Wheeze is one of the most common presenting complaints of children visiting emergency department of any busy hospital and the list of causes is exhaustive.
What Causes Wheeze
Wheeze is the whistling sound, which can be heard by stethoscope, which is heard due to partial obstruction of the airway when the air comes out of the lung during expiration. The reasons for such a symptom can be infective (viral or bacterial pneumonia) or non-infective (asthma, reactive airway diseases) and depending on the reason, the treatment is given. Children, especially infants and toddlers will find it difficult to feed while having wheeze and it is in fact a very debilitating condition. Nevertheless, we now have effective drugs and modalities of drug delivery to improve the airway obstruction
Use of Salbutamol In the Management of Wheeze
To understand wheeze and how salbutamol acts, we need to understand the pathology of wheeze. Whenever there is some infection (as in pneumonia) or exposure to any allergen (as in asthma), the sensitive airway of child hyper reacts to the stimuli and thereby initiates a cascade of reactions leading to pooling of secretions at airway and contraction of muscles of airways leading to narrowing of airway. As resistance of airway is inversely proportional to the fourth power of radius of airway, even a slight decrease in radius will exponentially increase the resistance of airflow. The child finds it difficult to exhale and does extra work to attain normal expiration, leading to increased work of breathing.
Efficacy of Salbutamol Nebulization Over Old Practices
In the yester decades, before the advent of salbutamol, wheeze was managed by intravenous medication and subcutaneous injection of adrenaline. All these medications had narrow therapeutic index (increased risk of adverse effects) and needed close monitoring of the patient. However, nebulization with salbutamol revolutionized the management of wheeze as it was an easy to administer drug with lesser adverse effects.
Salbutamol not only was safe but also decreased the morbidity and mortality associated with wheezing episodes.
As nebulizers became easily available in the market, people started to nebulize their kids at home and that has resulted in some harmful events. Salbutamol had an effect of abolishing hypoxia mediated vasoconstriction which can consequently lead to ventilation-perfusion mismatch. This effect will be explained in the subsequent paragraphs, and also the need to have oxygen while nebulizing with salbutamol.
Salbutamol is usually given whenever there is bronchospasm (can be due to asthma, other reactive airway diseases etc.) which can lead to hypoxia(less oxygen in blood).
How Salbutamol Works
Salbutamol, via beta receptors, causes relaxation of muscles of airways, thereby leading to widening of airways. Hypoxia causes constriction of the blood vessels in lungs (vasoconstriction) contrary to what it causes in the other parts of the body. Bronchospasm (narrowing of airway) is not uniform at all areas of lung. At some lobules, there will be better air entry and at some, there won’t be. Wherever there is low ventilation due to bronchoconstriction, there is vasoconstriction mediated by hypoxia. This is actually a protective mechanism by the body to channelize the blood to better ventilated areas so that more oxygen can be taken up from the alveoli.
Do’s and Don’ts When Giving Salbutamol Nebulization
Being a beta agonist, salbutamol has the capacity to dilate airways by virtue of its smooth muscle dilating property. But, it also dilates the blood vessels (vasodilation) present in the lungs which were actually constricted due to hypoxia. So, if we give just salbutamol, blood may also flow at those areas which are not adequately ventilated. This results in increased intrapulmonary shunting i.e. increasing perfusion to poorly ventilated lung lobules and hence ventilation-perfusion mismatches which can lead to worsening of hypoxemia.
The above said ventilation-perfusion mismatch can easily be prevented by giving oxygen driven nebulization. The cirrus chamber (the chamber of nebulization mask where nebulization solution is kept) can be directly attached to an oxygen cylinder or oxygen source. An oxygen flow of 6 liters/ minute will produce adequate fumes required for nebulisation. The mixture of salbutamol with oxygen will provide adequate bronchodilation without worsening hypoxemia. Salbutamol can also cause electrolyte disturbances like hypokalemia as well.
Recommends To Do a Nebulization Only at Hospital
The primary health care professionals and even caretakers should know about this effect and should avoid using nebulizers at home for salbutamol. This deleterious effect doesn’t happen with inhalers because the amount of drug administered drug through an inhaler is so small that it can’t cause vasodilation. So, inhalers are safe to use at home while nebulization needs to be done at hospital.
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