therapy overview

Essential Humidity to maximize tolerance of noninvasive ventilation One key factor to a successful noninvasive ventilation strategy is the use of heated humidification.

The high pressures and flow rates of the gases used with noninvasive positive pressure ventilation (NPPV or NIV) can overwhelm the patient’s natural conditioning system. Overwhelming the airways with large volumes of cool, dry gas can often cause the patient’s respiratory system to deteriorate further. Delivering Essential Humidity (31 °C, 32 mg/L absolute humidity (AH)) with NIV increases patient comfort and tolerance to the therapy and alleviates side effects, such as airway drying and reduced secretion clearance. A patient who tolerates the therapy provided will require fewer breaks in ventilation and the risk of NIV failure, resulting in possible intubation, is considerably reduced. NIV is any form of ventilatory support applied without the use of an endotracheal tube and covers both bi-level ventilation and continuous positive airway pressure (CPAP) with or without inspiratory pressure support.1 NIV promotes gas exchange in the lungs, providing a bulk flow of fresh gas to the alveoli on each inspiration. The use of inspiratory and expiratory positive pressure helps to reduce the work of breathing for the patient. NIV is used most successfully on hypercapnic patients with a chronic obstructive pulmonary disease (COPD) exacerbation, patients with acute pulmonary edema resulting in respiratory failure, immuno-compromised patients and to facilitate extubation in COPD patients. It is also commonly used in other patient groups, such as asthmatics, in post-operative respiratory failure and with do-not-intubate patients.2

THERAPY OVERVIEW | Essential Humidity to maximize tolerance of noninvasive ventilation

WHY IS HUMIDIFICATION ESSENTIAL? When breathing naturally the air is warmed and humidified in the upper airway before

Nasal 31 °C, 31 mg/L, 96% RH

it passes into the lower airways of the lungs. A normal subject breathing in ambient air

Oral 27 °C, 20 mg/L, 75% RH

(22 °C, 28% Relative Humidity (RH)) warms and humidifies the air on inspiration to an

22 °C, 7 mg/L

average of 31 °C, 96% RH with nasal breathing and 27 °C, 75% RH with mouth breathing, by the time it reaches the pharynx.3

37 °C, 44 mg/L

It is often considered that patients on NIV do not require humidification as they are not intubated and have an intact upper airway that may be utilized. However, patients who are receiving NIV breathe gas at much higher pressures and flows than normal breathing. In addition, users of the therapy often have compromised airways which are less efficient at warming and humidifying gas due to the

Conditions associated with the typical NIV patient

nature of their respiratory failure.

Airway Drying

The airways of hospital patients may be further

The airway lumen is lined by epithelial cells with

compromised as they receive respiratory

many hair-like cilia on the lumen surface, which

interventions in the form of either:

move in unison to transport mucus and foreign

• cold, dry medical gas, which absorbs heat and moisture from the airway surface as it passes down the airway; or • gas that has been warmed by a ventilator

particles out of the lungs. The removal of heat or moisture from the oral and nasal airways can cause the mucus lining the airway to become dry and sticky, inhibiting the movement of the cilia.4 Salah et al. (1988) found that breathing

but has not received any additional

dry air for 30 minutes resulted in excessive

humidification. This heating will lower the

water loss from the nasal mucosa which caused

relative humidity of the gas, causing it to

mucociliary transport to slow.5 Evidence suggests

remove further moisture from the airway.

that damage is caused to the epithelia after only one hour of dry gas.6

High Respiratory Rate Patients using NIV therapy are often dyspneic and have short, rapid breathing. This is because they try to inhale greater quantities of air into their lungs to improve gas exchange. This rapid breathing rate, combined with the higher-thannormal pressures and gas flows delivered with NIV, leads to increased loss of moisture from the upper airways.7

Oral Breathing Reduces Work of Breathing Many patients using NIV are in respiratory distress and tend to breathe through their mouth as this is easier. By mouth breathing instead of nose breathing, the gas that reaches the airways is 4 °C cooler and, more importantly, contains 11 mg/L less water than if it had been inhaled through the nose.3

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THE CONSEQUENCES of inadequate humidification FOR THE PATIENT The consequences of inadequate use of humidification during NIV are widely recognised. The NIV guidelines of the American Thoracic Society (ATS) state that “Inadequate humidification may cause patient distress, especially if pipeline or cylinder gas is used”.1 For the NIV patient, this deficiency of heat and humidity can result in various symptoms, as outlined below. These effects may combine to cause increased difficulties in ventilation. This can include reduced pressure in the lower airways, caused by restriction in the upper airways, leading to an increased work of breathing.8 9

Patient complications resulting from poor humidification

• Drying of the oral and nasal airways causing a sore, dry and inflamed throat and nasal passages.7 10 • Increased rhinitis/rhinorrhea and nasal congestion.11 12 This is worse in elderly patients.13 • Thickened secretions reducing mucociliary clearance from the airways and, in extreme circumstances, resulting in the formation of a life-threatening mass of thick secretions which can occlude the airways and require emergency removal.14 • Increased bronchoconstriction, further restricting the flow of gas into the lungs.9 • Cracked lips, nosebleeds and swollen tongue.

CASE STUDY

Wood et al., 200014

Figure 1

A 66-year-old male underwent abdominal surgery for rectal carcinoma. During recovery the patient was transferred to CPAP for 48 hours and was then transferred to NIV using a full face mask for six days. After six days of NIV, the patient had dry oral mucosa and dried secretions in the posterior pharynx. NIV was substituted with an 80% aerosol mask. After one hour the patient developed progressively worsening respiratory stridor associated with tachypnea and increased work of breathing. The nasogastric tube was removed and respiratory distress developed immediately. Intubation was attempted revealing a large object occluding the vocal cords which was removed using forceps (Figure 1). The removed object was a 5x7 cm mass consisting of inspissated secretions and blood. The patient returned to a 90% aerosol mask and complete respiratory recovery occurred without further NIV.

Life-threatening compromises in airway patency may increase in frequency as the use of NIV continues to grow. Such events could be limited by the use of adequate humidification, a heightened sense of awareness and limiting the duration of NIV.

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THERAPY OVERVIEW | Essential Humidity to maximize tolerance of noninvasive ventilation

THE BENEFITS OF HEATED HUMIDIFICATION The benefits of heated humidification during NIV are widely accepted. In their recent review on NIV, Nava and Hill 2009 stated that “Humidification of the upper airway is important to improve comfort and tolerance.” 15

This level of conditioning is the average

humidity of the gas delivered on their face

temperature and humidity in the pharynx of

in order for them to accept the therapy. With

a normal subject breathing in ambient air on

Essential Humidity the gas is delivered at 31 °C

inspiration through the nose.3 The delivery of

(fully saturated); this is the lower temperature

Essential Humidity ensures that the gases are

in the range of normal facial skin temperatures

conditioned so that heat and moisture are not

(31.1 °C to 35.4 °C).16 Delivering gas at a

lost from the airway surface.

temperature lower than skin temperature

During NIV, patients typically wear a face mask

Delivering Essential Humidity (31 °C, 32 mg/L)

to receive the therapy. It is important that

during NIV is beneficial to patient outcome.

the patient can tolerate the temperature and

Maximize patient tolerance to the therapy It is estimated that up to 70% of NIV patients experience adverse effects from the therapy, to the extent that 25 to 33% have great difficulty tolerating NIV in both the acute and chronic settings.7 Windisch et al. (2008) reported that 31 out of 85 (37%) of domicile NIV patients experienced a dry throat.17 Many of these adverse effects may be reversed by the introduction of heat and humidification. This improves the patient’s comfort and tolerance to NIV, allowing them to use the therapy for longer with fewer breaks in ventilation. Several researchers have reported increased patient comfort using heated humidification. Tuggey et al. (2007) showed that in healthy volunteers using nasal bi-level NIV, heated humidification had significantly higher comfort scores compared to no humidification.11 This work is supported by Massie et al. (1999) who found the same results using nasal CPAP and also demonstrated that these benefits were obtainable only with heated humidification and not with cold passover humidification.18 In another study, Wiest et al. (1999) concluded that the increased comfort from using heated humidification in CPAP patients led to them using the therapy for longer.19 Long-term studies on domicile patients also reflect this.20 After 12 months of use, 10 out of 14 patients chose to continue using heated humidification with their NIV therapy.

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means condensation, which can cause discomfort, will not form on the patient’s face.

Minimize airway drying

Improve secretion clearance

Delivering Essential Humidity avoids drying

Drying of the airways causes mucus

of the oro-nasal airway, preventing patient

secretions to become viscous and sticky,

discomfort. There are many reports of

which allows them to build up in the airway

this in the literature. Tuggey et al. (2007)

causing an obstruction to the flow of gas.14

demonstrated that if a person has their

Heated humidification reduces the build

mouth open while using nasally delivered

up of secretions by preventing dehydration

bi-level ventilation, the resulting mouth leak

of the airways.24 This is achieved by two

is a highly unidirectional nasal air-flow.11

mechanisms: heat and humidification, which

This mouth leak dries the airways and

prevent damage to the mucociliary transport

causes a large increase in nasal resistance.

system and inhibit dehydration of the

Heated humidification prevented the

airways’ mucus secretions so that they may

adverse effects of mouth leak, reducing nasal resistance and increasing the effective

Normal

Bronchoconstriction

move more easily. Chalon et al. (1972) found that dry anesthetic

tidal volume. The same was also found for

gas caused damage to epithelial cells,

nasally delivered CPAP.8

including the cilia, of patients after one hour.6

The benefits of heat and humidification in

nasal mucosal blood flux. This is likely to

However, this damage did not occur if the

reducing resistance in the nasal airway equate

be part of the mechanism by which nasal

patients received 100% RH at 37 °C. There

to pressure drops of 5 to 7.5 cm H2O/L across

resistance is increased and can be prevented

is other direct evidence of the benefits of

the nose. For NIV patients, a pressure drop of

by humidifying the air.21

heated humidification. It has been shown that

Delivering heat and humidity during NIV

the mucociliary beat frequency and mucus

also prevents airway drying when the patient

transport velocity of ovine trachea are both

this size may cause a critical decrease in the positive pressure delivered to the patient’s lower airways and affect their ventilation.8

keeps their mouth closed and mouth leak

reduced when the air temperature is 34 °C,

Other researchers have shown that when

is not present. This reduces the water lost

100% RH or 30 °C, 100% RH but not when it

patients keep their mouth open during nasal

from the airways by 38% compared to cold

is 37 °C, 100% RH.4

CPAP, the mouth leak causes an increase in

humidification.22 Fontanari et al. (1996) found that nasal inhalation of cold, dry air (-4 °C, 0.3% RH) or dry-only air (23 °C, 0.3% RH) both caused an increase in nasal resistance

Resistance (cmH2O.L/s)

Effect of humidification on airway resistance during NIV after 5-minute leak challenge

when compared to inhaling room-temperature moist air (23 °C, 97% RH).23

8

The delivery of Essential Humidity can also

7

minimize airway constriction, reducing the

6 5

baseline resistance

4 3

work of breathing. In a study on asthmatics, Moloney et al. (2002) gave a dry air challenge which caused airway dehydration, triggering

2

bronchoconstriction and a drop in the forced

1

With Heated Humidification

Without Humidification

expiratory volume over one second (FEV1 ). This was prevented when the asthmatics were given heated and humidified air.9

Adapted from Tuggey et al. (2007)11

Normal

Occluded Airway

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THERAPY OVERVIEW | Essential Humidity to maximize tolerance of noninvasive ventilation

Key factors to predict success with NIV The table below shows factors that can predict whether NIV succeeds or fails.

Factor

Hypercapnic respiratory failure

Hypoxemic respiratory failure

Improvement after 1 to 4 hours of NIV

Predicts Success 25 26

–

Low pH on admission

Predicts Failure 27 28

–

Severity of illness

Predicts Failure 28 29

Predicts Failure 30

Comfort/Tolerance

Predicts Success 28 31

–

PaO2/FiO2

Not Predictive 29 32

Predicts Failure 30

Expectoration difficulties

Predicts Failure 28 31

–

Age

Not Predictive 25 29

Predicts Failure 30

Pneumonia on admission

Predicts Failure 26 31

Predicts Failure 30

The factors highlighted can be modified and patient outcome improved by hospital care.

Modifiable predictive factors • Improvement after 1 to 4 hours of NIV: can be influenced by efficient gas exchange causing physiological improvements in pH, partial pressure of oxygen in arterial blood (PaO2 ) and respiratory rate. Heat and humidification prevent increases in upper airway resistance and may improve gas exchange.8 11 23 • Comfort and tolerance to NIV: is affected by nasal congestion, drying of the upper airways, mask comfort, ulcerations and patient-ventilator synchrony. Humidification helps to prevent nasal congestion and drying of the upper airway mucosa, which occurs in 36 to 89% of all NIV patients.7 9 11 33 • Expectoration: is influenced by the secretion clearance rate, viscosity, abundance of secretions and ability to cough. Heat and humidification improve mucociliary transport and expectoration.4 5

WHAT ABOUT OTHER HUMIDIFICATION DEVICES? A heat and moisture exchanger (HME) is

breath from the patient will exit through this

is reduced by up to 50% with leaks during

sometimes used to provide a degree of

leak and never reach the HME. This results

NIV35 and is likely to be ineffective at providing

humidification during invasive ventilation;

in it collecting almost no heat or moisture

the level of humidification required by the

however, there are specific reasons for not

and being unable to return any to the patient

airways. The use of HMEs during NIV has also

using a HME during NIV with both single and

on inspiration, rendering the HME useless.

been shown to modify the ventilatory pattern

dual-limb circuits. If NIV is being provided by

During NIV with a dual-limb circuit, there is no

and gas exchange and to increase inspiratory

way of a single-limb circuit, there is always a

controlled leak in the system. However, most

effort.36 In addition, HMEs add resistance

controlled leak, either through an exhalation

masks, even when well fitted, will have some

and dead space to the circuit, increasing the

port or vents in the mask. Most of the exhaled

leak when used under pressure.34 HME function

patient’s work of breathing.34

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references 1. Evans T. International Consensus Conferences in Intensive Care Medicine: non-invasive positive pressure ventilation in acute respiratory failure. Organised jointly by the American Thoracic Society, the European Respiratory Society, the European Society of Intensive Care Medicine, and the Societe de Reanimation de Langue Francaise, and approved by the ATS Board of Directors, December 2000. Intensive Care Med 2001;27(1):166-78.Garpestad E, Brennan J, Hill NS. Noninvasive ventilation for critical care. Chest 2007;132(2):711-20. 2. Garpestad E, Brennan J, Hill NS. Noninvasive ventilation for critical care. Chest 2007;132(2):711-20. 3. Primiano FJ, Saidel G, Montague FJ, Kruse K, Green C, Horowitz J. Water vapour and temperature dynamics in the upper airways of normal and CF subjects. Eur Respir J 1988;1(5):407-14. 4. Kilgour E, Rankin N, Ryan S, Pack R. Mucociliary function deteriorates in the clinical range of inspired air temperature and humidity. Intensive Care Med 2004. 5. Salah B, Dinh XA, Fouilladieu J, Lockhart A, Regnard J. Nasal mucociliary transport in healthy subjects is slower when breathing dry air. Eur Respir J 1988;1(9):852-5. 6. Chalon J, Loew D, Malebranche J. Effects of dry anesthetic gases on tracheobronchial ciliated epithelium. Anesthesiology 1972;37(3):338-43. 7. Hill N. Complications of noninvasive positive pressure ventilation. Resp Care 1997;42(4):432-442. 8. Richards GN, Cistulli PA, Ungar RG, BerthonJones M, Sullivan CE. Mouth leak with nasal continuous positive airway pressure increases nasal airway resistance. Am J Respir Crit Care Med 1996;154(1):182-6. 9. Moloney E, O’Sullivan S, Hogan T, Poulter LW, Burke CM. Airway dehydration: a therapeutic target in asthma? Chest 2002;121(6):1806-11. 10. Togias AG, Naclerio RM, Proud D, Fish JE, Adkinson NF, Jr., Kagey-Sobotka A, et al. Nasal challenge with cold, dry air results in release of inflammatory mediators. Possible mast cell involvement. J Clin Invest 1985;76(4):1375-81. 11. Tuggey JM, Delmastro M, Elliott MW. The effect of mouth leak and humidification during nasal noninvasive ventilation. Respir Med 2007. 12. Cruz AA, Togias A. Upper airways reactions to cold air. Curr Allergy Asthma Rep 2008;8(2):111-7. 13. Lindemann J, Sannwald D, Wiesmiller K. Age-related changes in intranasal air conditioning

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Antonelli 2001.

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26. Ferrer M, Ioanas M, Arancibia F, Marco MA, de la Bellacasa JP, Torres A. Microbial airway colonization

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