Structured Handover

Transfer from the operating theatre to the ICU is one of the most vulnerable times in the patient’s postoperative course. Information transfer must include the child’s preoperative status, intraoperative management (anaesthetic, perfusion and surgical management), concerns regarding residual anatomic or physiological states, potential complications and anticipation of the postoperative course. During the time of handover, the anaesthetist is primarily responsible for the care of the patient. After the transfer of information and assessment, the intensivist assumes responsibility.

Generally, the child falls into one of three groups:

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   1. Uncomplicated and relatively straightforward surgery. A rapid recovery is anticipated and the child can be rapidly weaned from mechanical ventilation and the trachea extubated.

   
   
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   2. Children where surgery has been more complex. Whilst they may currently appear stable with satisfactory clinical and echocardiographic findings, they may be vulnerable to a low CO state (LCOS) or a worsening systemic inflammatory response. Until the clinician is satisfied that the period of vulnerability is over, these children are kept ventilated and sedated with progression following a period of stability.

   
   
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   3. Unstable children with an established LCOS. Multidisciplinary discussion and planning is essential. Important considerations include: has a residual lesion been excluded, are there other physiological problems, for example PHT and is extracorporeal life support (ECLS) indicated?

Mechanical Ventilation

Most children will be extubated relatively quickly. It is important to have an understanding of the source of the pulmonary blood flow (PBF) and the cardiopulmonary interactions of different circulations. Whilst oxygenation targets are tailored to an individual child, an SaO₂ of 75–80% in a single ventricle circulation will usually equate to a Q_P:Q_S ratio of approximately 1.

In children with a limited PBF, particularly when dependent on passive systemic venous return, early extubation is helpful. In contrast, the volume-loaded single ventricle or the impaired LV may struggle with the associated increase in systemic afterload, particularly in the setting of coexisting atrioventricular (A-V) valve regurgitation. Management of PaCO₂ is particularly important in the setting of PHT.

Metabolic State

Infants are at a particular risk of hypothermia. Hyperthermia may occur with LCOS, increasing oxygen demand and myocardial work, putting the child at greater risk of neurological injury.

Fluid and Electrolyte Management

Derangements are common. The clinical spectrum ranges from mild fluid overload to severe oedema, capillary leak, vasodilatation and hypotension, merging into the systemic inflammatory response state. The stress response, triggered as a normal response to surgical stimulation and bypass, leads to antidiuretic hormone (ADH) production.

With prolonged surgery and significant capillary leak, or where there is felt to be a significant chance of the child requiring postoperative renal replacement therapy (RRT), a peritoneal dialysis (PD) catheter may be placed in theatre. Even if PD is not required the continuous drainage of peritoneal (ascitic) fluid may benefit renal perfusion and mechanical ventilation.

Maintenance fluids are restricted to 25% in the initial 24 hours after surgery. Oliguria is common but diuretics are unlikely to be effective during this time until the CO increases and ADH levels fall.

The fluid management plan is reviewed and adjusted according to the clinical status. Avoidance of hypokalaemia and hypocalcaemia is important. Hyperglycaemia is common but there is no evidence that tight glycaemic control improves outcomes.

Blood transfusion may be required for adequate oxygen delivery, particularly with single ventricle circulations where the target Hb is generally 120–140 g l^–1.

Nutrition

Adequate nutrition is critical as these children may be malnourished preoperatively. The basal metabolic rate is raised proportionally to the illness severity with high caloric requirements – up to 150 kcal kg^–1 per day in infants.

Ideally, nutrition is enteral. Where there has been gut ischaemia or concern regarding splanchnic perfusion, then caution is indicated and, occasionally, a period of parenteral nutrition is needed.

Systemic Inflammatory Response

An exaggerated inflammatory response is commoner in infants, especially following protracted complex surgery. This leads to endothelial failure, capillary leak and multi-organ dysfunction. Clinical manifestations include generalized tissue oedema, third-space fluid losses (peritoneal and pleural), a persistent volume requirement, vasoplegia and increasing vasoactive infusion requirements.

Low Cardiac Output Syndrome

LCOS affects up to 25% of infants post CPB. The nadir typically occurs 6–18 hours post surgery. In high-risk cases, the sternum is left open to minimize any mechanical tamponade effect on the heart. Equally, where the chest is closed and there is a significant LCOS, consideration should be given to reopening.

Postoperative bleeding may be significant with a dilutional coagulopathy. This should be corrected and a low threshold maintained for surgical review and/or re-exploration if bleeding continues despite appropriate product replacement. In managing LCOS consider:

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  Preload: Children with passive systemic venous return as their source of PBF or who have restrictive physiology or diastolic dysfunction require higher preload.

  
  
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  Heart rate: Neonates have a fixed SV and thus are critically dependent on adequate chronotropy. Loss of A-V synchrony reduces the CO by 30%. Excessive tachycardia compromises coronary perfusion. Loss of rate variability is an important early sign of impending arrhythmia, reduced ventricular function or circulatory collapse.

  
  
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  Contractility: Consider potential residual lesions, particularly if the reduction in function persists beyond the first 24 hours.

  
  
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  Afterload: Consider in the context of both biventricular and univentricular circulations, and the potential benefit of positive pressure ventilation on afterload reduction, versus the preload impact.

In the univentricular circulation, the adequacy of systemic oxygen delivery is dependent on the balance between Q_P and Q_S, which in turn is dependent on the PVR and SVR. In the setting of a high SVR relative to PVR, the Q_P:Q_S ratio will often be greater than 1 and the infant will have a high SaO₂ (often >90%) at the expense of inadequate systemic perfusion. Manipulation of the SVR is important in this situation and is in general easier to control than manipulating the PVR.