Lecture Notes

Chapter 2: Introduction to Respiratory Failure

Objectives

Define respiratory failure, ventilatory failure, and

oxygenation failure

List the causes of respiratory failure

Describe the effects of respiratory failure on the

lung, heart, and other body systems

Recognize the clinical features associated with

respiratory failure

Describe the treatment of respiratory failure

Introduction

Respiratory failure

Failure of the lungs to provide adequate

oxygenation or ventilation

Oxygenation failure

PaO2 < 60 mm Hg at FiO2 > .50

Ventilatory failure

Inadequate ventilation between the lungs and

atmosphere that results PaCO2 > 45 mm Hg

Introduction

The amount of oxygen consumed and CO2

produced each minute is dictated by the

metabolic rate of the patient.

Exercise and fever are examples of factors that

increase the metabolic rate

Patients with acute respiratory failure have

inadequate oxygenation of the arterial blood or

elevation of CO2 levels or both.

Etiology: Oxygenation Failure

Hypoxemia has potentially serious consequences

because it can lead to inadequate tissue oxygenation

(hypoxia).

Tissue hypoxia of the heart complicates the problem by

causing dysrhythmias and poor contractility.

V/Q mismatch Hypoxemia

Mild: PaO2 60–79 mm Hg

Moderate: PaO2 40–59

mm Hg

Severe: PaO2 < 40 mm Hg

Shunt is the movement of blood from

the right side of the heart to the left side

of the heart without coming into contact

with ventilated Alveoli

Anatomical congenital heart defect

Physiologic collapsed or unventilated

alveoli

Etiology: Ventilatory Failure

Depression of respiratory centers by drugs

Cerebral disease

Spinal cord abnormalities

Muscular disease

Thoracic cage abnormalities

Upper and lower airway obstruction

Malnutrition and electrolyte disturbances

Pathophysiology: Oxygenation

Failure

Patient’s response to hypoxemia depends on

Pre-existing condition (cardiopulmonary patient,

healthy).

Severity of hypoxemia

Tachypnea and tachycardia are the most

common responses

Pathophysiology: Oxygenation

Failure

Increased right ventricular workload

Right ventricular failure

Increased pulmonary vascular resistance

Cor pulmonale abnormal enlargement of the right side of the heart as a result of disease of the lungs or the pulmonary blood vessels

Hypoxemia stimulates the pulmonary capillaries to constrict in the affected

regions.

pulmonary vasoconstriction Increase pulmonary vascular resistance

(PVR)

Cardiac muscles contraction and rate are increased as result of hypoxemia

which is can lead to ischemia and irreversible damage (infarction).

Pathophysiology: Ventilatory

Failure

e.g. Drug overdose

Change in respiration

Acidosis

Elevated PaCO2

Ventilatory failure is defined as a change in respiration resulting in an

elevated PaCO2.

Clinical Features: Oxygenation

Failure

Physical exam

Central cyanosis

Tachycardia, tachypnea, hypertension

Altered mental status

PVCs

Cor pulmonale: hepatomegaly, JVD, pedal

edema

Clinical Features: Oxygenation

Failure

Laboratory abnormalities

Low PaO2

Low SaO2

Low CaO2

Polycythemia if chronic

Chest radiograph

Often normal if extrapulmonary cause

Clinical Features: Ventilatory

Failure

Clinical findings (nonspecific)

Headache

Diminished alertness

Warm and flushed skin

Bounding peripheral pulses

Hypothermia and altered mental status = drug OD

Tachycardia and hypertension = tricyclics

Respiratory alternans or abdominal paradox = diaphragmatic fatigue

Clinical Features: Ventilatory

Failure

Laboratory abnormalities

High PaCO2

Acidosis

Elevated total CO2 on electrolyte panel

Treatment: Oxygenation Failure

Supplemental oxygen (V/Q mismatching)

Positive pressure ventilation-CPAP (shunt)

If PaO2 < 60 mm Hg at FiO2 > .50

Mechanical ventilation

If mask CPAP unsuccessful

Treatment: Ventilatory Failure

Mechanical ventilation

VT 5–10 ml/kg IBW

Keep Pplateau < 35 cm H2O

Respiratory rate according to age and metabolic

rate

FiO2 adjusted with pulse oximetry

Treatment: Ventilatory Failure

Weaning criteria

Etiology of ventilatory failure resolved

Patient’s condition stable and improving

Vital capacity > 10–15 mL/kg

Resting minute volume < 10 L/min

MIP > -20 cm H2O

Adequate oxygenation on FiO2 < .50

Spontaneous respiratory rate < 35 breaths/min

Spontaneous tidal volume > 325 mL

Treatment: Ventilatory Failure

Weaning methods

IMV

Decrease number of mechanical breaths until support is no longer necessary

Pressure Support

Set to acceptable tidal volume and rate without use of accessory muscles and wean thereafter

T-Piece

Temporary discontinuation of mechanical ventilation

“Blow-by” of appropriate FiO2