Transcript ABG’s
ABG’s Blood gas slip Data • • • • • Blood gases Electrolytes Haemoglobin Calculations Glucose • “Balance” What am I thinking ? Importance of gases and acid base balance • Need oxygen to live • Need to get rid of CO2 a waste product • Enzymes need pH 7.35 to 7.45 for optimal working Gas exchange in the body Carbon dioxide Oxyygen Lungs Heart Body Tissues Chemistry • C6H12O6 + 6O2 > 6CO2 + 6H2O • Glucose + Oxygen > Carbon dioxide + water • CO2 + H2O > H2CO3 > H+ + HCO3• Carbon dioxide + water > carbonic acid > acid + bicarbonate • pH depends on H+ Energy use in the body Glucose Pyruvate TCA cycle Oxygen ATP Energy Ways to loose acid • Lungs • Kidney Glucose metabolism I Glucose Liver Muscle Insulin Rest of body Glucose metabolism II • Glucose uptake depends on – Serum glucose – Blood flow – Insulin availability • Glucose doesn’t always cause acidosis Lactic acid I Glucose No oxygen Pyruvate Lactic acid TCA cycle Oxygen ATP Energy Lactic acid II - Lactic acidosis • Increased production – Tissue Hypoxia – Circulatory shock • Decreased utilisation – Liver failure – Circulatory shock • Acidosis dangerous, Lactate harmless • BE as surrogate marker Calcium • • • • Total calcium = free Ca2+ and Protein bound Ca2+ Active form is free Ca2 Myocardial contraction and vasoconstriction NOT with radial artery • Calcium chloride and gluconate Hct and haemoglobin • Bleeding – revealed – concealed • Chest • GIT • Retro peritoneum (IABP, recent angio) Balance I • Most are 500mL to 2.0 L +Ve by am • Depend on – fluids/loses in theatre – pre op dehydration • An aid to diagnosing internal bleeding and excessive vasodilatation Balance II • Always think (especially if CVP low) • Cold & 1.5L+Ve > CXR • Warm & 2.0 to 2.5L+Ve > CXR • Intra thoracic bleeding can occur regardless of chest tube drainage Acid - Base balance • Metabolic “HCO3/other acid problem” – Produce / loose acid / alkali • Respiratory “CO2” problem – Produce / retain CO2 Base excess (BE) or How much extra alkali • Meaning • Observation • Treatment BE I - meaning • Normal ~ 0 • If –Ve acidosis of any cause is present – Circulatory insufficiency • Cardiac • Circulatory volume – – – – – Renal failure Liver failure Ischaemic limb eg IABP Ischaemic bowel Respiratory • If +Ve alkalosis – Chronic hypokalaemia BE II - observation • A guide that patient is ok • If increasing negative monitor continuously • Can change from hour to hour BE III - treatment • If BE < -6.0 to –8.0 negatively inotropic • Acknowledge there is a problem, give bicarb, monitor BE frequently to reassess Blood gases I acid base balance • Uncompensated – No respiratory compensation when fully ventilated • Compensated – Most extreme value is usually primary problem • pO2 “unimportant” • CO2 + H2O > H2CO3 > H+ + HCO3• Carbon dioxide + water > carbonic acid > acid + bicarbonate Blood gases II acid base balance Uncompensated HCO3 Metabolic acidosis Metabolic alkalosis Respiratory acidosis Respiratory alkalosis CO2 pH > ^ > > ^ > ^ ^ Blood gases III acid base balance Compensated HCO3 Metabolic acidosis Metabolic alkalosis Respiratory acidosis Respiratory alkalosis CO2 pH >/ ^ ^ >/^ ^ ^ >/ >/^ Predicted response Anion gap • What you can’t measure • (Na+ + K +) - (Cl - + HCO3 -) • Causes “KUSMAL” – – – – – – Ketones Uraemia Salicylates Methyl alcohol Acid poisoning Lactate Frequency of blood gases ? ½ Hr, 1 Hr, 2 Hr • • • • • Recent admission Unstable Bleeding Oliguria/ renal failure Liver failure • “just unwell” or “just not right” • Previously abnormal result • Change in ventilation – Good lungs 5 minutes poor lungs 20 to 25 minutes Juniors and Fio2 ABG verses pulse oximetry • CO2 • Carbon monoxide Calculated verses Measured oxygen • Different types of Haemoglobin – – – – Oxyhaemoglobin Reduced (Normal, but no oxygen bound) Carboxyhaemoglobin (CO poisoning) Methemoglobin • DPG, blood transfusions • Haemoglobinopathies Thank you