Dead Space Ventilation and ARDS


Acute Respiratory Distress Syndrome (ARDS) is a critical illness that increases morbidity and mortality rates in the world. ARDS is a chronic reaction to “acute infections or injuries of the lungs” (Forel, Voillet, Pulina, Gacouin, Perrin, Barrau, Jaber, Arnal, Fathallah, Auquier, Roch, Azoulay, & Papazian, 2012, p.1). ARDS is not a disease but rather a syndrome triggered by diverse direct and indirect factors. Some of these factors include “intense arterial hypoxemia, which is an immunological response that causes a diffuse alveolar damage, pulmonary edema and noncompliant lungs” (Bhadade, De Souza, Harde, & Khot, 2011, p.1). ARDS causes a reduction in lung capacity to become available for ventilation, or a “baby lung” condition (Charron, Repesse, Bouferrache, Bodson, Castro, Page, Jardin, & Vieillard-Baron, 2011, p.2; Sundaresan, Chase, Shaw, Chiew, & Desaive, 2011).

Several Americans suffer from this condition, and there is a risk of an increase in the number of people who have become infected. The widespread of ARDS become attributed to the fact that many cases of respiratory diseases become treated through ventilation ways that may cause damage or injuries to the lungs. One such procedure is dead space ventilation. Dead space ventilation involves the use of gas that does not interact with pulmonary blood at any one time (Niklason, Eckerstrom, &Jonson, 2008). The energy spent to move gas that does not have any physiologic benefits is the clinical significance of dead space ventilation. A vast amount of energy must become used in moving extra gas to support ventilation. The effectiveness of pulmonary blood flow is another clinical significance of dead space ventilation that must get consideration. Insufficient pulmonary blood flow augments dead space ventilation as there exists a limit of blood flow through the lungs for perfusion.

ARDS can deplete the role of the lungs in ventilation. Patients acquiring this disease are, thus, admitted into the intensive care unit where they need mechanical ventilation (Sundaresan et al., 2011). Through artificial management of ventilation, the number of deaths of patients suffering from ARDS has become increased. This increase has arisen because of limiting the tidal volume and maintenance of plateau pressure (Pplat) below 30cmH2O. A bronchial collapse partially or totally excludes certain compartments of the lung from ventilation. ARDS does not respond to the administration of a high concentration of inspiratory oxygen. The ratio of dead space ventilation becomes increased when the patient is undergoing mechanical ventilation, while a ratio of 0.50 is considered normal. A ratio below 0.60 does not let any reason obstruct natural respiration, while a ratio of 0.60-0.80 portends chronic disease and indicates that the patient cannot handle prolonged natural respiration. This paper is an analysis of the relationship between ARDS and Dead space ventilation.

ARDS is known for promoting a severe respiratory insufficiency of the lung parenchyma as a result of progressive hypoxemia and an abnormality in permeating through the alveolar-capillary membrane. On the other hand, dead space ventilation may cause abnormalities in the lung structure and damages to the lung tissues thus resulting in ARDS.

ARDS and dead space ventilation relate and differ in various ways. A key difference between ARDS and space ventilation becomes articulated in the definition of the two conditions. While ARDS is a chronic condition to acute infections and injuries of the lungs, dead space ventilation refers to the used gas that does not interact with pulmonary blood.

Another difference between ARDS and dead space ventilation is that ARDS causes impairment in the process of gas exchange, while dead space ventilation enhances the use of gas that does not interact with pulmonary blood. This implies that ARDS causes the problem while dead space ventilation seeks to solve the problem. In ARDS, the parenchyma of the lung becomes inflamed, causing impairment in the process of gas exchange. Sufficient oxygenation becomes attained through decreasing intrapulmonary shunts using ventilation processes.

Dead space ventilation and ARDS have a relationship since dead space ventilation causes ARDS and the other way around. Dead space ventilation is a form of mechanical ventilation, which may cause abnormalities in the lung structure and damage to the lung tissues. Further understanding on how to balance gas exchange during dead space ventilation may enhance treatment of ARDS. Conversely, in ARDS, intrapulmonary force relies on malformed, lung departments that are not aerated but get perfused (Niklason et al., 2008). As a result, a part of venous blood leaves the lungs with no carbon dioxide replacement before combining with arterial blood (Niklason et al., 2008). Venous blood has more levels of carbon dioxide than arterial blood from perfused and ventilated lung units and thus, a thrust causes augmentation in levels of arterial carbon dioxide tension (PaCO2) (Aboab, Niklason, Uttman, Brochard, & Jonson, 2012). Hence, a right to left shunt increases the gap between PaCO2 and alveolar carbon dioxide tension (PaCO2), which describes the alveolar dead space. This shunt causes a dead space, and when it attains a level of 50 % cardiac output or more, it creates the need for dead space ventilation. Hence, this paper supports that ARDS and dead space ventilation relate in various ways.

Definition of Terms

Dead space ventilation is a form of mechanical ventilation. It becomes recommended for patients requiring support in the removal of carbon dioxide and maintaining oxygen. Ventilated patients usually suffer from abnormalities in the lung structure and obstructions in the airways the lung. Mechanical ventilation becomes anchored on the concept that the behavior of air is like that of fluid since both air and fluid follow the path that has the least resistance as they enter a surface.

The maximal pressure in the airways during respiration is known as Peak Inspiratory Pressure (PIP). PIP becomes used in measuring the pressure in the vital air paths in the lungs. Acute or Rapid changes in PIP normally show severe complications such as bronchospasm or plugging of mucus. Plateau Pressure (Pplat), however, measures the pressure of airways at the last stages of inspiration and normally indicates the pressure in the alveoli. Pplat determines complications that result from the ventilator such as volutrauma and must always be kept between 30 and 35 cm H2O pressure.

The volume of air that becomes inhaled and exhaled during a respiratory cycle gets called tidal volume (Vt). Minute ventilation determines (MV) the levels of carbon dioxide in the blood. “It can be calculated by multiplying the tidal volume with the respiratory rate” (Charron et al., 2011, p.2). Increasing Minute Ventilation decreases the level of carbon dioxide in the blood by increasing the rate at which the elimination of carbon dioxide from the blood takes place. Decreasing the M.V increases the level of pulmonary carbon dioxide by reducing the rate at which carbon dioxide gets eliminated from the blood. The non-perfused areas in the natural respiratory tract become referred to as Dead Space (VDS). Dead space describes the parts and components of the respiratory system that do not indulge in the removal of carbon dioxide.

The Mean Distribution Time (MDT) defines the time available for alveolar diffusion and “distribution of tidal gas” (Aboab et al., 2012, p.1). The ratio of the dead space versus that of the tidal volume determines the lung’s capability to transport carbon dioxide. This process gets affected by pathology as well as by the settings of the ventilator. When blood perfusion and air ventilation do not match, there is an abnormal dead space, which manifests itself in the form of disorders such as pulmonary embolism. The condition becomes characterized by ventilation of the alveoli while blood perfusion is not taking place. Increased dead space to tidal volume (VDS/VT) ratio causes abnormal oxygenation and irregular ventilation.

The Fraction of Inspired Oxygen (FiO2) connotes the percentage of oxygen in the air that the ARDS patient inhales. The FiO2 of room air is twenty-one percent. An increase in the amount of inspired oxygen to levels beyond sixty percent gets attributed to an increase in the release of free radical oxygen, which could harm the cells due to the poisonous nature of oxygen. Arterial carbon dioxide (PACO2) decreases because of a reduction in ventilation (Charron et al., 2011, p.2). Patients suffering from ARDS have poor respiratory systems and need the number of inspired oxygen levels to stay over sixty percent (Forel et al., 2012). High levels of Fraction of Inspired Oxygen become recommended for them even when they are in danger of oxygen toxicity. Mechanical ventilators get used to cut the FiO2 to safe levels. Dead space ventilation allows the alveoli that do not take part in the ventilation process to expand. This will increase the surface area available for oxygenation and ventilation. The method gets called alveolar recruitment and it becomes achieved through maximizing the capillaries of the alveoli (Niklason et al., 2008). Alveolar sacs containing dead spaces are capable of remaining open and functioning effectively.

Associated Diseases

ARDS becomes associated with ALI (Acute Lung Injury). This disease becomes characterized by the injury of the lungs due to hypoxemic-related disorders (Bhadade et al., 2011). It occurs when sepsis triggers systematic inflammation of the lung. Sepsis is a negative response by the body towards a disease or an infection. It gets caused by the invasion and a quick spread of bacteria within the bloodstream. The normal response of the body’s immune system is to fight diseases, but on the happening of sepsis, the immune system becomes agitated and overwhelmed. Primary ALI occurs when the liver becomes injured directly. For instance, it occurs when a person suffers from pneumonia disease (Arnal, Fathallah, Auquier, Roch, Azoulay, & Papazian, 2012). Secondary ALI is normally caused by indirect injury on another organ of the body such as an illness of the pancreas. It becomes considered quite severe but is not as fatal as ARDS.

Clinical Effects

It becomes estimated that a third of the people who suffer from ARDS, end up dying from the disease. The survivors are able to recover the normal functioning of their lungs, though most of them still contract mild permanent damage to the lungs. During the time that the lungs are not functioning properly, the brain does not receive enough oxygen and, as a result, may cause brain damage to occur (Forel et al., 2012). Patients with ARDS thus suffer from memory loss and a host of other psychological problems.

Current Therapy

Dead space ventilation can take on various forms. In Controlled Mechanical Ventilation, the ventilator takes up the complete role of breathing. A rate and volume get set for the ventilator. The patient breathes naturally in this mode because he is entirely sedated and almost paralyzed. This mode is not comfortable for the patient and is highly discouraged.

In Intermittent Mechanical Ventilation, the mechanical ventilator becomes set in such a way that it conveys a certain amount of breaths each minute with a regulated tidal volume. The patient has the freedom to breathe in and out without depending on help from the ventilator. The pressure becomes added to the breaths generated by Intermittent Mandatory Ventilation (IMV). The extra pressure supports the patient when they are taking their own breaths since much energy becomes expended in inhalation. The workload of breathing reduces by increasing the pressure, and the patient can generate high spontaneous tidal pressure (Bhadade et al., 2011). The intermittent mechanical ventilator method was traditionally used to wean the patient, but modern physicians have stopped using it as it causes tremendous muscle fatigue on a respiratory system that has not fully recovered.

Pressure control ventilation modes can become recommended over volume control ventilation modes because they pose little risk of injuring the alveolar sac. This is because they decrease the level of stretching that the alveoli undergo, in weak lungs, such as those of people suffering from ARDS (Niklason et al., 2008). The tidal volume is not set, but it gets achieved through changes in pressure. Patients become encouraged to breathe spontaneously when pressure is at the highest level.

High-frequency ventilators use a technique similar to the airways pressure ventilation, but small breaths are rapidly delivered to the patient (Aboab et al., 2012). The rapid frequency of delivering breath keeps the alveoli open, thus, allowing oxygen to become delivered easily, and carbon dioxide to become eliminated without complications. This method requires the patient to become sedated and paralyzed. In the pressure support system, the ventilator “conveys a controlled amount of pressure when the patient starts a natural breath” (Sundaresan et al., 2011, p.2). Positive End Expiratory Pressure (PEEP) becomes hailed as one of the most fundamental mechanisms in treatment of ARDS patients. It promotes alveolar recruitment at the end by maintaining the unstable units of the lung in an open state (Sundaresan et al., 2011).

Effects of Therapy

Dead space ventilation mechanisms usually create complications such as volutrauma, hypotension, and in some cases, Ventilator Associated Pneumonia (VAP). Volutrauma increases the risk of death and multiple organ failure and becomes related with high chances of death in the intensive care unit (Forel et al., 2011, p.8). Volutrauma can become avoided by keeping plateau pressures as low as possible. Hypotension becomes caused by reduced pleural pressure resulting from the bringing in of positive pressure. It can become reversed by administering fluids and adjusting the ventilator. Ventilator associated pneumonia is a fatal complication that arises from dead space ventilation. It increases the patient’s mortality, morbidity, and the time span during which the patient gets supported by the ventilator.

Ventilator associated pneumonia is usually treated by the use of antibiotics that act on the pathogens that are under suspicion and employment of bronchoscopic mechanisms. The condition can become prevented by shortening the periods during which the patient undergoes mechanical ventilation (Niklason et al., 2008). The patient should also be placed in a semi-recumbent position as opposed to a supine position. Patients most likely may suffer from deep vein thromboses, a decline in nutritional condition and pressure ulcers. Noninvasive ventilation rules are in high demand, and they will soon phase out mechanical ventilation rules. The methods use both nasal and oral face masks in place of tubes.

Role of the Respiratory Therapist

Respiratory therapists assess, treat and care for persons who have breathing and other cardiopulmonary problems. They conduct all therapeutic treatments and diagnostic processes involved in respiratory care. They also oversee the work of respiratory therapy technicians and give them precise rules for use when delivering care.

Most duties of respiratory therapists interact with those of respiratory technicians. Nevertheless, the responsibilities of therapists are superior to those of technicians. For instance, respiratory therapists offer physicians guidance on how to structure and adjust plans for patient care. Also, respiratory therapists tend to offer a complex remedy that requires significant, a sovereign evaluation like caring for patients in intensive care units.

Respiratory therapists assess and give care to patients in different groups ranging from infants to elderly patients. They offer emergency treatment to victims of shock and heart failure and short-term care to patients with chronic asthma.

Therapists interrogate patients and do physical evaluations as well as diagnostic assessments to study patients (Niklason et al., 2008). For instance, they test the PH levels of a patient to find out concentration levels of blood. They also check the level of inhalation in a patient to find out the absorption of gases in the blood.

Respiratory therapists ask patients to inhale through a gadget that records oxygen stream and volume during breathing to assess the working of lungs. This becomes realized through evaluating the reading through the respiratory device against the height, sex, age and weight of the patient to search for any lung problems.

Respiratory therapists train patients on how to inhale the aerosol and enhance a patient’s concentration of oxygen, by using oxygen masks and setting levels of oxygen flow that physicians recommend.

Therapists should conduct frequent examinations on equipment and patients. When patients show breathing problems or abnormal levels of acidity and alkalinity in blood therapists adjust settings of the ventilator according to doctors’ instruction. They also check machinery for any mechanical problems in case of breathing problems.

Respiratory therapists carry out chest physiotherapy on patients to boost breathing and remove mucus. Therapists shake the rib cages of patients by drumming their upper bodies to draw off mucus.

Therapists also work in home care settings. They teach patients along with their families on how to use life support systems and ventilators (Bhadade et al., 2011). Therapists who work in home care settings visit patients at home to check on them as well as to clean the equipment. They check the home environment and make necessary recommendations to patients and family members.

Respiratory therapists also engage in providing the proper nutrients to patients who have undergone dead space ventilation. Therapists design regimens of nutrition that are patient-specific (Bhadade et al., 2011). In addition, they always make sure that adequate oxygenation gets provided and that the hemodynamic function and airways get supported. They have to undertake these actions because perfusion of the ARDS patient should become maximized, in the blood capillary system, and this can only be done by increasing fluids to make sure that oxygen is readily transported between the pulmonary capillaries and the alveoli. The therapist must thus constantly test the patient’s blood pressure, pulse pressure of the arteries, cardiac index, and the level of oxygen saturation.

Respiratory therapists also position patients in most proper ways to aid quick recovery. The Prone Position (PP) becomes advocated for as the most efficient one in critical care. This is because it permits the slow compartments of the lungs that have become excluded from respiration by ARDS to face recruitment (Charron et al., 2011).

Respiratory therapists do a blend of kinetic therapy and lateral, rotational therapy. They develop a structured routine in monitoring the patient for changes in the respiratory cycle and status such as reduced oxygenation, decreased saturation, increase in the rate of respiration and quick breath sounds (Niklason et al., 2008).

Therapists may want to give dexterous skin care to the patient to avoid pressure ulcers, as well as utilize devices that relieve pressure such as air mattresses, and continuously monitor the patient’s nutrition condition. Other areas that need the services of respiratory therapists include cessation counseling, pulmonary rehabilitation, disease prevention and diagnosis of apnea. They also care for critical patients in hospitals.


ARDS and dead space ventilation relate in various ways because dead space ventilation is a form of mechanical ventilation used in ARDS patients. A chief difference between ARDS and dead space ventilation is that ARDS causes impairment in the process of gas exchange, while dead space ventilation enhances the use of gas that does not interact with pulmonary blood. Conversely, dead space ventilation may cause abnormalities in the lung structure and damages to the lung tissues. This relationship points out that respiratory therapists and physicians, working with ARDS patients that are undergoing dead space ventilation should have extensive knowledge of the entire ventilation process so that they can give the best medical care possible.

Therapists must also conduct frequent examinations on equipment and patients so that they can adjust ventilator settings when patients show breathing problems or abnormal PH levels in the blood. Therapists must also check machinery and regulate them to make sure they are functioning appropriately without injuring their lungs. Therapists operating in home care settings should teach patients as well as their relatives how to use ventilators without causing excess force on lungs. Therapists must also constantly test the patient’s blood pressure, pulse pressure of the arteries, cardiac index, and the level of oxygen saturation in home care settings.

Pharmacological and ventilation technologies and therapies are evolving rapidly, and physicians must stay on the lookout for the new regimens and their advantages over traditional approaches. Respiratory therapists must always keep in mind that the modes of mechanical ventilation used will affect the delivery of medication, analgesia, and sedation to the patient. Respiratory therapists can adopt noninvasive ventilation techniques that involve the use of masks to give the best critical care to ARDS patients.


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