Introduction
Respiratory illnesses often complicate anesthetic management of patients in elective as well as emergency surgeries. Patients with respiratory diseases are at risk of desaturation, laryngospasm, and bronchospasm during the perioperative period. Anesthetists need to be acquainted with commonly encountered respiratory illnesses and acquire appropriate airway skills to provide optimal patient care. This chapter will discuss the following respiratory illnesses in detail, including anesthetic considerations:
Asthma
Asthma is characterized by episodes of recurrent wheezing, dyspnea, and dry cough caused by airway obstruction, airway inflammation, and airway hyperresponsiveness.
Preoperative Assessment
Preoperative evaluation should focus on:
Physical Examination
It should focus on the assessment of wheeze, the presence of prolonged expiratory wheeze, and signs of respiratory distress. Cyanosis and drowsiness should be noted and documented. Oxygenation status should be confirmed using pulse oximeter and blood gas analysis
(if required).
Anesthetic Management
The goal of anesthetic management is to avoid airway manipulations to the minimum, ensure adequate depth of anesthesia as well as analgesia during airway handling, and use anesthetic drugs with maximal bronchodilation properties. Induction of general anesthesia (GA), airway manipulation, and emergence from anesthesia represent the most critical times for potential airway complications during a general anesthetic. The effects of various anesthetic agents and airway devices on the airway are as follows:
Fentanyl is preferred over morphine due to the histamine-releasing property of the latter.
All volatile anesthetics have direct bronchodilation properties except desflurane. Halothane followed by sevoflurane is the most effective bronchodilator.
Desflurane is an airway irritant and is avoided in asthmatics.
Propofol is superior to etomidate and thiopental in terms of lowering airway resistance but has inferior bronchodilator properties compared to volatile anesthetics.
Ketamine has a direct bronchodilation activity and blunts airway reflex; bronchoconstriction, although coming at the cost of increased secretions, can complicate airway management.
Neuromuscular blocking drugs (NMBDs) improve intubating conditions in adults. Preferred ones are rocuronium and vecuronium. Atracurium has histamine-releasing properties.
The use of noninvasive such as supraglottic airway (SGA) carries a lower risk of postoperative hypoxemia and coughing compared to the endotracheal tube (ETT) in adults.
In patients with airflow obstruction, prolongation of the expiratory phase of ventilation occurs. Increase the inspiratory:expiratory (I:E) ratio to allow ample time for expiration, in order to avoid dynamic hyperinflation (autopositive end-expiratory pressure [PEEP] or breath stacking).
Extubation in a deep plane of anesthesia should theoretically decrease the risk of bronchospasm caused by the stimulus of the ETT.
Chronic Obstructive Pulmonary Disease
COPD is a chronic progressive, an irreversible inflammatory condition resulting in expiratory airflow limitation. It includes:
Risk factors for COPD include:
Increased airway responsiveness to various exogenous stimuli.
Occupational exposures (coal mining, gold mining, and cotton textile dust).
Preoperative Evaluation
History should focus on exercise tolerance, change in trend of symptoms, addition of new medication or escalation of previous medications, number of hospitalizations related to exacerbations, need of mechanical ventilation, and presence of any comorbid illness.
Nutritional status: Body mass index (BMI), outside the normal range, increases the risk of pulmonary complications.
Auscultation: The presence of diminished breath sounds, prolonged expiration, wheeze, and rhonchi are predictors of postoperative pulmonary complications.
Fever, purulent sputum, worsening cough, and dyspnea also add to the risk of complications.
Preoperative Preparation
Preoperative preparation should target on smoking cessation. Smoking cessation anytime before surgery has been found to reduce complications (e.g., pneumonia, length of intensive care stay, and need for mechanical ventilation), but maximum benefit is seen with at least 8 weeks of abstinence before surgery. Chest physiotherapy is warranted in patients with a large volume of sputum to optimize patient outcomes.
Anesthetic Management
GA with tracheal intubation is associated with laryngospasm, bronchospasm, cardiovascular instability, barotraumas, and hypoxemia, resulting in increased rates of postoperative pulmonary complications. Therefore, regional anesthesia (RA) is preferred.
General Anesthesia
Preoxygenation should be used in any patient who is hypoxic on-air before induction. The use of continuous positive airway pressure (CPAP) during induction may be used to improve the efficacy of preoxygenation and reduce the development of atelectasis in patients with severe hypoxia. Ventilatory management is an essential consideration in a patient of COPD, and the following points are noteworthy:
Avoid auto-PEEP: It can be achieved by reducing the frequency of breaths or I:E ratio. Exhalation time should be more to prevent breath stacking.
Application of PEEP: Extrinsic PEEP (usually 80% of intrinsic PEEP) helps to decrease the work of breathing.
Treatment of bronchospasm: It can be treated with any of the following:
At the end of the surgery, extubation should be done cautiously and preferably in the presence of an experienced anesthetist. Before extubation, oxygenation and reversal of the neuromuscular blockade must be ensured. Switching from tracheal intubation to noninvasive ventilation (NIV) may lessen the work of breathing and air trapping in select high-risk patients.
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