This course presents you with a general overview of the principles of pharmacology and the mechanisms and effects of cardiovascular and respiratory drugs. While the focus is predominantly on disorders of the pulmonary system, the inter-relatedness of the two systems requires a review of the medications focused on heart problems. Since the respiratory system cannot be disassociated from cardiac and vascular systems, cardiovascular-respiratory pharmacology necessarily involves a relatively broad scope of drug classes.

Nurses are on the front lines in administering drugs that are specifically designed to treat the so-called pathological triad of pulmonary disease: bronchospasm, airway inflammation, and retained secretions. Their front line arsenal for treating cardio-pulmonary diseases includes bronchodilators, antimuscarinics, corticosteroids, mucokinetics, mucolytics, and decongestants. There are also a variety of other agents available for treating pulmonary ailments, including: oxygen, antibiotics, local anesthetics, respiratory stimulants, and muscle relaxants. Because of the inter-connectedness of the body systems, additional groups of drugs that may be administered to patients with respiratory diseases include: anti-infectives, CNS drugs, antiarrhythmic agents, anticoagulants, antihypertensives, and diuretics.

The course includes lengthy explanations of the uses for aerosol therapy, nebulizers, and humidifiers. Therapeutic procedures and medication functions are reviewed and you will learn about the broad categories of medications used, subgroups of medications, read articles published about those medications, and, finally, learn about some of the equipment used to deliver medications to patients. The resources drawn upon for the following material can be found in the References section at the end of the course.

Upon successful completion of this course, you will be able to:

• List the general categories of medications used to treat cardio-pulmonary disorders.
• Identify indications, contradictions, and possible side effects of four of these most commonly prescribed medications.
• Explain the functions of the various types of equipment used to deliver some of these medications
• Cite the clinical practice guidelines for selecting and using equipment to deliver medications.

Introduction

Before we begin reviewing the medications used to treat respiratory (and cardio-respiratory) problems, we believe it would be good to first present you with a brief review of the respiratory system:

a. Respiration. Respiration is the exchange of gases between the atmosphere and the cells of the body. It is a physiological process. There are two types of respiration-external and internal. External respiration is the exchange of gases between the air in the lungs and blood. Internal respiration is the exchange of gases between the blood and the individual cells of the body.

b. Breathing. Breathing is the process that moves air into and out of the lungs. It is a mechanical process. There are two types of breathing in humans--costal (thoracic) and diaphragmatic (abdominal). In costal breathing, the major structure causing the movement of the air is the rib cage. In diaphragmatic breathing, interaction between the diaphragm and the abdominal wall causes the air to move into and out of the lungs.

1-2. COMPONENTS AND SUBDIVISIONS OF THE HUMAN RESPIRATORY SYSTEM

See Figure 1-1 for an illustration of the human respiratory system.

a. Components. The components of the human respiratory system consist of air passageways and two lungs. Air moves from the outside of the body into tiny sacs in the lungs called alveoli (pronounced al-VE-oh-lie).

b. Main Subdivisions. The main subdivisions of the respiratory system may be identified by their relationship to the voice box or larynx. Thus, the main subdivisions are as follows:

Figure 1-1. The human respiratory system.

1-3. SUPRALARYNGEAL STRUCTURES

a. External Nose. The external nose is the portion projecting from the face. Primarily cartilages support it. It has a midline divider called the nasal septum, which extends from the internal nose. Paired openings (nostrils lead to paired spaces (vestibules). Guard hairs in the nostrils filter inflowing air.

Figure 1-2. Supralaryngeal structures.

b. Nasal Chambers (Internal Nose). Behind each vestibule of the external nose is a nasal chamber. The two nasal chambers together form the internal nose. These chambers too are separated by the nasal septum.

1. Mucoperiosteum. The walls of the nasal chambers are lined with a thick mucous-type membrane known as the mucoperiosteum. It has a ciliated epithelial surface and a rich blood supply, which provides warmth and moisture. At times, it may become quite swollen.
   CILIATED = Provided with cilia (hair like projections that move fluids to the rear)
2. Conchae. The lateral wall of each chamber has three scroll-like extensions into the nasal chamber, which help to increase the surface area exposed to the inflowing air. These scroll-like extensions are known as conchae.
   CONCHA =sea shell CONCHA (singular), CONCHAE (plural) (pronounced KON -kah)
3. Olfactory epithelium. The sense of smell is because of special nerve endings located in the upper areas of the nasal chambers. The epithelium containing the sensory endings is known as the olfactory epithelium.
4. Paranasal sinuses. There are air "cells" or cavities in the skull known as paranasal sinuses. The paranasal sinuses are connected with the nasal chambers and are lined with the same ciliated mucoperiosteum. Thus, these sinuses are extensions of the nasal chambers into the skull bones. For this reason, they are known as paranasal sinuses.

c. Pharynx. The pharynx (FAIR-inks) is the common posterior space for the respiratory and digestive systems.

1. Nasopharynx. That portion of the pharynx specifically related to the respiratory system is the nasopharynx. It is the portion of the pharynx above the soft palate. The two posterior openings (nares) of the nasal chambers lead into the single space of the nasopharynx. The auditory (eustachian) tubes also open into the nasopharynx. The auditory tubes connect the nasopharynx with the middle ears (to equalize the pressure between the outside and inside of the eardrum). Lying in the upper posterior wall of the nasopharynx are the pharyngeal tonsils (adenoids). The soft palate floor of the nasopharynx is a trap door that closes off the upper respiratory passageways during swallowing.
2. Oropharynx. The portion of the pharynx closely related to the digestive system is the oropharynx. It is the portion of the pharynx below the soft palate and above the upper edge of the epiglottis. (The epiglottis is the flap that prevents food from entering the larynx (discussed below) during swallowing.) (3) Laryngopharynx. That portion of the pharynx that is common to the respiratory a digestive systems is the laryngopharynx. It is the portion of the pharynx below the upper edge of the epiglottis. Thus, the digestive and respiratory systems lead into it from above, and lead off from it below.

1-4. LARYNX

The larynx, also called the Adam’s apple or voice box, connects the pharynx with the trachea. The larynx, located in the anterior neck region, has a box-like shape. See Figure 1-3 for an illustration. Since the voice box of the male becomes larger and heavier during puberty, the voice deepens. The adult male’s voice box tends to be located lower in the neck; in the female, the larynx remains higher and smaller and the voice is of a higher pitch.

Figure 1-3. The larynx.

a. Parts and Spaces. The larynx has a vestibule ("entrance hallway") that can be covered over by the epiglottis. The glottis itself is the hole between the vocal cords. Through the glottis, air passes from the vestibule into the main chamber of the larynx (below the cords) and then into the trachea. The skeleton of the larynx is made up of a series of carti1ages.

b. Muscles. The larynx serves two functions and there are two sets of muscles- -one for each function.

1. One set controls the size of the glottis. Thus, it regulates the volume of air passing through the trachea.
2. The other set controls the tension of the vocal cords. Thus, it produces vibrations of selected frequencies (variations in pitch) of the moving air to be used in the process of speaking.

1-5. INFRALARYNGEAL STRUCTURES

a. Trachea and Bronchi. The respiratory tree (Figure 1-4) is the set of tubular structures that carry the air from the larynx to the alveoli of the lungs. Looking at a person UPSIDE DOWN, the trachea is the trunk of the tree and the bronchi are the branches. These tubular parts are held open (made patent) by rings of cartilage. Their lining is ciliated to remove mucus and other materials that get into the passageway.

b. Alveoli. The alveoli (alveolus, singular) are tiny spherical (balloon-like) sacs that are connected to the larger tubes of the lungs by tiny tubes known as alveolar ducts and bronchioles. The alveoli are so small that there are millions in the adult lungs. This very small size produces a maximum surface area through which external respiration takes place. External respiration is the actual exchange of gases between the air in the alveolar spaces and the adjacent blood capillaries through their walls.

c. Lungs. A lung is an individual organ composed of tubular structures and alveoli, bound together by fibrous connective tissue (FCT). In the human, there are two lungs, right and left. Each lung is supplied by a primary or mainstem bronchus leading off from the trachea. The right lung is larger in volume than the left lung. The left lung must leave room for the heart. The right lung is divided into 3 pulmonary lobes (upper, middle and lower) and 10 bronchopulmonary segments (2 + 3 + 5). The left lung is divided into 2 pulmonary lobes upper and lower) and 8 bronchopulmonary segments (4 + 4). A pulmonary lobe is a major subdivision of a lung marked by fissures (deep folds. Each lobe is further partitioned into bronchopulmonary segments. Each lobe is supplied by a secondary or lobar bronchus. A tertiary or segmental bronchus, a branch of the lobar bronchus supplies each segment.

d. Pleural Cavities. Each serous cavity has inner and outer membranes. In the case of the lungs, the inner membrane, is known as the visceral pleura which very closely covers the surface of the lungs. The outer membrane is known as the parietal pleura, forming the outer wall of the space. The pleural spaces are the potential spaces between the inner and outer membranes. The opening between the pleural layers contains a slick fluid called pleural fluid. The pleural fluid serves as a lubricant and allows the lungs to move freely with a minimum of friction.

Figure 1-4. Infralaryngeal structures.

1-6. INTRODUCTION

a. Boyle’s law tells us that as the volume (V) of a gas-filled container increases, the pressure (P) inside decreases; as the volume (V) of a closed container decreases, the pressure (P) inside increases. When two connected spaces of air have different pressures, the air moves from the space with greater pressure to the one with lesser pressure. In regard to breathing, we can consider the air pressure around the human body to be constant. The pressure inside the lungs may be greater or less than the pressure outside the body. Thus, a greater internal pressure causes air to flow out; a greater external pressure causes air to flow in.

b. We can compare the human trunk to a hollow cylinder. This cylinder is divided into upper and lower cavities by the diaphragm. The upper is the thoracic cavity and is essentially gas-filled. The lower is the abdominopelvic cavity and is essentially water-filled.

1-7. COSTAL (THORACIC) BREATHING

a. Inhalation. Muscles attached to the thoracic cage raise the rib cage. A typical rib might be compared to a bucket handle, attached at one end to the sternum (breastbone) and at the other end to the vertebral column. The "bucket handle" is lifted by the overall movement upward and outward of the rib cage. These movements increase the thoracic diameters from right to left (transverse) and from front to back (A-P). Thus, the intrathoracic volume increases. Recalling Boyle’s law, the increase in volume leads to a decrease in pressure. The air-pressure outside the body then forces air into the lungs and inflates them.

b. Exhalation. The rib cage movements and pressure relationships are reversed for exhalation. Thus, intrathoracic volume decreases. The intrathoracic pressure increases and forces air outside the body.

1-8. DIAPHRAGMATIC (ABDOMINAL) BREATHING

The diaphragm is a thin, but strong, dome-shaped muscular membrane that separates the abdominal and thoracic cavities. The abdominal wall is elastic in nature. The abdominal cavity is filled with soft, watery tissues.

a. Inhalation. As the diaphragm contracts, the dome flattens and the diaphragm descends. This increases the depth (vertical diameter) of the thoracic cavity and thus increases its volume. This decreases air pressure within the thoracic cavity. The greater air pressure outside the body then forces air into the lungs.

b. Exhalation. As the diaphragm relaxes, the elastic abdominal wall forces the diaphragm back up by pushing the watery tissues of the abdomen against the underside of the relaxed diaphragm. The dome extends upward. The process of inhalation is thus reversed.

1-9. INTRODUCTION

Many conditions affect the respiratory system. Some of the conditions are life-threatening, while many are chronic conditions which affect thousands of patients. Many of the patients who suffer from these conditions will be standing in front of the outpatient pharmacy in order to receive prescriptions to obtain some relief.

1-10. PNEUMONIA

Pneumonia is caused by an infection of the lung. This infection is caused by either bacteria (like the pneumococcus bacterium) or viruses. In pneumonia the walls of the alveoli become inflamed and filled with fluid and the air spaces in the alveoli become filled with blood and fluid.
As you might expect, the exchange of gases in the alveoli becomes impaired. Death can result from pneumonia.

1-11. ASTHMA

Asthma, a condition usually caused by allergic reactions to substances in the environment, affects many people. The allergic reactions cause the bronchioles to spasm. Hence, the flow of air into and out of the lungs becomes impaired. For some unknown reason, the flow of air out of the lungs is more impeded than the flow of air into the lungs. Hence, the person with asthma often finds it more difficult to expire (expel the air) than to inspire. Furthermore, such labored breathing, after many years, often results in the asthma-sufferer having a barrel-shaped chest.

1-12. STATUS ASTHMATICUS

Status asthmaticus is a very sudden, continuous, and intense asthmatic attack.

1-13. EMPHYSEMA

Emphysema is a condition in which the patient has large portions of the alveolar walls destroyed. Consequently, the patient finds it necessary to breathe faster and more deeply in order to obtain the oxygen needed to live. Emphysema is often associated with smoking. Emphysema may also be referred to as Chronic Obstructive Pulmonary Disease (COPD).

1-14. PULMONARY EDEMA

Pulmonary edema is a condition in which fluid collects in the interstitial spaces of the lungs and in the alveoli. Obviously, the exchange of gases in the alveoli becomes impaired. Pulmonary edema is usually caused when the left side of the heart fails to pump efficiently; when this happens blood backs up into the pulmonary circulation and causes fluid in the lungs.

Pharmacology involves the study of drugs, and drugs are defined as chemical substances that exert a biologic effect on the recipient. Medical drugs are used for the treatment or prevention of disease, and drugs are considered useful when they can maintain, enhance or alter bodily function when a patient is cannot cope with a particular disease. Pharmacology is concerned with the following:

• the chemical and physical properties of drugs
• the physiologic effects and site of action of drugs
• how drugs exert their effects
• how the body absorbs, distributes, metabolizes, and excretes the drugs
• dosages and routes of administration of drugs
• side effects, toxicity, and contraindications

The safe administration of drugs requires awareness of the following factors:

• mode of action
• side effects
• toxicity
• range of common dosages
• rate and route of excretion
• individual differences in responses
• interaction with other drugs or food
• contraindications

For drugs to exert their expected therapeutic benefits, they need to be made available for absorption in the body’s systems. Availability depends to a large extent on the route of administration of the drug. Drugs can be administered gastrointestinally, parenterally, or topically. Topical administration includes application to the skin and directly to the lungs by inhalation.

In order for a drug to be administered via inhalation, it must first either be vaporized or placed in an aerosol suspension. This generally requires the use of special equipment. The following discussion reviews the types of equipment available for administering drugs via inhalation.

In addition to activities related to gas exchange, the respiratory system is responsible for a variety of other vital functions. One function of the upper airway to assure that inspired gases are warmed and adequately humidified. Another function involves protecting the lungs by filtering inspired gas. RCPs need to understand basic concepts of humidification and aerosol systems in order to treat patients whose airway mechanisms are compromised.

Aerosol and humidity therapy are provided to maintain normal physiologic conditions and as therapy for pathologic conditions. One of the most important, but least understood, aspects of pulmonary care is the role of humidity therapy. Many care providers and most patients do not appreciate the role of hydration in liquifying secretions and facilitating the natural flow of mucus from the lower airways.

Pulmonary patients need adequate humidification of their inspired gases and controlled fluid balance, otherwise patients can become dehydrated. Dehydration can make secretions more viscous and inhibit the mucociliary escalator activity of the airways, making secretions difficult to dislodge. If this blocks functional gas flow through the distal airways, infections, atelectasis and other respiratory problems can easily occur.

Since humidification and humidity therapy are so important to respiratory well-being, you need to take a moment and review the basic physical principles of humidity. Humidity is essentially the water vapor in a gas. This water vapor can be described in several ways, as:

1. Absolute humidity -The actual content of water vapor in a gas measured in milligrams per liter.

2. Potential humidity -The maximum amount of water vapor a gas can hold at a given temperature.

3. Relative humidity -The amount of water vapor in a gas as compared to the maximum amount possible, expressed as a percentage.

When these three are presented in equation form, their relationship becomes more clear:
Relative Humidity = Absolute Humidity/Potential Water Vapor Content x 100

When a gas or air becomes heated, it expands and more spaces are created between the molecules. The resulting warmer gases have greater capacity for “holding” more water vapor than do cooler gases. Therefore, potential humidity increases as the temperature of a gas increases. As a result, warm, humidified gas traveling through tubing tends to “rain?out” water vapor as the gas cools and has a lower water?carrying capacity. The table below illustrates the relationship of temperature and potential humidity:

Water Vapor Content of Air

One of the more important gases found in air is water vapor. The amount of water vapor in the air can vary widely day-to-day, while gases like oxygen and nitrogen are present in relatively constant amounts. In general, water in vapor form is governed by gas laws and can be treated as a gas.

All bodies of water or moist organic bodies are capable of giving off water vapor. When water enters the air as a gas, the air’s humidity increases. The measure of how much water vapor is contained in the air is identified as the humidity level, and the factors determining the humidity include:

1. The availability of water. Clearly the air over a desert has less chance of picking up water vapor than the air over a lake.
2. Temperature is also a factor since the spacing of warmer air’s molecules allows water vapor’s molecules to fit more easily. Recalling the principles of Charles’ law, the volume of a gas increases as its temperature increases. If the number of molecules of the gases increases as the temperature rises, the humidity will not increase as much.

Summarizing, if there is water available there will be a specific amount of water vapor in the air at each ambient temperature. That amount equals the air’s total capacity for water vapor at that temperature. Air that contains its total capacity for water vapor at a specific temperature is said to be 100% saturated.

Amounts of water found in air are generally measured as grams per cubic meter of air (gm/ml) or as milligrams per liter of air (mg/1). These measurements can then be converted to moles of water by dividing by the gram molecular weight of water (which is 18). The total capacity of the air for water vapor is measured in milligrams per liter, with total capacity of the air for water vapor in milligrams per liter is referred to as the air’s potential water vapor. Table 1 identifies the various values of the potential water vapor content at several different temperatures.

THE POTENTIAL WATER VAPOR IS THE MAXIMUM THE AIR CAN HOLD AT A CERTAIN TEMPERATURE.

Air’s capacity for water cannot be met if there is not enough water available, and to discover the actual amount of water vapor present in the air it is necessary to measure the absolute humidity.

Relative humidity is another important measurement, and it represents the actual amount of water vapor in the air (absolute humidity) compared to the total possible water vapor content of the air at the given ambient temperature (potential water vapor). The measurement of relative humidity is expressed as a percentage (of saturation). For example, if the air contained only 17 mg/l of water vapor at 25°C, then it would not be totally saturated (see Table 1).

Calculating the relative humidity involves dividing the absolute humidity (actual water vapor content of the air) by the potential water vapor (maximum possible water vapor content of the air), and multiplying by 100 to convert the decimal percentage:
Relative Humidity = Absolute Humidity/Potential Water Vapor Content x 100

For the example above where the air had 17 mg/l of water vapor at 25°C:
Relative Humidity = 17/23 x 100
Therefore: Relative Humidity = 73.9%

Humidity Deficit

Another factor to consider is the humidity deficit. For example, if the atmosphere’s relative humidity is less than 100%, the air of the atmosphere has what is referred to as a humidity deficit. If outside air at 20°C has 14 mg/l of water vapor, and needs to have 17.3 mg/l to be fully saturated, it is said to have a primary humidity deficit of 3.3 mg/l. To calculate the primary humidity deficit simply subtract the absolute humidity of the air from its potential water vapor at the appropriate temperature and the difference between the two is the primary humidity deficit:

Primary Humidity Deficit = Potential Water Vapor Content - Actual Water Vapor Content

The secondary humidity deficit also needs to be considered. This is the moisture deficit in the inspired air that the nose and upper airway needs to compensate for. When air is breathed into the nasal cavity and heated to body temperature, its potential water vapor rises to 44 mg/l that is the potential water vapor content of air at 37°C.

Therefore, unless the air of the atmosphere is at least 37°C and fully saturated, there exists a moisture deficit. For example, if the atmosphere’s air was 98.6°F (37°C) and the relative humidity 100%, people in such conditions would be very hot and sweaty! Luckily, inspired air is generally not that warm or humid, so most inspired air does have a secondary humidity deficit.

The secondary humidity deficit is calculated by subtracting the absolute humidity of the air from the potential water vapor content. The difference from the calculations for primary humidity deficits is that the potential water vapor content is always 44 mg/l, the potential water vapor of air at body temperature:
Secondary Humidity Deficit = 44 mg/l - Absolute Humidity.

Therefore, if inspired air’s absolute humidity is 16 mg/l at 25°C before being warmed in the nasal cavity, there is a primary humidity deficit of:
Primary Humidity Deficit = 23 mg/l - 16 mg/l = 7 mg/l

For this same absolute humidity for the atmosphere, the secondary humidity deficit is
Secondary Humidity Deficit = 44 mg/l -16 mg/l = 28 mg/l

Here are some other calculations for you to consider:

If the absolute humidity of the same inspired air at 25°C were 23 mg/l, there would be no primary humidity deficit because the potential water vapor of air at 25°C is 23 mg/l (see Table above). There would still be a secondary humidity deficit of 21 mg/l because 44 mg/l minus 23 mg/l is 21 mg/l. This illustrates that at 100% relative humidity, it is still possible that the nasal cavity’s lining will have to supply moisture to the inspired air.

• You may sometime need to calculate a primary or secondary humidity deficit when you only know the relative humidity. To perform this calculation, you first need to convert the relative humidity into absolute humidity before calculating the humidity deficit. Remember the formula for relative humidity:
  Relative Humidity = Absolute Humidity/Potential Water Vapor Content x 100
  
  
• When the temperature and relative humidity are known, you can look up the potential water vapor for the air temperature by using the Table shown above. Then substitute into the above formula the values for relative humidity and potential water vapor and calculate the absolute humidity. For example, the relative humidity at 10°C is 75% for the air in the atmosphere. Using the Table, you can see that the potential water vapor content at 10°C is 9.5 mg/l, so:
  
  Relative Humidity = Absolute Humidity/Potential Water Vapor Content x 100
  
  Absolute Humidity = 7.125 mg/l

This measurement of the absolute humidity can be used to calculate the primary and secondary humidity deficits of the same air. At 10°C, we know that the potential water vapor content is 9.5 mg/l, so the primary humidity deficit is:

Primary Humidity Deficit = Potential Water Vapor Content - Absolute Humidity
9.5 -7.125 = 2.375 mg/l

The secondary humidity deficit for the same air would be:

Secondary Humidity Deficit = 44 - Absolute Humidity
44 -7.125 = 36.875 mg/l

To summarize:

· The primary humidity deficit occurs in the atmosphere and represents the difference between what humidity there is and what there could be.

· The secondary deficit occurs in the body and represents the difference between what humidity there is and what there needs to be at body temperature (37°C).

Water Vapor Correction

Since we’ve already ascertained that water vapor acts in most ways like any other gas, air creates a partial pressure when its in a mixture of gases.

That partial pressure depends on the amount of water vapor present, which in turn depends on the temperature. However, water vapor differs from the behavior of other gases in the air since changes in the barometric pressure of the atmosphere under normal conditions do not have much impact on the partial pressure of water.

As a result, it is best to calculate the partial pressures of the other gases in the air after the partial pressure of water vapor has been determined—especially when measuring the air within the lungs. Inside the lungs, the partial pressure of water vapor is approximately 47 mm Hg. This value is relatively constant because the air entering the lungs is normally saturated and at 37°C.

By subtracting the partial pressure of the water vapor from the total atmospheric pressure, you will find what is referred to as the dry gas pressure. In the lungs:

Dry Gas Pressure = Atmospheric Pressure - 47 mmHg

At one atmosphere (760 mmHg), the dry gas pressure would be:
Dry Gas Pressure = 760 -47 = 713 mmHg

As you have seen from the previous discussion, there are a number of reasons why humidity is an important aspect of the pulmonary system, including:

• It is needed to maintain normal bronchial hygiene
• It promotes functions of the normal mucociliary escalator
• It maintains the body’s vital homeostasis
• Without humidity the cleansing activities of the cilia could not function properly, and the nearly 100 ml of mucus secreted daily would become quite thick and tenacious.
• Without humidity the actual lung parenchyma would dry up, causing a loss of normal compliance which would restrict lung movement and reduce ventilation.

If normal use of the route of humidification and recapture of water were lost, problems would most certainly present themselves. If the upper airway were bypassed or dry gases were inhaled, a series of adverse reactions could occur, including:

• Impairment of ciliary activity
• Slowing of mucus movement
• Inflammatory changes and possible necrosis of pulmonary epithelium
• Retention of thick secretions and encrustation
• Bacterial infiltration of mucosa (bronchitis)
• Atelectasis
• Pneumonia

As a result of the importance of maintaining humidity, humidity and aerosol therapy are also important, and their general goals are to:

1. Promote bronchial hygiene
2. Loosen dried and/or thick secretions
3. Promote a effective coughs to clear secretions
4. Provide adequate humidity in the presence of an artificial airway
5. Deliver adequate humidity when administering dry gases therapies
6. Delivering prescribed medications

Clinical Evaluation of the Need for Humidity and/or Aerosol Use

There are a variety of factors to be considered when deciding to add humidity to dry gas therapies, including:

• patient’s age and ability to move normal secretions
• neuromuscular status
• recent or planned surgeries
• trauma
• disease conditions

The presence of any of these may impair the patient’s ability to cough and move secretions. Another problem may occur when patients develop very thick and abundant amounts of secretions that cannot be moved with normal muscle activity—making humidity or aerosol therapy necessary.

Indications for delivery of humidified gases and aerosols

Primary indications for humidifying inspired gases include:

• Administration of medical gases
• Delivery of gas to the bypassed upper airway
• Thick secretions in non-intubated patients

Additional indications for warming inspired gases:

• Hypothermia
• Reactive airway response to cold inspired gas

Primary indications for aerosol administration:

• Delivery of medication to the airway
• Sputum inductions

Sources of Mucus

Mucus generally comes from two sources: secretion from goblet cells and bronchial (mucous) glands. The goblet cells, which are distributed throughout the epithelium of the mucosa, synthesize and secrete mucus into the airway. The mucous glands, which are in the submucosa, are the greater source of mucus. Chronic irritation or disease can cause the number and size of goblet cells and mucous glands to increase, resulting in a larger and more viscous mucous blanket.

Effects of Mucous Layer

Ciliary activity, which moves the mucus, can be adversely affected if the mucous layer is changed. Changes in the ratio of gel to sol layer will affect the flow of mucus. A higher ratio, due either to a decrease in the watery sol layer or an increase in the viscous gel layer, could make the workload of the cilia too difficult to be effective. The cilia are capable of continuing to beat even if the workload increases, but only to a certain level. If the cilia become tangled in the thick mucus or are unable to penetrate the dense layer, the transport of the mucous blanket would stop, causing secretions to become retained in the respiratory tract.

Increases in the amount of watery sol fluid would also decrease the transport of mucus. The cilia must be able to extend through the sol layer to the gel layer to transport the mucus. Transport would be impaired if the thickness of the sol layer were to eliminate ciliary contact with the gel layer.

Other factors that can impede ciliary activity and the flow of mucus include:

• tobacco smoke
• local environmental conditions
• and pathology of the airway can impede clearance due to changes in the epithelium.

Humidification Devices

The effectiveness of humidifiers' ability to adequately supply vapor to a gas depends on three factors: temperature, surface area and time.

Temperature increases cause increases in vapor pressure and potential humidity. The greater the surface area of water/gas contact and the longer time this contact takes place, the greater the number of water molecules that can enter the gas mixture. These principles are used by humidifiers to provide increased relative humidity to the gas.

Blow-By Humidifier

Figure 1. The blow-by humidifier.