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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?