Diagnosis and Management of Acute Respiratory Failure

Transcription

1 Diagnosis and Management of Acute Respiratory Failure Steven B. Leven, M.D., F.C.C.P. Clinical Professor, Pulmonary/Critical Care Medicine UCI Director MICU and Respiratory Therapy, UCI Medical Center 1

2 Objectives Understand the causes of hypoxia and hypercapnea Know the clinical manifestations of respiratory failure Be familiar with various oxygen delivery systems Know indications and contraindications to noninvasive positive pressure ventilation Know indications for endotracheal intubation Be familiar with basic modes of mechanical ventilation 2

3 CASE # 1 J.T. is a 68-kg, 42-yr old female admitted after a drug overdose complicated by emesis and aspiration. Intubation and mechanical ventilation are initiated in the emergency department. 3

4 CASE # 1 Mechanical ventilation AC (volume) mode Tidal volume 750 ml 16 breaths/min FIO PEEP 5 cm H 2 O 4

5 CASE # 1 Peak airway pressure 52 cm H 2 O Inspiratory plateau pressure (IPP) 48 cm H 2 O ph 7.38, PaCO 2 36 PaO 2 57 Sinus tach at 166, BP 75/50, no urine output Patient very agitated and fighting vent What would you do? 5

6 CASE #2 L.W. is a 62-yr-old, 52-kg female with severe emphysema. For 2 days she has had progressive dyspnea and was found unresponsive. ABG on 5liters NC ph 7.07 pco2 87 po2 62. She required intubation and initiation of mechanical ventilation. 6

7 CASE #2 ICU ventilator settings AC, rate 12 breaths/min Tidal volume 500 ml FIO 2 100% PEEP 5 cm H 2 O 7

8 CASE #2 RR 24 I:E ratio = 1:1.5 Peak pressure 50 cm H 2 O, IPP 35 cm H 2 O End expiratory pressure is 20 cm ph 7.20, PaCO 2 60, PaO Sinus tach 157 BP 78/45 No urine output Patient very agitated What would you do? 8

9 CASE #3 37 year old healthy malpractice plaintiff attorney presents to ER with 24 hour history of generalized weakness. Last week he had a mild bout of gastroenteritis after eating under cooked chicken. He could walk with difficulty when he arrived at ER 8 hours ago. Now he needs help to reposition himself in bed and he coughs when he attempts to drink. 9

10 CASE #3 Exam normal except weakness Chemistries and CBC normal RA ABG ph 7.41 pco2 41 po2 84 Vital Capacity 840cc (12cc/Kg) CXR at left 10

11 CASE #3 Where should this patient be cared for? ICU? Tele? Ward? Home? Should this patient be fed? Should he be advised to call a lawyer? Would you put him on BiPAP? Anything else you would do? 11

12 Case # 4 A 25-year-old lady, Miss. Poor Compliance, is rushed into your Emergency Department. She is an asthmatic who on arrival is sitting forward in the tripod position, using her accessory muscles to breath. She is tachypneic, diaphoretic, agitated and unable to talk. During a nebulizer tx with albuterol she becomes dusky and poorly responsive. 12

13 Case # 4 13

14 Get ABG? Start BiPAP? Plan of care? Discuss patient s feelings about being ill? Get advice from resident (oops, he is running a code) Other? 14

15 Acute Respiratory Failure Hypoxemic Room air PaO 2 50 torr Hypercapnic PaCO 2 50 torr Acute vs chronic Often Multifactorial ARF 15

16 Pathophysiology of Hypoxemia Ventilation/perfusion mismatch Shunt effect (intracardiac or intrapulmonary) Decreased diffusion of O 2 Alveolar hypoventilation FIO2 < 21% (eg. High altitude) ARF 16 16

17 Pathophysiology of Hypercapnia Alveolar ventilation is the prime determinant of CO 2 exchange during mechanical ventilation V A ~ 1/pCO 2 V A =(V T -V D )f Change in any variable affects pco 2 17

18 Causes of Hypercapnia Inability to sense elevated PaCO 2 Inability to signal respiratory muscles Inability to effect a response from respiratory muscles Increased dead space 18

19 Inability to effect adequate response from respiratory muscles Imbalance between demand for respiratory muscle work and the ability to supply that work Examples of increased demand: bronchospasm, fever, low lung compliance, pleural effusion Decreased supply: poor cardiac output, malnutrition, deconditioning 19

20 Increased Dead Space (wasted ventilation) Hypovolemia Low cardiac output Pulmonary embolus High airway pressures Short-term compensation by increasing tidal volume and/or respiratory rate 20

21 Manifestations of Respiratory Distress Altered mental status especially anxiety!!! Anxiety is a result of respiratory distress, almost NEVER the cause. Increased work of breathing Tachypnea, nasal flaring Accessory muscle use, retractions, paradoxical breathing pattern, respiratory alternans Catecholamine release Tachycardia, diaphoresis, hypertension Abnormal ABG not always!!! Neuromuscular failure is different from above monitor vital capacity intubate near 15cc/kg 21

22 Oxygen Supplementation low flow systems 1-10 LPM 100% O2 mixes with room air to determine FIO2 - definition FIO2 varies with patient s breathing pattern Rapid inspiration entrains more room air Deep breaths entrain more room air Rapid respiratory rate entrains more room air Patients in more distress get lower FIO2 FIO2 is unknown since amount of entrainment is unknown Any humidity in gas comes from entrained air- wall O2 has 0% relative humidity Low flow devices Simple Nasal Cannulas Simple masks 22

23 High Flow O2 Devices > lpm Device provides 100% of gas to patient - definition No entrainment of room air if mask fits FIO2 is known and exact Relative humidity depends on the device High flow devices: High flow nasal cannula Venturi mask Aerosol mask heated or cool Nonrebreather mask some characteristics of both high and low 23

24 O2 Devices 24

25 Aerosol O2 devices 25

26 BiPAP or NPPV Contraindications Cardiac or respiratory arrest Need for emergent intubation Inability to cooperate, protect the airway, or clear secretions Nonrespiratory organ failure, esp shock Facial surgery, trauma, or deformity Prolonged duration of mechanical ventilation anticipated Recent esophageal anastomosis Never restrain patients on BiPAP Precedex (dexmedetomidine) drip may be considered if the patient is anxious. Patient will often be calm if the physician stands by with the patient during initiation. 26

27 BiPAP Settings IPAP 10/CPAP 5 is almost never correct Determine EPAP (PEEP) first based on degree of hypoxia and uniformity of infiltrates. IPAP EPAP determines ventilatory assist. Adjust this at the bedside as you watch the patient. Adjust this delta to achieve exhaled tidal volume of cc assuming small mask leak. You have succeeded if the patient begins to look more comfortable. Rate is a floor, patient sets the actual rate. If patient is functioning on a hypoxic drive, set FIO2 to target O2sat 88% to 92%. 27

28 Endotracheal Intubation.An opening must be attempted in the trunk of the trachea, into which a tube or cane should be put; You will then blow into this so that lung may rise again.and the heart becomes strong. (1555) -Andreas Vesalius 28

29 Indications for Endotracheal Intubation Airway protection (outside ICU?) Relief of airway obstruction Respiratory failure or impending respiratory failure Hypoxic or Hypercapneic or both Need for hyperventilation - ICP Unsustainable work of breathing Facilitate suctioning/pulmonary toilet Shock!!!!!!!!!!! 29

30 Decision to intubate Clinical decision-not based on ABG Error on the side of patient safety What is the safest way to navigate illness? Intubation is not an act of weakness Think ahead- if need to intubation is expected in next 24hr, intubate now Endotracheal tubes are not a disease and ventilators are not an addiction i.e. Intubation does not cause ventilator dependence 30

31 Modes of Mechanical Ventilation Point of Reference: Spontaneous Ventilation 31

32 Continuous Positive Airway Pressure (CPAP) No machine breaths delivered Allows spontaneous breathing at elevated baseline pressure Patient controls rate and tidal volume 32

33 Assist-Control Ventilation You set tidal volume and minimum rate Additional breaths delivered with minimal inspiratory effort - pt sets actual rate Advantages: reduced work of breathing; allows patient to modify minute ventilation Most patients should start with this mode Rate 12, TV 8-10 cc/kg, FiO2 100% PEEP 5 33

34 Synchronized Intermittent Mandatory Ventilation (SIMV) Volume cycled breaths at a preset rate Additional spontaneous breaths at tidal volume and rate determined by patient Invented as weaning mode Best weaning mode is sink or swim Best use is to mitigate AutoPEEP 34

35 Pressure-Support Ventilation Pressure assist during spontaneous inspiration with flow-cycled breath Pressure assist at constant pressure continues until inspiratory effort decreases Delivered tidal volume dependent on set pressure, inspiratory effort and resistance/compliance of lung/thorax 35

36 Inspiratory Plateau Pressure Airway pressure measured at end of inspiration with no gas flow present Estimates alveolar pressure at end-inspiration IPP is best indicator of alveolar distension PIP IPP ~ airway resistance Peak pressure Plateau pressure Inspiration Expiration 36

37 Inspiratory Plateau Pressure High inspiratory plateau pressure stiff lungs Barotrauma - no Volutrauma yes pneumothorax, etc Decreased cardiac output Methods to decrease IPP Decrease tidal volume??? Decrease PEEP Goal IPP usually 30 cm H 2 O ARDS protocol: tidal volume 6 cc/kg IBW 37

38 Auto-PEEP - common Occurs in setting of severe COPD or asthma Very uncomfortable for patient - agitation Can be measured on most ventilators Increases peak, plateau, and mean airway pressures Hypotension impaired venous return Suspect in setting of COPD or asthma pt who is agitated or hypotensive this is common!!! 38

39 I:E Ratio during Mechanical Ventilation If expiratory time too short for full exhalation Breath stacking Auto-PEEP Reduce auto-peep by reducing inspiratory time/increasing expiratory time Increase peak inspiratory flow rate 100 lpm Decrease respiratory rate (use IMV without PSV) rate of 12 usually is good Decrease tidal volume to 8 cc per kg IBW 39

40 CASE # 1 J.T. is a 68-kg, 42-yr old female admitted after a drug overdose complicated by emesis and aspiration. Intubation and mechanical ventilation are initiated in the emergency department. 40

41 CASE # 1 Mechanical ventilation AC (volume) mode Tidal volume 700 ml 10 breaths/min FIO always start at 100% PEEP 5 cm H 2 O 41

42 CASE # 1 Peak airway pressure 52 cm H 2 O Inspiratory plateau pressure (IPP) 48 cm H 2 O ph 7.38, PaCO 2 36 torr PaO 2 57 torr Sinus tach at 166, BP 75/50 Patient very agitated and fighting vent What are the issues here? 42

43 CASE # 1 What is diagnosis? What are the consequences of FIO 2 100%? TV 10cc/Kg? High inspiratory plateau pressure? Hypotension and tachycardia? agitation and fighting vent What variables should be changed to improve PaO 2? BP? Protect lungs? 43

44 ARDS Decreased lung compliance results in high airway pressures Tidal volume goal 6cc/Kg Maintain IPP 30 cm H 2 O PEEP to improve oxygenation Aim for FIO2 50% - O2 toxic at > 50% Patients often need volume loading Sedation usually needed and sometimes also paralytic 44

45 CASE #2 L.W. is a 62-yr-old, 52-kg female with severe emphysema. For 2 days she has had progressive dyspnea and was found unresponsive. ABG on 5 liters NC ph 7.07 pco2 87 po2 42. She required intubation and initiation of mechanical ventilation. 45

46 CASE #2 ICU ventilator settings AC, rate 12 breaths/min FIO Tidal volume 600 ml Peak flow 50 l/sec PEEP 5 cm H 2 O 46

47 RR 24 I:E ratio = 1:1.5 CASE #2 Peak pressure 50 cm H 2 O, IPP 35 cm H 2 O End Expiratory Alveolar Pressure 20 cm H 2 O ph 7.28, PaCO 2 60 torr, PaO torr Sinus tach 157 BP 78/45 No urine output Patient very agitated 47

48 CASE #2 What complication of therapy is at work? What variable(s) should be changed to improve the ABG? BP? UO? Agitation? change in peak flow rate? change in respiratory rate? change in ventilator mode? bronchodilators? 48

49 Analysis - Patient L.W. Hypercapnia acceptable if ph OK High peak airway pressure can be OK Wide peak-plateau pressure difference indicates obstructive disease Be alert for auto-peep Hypotension and tachycardia suggest auto-peep and or inadequate preload 49

50 Obstructive Airway Disease Obstructive diseases require adequate expiratory time PaCO 2 should be kept at patient s baseline level 50

51 CASE #3 37 year old healthy lawyer admitted from ER with 24 hour history of generalized weakness. Last week he had a mild bout of gastroenteritis. He could walk with difficulty when he arrived at ER 12 hours ago. Now he needs help to reposition himself in bed and he coughs when he attempts to drink. 51

52 CASE #3 Exam normal except weakness Chemistries and CBC normal RA ABG ph 7.41 pco2 41 po2 84 Vital Capacity 840cc (12cc/Kg) 52

53 CASE #3 What is this patient s diagnosis? Is this patient in respiratory failure? What is this patient s most urgent need? 53

54 CASE #3 Neuromuscular Respiratory Failure Patients do not appear to struggle ABG does not tell you when to intubate Delay may result in aspiration and arrest Follow vital capacity closely in ICU Intubate when VC approaches 15cc/Kg 54

55 Case # 4 A 25-year-old lady, Miss. Poor Compliance, is rushed into your Emergency Department. She is an asthmatic who on arrival is sitting forward in the tripod position, using her accessory muscles to breath. She is tachypneic, diaphoretic, agitated and unable to talk. During a nebulizer tx with albuterol she becomes dusky and poorly responsive. 55

56 Case # 4 56

57 Get ABG? Start BiPAP? Plan of care? Discuss patient s feelings about being ill? Check her health insurance Get advice from resident (oops, he is running a code) Other? 57