Alveolar Ventilation During General Endotracheal Anesthesia Valentyna Groelle, RN, BSN, SRNA

Objectives Review the physiology of alveolar ventilation Discuss pulmonary changes after induction of general endotracheal anesthesia Describe how to perform two major types of alveolar recruitment maneuvers

Conducting vs Gas Exchange Airways

Alveolar-Capillary Gas Exchange

Physiology of Gas Exchange Ventilation External Respiration Internal Respiration

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

ARDS

Asthma

COPD and Air Trapping NORMAL COPD

Atelectasis

A-a Gradient A-a Gradient= PAO2-PaO2 PAo2=FiO2(Patm-PH2O)-PaCO2/0.8

Increased A-a gradient Causes of Hypoxemia Normal A-a gradient Increased A-a gradient Hypoventilation Low Inspired O2 Right to Left Shunt V/Q Mismatch Diffusion Impairment

Causes of Hypoxemia Normal A-a gradient Hypoventilation Neuromuscular disorder CNS disorder Depression of CNS by drugs Low Inspired Oxygen PiO2=(Patm-PH2O)xFiO2 High altitude Low FiO2

Causes of Hypoxemia Increased A-a gradient Right to Left Shunt (alveoli blocked from ventilation) CHF ARDS Drowning (due to congenital abnormalities) Intra-cardiac shunt Intra-pulmonary fistulas

Causes of Hypoxemia Increased A-a gradient V/Q Mismatch (due to lung dead space or shunt) PE Atelectasis PNA Obstructive lung disease (asthma, COPD) Pneumothorax “Shunt-like” “Dead-space” VA= 4-6 L/min Q=5-6 L/min V/Q= 0.8-1.2

Causes of Hypoxemia Increased A-a gradient Diffusion impairment Interstitial lung disease 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 P Transpulmonary 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 mmHg PEEP of 10cmH2O= 7.35 mmHg PEEP of 13cmH2O= 9.55mmHg Normal CVP: 0-8 mmHg Normal PAP (systolic): 15-25 mmHg Normal PAP (diastolic): 8-15mmHg

Cycling Maneuvers

SI vs Cycling Recruitment Maneuvers

Questions