Shallow, monotonous breathing may decrease ventilation to dependent lung regions and may contribute to the development of atelectasis. Incisional pain, residual anaesthetic effects, and lying in bed for prolonged periods are also contributive factors. Although postoperative atelectasis usually improves spontaneously, if the collapsed regions of the lungs do not become re-inflated then infection may arise as a secondary event (Chumillas 1998; Kips 1997; Stock 1985). Other serious postoperative complications such as intraperitoneal infection, wound infection, cardiac and haemodynamic complications (Hall 1996) can also develop and worsen the patients' outcomes. It is particularly important to identify patients at risk of postoperative pulmonary complications as these are the most frequently reported cause of morbidity and mortality in the postoperative period (Doyle 1999). The occurrence of pulmonary complications is linked to the presence of risk factors, many of which are identifiable at the patient's preoperative evaluation. They include age, smoking status, obesity, pre-existing chronic lung disease, and co-morbidities (Chumillas 1998; Kips 1997). The anaesthetic factors include the type and duration of anaesthesia as well as the different drugs used for anaesthesia and pos