Anesthetic Management of Pt. with Bronchial Asthma
Definition:
➧ It is an acute obstructive pulmonary disease. It is due to the hyperreactivity of the tracheobronchial tree, in which some exogenous or endogenous stimuli can produce reversible airway obstruction.
➧ Histamine and the leukotrienes are the most active chemical mediators, while acetylcholine contributes via a disturbance in autonomic balance by stimulation of M3 cholinergic receptors on bronchial smooth muscles causing bronchospasm.
Pathological changes: (Figure 1)
-Prolonged expiration
-Increased residual volume and functional residual capacity
-Increased work on breathing
-Reduced vital capacity, inspiratory capacity, and expiratory reserve volume
-Ventilation-perfusion inequalities
-Hypoxia
-Bronchospasm
-Mucus secretion
-Edema of the bronchial mucosa
-Epithelial desquamation
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| Figure 1: Pathological changes in Br. Asthma |
Anesthetic Management:
Preoperative:
a) Assessment:
1-History:
-Wheezing, dyspnea, cough, and sputum production.
2-Classification of Asthma:
-Mild Intermittent: Mild symptoms up to two days a week and up to two nights a month
-Mild Persistent: Symptoms more than twice a week, but no more than once in a single day
-Moderate Persistent: Symptoms once a day and more than one night a week
-Severe Persistent: Symptoms throughout the day on most days and frequently at night
3-Drug Therapy:
-β2-adrenoceptor agonists (albuterol, levalbuterol, salbutamol, terbutaline, salmeterol, formoterol)
-Xanthine derivatives (theophylline, aminophylline)
-Anticholinergics (Ipratropium bromide)
-Corticosteroids (beclometasone, budesonide, fluticasone, flunisolide, ciclesonide, mometasone).
-Mast cell stabilizers (sodium cromoglycate, nedocromil sodium)
-Leukotriene modifiers (montelukast, pranlukast, zafirlukast, zileuton)
-Allergy medications (allergy shots (immunotherapy), omalizumab)
4-Examination:
-Pulsus paradoxus
-Chest auscultation: The chest may be hyper resonant, with diminished breath sounds, prolonged expiration, and audible wheezes. In very severe cases the wheezes disappear
5-Investigations:
1. CBC:
-Polycythemia (if there is chronic hypoxemia)
-Eosinophilia: indicates the degree of airway inflammation
-Neutrophilia: bacterial infection
-Lymphocytosis: viral infection
2. Chest X-ray (CXR):
-Baseline for postoperative follow up
-May show an increase in bronchovascular markings and hyperinflation
-In the later stages, may show some degree of emphysema
-In an acute asthma attack, a CXR is essential to exclude pneumothorax
3. Arterial Blood Gases (ABG):
-Hypoxemia, Hypercarbia
4. Pulmonary Function Tests (PFT):
a) Tests indicate Severe Obstruction:
-Peak Expiratory Flow Rate (PEFR) of less than 120 l/min.
-Maximum Voluntary Ventilation (MVV) of less than 50% of predicted
b) Tests indicate the need for Postoperative Mechanical Ventilation (MV):
-FEV1 of less than 1 liter
-FEV1/VC ratio of less than 40% of predicted
-Increased PaCO₂ > 50 mmHg
c) Assessment of Severity of Asthma by PFT:
-Mild, Moderate, Severe, Very severe (Status asthmaticus or Respiratory failure)
d) Prediction of Postoperative Elective MV:
-PaCO₂ > 50 mmHg, PaO₂ < 50 mmHg, PFT < 50% of predicted
6-Risk assessment:
-Respiratory risk index score: predict postoperative respiratory complications or failure
b) Preparation:
1-Elective surgery should not take place in the presence of infection or untreated bronchospasm
2-Continue treatment: (Bronchodilators, Corticosteroids, …) up to the time of surgery
3-Pulmonary function tests and blood gases can be improved after the administration of bronchodilators
4-Stop smoking
5-Treatment of respiratory tract infection: Antibiotics after culture and sensitivity tests
6-Wait 2-3 weeks after clinical recovery of URTI (due to increased airway reactivity)
7-Treatment of complications if present: Dysrhythmia, Pulmonary HTN, Cor-pulmonale, Congestive heart failure
8-Chest physiotherapy: to remove secretions
9-Incentive spirometry: to improve lung expansion
10-Weight reduction of obese patients prepared for elective surgery
11-In severe cases it is important to assess the need for postoperative mechanical ventilation and reserve an ICU bed
c) Premedication:
1-Sedation:
-Anxiety may be a significant feature in the asthmatic patient, but a sedative premedication, such as an antihistaminics or benzodiazepine, is advantageous.
2-Anticholinergic:
-Atropine (to decrease bronchial secretions and vagal tone) 1-Atropine may be desirable for a smooth induction. It has a drying effect on secretions and can also improve dilatation in the larger bronchi by blocking vagal constrictor effects.
3-Corticosteroid Cover: if steroids have been used within the previous 3 months.
4-Avoid H2 blockers: lead to unopposed H1 bronchoconstriction.
Intraoperative:
a) Monitoring:
-ECG, NIBP, Pulse Oximeter, Capnography
-Pulsus paradoxus is present with Severe asthma & Tension pneumothorax (drop-in SBP ≥ 10 mmHg during inspiration) (Figure 2)
-Ventilator waveforms: Flow-Time scalar
-Spirometry: Volume-Pressure & Flow-Volume loops
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| Figure 2: Pulsus Paradoxus |
b) Precautions:
1-Avoid:
-β-blockers
-Histamine releasing drugs (Thiopental, Succinylcholine, Atracurium, Morphine, Meperidine)
2-Drug interactions:
-Ketamine + Theophylline → Seizures
-Halothane + (Aminophylline, β2-agonists, Hypercapnia) → Dysrhythmia
c) Regional anesthesia:
1-Avoid block above T6 as it leads to decreased Expiratory Reserve volume and decreased use of accessory m. → Ineffective cough and Retention of secretions → Postoperative respiratory complications.
2-Regional a. may be used for surgery or during labor. Epidural anesthesia could be safely administered to asthmatic parturients, even during acute exacerbations of asthma.
d) General anesthesia:
Induction:
1-Preoxygenation
2-Smooth induction, Warm, Humidified gases.
3-Blunt reflex bronchospasm induced by intubation (increase depth of anesthesia, Lidocaine, β2-agonist inhaler).
4-The use of IV lidocaine (1-1.5 mg/kg) before induction has been recommended, as it can prevent reflex bronchospasm, but not that resulting from the release of allergic mediators. However, topical lidocaine spray is not effective and can induce bronchoconstriction in asthmatic patients.
5-Bronchoconstriction can arise from the drug itself, or directly from tracheal intubation. Even when attacks are infrequent, tracheal intubation is one of the commonest causes of intraoperative bronchospasm in patients who have any history of asthma. The carina is particularly sensitive to stimulation.
6-Use of a laryngeal mask airway (LMA) has been shown to avoid the reversible bronchoconstriction associated with tracheal intubation.
Induction agents:
-Avoid Thiopental as it causes histamine release.
-Propofol, Ketamine, Etomidate, Benzodiazepines: are suitable agents.
-Ketamine: is a suitable induction agent for emergency anesthesia in asthmatics when a rapid sequence induction is required, as it has a protective effect against bronchospasm through sympathomimetic action by inhibition of noradrenaline reuptake, which was abolished by beta-adrenoceptor blockers.
-Inhalational induction:
-With Halothane or Sevoflurane in pediatric patients.
-With Sevoflurane can be given for emergency cesarean section in a patient with status asthmaticus.
Neuromuscular blockers:
-Succinylcholine: causes histamine release.
-Atracurium: constricts peripheral airways in doses that produce significant cardiovascular effects, and this probably results from histamine release which acts on H2 receptors. The peak effects occur 3 min. after a dose of 0.5 mg/kg.
-Cis-atracurium, Rocuronium, Vecuronium, and Pancuronium: are suitable agents.
Inhalational agents:
1-Avoid N₂O if there is large emphysematous bullae (rupture, tension pneumothorax) or pulmonary HTN (increased PVR → pulmonary edema).
2-Inhalational agents are potent bronchodilators, however, in severe asthma, they can worsen ventilation-perfusion inequalities and increase hypoxia, by reducing hypoxic pulmonary vasoconstriction.
3-Halothane can interact with Aminophylline to produce serious arrhythmias (ventricular fibrillation and ventricular tachycardia), even when theophylline levels are within the therapeutic range. Halothane also sensitizes the heart to the effect of exogenous and endogenous catecholamines.
4-Halothane, Isoflurane, and Enflurane are all effective at reversing antigen-induced bronchospasm. The effect of halothane is secondary to the blocking of baseline vagal tone.
5-The choice of Isoflurane, Sevoflurane, and Enflurane may therefore be more appropriate.
Controlled MV:
1-Use warmed, humidified gases
2-Parameters: VT: 10-15 ml/kg, RR: 6-10 b/min., decrease TI, increase TE, decrease inflating pressure
3-Avoid PEEP
Fluid management:
-Adequate hydration: (less viscid secretions)
Intraoperative Complications:
1-Bronchospasm: There is an increased sensitivity to airway manipulations during light anesthesia. Tracheal tube insertion can induce reversible bronchoconstriction (acute bronchospasm), triggered by mechanical stimuli, but not with an LMA.
Treatment of Acute Bronchospasm:
-Identify the cause
-If this occurs following tracheal intubation, the easiest initial maneuver is to deepen the anesthetic using a volatile agent or β2 agonist inhalation through the inspiratory limb of the breathing circuit or ETT adaptor (Figure 3)
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| Figure 3: Application of β2-agonist inhaler through ETT adaptor |
-IV Salbutamol 5-15 µg/kg in 10 ml saline over 10 min., for continued problems, a salbutamol infusion, 1-5 µg/kg/min. (with ECG monitoring)
-IV Aminophylline 5-6 mg/kg over in saline over 20 min. then 0.5-1 mg/kg/h. (with ECG monitoring)
N.B.1: Reduce aminophylline infusion rate by 30% because GA decreases hepatic blood flow by 30% and consequently aminophylline metabolism
N.B.2: Aminophylline has a narrow therapeutic index so, plasma theophylline levels must be measured if treatment is prolonged for more than 24 h. The therapeutic range is 10-20 mg/l but toxic effects such as fits, arrhythmias, and cardiac arrest have been described with plasma levels as low as 25 mg/l. Extreme caution is necessary if the patient has already been taking sustained-release theophylline preparations
-IV Hydrocortisone 1-2 mg/kg
-IV Ketamine in subanesthetic dose (bolus dose 0.75 mg/kg, infusion of 0.15 mg/kg/h) has been used to treat intractable bronchospasm
-IV Epinephrine 1 in 10 000 should be given in divided doses, 1-10 ml if there is complete airway closure. This may need to be repeated
2-Air trapping (Auto-PEEP, Intrinsic PEEP): due to decreased expiratory time, increased airway pressure, congested neck veins, decreased pulse pressure, hypotension due to decreased venous return and consequently cardiac output
3-Cardiac Dysrhythmias: can occur more frequently in the presence of hypoxia, hypercarbia, and acidosis, or following the overuse of sympathomimetic agents
4-Complications due to Drug interactions: mentioned before
5-Sudden Death: has been attributed to the combination of nebulized high dose β2-sympathomimetics and long-acting theophylline derivatives
The reverse of Neuromuscular blockers:
-Anticholinergic (Atropine) first then Cholinesterase inhibitor (Neostigmine)
Extubation:
-Deep extubation
-Awake extubation: blunt reflexes with IV lidocaine (1-1.5 mg/kg) first
Postoperative:
1-Monitoring, Semi sitting, Humidified O₂
2-Analgesia: NSAIDs (with caution), Local or regional a., Avoid Opioids can cause respiratory depression
3-Continue preoperative treatment
4-Avoidance of MV in a severe asthmatic was achieved by administration of a subanesthetic dose of halothane in 100% oxygen using a close-fitting mask
5-Elective MV if predicted preoperative or if indicated postoperative
Indications for Postoperative MV in Asthmatic Patients:
1-Distress and exhaustion
2-Deterioration in ABG. PaO₂ < 6.7 kPa (50 mmHg) or PaCO₂ > 6.7 kPa (50 mmHg), and increasing metabolic acidosis
3-Cardiac dysrhythmias or hypotension
4-Acute crises such as cardiorespiratory arrest, decreased conscious level due to sedatives, or a collapsed lung
5-Refractory asthma has been treated in the ICU with Magnesium sulphate, Halothane, and Propofol
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