Liquid ventilation improves pulmonary function and cardiac output in a neonatal swine model of cardiopulmonary bypass

Effects of socio-emotional stressors on ventilation rate and subjective workload during simulated CPR by lay rescuers

Several studies have documented the occurrence of high ventilation rates during cardiopulmonary resuscitation, but to date, there have been no scientific investigation of the causes of hyperventilation. The objective of the current study was to test the effects of socio-emotional stressors on lay rescuers' ventilation rate in a simulated resuscitation setting using a manikin model. A within-subjects experiment with randomized order of conditions tested lay rescuers' ventilation rate on an intubated manikin during exposure to socio-emotional stressors and during a control condition where no external stressors were present. Ventilation rates and subjective workload were significantly higher during exposure to socio-emotional stressors than during the control condition. All but one of the nine participants ventilated at a higher ventilation rate in the experimental condition. All nine participants rated the subjective workload to be higher during exposure to socio-emotional stressors. Hence, exposure to socio-emotional stressors is associated with increased ventilation rates performed by lay rescuers during simulated cardiac arrest using a manikin model. These findings might have implications for the understanding of the type of situations which hyperventilation may occur. Awareness of these situations may have implications for training of lay rescues.

Total Liquid Ventilation Reduces Lung Injury in Piglets After Cardiopulmonary Bypass

BACKGROUND

Cardiopulmonary bypass may cause lung injury that does not respond to traditional therapies. Total liquid ventilation has been developed as an alternative ventilatory strategy for severe lung injury. The aim of this study is to investigate the effect of total liquid ventilation on lung injury in piglets after cardiopulmonary bypass.

METHODS

After exposure to 60 minutes of cardiac arrest and weaning from cardiopulmonary bypass, 12 piglets (4.2 +/- 0.3 kg) were randomly treated with conventional gas ventilation (control group) or total liquid ventilation (study group) for 240 minutes. Samples for blood gas analysis were collected before, and at 30-minute intervals after, cardiopulmonary bypass. The degree of lung injury was quantified by histologic examination. The inflammatory cells and the levels of interleukin-6, interleukin-8, and myeloperoxidase in bronchoalveolar lavage were analyzed.

RESULTS

Neutrophil and macrophage count in bronchoalveolar lavage were significantly decreased in the study group (52.4 +/- 6.82 vs 0.46 +/- 0.11 10(4)/mL; 58.33 +/- 0.88 vs 4.37 +/- 0.90 10(5)/mL; p < 0.001, respectively). The inflammation score and the total lung injury score were also reduced in the study group (4.39 +/- 1.14 vs 2.61 +/- 1.09; 11.06 +/- 1.66 vs 6.94 +/- 1.43; p < 0.05, respectively). The concentrations of interleukin-6 and myeloperoxidase in bronchoalveolar lavage were significantly reduced in the study group (81.32 +/- 15.23 vs 53.55 +/- 15.48 pg/mL, 75.00 +/- 9.19 vs 50.00 +/- 7.37 u/mL; p < 0.05, respectively), whereas the interleukin-8 levels were similar between both groups (551.63 +/- 119.34 vs 563.68 +/- 137.14 pg/mL, p > 0.05).

CONCLUSIONS

Total liquid ventilation with FC-77 (3M, St. Paul, MN) reduces biochemical and histologic lung injury in piglets after cardiopulmonary bypass.

Inhaled nitric oxide results in deteriorating hemodynamics when administered during cardiopulmonary bypass in neonatal swine

OBJECTIVE

To evaluate if inhaled nitric oxide (iNO) has a lung-protective effect when it is delivered during the ischemic phase of neonatal cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, controlled study.

SETTING

Surgical research laboratory in a university hospital.

SUBJECTS

Thirty-five neonatal swine.

INTERVENTIONS

One-week-old swine (2.1-3.4 kg) were exposed to cool, low-flow CPB bypass designed to mimic the bypass used during neonatal congenital heart repair. Animals were randomized to four groups: a) CPB without exposure to iNO (n = 9); b) iNO delivery only during CPB with discontinuation of iNO at the start of reperfusion (n = 7); c) iNO delivery both during CPB and during the 90-min post-CPB observation period (n = 7); and d) iNO delivery only after separation from CPB (n = 7). Each animal was placed on nonpulsatile CPB and cooled to a nasopharyngeal temperature of 18 degrees C (64 degrees F). Low-flow CPB (35 mL.kg(-1).min(-1)) was instituted for 90 mins. The blood flow then was returned to 100 mL.kg(-1).min(-1), and the animals were warmed to 36 degrees C (96.8 degrees F) before separation from CPB. Animals were followed 90 mins post-CPB. Lung tissue was harvested and evaluated for myeloperoxidase activity, wet/dry weight, and lung pathology. Five animals underwent sham protocol, receiving instrumentation but not exposure to CPB or iNO.

MEASUREMENTS AND MAIN RESULTS

We measured pulmonary vascular resistance, right ventricular output, and pulmonary artery pressure in all animals at 30, 60, and 90 mins following separation from CPB. Study animals that received iNO during the ischemic period of CPB were not protected against CPB-induced lung injury. Those animals treated with iNO both during and after CPB trended worse than those receiving iNO only after CPB. Inhaled nitric oxide delivered only after separation from CPB improved the hemodynamic variables compared with all other groups. Differences in lung wet/dry weight, myeloperoxidase, and pathology were not significantly different among groups.

CONCLUSIONS

The delivery of iNO during the ischemic period of CPB does not protect against CPB-induced lung injury in a neonatal piglet CPB model. Delivery of iNO during this phase of CPB may, in fact, worsen the post-CPB hemodynamic condition. Inhaled nitric oxide should be used with caution during periods of low pulmonary blood flow CPB. Inhaled nitric oxide remains effective for reducing pulmonary vascular resistance after CPB.

Routine use of mechanical ventricular assist following the Norwood procedure

Conventional postoperative management after the Norwood procedure in patients with hypoplastic left heart syndrome suffers from three main shortfalls. First, the early postoperative care is often labor-intensive and ironically (despite sometimes heroic efforts), when babies die, health care providers often feel like failures, and in the worst scenarios, surgeons or other physicians create cultures of blame. Second, hospital survival is inconsistent in most centers, especially the ones with small surgical volume and limited experience. Third, survivors often show evidence of significant neurologic impairment. To address these postoperative problems, we have adopted the strategy of routinely placing all our patients with hypoplastic left heart syndrome on mechanical circulatory support immediately after their Norwood procedure. No attempt was made to balance the systemic and pulmonary circulation. Because an oxygenator was not used in the circuit, a much lower level of anticoagulation was used. Once the lactate level normalized, the amount of mechanical circulatory support was weaned. Since January of 2001, 23 patients have been managed using this strategy. The average time of mechanical circulatory support was approximately 3 days and has decreased to 2 days in more recent experience. The overall incidence of complications was 22%, and overall hospital survival was 87%. Neurodevelopmental testing before the Glenn procedure was normal for all patients tested. Routine postoperative use of mechanical ventricular assist device can support the increased cardiac output demands of infants following Norwood procedure and results in a stable postoperative convalescence. This strategy can simplify postoperative management, lead to excellent hospital survival, and possibly augment cerebral oxygen delivery resulting in improved neurologic outcomes for these patients.

Cardiopulmonary bypass in infants and children

Cardiopulmonary bypass (CPB) systems have evolved from futuristic visions of surgical pioneers to a safe and efficient tool in the therapy of treatment of cardiac disorders. There are many significant differences in the physiology between neonates and adult patients. There are currently very few congenital cardiac malformations that cannot be addressed effectively with surgical therapy. Yet, the necessity of CPB in the repair of these patients can still result in significant morbidity. A clearer understanding of the effects of CPB, hypothermia, and circulatory arrest is evolving and there is a considerable amount of research in these areas. It seems likely that modification of current CPB systems, minimization of exposure, and surgical techniques to avoid or limit the adverse effects may reduce mortality and morbidity in the future. The problems faced in these complex patients and procedures require that infant and neonatal cardiac surgery be performed in specialized centers with a multidisciplinary approach and specialized personnel. Future improvements in technology will likely result in improved long term outcome for children with congenital cardiac disease. Copyright 2000 by W.B. Saunders Company

Liquid lung ventilation reduces neutrophil sequestration in a neonatal swine model of cardiopulmonary bypass

OBJECTIVE

Liquid lung ventilation has been demonstrated to improve cardiorespiratory function after cardiopulmonary bypass. We hypothesized that liquid lung ventilation (LLV) would decrease the pulmonary inflammatory response after cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, experimental, controlled, nonblinded study.

SETTING

Animal research laboratory at a university setting.

SUBJECTS

A total of 24 neonatal piglets.

INTERVENTIONS

After intubation with a cuffed endotracheal tube, swine were conventionally ventilated. After surgical cannulation, each piglet was placed on conventional nonpulsatile CPB and cooled to 18 degrees C (64.4 degrees F). Subsequently, the animals were exposed to 90 mins of low-flow CPB (35 mL/kg/min). Animals were rewarmed to 37 degrees C (98.6 degrees F), removed from CPB, and ventilated for 90 min. Ten animals received conventional gas ventilation only (control), seven received initiation of LLV before CPB (prevention), and seven received initiation of LLV during the rewarming phase of CPB (treatment). After the animals were killed, the lungs were removed en bloc. The left lobe was dissected and formalin-fixed at 20 cm H2O overnight, followed by paraffin embedding. Sections were taken from the paraffin-embedded lungs. Neutrophil accumulation and lung injury were assessed by histochemical staining with leukocyte esterase and morphometrics, respectively. One hundred microscopic images were digitized from each tissue sample for lung morphometrics, and neutrophil counts were obtained from every fifth image.

MEASUREMENTS AND MAIN RESULTS

Lung tissue sections showed a significantly lower number of neutrophils per alveolar area in the prevention and treatment groups than in the control group (control 681 +/- 65, prevention 380 +/- 49, treatment 412 +/- 101 neutrophils per alveolar area [cells/mm2]; p <.05 for both prevention and treatment compared with control). There were no differences in lung injury as assessed with morphometrics or hemodynamic measurements between any of the three groups.

CONCLUSIONS

The data suggest that LLV reduces the CPB-induced neutrophil sequestration in the pulmonary parenchyma independent of its effects on the circulatory physiology or evidence of early lung injury.