Chapter 46 Monitoring the Patient in the Intensive Care Unit

1. Chapter 46Monitoring the Patient in the Intensive Care Unit

2. Learning Objectives • Discuss the principles of monitoring the respiratory system, cardiovascular system, neurological status, renal function, liver function, and nutritional status of patients in intensive care. • Discuss the risks and benefits of intensive care unit (ICU) monitoring techniques. • Discuss why the caregiver is the most important monitor in the ICU. • Describe how to evaluate measures of patient oxygenation in the ICU.

3. Learning Objectives (cont.) • Define why Paco2 is the single best index of ventilation for critically ill patients. • Describe the approach used to evaluate changes in respiratory rate, tidal volume, minute ventilation, Paco2, and end-tidal Pco2 values for monitoring purposes. • Discuss monitoring techniques used in the ICU to evaluate lung and chest wall mechanics and work of breathing. • Discuss the importance of monitoring peak and plateau pressures in patients receiving mechanical ventilatory support.

4. Learning Objectives (cont.) • Introduce monitoring techniques that have become available recently such as stress, strain, FRC, stress index, Electrical Impedance Tomography and Acoustic Respiratory Monitoring. • Describe the approach used to interpret the results of ventilator graphics monitoring. • Describe the cardiovascular monitoring techniques used in the care of critically ill patients and how to interpret the results of hemodynamic monitoring.

5. Learning Objectives (cont.) • Discuss the importance of neurological status monitoring in the ICU and the variables that should be monitored. • Discuss evaluation of renal function, liver function, and nutritional status in intensive care. • Describe and discuss the use of composite and global scores to measure patient status in the ICU, such as the Murray lung injury score and the APACHE severity of illness scoring system. • Discuss monitoring and troubleshooting of the patientventilator system in the ICU.

6. Introduction to Monitoring • Continuous monitoring or periodic checks • Gray area between diagnostic and monitoring procedures • Risk/benefit ratio

7. Monitored Values • All data must be evaluated in context of overall clinical presentation • Instrument inaccuracyrecalibrate • Artifacts • Factitious events: true but temporary (cough) • Treat pathology, not errant number • All values monitored must be considered in relation to what pathology has altered them and how best to treat the pathology

8. Respiratory Monitoring • Gas Exchange • Arterial Blood Gas • pH • PaCO2 • PaO2 • Calculated HCO2 • Estimated base excess or deficit • SaO2 • Oxygenation • Ventilation

9. Monitoring

10. Monitoring Oxygenation • Tissue oxygenation depends on CaO2 (PaO2 and SaO2), cardiac output, and oxygen uptake • Pulse oximetry (“fifth vital sign”) • Provides noninvasive measurement of SaO2, referred to as SpO2 • Monitors only oxygen, not ventilation • Significant limitations

11. All of the following are true about pulse oximetry monitoring, except: • Provides an SpO2 reading • Provides invasive measurement of SaO2 • Monitors only oxygen, not ventilation • Significant limitations

12. Monitoring Oxygenation (cont.)

13. All of the following values affect pulse oximetry, except: • Nail polish • Deeply pigmented skin • Anemia • CO2 buildup

14. Other Oxygen Indices • Oxygen consumption • Difficult to measure, so seldom used • Normal 250 ml/min, 25% of oxygen delivery • P(A  a)O2 • Healthy patient • 21% O2, gradient is 5 to 15 mm Hg • 100% O2, gradient is 100 to 150 mm Hg • Abnormal increase associated with gas exchange problems

15. Other Oxygen Indices (cont.) • PaO2/FIO2 ratio (P/F ratio) • Normal P/F ratio is 400 to 500. • In Acute Lung Injury - ALI, this falls below 300. • In Acute Respiratory Distress Syndrome - ARDS, will be < 200. • Most reliable index of gas exchange if FIO2 > 0.50 and PaO2 < 100 mm Hg • QS/QT (physiologic shunt) • Increased if pulmonary venous admixture occurs (mixed venous blood exits A/C membrane unchanged)

16. Which of the following PaO2/FIO2 ratio identifies a patient with ARDS? • 500-600 • 300-500 • >200 • <200

17. Monitoring Ventilation • Routine monitoring includes • PaCO2, which defines adequacy of ventilation • VT, f, and VE • Low VT and high f often indicate distress • VD/VT • Normal 0.20 to 0.40 • Higher ratio indicates more wasted ventilation • ICU common to be > 0.60 • >0.60, patient is unlikely to sustain spontaneous ventilation . . V V

18. Monitoring Ventilation (cont.) • Inspired vs. Expired Tidal Volume • Normal Inspired – (VTI) and expired tidal volume (VTE) should be nearly equal. • Air leak will result in higher VTI than VTE. • Capnography • Capnometry

19. Monitoring Ventilation (cont.)

20. All of the following are true regarding VD/VT ratio, except: • Normal 0.40 to 0.60 • Higher ratio indicates more wasted ventilation • ICU common to be >0.60 • If >0.60, patient is unlikely to sustain spontaneous ventilation

21. Compliance • Compliance is ΔV/ΔP or effective VT/(Pplat  PEEP) . • Normally, is 60 to 100 ml/cm H2O • In severe ARDS, may be <25-30 ml/cm H2O • Many pulmonary diseases alter compliance • See Box 46-7.

22. Resistance • Resistance (Raw) = (PIP Pplat)/flow • Normally 1 to 2 cm H2O/L/sec • Intubated, typically 5 to 10 cm H2O/L/sec or more • See Box 46-7 for diseases that alter Raw

23. Auto-PEEP • If exhalation is incomplete, intrinsic or auto-PEEP occurs • Causes ⇑FRC and mean alveolar pressure • Often causes patientventilator asynchrony • Ways to decrease auto-PEEP • Decrease VE • Increase ET • Decrease IT

24. Auto-PEEP (cont.) • Adding extrinsic PEEP may overcome the trigger sensitivity issue and facilitate lung emptying • Slowly increase in 1-2 cm H2O increments until either: • Patient can trigger the ventilator • Auto-PEEP increases

25. Measuring Auto-PEEP • Presence noted by expiratory flow at end of expiration • Measured by • End-expiratory hold: most common method • Allows alveolar pressure to equalize with ventilator pressure. • Esophageal balloon • Increase PEEP until end-expiratory flow is zero • PEEP applied estimates auto-PEEP

26. Auto-PEEP can be measured by all of the following, except: • Esophageal balloon • Inspiratory pause • Increase PEEP until end-expiratory flow is zero • End expiratory hold

27. Monitoring Breathing Effort & Pattern • P0.1 assesses ventilator drive • Occlusion pressure 100 ms after initiation of inspiration • <6 cm H2O is indicative of patient’s ability to wean from MV • RSBI (f/VT) • Respiratory muscle fatigue tends toward rapid shallow breathing • RSBI < 105 indicates patient likely to wean from MV • The lower the RSBI the better

28. Monitoring Breathing Effort & Pattern (cont.) • Vital capacity (VC) • Effort dependent • VC less than 10 to 15 ml/kg, need for MV • Maximal inspiratory pressure (MIP) • Not effort dependent, as prolonged occlusion of airway stimulates maximal effort • More negative is better • 20 to30 cm H2O acceptable

29. MIP

30. Work of Breathing

31. Monitoring During Lung Protective Ventilation • Commonly used for ALI/ARDS patients to avoid ventilator-induced lung injury (VILI) • Three principles confirmed • Limit Pplat to < 28 cm H2O • Reduce VT to 4–8 ml/kg • Use adequate PEEP to avoid opening/closing injury • Permissive hypercapnia is often used as a lung protective strategy avoid VILI

32. Cardiac & Cardiovascular Monitoring • Arterial blood pressure • Invasive or noninvasive • Central venous pressure (CVP) • Pulmonary arterial catheter: high risk-to-return ratio, so only used on most complicated patients • Allows monitoring of • Cardiac output/cardiac index • Pulmonary arterial pressure • Pulmonary capillary wedge pressure • Pulmonary vascular resistance • Systemic vascular resistance

33. Cardiac & Cardiovascular Monitoring

34. Cardiac & Cardiovascular Monitoring

35. Pulmonary arterial catheter allows monitoring of all of the following, except: • Cardiac output/cardiac index • Pulmonary and Systemic vascular resistance • Peripheral vascular wedge pressure • Pulmonary arterial pressure

36. Hemodynamic Monitoring • Complete hemodynamic profile from PA catheter eases determination of cause for altered hemodynamic status • Table 46-4 shows expected changes in hemodynamic values associated with clinical presentation of cardiac or cardiovascular dysfunction

37. Neurologic Monitoring • Neurologic dysfunction is difficult to recognize in sedated patient • Obtain history, from family if not from patient • Neurologic examination • Mental status • Pupillary response and eye movement • Corneal and gag reflex • Respiratory rate and pattern • ICP monitoring (10 to 15 mm Hg normal) • Glasgow Coma Scale (see Table 46-6)

38. Monitoring Renal Function • Kidney functions • Filtering and excretion of wastes • Regulates fluid and electrolyte composition • Renal failure is noted by • BUN increases of 10 to 15 mg/dl/day • Creatinine increases of 1 to 2.5 mg/dl/day • Urine volume reflects renal perfusion • Oliguria <400 ml/day in average-sized adult • Anuria occurs with <50 ml/day

39. Monitoring Nutritional Status • Adequate nutrition key for healing • Assessment for malnutrition important • Including organ function and muscle wasting • Serum albumin concentration most common • <2.2 g/dl reflects severe malnutrition; shows chronic, not acute, change • Also altered by sepsis, dehydration, trauma

40. Estimating Nutritional Needs • First step is estimating caloric need • Estimate the basal energy expenditure, or BEE • Harris-Bennedict equation estimates BEE • Men = 66 + (13.7) (wt) + 5 (ht) – 6.8 (age) • Women = 65 + (9.6) (wt) + 1.8 (ht) – 4.7 (age) • For ill patients, often multiply the result by a stress factor of 0.5 to 2.5.