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Mohammad Rezaei Fellowship of Pediatric Pulmonology

Respiratory distress  Respiratory distress is a clinical impression

Respiratory failure  inability of the lungs to provide sufficient oxygen (hypoxic respiratory failure) or remove carbon dioxide (ventilatory failure) to meet metabolic demands.

Respiratory failure  Pao 2 < 60 torr with breathing of room air and  Paco 2 > 50 torr resulting in acidosis,  the patient's general state, respiratory effort, and potential for impending exhaustion are more important indicators than blood gas values.

 Respiratory distress can occur in patients without respiratory disease, and  respiratory failure can occur in patients without respiratory distress.

Respiratory failure  Acute  Chronic

The physiologic basis of respiratory failure determines the clinical picture.  normal respiratory drive are breathless and anxious  decreased central drive are comfortable or even somnolent.

The causes:  conditions that affect the respiratory pump  conditions that interfere with the normal function of the lung and airways

Respiratory Pump Dysfunction ● Decreased Central Nervous System (CNS) Input  — Head injury  — Ingestion of CNS depressant  — Adverse effect of procedural sedation  — Intracranial bleeding  — Apnea of prematurity ● Peripheral Nerve/Neuromuscular Junction  — Spinal cord injury  — Organophosphate/carbamate poisoning  — Guillian-Barre´ syndrome  — Myasthenia gravis  — Infant botulism ● Muscle Weakness  — Respiratory muscle fatigue due to increased work of breathing  — Myopathies/Muscular dystrophies

Airway/Lung Dysfunction ● Central Airway Obstruction  — Croup  — Foreign body  — Anaphylaxis  — Bacterial tracheitis  — Epiglottitis  — Retropharyngeal abscess  — Bulbar muscle weakness/dysfunction ● Peripheral Airways/Parenchymal Lung Disease  — Status asthmaticus  — Bronchiolitis  — Pneumonia  — Acute respiratory distress syndrome  — Pulmonary edema  — Pulmonary contusion  — Cystic fibrosis  — Chronic lung disease (eg, bronchopulmonary dysplasia)

Arterial gas composition depends on :  the gas composition of the atmosphere  the effectiveness of alveolar ventilation  pulmonary capillary perfusion  diffusion across the alveolar capillary membrane

Alveolar Gas Composition  P A O2 = P I O2 – (PCO2/R)  P I O2 = (BP – P H2O ). Fio2  P A O2 = [(BP – P H2O ). Fio2] – (PCO2/R)

Hypoventilation  V A = V T. RR  low respiratory rate and shallow breathing are both signs of hypoventilation.

Dead Space Ventilation  Anatomical  Physiological V D / V T = (P a CO2-P E CO2)/ P a CO2 = 0.33 Increases in decreased pulmonary perfusion: PHTN, hypovolemia, decreased cardiac output

Alveolar Ventilation V A = (V T -V D ). RR

Hypoventilation  The Paco2 increases in proportion to a decrease in ventilation.  Pao2 falls approximately the same amount as the Paco2 increases.

Hypoventilation  The relationship between oxygenation and hypoventilation is complicated by the shape of the Hb-dissociation curve  Because of the dissociation curve, a patient who exhibits alarming CO2 retention might have a near normal oxygen saturation.

1. PO2 100 mm Hg= SpO2 of 97% 2. PO2 60mm Hg= SpO2 of90% When Paco2 increases from 40 to 70 mm Hg, a dangerous level of hypoventilation, might have a Pao2 that has decreased from 100 to 60 mm Hg and, therefore, maintain an oxygen saturation of 90%.

Thus: oximetry is not a sensitive indicator of the adequacy of ventilation. This is particularly true when a patient is receiving oxygen.

Lung/Airway Disease  Diseases of the lung or airways affect gas exchange most often by disrupting the normal matching of V/Q or by causing a shunt.  usually can maintain a normal Paco2 as lung disease worsens simply by breathing more.  hypoxemia is the hallmark of lung disease

Ventilation-Perfusion Mismatch

 hypoxemia due to V/Q mismatch &  hypoxemia due to shunt administering Oxygen

Intrapulmonary Shunt

Diffusion  diffusion defects manifest as hypoxemia rather than hypercarbia.  Examples : interstitial pneumonia, ARDS, Scleroderma, Pulmonary lymphangiectasia,…

Monitoring a Child in Respiratory Distress and Respiratory Failure

Clinical Examination  Clinical observation is the most important component of monitoring.

ABG & Oximetry  ABG /CBG/ VBG  Oximetry - Oximetry provides an invaluable and usually accurate measurement of oxygenation. - important to recognize its technical limitations

ConditionLimitation Dark skin pigment Anemia Causes inadequate signal Bright external light Motion Decreased perfusion Venous pulsations — Severe right heart failure — Tricuspid regurgitation — Tourniquet or blood pressure cuff above site Results in low reading Abnormal hemoglobin concentration — Methemoglobin Unreliable reading (tends to read 80% to 85% saturation regardless of actual saturation) — SS hemoglobin Saturationaccurate, but hemoglobin dissociation curve shifted to right — CarboxyhemoglobinSpuriously high saturation readings

Acute Respiratory Failure

ARF  most common cause of cardiac arrest in children. When presented with a child who has:  a decreased level of consciousness,  slow/shallow breathing, or increased  respiratory drive, the possibility of ARF should be considered

First:  to assure adequate gas exchange and circulation (the ABCs).  Oxygen Administration to maintain ….  If Ventilation is or appears to be inadequate …..  Intubation ? Need ICU

Chronic Respiratory Failure

CRF is seen most commonly in children who have:  Respiratory muscle weakness (muscular dystrophy, anterior horn cell disease) or  severe chronic lung diseases (BPD, end- stage cystic fibrosis)

 usually has an insidious onset  Most children do not have dyspnea.  PH normal or near normal, unless…..  Recognizing need careful monitoring of children at risk for CRF

 Disordered sleep  Daytime hypersomnolence  Morning headaches  Altered mental status  Increased respiratory symptoms  Cardiomegaly  Decreased baseline oxygenation  CRF often presents first during sleep  Develops an intercurrent illness, Fever