Effects of severe hypoxemia on mesenteric blood flow in neonatal piglets

Cardiovascular Supportive Therapies for Neonates With Asphyxia - A Literature Review of Pre-clinical and Clinical Studies

Asphyxiated neonates often have hypotension, shock, and poor tissue perfusion. Various "inotropic" medications are used to provide cardiovascular support to improve the blood pressure and to treat shock. However, there is incomplete literature on the examination of hemodynamic effects of these medications in asphyxiated neonates, especially in the realm of clinical studies (mostly in late preterm or term populations). Although the extrapolation of findings from animal studies and other clinical populations such as children and adults require caution, it seems appropriate that findings from carefully conducted pre-clinical studies are important in answering some of the fundamental knowledge gaps. Based on a literature search, this review discusses the current available information, from both clinical studies and animal models of neonatal asphyxia, on common medications used to provide hemodynamic support including dopamine, dobutamine, epinephrine, milrinone, norepinephrine, vasopressin, levosimendan, and hydrocortisone.

Bronchoscopy is associated with decreased mesenteric arterial flow

BACKGROUND

We hypothesized that fiberoptic bronchoscopy can contribute to mesenteric ischemia and bacterial translocation.

OBJECTIVE

To test this hypothesis we investigated in patients undergoing bronchoscopy mesenteric blood flow and markers in association with ischemia reperfusion injury.

PATIENT

Forty-seven consecutive patients requiring diagnostic fiberoptic bronchoscopy were studied.

MEASUREMENTS

Parameters evaluated were superior mesenteric artery Doppler sonography, oxidative stress mediators, arterial blood gases, blood cultures pre-fiberoptic bronchoscopy, and 1st, 4th, and 24th hr post-fiberoptic bronchoscopy.

MAIN RESULTS

After bronchoscopy; PaO2 decreased by 21.8% +/- 1.5% (range 6-40), and remained low at all time points (p = 0.0001, p = 0.0001, p = 0.008). Flow volume decreased by 38.8% +/- 14.9% (range 6-72), and remained low at 1st and 4th hr (p = 0.0001, p = 0.01). Resistive and pulsatile index increased at 1st hr (p = 0.0001, p = 0.001) and 4th hr (p = 0.018, p = 0.045). Myeloperoxidase and malondialdehyde increased at 1st hr (p = 0.0001) and 4th hr (p = 0.037, p = 0.028). Corresponding glutathione and catalase decreased at 1st hr (p = 0.0001), and glutathione remained significant at 4th and 24th hr (p = 0.0001, p = 0.003). Correlation between flow volume and PaO2 (r = .71, p = 0.0001), myeloperoxidase (r = -.39, p = 0.05), glutathione (r = .41, p = 0.03) was significant. Nine of 47 (19.1%) had fever, and 3 of 47 (6.4%) had gram-negative bacteremia.

CONCLUSION

Fiberoptic bronchoscopy is associated with decreased mesenteric blood flow, which may place the patient at risk for mesenteric ischemia and gastrointestinal bacterial translocation.

Effects of acute hypobaric hypoxia on resting and postprandial superior mesenteric artery blood flow

Reduced blood flow to the gut may contribute to weight loss and gastrointestinal symptoms of acute mountain sickness (AMS) at altitude. A study in humans tested the hypothesis that acute hypobaric hypoxia (ALT) would attenuate the normal postprandial hyperemia in the superior mesenteric artery (SM). Blood pressure, cardiac output (CO), and (SM) were measured with previously validated noninvasive Doppler ultrasonic flowmetry in 9 (3 women) healthy young adults (mean age: 23; range: 18-33 yr) residing at 1700 m. Baseline measurements were made after 2 h at ALT in a chamber at 430 mmHg (asymptotically equal to 4800 m = 15,750 ft) after 10-12-h fasting, and the next day the control (CON) measurements were made at 615 mmHg (1850 m). Postprandial measurements were made 45 to 60 min after ingesting a 1000-cal liquid meal under both conditions. At ALT, 5 of the 9 subjects had AMS by the Lake Louise score criteria of headache > or =1 and total score > or =3. ALT significantly reduced fasting, baseline SM relative to CON by 15%, and increased CO by 16%. The postprandial CO increase was not different between ALT and CON, but (SM) increased 115% at CON, but only 75% at ALT, the attenuation being significant (p < 0.006). Neither the diminution of fasting (SM) at ALT nor the attenuation of the postprandial increase in (SM) correlated significantly with AMS symptom scores. These results suggest that baseline and postprandial gut blood flow are altered during acute altitude exposure because of increased intestinal sympathetic tone, inferred from increased local resistance, and may be related to reduced energy intake if sustained during prolonged exposure.

Resuscitation with 100% oxygen causes intestinal glutathione oxidation and reoxygenation injury in asphyxiated newborn piglets

OBJECTIVE

To compare mesenteric blood flow, oxidative stress, and mucosal injury in piglet small intestine during hypoxemia and reoxygenation with 21%, 50%, or 100% oxygen.

SUMMARY BACKGROUND DATA

Necrotizing enterocolitis is a disease whose pathogenesis likely involves hypoxia-reoxygenation and the generation of oxygen-free radicals, which are known to cause intestinal injury. Resuscitation of asphyxiated newborns with 100% oxygen has been shown to increase oxidative stress, as measured by the glutathione redox ratio, and thus may predispose to free radical-mediated tissue injury.

METHODS

Newborn piglets subjected to severe hypoxemia for 2 hours were resuscitated with 21%, 50%, or 100% oxygen while superior mesenteric artery (SMA) flow and hemodynamic parameters were continuously measured. Small intestinal tissue samples were analyzed for histologic injury and levels of oxidized and reduced glutathione.

RESULTS

SMA blood flow decreased to 34% and mesenteric oxygen delivery decreased to 9% in hypoxemic piglets compared with sham-operated controls. With reoxygenation, SMA blood flow increased to 177%, 157%, and 145% of baseline values in piglets resuscitated with 21%, 50%, and 100% oxygen, respectively. Mesenteric oxygen delivery increased to more than 150% of baseline values in piglets resuscitated with 50% or 100% oxygen, and this correlated significantly with the degree of oxidative stress, as measured by the oxidized-to-reduced glutathione ratio. Two of eight piglets resuscitated with 100% oxygen developed gross and microscopic evidence of pneumatosis intestinalis and severe mucosal injury, while all other piglets were grossly normal.

CONCLUSIONS

Resuscitation of hypoxemic newborn piglets with 100% oxygen is associated with an increase in oxygen delivery and oxidative stress, and may be associated with the development of small intestinal hypoxia-reoxygenation injury. Resuscitation of asphyxiated newborns with lower oxygen concentrations may help to decrease the risk of necrotizing enterocolitis.

Spontaneous localized intestinal perforation in very-low-birth-weight infants: a distinct clinical entity different from necrotizing enterocolitis

BACKGROUND

Idiopathic spontaneous intestinal perforation (SIP), a distinct clinical entity different from necrotizing enterocolitis (NEC), has an increasing prevalence in very-low-birth-weight infants. The aims of our study were to define patient characteristics and potential risk factors for premature infants with SIP compared with infants subjected to surgical treatment for NEC.

STUDY DESIGN

The medical records of 29 premature infants with either SIP (n = 13) or NEC (n = 16) were reviewed retrospectively.

RESULTS

Infants who experienced SIP were smaller at birth, had lower Apgar scores, and required more intensive neonatal resuscitation. An increased rate of premature rupture of membranes in infants with SIP (8/13 versus 6/16) was not associated with a higher rate of infection in mothers or infants. The onset of illness in SIP was significantly earlier than in NEC (p = 0.022). In contrast to patients with NEC (7/16), 11 of 13 patients in the SIP group had received indomethacin (p = 0.02). Bluish discoloration of the abdomen (8/13), a gasless abdomen (8/13), and the absence of pneumatosis intestinalis (0/13) were further significant markers in infants with SIP. At operation, SIP was always located in the terminal ileum in an antimesenteric position (13/13), and the remaining bowel appeared grossly normal. In most cases of SIP (10/13), the histologic investigation revealed an area of hemorrhagic necrosis without the typical coagulation necrosis seen predominantly in NEC.

CONCLUSIONS

Based on clinical presentation and radiologic and intraoperative findings, SIP is a distinct pathologic entity in very-low-birth-weight infants and can be differentiated from classic NEC. Detected early, SIP can be treated by simple procedures (sutures, or resection and primary anastomosis) with a low rate of morbidity and mortality.

Effect of hypoxia on DNA fragmentation in different brain regions of the newborn piglet

DNA fragmentation has been studied in different regions of the newborn piglet brain following different times of normobaric hypoxia (5% O(2), 95% N(2)). After 1 hr of hypoxia, fragmented DNA was observed in cerebellum, cortex, hippocampus, and striatum but not in hypothalamus. More fragmentation occurred in these areas of the brain when the animals were kept under hypoxia for times up to 8 hr 45 min. When the animals were submitted to hypoxia for two and a half hours, integrity of DNA was recovered respectively after 3 hr of exposure to the ambient atmosphere in hippocampus and striatum, but 4 hr of recovery were necessary for cerebellum and cortex. These results are discussed in terms of the consequences of neonatal hypoxia and apnea for newborn infants and economical impact for farm animals.

Necrotizing enterocolitis in infants with very low birth weight

Necrotizing enterocolitis (NEC) is a disease in which the primary risk factor is prematurity. Despite, and partially as a result of, the tremendous strides neonatal care has taken, it is a major cause of morbidity and mortality of the newborn. The infant with very low birth weight is particularly susceptible, and the management of the condition in this group differs somewhat from other neonates. The outcomes continue to improve, but there are significant sequelae. Prevention, which would be the best "cure," is elusive, in no small part because of the multifactorial nature of the etiology of NEC.

Post-treatment Dopexamine Infusions Partially Reverse Reductions in Cranial Mesenteric Blood Flow and Mucosal Oxygenation Induced by Hypoxia in Newborn Piglets

A severe hypoxic insult is known to induce dramatic reductions in newborn intestinal blood flow and is, thus, considered a vector for the development of neonatal intestinal ischemic diseases. Dopexamine (DPX) is a novel synthetic agent that has potent B2-adrenoceptor and dopaminergic activity, the clinical effects of which include an increase in cardiac output and in mesenteric blood flow. Having previously shown that infusion of DPX before hypoxia (HYP) mitigated the reduction in newborn mesenteric blood flow, we sought to define its efficacy when given after an established hypoxic insult. Ultrasonic transit time blood flow probes were placed around the ascending aorta and cranial mesenteric artery of anesthetized, mechanically ventilated 0 to 2-day-old piglets. Small bowel mucosal oxygenation was observed with a tissue oxygen monitoring system. After stabilization, animals were subjected to one of the following: HYP (FIO2 = 0.12) for 60 minutes (n = 12); DPX (5 μg/kg/min) infusion begun 10 minutes after induction of HYP/DPX (n = 11). Almost no alterations in any of the monitored variables were shown in a group (n = 5) of similarly instrumented, untreated animals. In contrast, although both hypoxic piglet groups experienced significant (P < 0.05, analysis of variance) declines from baseline cardiac output, mesenteric blood flow, and mucosal oxygenation, each of these deleterious effects was significantly (P < 0.05) blunted in the DPX-treated animals. During periods of systemic hypoxemia, the reductions in neonatal mesenteric blood flow and oxygenation can be somewhat blunted by DPX. As such, this agent may prove of clinical benefit when an infant is threatened by a hypoxic episode.