Anesthesiology

Left-to-right shunts

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What the Anesthesiologist Should Know before the Operative Procedure

Left-to-right shunt occurs almost exclusively in the setting of ventricular septal defect (VSD), most commonly in neonates and small children. VSD size (combined cross-sectional area in case of multiple VSDs) is the primary determinant of initial pathology and progression of disease in these patients.

"Large" VSD =

same size as aortic valve annulus or larger. In this case there is no restriction to flow across the ventricular septum and the RV pressure equals LV pressure, and pulmonary blood flow (Qp) is determined solely by ratio of pulmonary vascular resistance (PVR) to systemic vascular resistance (SVR) [usually 1:10-1:20].

"Small" VSD =

restrictive and RVp is either normal or minimally elevated. The Qp:Qs ratio (pulmonary blood flow:systemic blood flow) is rarely greater than 1.5.

"Moderate" VSD =

intermediate size where the RV pressure is less than or equal to ½ systemic and the Qp:Qs ratio is ~2.5-3.

Most VSDs are closely associated with ventricular inlet or outlet valves or tricuspid valve chordae, making them suitable only for surgical closure. Muscular VSDs are often amenable to catheter-delivered device closure in the cardiac catheterization laboratory. The chief limitation to device closure of muscular VSDs is patient size as large sheaths are required for device delivery [patients should be at least 8-10 kg]. Surgical VSD correction will be considered in this chapter.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Generally, VSDs are repaired electively after failure of aggressive medical management.

Emergent: There are generally no indications for emergent VSD closure.

Urgent:Repair of VSD is indicated urgently to semiurgently if infant is rapidly developing congestive heart failure (CHF) or has rapidly worsening CHF despite maximum medical management with diuretics and/or digitalis. Allowing CHF to continue to worsen will make the patient much less able to tolerate cardiopulmonary bypass and will lengthen and complicate the postoperative course. Continued exposure of the pulmonary vasculature to systemic pressure and high blood flow significantly increase the risk of developing pulmonary vascular occlusive disease and irreversible elevation of PVR, making the patient not a candidate for VSD closure.

Elective: Approximately 30% of infants with VSD will require surgery in the first year secondary to unmanageable CHF, frequent respiratory infections, or (most commonly) failure to thrive. Considerable controversy exists as to benefit of closure of smaller VSD in asymptomatic teen or young adult. Some suggest that closure reduces the ongoing risk of bacterial endocarditis, and closure of small defects obviates the need for regular surveillance of aortic valve function. Whether closure of these defects reduces the risk of endocarditis is debatable and it has been suggested that ongoing antibiotic prophylaxis should be continued even if the defect is closed.

2. Preoperative evaluation

Approximately 25% of symptomatic patients with a VSD also have a large patent ductus arteriosus and a hemodynamically significant aortic coarctation is present in 10% of these patients as well. Older patients may develop aortic valve incompetence secondary to prolapse of the right or noncoronary leaflet through the VSD.

These associated lesions can lead to significant increase in risk for serious respiratory infection due to substantial pulmonary overcirculation. Preoperative severe respiratory complications have been shown to lead to much higher perioperative morbidity and mortality rates. Mild-moderate symptoms are unlikely to resolve if patient is in overt failure and should not be cause for cancellation of the case.

Objective data (i.e., echocardiography and/or cardiac catheterization data) may be several months old when the patient presents for surgery, and recent clinical observation by the family may most accurately reflect the patient's current cardiac status.

Patients presenting in overt CHF warrant medical therapy to maximize their suitability for surgical correction. Surgical correction may be cancelled if patient is in overt failure without medical intervention. Frequently these patients are described by the parents as sweaty, dyspneic, and easily tiring and commonly with circumoral pallor/cyanosis during feeding. Older children may simply be unable to keep pace with siblings/playmates.

3. What are the implications of co-existing disease on perioperative care?

Generally, younger patients with VSDs have little or no other systemic illness.

Perioperative evaluation: Shunt localization is most often accomplished angiographically and quantified by oxygen saturation measurements in the pulmonary veins, SVC and IVC, Right heart chambers, left heart chambers, aorta, and pulmonary artery.

Perioperative risk reduction strategies: Smaller patients with congenital VSD's may be optimized for surgery with diuretic therapy to improve pulmonary function and possibly reduce Right ventricle volume overload.

b. Cardiovascular system

Baseline coronary artery disease or cardiac dysfunction

These patients virtually never have coronary artery disease. They have left atrial and left ventricular volume overload. Right ventricle volume overload and possibly decreased RV function may occur as well.

c. Pulmonary

COPD is unlikely to be present in the pediatric population.

Reactive airway disease (Asthma): Smaller airway obstruction and wheezing may occur in cases of chronic severe volume overload or with very high Qp:Qs ratio.

Pulmonary vascular occlusive disease (PVOD) involves structural changes in the pulmonary vasculature (increased muscularity of small pulmonary arteries, small artery intimal hyperplasia, scarring, thrombosis, and reduced numbers of intra-acinar arteries) secondary to prolonged increased pulmonary blood flow), which result in progressive/irreversible elevations in PVR and PA pressure. These changes are markedly accelerated and occur at a much younger age (as early as 4-6 months) in trisomy 21 syndrome patients

d. Renal-GI:

Pediatric patients with VSDs typically have normal renal function. They may have substantial electrolyte abnormalities secondary to significant diuretic exposure, which could warrant intervention preoperatively. The most typical abnormality is a hypochloremic metabolic alkalosis.

e. Neurologic:

These patients rarely present with neurologic issues.

Acute issues: Very rare in the pediatric patient. Usually only occur in the setting of right-to-left shunting at the atrial level due to elevated RA pressures if a PFO is present or if there is bidirectional flow across the VSD (with elevated PVR). These events would most commonly be secondary to paradoxical air/thrombus embolization

Chronic disease: Not typically found in this population.

f. Endocrine:

Rarely, if ever, associated with this pathology.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

Rarely an issue in the patient population.

4. What are the patient's medications and how should they be managed in the perioperative period?

These patients generally are very healthy and infrequently have associated diseases that require pharmacologic therapy.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

VSD surgery patients typically will be on diuretic therapy preoperatively. It is not unusual for these patients to be taking two diuretics (typically furosemide and hydrochlorothiazide) and to have electrolyte imbalances secondary to that therapy. Some patients with severe CHF may also be taking ACE inhibitors.

i. What should be recommended with regard to continuation of medications taken chronically?

Cardiac:

Diuretics are generally continued to the morning of surgery to prevent volume overload and pulmonary deterioration.

Pulmonary:

Generally not applicable except as above

j. How To modify care for patients with known allergies -

This is generally not an issue with this patient population. It usually only involves antibiotic administration. For known penicillin allergy, we still recommend proceeding with the usual cefazolin AFTER A NEGATIVE SMALL TEST DOSE. The most common alternative is to administer vancomycin instead of cefazolin. This is a surgical decision but is included here as the anesthesiologist is most frequently administering the antibiotic.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

Most pediatric operating rooms/facilities are almost completely latex-free at this point. In our facility, the only alteration in care required for latex-allergic patients is the use of non–latex-containing tourniquets for the cardiac cannulation sites.

l. Does the patient have any antibiotic allergies- - Common antibiotic allergies and alternative antibiotics]

A cephalosporin (specifically cefazolin) is the antibiotic most commonly given intraoperatively for VSD closure. It is given within 30 minutes of incision and repeated just after separation from cardiopulmonary bypass.

Penicillin-allergic patients are either given the standard cephalosporin after a negative test dose or, alternatively, given vancomycin. Vancomycin is given preincision and is not repeated post bypass.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH)

Documented- avoid all trigger agents such as succinylcholine and inhalational agents:

  1. Proposed general anesthetic plan: Younger patients may be maintained under general anesthesia with bolus doses of fentanyl (or sufentanil) and midazolam without inhaled agent. Older children/ adults may be maintained with fentanyl plus midazalam with a continuous propofol infusion with or without nitrous oxide.

  2. Ensure MH cart available:

Family history or risk factors for MH: We generally maintain general anesthesia for these patients with a clean technique as noted above.

Local anesthetics are generally not used for these patients in the perioperative period as they are usually not candidates for rapid wakeup due to temperature, blood pressure control, and hemostasis considerations. If the patient has a documented allergy to a steroid-based nondepolarizing neuromuscular blocking agent, cis-atricurium is useful.

5. What laboratory tests should be obtained and has everything been reviewed?

Extensive preoperative laboratory evaluation is rarely indicated. As noted above, these patients frequently have electrolyte abnormalities when receiving preoperative diuretic therapy. Preoperative electrolytes must be evaluated. It is helpful to have a preoperative hematocrit for cardiopulmonary bypass pump prime planning.

Hemoglobin levels:

Preoperative hematocrit values are important for calculating the prime volumes for the cardiopulmonary bypass pump. The goal is generally to have a hematocrit value of 30 on bypass. Hematocrit levels >65% are associated with markedly increased blood viscosity which would predispose the patient to neurologic sequelae in the peri-operative period--especially on bypass. These patients must be considered for exchange transfusion prior to surgery. [Cyanosis is a late finding in VSD patients at which time they are suitable only for palliative surgery which does not include hemodilution on bypass, making pre-procedure exchange transfusion doubly important.

Electrolytes:

Preoperative diuretic therapy will have substantial effect on electrolytes, especially potassium levels which must be checked and possibly replaced prior to surgery. Children in congestive heart failure may have an iron deficiency due to increased metabolic needs which may be associated with significant anemia. Hypocalcemia is also fairly common in children with CHF.

Coagulation panel:

Baseline coagulation studies (PT/PTT and platelet count) are an important reference to be used when ordering coagulation products for post-bypass administration and for reference in the Cardiac Intensive Care Unit postoperatively.

Imaging

1. Chest radiograph: Will confirm other clinical and diagnostic findings such as cardiomegaly, pulmonary blood flow quantity, previous surgical procedures, and presence or absence of pulmonary infections.

2. Electrocardiogram: Confirms presence/absence of dysrhythmias and or ventricle enlargement.

3. Echocardiogram: The diagnostic modality of choice for preoperative evaluation of VSD size/ location, blood flow direction/ velocity, valve morphology/function, chamber size, and function evaluation and to rule out associated intracardiac lesions.

4. Cardiac catheterization data: Generally confirms and enhances echocardiogram data. Most frequently used in older patients where concerns remain regarding pulmonary artery pressure, pulmonary vascular resistance and whether or not the VSD is restrictive.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Patients undergoing surgical correction of VSD(s) require cardiopulmonary bypass and therefore general anesthesia.

If the patient is minimally symptomatic preoperatively, they may be a candidate for early wake-up/extubation and therefore benefit from local anesthetic infiltration at the sternotomy incision.

a. Regional anesthesia -

;;; Due to multiple (most notably coagulation) issues these patients are not generally considered for regional anesthesia.

Neuraxial

Benefits: There may be a potential benefit of postoperative sternotomy pain relief in these patients but neuraxial anesthesia is rarely, if ever conducted on patients undergoing open heart operations in the Western world.

Drawbacks: Patients undergoing open heart surgery are fully anticoagulated, frequently have low platelet counts and coagulation factor values and the platelets present may be of diminished activity. All of these factors combined lead to substantially increased risk injurious bleeding if epidural catheter placement is attempted.

Peripheral nerve block

Benefits: Local anesthetic administration around the sternotomy incision and chest tube exit sites are useful in patients who are asymptomatic prior to surgery, have an uncomplicated/quick repair with no intraoperative issues, are warm, and therefore are potential candidates for early wakeup and extubation (within 6 hours). Local anesthetic in these patients can make for easier pain management with more stable/easier blood pressure control and lower narcotic pain medication requirement, which lets them wake up much quicker.

Drawbacks: If the case involves a complex/lengthy repair or the patient was in significant failure prior to surgery, they are generally NOT candidates for rapid wakeup and extubation. These patients receive far less benefit from local anesthetic administration and, in the smallest patients, toxicity risks may well outweigh any benefit.

b. General Anesthesia

Benefits: Maintenance of baseline vital signs, control of airway/ prevention of worsening preexisting pulmonary congestion and amnesia.

Drawbacks: No alternative exists in the Western world.

Airway concerns: Maintenance of general anesthesia on ROOM AIR with continuous PEEP helps treat/ prevent worsening of pulmonary overcirculation and pulmonary edema. This situation is also aided by keeping the PCO2 above 40 in the pre-bypass period.

c. Monitored Anesthesia Care

Patients presenting for open-chest cardiac surgery cannot be considered for monitored anesthesia care.

6. What is the author's preferred method of anesthesia technique and why?

What prophylactic antibiotics should be administered?

Cefazolin is generally given within 1hr of incision, repeated dose given by perfusionists at the beginning of cardiopulmonary bypass and repeat dose given by the anesthesia team post-bypass.

What do I need to know about the surgical technique to optimize my anesthetic care?

These surgeries always take place through median sternotomy with the patient in the supine position with arms at the sides. Cardiopulmonary bypass with bicaval and aortic cannulation is necessary. Aortic cross-clamping and cardioplegia induced diastolic arrest are standard.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Care must be given to avoid exacerbating pulmonary overcirculation--i.e., keep CO2 level at mid 40s or higher pre-bypass, keep patient at the lowest possible FiO2 pre-bypass (while maintaining adequate SaO2). PEEP can be used to optimize lung volumes as long as lung expansion does not compromise surgical exposure. Cell saver is rarely helpful for first-time operations.

What are the most common intraoperative complications and how can they be avoided/treated?

  1. Hypoxia/difficult ventilation secondary to high intra-alveolar water content; avoided by above maneuvers.

  2. Significant intravascular volume loss during surgical dissection/ bypass cannulation; large-bore IV access ALWAYS warranted.

  3. Significant arrhythmias during electrocautery dissection; -necessitates immediate availability of defibrillator/paddles.

Complications

Cardiac:

Intracardiac electrical conduction delays due to surgical injury. Thromboembolic vs. air embolus.

Pulmonary:

Worsened intra-alveolar water content and/or atelectasis.

Neurologic:

Possible focal neurologic deficit secondary to embolization or inadequate cardiac output on cardiopulmonary bypass.

Coagulation:

Coagulopathy secondary to platelet/ coagulation factor depletion on bypass and/or inadequate heparin reversal.

a. Neurologic:

These patients, as noted above, are clearly at risk for neurologic complications secondary to thromboembolization, air embolization, low cardiac output, or inadequate perfusion on bypass and hemorrhagic events during complete heparinization.

b. If the patient is intubated, are there any special criteria for extubation?

Patients undergoing open heart surgery are generally considered for extubation once they are (1) fully rewarmed, (2) have no ongoing bleeding issues, (3) have no uncontrolled arrhythmia issues, (4) have achieved good pain control, and (5) have no oxygen or ventilatory support needs.

c. Postoperative management

These patients are almost always taken to the cardiac intensive care unit intubated postoperatively.

What analgesic modalities can I implement?

Younger patients are generally treated with intermittent boluses of morphine. Older patients may be considered for patient-controlled Analgesia based on their maturity and ability to follow instruction.

What level bed acuity is appropriate?

These patients can only be sent to the cardiac intensive care unit postoperatively.

What are common postoperative complications, and ways to prevent and treat them?

  • Inadequate closure of the VSD(s) or the presence of an unrecognized VSD(s) may prevent separation from bypass. [These are most frequently evaluated using trans-esophageal echocardiography (or surface echo if the patient is too small for TEE)].

  • Tricuspid regurgitation secondary to leaflet damage due to difficult transatrial approach.

  • Subaortic or subpulmonic stenosis from VSD patch bowing.

  • Transient heart block requiring pacing (AV node and His bundle are near operative site and can be injured).

What's the Evidence?

DiNardo, JA, Zvara, DA. Anesthesia for cardiac surgery. Blackwell. 2007.

(Textbook that describes the anesthetic management of patients with underlying congenital heart disease.)

Jonas, RA. Comprehensive surgical management of congenital heart disease. Hoder-Arnold. 2004.

(Textbook that describes the surgical approach as well as the pathophysiology of various congenital cardiac lesions.)
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