**14. Discontinuation of cardiopulmonary bypass and postoperative management**

A co-ordinated approach must be used during weaning so that a smooth transition can be ensured - there should be close communication between surgeon, anesthesiologist and perfusionist. The need for vasopressors and inotropes is decided by close observation of the heart during re-warming period. Once adequate temperature is reached, ventilation is restarted after a good inflation of the lungs to prevent atelectasis and for deairing. Acid base status is normalized, adequate heart rate is ensured and the drainage from venous cannula is slowly reduced and CPB is stopped.

Myocardial edema and secondary fall in cardiac output by 20-30% is common in neonate in the first 6 – 12 hrs following surgery. Sternal closure is frequently delayed in neonates due to this reason. Avoiding hypothermia and hypoglycaemia, maintenance of optimal filling pressures, and preventing abdominal distension due to ascites by using catheter which can be used for peritoneal dialysis are important in the early postoperative period. An LA line and PA line may be inserted by the surgeons in the theatre in situations when LV dysfunction is anticipated or when pulmonary artery pressures are labile. This would help to fine tune management and help in decision making with regards to inotropes and ventilation manage‐ ment.

Postoperative management requires a precise knowledge about the anatomy, pathophysiology and details of the surgical and CPB technique. For most patients the recovery is uncomplicated and whenever the clinical progress does not follow the expected course possible residual or additional defects should be investigated.

#### **14.1. Analgesia and sedation**

Inadequate analgesia while the patient is on ventilator may be manifested by tachycardia, hypertension, pupillary dilation, diaphoresis etc, Changes in the respiratory pattern like tachypnea, grunting and splinting of the chest wall may also be seen. Fever, hypoxemia, hypercapnia, seizures, vasoactive infusions, early low cardiac output may also present in similar fashion and should be ruled out.

Opioid analgesics are the mainstay of pain management as they blunt hemodynamic response to procedures such as endotracheal suctioning. Morphine in intermittent or continuous infusion (50-100 ug/kg) is an excellent analgesic with sedative property. Disadvantage is that it can cause histamine release with systemic vasodilation and elevation of PVR.Fentanyl (5-10ug/kg/hr) is an alternative drug with less sedative action, and does not cause histamine release. There is wide variation in the metabolism of fentanyl, tolerance and dependence develops rapidly and chest wall rigidity can develop as a rare idiosyncratic reaction. It blocks the stress response and maintains systemic and pulmonary hemodynamic stability.

during narcotic induction but can cause hypotension in patients with high sympathetic drive. Isoflurane and midazolam can be used during bypass for maintenance and blunt awareness.

Reducing stress response using high dose opioid anesthesia and extending this to immediate postoperative period was considered important to reduce morbidity and mortality. With changes in surgical practice and particularly the timing of surgery, a strategy of using high dose opiod may be a less critical determinant of outcome. The main aim however is to maintain hemodynamic stability so that the team can focus on surgery without the distraction of side

**14. Discontinuation of cardiopulmonary bypass and postoperative**

A co-ordinated approach must be used during weaning so that a smooth transition can be ensured - there should be close communication between surgeon, anesthesiologist and perfusionist. The need for vasopressors and inotropes is decided by close observation of the heart during re-warming period. Once adequate temperature is reached, ventilation is restarted after a good inflation of the lungs to prevent atelectasis and for deairing. Acid base status is normalized, adequate heart rate is ensured and the drainage from venous cannula is

Myocardial edema and secondary fall in cardiac output by 20-30% is common in neonate in the first 6 – 12 hrs following surgery. Sternal closure is frequently delayed in neonates due to this reason. Avoiding hypothermia and hypoglycaemia, maintenance of optimal filling pressures, and preventing abdominal distension due to ascites by using catheter which can be used for peritoneal dialysis are important in the early postoperative period. An LA line and PA line may be inserted by the surgeons in the theatre in situations when LV dysfunction is anticipated or when pulmonary artery pressures are labile. This would help to fine tune management and help in decision making with regards to inotropes and ventilation manage‐

Postoperative management requires a precise knowledge about the anatomy, pathophysiology and details of the surgical and CPB technique. For most patients the recovery is uncomplicated and whenever the clinical progress does not follow the expected course possible residual or

Inadequate analgesia while the patient is on ventilator may be manifested by tachycardia, hypertension, pupillary dilation, diaphoresis etc, Changes in the respiratory pattern like tachypnea, grunting and splinting of the chest wall may also be seen. Fever, hypoxemia, hypercapnia, seizures, vasoactive infusions, early low cardiac output may also present in

effects of anesthetic drugs.

244 Principles and Practice of Cardiothoracic Surgery

slowly reduced and CPB is stopped.

additional defects should be investigated.

similar fashion and should be ruled out.

**14.1. Analgesia and sedation**

**management**

ment.

Dexmedetomidine (commonly called the dexmed) is alpha-2 agonist which is increasingly being used due to its sedative, anxiolytic, and its non-respiratory depressant property. This can cause hypotension and bradycardia and should be used with caution in children with CHD.

Recognition and early intervention for the management of low cardiac output is one of the pivotal roles of the intensivists. The following are some of the clues and the entire clinical picture should be considered rather than a isolated finding.

Physical examination: Core hyperthermia, tachycardia, cool peripheries with impalpable peripheral pulses, hypotension with narrow pulse pressure, ascites, hepatomegaly, oliguria, obtundation of sensorium.

Monitoring – Dampened arterial upstroke, narrow pulse pressure, elevated venous pressures (systemic or pulmonary – loss of sinus rhythm, residual outflow obstruction, tamponade, AV valve regurgitation should be ruled out)

Laboratory – Metabolic acidosis, low mixed venous oxygen saturation (or increased arterio‐ venous oxygen difference > 25 – 30%), increased arterial lactate, potassium, liver transaminases and Increased BUN and creatinine.

Strategies for management of Low CO should focus on optimizing the balance between oxygen supply and demand.

Demand – Maintaining adequate analgesia, sedation and paralysis when necessary, strict avoidance of hyperthermia and occasionally using mild hypothermia to reduce metabolic rate.

For optimizing delivery – Oxygen content can be optimized by managing Hemoglobin and fiO2, and the factors which determine output

Contractility – Dopamine (5-10ug/kg/min), dobutamine (5-10 ug/kg/min), epinephrine (upto 0.1ug/kg/min is considered acceptable. Requirement greater than 0.3 – 0.5ug/kg would make one assess the possibility of mechanical circulatory support. Calcium infusion may also be necessary especially in patients with diGeorge syndrome and 22q11 deletion.

Afterload – Milrinone (0.2- 0.75 ug/kg/min) has inotropic and peripheral and pulmonary vasodilating property and is useful for patients with ventricular dysfunction and increased afterload. Nitroprusside and GTN can be used in the setting of normal ventricular function. Norerpinephrine (upto -0.2ug/kg/min) and vasopressin (10-120 milliunits/kg/hr is a potent vasopressor) can be used in situations with low SVR ('warm' shock) [23]

Heart rate and sinus rhythm –temporary atrial and ventricular pacing wires are kept after any major cardiac procedure and can be used to optimize the heart rate, though a little trial and error would be required to find the best settings for the individual patient

circulatory arrest pioneered by Barrat- Boyes and Castaneda. Progressive improvement in circuit design and perfusion techniques has now brought the overall mortality to less than 5%. Even now the morbidity associated with the use of CPB is held to be the major limitation for

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Due to immature organ function, fetal contractile protein isoforms, immature calcium cycling, pulmonary dysfunction and exaggerated stress and inflammatory response the morbidity

**1.** Oxygenators - microporous membrane(0.05 – 0.25um) pores which allows more efficient oxygenation but lasts shorter are used for cardiac surgery, the nonporous folded sheet silicone membrane oxygenator is usually selected for longer term circulatory support

**2.** Pumps – Roller pumps are used and the flow rate is governed by the revolutions per minute, occlusion produced by the rollers and the internal diameter of the tubing. **3.** Tubing – usually ¼ inch tubing in used on arterial and venous limbs, the pump is situated close to the field to reduce the tubing length which contributes to the priming volume. **4.** Venous reservoirs – Open rigid reservoirs are usually used to which the blood flows by gravity, the level of blood in the reservoir is an important safety mechanism – source of volume for arterial inflow and to judge adequacy of venous return. Malposition of venous cannulas and lost blood in the surgical field can reduce the venous volume which may need urgent attention. Collapsible venous reservoir with reduced air blood contact is increasingly being used. Vacuum can improve drainage through small venous cannulas and tubing which can theoretically reduce organ edema and improve organ function;

**5.** Arterial cannula – aorta is the usual site of cannulation, the location needs to be tailored according to surgery. Alternate sites are carotid artery in small infants and femoral artery

**6.** Venous cannula – SVC and IVC cannulas are used to maximize venous return and to minimize interference with the operative field, and optimally sited to prevent obstruction

**7.** Filters – 0.2 um filters are used in gas inflow and for crystalloid and cardioplegia solutions. 40um filters are used in cardiotomy suction return lines to remove macro and micro aggregates and debris returning from the surgical field. Arterial filter (40um) may reduce

**8.** Prime – The fluid used to fill the oxygenator, minimum level required in the reservoir and the tubing is the priming volume. The prime consists of physiologic crystalloid solutions, packed red cells, colloids like albumin and FFP, and mannitol (used for its membrane stabilization, antioxidant and osmotic diuretic properties). The hematocrit during CPB should be maintained around 25 – 30 %. At low temperature and low flows, low hematocrit

associated with CPB is more profound in infants and neonates.

venoarterial air embolism is a potential complication.

microemboli, though some consider its use optional.

in bigger children (> 10-15kg).

and kinking.

The Cardiopulmonary bypass circuit consists of

completely successful outcomes.

applications.

Stress dose steroid – hydrocortisone (50mg/m2/day) has been demonstrated to increase systemic blood pressure and lower inotropic scores and should be used when the pressures are recalcitrant to inotropes. No consistent correlation has been found between the serum cortisol level and low cardiac output state. Due to risks of infection and poor wound healing its use should be restricted to 3- 5 days.

T3 at dose of 0.05ug/kg/hr has been shown to be beneficial in neonates due to sick euthyroid state when there is reduced conversion of thyroxine to active T3.

Fluid management – the first 24 hrs the maintenance fluids should be 50% of full maintenance and volume replacement should be titrated to filling pressures and hemodynamic response. Furosemide (0.2-0.3 mg/kg/hr is used after iv bolus of 1 mg/kg can provide consistent and sustained diuresis. Fenoldopam is a new selective dopamine DA1 receptor agonist with renal and mesenteric vasodilating properties (0.1-0.5 ug/kg/min).

Peritoneal dialysis, hemodialysis and continuous veno-venous hemofiltration provide renal replacement therapy for patients with persistent oliguria and renal failure. Besides helping in solute and water clearance, they help in nutritional support by allowing additional volume, and may also remove the inflammatory mediators. [24]

Weaning from ventilation and extubation should be possible once patients are hemodynami‐ cally stable and normothermic with good cardiac output. Patients after closed heart surgery like PDA ligation, ASD, small to moderate VSD, RV to PA conduit change, bidirectional Glenn shunt and Fontan procedure with fenestration are suitable for early extubation.Neonates undergoing surgery like TGA, Truncus, TAPVC, TOF would require elective ventilation for 48 hrs for the physiology to normalize.

Extubation of an infant after a major cardiac procedure is both an art and science.Upto to 25% of 1st extubation can end in reintubations, and if more than 3 attempts fail serious consideration should be given to the following conditions. Residual volume and pressure load, ventricular dysfunction. Phrenic nerve injury, bronchomalacia, retained secretions, vocal cord injury, Diuretic therapy with contraction alkalosis, Inadequate nutrition and an evolving sepsis are all factors to be considered for failed extubation. Early tracheostomy can sometimes help if there is no correctable lesions, and if predominantly retained secretions and nutrition are the major causes of failed extubation. [25,26]

#### **14.2. Cardiopulmonary bypass and extracorporeal life support**

Cardiopulmonary bypass machine essentially takes over the function of pumping and oxygenating the blood allowing surgery to be performed on arrested still heart.

Gibbon developed the first cardiopulmonary bypass machine used for closing an atrial septal defect in 1953, Throughout the 1960's the typical survival rate for open heart surgery remained around 50%. During the 1970's the mortality of CPB was reduced by using deep hypothermic circulatory arrest pioneered by Barrat- Boyes and Castaneda. Progressive improvement in circuit design and perfusion techniques has now brought the overall mortality to less than 5%. Even now the morbidity associated with the use of CPB is held to be the major limitation for completely successful outcomes.

Due to immature organ function, fetal contractile protein isoforms, immature calcium cycling, pulmonary dysfunction and exaggerated stress and inflammatory response the morbidity associated with CPB is more profound in infants and neonates.

The Cardiopulmonary bypass circuit consists of

Heart rate and sinus rhythm –temporary atrial and ventricular pacing wires are kept after any major cardiac procedure and can be used to optimize the heart rate, though a little trial and

Stress dose steroid – hydrocortisone (50mg/m2/day) has been demonstrated to increase systemic blood pressure and lower inotropic scores and should be used when the pressures are recalcitrant to inotropes. No consistent correlation has been found between the serum cortisol level and low cardiac output state. Due to risks of infection and poor wound healing

T3 at dose of 0.05ug/kg/hr has been shown to be beneficial in neonates due to sick euthyroid

Fluid management – the first 24 hrs the maintenance fluids should be 50% of full maintenance and volume replacement should be titrated to filling pressures and hemodynamic response. Furosemide (0.2-0.3 mg/kg/hr is used after iv bolus of 1 mg/kg can provide consistent and sustained diuresis. Fenoldopam is a new selective dopamine DA1 receptor agonist with renal

Peritoneal dialysis, hemodialysis and continuous veno-venous hemofiltration provide renal replacement therapy for patients with persistent oliguria and renal failure. Besides helping in solute and water clearance, they help in nutritional support by allowing additional volume,

Weaning from ventilation and extubation should be possible once patients are hemodynami‐ cally stable and normothermic with good cardiac output. Patients after closed heart surgery like PDA ligation, ASD, small to moderate VSD, RV to PA conduit change, bidirectional Glenn shunt and Fontan procedure with fenestration are suitable for early extubation.Neonates undergoing surgery like TGA, Truncus, TAPVC, TOF would require elective ventilation for

Extubation of an infant after a major cardiac procedure is both an art and science.Upto to 25% of 1st extubation can end in reintubations, and if more than 3 attempts fail serious consideration should be given to the following conditions. Residual volume and pressure load, ventricular dysfunction. Phrenic nerve injury, bronchomalacia, retained secretions, vocal cord injury, Diuretic therapy with contraction alkalosis, Inadequate nutrition and an evolving sepsis are all factors to be considered for failed extubation. Early tracheostomy can sometimes help if there is no correctable lesions, and if predominantly retained secretions and nutrition are the

Cardiopulmonary bypass machine essentially takes over the function of pumping and

Gibbon developed the first cardiopulmonary bypass machine used for closing an atrial septal defect in 1953, Throughout the 1960's the typical survival rate for open heart surgery remained around 50%. During the 1970's the mortality of CPB was reduced by using deep hypothermic

oxygenating the blood allowing surgery to be performed on arrested still heart.

error would be required to find the best settings for the individual patient

state when there is reduced conversion of thyroxine to active T3.

and mesenteric vasodilating properties (0.1-0.5 ug/kg/min).

and may also remove the inflammatory mediators. [24]

its use should be restricted to 3- 5 days.

246 Principles and Practice of Cardiothoracic Surgery

48 hrs for the physiology to normalize.

major causes of failed extubation. [25,26]

**14.2. Cardiopulmonary bypass and extracorporeal life support**


may improve microvascular flow and oxygen delivery. For patients with myocardial dysfunction and complex prolonged surgeries a target of around 40% at the end of surgery may improve oxygen delivery.

**3.** Arterial and venous blood gases are measured every 15-30 minutes. Oxygen saturation of venous blood (SvO2) and blood lactates are an important index of tissue perfusion and SvO2 can also be measured continuously using calibrated inline monitor. Values < 60-70% should raise concerns of inadequate tissue oxygen delivery. At low temperature, due to

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249

increased affinity of Hb to oxygen, higher levels (90%) may have to be targeted

are prone to hypoglycemia due to low glycogen reserves.

**5.** pH management – There are two methods –

and to increase systemic flow.

**15. Bleeding and organ injury**

after complex surgeries and in infants.

**16. Extracorporal life support**

ical ventilation.

useful during **mild and moderate** hypothermia.

**4.** Blood glucose should be monitored frequently particularly in neonates and infants who

**6.** Alpha stat - maintains electrical neutrality at lower temperatures, pH measured is 7.7 at 20° C. Advantages are better preservation of metabolic functions and buffering capacity,

**7.** pH stat - Adds CO2 to the circuit to correct pH for the fall of temperature, useful during **deep** hypothermia to increase cerebral blood flow and decrease metabolic rate, and also for management of aortopulmonary collaterals to increase pulmonary vascular resistance

The coagulation factors reach the adult level at 6 – 12 months of age. The effects of CPB on blood activation and coagulation is far greater in neonates and infants because of hemodilu‐

Platelets are the initial therapy for bleeding after adequate heparin reversal. 1 unit of platelets per 10 Kg raises the platelet count by approximately 50,000/mm3. Cryoprecipitate which is a good source of fibrinogen is the next blood component usually used. Antifibrinolytic agents like aprotinin, e-aminocaproic acid, tranexamic acid have become popular to reduce bleeding

Lung, kidney and brain are at risk of injury during CPB. The stress and inflammatory response is 5-10 times greater in neonates and infants. High dose steroids have been used to mask the response and have been shown to be more beneficial in neonates and infants. Ultrafiltration, both conventional and modified are being used for hemoconcentration, removing inflamma‐ tory mediators, and decreasing total body water, with beneficial effects being shown for hematocrit, oxygenation, pulmonary vascular resistance and decreasing duration of mechan‐

Modalities include extracorporeal membrane oxygenation (ECMO), intra-aortic balloon pump (IABP) counter pulsation and ventricular assist devices. Wide application in pediatric age

tion, hypothermia, greater shear stress, and more blood- air contact activation.

#### **14.3. Initiation, monitoring and termination of CPB**

Heparin at a dose of about 4mg/kg is given to bring activated clotting time(ACT) of more than 400 seconds. ACT should be maintained between 400- 600 seconds to prevent activation of blood coagulation and clot formation. Inadequate concentration of heparin is believed to contribute to excess coagulation and fibrinolytic system activation.

Once the arterial and venous cannulae are in place, after confirming adequate anticoagulation and absence of air (especially at the arterial cannula and tubing) is confirmed, CPB is slowly initiated by beginning arterial inflow and unclamping the venous line. Any systemic to pulmonary shunts should be closed prior to, or immediately after CPB initiation. These can contribute to systemic runoff, contributing to organ malperfusion, increased left heart return, heart distension, and inadvertent rewarming. It is absolutely essential to prevent myocardial distension at all times after initiation of CPB.

The important CPB circuit variables that are monitored are:


Hypothermia delays loss of ionic hemostasis, slows consumption of ATP, decreases free radical generation, inflammatory cytokine production, white cell activation and leucocyte adhesion molecule synthesis, suppresses the release of excitatory amino acid neurotransmitters. It continues to be the mainstay for cerebral and other organ protection during CPB.

The important patient variables monitored are


may improve microvascular flow and oxygen delivery. For patients with myocardial dysfunction and complex prolonged surgeries a target of around 40% at the end of surgery

Heparin at a dose of about 4mg/kg is given to bring activated clotting time(ACT) of more than 400 seconds. ACT should be maintained between 400- 600 seconds to prevent activation of blood coagulation and clot formation. Inadequate concentration of heparin is believed to

Once the arterial and venous cannulae are in place, after confirming adequate anticoagulation and absence of air (especially at the arterial cannula and tubing) is confirmed, CPB is slowly initiated by beginning arterial inflow and unclamping the venous line. Any systemic to pulmonary shunts should be closed prior to, or immediately after CPB initiation. These can contribute to systemic runoff, contributing to organ malperfusion, increased left heart return, heart distension, and inadvertent rewarming. It is absolutely essential to prevent myocardial

**1.** Arterial line pressures (typically in the range of 200-250mm Hg to drive blood through the infant arterial cannula and tubing to maintain mean pressures around 40-60 mm Hg).

**2.** Pump flow rate - which is a calculated value in roller pumps based on rotation, internal

**3.** Oxygenator gases – the flow rate ('sweep speed') and oxygen concentration controlled with blender and flow meter, usually started with 1: 1 ratio with the flow rates in mem‐

**4.** Temperature- thermistors measure the temperature of the water bath, arterial and venous blood. The gradient between the patient and the perfusate should not exceed 10 degree

Hypothermia delays loss of ionic hemostasis, slows consumption of ATP, decreases free radical generation, inflammatory cytokine production, white cell activation and leucocyte adhesion molecule synthesis, suppresses the release of excitatory amino acid neurotransmitters. It

**1.** Patient mean arterial and venous pressures – femoral arterial line preferred especially in

**2.** Nasopharyngeal (reflecting brain temperature), rectal or bladder (core) and esophageal (aortic) temperatures are measured using appropriate thermistors, slow cooling over a period of 15-20 minutes- is necessary whenever deep hypothermic circulatory arrest

C, especially during rewarming to prevent formation of gaseous bubbles.

continues to be the mainstay for cerebral and other organ protection during CPB.

(DHCA) is planned. Hct of 25% is favoured at this temperature.

may improve oxygen delivery.

248 Principles and Practice of Cardiothoracic Surgery

distension at all times after initiation of CPB.

tubing diameter and occlusion pressure.

The important patient variables monitored are

small infants and in deep hypothermia.

brane oxygenators.

The important CPB circuit variables that are monitored are:

**14.3. Initiation, monitoring and termination of CPB**

contribute to excess coagulation and fibrinolytic system activation.

