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Basic Physics in Anesthesia
Davis & Kenny 5th edition Ch 17 Blood Pressure Measurement
41
Medical
Graduate
03/07/2009

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Cards

Term
Blood Pressure
Definition
The force of contraction of the myocardium acting on the blood contained in the heart
Term
Laplace's Law in BP measurement
Definition
P = 2T/R
Term
Laplace's Law in a distended failing heart
Definition
a distended failing heart has a larger radius than normal so it produces less pressure, unless it can contract proportionately more forcefully
Term
Starling's law of the heart
Definition
In a normal heart, slight distension cause by an increased venous return and the consequent lengthening of cardiac muscle increases the force of contraction and the pressure is maintained.
Term
Mechanical work of heart
Definition

Work = Pressure X stroke volume

(increase in stroke volume or BP, increases work)

Term
Elastic tissue of aorta and main vessels
Definition
Stores the work of the heart in systole to maintain blood flow during diastole.
Term
Standard reference point for BP measurement
Definition
The level of the right atrium
Term
BP variations
Definition
  • Varies with the site of measurement, caliber of vessel and its distance from the heart.
  • BP is pulsatile and changes in the wave pattern in different vessels alter the systolic pressures. * BP is posture dependent.
  • BP has a diurnal variation, lower at HS
  • IPPV decreases BP
  • Anxiety increases BP.
Term
Peripheral resistance
Definition
Mean (aortic) blood pressure/Cardiac output
Term
Mean arterial pressure
Definition
Peripheral resistance X Cardiac output
Term
Mean Blood Pressure
Definition

(2DBP + SBP)/3

 

An MAP of about 60 is necessary to perfuse coronary arteries, brain, kidneys.

Term
Advantages of a cuff pressure
Definition
simplest noninvasive.
Term
How a BP cuff works
Definition
Identifies the pressure at which the pulse returns after occlusion.
Term
Correct Use of BP cuff
Definition

Placed where center of its bladder is on medial side of arm over brachial artery and width should be 20% greater than diameter of arm.

The mercury manometer must read zero before use and should be used vertically.

Partial blockage of air vent in manometer or of connecting tubings may lead to inaccurate or sluggish readings.

Term
Correct Use of BP dectector
Definition
Inflate cuff above expected systolic pressure. Slowly release at a rate of 2-3mmHg/sec. (for sound) Systolic pressure is indicated by reappearance of peripheral pulse by manual palpation of radial pulse or auscultation over brachial artery. Listen throughout whole cycle for Korotkoff sound (5 phases).
Term
Correct use of Oscillometry
Definition
As bp cuff deflated from above systolic, needle on an aneroid gauge starts to oscillate when systolic pressure is reached. The oscillations increase in amplitude to a maximum at the mean BP, then decrease at a less precise point about the diastolic.
Term
Automated Oscillometric Technique
Definition
A single cuff collected to a pressure transducer measures both the pressure and oscillations. The processing unit analyzes the signal from the transducer to detect the ONSET of oscillations at the systolic pressure AND the point of MAXIMUM oscillation at mean pressure and to give an indication of the diastolic pressure.
Term
NIBP and time intervals
Definition

If the interval between readings is too short, impeded blood flow may result.

 

A minimum interval is preferred of 2 minutes per inflation.

Term
NIBP and ectopy
Definition
Readings are less accurate if the pt has a dysrhythmia.
Term
Radial Artery Compression
Definition
This technique is used to reduce the potential for injury resulting from repeated rapid inflation of a bp cuff. It uses a pressure sensor strapped to the wrist over the radial artery. The sensor is driven hydraulically by a control system and is used both to apply pressure to the wall of the radial artery and to measure pressure fluctuations at the wall of the artery due to pulsations during the cardiac cycle. Approx 12-15 heart beats are required to obtain a measurement.
Term
The Penaz Technique
Definition
Used to give continuous measurement of finger blood pressure. Cuff is placed on finger and attached to a transducer to measure pressure and to an air pump. The apparatus detects the mean pressure from the point of maximum oscillation. The system also includes an infrared light-emitting diode and a photocell which act as a photoplethysmograph.
Term
Other Automated Techniques for BP measurement
Definition

A microphone may be positioned over the brachial artery to detect either audible sound or infrasound.

 

An ultrasonic transmitter and receiver used to detect Doppler changes of frequency from arterial wall movement.

Term
Problems with NIBP
Definition
Have problems with pts with an irregular pulse and it does not measure BP continuously.
Term
Invasive BP techniques
Definition
A peripheral artery is preferred for arterial cannulation so the whole limb is not threatened if a clot or hematoma forms. Radial artery is most preferred site, after Allen’s test performed.
Term
Possible complications of invasive BP techniques
Definition
Intra-arterial cannulations may rarely cause thrombosis to occur.
Term
Steps to minimize complications with IBP techniques
Definition

To prevent thrombosis, the cannula should be constructed of Teflon, be short with parallel sides.

 

To prevent dislodgement, it should be sutured in place

Term
Care of IBP devices after insertion
Definition

The cannula and its connections must be fixed securely to avoid leakage resulting in blood loss.

To avoid clotting, intermittent flushing is recommended.

Care should be taken when flushing, and syringes smaller than 5ml should not be used because they generate high pressures that can damage arterial walls or the diaphragm of the pressure transducer.

Term
Allen test
Definition

1) The hand is elevated and the patient/person is asked to make a fist for about 30 seconds.

2) Pressure is applied over the ulnar and the radial arteries so as to occlude both of them.

3) Still elevated, the hand is then opened. It should appear blanched (pallor can be observed at the finger nails).

4) Ulnar pressure is released and the color should return in 7 seconds.

If color does not return or returns after 7-10 seconds, then the ulnar artery supply to the hand is not sufficient and the radial artery therefore cannot be safely pricked/cannulated.

Term
Fiberoptic Catheter Tip Transducer
Definition
Employs a mirror-coated moving diaphragm which reflects light carried to the tip by an optical fiber
Term
Arterial Pressure Recordings
Definition
The form of the pressure wave alters as blood flows to the periphery. Systolic pressure is found to be an average of 5 mmHg higher and diastolic 8mmHg lower with direct measurement at the radial artery than with indirect techniques. The frequency range of the arterial pressure wave is 0 Hz to 40 Hz.
Term
Advantages of IBP
Definition
Main advantages of invasive = bp accuracy and bp can be monitored continuously.
Term
Disadvantages of IBP
Definition
Arterial damage,
costly,
technical skill
Term
Conversion of BP into an electrical signal
Definition
Movement of the diaphragm of the pressure transducer converts the BP change into an electrical signal. This movement of the diaphragm is associated with a very small movement of saline to and fro along the catheter with changes of pressure.
The system possesses a resonant frequency at which oscillations can occur and produce a blood pressure waveform
Term
Resonance in Waveform
Definition
Occurs if the resonant frequency is outside the range of frequencies in the BP waveform.
Term
Ways to avoid Resonance in arterial pressure tracings
Definition
Use a shorter, wider, or stiffer cathter.
Term
Dampened arterial tracings
Definition
Caused by restriction to the transmission of the BP from the artery to the transducer diaphragm.
Produced by air bubbles in the catheter or in the transducer chamber OR by blood clot in the cannula.
Term
Placement of CVP catheter
Definition
To measure CVP, a catheter is inserted via an arm or neck vein and advanced so that it reaches the superior vena cava.
Term
Complications of CVP
Definition
Faulty techniques can increase the risk of pneumothorax, hemothorax, or hydrothorax and of infection.
Term
Balancing a CVP
Definition
Before CVP reading is taken, pt is placed in horizontal position. The transducer is zeroed to the pt midaxillary line, which represents the level of the right atrium.
Term
Venous Pressure
Definition
The filling of the heart depends on adequate venous pressure. If venous pressure rises, the normal heart fills to a greater extent and automatically increases its output. If there is appreciable blood loss, venous pressure falls.
Term
Wedge Pressure
Definition
Measurement of pulmonary wedge pressure gives an indication of the left arterial pressure. It is obtained by advancing a special venous catheter through the right heart and pulmonary artery until it wedges into a small branch of the pulmonary artery, where it would be used to measure the pressure of the pulmonary capillaries.
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