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RESPIRATORY FAILURE

Mohammad RezaeiFellowship 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

Pao2 < 60 torr with breathing of room air and Paco2 > 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

PAO2 = PIO2 – (PCO2/R)

PIO2 = (BP – PH2O) . Fio2 PAO2 = [(BP – PH2O) . Fio2] – (PCO2/R)

Hypoventilation VA = VT . RR

low respiratory rate and shallow breathing are both signs of hypoventilation.

Dead Space Ventilation

Anatomical Physiological

VD/ VT = (PaCO2-PECO2)/ PaCO2 = 0.33

Increases in decreased pulmonary perfusion: PHTN, hypovolemia, decreased cardiac output

Alveolar Ventilation

VA = (VT-VD). 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

Condition LimitationDark skin pigmentAnemia Causes inadequate signalBright external lightMotion

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 read80% to 85% saturation regardless of actual saturation)

— SS hemoglobin Saturation accurate, but hemoglobin dissociation curve shifted to right

— Carboxyhemoglobin Spuriously 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

CRFis 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