff learning curve and the time demands of nursing and respiratory therapy (Table 12-2) . Another important consideration is the potential for delay in definitive therapy.
Patient lnterfaces and Mask Devices
NIV differs from invasive ventilation by nature of the interface between the patient and the ventilator. Invasive ventilatory support is provided via either an ETT or tracheostomy tube. NIV support uses a variety of interfaces, and these have continued
to evolve with modifications based on patient comfort and efficacy. Nasal masks and orofacial masks were the earliest interfaces, followed by the subsequent development and use of full-face masks, mouthpieces, and nasal pillows. Nasal masks and orofacial masks are still the most commonly used devices. Orofacial masks are used almost twice as frequently as nasal masks.
Proper fitting of the mask is a key component to successful NIV. The mask should be held in place without straps first by the therapist to familiarize the patient with the mask and the ventilator. Typically, the smallest mask providing a proper fit is the most effective. Straps hold the mask in place. Leaking masks are the biggest problem in the use of all masks. Care must be taken to minimize excess pressure on the face or nose, which would otherwise create pressure ulcers. Excess pressure increases the risk of pressure necrosis and skin breakdown. Any cuff used in these interfaces should be kept below 25 mm Hg to prevent tissue necrosis. The main considerations regarding the choice of an orofacial mask or nasal mask are outlined in Tables 12-3 and 12-4.
Ventilators Used in NIV Support
Ventilator options providing NIV have continued to increase. The specialty ventilators have fewer options and range, but are more leak tolerant. Many critical care ventilators currently in use also have an NIV option, either as part of the original device or available as an upgrade option. Selection of the ideal device is dependent on a number of factors, including familiarity of the staff with the equipment chosen and the availability of alternative options. Many hospitals continue to provide noninvasive support with the specialty ventilator.
Modes of Noninvasive Ventilation
Most patients treated with NIV receive PSV, with CPAP, which is the most basic level of support. BiPAP is the most common mode of support and requires provision
and control in the amount of both IPAP and EPAP. The difference between IPAP and EPAP is the amount of pressure support provided to the patient by the ventilator. EPAP is equivalent to positive end-expiratory pressure (PEEP) . While volume ventilators can be used to provide NIV support, the previously described dedicated models are the best. Less sedation is needed because of increased patient comfort with the use of NIV.
Initial Ventilator Settings and Adjustments
The primary goals of NIV are: (1) adequate ventilation and oxygenation, (2) correction of respiratory failure, and (3) an acceptable level of patient tolerance and comfort. Adjustments are often necessary to achieve these endpoints. The initial settings should focus on achieving adequate tidal volumes, usually in the range of 5 to 7 mL/kg. Additional support is provided to reduce the respiratory rate to be <25 breaths/minute. FIO2 is adjusted to achieve adequate oxygenation with a pulse oximetry level of 90% to 92%. Serial ABG measurements are essential to monitor the response to therapy and guide further adjustments.
lnitial IPAP/EPAP Settings
Start at 10 cm H2O IPAP/5 cm H2O EPAP, pressures < 8 cm H2O IPAP/4 cm H2O EPAP are not advised as this may be inadequate, make adjustments to achieve tidal volume of 5 to 7 mL/kg (IPAP and/or EPAP).
Subsequent Adjustments Based on Arterial Blood Gas Values
- Increase IPAP by 2 cm H2O if persistent hypercapnia exists.
- Increase IPAP and EPAP by 2 cm H2O if persistent hypoxemia exists.
- IPAP limited to 20 to 25 cm H2O ( avoids gastric distension, improves patient comfort) .
- Maximal EPAP should b e limited to 10 to 15 cm H2O.
- Begin FIO2 of 100% and adjust to the lowest level with an acceptable pulse oximetry value.
- Back up the respiratory rate to 12 to 16 breaths/minute.
Predictors of success include a good response to a trial of NIV for 1 to 2 hours with a decrease in PACO2 >8 mm Hg from baseline and an improvement in pH >0.06 units. Predictors of failure include an increased severity of illness and acidosis (pH < 7.25 ) especially if due to hypercapnia ( PACO2 >80 ) . Certain patients may benefit from a trial of NIV, limiting the duration of trials is important to avoid delays in definitive therapy. NIV trials may be as short as a few minutes in patients with immediate failure and probably should not exceed 2 hours if patients fail to improve. Follow intubation criteria when NIV fails. It is important to use the following guidelines to assist in the decision of when to intubate a patient.
COMPLICATIONS OF NIV
Complications common to both NIV and invasive ventilation occur less frequently in patients undergoing NIV. When compared to CPAP, BiPAP has less morbidity, lower mortality, fewer adverse events, and lower medical utilization in adults with COPD and acute respiratory failure. NIV is also effective in the perioperative and post transplantation settings. Facial and nasal pressure sores and air leaks are the main complications of NIV. This pressure can be minimized by intermittent NIV application at scheduled breaks of 30 to 90 minutes. Rebalancing of strap tension to minimize mask leaks without excessive mask pressures is also helpful. Early wound care is important. Gastric distension can be avoided by limiting peak inspiratory pressures to <25 cm of H2O. Nasogastric tubes can be placed but can increase leaks from the mask. The use of nasogastric tubes also bypasses the lower esophageal sphincter and permits reflux to occur with more ease. Aspiration of gastric contents especially with emesis during NIV can also occur. NIV should be avoided in patients with ongoing emesis or hematemesis.
Barotrauma complicates both NIV and invasive ventilation, but occurs less frequently with NIV. Hypotension related to increased positive intrathoracic pressure can be reversed with increased intravenous fluids. Sedatives were used in <15 % of NIV patients. It is used extensively in Europe ( >80% of ICU patients ). Current NIV practice guidelines suggest an increase in the usage of NIV because of the increased use of protocol, which avoids the costs of endotracheal intubation and mechanical ventilation, provides shorter ICU and hospital stays, and eliminates costs associated with infectious complications. Episodes of ventilator-associated pneumonia are reduced by half or more when NIV is used.
CONCLUSIONS
COPD is the most suitable condition for NIV. It is most effective in patients with moderate to severe disease. Those with hypercapneic respiratory acidosis are generally the best responders (pH 7.20-7.30) . CPAP and BiPAP modalities are effective, with CPAP possibly being more effective. The greatest benefits are realized in the relief of symptoms and dyspnea. A decrease in intubation and mortality rates is not a universal experience. NIV is effective as a bridge support to freely breathing patients after early extubation. Patients with underlying COPD are most likely to benefit from this modality after early extubation. NIV has not shown benefit in patients with community-acquired pneumonia (CAP ). Secretions may be a limiting factor to the use of NIV.
NIV is effective in patients with muscular dystrophy, kyphoscoliosis, and postpolio syndrome, as well as in cases of obesity-hypoventilation or obstructive sleep apnea (OSA ). In OSA, NIV corrects hypercapnia, facilitates diuresis, and provides an opportunity for restorative sleep. NIV should be used carefully in cases of partial upper airway obstruction, but an even greater caution should be used if a potential for complete obstruction exists. NIV is also used during invasive procedures such as bronchoscopy, percutaneous gastrostomy.
CLINICAL CASE CORRELATION
- See also Case 8 (Airway Management/Respiratory Failure), Case 9 (Ventila, tor Management), Case 10 (Respiratory Weaning), and Case 11 (Asthmatic Exacerbation).
COMPREHENSION QUESTIONS
12.1 NIV is started on a 72-year-old man who presents to the emergency department with a non-ST-segment elevation myocardial infarction and acute onset of pulmonary edema. He has a medical history of chronic obstructive pulmonary disease with a 40 pack per year history of cigarette smoking. He complains of air hunger and is breathing at 30 breaths/minute with pursed lip breathing and accessory muscle use. His heart rate is 120 beats/minute and regular. His blood pressure is 140/80 mm Hg and he has a temperature of 98°F. His oxygen saturation is 90% while breathing on 1 L of oxygen via nasal cannula. He is awake and cooperative and free of chest pain on a nitroglycerin drip. What initial treatment with noninvasive ventilation would be best for this patient ?
A. BiPAP at a pressure of 10 cm H2O IPAP and 5 cm H2O of EPAP
B. Intermittent positive pressure breathing
C. CPAP at 5 cm H2O
D. Nasal CPAP
E. CPAP at 35 cm H2O
12.2 A 35-year-old woman has been receiving BiPAP for 2 days because of CAP and an exacerbation of asthma with moderate respiratory distress. On day 3 she is now afebrile, alert, and cooperative; secretions are well controlled, the respiratory rate is 10 breaths/minute, wheezing cannot be heard, and breath sounds are normal. There is no use of accessory muscles while breathing. The O2 saturation reads 95% on the current settings of 8 cm H2O IPAP and 4 cm H2O EPAP with an FIO2 of 30%. These settings have been decreased from the admission values of 10 cm H2O IPAP and 5 cm H2O EPAP with an FIO2 of 50%. What should be the next best step in the use of BiPAP in this patient?
A. Continue present BiPAP settings.
B. Stop BiPAP and observe the patient closely.
C. Further decrease the IPAP and EPAP.
D. Switch to CPAP.
E. Apply BiPAP use for nighttime use only.
ANSWERS TO QUESTIONS
12.1 A. When a patient has respiratory distress especially if caused by COPD or cardiogenic pulmonary edema (CPE) the application of NIV is the treatment of choice. Delivery of NIV would be best accomplished by the use of BiPAP at minimum starting level of 10 cm H2O of iPAP, and 5 cm H2O of EPAP with an appropriate oxygen concentration (FIO2) for acceptable ABG. This provides a PEEP of 5 cm H2O or the same as the EPAP and a net pressure support of 5 cm H2O, the difference between IPAP and EPAP. The maximum numbers that are usually effective are 15 IPAP, 8 EPAP, and minimum numbers of support during weaning off BiPAP 8 IPAP and 4 EPAP.
12.2 B. An improving clinical picture with the use of NIV should lead to a trial discontinuation of the NIV. The improvement and stability of the patient's condition would suggest the discontinuation of the NIV and a continued clinical evaluation of the patient. The blood gases are acceptable with BiPAP settings at the minimum recommended pressures of 8 IPAP and 4 EPAP. Follow the patient closely after extubation but with continuous ECG/O2 saturation monitoring. Use ABGs as needed. Being on the minimum BiPAP settings is equivalent to a spontaneous breathing trial and a successful respiratory stress test. Do not prolong these trials since in some cases they may lead to fatigue and failure. Liberate the patient from NIV once the patient shows she can breathe on her own.
CLINICAL PEARLS
⯈ NIV is best used for patients with moderate exacerbations of chronic obstructive pulmonary disease and/or cardiogenic pulmonary edema.
⯈ Nasal masks and orofacial masks are the most commonly used NIV interfaces, with orofacial masks more commonly used in the acute setting.
⯈ BiPAP is the most commonly used NIV.
⯈ NIV works best in patients in moderate distress, is less useful in severe or mild conditions, and should be avoided in patients with decreased mental status.
⯈ The complications of NIV are similar to but occur less often than associated with invasive (intubated) mechanical ventilation.
⯈ Rates of intubation and mechanical ventilation have decreased with the increased use of NIV.
References
Bordow RA, Ries AL, Morris TA. Manual of Clinical Problems in Pulmonary Medicine . Philadephia: Lipp incott Williams and Wilkins, 6th ed. , 2005 .
Rabe KF, Hurd S, Anzueto A, et al. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease: GOLD executive summary. Am ] Respir Crit Care Med . 2007 ; 1 7 6 ( 6 ) : 5 3 2 -5 5 5 .
Tobin MJ , ed. Principles and Practice of Mechanical Ventilation. 2nd ed. New York, NY: McGraw-Hill; 2006 : 1 442; ISBN : 9 78-0-07 - 1 44767-6.
Toy EC, Simon B, Takenaka L, Liu T, Rosh A. Case Files Emergency Medicine. 2nd ed. McGraw-Hill Medical, 2009.
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