Arterial Pressure Monitoring

Steps for ABP with manual cuff

Select appropriate size. Secure cuff around upper arm at heart level. Inflate to 30 mmHg over normal ABP to occlude flow. Place bell over brachial artery while cuff deflates 3 mmHg/second. P at first sound = SBP, P at sound disappearance = DBP.

manual cuff advantages

noninvasive, easy to apply, low risk, widely available, appropriate for many stable patients

manual cuff disadvantages

Time between measurements misses rapid hemodynamic changes, accuracy depends on fit and positioning, no direct waveform or blood sampling, confounded by motion, arrhythmias, poor perfusion, vascular disease.

other non-invasive BP monitoring techniques

manual auscultation, oscillometric cuff, doppler-assisted, finger cuffs

arterial catheter sites

Radial preferred, then femoral (central) and axillary. Brachial and dorsalis pedis in peds

Arterial line placement complications

Bleeding, hematoma, thrombosis/occlusion, emboli, distal ischemia, infection, disconnection/dislodgement

peripheral vs central arterial waveforms

Peripherals show widened pulse pressure and a slid down dicrotic notch due to decreased compliance and energy absorption compared to more elastic central arteries.

pulse pressure

SBP - DBP

blood pressure by age

Vessels get less compliant, BP increases and pulse pressure widens

preload

volume of blood in both ventricles at the end of diastole. measured by CVP/RVEDV (R) and PCWP/LVEDV (L)

afterload

resistance the ventricles must overcome to eject their blood volume. measured by PVR (R) and SVR (L)

contractility

force with which the heart muscle contracts. measured by SV & EF. Increased by inotropes

preload modulation

Giving volume and blood increase, giving diuretics decreases (more fluid excreted)

afterload modulation

vasoconstrictors increase, vasodilators increase

CO

HR x SV

CI

CO / BSA

SV

EDV - ESV. Normal = 50-100 ml/beat

stroke volume index (SVI)

SV / BSA

systemic vascular resistance (SVR)

(MAP - CVP) / CO x 80. Normal = 900-1440 dynes x s x cm^-5

Frank Starling curve of contractility

As preload (x- axis) increases, SV (y-axis) also increases up to a point. Past which the heart over-distends and can’t pump efficiently (SV decreases)

MAP

(1/3) systolic + (2/3) diastolic

pulmonary vascular resistance (PVR)

(mPAP - LAP) / CO x 80. Normal = 20-120 dynes x s x cm^-5

components of arterial pressure waveform

anacrotic limb, systolic peak, dicrotic limb, dicrotic notch, end diastolic pressure

anacrotic limb of arterial pressure waveform

rapid pressure rise during ventricular ejection

systolic peak of arterial pressure waveform

Anacrotic notch is the waveform’s highest peak and reflects SBP

dicrotic limb of arterial pressure waveform

pressure falls as blood moves into the peripheral circulation

dicrotic notch

Late dip in arterial pressure wavform associated with aortic valve closure. Marks the start of diastole

end diastolic pressure

Lowest trough in arterial pressure waveform immediately before the next systolic upstroke

peripheral arteries

High-resistance vessels with branch points create reflected pressure waves that travel back toward the heart. These combine with the forward wave during systole to amplify distal diastolic pulses.

aorta and vena cavae

Lowest cross-sectional area, highest flow velocity