Alveolar Ventilation During General Endotracheal

Anesthesia

Valentyna Groelle, RN, BSN, SRNA

1. Review the physiology of alveolar ventilation

2. Discuss pulmonary changes after induction of general endotracheal anesthesia

3. Describe how to perform two major types of alveolar recruitment maneuvers

Objectives

Conducting vs Gas Exchange Airways

Alveolar-Capillary Gas Exchange

L

CDA

t

Q

Physiology of Gas Exchange

Internal Respiration

External Respiration

Ventilation

West’s Zones of the Lung

“Dead space”

“Shunt-like”

Alveolar Ventilation

Alveolar Ventilation VA= RR x (VT-VD)

Physiologic Dead Space VD/VT = (PaCO2−PECO2)/PaCO2

Alveolar Gas Exchange in Lung Disease

L

CDA

t

Q

ARDS

Asthma

COPD and Air Trapping

NORMAL COPD

Atelectasis

A-a Gradient

A-a Gradient= PAO2-PaO2 PAo2=FiO2(Patm-PH2O)-

PaCO2/0.8

Causes of Hypoxemia

Normal A-a gradient

1. Hypoventilation2. Low Inspired O2

Increased A-a gradient

1. Right to Left Shunt 2. V/Q Mismatch 3. Diffusion Impairment

Causes of HypoxemiaNormal A-a gradient

Hypoventilation

a. Neuromuscular disorder

b. CNS disorderc. Depression of CNS

by drugs

Low Inspired OxygenPiO2=(Patm-PH2O)xFiO2a. High altitudeb. Low FiO2

Causes of HypoxemiaIncreased A-a gradient

Right to Left Shunt(alveoli blocked from ventilation) a. CHFb. ARDSc. Drowning(due to congenital abnormalities)d. Intra-cardiac shunte. Intra-pulmonary fistulas

Causes of HypoxemiaIncreased A-a gradient

V/Q Mismatch (due to lung dead space or shunt)a. PEb. Atelectasisc. PNAd. Obstructive lung

disease (asthma, COPD)

e. Pneumothorax

“Shunt-like” “Dead-space”

VA= 4-6 L/minQ=5-6 L/minV/Q= 0.8-1.2

Causes of HypoxemiaIncreased A-a gradient

Diffusion impairment

a. Interstitial lung disease

b. Environmental disease

Induction of General Anesthesia

Cessation of Sigh Breaths

Absorption Atelectasis

Solubility of gases in blood plasma:Carbon dioxide>oxygen>nitrogen

Airway Closure from ↓ FRC

Compressive Atelectasis

Transpulmonary P =Intrapulmonary/Alveolar P-Intrapleural PTranspulmonary P= 760mmHg-756mmHg= +4mmHg

Open Lung Ventilation

Alveolar Recruitment Maneuvers

Low Tidal Volumes

PEEP

Alveolar Recruitment Maneuvers

1. The lung’s opening

pressure

2. The lung’s closing

pressure

3. The open-lung PEEP

Sustained Inflation Recruitment Maneuvers

Cycling Maneuvers

Hemodynamic Pre-Conditioning Phase

PEEP of 5 cmH2O= 3.67 mmHgPEEP of 10cmH2O= 7.35 mmHgPEEP of 13cmH2O= 9.55mmHg

Normal CVP: 0-8 mmHgNormal PAP (systolic): 15-25 mmHgNormal PAP (diastolic): 8-15mmHg

Cycling Maneuvers

SI vs Cycling Recruitment Maneuvers

Questions