1. Chapter 46 Respiratory Monitoring and Management of the Patient in the Intensive Care Unit

2. Objectives Discuss the principles of monitoring the respiratory system
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. 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. Objectives (cont.)
Describe the approach used to interpret the results of ventilator graphics monitoring.

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

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

7. 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

8. Monitoring Oxygenation (cont.)

9. Other Oxygen Indices Oxygen consumption P(A  a)O2
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
An abnormal increase is associated with gas exchange problems.

10. Other Oxygen Indices (cont.)
PaO2/FIO2 ratio (P/F ratio)
Normal P/F ratio is 400 to 500.
In ALI, this falls below 300.
In ARDS, it 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)

11. Monitoring Ventilation
Routine monitoring includes
PaCO2, which defines adequacy of ventilation
T, f, and E
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 >0.70
>0.60, patient is unlikely to sustain spontaneous ventilation . . V V . .

12. Compliance Compliance is ΔV/ΔP or effective VT/(Pplat  PEEP) .
Normally, this is 60 to 100 ml/cm H2O .
In severe ARDS, it may be <25 ml/cm H2O .
Many pulmonary diseases alter compliance.
See Box 46-7.
ΔV/ΔP – change in volume divided by change in pressure

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

14. Auto-PEEP If exhalation is incomplete, 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 .
ET – Expiratory time, IT – inspiratory time

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

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

17. Monitoring Breathing Effort and 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 < 100 indicates patient likely to wean from MV
The lower the RSBI the better

18. Monitoring Breathing Effort and 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

19. Monitoring During Lung Protective Ventilation
Commonly used for ALI/ARDS patients to avoid ventilator-induced lung injury (VILI)
Three principles confirmed
Limit Pplat to <30 cm H2O
Reduce VT to 6–8 ml/kg
Use adequate PEEP to avoid opening/closing injury
Permissive hypercapnia is often used as a lung protective strategy avoid VILI.
VILI - ventilator-induced lung injury: Associated with overdistention which leads to volutrauma and biotrauma), as well as and recruitment/derecruitment injury calle atelectrauma.