Cardiovascular Monitoring

1. Cardiovascular Monitoring Drabdollahi

2. Although a stethoscope should be present in every anesthetizing location, continuous stethoscopy is an insensitive method for early detection of untoward hemodynamic events.

3. Most automated noninvasive blood pressure measuring devices use an oscillometric measurement technique and rarely cause complications. Caution should be exercised in patients: • Who cannot complain of arm pain • Those with irregular rhythms that force repeated cuff inflation • Individuals receiving anticoagulant therapy

4. Direct arterial pressure monitoring should be widely used in operative patients with severe cardiovascular diseases or those undergoing major surgical procedures that involve significant blood loss or fluid shifts.

5. The Allen test for palmar arch collateral arterial flow is not a reliable method to predict complications from radial artery cannulation. Despite the absence of anatomic collateral flow at the elbow, brachial artery catheterization for perioperative blood pressure monitoring is a safe alternative to radial or femoral arterial catheterization.

6. The accuracy of a directly recorded arterial pressure waveform is determined by the natural frequency and damping coefficient of the pressure monitoring system. Optimal dynamic response of the system will be achieved when the natural frequency is high, thereby allowing accurate pressure recording across a wide range of damping coefficients.

7. Rather than the common placement at the midaxillary line, the preferred position for alignment (or “leveling”) of external pressure transducers is approximately 5 cm posterior to the sternomanubrial junction. When using external transducers and fluid-filled monitoring systems, this transducer location will eliminate confounding hydrostatic pressure measurement artifacts

8. Selecting the best site, catheter, and method for safe and effective central venous cannulationrequires that the physician consider the purpose of the catheterization, the patient's underlying medical condition, the intended operation, and the skill and experience of the physician performing the procedure. Right internal jugular vein cannulation is favored by most anesthesiologists because of its consistent, predictable anatomic location and its relative ease of access intraoperatively

9. Methods to reduce mechanical complications from central venous catheters include the use of ultrasound vessel localization, venous pressure measurement before insertion of large catheters, and radiographic confirmation that the catheter tip rests outside the pericardium and parallel to the walls of the superior vena cava.

10. When using CVP as a measure of intravascular volume, the influences of ventricular compliance and intrathoracic pressure must be taken into consideration. In general, a trend in CVP values or its change with therapeutic maneuvers is more reliable than a single measurement. Important pathophysiologic information can be obtained by careful assessment of the CVP waveform morphology.

11. Of the many complications of central venous and pulmonary artery catheters, catheter misuse and data misinterpretation are among the most common.

12. Pulmonary artery wedge pressure is a delayed and damped reflection of left atrial pressure. The wedge pressure provides a close estimate of pulmonary capillary pressure in many cases but may underestimate capillary pressure when postcapillary pulmonary vascular resistance is increased, as in patients with sepsis.

13. Use of central venous, pulmonary artery diastolic, or pulmonary artery wedge pressure as an estimate of left ventricular preload is subject to many confounding factors, including changes in diastolic ventricular compliance and juxtacardiac pressure.

14. Most randomized prospective clinical trials have failed to show that pulmonary artery catheter monitoring results in improved patient outcome. Reasons cited for these results include misinterpretation of catheter-derived data and failure of hemodynamic therapies that are guided by specific hemodynamic indices.

15. Thermodilution cardiac output monitoring, the most widely used clinical technique, is subject to measurement errors introduced by rapid intravenous fluid administration, intracardiac shunts, and tricuspid valve regurgitation.

16. Mixed venous hemoglobin oxygen saturation is a measure of the adequacy of cardiac output relative to body oxygen requirements. It is also dependent on arterial hemoglobin oxygen saturation and hemoglobin concentration.

17. Introduction to Cardiovascular Monitoring: Focused Physical Examination • Although cardiovascular monitors receive prime emphasis, the fundamental basis for circulatory monitoring remains in the eyes, hands, and ears of the anesthesiologist.

18. اعتماد بيش از حد به مانيتورينگ هاي الكترونيكي باعث كاهش در مهارت و تشخيص فيزيكي مي گردد

19. The most obvious, perhaps trivial, example is a patient whose electrocardiogram (ECG) shows asystole. Detection of a normal pulse by direct palpation focuses the anesthesiologist on correcting the monitoring artifact rather than initiating cardiopulmonary resuscitation.

20. During cardiac surgery the beating heart may be observed directly, and palpation of the ascending aorta by the surgeon provides a useful estimate of aortic blood pressure. In fact, the surgeon's evaluation of any arterial pulse within the surgical field should be considered whenever severe hemodynamic instability develops.

21. Stethoscopy • Laennec is credited with introducing the stethoscope into general medical practice in 1818, nearly a century elapsed before Harvey Cushing proposed in 1908 that the stethoscope be used as a routine cardiopulmonary monitoring device during surgery. For many years thereafter, intraoperative monitoring with either a precordial or an esophageal stethoscope became the most common simple method for monitoring ventilation and circulation in anesthetized patients.

22. Though minimally invasive and practical only for patients receiving general endotracheal anesthesia, the esophageal stethoscope provides monitoring benefits not available with its precordial cousin.

23. Clear breath sounds and distinct heart sounds are audible in most patients when the tip of the stethoscope is positioned 28 to 30 cm from the incisors, and esophageal temperature can be measured with an incorporated thermistor

24. complications • Hypoxemiafrom unintended tracheobronchial placement or compression of the membranous posterior portion of the trachea in small infants, loss down the esophagus, detachment of the acoustic cuff, and distortion of surgical anatomy in the neck. Placement of the esophageal stethoscope may also cause pharyngeal or esophageal trauma and interfere with NGT positioning or TEE.

25. The current role of intraoperative stethoscopy as a continuous monitor has become limited to special applications (e.g., pediatric anesthesia) and to institutions with insufficient resources to purchase electronic monitors

26. از استتوسكوپ ايزو فاژيال براي تنظيم حرارت (تشخيص حرارت بدن) وبه عنوان ليد ECG براي تشخيص اريتمي دهليزي ايسکمی بطن راست وايسكمی Posteaior L.V. و همچنين براي استفاده جهت Pace قلبي در موارد برادي كاردي سينوسي وريتم جانكشنال استفاده مي شود.

27. Heart Rate Monitoring • The simplest and least invasive form of cardiac monitoring remains measurement of the heart rate. Under most circumstances in modern anesthesia practice, electronic devices are used to continuously monitor this vital sign and provide an important guide to the influence of anesthetics and surgical stimuli on the patient's condition. The ability to estimate the heart rate quickly with a “finger on the pulse” is a skill as important as this expression is common.

28. Although any monitor that measures the period of the cardiac cycle can be used to determine the heart rate, the ECG is the most common method used in the operating room.

30. Artifacts • Electrical interference in the ECG trace may arise from sources other than the electrosurgicalunit. • Muscle twitching and fasciculations, as well as from various medical devices, including lithotripsy machines, cardiopulmonary bypass equipment, and fluid warmers.

31. Pulse Rate Monitoring • The distinction between heart rate and pulse rate centers on whether a given electrical depolarization and systolic contraction of the heart (heart rate) generate a palpable, peripheral arterial pulsation (pulse rate).

32. Pulse deficit • Pulse deficit describes the extent to which the pulse rate is less than the heart rate. Such deficit is typically seen in patients with: • Atrial fibrillation, in which short R-R intervals compromise cardiac filling during diastole and result in reduced stroke volume and an imperceptible arterial pulse

33. 2- Electrical-mechanical dissociation, 3- Pulseless electrical activity, seen in patients with cardiac tamponade, extreme hypovolemia, 4- Other conditions in which cardiac contraction does not generate a palpable peripheral pulse.

34. IABP - increase PR • AI (Bisference pulse)- increase PR • Pulsusalternans - decrease PR

35. Arterial Blood Pressure Monitoring • Like the heart rate, blood pressure is a fundamental cardiovascular vital sign and a critical part of monitoring anesthetized or seriously ill patients. The importance of monitoring this vital sign is underscored by the fact that standards for basic anesthetic monitoring mandate measurement of arterial blood pressure at least every 5 minutes in all anesthetized patients.

36. Techniques for measuring blood pressure fall into two major categories: • Indirect cuff devices • Direct arterial cannulation and pressure transduction

37. Although direct arterial blood pressure measurement is the reference standard against which other methods are compared, even this technique can yield spurious results. Consequently, blood pressure measured in clinical practice with different techniques often yields significantly different values.

38. Indirect Measurement of Arterial Blood Pressure • Manual Intermittent Techniques: • Most indirect methods of measuring blood pressure rely on a sphygmomanometer similar to the one first described by Riva-Rocci in 1896. This apparatus included an arm-encircling inflatable elastic cuff, a rubber bulb to inflate the cuff, and a mercury manometer to measure cuff pressure.

39. Riva-Rocci described the measurement of systolic arterial blood pressure by determining the pressure at which the palpated radial arterial pulse disappeared as the cuff was inflated.

40. A commonly used variation of the Riva-Rocci method, termed the “return-to-flow technique,” records the pressure during cuff deflation at which the pulse reappears and is detected by palpation. When the patient has a finger pulse oximeter or an indwelling arterial catheter in the ipsilateral arm, return to flow can be detected by reappearance of the plethysmographic or arterial pressure waveforms

41. Return-to-flow methods provide a simple, rapid estimation of systolic blood pressure during urgent situations but do not allow measurement of diastolic blood pressure.

42. To measure both systolic and diastolic arterial pressure, the most widely used intermittent manual method is the auscultatory technique, originally described by Korotkoffin 1905

43. Using a sphygmomanometer, cuff, and stethoscope, Korotkoff measured blood pressure by auscultating sounds generated by arterial blood flow. These sounds are a complex series of audible frequencies produced by turbulent flow beyond the partially occluding cuff.

44. The pressure at which the first Korotkoff sound is heard is generally accepted as systolic pressure (phase I). The character of the sound progressively changes (phases II and III), becomes muffled (phase IV), and is finally absent (phase V). Diastolic pressure is recorded at phase IV or V.

45. phase V may never occur in certain pathophysiologic states such as aortic regurgitation.

46. Pathologic or iatrogenic causes of decreased peripheral blood flow, such as cardiogenic shock or high-dose vasopressor infusion, can attenuate or obliterate the generation of sound and result in significant underestimation of blood pressure.

47. In contrast, low compliance of the tissues underlying the cuff, as encountered in a shivering patient, will require an excessively high cuff-occluding pressure and produce “pseudohypertension.” A similar situation exists in patients with severe calcific arteriosclerosis, whose noncompressible arteries may be palpated distal to a fully inflated cuff (positive Osler sign).

48. Other common sources of error during intermittent manual blood pressure measurement include selection of an inappropriate cuff size and excessively rapid cuff deflation. The optimal cuff should have a bladder length that is 80% and a width at least 40% of arm circumference.

49. The cuff should be applied snugly, with the bladder centered over the artery and any residual air squeezed out. Although too large a cuff will generally work well and produce little error, use of cuffs that are too small will result in overestimation of blood pressure. The cuff deflation rate is another important variable that influences manual blood pressure measurement.

50. Automated Intermittent Techniques • Many limitations of manual intermittent blood pressure measurement have been overcome by automated NIBP devices, which are now used widely. In addition, automated NIBP devices provide audible alarms and can transfer data to a computerized information system.