How does blood shunting work

The subclavian or innominate artery is controlled with a vascular clamp and an end-to-side anastamosis is performed between a polytetrafluoroethylene PTFE: Goretex, Impra graft usually 3.

The heparin is typically not reversed unless excessive bleeding is present. Classic Blalock-Taussig shunt: Via a right thoracotomy with connection of the proximal portion of the right subclavian artery, directly to the right pulmonary artery.

The distal subclavian artery is oversewn, resulting in decreased or absent pulses in the corresponding arm. Support cardiac output and pulmonary blood flow: Adjust ventilation to facilitate surgical exposure without compromising oxygenation; manual ventilation is sometimes necessary.

Prevent sometimes possible and treat hypercyanotic spells during manipulation of the pulmonary arteries. Discuss strategy with the surgeon to prevent early shunt thrombosis. Hypercyanotic spell: Tet spells can occur during induction and maintenance of anesthesia, particularly in the Trendelenberg position for central venous line insertion, during positioning in the lateral decubitus position, or surgical manipulations.

Tet spells can possibly be prevented by close monitoring and attention to oxygenation and ventilation, hemodynamics, depth of anesthesia, analgesia, and the operative field. A very early indication is an increase in duskiness of the right atrial wall. Prevention and treatment comprise of i good airway control and high FiO2. Hypoxemia during thoracotomy, vessel manipulation, and shunt insertion: Careful adjustment of ventilation, FiO2 1.

Use of cardiopulmonary bypass if hypoxemia is unacceptable or associated with significant hemodynamic compromise. Hypoxemia after release of clamps: The differential diagnosis includes shunt obstruction either due to mechanical factors kinking, torsion external compression, too small a shunt or early shunt thrombosis, inadequate perfusion pressure low cardiac output, bleeding , or lung disease atelectasis, pulmonary hemorrhage, or inadequate ventilation settings.

Treatment is directed toward the most likely cause. Occasionally, flow through the shunt needs to be restricted by placing small clips on the tube graft. Pulmonary hemorrhage: Caused by manipulation of the pulmonary artery, pulmonary overcirculation, or coagulopathy. Treated with frequent suctioning, lavage, and adequate ventilation with PEEP. In addition to standard monitoring and a urinary catheter, invasive monitoring with an arterial catheter and a central venous line usually right internal jugular vein is necessary for optimal hemodynamic and ventilatory management and inotrope and fluid administration during a cardiothoracic procedure with cardiopulmonary bypass in a small infant.

Cerebral oximetry with near infrared spectroscopy NIRS has become routine. Repair of tetralogy of Fallot with pulmonary stenosis and infundibular obstruction: After midline sternotomy, subtotal resection of the thymus and opening of the pericardium, cardiopulmonary bypass is initiated in the standard fashion, with either bicaval or single atrial venous cannulation, depending on the size of the patient and competence of the tricuspid valve. For infants, less than 2 to 2.

Immediately after commencing bypass, the PDA or previous shunt is ligated with a concomitant increase in the mean arterial pressure. During the cooling phase, the pulmonary arteries are dissected free and the size of the pulmonary valve annulus inspected to determine the need for a transannular patch.

The coronary artery distribution over the RV outflow tract is examined to find the best location for the ventriculotomy if the ventricular approach rather than atrial approach is chosen. Once the aortic cross-clamp is placed and cardioplegia given, resection of infundibular muscle bundles and VSD closure is performed via the ventriculotomy or via an atrial approach.

If the pulmonary valve annulus is severely hypoplastic, a transannular pericardial patch is placed. If there is mild-moderate annular hypoplasia, a hybrid approach with balloon dilation of the pulmonary valve in the operating room is increasingly being performed in an attempt to preserve as much function of the pulmonary valve as possible. If the annulus is of adequate size, a valve-sparing technique with 2 separate patches is preferred to avoid free pulmonary regurgitation and RV volume overload: one patch is placed over the main pulmonary artery for supravalvular stenosis and one over the infundibular area.

A left atrial line may be placed prior to separation from bypass, and, occasionally, a PA or RV line to monitor PA or RV pressures in the postoperative period. Residual VSDs, RV outflow tract obstructions, pulmonary valve function, and ventricular performance can be assessed by transesophageal or epicardial echocardiography, depending on the size of the patient.

Atrial and ventricular epicardial pacing wires and chest tubes are placed, and the chest closed in the usual fashion. In very small babies with significant myocardial edema and RV dysfunction, the chest may be left open and covered with part of an Esmarch bandage.

After 3 to 4 days, once RV function has improved, adequate diuresis is established and the tissue swelling has subsided, the chest can be closed. Adjust ventilation to facilitate and optimize surgical exposure without compromising oxygenation, using manual ventilation as necessary. Treat hypercyanotic spells during surgical manipulations. Initiate vasoactive support with dopamine, phenylephrine, or epinephrine to treat low output syndrome and maintain adequate perfusion pressures as necessary.

Ensure that functional temporary pacemaker and antiarrhythmic drugs for treatment of complete heart block or JET are immediately available. Tet spells possibly can be prevented by close monitoring and attention to oxygenation and ventilation, hemodynamics, depth of anesthesia, analgesia, and the operative field.

Coronary Ischemia: May occur if a coronary artery crossing the RVOT is inadvertently transected or the outflow tract patch results in coronary artery obstruction. This is evidenced by poor ventricular function, myocardial duskiness, ST segment changes, and arrhythmias during rewarming and separation from bypass.

Careful evaluation of coronary artery distribution in infundibular area and limitation of ventricular incision can help to prevent this complication. Treatment depends on severity of injury and ranges from return to bypass with surgical revision to increased inotropic support, nitroglycerin administration, and other measures to maintain adequate coronary perfusion. It is often temporary due to traction or edema around the conduction system.

If resolution of conduction occurs, it usually happens within 8 to 10 days postoperatively. Treatment with defibrillation, antiarrhythmic medications, support of RV function, and correction of electrolyte abnormalities.

Rates may be as high as to bpm and associated with significant hemodynamic compromise. Adequate anesthesia; analgesia and sedation ICU ; lower levels of inotropic support, if possible; and avoidance of hyperthermia might help to reduce the incidence. If the rate is relatively low, atrial pacing at a slightly higher rate may improve cardiac output. Dexmedetomidine has also been used to treat JET. Bleeding: Usually causes of bleeding include leaking suture lines, bypass-induced coagulopathy, and preexisting clotting abnormalities in a cyanotic patient.

Adequate rewarming, protamine reversal of heparin effects, exploration of the operative field for potential surgical causes, and transfusion of blood products platelets, cryoprecipitate, and packed red blood cells to maintain adequate hematocrit are important management steps. Postoperative RV dysfunction and low cardiac output syndrome: Causative factors include poor RV function, high PVR, residual lesions, myocardial ischemia due to coronary artery injury, and cardiac tamponade.

Chest X-ray to determine and thereby treat atelectasis, hemothorax, pneumothorax, and right mainstem intubation. Echocardiography to determine if residual lesions or significant pericardial effusion. Bronchodilators if necessary. Neurologic: Embolic or hypoxic-ischemic injury in the early postoperative period can present as stroke ischemic, hemorrhagic , seizures, or, rarely, choreoathetosis. Unique to procedure: Embolic stroke air or thrombotic material , ischemic stroke, intracerebral hemorrhage, seizures, choreoathetosis.

Patients are mechanically ventilated for at least 12 to 24 hours, particularly to assess shunt and pulmonary function. Excessive flow across the shunt with pulmonary overcirculation can result in pulmonary edema, pulmonary hemorrhage can be unilateral , and systemic hypotension. Inadequate shunt flow see below can result in profound hypoxemia. Patients are mechanically ventilated in the ICU, with most patients being eligible for extubation within the first 24 hours. Neonates and very sick young infants with RV dysfunction and high PVR may need a few days to a week or so of mechanical ventilation.

Respiratory factors include atelectasis, large pleural effusions, hemothorax or pneumothorax, and phrenic nerve injury. Patients usually remain intubated and ventilated for at least several hours after the procedure. Pain is initially treated with intravenous opioids, either intermittent doses of morphine or continuous infusions of morphine or fentanyl, depending on hemodynamic stability and the expected time to extubation.

Acetaminophen rectal or intravenous is a useful adjunct and is also used to reduce fever. Once any existing postoperative coagulopathy has resolved, bleeding has stopped, and there are no concerns regarding renal function, nonsteroidal anti-inflammatory agents such as ketorolac can be added to the analgesic regimen.

Following extubation and establishment of oral intake, there is a transition to oral analgesics. Postoperative admission to a Pediatric Intensive Care Unit with expertise in the perioperative management of pediatric cardiac surgical patients. ICU admission is necessary to ensure close monitoring and immediate availability of staff and equipment to treat postoperative complications such as bleeding, cardiac tamponade, myocardial ischemia, low output syndrome, and arrhythmias.

Hypoxemia: May be due to pulmonary, hemodynamic, or shunt factors. Pulmonary causes include high PVR; endotracheal tube obstruction; circuit disconnection; atelectasis; contusion following lung retraction; pulmonary hemorrhage; hemo-, pneumo-, or chylothorax damage to thoracic duct ; poor ventilator settings; and interstitial and alveolar edema following prolonged pulmonary overcirculation.

Shunt factors, usually beyond the control of the anesthesiologist and intensivist, are associated with decreased shunt flow and include too small a shunt, thrombosis, compression, torsion and kinking; the chest may need to be opened emergently in the ICU and the shunt problem addressed.

Hypotension can also be due to excessive PBF or pulmonary overcirculation. Diastolic hypotension with a volume-loaded ventricle and high heart rate can result in myocardial ischemia. These holes in the walls are sometimes associated with strokes. More rarely, this can lead to heart rhythm problems, heart failure , and pulmonary hypertension. Most often, these holes exist within the wall of the heart that divides the top chambers of the heart atria , called the interatrial septum.

Less frequently, these holes exist within the lower part of the septum, called the interventricular septum. In the lower heart, they are called ventricular septal defects VSD. All of us have a PFO early in our development. In fact, PFOs are necessary to support our circulation in fetal life. Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys. Updating… Please wait. Unable to process the form. Check for errors and try again.

Thank you for updating your details. Log In. Sign Up. Become a Gold Supporter and see no ads. Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. View revision history Report problem with Article. Citation, DOI and article data. Knipe, H. Question Why is a person less likely to strain a muscle if they have warmed up before taking part in exercise? Reveal answer up. Increase in stroke volume SV ; increase in heart rate HR ; increase in cardiac output Q ; increase in blood pressure BP ; redistribution of blood flow.

Increase in breathing rate f ; increase in tidal volume TV ; increase in minute ventilation VE. Increase in oxygen uptake and transport to the working muscles; increase in carbon dioxide removal. Increase in lactic acid lactate production. Increase in temperature of muscles; increased pliability elasticity ; muscle fatigue.