Cardiac output, pulmonary artery pressure, and patent ductus arteriosus during therapeutic cooling after global hypoxia-ischaemia

Lactate acidosis and cardiac output during initial therapeutic cooling in asphyxiated newborn infants

Aim

We hypothesized that compromised cardiac output in asphyxiated infants may influence on the rate of disappearance of lactate due to insufficient perfusion.

Methods

The study was a prospective, observational study, where infants with perinatal asphyxia who met the criteria for therapeutic hypothermia were included. Cardiac output, stroke volume and heart rate were measured by electrical velocimetry in 15 newborn infants with perinatal asphyxia during the first six hours of active therapeutic hypothermia. Results from routine blood samples were collected retrospectively. Cardiac parameters were also measured in 10 healthy, term infants after caesarian section. Cardiac parameters were compared between the asphyxiated group and the control group prior to and during hypothermia. Rate of disappearance of lactate was correlated to cardiac output in the asphyxiated infants.

Results

Cardiac output was stable in the healthy infants from 0.5 to 6 hours postnatally. The infants with perinatal asphyxia had lower cardiac output prior to and during therapeutic hypothermia compared to the control group. Rate of disappearance of lactate was not related to cardiac output.

Conclusion

An association between disappearance of lactate acidosis and low cardiac output was not confirmed. A low rate of disappearance of lactate may rather be an indicator of organ injury due to asphyxia.

Noninvasive continuous cardiac output and cerebral perfusion monitoring in term infants with neonatal encephalopathy: assessment of feasibility and reliability

BackgroundNoninvasive hemodynamic monitoring of infants with neonatal encephalopathy (NE) undergoing therapeutic hypothermia (TH) would be a potentially useful clinical tool. We aimed to assess the feasibility and reliability of noninvasive cardiac output monitoring (NICOM) and near-infrared spectroscopy (NIRS) in this cohort.MethodsNICOM and NIRS were commenced to measure cardiac output (CO), systemic vascular resistance (SVR), blood pressure (BP), and cerebral regional oxygen saturations (SctO₂) during TH and rewarming. NICOM measures of CO were also compared with simultaneous echocardiography-derived CO (echo-CO).ResultsTwenty infants with a median gestation of 40 weeks were enrolled. There was a strong correlation between NICOM- and echo-CO (r²=0.79, P<0.001). NICOM-CO was systematically lower than echo-CO with a bias of 27% (limits of agreement 3-51%). NICOM illustrated lower CO during TH, which increased during rewarming. SctO₂ increased over the first 30 h of TH and stayed high for the remainder of the study. There was a rise in SVR over the first 30 h of TH and a decrease during rewarming (all P<0.05).ConclusionsNoninvasive hemodynamic assessment of infants with NE is feasible and illustrates potentially important changes. Larger studies are needed to assess the clinical applicability of those methods in this cohort.

Feasibility of a Miniature Esophageal Heat Exchange Device for Rapid Therapeutic Cooling in Newborns: Preliminary Investigations in a Piglet Model

Therapeutic hypothermia (TH) after neonatal encephalopathy, commonly provided by 72 hours of whole-body cooling using a wrap, limits parents' physical contact with their infants affecting bonding and may not be suitable for encephalopathic preterm infants with fragile skin. Alternative cooling methods are unavailable for this population. We investigated in a neonatal pig model the feasibility of achieving a 3.5°C reduction in rectal temperature (T_rectal) similar to clinical TH protocols from 38.5°C (normothermia for pigs) to a target of 35°C ± 0.2°C, using a novel neonatal esophageal heat exchanger (NEHE), compared its efficacy to passive cooling, and investigated its ability to maintain target T_rectal. Ventilated and anesthetized Landrace/Large white newborn pigs had the NEHE inserted. Water at adjustable temperatures and rates flowed down a central tube, returning up a surrounding distensible blind ending latex tube in a continuous loop. An initial experiment guided four subsequent cycles of passive cooling (30 minutes), rewarming to 38.5°C, active esophageal cooling to 35°C ± 0.2°C, active maintenance of target T_rectal (30 minutes), and rewarming. We compared surface, rectal temperature, and hemodynamic changes among passive, active, and maintenance phases, and esophageal histopathology against control. Compared with passive cooling, esophageal cooling achieved target T_rectal significantly earlier (71.3 minutes vs. 17.25 minutes, p = 0.003) with significantly greater rates of reduction in rectal (p = 0.0002) and surface (p = 0.005) temperatures and heart rate (p = 0.04). A water temperature of 39.1°C-40.2°C at a flow of 108-120 mL/min maintained T_rectal around 35°C ± 0.2°C. The higher peak heart rate and blood pressure within 8 minutes of the maintenance phase (p = 0.04) subsequently stabilized. Histopathology showed congestion, edema, and neutrophil infiltration with increasing cycles. Esophageal cooling is feasible and effective in achieving rapid cooling in newborns. Subsequent maintenance at this temperature required continued circulation of warm water. Esophageal histopathology needs further evaluation after 72 hours servo-control cooling with a narrower range of water temperatures in a larger group of animals.

Reduced cardiac output and its correlation with coronary blood flow and troponin in asphyxiated infants treated with therapeutic hypothermia

Perinatal asphyxia can lead to multi-organ insult which includes cardiovascular dysfunction. The objective was to study the relationship between cardiac function, perfusion and troponin. Unit database was accessed to identify infants with perinatal asphyxia over the last 2 years. Information from medical records and archived echocardiographic images was retrieved. Comparisons for echocardiographic information were made with healthy term infants. Seventeen infants with perinatal asphyxia were identified, of which three were excluded (one-33 weeks gestation, two-coagulopathy and pulmonary hypertension); 14 infants received therapeutic hypothermia. Median (range) gestation and birthweight were 39 (37-42) weeks and 3,550 (2,380-3,992) g respectively. Mean (S.D.) rectal temperature and time of echocardiogram were 33.5 ± 0.5 °C and median (range) 7.7 h [3-10] respectively. Majority of infants had low biventricular outputs. Median (range) SVC flow was 29.8 ml/kg/min (13-96.2). Median (range) troponin was 0.77 μg/L (0.17-2.6); normal ≤ 0.08 μg/L. Markedly low coronary flows (diastolic VTI median (range) 2.1 (1.3-2.9) cm were noted compared to controls. Coronary flow had a significantly positive correlation with left ventricular output. Higher troponin levels were associated with lower aortic stroke velocity. A close association between cardiac output, perfusion and troponin was noted. A dichotomy between blood pressure and flow parameters was noted, indicating the wide variation in vascular resistance in these infants. Biventricular output, coronary and SVC flows were significantly higher in the control population. In conclusion, inter-variable relationship between cardiac output, coronary flow and troponin is an important addition to the understanding of cardiovascular impact of perinatal asphyxia.

Xenon offers stable haemodynamics independent of induced hypothermia after hypoxia-ischaemia in newborn pigs

PURPOSE

To assess the effect of 18 hour (h) 50% xenon (Xe) inhalation at normothermia (NT, 38.5°C) or hypothermia (HT, 33.5°C) on mean arterial blood pressure (MABP), inotropic support and heart rate (HR) following an induced perinatal global hypoxic-ischaemic insult (HI) in newborn pigs.

METHODS

Newborn pigs ventilated under inhalational anaesthesia, following a 45 min HI (inhaled oxygen fraction reduced until amplitude integrated electroencephalogram was less than 7 μV), were randomised to three Xe (n = 45) (50% Xe 18 h with NT, HT 12 h or HT 24 h) or three non-Xe groups (n = 53) (0% Xe with NT, HT 12 h or HT 24 h) under otherwise identical conditions. We measured MABP and HR every minute. Hypotension (MABP <40 mmHg) was treated sequentially with 2 × 10 mL/kg saline, dopamine, norepinephrine and hydrocortisone if required.

RESULTS

Xe maintained higher MABP during HT (5.1 mmHg, 95% CI 2.34, 7.89), rewarming (10.1 mmHg, 95% CI 6.26, 13.95) and after cessation (4.1 mmHg, 95% CI 0.37, 7.84) independent of HT, inotropic support and acidosis. Xe reduced the duration of inotropic support by 12.6 h (95% CI 5.5, 19.73). Inotropic support decreased the HR reduction induced by HT from 9 to 5 bpm/°C during cooling and from 10-7 to 4-3 bpm/°C during rewarming. There was no interaction between Xe, HT, inotropic support and acidosis. Xe during HT cleared lactate faster; 3 h post-HI median (IQR) values of (Xe HT) 2.8 mmol/L (0.9, 3.1) vs. (HT) 5.9 mmol/L (2.5, 7.9), p = 0.0004.

CONCLUSION

Xe maintained stable blood pressure, thereby reducing the inotropic support requirements during and after administration independently of induced HT-current neonatal encephalopathy treatment. Xe may offer haemodynamic benefits in clinical neuroprotection studies.

Shock: a common consequence of neonatal asphyxia

Neonatal asphyxia is associated with multi-organ hypoxia-ischemia and subsequent dysfunction. The cardiovascular system is frequently affected, causing signs of shock and complicating the neonatal circulatory transition. Hypothermia therapy can improve outcome from neonatal asphyxia without adversely affecting cardiovascular stability. Therapy directed at the cardiovascular system can improve short-term measures of systemic blood flow, but to date has not been demonstrated to improve long-term outcome.

A tertiary care center's experience with therapeutic hypothermia after pediatric cardiac arrest

OBJECTIVE

To describe the use and feasibility of therapeutic hypothermia after pediatric cardiac arrest.

DESIGN

Retrospective cohort study.

SETTING

Pediatric tertiary care university hospital.

PATIENTS

Infants and children (age 1 wk to 21 yrs) without complex congenital heart disease with return of spontaneous circulation after in-hospital or out-of-hospital cardiac arrest from 2000 to 2006.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

We studied 181 patients after cardiac arrest, of which 91% were asphyxial in etiology (vs. cardiac) and 52% occurred in-hospital. Overall survival to hospital discharge was 45%. Forty patients received therapeutic hypothermia; all were admitted during or after 2002. Sixty percent of patients in the therapeutic hypothermia group had an initial temperature <35 degrees C. The median therapeutic hypothermia target temperature was 34.0 degrees C (33.5-34.8 degrees C), was reached by 7 hrs (5-8 hrs) after admission in patients who were not hypothermic on admission, and was maintained for 24 hrs (16-48 hrs). Re-warming lasted 6 hrs (5-8 hrs). In the therapeutic hypothermia group, temperature <32 degrees C occurred in 15% of patients and was associated with higher hospital mortality (29% vs. 11%; p = .02). Patients treated with therapeutic hypothermia differed from those treated with standard therapy, with more un-witnessed cardiac arrest (p = .04), more doses of epinephrine to achieve return of spontaneous circulation (p = .03), and a trend toward more out-of-hospital cardiac arrests (p = .11). After arrest, therapeutic hypothermia patients received more frequent electrolyte supplementation (p < .05). Standard therapy patients were twice as likely as therapeutic hypothermia patients to have a fever (>38 degrees C) after arrest (37% vs. 18%; p = .02) and trended toward a higher rate of re-arrest (26% vs. 13%; p = .09). Rates of red blood cell transfusions, infection, and arrhythmias were similar between groups. There was no difference in hospital mortality (55.0% therapeutic hypothermia vs. 55.3% standard therapy; p = 1.0), and 78% of the therapeutic hypothermia survivors were discharged home (vs. 68% of the standard therapy survivors; p = .46). In multivariate analysis, mortality was independently associated with initial hypoglycemia or hyperglycemia, number of doses of epinephrine during resuscitation, asphyxial etiology, and longer duration of cardiopulmonary resuscitation, but not treatment group (odds ratio for mortality in the therapeutic hypothermia group, 0.47; p = .2).

CONCLUSIONS

This is the largest study reported on the use of therapeutic mild hypothermia in pediatric cardiac arrest to date. We found that therapeutic hypothermia was feasible, with target temperature achieved in <3 hrs overall. Temperature below target range was associated with increased mortality. Prospective study is urgently needed to determine the efficacy of therapeutic hypothermia in pediatric patients after cardiac arrest.

Does head cooling with mild systemic hypothermia affect requirement for blood pressure support?

OBJECTIVE

Our goal was to evaluate whether head cooling with mild systemic hypothermia for neonatal encephalopathy is associated with greater requirement for volume or inotrope support.

PATIENTS AND METHODS

We studied term infants (>/=36 weeks) with moderate-to-severe neonatal encephalopathy plus abnormal amplitude integrated electroencephalography, randomly assigned to head cooling for 72 hours starting within 6 hours of birth, with the rectal temperature maintained at 34.5 degrees C +/- 0.5 degrees C (n = 112), or conventional care (n = 118).

DESIGN

This was a multicenter randomized, controlled study (the CoolCap trial). The primary outcome was the time relationship between mean arterial blood pressure and subsequent administration of inotropes or volume administration.

RESULTS

Pooled data from 0 to 76 hours after randomization revealed no difference in mean arterial blood pressure between groups and significantly lower mean heart rate during cooling. The use of inotropes or volume was related to preceding mean arterial blood pressure and not to treatment group in the first 24 hours. In contrast, from 24 to 76 hours, there was no effect of mean arterial blood pressure, but there was an overall reduction in pressure support over time and significantly more frequent pressure support in the cooled group than in controls.

CONCLUSIONS

Mild systemic hypothermia did not affect arterial blood pressure or initial treatment with inotropes or volume in infants with moderate-to-severe encephalopathy but was associated with an apparent change in physician behavior, with slower withdrawal of therapy in cooled infants.

Rapid progressive central cooling to 29 degrees C by extracorporeal circuit preserves cardiac function and hemodynamics in immature swine

The International Liaison Committee on Resuscitation (ILCOR) consensus statement includes recommendations and guidelines for therapeutic hypothermia in infants and children. The information supporting these recommendations is sparse, and reveals a need for target temperature and cooling mode data in age-appropriate animal models. Accordingly, we determined cardiac function and hemodynamic indices in immature piglets (<28 days) undergoing graded and rapid central cooling from 36 to 20 degrees C over 20 min by directing cardiac output through an extracorporeal circuit. Functional parameters were recorded continuously using aortic flow probes and left ventricular (LV) pressure capacitance catheters. Stroke volume and work increased during temperature reduction, peaking at 29 degrees C, while systemic vascular resistance did not change. Although, heart rate decreased steadily, cardiac output, power, and LV dP/dt(max) was maintained until 29 degrees C. All function parameters decreased below 29 degrees C, implying a critical threshold had been exceeded at lower temperatures. These data show that the temperature range (30+/-1) degrees C maintains cardiac function and that this target should be further evaluated as a target for therapeutic hypothermia.

The influence of thermal environment on pulmonary hemodynamic acclimation to extrauterine life in normal full-term neonates

OBJECTIVE

To assess chronological changes of pulmonary blood flow in response to ambient temperature load in normal full-term neonates.

METHODS

Group I (n=8) neonates were maintained at 25-26 degrees C for the first 24 h after birth, with Group II (n=7) at 32-33 degrees C. Left pulmonary artery flow volume (Vp) and ductus arteriosus diameter were measured at 2, 4, 6, 12, and 24 h using Doppler ultrasound. Core and peripheral temperatures, as a marker for cold stress, were also evaluated over the same time frame.

RESULTS

For Group I, Vp was steady for the first 6 h after birth before gradually decreasing. In contrast, Vp for Group II significantly decreased from 2-6 h, without later changes. At 6 h after birth in Group II, mean values of both Vp and ductus arteriosus diameter were significantly lower, whereas mean value of peripheral temperature was significantly higher than values in Group I (P<0.05).

CONCLUSION

Pulmonary blood flow in neonates placed at neutral ambient temperature stabilizes earlier than that of neonates placed at room temperatures. Changes of peripheral flow in response to ambient temperature load may be associated with decreased pulmonary blood flow through a left-to-right ductal shunt.

Hemodynamics among neonates with hypoxic-ischemic encephalopathy during whole-body hypothermia and passive rewarming

OBJECTIVE

To assess changes in cardiac performance, with Doppler echocardiography, among newborns with hypoxic-ischemic encephalopathy during mild therapeutic hypothermia and during rewarming.

METHODS

For 7 asphyxiated neonates (birth weight: 1840-3850 g; umbilical artery pH: 6.70-6.95) who received mild whole-body hypothermia, the following hemodynamic parameters were determined immediately before rewarming (33 degrees C) and during passive rewarming (35 degrees C and 37 degrees C): heart rate, systolic and diastolic blood pressure, core and peripheral temperatures, left ventricular ejection time, mean velocity of aortic flow, stroke volume, and cardiac output.

RESULTS

Heart rate decreased during hypothermia. Bradycardia, with heart rates below 80 beats per minute, did not occur. The median difference between core and peripheral temperatures decreased from 2.0 degrees C (range: 0-6.2 degrees C) during hypothermia to 0.7 degrees C (range: 0.4-1.9 degrees C) at normothermia. Cardiac output was reduced to 67% and stroke volume to 77% of the posthypothermic level. The median heart rate was 129 beats per minute before rewarming and increased to 148 beats per minute during complete rewarming. Before and during passive rewarming, hypotension was not observed. Before, during, and at the end of rewarming, the following parameters increased: mean velocity of aortic flow (median: 44, 55, and 58 cm/second, respectively), stroke volume (median: 1.42, 1.55, and 1.94 mL/kg, respectively), and cardiac output (median: 169, 216, and 254 mL/kg per minute, respectively). Left ventricular ejection time remained unchanged.

CONCLUSIONS

Whole-body hypothermia resulted in reduced cardiac output, which reached normal levels at the end of passive rewarming, at normothermia. Physiologic cardiovascular mechanisms seemed to be intact to provide sufficient tissue perfusion, with normal blood lactate levels.

Restoration of cardiopulmonary function with 21% versus 100% oxygen after hypoxaemia in newborn pigs

OBJECTIVE

To assess the consequences of hypoxaemia and resuscitation with room air versus 100% O(2) on cardiac troponin I (cTnI), cardiac output (CO), and pulmonary artery pressure (PAP) in newborn pigs.

DESIGN

Twenty anaesthetised pigs (12-36 hours; 1.7-2.7 kg) were subjected to hypoxaemia by ventilation with 8% O(2). When mean arterial blood pressure fell to 15 mm Hg, or arterial base excess was < or = -20 mmol/l, resuscitation was performed with 21% (n = 10) or 100% (n = 10) O(2) for 30 minutes, then ventilation with 21% O(2) for 120 minutes. Blood was analysed for cTnI. Ultrasound examinations of CO and PAP (estimated from tricuspid regurgitation velocity (TR-Vmax)) were performed at baseline, during hypoxia, and at the start of and during reoxygenation.

RESULTS

cTnI increased from baseline to the end point (p<0.001), confirming a serious myocardial injury, with no differences between the 21% and 100% O(2) group (p = 0.12). TR-Vmax increased during the insult and returned towards baseline values during reoxygenation, with no differences between the groups (p = 0.11) or between cTnI concentrations (p = 0.31). An inverse relation was found between increasing age and TR-Vmax during hypoxaemia (p = 0.034). CO per kg body weight increased during the early phase of hypoxaemia (p<0.001), then decreased. Changes in CO per kg were mainly due to changes in heart rate, with no differences between the groups during reoxygenation (p = 0.298).

CONCLUSION

Hypoxaemia affects the myocardium and PAP. During this limited period of observation, reoxygenation with 100% O(2) showed no benefits compared with 21% O(2) in normalising myocardial function and PAP. The important issue may be resuscitation and reoxygenation without hyperoxygenation.

Moderate hypothermia in neonatal encephalopathy: safety outcomes

Hypoxic-ischemic injury may cause multisystem organ damage with significant aberrations in clotting, renal, and cardiac functions. Systemic hypothermia may aggravate these medical conditions, such as bradycardia and increased clotting times, and very little safety data in neonatal hypoxic-ischemic injury is available. This study reports a multicenter, randomized, controlled pilot trial of moderate systemic hypothermia (33 degrees C) vs normothermia (37 degrees C) for 48 hours in infants with neonatal encephalopathy instituted within 6 hours of birth or hypoxic-ischemic event. The best outcome measures of safety were determined, comparing rates of adverse events between normothermia and hypothermia groups. A total of 32 hypothermia and 33 normothermia neonates were enrolled in seven centers. Adverse events and serious adverse effects were collected by the study team during the hospital admission, monitored by an independent study monitor, and reported to Institutional Review Boards and the Data and Safety Monitoring Committee. The following adverse events were observed significantly more commonly in the hypothermia group: more frequent bradycardia and lower heart rates during the period of hypothermia, longer dependence on pressors, higher prothrombin times, and lower platelet counts with more patients requiring plasma and platelet transfusions. Seizures as an adverse event were more common in the hypothermia group. These observed side effects of 48 hours of moderate systemic hypothermia were of mild to moderate severity and manageable with minor interventions.