RESPIRATORY FAILURE Mohammad Rezaei Fellowship of Pediatric Pulmonology

RESPIRATORY FAILURE Mohammad Rezaei Fellowship of Pediatric Pulmonology

Respiratory distress � Respiratory impression distress is a clinical

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 � PAO 2 = PIO 2 – (PCO 2/R) � PIO 2 = (BP – PH 2 O). Fio 2 � PAO 2 = [(BP – PH 2 O). Fio 2] – (PCO 2/R)

Hypoventilation � VA = � low VT. RR respiratory rate and shallow breathing are both signs of hypoventilation.

Dead Space Ventilation Anatomical � Physiological � VD/ VT = (Pa. CO 2 -PECO 2)/ Pa. CO 2 = 0. 33 Increases in decreased pulmonary perfusion: PHTN, hypovolemia, decreased cardiac output

Alveolar Ventilation VA = (VT-VD). RR

Hypoventilation � The Paco 2 increases in proportion to a decrease in ventilation. � Pao 2 falls approximately the same amount as the Paco 2 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 CO 2 retention might have a near normal oxygen saturation.

When Paco 2 increases from 40 to 70 mm Hg, a dangerous level of hypoventilation, might have a Pao 2 that has decreased from 100 to 60 mm Hg and, therefore, maintain an oxygen saturation of 90%. 1. PO 2 100 mm Hg= Sp. O 2 of 97% 2. PO 2 60 mm Hg= Sp. O 2 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 Paco 2 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 Limitation 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 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

CRF is seen most commonly in children who have: � Respiratory muscle weakness (muscular dystrophy, anterior horn cell disease) or � severe chronic lung diseases (BPD, endstage 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