Oxygen Therapy

The atmosphere contains 20.95% oxygen, the most essential element needed to sustain human life. Oxygen exerts a partial pressure of 159.6 mm Hg at sea level (dry air) and approximately 97 mm Hg (Torr) in arterial blood. The normal range, as measured by arterial blood gas (ABG) analysis, is 80 to 100 mm Hg (Torr). Under normal circumstances, oxygen molecules travel from the atmosphere to the mitochondria at the cellular level, where it is used to produce ATP in a process called aerobic metabolism (oxygen transport mechanisms). The oxygen transport pathway involves the airways and lungs, heart and peripheral vasculature, and the muscle tissue in which the mitochondria reside. Any process that inhibits the transport of oxygen from the atmosphere to the cellular level can cause hypoxemia, decreased patient function, and, ultimately, death.

When oxygen is prescribed, it should be considered a drug. A particular dosage must be ordered by a set prescription. In general, physical therapists do not instruct patients to increase or decrease medication they are taking without a physician’s order. Some practices have standing orders that allow the health care team to change oxygen settings by following a standardized protocol. For example, a prescription may be for 1 L/min of oxygen by nasal cannula at rest titrated up to 6 L/min to keep oxygen saturation above 90%. Although higher-flow oxygen cannulas can deliver increased liter flow, it is more standard in practice to increase titration according to a prescribed protocol.

Patients with cardiovascular and pulmonary impairments frequently need oxygen supplementation.¹ Respiratory care practitioners and the nursing staff are generally responsible for administration of this drug under a physician’s order. Therapists have a variety of methods from which to choose to deliver oxygen in the most effective way (individual methods are discussed later in this chapter). Long-term oxygen therapy for patients with chronic obstructive pulmonary disease (COPD) who are hypoxemic has been reported to improve quality of life and life expectancy.^2–5 However, even though the benefits of long-term oxygen therapy have been established, U.S. congressional mandates for competitive bidding and caps in rental agreement programs have led to cutbacks. As a consequence, the dose of oxygen and its mode of delivery may need to be modified at rest and during activity.⁶ This is an issue of significant concern. As practitioners working with patients requiring oxygen, physical therapists need to advocate for their patients to ensure that they receive appropriate oxygen therapy.

The purpose of oxygen therapy is to treat and prevent hypoxemia, excessive work of breathing, and excessive myocardial work.⁷ Although individual oxygen appliances offer suggested guidelines regarding oxygen administration, the only way to ensure effective delivery from a given device is by blood gas monitoring of PaO₂ (partial pressure of oxygen in the arterial blood) or monitoring hemoglobin saturation by oximetry. Medicare and third-party payers have specific indications for oxygen therapy. These indications may differ and physical therapists need to identify these in the practice setting and provide the documentation required for patients to receive the oxygen they need. Initially, a patient may need oxygen only with higher levels of activity or exercise; that needs to be documented by an exercise test that shows desaturation by oximetry. As a patient’s disease progresses, continuous oxygen may be indicated. Careful monitoring of patients will determine when the need for continuous oxygen occurs. Oxygen therapy is usually administered by one of two methods: low-flow or high-flow systems.

Low-Flow Systems

A low-flow oxygen system is one that is not intended to meet the total oxygen requirements of the patient (does not deliver atmospheric oxygen concentration to the patient). For example, using a normal minute ventilation (minute ventilation = tidal volume [TV] × respiratory rate [RR]) of 8 L/min (500 mL × 16 breaths per minute) with a patient receiving 1 L/min of oxygen, the patient is breathing 8 L/min but the device only provides 1 L/min. Thus 7 L/min are contributed from room air. Each time there is a change in the patient’s breathing pattern, tidal volume, and respiratory rate, the fraction of inspired oxygen (FiO₂) may also change. Ideally, for efficient use of a nasal cannula, the patient should have a normal tidal volume, respiratory rate, and breathing pattern. This is often not the case, but the cannula is used because it is well tolerated by the patient. This method of oxygen delivery is not used when a specific concentration of oxygen is needed.⁸

Nasal Cannulas

The nasal cannulas (also called nasal prongs) are one of the most common low-flow devices encountered because of low expense and high patient compliance (Figure 43-1). This device supplies an FiO₂ of approximately 24% to 40% oxygen with flow rates from 1 L/min to 6 L/min. Flow rates greater than 6 L/min can cause nasal mucosal irritation and drying. The approximate liter flow and resultant FiO₂ values are shown in Table 43-1.

Table 43-1

Approximate Liter Flow and Resultant FiO₂ Values

Flow (L/min)	FiO2 (%)
1	24
2	28
3	32
4	36
5	40
6	44

Adapted from the American College of Sports Medicine: Guidelines for exercise testing and prescription, ed 6, Philadelphia: Lippincott, Williams & Wilkins, 2000.

Nasal cannulas deliver 100% oxygen; however, this percentage significantly lessens as the oxygen mixes with inspired air from the room. The amount of oxygen delivered depends on the flow rate and the ventilatory pattern of the patient. A larger minute volume (TV × RR) would dilute the oxygen at any given flow rate and cause a greater decrease in the percentage delivered to the lungs. In other words, the faster and deeper a patient breathes, the more diluted the oxygen becomes. On the other hand, if a patient has a low minute volume, the oxygen percentage delivered increases.⁷ If precise control of FiO₂ is needed, the nasal cannula should not be used.⁹ In these cases a high-flow system (i.e., a Venturi mask) may be used.

Skin integrity, especially behind the ears, needs to be evaluated because the pressure of the cannula can cause skin breakdown. Patients at times will pull on the cannula or take the oxygen off. It is important to check for skin breakdown behind the ears, especially if patients are not able to communicate.

Mouth-breathing by patients using a nasal cannula typically causes concern from some of the health care team. This concern, however, may be unnecessary. If the nasal passages are unobstructed, then oxygen is able to collect in the oral and nasal cavity (anatomical reservoir). On inspiration, the oxygen collected in this area is drawn into the airways and lungs. If a patient with a nasal cannula is mouth-breathing, the practitioner should ensure the nasal passages are unobstructed. If there is concern that the patient is not receiving adequate oxygen, a blood gas or oxygen saturation measurement should be obtained. If this is not feasible, or if the patient is unable to breathe through the nose, it may be appropriate to switch the patient to a mask.

The patient should be encouraged to breathe through the nose to receive maximum benefit from the nasal cannula; however, mouth breathing does not mean the patient will not receive appropriate oxygen.¹⁰ Clinically, it is found that some patients who mouth-breathe do so because of nasal polyps, sinus congestion, deviated septum, or other physical issues. If the work of breathing is increased when the patient tries to breathe through the nose, it may be counterproductive.

Nonrebreathing Mask

Another low-flow delivery device, the nonrebreathing mask, also contains a bag reservoir, but it can deliver up to 100% oxygen. This mask has valves on the reservoir bag and side vents. This feature prevents ambient air mixing on inspiration and exhaled air mixing on expiration. For this mask to operate effectively, a good seal between the patient’s face and the mask must be achieved. The bag should partially deflate during inspiration (Figure 43-2).

High-Flow Systems

A high-flow oxygen delivery system delivers a specific oxygen concentration (FiO₂) despite the patient’s ventilatory pattern. This system delivers atmospheric oxygen pressure to the patient, which means that the entire volume that is breathed is delivered through the device. A patient requires oxygen delivered at specific FiO₂ of 50% to keep the arterial oxygen and oxygen saturation at a safe level, then a high-flow system is the method of choice. If a patient has CO₂ retention and a hypoxic drive to breathe, a high-flow system with an exact FiO₂ can be used. This is often the case when a patient with COPD who is a CO₂ retainer has pneumonia and goes into respiratory failure. The physician wants to provide adequate oxygen to the patient and avoid having to mechanically ventilate. The ideal choice would be a high-flow device at a lower FiO₂ to prevent CO₂ retention while not reducing the hypoxic drive to breathe. Unfortunately, patient tolerance of the high-flow oxygen-delivery mask, which covers both the nose and mouth, is often less than optimal. Patients who are acutely ill and very dyspneic or those who have decreased cognitive awareness may tolerate the mask, but as these patients begin to improve, they may have a claustrophobic reaction to the mask and the high flow of gas.

Venturi Mask

The Venturi mask is a common method of delivering high-flow oxygen concentrations from 24% to 50%. This mask operates via the Venturi principle, which provides for a mixing of 100% oxygen and entrained ambient air. The oxygen flows though a narrow orifice at a high velocity, causing a subatmospheric pressure. This drop in pressure is what causes the ambient air to be entrained through a port. The size of the port determines the amount of air that is entrained, thus the percentage of oxygen delivered. The Venturi mask has a rotating air entrainment port that allows the health care provider to “dial in” the desired FiO₂ (Figure 43-3). Flow rates of 40 to 80+ L/min provide minute ventilation at rates that are higher than those the patient could breathe without assistance; consequently, the mask provides the entire inspired atmosphere to the patient. This means that regardless of the patient’s respiratory rate, tidal volume, or breathing pattern, the oxygen delivery (FiO₂) will be consistent.

Mechanical aerosol systems also operate via air entrainment, but the mask is connected to the aerosol unit by large-bore tubing to allow a specific FiO₂ to be delivered with high humidity (Figure 43-4). Although drainage bags are usually attached to the tubing to collect condensation, the tubing must be monitored for possible pooling of water, which causes flow obstruction to the patient. If partial obstruction occurs, a mild back pressure results in the tubing, causing less air entrainment. This means that a higher concentration of oxygen results and potentially a higher dosage of oxygen than desired may be delivered to the patient.

Portable Oxygen

As health care continues to move out of the hospital setting and into the home, more health care practitioners will provide care to patients who require oxygen in their homes. When this is the case, it is essential that a sign be posted about the use of oxygen in the home. Patient teaching before hospital discharge should include a discussion of safety concerns—for example, not cooking with a gas stove, not smoking, and allowing anyone to smoke in the home (or anywhere around the patient). In addition, it must be made clear to the patient that oxygen is considered a prescription medication and thus the amount of oxygen delivered should not be changed unless ordered by the doctor.

Oxygen is most commonly provided in the home for those patients with long-term oxygen needs, usually patients with COPD who are hypoxemic. Generally 1 to 2 L/min is prescribed via nasal cannula, but the flow rate will depend on the patient’s need.

Home oxygen-delivery systems include high-pressure oxygen cylinders, low-pressure liquid oxygen,¹⁸ and oxygen concentrators.⁸ Additional options include continuous flow versus demand or pulsed oxygen delivery.^19–21 There are also a number of oxygen-conserving devices from which to choose.²² When a continuous system is changed to either a demand or pulsed system, or when a new oxygen-conserving device is started, the patient must be monitored carefully. Clinical experience has shown that some patients may not tolerate the same liter flow with a pulsed system, and oximetry and perceived exertion must be evaluated when there is any change in oxygen delivery. The oxygen delivery may not be as effective as a continuous flow device when changing to a pulsed oxygen system. Unfortunately, there is no mandate for clinical testing of the devices before they come to market, so documented effectiveness of one versus another in clinical use is not available.²³

Heliox, a combination of 21% oxygen and 79% helium, has been used in acute care for patients who have upper airway obstruction and increased work of breathing (spontaneously breathing patients, as well as those on a ventilator). However, use of heliox has not been widespread because of its cost, which has been estimated to be 13 times that of oxygen. Heliox for portable oxygen and home use has been documented as effective for patients with asthma and COPD. It has been shown to decrease airway resistance and decrease the work of breathing and has also been effective with patients who have increased mucus secretions. Studies have demonstrated an increase in patients’ ability to exercise using heliox; however, it has not been shown to significantly decrease dyspnea.24–26

High-pressure oxygen tanks are not used as frequently as are low-pressure tanks, but they are used in some settings. High-pressure tanks come in various sizes. The larger ones, such as the H and K sizes, are used as a base unit or reservoir. Long oxygen tubing connected to these tanks allows for patient mobility. Smaller tanks (such as E cylinders) are used for portability and can provide up to 3 hours of use depending on the liter flow of oxygen. Some systems allow for the smaller tank to be refilled by transferring gas from the larger reservoir tank. The primary concern with the high-pressure tanks is guarding them against tipping over. They must be well tied and secured because if a tank tips over or falls, the neck that holds the regulator could break. If this happens, the high pressure inside can propel the tank at a very high velocity, causing damage to surrounding structures and posing a danger to anyone around. The tanks are usually tied to a bed, put in a standard box, or secured on a portable wheeled cart. Thus the high-pressure tanks are difficult to move and maneuver, especially up and down stairs, making their use less than optimal for most patients, especially those who wish to be more active. In terms of cost, the high-pressure tanks are less expensive overall, but deliveries and replacements need to occur regularly.

Liquid oxygen, a low-pressure oxygen delivery method, tends to be more convenient than the high-pressure oxygen tanks, especially for active patients on oxygen. The canisters are lightweight and allow patients to be away from the home reservoir for up to 8 hours. The downside is that liquid oxygen costs more and, with heavy use, the reservoirs may need to be filled up to twice a week. If high flows are needed, these units are not recommended.

Oxygen concentrators are commonly used in the home health setting, especially because Medicare offers coverage for these devices (Figure 43-5). They are electrically powered and create oxygen by drawing ambient air across a semipermeable membrane, separating oxygen from nitrogen. They generally operate at 2 L/min and provide FiO₂ 90% oxygen output. Long oxygen tubing, up to 50 feet, allows patients extra mobility. Patients using concentrators should have a back-up device, such as a portable tank, in case of a power outage. In addition, the electrical power company should be notified of any patient who is using oxygen by concentrator so that the patient’s location is designated as a high priority for backup and restoration of power if an outage occurs.

The local fire department should also be informed of any patient who is on oxygen therapy, especially if the patient is limited physically. Oxygen devices will not “explode,” but oxygen does support combustion. As noted, high-pressure tanks, if knocked over, have a tremendous force due to the pressurized oxygen and there have been reports of these tanks going through walls. Firefighters, or any emergency personnel, should be informed that oxygen is in use so that in the case of a fire or other emergency, they are aware of this potential danger.

Continuous (Constant) Positive Pressure Breathing

Continuous positive airway pressure (CPAP) is oxygen delivered with pressure above atmospheric pressure (i.e., positive airway pressure). Whereas normally during the respiratory cycle there is a negative pressure during inspiration, the pressure curve in CPAP is always above atmospheric pressure (positive pressure) on the airways.

CPAP may be used to improve oxygenation27,28 in patients for whom the usual means of oxygen delivery is not effective or for those with obstructive sleep apnea.²⁹ Sleep apnea and COPD often occur together; recently, recognition of when “overlap syndrome” occurs there is higher mortality than either disease process alone.³⁰ CPAP has also been used to help the transition of weaning patients from mechanical ventilation,³¹ including infants who have had cardiac surgery. CPAP can help stabilize these infants and normalize their spontaneous breathing pattern.³² It has also been useful in the management of respiratory distress in premature babies and decreases the need for invasive mechanical ventilation.³³ Early intervention using CPAP in older patients with cardiogenic pulmonary edema has also been effective.³⁴ Quality-of-life predictors have been shown to be positive a year after initiation of CPAP; improvement was noted at 3 months after initiation of CPAP and continued at 1 year.^35,36

Patients who are mouth breathers may have difficulty adjusting to CPAP, thus rendering it less effective in these cases. Those with moderate to severe sleep-disordered breathing have been found to be less adherent to CPAP therapy than are who are nose breathers. This is related to a leak that compromises the CPAP.³⁷

Use of Oxygen to Improve Exercise

Oxygen has been shown to increase exercise performance in patients with COPD who have moderate to severe airflow obstruction and mild hypoxemia at rest.38–40 It has also been shown to benefit patients with COPD who are nonhypoxemic at rest.^41,42 Breathlessness is the most common symptom that limits exercise tolerance. Oxygen supplementation will often provide an increased driving pressure of oxygen, which allows the patient to decrease the work of breathing.⁴³ Peripheral muscle weakness has been found in many patients with COPD. Improving exercise tolerance will result in improved muscle strength and endurance. Another consideration, if hyperoxia is not enough, is the use of noninvasive positive pressure (NPPV). This is still somewhat controversial and requires more study, but in this author’s clinical opinion, NPPV can be very beneficial.⁴⁴ As previously discussed in this chapter, heliox has been shown to improve exercise tolerance in patients with asthma and COPD who have upper airway obstruction, inflammation, and increased mucus secretions.

Noninvasive ventilation will be discussed later in the chapter, but it is interesting to note that in some pulmonary rehabilitation programs it is being used in addition to supplemental oxygen with very positive results. The combination of oxygen and noninvasive ventilation was shown to be better than supplemental oxygen alone.⁴⁵ The rationale for this improvement when using both oxygen and noninvasive ventilation is that in patients with severe COPD, the ventilatory muscles can be “unloaded” and this may promote higher levels of exercise.⁴⁶

Incentive spirometry (IS), also called sustained maximum inspiration (SMI), is a visual and/or audio feedback device that encourages slow, deep inspiration (Figure 43-6). Generally this treatment is performed frequently, up to every hour, and its purpose is to treat and prevent atelectasis and pneumonia, especially in postoperative patients who are considered a high risk for postoperative complications.^47–51 In many acute care settings, IS is done routinely. Several articles challenge the routine use of IS and have found that the addition of IS added no benefit to breathing exercise postoperatively.^52–55 In a study of patients scheduled for lung resection, when a combination of inspiratory muscle training and IS was performed before and after lung resection, there were significant lung function improvements in FEV₁ that were higher postoperatively than preoperatively.⁵²

There may be potential benefits to using IS with patients with neuromuscular and musculoskeletal impairments as well. They often demonstrate a decreased vital capacity and decreased chest wall mobility. IS devices encourage deep breathing and a sustained inspiration. During the sustained inspiration, collateral ventilation can occur as well-ventilated areas of the lung equilibrate with areas that are poorly ventilated. This is an area for future research, perhaps combining inspiratory muscle training and IS.

Many commercial incentive spirometers are available. Some are focused on volume, others on flow rates. Regardless of the type, the importance of patients using them should be stressed. Patients with COPD may have these devices prescribed when they are undergoing surgical procedures. Care must be taken not to have patients continue to use them when the acute episode is over. Patients with COPD have air trapping, which can be made worse by using an incentive spirometer and will not take deeper breaths needed to prevent respiratory problems post op when they have pain.

Under normal circumstances, when inhalation takes place, air becomes 100% saturated with water vapor before entering the lower airway tracts below the carina. This humidification process is important to mucus production, ciliary activity, and a healthy respiratory tract. When this normal humidification process is interfered with, such as in patients with endotracheal or tracheostomy tubes, other methods of adding moisture to the respiratory system must be employed.

Humidification is the addition of water vapor in its molecular form to a gas. When a dry gas is administered to a patient (e.g., via a nasal cannula), some type of humidification appliance is used to prevent unnecessary complications. Flows of 2 L/min or less may not require humidification when using a nasal cannula. Humidification therapy is also indicated in the presence of thick tenacious secretions and when an artificial airway is in place. Artificial airways, such as endotracheal and tracheostomy tubes, bypass the normal humidification system (the upper airway); therefore supplementation is essential.⁵⁶

There are basically two types of humidifiers. Bubble-through humidifiers are those that are generally used with simple oxygen appliances. The passover type of humidifier is usually found in conjunction with a mechanical ventilator. Both bubble-through and passover humidifiers are available for ventilators,⁵⁷ and they are usually heated to warm the humidified air to body temperature before it enters the airway.⁷

Aerosol Therapy

An aerosol is created when a suspension of liquid or solid particles exists in a gas. Two common forms of aerosol medication delivery in the clinical setting are the small-volume nebulizer (SVN) and the metered-dose inhaler (MDI). A bland aerosol is administration of water or saline solution to the patient’s lungs.⁵⁸

In general the goals of aerosol therapy are to hydrate dried retained secretions, to improve cough efficiency, to restore and maintain function of the mucociliary escalator, to deliver medications, and to humidify gases delivered through artificial airways. The MDI is strictly used for medication delivery (see Chapter 45).

Other forms of aerosol delivery are the spinning disk (such as in a room humidifier or mist ) and the ultrasonic nebulizer. Both of these are electrically powered as opposed to the SVN, which is pneumatically powered (Figure 43-7).⁵⁹

A key element in aerosol delivery is particle size. The size of the aerosol particle will determine its ability to penetrate the airway before depositing or raining out. The therapeutic range is considered 1 micron, with the smaller range of particles having the greatest penetrating ability. The larger particles deposit sooner. If they are greater than 5 microns, then the chances of entry into the airway are less. The particles may deposit in the nose and proximal airway. The greatest amount of alveolar deposition (95% to 100%) occurs in the 1 to 2 micron range. On the other hand, aerosol particles smaller than 1 micron are so stable that they may not deposit at all.⁷

Although particle size is important in determining appropriate deposition, a patient’s ventilatory pattern is probably more important in that it is the more variable and controllable of the two. Gravity also plays a factor, and it too can be used to benefit particle deposition. Patients should be sitting up as much as possible while taking slow, deep breaths with a short 3- to 4-second inspiratory hold. Mouth breathing is encouraged if aerosol therapy is delivered by mask. Nasal breathing may filter out particles of optimal size. Not all patients will be able to achieve this position and ventilatory pattern, and the therapist must modify accordingly.

Comparisons between the ability of SVNs and MDIs to deliver medications have found that the MDI is either equal in efficacy or outperforms nebulizers. Significant cost savings are also realized by those institutions that recognize MDI usage as an effective means of aerosol medication delivery over SVN.⁶⁰

To further enhance the efficacy of the MDI treatment, the recommendation is that a spacer or holding chamber may be attached to hold the aerosol particles before inhalation. This device allows greater drug particle deposition to the airways and reduces oropharyngeal deposition.⁶¹ Ventilator patients who are receiving drug aerosol therapy also receive greater benefit from an in-line MDI with a holding chamber compared with a jet nebulizer.⁶²

Aerosol-Therapy Precautions

It should be mentioned that there are hazards associated with aerosol therapy. Bronchospasm may occur as the smooth muscles of the bronchial passages react to foreign particles entering the lung. Shortness of breath and respiratory distress may also occur as a result of dried retained secretions swelling and occluding portions of the lung. Cross contamination is a concern in that aerosol devices may harbor organisms that can be transmitted to patients. Frequent equipment changes and proper sterilization and cleaning techniques are key in preventing this occurrence.

Intermittent Positive Pressure Breathing

Intermittent positive pressure breathing (IPPB) continues to be used in some settings, but there is little evidence to support its efficacy as a treatment modality.⁵⁸

This particular technology was developed during World War II to assist pilots breathing in unpressurized cabins at high altitudes. IPPB subsequently became a very popular respiratory therapy device in the 1960s and 1970s (Figure 43-8). Its use began to decline in the 1980s. In 1983 the National Heart, Lung, and Blood Institute reported that IPPB has limited therapeutic benefit. This clinical trial is only one of several studies that show IPPB is an outmoded medical technology. Research dating back to the 1950s questions the efficacy of this device.⁶³

The purpose of the IPPB machine is to increase alveolar ventilation, improve the ventilation-perfusion ratio, mobilize and facilitate expectoration of thick secretions, decrease the work of breathing, and deliver aerosolized medications. It is a pressure-cycled ventilator that, when triggered by a patient’s inhalation, delivers ambient air or oxygen to the patient until a preset pressure is reached. It is basically a lung expansion device that helps deliver an increased tidal volume. IPPB is used for a variety of pulmonary conditions, and treatment sessions usually last 10 to 15 minutes.

The modality of IPPB comes into question in the clinical setting because it has not been shown to provide benefits over that of other simpler respiratory treatment methods. It also introduces potential complications and hazards that the other treatments do not. Typically, IPPB has been used to treat asthma, COPD, and postoperative atelectasis; however, other therapies, such as IS, airway clearance techniques and devices, and aerosol therapy, tend to prevail as the treatment of choice over IPPB, which is virtually no longer used. This discussion is included because IPPB is the precursor to mechanical ventilation.

Although the use of IPPB is questionable in regard to its clinical efficacy, it may be a beneficial form of treatment in acute asthma or COPD that is refractory to standard therapy, atelectasis that has not responded to simpler therapy, and the prevention of respiratory failure in patients with kyphoscoliosis and neuromuscular disorders.⁶⁴

Mechanical Ventilation

Many disease states that lead to cardiac and/or respiratory failure will require mechanical ventilation to support the patient’s effort to ventilate and oxygenate (Figure 43-9). Patients receiving mechanical ventilator support can be found in many settings, from the acute care hospital to skilled nursing facilities and home care. Children needing continuous mechanical ventilation who live in the home and community need to be integrated into the school system and community recreational facilities. Patients with acute exacerbations of disorders such as emphysema, COPD, and chronic bronchitis may require mechanical ventilation and are generally seen in hospital intensive care units and weaned before they are discharged home. Patients with disorders requiring long-term ventilation, such as spinal cord injury, brain injury, and certain neuromusculoskeletal diseases, may be found receiving mechanical ventilation in rehabilitation hospitals, the home, or a long-term care facility. According to the American Association for Respiratory Care (AARC), the scope of practice for the respiratory therapist has expanded to include anywhere that patients with respiratory disease present. Therapists currently practice in hospitals, long-term care, pulmonary rehabilitation, patients’ homes, and pulmonary physicians’ offices.

Mechanical ventilator assistance in the past was provided primarily by machines that deliver preset volume and/or positive pressure breaths to the patient. Positive pressure ventilation is the opposite of normal physiological ventilation in that normal ventilation occurs when negative pressure, created by contraction of the diaphragm, causes air to enter the lungs. Whereas normal inspiration occurs by pulling air into the lungs, ventilators push air into the lungs (positive pressure) or apply pressure to the airways and thus increase ventilation. This is important because the thoracic cavity becomes an area of higher pressure, which may create adverse cardiovascular and hemodynamic events. Monitoring of heart rate and blood pressure is vital when patients are placed on a mechanical ventilator to make sure there are not cardiovascular compromises with increase in pressure and/or volume in the lungs.

Over the past 20 years there has been an increase in the use of noninvasive mechanical ventilation (NIMV) in patients with respiratory failure to avoid the risks involved with intubation. It is becoming the standard “first line therapy in several situations” in acute care.⁶⁵

Several other patient populations have also been supported and their health and sleep improved through the use of NIMV, among them patients with end-stage Duchenne muscular dystrophy, cystic fibrosis, and other neuromuscular dysfunction. In patients with Duchenne MD the pulmonary function data are monitored and the patient may be started on NIMV only at night, progressing to continuous ventilation as needed.⁶⁶ This has also been shown to prolong life and eliminate the need for tracheostomy in these patients needing ventilation.⁶⁷ In patients with cystic fibrosis, as the disease process progresses, a heavier workload is placed on the respiratory muscles. The patient will often develop a rapid, shallow breathing pattern that results in decreased alveolar ventilation. NIMV may reduce respiratory muscle work of breathing and improve gas exchange. It can decrease oxygen desaturation during exercise and airway clearance and help in patient recovery following an exacerbation. More data are needed to evaluate long-term benefits and criteria for the use of NIMV in people with cystic fibrosis.⁶⁸

Alarm Management and Precautions

When patients are using mechanical ventilators, it is inevitable that alarms will sound. Alarms are important indicators of a change in patient condition or a machine malfunction. All alarms should be recognized and valued as excellent sources of information. If alarms are silenced or ignored without interpretation, patient fatalities may result. Alarms should not be turned off. When therapy is being delivered, the alarms are a valuable tool. Therapists, however, need to realize they are treating the patient, not the machine. If an alarm sounds during a therapy treatment, stop the intervention and wait a few seconds to see whether the alarm stops. Before continuing therapy, identify which alarm went off and evaluate why. If it is not clear why the alarm sounded, contact the respiratory care practitioner or the patient’s nurse immediately.

The most common alarms are those that monitor high and low pressure, FiO₂, apnea, disconnection, and volume. The high-pressure alarm is the one that sounds most commonly when the patient is receiving physical therapy. This alarm indicates that more than the preset pressure is needed to deliver the volume of ventilation. Generally, if the high-pressure alarm continues to sound, the patient should be checked for secretions. Suctioning can remedy this problem. The ventilator tubing should also be checked for possible occlusion from compression or excessive water buildup (Figure 43-10). High-pressure alarms may also sound in the case of bronchospasm or breath holding. Do not use strong resistance exercise with patients on mechanical ventilation because they may hold their breath and perform a Valsalva maneuver, which will cause increased circuit pressure to deliver the tidal volume to the patient. Low pressure alarm may signify a leak in the ventilator circuitry or a disconnection from the machine. Before turning a patient or performing upper extremity exercise, make sure there is clearance and ease of movement in the ventilator circuit tubing to prevent it from coming off during the interventions. In one case (in an unnamed medical center’s intensive care unit) a patient’s low-pressure alarm sounded and the patient was bagged while the cause was evaluated. The source was a disconnection that occurred when a new employee from the housekeeping department unplugged the ventilator to use the plug for a cleaning machine. When the low-pressure alarm sounds, first consider that the patient is not being ventilated.

If you are unfamiliar with a particular ventilator and an alarm sounds that you are unable to identify and/or remedy, first ensure the patient is not in any extra distress. Assess the overall appearance of the patient and, most important, the rise and fall of the patient’s chest as the ventilator cycles. If the patient does not appear to be receiving breaths, immediate action should be taken to remove the ventilator from the patient and begin manual ventilation with a self-inflating bag. The respiratory care practitioner should be called to rectify the situation. When the problem is resolved, the patient should be returned to the mechanical ventilator.

Another significant precaution to take when working with a patient on a ventilator is to watch for condensation in the tubing that could accidentally be poured directly into the patient’s lungs, especially during turning. When moving a patient who is using a ventilator, plan ahead by securing all lines, wires, and tubing. Follow the appropriate procedure for emptying any water from the ventilator tubing before moving the patient. If the patient aspirates water from ventilator tubing, it can be fatal.

Role of the Physical Therapist

The physical therapist can have a significant role in keeping the patient who is mechanically ventilated from having decreased aerobic capacity by helping the patient perform aggressive mobilization (see Chapters 18, 19, and 20), exercise, airway clearance techniques, and breathing strategies and interventions (see Chapters 21, 22, and 23). The physical therapist can also play a role in finding optimal positions to support the patient who is being weaned. Therapists who have been working on breathing strategies can be a source of comfort and encouragement for the patient during the weaning periods. Active mobilization early in the course of mechanical ventilation will result in more successful outcomes.

Evidence now supports the use of early physical and occupational therapy by giving patients sedation breaks and rousing patients to exercise. This has been shown to result in better functional outcomes at discharge, fewer ventilator days, and fewer days of delirium compared with standard ventilator treatment without waking patients for therapy.81,82

Summary

Physical therapists need to understand the basic equipment and principles of respiratory care in order to optimize the functional outcomes of their patients. The interprofessional team approach is vital in acutely ill patients. Working in collaboration with respiratory care practitioners and nurses will maximize interventions and improve patient outcomes.