Joel R. Lopes Jr., M.D.

Director Trauma/Critical Care Anesthesia

Department Of Anesthesiology

Boston University Medical Center

Mechanical Properties of the respiratory Mechanical Properties of the respiratory System in Morbidly Obese patientsSystem in Morbidly Obese patients

Decreased Functional Decreased Functional residual capacityresidual capacity

Increased Intra-abdominal Increased Intra-abdominal PressurePressure

Increased Alveolar-arterial Increased Alveolar-arterial Oxygenation gradientOxygenation gradient

Supine Position under General AnesthesiaSupine Position under General Anesthesia HYPOXEMIAHYPOXEMIA

FRC FRC << Closing Capacity Closing Capacity Unopposed Intra-Abdominal PressureUnopposed Intra-Abdominal Pressure

Options for VentilationOptions for Ventilation

P.E.E.P.P.E.E.P. Tidal VolumeTidal Volume Respiratory RateRespiratory Rate

P.E.E.P.P.E.E.P.

Maintain the highest mean Maintain the highest mean PaO2 intraOpPaO2 intraOp

NOT sustained postOpNOT sustained postOp

?benefits in the Morbidly ?benefits in the Morbidly ObeseObese

Yakaitis RW Anesth Analg 1975;54:427-32

““Does PEEP Improve Intraoperative Arterial Does PEEP Improve Intraoperative Arterial Oxygenation in Grossly Obese Patients?”Oxygenation in Grossly Obese Patients?”

Constant Tidal Volume = 1000-1200ccConstant Tidal Volume = 1000-1200cc Respiratory Rate = 9–12/minRespiratory Rate = 9–12/min PEEP = 10 – 12cm H2OPEEP = 10 – 12cm H2O

ABG analysis 5 minutes before and at 2, 4, 20, and 30 minutes following discontinuation of PEEP

Salem MR Anesth 1978:48:280-81

Effects of Discontinuing PEEP on A-a pO2Effects of Discontinuing PEEP on A-a pO2

300

320

340

360

380

B 2 5 20 30

Time

A-a

pO

2 G

radi

ent

Salem MR Anesth 48:281,1978

DiscontinuationDiscontinuation of PEEP resulted in of PEEP resulted in significant increase in Arterial O2 tensionsignificant increase in Arterial O2 tension

high Tidal Volumeshigh Tidal Volumes Redistribution of Pulmonary Blood flowRedistribution of Pulmonary Blood flow Increased intrathoracic pressIncreased intrathoracic press

Gas Exchange at Different PEEP levelsGas Exchange at Different PEEP levels

0cm H2O0cm H2O 10cm H2O10cm H2O 0cm H2O0cm H2O 10cm H2O10cm H2OPaO2PaO2 (mmHg)(mmHg) 218 218 ++ 47 47

215 215 ++ 47 47 110 110 ++ 29 29130 130 ++ 28 28

Diff (A-a)O2Diff (A-a)O2 (mmHg)(mmHg)

110 110 ++ 45 45113 113 ++ 86 86

208 208 ++ 30 30187 187 ++ 30 30

PaCO2PaCO2 (mmHg)(mmHg) 28.4 28.4 ++ 3.1 3.1

27.8 27.8 ++ 5.7 5.737.8 37.8 ++ 6.8 6.8

39.4 39.4 ++ 4.9 4.9

Normal Obese

Pelosi P Anesth:1999:91,1228

0 cm H2O0 cm H2O 10cm H2O10cm H2O 0cm H2O0cm H2O 10cm H2O10cm H2O

Intra Abd PressIntra Abd Press 9 9 ++ 2.4 2.4 18.8 18.8 ++ 7.8 7.8

End Exp VolEnd Exp Vol 2.15 2.15 ++ 0.58 0.58 2.75 2.75 ++ 0.59 0.59 0.58 0.58 ++ 0.17 0.17 1.03 1.03 ++ 0.28 0.28

ElastanceElastance

Resp SystemResp System

16.39 16.39 ++ 3.6 3.6 15.68 15.68 ++ 3.23 3.23 26.8 26.8 ++ 4.2 4.2 18.54 18.54 ++ 3.06 3.06

Obese

IntraAbd Press, Lung Volume, and Elastance at different Levels of PEEP

Pelosi P Anesth 1999:91;1225

Normal

Rev. Trendelenburg effect on Pao2Rev. Trendelenburg effect on Pao2

IntubationIntubation LaparotomyLaparotomy RetractorsRetractors Rev TBurgRev TBurg

P(A-a)O2P(A-a)O2 132 132 ++ 60 60 162 162 ++ 69 69 207 207 ++ 33 33 159 159 ++ 63 63

PaO2PaO2 177 177 ++ 68 68 152 152 ++ 52 52 115 115 ++ 41 41 156 156 ++ 55 55

Paw Paw peakpeak 3 3 ++ 6 6 30 30 ++ 5 5 31 31 ++ 2 2 26 26 ++ 3 3

C C tottot 32 32 ++ 5 5 31 31 ++ 6 6 32 32 ++ 5 5 41 41 ++ 5 5

Perilli V Anesth Analg 2000;91:1520-3

……Morbid Obesity, Pneumoperitoneum, and Posture on Morbid Obesity, Pneumoperitoneum, and Posture on Respiratory Mechanics and Oxygenation During LaparoscopyRespiratory Mechanics and Oxygenation During Laparoscopy

15

25

35

45

55

65

nl wtMO

Sprung J.Anesth Analg 2002;94:1345-50

Static Compliance

Pneumoperitoneum,

50

75

100

125

150

175

nl WtMO

A-a DO2

Sprung J Anesth Analg 2002;94:1345-50

Effect of Tidal Volume and Respiratory Rate on Effect of Tidal Volume and Respiratory Rate on Respiratory Mechanics During Laparoscopy…Respiratory Mechanics During Laparoscopy…

600-700ml600-700ml 10 bpm10 bpm

1200-1400ml1200-1400ml 10 bpm10 bpm

600-700ml600-700ml 20 bpm20 bpm

Baseline

Double Vt

Double RR

Tidal Volume Resp Rate

Sprung J Anesth Analg 2003;97:268-74

Static Compliance in Normal Weight PatientsStatic Compliance in Normal Weight Patients

20

30

40

50

60

70

80

Baseline

Double Vt

Double RR

Pneumoperitoneum

Sprung J Anesth Analg 2003;97:268-74

Static Compliance in Morbidly Obese PatientsStatic Compliance in Morbidly Obese Patients

10

20

30

40

50

60

70

Baseline

Double Vt

Double RR

Pneumoperitoneum

Sprung J Anesth Analg 2003;97:268-74

Effect of Weight, Position, and Pneumoperitoneum on Effect of Weight, Position, and Pneumoperitoneum on Alveolar-arterial difference in O2 tensionAlveolar-arterial difference in O2 tension

40

60

80

100

120

140

160S

up

ine

Tre

nd

Rev

Tre

nd

Su

pin

e

Tre

nd

Rev

Tre

nd

Baseline

Double Vt

Double RR

Baseline

Double Vt

Double RR

Pneumoperitoneum

A-aDO2 mmHg

Sprung J Anesth Analg 2003;97:268-74

mo

nw

P.E.E.P.P.E.E.P.

5-10cm H2O

10cc/kg IBW

Pressure Control

I : E

Adjust RR for EtCO2 = 32-40

Tidal Volume

Respiratory Rate