Acute Respiratory Failure

Yoon Jung Oh,M.D.

Departments of Pulmonary and Critical Care MedicinAjou University School of Medicine

Hypoxemic respiratory failure PaO2 < 55 mmhg , FiO2 ≥ 0.6• Acute : develops in min to hr• Chronic : develops over several days or longer

Hypercapnic respiratory failure PaCO2 > 45 mmHg • Acute : develops in min to hr( pH < 7.3)• Chronic : develops over several days or longer

Hypercapnic and hypoxemic respiratory failure coexist.

Definition

Acute Respiratory Failure

PaCO2 < 45 mmHgType 1 respiratory failure

PaCO2 > 45 mmHgType II ventilatory failure

CXRCXR Black• acute pulmonary embolism• vascular obstruction• R-L shunt

WhiteDiffuse• ARDS• Pulmonay edema• Pulmonary fibrosisLocalized• Pneumonia• atelectasis

Black• COPD• Status asthmaticus• Alveolar hypoventilation• Drug overdose• Neuromuscular disease

WhiteDiffuse• ARDS• Pulmonary edema• Pulmonary fibrosisLocalized• Pneumonia + COPD• Drug overdose

ABGA

Ventilatorysupply

Ventilatorydemand

Ventilatory supply exceeds ventilatory demand.

Ventilatorysupply

Ventilatorydemand

Ventilatory supply equals ventilatory demand.

Ventilatorysupply

Ventilatorydemand

Ventilatory demand exceeds ventilatory supply.

A

B

C

TABLE 165-3 Factors That Increase Ventilatory Demand

Factors Clinical Examples

Increased VD/VT

Increased Vo2

Increased RQ

Decreased Pa CO2

Acute asthma, emphysema, late phase of acute respirat

ory distress syndrome, pulmonary emboli

Fever, sepsis, trauma, shivering, increased work of brea

thing, massive obesity

Excessive carbohydrate feeding

Hypoxemia, metabolic acidosis, anxiety, sepsis, renal fa

ilure, hepatic failure

SOURCE: Data from Lanken. 23

TABLE 165-2 Factors That Diminish Ventilatory Supply

Factors Examples

Decreased respiratory muscle strength Muscle fatigue

Disuse atrophy

Malnutrition Electrolyte abnormalities Arterial blood gas abnormalities Fatty infiltration of diaphragm Unfavorable alteration in diaphragm length-tension relationshipIncreased muscle energy requirement or decreased substrate supply High elastic work of breathing High resistive work of breathing Reduced diaphragm perfusionDecreased motor neuron function Decreased phrenic nerve output

Decreased neuromuscular transmissionAbnormal respiratory mechanics Airflow limitation Loss of lung volume Other restrictive defects

Recovery from acute respiratory failure, high respiratory rates, increased Pdi/Pdimax,* increased inspiratory timeProlonged mechanical ventilation, following phrenic nerve injuryProtein-calorie starvationLow serum phosphate or potassium concentrationsLow pH, low PaO2, high PaCO2

ObesityFlattened domes of diaphragm caused by hyperinflation

Low lung or chest wall compliance, high respiratory rate Airway obstructionShock, anemia

Polyneuropathy, Guillain-Barré syndrome, phrenic nerve transection or injury, poliomyelitisMyasthenia gravis, use of paralyzing agents

Bronchospasm, upper-airway obstruction, excessive airway secretionsAfter lung resection, large pleural effusionPain-limited inspiration; tense abdominal distention due to ileus peritoneal dialysis fluid, or ascites

Hypoxemic Respiratory Failure

Alveolar hypoventilatio

n

Drug overdose Normal D(A-a)O2, PaCO2 > 40 mmHg

V/Q mismatching

COPD, asthma Corrected by oxygen

R-L shunt ARDS, pneumonia Not corrected by oxygen

Diffusion disturbance

Interstitial disease Same to V/Q mismatching

Low FiO2 High altitude Normal D(A-a)O2

Pathophysiology(1)

Hypercapnic Respiratory Failure

↓Alveolar ventilation Central-drug overdose,NM drug, flail chest, COPD, asthma

↑ Anatomic/physiologic dead space(Vd/Vt)

COPD, ARDS,bronchospasm

↑ CO2 production fever,sepsis,burn,infection,exercise, hyperalimentation

Pathophysiology(2)

Hx : 3 년전 bronchial asthma 진단받았으며 3 일전 URI 후 악화된 호흡곤란을 주소로 내원 . ABGA : pH 7.5 PaO2 50 mmHg, PaCO2 30 mmHg HCO3 22 mmol/L at room air O2 5 L/min PaO2 65 mmHg

P/E : RR 30/min, use of accessory muscle wheezing on whole lung field

CXR : hyperinflation

Case 1.1 F/30

Acute hypoxemic respiratory failure

due to acute exacerbation of asthma

Diagnosis 1.

병동에서 치료중 호흡곤란을 계속 호소함 .

ABGA : pH 7.4 PaO2 65 mmHg PaCO2 40 mmHg

O2 sat 92%

Case 1.2

Case 1.3

다음날 아침 , 밤새 호흡곤란으로 한숨도 자지 못했다하며

지속적인 호흡곤란을 호소함 .

ABGA : pH 7.35 PaO2 60mmHg PaCO2 50mmHg

O2sat 90%

Case 2. F/19

남자친구와 다툰 후 수면제 100 알을 복용후 응급실로 내원 .

ABGA : pH 7.25 PaO2 60mmHg PaCO2 70mmHg

HCO3 27 mmol/L O2sat 90%

Acute hypercapnic respiratory failure

due to drug overdose

Diagnosis 2

50 pack year smoker, 평소 100m 정도 걸으면 심해지는 DOE 있었으며 최근 감기앓은 후 fever,cough,dyspnea 로 내원 .

P/E : RR 28/min wheezing on whole lung field

ABGA : pH 7.4 PaO2 50 mmHg PaCO2 50 mmHg

HCO3 28 mmol/L O2sat 85% at room air

Nasal O2 투여후 O2 sat 92% 로 증가

Case 3.1 M/67

Chronic obstructive pulmonary disease ( Emphysema )

Diagnosis 3.1

응급실에서 산소를 투여한지 4 시간 후 , 환자가 헛소리를

하고 자꾸 자려고만 한다고 보호자가 호소함 .

ABGA : pH 7.2 PaO2 80 mmHg PCO2 90 mmHg

nasal O2 5L/min

Case 3.2

Acute hypercapnic respiratory failure

CO2 narcosis

Diagnosis 3.2

CNSEfferentsCNSEfferents

Effector Components

Perepheral Nerves

Perepheral Nerves

Repiratory m.Chest wall

Repiratory m.Chest wall

AirwayAlveoliAirwayAlveoli

AfferentIntegration

In CNS

AfferentIntegration

In CNS

Chemo-receptorsChemo-receptors

PaO2PaCO2PaO2

PaCO2VA, VEVA, VE

Failed respiratory component pH PaCO2 PaO2 P(A-a)O2 VE VA

Central nervous system ↓ ↑ ↓* NL or ↑# ↓ ↓

Peripheral nervous system or chest wall

↓ ↑ ↓* NL or ↑# ↓ ↓

Airways In acute asthma

Early phase(before respiratory failure)

↑ ↓ NL ↑ ↑ ↑

“Crossover point” NL NL NL or ↓

↑ ↑ NL

With respiratory muscle fatigue

↓ ↑ ↓ ↑ ↓$ ↓$

*PaO2 may decrease when pneumonia or atelectasis occurs as a complication#P(A-a)O2 widens when pnumonia or atelectasis occurs as a complication$VE declines when frank respiratory muscle failure occurs.

Failed respiratory component

pH PaCO2 PaO2 P(A-a)O2 VE VA

In COPD

Non-CO2 retainer ↓ NL or ↑& ↓ ↑ ↑ ↓

CO2 retainer

Basseline NL or ↓ ↑ ↓ ↑ NL or ↑ ↓

Flare ↓ ↑ ↑ ↓ ↓ ↑ NL or ↑Or ↓

↓

Alveoli

Before resp. m. fatigue ↑ ↓ ↓ ↓ ↑ ↑ ↑ ↑

After resp.m. fatigue ↓ ↑ ↓ ↓ ↑ ↑ ↓ ↓

&PaCO2 may increase during an exacerbation

• Correct hypoxemia/respiratory acidosis

• Patent upper airway

• Adequate ventilation

• Supplemental oxygen

Treatment of Acute Respiratory Failure

• Increase VA

• Bronchodilator

• Control of infection

• Oxygen therapy

Treatment of Respiratory Failure

To decrease VCO2

• Antipyretics

• Cooling blanket

• Decrease muscle activity

To increase VA

• Prevent airflow obstruction

• Respiratory training

• Intubation & mechanical ventilation

• Cautious administration of sedatives

Ventilatory Failure