Acid–base optimization during hypothermia

The Complex Interrelationship Between Mechanical Ventilation and Therapeutic Hypothermia in Asphyxiated Newborns. A Review

Asphyxiated newborns often require both therapeutic hypothermia (TH) and mechanical ventilation (MV) and the complex interrelationship between these two therapeutic interventions is very interesting, which could not only have several synergistic positive effects but also some risks. Perinatal asphyxia is the leading cause of neonatal hypoxic-ischemic encephalopathy (HIE) and TH is the only approved neuroprotective treatment to limit brain injury, improving the mortality rate and long-term neurological outcomes. HIE is often associated with severe respiratory failure, requiring MV, due to different lung diseases or an impairment of the respiratory drive. The respiratory support management of asphyxiated newborns is very difficult, considering (a) various pathophysiological contexts, (b) the strong impact of TH on gas metabolism and (c) on lung mechanics, and (d) complex TH-MV interactions. Therefore, it is necessary to evaluate the real indications of MV for cooled newborns, considering the risks of respiratory overassistance (hypocapnia/hyperoxia), as well as the adequate monitoring systems. To date, specific randomized studies about the optimal respiratory approach for cooled newborns are lacking, and strategies for MV support vary from center to center. Moreover, there are many open questions about the real effects of cooling on lung mechanics and on surfactant, most appropriate method of blood gas analysis, and clear indications for pharmacological sedation. The aim of this review is to propose a reasoned approach for respiratory management of cooled newborns, considering the pathophysiological context, multiple actions of TH, and consequences of TH-MV matched action and its related risks.

The early change in pH values after out-of-hospital cardiac arrest is not associated with neurological outcome at hospital discharge

Background

The association between pH values and outcome for patients after out-of-hospital cardiac arrest (OHCA) was not fully elucidated; besides, the relationship of change in pH values and neurological outcome was unknown. The aim was to explore the association of pH values as well as change in pH values and neurological outcome for OHCA cardiac patients.

Methods

The adult patients with non-traumatic out-of-hospital cardiac arrest, shock-refractory ventricular fibrillation or pulseless ventricular tachycardia, and at least two arterial blood gases analysis recorded after admission were included. The change in pH values is calculated as the difference between the second and first pH value, and divided by time interval got the rate of change in pH values. The primary outcome was modified Rankin Score (mRS), dichotomized to good (mRS 0-3) and poor (mRS 4-6) outcomes at hospital discharge. The independent relationship of the first pH value, second pH value, and changes in pH values with neurological outcome was investigated with multivariable logistic regression models, respectively.

Results

A total of 1388 adult patients were included for analysis, of which 514 (37%) had good neurological outcome. The median first pH value and second pH value after admission were 7.21 (interquartile range [IQR] 7.09-7.29) and 7.28 (IQR 7.20-7.36), respectively. The median absolute, relative change, and rate of changes in pH values were 0.08 (IQR 0.01-0.16), 1.10% (IQR 0.11-2.22%), and 0.02 (IQR 0-0.06) per hour, respectively. After adjusting for confounders, the higher first pH value (odds ratio [OR] 3.81, confidence interval [CI] 1.60-9.24, P = 0.003) and higher second pH value (OR 9.54, CI 3.45-26.87, P < 0.001) after admission were associated with good neurological outcome, respectively. The absolute (OR 1.58, CI 0.58-4.30, P = 0.368) and relative (OR 1.03, CI 0.96-1.11, P = 0.399) change as well as the rate of change (OR 0.98, CI 0.33-2.71, P = 974) in pH values were not associated with neurological outcome.

Conclusions

For OHCA patients, abnormality in pH values was very common, with a more acidic pH value indicating poor neurological outcome. However, the change in pH values was not associated with outcomes.

Challenges in respiratory management during therapeutic hypothermia for neonatal encephalopathy

Neonatal encephalopathy (NE) is a serious condition with devastating neurological outcomes that can impact oxygenation and ventilation. The currently recommended therapeutic hypothermia (TH) for these infants may also has several respiratory implications. It decreases metabolic rate and oxygen demands; however, it increases oxygen solubility in the blood and impacts its release to peripheral tissue including the brain. Respiratory management of infants treated with TH should aim for minimizing exposure to hypocapnia or hyperoxia. Inspiratory gas should be heated to 37 °C and humidified to prevent airway and alveolar injury. Blood gas values should be corrected to the core temperature during TH and the use of alkaline buffers is discouraged. While mild sedation/analgesia may ameliorate the discomfort related to cooling, paralytic agents/heavy sedation should be used with caution considering their side effects. Finally, the use of caffeine still needs careful investigation in this population.

Respiratory management during therapeutic hypothermia for hypoxic-ischemic encephalopathy

Therapeutic hypothermia (TH) has become the standard of care treatment to improve morbidity and mortality in infants with hypoxic-ischemic encephalopathy (HIE). Although TH has clearly proven to be beneficial, recent studies suggest optimization of respiratory management as an approach to prevent further damage and improve neurodevelopmental outcome. The ventilatory management of asphyxiated neonates presents a challenge because both the hypoxic insult and TH have an impact on respiratory functions. Although the danger of recurrence of hypocapnia is well recognized, a brief period of severe hyperoxia also can be detrimental to the previously compromised brain and have been shown to increase the risk of adverse neurodevelopmental outcomes. Therefore, judicious ventilatory management with rigorous monitoring is of particular importance in patients with HIE. In the present review, we provide an overview of the currently available evidence on pulmonary function, respiratory morbidities, and ventilation strategies in HIE and we highlight possible future research directions.