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Why How Exploring (some of) the equations, physiology and mechanisms which inform and underlie our practice. Adam Bell, BS, CCEMT-P, CPTC, Donor Network of Arizona, AZOB NATCO Annual Meeting Aug 8, 2015

Why ⇌ How NATCO version

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Page 1: Why ⇌ How NATCO version

Why ⇌ HowExploring (some of) the equations, physiology and mechanisms which inform and underlie our practice.

Adam Bell, BS, CCEMT-P, CPTC,

Donor Network of Arizona, AZOB

NATCO Annual Meeting

Aug 8, 2015

Page 2: Why ⇌ How NATCO version

“What senses do we lack that we cannot see or hear another world all around us?”-Frank Herbert, DUNE

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Objectives

Provide an example of an order for a bicarbonate drip which will also lower sodium in the setting of hypernatremia and an indication for the same and define a % solution

Calculate a mean airway pressure given PIP, PEEP and I:E ratio

Demonstrate how to predict CO2 with vent rate change assuming apneic pt on vent with constant compliance and volume

Verbalize the two most significant factors in delivery of O2 to tissues and two interventions to support each factor

Which sounds hard, right?

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“…A lot of what we do in the (ICU)…at least the biology and the chemistry, is

really strongly founded on what I learned in high school science…A lot of the science

really isn’t that highbrow…”

-Dr. Jeffery Guy,

ICU Rounds Podcast, “Colloids: Details and Myths” 2012

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“All vague notions must fall before the pupil can call himself a master”- Bruce Lee

• Why do we breathe?

• How many of us were told “CO2 Level?”

• Typical DKA ABG: 7.19/27/110/15/98%

• pH of CSF

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DEFINITIONS & PRECISION

How does a tension pneumothorax kill you?

What does CVP Measure?

What are preload and afterload?

Where does vasoconstriction mostly occur?

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Mean Airway Pressure (MAWP)

• What is the formula for Mean Arterial Pressure and why does it make sense?

Hint: Time Averaged Pressure

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Calculating MAWP

• Find I:E ratio, for each unit of I time add 1x PIP, for each unit of E time: add 1x PEEP, then divide by total units of time

• e.g. PIP 25 PEEP 5, I:E 4:1:

4 x 25 =100 ( for this 4 units of PIP)

+ 1 X 5 [ for single unit of PEEP] = 105 / 5

( the total units of PIP + units of PEEP) = MAWP of 21 cm H2O

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I:E Ratio 1:2 1:1 3:1 11:1 1:2

PIP 30 30 30 30 40

PEEP 5 5 5 0 15

Equation (30+5+5)/3 (30+5) /2 (30+30+30+5) /4

(30x11) +0/12

(40 +15+15)/3

MAP 13.3 17.5 23.75 27.5 23.3

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MV changes and PaCO2Master Equations

• Minute Volume (MV) =

(tidal volume/ breath) X (breaths/ min)

• (MV X PaCO2) / desired PaCO2 = Desired MV

&

• (MV X PaCO2) / New MV = Predicted PaCO2

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Predicting CO2 changes w/volume changes

• Vent volume assuming you keep same rate:

• (Current PaCO2 x Current tidal volume)/ Desired PaCO2 = Desired tidal volume to normalize CO2

• And so:

(Current PaCO2 x Current tidal volume)/ New Tidal Volume = new predicated PaCO2

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Rate Changes and PaCO2:

Vent Rate assuming constant tidal volume:

(Current PaCO2 x Current Vent Rate)/Desired PaCO2 = Desired Vent Rate

“Repetition of error is not experience”-Dr. Jeffery Guy, ICU Rounds Podcast

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Same Donor, top ABG is earlier,No Bicarb given

BD Donors still compensate for hyperventilation

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Anion Gap, AG (in one slide)

• The body must be electrically neutral. Charges must balance.

• <12 (+/-2)

• Na+ - ( Cl- + HCO3-)

• The “gap” represents other normally unmeasured anions such as phosphate, sulfates and proteins in serum plasma

• Low Albumin lowers Anion gap drop of 1gm Albumin yields drop of 2.5 in gap calculation

• w/ Acidosis: Pos AG: treat cause, Neg AG: give bicarb

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Bicarb Drips (back to chemistry class)

• mEq measure electrical charge

• mg measure mass

• % solution means:

X grams solute/100ml fluid where X= the %

Mass Charge

23 mg Na + 1 mEq

39 mg K+ 1 mEq

36 mg Cl- 1 mEq

30 mg HCO3- 1 mEq

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The solution to pollution is dilution?!

Serum NamEq/L

DONORS

3% NaCl

mEq/LNa, Cl

0.9 % NaClmEq/LNa, Cl

(5% alb is in NS)

3 “amps” bicarb/L Sterile H2O

LRmEq/LNa:

0.45 % NS

& D5 ½ NS

mEq/L Na:

D5W

50 gm Dextrose/L

mEq/L Na:

175 513, (513 Cl)

154, (154 Cl)

150(0 Cl)

130 (110 Cl)

77(77 Cl)

0 (0 Cl)

155 513 154 * 150(0 Cl)

130 77 0 (0 Cl)

145 513 154 150(0 Cl)

130 77 0 (0 Cl)

135 513 154 150(0 Cl)

130 * 77 0 (0 Cl)

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Bicarb Drips Cont.

• 0.45% NaCl has 450 mg NaCl/ 100ml or 4,500 NaCl mg/L which =

• 77 mEq each of Na+ and Cl- /L

Thus 1771 mg Na+ electrically balance 2772 mg Cl- for total mass of 4543 mg /L

Why do you care???

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Bicarb Drips Cont.

• In hypernatremia we’d like to lower Na+

• Thus if we want a bicarb gtts w/ same Na+ of 0.45% NaCl:

We can calculate how much bicarb to use and not let our Na+ rise!

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Replacement Formulae

• Bicarb Replacement:• 0.15 x weight {in kg} x Base Deficit = mEq

NaHCO3 for replacement of 50% of Deficit

• K+ Replacement (assumes no continuing losses)

• Desired K - Current K x 20 = mEq to replace

• Note: K-Phos has:

approx. 1.5 mEq K+/mmol K-Phos(30 mmol k-Phos = 44- 45 mEq K+)

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Delivered O2

Delivered O2 = CO x {1.36 x Hbg x SaO2} + {0.0031 x PaO2}

BP 48/33 Good? Bad?

ECMO pt: Flow 4.5 L/min

If you double the diameter of a tube: flow increases 16X, and speed & pressure drop.

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Putting it all together

Consider a brain dead pt:Cardiac/Fluid Status:

200 mcg/min Neo, 60mcg/min Levo, Vasopressin 0.04u/min, Fluid -2L, 100/86,

CVP 8, CO 3, CI 1.2, SVV 38,

SVI 24

Respiratory/Pulmonary Status:

Peep +15, , FiO2 1.0, SpO2 92%

Chemistry Status:

lactate 7, Alb 1.9, TP 3.8,

Hbg 8.6,

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Sources Used

· Mosby’s Pocket Guide to Fluids and Electrolytes 4th Ed.· Quick Reference to Critical Care 3rd Ed.

· Online Database of “Progress in Transplantation”· The ICU Book 2nd Ed.

· ICU Rounds Podcast by Dr. J Guy· Critical Care Medicine 3rd Ed.

· Egans- Fundamentals of Respiratory Care· Oaks- Guides to: Hemodynamics and Ventilator Management

· Robbins- Pathologic Basis of Disease· Pulmonary Physiology and Pathophysiology 2nd Ed.

· Jones and Bartlett – Critical care Transport· Epocrates Free Version Apple app.

· Principles of Anatomy and Physiology 9th Ed. · Sauders- Pharmacology for Nursing Care 4th Ed.

· Harrison’s Internal Medicine, e-book Ed. · Lehninger- Principles of Biochemistry