Understanding Humidification, Medical Gas and Medical Aerosols

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The exchange of heat and moisture occurs in the upper respiratory tract, primarily in the nose. The inspired air is filtered, heated, and humidified before moving down through the lungs, in order to achieve the BTPS condition (body temperature, ambient pressure, saturated with water vapor). Unlike the BTPS condition, the normal ISB (isothermic saturation boundary) occurs 5 cm below the carina, where the relative humidity and temperature remain constant. However, the ISB can be shifted when a person breathes in dry, cold air and/or when the upper airway is bypassed. The primary goal for humidification is to maintain the normal BTPS and ISB conditions because inadequate humidification can potentially cause atelectasis, increased airway resistance and incidence of infection as well as thick, dehydrated secretions1.

Medical gas is used in oxygen therapy, which may be beneficial for patients with suspected hypoxemia, major trauma, and acute myocardial infarction, where PaO2 is less than 60 mmHg and SaO2 is less than 90% breathing on room air. Supplemental oxygen can help decrease the demands on the heart and lungs. Hypoxemia causes the cardiopulmonary system to increase both cardiac output and ventilation due to the decrease in oxygen circulating in the blood and tissues1. Supplemental oxygen can be provided through low-flow and high-flow systems. Low-flow systems include the nasal cannula, nasal catheter and transtracheal catheter. These devices do not meet or exceed the inspiratory flow demands of the patient. The nasal cannula consists of two prongs that fit directly into the nose, which is connected to the oxygen supply tubing. When the input flow is 4 L/min or greater, humidification is required in order to avoid patient discomfort from bleeding and nasal dryness. High-flow systems include air-entrainment mask (AEM), air-entrainment nebulizer, blending system, and high-flow nasal cannula system. These devices meet or exceed the inspiratory flow demands of the patient. The air-entrainment nebulizer can achieve humidification by producing an aerosol, and temperature can be controlled by adding heating components2.

The utilization of medicated aerosol therapy may be beneficial for patients suffering from pulmonary disorders. The medicated aerosol delivers therapeutic doses into the lungs while reducing systemic side effects. Some of the aerosol devices that can be used for the treatment of children and adults include metered dose inhalers (MDI) and dry power inhalers (DPI). Selecting the device is based on the need for a specific drug and the target area. MDIs are light, portable, and provide consistent drug delivery. The breath-actuated MDI design has several advantages over the conventional MDI when using with children because less coordination is required while reducing the amount of medication deposited into the oropharyngeal area.  DPIs are small, portable, and breath-actuated; the patient creates an aerosol by breathing in deeply and rapidly through the inhaler because there is no propellant. These devices may be more suited for older children because of the high inspiratory flow required to deliver the medication3.

 

References:

 

  1. Kacmarek R, Stoller J, Heur A, Egan DF. Humidity Therapy and Oxygen Therapy. In: Egan’s Fundamentals of Respiratory Care, 10th edition Elsevier; 2013:818-822, 910-911.
  2. Cairo JM. Devices for Administering Medical Gases. In: Mosby’s Respiratory Care Equipment, 9th edition Elsevier; 2014:87-105.
  3. Ari A, Fink JB. Aerosol Drug Delivery to Infants and Pediatric Patients. RT 2012;25(1):14-17 4p.

 

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