Ch 27 Anaesthesia For Chest Surgery

CHAPTER 27

ANAESTHESIA FOR CHEST SURGERY (Thoracic Anaesthesia)

Outline: (This topic will be considered only briefly) Introduction Problems associated with chest surgery: The open chest Secretions Air leak General state of the patient Blood loss Cardiac problems Atelectasis (Only the first two of these will be dealt with in the text following. For more detail consult a specialist text) Anaesthetic management of a patient for chest surgery The underwater drain

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INTRODUCTION Chest surgery may be elective or emergency surgery and may involve operations on the following structures: • •

• • • •

Chest wall: for instance for a tumour, or repair of chest wall injury Lungs, e.g. Lobectomy (removal of a lobe) Pneumonectomy (removal of a lung) Closure of a bronchopleural fistula (i.e. of a communication between the bronchus and the pleural cavity) Heart + great vessels Oesophagus Diaphragmatic hernia Others eg pleurectomy, drainage of abscesses, decortication.

PROBLEMS ASSOCIATED WITH CHEST SURGERY The problems of the open chest Collapse of the lung. When the chest is opened the negative pressure in the pleural cavity is replaced by atmospheric pressure. This positive pressure collapses the lung. If the chest is opened and the patient breathes spontaneously, two other strange phenomena occur, paradoxical respiration and mediastinal flap. Paradoxical respiration. Here, air passes from the collapsed lung into the healthy lung during inspiration. During expiration air passes out from the healthy lung, not into the atmosphere but back into the collapsed lung. This cycle is repeated. It leads to hypoxia and hypercarbia, if the patient continues to breathe spontaneously. Mediastinal flap. The mediastinum is the space between the two lungs. It is centrally situated and contains the heart, great vessels, oesophagus etc. It is kept central by the equal pressures on the two sides of the chest. If the chest cavity is opened on one side, the negative pressure is replaced by a positive pressure. During inspiration the negative pressure on the healthy side increases and this negative pressure draws the mediastinum towards the healthy lung. During expiration the negative pressure (on the healthy side) decreases and this pushes the mediastinum away from it. The mediastinum therefore moves to and fro with each respiration. This is called mediastinal flap.

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Mediastinal flap has two effects: • The pressure of the mediastinum against the sound lung during inspiration interferes with the exchange of gases in this lung. The patient therefore becomes even more hypoxic and hypercarbic. • This intermittent movement causes obstruction of the great vessels (inferior and superior vena cava) at the opening into the heart. The patient therefore becomes hypotensive. Respiration is affected by collapse, paradoxical respiration and mediastinal flap. Circulation is affected by mediastinal flap and also by the absence of negative pressure in the chest and the position of the patient. For all forms of chest surgery, where the chest is opened, IPPV must be used. IPPV will distribute the gases equally on both sides of the chest. This will eliminate the problems of paradoxical respiration and mediastinal flap. Further, it will prevent the collapse of the lung on the side of the open chest. Secretions This is another major problem with chest surgery. The affected lung may contain pus, blood or secretions and these may contaminate the unaffected side. Various techniques are used to reduce the danger of contamination: • Position • Suction • An endobronchial tube (thus anaesthetising only the healthy lung) • A bronchial blocker • A double lumen tube. These techniques are simply mentioned. A textbook of anaesthesia should be consulted for more details.

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ANAESTHETIC MANAGEMENT OF A PATIENT FOR CHEST SURGERY Consultation with the surgeon is necessary in planning the anaesthetic and choice of tube Pre-operative care Assess the patient’s general condition. Especially check the patient for secretions and for pneumothorax/bronchopleural fistula. Premedication: Oral benzodiazepine or opioids + atropine or glycopyrrolate. Intra-operative care Induction: Use thiopentone, propofol or ketamine IV depending on the state of the patient, followed by suxamethonium and intubation. Use an ordinary PVC cuffed ETT. If a special tube (e.g. double lumen) is required, it must only be used by someone experienced. Maintenance: Ether/Air/O2/opioid/non-depolarising muscle relaxant. (EMO) OR Air or N2O/O2/ volatile/opioid/non-depolarising relaxant. Analgesia can be supplemented by intercostal nerve blocks performed by the surgeon under direct vision. Good analgesia helps the patient cough up secretions post-operatively. Reversal: If the chest is closed without a drain, inflate the collapsed lung before the last few stitches are inserted. Post-operative care If an underwater drain is inserted, it must be checked regularly, in addition to other post-operative observations.

THE UNDERWATER DRAIN This has been devised to prevent air entering the pleural space, at the same time allowing free drainage of fluid and air (if the intrapleural pressure rises above atmospheric level).

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Apparatus A large wide-mouthed bottle (Winchester bottle) with a rubber stopper through which two glass tubes pass. The upper end of the longer tube is connected to the drainage tube or catheter by rubber or plastic tubing and a glass connection. The lower end of the tube should be below the level of the sterile solution in the bottle. The shorter tube is open to the atmosphere and its lower end projects just beyond the rubber stopper. It allows air to escape naturally, or it could be connected to a suction pump. There are also disposable commercially produced units available for chest drainage (e.g. Thoraseal). If a clear passage exists between the bottle and the pleural space, the column of liquid will swing. If the pressure in the intrapleural space is below atmospheric pressure, a column of liquid will be drawn up the tube. This column will swing during respiration.

Fig 27.1 Underwater seal chest drainage system If a broncho-pleural fistula exists the intrapleural pressure becomes positive at the end of each expiration and air will bubble through the end of the tube. If the patient coughs, a continuous stream of bubbles in the bottle suggests a fistula is present.

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Obstruction of the drainage system This is suggested by the absence of the respiratory swing in the tube. Commonest sites of obstruction: • In the dressings or bedding. These two sites of obstruction must be investigated first. • In the tube from outside, by pressure from the chest wall, the tubing being too thin. In the lumen, a slough or a clot. • At the end of the tube, debris causing occlusion against re-expanding lung. Management of blocked tube: • Check for the site of blockage. • Milk the tube in either direction or readjust its position but be careful not to push it further into the chest as this may introduce infection. • Irrigate with sterile saline. • If these measures fail, remove the tube and replace it with a fresh one.

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