Correlation of thromboelastography with standard tests of anticoagulation in paediatric patients receiving extracorporeal life support.

UNLABELLED: Children requiring extracorporeal life support (ECLS) are at significant risk for thrombotic and haemorrhagic complications. Thromboelastography (TEG) is increasingly being used to assist in monitoring the coagulation status of critically ill patients. Its role in heparinised children receiving ECLS is unknown. METHODS: A retrospective review of TEG in 27 children (mean age 2 years and 8 months) receiving ECLS in a tertiary paediatric intensive care unit between December 2006 and April 2008. Paired TEG (kaolin and heparinase) analysis was performed on 171 occasions. On all occasions activated partial thromboplastin time (APTT) and platelet count were performed within 4 hours of the TEG (mean 6.5 minutes after TEG). On 158 occasions, the activated clotting time (ACT) was measured simultaneously with TEG. RESULTS: The TEG (kaolin) sample was not interpretable due to the heparin effect in 89 (52%) samples. There was a weak correlation between TEG (heparinase) variables and APTT, and between TEG and ACT with a stronger correlation between TEG (Maximum amplitude) and platelet count. CONCLUSION: TEG monitoring should always include paired samples in heparinised children on ECLS. In this heterogeneous population, weak, and moderate correlations exist between TEG and standard haematological tests. Prospective studies, with simultaneous sampling for TEG and conventional laboratory tests, must be performed in order to establish its absolute utility as a clinical tool in this population.

Influences on lactate levels in children early after cardiac surgery: prime solution and age.

OBJECTIVE: Hyperlactataemia is often seen after cardiac surgery in children and is associated with an increased risk of adverse outcome, especially in infants and young children. However, we noticed that many older children after cardiac surgery had elevated lactate levels in the absence of other markers of oxygen debt or cardiovascular instability and had an uncomplicated postoperative course. Many older children undergo surgery without blood products being used in the cardiopulmonary bypass (CPB) circuit prime. The aim of this study was to determine whether lactate levels in children after CBP are influenced by age and/or pump prime solutions. METHODS: We studied 100 children undergoing open heart surgery in a tertiary paediatric cardiac surgical unit. Fifty children were aged 2 months to 4 years (Group 1) and 50 were aged 4 years or older (Group 2). Blood samples were obtained from an arterial catheter and serum lactate levels were collected at the time of admission to the paediatric intensive care unit (PICU) and 4 hours later. The following data were collected from the medical records or laboratory databases: weight, age, lowest haemoglobin during CPB, total bypass time, aortic cross clamp time, priming solution used, length of postoperative ventilation and PICU stay, type of surgery and occurrence of adverse perioperative events, including cardiac arrest, need for extracorporeal support or death. RESULTS: All children in Group 1 had a blood prime. All children in Group 2 had a bloodless prime. Although there were differences in the types of anomalies and surgical procedures performed, there were no significant differences between the two groups in terms of surgical complexity, CBP time, aortic cross clamp time and haemoglobin during CPB. Lactate levels in children in Group 2 were higher than in Group 1. Sixteen children (32%) in Group 2 had a lactate level of > 4 mmol/L, whereas only 3 children (6%) in Group 1 had a lactate level of > 4 mmol/L (Fisher's exact test p = 0.0002). Using multivariate analysis the pump prime solution was independently associated with high lactate levels after CPB. CONCLUSIONS: Lactate levels after cardiac surgery in older children who have a bloodless prime may not have the same physiological or prognostic implications as in infants who have a blood prime.

Predicting outcome in ex-premature infants supported with extracorporeal membrane oxygenation for acute hypoxic respiratory failure.

OBJECTIVE: To identify predictors of outcome in ex-premature infants supported with extracorporeal membrane oxygenation (ECMO) for acute hypoxic respiratory failure. METHODS: Retrospective review of ex-premature infants with acquired acute hypoxic respiratory failure requiring ECMO support in the United Kingdom from 1992 to 2001. Review of follow up questionnaires completed by general practitioners and local paediatricians. RESULTS: Sixty four ex-premature infants (5-10 each year) received ECMO support, despite increased use of advanced conventional treatments over the decade. The most common infective agent was respiratory syncytial virus (85% of cases). Median birth gestation was 29 weeks and median corrected age at the time of ECMO support was 42 weeks. Median ECMO support duration was relatively long, at 229 hours. Survival to hospital discharge and to 6 months was 80%, remaining similar throughout the period of review. At follow up, 60% had long term neurodisability and 79% had chronic pulmonary problems. Of pre-ECMO factors, baseline oxygen dependence, younger age, and inpatient status were associated with non-survival (p < or = 0.05). Of ECMO related factors, patient complications were independently associated with adverse neurodevelopmental outcome and death (p < 0.01). CONCLUSIONS: Survival rates for ex-premature infants after ECMO support are favourable, but patients suffer a high burden of morbidity during intensive care and over the long term. At the time of ECMO referral, baseline oxygen dependence is the most important predictor of death, but no combination of the factors considered was associated with a mortality that would preclude ECMO support.

Improved early ventricular performance with a right ventricle to pulmonary artery conduit in stage 1 palliation for hypoplastic left heart syndrome: evidence from strain Doppler echocardiography.

OBJECTIVE: To quantify non-invasively right ventricular (RV) performance in infants after stage 1 palliation for hypoplastic left heart syndrome (HLHS). DESIGN: Prospective, observational study with two dimensional and strain Doppler echocardiography. SETTING: Single tertiary paediatric cardiology centre. PATIENTS: Convenience sample of nine consecutive infants with HLHS. Four whose surgery involved a systemic to pulmonary artery (S-PA) shunt were compared with five whose surgery incorporated a right ventricle to pulmonary artery (RV-PA) conduit. METHODS: Basal RV free wall longitudinal strain rate, systolic strain (epsilon), and RV percentage area change were calculated during a single assessment between 27-50 days after surgery. RESULTS: Cardiopulmonary bypass time was longer in patients who underwent RV-PA (226 (30) minutes v 181 (18) minutes, p = 0.03), but cross clamp time, duration of ventilation, and inotrope use did not differ. Two patients in the S-PA group died, on days 29 and 60 after surgery. Peak systolic strain rate (-1.24 (0.19)/s v -0.91 (0.21)/s, p = 0.048), peak epsilon (-17.8 (1.8)% v -13.4 (2.0)%, p = 0.01), and RV percentage area change (56 (6)% v 25 (6)%, p < 0.01) were all greater among RV-PA patients. These indices also tended to be greater in survivors as a group. Ventricular loading conditions (oxygen saturations, diuretic treatment, and blood pressure) were similar in both groups. CONCLUSION: Strain Doppler echocardiography shows improved RV longitudinal systolic contractility in patients during convalescence after the RV-PA modification of stage 1 palliation for HLHS compared with those with an S-PA shunt.

Early extubation after surgical repair of tetralogy of Fallot.

In recent years, post-operative intensive care of the child with congenital cardiac disease has placed an emphasis on earlier weaning from mechanical ventilation. We describe our experience of postoperative fast-tracking of children undergoing cardiac surgery during a charitable mission in Venezuela, where resources and equipment were severely limited. During our stay, 11 children, with a median age of 2 years, underwent total correction of tetralogy of Fallot. The median duration of ventilation was 2.5 hours, and all patients were extubated within 12 hours of surgery. Effective analgesia was achieved without the need for continuous intravenous infusions of opiates. This experience shows that early extubation can safely be carried out in well-selected patients after surgery to correct congenital cardiac malformations. This allows faster throughput of patients, and helps provide an efficient and cost-effective service.

Negative pressure ventilation as haemodynamic rescue following surgery for congenital heart disease.

A low cardiac output state is an important cause of morbidity and mortality following repair of tetralogy of Fallot (ToF). This is often refractory to conventional measures. The cardiac output of these patients is highly dependent on diastolic pulmonary arterial flow which is enhanced during spontaneous respiration, but much reduced by intermittent positive pressure ventilation (IPPV). We report the successful use of negative pressure ventilation (NPV) as haemodynamic therapy in three children with a low output secondary to restrictive right ventricular (RV) physiology following ToF repair. NPV produced a significant haemodynamic improvement, with increases in cardiac output of greater than 100 % in two of the children. By augmenting pulmonary blood flow, and hence cardiac output, NPV has a role as adjunctive haemodynamic therapy in patients with a low output secondary to diastolic RV dysfunction, in whom early extubation is not possible.

Cardiorespiratory responses to negative pressure ventilation after tetralogy of fallot repair: a hemodynamic tool for patients with a low-output state.

OBJECTIVES: We hypothesized that a period of cuirass negative pressure ventilation (NPV) would augment the cardiac output of patients in the early postoperative period after complete correction of tetralogy of Fallot (TOF). BACKGROUND: Diastolic right ventricular dysfunction can lead to a low-output state in an important minority of patients after TOF repair. In these patients, the diastolic pulmonary arterial flow, which characterizes restrictive right ventricular physiology, and on which the cardiac output is so dependent, is highly sensitive to changes in intrathoracic pressure. METHODS: The effects of NPV on pulmonary blood flow were investigated in 23 intubated children who were initially ventilated using intermittent positive pressure ventilation after TOF repair. Eight patients had restrictive right ventricular physiology. All children received a 15-min period of NPV, and eight received a prolonged period (45 min) of NPV. RESULTS: A brief period of NPV increased pulmonary blood flow by 39%, and the improvement further continued if the study period was extended, with a total increase of 67% after 45 min. Patients with restrictive physiology had a somewhat delayed response to NPV, but the ultimate increase during an extended period of NPV was greater in restrictive patients (84%) than nonrestrictive patients (50%). CONCLUSIONS: By manipulating important cardiopulmonary interactions, NPV improves the cardiac output of patients after TOF repair, and has a role as a hemodynamic tool in the management of the low-output state in selected cases.

Cardiopulmonary interactions after Fontan operations: augmentation of cardiac output using negative pressure ventilation.

BACKGROUND: The low-output state is the chief cause of morbidity and mortality after Fontan operations. An alternative hemodynamic tool would be a welcome addition for these patients, who are typically resistant to conventional therapeutic measures. METHODS AND RESULTS: The hemodynamic effects of conversion from conventional intermittent positive pressure ventilation (IPPV) to cuirass negative pressure ventilation (NPV) was investigated in nine acute postoperative Fontan patients on the pediatric intensive care unit and nine anesthetized patients undergoing cardiac catheterization in the convalescent phase after Fontan operations. Pulmonary blood flow was measured using the direct Fick method during IPPV and after a brief period of NPV. In one subgroup of patients, pulmonary blood flow was measured again after reinstitution of IPPV, and in a second subgroup, pulmonary blood flow was measured after an extended period of NPV. A brief period of NPV increased pulmonary blood flow from 2.4 to 3.5 L x min(-1) x /m(-2), with a mean increase of 42%. Pulmonary blood flow continued to improve, with a total increase of 54% after an extended period of NPV. Values fell toward baseline after reinstitution of IPPV. Heart rate was unchanged during NPV, and the improvement in pulmonary blood flow was achieved by an increase in stroke volume from 25 mL/m2 to 37 mL/m2. CONCLUSIONS: Through improvement of the stroke volume alone, NPV brought about a marked increase in the pulmonary blood flow and, hence, cardiac output of Fontan patients. An improvement in cardiac output of this order, and by this mechanism, is currently unmatched by any therapeutic alternatives.

Cardiopulmonary interactions in healthy children and children after simple cardiac surgery: the effects of positive and negative pressure ventilation.

OBJECTIVE: To investigate the effects of cuirass negative pressure ventilation on the cardiac output of a group of anaesthetised children after occlusion of an asymptomatic persistent arterial duct, and a group of paediatric patients in the early postoperative period following cardiopulmonary bypass. DESIGN: Prospective study. SETTING: The paediatric intensive care unit and catheter laboratory of a tertiary care centre. PATIENTS: 16 mechanically ventilated children were studied: seven had undergone surgery for congenital heart disease, and nine cardiac catheterisation for transcatheter occlusion of an isolated asymptomatic persistent arterial duct. INTERVENTIONS: Cardiac output was measured using the direct Fick method during intermittent positive pressure ventilation and again after a short period of negative pressure ventilation. In five of the postoperative patients a third measurement was made following reinstitution of positive pressure ventilation. RESULTS: Negative pressure ventilation was delivered without complication, with no significant change in systemic arterial oxygen and carbon dioxide tension. The mixed venous saturation increased from 74% to 75.8% in the healthy children, and from 58.9% to 62.3% in the postoperative group. Negative pressure ventilation increased the cardiac index from 4.0 to 4.5 l/min/m2 in the healthy children, and from 2.8 to 3.5 l/min/m2 in the surgical group. The increase was significantly higher in the postoperative patients (28.1%) than the healthy children (10.8%). CONCLUSIONS: While offering similar ventilatory efficiency to positive pressure ventilation, cuirass negative pressure ventilation led to a modest improvement in the cardiac output of healthy children, and to a greater increase in postoperative patients. There are important cardiopulmonary interactions in normal children and in children after cardiopulmonary bypass, and by having beneficial effects on these interactions, negative pressure ventilation has haemodynamic advantages over conventional positive pressure ventilation.

Negative-pressure ventilation improves cardiac output after right heart surgery.

BACKGROUND: A low cardiac output state can complicate the postoperative course of patients undergoing Fontan-type operations and tetralogy of Fallot repair. METHODS AND RESULTS: We investigated the effect of negative-pressure ventilation on cardiac output in 11 children in the early postoperative period after right heart surgery. All patients were initially ventilated with volume-cycled intermittent positive-pressure ventilation, and negative-pressure ventilation was delivered with the Hayek external high-frequency oscillator. Cardiac output was calculated by the direct Fick method, oxygen consumption being measured by respiratory mass spectrometry. Cardiac output was measured during intermittent positive-pressure ventilation and after 15 minutes of negative-pressure ventilation. Negative-pressure ventilation improved the cardiac output by a mean of 46% (P = .005). Heart rate did not change, and stroke volume increased by a mean of 48.5% (P = .005). Mixed venous saturation increased by 4.6% (P < .02), and consequently arteriovenous oxygen content difference fell significantly (P = .01). The systemic and pulmonary vascular resistances were reduced significantly during negative-pressure ventilation (P < .05 and P < .03, respectively). CONCLUSIONS: Negative-pressure ventilation improves cardiac output in children after total cavopulmonary connection and tetralogy of Fallot repair and may prove to be an important therapeutic option in children with the low cardiac output state.