Strategies to reduce post-operative pulmonary complications

Question 1

Preoperative

Answer 1

• Smoking cessation as early as possible; stopping smoking for 8wk or longer is more likely to be beneficial.
• Regular ipratropium or tiotropium for all patients with clinically significantCOPD.
• Inhaled β-agonists, as required, for patients with COPD or asthma who have wheeze or dyspnoea.
• Preoperative glucocorticoids for patients with COPD or asthma who are not optimized and whose airway obstruction has not been maximally reduced.
• Delay elective surgery if respiratory tract infection is present.
• Antibiotics only for patients with lower respiratory tract infection (LRtI).
• Preoperative inspiratory muscle training and chest physiotherapy. this involves breathing exercises, aerobic exercise, incentive spirometry (deep breathing facilitated by a simple mechanical device), education on active breathing, and forced expiration techniques

Question 2

Intra-operative

Answer 2

• Choose an alternative procedure lasting <4hr when possible.
• Surgery other than upper abdominal or thoracic when possible. For example, percutaneous cholecystostomy could be substituted for open cholecystectomy in a critically ill, high-risk patient with acute cholecystitis.
• Regional anaesthesia—if an option in very high-risk patients.
• Epidural or spinal anaesthesia may confer lower risk than gA, though this remains an area of debate.
• Avoid long-acting muscle relaxants in very high-risk patients. Residual nMB is associated with post-operative hypoventilation which may increase post-operative complications.
• Choosing laparoscopic, rather than open, surgery may be beneficial.
• Lung protective ventilation. Alung protective strategy of low tidal volume (Vt) ventilation (6–8mL/kg of ideal body weight (IBW), PEEP at 6–8cmH2O, and recruitment manoeuvres every 30min) is associated with a reduction in adverse pulmonary events (see E p. 94).

Question 3

Post-operative

Answer 3

• If possible, aim for upright posture post-operatively. Respiratory performance, FRC, and clearance of secretions are improved when sitting or standing, compared with the supine position.
• Early mobilization reduces the incidence of thromboembolic disease.
• Ensure regular clinical review, and monitor the respiratory rate and O2 saturation. Respiratory deterioration may present in a non-specific way (confusion, tachycardia, fever, malaise). Regular review allows urgent investigation and aggressive therapy. Seek assessment and advice of the intensive care/outreach team early if the patient does not respond to initial treatment.
• Early post-operative chest physiotherapy, including incentive spirometry and breathing exercises, aids clearance of secretions and reduces atelectasis.
• Administer supplemental O2 for up to 72hr post-operatively, particularly if the patient is receiving opioids. Anaesthetic agents exert a dose-dependent depression on the sensitivity of central chemoreceptors, reducing the stimulatory effect of CO2. this effect can occur for up to 72hr post-operatively and is commonest at night. Preoperative measurement of PaO2, SaO2, and PaCO2 is essential to establish a realistic target for each patient.
• Patients who chronically retain CO2 (advanced COPD) may be dependent on hypoxaemia as their main ventilatory drive due to downregulation of central chemoreceptors. the concentration of delivered O2 should be controlled (e.g. by Venturi mask) and titrated, in order to optimize oxygenation and prevent hypoventilation. Adequate monitoring should be available, ideally using serial ABg measurement (pulse oximetry shows onlySpO2).
• Humidification of O2 aids physiotherapy and sputum clearance.
• Accurate management and documentation of fluid balance is essential. Adequate intravascular filling is required to maintain perfusion of organs such as the kidney and gut. However, patients with lung disease are at increased risk of pulmonary oedema. (A dilated right ventricle may mechanically compromise the function of the left ventricle.) Fluid overload is poorly tolerated in these patients, and a high index of suspicion should be maintained.
• good analgesia is essential for the maintenance of efficient respiratory function, compliance with physiotherapy, early mobilization, and minimizing cardiac stress. Regular PO or IV paracetamol and, where not contraindicated, nSAIDs should be prescribed. nSAIDs should be used with caution in the elderly, as renal function may be compromised and they may induce fluid retention.
• Patients with lung dysfunction may benefit from local or regional anaesthesia. the surgeon may be able to place a catheter for regional anaesthesia at the time of operation (e.g. paravertebral catheter for thoracotomy). the benefits of opioid-based analgesia (patient control, mobility, and avoidance of bladder catheterization) should be weighed against the benefits of regional analgesia (avoidance of high-dose systemic opioids, preservation of respiratory function) and discussed with the patient preoperatively.
• Involve the pain management team early in the post-operative period, requesting at least daily reviews

Question 4

Lung protective ventilation

Answer 4

• In 2000, the ARDSnet study showed that the use of low Vt (6–8mL/ kg IBW) during mechanical ventilation significantly reduced mortality in acute respiratory distress syndrome (ARDS).
• the IMPROVE study randomized 400 patients undergoing elective abdominal surgery into two groups.17 One group received low Vt ventilation:6–8mL/kg IBW, PEEP 6–8cmH2O, and recruitment manoeuvres every 30min. the other group received standard mechanical ventilation (10–15mL/kg with PEEP and recruitment manoeuvres provided, according to the anaesthetist’s discretion). In both groups, the anaesthetists tried to keep plateau pressures under 30cmH2O. the rate of post-operative pulmonary complications was significantly lower in the group receiving low Vt ventilation.

Question 5

Respiratory tract infection and elective surgery

Answer 5

• Patients who have respiratory tract infections producing fever and cough with or without chest signs on auscultation should not undergo elective surgery under gA due to the increased risk of post-operative pulmonary complications.
• Adult patients with simple coryza are not at significantly increased risk of developing post-operative pulmonary problems, unless they have pre-existing respiratory disease or are having major abdominal or thoracic surgery.
• Laryngospasm may be more likely in patients with a recent history of upper respiratory tract symptoms who are asymptomatic at the time of surgery.
• Compared with asymptomatic children, children with symptoms of acute or recent upper respiratory tract infection (URtI) are more likely to suffer from transient post-operative hypoxaemia (SpO2 <93%). this is most marked when intubation is necessary

Question 6

Smoking

Answer 6

• Cigarette smoke contains nicotine, a highly addictive substance, and at least 4700 other chemical compounds, of which 43 are known to be carcinogenic. Long-term smoking is associated with serious underlying problems such as COPD, lung neoplasm, IHD, and vascular disorders.20
• Respiratory tract mucus is produced in greater quantities, but mucociliary clearance is less efficient. Smokers are more susceptible to respiratory events during anaesthesia and to post-operative atelectasis/ pneumonia. Abdominal or thoracic surgery and obesity increase theserisks.
• Carboxyhaemoglobin (COHb) levels may reach 5–15% in heavy smokers, causing reduced O2 carriage by the blood. COHb has a similar absorption spectrum to oxyhaemoglobin and will cause falsely high O2 saturation readings.
• Increased airway irritability increases coughing, laryngospasm, and desaturation during induction and airway manipulation (e.g. laryngeal mask insertion). Avoid by using a less irritant volatile (e.g. sevoflurane) and deepening anaesthesia slowly.
• Maintaining spontaneous breathing via an endotracheal tube (Ett) or laryngeal mask airway (LMA) may be awkward due to airway irritation—consider LA to the vocal cords, opioids, relaxants, andIPPV.

Question 7

Smoking Risk reduction

Answer 7

• Abstinence from smoking for 8wk is required to decrease morbidity from respiratory complications to a rate similar to that of non-smokers.
• Smokers unwilling to stop preoperatively will still benefit by refraining from smoking for 12hr before surgery. During this time, the effects of nicotine (activation of the sympathoadrenergic system with raised coronary vascular resistance) and COHb will decrease.