Chronic obstructive pulmonary disease and anaesthesia

Abstract

Chronic obstructive pulmonary disease (COPD) is a commonly encountered respiratory disorder. Patients with COPD pose a challenge to the anaesthetist because intraoperative and post- operative complications occur more commonly than in those without the disease, and can lead to prolonged hospital stay and increased mortality. This article provides an overview of COPD and discusses implications for the anaesthetic management of patients with the disease. Pathophysiology COPD is a chronic and progressive inflammatory condition affecting central and peripheral airways, lung parenchyma, and pulmonary vas- culature. This leads to poorly reversible narrow- ing of the airways, remodelling of airway smooth muscle, increased numbers of goblet cells and mucus-secreting glands, and pulmon- ary vasculature changes resulting in pulmonary hypertension. It is widely accepted that cigarette smoking is the key noxious stimulus leading to the devel- opment of COPD. However, more recently it has been suggested that genetic factors are also implicated, with the finding that a genetic variant (FAM13A) is associated with the devel- opment of COPD in the COPDGene study. 1 COPD is characterized by expiratory airflow limitation because of a combination of small airway inflammation (obstructive bronchiolitis) and parenchymal destruction (emphysema). In the former, inflammation in the small airways causes obstruction and air trapping, leading to dynamic hyperinflation, which adversely affects both ventilation/perfusion (V/Q) matching and the mechanics of the respiratory muscles. In em- physema the end result of inflammation is elastin breakdown and subsequent loss of alveolar structural integrity leading to decreased gas transfer, reduction in the pulmonary capillary bed, and further worsening of V/Q matching. Further airflow limitation results from reduced parenchymal support of small airways. Often it is not possible to make clear distinctions between the two subtypes and the relative contri- bution of each varies from patient to patient. In patients with advanced COPD, the combin- ation of V/Q mismatch, decreased gas transfer, and alveolar hypoventilation ultimately leads to respiratory failure. COPD is often associated with a number of coexisting diseases that may complicate the an- aesthetic management of these patients. A high proportion of patients with COPD are smokers, hence the disease is associated with the develop- ment of lung cancer. Pulmonary hypertension is prevalent in a third of patients with COPD and has been shown to be an indicator of poor long- term survival. Inflammatory processes in the lung not only cause pulmonary effects but also contribute to the extrapulmonary effects of the disease. The origin of this systemic inflamma- tion is unclear and probably multifactorial, but results in weight loss, skeletal muscle dysfunc- tion (with further adverse effects on respiratory muscle function), cardiovascular disease, de- pression, and osteoporosis. Weight loss occurs in 50% of patients with severe COPD and indi- cates a poor prognosis. Clinical features Epidemiology It has been estimated that 3 million people have COPD in the UK, two-thirds of these being undiagnosed. Diagnosis is most common in the sixth decade of life. COPD confers increased risk of hospitaliza- tion in general, and in the critically ill it has been shown to increase mortality both in those with ventilator-associated pneumonia and in those with non-exacerbated disease. The long- term survival of patients with severe COPD undergoing surgery is poor, with postoperative pulmonary complications being common. A recent study identified COPD as an independent Key points Chronic obstructive pulmonary disease (COPD) is a progressive inflammatory condition resulting in expiratory airflow limitation. Treatment involves smoking cessation, inhaled therapy, pulmonary rehabilitation, and appropriate and timely treatment of exacerbations. Patients with COPD are at increased riskof developing perioperative complications and have an increased mortality. Anaesthetic management centres on preoperative optimization and the use of regional techniques wherever possible. If general anaesthesia is used, then artificial ventilation is challenging because of the development of intrinsic positive end-expiratory pressure.