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بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم. قالوا سبحانك لا علم لنا الا ما علمتنا انك أنت العليم الحكيم. صدق الله العظيم. البقرة (23). Mansoura University. Faculty of Medicine. Anaesthesia & Surgical ICU Department. Cardiothoracic Anaesthesia Unit. CARDIAC ANAESTHESIA. Weaning From Cardiopulmonary Bypass.

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بسم الله الرحمن الرحيم

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  1. بسم الله الرحمن الرحيم قالوا سبحانك لا علم لنا الا ما علمتنا انك أنت العليم الحكيم صدق الله العظيم البقرة (23)

  2. Mansoura University Faculty of Medicine Anaesthesia & Surgical ICU Department Cardiothoracic Anaesthesia Unit

  3. CARDIAC ANAESTHESIA Weaning From Cardiopulmonary Bypass By: Mohamed R. El Tahan, M.D Lecturer of Anaesthesia&Surgical ICU 2006

  4. Objectives • To understand: • Pathophysiology of weaning from CBP. • Grouping of patients during weaning from CBP. • Preparation for weaning from CBP. • Discontinuation of CBP. • Difficult weaning from CBP.

  5. Introduction ☼Weaning Off CBP is: ► Simple process, that may occasionally prove very difficult or virtually impossible. ►Period of potential stress for the heart. ►Time of planned action among the cardiac operating team. ►Critical time. ►The time that the anaesthetist must be patient & well communicable with both the surgeons &the perfusionist. Souza&Elias (1997), andVegas (2000)

  6. Pathophysiology Cardiopulmonary Bypass is associated with various insults to normal physiology. Activationof complement. ElectrolyteDisturbances. ▲Cathecholamines. Vasopressin Release. Platelet Activation. CardiacArrest. Haemodilution. Anticoagulation. Hypothermia. SIRS Moyers & Tinker (1989)

  7. Pathophysiology Recovery Pattern: ☻Following separation from CBP, ventricular function improves initially, but then begins to worsen & reaches a nadir between 4-6hrs after surgery with full recovery occurring around 24 hrs post – operatively. ☻However, in patients withpre – operative ventricular dysfunction, the depression of ventricular function is more severe& recovery is longer. Preop. CBP end Post CBP hours Graphic illustration of myocardial performance following CBP changes Royster(1993)

  8. Grouping Of Patients Majority ■Group(A): • No difficulties to remove from CPB. • ±Slow infusion of inotropes/V.D. ■Group(B): • Mild to Moderate dysfunction. • Physiological (Starling’s law) orPharmacological (inotropes,vasoactive) • support. ■Group(C): • Poor or No cardiac action. • Aggressive Pharmacological support or Prolonged Mechanical support. Souza&Elias (1997)

  9. Preparation For Weaning [1.] Responsiveness. ☻Requirements of analgesic,narcotic and paralyzing drugs usually increase during re warming and the necessary adjustments are made to avoid awareness or the increase of the oxygen demand withavoidance of myocardial and circulatory depressant agents. Hemmings & Thomas (1993)

  10. Preparation For Weaning [2.] Rewarming. ►Temperature changes. ☻CPB is accompanied by heat loss even when hypothermia is not employed. ☻Re-warming should be initiated as early as necessary so that its completion coincides with completion of the surgical procedure or soon afterwards. ►Monitoring. ☻Patient temperature is monitored in atleast two sites such as: ☼Nasopharyngeal. ☼Esophageal. ☼Rectal. ☼Bladder. ☼Tympanic.

  11. Preparation For Weaning [2.] Rewarming. ►Goals. ☻Nasopharyngeal(36.5–37 C○). ☻Rectal(37 C○). ☻Bladder(35–37 C○). ☻Toe(>30 C○). ►A larger than 4C○ gradient between the nasopharyngeal and rectal temperatures is indicative of inadequate re – warming or increased vasoconstriction. ►This may predispose the patients to unstable cardiac, rhythm, shiveringandincreased SVR.

  12. Preparation For Weaning [2.] Rewarming. ►After Drop Phenomenon. ♦ 2 – 3C○decrease in nasopharyngeal temperature during sternal closure and transfer to ICU. ♦This may be attributed to redistribution of heat within the body as the normal pulsatile blood flow opens up some relatively colder and constricted vascular beds. ♦This may be corrected with: ☻Aslow infusion of nitroprusside or other vasodilators may provide a more homogenous re warming. ☻High CBP flow. ☻Pulsatile flow. Hemmings & Thomas (1993) Williams et al (1993)

  13. Preparation For Weaning [3.] Adequacy of anticoagulation. ☻The recovery of the metabolic functions speeds the elimination of heparin with re–warming, so , activated clotting time (ACT) should repeated more frequently at normothermia and additional 100u.Kg-1 of heparin may be needed to maintain ACT >480 seconds.

  14. Preparation For Weaning [4.] Reperfusion. ☻Regardless of the myocardial protection strategy and method used,even short periods of aortic cross–clamping can be followed by temporary functional depression. ☻Most hearts will benefit from a period of rest(reperfusion time) after releasing the aortic cross – clamp toreplenish myocardial ATP stores andwashout metabolitesfrom the coronary circulation. ☻Partial bypass may help to eliminate untowardpulmonaryV.C. ☻An average of15to 20minutesof supportive CPB will usually provide a good recovery timefor eachhourof clamping time. Moyers & Tinker (1989)

  15. Preparation For Weaning [5.] Electrolytes. POTASSIUM: ◙Potassium has pronounced effects on cardiac conduction. HYPERKALEMIA ◙Hyperkalemia during cardiac surgery may be caused bycardioplegia, haemolysis,acidosis,massive depolarization of muscle, andtissue cell death. ◙After adoption of blood cardioplegia a higher potassium level is more commonly seen at the end of perfusion. ◙High potassium level may be responsible for the presence of aheart blockorbradycardia. Hemmings & Thomas (1993)

  16. Preparation For Weaning [5.] Electrolytes. POTASSIUM: ◙Potassium has pronounced effects on cardiac conduction. HYPERKALEMIA ●Mild hyperkalemiarepresented by a serum level of 6 mEq/L will not require special treatment and resolve spontaneously. ●Severe hyperkalemiarepresented by a serum level > 6 mEq/L: ▄ Treatment :■ Frusemide:[3,10,30,300 mg]. ■1.0 gm glucose per kilogram and 1 unit of regular insulin per 4.0gm of glucose administered. ■ CaCl2:[1 – 2gm]. ■NaHCO3:[50mEq].

  17. Preparation For Weaning [5.] Electrolytes. POTASSIUM: ◙Potassium has pronounced effects on cardiac conduction. HYPOKALEMIA ●Hypokalemia if present should be treated to avoid the risks of atrial and ventricular arrhythmias. ●Hypokalemia may be caused by haemodilution with non–potassium priming solutions,diuresis,orincreased sympathetic tone during nonpulsatile perfusion. ●Hypokalemia predisposes to atrial arrhythmias, ventricular ectopy, anddigitalis toxicity. ▄ Treatment :■ KCL 5 –10mEq. Cheung&Chernow(1991)

  18. Preparation For Weaning [5.] Electrolytes. CALCIUM: ◙Ionized calcium levels usually decrease during CPB and appear to recoverfast thereafter. ◙Evidence suggests that calcium influx during ischemia – reperfusion contributes to myocardial dysfunction after CPB.

  19. Preparation For Weaning [5.] Electrolytes. CALCIUM: CaCl2:☻ Indications:►Valvural surgery. ►Pediatric surgery. ☻ Time:After reperfusion time or>8 minutes. ☻ Dose:10 – 15mg.Kg -1. ☻ Advantages:* ++ SVR. * Correction of ionized hypocalcaemia. *Correction of hyperkalemia. ☻ Drawbacks:*Ischemic cellular injury. *Coronary artery spasm. * IMA graft spasm. * Post – operative pancreatitis. *Blunt the responseto epinephrine & dobutamine. Prielipp & Butterworth (1997)

  20. Preparation For Weaning [5.] Electrolytes. MAGNESIUM: ◙Magnesium,essential to the normal electro–mechanical function of myocardial cells, has an important role in protecting the myocardium against the damaging effects of intracellular accumulation of Ca++. ◙Exogenous Mg++ has been considered in the management of cardiac dysrhythmias, myocardial infarction, and for improving myocardial performance after cardioplegic arrest.

  21. Preparation For Weaning [5.] Electrolytes. MAGNESIUM: MgSo4 : ☻ Dose: 50mg. Kg -1. ☻ Advantages:* Magnesiumprevents hypomagnesaemia in 1stpost – operative day. * less need for pacing,inotropes, & defibrillation during separation from CPB. * Magnesium inhibits platelet function. *Magnesium has neuroprotective effects as proved by reduced incidence of neurocognitive dysfunction in post – CABG. Gathwala(2001)

  22. Preparation For Weaning [6.] Optimizaion of oxygen delivery. • HAEMATOCRIT: • ◙ Haemodilution is universally used as an adjunct to CBP. • ◙Haematocrit values from 20 to 25% are usual with most perfusion • protocols. • ◙By the end of re warming, depending on renal function and the use • of diuretics haematocrit may reach24 to 30%. • ◙Hearts with severe preoperative myocardial dysfunction will perform • better immediately after termination of CPB with a haematocrit • level above 34%. • ◙Red blood cells transfusion during re – warming may be necessary • to adjust the haematocrit prior to discontinuing perfusion. DO2=1.34xHb[gm.dl-1]xSaO2 x COP Martineau(1996)

  23. Preparation For Weaning [6.] Optimizaion of oxygen delivery. B.Tissue oxygenation: ◙ A progressive disparity develops between arterial & mixed venous blood gases with regard to both acid-base status and oxygenation. ◙ Optimum ABGs will best reflect the adequacy of the oxygenator performance. ◙ Mixed venous blood gases analysis is well correlated to the adequacy of the tissues perfusion. ◙ Inadequate tissue perfusion & oxygenation is manifested by increased lactate production,decreased pH, decreasedSvO2and PvO2. ◙ A SvO2 of 75% and a minimum venous PvO2of 35mmHg are satisfactory to start weaning from CPB. DO2=1.34xHb [gm.dl-1]xSaO2x COP Souza&Elias (1997)

  24. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: ◙Assessment of cardiac functionimmediately prior to discontinuing perfusion is usually performed by: ☻Direct visualization: Simple visual observation of heart contraction and relaxation may provide valuable information on myocardial performance. ☻PAC. ☻TEE. DO2=1.34xHb [gm.dl-1]xSaO2 x COP Souza&Elias (1997)

  25. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Heart Rate & Rhythm: • ►Weaning from CBP requires a heart rate of70–100 bpmfor • adequate cardiac output to compensate for a lower stroke • volume associated with myocardial dysfunction. • ►Sinus rhythm is preferred for adequate atrial kick particularly • in the presence of a non – compliant thick walled ventricle.

  26. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Heart Rate & Rhythm: A- Asystole/ Heart block: ►Frequently, temporarily A.V block is found at the end of CBP because of pre–existing heart block, K+ cardioplegia & ischemic insult during aortic cross–clamping. (1.) Correction of hyperkalemia:CaCl2:(1−2g). Insulin (10U)± Glucose (40gm). Fursemide: (1,3,0,100 mg). NaHCO3: (50mEq). (2.) Atropine(2-2.5mg /70KgBWT). (3.) Temporary Epicardial Pacing:Types: A−V sequential,Ventricular.  Pacing Rate: 80– 100Bpm. (4.) Isoproterenol(0.01 −0.1 μg.Kg-1.min-1).

  27. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Heart Rate & Rhythm: B- Ventricular fibrillation/ Tachycardia: (1) DC defibrillator:(10- 40Watt/Sec). (2)Temperature:++ to 37 Cº. (3)Electrolytes:K+, MgSO4[1 –2gm]. (4) ABGs:pH , PaO2 , PaCO2. (5)Haematocrit:>30%. (6) CheckPAcatheter position. (7) SatisfactoryMAP[ ≥ 80mmHg], PAOP&COP. (8) Lidocaine:(1.5,1,0.5mg.Kg-1 i.v). (9) Amiodarone:( 5mg.Kg-1i.v). (10)Bretylium:(5–10mg.Kg-1 i.v followed with1 –2mg.min-1i.v.i).

  28. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Heart Rate & Rhythm: B- Ventricular fibrillation/ Tachycardia: ◙Baraka et al (2000) suggested that a bolus of 100mg of lidocaine administered 2minutes before release of the ACC can safely decrease the incidence of reperfusion ventricular fibrillation after weaning from CBP. ◙Turkoz et al (2002) concluded that a termination of persistent refractory VF, which can be difficult to treat, can be done by re – cross– clamping the ascending aorta while the patient is still on CBP,infusing 37Cº buffered K+ cardioplegic solution into the coronary system,and, after having achieved flaccid standstill,pacing the heart by the ventricular mode.

  29. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Heart Rate & Rhythm: C- Supra – ventricular arrythmias: (1.) Temperature:++ to 37 C○. (2.) Electrolytes:K+, Mg++. (3.) ABGs:.pH , PaCO2. (4.) Haematocrit. (5.) Check CVP catheter position. (6.) Overdrive Pacing. (7.) Synchronized DC:(5−10Watt/Sec). (8.) Adenosine:(6−12mg). (9.) β-blockers:Esmolol /Propranalol. (10.) CCB:Diltiazem(5−25mg i.v). (11.) Procainamide:(100mgq.5.00min to effect OR15mg.Kg-1).

  30. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Preload: ●●Preload is indirectly evaluated byventricular filling pressures. ◙Left ventricular preloadis inferred from the left atrial mean pressure or pulmonary artery diastolic pressure. ◙Right ventricular preloadis inferred from the right atrial pressure.

  31. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Preload: ►During weaning preload is pump– dependent and can be adjusted by balancing blood volume between patient and oxygenator. ►If there isenough volumein the pump it will come off CPB. ►In theabsence of sufficient volume, the perfusionist may administer additionalblood,PRBCs,colloidsorcrystalloids. ►It is preferred to givebloodandblood productsthrough a peripheral lineto avoid trauma to cells associated with the pump.

  32. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Afterload: ●Left ventricular afterload is evaluated by the status of peripheral vascular resistance [SVR]. ●Right ventricular afterload is evaluated by the status of pulmonary vascular resistance [PVR]. ► Elevated peripheral resistance can be reduced by the administration of vasodilators. ► Decreased peripheral resistance will require a vasoconstrictor infusion [norepinephrine,phenylephrine]to restore a normal peripheral resistance.

  33. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Afterload: • ►Elevated PVRcan be reduced by: • ▀ Correction and /or/ avoidance of the factors that increase PVR: • Hypoxia. • Hypercarbia. • Acidosis. • Sympathetic stimulation. • Hypervolemia / Hypovolemia. • ++ ITP[eg .PEEP]. • Drugs:■Ketamine. • ■Nitrous Oxide. • ▀Administration of pulmonary vasodilators: • [NO, PGEI, PDIs, Dobutamine, SNP, NTG].

  34. Preparation For Weaning [6.] Optimizaion of oxygen delivery. C.Cardiac output: DO2=1.34xHb [gm.dl-1]xSaO2 x COP • Contractility: ☻The usual situation is represented by a mild and very transient functional impairment shortly followed by resumption of effective cardiac action. ☻Most patients tolerate a relatively low B.P [SBP60–80 mmHg]for 3–5minutes and often it is a short time before the patient’s heart begins to function well without inotropes. Vegas (2000)

  35. Preparation For Weaning [7.] Ventilation. ►The lungs should be re – expanded with 2 – 3breaths to a peak pressure of 30 – 40 cmH2O with visual confirmation of bilateral lung expansion. ►This may help removal of trapped air in the pulmonary veins. ►Vaporizers are turned off 15–30minutes prior to termination of CBP as agents may take a long time to clear from the pump circuit, particularly the oxygenator. Vegas (2000)

  36. Preparation For Weaning [8.] Monitors. ►All pressure transducers are zeroed. ►There is frequently discrepancy between the radial arterial pressureand the centralaortic pressure, though the pressures gradually equilibrate over 10 – 30minutes. ►When a clinician is unsure of the blood pressure during separation from CPB, direct measurement of central aortic blood pressure, femoral arterial pressure,oscillometric, aortic line of the CPB circuit,anddigital palpationis advised. Vegas (2000)

  37. Preparation For Weaning [9.] Venting of arterial air. ●Cardiac Chambers,air could be evaluated byTEE. ●Aorta. ●Saphenous graft. ●Head – down position. ●Carotid Artery Compression. Miller (2000)

  38. Termination of CBP * Decreasing venous return to the pump. ☻The venous line is partially occluded by the surgeon or perfusionist and the patient’s heart is allowed to fill. ☻Watch the filling pressures and observe the right heart filling. ☻Try not to overfill the heart, even if the systemic blood pressure appears low, as over distension impairs ventricular contractility and subendocardial blood flow which may predispose to mitral regurgitation. Vegas (2000)

  39. Termination of CBP * Decreasing pump flow into the aorta. ☻As the heart ejects blood flows through the aorta, the aortic pump flow is lowered by 0.5 –1.0 L.minute-1. ☻If the heart function is expected to be good, the venous line is clamped and the heart weaned from CPB quickly. Vegas (2000)

  40. Termination of CBP * Termination bypass. ☻The venous line is completely clamped and the aortic pump head is turned off.*Rapid weaning:if good myocardial function. *Slow weaning:if poor myocardial function. ☻If needed, additional volume in increments of 50–100cc to optimize the preload with the aid of head – up position±venodilators. ☻Low preloadmay be due to: a.Continued volume redistribution due to vasodilatation. b.Changes in ventricular diastolic compliance. c.Ongoing bleeding in the chest. ☻Following CPB try to maintain an optimal SBP of 90–120mmHg. ☻Monitor adequacy of systemic perfusion by observing patient colour, urine output and absence of acidosis. Vegas (2000)

  41. Termination of CBP * After discontinuation of CBP. ☻Surgical control of major bleeding. ☻Decanulation of venous cannulae. ☻Decannulation of aortic cannula. ☻Reversal of anticoagulation. ☻Maintenance of circulating volume. ☻Maintenance of adequate coagulation. ☻Haemodynamic adjustment. ☻Anaesthesia. ☻Transfer to CVICU. Miller (2000)

  42. Break

  43. Scenario Discussion

  44. 60year aged male patient underwent successful LCA bypass & Aortic valve replacement. Hypothermic CBP was non – pulsatile & continued for80min.. Last cold cardioplegia was given20min. ago. Now, it’s the time of weaning from CBP, What do you want to ask me? Cardiac F. Fair • Pre–operative myocardial function status. • What’s about the depth of anaesthesia? • What’s the value of his body temperature? • What’s the value of ACT, now? • What’s the Haematocrite value? • What’s the value of SaO2? • What’s the heart rate & rhythm? • What’s the value of RV and LV preload? • What’s about the myocard. contractility? • What’s the value of RV and LV afterload? Anaesthesia ? Temperature 37 C○ ACT 390 sec. Hct. 21% SaO2 92% Heart R&R VF Preload Empty Contractility Weak Afterload PVR + +

  45. 60year aged male patient underwent successful LCA bypass & Aortic valve replacement. Hypothermic CBP was non – pulsatile & continued for80min.. Last cold cardioplegia was given20min. ago. Now, it’s the time of weaning from CBP, What are your next steps? • I’m already prepared my drugs and they areSTAND – BY. • I’ll ensure the adequate depth of anaesthesia [BY ?……. ]. • Re – warming was started to the value of Nasopharyngeal(36.5–37 C○) • Rectal(37 C○). • Additional Heparin was considered to maintain ACT > 460 seconds. • Re – perfusion for20 – 25min. • Additional Lasix or PRBCs was given to maintain Hct value20to25% • Maintain adequate tissue oxygenationABGs, SvO2andPvO2. • VF protocol? ± Electrolytes [K+, Ca++, Mg++]. • I’ll consider additional filling of the empty heart. • I’ll start my inotropic support after 2/3 of the re – perfusion time. • I’ll start my V.D to optimize the values of RV and LV afterload.

  46. Difficult Weaning Off CBP • ☻Difficult Separation From CBP (DSB): • 1.Systolic arterial pressure<80mmHg. • 2. Diastolic pulmonary artery pressure>15mmHg.During progressive • separation from CPB without inotropic, mechanical support of • cardiac function. • 3. Haemodynamic instability resulting in the re-introduction of CBP. • 4.The insertion of an intra – aortic balloon pump(IABP). • 5. Patients with successful weaning from CPB but requiring a significant • amount of: • Vasopressors(norepinephrine> 4µg.min-1 or epinephrine>2µg.min-1). • Inotropic drugs(dobutamine> 2µg.kg-1.min-1 or the use of amrinone and milrinone) during the first 12 hours after surgery. • IABP, or both. Bernardet al (2001)

  47. Difficult Weaning Off CBP ☻Factors of Difficult Weaning from CBP: 1. Aortic cross clamp time>120minutes. 2. Incomplete surgical repair: ►Valve replacement:a. small size. b. Failed prosthetic valve. c. Failed native repair. ►Incomplete revascularization:a. Graft failure [kink, debris,air]. b. Small vessels. c. Distal disease. 3. Inadequate myocardial protection: a.Non – systolic ECG. b.Prolonged ventricular fibrillation prior to aortic–cross clamp and un–clamping. c.Warm myocardium: due to* LVH [incomplete cardioplegic protection]. * High grade coronary stenosis. * Choice of graft order. * Non – coronary collateral flow. * Poor LV venting. 4. Reperfusion injury. 5. Ventricular distension [volume overload]. 6. Under–filled ventricles [inadequate preload]. Vegas (2000)

  48. Difficult Weaning Off CBP ☻The Consequences of Prolonged Weaning from CBP: 1. More prolonged pump time. 2. Potential systemic hypotension&organ damage. 3. Increase the need for multiple inotropes. 4. The use of mechanical assistance. 5. Potential need for blood products. Vegas (2000)

  49. Difficult Weaning Off CBP • ☻Predictors of The Needs of The Inotropic support: • Pre–Operative: • Age > 60years. • Low LVEF< 0.4. • Female sex. • Cardiomegally. • CHF. • Recent M.I < 6months. • D.M. • Three vessels coronary grafts. • Redo surgery. • Emergency surgery. • Intra–Operative: • CBP time >150 minutes.. • Aortic cross clamp time >120 minutes.. Royster (1993), Rao (1996)& Butterworth (1998)

  50. Difficult Weaning Off CBP • ☻Predictors of The Needs of The Vasopressor Support: • Pre – Operative: • Low LVEF<0.35−0.4. • Advanced Age. • D.M. • Peripheral vascular disease. • Drugs : eg :ACEIs, diuretics. • Recent M.I < 6months. • Intra – Operative: • Normothermic CBP.. • Longer perfusion time. • Hypothermic CPB -----------►Longer CPB time. • -----------►larger volume of cardioplegia. Argenziano(1998) & Christakis (1994)

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