Lung isolation techniques
This case aims to highlight the available lung isolation techniques for pulmonary resection, the indications for their use, and troubleshooting commonly occurring problems.
1 Outline the pre-assessment principles for a patient preparing for intrathoracic surgery
2 Discuss the different techniques for employing one-lung ventilation (OLV) anaesthesia.
2A01; 2A03
You are scheduled to anaesthetize a 61-year-old gentleman for a right-sided pneumonectomy and have been called to see him in the pre-admission clinic. He has a diagnosis of non-small cell lung cancer, and his surgery is intended to be a curative procedure. He is a lifelong heavy smoker and suffers from hypertension, AF, and angina. He has a BMI of 22.
The pre-assessment nurse has taken some baseline observations and performed an ECG for you on your arrival. Current observations are: BP 176/110 (remains raised on three repeated measurements in clinic), pulse rate 58 bpm, RR 21 breaths/min, temperature 36.8°C. His ECG shows rate-controlled AF, with no obvious signs of current or previous ischaemia.
This patient should be assessed, based on the recommendations set out by the British Thoracic Society guidelines of 2001 and the more recent NICE guidelines of 2011 (lung cancer).
◆ Patients should be assessed, using a global risk score such as THORACOSCORE
◆ Age is not a barrier to surgery; it is, however, known that patients of advancing age will require greater levels of perioperative support and, as a result, have higher morbidity and mortality rates
◆ Assessment should be made of the cardiovascular function, and surgery delayed if the patient has had an MI within 30 days. If the patient has an active cardiac condition or three or more risk factors, they should be seen preoperatively by a cardiologist. If they have no active conditions and two or fewer risk factors, no further cardiac investigation is indicated
◆ Respiratory function should be measured. This should be done in the sequence outlined below for patients undergoing a pneumonectomy
1 Spirometry: if normal spirometry and good exercise tolerance, no further investigation is required. If, however, the post-bronchodilator FEV1 is <55% of the predicted value (<2 L), further investigation is required
2 Perform a quantitative perfusion scan, and calculate the patient’s estimated post-operative FEV1
3 Perform the transfer factor test TLCO, and calculate the estimated post-operative transfer factor
4 Express both post-operative transfer factor and FEV1 as a percentage of predicted values, and assess oxygen saturations on room air. If these variables are <40% predicted, then the patient is considered high risk, and surgery should only be offered if the patient accepts the risk of complications and persistent dyspnoea post-operatively. If the measured values are >40% predicted, then surgery should be undertaken without further assessment. Any other combination of findings should precipitate further exercise testing
5 Exercise testing should take the form of a full CPET; however, if this is not available, then the shuttle walk test may be conducted. If the patient has a VO2 max of >15 mL/kg/min, then surgery should proceed as planned, or alternatively if they manage >25 shuttles with <4% oxygen desaturation, they should be listed for theatre. If they do not meet either of these criteria, consideration should be given to a less extensive resection or to radical radiotherapy.
◆ Current level of dyspnoea
◆ Exercise tolerance
◆ Smoking status
◆ Presence of cardiac risk factors
◆ Associated comorbid conditions
◆ Nutritional status: a poor nutritional status has known associations with increased post- operative complications
◆ Treatment to date
◆ Medication history
◆ Anaesthetic history
◆ Presence or absence of reflux disease.
◆ Cardiorespiratory exam looking specifically for signs of congestive cardiac failure or pulmonary hypertension which are associated with high levels of perioperative morbidity and mortality
◆ Airway assessment
◆ Assessment of dentition.
◆ ECG
◆ Pulmonary function tests (as outlined earlier in the text)
◆ ABG (if the pulmonary function test results are borderline)
◆ Baseline haematology, coagulation, and biochemistry blood tests; ensure that cross-matched blood will be available.
The patient will already have had a plain CXR film and high-resolution CT thorax, and these should be reviewed by the anaesthetist.
Your patient has three cardiovascular risk factors in the form of rhythm other than sinus, uncontrolled hypertension, and mild angina pectoris; you therefore arrange for the patient to be seen by a cardiologist. Following review by your cardiology colleagues, who have rationalized the patient’s antihypertensives and continued all the other cardiac medications, you ask for the patient to undergo pulmonary function testing. Based on the steps mentioned earlier, the patient is declared fit for pneumonectomy.
◆ Patients will require general anaesthesia with mandatory ventilation which, in most centres, will be combined with a regional technique such as an epidural, a paravertebral block, or intercostals nerve blocks
◆ The ability to isolate the lungs and perform OLV, although not an absolute requirement, is highly desirable
◆ Aims are to avoid inhibition of hypoxic pulmonary vasoconstriction, reduce airway irritability, and maintain cardiovascular stability
◆ Intraoperative fluid administration should be restricted as far as possible, as the handling of the lung tissue impairs pulmonary capillary function, placing the patient at high risk of post-operative pulmonary oedema
◆ Consideration should be given to patient positioning in the lateral decubitus position.
There are three devices which allow lung isolation and therefore OLV.
1 Double-lumen tubes (DLTs):
• These are the most commonly used devices to achieve lung isolation. Their popularity stems from the fact that they allow independent control of each lung
• These devices can be either right- or left-sided and come in several different sizes and designs
• As the name suggests, the tube has two lumens, one of which is long enough and appropriately angulated to reach the right or left main bronchus, and the other lumen is shorter and terminates in the distal trachea. The bronchial lumen has a bronchial cuff which allows separation of the lungs. The tube also has a tracheal cuff that separates the lungs from the oropharynx and the environment
• Anatomically, the left main bronchus is longer than the right, making it much easier to correctly position a left-sided tube
• The DLT has two curves; the bronchial lumen curve, being orientated initially anteriorly in order to pass into the tracheal inlet and then being rotated in the direction of the bronchus you are aiming to intubate
• After ETCO2 has been detected, appropriate tube positioning is confirmed by visual inspection of chest movement and by auscultation of the chest, whilst alternately clamping one lumen and ventilating the other. A fibreoptic bronchoscope is used to further check appropriate tube positioning
2 Bronchial blockers:
• These are reserved for use in situations where DLTs are deemed unsuitable. For example, in children where DLTs may be too large, in distorted airway anatomy that prevents the passage of the DLT, in critically ill patients who already have single-lumen ETT in situ and in whom a tube change is deemed dangerous, or when DLT insertion has been difficult or impossible
• Bronchial blockers are single-lumen, balloon-tipped endoluminal catheters
• A single-lumen, cuffed orotracheal tube is placed first, and, through it, the bronchial blocker is advanced into the main bronchus under direct vision using a bronchoscope
• The selected bronchus is then occluded by inflating the balloon
• The central lumen allows passive lung deflation, suction, and insufflations with oxygen, if required
• The main disadvantage to the use of bronchial blockers is that, in order to ventilate both lungs, the isolation of the lungs is lost
3 Endobronchial intubation with single-lumen ETT:
• Mainly reserved for the emergency separation of the two lungs, e.g. in severe pulmonary haemorrhage
• An uncut single-lumen ETT is used and will normally intubate the right main bronchus if it is not guided using a bronchoscope.
◆ Isolation of the lungs to prevent cross-contamination, particularly in cases of pulmonary haemorrhage or in the presence of infections affecting a single lung
◆ Bronchopleural fistula where OLV allows a controlled distribution of ventilation.
◆ Facilitation of surgical procedure.
You have opted to use a double-lumen tube in order to achieve lung separation in your patient. You have selected a 39F left-sided DLT and successfully placed it within the left main bronchus, confirmed by using ETCO2 monitoring, auscultation, visual inspection, and bronchoscopy. The patient has been positioned and draped for surgery, and the surgeon asks you to initiate OLV.
1 Establishing one-lung anaesthesia using a DLT:
• A clamp is placed on the tracheal lumen to ensure all ventilation is delivered to the dependent (left) lung
• The tracheal lumen of the DLT is then opened to air to facilitate the deflation of the right lung
2 Ventilator strategies for OLV:
• ALI, following pneumonectomy, occurs in 2–4% of cases, despite fluid restrictive management, and is associated with a mortality of 25–50%; it has been established that this may be due to volutrauma and barotrauma during OLV
• Maintain FiO2 as low as possible
• Avoid atelectasis with frequent recruitment manoeuvres
• Tidal volume 5–6 mL/kg; external PEEP of 4–10 cmH2O; RR of 15–20 breaths/min
• Pressure control ventilation (peak inspiratory pressure <35 cmH2O)
• Permissive hypercapnia is an accepted consequence of lung-protective strategies.
Your patient has been established on OLV for approximately 40 min, and surgery is progressing well. However, you notice that his oxygen saturations have begun to fall from 96%, with an FiO2 of 0.4, to 88%.
◆ Hypoxaemia affects post-operative outcomes, with an increased incidence of cognitive dysfunction, AF, renal failure, and pulmonary hypertension
◆ Increase FiO2 to 1.0
◆ Confirm the position of the DLT, using a fibreoptic bronchoscope, and confirm that the anaesthetic machine and equipment are functioning appropriately
◆ If airway pressures are high, suctioning to clear any blood or secretions from the tube and an assessment for bronchospasm should be performed
◆ Ensure adequate cardiac output and Hb for oxygen delivery
◆ Supply passive oxygen flow to the non-ventilated lung, e.g. 2–4 L/min via a C-circuit. This may be enough to reduce the V/Q mismatching and improve oxygenation
◆ If hypoxaemia is persistent, then applying CPAP of 5–10 cmH2O to the non-ventilated lung would be the next step. However, this may impede surgical progress, and so communication of the situation with the surgeon is important
◆ Intermittent ventilation of both lungs may be required
◆ Clamping of the appropriate pulmonary artery will essentially remove the shunting of blood through the non-ventilated lung and treat the hypoxaemia.
Summary
Anaesthesia for lung resection and lung isolation are challenging techniques and should only be carried out by those individuals who are familiar with the use of lung isolation equipment and the techniques required to troubleshoot any resultant complications. An in-depth knowledge of cardiorespiratory anatomy and physiology is an absolute requirement, and the thoracic anaesthetist should be involved in patient selection and meticulous preparation.
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