Acid-base and Blood Gases in the Fetus My perpetual AIM with our - - PowerPoint PPT Presentation

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Acid-base and Blood Gases in the Fetus My perpetual AIM with our - - PowerPoint PPT Presentation

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6/10/2016 No disclosures Acid-base and Blood Gases in the Fetus My perpetual AIM with our erudite & wonderful J T Parer, MD, PhD Maternal Fatal Medicine UCSF OB/GYN residents is University of California San Francisco after 4 years to

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Acid-base and Blood Gases in the Fetus

J T Parer, MD, PhD Maternal Fatal Medicine University of California San Francisco

40th Meeting Antepartum and Intrapartum Management San Francisco, California June, 2016

No disclosures My perpetual AIM with our erudite & wonderful UCSF OB/GYN residents is after 4 years to have at least 50%

  • f them be able to explain and

understand the clinical significance

  • f

BASE EXCESS Teenage G1P0 at 40 2/7 wks, uneventful PNC

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SVD at 08:52 What is pH?

pH is the negative log, to the base 10, of the concentration of [H+] ions

Concentration of acid, or hydrogen ions, or [H+] in blood: 0.0000004 mM/lit or 4 X 10 -7 or 10 -7.4

The pH is therefore 7.4

The Dreaded Henderson- Hasselbalch Equation

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Henderson-Hasselbalch Equation

[H+] = K.[acid]/[base]

Henderson-Hasselbalch Equation

For convenience this is changed to negative logarithm notation:

  • -log [H+]= -log K + log [base]/[acid]

For the H2CO3 and HCO3

  • acid base pair:
  • pH= pK + [HCO3
  • ]/H2CO3]
  • pH= 6.1 + log 24/1.2
  • = 6.1 + log 20
  • = 6.1 + 1.3
  • = 7.4

Normal Values for Arterial Blood in Adults

Nonpreg Pregnant

pH 7.40 7.40 PCO2 mmHg 40 34 HCO3

  • mM/lit

24 20 BE mM/lit

  • 4

I can easily and comfortably define Base Excess

  • A. True
  • B. False

86% 14%

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Summary of normal values in utero

Nicholaides et al, 1986

Umbilical Artery

Mean ± 2 SD

Umbilical Vein

Mean ± 2 SD

pH 7.33 ± 0.07 7.38 ± 0.06 Carbon dioxide pressure (mmHg) 45 ± 10 38 ± 8 Bicarbonate (mEq • L–1) 23 ± 5 23 ± 5 Base excess (mEq • L–1) – 3 ± 3 +0.5 ± 4 Oxygen content (mM • L–1) ─ 6.7 ± 0.6 Oxygen pressure (mmHg) 35 ± 15 41 ± 20 Hemoglobin (g • dl–1) 13 13

The Tyranny of 3 Variables: pH, HCO3

  • and H2CO3
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Before & after labour

Rooth et al, 1972

Before Labor Second Stage of Labor

pH 7.37 7.30 Carbon dioxide pressure (mmHg) 38 43 Bicarbonate (mEq • L–1) 21 21 Base excess (mEq • L–1) –3 –5

Respiratory acidosis is due to CO2 Metabolic acidosis is caused (mainly) by lactic acid Blood Gases

Umb artery Umb vein

pH 6.88 6.91 PCO2 mmHg 112 99 HCO3

  • mM/lit

20 20 Base Excess mM/lit

  • 13
  • 13

Normal Values for Arterial Blood in Adults

Nonpreg Pregnant

pH 7.40 7.40 PCO2 mmHg 40 34 HCO3

  • mM/lit

24 20 BE mM/lit

  • 4
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Base Excess

Bicarbonate, HCO3

  • can change in 2 ways:
  • By reacting with fixed acids, eg lactic, beta

hydroxybutyric, acetoacetic acids

  • By changes in CO2; if more CO2, higher HCO3
  • Because of this [HCO3
  • ] is only useful as a measure of

metabolic acid derangement when PCO2 is 40 mmHg

  • Base Excess/Base Deficit was introduced as a

measure of metabolic change from normal, even in the presence of CO2 changes from normal

Umbilical blood gases from clamped segment of cord at birth

n=15000 normal births, Helwig

Mean Standard Deviation Median 2.5 %tile 97.5th %tile UA pH 7.26 0.07 7.27 7.10 7.38 UA pCO2 (mmHG) 53 10 52 35 74 UA pO2 (mmHG) 17 6 17 6 30 UA base excess (mEQ • L–1) –4 3 –4 –11 1 UV pH 7.34 0.06 7.35 7.20 7.46 UV pCO2 (mmHg) 41 7 41 28 57 UV pO2 (mmHG) 29 7 29 16 43 UV base excess (mEQ • L–1) –3 3 –3 –8 2

Threshold of Acceptable Acidemia in Umbilical Arterial Blood at Birth

  • pH > 7.1
  • Base excess >-12 meq/lit

Helwig et al, AJOG

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FHR Management- King’s Kascade

26

IIa Recurrent decelerations IIb Variability diminishing IIb Decelerations getting deeper +/- tachycardia

Conservative measures and reevaluate in short period

  • f time

Conservative measures Consult and make a plan for reevaluation in short period of time Bedside evaluation by clinicians Consider delivery in short period of time and and

Category II Category I Category III

Expectant management consider Intermittent auscultation Deliver as soon as possible

Pathologic fetal acidemia pH < 7.0 BE < -12, or -16, or -20

  • Goldaber
  • Gilstrap
  • Goodwin
  • Low
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Newborn Cooling Protocol Blood Gas Criteria pH < 7.0 BE< -12 SVD at 08:52 Blood Gases

Umb artery Umb vein

pH 6.88 6.91 PCO2 mmHg 112 99

HCO3- mM/lit

Base Excess mM/lit

  • 13
  • 13

The most likely outcome for this baby is:

  • A. Brain damage
  • B. Impossible to say

C.Normal outcome

9% 48% 43%

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Rate of change after acute cessation of oxygen delivery in a monkey fetus- Myers pH fell 0.04 units/min CO2 increased 6 mmHg/min Base Excess fell ca 1 mEq/lit/min SVD at 08:52 SVD at 08:52 3270 gm girl Apgars 1, 7, 10 Glucose @ 30 min-14 Glucose @ 2 hrs-66 Home age 18 hrs I am now much more comfortable defining and understanding the clinical significance of fetal Base Excess

  • A. True
  • B. False

40% 60%

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THANK YOU!

Fick equation

Cardiac output = (O2 consumption) / (arterio- venous O2 concentration difference) or O2 consumption = (cardiac output) x (A-V O2 difference)