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Humidication in NICU Dr Padmesh

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Humidification in NICU - the concepts

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Humidication in NICU Dr Padmesh

  1. 1. HUMIDIFICATION IN NICU Dr Padmesh V DNB (Ped), DM (Neonatology)
  2. 2. • Ambient air is cooler and contains less water. • Alveolar air is fully saturated with water vapor at core body temperature. • This gradient in heat and water vapor pressure is maintained along the nose and upper airways.
  3. 3. • The inspired air gains heat and water vapor from the upper airway lining which is partly recovered when the expired gas loses heat and water condenses back to the airway surface. This recovery occurs because the upper airway temperature remains below core body temperature during expiration. • Breathing is associated with a net heat loss and water loss because the expired air temperature is higher than ambient temperature under normal circumstances.
  4. 4. Alveoli fully saturated with water vapor at core body temp Ambient air is cooler, with less water vapor INSPIRATION EXPIRATION Upperairway Upperairway Temperature of expired air is higher than ambient temperature
  5. 5. • The term “absolute humidity” (AH) is defined as the amount of water vapor per gas volume at a given temperature. (mg/L) • “Relative humidity” (RH) is the actual water vapor content of the gas volume (in milligrams) relative to the water vapor content (in milligrams) of this same gas volume at saturation at the same temperature. • There is a fixed relationship between AH, RH, and temperature.
  6. 6. • Absolute humidity is the amount of water vapour per litre of gas, expressed in mg/l. • Relative humidity is a measure of how much water vapour is in a gas compared to its capacity to hold water vapour. It is measured as a percentage.
  7. 7. • Water vapor in air will exert a gaseous pressure which amounts to a partial pressure of water of 47 mmHg when air is fully saturated with water vapor at 37 °C. This corresponds to a water vapor mass of 44 mg of water per liter of gas. • The partial pressure of water vapor at saturation depends solely on the temperature. • The fraction of water vapor pressure at saturation, 37 °C, and 760 mmHg ambient pressure is therefore FH2O = 47 mmHg/760 mmHg = 0.062, i.e., 6.2 %.
  8. 8. 1. Heated Humidifiers 2. Heat and Moisture exchangers (Artificial noses)
  9. 9. • Heated Humidifiers: • Should deliver inspiratory gas at or close to core body temperature and full saturation to endotracheally intubated infants. • Respiratory gas is warmed inside the humidification chamber to a set target temperature, and water vapor is added from the heated water reservoir.
  10. 10. • Heated Humidifiers: • A heated wire inspiratory circuit tubing is then used to maintain or slightly raise the gas temperature so as to prevent water rainout before the gas reaches the infant. • At a set humidifier chamber temperature of 37 °C, the gas will absorb a maximum of 44 mg/L of water which corresponds to full saturation (100 % RH).
  11. 11. • Heated Humidifiers: • Position of three temperature probes of a heated wire humidification system for infants. The user sets the target temperature to be reached at the endotracheal tube adaptor. This temperature is commonly set at or slightly above 37.0 °C. The temperature inside the humidifier chamber must be high enough to vaporize an amount of water near the absolute water content of gas saturated at 37 °C (44 mg/L). • Flow rate: 5L/min
  12. 12. • Recording the water consumption of the chamber over time is a simple test to check for sufficient vaporization. • Because most infant ventilators use a continuous constant circuit flow of known size, the absolute and relative humidity delivered at the chamber outlet can be calculated from the humidifier’s water consumption rate.
  13. 13. • Any decrease in gas temperature along the way from the humidification chamber to the Y adaptor will induce condensation if the gas was saturated at the chamber outlet. • This implies that any rainout in the tubing indicates a moisture loss of the respiratory gas. The gas will then reach the infant underhumidified. • It must be emphasized that rainout in the inspiratory limb of the ventilator circuit does not indicate proper humidification in such situations. To the contrary, condensation will necessarily be associated with underhumidification.
  14. 14. As temperature decreases, amount of water vapor the gas can hold also decreases. So if temp of inspiratory limb decreases, water will be lost from the gas, which will cause rain out, which ultimately causes under-humidification.
  15. 15. • The inspiratory gas can rapidly cool down in unheated segments of the circuitry. This is promoted by – large outer surface area of small-diameter tubings (particularly when corrugated), – by drafts around the tubing (air conditioned rooms), and – by a low room temperature. • The decrease in temperature will be larger with smaller gas flow rates due to the longer contact time. • Insulating unheated segments of the inspiratory circuit may partly obviate these problems.
  16. 16. • Therefore, in a regular application for an intubated subject, a heated humidifier can be set up with: – a chamber temperature of 37 °C (in order to saturate the gas with 44 mg/L of water). – To avoid loss of moisture in the inspiratory limb of the heated circuit, the target gas temperature at the Y adaptor can be set at 39 °C so that the gas arrives with slightly less than full saturation.
  17. 17. • The technology required for preterm infants is slightly more complex because the ventilator circuit passes through two different environments: – the room and – the incubator or radiant warmer. • Temperature probe close to patient connection monitors the inspiratory gas temperature. • It is commonly part of a servo control which aims at maintaining the set gas temperature at the Y adaptor by controlling the heated wire circuit’s power output.
  18. 18. • If temperature probe is in a heated field, it may register a temperature higher than actual inspiratory gas temperature as a result of radiation or convection from the warmer  Servo decreases heating output of the ventilator heated wire circuit  Loss of gas temperature and rainout. Note that the temperature probe controls servo of heated wire circuit and not the heating chamber of humidifier
  19. 19. • Insulating the temperature probe by a light-reflective patch or other material can improve performance of the system. • Another way to alleviate this problem is to place temperature probe just outside the heated field and use an unheated extension adaptor tubing to carry the gas through the heated field to the infant. The extension tube does not need to incorporate heated wires because its temperature is maintained by the heated field. • Using a circuit with two temperature probes, one outside the heated field and another one close to the Y adaptor. two temperature probes
  20. 20. • Note: Expiratory limb should pass down-hill from the patient manifold to prevent water trickling back into the patient • Minimum Humidification Requirements: • International standards recommend an absolute humidity level of inspired gas >33 mg/L in patients whose supraglottic airway is bypassed. (44 mg/L, 33 mg/L !)
  21. 21. 1. Heated Humidifiers 2. Heat and Moisture exchangers (Artificial noses)
  22. 22. • Artificial Noses (HME) • Heat and moisture exchangers (HMEs) are designed to recover part of heat and moisture contained in expired air. • A sponge material of low thermal conductivity inside clear plastic housing absorbs heat and condenses water vapor during expiration for subsequent release during inspiration. • Some HMEs are additionally coated with bacteriostatic substances and equipped with bacterial or viral filters (HMEF).
  23. 23. • Artificial Noses (HME) • HMEs may be an alternative to heated humidifiers because: – Simplification of ventilator circuit – Passive operation without requirement of external energy and water sources – No ventilator circuit condensate – Low risk of circuit contamination – Low expense
  24. 24. • Artificial Noses (HME) • Use of heat–moisture exchangers, or artificial noses, in neonates should be discouraged because they: – increase ventilation requirements, – increase CO2 levels, – lower body temperature, and – increase artificial airway blockage. May be used only for short term: eg: neonatal transport.
  25. 25. • Side effects of inadequate humidification: • Even if all other forms of infant warming are provided, ventilation with nonhumidified gases is a major reason for hypothermia in neonates. • Inadequate humidification of the respiratory tract may reduce mucociliary clearance: – airway obstruction by secretions, – gas trapping – VAP • Dry gases  Severe lung injury.
  26. 26. • What happens if hot air without humidity is given? • The increased temperature of a gas shifts the isothermal boundary (point at which gas completes equilibrium to body temp & humidity levels) to a point closer to airway opening. • At first glance, this seems beneficial because less mucosa is exposed to humidity deficit. However, because the effect of a given humidity deficit is concentrated on a smaller area of the mucosa, there is potential for a greater degree of damage.
  27. 27. • What happens if hot air without humidity is given? • Moreover, use of higher airway temperatures means that, even with lower humidity, there is relatively less opportunity for exhaled humidified air from within the lung to recondense some of its humidity. The result is an increase in the humidity deficit . • Thus, potential for adverse effects with use of heated wire circuit is exacerbated by inadequate humidity levels.