Cardio-renal recovery of hypoxic newborn pigs after 18%, 21% and 100% reoxygenation

Sustained inflation with 21% versus 100% oxygen during cardiopulmonary resuscitation of asphyxiated newborn piglets - A randomized controlled animal study

BACKGROUND

Current neonatal resuscitation guidelines recommend using 100% oxygen during chest compressions (CC), however the most effective oxygen concentration during cardiopulmonary resuscitation remains controversial.

AIM

In term newborn piglets with asphyxia-induced cardiac arrest does 21% oxygen compared to 100% oxygen during resuscitation using CC during sustained inflation (SI; CC + SI) will have a reduced time to return of spontaneous circulation (ROSC).

INTERVENTION AND MEASUREMENTS

Twenty-two mixed breed piglets (1-3 days old, 1.7-2.4 kg), were obtained on the day of the experiment and anesthetized, intubated, instrumented, and exposed to 30-min normocapnic hypoxia followed by asphyxia. Piglets were resuscitated using CC + SI and randomized to 21% oxygen (n = 8) or 100% oxygen (n = 8). Heart rate, arterial blood pressure, carotid blood flow, cerebral oxygenation, and respiratory parameters were continuously recorded throughout the experiment.

MAIN RESULTS

Baseline parameters were similar between 21% and 100% oxygen groups. There was no difference in asphyxiation (duration and degree) between groups. Time to ROSC was similar between 21% and 100% oxygen groups: median (interquartile range - IQR) 80 (70-190)sec vs. 90 (70-324)sec, (p = 0.56). There was no significant difference in the rate of ROSC between 21% and 100% oxygen groups: 7/8 (88%) vs. 5/8 (63%), (p = 0.569). All piglets that achieved ROSC survived to four hours post-resuscitation. Hemodynamics and regional perfusion were not significantly different between groups.

CONCLUSIONS

In term newborn piglets resuscitated by CC + SI, the use of 21% oxygen resulted in a similar time to ROSC, short-term survival, and hemodynamic recovery compared to 100% oxygen.

Gradually increased oxygen administration promoted survival after hemorrhagic shock

Gradually increased oxygen administration (GIOA) seems promising in hemorrhagic shock. However, the effects of GIOA on survival remain unclear, and details of GIOA are to be identified. After the induction of hemorrhagic shock, the rats were randomized into five groups (n = 9): normoxic group (Normo), hyperoxic group (Hypero), normoxic to hyperoxic group (GIOA1), long-time hypoxemic to hyperoxic group (GIOA2), and short-time hypoxemic to hyperoxic group (GIOA3). Survival was recorded for 96 h, plasma alanine transaminase, oxidative stress, hemodynamics, and blood gas were measured. The mean survival time of the GIOA3 was significantly longer than that of the Normo, Hypero, and GIOA2. Plasma alanine transaminase levels were significantly lower in the Normo, GIOA1, and GIOA3 compared to the Hypero and GIOA2 at 2 h post-resuscitation (PR). Plasma 3-nitrotyrosine levels at 2 h PR were significantly lower in the GIOA2 and GIOA3 compared to the Normo and Hypero. Central venous oxygen saturation at 2 h PR in the GIOA3 was significantly higher than the Normo; however, no significant difference was observed between GIOA1 and Normo. Besides, at 2 h PR, mean arterial pressure in the GIOA3 was significantly higher than the GIOA2; however, no significant difference was observed between GIOA1 and GIOA2. (1) GIOA could significantly prolong survival time compared to normoxemic resuscitation and hyperoxic resuscitation; (2) early moments of GIOA are critical to the benefits; and (3) hypoxemia at onset of resuscitation may be imperative, more works are needed to determine the optimal initial oxygen concentration of GIOA.

Effects of Oxygen Concentrations on Postresuscitation Myocardial Oxidative Stress and Myocardial Function in a Rat Model of Cardiopulmonary Resuscitation

OBJECTIVE

Lipid peroxidation induced by free-radical species plays a prominent role in myocardial injury following ischemia and reperfusion. However, there is a lack of data in different oxygen concentrations on myocardial lipid peroxidation during the early phase of reperfusion. In this study, we investigated whether ventilation with medium or normal concentration of oxygen would decrease the severity of myocardial lipid peroxidation and postresuscitation myocardial dysfunction.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University-affiliated animal research institution.

SUBJECTS

Sixty-three healthy male Sprague-Dawley rats.

INTERVENTIONS

Animals were randomized into three groups: 1) 100% group, 2) 50% group, and 3) 21% group. Ventricular fibrillation was induced and untreated for 8 minutes, and defibrillation was attempted after 8 minutes of cardiopulmonary resuscitation. Ventilation with 100%, 50%, or 21% oxygen was initiated in all groups during cardiopulmonary resuscitation and 1 hour following the return of spontaneous circulation. Normoxic ventilation was maintained thereafter.

MEASUREMENTS AND MAIN RESULTS

Myocardial function, including ejection fraction and myocardial performance index, were measured at baseline, 4, or 72 hours after resuscitation. Blood samples were drawn at baseline, 15 minutes, 1, 4, or 72 hours after resuscitation for the measurements of blood gas or biomarkers. Significantly better myocardial function and longer duration of survival were observed in the 50% group. Compared with the 21% and 100% groups, a mild hyperoxia and greater oxygen extraction with lower 8-iso-prostaglandin F2α were observed in the 50% group. Pearson correlation analysis confirmed that 8-iso-prostaglandin F2α was positively correlated with myocardial performance index at 4 hours postresuscitation.

CONCLUSIONS

In a rat model of cardiac arrest and resuscitation, ventilation with 50% inspired oxygen during early postischemic reperfusion phase contributed to a decreased lipid peroxidation and a better myocardial function and duration of survival.

Cardiopulmonary resuscitation with chest compressions during sustained inflations: a new technique of neonatal resuscitation that improves recovery and survival in a neonatal porcine model

BACKGROUND

Guidelines on neonatal resuscitation recommend 90 chest compressions (CCs) and 30 manual inflations (3:1) per minute in newborns. The study aimed to determine whether CC s during sustained inflations (SIs) improves the recovery of asphyxiated newborn piglets in comparison with coordinated 3:1 resuscitation.

METHODS AND RESULTS

Term newborn piglets (n=8/group) were anesthetized, intubated, instrumented, and exposed to 45-minute normocapnic hypoxia followed by asphyxia. Piglets were randomly assigned to receive either 3:1 resuscitation (3:1 group) or CCs during SIs (SI group) when the heart rate decreased to 25% of baseline. Piglets randomly assigned to the SI group received SIs with a pressure of 30 cm H2O for 30 s. During the SI, CCs at a rate of 120/min were provided. SI was interrupted after 30 s for 1 s before a further 30-s SI was provided. CCs were continued throughout SIs. CCs and SI were continued until the return of spontaneous circulation. Continuous respiratory parameters, cardiac output, mean systemic and pulmonary artery pressures, and regional blood flows were measured. Mean (standard deviation) time for return of spontaneous circulation was significantly reduced in SI group versus 3:1 group (32 [11] s versus 205 [113] s, respectively). In the SI group, administration of oxygen and epinephrine was significantly lower, whereas minute ventilation and exhaled CO2 were significantly increased. The SI group had significantly higher mean systemic and pulmonary arterial pressures during resuscitation in comparison with the 3:1 group (51 [10] versus 31 [5] mm Hg; 41[7] versus 31 [7] mm Hg, respectively; all P<0.05), with improved cardiac output and carotid blood flow.

CONCLUSIONS

Combining CCs and SIs significantly improved the return of spontaneous circulation with better hemodynamic recovery in asphyxiated newborn piglets in comparison with standard coordinated 3:1 resuscitation.

Impaired diastolic function and disruption of the force-frequency relationship in the right ventricle of newborn pigs resuscitated with 100% oxygen

BACKGROUND

Resuscitation with 100% oxygen increases oxidative stress and is detrimental for organ function.

OBJECTIVE

To study the effects of resuscitation with 100% oxygen compared to room-air on myocardial function.

METHODS

Twenty-eight newborn pigs underwent global hypoxia (8% oxygen/N2) until base excess reached -20 mmol/l. The animals were randomized into two groups and resuscitated with either 100% or room air for 30 min. Myocardial tissue Doppler velocities and acceleration of the mitral and tricuspid valve annuli during systole and diastole were assessed before global hypoxia and after resuscitation together with troponin I.

RESULTS

Peak early diastolic velocity (E') and acceleration (pEac) in the septum and pEac in the lateral tricuspid valve annulus were lower after resuscitation with 100% oxygen, suggesting impaired diastolic relaxation in the right ventricle. Lower systolic velocities and acceleration in the right ventricle relative to heart rate indicate disruption of the right ventricular force-frequency relationship after resuscitation with 100% oxygen. Troponins were higher in the 100% oxygen group, suggesting increased myocardial damage in this group.

CONCLUSION

Resuscitation with 100% oxygen compared to room air induces diastolic dysfunction, disrupts the systolic force-frequency relationship and increases myocardial damage in the newborn pig.

A swine model of neonatal asphyxia

Annually more than 1 million neonates die worldwide as related to asphyxia. Asphyxiated neonates commonly have multi-organ failure including hypotension, perfusion deficit, hypoxic-ischemic encephalopathy, pulmonary hypertension, vasculopathic enterocolitis, renal failure and thrombo-embolic complications. Animal models are developed to help us understand the patho-physiology and pharmacology of neonatal asphyxia. In comparison to rodents and newborn lambs, the newborn piglet has been proven to be a valuable model. The newborn piglet has several advantages including similar development as that of 36-38 weeks human fetus with comparable body systems, large body size (~1.5-2 kg at birth) that allows the instrumentation and monitoring of the animal and controls the confounding variables of hypoxia and hemodynamic derangements. We here describe an experimental protocol to simulate neonatal asphyxia and allow us to examine the systemic and regional hemodynamic changes during the asphyxiating and reoxygenation process as well as the respective effects of interventions. Further, the model has the advantage of studying multi-organ failure or dysfunction simultaneously and the interaction with various body systems. The experimental model is a non-survival procedure that involves the surgical instrumentation of newborn piglets (1-3 day-old and 1.5-2.5 kg weight, mixed breed) to allow the establishment of mechanical ventilation, vascular (arterial and central venous) access and the placement of catheters and flow probes (Transonic Inc.) for the continuously monitoring of intra-vascular pressure and blood flow across different arteries including main pulmonary, common carotid, superior mesenteric and left renal arteries. Using these surgically instrumented piglets, after stabilization for 30-60 minutes as defined by Z<10% variation in hemodynamic parameters and normal blood gases, we commence an experimental protocol of severe hypoxemia which is induced via normocapnic alveolar hypoxia. The piglet is ventilated with 10-15% oxygen by increasing the inhaled concentration of nitrogen gas for 2h, aiming for arterial oxygen saturations of 30-40%. This degree of hypoxemia will produce clinical asphyxia with severe metabolic acidosis, systemic hypotension and cardiogenic shock with hypoperfusion to vital organs. The hypoxia is followed by reoxygenation with 100% oxygen for 0.5 h and then 21% oxygen for 3.5 h. Pharmacologic interventions can be introduced in due course and their effects investigated in a blinded, block-randomized fashion.

Quantification of compensatory processes of postnatal hypoxia in newborn piglets applying short-term nonlinear dynamics analysis

Background

Newborn mammals suffering from moderate hypoxia during or after birth are able to compensate a transitory lack of oxygen by adapting their vital functions. Exposure to hypoxia leads to an increase in the sympathetic tone causing cardio-respiratory response, peripheral vasoconstriction and vasodilatation in privileged organs like the heart and brain. However, there is only limited information available about the time and intensity changes of the underlying complex processes controlled by the autonomic nervous system.

Methods

In this study an animal model involving seven piglets was used to examine an induced state of circulatory redistribution caused by moderate oxygen deficit. In addition to the main focus on the complex dynamics occurring during sustained normocapnic hypoxia, the development of autonomic regulation after induced reoxygenation had been analysed. For this purpose, we first introduced a new algorithm to prove stationary conditions in short-term time series. Then we investigated a multitude of indices from heart rate and blood pressure variability and from bivariate interactions, also analysing respiration signals, to quantify the complexity of vegetative oscillations influenced by hypoxia.

Results

The results demonstrated that normocapnic hypoxia causes an initial increase in cardiovascular complexity and variability, which decreases during moderate hypoxia lasting one hour (p < 0.004). After reoxygenation, cardiovascular complexity parameters returned to pre-hypoxic values (p < 0.003), however not respiratory-related complexity parameters.

Conclusions

In conclusion, indices from linear and nonlinear dynamics reflect considerable temporal changes of complexity in autonomous cardio-respiratory regulation due to normocapnic hypoxia shortly after birth. These findings might be suitable for non-invasive clinical monitoring of hypoxia-induced changes of autonomic regulation in newborn humans.

Oxygen supplementation in the delivery room: updated information

Resuscitation is the most common procedure performed in neonatology. However, new contributions based on scientific evidence challenge the traditional procedures. Of these new contributions, the use of room-air instead of 100% oxygen and titration of the oxygen inspiratory fraction according to oximetry and heart rate represent a new approach in the resuscitation of both term and preterm newborns.