Blood Pressure

Mean Arterial Pressure (MAP)

is the most useful parameter for assessing organ perfusion. It is a time-weighted average of arterial pressures during a pulse cycle.

Brachial Artery as a site for a line

large and easily identifiable in the antecubital fossa. Proximity to the aorta provides less waveform distortion.

Underdamp=

leading to overshoot: SBP falsely high

Low dicrotic notch

low stroke volume (hypovolemic)

Pressure Transducers:

miniaturized, disposable that contains a diaphragm that is distorted by an arterial pressure wave.

Ulnar Artery as a site for a line

more difficult due to artery's deeper and more tortuous course. Do not attempt if radial artery on that wrist has already been tried due to risk of compromising blood flow to the hand.

Radial Artery as a site for a line

most common site-superficial location and collateral flow 5% of patients lack adequate collateral blood flow

Indications for invasive BP monitoring

1. Elective hypotension 2. Anticipation of wide intraoperative blood pressure swings 3. End organ disease necessitating beat to beat blood pressure regulation 4. Need for multiple analyses of arterial blood gases 5. Single lung ventilation 6. Cardiac/major vascular surgery 7. Procedures requiring strict control of blood pressure

Complications of a lines

1. Hematoma 2. Bleeding - separation of transducer tubing from catheter hub 3. Vasospasm 4. Arterial thrombosis 5. Embolization of air bubbles or thrombi 6. Necrosis of skin overlying the catheter 7. Nerve damage 8. Infection 9. Loss of digits 10. Unintentional intra-arterial drug injection

Minimize risks of a lines by:

1. Keeping ratio of catheter to artery site small 2. Heparinized saline continuously infused at 2-3 ml/hr 3. Limit flushing of catheter 4. Meticulous attention paid to aseptic technique 5. Monitor adequacy of perfusion during radial artery cannulation by placing pulse oximeter on same side finger

Keys to accurate waveform:

1. Minimize tubing length 2. Eliminate unnecessary stopcocks 3. Remove air bubble 4. Use low compliance tubing 5. Smaller catheters improve underdamped systems and less apt to result in vascular complications

How do you determine an adequate blood pressure?

1. Patient baseline and history 2. Surgical procedure

Factors associated with increased rate of complications of a lines

1. Prolonged cannulation 2. Hyperlipidemia 3. Repeated insertion attempts 4. Female gender 5. Cardiopulmonary bypass 6. Use of vasopressors 7. Prolonged shock 8. Preexisting peripheral vascular disease

The width of a non invasive BP should be

20-50% greater than diameter of extremity

Outcomes for Allens Test

< 5 seconds is adequate collateral flow 5-10 seconds an equivocal test >10 seconds is inadequate circulation

Most transducers have frequencies of...

> 200 Hz.

Doppler technique

A Doppler probe is substituted for anesthesia provider's finger. It transmits an ultrasonic signal. Need coupling gel between probe and skin and correct position of probe above an artery is crucial. Also only provides systolic blood pressure.

How does oscillometry work

A microprocessor derives systolic, mean, and diastolic pressures by using an algorithm. Arterial pulsations cause oscillations in cuff pressure. These oscillations are small when cuff is inflated above systolic pressure. When cuff pressure decreases to systolic pressure the pulsations are transmitted to the entire cuff and oscillations are markedly increased. Maximal oscillations occur at mean arterial pressure after which oscillations decrease. Electronically measure pressures at which oscillation amplitudes change.

To test for collateral flow:

A. Doppler Probe B. Plethysmography C. Pulse Oximetry D. Allen's test; not reliable and requires patient cooperation ∙to do: exsanguinate hand by patient making fist, manually compress radial and ulnar arteries, relax hand, release pressure over ulnar artery and observe return of color

Plethysmography:

Arterial pulsations transiently increase blood volume in an extremity. Finger photoplethysmograph consists of light-emitting diode and photoelectric cell. Unreliable in patients with poor perfusion.

Contraindications for invasive BP monitoring

Avoided in arteries without documented collateral blood flow or extremities where there is a suspicion of pre-existing vascular insufficiency. The hand is supplied by both the ulnar and radial arteries.

When auscultating, Disappearance of sounds=

DBP

When should you treat it blood pressure.

Depends based on: 1. Patient baseline and history 2. Cause

Ausculatating BP

Inflation of cuff to a pressure between systolic and diastolic pressures will partially collapse an underlying artery, producing turbulent flood flow and the characteristic Korotkoff sounds. Auscultated with a stethoscope placed under or just beyond the distal third of an inflated blood pressure cuff.

Equation for MAP

MAP= SBP+2(DBP)/ 3

Arterial Tonometr

Noninvasively measures beat to beat pressure by sensing the pressure required to partially flatten a superficial artery that is supported by a bony structure (i.e. radial artery). Needs frequent calibration and is sensitive to movement.

Position of dichrotic notch on descending limb depends on

cardiac output

Accuracy of non invasive BP is dependent upon:

Proper cuff size Positioning Heart rate

When auscultating, Onset of sounds=

SBP

Pros and cons of palpating BP

This underestimates the systolic pressure due to the insensitivity of touch and does not provide diastolic or mean arterial pressure. Simple and inexpensive

The sensing elements are arranged as

a Wheatstone bridge circuit so that the voltage output is proportionate to the pressure applied to the diaphragm.

In the palpation technique, Systolic blood pressure determined by

a. locating a palpable peripheral pulse b. inflating blood pressure cuff proximal to pulse until flow is occluded c. releasing cuff pressure by 2-3 mm Hg per heart beat d. measuring the cuff pressure at which pulsations are palpable

Femoral Artery as a site for a line

access of last resort. Prone to pseudoaneurysm and atheroma formation. It has an increased incidence of infectious complications and arterial thrombosis. In kids, aseptic necrosis of the femur head is rare but tragic complication.

That mechanical energy in a pressure transducer is converted to

an electrical signal.

The natural frequency of the measuring system must

exceed the natural frequency of the arterial pulse.

Dichrotic notch =

closure of aortic valve

Upstroke of a line wave form =

contractility

Systolic Blood Pressure (SBP)

correlates with changes in myocardial oxygen consumption. It is the peak pressure generated during systolic contraction.

Adding stopcocks, air in the line, and adding tubing all ________ frequency.

decrease

Quality of the transduced waveform depends on the

dynamic characteristics of the catheter-tubing-transducer system

In seated patient the arterial pressure in brain differs significantly from left ventricle pressure, so level at the...

ear, which approximates the circle of Willis

Arterial blood pressure is an indicator of

end-organ perfusion

Dorsalis Pedis and Posterior Tibial Arteries as site for a line

far from aorta and therefore distorted waveforms.

every patient receiving anesthesia shall have arterial blood pressure and heart rate determined and evaluated at least every

five minutes.

Overdamp=

frequency response too low: SBP underestimated

The rubber bladder of a noninvasive BP cuff should extend

halfway around extremity

High dicrotic notch

high stroke volume

Exaggerated variation in size of a line waveform during respirations =

hypovolemia

A slow upstroke on an a line waveform indicates

increased SVR or decreased contractility

A fast upstroke on an a line waveform indicates

increased contractility or decreased SVR

Diastolic Blood Pressure (DBP)

is an important determinant of adequate coronary perfusion. It is the trough pressure during diastolic relaxation.

If a noninvasive BP cuff is too narrow

overestimate SBP

If a noninvasive BP cuff is too wide

overestimate SBP

Downstroke of a line wave form=

peripheral vascular resistance

Oscillometry

preferred NIBP monitor. Versatile, quick, accurate

To Zero an a line

stopcock at level of midaxillary line, open, hit zero.

This mechanism of a pressure transducer is based on the

strain gauge principle; stretching a wire or silicone crystal changes its electrical resistance.

Axillary Artery as a site for a line

surrounded by the axillary plexus and nerve damage can result from hematoma or traumatic cannulation. Air or thrombi will quickly gain access to the cerebral circulation during retrograde flushing of left axillary artery.

Pulse Pressure

the difference between the systolic and diastolic pressures.

If no choice but to place on I.V. line side (i.e. shoulder surgery) place I.V. tubing where?

underneath cuff to prevent extravasations.