General Anesthetic Consideration in Respiratory Diseases
General Anesthetic Consideration in Respiratory Diseases
Respiratory disease is pathological conditions; affecting the upper respiratory tract (nose, pharynx, larynx), trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity which ranges from self limiting common cold to severe pneumonia and lung cancer. Patients with respiratory disease have an increased chance of developing complications perioperatively. Most problems are seen postoperatively and are usually secondary to shallow breathing, poor lung expansion, basal lung collapse and subsequent infection. To minimize the risk of complications these patients should be identified preoperatively and their pulmonary function optimized. This involves physiotherapy, a review of all medications and may require referral to seniors and medical specialist. The benefits of the proposed surgery must therefore be weighed against the risks involved.
Effects of General Anesthesia
It is relatively minor and do not persist beyond 24 hours. However, they may tip a patient with limited respiratory reserve into respiratory failure.
- Manipulation of the airway (laryngoscopy and intubation) and surgical stimulation may precipitate laryngeal or bronchial spasm.
- Endotracheal intubation bypasses the filtering, humidifying and warming functions of the upper airway allowing the entry of pathogens and the drying of secretions. Adequate humidification and warming of the anaesthetic gases with a Heat and Moisture Exchanger (HME) is ideal (if available).
- Volatile anaesthetic agents depress the respiratory response to hypoxia and hypercapnia, and the ability to clear secretions is reduced. Functional residual capacity (FRC) decreases and pulmonary shunt increases; these are unfavorable changes leading to hypoxia and occur especially in lithotomy and head-down positions, and in the obese.
- Intermittent positive pressure ventilation causes an imbalance in ventilation and perfusion matching in the lung, and necessitates an increase in the inspired oxygen concentration.
- Neuromuscular blockade is reversed before extubation. In the recovery room residual effects of anesthesia depress upper airway muscular tone, and airway obstruction may occur.
- The intravenous induction agents thiopentone, propofol and etomidate produce an initial transient apnoea. Ketamine preserves respiratory drive and is better at maintaining the airway, although secretions increase.
- Thiopentone increases airway reactivity.
- Volatile anesthetics depress respiratory drive.
- Atracurium release histamine and may result in bronchospasm. They are best avoided in asthma.
- Opioid drugs and benzodiazepines depress respiratory drive and response to hypoxia and hypercapnia. Morphine may result in histamine release and occasionally bronchospasm. Non- steroidal anti-inflammatory drugs (NSAIDS) may exacerbate asthma. Pethidine is a useful alternative analgesic for asthmatics.
Effects of Surgery
- Upper abdominal surgery limits their ability (pain) to take deep breaths and increases the risk of postoperative pulmonary complications. Surgery on the limbs, lower abdomen or body surface surgery has less effect.
- A laparotomy may remove fluid or masses that cause diaphragmatic splinting and respiratory difficulty. However, gas (especially nitrous oxide) and fluid may accumulate within the bowel and peritoneal cavity exacerbating post-operative distension and splinting.
- Surgery lasting more than 3 hours is associated with a higher risk of pulmonary complications.
- Postoperatively, return of lung function to normal may take one to two weeks
- General assessment: This involves history, examination and investigation. A medical, anesthesia, specialist, surgeon, senior anesthetist may help you in examination, interpreting investigation and the need for referral or to proceed will be decided after consultation.
- History: Ask about symptoms of wheeze, cough, sputum production, hemoptysis, chest pain, exercise tolerance, orthopnea and paroxysmal nocturnal dyspnea. The diagnosis of chronic chest complaints such as asthma is often known. Present medication and allergies are noted, and a history of smoking sought. Previous anaesthetic records may be available and can help in planning care (Table4.1).
- Examination: Inspect for cyanosis, dyspnea, and respiratory rate, asymmetry of chest wall movement, scars, and cough and sputum color. Percussion and auscultation of chest may suggest areas of collapse and consolidation, pleural effusions, pulmonary edema or infection.
- Investigations: Leucocytosis may indicate active infection, and polycythemia chronic hypoxemia. Preoperative hypoxia or carbon dioxide retention indicates the possibility of postoperative respiratory failure which may require a period of assisted ventilation post operatively.
- Chest X-rays and electrocardiogram
- Pre-medication: In patients with poor respiratory function premedication (if used) must not cause respiratory depression. Opiates and benzodiazepines can both do this, and are best avoided if possible, or used with caution. Humidified oxygen may be administered. Anticholinergic drugs (e.g. atropine) may dry airway secretions and may be helpful before ketamine
Table 4.1 Preoperative Consideration on Health Status of the Patient in All Patient With Respiratory Diseases
|Smoking||Active and passive smokers have hyper-reactive airways with poor muco-ciliary clearance of secretions. They are at increased risk of perioperative respiratory complications, such as atelectasis or pneumonia. It takes 8 weeks abstinence for this risk to diminish. Even abstinence for the 12 hours before anesthesia will allow time for clearance of nicotine, a coronary vasoconstrictor (affecting blood supply to the heart which cause angina or chest pain), and a fall in the levels of carboxyhemoglobin (carbon monoxide, a toxic gas combined with Hgb reducing the oxygen carrying capacity of hemoglobin which causes hypoxia) thus improving oxygen carriage in the blood.|
|Obesity||The normal range for BMI (Body Mass Index - defined as weight (Kg) divided by the square of the height (m) is 22-28. Over 35 is morbidly obese. Normal weight (Kg) is height (cm) minus 100 for males, or height minus 105 for females. Obese patients may present a difficult intubation and have perioperative basal lung collapse leading to postoperative hypoxia. A history of sleep apnea may lead to post-operative airway compromise. If possible, obese patients should lose weight preoperatively, and co-existent diabetes and hypertension stabilized.|
|Physio-therapy||Teaching patients in the preoperative period to participate with techniques to mobilize secretions and increase lung volumes in the postoperative period will reduce pulmonary complications. Methods employed are early mobilization, coughing, deep breathing, chest percussion and vibration together with postural drainage.|
|Pain Relief||Effective analgesia is important as it allows deep breathing and coughing and mobilization. This helps prevent secretion retention and lung collapse, and reduces the incidence of postoperative pneumonia.|