Pulmonary Artery Catheter (PAC, Swan-Ganz catheter)
Overview
Pulmonary artery catheter (PAC) หรือ Swan-Ganz
catheter ใช้สำหรับ:
- Advanced
hemodynamic monitoring
- Shock
evaluation
- Pulmonary
hypertension assessment
- Cardiac
output measurement
ช่วยแยกประเภท shock และประเมิน
cardiac/pulmonary hemodynamics ได้ละเอียด
Parameters Measured by PAC
Direct measurements
Right-sided pressures
- CVP /
RAP
- RV
pressure
- PAP
- PAOP/PCWP/PAWP
Cardiac output (CO)
Mixed venous oxygen saturation (SvO₂)
Derived calculations
Cardiac index (CI)
[CI = CO / BSA]
Normal:
2.8–4.2 L/min/m²
Systemic vascular resistance (SVR)
SVR = 80 x (MAP-CVP)/(CO)
Pulmonary vascular resistance (PVR)
PVR = 80 x (mPAP-PAOP) / (CO)
Pulmonary artery pulsatility index (PAPI)
PAPI = (PASP-PADP) / (CVP)
ใช้ประเมิน RV failure
Cardiac power output (CPO)
CPO = (CO x MAP) / 451
Strong prognostic marker in cardiogenic shock
Ensuring Accurate Measurements
1. Zeroing
ต้อง zero transducer ที่ phlebostatic
axis
Repeat when:
- Patient
repositioned
- Time
elapsed
- Accuracy
questionable
2. Correct catheter position
ใช้:
- Pressure
waveform
- Fluoroscopy
- TEE
3. Dynamic response test (fast flush)
Normal
Square wave + 1–2 oscillations
Overdamped
No oscillation
Causes:
- Air
bubbles
- Clot
- Kink
- Low
flush pressure
Effects:
- False
low systolic
- Narrow
pulse pressure
Underdamped
Excess oscillation
Causes:
- Long
tubing
- Stopcocks
- Hyperdynamic
state
- Tachycardia
Effects:
- False
high systolic
Right Atrial Pressure (RAP/CVP)
Normal:
0–7 mmHg
Reflects:
- Venous
return
- RV
preload
- RV
end-diastolic pressure
Causes of Elevated RAP
RV pathology
- RV
infarction
- RV
failure
- Pulmonary
hypertension
Volume overload
- Hypervolemia
Pericardial disease
- Tamponade
- Constrictive
pericarditis
Tricuspid disease
- TR
- TS
RA Waveform Components
a wave
Atrial contraction
c wave
Tricuspid closure
v wave
Venous filling during ventricular systole
x descent
Atrial relaxation
y descent
RV filling after tricuspid opening
Abnormal RA Waveforms
Large v waves
Suggest:
- Tricuspid
regurgitation
Cannon a waves
Suggest AV dissociation:
- VT
- Complete
heart block
- Ventricular
pacing
- Tricuspid
stenosis
Loss of a wave
Suggest:
- Atrial
fibrillation
- Atrial
flutter
Rapid y descent
Suggest:
- Constrictive
pericarditis
- Restrictive
cardiomyopathy
- Severe
TR
Loss of y descent
Suggest:
- Cardiac
tamponade
Right Ventricular Pressure
Normal:
- RV
systolic: 15–25 mmHg
- RVEDP:
3–12 mmHg
Elevated RV systolic pressure
Suggest:
- Pulmonary
hypertension
- Pulmonic
stenosis
- Pulmonary
embolism
Elevated RVEDP
Suggest:
- RV
infarction
- RV
failure
- Tamponade
- Constrictive
disease
Pulmonary Artery Pressure (PAP)
Normal:
- PASP:
15–25 mmHg
- PADP:
8–15 mmHg
- Mean
PAP: ~16 mmHg
Pulmonary hypertension:
mPAP >22 mmHg
Causes of Elevated PAP
Group 1
Pulmonary arterial hypertension
Group 2
Left heart disease
Group 3
Lung disease/hypoxia
Group 4
Chronic thromboembolic PH
Group 5
Multifactorial PH
Important Pearl
Acute PE rarely causes PAP >40–50 mmHg
Very high PAP usually suggests chronic PH
PA Waveform
Components:
- Systolic
upstroke
- Diastolic
runoff
- Dicrotic
notch (pulmonic valve closure)
Pulmonary Artery Occlusion Pressure (PAOP/PCWP)
Normal:
6–15 mmHg
Best estimate of:
- Left
atrial pressure
- LV
preload
if:
- No
mitral obstruction
- Normal
LV compliance
Conditions Causing Elevated PAOP
LV dysfunction
- HFrEF
- HFpEF
Valve disease
- MR
- MS
- AS
- AR
Hypervolemia
Pericardial disease
- Tamponade
- Constriction
Low PAOP
Suggest:
- Hypovolemia
- Massive
PE
- Volume
depletion
PAOP Waveform
a wave
LA contraction
v wave
LA filling during ventricular systole
Large a wave
Suggest:
- Mitral
stenosis
- LV
stiffness
- Diastolic
dysfunction
Large v wave
Suggest:
- Mitral
regurgitation
Important Limitations of PAOP
PAOP ≠ LVEDV directly
May be unreliable when:
- LV
compliance abnormal
- Positive
pressure ventilation
- Tamponade
- RV
overload
Sources of Error in PAOP
1. Incomplete wedge
Causes falsely elevated PAOP
Check wedge saturation:
- 90%
- Near
systemic saturation
2. Non-zone 3 placement
Correct wedge requires zone 3
Otherwise PAOP overestimated
3. Respiratory effects
Always measure:
- End
expiration
Mechanical ventilation
Spontaneous breathing
Measure at expiratory peak
Positive pressure ventilation
Measure at expiratory trough
PEEP Effects
PEEP may falsely elevate PAOP
Approximate correction:
- Subtract
½ PEEP if normal compliance
- Subtract
¼ PEEP if low compliance
But effect usually clinically modest
Cardiac Output Measurement
Thermodilution Method
Standard PAC method
Cold saline injected →
thermistor detects temperature change
Inverse relation:
- Larger
area under curve →
lower CO
Thermodilution Errors
TR
Underestimates CO
Intracardiac shunts
Can overestimate CO
Fick Method
CO = (VO_2) / (10 x (1.34 x Hb x (SaO_2-SvO_2)))
More accurate in some settings
Needs:
- Oxygen
consumption
- Arterial
saturation
- Mixed
venous saturation
Mixed Venous Oxygen Saturation (SvO₂)
Reflects balance between:
- Oxygen
delivery
- Oxygen
consumption
Low SvO₂
Suggest:
- Low
CO
- Shock
- Hypoxemia
- Anemia
- Increased
metabolic demand
High SvO₂
Suggest:
- Sepsis
- Cyanide
toxicity
- Mitochondrial
dysfunction
- Excess
oxygen delivery
Detection of Left-to-Right Shunts
Look for oxygen saturation step-up:
- RA
- RV
- PA
Suggests:
- ASD
- VSD
- Other
shunts
Shock Hemodynamics
|
Shock Type |
CO |
SVR |
PAOP |
|
Hypovolemic |
↓ |
↑ |
↓ |
|
Cardiogenic |
↓ |
↑ |
↑ |
|
Obstructive |
↓ |
↑ |
Variable |
|
Septic/distributive |
↑/↓ |
↓ |
↓/normal |
Pulmonary Vascular Resistance
Useful in:
- Pulmonary
hypertension
- RV
failure
But relatively error-prone because depends on multiple
measured variables
Important Clinical Pearls
- PAC
provides comprehensive hemodynamic assessment
- PAOP
estimates LA pressure, not true LVEDV
- Measure
wedge at end expiration
- Zone
3 positioning is critical for accurate PAOP
- Large
v waves suggest MR or TR
- Equalization
of pressures suggests tamponade/constriction
- PAP
>50 mmHg usually chronic PH rather than acute PE
- Thermodilution
inaccurate in severe TR/shunts
- SvO₂
reflects global oxygen balance
- Dynamic
interpretation more important than isolated values
