1. Invasive blood pressure monitoring in critical care Presented by Ri 施易青

2. Outline • Introduction • Arterial pressure waveform • Controversial aspect of IBP monitoring • Conditions that affect arterial waveform morphology • Pros and cons of various cannulation sites

3. History • First invasive blood pressure monitoring: Stephen Hales’ horse (1733) • First attempt in human: Faivre’s amputee (1856) • Clinical use: Lambert and Wood (1947) • Modern cannulation technique: Barr (1961) • CV surgery in the 60s

4. Indications • Continuous monitoring of BP • Serial external monitoring inadequate • Hypotension or hypertension requiring vasoactive drugs • Respiratory illness or mechanical ventilation requiring frequent blood gases: >3X/D for arterial sticks >5X/D for combined arterial and/or venous sticks • Major Surgery: Especially CV or neuro. procedures

5. Contraindications • Absence of collateral flow • Raynaud's disease and cold infusions • Angiopathy, coagulopathy (recent anti-coag. or thrombolytic infusion increases risk of hematoma and compressive neuropathy), atherosclerosis: Use Caution! • Avoid locating near A-V fistula, and inserting through synthetic graft • Diabetics at increased risk of complications • Avoid local infection, burn or traumatic sites • Avoid extremities with carpal tunnel syndrome

7. The Pressure-pulse • 1st shoulder (the Inotropic Component): early systole, opening of aortic valve, transfer of energy from contracting LV to aorta • 2nd shoulder (the Volume Displacement Component): produced by continuous ejection of stroke volume from LV, displacement of blood, and distention of the arterial wall • Diastole: when the rate of peripheral runoff exceeds volume input to the arterial circulation

8. Possible Information gained from a pressure waveform • Systolic, diastolic, and mean pressure • Myocardial contractility (dP/dt) • Peripheral vascular resistance (slope of diastolic runoff) • Stroke volume (area under the pulse pressure curve) • Cardiac output (SV x HR)

9. Is arterial waveform predictive of cardiac contractility? • It is only “aortic arch pressure” that can be used to measure LV contractility, not “peripheral pressure”

11. As BP is measured farther into periphery: • The anacrotic and dicrotic notches disappear • The waveform appears narrower • The systolic and pulse pressure increase • The upstroke becomes steeper • The diastolic and mean pressure decrease

12. Morphology changes as a result of peripheral reflexions: • Reflexion of waves due to the tapering diameter • Reflexion due to changing content of the arterial wall • Reflexion also occur at branching points of vessels

13. Is the arterial waveform predictive of stroke volume? • The pressure does not predict flow • The distensible aortic arch act as a “fixed-capacity, high pressure reservoir” • Flow in the arterial tree is continuous, with 10-20 percent of LV power being pulsitile

14. Cullen et al: Correlation coefficient of 0.82 between changes in stroke volume and changes in peripheral systolic pressure in halothane-induced anesthesia status, where peripheral vascular resistance remained essentially unchanged Interpretation of blood pressure measurement in anesthesia Anesthesiology, 40:6 1974

15. Role of direct arterial pressure monitoring • Provides trends over a wide range • Unreliable as absolute hemodynamic values • As a reminder • “A needle in an artery does not guarantee a pressure or accuracy any more than an endotracheal tube guarantee a patent airway.”

16. Conditions that affect arterial waveform morphology • Hyperdynamic pulse • Pulsus paradoxus • Reverse pulsus paradoxus • Pulsus alternans • Pulsus bisferens

17. Hyperdynamic pulse • Aortic regurgitation • AV fistula • Thyrotoxicosis • Anemia • Pregnancy • sepsis

18. Pulsus paradoxus

19. Cause of pulsus paradoxus • Change in pleural pressure associated with breathing • Anatomic relationship between two ventricle chambers

20. D/D of Pulsus paradoxus • Constrictive pericarditis or cardiac tamponade • COPD • Asthma • Tension pneumothorax

21. Reverse pulsus paradoxus • An exaggeration of the rise in systolic BP during mechanical ventilation • A sensitive indicator of hypovolemia in mechanically ventilated p’t

22. Pulsus alternans

23. Cause of pulsus alternans • A sign of decreased myocardial contractility (deletion of the number of myocardial cells contracting on alternate beats) • An alteration in diastolic volume leading to beat-to-beat variation in preload

24. D/D of pulsus alternans • LV dysfunction • Pericardial effusion

25. Pulsus bisferens

26. Pulsus bisferens • Hypertrophic cardiomyopathy • Aortic regurgitation

27. Advantages and disadvantages on various cannulation sites • Radial artery • Brachial artery • Femoral artery • Axillary artery • Dorsalis pedis artery

28. Radial artery • Advantages: easy to cannulate, accessible during most type of surgery, good collateral circulation, patient comfort, Allen’s test • Disadvantages: thormbus formation, possible injury to nerve, augmentation of SBP,

29. Brachial artery • Advantages: easy to cannulate, larger catheter, less SBP augmentation, collateral vessels • Disadvantage: uncomfortable for p’t, median nerve damage

30. Femoral artery • Advantages: prolonged use, useful in shock p’t, largest catheter • Disadvantages: atherosclerotic plaque may break off, massive hematoma, difficult to immobilize

31. Axillary artery • Advantages: large size, useful in peripheral artery dz and shock, proximity to aorta, • Disadvantages: neurologic complication, technically difficult

32. Dorsalis pedis artery • Advantages: dual circulation • Disadvantages: greatest SBP augmentation, thrombus formation, difficult to immobilize, impossible to walk

33. Take home message • The arterial system functions as a damped, resonant, transmission line, transmitting various frequencies with different degrees of attenuation. • The clinician must dissuade himself from the belief that the peripheral pressure accurately reflects aortic arch pressure.

34. reference • Monitoring in Anesthesia and Critical Care Medicine, 2nd edition. 1990 • Hemodynamic monitoring: Invasive and Noninvasive Clinical application, 2nd edition.1995 • Cullen et al: Interpretation of blood pressure measurement in anesthesia. Anesthesiology, 40:6 1974

35. Thanks for your attention!