degenerative changes progressively decrease pulmonary function and physical changes
occur in the lungs and chest wall. There is reduced alveolar surface area and diffusion
capacity, pulmonary fibrosis, reduced lung elasticity, and reduced mechanical ventilation
reserve. Chronic obstructive lung disease is common in old dogs and cats.
All of these changes impair gaseous exchange during anaesthesia
hence oxygen supplementation is beneficial, and in some cases the use of bronchodilators
may be indicated.
Impaired laryngeal function (sometimes laryngeal paralysis
in older dogs - particularly Labrador retrievers) and increased respiratory dead
space necessitate correct endotracheal intubation during anaesthesia and careful
preparation of the patient to avoid vomiting. The use of antiemetic drugs (e.g. metoclopramide)
might be indicated in patients requiring emergency surgical treatment, those with
oesophageal or gastric motility problems or
those with conditions likely to cause nausea (e.g. uraemia).
A recent study suggests that older animals have a greater risk of developing gastro-oesophageal reflux
Pulmonary embolism is a common postoperative complication
in old people, and may be more common than is currently appreciated in veterinary
patients. In human general surgery patients the incidence of deep vein thrombosis
is reported to be as high as 45% in those aged over 40, and 65% in patients over
71 (Consensus Conference 1986; Borow and Goldson 1981).