One. Background
There are three main types of pulmonary ventilatory dysfunction: 1. obstructive, and the typical disease is COPD, which is caused by airway obstruction; 2 is restrictive, the typical disease is pulmonary fibrosis, which is caused by a decrease in lung volume; 3 is mixed, both blocking and limiting factors exist.
How to identify mainly depends on three indicators: (1) FEV1% predicted value (2) FVC % predicted value (3) FEV1/FVC. (FVC refers to the expiratory spirometry obtained by exhaling with maximum effort and speed after the maximum inspiration.) FEV1 refers to the amount of breath exhaled in the first second of FVC, and the ratio of measured value to predicted value > 80% is normal. The ratio of FEV1 to FVC is a one-second rate (FEV1.0%), with FEV1.0% being an indicator of airway obstruction, > 70% normal, and decreasing in airway obstruction and/or emphysema. If (1) (3) falls and (2) does not fall, it is blocked; If (1) (2) is down and (3) is not down; If all three are lowered, it is mixed ventilatory dysfunction.
Preoperative pulmonary function abnormalities are not an absolute contraindication to surgery, but the risk of surgery is related to various factors such as the patient's age, nutritional status, body mass index (BMI), surgical site and scope, anesthesia time, preoperative underlying lung disease, and chronic inflammation control. Patients who are assessed as high-risk before surgery must receive adequate preoperative preparation and strict management during and after surgery.
Two. Preoperative evaluation
A detailed history and physical examination are the most important part of the preoperative risk assessment. History may reveal a history of previously diagnosed chronic lung disease and a history of occult underlying lung disease or heart failure, such as exercise intolerance, unexplained dyspnea, or cough. Physical examination can directly suggest chronic obstructive pulmonary disease (COPD), such as barrel chest, hyperresonance on lung percussion, decreased breath sounds, rales, and prolonged expiratory phase. In patients at high risk of abnormal lung function, laboratory tests may be added. Pulmonary ventilation function is the most widely used in clinical practice, mainly for the determination of lung volume, lung ventilation, pulmonary ventilation function, including bronchodilation test, bronchial provocation test and exercise cardiopulmonary function measurement. Clinically, selective screening is required according to the patient and surgery-related factors, such as age > 60 years, ASA grade ≥2, COPD, congestive heart failure, and the estimated time of surgery >3 hours.
Before surgery, a respiratory physician needs to be consulted to develop an appropriate plan to improve lung function. Reasonable medication and oxygen therapy are used to maintain the patient's arterial oxygen partial pressure ≥ 60mmHg or pulse oximetry >90% in the preoperative resting state. Medications such as bronchodilators and hormones are recommended until the morning of surgery.
Three. Perioperative management
Patients who are at high risk of postoperative pulmonary complications should be adequately preoperatively prepared, intraoperatively managed, and prevented and managed after surgery. Chronic lung diseases (e.g., COPD, asthma, obstructive sleep apnea, pulmonary hypertension, etc.) can be operated on if the symptoms are controlled and stable; If symptoms are not controlled, it is recommended to postpone elective surgery and optimize treatment to achieve optimal control before proceeding with surgery.
1. Preoperative preparation
Smoking cessation, intensive nutritional support (correction of hypoalbuminemia), infection control, respiratory exercises, and pulmonary medication (continued use of bronchodilators, expectorants, and hormones in the perioperative period of lung disease).
2. Intraoperative management
The anesthesia method is to use low-risk endotracheal intubation general anesthesia as much as possible, without long-acting neuromuscular blocking agents as much as possible, limit fluids, and control the duration of surgery (less than 3 hours as much as possible).
(1) Respiratory management
(1) It is recommended to ventilate with small tidal volume, which can be set at 6ml/kg for patients with poor lung compliance such as ARDS, pulmonary edema, and atelectasis. However, COPD patients are more likely to have hypercapnia before surgery, and long-term low tidal volume ventilation has the risk of hypoventilation aggravating hypercapnia, so the goal of intraoperative mechanical ventilation is to maintain the arterial partial pressure of carbon dioxide (PaCO2) at the preoperative baseline level.
(2) Breath-to-exhale ratio. The inspiration-exhalation ratio is 1:2~2.5 with slow frequency in obstructive ventilation disorder, and 1:1.5 with faster frequency in restrictive ventilation disorder.
(3) Positive end-expiratory pressure (PEEP). Patients with COPD have endogenous PEEP due to early closure of the small airways during expiratory periods. PEEP of 3 to 5 cm H2O for mechanical ventilation can delay small airway closure and improve lung dynamic compliance.
(4) Inhaled oxygen concentration. Patients with COPD are more likely to develop atelectasis if the inspired oxygen concentration is too high, and the intraoperative inspired oxygen concentration should not exceed 50%, generally about 40%, and the partial pressure of oxygen in the target artery should be maintained below 120mmHg.
(2) Treatment of intraoperative bronchospasm
Spray β2 agonists such as albuterol through the endotracheal tube for 4~5 sprays, or even more (8~10 sprays); In severe cases, 0.1mg of epinephrine can be instilled through endotracheal intubation, or 5μg~10μg of intravenous epinephrine, and then 0.5~2μg/min continuous pumping; At the same time, intravenous corticosteroids methylprednisolone 1 mg/kg or hydrocortisone 100 mg are given.
(3) Extubation
When explaining the risks to the family, we are most worried about whether we can be extubated in time after surgery. For patients, early extubation is certainly beneficial, reducing lung injury associated with mechanical ventilation and reducing the risk of infection upon admission to the ICU. How to extubate safely? We need to consider the following:
(1) Muscle relaxation and sedative drug metabolism is complete, the patient is conscious, and spontaneous breathing is stable. Cholinergic drugs such as neostigmine can induce asthma, so according to the time of surgery, try to choose short-acting muscle relaxants without antagonism.
(2) Satisfactory analgesia. For relatively large surgeries, we need to use nerve blocks or local infiltration anesthesia as much as possible with short-acting opioids and NSAIDs. Of course, ESD surgery is less invasive and does not require a nerve block.
(3) Before extubation, the inhaled oxygen concentration should be reduced, and the goal is to maintain pulse oximetry at 88%~92% or the preoperative baseline level to restore the stimulating effect of hypoxia on spontaneous breathing. Arterial blood gas analysis may be done if necessary to accurately assess arterial oxygenation status and PaCO2 levels. Safe extubation may be considered in patients who have no anesthetic drug residue and are able to maintain blood gases at baseline or acceptable levels. If you can't pull the tube, it may be safe to send it to the ICU and wait for a transition to a non-invasive ventilator.
3. Postoperative prophylaxis
Regional analgesia, anti-infection, respiratory management (oxygen therapy, non-invasive positive pressure ventilation), chest physiotherapy (intensive cough training, back patting and expectoration), early mobilization, nutritional support (malnutrition can lead to immunocompromise and poor wound healing), continued use of drugs (including bronchodilators, expectorants, and hormones) and prevention of blood clots in the lower extremities (early postoperative mobilization, compression stockings, and low molecular weight heparin).
Four. brief summary
Patients who undergo thoracic surgery and have abnormal pulmonary function need to be stratified according to patient-related and surgery-related risk factors, and lung function should be evaluated and surgical modality determined. Abnormal pulmonary function is not an absolute contraindication to surgery, and perioperative management requires multidisciplinary collaboration between thoracic surgery, respiratory medicine, and anesthesiology to reduce perioperative complications and improve patients' quality of life.
Wang Danyang, Department of Anesthesiology, Shanghai Pulmonary Hospital, Tongji University
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