3. Arterial P
Arterial PO
O2
2 (Pa
(PaO
O2
2)
)
z
z Normal: 80
Normal: 80 –
– 100 mm Hg breathing room air
100 mm Hg breathing room air
at sea level in healthy young adults (103
at sea level in healthy young adults (103-
- 0.5
0.5
x age)
x age)
z
z PaO
PaO2
2 affected by
affected by
–
– F
FI
IO
O2
2 PEEP
PEEP Lung function
Lung function
–
– Age Ventilation Altitude
Age Ventilation Altitude
PAO
PAO2
2 = FIO
= FIO2
2(P
(PB
B-
-PH
PH2
20)
0) –
– PaCO
PaCO2
2 x 1.2
x 1.2
PAO
PAO2
2 = FIO
= FIO2
2(700)
(700) -
- PaCO
PaCO2
2 x 1.2
x 1.2
Always interpret PaO2 in relation to FIO2
5. PaO
PaO2
2/SaO
/SaO2
2
Shifting of the Oxyhemoglobin Dissociation curve
-Temperature
-pH
-2,3, DPG (stored blood loses 2,3, DPG)
-Dyshemoglobins (carboxy, fetal, methhgb)
Shift to left facilitates Oxygen loading
Shift to right facilitates Oxygen unloading
6. PaO
PaO2
2/SaO
/SaO2
2
30 mm Hg = 60% saturation
60 mm Hg = 90% saturation
40 mmHg = 75% saturation
Oxygen delivery = Oxygen content x cardiac output
Oxygen content = PaO2 (0.003) + Hgb(1.34)%sat
Once PaO2 exceeds 70 mmHg further increases do
not increase oxygen delivery
7. Arterial P
Arterial PCO
CO2
2 (Pa
(PaCO
CO2
2)
)
z
z Normal: 35 to 45 mm Hg
Normal: 35 to 45 mm Hg
z
z ↑
↑ PaCO
PaCO2
2 = hypoventilation
= hypoventilation
–
– Respiratory center depression
Respiratory center depression
–
– Neuromuscular disease
Neuromuscular disease
–
– Pulmonary disease
Pulmonary disease
z
z ↓
↓ PaCO
PaCO2
2 = hyperventilation
= hyperventilation
–
– Central
Central
–
– Pain
Pain
–
– Anxiety
Anxiety
–
– Iatrogenic
Iatrogenic
8. Acid
Acid-
-Base Balance
Base Balance
pH = 6.1 + log
HCO3
-
0.03 × PCO2
pH ~
~
HCO3
-
PCO2
metabolic component
respiratory component
When HCO3
- is 24 mmol/L and PaCO2 is 40 mm Hg, the pH is 7.40
9. Normal Values
Normal Values
z
z pH 7.35
pH 7.35 –
– 7.45
7.45
z
z PaCO2 35
PaCO2 35-
-45 mmHg
45 mmHg
z
z HCO3
HCO3-
- 22
22-
-26 meq/L
26 meq/L
z
z BE/BD
BE/BD –
–2 to +2
2 to +2
z
z Base Excess or Base Deficit reflects the non
Base Excess or Base Deficit reflects the non-
-
respiratory portion of acid
respiratory portion of acid-
-base balance
base balance
z
z Includes RBC buffering
Includes RBC buffering
10. Acid
Acid-
-Base Disorders
Base Disorders
z
z Primary disturbance
Primary disturbance
–
– Acidosis: pH < 7.35
Acidosis: pH < 7.35
•
• Respiratory:
Respiratory: ↑
↑ Pa
PaCO
CO2
2
•
• Metabolic:
Metabolic: ↓
↓ HCO
HCO3
3
-
-
•
• BE: normal
BE: normal
–
– Alkalosis: pH > 7.45
Alkalosis: pH > 7.45
•
• Respiratory:
Respiratory: ↓
↓ Pa
PaCO
CO2
2
•
• Metabolic:
Metabolic: ↑
↑ HCO
HCO3
3
-
-
•
• BE: normal
BE: normal
11. Acid
Acid-
-Base Disorders
Base Disorders
Rules
Rules
For a 0.08 change in pH
For a 0.08 change in pH –
– PaCO
PaCO2
2 changes 10
changes 10
mmHg
mmHg
7.40 40 7.32 50 7.48 30
7.40 40 7.32 50 7.48 30
Respiratory compensation is rapid
Respiratory compensation is rapid
Metabolic compensation is slow
Metabolic compensation is slow
12. Acid
Acid-
-Base Disorders
Base Disorders
z
z Compensation
Compensation
–
– Change in Pa
Change in PaCO
CO2
2 to correct pH with
to correct pH with
metabolic acid
metabolic acid-
-base imbalance
base imbalance
•
• e.g., hyperventilation occurs with
e.g., hyperventilation occurs with
metabolic acidosis
metabolic acidosis
–
– Change in HCO
Change in HCO3
3
-
- to correct pH with
to correct pH with
respiratory acid
respiratory acid-
-base imbalance
base imbalance
•
• e.g., HCO
e.g., HCO3
3
-
- increases with respiratory
increases with respiratory
acidosis
acidosis
pH ~
~
HCO3
-
PCO2
↓
↓
↓
↔
↑
↑
↓
↔
13. Respiratory Acidosis
Respiratory Acidosis
z
z Uncompensated:
Uncompensated: ↓
↓ pH,
pH, ↑
↑ Pa
PaCO
CO2
2, nl BE,
, nl BE,
HCO
HCO3
3
-
-
z
z Compensated: nl pH,
Compensated: nl pH, ↑
↑ Pa
PaCO
CO2
2,
, ↑
↑ BE, HCO
BE, HCO3
3
-
-
z
z Causes: respiratory center depression,
Causes: respiratory center depression,
neuromuscular disease, lung disease
neuromuscular disease, lung disease
z
z Treatment: treat cause, mechanical
Treatment: treat cause, mechanical
ventilation, buffers
ventilation, buffers
14. Respiratory Alkalosis
Respiratory Alkalosis
z
z Uncompensated:
Uncompensated: ↑
↑ pH,
pH, ↓
↓ Pa
PaCO
CO2
2, nl BE,
, nl BE,
HCO
HCO3
3
-
-
z
z Compensated: nl pH,
Compensated: nl pH, ↓
↓ Pa
PaCO
CO2
2,
, ↓
↓ΒΕ,
ΒΕ, HCO
HCO3
3
-
-
z
z Causes: respiratory center stimulation,
Causes: respiratory center stimulation,
iatrogenic
iatrogenic
z
z Treatment: treat cause
Treatment: treat cause
15. Metabolic Alkalosis
Metabolic Alkalosis
z
z Uncompensated:
Uncompensated: ↑
↑ pH,
pH, ↑
↑ HCO
HCO3
3
-
-, nl Pa
, nl PaCO
CO2
2
z
z Compensated: nl pH,
Compensated: nl pH, ↑
↑ HCO
HCO3
3
-
-,
, ↑
↑ Pa
PaCO
CO2
2
z
z Causes: hypokalemia, nasogastric suctioning
Causes: hypokalemia, nasogastric suctioning
or vomiting, contraction alkalosis, bicarbonate
or vomiting, contraction alkalosis, bicarbonate
administration, steroid therapy
administration, steroid therapy
z
z Treatment: treat cause, KCl, volume, diamox,
Treatment: treat cause, KCl, volume, diamox,
NH
NH4
4Cl, arginine monohydrochloride, HCl
Cl, arginine monohydrochloride, HCl
16. Metabolic Acidosis
Metabolic Acidosis
z
z Uncompensated:
Uncompensated: ↓
↓ pH,
pH, ↓
↓ HCO
HCO3
3
-
-, nl Pa
, nl PaCO
CO2
2
z
z Compensated: nl pH,
Compensated: nl pH, ↓
↓ HCO
HCO3
3
-
-,
, ↓
↓ Pa
PaCO
CO2
2
z
z Causes: hypoxia (lactic acidosis), diabetes
Causes: hypoxia (lactic acidosis), diabetes
(ketoacidosis), renal failure (uremic acidosis),
(ketoacidosis), renal failure (uremic acidosis),
GI loss of HCO
GI loss of HCO3
3
-
- (diarrhea), renal loss of
(diarrhea), renal loss of
HCO
HCO3
3
-
- (renal tubular acidosis, diamox),
(renal tubular acidosis, diamox),
poisons (aspirin, methanol, ethylene glycol)
poisons (aspirin, methanol, ethylene glycol)
z
z Treatment: treat cause, buffer
Treatment: treat cause, buffer
17. Acid
Acid-
-Base Interpretation
Base Interpretation
z
z Classify the disturbance: acidosis, alkalosis,
Classify the disturbance: acidosis, alkalosis,
metabolic, respiratory
metabolic, respiratory
z
z Determine the degree of compensation:
Determine the degree of compensation:
uncompensated, partially compensated, fully
uncompensated, partially compensated, fully
compensated
compensated
z
z Identify the cause of the disturbance
Identify the cause of the disturbance
z
z Develop a treatment plan
Develop a treatment plan
18. Disorder pH PaCO2 HCO3
-
Respiratory acidosis
Uncompensated ↓↓ ↑↑ N
Partially compensated ↓ ↑↑ ↑
Fully compensated N ↑↑ ↑↑
Respiratory alkalosis
Uncompensated ↑↑ ↓↓ N
Partially compensated ↑ ↓↓ ↓
Fully compensated N ↓↓ ↓↓
Metabolic acidosis
Uncompensated ↓↓ N ↓↓
Partially compensated ↓ ↓ ↓↓
Fully compensated N ↓↓ ↓↓
Metabolic alkalosis
Uncompensated ↑↑ N ↑↑
Partially compensated ↑ ↑ ↑↑
Fully compensated N ↑↑ ↑↑
Acid
Acid-
-Base Interpretation
Base Interpretation
19. Test Your Skills
Test Your Skills
pH~
~
HCO3
-
PCO2
pH = 7.25
PaCO2 = 57
HCO3
- = 24
↓
↑
↔
20. Test Your Skills
Test Your Skills
pH~
~
HCO3
-
PCO2
pH = 7.25
PaCO2 = 40
HCO3
- = 17
↓ ↔
↓
21. Test Your Skills
Test Your Skills
pH~
~
HCO3
-
PCO2
pH = 7.38
PaCO2 = 60
HCO3
- = 34
↔
↑
↑
22. Test Your Skills
Test Your Skills
pH~
~
HCO3
-
PCO2
pH = 7.28
PaCO2 = 28
HCO3
- = 13
↓
↓
↓
23. Mechanical Ventilation
Mechanical Ventilation
z
z Variables
Variables
z
z Mode
Mode
z
z FIO2 and PEEP
FIO2 and PEEP
z
z Tidal Volume and frequency
Tidal Volume and frequency
z
z I:E ratio, inspiratory time
I:E ratio, inspiratory time
24. Modes
Modes
z
z CMV or assist control
CMV or assist control –
– every breath is the
every breath is the
same volume or pressure, time
same volume or pressure, time
z
z IMV
IMV –
– spontaneous breaths are allowed
spontaneous breaths are allowed
between mandatory breaths
between mandatory breaths
z
z Pressure support
Pressure support –
– a set pressure is delivered
a set pressure is delivered
with each breath the patient takes (a boost)
with each breath the patient takes (a boost)
z
z CPAP/PEEP
CPAP/PEEP –
– elevated end expiratory
elevated end expiratory
pressure
pressure
25. Tidal Volume & Frequency
Tidal Volume & Frequency
z
z Control minute ventilation & PaCO
Control minute ventilation & PaCO2
2
z
z V
VE
E =
= f
f x V
x VT
T
z
z PaCO
PaCO2
2 = VCO
= VCO2
2/V
/VA
A
z
z V
VA
A = V
= VT
T –
– Vds
Vds
z
z Postop
Postop –
– 8
8-
-12 mL/kg
12 mL/kg
z
z Restrictive
Restrictive –
– 4
4-
-8 mL/kg
8 mL/kg
z
z Obstructive
Obstructive –
– 8
8-
-10 mL/kg
10 mL/kg
26. Tidal Volume
Tidal Volume –
– Weight & Height
Weight & Height
The major determinant of lung volume is height
The major determinant of lung volume is height
not weight
not weight
Women
Women –
– 45.5 + 2.3 (Ht in inches
45.5 + 2.3 (Ht in inches -
-60)
60)
Men
Men -
- 50 + 2.3 (Ht in inches
50 + 2.3 (Ht in inches –
– 60)
60)
Modify tidal volume to maintain airway plateau
Modify tidal volume to maintain airway plateau
pressure < 30 cm H2O
pressure < 30 cm H2O
27. PEEP and FIO2
PEEP and FIO2
z
z Control oxygenation
Control oxygenation
z
z FIO
FIO2
2 start at 100% and move down using SpO
start at 100% and move down using SpO2
2
z
z PEEP
PEEP –
– 5 cm H
5 cm H2
20 minimum
0 minimum
z
z ARDS
ARDS –
– 10
10 –
– 20 cm H2O
20 cm H2O
z
z COPD
COPD –
– 5
5-
-10 cm H2O
10 cm H2O
z
z PEEP is titrated to oxygenation, lung mechanics,
PEEP is titrated to oxygenation, lung mechanics,
oxygen delivery or other clinician determined
oxygen delivery or other clinician determined
endpoints
endpoints
28. Writing Ventilator Orders
Writing Ventilator Orders
z
z Mode (A/C, IMV, PSV)
Mode (A/C, IMV, PSV)
z
z Pressure or tidal volume
Pressure or tidal volume
z
z Frequency
Frequency
z
z FIO2
FIO2
z
z PEEP
PEEP
z
z Goals of support
Goals of support
z
z Better to write adjust FIO2 to maintain SpO2 > 92%
Better to write adjust FIO2 to maintain SpO2 > 92%
then to write six orders to reduce FIO2
then to write six orders to reduce FIO2
29. Terminology
Terminology
z
z Weaning implies the gradual withdrawal of
Weaning implies the gradual withdrawal of
support
support
z
z Liberation from mechanical ventilation is more
Liberation from mechanical ventilation is more
appropriate
appropriate
z
z Liberation may not require weaning
Liberation may not require weaning
z
z Extubation is removal of the ET tube
Extubation is removal of the ET tube
z
z Decannulation is removal of the tracheostomy
Decannulation is removal of the tracheostomy
tube
tube
31. WHEANS NOT
WHEANS NOT
z
z W
Wheezes
heezes
z
z H
Heart disease
eart disease
z
z Electrolytes
Electrolytes
z
z A
Anxiety, airway problems, alkalosis
nxiety, airway problems, alkalosis
z
z N
Neuromuscular disease
euromuscular disease
z
z S
Sepsis, sedation
epsis, sedation
z
z N
Nutrition (over and underfeeding)
utrition (over and underfeeding)
z
z O
Opiates, obesity
piates, obesity
z
z T
Thyroid disease
hyroid disease
Ely EW, RCCNA 2000;6:303
32. Weaning Readiness
Weaning Readiness
Daily Screen
Daily Screen –
– 5 Criteria
5 Criteria
z
z Patient coughs when suctioned
Patient coughs when suctioned
z
z No continuous vasopressor or sedative
No continuous vasopressor or sedative
infusions
infusions
z
z PaO
PaO2
2//FIO
//FIO2
2 > 200
> 200
z
z PEEP
PEEP <
< 8 cm H
8 cm H2
2O
O
z
z f
f/V
/VT
T < 105 for one minute
< 105 for one minute
Ely NEJM 1996;335:1864
33. Spontaneous Breathing Trials
Spontaneous Breathing Trials
z
z All pts who pass the daily screen
All pts who pass the daily screen –
– SBT 30
SBT 30 mins
mins
Termination of the SBT
Termination of the SBT
z
z Resp
Resp rate > 35 for > 5
rate > 35 for > 5 mins
mins
z
z SpO2 < 90% for > 30
SpO2 < 90% for > 30 secs
secs
z
z 20% increase or decrease in heart rate for > 5
20% increase or decrease in heart rate for > 5 mins
mins
z
z SBP > 180 or < 90 for 60
SBP > 180 or < 90 for 60 secs
secs consecutively
consecutively
z
z Agitation, anxiety, diaphoresis > baseline for > 5
Agitation, anxiety, diaphoresis > baseline for > 5
minutes
minutes
Ely NEJM 1996;335:1864
