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PICU Primer I

Kevin M. Creamer M.D. Pediatric Critical Care Walter Reed AMC. PICU Primer I. Physiology Hypoxia / Hypoxemia ABG’s and Acidosis Sodium and H 2 O metabolism Hemodynamics and Cardiopulmonary interactions. ICU Care & Common Problems Head trauma Toxicology Postoperative issues

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PICU Primer I

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  1. Kevin M. Creamer M.D. Pediatric Critical Care Walter Reed AMC PICU Primer I

  2. Physiology Hypoxia / Hypoxemia ABG’s and Acidosis Sodium and H2O metabolism Hemodynamics and Cardiopulmonary interactions ICU Care & Common Problems Head trauma Toxicology Postoperative issues Mechanical Ventilation The Primer Outline

  3. Can you have hypoxia without hypoxemia? • Can you have hypoxemia without hypoxia?

  4. Oxygen and Hypoxemia • Define • Hypoxemia • Hypoxia

  5. Hypoxemia • Ventilation/Perfusion mismatch • Hypoventilation • Shunt • Diffusion • Decreased Ambient O2

  6. Oxyhemoglobin Curve >> low pH, high Temp

  7. Shunt / Dead Space Spectrum V/Q = 0 V/Q = infinity No amount of  O2  difference will fixbetween EtCO2 and PaCO2

  8. Ventilation / Perfusion mismatch • Blood • Pus • Air • Water • Atalectasis • Quantitate using A – a Gradient

  9. A – a Gradient (Pb-PH2O) x FIO2 - (PCO2/.8) - PaO2 • Other useful equations • Dead Space = 1 - (EtCO2/PaCO2) • OI = (Paw x FIO2 x 100)/ PaO2 • Positive vs. negative pressure

  10. Cause for desaturations • Anesthesia – hypoventilation • Atalectasis – V/Q mismatch • Edema - V/Q mismatch • Asthma– dead space/ V/Q mismatch • Dysfunctional Hemoglobin • You may need a CXR and or ABG in addition to H+P to answer the question

  11. Non respiratory Physiologic causes of a low PaO2 Causes Effect on P(A­a)O2 • Nonrespiratory • Right­to­left intracardiac shuntDecreased PIO2Low barometric pressureLow FIO2Decreased R valueLow mixed venous oxygen content* • Artifact • Very high white blood cell countPatient hyperthermia Increased Normal Normal Increased Increased Increased *Only in presence of increased venous admixture

  12. Hypoxia • Hypoxic - ex. pulmonary disease • Anemic – ex. low CaO2 , CO poisoning • Distributive - ex. sepsis, emboli • Histotoxic – ex. cyanide

  13. Oxygen Debt/ Oxygen Deficit Death>? MODS > Inadequate Resuscitation

  14. Oxygen Content • Which has the biggest impact on O2 delivery to the tissues? • Hemoglobin, Sat, Cardiac Output, or PaO2 • Which patient has more oxygen in the blood? • Patient A, PaO2 89, Sat% 97%, Hg 9.8 • Patient B, PaO2 60, Sat% 85%, Hg 13.1

  15. V A Hb 15 20 // 15 O2 content cc/dl Hb 10 // 10 // Hb 7.5 Hb 0 // PO2 25 50 75 100 150 600 Sat% 50 75 90 99 100

  16. Preload HR CO Contractility SV DO2 Afterload Hg CaO2 PaO2 Sat %

  17. “Normal” Values • CaO2 = (Hg X 1.34 X Sat%) + (PaO2 X 0.003) • 17-20cc O2 /dL • DO2 = CI X CaO2 • 400-600 ml X min / M2 • VO2 = CI X avDo2 • 140-160 ml X min / M2 Arterial sat 100% minus Consumption = Venous sat 75-80%

  18. Oxygen Rules of Thumb • Give enough • high flow non-rebreather if needed • Look for a reason for low Saturations • Postop Posterior Spinal Fusion Pt with Sats 88% • Don’t be fooled by a little • 5 kg baby , RR 40, I:E 1:2, on 2L NC • What’s the FiO2?

  19. Questions? • NEXT UP • ABG’s and acidosis

  20. Acidosis • Respiratory vs. Metabolic? • Anion gap or not? • Acute vs. Chronic? • Primary or Secondary? • Rule • every 10 torr change in PCO2 should result in 0.08 change in pH • Every HCO3 drop you should see 1:1 increase in base excess

  21. ABG quiz 1. 1° Respiratory Alkalosis 2. 1° Respiratory and 1° metabolic acidosis 3. 1° Resp acidosis and 2° Metabolic alkalosis 4. 1° Metabolic acidosis and 2° Resp alkalosis

  22. ABG quiz 1. Crying healthy infant 2. Former preemie with bad BPD 3. Salicylate toxicity 4. Postop spinal fusion patient 5. Moderate Asthma attack on O2 6. DKA

  23. Acidosis - Anion Gap? • Pay attention to the frequently overlooked HCO3 on the Chem-7 • It’s measured not calculated • Does the Chloride rise as the HCO3 drops?

  24. Acidosis - Osmole Gap ? • IF AG is + then calculate the osmole gap • Difference between measured and calculated OSMs • Osm = 2(Na+) + BUN/2.8 +Glu/18

  25. Methanol Uremia DKA Paraldehyde Iron/INH/inhale CO Lactic Acid Ethanol/Ethylene Glycol Salicylates GI HCO3 losses Renal tubular acidosis Carbonic Anhydrase inhibition TPN? Hypoaldosteronism Anion Gap vs. Non Anion Gap

  26. Potassium? OSM Gap?

  27. Acidosis treatment • Correct underlying problem • restore perfusion !!! • NaHCO3 usually not necessary • Paradoxical CNS acidosis • Left shift of oxyhemoglobin curve • Think about funky metabolic disorders if the story doesn’t fit

  28. Funky Acidosis Workup • First 1-2 hours • ABG • Chem 10 • Lactate • Ammonia • Ketones • Urinalysis • consider CBC and LFTs’

  29. Questions? • NEXT UP • Sodium and water metabolism • “There is no such thing as free water, sooner or later you have to pay for it”

  30. Sodium and Water H+P • HX- intake, output of water and salt • Ex. (V/D) , boiled milk or home-made solutions • Intravascular Volume (Hi, Low, Nl) • Urine volume and concentration • Renal Fxn • BUN, Cr, K+ • FeNa+ = (UNa+/PNa+)/(Ucr/PCr) • <1% Low effective ECF

  31. Hypernatremia Common in under watered ICU patients

  32. DI Central - responds to ADH look for a CNS lesion Nephrogenic - doesn’t respond to ADH Don’t forget Mineralocorticoid Excess Renal d/o with High PRA Hypernatremia - Other

  33. Goal of any hyperosmolar state correction is to fix problem while avoiding cerebral edema Pesky idiogenic osmoles  correct over 48 hours Hypertonic state may mask symptoms Correct both Na+ and H2O deficits Treatment

  34. Correct at rate 0.5-.75 mEq/L/hr Check lytes q4-6° Watch for Hypogylcemia, Hypocalcemia Assume all losses are 140 meq/L Na+ Treatment If Na+ < 160 Fluid = 1/2 NS If Na+ > 160Fluid = NS

  35. 10 d.o. 3.3 kg patient presents with Na+ 172, Birth wt 3.9 Kg assume 600 cc lost is all 140 meq/L Na+ add daily Na+ and H2O X 2 calculations yield 1/2 NS at 28cc/hr *remember rule and use NS USE NS and make the patient NPO for at least the first 12 hours Hypernatremia Example

  36. Hyponatremia • Pseudohyponatremia? i.e. DKA • Volume status? • High - CHF, Renal or Liver failure, hypoalbuminemia • Normal - excess free H2O intake, or SIADH, hypothyroidism • Low - GI, Skin,CSF or tissue losses, diuretics, CSW, adrenal insufficiency

  37. Hyponatremia • Checking urine sodium is invaluable • Remember iatrogenic losses • Drains • Lumbar, or JP, etc • Lasix • hyponatremic, hypokalemic, metabolic alkalosis • fix by replacing Cl- , not Na+ • give KCL

  38. Treatment • One goal of hyponatremia correction is to avoid Central Pontine Myelinolysis • Correct both Na+ and H2O deficits • Correct at rate 0.5 mEq/L/hr • Treat Shock with NS then fix other deficits more slowly

  39. Special Situations • SIADH • Restrict free H2O • 3/4 maintenance NS • 3% Saline only for seizures • push 2-4 ml/kg over 5 -10 minutes until seizure stops • Lasix isn’t going to work • CSW • Replace ongoing Na+ and H2O losses with combination of 3% and NS

  40. Questions? • NEXT UP • Hemodynamics and Cardiopulmonary interactions • Pop quiz • What are the five determinants of Cardiac output??

  41. Hemodynamic Determinants • CO = HR X SV • Preload -Volume • Afterload -Resistance to LV emptying • Contractility -Squeeze • Heart Rate - rate =  SV • Rhythm -Atrial kick 10% CO • Ohm’s Law(V= I X R) or BP = CO X SVR

  42. Cardiac output I • Pulse quality • Central vs. Peripheral pulses • Differential Temperatures • Capillary refill time (CRT) • Organ Perfusion • CNS - AVPU? • Renal - UOP • only organ with easily measured output • Acidosis?

  43. Hemodynamic Assessment • Stroke volume - pulse quality • Preload - Liver size, CXR - heart size • SVR - CRT, Pulse pressure, differential temperatures

  44. Altered Hemodynamics • Common features • Elevated HR - attempt to  CO • Elevated RR - beware Resp. alkalosis • Decreased pulses -  CO • Depressed LOC -  CO • Acidosis -  CO • Falling UOP -  CO

  45. Distinguishing Exam

  46. Treatment priorities Preload Contractility Afterload

  47. Cardiopulmonary Interactions • Heart and Lungs intimately linked especially during critical illness • Ex. Valsalva can cause  intrathoracic pressure which results in  in CO via  venous return • RV filling inversely proportional to Thoracic pressure • Spectrum • Pulsus paradoxicus PEA 2° Tension pneumo Too much - Too much +

  48. Cardiopulmonary Interactions • Influence of negative pressure ventilation on healthy hearts is negligible • Normally systemic venous return is the main determinant of CO • Lung volume or (stretch) can PVR Lung volume PVR FRC

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