is there a role for sodium bicarbonate in nicu? · 1950s hypoglycaemia, azotaemia, hyperkalaemia...
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Is there a role for Sodium Bicarbonate
in NICU?
Stephen Wardle
Consultant Neonatologist
Nottingham University Hospitals
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Aim / Objectives
To persuade you:-
• there is no evidence in favour of using bicarbonate
and some significant adverse effects
• to think about acid base and fluid management
in a different way to avoid the need for bicarbonate
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Possible Uses of Bicarbonate
on NICU
1. During resuscitation
2. To correct acidosis in babies with
pulmonary hypertension (PPHN)
3. To correct ‘metabolic’ acidosis in preterm infants
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Examples
28 week baby
6 hours old
pH 7.19
CO2 5.5 kPa
BE -12
Lactate 8.2 mmol/l
25 week baby
6 days old
pH 7.19
CO2 5.5 kPa
BE -12
Lactate 1.2 mmol/l
Term infant
FiO2 100%
SpO2 89%
pH 7.26
CO2 4.5
BE -10
Lactate 6.5
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Resuscitation
Recommended for use by NLS / AAP
‘May reverse intra-cardiac acidosis...
But ..lack of evidence …
Strong opinions in both directions
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A study from 1966 in five fetal monkeys
which infused TRIS and glucose together Daniel, Dawes et al BMJ 1966
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Arguments against:
• Lack of effectiveness in animal and human studies
• Increases CO2 (and increases acidosis)
• Even if arterial CO2 is normal, Increased
venous CO2 causes decreased intra-cellular pH
• Reduces pH of CSF
Roberton text book
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PPHN
Meconium Aspiration
Congenital diaphragmatic hernia
Pulmonary hypoplasia etc
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Strategy to maintain high pH using bicarb is possible
But
No evidence of effectiveness
Very high pH is needed to improve PaO2
Other strategies (e.g. NO) have more evidence / more effective
Maintain normal pH and avoid acidosis – can be achieved
without bicarb
Many adverse effects:
Hypernatraemia
Effect on intracellular pH
Effect on CBF / oxygen availability
PPHN
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Pretem Babies - Historical Perspective
1950s Hypoglycaemia, azotaemia, hyperkalaemia and metabolic acidosis
common before death in premature infants
1963 Usher - IV glucose and bicarbonate proposed
reduced mortality compared to historical controls
1967 Usher - bicarb to correct acidosis in RDS
mortality increased, IVH rate doubled
1977 Corbett RCT of bicarb
No effect on mortality / IVH rate pH improved without bicarb
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Rennie Roberton 3rd Edition 1999
Bicarbonate 14 page references
Rennie Roberton 4th Edition 2005
Bicarbonate 2 page references
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Why not just use bicarbonate?
• Increased risk of IVH (Usher 1968)
• Effects on CBF
• Possible detrimental effect on cardiac function
• Increased CO2
• Hypernatraemia
• Skin damage
Giving bicarb may cause:-
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Preterm Babies
What is the cause of the
acidosis?
Most early acidosis is lactic acidosis
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Prevalence and Severity
• 23 infants <1000g were studied
• 56.5% became acidotic in the 1st 7 days
• 30% became acidotic on the 1st day, always with an increased lactate concentration
• 100% showed a low base excess in the 1st 7 days
Acidotic babies more likely to die (p = 0.012)
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Lactic Acidosis
Requires treatment of the cause:
• Peri-partum hypoxia-ischaemia
• Low systemic output
• NEC
• Significant IVH
• Significant acute blood loss etc
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If lactate is normal what is the cause
of the acidosis?
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Conventional Acid-Base balance
• Henderson - Hasselbach Equation:
pH = 6.1 + ‘metabolic’ [HCO3-]
‘respiratory’ 0.03 pCO2
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Metabolic Acidosis – conventional approach
• Accumulation of acid other than CO2 and
associated with a decrease in [HCO3-]
• The acid can be
• Lactic
• Something else – bicarb loss??
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The Anion Gap
Na+ Na+ Na+
Alb-
HCO3
XA- Alb-
HCO3-
Cl-
Alb-
HCO3-
Cl- Cl-
Normal
pH
Metabolic
Acidosis
Lactic
Acidosis
N N Raised
Durward 2002
Difference between measured plasma cations
and anions
([Na+] + [K+]) – ([HCO3-] + [Cl-])
K+ K+ K+
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Giving sodium chloride generates an acidosis
This cannot be easily explained by Henderson
Hasselbach
This is the commonest cause of non-lactic acidosis
in preterm babies
not bicarb loss!
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Stewart’s Strong Ion Theory Can. J. Physiol. Pharm. 1983
pH is affected by 3 independent variables
• PCO2 (↑ in acidosis)
• Weak acids (albumin and phosphate) (↑ in acidosis)
• Strong ion difference (SID) (↓ in acidosis)
Peter Stewart
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All of which affect bicarbonate concentration
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Strong Ion Difference (SID)
• Strong ions are fully dissociated at physiological pH
• SID = [Strong cations] – [Strong anions]
Cl to Na ratio is a good approximation
Durward 2002
Na+
K+
Mg2+
Ca2+
SID
Cl-
Alb-
Pi-
HCO3-
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Strong Ion Gap (SIG)
Na+
K+
Mg2+
Ca2+
Cl-
HCO3-
Alb-
Pi- SID Na+
K+
Mg2+
Ca2+ Cl-
HCO3-
Alb-
Pi-
XA- SIG
(Strong Cations – Strong anions)
= Weak anions
(Strong Cations – Strong anions)
≠ Weak anions
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SID of Infusions
Fluid Sodium Chloride SID
mmol/l mmol/l
Blood (plasma) 140 100 40
0.9% saline 150 150 0
4.5% HAS 150 150 0
Ringers Lactate 130 109 21
Hartmanns 129 109 27
PN (typical) 33 0 33
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Acidosis is therefore usually due to infusions of fluid
with low Strong Ion Difference
E.g. Sodium chloride 0.9% at 0.5 ml/hr in 500g baby
= 24 mls / kg / day
Plus flushes, other infusions etc
= significant amount of low SID fluid
significant acidosis
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How can this be avoided?
Avoid low SID fluids where possible
Avoid saline / albumin
Acetate in TPN instead of chloride (Peters ADC 1997)
Do not treat base deficit – determine the cause and
manage appropriately
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No evidence for sodium bicarb in resuscitation
Better approaches to managing PPHN
Conclusions
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Avoid acidosis in preterm babies with:
• Better understanding of Stewart strong ion theory
• Greater use of infusions with higher strong ion
difference (acetate in PN)
• Avoid infusions of low strong ion difference fluids
(saline)
Conclusions