Hemodynamic Monitoring Flashcards
Radial Artery Catheterization
The radial artery is the most common site for invasive blood pressure monitoring because it is technically easy to cannulate and complications are uncommon.
Radial Artery Catheterization Technique
Needle Held 30- 45 degrees.
Dorsiflexion of the wrist should be mild at most to avoid attenuating the pulse by stretch or extrinsic tissue pressure. The course of the radial artery proximal to the wrist is identified by gentle palpation, the skin is prepared with an antiseptic, and a local anesthetic is injected intradermally and subcutaneously beside the artery. Arterial catheterization can be performed with a standard IV catheter or an integrated guidewire-catheter assembly designed for this purpose.
Radial Artery Catheterization Care
Extreme wrist dorsiflexion following establishment of an A line should be avoided to prevent injury to the median nerve.
Complication Risk: Radial A-line
Overall low risk Increased Risk: vasospastic arterial disease previous arterial injury thrombocytosis, protracted shock high-dose vasopressor administration, prolonged cannulation infection.
Allen Test
Technique: compress both the radial and ulnar arteries and asks the patient to make a tight fist, exsanguinating the palm. The patient then opens the hand, avoiding hyperextension of the wrist or fingers. As occlusion of the ulnar artery is released, the color of the open palm is observed.
Normally, the color will return to the palm within several seconds; severely reduced ulnar collateral flow is present when the palm remains pale for more than 6 to 10 seconds.
Predictive value of this test is poor
Ischemic injuries seen even in patients with Normal Allen test
Indications for A-line
Elective deliberate hypotension Wide swings in intra-op BP Risk of rapid changes in BP Rapid fluid shifts Titration of vasoactive drugs End organ disease Repeated blood sampling Failure of indirect BP measurement
A-line Transducer System
Transducer system- continuous flush device
System dynamics and accuracy improved by minimizing tube length, limit stop cocks, no air bubbles, the mass of fluid is small, using non compliant stiff tubing
calibration at level of heart (mid-axillary line/right atrium or meatus of ear/circle of Willis if concerned about cerebral perfusion as in sitting pt)
Zeroing and Leveling Transducer
All pressures displayed on the monitor are referenced to local atmospheric pressure
The phlebostatic axis is on the 4th intercostal space along the mid axilla line.
The phlebostatic axis is relevant for supine and up to 60 degrees of head-up tilt.
If the transducer has not been levelled to the phlebostatic axis, pressure readings will be either falsely high or falsely low.
A 20-cm difference in height produces a 15-mm Hg difference in pressure
High-low
Low- high
Position and A-line
This point must be specifically positioned relative to the patient to ensure correct transducer level. When a significant or unexpected change in pressure occurs, the zero reference value can be rechecked quickly by opening the stopcock and noting that the pressure value on the bedside monitor is still zero.
Despite successful transducer zeroing, the measured blood pressure values seem erroneous, and a malfunctioning pressure transducer, cable, or monitor should be suspected
Underdamped
Underdamped- Systolic pressure overshoots and additional small, non-physiologic pressure waves distort the waveform and make it hard to discern the dicrotic notch (If visible, dicrotic notch will be exaggerated).
Several oscillations during square wave test.
Saltatory rather than gradual transitions. Systolic will reported higher and diastolic lower.
Overdamped
Overdamped- waveform is recognizable by its slurred upstroke, absent dicrotic notch, and loss of fine detail. Such waves display a falsely narrowed pulse pressure, although MAP may remain reasonably accurate.
One oscillation during square wave test. Dicrotic notch will be hard to visualize. Low systolic and overestimated diastolic.
Causes of Underdamped:
Catheter whip or artifact
Stiff non-compliant tubing
Hypothermia
Tachycardia or dysrhythmia
Causes of Overdamped:
Loose connections Air bubbles Kinks Blood clots Arterial spasm Narrow tubing
Actions to assess and fix damped wave forms:
Actions: Damped Waveforms Pressure bag inflated to 300 mmHg Reposition extremity or patient Verify appropriate scale Flush or aspirate line Check or replace module or cable
Square Wave Test
Square Wave Testing
Square wave testing can have a direct impact on the validity and accuracy of the hemodynamic values which are obtained from the invasive monitoring device.
It assesses for adequately damped, over-damped, and under damped.
Adequately- damped waveform is when there are only two oscillations that follow the fast-flush wave. Oscillations should be no more than 1/3 the height of the previous oscillation. The subsequent transducing should demonstrate a clear arterial waveform with a discernable dicrotic notch.
Aline Complications
Nerve Damage Hemorrhage/ Hematoma Infection Thrombosis Air embolus Skin necrosis Loss of digits Vasospasm Arterial aneurysm Retained guide wire
ASA closed claims for A-lines
ASA closed claims for A-lines: 54% were related to radial artery use (ischemic injury, median or radial nerve injury, or retained wire fragment), less than 8% were associated with use of the brachial artery, and the remainder followed severe thrombotic or hemorrhagic complications after femoral artery monitoring
Complications of Direct Arterial Pressure Monitoring
Distal ischemia, pseudoaneurysm, arteriovenous fistula Hemorrhage
Arterial embolization
Infection
Peripheral neuropathy Misinterpretation of data Misuse of equipment
Aortic Stenosis
Aortic stenosis Pulsus parvus (narrow pulse pressure) Pulsus tardus (delayed upstroke)
Aortic Regurgitation
Aortic regurgitation Bisferiens pulse (double peak) Wide pulse pressure
Hypertrophic cardiomyopathy
Spike and dome (mid-systolic obstruction)
Systolic left ventricular failure
Pulsus alternans (alternating pulse pressure amplitude) inspiration)
Cardiac tamponade
Pulsus paradoxus (exaggerated decrease in systolic blood pressure during spontaneous
Pulse pressure variation
Pulse pressure variation (PPV) is calculated as the difference between maximal (PPMax ) and minimal (PPMin ) pulse pressure values during a single mechanical respiratory cycle, divided by the average of these two values.
Yields a %- PPV: grey zone of 9% to 13%, such that those below 9% should receive intravascular volume expansion, whereas those above 13% should not. For those between the two values, the measurement is not able to provide meaningful information and the decision should be made on other criteria
During positive pressure ventilation, increases in lung volume compress lung tissue and displace blood contained within the pulmonary venous reservoir into the left heart chambers, thereby increasing left ventricular preload. Simultaneously, the increase in intrathoracic pressure reduces left ventricular afterload. The increase in left ventricular preload and decrease in afterload produce an increase in left ventricular stroke volume, an increase in cardiac output, and in the absence of changes in peripheral resistance, an increase in systemic arterial pressure. In most patients the preload effects are more prominent, but in patients with severe left ventricular systolic failure, the reduction in afterload plays an important role in increasing ventricular ejection.
To measure PPV accurately: In general, mechanical ventilation with tidal volumes of 8 to 10 mL/kg, positive end-expiratory pressure of 5 mm Hg or greater, regular cardiac rhythm, normal intraabdominal pressure, and a closed chest are necessary to duplicate the experimental conditions.
