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Applied Pulmonary Physiology
Jeremy S. Heiner CRNA
Non-Respiratory Functions n Filtration n Warming n Humidification n Metabolism n Surfactant
Other Factors That Can Alter Respiration n Hering-Breuer reflex n Higher respiratory centers n Proprioreceptors and peripheral
mechanoreceptors n Juxtacapillary receptors n Chemical stimulation
Central Chemoreceptors
H+ stimulates the chemosensitive area
How is the manipulation of CO2 applicable to anesthesia?
Peripheral Chemoreceptors
Compliance
Respiratory Muscles
Mechanics of Respiration
Elastic Forces within the Chest
Transpulmonary Pressure
Lung Volumes and Capacities
Anesthetic Effects on FRC
40-50% ↓ in FRC
Pulmonary Function Tests
Obstructive Lung Disease
Restrictive Lung Disease
60+ year old
O2 and CO2 Gas Exchange
O2 CO2
O2 and CO2 Diffusion
Oxygen Content in Blood
n Oxygen content = % Saturation x Oxygen binding capacity + dissolved oxygen
n (0.003 ml/dl/mmHg x PaO2) + (SaO2 x Hgb x 1.34 ml O2/gm Hgb)
n PaO2 = 100 n SaO2 = 100% n Hgb = 15
n (0.003 x 100) + (1 x 15 x 1.34) = 20.4 ml/dL
Calculate the O2 content based on these values. n PaO2 = 95 mmHg n SaO2 = 97% n Hgb = 15 g/dL n (0.003 x 95) + (0.97 x
15 x 1.34) = 19.8 mL/dL
n PvO2 = 40 mmHg n SvO2 = 75% n Hgb = 15 g/dL n (0.003 x 40) + (0.75 x
15 x 1.34) = 15.1 mL/dL
O2 Consumption
n Adult = 3-4 mL/kg n Neonate/infant = 6-8 mL/kg
Your patient weighs 100 kg and has an FRC of 2000 ml. She is breathing room air. Approximate how much apneic time do you have before she desaturates assuming she has a normal O2 consumption rate? How much time is increased if you provide Preoxygenation of 100% O2 for 5 minutes?
n 4 x 100 = 400 mL/O2/min (O2 consumption) n 0.21 x 2000 = 420 mL/O2 n 420/400 = 1.05 minutes or about 60 seconds n 1.0 x 2000 = 2000 mL/O2 n 2000/400 = 5 minutes
Oxyhemoglobin Dissociation Curve
90
26.6
Pulmonary Capillaries
Alveolus
Difference between ETCO2 and PaCO2 is due to dead space
ventilation
Why would slower deep breathing be more effective than rapid shallow breathing?
n 75 kg male 1. 300 mL tidal volume with RR of 20 2. 600 mL tidal volume with RR of 10 n Dead space ventilation is 2 mL/kg = 150 mL 1. 300 – 150 x 20 = 3000 mL/min 2. 600 – 150 x 10 = 4500 mL/min
Right-to-Left Shunt Normal Ventilation Shunt
Alveolus is being perfused, but no gas exchange is occurring
which leads to a shunt and hypoxemia
Physiologic Shunt
Lung Zones
Awake Upright Spontaneously Breathing
CO2 Response Curve
Depressive effects of anesthetics on the CO2 response curve
Anesthetic Effects on FRC n FRC ↓ 10-15% in supine
position n Controlled ventilation ↓ FRC n General Anesthesia ↓ FRC
an additional 5-10% n Paralysis ↓ FRC further n Surgical displacement of
abdominal organs
QUESTIONS?