ANAESTHESIA FOR AORTIC ANEURYSM REPAIR SURGERY

ANAESTHESIA FOR THORACOABDOMINAL AORTIC ANEURYSM REPAIR SURGERY: 

ANAESTHESIA FOR THORACOABDOMINAL AORTIC ANEURYSM REPAIR SURGERY DR. RAFIA TABASSUM ANAESTHETIST, DEPT: ANAESTHESIA & SICU, PMCH NAWABSHAH,SIND-PAKISTAN

DEFINITION: 

DEFINITION An aneurysm is an area of a localized widening (dilation) of a blood vessel. (The word "aneurysm" is borrowed from the Greek "aneurysma" meaning "a widening"). A true aortic aneurysm is a dilation of the entire aorta, as measured across from the adventitia to the adventitia, and it is associated with degenerative changes of the aortic wall where the original histological constituents can still be recognized. The abdominal aorta is aneurysmal when its diameter is greater than 3.0 cm.

PREVALENCE: 

PREVALENCE 1-4% of the population over 50 years of age Ascending Aorta 45% Arch of Aorta 10% Descending Aorta 35% Thoraco-abdominal Aorta 10% Men are 5 to 10 times more likely than women Rupture of a thoracic aneurysm has a greater than 97% fatality rate

RISK FACTORS: 

RISK FACTORS Age over 60 years Smoking history Male gender High blood pressure High cholesterol Obesity

ETIOLOGY: 

ETIOLOGY Atherosclerotic >50% Genetic/hereditary: Post Trauma-- heart valve surgery Mycotic (fungal) infection IV drug abuse -- cocaine Syphilitic aortitis Arteritis: Inflammation of blood vessels as occurs in Takayasu disease , giant cell arteritis, and relapsing polychondritis . Connective tissue diseases involving the aortic Wall; Marfan syndrome Ehlers-Danlos syndrome Cystic medial degeneration R heumatoid arthritis

PATHOPHYSIOLOGY: 

PATHOPHYSIOLOGY Nutritional blood flow to the aorta is compromised, and the increasing diameter is associated with increased wall tension (LaPlace’s law), even when arterial pressure is constant.

CLASSIFICATION: 

CLASSIFICATION Crawford classified TAAA in type I, II, III, and IV according to the anatomic extent Dr Cinà classified into a broader range of anatomical situations found in clinical practice DeBakey Classification Stanford Classification

PowerPoint Presentation: 

Cina’s proposed classification of aneurysmal disease of the entire thoracoabdominal aorta.

SYMPTOMS OF AN ABDOMINAL AORTIC ANEURYSM : 

SYMPTOMS OF AN ABDOMINAL AORTIC ANEURYSM Asymptomatic “watchful waiting.” A rapidly expanding aneurysm is also at imminent risk of rupture. Actual rupture of an abdominal aneurysm can cause sudden onset of back and abdominal pain , sometimes associated with abdominal distension, a pulsating abdominal mass, and even shock (severe low blood pressure due to massive blood loss).

CLINICAL DIAGNOSIS : 

CLINICAL DIAGNOSIS Careful palpation or feeling of the abdomen may reveal the abnormally wide pulsation of the abdominal aorta. This is characteristically felt on both sides of the aorta which is in the midline of the abdomen. Even large aneurysms can be very difficult to detect on physical examination in overweight people. Aneurysms on the verge of rupture and that are rapidly enlarging, are often tender . Listening with a stethoscope may also reveal a bruit or abnormal sound from turbulence of blood within the aneurysm.

INVESTIGATIONS : 

INVESTIGATIONS X-rays show calcium deposits in the aneurysm wall. Ultrasound has about 98% accuracy in measuring the size of the aneurysm, and is safe and noninvasive Computerized tomography of the abdomen, is highly accurate in determining the size and extent of the aneurysm, and its relation to the renal arteries. Angiography . Angiography also uses a special dye injected into the blood stream to make the insides of arteries show up on x-ray pictures. An angiogram shows the amount of damage and blockage in blood vessels. An Aortogram is an angiogram of the aorta. It may show the location and size of an aortic aneurysm, and the arteries of the aorta that are involved. In patients with kidney diseases, the doctor may consider an MRA (magnetic resonance angiography), which is a study of the aorta and the other arteries using MRI scanning.

NATURAL HISTORY OF TAAA: 

NATURAL HISTORY OF TAAA The natural history of aortic aneurysms depends on their size and the speed of expansion . Rupture of aneurysms is uncommon when they are less than 5.5 cm wide and are expanding slowly. Surgical repair is therefore usually recommended for Aneurysms over 5.5 cm wide Aneurysm reached at least 5.5 cm in diameter Enlarged by at least 0.7 cm in 6 months Enlarged by at least 1.0 cm in 1 year Rupture is far more common in aneurysms that are over 5.5 cm wide and are expanding rapidly >0.5 cm/year.

COMPLICATIONS OF TAAA: 

COMPLICATIONS OF TAAA Rupture is a feared catastrophe. It is highly lethal and is usually preceded by excruciating pain in the lower abdomen and back, with tenderness of the aneurysm. Rupture of an abdominal aneurysm causes profuse bleeding and leads to shock. Death may rapidly follow. Half of all persons with untreated abdominal aortic aneurysms die of rupture within five years . Abdominal aortic aneurysms are the 13th leading cause of death in the U.S.

COMPLICATIONS OF TAAA Cont:: 

COMPLICATIONS OF TAAA Cont: A pseudoaneurysm forms when the intima and media are ruptured and only adventia or blood clot forms the outer layer Peripheral embolization of clot within the aneurysm can occur when a piece of clot comes loose and travels further out in the arterial system. This clot fragment can lodge in a smaller artery and block the flow of blood.

COMPLICATIONS OF TAAA Cont:: 

COMPLICATIONS OF TAAA Cont: Infection of aneurysms can occur from turbulent blood flow from the rough inner surface of the affected aorta. Aortic regurgitation Tracheal compression and/or deviation, bronchial compression , hemoptysis Compression of the left recurrent laryngeal nerve produces hoarseness and left vocal cord paralysis Superior vena cava syndrome Distortion of the normal anatomy may also complicate endotracheal or endobronchial intubation or cannulation of the internal jugular and subclavian veins.

MEDICAL MANAGEMENT (NON-SURGICAL MANAGEMENT) OF TAAA : 

MEDICAL MANAGEMENT (NON-SURGICAL MANAGEMENT) OF TAAA The goals of treatment are to; Prevent the aneurysm from growing Prevent or reverse damage to other body organs Prevent a rupture Allow to continue to participate in normal daily activities.

PowerPoint Presentation: 

For patients who are not surgical candidates (for example for patients with aneurysm smaller than 5 cm); medical treatment to prevent aneurysm expansion and rupture include: Stopping cigarette smoking Controlling high blood pressure Lowering high blood cholesterol-- Statins B eta blockers , like propanolol , atenolol or metoprolol which block adrenaline receptors and lower pressure within the blood vessel. Close monitoring of the aneurysm size with ultrasound or CT scan every 6 to 12 months (sooner in high risk patients )

How are abdominal aortic aneurysms repaired ? : 

How are abdominal aortic aneurysms repaired ? The goal of surgical treatment of abdominal aortic aneurysm is to prevent aneurysm rupture. Traditionally, repair of aortic aneurysms has been surgical . The operation consists of opening the abdomen, finding the aorta and removing (excising) the aneurysm. A synthetic Dacron tube that replaces the removed piece of aorta is sewn into place. A less invasive procedure for aortic aneurysm is endovascular surgery. This minimally invasive procedure that allows the grafts (stent) to be guided within the blood vessel itself to the site of the aneurysm without the need to cut open the abdomen.Though the post-operative course is shorter, there is a need for closer follow-up and testing.

Physiologic Changes with Aortic Cross-Clamping : 

Physiologic Changes with Aortic Cross-Clamping Hemodynamic Changes ↑ Arterial blood pressure above the clamp ↓ Arterial blood pressure below the clamp ↑ Segmental wall motion abnormalities ↑ Left ventricular wall tension ↓ Ejection fraction ↓ Cardiac output ↓ Renal blood flow ↑ Pulmonary occlusion pressure ↑ Central venous pressure ↑ Coronary blood flow Metabolic Changes ↓ Total-body oxygen consumption ↓ Total-body carbon dioxide production ↑ Mixed venous oxygen saturation ↓ Total-body oxygen extraction ↑ Epinephrine and norepinephrine Respiratory alkalosis Metabolic acidosis

Therapeutic Interventions : 

Therapeutic Interventions Afterload reduction Sodium nitroprusside Inhaled anesthetics Amrinone Shunts and aorta-to-femoral bypass Preload reduction Nitroglycerin Controlled phlebotomy Atrial-to-femoral bypass Renal protection Fluid administration Distal aortic perfusion techniques Selective renal artery perfusion Mannitol Drugs to augment renal perfusion Others Hypothermia ↓ Minute ventilation Sodium bicarbonate

Physiologic Changes with Aortic Unclamping : 

Physiologic Changes with Aortic Unclamping Hemodynamic Changes ↓ Myocardial contractility ↓ Arterial blood pressure ↑ Pulmonary artery pressure ↓ Central venous pressure ↓ Venous return ↓ Cardiac output Metabolic Changes ↑ Total-body oxygen consumption--- Hypoxaemia ↑ Lactate ↓ Mixed venous oxygen saturation ↑ Prostaglandins ↑ Activated complement ↑ Myocardial depressant factor ↓ Temperature Metabolic acidosis

Therapeutic Interventions : 

Therapeutic Interventions ↓ Inhaled anesthetics ↓ Vasodilators ↑ Fluid administration ↑ Vasoconstrictor drugs Reapply cross-clamp for severe hypotension Consider mannitol Consider sodium bicarbonate Avoidance of significant hypotension with unclamping requires; Close communication with the surgical team Awareness of the technical aspect of the surgical procedure Appropriate administration of fluids and vasoactive agents

EFFECTS OF AORTIC CROSS-CLAMP : 

EFFECTS OF AORTIC CROSS-CLAMP ↑ left ventricular afterload. ↓ distal organ perfusion. Worsening of severe HTN, myocardial ischemia, and valvular regurgitation. Renal failure secondary to hypoperfusion. Paraplegia from compromised flow to the spinal cord via the artery of Adamkiewicz.

EFFECTS OF AORTIC CROSS-CLAMP RELEASE: 

EFFECTS OF AORTIC CROSS-CLAMP RELEASE Cross-clamp release causes hypotension as a result of: Sudden ↓ in afterload----SVR Coagulopathy and ↑ bleeding. Release of metabolites vasoactive cytokines from ischemic lower body, causing diffuse vasodilatation. Redistribution of blood to lower extremity Central hypovolaemia due to sequestration of blood in the reperfused organs The release of myocardial depressant factors Prevention: Slow release of clamp, volume loading, briefly ↓ing anesthetic depth, and intermittent dosing of vasopressors can alleviate the amount of hypotension.

Complications Of Surgery: 

Complications Of Surgery Mortality 2% to 4% Paraplegia and spinal cord ischemia caused by surgical damage to artery of Adamkiewicz, which is the major artery supplying lower thoracic and lumbar spinal cord. Monitoring motor and somatosensory evoked potentials may be useful in preventing paraplegia . Anterior spinal artery syndrome : Loss of motor function and sensation to pinprick, with intact proprioception and vibration. Protection against spinal cord injury : Short cross-clamp time <30 min:, higher perfusion pressures, shunts, partial cardiopulmonary bypass (CPB), steroids, hypothermia, mannitol, cerebrospinal fluid drainage via lumbar drain

PowerPoint Presentation: 

Heart attack Respiratory tract failure Deprivation of blood supply to colon Prosthetic graft infection Renal failure : Risk factors: Preexisting renal disease with emergency cases, prolonged cross-clamp times, prolonged hypotension. Greater incidence with suprarenal over infrarenal clamping. Prevention : Loop diuretics (e.g. Furosemide), dopamine, mannitol, fenoldapam and N-acetylcysteine are proposed renal protective agents. Adequate fluid resuscitation Avoidance of nephrotoxins (NSAID’S, ACEI, aminoglycosides).

PowerPoint Presentation: 

Anesthetic Management

PRE-OPERATIVE EVALUATION: 

PRE-OPERATIVE EVALUATION

NUTRITIONAL STATUS: 

NUTRITIONAL STATUS The preoperative nutritional status is important and needs to be carefully evaluated and, if necessary, improved. Low preoperative serum albumin level has been associated with postoperative negative outcomes in surgical patients With clinical evidence of malnutrition supplement with a high protein/ calorie beverage (e.g. Ensure 2 cans per day) during the month before surgery

AIRWAY & CHEST: 

AIRWAY & CHEST The chest x-ray should be available in the operating room and should be examined preoperatively for evidence of aneurysmal compression of the left main stem bronchus Preoperative pulmonary assessments provide a baseline measurement to aid in risk stratification, and to identify patients whose preoperative respiratory status may be improved. Poor pulmonary function is associated with prolonged respiratory ventilation and increased mortality. All patients should have spirometry , arterial blood gas and analysis study of gas diffusion. The lower limit for FEV1 is around 0.6 to 0.7 L . In patients with carbon dioxide retention, the five year survival is less than 10%.

CARDIAC ASSESSMENT: 

CARDIAC ASSESSMENT Coronary angiography Two dimensional echocardiography, exercise stress test or Persantin Thallium investigation and Holter electrocardiography Patients with coronary artery disease are considered for preoperative revascularization (either with percutaneous transluminal dilatation and stenting or with coronary artery bypass graft) before surgery Beta-blocker therapy usually starts preoperatively unless such therapy is contraindicated. Perioperative ß-blockers may decrease the risk of major perioperative cardiovascular events but increase the risk of bradycardia and hypotension needing treatment

Preoperative Patient Preparation: 

Preoperative Patient Preparation Cessation of smoking Structured exercise programmes Antiplatelet medication Statins ß- blockers Coronary revascularisation prior to non- cardiac surgery in patients with severe triple vessel disease with impaired left ventricular function).

Conduct of Anaesthesia: 

Conduct of Anaesthesia Patients should receive all their regular medication on the day of surgery. The aim of anaesthesia is to have a Haemodynamically stable Normothermic Pain free patient on completion of surgery. Use a balanced general anaesthetic technique (high dose opioid, oxygen, air, low dose volatile agent) with a thoracic epidural.

Thoracic Epidurals: 

Thoracic Epidurals Advantages Ameliorate the stress response to surgery Reducing cardiovascular demands Provide high quality postoperative analgesia Facilitating early extubation Reducing the incidence of pulmonary complications. There is no evidence that epidurals reduce mortality. It is safe to insert epidurals on patients taking aspirin If an epidural is inserted in a patient taking Clopidogrel careful documentation of the risk benefit ratio is essential. Patients should be monitored closely for the symptoms and signs of spinal haematoma (back pain, bladder dysfunction, leg weakness)

Monitoring: 

Monitoring Standard monitoring Direct measurement of arterial and central venous pressure Temperature Urine output A 5 lead ECG will aid detection of ST segment changes Pulmonary artery flotation catheters Transoesophageal echocardiography (TOE) Oesophageal doppler monitoring Cardiac output monitoring (LiDCO™ and PiCCO ™) A ctivated clotting time (ACT) is used to monitor anticoagulation

Heparinisation: 

Heparinisation A dose of 100 units/kg prior to cross clamping has been shown to reduce thrombotic and embolic events. Additional heparin may be required in the presence of prolonged clamp times. Heparin can be reversed by protamine if bleeding is thought to be due to excessive heparinisation. Protamine should be used with caution as it may lead to myocardial depression, anaphylaxis and pulmonary hypertension.

Temperature Control: 

Temperature Control Perioperative hypothermia is associated with myocardial ischaemia and dysrhythmias. It contributes to a coagulopathy and increases wound infections. Shivering can increase oxygen consumption up to six fold placing excessive demands on the cardiovascular system. Forced air warming devices, fluid warmers and increasing ambient theatre temperatures are used to minimise heat loss. The legs should not be actively warmed during cross clamping

Blood Losses and Blood Products Utilization: 

Blood Losses and Blood Products Utilization Repair of TAAA is associated with major blood losses, often exceeding the patient’s intravascular volume, and complex intraoperative and postoperative coagulopathies necessitating large-volume transfusion of blood products. Massive haemorrhage results in a dilutional coagulopathy requiring fresh frozen plasma, cryoprecipitate and platelet transfusions Appropriate administration of clotting factors is best guided by using a thromboelastograph

Blood Losses and Blood Products Utilization Cont:: 

Blood Losses and Blood Products Utilization Cont: Blood loss can result from malpositioned clamps or from leaking anastomoses. Homologous blood transfusion can be minimised by intraoperative cell salvage (ICS). Since vascular patients have a high incidence of coronary disease the haematocrit should be kept greater than 27% (Hb > 9g/dl) Appropriate goals are an International Normalised Ratio (INR) of less than 1.5, a platelet count of greater than 50 x 109/l and fibrinogen levels greater that 1g/dl

Perioperative Problems Of TAAA: 

Perioperative Problems Of TAAA

SURGERY ON THE ASCENDING AORTA: 

SURGERY ON THE ASCENDING AORTA Involves sternotomy and CPB. Intraoperative course can be complicated by large volume shifts, blood loss, long cross-clamp times, and new or worsening aortic regurgitation, often requiring valve replacement. Nitroglycerin or nitroprusside is often used for precise blood pressure control . ß blockers should be used with caution, as bradycardia can worsen aortic regurgitation.

SURGERY ON THE ASCENDING AORTA Cont:: 

SURGERY ON THE ASCENDING AORTA Cont: TEE monitoring is extremely useful. Blood loss can be reduced by administration of aprotinin The left radial artery should be used to monitor arterial blood pressure, because clamping of the innominate artery may be necessary during the procedure; the femoral and dorsalis pedis arteries are suitable alternatives

Aprotinin: 

A protinin A protinin is an inhibitor of serine proteases It preserve platelet function (adhesiveness and aggregation). Aprotinin therapy is highly effective in reducing perioperative blood loss and transfusion requirements (by 40–80%). It also appears to blunt the intense inflammatory response associated with CPB. Serious allergic reactions, including anaphylaxis (< 0.5%), may be encountered with aprotinin. Reactions are more likely to occur upon repeat exposure. A test dose of 1.4 mg (10,000 KIU) is given prior to a loading dose of 280 mg (2 million KIU) over 20–30 min via a central venous catheter. The drug is then infused at 70 mg/h (500,000 KIU/h) for the duration of the surgery. The celite-ACT should not be used because it is artificially prolonged by aprotinin in the presence of heparin .. The kaolin-ACT is affected less by aprotinin therapy

SURGERY ON THE AORTIC ARCH: 

SURGERY ON THE AORTIC ARCH Involves sternotomy , CPB, and hypothermic circulatory arrest. Cooling to 15-l8°C , steroids ( methylprednisolone or dexamethasone ) , mannitol, phenytoin and thiopental infusion to maintain a flat EEG,, can be used to achieve cerebral protection. Associated coagulopathies should be corrected during rewarming period

SURGERY ON THE DESCENDING THORACIC AORTA: 

SURGERY ON THE DESCENDING THORACIC AORTA Involves left thoracotomy without CPB for open procedures. One-lung anesthesia using double-lumen tube or bronchial blocker can facilitate surgical exposure. Shunts and left atrial-femoral artery and femoral vein-femoral artery bypasses can reduce complications caused by cross-clamping. Elective cases can benefit from a thoracic epidural for postoperative pain management but may be complicated with use of anticoagulation.

SURGERY ON THE DESCENDING THORACIC AORTA Cont:: 

SURGERY ON THE DESCENDING THORACIC AORTA Cont: Right radial arterial line , as clamping of left subclavian artery may be necessary. Cross-clamping causes HTN above clamp and hypotension below clamp. Vasodilator agents (nitroglycerin and nitroprusside) ↓ blood pressure in the acute setting. Correction of coagulopathy and dosing of calcium chloride may benefit those receiving massive transfusions

SURGERY ON THE ABDOMINAL AORTA: 

SURGERY ON THE ABDOMINAL AORTA Involves anterior abdominal or anterolateral retroperitoneal approach. Combined epidural-general anesthesia may provide benefit by ↓ release of stress hormones and ↓ requirements for inhalation agents. More distal cross-clamping produces less effect on left ventricular afterload and hemodynamics. Fluid replacement is of concern due to large surgical exposure up to 10–12 mL/kg/h

Postoperative Care: 

Postoperative Care Most patients undergoing surgery to the ascending aorta, the arch, or the thoracic aorta should remain intubated 2–24 h postoperatively and ventilated for the immediate postoperative period. Most patients undergoing surgery of the abdominal aorta can be extubated . Immediate postoperative goal is to maintain stable hemodynamic parameters and correct coagulopathies Early enteral nutrition Tight glycaemic control Antacid and thromboembolic prophylaxis

Emergency AAA surgery: 

Emergency AAA surgery Shocked patients require immediate transfer to the operating theatre and laparotomy. Aortic cross clamping is a life saving manoeuvre Surgery may be futile inpatients with severe pre-existing co-morbidity. Aggressive preoperative fluid resuscitation is contraindicated as it will only serve to increase bleeding and dilute clotting factors

Preparation Prior To Induction: 

Preparation Prior To Induction Patient Insertion of two wide bore cannulae Baseline bloods (blood count, electrolytes, coagulation screen) Arterial line (if time permits) Insertion of urinary catheter Equipment Rapid fluid infusor Cell salvage equipment Forced air warming device Invasive lines and cardiac output monitors Nasogastric tube and temperature probe

PowerPoint Presentation: 

Drugs and Fluids 6 - 10 units of cross matched blood, FFP and platelets Routine anaesthetic drugs, crystalloids and colloids Inotropes (adrenaline 1:100 000, ephedrine 3mg/ml) Vasopressors (metaraminol 0.5mg/ml, phenylephrine 100 mcg/ml) Other Intensive Care Unit informed

PowerPoint Presentation: 

The patient is draped and skin prepared prior to a rapid sequence induction. Loss of abdominal tone combined with the negative inotropic and vasodilatory effects of the anaesthetic agents may result in severe hypotension post induction . Skin incision is made as soon as the airway is secure. Heparinization is not required. After the aorta is cross clamped aggressive fluid resuscitation can be instituted with blood and colloid solutions. A dilutional coagulopathy should be anticipated and FFP and platelets ordered. Once haemodynamc stability is obtained arterial and central venous catheters can be inserted, a nasogastric tube passed, and temperature monitoring commenced. There is a high incidence of myocardial ischaemia and renal failure

CONCLUSION: 

CONCLUSION An aneurysm is an abnormal area of localized widening of a blood vessel. Aortic aneurysms are typically spindle-shaped and involve the aorta below the arteries to the kidneys. Five percent of men over 60 develop an abdominal aortic aneurysms. The most common cause of an aneurysm is arteriosclerosis. Abdominal aortic aneurysms often do not cause symptoms . If they do, they may cause deep pain in the lower back or abnormally prominent abdominal pulsation. X-rays of the abdomen and other radiologic tests can be used in diagnosing an aneurysm. Rupture of an aortic aneurysm is a catastrophe. Repair of the aneurysm can be done by surgery or endovascular stenting.