RESPIRATORY SYSTEM PART II PATHOPHYSIOLOGY

1. RESPIRATORY SYSTEMPART IIPATHOPHYSIOLOGY DENNIS STEVENS CRNA, MSN, ARNP FEBRUARY 2010 FLORIDA INTERNATIONAL UNIVERSITY ADVANCED BIOSCIENCE IN ANESTHESIOLOGY I NGR 6404

2. RESPIRATORY SYSTEMPART II OBJECTIVES Discuss risk factors related to pulmonary disease and associated anesthetic implications. Explain preoperative and intraoperative anesthetic considerations associated with obstructive pulmonary disease including treatment modalities. Describe the anatomic and related physiologic changes that occur in airways secondary to advanced pulmonary disease. Discuss anesthetic considerations associated with restrictive pulmonary disease. Explain the pathogenesis of pulmonary embolism and the treatment for intraoperative pulmonary embolism.

3. RESPIRATORY SYSTEMPART II INTRODUCTION The association of preexisting respiratory disease on respiratory function during anesthesia and in the postoperative period is predictable More marked intraoperative alterations in respiratory function and higher rates of postoperative complications are associated with greater degrees of preoperative pulmonary impairment Important to recognize patients at increased risk of potential pulmonary complications in the preoperative period

4. RESPIRATORY SYSTEMPART II PULMONARY RISK FACTORS Pulmonary dysfunction a common postoperative complication Incidence of atelectasis, pneumonia, pulmonary embolism, and respiratory failure following surgical procedures varies Risk factors for postoperative pulmonary complications: Preexisting pulmonary disease Thoracic or upper abdominal surgery Smoking Obesity Age (> 60 years) Prolonged general anesthesia (> 3 hours)

5. RESPIRATORY SYSTEMPART II OBSTRUCTIVE PULMONARY DISEASE Obstructive lung diseases are the most common form of pulmonary dysfunction Includes; asthma, emphysema, chronic bronchitis, cystic fibrosis, bronchiectasis, and bronchiolitis Hallmark of these disorders is resistance to airflow Elevated airway resistance and air trapping increases the WOB and respiratory gas exchange is impaired because of ventilation/perfusion imbalance Wheezing is a common finding representing turbulent airflow

6. RESPIRATORY SYSTEMPART II ASTHMA Common disorder affecting 5-7% of the population Classified as a chronic inflammatory disorder of the airways characterized by increased responsiveness of the tracheobronchial tree to various stimuli Many cells and cellular elements play a role Inflammation characterized by: Recurrent episodes of wheezing, breathlessness, chest tightness, and cough Episodes are associated with widespread but variable airflow obstruction that is often reversible

7. RESPIRATORY SYSTEMPART II ASTHMA Significant consideration is the identification of exacerbating factors Extrinsic asthma: Most commonly affects children and young adults and involves infectious, environmental, psychologic, or physical factors Intrinsic asthma: Develops in middle age without specific identifiable stimuli Incidence; up to 15 million people in the US have asthma

8. RESPIRATORY SYSTEMPART II ASTHMA Pathogenesis and pathophysiology: Clinical syndrome characterized by episodes in which the airways are hyperresponsive Involves the local release of various chemical mediators in the airway resulting in bronchoconstriction Permanent changes in airway anatomy (airway remodeling) are associated with the inflammatory response During an asthma attack, bronchoconstriction, mucosal edema, and secretions increase resistance to gas flow at all levels of the lower airways

9. RESPIRATORY SYSTEMPART II ASTHMA Pathogenesis and pathophysiology: Airway resistance normalizes first in the larger airways and then in more peripheral airways as an attack resolves TLC, RV, and FRC are all increased, prolonged or severe attacks markedly increase the WOB and can fatigue respiratory muscles Number of alveolar units with low V/Q ratios increases Tachypnea is due to stimulation of bronchial receptors and typically produces hypocapnia

10. RESPIRATORY SYSTEMPART II ASTHMA Treatment: Medication administration: �-adrenergic agonists, methylxanthines, glucocorticoids, anticholinergics, leukotriene blockers, and mast cell stabilizing agents Sympathomimetic agents are the most useful and most commonly used agents. They produce bronchodilation via �2-agonist activity Usually administered via a metered-dose inhaler or by aerosol

11. RESPIRATORY SYSTEMPART II ASTHMA Anesthetic considerations: Preoperative management: Determine recent course of disease H&P; no or minimal dyspnea, wheezing, or cough is optimal Diagnostic studies: PFTs, CXR, ABGs Asthmatic patients with active bronchospasm presenting for emergent surgery; intensive treatment Bronchodilators continued to time of surgery, consider preoperative sedation and steroid therapy

12. RESPIRATORY SYSTEMPART II ASTHMA Intraoperative management: Most critical time for asthmatic patient receiving anesthesia is during instrumentation of the airway Avoid medications associated with histamine release Goal of GA; smooth induction and emergence, with anesthetic depth adjusted to stimulation Achieve deep anesthesia before intubation and surgical stimulation Volatile anesthetics used for maintenance of anesthesia CV with warmed humidified gases

13. RESPIRATORY SYSTEMPART II ASTHMA Intraoperative bronchospasm: Manifested as wheezing, increased PIPs, decreasing exhaled tidal volumes, or a slow rising capnograph waveform Treatment: Deepen the anesthetic If wheezing not resolved consider less common causes Pharmacologic intervention End of surgery; consider reversal, emergence, and deep extubation

14. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Preoperative considerations: COPD most common pulmonary disorder encountered Strongly associated with cigarette smoking Majority of patients are asymptomatic or mildly symptomatic With advancing disease maldistribution of both ventilation and pulmonary results in areas of: Low V/Q ratios High V/Q ratios

15. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Chronic Bronchitis: Defined by the presence of a productive cough Responsible factors; cigarette smoking, air pollutants, occupational exposure to dust, recurrent pulmonary infections, and familial factors Airflow obstruction is produced by secretions and inflammation Bronchospasm may be present Recurrent pulmonary infections are common RV is increased but TLC is often normal

16. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Chronic Bronchitis: Intrapulmonary shunting is prominent and hypoxemia is common Chronic hypoxemia leads to �blue bloater syndrome�: Erythrocytosis Pulmonary hypertension Eventual RV failure With progression of disease patients gradually develop chronic CO2 retention Ventilatory drive less sensitive to arterial CO2 tension

17. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Emphysema: Pathologic disorder with irreversible enlargement of the airways distal to terminal bronchioles and destruction of alveolar septa Nearly always related to cigarette smoking Less commonly occurs at an early age and is associated with a homozygous deficiency of antitrypsin Associated with premature closing of the small airways Characteristic increases in; RV, FRC, TLC, and RV/TLC ratio

18. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Emphysema: Inevitably leads to pulmonary hypertension in the terminal stages of the disease Large cystic areas or bullae may develop Increased deadspace is a prominent feature Dyspneic patients with emphysema often purse their lips to delay closure of the small airways �pink puffers� Majority of patients have a combination of bronchitis and emphysema

19. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Treatment: Treatment for COPD is primarily supportive Cessation of smoking most important intervention Bronchodilator therapy if reversible airway obstruction presents Inhaled �2-adrenergic agonists, glucocorticoids, and ipratropium are useful Hypoxemia carefully treated with supplemental oxygen Chronic hypoxemia and pulmonary hypertension require low-flow oxygen therapy

20. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Treatment: O2 therapy can elevate PaCO2 levels in patients with CO2 retention If cor pulmonale present diuretics are used to control peripheral edema Broad-spectrum antibiotic therapy may be necessary to treat exacerbations related to bronchitis

21. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Anesthetic Considerations/Preoperative Management: Patients with COPD should be optimally prepared prior to elective surgical procedures Recent changes in dyspnea, sputum, and wheezing should be questioned Pulmonary function studies, CXRs, and ABG measurements should be reviewed Many patients have concomitant cardiac disease and should receive a CV evaluation Only limited improvement in respiratory function may be seen after a period of intensive preoperative preparation

22. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Anesthetic Considerations/Preoperative Management: Preoperative interventions may decrease the incidence of postoperative pulmonary complications Possibility of postoperative ventilation necessary in high risk patients should be discussed with the patient and surgeon Smoking should be discontinued 6-8 weeks prior to the surgical procedure Carboxyhemoglobin levels and methemoglobin levels may be increased

23. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Anesthetic Considerations/Preoperative Management: Preoperative chest physiotherapy and antibiotics may be administered Administration of bronchodilators and/or glucocorticoids may be useful Pulmonary hypertension should be optimized Malnutrition if present should be addressed Treatment of cor pulmonale especially if right ventricular failure presents

24. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Anesthetic Considerations/Intraoperative Management: Regional anesthesia often considered preferable to general anesthesia, yet there are pitfalls...! Preoxygenation necessary prior to the induction of general anesthesia Bronchodilating anesthetics improve only the reversible component of airflow obstruction bronchospasm Enhanced respiratory depression is present with moderate to severe disease Ventilation should be controlled with small to moderate tidal volumes and slow rates

25. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Anesthetic Considerations/Intraoperative Management: Consider the use of humidified gases Nitrous oxide should be avoided in certain patients Inhibition of HPV by inhalational agents not clinically significant at usual doses Measurement of ABGs helpful for certain procedures Deadspace has an effect on normal arterial-EtCO2 gradient Ventilation adjusted to maintain a normal arterial pH Hemodynamic monitoring considered for any underlying concomitant pathology

26. RESPIRATORY SYSTEMPART II CHRONIC OBSTRUCTIVE PULMONARY DISEASE Anesthetic Considerations/Intraoperative Management: Completion of surgery and timing of extubation�! Early extubation versus awake extubation Benefits of both Detriments of both Certain patients most likely to require a period of postoperative ventilation

27. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Characterized by decreased lung compliance Lung volumes are typically reduced with preservation of normal expiratory flow rates: FEV1 and FVC are reduced, FEV1/FVC ratio is normal Restrictive pulmonary diseases include acute and chronic intrinsic pulmonary disorders and extrinsic disorders Increased WOB results in rapid but shallow breathing pattern Respiratory gas exchange eventually affected

28. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Acute Intrinsic Pulmonary Disorders: Includes; pulmonary edema, ARDS, infectious pneumonia, and aspiration pneumonitis Preoperative consideration: Reduced lung compliance primarily due to an increase in extravascular lung water Increased pressure occurs with LV failure and fluid overload, and increased permeability is present with ARDS Increased permeability also occurs following aspiration or infectious pneumonitis

29. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Acute Intrinsic Pulmonary Disorders: Anesthetic Considerations/Preoperative Management: Elective surgery should be postponed with acute pulmonary disease Preparation for emergent surgical procedures: Oxygenation and ventilation should be optimized Fluid overload and heart failure addressed Drainage of large pleural effusions considered PPV and PEEP may be required for persistent hypoxemia Hypotension or infection aggressively treated

30. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Acute Intrinsic Pulmonary Disorders: Anesthetic Considerations/Intraoperative management: Selection of anesthetic agents should be patient specific Anesthesia often provided with IV and inhalational agents in addition to a NDMR High FIO2 and peep may be required Increased risk of barotrauma and volutrauma TV reduced to 4-8 mL/kg with compensatory rate 14-18 Airway pressure should generally not exceed 30 cm H2O Sophisticated ventilatory modes may be needed Aggressive hemodynamic monitoring is recommended

31. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Chronic Intrinsic Pulmonary Disorders: Referred to as interstitial lung diseases Disease process characterized by; insidious onset, chronic inflammation of alveolar walls and peri-alveolar tissue, and progressive pulmonary fibrosis Inflammatory process may be confined to the lungs Causes include; hypersensitivity pneumonitis, drug toxicity, radiation pneumonitis, idiopathic pulmonary fibrosis, autoimmune diseases, and sarcoidosis Chronic fibrosis may be caused by O2 toxicity, severe ARDS, and chronic pulmonary aspiration

32. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Chronic Intrinsic Pulmonary Disorders: Preoperative considerations: Typically present with DOE and at times a nonproductive cough Symptoms of cor pulmonale with advanced disease Physical exam; fine (dry) crackles over lung bases Progressive changes associated with CXR ABGs; mild hypoxemia with normocarbia Treatment; abating disease process, possibly O2 therapy, and glucocorticoid and immunosuppressive therapy

33. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Chronic Intrinsic Pulmonary Disorders: Anesthetic Considerations/Preoperative Management: Evaluation should focus on determining degree of impairment and underlying disease process DOE (or at rest) further evaluated with PFTs and ABGs VC less than 15 mL/kg indicative of severe dysfunction CXR to assess disease severity

34. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Chronic Intrinsic Pulmonary Disorders: Anesthetic Considerations/Intraoperative Management: Management is complicated by a predisposition to hypoxemia and the need to control ventilation to ensure optimum gas exchange Patients predisposed to rapid hypoxemia following induction Inspired FIO2 should be kept to minimum Ventilator management should limit high PIPs thereby decreasing the potential risk of pneumothorax

35. RESPIRATORY SYSTEMPART II RESTRICTIVE PULMONARY DISEASE Extrinsic Restrictive Pulmonary Disorders: Alter gas exchange by interfering with normal lung expansion Includes; pleural effusions, pneumothorax, mediastinal masses, kyphoscoliosis, pectus excavatum, neuromuscular disorders, and increased intra-abdominal pressure from ascites, pregnancy, or bleeding Marked obesity produces a restrictive ventilatory defect Anesthetic considerations similar to intrinsic restrictive disorders

36. RESPIRATORY SYSTEMPART II PULMONARY EMBOLISM Preoperative Considerations: Results from the entry of blood clots, fat, tumor cells, air, amniotic fluid, or foreign material into the venous system Venous stasis or hypercoagulability is often contributory to the development of clots Pulmonary embolism, fat embolism, and air embolism can occur intraoperatively in normal individuals undergoing certain surgical procedures Factors associated with DVT and PE

37. RESPIRATORY SYSTEMPART II PULMONARY EMBOLISM Pathophysiology: Increased dead space secondary to embolic occlusions in the pulmonary circulation Clinically, hypoxemia often seen Net effect is increase in pulmonary shunt and hypoxemia Affected area loses its surfactant within hours Pulmonary infarction may occur if a large vessel involved Pulmonary hypertension may develop Sustained increase in RV afterload can precipitate acute RV failure

38. RESPIRATORY SYSTEMPART II PULMONARY EMBOLISM Diagnosis: Clinical manifestations include; sudden tachypnea, dyspnea, chest pain, or hemoptysis Wheezing may be present ABG analysis, CXR, and ECG�! Hypotension with elevated CVP indicative of RV failure Pulmonary angiography most accurate means of diagnosing PE, V/Q scans may be useful Helical CT scanning may be used

39. RESPIRATORY SYSTEMPART II PULMONARY EMBOLISM Treatment: Prevention is the best treatment! Minidose heparin, oral anticoagulation, ASA, or dextran therapy together with early ambulation may decrease the incidence of postoperative emboli High elastic stockings and pneumatic compression of the legs may decrease the incidence of venous thrombosis in the legs Heparin therapy and low molecular weight heparin (LMWH) IVC filter and pulmonary embolectomy may be indicated

40. RESPIRATORY SYSTEMPART II PULMONARY EMBOLISM Anesthetic Considerations/Preoperative Management: Patients with acute PE may present to the OR for IVC filter placement or pulmonary embolectomy Patient with h/o PE presenting for unrelated surgery Perioperative management; prevention of new episodes Anesthetic Considerations/Intraoperative Management: IVC filters placed percutaneously with LA and sedation Regional anesthesia versus general anesthesia� Inotropic support until the clot is removed and CPB may be necessary

41. RESPIRATORY SYSTEMPART II PULMONARY EMBOLISM Intraoperative Pulmonary Embolism: Significant PE is rare occurrence during anesthesia Air embolism�, fat embolism�, amniotic fluid embolism�! Thromboembolism may occur intraoperatively during prolonged procedures Manipulation of tumors with intravascular extension�! Intraoperative PE usually presents as unexplained sudden hypotension, hypoxemia, or bronchospasm Decrease in EtCO2 concentration is suggestive Elevated CVP and PA pressures

42. RESPIRATORY SYSTEMPART II PULMONARY EMBOLISM Intraoperative Pulmonary Embolism: Treatment: Transesophageal echocardiogram may be of use Air identified or suspected in the RA: Emergent central vein cannulation and aspiration of air For all other emboli treatment is supportive, with intravenous fluids and inotropes Placement of an IVC filter should be considered postoperatively

43. RESPIRATORY SYSTEMPART IIPATHOPHYSIOLOGY REFERENCES Morgan, G.E., Mikhail, M.S., and Murray, M.J. (2006). Clinical Anesthesiology. (4th Ed.) New York, NY: McGraw-Hill. Nagelhout, J.J. and Zaglaniczny, K.L. (2005). Nurse Anesthesia. (3rd Ed.) St. Louis, MO: Elsevier- Saunders.