Respiratory gas humidification

Last updated May 13, 2024

Respiratory gas humidification is a method of artificially conditioning respiratory gas for the patient during therapy, and involves humidification, warming, and occasionally filtration of the gas being delivered. If these three measures are not performed to compensate for the natural conditioning of air by the respiratory system, lung infections and lung tissue damage may occur. This is particularly problematic in high gas-flow therapies such as [mechanical ventilation], in patient populations with highly sensitive respiratory tracts (i.e. asthmatics), or among those requiring ventilation for longer periods of time. The two methods currently available for this purpose are active or passive respiratory gas humidification.

Active respiratory gas humidifiers

An active respiratory gas humidifier ensures that patients on mechanical ventilation are supplied with optimally conditioned respiratory gas. In active humidifying processes, moisture and heat is input to respiratory gas by an electrically powered humidifier. Performance data and safety-related requirements for active respiratory gas humidifiers are specified by the standard ISO 8185. According to that standard, the minimum water content of inspired respiratory gas is ca. 33 mg/dm³ and the maximum respiratory gas temperature is ca. 42 °C.

The aggregation of water in the gas produced by an active respiratory gas humidifier may be a suspension, or aerosol, which is produced by a nebulizer; or particulate water, output from an evaporator or bubble humidifier.

Nebulizers

Nebulizers generate aerosols consisting of droplets of various sizes that are admixed to the inspired respiratory gas. Types of nebulizers currently on the market include

Small volume nebulizers, which are used to administer medications such as salbuterol or albuterol.
Large volume nebulizers, which are similar to bubble humidifiers except for the addition of an air entrainment port, and
Ultrasonic nebulizers, which may carry a risk of overwatering the patient.

The high density mist produced by nebulizers is useful in decreasing the viscosity of respiratory secretions in those suffering from conditions such as cystic fibrosis, croup, epiglottitis, and bronchiectasis.

Evaporators

Evaporators enrich the inspired respiratory gas with water vapor. In a throughflow evaporator, the inspiration flow is led through a warmed up water bath, in case of a surface evaporator however the inspiration flow is guided along the surface of the water level. Consequently, a surface evaporator transports only water vapor and no water droplets into the patient. Therefore, the risk of passing on germs by surface evaporators is minimal^{[ citation needed ]}.

Bubble humidifiers

In a bubble humidifier, or bubble bottle as they are affectionately known by respiratory therapists, the inspiration flow is guided through a capillary system. In this capillary system warmed up water is circulating. Although the humidifying capacity of a bubble respiratory gas humidifier is rather low, it may be improved by increasing the water temperature. A bubble bottle is mostly used in oxygen therapy with high flow rates via a mask, nasopharyngeal catheter, or nasal cannula in order to prevent drying of the mucous membranes in the nose and mouth.^[1]^[2]

Passive respiratory gas humidifiers

Passive respiratory gas humidifiers are independent from any external energy source or external water supply. They function as heat and moisture exchangers (HMEs) and are placed like an artificial nose between a tube and Y piece.^{[ clarification needed ]}^{[ citation needed ]} Here they withdraw heat and moisture from expirations, which they resupply to the inspired gas during the following inspiration. As there are significant functional differences among the various HMEs on the market, respiratory therapists should test the efficacy of each individual model. The ideal HME has high reversible water retention capacity, small internal volume, and low flow resistance.^{[ citation needed ]}

To enable the absorption of sufficient amounts of water and heat, the expiratory stream of respiratory gas must be fully filtered through the HME. Leakages in the system, such as may be caused by bronchial fistulae, will render this system less effective.^{[ clarification needed ]} Other negative effects of this technology include increased secretions (i.e. mucus) and nosebleeds, either or which may clog an HME. In such cases, the application of active respiratory gas humidifiers is recommended.^{[ citation needed ]}

Related Research Articles

Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.

An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be generated from natural or human causes. The term aerosol commonly refers to the mixture of particulates in air, and not to the particulate matter alone. Examples of natural aerosols are fog, mist or dust. Examples of human caused aerosols include particulate air pollutants, mist from the discharge at hydroelectric dams, irrigation mist, perfume from atomizers, smoke, dust, sprayed pesticides, and medical treatments for respiratory illnesses.

A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons, or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rinks and swimming pools, as well as manufacturing plants or storage warehouses. Typical air conditioning systems combine dehumidification with cooling, by operating cooling coils below the dewpoint and draining away the water that condenses.

Mechanical ventilation or assisted ventilation is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air into and out of the lungs, with the main goal of helping the delivery of oxygen and removal of carbon dioxide. Mechanical ventilation is used for many reasons, including to protect the airway due to mechanical or neurologic cause, to ensure adequate oxygenation, or to remove excess carbon dioxide from the lungs. Various healthcare providers are involved with the use of mechanical ventilation and people who require ventilators are typically monitored in an intensive care unit.

Aquatic respiration is the process whereby an aquatic organism exchanges respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excreting carbon dioxide and some other metabolic waste products into the water.

<span class="mw-page-title-main">Positive airway pressure</span> Mechanical ventilation in which airway pressure is always above atmospheric pressure

Positive airway pressure (PAP) is a mode of respiratory ventilation used in the treatment of sleep apnea. PAP ventilation is also commonly used for those who are critically ill in hospital with respiratory failure, in newborn infants (neonates), and for the prevention and treatment of atelectasis in patients with difficulty taking deep breaths. In these patients, PAP ventilation can prevent the need for tracheal intubation, or allow earlier extubation. Sometimes patients with neuromuscular diseases use this variety of ventilation as well. CPAP is an acronym for "continuous positive airway pressure", which was developed by Dr. George Gregory and colleagues in the neonatal intensive care unit at the University of California, San Francisco. A variation of the PAP system was developed by Professor Colin Sullivan at Royal Prince Alfred Hospital in Sydney, Australia, in 1981.

Oxygen therapy, also referred to as supplemental oxygen, is the use of oxygen as medical treatment. Supplemental oxygen can also refer to the use of oxygen enriched air at altitude. Acute indications for therapy include hypoxemia, carbon monoxide toxicity and cluster headache. It may also be prophylactically given to maintain blood oxygen levels during the induction of anesthesia. Oxygen therapy is often useful in chronic hypoxemia caused by conditions such as severe COPD or cystic fibrosis. Oxygen can be delivered via nasal cannula, face mask, or endotracheal intubation at normal atmospheric pressure, or in a hyperbaric chamber. It can also be given through bypassing the airway, such as in ECMO therapy.

<span class="mw-page-title-main">Nebulizer</span> Drug delivery device

In medicine, a nebulizer or nebuliser is a drug delivery device used to administer medication in the form of a mist inhaled into the lungs. Nebulizers are commonly used for the treatment of asthma, cystic fibrosis, COPD and other respiratory diseases or disorders. They use oxygen, compressed air or ultrasonic power to break up solutions and suspensions into small aerosol droplets that are inhaled from the mouthpiece of the device. An aerosol is a mixture of gas and solid or liquid particles.

A humidifier is a household appliance or device designed to increase the moisture level in the air within a room or an enclosed space. It achieves this by emitting water droplets or steam into the surrounding air, thereby raising the humidity.

<span class="mw-page-title-main">Nasal cannula</span> Medical device to deliver supplemental oxygen

The nasal cannula (NC) is a device used to deliver supplemental oxygen or increased airflow to a patient or person in need of respiratory help. This device consists of a lightweight tube which on one end splits into two prongs which are placed in the nostrils curving toward the sinuses behind the nose, and from which a mixture of air and oxygen flows. The other end of the tube is connected to an oxygen supply such as a portable oxygen generator, or a wall connection in a hospital via a flowmeter. The cannula is generally attached to the patient by way of the tube hooking around the patient's ears or by an elastic headband, and the prongs curve toward the paranasal sinuses. The earliest, and most widely used form of adult nasal cannula carries 1–3 litres of oxygen per minute.

Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body.

The venturi mask, also known as an air-entrainment mask, is a medical device to deliver a known oxygen concentration to patients on controlled oxygen therapy. The mask was invented by Moran Campbell at McMaster University Medical School as a replacement for intermittent oxygen treatment. Dr. Campbell was fond of quoting John Scott Haldane's description of intermittent oxygen treatment; "bringing a drowning man to the surface – occasionally". By contrast the venturi mask offered a constant supply of oxygen at a much more precise range of concentrations.

<span class="mw-page-title-main">Thermospray</span>

Thermospray is a soft ionization source by which a solvent flow of liquid sample passes through a very thin heated column to become a spray of fine liquid droplets. As a form of atmospheric pressure ionization in mass spectrometry these droplets are then ionized via a low-current discharge electrode to create a solvent ion plasma. A repeller then directs these charged particles through the skimmer and acceleration region to introduce the aerosolized sample to a mass spectrometer. It is particularly useful in liquid chromatography-mass spectrometry (LC-MS).

Heated humidified high-flow therapy, often simply called high flow therapy, is a type of respiratory support that delivers a flow of medical gas to a patient of up to 60 liters per minute and 100% oxygen through a large bore or high flow nasal cannula. Primarily studied in neonates, it has also been found effective in some adults to treat hypoxemia and work of breathing issues. The key components of it are a gas blender, heated humidifier, heated circuit, and cannula.

Heat and moisture exchangers (HME) are devices used in mechanically ventilated patients intended to help prevent complications due to "drying of the respiratory mucosa, such as mucus plugging and endotracheal tube (ETT) occlusion." HMEs are one type of commercial humidification system, which also include non-heated-wire humidifiers and heated-wire humidifiers.

Heat and moisture exchangers (HME) are used after laryngectomy to help reduce breathing restrictions and compensate nasal functions.

Surgical humidification is the conditioning of insufflation gas with water vapour (humidity) and heat during surgery. Surgical humidification is used to reduce the risk of tissue drying and evaporative cooling.

Ventilation-perfusion coupling is the relationship between ventilation and perfusion processes, which take place in the respiratory system and the cardiovascular system. Ventilation is the movement of gas during breathing, and perfusion is the process of pulmonary blood circulation, which delivers oxygen to body tissues. Anatomically, the lung structure, alveolar organization, and alveolar capillaries contribute to the physiological mechanism of ventilation and perfusion. Ventilation-perfusion coupling maintains a constant ventilation/perfusion ratio near 0.8 on average, while the regional variation exists within the lungs due to gravity. When the ratio gets above or below 0.8, it is considered abnormal ventilation-perfusion coupling, also known as a ventilation–perfusion mismatch. Lung diseases, cardiac shunts, and smoking can cause a ventilation-perfusion mismatch that results in significant symptoms and diseases, which can be treated through treatments like bronchodilators and oxygen therapy.

A breathing apparatus or breathing set is equipment which allows a person to breathe in a hostile environment where breathing would otherwise be impossible, difficult, harmful, or hazardous, or assists a person to breathe. A respirator, medical ventilator, or resuscitator may also be considered to be breathing apparatus. Equipment that supplies or recycles breathing gas other than ambient air in a space used by several people is usually referred to as being part of a life-support system, and a life-support system for one person may include breathing apparatus, when the breathing gas is specifically supplied to the user rather than to the enclosure in which the user is the occupant.

References

↑ "What options exist for humidification of oxygen delivered to patients?". Open Critical Care. Retrieved 2024-05-10.
↑ "Oxygen Therapy". saralmind.com. Retrieved 2024-05-10.

W. Oczenski, H. Andel und A. Werba: "Atmen - Atemhilfen." Thieme, Stuttgart 2003, ISBN 3-13-137696-1
J. Rathgeber: "Grundlagen der maschinellen Beatmung." Aktiv Druck, Ebelsbach 1999, ISBN 3-932653-02-5
S. Schäfer, F. Kirsch, G. Scheuermann und R. Wagner: "Fachpflege Beatmung." Elsevier, 2005, ISBN 3-437-25182-1
A. Schulze: "Respiratory Gas Conditioning and Humidification." In: Clin Perinatol, 2007; 34: 19–33, ISSN 0095-5108
M.P. Shelly, G.M. Lloyd und G.R. Park: "A review of the mechanism and methods of humidification of inspired gases." In: Intens Care Med, 1988; 14:1, ISSN 0342-4642
F. Kapadia, M. Shelly, J.M. Anthony, et al.: "An active heat and moisture exchanger." In: Br. J. Anaest. 1992; 69: 640–642, ISSN 0007-0912cx

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[1] "What options exist for humidification of oxygen delivered to patients?". Open Critical Care. Retrieved 2024-05-10.

[2] "Oxygen Therapy". saralmind.com. Retrieved 2024-05-10.

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