Pre operative evaluation of respiratory system before surgery full details for md exam answer 15 marks

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Preoperative Evaluation of the Respiratory System Before Surgery

Introduction

Postoperative pulmonary complications (PPCs) include atelectasis, pneumonia, bronchospasm, aspiration, hypoxemia, respiratory failure, prolonged mechanical ventilation, and pulmonary embolism. They increase postoperative morbidity, mortality, ICU stay, and hospital cost.

The objectives of respiratory evaluation are to:

Identify existing respiratory disease and perioperative pulmonary risk.
Detect and correct reversible factors.
Assess functional reserve and suitability for the proposed surgery.
Plan anesthesia, postoperative analgesia, monitoring, and respiratory support.
Decide whether surgery should proceed, be deferred for optimization, or be modified.

All patients undergoing noncardiac surgery should have clinical assessment for pulmonary risk. High-risk procedures include thoracic, upper abdominal, major vascular, neurosurgical, head and neck surgery; emergency surgery; procedures lasting more than 3 hours; and surgery under general anesthesia. Harrison's Principles of Internal Medicine, p. 3952.

1. Risk Factors for Postoperative Pulmonary Complications

A. Patient-related factors

Age above 60 years
Current cigarette smoking
COPD, asthma, bronchiectasis, interstitial lung disease
Recent upper or lower respiratory tract infection
Obstructive sleep apnea (OSA), obesity hypoventilation syndrome
Obesity or malnutrition
Poor functional capacity or functional dependence
Congestive cardiac failure, pulmonary hypertension
Neuromuscular disease or impaired cough
Altered sensorium
Alcohol misuse
Low serum albumin, usually less than 3.5 g/dL
Anemia
Poor oxygen saturation at rest
Abnormal chest examination
Previous postoperative respiratory complication

Important predictors listed in standard risk assessment include COPD, cigarette use, OSA, age above 60 years, CHF, low albumin, functional dependence, recent respiratory infection, and abnormal chest findings. Harrison's Principles of Internal Medicine, p. 3952.

B. Procedure-related factors

Emergency surgery
Duration more than 2 to 3 hours
Upper abdominal surgery
Thoracic surgery
Aortic aneurysm repair and major vascular surgery
Head and neck surgery
General anesthesia, especially prolonged anesthesia
Use of long-acting neuromuscular blockers or excessive opioids
Poorly controlled postoperative pain causing splinting and inability to cough

2. History

A focused respiratory history is the most useful initial step.

A. Present respiratory symptoms

Ask about:

Cough: dry or productive; amount, color, and purulence of sputum
Breathlessness: at rest, on exertion, orthopnea, paroxysmal nocturnal dyspnea
Wheeze, chest tightness, episodic symptoms suggesting asthma
Hemoptysis
Fever, sore throat, nasal discharge, and symptoms of recent respiratory infection
Pleuritic chest pain
Nocturnal symptoms, snoring, witnessed apnea, daytime somnolence
Change from baseline exercise capacity

Acute infection, uncontrolled wheeze, copious purulent sputum, or acute COPD/asthma exacerbation requires optimization and usually postponement of elective surgery.

B. Past respiratory illness

Asthma: severity, triggers, recent exacerbations, hospital admission, ICU admission, intubation, steroid requirement, current inhaler use
COPD: baseline dyspnea, exacerbation frequency, home oxygen, noninvasive ventilation, prior intubation
Tuberculosis and sequelae
Bronchiectasis and chronic sputum production
Interstitial lung disease/pulmonary fibrosis
Previous pneumonia, aspiration, COVID-19 sequelae where relevant
Previous pneumothorax or thoracic surgery
Pulmonary embolism
Lung malignancy
Pulmonary hypertension
Neuromuscular disorders: myasthenia gravis, muscular dystrophy, motor neuron disease

C. Smoking history

Document pack-years, current smoking, smoking cessation attempts, vaping, and biomass exposure. Advise cessation in every smoker. Longer cessation before surgery is better, but smoking cessation should be encouraged even if surgery is soon.

D. Drug history

Inhaled beta-agonists, anticholinergics, inhaled corticosteroids
Oral corticosteroids and duration of therapy
Theophylline
Antibiotics
Sedatives, benzodiazepines, opioids
Drugs causing pulmonary toxicity: amiodarone, bleomycin, methotrexate, etc.
Allergies and previous anesthetic/respiratory complications

E. Functional capacity

Assess activities of daily living and exercise tolerance:

Ability to walk on level ground
Ability to climb stairs
Ability to perform household work
Limitation due to breathlessness versus joint disease/cardiac symptoms

A patient able to climb two flights of stairs without stopping generally has reasonable reserve for lung resection assessment. Miller's Anesthesia, 10e, p. 7076.

3. Physical Examination

A. General examination

Build, obesity, cachexia
Cyanosis, pallor, clubbing
Respiratory rate and pattern
Use of accessory muscles
Ability to speak full sentences
Level of consciousness
Signs of chronic steroid use
Peripheral edema, raised JVP, signs of cor pulmonale

B. Airway examination

Assess for:

Difficult airway
Neck movement
Mouth opening and dentition
Facial or neck mass
Tracheal deviation
Stridor
Retrosternal goiter or mediastinal mass

Stridor, positional dyspnea, or superior mediastinal obstruction requires urgent evaluation and individualized anesthetic planning.

C. Respiratory system examination

Chest shape: barrel chest, kyphoscoliosis
Symmetry of chest movement
Tracheal position
Percussion note
Breath sounds: reduced/absent, bronchial breathing
Added sounds: wheeze, crackles, pleural rub
Sputum and effectiveness of cough

D. Cardiovascular examination

Look for:

Pulmonary hypertension
Right heart failure/cor pulmonale
Cardiac failure or valvular disease as alternative/additional causes of dyspnea

4. Investigations

Investigations should be selective and guided by clinical findings and the surgical procedure. Routine chest radiography, arterial blood gas analysis, and spirometry are not indicated for every patient undergoing non-thoracic surgery.

A. Pulse oximetry

Record resting room-air SpO₂ in all patients at risk.
SpO₂ 91% to 95% and especially ≤90% indicates increased PPC risk and requires evaluation/optimization.

B. Chest radiograph

Indications:

New or unexplained respiratory symptoms
Abnormal chest examination
Known active chest disease
Suspected infection, pleural effusion, mass, pneumothorax, or cardiac failure
Thoracic or intrathoracic surgery
Recent deterioration in chronic lung disease

Routine chest radiography based on age alone is not justified because it rarely changes management. Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e, p. 1791.

C. ECG and echocardiography

Consider where dyspnea may be cardiac, or where pulmonary hypertension, right ventricular dysfunction, heart failure, or ischemic heart disease is suspected.

D. Hemogram and biochemistry

Hemoglobin: identify anemia
Serum albumin: low albumin predicts poor outcome
Electrolytes and renal function
Serum bicarbonate: an elevated value may suggest chronic CO₂ retention

E. Arterial blood gas analysis

Indications:

Severe COPD or suspected chronic hypercapnia
Resting hypoxemia
Morbid obesity/obesity hypoventilation
Severe restrictive disease
Pulmonary hypertension
Patients on home oxygen or noninvasive ventilation
Major thoracic surgery/lung resection

ABG establishes baseline PaO₂ and PaCO₂ and helps plan postoperative ventilation. PaO₂ <60 mmHg or PaCO₂ >45 mmHg are warning indicators of increased risk in lung resection, though not absolute contraindications. Miller's Anesthesia, 10e, p. 7074.

F. Pulmonary function tests

Spirometry

Measures:

FEV₁
FVC
FEV₁/FVC ratio
Flow-volume loop, where upper airway obstruction is suspected

Role: PFTs are not routinely useful for predicting PPCs in non-thoracic surgery. They are indicated when there is unexplained dyspnea, suspected undiagnosed lung disease, poor clinical control of known disease, or planned lung resection.

For noncardiothoracic surgery, guidelines discourage routine spirometry solely for PPC prediction because history and examination provide more useful clinical risk information. Miller's Anesthesia, 10e, p. 4030.

Diffusing capacity for carbon monoxide (DLCO)

DLCO assesses alveolar-capillary gas transfer. It is particularly useful in:

Emphysema
Interstitial lung disease
Pulmonary vascular disease
Lung resection evaluation

G. Exercise testing

Stair-climbing test
Six-minute walk test (6MWT)
Formal cardiopulmonary exercise testing (CPET)

The 6MWT is simple and correlates with maximal oxygen consumption. A distance below 400 m is associated with higher cardiopulmonary complication risk after lobectomy. Miller's Anesthesia, 10e, p. 7076.

CPET measures peak oxygen consumption (VO₂max) and is the gold-standard assessment when functional reserve is uncertain. Miller's Anesthesia, 10e, p. 7077.

5. Risk Stratification: ARISCAT Score

The ARISCAT score predicts risk of postoperative pulmonary complications.

Risk variable	Score
Age 51-80 years	3
Age >80 years	16
SpO₂ 91%-95%	8
SpO₂ ≤90%	24
Respiratory infection in last 1 month	17
Hemoglobin ≤10 g/dL	11
Upper abdominal incision	15
Intrathoracic incision	24
Duration 2-3 h	16
Duration >3 h	23
Emergency surgery	8

Total score	Risk category	Approximate PPC rate
<26	Low	1.6%
26-44	Intermediate	13%
≥45	High	42%

Goldman-Cecil Medicine, Table 399-5.

Special Section: Evaluation Before Lung Resection

This must be written separately in an MD answer because lung resection requires quantitative assessment of postoperative respiratory reserve.

The evaluation rests on a three-legged stool:

Respiratory mechanical function: predicted postoperative FEV₁.
Pulmonary parenchymal/gas-exchange function: predicted postoperative DLCO.
Cardiopulmonary interaction: exercise capacity and peak VO₂.

Miller's Anesthesia, 10e, pp. 7073-7079.

A. Spirometry and predicted postoperative FEV₁

All candidates for pulmonary resection need baseline spirometry.

[ \text{ppoFEV}{1} = \text{preoperative FEV}{1} \times \left(1 - \frac{% \text{ functional lung removed}}{100}\right) ]

Interpretation:

ppoFEV₁ >40% predicted: relatively low risk for respiratory complications.
ppoFEV₁ 30%-40%: increased risk, further exercise assessment needed.
ppoFEV₁ <30%: high risk.

Miller's Anesthesia, 10e, p. 7073.

B. DLCO and predicted postoperative DLCO

Calculate ppoDLCO similarly:

[ \text{ppoDLCO} = \text{preoperative DLCO} \times \left(1 - \frac{% \text{ functional lung removed}}{100}\right) ]

ppoDLCO <40% predicted is associated with increased respiratory and cardiac complications.
Risk assessment requires DLCO even when FEV₁ is relatively preserved, as the two are independent predictors.

Miller's Anesthesia, 10e, p. 7074.

C. Estimating postoperative function

Lobectomy: segment counting method.
Pneumonectomy: ventilation-perfusion scan is useful to determine the contribution of the lung to be removed.

V/Q scanning is particularly valuable for pneumonectomy when FEV₁ or DLCO is below 80% predicted. Miller's Anesthesia, 10e, p. 7077.

D. Exercise testing and VO₂max

Climbing 2 to 3 flights of stairs suggests lower risk.
CPET is indicated if ppoFEV₁ or ppoDLCO is reduced, particularly below 30% to 40%.

Interpretation of peak VO₂:

Peak VO₂max	Interpretation
>20 mL/kg/min	Low risk
15-20 mL/kg/min	Intermediate risk
<15 mL/kg/min	High risk
<10 mL/kg/min	Very high/prohibitive risk for major resection

Miller's Anesthesia, 10e, p. 7077; Morgan and Mikhail's Clinical Anesthesiology, 7e, pp. 1038-1039.

6. Preoperative Optimization

A. Smoking cessation

Advise cessation to every smoker.
Ideally stop at least 4 weeks before surgery when feasible, but do not deny cessation advice or treatment because surgery is imminent.
Offer nicotine replacement therapy, varenicline, bupropion, and behavioral support as appropriate.

B. Treat infection

Identify and treat pneumonia, infective exacerbation of COPD, sinus infection with purulent secretions, and bronchiectasis exacerbation.
Elective surgery should generally be postponed until acute infection resolves.

C. Optimize asthma

Continue inhaled beta₂-agonist and inhaled corticosteroid.
Treat active wheeze with bronchodilators.
Add a short course of systemic corticosteroid when required for poor control.
Ensure no active exacerbation before elective surgery.

D. Optimize COPD

Continue usual inhaled bronchodilators and corticosteroids.
Treat bronchospasm with beta₂-agonist and anticholinergic therapy.
Treat exacerbation and infection where present.
Chest physiotherapy and secretion clearance for patients with copious sputum.
Teach breathing exercises and coughing technique.
Consider pulmonary rehabilitation before major elective thoracic or upper abdominal surgery.

E. Obstructive sleep apnea

Screen high-risk patients using a validated tool such as STOP-Bang.
Ask patient to bring and use home CPAP.
Plan opioid-sparing multimodal analgesia.
Consider postoperative continuous oximetry, monitored bed, or CPAP/NIV.

F. Nutrition, anemia, and physiotherapy

Correct anemia where practical.
Correct malnutrition and optimize albumin/protein intake.
Preoperative physiotherapy, inspiratory muscle training, incentive spirometry instruction, and airway clearance techniques are useful in selected high-risk patients.

7. Perioperative Plan Based on Respiratory Assessment

Document:

Baseline SpO₂ and ABG, if indicated
PFT, DLCO, exercise capacity, and lung-resection risk assessment
Need for bronchodilator treatment before induction
Need for arterial line or postoperative ICU/HDU
Plan for lung isolation in thoracic surgery
Need for postoperative CPAP/NIV
Opioid-sparing analgesia, thoracic epidural or regional analgesia where suitable
Early mobilization, chest physiotherapy, deep-breathing exercises, cough support, and adequate pain relief

For high-risk patients, postoperative prevention includes deep breathing, coughing, early ambulation, chest physiotherapy, incentive spirometry in selected cooperative patients, CPAP/NIV where indicated, and adequate analgesia. Harrison's Principles of Internal Medicine, p. 3952.

Conclusion

Preoperative respiratory evaluation is primarily clinical and risk-based. A detailed history, focused examination, pulse oximetry, and selective investigations identify patients at risk of PPCs. Routine chest radiography, ABG, and spirometry are not indicated for all patients. In lung-resection surgery, quantitative assessment with ppoFEV₁, ppoDLCO, V/Q scanning where required, and CPET is essential. The key to improved outcomes is identification of risk, correction of reversible factors, appropriate choice of surgery/anesthesia, and planned postoperative respiratory support.

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