Asthma Anesthesia

Function

Airway hyperresponsiveness and inflammation are key features of asthma. Bronchial smooth muscle constriction and airway inflammation lead to the obstructive process known as bronchospasm. Triggers of bronchospasm include allergens (e.g., medications or latex-based medical equipment), respiratory infection, smoke, cold air, exercise, stress, and physical stimulus/trauma to the airway, among others.[6] Clinically, bronchospasm may present as shortness of breath, wheezing, coughing, or chest tightness.  In the operating room, an endotracheally intubated patient will be unable to relay these symptoms. In these situations, bronchospasm will present as a sudden acute rise in peak inspiratory pressures on the ventilator. As a side note, bronchospasm should be differentiated from anaphylaxis by the absence of hypotension, flushing, rash, and/or angioedema.

Issues of Concern

When presenting for surgery, determining whether a patient's asthma is well-controlled or poorly controlled is key to mitigating perioperative complications. Elective surgery should be postponed until asthma is well controlled.[4][3] 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.[7]

During the preoperative interview, a history of recent asthma exacerbations, recent hospitalizations, as well as any prior history of tracheal intubation and mechanical ventilation due to asthma is important information to obtain. During the review of systems, the patient should provide a history of any recent wheezing, chest tightness, cough, or shortness of breath. 

In addition to a diagnosis of asthma, the following factors have been shown to increase the risk of PRAE in children and should be reviewed before administration of anesthesia[8]:

• Wheezing with exercise
• Wheezing > three times in last 12 months
• Nocturnal dry cough
• Recent upper respiratory tract infection (< 2 weeks) (Also a risk factor for intraoperative airway complications)
• Hayfever
• Eczema
• Second-hand smoking
• Family history of asthma, hay fever, or eczema
• Young age (age < 6 years also a risk factor for intraoperative airway complications[9])
• Higher ASA classification
• History of congenital heart disease
• Prematurity
• Low birth weight
• Obesity
• Obstructive sleep apnea 

Some of the prophylactic and abortive medications that patients with asthma 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 is using routine asthma medications as prescribed, it is at the discretion of the anesthesia provider as to whether to administer prophylactic therapy such as inhaled beta-2 agonists (e.g., albuterol) or systemic corticosteroids (e.g., methylprednisolone) before proceeding to the OR. Preoperative steroids have shown little benefit unless started 2 or 3 days in advance of surgery. In one study, systemic corticosteroids plus inhaled beta-2 agonists for five days before surgery was shown to markedly decrease the incidence of bronchospasm following intubation.[10]

Clinical Significance

Induction of general anesthesia, airway manipulation, and emergence represent the most critical times for perioperative respiratory complications in patients with asthma. Ensuring that expert team members 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.[11]

Choosing an inhaled induction over an intravenous is typically a major point of consideration in the pediatric population because most children do not tolerate pre-induction peripheral IV placement. All volatile anesthetics - sevoflurane, isoflurane, desflurane, have direct bronchodilating properties. However, at higher concentrations, desflurane increases bronchial smooth muscle tone and airway resistance and should be avoided in patients with asthma.[12] In terms of IV agents, propofol demonstrates an excellent ability to blunt airway reflex bronchoconstriction, but this bronchodilation is inferior to volatile anesthetics. Compared to etomidate and thiopental, propofol is associated with lower airway resistance.[13] Ketamine has direct bronchodilating effects and blunts airway reflex bronchoconstriction, but it also causes increased secretions, which can complicate airway management.  

Neuromuscular blocking drugs (NMBDs) are given to improve intubating conditions. In children, depolarizing NMBDs are often avoided, given the risk for hyperkalemic cardiac arrest in the setting of a possible undiagnosed myopathy. Topical lidocaine applied to the airway before endotracheal intubation is controversial as there is evidence to suggest an increased incidence of desaturation using this technique in children.[16][14]

In the acute setting, the use of cardioselective beta-blockers (i.e., beta-1 > beta-2 antagonism) is preferred when indicated for patients with asthma.[13]

Noninvasive airway management, such as placement of a supraglottic airway (SGA), is associated with a decreased risk of postoperative hypoxemia and coughing compared to the use of an endotracheal tube (ETT) in adults.[14] When comparing SGA to ETT use for airway control in children, the incidence of PRAE was lower with SGA use. However, there was no statistically significant difference in bronchospasm or aspiration between the two groups.

In patients with well-controlled asthma, routine mechanical ventilation can be used. However, when airflow obstruction is present, mechanical ventilation becomes a challenge. Bronchospasm causes an obstructive respiratory pattern, and 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 in patients with asthma.

Before emergence from general anesthesia, reversal of neuromuscular blockade is administered. The cautious use of cholinesterase inhibitors is vital because neostigmine may contribute to the risk of bronchoconstriction by inhibiting the breakdown of acetylcholine. Alternatively, sugammadex may also be used for the reversal of the non-depolarizing neuromuscular blockers - rocuronium and vecuronium, with no associated increased risk of bronchospasm. 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 the benefit of this technique. A recent randomized control trial data failed to show a difference between awake versus deep extubation as it related to PRAE.[15]

Other Issues

"All That Wheezes Is Not Asthma"

When caring for an anesthetized patient with asthma, bronchospasm is likely to be at the top of the list of differential diagnoses for an episode of wheezing. However, the following list presents other entities to consider:

• Anaphylaxis
• Aspiration of stomach contents
• Aspiration of a foreign body (e.g., tooth, a piece of medical equipment)
• Upper airway obstruction (non-intubated)
• Mainstem intubation
• ETT on carina
• ETT obstruction
• ETT cuff herniation
• Pneumothorax
• Pulmonary edema
• Pulmonary thromboembolism
• Drug-induced (histamine release, anticholinesterase)
• Carcinoid syndrome or crisis

Enhancing Healthcare Team Outcomes

Interprofessional communication is paramount in the perioperative care of patients with asthma. This involves effective communication between the anesthesiologist, nurse anesthetist or anesthesia assistant, and the recovery room nurse. In the preoperative period, patients and families should be counseled to continue all routine asthma-related medications, including oral medications with a small sip of water on the morning of surgery.[5] Intraoperatively, the anesthesia care team should tailor and execute an anesthetic plan that aims to avoid bronchospasm in the perioperative period. Postoperatively, patients should be monitored very closely, and they should return to the pre-anesthetic asthma regimen as soon as possible.

The key to minimizing post-anesthesia complications is to be vigilant about bronchospasm.  The recovery room nurses should auscultate the chest frequently and report any abnormal findings to the physician. Besides bronchodilator therapy, the nurse should ensure that the patient is performing deep breathing exercises, using the incentive spirometer, and ambulating as appropriate. Also, the anesthesiologist should ensure that the patient has optimal pain control and is awake and alert. All team members are responsible for monitoring the patient’s respiratory status. At the end of each shift, a thorough handoff should be completed to ensure continuity of care. Effective and open communication within the team can help reduce the morbidity and mortality associated with asthma.