Respiratory Failure and Mechanical Ventilation P Vorrakitpokatorn Respiratory

Respiratory Failure and Mechanical Ventilation P. Vorrakitpokatorn

Respiratory Function Maintain Adequate Oxygenation and Ventilation : drive : pump : gas exchange

Respiratory Failure Definition: Inability to maintain • Oxygenation • Ventilation(pump)

Dx: RESPIRATORY FAILURE 2/4 of • OXYGENATION…. Pa. O 2<60 mm. Hg • VENTILATORY …. Pa. CO 2>50 mm. Hg • p H<7. 3 • DYSPNEA

�������� of Respiratory failure Stimulation and then depression

Central cyanosis: hypoxemia

Hypercarbia: vasodilatation, warm moist slow capillary refilled> 3 seconds

The tripod sign used to describe the classic position of a person desperate for more air:

RESPIRATORY FAILURE : Classification • Type 1. Oxygenation failur • type 2. Ventilatory failure • and mixed type

������ hypoxemia (A-a)O 2 normal (A-a)O 2 Increase ������������������ ������ Diffusion defect • Decrease Fi. O 2 V/Q mismatch • CO 2 retention True shunt Delivery≠demand

Alveolar Air Equation PAO 2= Fi. O 2 (PB-PH 2 O) - PAO 2/ R R = 0. 8 …… Fi. O 2 < 0. 6 R = 1. 0 …… Fi. O 2 ≥ 0. 6

������ Oxygenation failure : A. normal (Aa)O 2, Fi. O 2. . . … A 1. Decrease Fi. O 2 PAO 2 CO 2 PA O 2 Pa. O 2 A 2. CO 2 retention

������ Oxygenation failure B. high (A-a)O 2 PA O 2 PAO 2 Pa. O 2 B 1. Diffusion defect B 2. V/Q mismatch B 3. Shunt.

��� MV-O 2 ������� Pa. O 2 �������� decrease CO Increase used PAO 2 Pa. O 2 80% SUPPLY. … P C O 2 100 %…. . . Shunt blood Tissue O 2 DEMAND organs MV-O 2 75%

(A-a)O 2 = 20 at room air (A-a)O 2 = 100 at FIO=1 Hypoxemia (A-a)O 2? (A-a)O 2 normal • How much Pa. CO 2? • How much FIO 2?

Hypoxemia : differential diagnosis (A-a)O 2��� PV-O 2 • RS • Delivery MV-O 2 ���� : resp system Gas exchange abnormal • Diffusion • V/Q • shunt • demand Hypoxemia (A-a)O 2 MV-O 2 ��� Delivery≠demand • CVS • increase metabolism

Hypoxemia (A-a)O 2��� PV-O 2 ���� Gas exchange abnormal Not response to increase Fi. O 2 True shunt Response to increase Fi. O 2 • Diffusion defect • V/Q mismatch

Diffusion defect: • response to oxygen therapy • Worse if inadequate time to exchange as tachycardia Abn diffusion ������ Pa. O 2 ���� second ������

������� CO 2 �� VA = Effective alveolar ventilation

Pa CO 2= CO 2 production /effective ventilation CO 2 Tissue metabolism

Effective Tidal volume Breath VT = Vd + Alv ventilation Vd = ventilate but not perfuse ��������

Deadspace ventilation and CO 2 retention

Ineffective alveolar ventilation : too large dead space Dead space 1 VT

Dead space

Hypercarbia: differential diagnosis (A-a)O 2 ��� RS, Delivery≠demand Hypercarbia ( A-a)O 2 ����� Minute ventilation (MV) MV���� CNS or neuromuscular • Depress rc: PIMax ������ • Pump abn: PIMax ��� MV ���� • Ineffective ventilation (airway obstruction, vd) • ��������� • CO 2 contamination

Obstructive sleep apnea Airway obstruction

Hypercarbia: differential diagnosis (A-a)O 2 ��� Severe gas exchange failure Hypercarbia ( A-a)O 2 ����� Minute ventilation (MV) MV���� CNS or neuromuscular • Depress rc: PIMax ������ • Pump abn: PIMax ��� MV ���� • Ineffective ventilation (airway obstruction, vd) • ��������� • CO 2 contamination

FO 2 Severity of gas exchange defect Pa. O 2/Fi. O 2>200 ~ shunt <20% Spontaneous resp_increase Fi. O 2 Pa. O 2/Fi. O 2 = 150 -200 ~ shunt >20% Need IPPV especially in CVS, CNS patients Pa. O 2/Fi. O 2 <150 ~ shunt >30% IPPV+ SPECIAL CARE

. 2 Inadequate Ventilation : PARAMETERS NORMAL IPPV needed Pa. CO 2 40 50 p. H 7. 4 7. 3 ������� /���� 12 -24 < 8, >30

������� . 3 Inadequate lung expansion : ������� PARAMETERS NORMAL VT �� /�� 6 -8 Vital Capacity �� /�� 65 -75 IPPV <5 < 10

����������� + oxygen supplement RMild oxygenation, ventilation, mechanic failure RRC intact RVt>5, <15 ml/kg Rrespiratory rate >8, <30

������� • CNS. . ��������� • CVS…. �� venous return ������ • RS…. ����� oxygenation, ventilation, barotrauma • Renal…. �� urine out-put ������� • GI…. . Abdomen distention, stress ulcer • Psychic trauma • Infection