Peripheral blood flow and oxygen extraction in the sick, newborn very low birth weight infant shortly after birth

Exogenous ketosis attenuates acute mountain sickness and mitigates normobaric high-altitude hypoxemia

Acute mountain sickness (AMS) represents a considerable issue for individuals sojourning to high altitudes with systemic hypoxemia known to be intimately involved in its development. Based on recent evidence that ketone ester (KE) intake attenuates hypoxemia, we investigated whether exogenous ketosis might mitigate AMS development and identified underlying physiological mechanisms. Fourteen healthy, male participants were enrolled in two 29-h protocols (simulated altitude of 4,000-4,500 m) receiving either KE or a placebo (CON) at regular timepoints throughout the protocol in a randomized, crossover manner. Physiological responses were characterized after 15 min and 4 h in hypoxia, and the protocol was terminated prematurely upon development of severe AMS (Lake Louise Score ≥ 10). KE ingestion induced a consistent diurnal ketosis (d-β-hydroxybutyrate, [βHB] of ∼3 mM), whereas blood [βHB] remained low (<0.6 mM) in CON. Each participant tolerated the protocol equally long or longer (n = 6 or n = 8, respectively) in KE. Protocol duration increased by 32% on average with KE, and doubled upon KE for severe AMS-developing participants (n = 9). Relative to CON, KE induced a mild metabolic acidosis, hyperventilation, and relative sympathetic dominance. KE also inhibited the progressive hypoxemia that was observed between 15 min and 4 h in hypoxia in CON, while concomitantly increasing cerebral oxygenation and capillary Po2 within this timeframe despite a KE-induced reduction in cerebral oxygen supply. These data indicate that exogenous ketosis attenuates AMS development. The key underlying mechanisms include improved arterial and cerebral oxygenation, in combination with lowered cerebral blood flow and oxygen delivery, and increased sympathetic dominance.NEW & NOTEWORTHY Ketone ester intake attenuated the development of acute mountain sickness at a simulated altitude of 4,000-4,500 m. This likely resulted from a mitigation of arterial and cerebral hypoxemia, reduced cerebral blood flow, and increased sympathetic drive.

Neonatal somatic oxygenation and perfusion assessment using near-infrared spectroscopy : Part of the series on near-infrared spectroscopy by the European Society of Paediatric Research Special Interest Group "Near-Infrared Spectroscopy"

In this narrative review, we summarize the current knowledge and applications of somatic near-infrared spectroscopy (NIRS), with a focus on intestinal, renal, limb, and multi-site applications in neonates. Assessing somatic oxygenation at various body locations in neonates may aid in the understanding of underlying pathophysiology of organ injury. Considering cerebral autoregulation may be active to protect the brain during systemic circulatory failure, peripheral somatic oxygenation may potentially provide an early indication of neonatal cardiovascular failure and ultimate hypoxemic injury to vital organs including the brain. Certain intestinal oxygenation patterns appear to be associated with the onset and course of necrotizing enterocolitis, whereas impaired renal oxygenation may indicate the onset of acute kidney injury after various types of hypoxic events. Peripheral muscle oxygenation measured at a limb may be particularly effective in the early prediction of shock in neonates. Using multi-site NIRS may complement current approaches and clinical investigations to alert for neonatal tissue hypoxemia, and potentially even guide management. However, somatic NIRS has its inherent limitations in regard to accuracy. Interpretation of organ-specific values can also be challenging. Last, currently there are limited prospective intervention studies, and clinical benefits need to be examined further, after the clarification of critical threshold-values. IMPACT: The assessment of somatic oxygenation using NIRS may contribute to the prediction of specific diseases in hemodynamically challenged neonates. Furthermore, it may give early warning signs for impending cardiovascular failure, and impaired cerebral circulation and oxygenation. We present a comprehensive overview of the literature on applications of NIRS to various somatic areas, with a focus on its potential clinical applicability, including future research directions. This paper will enable prospective standardized studies, and multicenter collaboration to obtain statistical power, likely to advance the field.

Evaluation of the Hypotensive Preterm Infant: Evidence-Based Practice at the Bedside?

Choosing the appropriate management approach for the preterm infant with low blood pressure during the transition period generally involved intervening when the blood pressure drifted below a certain threshold. It is now clear that this approach is too simplistic and does not address the underlying physiology. In this chapter, we explore the many monitoring tools available for evaluation of the hypotensive preterm and assess the evidence base supporting or refuting their use. The key challenge relates to incorporating these outputs with the clinical status of the patient and choosing the appropriate management strategy.

Peripheral fractional oxygen extraction measured with near-infrared spectroscopy in neonates-A systematic qualitative review

BACKGROUND

Peripheral fractional oxygen extraction (pFOE) measured with near-infrared spectroscopy (NIRS) in combination with venous occlusion is of increasing interest in term and preterm neonates.

OBJECTIVE

The aim was to perform a systematic qualitative review of literature on the clinical use of pFOE in term and preterm neonates and on the changes in pFOE values over time.

METHODS

A systematic search of PubMed, Embase and Medline was performed using following terms: newborn, infant, neonate, preterm, term, near-infrared spectroscopy, NIRS, oximetry, spectroscopy, tissue, muscle, peripheral, arm, calf, pFOE, OE, oxygen extraction, fractional oxygen extraction, peripheral perfusion and peripheral oxygenation. Additional articles were identified by manual search of cited references. Only studies in human neonates were included.

RESULTS

Nineteen studies were identified describing pFOE measured with NIRS in combination with venous occlusion. Nine studies described pFOE measured on the forearm and calf at different time points after birth, both in stable preterm and term neonates without medical/respiratory support or any pathological findings. Nine studies described pFOE measured at different time points in sick preterm and term neonates presenting with signs of infection/inflammation, anemia, arterial hypotension, patent ductus arteriosus, asphyxia or prenatal tobacco exposure. One study described pFOE both, in neonates with and without pathological findings.

CONCLUSION

This systematic review demonstrates that pFOE may provide additional insight into peripheral perfusion and oxygenation, as well as into disturbances of microcirculation caused by centralization in preterm and term neonates with different pathological findings.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42021249235].

Investigating the effects of cerebrospinal fluid removal on cerebral blood flow and oxidative metabolism in infants with post-hemorrhagic ventricular dilatation

BackgroundPost-hemorrhagic ventricular dilatation (PHVD) is predictive of mortality and morbidity among very-low-birth-weight preterm infants. Impaired cerebral blood flow (CBF) due to elevated intracranial pressure (ICP) is believed to be a contributing factor.MethodsA hyperspectral near-infrared spectroscopy (NIRS) method of measuring CBF and the cerebral metabolic rate of oxygen (CMRO₂) was used to investigate perfusion and metabolism changes in patients receiving a ventricular tap (VT) based on clinical management. To improve measurement accuracy, the spectral analysis was modified to account for compression of the cortical mantle caused by PHVD and the possible presence of blood breakdown products.ResultsFrom nine patients (27 VTs), a significant CBF increase was measured (15.6%) following VT (14.6±4.2 to 16.9±6.6 ml/100 g/min), but with no corresponding change in CMRO₂ (1.02±0.41 ml O₂/100 g/min). Post-VT CBF was in good agreement with a control group of 13 patients with patent ductus arteriosus but no major cerebral pathology (16.5±7.7 ml/100 g/min), whereas tissue oxygen saturation (StO₂) was significantly lower (58.9±12.1% vs. 70.5±9.1% for controls).ConclusionCBF was impeded in PHVD infants requiring a clinical intervention, but the effect is not large enough to alter CMRO₂.

Microvascular oxygen extraction during maximal isometric contraction in patients with chronic obstructive pulmonary disease

Abstract Introduction: COPD presents decrease in oxidative metabolism with possible losses of cardiovascular adjustments, suggesting slow kinetics microvascular oxygen during intense exercise. Objective: To test the hypothesis that chronic obstructive pulmonary disease (COPD) patients have lower muscle performance in physical exercise not dependent on central factors, but also greater muscle oxygen extraction, regardless of muscle mass. Methods: Cross-sectional study with 11 COPD patients and nine healthy subjects, male, paired for age. Spirometry and body composition by DEXA were evaluated. Muscular performance was assessed by maximal voluntary isometric contraction (MVIC) in isokinetic dynamometer and muscle oxygen extraction by the NIRS technique. Student t-test and Pearson correlation were applied. A significance level of p<0.05 was adopted. Results: Patients had moderate to severe COPD (FEV1 = 44.5 ± 9.6% predicted; SpO2 = 94.6 ± 1.6%). Lean leg mass was 8.3 ± 0.9 vs. 8.9 ± 1.0 kg (p =0.033), when comparing COPD and control patients, respectively. The decreased muscle oxygen saturation corrected by muscle mass was 53.2% higher (p=0.044) in the COPD group in MVIC-1 and 149.6% higher (p=0.006) in the MVIC-2. Microvascular extraction rate of oxygen corrected by muscle mass and total work was found to be 114.5% higher (p=0.043) in the COPD group in MVIC-1 and 210.5% higher (p=0.015) in the MVIC-2. Conclusion: COPD patients have low muscle performance and high oxygen extraction per muscle mass unit and per unit of work. The high oxygen extraction suggests that quantitative and qualitative mechanisms can be determinants of muscle performance in patients with COPD.

Peripheral Muscle Near-Infrared Spectroscopy in Neonates: Ready for Clinical Use? A Systematic Qualitative Review of the Literature

BACKGROUND

Peripheral muscle near-infrared spectroscopy (NIRS) measurements are of increasing interest especially in the care of critically ill patients.

OBJECTIVE

The aim was to perform a systematic qualitative review on peripheral muscle NIRS measurements in the clinical care of term and preterm neonates.

METHODS

A systematic search of PubMed and Ovid Embase was performed using the following terms: neonate, neonates, newborn, newborns, infant, infants, near-infrared spectroscopy, NIRS, oxygenation, perfusion, oxygen extraction, peripheral, tissue, muscle, calf, forearm and thigh. Additional articles were identified by a manual search of the cited references. Only human studies were included.

RESULTS

Twenty-one studies were identified to use peripheral muscle NIRS measurements as a single method, 17 studies combined cerebral and peripheral muscle NIRS measurements and 1 study used multi-site NIRS measurements in human neonates. Two randomized studies were identified. Two additional publications were included because they provided important general information about peripheral muscle NIRS measurements.

CONCLUSION

In the care of critically ill neonates peripheral muscle NIRS measurements alone or in combination with cerebral or multi-site NIRS measurements provide useful additional information about peripheral circulation and oxygenation. This method is a promising tool in the recognition of early states of centralization (compensated shock) in this vulnerable group of patients. However, before this method can be used in the clinical routine it has to be tested as monitoring to guide interventions in further studies.

Assessment of global tissue perfusion and oxygenation in neonates and infants after open-heart surgery

OBJECTIVES

Monitoring and preserving adequate perfusion and oxygen balance is a primary objective of critical care. This prospective observational study aimed to assess the relationship between global haemodynamic parameters and variables reflecting tissue oxygenation during the early period following corrective cardiac surgery in neonates and infants. The postoperative time course of oxygen delivery and consumption was evaluated. As surrogate markers of oxygen balance, the central venous oxygen saturation (ScvO2) and venoarterial PCO2 difference (PvaCO2) were thoroughly investigated.

METHODS

Thirteen children <1 year of age who underwent open-heart surgery were prospectively enrolled. In addition to conventional postoperative monitoring, transpulmonary thermodilution (TPTD) was used to monitor cardiac output and calculate oxygen delivery and consumption. In parallel with each TPTD measurement, arterial and central venous blood gas values were recorded. Global haemodynamic parameters and oxygenation measurements were compared with weighted linear regression statistics and Pearson's correlation coefficient.

RESULTS

Data from 145 TPTD measurements and 304 blood gas samples were recorded. The early postoperative period was characterized by a supply-dependent oxygen consumption, as demonstrated by the direct correlation between the change in oxygen delivery and consumption (r = 0.62, P < 0.001). Regarding haemodynamic parameters, none of the heart rate, mean arterial pressure or cardiac index correlated with the measured ScvO2. However, the ScvO2 and PvaCO2 were found to correlate significantly (r = -0.49, P < 0.001), and both strongly related to oxygen extraction.

CONCLUSIONS

Both the ScvO2 and PvaCO2 are reliable and comparable parameters in following tissue oxygen balance during the early postoperative course after open-heart surgery in neonates and infants. As part of multiparameter monitoring, our data highlight the importance of regular ScvO2 measurements and PvaCO2 calculations in paediatric intensive care.

Partial exchange transfusion results in increased cerebral oxygenation and faster peripheral microcirculation in newborns with polycythemia

AIM

The aim of this study was to assess cerebral and peripheral oxygenation, by using near infrared spectroscopy (NIRS) and microcirculation by using side stream dark field (SDF) imaging in newborns with polycythemia before and after partial exchange transfusion (PET) therapy to investigate treatment effect on tissue oxygenation and microcirculation.

METHODS

Polycythemic newborns with venous haematocrit (Htc) >70% or ≥65% with symptoms were included. NIRS measurements for cerebral and peripheral oxygenation and SDF recordings for microcirculatory flow assessment were obtained before and after PET. Fractional tissue oxygen extraction (FTOE) was calculated based on tissue oxygenation index and oxygen saturation. Wilcoxon test was used for statistical analysis.

RESULTS

Fifteen newborns were included. Cerebral tissue oxygenation index, microvascular flow index and % of vessels with hyperdynamic flow increased after PET; median (range): 61.27 (51.36-61.87) versus 64.54 (54.1-74.38), 2.74 (2.46-3) versus 3.22 (2.64-3.75) and 0 (0-2.8) versus 3 (0-99.3), respectively. Whereas cerebral fractional tissue oxygen extraction (CFTOE), % of vessels with sluggish flow decreased after treatment; 0.36 (0.22-0.44) versus 0.31 (0.17-0.46), 1.4 (0-69) versus 0 (0-0.9), respectively. Peripheral oxygenation was unchanged.

CONCLUSION

Partial exchange transfusion improves microcirculation in polycythemic newborns. Cerebral oxygenation increases and cFTOE decreases suggesting increased blood flow. Microvascular flow increases possibly representing reactive hyperperfusion after hemodilution. Whether these effects are beneficial require further research.

Regional oxygen saturation of the brain and peripheral tissue during birth transition of term infants

OBJECTIVE

To evaluate regional tissue oxygenation of the brain and preductal and postductal peripheral (muscle) tissue during immediate transition after birth, and to correlate with peripheral preductal and postductal arterial oxygen saturation.

STUDY DESIGN

We conducted a prospective observational study. With near-infrared spectroscopy (NIRS), changes in regional oxygen saturation of the brain (rSO2brain), peripheral preductal tissue (rSO2pre), and peripheral postductal tissue (rSO2post) were measured during the first 10 minutes of life in 59 healthy term infants after elective caesarean delivery. Fractional tissue oxygen extraction was calculated for all 3 regions.

RESULTS

Mean rSO2brain increased rapidly from 44% (3 minutes) to 76% (7 minutes); thereafter no significant change occurred. Mean rSO2pre and rSO2post increased constantly from minute 3 to minute 10, from 36%(pre)/27%(post) to 66%(pre)/58%(post). Fractional tissue oxygen extraction decreased in all 3 regions during the first minutes of life. Fractional tissue oxygen extraction of the brain did not change significantly after 5 minutes, and preductal and postductal fractional tissue oxygen extraction did not change significantly after 8 minutes.

CONCLUSIONS

During transition, the brain had the highest saturation levels, indicating a preference of oxygen delivery to the brain. Fractional tissue oxygen extraction of the brain reached a plateau earlier compared with peripheral tissue.

Peripheral oxygenation and management in the perinatal period

The mechanisms for the adequate provision of oxygen to the peripheral tissues are complex. They involve control of the microcirculation and peripheral blood flow, the position of the oxygen dissociation curve including the proportion of fetal and adult haemoglobin, blood gases and viscosity. Systemic blood pressure appears to have little effect, at least in the non-shocked state. The adequate delivery of oxygen (DO(2)) depends on consumption (VO(2)), which is variable. The balance between VO(2) and DO(2) is given by fractional oxygen extraction (FOE=VO(2)/DO(2)). FOE varies from organ to organ and with levels of activity. Measurements of FOE for the whole body produce a range of about 0.15-0.33, i.e. the body consumes 15-33% of oxygen transported.

Peripheral haemodynamics in newborns: best practice guidelines

Peripheral haemodynamics refers to blood flow, which determines oxygen and nutrient delivery to the tissues. Peripheral blood flow is affected by vascular resistance and blood pressure, which in turn varies with cardiac function. Arterial oxygen content depends on the blood haemoglobin concentration (Hb) and arterial pO2; tissue oxygen delivery depends on the position of the oxygen-dissociation curve, which is determined by temperature and the amount of adult or fetal haemoglobin. Methods available to study tissue perfusion include near-infrared spectroscopy, Doppler flowmetry, orthogonal polarisation spectral imaging and the peripheral perfusion index. Cardiac function, blood gases, Hb, and peripheral temperature all affect blood flow and oxygen extraction. Blood pressure appears to be less important. Other factors likely to play a role are the administration of vasoactive medications and ventilation strategies, which affect blood gases and cardiac output by changing the intrathoracic pressure.