Introduction		Postoperative Care
General Considerations		Postoperative Respiratory Problems
Preoperative Preparation		Further Reading
Anaesthesia - Techniques

Introduction

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 minimise the risk of complications these patients should be identified preoperatively and their pulmonary function optimised. This involves physiotherapy, a review of all medications and may require the help of a respiratory physician. Elective surgery is postponed until the patient is ready.

In the general surgical population thoracic and upper abdominal procedures are associated with the highest risk (10-40%) of pulmonary complications. The benefits of the proposed surgery must therefore be weighed against the risks involved. 

General Considerations

General health status

The American Society of Anesthesiologists classification (1 to 5) correlates well with the risk of post-operative pulmonary complications. Poor exercise tolerance also predicts those at risk.

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 anaesthesia will allow time for clearance of nicotine, a coronary vasoconstrictor, and a fall in the levels of carboxyhaemoglobin 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 apnoea may lead to post-operative airway compromise. If practical obese patients should lose weight preoperatively, and co-existent diabetes and hypertension stabilised.

Physiotherapy

Teaching patients in the preoperative period to participate with techniques to mobilise secretions and increase lung volumes in the postoperative period will reduce pulmonary complications. Methods employed are early mobilisation, 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 mobilisation. This helps prevent secretion retention and lung collapse, and reduces the incidence of postoperative pneumonia. Epidurals appear particularly good at this for abdominal and thoracic surgical procedures, although they are not available everywhere (see Epidural analgesia section).

The method of postoperative analgesia should always be discussed with the patient before surgery.

Effects of General Anaesthesia

These are 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.
• 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 unfavourable 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.
• Excessive fluid therapy can result in pulmonary oedema in patients with cardiac failure.
• Neuromuscular blockade is reversed before extubation. In the recovery room residual effects of anaesthesia depress upper airway muscular tone, and airway obstruction may occur.

Anaesthetic Drugs

• 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 anaesthetics depress respiratory drive in decreasing order as follows:
  Enflurane>Desflurane>Isoflurane> Sevoflurane>Halothane.
  Ether however stimulates respiratory drive and increases minute ventilation. It is, however, irritant to the airway, stimulates saliva production and may induce coughing.
• Atracurium and tubocurare 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

• To immobilise upper abdominal and thoracic incisions and limit pain, patients splint these areas postoperatively with their intercostal and diaphragmatic muscles. This limits their ability 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. 

(Continued ...)

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