Applied Physiology: Lecture 6 - Respiratory Phys

Question 1

TOTAL LEFT PNEUMONECTOMY

Answer 1

Surgical removal of an entire left lung.
❖
Higher mortality rate
❖
Post op hypoxemia
❖
Post op bleeding
❖
Will your patient tolerate utilizing one lung after the case? How can you predict this?

Question 2

V/Q Scan

Answer 2

Preop Scans

V/Q scan:
V/Q scan is a scan where a patient ingests small amount of radioactive tracer to show how well the lung is able to ventilate.

Small amount of tracer injected in the IV to show how well the lung is being perfused.

Question 3

Lung Anatomy

Answer 3

Tube placement for a male:
5’8” = 41F
<5’8” = 39F
99.9% of the time you go left sided tube even if the surgery is on the left lung

Female:
5’3”-5’7” = 37F
<5’2” = 35F

Question 4

THORACIC CAGE ANATOMY

Answer 4

Hoarseness is not uncommon on a lungectomy due to proximity to recurrent laryngeal nerve

Question 5

POST OPERATIVE
CONCERNS

Answer 5

Respiratory Stats… MR? (ROC) Reversal? (Suggamadex)
Disposition
Extubation Plans
Post Op Labs
Chest Tube Maintenance

Want:
2 RBC
A-Line
FOB Scope
2 Large bore IVs
DL- 39F L
Temp
Foley

Question 6

BLOOD FLOW TO THE LUNGS

Answer 6

The lungs have 2 blood flows!

1: High pressure low flow. This is the systemic arterial blood flow to the trachea, bronchioles, and supporting tissues of the lungs. Branches off thoracic aorta. Oxygenated blood. Bronchial vein deoxygenated blood empty into the pulmonary veins. This creates a small shunt. (FIND PICTURE TO UPLOAD FOR THIS!!!)

2: Low pressure High flow circulation. Deoxygenated Blood from the RV into the pulmonary arteries and eventually into the alveolar capillaries for O2 and CO2 exchange.

Lungs hold about 500cc of blood. A small reservoir.

Blood flow to the lungs is essentially equal to CO.

Lymphatics: important to have a functioning system to help prevent pulmonary edema. Empty into the right thoracic lymph duct. (Provide negative pressure???)

Lets focus more on Low Pressure High flow circulation from the RV

Normal PA Pressure: 25/10
Lung Tissue Blood Flow: Thoracic aorta
R to L shunt

Question 7

BLOOD FLOW FROM THE RV

Answer 7

Main PA:
❖
About 5cm long from the apex of the RV to the bifurcation to R and Left PA.
❖
Pulmonary arteries are distensible, and have large diameters giving them a large degree of compliance. (This may be important for later).
❖
Normal RV pressure: 25/8 mmHg. Mean RV pressure 15mmHg
❖
Mean pulmonary capillary pressure 8mmHg
❖
Left Atrial pressure: Hard to measure directly.
❖
We can “Wedge” a catheter into a distal pulmonary artery via central line into the RV and into the PA. This pressure is normally 5mmHg. We use this to indirectly measure correlate and trend LA pressure. (2-3mmHg higher than LA pressure)
This is a Swan Ganz catheter (LOOK UP HOW TO PUT THIS IN EVEN THOUGH RARELY USED)

Question 8

PRESSURES WITHIN PULMONARY VESSELS

Answer 8

Pul to Sys difference about 10x

Question 9

PRESSURES WITHIN PULMONARY BLOOD VESSELS

Answer 9

Transmural pressure: The pressure difference between the inside and outside of capillaries.

Alveolar vessels
-are exposed to alveolar pressure and are compressed if this increases.

Extra-Alveolar vessels-as lung expands, larger blood vessels (pulm. Arteries and veins) are pulled open by the radial traction of the elastic lung parenchyma that surrounds them—so effective pressure around them is low.

Question 10

PULMONARY VASCULAR RESISTANCE

Answer 10

Ohms Law

V=IR (Potential = Current x Resistance)
Rearranged and converted for fluid flow in a tube

Vascular Resistance = (Input Pressure –Output Pressure) / Blood Flow
Lets do an Example….

What is the Ratio of Systemic to Pulmonary Vascular Resistance? (NEED TO LOOK THIS UP MORE!!!)
25 - 15??? from SLIDE 14

Must make the assumption that blood flow between the two systems is identical (which it should be)

Question 11

PULMONARY VASCULAR RESISTANCE (Part 1)

Answer 11

Ohms law is an over simplification of PVR

What happens to Resistance as pressure increases
Interestingly, PVR decreases as Pulmonary
Artery or Venous Pressure increases. Why?

Question 12

PULMONARY VASCULAR RESISTANCE (Part 2)

Answer 12

Why?
Two Mechanisms

Recruitment –primary reason for drop in PVR with increase pressure

Some capillary beds or vessels are closed or open so little that no blood flow occurs

Distention–widening of existing pathways

Since each vessel is already open and surrounded by the low pressure alveoli, they simply increase their diameter

Question 13

PULMONARY VASCULAR RESISTANCE (Part 3)

Answer 13

Other MAJOR determinant of PVR = LUNG VOLUME

The larger “Extra-alveolar vessels” contain smooth muscle walls and elastic tissue, if the lung volume is very small (ex. Collapsed lung), PVR is extremely high. In fact pulmonary artery pressure must be increased for any flow to occur. –this is called the CRITICAL OPENING PRESSURE (Pressure that opens valves)

Additionally, if the lung volume is really high, the thin walled capillaries are stretched and their diameters actually decreased.

Question 14

PULMONARY VASCULAR RESISTANCE (Summary)

Answer 14

Summary

PVR is normally low

PVR will decrease with exercise because of recruitment & distention of capillaries (QUESTION ON TEST)

PVR increases at the low and high lung volumes

You want to find the sweet spot (critical opening pressure)

PVR increases with alveolar hypoxia (HPV) because of constriction of small pulmonary arteries.

Question 15

HPV (HYPOXIC PULMONARY
VASOCONSTRICTION)

Answer 15

This directs blood flow away from poorly ventilated
areas of diseased lung in the adult.

Ex: Right mainstem of ETT or One Lung Ventilation

Most important at birth: fetal circulation has very
high PVR (from HPV) with only 15% of CO going
through lungs. At first breath, the alveoli are
oxygenated and vasoconstriction ceases leading to
decreased pulmonary vascular resistance.

(LOOK UP MORE ABOUT SHUNT FRACTION!!!)

Question 16

OTHER INCREASES OF PVR

Answer 16

Things as an anesthesia provider in charge of.

Question 17

MEASUREMENTS OF PULMONARY BLOOD FLOW

Answer 17

The VOLUME of blood passing through the lungs every
minute can be calculated. Flow = volume / unit time = (Q)

Fick Principle: O2 consumption per minute measured at
the mouth is equal to the amount of O2 taken up by the blood in the lungs per minute. (VO2)

How we calculate the volume of blood passing through
the lungs each minute.

Question 18

FICK PRINCIPLE

Answer 18

KNOW THIS EQUATION and HOW IT MEASURES BLOOD IN THE LUNGS

Question 19

HOW DO WE MEASURE THESE VALUES?

Answer 19

VO2 measured by collecting expired gas in a large spirometer and measuring its O2 concentration
Mixed venous blood is taken via a catheter in the pulmonary artery

Provides the CvO2
Arterial blood by radial or brachial artery

Provides the CaO2

I’ll bet money you might see a test question about this in the next few weeks.

Question 20

DISTRIBUTION BLOOD FLOW THROUGH LUNGS

Answer 20

Everything to this point makes the assumption that blood flow through the pulmonary
circulation is identical.
Not the case in the upright human

In the upright human, blood flow decreases almost linearly from the bottom of the
lungs to the apex.

This uneven flow changes when patients lie flat.
Apex (top of lung) flow increases; basal flow remains nearly unchanged
Apex to basal flow distribution is nearly identical
However the distribution gradient changes between posterior and anterior lung regions.

What explains this uneven distribution of blood flow between apex and basal
regions?
Hydrostatic Pressure Difference

Question 21

DISTRIBUTION BLOOD FLOW THROUGH LUNGS

Answer 21

Hydrostatic Pressures; Assume that the pressure within the Pulmonary Circulation is a
constant pressure & therefore a constant “Column of Water.”
However the apex is approx. 30cm “above” the basal region

As a result, pressure required to perfuse the apex would need to be 30cmH2O above the pressure required to perfuse the base. (approx. 23mmHg)

Remember your pressures….What is the mean PA pressure? (15mmHg)
As a result, we create “physiologic zones” in the lungs based on the pressures in the
alveoli, arterial & venous pressures.

Question 22

DISTRIBUTION BLOOD FLOW THROUGH LUNGS (Part 2)

Answer 22

West Lung Zones (Zones 1, 2 & 3)
– not going to cover the sometimes mentioned Zone 4

Question 23

DISTRIBUTION BLOOD FLOW THROUGH LUNGS (West Lung Zone 1)

Answer 23

West Lung Zone 1

Alveolar Dead Space

Ventilated but not perfused

Does occur if

Decrease Pa (ex. Hemorrhage)

Increased PA (ex. Positive Pressure Ventilation)

Question 24

DISTRIBUTION BLOOD FLOW THROUGH LUNGS (West Lung Zone 2)

Answer 24

West Lung Zone 2

Lower in height

Requires a lower Pa to perfuse

Here Pa greater than PA

Blood flow dependent on Pressure difference between Pa and PA (venous pressure is NOT an influence here)

Question 25

DISTRIBUTION BLOOD FLOW THROUGH LUNGS (West Lung Zone 3)

Answer 25

West Lung Zone 3  Lowest in Height (basal)  Requires a lower Pa to perfuse  Here Pa > PV > PA  Blood flow now dependent on the pressure gradient difference between Pa - Pv

Question 26

ACTIVE CONTROL OF THE PULM. CIRCULATION

Answer 26

Hypoxic Pulmonary Vasoconstriction  When alveolar Po2 drops → contraction of smooth muscle  Mechanism unknown  Occurs in “excised” & non-innervated lung, therefore not CNS dependent. Nitric Oxide (NO) – don’t confuse this with Nitrous Oxide  NO is endothelium derived vasoactive substance  Also available as an inhaled medication  Requires an inhaled concentration of approx. 20ppm (very low concentration)

Question 27

WATER BALANCE IN LUNG

Answer 27

Lungs can easily become fluid filled because only 0.3 micrometers of tissue separates capillary blood from air in alveoli. Fluid exchange across capillary endothelium obeys Starling’s law → illustrates role of hydrostatic and oncotic forces in movement of fluid across capillary membranes.

Question 28

WATER BALANCE IN LUNG (STARLING’S LAW)

Answer 28

Question 29

WATER BALANCE IN LUNGS (Part 2)

Answer 29

Force tending to push fluid out of capillary is capillary hydrostatic pressure minus the hydrostatic pressure in the interstitial fluid (Pc-Pi). Force tending to pull fluid in is the colloid osmotic pressure of the proteins of the blood minus that of the proteins of the interstitial fluid (πc-πi) PROTEINS "SUCK" THE FLUID Most likely, net pressure is outward, causing a small lymph flow in humans under normal conditions. When fluid leaves capillaries it leaks into interstitium of the alveolar wall tracks through the interstitial space to the perivascular and peribronchial space within the lung. Lymphatics in perivascular spaces help transport the fluid to the hilar lymph nodes Early pulmonary edema=engorgement of perivascular and peribronchial spaces. Called interstitial edema In later stage of pulmonary edema, fluid may cross alveolar epithelium into alveolar spaces. Alveoli then fill with fluid one by one.

Question 30

OTHER FUNCTIONS OF PULMONARY CIRCULATION

Answer 30

Acts as a reservoir for blood Lungs filter blood —remove small blood thrombi from circulation before it can reach brain (one reason a right to left shunt with VSD/ASD can be dangerous) Lungs trap WBCs and release later (unclear value).

Question 31

METABOLIC FUNCTIONS OF LUNG

Answer 31

Lung is only organ except heart that receives whole circulation. Vascular endothelium has many important pharmacologic features. Most notably:  Angiotensin I→Angiotensin II (by angiotensin converting enzyme)  ACE lives in small pits in surface of capillary endothelial cells.  *Renin-angiotensin system was covered in renal physiology . . . but

Question 32

RAS

Answer 32

One of main regulators of blood pressure and fluid balance Blood volume is low: juxtaglomerular cells in kidneys secrete renin into circulation. Plasma renin converts angiotensinogen (released by liver) to Angiotensin I. Angiotensin I converted by ACE to AngII. Angio II—vessel constriction→increased BP, aldosterone secretion from adrenal cortex Aldosterone -triggers kidney tubules to increase reabsorption of sodium (and thus water) into the blood which increases total fluid volume and also increases BP.

Question 33

LEFT TOTAL PNEUMONECTOMY Scenerio

Answer 33

60 YO male ❖ You have done aTHOROUGH Pre-operative evaluation ❖ Now, I go down stairs and get coffee and mingle with my coworkers..while YOU… ❖ Set up the room ❖ What will you have set up and ready before patient rolls in?

Question 34

LEFT TOTAL PNEUMONECTOMY Plan

Answer 34

Induction:Preoxygenate! Versed, Fentanyl, Propofol, Roc Intubation: Lube, Get your view, tube past cords (may have to turn right to point tube anterior) Lines: a-line (R Side down???, 2 large bore IVs Positioning: R Lateral, jacknife, reverse trendelenberg, check tube position Maintenance: OLV - clamp bronchial, open port to let lung exhale Post op Concerns: bleeding, hypoexemia, hypoxia Double Lumen tube Left and right sided. We use Left almost 100% of the time. Why? Sizing: Based on sex and height. 39F, 41F for males 35F 37F for females Lung Isolation: Left DLT: Bronchial lumen goes…? How do we isolate? How do we verify? We have isolated the lung Surgeon is happy Is the patients O2 sats happy? Someone tell me about HPV and how it applies here Someone tell me about his V/Q scan and how it applies here Surgeon tells you he is going to take the pulmonary artery What are you watching for? Make sure taking the artery for the correct lung SURGEON TELLS YOU HE IS TAKING THE LEFT MAIN BRONCHUS. BUT WAIT!! (Pull tube back with scope) Chest tube? Yes On gravity/waterseal (no suction - so you dont cause mediatinal shift) Watching for Blood

Question 35

POST THORACOTOMY PAIN SYNDROME

Answer 35

PTPS is defined as a constant or intermittent pain along the thoracotomy scar line greater than 2 months after surgery 30% to 50% of patients undergoing thoracotomy will develop PTPS PTPS is likely multifactorial in etiology – intercostal nerve injury is thought to play a role. Hyper-responsiveness is less well accepted as having a part in this syndrome

Question 36

POST THORACOTOMY PAIN SYNDROMEWHAT HELPS?

Answer 36

Thoracic epidural is the only intervention that has been proven to decease the incidence of PTPS Celebrex improves pain scores post -op, but has not yet been associated with a decrease in PTPS A VATS/thoracotomy pain protocol has been developed for CU. Consult with OR attending before ordering all meds on this protocol.