Ch 28 Anaesthesia For Abdominal Surgery

CHAPTER 28

ANAESTHESIA FOR ABDOMINAL SURGERY

Outline: Points of importance associated with anaesthesia for abdominal surgery Techniques for anaesthesia Regional General Anaesthesia for Laparoscopy

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POINTS OF IMPORTANCE ASSOCIATED WITH ANAESTHESIA FOR ABDOMINAL SURGERY Good relaxation of the anterior abdominal wall muscles The posterior sheath of the rectus and the transversus muscles are fused with the peritoneum in the upper abdomen. Hence when the peritoneum is sutured at the end of the operation the muscles need to be well relaxed. If the surgeon is unable to close the peritoneum due to inadequate muscle relaxation, a further dose of relaxant may be given. It is, however, important to make sure that the problem is due to a lack of relaxant and not to some other factor, e.g. gastric distension. If the patient has not had any relaxant drugs for a period of 20 minutes and if there is no contraindication, then another small dose of relaxant may be given to assist the surgeon. The maintenance of adequate ventilation This is achieved by IPPV using a relaxant technique. However, ventilation may be impaired by the presence of packs and retractors in the upper abdomen. The prevention of shock and cardiovascular depression This may be caused by: • Pre-operative hypovolaemia • Intra-operative bleeding • Loss of fluid from the gut, by prolonged exposure during surgery. • Handling of the gut and traction on the mesentery. • Compression of the inferior vena cava by packs, retractors and even abdominal tumours. Cardiac arrhythmias These may occur if there is excessive traction on the gut or mesentery. Protection of the airway and prevention of aspiration. This precaution is necessary in all types of surgery but especially in abdominal surgery. A naso-gastric tube must be used for aspiration of stomach contents if a full stomach is suspected. A rapid sequence induction is indicated if there is any danger at all of vomiting or regurgitation. Hiccups This may be encountered, especially in upper abdominal surgery. The topic is covered in Anaesthetic complications involving the Gastro-intestinal system in Chapter 46.

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Respiratory complications These are common in the post-operative period. Patients who have upper abdominal surgery are more prone to post-operative respiratory complications than others. Adequate ventilation during the operation and attention to adequate analgesia (e.g. opioids) to enable the patient to cough and take deep breaths post–operatively, is vital to prevent post–operative pneumonia. It is important to give opioids both during and after surgery. An appropriate regime would be: − Intra–operatively boluses of up to 0.1–0.2 mg/kg of morphine IV. − Post–operatively 0.1mg/kg IM 3 hourly. Unless otherwise indicated, the patient is best nursed supported in a semisitting position in the post-operative period. Good preoperative and postoperative physiotherapy are very important in preventing chest complications. It cannot be stressed enough that adequate pain relief in the post-operative period is very important. Deep vein thrombosis This is more likely after lower abdominal and pelvic surgery. Prophylactic measures include: • The use of calf stimulators • Elastic stockings • The peri–operative use of sub-cutaneous heparin preparations • Avoidance of hypotension • Early ambulation • Physiotherapy in the post–operative period. Post-operative nausea and vomiting This is discussed under Anaesthetic complications in Chapter 46 TECHNIQUES FOR ANAESTHESIA Regional techniques. Spinal anaesthesia is usually the method of choice for surgery below the level of the umbilicus, provided there is no contraindication. The advantages of a spinal anaesthetic are detailed in Chapter 19. Ensure adequate fluid replacement. Local infiltration. If a general or spinal anaesthetic is contraindicated (e.g. in a moribund patient), then it may be necessary to resort to local infiltration by the surgeon.

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General anaesthesia The techniques of controlled ventilation are outlined in Chapters 14 and 16. A rapid sequence induction technique must be used for patients with a full stomach. For a full description of this technique see Chapter 16. The depth of anaesthesia needs to be greatest during: − The skin incision − Initial abdominal exploration − Closure of the peritoneum. If the patient is very hypotensive or moribund, ventilate with oxygen and a very small dose of ketamine or N2O to prevent awareness. At the earliest sign of the patient beginning to waken, increase these agents and/or give a small dose of opioid or halothane. ANAESTHESIA FOR LAPAROSCOPY Most anaesthetists favour general anaesthesia, although local and regional anaesthetics have been used. The following points should be noted: • Endotracheal intubation (using a cuffed tube) is advisable: − For controlling ventilation. The insufflation of gas into the peritoneal cavity raises the diaphragm and interferes with breathing. It is important that the patient be paralysed and ventilated. − To prevent regurgitation of gastric contents. This is more likely with the high intra-abdominal pressure. In spite of these potential risks some anaesthetists will use a LMA and ventilation with a short acting muscle relaxant (eg mivacurium/ atracurium/ vecuronium) for elective surgery of short duration, (e.g. gynaecology) in fasted, non-obese patients. • The introduction of gas into the peritoneal cavity can result in hypotension (secondary to inferior vena caval obstruction) and also cardiac arrhythmias. Carbon dioxide embolus can cause hypotension and cardiac arrest. It is important to limit intraperitoneal pressures to no greater than 15mmHg. Laparoscopy is often associated with bradycardia. Careful monitoring is essential. Atropine or glycopyrrolate is often required and should be readily available. • The patient is placed in a steep Trendelenburg position (head down) which carries its own hazards. (See Chapter 30)

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