ACID-BASE DISORDERS

I.M.SIALA, MD

Acid-base disorders

Pulse

Pulse

HemoglobinHemoglobin

Blood Pressure

Blood Pressure

TemperatureTemperature

Hydro

gen Io

n

Conce

ntrat

ion

Hydro

gen Io

n

Conce

ntrat

ion

ProperCell

Function

ProperCell

FunctionCa, K, …

Ca, K, …

may change out of the normal range:

1- physiological: during daily metabolism

2- Pathological: e.g diabetic keto-acidosis

If not corrected major cell dysfunction

Hydrogen Ion ConcentrationHydrogen Ion Concentration

pH and H+ concentration

Compensatory mechanisms

Body buffers CO2-bicarbonate system

H+ + HCO3 H2CO3 H2O + CO2

Hemoglobin Hydroxyapatite

REGULATED BY KIDNEY

REGULATED BY LUNG

Lungs Hyperventilation wash out CO2 Hypoventilation retain CO2 Response is immediate

Kidneys Proximal tubule:

All HCO3 is filtered body reabsorb ONLY its requirements rest lost in urine

Distal tubule Na is reabsorbed in exchange of K or H+. KK H+H+ is excreted more alkalosis KK H+H+ is excreted less acidosis

Kidney needs 6 – 12 hours to start its compensating mechanisms.

+ CO2H2OH2CO3HCO3H++

Alkalosis

Acidosis

PHPH 7.36-7.447.36-7.44 7.4 7.4 ++.04.04

PaCO2PaCO2 35 – 45 mmHg35 – 45 mmHg 40 40 ++ 5 5

HCO3HCO3 21 – 28 mmol\l21 – 28 mmol\l 25 25 ++33

PaO2PaO2 83 – 108 mmHg83 – 108 mmHg

Acid base disturbancesArterial blood sampleArterial blood sample Normal valuesNormal values

Heparinized Heparinized syringesyringe

Radial Radial arteryartery

•A 2 ml syringe•Heparinized•Radial/ femoral artery•Draw 1 ml of blood•Send for analysis immediately or send in an ice pack

Acid-base disorders

AcidosisAlkalosis

ACIDOSISACIDOSIS

ACID ACID PaCOPaCO22

ALKALI ALKALI HCOHCO33

ACID ACID PaCOPaCO22

ALKALI ALKALI HCOHCO33

7.367.36 7 .447 .44

HCOHCO33COCO22

HCOHCO 33

COCO 22

COCO22

7.36 7 .44

METABOLIC ACIDOSISCOMPANSATED METABOLIC ACIDOSIS

HCOHCO33

COCO 22

ACID ACID PaCOPaCO

22

ALKALI ALKALI HCOHCO33

HCOHCO33COCO22

HCOHCO 33

COCO 22

HCOHCO 33

HCOHCO33COCO22

7.36 7 .44

RESPIRATORY ACIDOSISCOMPANSATED RESPIRATORY ACIDOSIS

HCOHCO33

COCO 22

COCO 22

COCO22

ACID ACID PaCOPaCO

22

ALKALI ALKALI HCOHCO33

ALKALOSISALKALOSIS

ACID ACID PaCOPaCO22

ALKALI ALKALI HCOHCO33

ACID ACID PaCOPaCO22

ALKALI ALKALI HCOHCO33

7.367.36 7 .447 .44

HCOHCO33COCO22

HCOHCO

33

COCO22

HCOHCO

33

HCOHCO33COCO22

7.36 7 .44

RESPIRATORY ALKALOSISCOMPANSATED RESPIRATORY ALKALOSIS

ACID ACID PaCOPaCO

22

ALKAALKALI LI

HCOHCO33

HCOHCO33COCO22

HCOHCO

33

COCO22

HCOHCO

33

HCOHCO33COCO22

7.36 7 .44

METABOLIC ALKALOSISCOMPANSATED METABOLIC ALKALOSIS

HCOHCO33

COCO22

COCO22

HCOHCO

33

ACID ACID PaCOPaCO

22

ALKAALKALI LI

HCOHCO33

Acid-base disorders

AcidosisMetabolicRespiratory

AlkalosisMetabolicRespiratory

Metabolic acidosis

a pH< 7.36 due to a reduction in plasma HCO3-.

PaCO2 will secondary to

hyperventilation .

a pH< 7.36 due to a reduction in plasma HCO3-.

PaCO2 will secondary to

hyperventilation .

Definition:Definition:

ANION GAP

Na+Na+

Anion GapAnion Gap

HCOHCO33__

ClCl--

“Anion gap represents the difference between readily measured anions and cations”

Anion gap = Plasma Na+ - (Cl- + HCO3-)

N= 8 – 14 mmol\l

Unmeasured Anions: albumin, phosphate, sulphate, lactate, ketoacids, others.

Unmeasured Cations: calcium, Mg, globulins, K.

Aetiology of metabolic acidosis

Na+Na+

Anion GapAnion GapHCOHCO33

__

ClCl--

Na+Na+

Anion GapAnion GapHCOHCO33

__

ClCl--

Increased Anion gap acidosis:Lactic acidosisKetoacidosis Diabetic

AlcoholToxins Methanol

Ethylene glycolSalicylate

Uraemia ARF CRF

Normal Anion gap acidosisHyperchloremic acidosis

GIT HCO3- lossDiarrheaPancreatic drainageUreterosigmoidostomy

Renal tubular acidosis

Drugs CA inhibitors

Anion GapAnion Gap

Metabolic acidosis

Clinical pictureClinical picture

A- due to acidosis:A- due to acidosis: Deep & rapid breathing, Kussmaul`s

breathing. Altered state of consciousness Hypotension in severe cases

B- Due to primary diseaseB- Due to primary disease

Arterial blood gas findings

pH low<7.36 or in the lower limit of

normal HCO3

- low <21 mmol\l

PaCO2 low < 35 mmHg

Treatment

A- treat the underlying disease.

B- control the acidosis; Correct fluid & electrolyte disturbances Indications of parentral Na HCO3:

in severe acidosis pH <7.1

GI loss or RTA HCO3 can be given as replacement therapy, usually orally.

RESPIRATORY ACIDOSIS

Definition:Definition: a pH < 7.36 due to increased retention of CO2 as a result

of alveolar ventilation

Definition:Definition: a pH < 7.36 due to increased retention of CO2 as a result

of alveolar ventilation

Respiratory Physiology

Aetiologya-Acutea-Acute Airway obstructionAirway obstruction

Foreign body Laryngospasm Severe bronchospasm

Respiratory center Respiratory center depressiondepression Morphine overdose CVA Trauma

NeuromuscularNeuromuscular High cervical cord

resection Myasthenia gravis Gullian Barre syndrome Organophosphorus

Restrictive defectsRestrictive defects Pneumothorax Flail chest

Cardiac Arrest & sever Cardiac Arrest & sever pulmonary oedemapulmonary oedema

COADCOAD

NeuromuscularNeuromuscular MS Muscular dystrophies Motor neuron disease Diaphragmatic paralysis

Chest wall deformitiesChest wall deformities Kyphoscolisis Ankylosing spodylitis

Primary alveolar Primary alveolar hypoventilation-hypoventilation-ObesityObesity

b-Chronicb-Chronic

RESPIRATORY ACIDOSIS Clinical Picture:Clinical Picture: A-Features of CO2 retention

Headache Altered level of consciousness(severe) Myoclonus &hyperreflexia Astrexis Central cyanosis Collapsing pulse Warm periphery Papilloedema

B-Features of the underlying illness.

AcuteAcute chronicchronic

pHpH low <7.36low <7.36 or atlower limit of

normal

PaCOPaCO22 high >45 mmHg high >45 mmHg

HCOHCO33 Normal high >28 mmol\l

RESPIRATORY ACIDOSIS

Respiratory failure

Type I respiratory failure: PaO2 < 60 mmHg with normal or low

PaCO2

Type II respiratory failure: PaCO2 >55 mmHg irrespective of O2

value.

A- Treat the underlying cause B- Treat carbon dioxide retention

Naloxone if Narcotic overdose is suspected Low oxygen concentration Mechanical ventilation in severe cases

Treatment

METABOLIC ALKALOSIS

Definition:Definition: a pH > 7.44 due to an increase in

plasma HCO3

PaCO2 may . In normal renal function it is rare,

why?

Definition:Definition: a pH > 7.44 due to an increase in

plasma HCO3

PaCO2 may . In normal renal function it is rare,

why?

Aetiology

Loss of H+, Cl, & NaAssociated with EC volume depletion

GIT loss Vomiting Aspiration of gastric

contentsLoss through kidney

DiureticsCarbenicillin, penicillins

K depletion

Mineralocorticoid excess

Bartter`s syndrome1o & 2o AldosteronismCushing syndromeAdrenal enzyme deficiencyHyperreninismExogenous mineralocorticoidsCarbenoxolone

Exogenous alkaliNaHCO3(Baking soda)Blood transfusions-citrateAntacids

METABOLIC ALKALOSISClinical picture A- Features of underlying illness

B- Features related to metabolic alkalosis;

Tetany Due to acute fall in ionized Ca level

Manifest Latent

Chvostok sign Traussau sign

Altered state of consciousness

Arterial blood gas picture

pH >7.44 or in the Upper limit of normal in

compensated cases

HCO3 >28 mmol\l

PaCO2 >45 mmHg or normal

Treatment

A- Correct the metabolic alkalosis; Correct EC volume depletion enhance HCO3

excretion

B- Treat the underlying cause; mineralocorticoid excess Correct K

RESPIRATORY ALKALOSIS

Definition:Definition: pH>7.44 due to CO2 washout as a

result of hyperventilation

Definition:Definition: pH>7.44 due to CO2 washout as a

result of hyperventilation

Aetiology

Hypoxia Voluntary CNS Disease

CVA Infections Trauma Tumours

DrugsAspirin Hepatic Failure Gram Negative Septicaemia Heat Exposure Mechanical overventilation

Clinical picture

A- features of the underlying cause. Anxiety

B- Features of Alkalosis; Tetany

Parasthesia, numbness around the mouth, tingling in hands & feet

Tetany

Arterial blood gas

pH high >7.44 PaCO2 low<35 mmHg

HCO3 normal or low<21 mmol\l

Treatment

A- Treat the underlying cause

B- Supportive measures; Rebreathing in a paper bag in

Hyperventilation syndrome + sedation

pHpH PaCO2PaCO2 HCO3HCO3

METABOLIC ACIDOSIS

(OR (OR LOWLOW NORMAL)NORMAL)

CompensatoryCompensatory

METABOLIC ALKALOSIS

(OR (OR HIGH HIGH NORMALNORMAL))

CompensatoryCompensatory

RESPIRATORY ACIDOSIS

(OR (OR LOWLOW NORMAL)NORMAL)

CompensatoryCompensatory

RESPIRATORY ALKALOSIS

(OR (OR HIGHHIGH

NORMAL)NORMAL)

CompensatoryCompensatory

SummarySummary