Pressure-regulated volume control vs volume control ventilation in infants after surgery for congenital heart disease

The objective of this investigation was to compare how two modes of positive pressure ventilation affect cardiac output, airway pressures, oxygenation, and carbon dioxide removal in children with congenital heart disease in the immediate postoperative period. The investigation used a one group pretest-post-test study design and was performed in the pediatric cardiac intensive care unit in a university-affiliated children's hospital. Nine infants were enrolled immediately after repair of tetralogy of Fallot (2) or atrioventricular septal defects (7) with mean weight = 5.5 kg (4.2-7.3 kg). Children were admitted to the pediatric cardiothoracic intensive care unit after complete surgical repair of their cardiac defect and stabilized on a Siemen's Servo 300 ventilator in volume control mode (VCV1) (volume-targeted ventilation with a square flow wave pattern). Tidal volume was set at 15 cc/kg (total). Hemodynamic parameters, airway pressures and ventilator settings, and an arterial blood gas were measured. Patients were then changed to pressure-regulated volume control mode (PRVC) (volume-targeted ventilation with decelerating flow wave pattern) with the tidal volume set as before. Measurements were repeated after 30 minutes. Patients were then returned to volume control mode (VCV2) and final measurements made after 30 minutes. The measurements and results are as follows: After correction of congenital heart defects in infants, mechanical ventilation using a decelerating flow wave pattern resulted in a 19% decrease in peak inspiratory pressure without affecting hemodynamics, arterial oxygenation, or carbon dioxide removal.

Postoperative hemodynamics after Norwood palliation for hypoplastic left heart syndrome

Hemodynamics after Norwood palliation for hypoplastic left heart syndrome (HLHS) have been incompletely characterized, although emphasis has been placed on the role that an excess pulmonary-to-systemic blood flow ratio (Qp/Qs) may play in causing hemodynamic instability. Studies suggest that maximal oxygen delivery occurs at a Qp/Qs < 1. However, it remains unclear to what extent cardiac output can increase with increasing pulmonary perfusion. One approach is to use the oxygen excess factor omega, an index of systemic oxygen delivery, and compare omega with measured Qp/Qs. We measured Qp/Qs and omega in neonates after Norwood palliation for HLHS, and determined how they were related. In addition, we determined the temporal course of surrogate indexes of systemic perfusion in the early postoperative period. Arteriovenous oxygen saturation difference, blood lactate, and omega were recorded on admission and every 3 to 12 hours for 2 days in 18 consecutive infants with HLHS or variant after Norwood palliation. Three infants required extracorporeal membrane oxygenation (ECMO) 6 to 9 hours after admission. These infants had higher Qp/Qs, blood lactate, arteriovenous oxygen saturation difference, and lower omega than non-ECMO patients. In non-ECMO patients between admission and 6 hours, omega decreased significantly despite no appreciable change in Qp/Qs. We conclude that: (1) Oxygen delivery is significantly decreased at 6 postoperative hours unrelated to Qp/Qs. This modest decline in oxygen delivery is insufficient to compromise tissue oxygenation. (2) Patients requiring ECMO have significant derangements in oxygen delivery.

Serial blood lactate measurements predict early outcome after neonatal repair or palliation for complex congenital heart disease

OBJECTIVES

Neonates with congenital heart disease may appear hemodynamically stable after operation and then suddenly experience catastrophic decompensation. An improved means of predicting which infants will suddenly die in the early postoperative period may lead to lifesaving interventions. Studies indicate that blood lactate level is proportional to tissue oxygen debt, but information linking lactate levels with outcome in infants after operation is limited. We sought to determine whether a change in lactate level over time was predictive of a poor outcome defined as death within the first 72 hours or the need for extracorporeal membrane oxygenation.

METHODS

To test this hypothesis, we studied prospectively 46 infants who were less than 1 month old and were undergoing complex cardiac surgical palliation or repair. Postoperative arterial oxygen saturation, bicarbonate, and lactate levels were recorded on admission to the intensive care unit and every 3 to 12 hours for the first 3 days.

RESULTS

Thirty-seven patients had a good outcome, and 9 patients had a poor outcome. Mean initial lactate level was significantly greater in patients with a poor outcome (9.4 +/- 3.8 mmol/L) than in patients with a good outcome (5.6 +/- 2.1 mmol/L; P =.03). However, an elevated initial lactate level of more than 6 mmol/L had a low positive predictive value (38%) for poor outcome. In contrast, a change in lactate level of 0.75 mmol/L per hour or more was associated with a poor outcome (P <.0001) and predicted a poor outcome with an 89% sensitivity value, a 100% specificity value, and a 100% positive predictive value.

CONCLUSIONS

Serial blood lactate level measurements may be an accurate predictor of death or the requirement for extracorporeal membrane oxygenator support for patients who undergo complex neonatal cardiac surgery.

Normalization of priming solution ionized calcium concentration improves hemodynamic stability of neonates receiving venovenous ECMO

The authors' objectives in this investigation were: 1) to prospectively determine whether a normocalcemic priming solution would result in elimination of hypocalcemia after the initiation of extracorporeal membrane oxygenation (ECMO); 2) to investigate whether normocalcemia would result in improvements in the patient's hemodynamics during the initiation of ECMO; and 3) to further define the relationship between ionized calcium measurements and total calcium, serum total protein, serum albumin, and total magnesium. This was a prospective study done in our neonatal intensive care unit, and included nine neonatal patients placed on ECMO for cardiopulmonary support. The bypass circuit was primed in the standardized manner with 100 mg calcium chloride. Circuit ionized calcium measurements were performed, and additional calcium chloride was added to normalize the ionized calcium in the priming solution. Ionized calcium was measured from the circuit and the patient before the initiation of ECMO, and then again from the patient 5, 10, 15, 30, 60, 120, and 240 minutes after the initiation of ECMO. The patients' mean arterial pressure was measured simultaneously with each ionized calcium measurement. Ionized calcium, serum total calcium, total protein, serum albumin, and total magnesium were measured from blood samples simultaneously collected four times daily. There was no significant change in the ionized calcium measured in the patients after the initiation of ECMO. There was, however, a significant increase in blood pressure 5 min after the initiation of ECMO (62 +/- 7 mmHg vs 53 +/- 6 mmHg, p = 0.01). Thereafter, there was no difference in blood pressure measured when compared with pre ECMO values. A poor correlation was demonstrated between ionized calcium and total calcium (r2 = 0.35), serum total protein (r2 = 0.26), serum albumin (r2 = 0.27), and total magnesium (r2 = 0.05). On the basis of the authors' data, the initiation of ECMO with a normocalcemic prime results in a minimal change in patient ionized calcium and resolution of the hypotension previously observed. In addition, there was poor correction between ionized calcium, total calcium, and other indirect measures of ionized calcium. Ionized calcium measurements are critical for patient hemodynamic stability before bypass and should be normalized in both the patient and priming solution before the initiation of bypass.

High-frequency jet ventilation for respiratory failure after congenital heart surgery

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) is considered when respiratory failure (RF) persists despite increasing conventional mechanical ventilation (CMV). High-frequency jet ventilation (HFJV) can improve ventilation with comparable mean airway pressure (PAW) to that found on CMV. This study was undertaken to determine whether HFJV is an effective treatment and alternative to ECMO for RF after congenital heart surgery.

METHODS AND RESULTS

HFJV was instituted in nine patients ranging in age from 6 days to 3.3 years with congenital heart disease meeting pulmonary criteria for ECMO. Indications for HFJV were pulmonary hypertension (six), adult-type respiratory distress syndrome (two), and pneumonitis (one). Seven patients (77%) were placed on HFJV within 24 hours of operation, and two patients required HFJV 2 weeks after operation. HFJV resulted in resolution of RF in eight of nine patients (89%). After 1 hour of HFJV, the arterial pH increased from 7.40 +/- 0.1 to 7.56 +/- 0.1 (p < 0.05) and the PaCO2 decreased from 44 +/- 15 to 29 +/- 12 mm Hg (p < 0.05). During HFJV there was no change in PaO2, although the FIO2 decreased from 0.99 +/- 0.0 to 0.73 +/- 0.2 (p < 0.05). There was no change in PAW, peak inspiratory pressures, positive end-expiratory pressures, heart rate, or mean arterial blood pressure during HFJV when compared with CMV. Mean duration of HFJV was 43 hours. Four patients were extubated and discharged from the hospital. Two patients were extubated but died from sepsis. Two patients had resolution of RF, but one died at reoperation and one from multisystem organ failure. The patient who failed HFJV therapy was placed on ECMO and died.

CONCLUSIONS

This study suggests that HFJV improves ventilation and is an alternative to ECMO in patients with RF after surgery for congenital heart disease.

High-frequency jet ventilation improves cardiac function after the Fontan procedure

Pulmonary vascular resistance is an important determinant of cardiac output after the Fontan procedure and is adversely affected by elevated mean airway pressure. High-frequency jet ventilation (HFJV) is an alternate form of mechanical ventilation which supports gas exchange at lower mean airway pressure. This study was performed to determine if HFJV could lower mean airway pressure and pulmonary vascular resistance and result in an increase in cardiac output after the Fontan procedure. We prospectively evaluated 13 patients ranging in age from 0.9 to 8.5 years (mean, 3.9 years) and in weight from 6.2 to 20.1 kg (mean, 13.9 kg). Right atrial, left atrial and pulmonary artery catheters were used to measure hemodynamic parameters. Cardiac index was measured by dye dilution technique, and pulmonary vascular resistance was calculated. The patients were stabilized on mechanical ventilation to achieve a PaCO2 = 30 +/- 5 mm Hg, and baseline hemodynamic and respiratory measurements were made. HFJV was begun at settings adjusted to achieve similar gas exchange. Respiratory and hemodynamic measurements were repeated after 30-60 minutes of HFJV. Mechanical ventilation was then resumed at baseline settings, and measurements were repeated 0.5-1 hour later. There was no significant change in gas exchange. HFJV resulted in a 50% reduction in mean airway pressure (9.2 +/- 0.2 cm H2O to 4.6 +/- 0.1 cm H2O, p less than 0.001), a 59% reduction in pulmonary vascular resistance (3.82 +/- 0.36 to 1.52 +/- 0.16 Woods units, p less than 0.001), and a 25% increase in cardiac index (2.32 +/- 0.12 l/min/m2 to 2.91 +/- 0.12 l/min/m2, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic instability after the initiation of extracorporeal membrane oxygenation: role of ionized calcium

OBJECTIVES

To prospectively document the occurrence of ionized hypocalcemia in infants and children treated with extracorporeal membrane oxygenation (ECMO), to determine if the type of calcium salt (calcium chloride or gluconate) used in priming the ECMO circuit affected ionized calcium, to determine if ionized calcium concentrations correlate with total calcium, protein, albumin, or total magnesium values, and to determine if the hypotension usually observed after ECMO initiation correlates with low circulating ionized calcium concentrations.

DESIGN

Prospective study.

SETTING

Pediatric ICU and neonatal ICU.

PATIENTS

Sixteen neonatal and three pediatric patients who were started on ECMO for cardiopulmonary support.

INTERVENTIONS

The ECMO circuit was primed in a standardized manner, 100 mg of calcium gluconate was added in group 1 patients and 100 mg of calcium chloride was added in group 2 patients.

MEASUREMENTS

Ionized calcium was measured from the circuit before initiation of ECMO and from the patient before, and then 5, 10, 15, 30, 60, 120, and 240 mins after initiation of ECMO. Total calcium and ionized calcium concentrations were measured simultaneously every 6 hrs. Serum total protein, albumin, magnesium, and ionized calcium values were measured from blood samples collected simultaneously twice daily.

RESULTS

A significant decrease in the mean serum ionized calcium value occurred 5 mins after the initiation of ECMO in both groups, p less than .001. The ionized calcium value remained significantly decreased until 30 mins after the initiation of ECMO. There were no differences between the ionized calcium concentrations obtained during priming with calcium gluconate vs. those concentrations obtained with calcium chloride priming (p = .79). Throughout the course of ECMO, the serum ionized calcium concentrations ranged from 0.60 to 1.86 mmol/L. Poor correlations existed between circulating ionized calcium values and total calcium (r2 = .30), total protein (r2 = .20), albumin (r2 = .20), and magnesium concentrations (r2 = .10). There was a good correlation between the patients' BP and ionized calcium concentrations after bypass was initiated (r2 = .87).

CONCLUSION

Our data demonstrate that ionized hypocalcemia is a frequent occurrence after the initiation of ECMO. Since there is a poor correlation between ionized calcium and total calcium, ionized calcium concentrations should be measured directly in these patients.