Copyright 2008 Society of Critical Care Medicine

Mechanical Ventilation 2

2Copyright 2008 Society of Critical Care Medicine

Objectives

Describe interactions between ventilatory parameters and modifications needed to avoid harmful effects of mechanical ventilationReview guidelines for initial ventilator management that apply to specific clinical situations

3Copyright 2008 Society of Critical Care Medicine

Case Study

18-year-old found unresponsive at a party (wt 60 kg, ht 64 inches [162.6 cm])

Vomitus in pharynx, difficult intubation

SpO2 87-88% on 100% oxygen

High pressure alarm sounding

What ventilator What ventilator settings are settings are

recommended? recommended?

4Copyright 2008 Society of Critical Care Medicine

Case Study

ModeFiO2Tidal volumeRatePEEP

Assist control (volume)1.0550 mL10 breaths/min5 cm H2O

®

Predicted body wt = 45.5 + 2.3 (ht in inches-60) = 55 kg

5Copyright 2008 Society of Critical Care Medicine

Case Study

SpO2

Blood gas

Ppeak

Pplat

Auto-PEEP

Respiratory rate

88%

pH 7.38, PaCO2 36 mm Hg (4.8 kPa), PaO2 57 mm Hg (7.6 kPa)

52 cm H2O

48 cm H2O

0 cm H2O

18 breaths/min

®

What parameters should be measured? What parameters should be measured?

6Copyright 2008 Society of Critical Care Medicine

Case Study

SpO2 88% (FiO2 1.0)Blood gas: pH 7.38, PaCO2 36 mm Hg (4.8 kPa), PaO2 57 mm Hg (7.6 kPa)Ppeak 52 cm H2OPplat 48 cm H2OAuto-PEEP 0 cm H2ORespiratory rate 18 breaths/min

®

What problems are present?What problems are present?

7Copyright 2008 Society of Critical Care Medicine

Case Study

Current Ventilator SettingsAssist control (volume)FiO2 1.0Tidal volume 550 mLRespiratory rate 10 breaths/minPEEP 5 cm H2O

®

What changes in ventilator settings would What changes in ventilator settings would improve oxygenation?improve oxygenation?

8Copyright 2008 Society of Critical Care Medicine

Determinants of Oxygenation

FIO2Mean airway pressure

Tidal volumeI:E ratioInspiratory flow ratePEEPAuto-PEEPInspiratory flow waveform

®

9Copyright 2008 Society of Critical Care Medicine

Case Study

Assist control (volume)FiO2 1.0Tidal volume 550 mLRespiratory rate 10 breaths/minPEEP 5 cm H2O

What are the consequences of the following What are the consequences of the following ventilator changes?ventilator changes?

−Increased PEEPIncreased PEEP−Increased tidal volumeIncreased tidal volume

10Copyright 2008 Society of Critical Care Medicine

Case Study

Current Ventilator SettingsAssist control (volume)FiO2 1.0Tidal volume 550 mLRespiratory rate 10 breaths/minPEEP 5 cm H2O

®

What changes in ventilator settings would What changes in ventilator settings would decrease inspiratory plateau pressure?decrease inspiratory plateau pressure?

11Copyright 2008 Society of Critical Care Medicine

Acute Lung Injury

Hypoxemic respiratory failureDecreased lung compliance high airway pressuresLower tidal volume needed (6 mL/kg PBW)Maintain Pplat 30 cm H2OPEEP to improve oxygenationPermissive hypercapnia may be necessary

12Copyright 2008 Society of Critical Care Medicine

Case Study

70-year-old with long smoking history failed NPPV for respiratory distress Intubated, sedated, and receiving mechanical ventilationWt 75 kg, ht 69 inches [175.3 cm])Low blood pressure alarm sounding

What ventilator settings are What ventilator settings are recommended? recommended?

13Copyright 2008 Society of Critical Care Medicine

Case Study

SIMV

1.0

700 mL

12 breath/min

5 cm H2O

Mode

FiO2

Tidal volume

Rate

PEEP

14Copyright 2008 Society of Critical Care Medicine

Case Study

Blood gas: pH 7.20, PaCO2 60 mm Hg (8 kPa), PaO2 215 mm Hg (28.7 kPa)Pplat 35 cm H2O, Ppeak 50 cm H2OAuto-PEEP 8 cm H2OI:E = 1:1.5Respiratory rate 18/minBlood pressure 90/60 mm Hg, heart rate 130 beats/min

®

What parameters should be measured?What parameters should be measured?

15Copyright 2008 Society of Critical Care Medicine

Case Study

Blood gas: pH 7.20, PaCO2 60 mm Hg(8 kPa), PaO2 215 mm Hg (28.7 kPa)Pplat 28 cm H2O, Ppeak 50 cm H2OAuto-PEEP 8 cm H2OI:E = 1:1.5Respiratory rate 18 breaths/minBlood pressure 90/60 mm Hg,heart rate 130 beats/min

®

What are the major problems?What are the major problems?

16Copyright 2008 Society of Critical Care Medicine

Case Study

Positive intrathoracic pressureAuto-PEEPHypovolemiaTension pneumothoraxMyocardial ischemia

®

What are possible causes of the patient’sWhat are possible causes of the patient’shypotension?hypotension?

17Copyright 2008 Society of Critical Care Medicine

Case Study

Current Ventilator SettingsSIMVFiO2 1.0Tidal volume 700 mLRespiratory rate 12 breaths/minPEEP 5 cm H2O

®

What immediate changes in ventilator What immediate changes in ventilator settings should be made?settings should be made?

18Copyright 2008 Society of Critical Care Medicine

Case Study

SIMV

Tidal volume 700 mL

Respiratory rate12 breaths/min

PEEP 5 cm H2O

pH 7.20, PaCO2 60 mm Hg (8 kPa), PaO2 215 mm Hg (28.7 kPa)

Auto-PEEP 8 cm H2O

I:E = 1:1.5

®

What are the consequences of the following What are the consequences of the following ventilator changes?ventilator changes?

−Decrease in tidal volumeDecrease in tidal volume−Decrease in respiratory rateDecrease in respiratory rate−Change to assist control (volume)Change to assist control (volume)

19Copyright 2008 Society of Critical Care Medicine

Obstructive Airway Disease

Initial tidal volume ~8-10 mL/kgOptimize expiratory time Beware of auto-PEEPAdjust minute ventilation tolow normal pHTreat obstruction with bronchodilators

20Copyright 2008 Society of Critical Care Medicine

Questions? Questions?

21Copyright 2008 Society of Critical Care Medicine

Key Points

The complex interactions of ventilator parameters must be appreciated to evaluate the effects in each patient.Primary determinants of oxygenation are FiO2 and mean airway pressure.Patients should be monitored closely during mechanical ventilation.Maintain Pplat 30 cm H2O.Hypotension after initiation of mechanical ventilation should be promptly evaluated.