Respiratory Failure in Children

1. Respiratory Failure in Children Daniel Sloniewsky, MD Associate Professor Division of Critical Care Department of Pediatrics Stony Brook University Hospital

2. Definitions: Acute Respiratory Failure ARF is the inability of the respiratory system to deliver O2 and remove CO2 at a sufficient rate to meet the body’s metabolic demands Can be hypoxic or hypercarbic ABG abnormalities • PaCO2 > 55 mm Hg (with low pH) • PaO2 < 60 mm Hg • SaO2 < 90% (in absence of cyanotic CHD)

3. Problems with Oxygenation Hypoxemia: Decrease in tissue O2 delivery • Hypoxic Hypoxemia -- Lung Disease • Ischemic Hypoxemia -- Decreased Blood Flow -- DO2 = O2 content x Cardiac Output • Anemic Hypoxemia -- Decreased O2-Carrying Capacity -- O2 Content = (1.39 x HgB x SaO2) + (0.003)(PaO2)

4. Hypoxic Hypoxemia: Where is the problem? FIO2 (Ex. Altitude) Decreased Air Entry -- Sedation (Ex. Opioid Overdose) -- Respiratory Muscle Weakness (Ex. SMA) -- Airway Obstruction (Ex. Croup, Asthma, etc) V/Q Mismatches (Ex. Atelectasis, ARDS) Shunting (Ex. CHD, pulmonary hypertension) Diffusion Abnormalities (Ex. Pulmonary Fibrosis, ARDS)

5. Acute Respiratory Failure: Problems with Ventilation Hypercapnea (increased CO2) can be seen with: 1. Increased Dead Space (areas not involved in gas exchange) (Ex. Asthma, Pulmonary HTN) 2. Decreased Alveolar Ventilation - Decreased Tidal Volume or Respiratory Rate (Ex. Coma, Overdose, MG, ARDS, etc) 3. Obstructed Airways (Ex. Asthma) 4. Increased CO2 production (Ex. Burns,Overfeeding) CO2 diffuses easily across alveolar-capillary membrane so diffusion problems usually do not cause hypercapnea

6. Acute Respiratory Failure: How to Diagnose Clinical Exam -- MOST IMPORTANT 1. Changes in RR and Breathing Effort: Question - Why do infants “tire out?” 2. Changes in lung exam (stridor, wheeze, etc.) 3. Cyanosis – definition? Flushing, tachycardia, HA, confusion – seen with acute hypercarbia Mental Status

7. Chronic Hypoxemia/Hypercarbia Clinical signs/lab evidence of chronic hypoxia: -- Clubbing – seen with chronic hypoxemia -- What might you see on abdominal exam? -- Labs: Polycythemia Lab evidence of hypercarbia

8. Hypoxic Hypoxemia: How to Diagnose Pulse oximetry – How does it work? What are its limitations? Arterial Blood Gas – What information does this provide that pulse-ox does not?

9. Pulse-oximetry: How does it work? Current pulse-ox machines measure 2 types of light: red (wavelength=660 nm) and infrared (wavelength= 940 nm) Red light is better absorbed by deoxy-Hgb, infrared light is better absorbed by oxy-Hgb, so the ratio gives you the SaO2

10. Pulse-oximetry Problems 1. Doesn’t work well with poor perfusion 2. Other light sources (Ex. phototherapy light) can interfere with the results 3. Abnormal Hgb can lead to overestimation of a true SaO2 (specifically carboxy-, and metHgb) What laboratory test do you order in someone with met- or carboxy-hgb

11. Arterial Blood Gas and Oxygenation ABG – can give you carboxy and metHgb levels (if you ask); will give you co-oximetry values (multiple wavelengths measured) -- will also give you a PaO2 which can help you diagnose a patient with hypoxemic hypoxia using an equation called ………..

12. Alveolar Gas Equation PAO2 = FIO2(PB-PH2O) – PCO2/R • PAO2 = Alveolar oxygen partial pressure • FIO2 = fraction of inspired oxygen • PB = barometric pressure (760 mm Hg at sea level) • PH2O = partial pressure of water vapor (47 mm Hg) • PCO2 = partial pressure of CO2 • R = respiratory quotient (usually ~ 0.8)

13. Alveolar Gas Equation So at room air at sea level, your PAO2 should be 100 On 100% FIO2 at sea level, your PAO2 should be 663 The difference between Alveolar (PAO2) and arterial (PaO2) oxygen is called the A-a gradient and should be less than 20; this will help you figure out if this is hypoxic hypoxemia and the degree of hypoxia

14. Given a PaO2, what is the SaO2 (and vice-versa) Curve moves to right with • Lower pH • Higher Temperature • Increased 2,3 DPG

15. Hypercarbic Respiratory Failure: Who cares about CO2 and pH? What makes you breathe? Primarily pH (can be PaO2 in some patients) What happens to you if you are too alkalotic or acidotic? Acidosis: AMS, impaired cardiac contractility, pulmonary vasoconstriction, metabolic abnormalities, etc. Alkalosis: tetany (sec. to decreased iCa), arrhythmias, etc. Does it matter what the source of the altered pH is? Yes. For example: metabolic acidosis is worse for you than respiratory acidosis.

16. Arterial Blood Gas, pH, and Ventilation pH < 7.35 with high CO2: respiratory acidosis pH > 7.35 with high CO2: compensated respiratory acidosis pH < 7.35 with low bicarb: metabolic acidosis pH > 7.35 with low bicarb: compensated metabolic acidosis What is a base deficit?

17. Base Deficit Given a normal pCO2, how much base would be needed to correct the pH. Ex. 7.35/28/80/-15

18. Arterial Blood Gas, pH, and Ventilation pH > 7.45 with low CO2: respiratory alkalosis pH < 7.45 with low CO2: compensated respiratory alkalosis pH > 7.45 with high bicarb: metabolic alkalosis pH < 7.45 with high bicarb: compensated metabolic alkalosis

19. How to Approach an ABG First – Is this an arterial or venous blood gas? Second - does the patient have an acidosis or an alkalosis • Look at the pH Third, what is the primary problem – metabolic or respiratory • Look at the pCO2 • If the pCO2 change is in the opposite direction of the pH change, the primary problem is respiratory • You never overcompensate

20. How to Approach an ABG Next, don’t forget to look at the effectiveness of oxygenation, (and look at the patient) • your patient may have a significantly increased work of breathing in order to maintain a “normal” blood gas • metabolic acidosis with a concomitant respiratory acidosis is concerning

21. Case 1 Sameer got into some of Dad’s barbiturates. He suffers a significant depression of mental status and respiration. You see him in the ER 3 hours after ingestion with a respiratory rate of 12. A blood gas is obtained. It shows pH = 7.16, pCO2 = 70, HCO3 = 22

22. Case 1 What is the acid/base abnormality? 1. Uncompensated metabolic acidosis 2. Compensated respiratory acidosis 3. Uncompensated respiratory acidosis 4. Compensated metabolic alkalosis

23. Case 2 You are evaluating a 15 year old female in the ER who was brought in by EMS from school because of abdominal pain and vomiting. Review of system is negative except for a 10 lb. weight loss over the past 2 months and polyuria for the past 2 weeks. She has no other medical problems and denies any sexual activity or drug use. On exam, she is alert and oriented, afebrile, HR 115, RR 26 and regular, BP 114/75, pulse ox 95% on RA.

24. Case 2 Exam is unremarkable except for mild abdominal tenderness on palpation in the midepigastric region and capillary refill time of 3 seconds. The nurse has already seen the patient and has sent off “routine” blood work. She hands you the result of the blood gas. pH = 7.21 pCO2=24 pO2 = 45 HCO3 = 10 BE = -10 saturation = 72%

25. Case 2 What is the blood gas interpretation? 1. Uncompensated respiratory acidosis with severe hypoxia 2. Uncompensated metabolic alkalosis 3. Combined metabolic acidosis and respiratory acidosis with severe hypoxia 4. Metabolic acidosis with respiratory compensation

26. Case 3 10 year old with history of ALL and neutropenia presents with tachypnea. He has no O2 requirement but is breathing 30 – 40 times/minute. Lung exam (other than the tachypnea) is normal. CXR shows no infiltrate. An ABG is done: 7.45/30/90/22 on room air. Does this patient need a bronchoscopy to diagnose his respiratory compromise? Why or why not?

27. Case 3 Answer: No; This is a trick question because he doesn’t have respiratory compromise The patient is tachypneic for some other reason than acidosis, hypercarbia, or hypoxia (i.e. increased intracranial pressure, burgeoning sepsis, etc)

28. Other Laboratory Findings in ARF CXR Abnormalities Complete Blood Count (look at WBC and Hgb, which may suggest chronic hypoxia) Electrolyte Abnormalities (look at bicarbonate)

29. Foreign Body Aspiration

30. Right Lung Atelectasis

31. Left Lung Pneumonia with Effusion

32. Pneumothorax

33. ARDS (Bilateral Infiltrates)

35. Flail Chest

36. A Case of Hypoxia 4 yo presents to the ER with fever and cough. On examination, the patient has the following vital signs: T 39.9, P 130, RR 32, O2 sats 87-90% on RA, Nl BP’s PE: Lungs – tachypneic with good breathing effort, clear lung sounds, Cardiac -- 2/6 SEM at LSB, good pulses in all extremities Extremities -- mild clubbing of fingers and toes Labs: WBC ct = 9.6, H/H = 14/41, platelets = 192k Elytes normal except bicarbonate = 20; LFT’s Nl except AP = 358 CXR showed normal sized heart, possible infiltrate in hilar area Patient is admitted to the hospital with a diagnosis of pneumonia and is started on appropriate abx and supplemental oxygen. He defervesces after 24 hours but still has O2 saturations in the low 90’s that increase to mid-90’s on 4L NC. Physical exam remains the same and the repeat CXR is negative. What is the cause of his hypoxia?

37. Clinical Scenario Decreased O2 Availability? No Decreased Air Entry? No V/Q Mismatches? Possible Shunt? Possible Diffusion Problems? Possible What lab test do you want to prove this?

38. Clinical Scenario Arterial Blood Gas: ABG on RA: 7.27 / 57 / 52 ABG on 100% O2: 7.29 / 60 / 69 What should his PaO2 be on RA and 100% FIO2? RA = 78.5 100% FIO2 (through NRB) > 353 Do these ABG’s confirm our suspicions about V/Q mismatch, shunt, or diffusion abnormalities? What role does the high pCO2 play? Now what tests do you want?

39. Clinical Scenario Echocardiogram = no lesions Chest CT = loss of volume in the LLL with small consolidation, patchy atelectasis of right lung; enlarged caliber of the pulmonary vasculature in the dependent lung zones; rapid injection of contrast showed early filling of the pulmonary veins Ventilation/perfusion scan = normal ventilation; no segmental defects in perfusion So, what test was done to get a diagnosis? Answer: Liver biopsy that confirmed the diagnosis of hepatopulmonary syndrome

40. ARF -- Treatment Monitoring • invasive (ABG, PAC) or noninvasive (pulse-oximeter) Prevention • Encourage coughing, frequent position changes, reflux precautions, decompress abdomen, etc.

41. ARF -- Treatment Surgical: Thoracostomy tubes Medications: • b-agonists • Anticholinergics • Anti-inflammatory agents (steroids, NSAIDS) • Surfactant • Nitric Oxide

42. ARF -- Treatment O2 Delivery Systems: Low vs. High Flow Low Flow: • Nasal Cannula: FIO2 < 40% (1L/min ~ 3%) • Blow-by O2 High Flow: • Head Hood: Flow >10 l/min • Venturi Face Masks: FIO2 ~ 50% • Nonrebreather Mask: FIO2 ~ 80-100% • Bag-Mask-Valve Units: FIO2 ~ 100%

43. ARF -- Treatment Continuous or Bilevel Positive Pressure (CPAP or BIPAP) -- applied through a tight-fitting mask Best applied in an awake, cooperative patient who is expected to improve in 48-72 hours.

44. ARF – Treatment with Mechanical Ventilation Always Remember: Bag-mask ventilation is an effective method to oxygenate patients: use BMV if conditions are not ideal for intubation Mechanical Ventilation: Indications • Airway Protection • Respiratory Failure • Shock • Treatment of Intracranial Hypertension • Other (for procedures, pulmonary toilet, etc.)

45. Mechanical Ventilation: Modes AC – assist control • no spontaneous breaths • delivers full breath with any ventilator and patient initiated effort SIMV -- synchronized intermittent mandatory ventilation • ventilator breaths synchronized with patient’s own breaths • weaning mode

46. Mechanical Ventilation: Modes Pressure Ventilation (Control) • the size of the breath is determined by the pressure that is set • the tidal volume then depends on the lung compliance (it is the dependent variable) Volume Ventilation (Control) • the size of the breath is determined by the volume that is set • the pressure is the dependent variable

47. Mechanical Ventilation: Goals Your goals for gas exchange when a patient is on a ventilator must not be so rigid as to cause further injury to the lung when trying to obtain them. Oxygenation is more important than ventilation You should try to keep the FIO2 < 60%, the PIP < 35-40 cm H20, and the TV ~6-8 cc/kg

48. Mechanical Ventilation: Terminology Mean Airway Pressure (MAP): the average pressure over a respiratory cycle, measured at the proximal airway Peak Inspiratory Pressure (PIP): the maximum amount of pressure needed to deliver a breath Positive End Expiratory Pressure (PEEP): pressure applied at the end of exhalation I time: total time spent during inspiration

49. Mechanical Ventilation: Terminology Tidal Volume: the size (volume) of the breath • goal ~ 6-10 cc/kg Minute Ventilation: total volume of air inspired in one minute Compliance: relationship of volume to pressure • C = DV / DP

50. Mechanical Ventilation Oxygenation • determined by FIO2 and Mean Airway Pressure • MAP is determined by PEEP, PIP, and inspiratory time (I time) Ventilation • determined by rate and TV • rate x TV = MV