Argon Inhalation for 24 h After Closed-Head Injury Does not Improve Recovery, Neuroinflammation, or Neurologic Outcome in Mice.

BACKGROUND/OBJECTIVE: In recent years, the noble gas argon (Ar) has been extensively studied for its organ protection properties. While mounting in vitro and in vivo evidence indicates that argon provides neuroprotection in ischemic brain injury, its neuroprotective potential in traumatic brain injury (TBI) has not been evaluated in vivo. We tested the hypothesis that prolonged inhalation of 70% or 79% argon for 24 h after closed-head injury (CHI) improves neurologic outcome and overall recovery at 36 days post-injury. We also compared effects of the 30% or 21% residual oxygen on argon's potential neuroprotective capacity. METHODS: Adult male C57/black mice (n = 240) were subjected to closed-head traumatic brain injury, followed by inhalation of 70% argon or nitrogen (30% oxygen), or 79% argon or nitrogen (21% oxygen) for 24 h. Neurologic outcome (rotarod, neuroscore, and Morris water maze) was evaluated for up to 36 days post-injury. Histologic parameters of neurologic degeneration (Fluoro-Jade staining) and inflammation (F4/80 microglia immunostaining) were assessed in subgroups at 24 h and on post-injury day 7. RESULTS: Our CHI protocol consistently resulted in significant brain injury. After argon inhalation for 24 h at either concentration, mice did not show significant improvement with regard to neuroscores, rotarod performance, Morris water maze performance, or overall recovery (body weight), compared to nitrogen controls, up to 36 days. At 7 days post-injury, histologic markers of neurodegeneration and inflammation, particularly in the hippocampus, consistently demonstrated significant injury. Notably, recovery was reduced in mice treated with the higher oxygen concentration (30%) after CHI compared to 21%. CONCLUSIONS: Prolonged argon treatment did not improve neurologic outcome, overall recovery (weight), nor markers of neurodegeneration or neuroinflammation after significant CHI compared to nitrogen. While neuroprotective in predominately ischemic injury, argon did not provide protection after TBI in this model, highlighting the crucial importance of assessing argon's strengths and weaknesses in preclinical models to fully understand its organ protective potential in different pathologies and gas mixtures.

Noninvasive Neurological Monitoring in Extracorporeal Membrane Oxygenation.

Optimal neurologic monitoring methods have not been characterized for patients on extracorporeal membrane oxygenation (ECMO). We assessed the feasibility of noninvasive multimodal neuromonitoring (NMN) to prognosticate outcome. In this prospective observational study, neurologic examinations, transcranial Doppler (TCD), electroencephalography (EEG), and somatosensory evoked potentials (SSEPs) were performed at prespecified intervals. Outcome at discharge was defined as favorable when modified Rankin Scale (mRS) 0-3; unfavorable when mRS >3. Of 20 patients (median age 60 years), 17 had TCDs, 13 had EEGs, and seven had SSEPs. With NMN, 17 (85%) were found to have neurologic complications. Fourteen (70%) had unfavorable outcomes. The unfavorable outcome was associated with absent EEG reactivity, coma, central cannulation, higher transfusion requirement, and higher Acute Physiology and Chronic Health Evaluation II and Sepsis-related Organ Failure Assessment scores. Seven patients had both SSEPs and EEGs and exhibited intact N20 responses despite poor outcomes. Four of these seven showed absent EEG reactivity despite intact N20. Eighteen thromboembolic events were observed, 14 of which had positive microembolic signals (MESs) in TCD. All 10 patients with arterial-sided thrombotic events had positive MES. NMN caused no adverse effects. NMN during ECMO is feasible and found high neurologic complication rate. EEG and TCD showed potential for prognostication of neurologic outcome.

A novel 8.7-kb mitochondrial genome deletion accurately detects endometriosis in the plasma of symptomatic women.

Aim: To evaluate an 8.7-kb mitochondrial DNA (mtDNA) deletion as a potential biomarker of endometriosis. Materials & methods: We tested the diagnostic accuracy of the 8.7-kb deletion real-time PCR assay using 182 prospectively collected blood samples from females presenting with symptoms of endometriosis in a case-control format. Results: The assay differentiated between endometriosis and controls (area under curve: 0.74-0.89) with a statistically significant difference (p < 0.05) in 8.7-kb deletion levels measured for all disease subtypes and stages. No correlation was seen between 8.7-kb deletion levels and participant or specimen age, hormone status or menstrual phase. Conclusion: The diagnostic accuracy of the 8.7-kb deletion for endometriosis suggests potential utility in the clinic to improve patient management.

Argon Inhalation for 24 Hours After Onset of Permanent Focal Cerebral Ischemia in Rats Provides Neuroprotection and Improves Neurologic Outcome.

OBJECTIVES: We tested the hypothesis that prolonged inhalation of 70% argon for 24 hours after in vivo permanent or temporary stroke provides neuroprotection and improves neurologic outcome and overall recovery after 7 days. DESIGN: Controlled, randomized, double-blinded laboratory study. SETTING: Animal research laboratories. SUBJECTS: Adult Wistar male rats (n = 110). INTERVENTIONS: Rats were subjected to permanent or temporary focal cerebral ischemia via middle cerebral artery occlusion, followed by inhalation of 70% argon or nitrogen in 30% oxygen for 24 hours. On postoperative day 7, a 48-point neuroscore and histologic lesion size were assessed. MEASUREMENTS AND MAIN RESULTS: After argon inhalation for 24 hours immediately following "severe permanent ischemia" induction, neurologic outcome (neuroscore, p = 0.034), overall recovery (body weight, p = 0.02), and infarct volume (total infarct volume, p = 0.0001; cortical infarct volume, p = 0.0003; subcortical infarct volume, p = 0.0001) were significantly improved. When 24-hour argon treatment was delayed for 2 hours after permanent stroke induction or until after postischemic reperfusion treatment, neurologic outcomes remained significantly improved (neuroscore, p = 0.043 and p = 0.014, respectively), as was overall recovery (body weight, p = 0.015), compared with nitrogen treatment. However, infarct volume and 7-day mortality were not significantly reduced when argon treatment was delayed. CONCLUSIONS: Neurologic outcome (neuroscore), overall recovery (body weight), and infarct volumes were significantly improved after 24-hour inhalation of 70% argon administered immediately after severe permanent stroke induction. Neurologic outcome and overall recovery were also significantly improved even when argon treatment was delayed for 2 hours or until after reperfusion.

Mitochondrial DNA deletions accurately detect endometriosis in symptomatic females of child-bearing age.

AIM: Accurate noninvasive diagnostic aids for endometriosis are needed. We evaluated mitochondrial DNA deletions as potential biomarkers for endometriosis. METHODS: The diagnostic accuracy of deletions was evaluated by quantitative polymerase chain reaction (QPCR) using well-characterized clinical specimens from all subtypes and stages of endometriosis in a case-control format (n = 182). RESULTS: Deletions (1.2 and 3.7 kb) detected in blood differentiated between endometriosis and controls (area under the curve [AUC] 0.71-0.90). Differences in deletion levels were statistically significant (p < 0.05) for all disease subtypes and stages. Neither deletion was correlated with patient or specimen age or hormone status. The 1.2 kb deletion was not correlated with menstrual stage; the 3.7 kb deletion was significantly correlated between two of the groups. CONCLUSION: Biomarkers of the mitochondrial genome, including the deletions described here, offer a promising and largely unexplored avenue in the pursuit of diagnostic markers for endometriosis that can be effectively translated to clinical application.

Early withdrawal of non-anesthetic antiepileptic drugs after successful termination of nonconvulsive seizures and nonconvulsive status epilepticus.

PURPOSE: Multiple antiepileptic drugs (AEDs) are often necessary to treat nonconvulsive seizures (NCS) and nonconvulsive status epilepticus (NCSE). AED polypharmacy places patients at risk for adverse side effects and drug-drug interactions. Identifying the likelihood of seizure relapse when weaning non-anesthetic AEDs may provide guidance in the critical care unit. METHOD: Ninety-nine adult patients with successful treatment of electrographic-proven NCS or NCSE on continuous critical care EEG (CCEEG) monitoring were identified retrospectively. Patients were determined to undergo an AED wean if the number of non-anesthetic AEDs was reduced at the time of discharge compared to the number of non-anesthetic AEDs at primary seizure cessation. Primary outcome was recurrent seizures either clinically or by CCEEG during hospitalization. Secondary outcome measures included hospital length of stay and discharge disposition. RESULTS: The rate of recurrent seizures in the wean group was not statistically different when compared to the group that did not undergo an AED wean (17% vs. 13%, respectively; p = 0.77). The wean group had a median value of 4 (IQR: 3-4) non-anesthetic AEDs at the time of primary seizure cessation compared with 3 (IQR: 2-3) in the non-wean group (p < 0.0001). However, both groups had similar values of AEDs at discharge (median of 2 (IQR: 2-3) vs. 3 (IQR: 2-3) for wean and non-wean groups respectively; p = 0.40). Discharge disposition (favorable, acceptable, or unfavorable) was similar between groups (p = 0.32). CONCLUSIONS: Early weaning of non-anesthetic AEDs does not increase the risk of recurrent seizures in patients treated for NCS or NCSE during their hospitalization.

A single mitochondrial DNA deletion accurately detects significant prostate cancer in men in the PSA 'grey zone'.

PURPOSE: To determine the clinical performance of a blood-based test for clinically significant (CS) prostate cancer (PCa) (grade group ≥ 2) intended for use in men with prostate serum antigen levels in the 'grey zone' (PSA < 10 ng/ml). The test quantifies a previously described 3.4 kb mitochondrial DNA (mtDNA) deletion. METHODS: In a first prospective study of an MRI-guided re-biopsy population (n = 126), the 3.4 kb deletion and 18S rRNA gene were amplified from plasma. A diagnostic threshold was selected from the coordinates of the receiver operating characteristic curve and tested in a second population of men who were (n = 92) biopsy naïve when the mtDNA deletion was assayed and for whom those diagnosed with cancer on initial biopsy were treated with radical prostatectomy. RESULTS: The 3.4 kb deletion was a good predictor of CS PCa in the image-guided re-biopsy population [AUC 0.84, (95% CI 0.73-0.95)] and the selected threshold corresponded to a sensitivity of 87% [95% CI, 70-96%], specificity of 68% [95% CI, 47-85%] and negative predictive value (NPV) of 97%. Applying this threshold to the second population showed this deletion to be a strong predictor of CS cancer [AUC 0.98, (95% CI 0.94-1.02)], independent of PSA or age [sensitivity 100% (95% CI, 93-100%), specificity 90% (95%CI 73-98%) and NPV 100%]. CONCLUSION: The 3.4 kb deletion in plasma is an accurate predictor of CS cancer for men in the PSA 'grey zone'. Used in advance of biopsy for improved patient selection, this deletion may reduce the number of biopsies needed to diagnose CS prostate cancers.

Mitochondria, prostate cancer, and biopsy sampling error.

Mitochondria and their associated genome are emerging as sophisticated indicators of prostate cancer biology. Alterations in the mitochondrial genome (mtgenome) have been implicated in cell proliferation, metastatic behavior, androgen independence, as a signal for apoptosis, and as a predictor of biochemical recurrence. Somatic mutation patterns in complete mtgenomes are associated with prostate specific antigen levels (PSA) in prostate cancer patients and a large-scale mtgenome deletion (3.4 kb) is consistent with a prostate "cancerization" field effect. This review will focus on the biological characteristics of mitochondria and their direct clinical application to prostate cancer. Mitochondrial science is currently influencing clinical prostate cancer diagnostics and the rapid progress in this area indicates future, break-through contributions in the general field of oncology.

Paired ductal carcinoma in situ and invasive breast cancer lesions in the D-loop of the mitochondrial genome indicate a cancerization field effect.

Alterations in the mitochondrial genome have been chronicled in most solid tumors, including breast cancer. The intent of this paper is to compare and document somatic mitochondrial D-loop mutations in paired samples of ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC) indicating a potential breast ductal epithelial cancerization field effect. Paired samples of these histopathologies were laser-captured microdissected (LCM) from biopsy, lumpectomy, and mastectomy tissues. Blood samples were collected as germplasm control references. For each patient, hypervariable region 1 (HV1) in the D-loop portion of the mitochondrial genome (mtGenome) was sequenced for all 3 clinical samples. Specific parallel somatic heteroplasmic alterations between these histopathologies, particularly at sites 16189, 16223, 16224, 16270, and 16291, suggest the presence of an epithelial, mitochondrial cancerization field effect. These results indicate that further characterization of the mutational pathway of DCIS and IBC may help establish the invasive potential of DCIS. Moreover, this paper indicates that biofluids with low cellularity, such as nipple aspirate fluid and/or ductal lavage, warrant further investigation as early and minimally invasive detection mediums of a cancerization field effect within breast tissue.

Concussive brain trauma in the mouse results in acute cognitive deficits and sustained impairment of axonal function.

Concussive brain injury (CBI) accounts for approximately 75% of all brain-injured people in the United States each year and is particularly prevalent in contact sports. Concussion is the mildest form of diffuse traumatic brain injury (TBI) and results in transient cognitive dysfunction, the neuropathologic basis for which is traumatic axonal injury (TAI). To evaluate the structural and functional changes associated with concussion-induced cognitive deficits, adult mice were subjected to an impact on the intact skull over the midline suture that resulted in a brief apneic period and loss of the righting reflex. Closed head injury also resulted in an increase in the wet weight:dry weight ratio in the cortex suggestive of edema in the first 24 h, and the appearance of Fluoro-Jade-B-labeled degenerating neurons in the cortex and dentate gyrus of the hippocampus within the first 3 days post-injury. Compared to sham-injured mice, brain-injured mice exhibited significant deficits in spatial acquisition and working memory as measured using the Morris water maze over the first 3 days (p<0.001), but not after the fourth day post-injury. At 1 and 3 days post-injury, intra-axonal accumulation of amyloid precursor protein in the corpus callosum and cingulum was accompanied by neurofilament dephosphorylation, impaired transport of Fluoro-Gold and synaptophysin, and deficits in axonal conductance. Importantly, deficits in retrograde transport and in action potential of myelinated axons continued to be observed until 14 days post-injury, at which time axonal degeneration was apparent. These data suggest that despite recovery from acute cognitive deficits, concussive brain trauma leads to axonal degeneration and a sustained perturbation of axonal function.

Titanic's unknown child: the critical role of the mitochondrial DNA coding region in a re-identification effort.

This report describes a re-examination of the remains of a young male child recovered in the Northwest Atlantic following the loss of the Royal Mail Ship Titanic in 1912 and buried as an unknown in Halifax, Nova Scotia shortly thereafter. Following exhumation of the grave in 2001, mitochondrial DNA (mtDNA) hypervariable region 1 sequencing and odontological examination of the extremely limited skeletal remains resulted in the identification of the child as Eino Viljami Panula, a 13-month-old Finnish boy. This paper details recent and more extensive mitochondrial genome analyses that indicate the remains are instead most likely those of an English child, Sidney Leslie Goodwin. The case demonstrates the benefit of targeted mtDNA coding region typing in difficult forensic cases, and highlights the need for entire mtDNA sequence databases appropriate for forensic use.

Calpain as a therapeutic target in traumatic brain injury.

The family of calcium-activated neutral proteases, calpains, appears to play a key role in neuropathologic events following traumatic brain injury (TBI). Neuronal calpain activation has been observed within minutes to hours after either contusive or diffuse brain trauma in animals, suggesting that calpains are an early mediator of neuronal damage. Whereas transient calpain activation triggers numerous cell signaling and remodeling events involved in normal physiological processes, the sustained calpain activation produced by trauma is associated with neuron death and axonal degeneration in multiple models of TBI. Nonetheless, the causal relationship between calpain activation and neuronal death is not fully understood. Much remains to be learned regarding the endogenous regulatory mechanisms for controlling calpain activity, the roles of different calpain isoforms, and the in vivo substrates affected by calpain. Detection of stable proteolytic fragments of the submembrane cytoskeletal protein alphaII-spectrin specific for cleavage by calpains has been the most widely used marker of calpain activation in models of TBI. More recently, these protein fragments have been detected in the cerebrospinal fluid after TBI, driving interest in their potential utility as TBI-associated biomarkers. Post-traumatic inhibition of calpains, either direct or indirect through targets related to intracellular calcium regulation, is associated with attenuation of functional and behavioral deficits, axonal pathology, and cell death in animal models of TBI. This review focuses on the current state of knowledge of the role of calpains in TBI-induced neuropathology and effectiveness of calpain as a therapeutic target in the acute post-traumatic period.

Circulatory arrest and low-flow cardiopulmonary bypass alter CREB phosphorylation in piglet brain.

BACKGROUND: The purpose of this study was to determine the effects of low-flow cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest followed by postbypass recovery on the phosphorylation state of transcription factor, cyclic adenosine 3', 5'-monophosphate response element-binding protein (CREB), in the striatum of neonatal brain. METHODS: Neonatal piglets (1.4 to 2.5 kg) anesthetized with isoflurane and fentanyl were put on CPB. The animals were cooled to 18 degrees C during a 20-minute period. The CPB circuit flow was then either reduced to 20 mL.kg(-1).min(-1) for 90 minutes (low-flow CPB) or turned off for 90 minutes (deep hypothermic circulatory arrest), following with a gradual increase in the flow and rewarming during a 30-minute period and a 2-hour recovery. At the end of the recovery period, the animals were rapidly euthanized, and the striata were removed and frozen for immunochemical analysis by Western blot technique using antibodies against phosphorylated and total CREB. The results are presented as mean +/- standard deviation (p < 0.05 was significant). RESULTS: Deep hypothermic circulatory arrest did not result in alteration in either the level of CREB or its degree of phosphorylation in the piglet striatum whereas after low-flow CPB, CREB phosphorylation was significantly increased (p < 0.005) and there was also an increase in CREB expression (p < 0.01). CONCLUSIONS: This study indicates that at 2 hours of recovery, low-flow CPB but not deep hypothermic circulatory arrest causes an increase in CREB phosphorylation and expression. Future studies will determine the degree to which the increase in CREB phosphorylation correlates with cell survival and neuronal injury after CPB.

CREB phosphorylation following hypoxia and ischemia in striatum of newborn piglets: possible role of dopamine.

The goal of the present study was to determine the effects of hypoxia and ischemia and the role of dopamine on phosphorylation of cAMP response element binding protein (CREB) in striatum of newborn piglets. Piglets, with and without prior injection of alpha-methyl-p-tyrosine (AMT), an inhibitor of dopamine (DA) synthesis, were subjected to 1 h of hypoxia (decreased inspired oxygen pressure, FiO2, from 21 to 6%) or 1 h of ischemia (ligation of both carotid arteries and hemorrhage to reduce the systemic arterial pressure to about 40 mmHg), followed by 2 h recovery. Microvascular oxygen pressure in the cortex (pCO2) was measured by quenching of phosphorescence. Extracellular DA was determined by in vivo microdialysis. Striatal levels of phosphorylated CREB (pCREB) and total CREB were determined by Western blots. In sham-operated animals, pCO2 was 49.7 +/- 8.2 mmHg. During hypoxia and ischemia, pCO2 decreased to 6.3 +/- 1.8 mmHg and 10.2 +/- 2.7 mmHg, respectively. There was statistical difference in the level of extracellular DA during hypoxia versus ischemia. At the end of ischemia and hypoxia, the levels of DA were 96 x 10(3) +/- 24 x 10(3)% and 26 x 10(3) +/- 12 x 10(3)% of control, respectively. The pCREB measured after 2 h recovery was not changed after hypoxia but was decreased to 47.8 +/- 24% of control after ischemia. Depletion of endogenous DA abolished the ischemia-induced decrease in pCREB level. Total CREB did not change after either condition. It can be concluded that observed decreases of CREB phosphorylation following ischemia can be at least partially due to the high extracellular DA level.

Cerebral oxygenation during repetitive apnea in newborn piglets.

This study examined the effect of repetitive apnea on brain oxygen pressure in newborn piglets. Each animal was given 10 episodes of apnea, initiated by disconnecting them from the ventilator and completed by reconnecting them to the ventilation circuit. The apneic episodes were ended 30 sec after the heart rate reached the bradycardic threshold of 60 beats per min. The oxygen pressure in the microvasculature of the cortex was measured by oxygen-dependent quenching of the phosphorescence. In all experiments, the blood pressure, body temperature, and heart rate were continuously monitored. Arterial blood samples were taken throughout the experiment and the blood pH, PaO2 and PaCO2 were measured. During pre-apnea, cortical oxygen was 55.1 +/- 6.4 (SEM, n = 7) mm Hg and decreased during each apnea to 8.1 +/- 2.8 mm Hg. However, the values of cortical oxygen varied during recovery periods. Maximal oxygen levels during recovery from the first two apneic episodes were 76.8 +/- 12 mm Hg and 69.6 +/- 9 mm Hg, respectively, values higher than pre-apnea. Cortical oxygen pressure then progressively decreased following consequent apnea. In conclusion, the data show that repetitive apnea caused a progressive decrease in cortical oxygen levels in the brain of newborn piglets. This deficit in brain oxygenation can be at least partly responsible for the neurological side effects of repetitive apnea.

Comparison of low-flow cardiopulmonary bypass and circulatory arrest on brain oxygen and metabolism.

BACKGROUND: In the neonatal brain we measured oxygen (Bo(2)), extracellular striatal dopamine (DA), and striatal tissue levels of ortho-tyrosine (o-tyr) during low-flow cardiopulmonary bypass (LFCPB) or deep hypothermic circulatory arrest (DHCA) and the post-bypass recovery period. METHODS: Newborn piglets were assigned to sham (n = 6), LFCPB (n = 8), or DHCA (n = 6) groups. Animals were cooled to 18 degrees C and underwent DHCA or LFCPB (20 mL x kg(-1) x min(-1)) for 90 minutes. The Bo(2) was measured by quenching the phosphorescence, DA by microdialysis, and hydroxyl radicals by o-tyr levels. The results are presented as the mean +/- SD (p < 0.05 was significant). RESULTS: Baseline Bo(2) was between 45 to 60 mm Hg. At the end of LFCPB, Bo(2) was 10.5 +/- 1.2 mm Hg. By 5 and 30 minutes of arrest during DHCA, Bo(2) fell to 4.2 +/- 2.5 mm Hg and 1.4 +/- 0.7 mm Hg, respectively. Compared with control, extracellular DA did not change during LFCPB. During DHCA extracellular levels of DA increased, by 750-fold from baseline at 45 minutes and to a maximum of 53000-fold at 75 minutes. After 2 hours of recovery from DHCA, the o-tyr within the striatum increased about sixfold as compared with control. There was no change in o-tyr measured after LFCPB. CONCLUSIONS: In DHCA, but not LFCPB, levels of DA and o-tyr increased considerably in the striatum of piglets, a finding that may indicate the exhaustion of cellular energy levels and contribute substantially to cellular injury.

Altered gene expression following cardiopulmonary bypass and circulatory arrest.

This study investigated the effects of normothermic cardiopulmonary bypass (CPB) and circulatory arrest (DHCA) on expression of specific genes in neonatal piglet brain. CPB was performed through the chest at 100 ml/kg/min for 2 hrs at 37 degrees C. In the second group of animals, CPB was begun as described above and then animals were cooled to a nasopharyngeal/brain temperature of 18 degrees C. When the brain temperature reached 18 degrees C, the CPB circuit was turned off. After 60 min of circulatory arrest (DHCA), CPB was resumed at 100 ml/kg/min, and the piglets were rewarmed to a temperature of 36 degrees C. In both groups, the animals remain sedated, paralyzed, mechanically ventilated, and continuously monitored throughout a four hour study period after CPB. Oxygen pressure in the microvasculature of the cortex was measured by oxygen dependent quenching of phosphorescence. The aRNA technique was used to assess mRNA steady-state levels in the brain tissue. Control oxygen pressure (pre-bypass) was 61 +/- 5 Torr and during CPB this decreased to 32 +/- 7 Torr on the beginning of bypass and to 36 +/- 5 Torr at the end of bypass. During the recovery period, cortical oxygenation steadily decreased, reaching 29 +/- 8 Torr at the end of the four hours period. Cortical oxygen decreased during DHCA to near zero and during rewarming and recovery increased to 35 +/- 6 Torr. Measurements of gene expression following CPB revealed significantly increased levels of mRNA for NMDAR1, DARPP-32, CamKII, GluR1, and D1AR. DHCA caused changes similar to those for CPB in levels of mRNA for NMDAR1, DARPP-32, CamKII and GluR1. In contrast, DHCA caused significantly increased levels of mRNA for GluR6 and GABRB1. There was no significant alteration in the level of D1AR following DHCA. The results showed that DHCA caused much larger alterations in gene expression in the critical metabolic signaling pathways tested than did CPB.

Tissue oxygen tension during regional low-flow perfusion in neonates.

OBJECTIVE: We examined cerebral cortical and peripheral organ tissue Po(2) values in a neonatal piglet model of regional low-flow perfusion. METHODS: Twenty-one neonatal piglets were placed on cardiopulmonary bypass, were cooled to 18 degrees C, then underwent either deep hypothermic circulatory arrest or regional low-flow perfusion at 20 or 40 mL/(kg x min) for 90 minutes. Regional low-flow perfusion was carried out by advancing the aortic cannula into the proximal innominate artery. Tissue mean Po(2) and Po(2) distribution were measured in the cerebral cortex, liver, small bowel, and skeletal muscle through the principle of oxygen-dependent quenching of phosphorescence. Measured quantities were compared by analysis of variance or the Fisher exact test. RESULTS: During regional low-flow perfusion, axillary and femoral arterial pressures, respectively, were 55 +/- 15 and 8 +/- 4 mm Hg at 40 mL/(kg x min) and 37 +/- 10 mm Hg (P =.04) and 17 +/- 5 mm Hg (P =.08) at 20 mL/(kg x min). Venous saturations were 95% +/- 6% at 40 mL/(kg x min) and 84% +/- 6% at 20 mL/(kg x min) (P =.03 at 15, 30, and 45 minutes). Cortical Po(2) was similar to prebypass values during regional low-flow perfusion at 40 mL/(kg x min) (53 +/- 5 mm Hg) but declined during reperfusion and recovery. Cortical Po(2) was lower than before bypass during low-flow perfusion at 20 mL/(kg x min) (38 +/- 7 mm Hg) but increased during reperfusion. Po(2) in liver and bowel was less than 10 mm Hg during low-flow perfusion at both 20 and 40 mL/(kg x min). Fraction of oxygen distribution with Po(2) lower than 15 mm Hg was less during perfusion at 40 mL/(kg x min) than at 20 mL/(kg x min) (P =.001). Three of 6 piglets that received a 40-mL/(kg x min) flow rate had significant upper torso edema, metabolic acidosis, and an unstable recovery period, whereas zero of 6 piglets that received a 20-mL/(kg x min) flow rate did. CONCLUSIONS: In a piglet model, regional low-flow perfusion at 20 mL/(kg x min) resulted in lower cortical tissue oxygenation but better recovery than did perfusion at 40 mL/(kg x min). Neither flow rate adequately oxygenated organs in the lower torso.