**13. Pediatric anesthesia and critical care**

The success of any pediatric cardiac surgical programme depends on a team effort and anesthetists and intensive care personnel are critical members of the team. The importance of effective communication between the various team members cannot be overemphasized.

Care of pediatric patients and care of the neonates in particular needs appreciation of the differences in **physiology** of the immature organ systems.

The neonate responds rapidly to any stressful situations which reflect in the sudden changes of various metabolic and hemodynamic parameters. The metabolic rate of neonates is 2-3 fold have increased compared to adults. The caloric requirement is between 100-150 Kcal/kg/day and neonatal gut is at risk of necrotizing enterocolitis with the use of hyperosmolar feeds.

The myocardium has only 30% contractile tissue as against 60% in mature myocardium. The myocardium has a reduced ability to respond to afterload stress and the compliance is reduced. Acute pressure afterload is poorly tolerated, and can lead to rapid ventricular dysfunction; chronic pressure load is longer tolerated than chronic volume load. Symptoms of CHF are rare unless the obstruction is severe and prolonged.

The stroke volume is relatively fixed and cardiac output is more heart rate dependent. They are more dependent on the trans-sarcolemma movement of calcium to initiate and sustain contraction as the sarcoplasmic reticulum and T-tubules are relatively underdeveloped.

Cardiorespiratory interactions and ventricular interdependence are particularly marked in infants. Positive pressure ventilation reduces the preload of both ventricles, increases the afterload of right ventricle and reduces the afterload of left ventricle. Implying that in situations where right ventricle is dysfunctional or in situations of single ventricle, early extubation with reduced afterload would be useful and in situations of left ventricular dysfunction, positive pressure ventilation would reduce the afterload of the heart and act as positive inotrope. This principle should be tempered against the background of ventricular interdependence where dysfunction of one ventricle can rapidly affect the other due to septal interactions.

Neonates rely on diaphragm as the main muscle of respiration. Only 25% of the diaphragm in neonates is made of type I fibre capable of slow and sustained activity against 55% by 8 months of age. Raised intra-abdominal pressure due to any cause like gastric distension, hepatic congestion and ascites can compromise its function. In neonates a larger portion of energy expenditure is used for ventilation and therefore they fatigue easily and have failure to thrive in the presence of increased work of breathing. They have increased closing capacity with airway closure occurring during normal tidal ventilation putting them at risk of developing hypoxemia and atelectasis. In addition dilated pulmonary arteries and left atrium can compress bronchi causing lobar collapse. [20]

Coils – are metal wires coated with thrombogenic Dacron strands, suitable for vessels < 6-7 mm, with an area of narrowing. The thrombus formation around the coil plugs the vessel.

Other defects which have been plugged are ruptured sinus of Valsalva especially the ones arising from the non-coronary sinus, aorta LV tunnels, veno-venous collaterals plugging

The success of any pediatric cardiac surgical programme depends on a team effort and anesthetists and intensive care personnel are critical members of the team. The importance of effective communication between the various team members cannot be overemphasized.

Care of pediatric patients and care of the neonates in particular needs appreciation of the

The neonate responds rapidly to any stressful situations which reflect in the sudden changes of various metabolic and hemodynamic parameters. The metabolic rate of neonates is 2-3 fold have increased compared to adults. The caloric requirement is between 100-150 Kcal/kg/day and neonatal gut is at risk of necrotizing enterocolitis with the use of hyperosmolar feeds.

The myocardium has only 30% contractile tissue as against 60% in mature myocardium. The myocardium has a reduced ability to respond to afterload stress and the compliance is reduced. Acute pressure afterload is poorly tolerated, and can lead to rapid ventricular dysfunction; chronic pressure load is longer tolerated than chronic volume load. Symptoms of CHF are rare

The stroke volume is relatively fixed and cardiac output is more heart rate dependent. They are more dependent on the trans-sarcolemma movement of calcium to initiate and sustain contraction as the sarcoplasmic reticulum and T-tubules are relatively underdeveloped.

Cardiorespiratory interactions and ventricular interdependence are particularly marked in infants. Positive pressure ventilation reduces the preload of both ventricles, increases the afterload of right ventricle and reduces the afterload of left ventricle. Implying that in situations where right ventricle is dysfunctional or in situations of single ventricle, early extubation with reduced afterload would be useful and in situations of left ventricular dysfunction, positive pressure ventilation would reduce the afterload of the heart and act as positive inotrope. This principle should be tempered against the background of ventricular interdependence where

Neonates rely on diaphragm as the main muscle of respiration. Only 25% of the diaphragm in neonates is made of type I fibre capable of slow and sustained activity against 55% by 8 months of age. Raised intra-abdominal pressure due to any cause like gastric distension, hepatic congestion and ascites can compromise its function. In neonates a larger portion of energy expenditure is used for ventilation and therefore they fatigue easily and have failure to thrive

dysfunction of one ventricle can rapidly affect the other due to septal interactions.

Embolization, incomplete closure and hemolysis are possible risks.

following cavopulmonary connection. [19]

242 Principles and Practice of Cardiothoracic Surgery

**13. Pediatric anesthesia and critical care**

differences in **physiology** of the immature organ systems.

unless the obstruction is severe and prolonged.

**Pulmonary hypertension** both pre and postoperatively plays an important role in the planning of surgery, anesthesia and postoperative care.

Preoperatively it can be due to large left to right shunt lesions, or due to pulmonary venous obstruction, rarely due to pulmonary vascular obstructive disease.

Intraoperatively- light anesthesia, hypoxemia, hypoventilation, lung hyperinflation or hypoinflation, hypothermia, respiratory and metabolic acidosis, protamine, blood products, prolonged bypass with inflammatory response and capillary leak, compression and atelectasis of lung, pulmonary edema from inadequate venting of left atrium can all contribute to increased pulmonary vascular resistance (PVR).

Intravenous drugs can be used to reduce the PVR, but they lack selectivity and can cause systemic hypotension. Nitroprusside, glyceroltrinitrate, milrinone, Prostaglandin E1 and I2, tolazoline and isoproterenol have been used. Inhaled NO is most selective pulmonary vasodilator currently available; it is rapidly taken up and inactivated by haemoglobin as it diffuses from the alveoli. Oral drugs in the form of PDE type V inhibitor, sildenafil and endothelin I blocking drugs bosentan have shown encouraging results. [21,22]

Preoperative evaluation should keep in mind the physiology of defect, and the changes that the preoperative treatment could have caused (diuretics causing hypokalaemia) and the presence and severity of cyanosis and pulmonary hypertension. Haematocrit greater than 65% can exacerbate tissue hypoxia and can cause stasis and potential thrombosis. Avoiding dehydration is very important to avoid tissue hypoxia and to maintain renal function postop‐ eratively.

Non-invasive monitoring using electrocardiography, pulse oximetry, capnography, noninvasive blood pressure is placed before induction, invasive arterial and central venous line should be planned according to procedure. Neurologic monitoring and cerebral protection is of concern during congenital heart surgery. Nasopharyngeal temperature, continuous EEG, transcranial Doppler, frontal lobe infrared spectroscopy and cerebral oximetry can be used to evaluate cerebral blood flow velocity and perfusion. Intraoperative echocardiography has achieved a significant role in repair of CHD. It helps in re-evaluation of anatomy before intervention, adequacy of surgical repair and de-airing after weaning from cardiopulmonary bypass and has become a integral part of monitoring in many units including ours.

Maintenance of diastolic pressure and coronary perfusion is important particularly in the setting of duct dependent lesions and in situations of altered coronary perfusion. There is a choice of induction techniques, inhalational, IV or IM.

Fentanyl (15-25 ug/kg), ketamine (1-3 mg/kg), Pancuronium (0.2mg/kg) or Suxamethonium (2mg/kg) in combination with glycopyrrolate (10ug/kg) allows prompt induction and airway control without significant increase in PVR. Midazolam (0.1-0.2mg/kg) is also a useful adjunct 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.

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

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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

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

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

Monitoring – Dampened arterial upstroke, narrow pulse pressure, elevated venous pressures (systemic or pulmonary – loss of sinus rhythm, residual outflow obstruction, tamponade, AV

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

Strategies for management of Low CO should focus on optimizing the balance between oxygen

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

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

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

necessary especially in patients with diGeorge syndrome and 22q11 deletion.

vasopressor) can be used in situations with low SVR ('warm' shock) [23]

the stress response and maintains systemic and pulmonary hemodynamic stability.

picture should be considered rather than a isolated finding.

with CHD.

obtundation of sensorium.

valve regurgitation should be ruled out)

fiO2, and the factors which determine output

and Increased BUN and creatinine.

supply and demand.

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 effects of anesthetic drugs.
