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Respiratory failure :airplane_departure: (:tokyo_tower:Introduction (:!:…
Respiratory failure
:airplane_departure:
:tokyo_tower:
Introduction
:!: Respiratory
distress
≠ Respiratory
failure
Primary Dx for ~50%
of children admitted to PICUs
Common cause
of cardiopulmonary arrests in children
Normally we check Oxygenation by looking at
O2 saturation
ABG to confirm
:!: Note that VBG (venous) & CBG (capillary blood gas) can't check
PaO2
[
only ABG can
]
:kiwifruit:
Definition
Acute RF occurs when Pulmonary system
no longer able to meet the metabolic demands of body
:banana:
Types
Type :one: respiratory failure
or
Hypoxemic
respiratory failure
or
Oxygenation
failure
PaO2
≤ 60 mmHg (SaO2 < 90%)
in room air
usu.
low PCO2
due to
hypoxemia
stimulate alveolar hyperventilation
Type :two: respiratory failure
or
Hypercapnic
respiratory failure
or
Ventilatory
failure
PaCO2
≥ 50 mmHg
usu. present with
hypoxemia
Mechanism :gear:
:arrow_down: CO2 elimination: Alveolar hypoventilation resulting in CO2 retention
:arrow_up:
excessive
CO2 production: Hypercatabolism
:explode:
Factors predisposing
to RF
Obligate nose breathers (หายใจผ่านรูจมูก เท่านั้น)
Relative macroglossia
Larger adenoid tissue
U-shaped &
floppy
(weak) epiglottis ➯ use
straight laryngoscope blade
Cricoid area -- narrowest part of airway (child's is smaller than adult's)
Smaller
caliber of airways with greater resistance
Fatigable diaphragm: Place NG tube to :arrow_down: gastric distention
Shorter
tracheal length ➯
ETT easily dislodge into Esophagus
Larynx is more
cephalad & anterior
Deficient collateral ventilation
:leaves:
Basic respiratory PSO
Major func of lung = Get O2 into body & Get CO2 out of body
Gas exchange
requires
Pressure gradient
between Alveolar air & Blood
Short distance for diffusion of gases
and intervening tissues which are permeable to O2 & CO2
:wind_blowing_face:
Getting O2 in
A
levolar partial pressure of O2 (P
A
O2)
depends on
Partial pressures of other gases in the alveolus
Total alveolar pressure
can be
increased by
:arrow_up: Alveolar pressure
:arrow_up: Proportion of O2 in the mixture
So CO2 passes into alveolus & O2 passes into blood ➯ PACO2 :arrow_up: & PAO2 :arrow_down:
*Ventilation - required to replenish Alveolar gas with Fresh gas
:explode:
Factors
that causes changes in PAO2
PACO2 / Ventilation
Alveolar pressure
Inspired O2 conc
Ventilation
:wind_blowing_face:
Getting CO2 out
CO2 elimination
depends on
Rate of Alveolar ventilation
Alveolar ventilation = RR x (Tidal volume - Dead space)
so we tachypnea to wash CO2 resulting in deeper tidal volume
A
lveolar partial pressure of CO2 (P
A
CO2)
changes
depend on
Respiratory rate (RR)
Tidal volume
Ventilation-perfusion matching (V/Q mismatching)
:gear:
Mechanism of RF
:one:.
Hypoventilation
Def: markedly :arrow_up: in PaCO2 & :arrow_down: in PaO2
PSO: CO2 passes into alveolus & O2 passes into blood ➯ Pressure gradients between alveolar gas & blood
gradually reduced
➯
Ventilation
- required to restore the pressure gradients
:green_apple:
Causes
Brainstem
Injury
Metabolic encephalopathy
Depressant drugs
Spinal cord
Trauma
Transverse myelitis
Nerves
Guillain Barre
Neuromuscular junction
Myasthenia gravis
Respiratory muscles
Faitgue
Myopathy
Malnutrtition
Respiratory system
Airway obstruction (Upper & Lower)
:arrow_down: lung compliance
:two:.
Intrapulmonary shunting
:clubs:
:three:.
Ventilation-perfusion (V/Q) mismatch
Def: Mismatched distribution of V & Q ➯
some
lung units receive
disproportionally High V
and others receive disproportionally
High Q
:hourglass_flowing_sand:
Interpretation
Low
V/Q
Asthma
Secretion obstruction
Bronchiolitis
Pneumonia
Pulmonary edema
Partial atelectasis
High
V/Q
(Dead space ventilation)
Shock
Pulmonary embolism
Ventilation
w/o Perfusion
Gas passes in and out of alveoli
but no gas exchange
cuz
Alveoli are not perfused
&
Ventilation is ineffective
#
so alveoli
ventilated but not take part in gas exchange
➯ Dead space ➯ :arrow_down: effective ventilation ➯ :arrow_up: PaCO2
:apple:
Causes of Dead space
Low cardio output
High intraalveolar pressure led to compression
or
stretching of alveolar capillary (mechanically ventilated pt)
Pulmonary thromboembolism
:four:.
Diffusion abnormality
Less common
Def: Abnormality of
alveolar mb
or :arrow_down:
no. of alveoli
➯ :arrow_down: alveolar surface area
:pineapple:
Causes
ARDS
Fibrotic lung disease
What is
Shunting?
Relatively
resistant to O2 therapy
:frowning_face:
as it can't reach alveoli where shunting occurs ➯ :arrow_up: inspired O2 conc has little effect
Def: Form of V/Q mismatch in which
Alveoli
which are
not ventilated
(eg due to collapse or edema fluid) but
still perfused
➯ Blood in these alveoli
not oxygenated
:fireworks:
Causes
:two_hearts:
Intracardiac
Any
cause of
Rt to Lt shunt
eg. TOF, Eisenmenger's syndrome
:clubs:
Intrapulmonary
Pneumonia
Pulonary edema
Atelectasis
Pulmonary hemorrhage
Pulmonary contusion
:film_projector:
Clinical signs
:film_frames:
Signs of respiratory compensation
:star:
Tachypnea - very good indicator
of severely ill pt
found this meaning there's impending RF
Use of accessory ms
Nasal flaring
Intercostal, suprasternal or subcostal retraction
:film_frames::arrow_up: Sympathetic tone
Tachycardia :<3:
easiest to know
Hypertension
may due to agitation
Sweating
:film_frames:End-organ hypoxia
Altered mental status
Bradycardia & Hypotension (
late signs
)
:film_frames:Hb desaturation
Cyanosis
Pulse oximetry saturation (SpO2) falls below 90%
Pulse oximetry: estimates Arterial saturation (
not PaO2
) by using Absorption of Two different wavelengths of Infrared light
small fall
in PaO2 ➯
sharp fall in SpO2
➯ O2 supplement as Rx ➯ if not better, insert ETT
:male-scientist::skin-tone-5:
Investigation
Arterial blood gas
analysis
PaO2 < 60 mmHg, PaCO2 > 50 mmHg
AND
pH < 7.25
or
PaCO2 > 40
AND
Severe respiratory distress
O2 saturation
SpO2 < 90% (FiO2 0.4)
Bedside pulmonary func test
(ไม่ค่อยทำ)
Vital capacity < 15 cc/kg
Negative inspiratory pressure < 25-30 cmH2O
:leaves:
Mx
1. O2 therapy
2. Hydration
:warning:
No sedation allowed
cuz sedation might cause hypoventilation
3. ± Intubation
:check:
I/C
Acute respiratory failure
:stars:Clinical signs of respiratory failure:stars:
PO2 < 60 mmHg
PCO2 > 50 mmHg
Apnea (multiple time)
Hypoventilation
Shock / Severe metabolic acidosis
Neurological resuscitation
GCS < 8
Status epilepticus
Airway protection
Inability to control secretions
:rosette:
Settings
PEEP
(positive end-expiratory pressure)
necessary
to :arrow_down: intrapulmonary shunt
Initial PEEP
should be ~
5 cmH2O
(if O2 remains
inadequate
can be inc.
incrementally up to 10-15 cmH2O
) goal SaO2 > 90%