Asthma is variable and often reversible airway obstruction with bronchial hyperreactivity. An estimated 8.4% of US citizens have asthma, while 4.3% of the worldwide population carry this diagnosis. Both the domestic and worldwide prevalence of asthma continues to rise.  Patients with asthma are at an elevated risk of perioperative morbidity and mortality due to bronchospasm and hypoxemia. Children are especially prone to perioperative respiratory adverse events (PRAE). Preoperative identification and optimization of asthmatics presenting for elective surgery are critical in preventing harm. A well-planned, meticulous anesthetic constitutes an essential component of the multidisciplinary approach to providing high-quality care for these patients in the perioperative environment.
Asthma begets airway hyperresponsiveness, causing bronchial smooth muscle constriction and airway inflammation leading to an obstructive dysfunctional process known as bronchospasm. Triggers of bronchospasm may include allergens (medications or medical equipment such as latex), respiratory infection, smoke, cold air, exercise, stress, and physical stimulus/trauma to the airway (endotracheal intubation or irritating secretions). Clinically, bronchospasm may present as shortness of breath, wheezing, coughing, or chest tightness. While endotracheally intubated in the operating room, patients are unable to relay these symptoms. In these situations, bronchospasm often presents as a sudden acute rise in peak inspiratory pressures as measured by the modern ventilator, though it can be a slower change that presents more insidiously. As a side note, bronchospasm should be differentiated from anaphylaxis by the absence of hypotension, flushing, rash, and/or angioedema with bronchospasm.
When presenting for surgery, determining whether a patient's asthma is well controlled or poorly controlled is key to mitigating complications. Elective surgeryshould be postponed until asthma is well controlled. A detailed history and focused cardiopulmonary physical examination are requisite in making this determination. Preoperative labs, chest radiographs, and tests to assess pulmonary function have not been shown to correlate with PRAE and are rarely recommended.
During the interview, a history of recent exacerbations, recent hospitalizations, as well as any prior history of tracheal intubation and mechanical ventilation due to asthma is important information to gather. During a review of systems, the patient should provide history about any recent wheezing, chest tightness, cough, or shortness of breath.
In addition to a diagnosis of asthma, the following risk factors have been shown to increase the incidence of PRAE in children, and should undergo a review before administration of any anesthetic :
Some of the prophylactic and abortive medications these patients may take include inhaled beta-2 agonists (e.g., albuterol, inhaled corticosteroids (e.g., budesonide), oral leukotriene antagonists (e.g., montelukast), oral or intravenous (IV) corticosteroids, and IV magnesium. Upon verification that the patient takes their routine asthma medications as prescribed, it is at the discretion of the anesthesia provider whether to administer prophylactic medications such as inhaled beta-2 agonists (e.g., albuterol) or systemic corticosteroids (e.g., methylprednisolone) prior to proceeding to the OR. Preoperative steroids have shown little benefit unless started 2-3 days in advance of surgery. In one study, systemic corticosteroids plus inhaled beta-2 agonists for five days prior to surgery was shown to markedly decrease the incidence of bronchospasm following intubation.
Induction of general anesthesia, airway manipulation, and emergence from anesthesia represent the most critical times for potential airway complications during a general anesthetic. Ensuring expert personnel are involved with the case is essential. As it pertains to children, the presence of an experienced pediatric anesthesiologist during airway management has been shown to reduce the risk for PRAE.
Choosing an inhaled volatile versus IV induction is typically a major point of consideration only in the pediatric population as most children will not tolerate pre-induction peripheral IV placement. While all volatile anesthetics have direct bronchodilating properties, sevoflurane appears to most possess this quality. Desflurane increases bronchial smooth muscle tone and airway resistance and should be avoided in asthmatics, especially pediatric asthmatics. Concerning IV agents, propofol demonstrates an excellent ability in blunting airway reflex bronchoconstriction but has inferior bronchodilator properties compared to volatile anesthetics. Propofol associates with lower airway resistance compared to etomidate and thiopental. Ketamine has a direct bronchodilating activity and blunts airway reflex bronchoconstriction though comes at the expense of increased secretions which can complicate airway management. Neuromuscular blocking drugs are often given to improve intubating conditions in adults, though should be avoided in children given the risk for hyperkalemic cardiac arrest in the setting of a possible undiagnosed myopathy. Topical lidocaine applied to the airway prior to endotracheal intubation is controversial as there is evidence to suggest an increased incidence of desaturation using this technique in children.
In the acute setting, use of cardioselective beta-blockers in the (i.e., those with beta-1 > beta-2 antagonism) is preferred when indicated for asthmatic patients but are not without risk.
Noninvasive airway management, such as with a supraglottic airway (SGA), carries associations with a decreased risk of postoperative hypoxemia and coughing compared to use of an endotracheal tube (ETT) in adults. When comparing SGA vs. ETT use for airway control in children, the incidence of PRAE was lower with SGA use, though there was no statistically significant difference in bronchospasm or aspiration between the two groups.
In patients with well-controlled asthma, general tenets of safe mechanical ventilation apply. However, when airflow obstruction is present, mechanical ventilation becomes a challenge. As bronchospasm causes an obstructive respiratory pattern, prolongation of the expiratory phase of ventilation occurs. Allowing ample time for exhalation during mechanical ventilation is critical to avoiding dynamic hyperinflation (also known as auto-PEEP or breath-stacking), a feared complication of mechanical ventilation of asthmatic patients.
Before emergence from general anesthesia, reversal of neuromuscular blockade with cautious use of cholinesterase inhibitors is a consideration, though some authors note that neostigmine may contribute to the risk of bronchoconstriction by inhibiting the destruction of acetylcholine.[ Use of sugammadex for reversal of the non-depolarizing neuromuscular blockers rocuronium and vecuronium may also be a consideration, and it is becoming a more accepted practice in the pediatric anesthesia realm. Extubation in a deep plane of anesthesia should theoretically decrease the risk of bronchospasm caused by the stimulus of the ETT. However, little research has been performed to show a benefit with this technique. Recent randomized control trial data failed to show a difference between awake versus deep extubation as it related to PRAE, though the awake extubation group was noted to have an increased incidence of coughing, while the deep extubation group showed a higher incidence of airway obstruction relieved by simple airway maneuvers.
"ALL THAT WHEEZES IS NOT ASTHMA"
When caring for an anesthetized asthmatic patient, bronchospasm is likely to be at the top of the list of differential diagnoses for wheezing. Below, however, are other entities to consider:
Interprofessional communication is paramount in the perioperative care of asthmatic patients. In the preoperative period, patients and patient's parents should be counseled to continue all asthma-related medications as routinely taken, including oral medications which may be taken with a small sip of water the morning of surgery. Intraoperatively, the anesthesia provider should tailor and execute an anesthetic which aims to avoid bronchospasm in the OR and during recovery from anesthesia. Postoperatively, patients should be monitored closely and return to the pre-anesthetic asthma medication regimen as soon as possible.