Decreased accuracy of pulse oximetry measurements during low perfusion caused by sepsis: Is the perfusion index of any value?

OBJECTIVE

To evaluate the effects of deteriorating perfusion caused by sepsis on the accuracy of pulse oximetry measurements using two more recently available techniques (Nellcor N-395 and Masimo Radical) and to evaluate the perfusion index as a marker of impaired peripheral perfusion to indicate that accuracy of pulse oximetry readings may be affected.

DESIGN AND SETTING

Interventional cohort study in a university animal research facility.

SUBJECTS

Thirty-seven adult anesthetized, ventilated rabbits.

INTERVENTIONS

Pneumonia/sepsis was induced by tracheal instillation of Escherichia coli.

MEASUREMENTS AND RESULTS

Oxygen saturation and perfusion index as a marker of peripheral perfusion were measured by pulse oximetry (SpO2) and recorded continuously for 8 h. Arterial oxygen saturation (SaO2) was measured every 30 min by CO oximetry, and bias (SpO2 - SaO2) was calculated at each time point for each device to assess time-dependent changes in bias. Bias increased significantly across time for both devices tested comparing the first with the second half of the experimental period. Bias measurements during the second half of the experimental time were beyond the +/-3% error limit in 21.4% of cases with Nellcor and in 22.6% with Masimo. A lower perfusion index was associated with increased bias, but sensitivity, specificity, and positive and negative predictive values of this marker for increased bias was very limited.

CONCLUSIONS

We conclude that accuracy of pulse oximetry measurements was considerably affected with both devices with progressively deteriorating hemodynamics in this animal model of severe sepsis. Perfusion index as a marker for increased risk of bias was not a useful tool.

Volume-controlled intermittent mandatory ventilation in preterm infants with hypoxemic episodes

OBJECTIVE

To test the hypothesis in ventilated very low birth weight infants with frequent hypoxemic episodes that volume-controlled synchronized intermittent mandatory ventilation (SIMV) vs. pressure-controlled SIMV reduces by at least 20% the time with hypoxemia (defined as SpO(2)<80%).

DESIGN

Randomized cross-over design.

SETTING

University-based tertiary neonatal intensive care unit.

PATIENTS

15 mechanically ventilated very low birth weight infants with frequent hypoxemic episodes.

INTERVENTIONS

The infants were exposed in random order to volume-controlled and pressure-controlled SIMV for 4 h each. The target tidal volume during volume-controlled SIMV was matched to the tidal volume measured during pressure-controlled SIMV. FIO(2) was adjusted using uniform criteria to maintain SpO(2) within the target range (SpO(2) 80-92%).

MEASUREMENTS AND RESULTS

Primary outcome measure was the time with an SpO(2)<80%. Although tidal volume was maintained better during desaturations with volume-controlled SIMV, there was neither a significant difference in time with an SpO(2)<80% (expressed as proportion of total experimental time; median, interquartile range)-volume-control 10.6% (9.2-13.7%) vs. pressure-control 10.8% (8.3-13.3%)-nor in FIO(2) exposure. During volume-controlled SIMV the infants spent less time with an SpO(2) above the target range and had fewer associated bradycardias.

CONCLUSION

Volume-controlled SIMV did not decrease the time with an SpO(2)<80%, although tidal volume was better maintained during these episodes and bradycardias were less frequent than with pressure-controlled SIMV in this population of very low birth weight infants with frequent hypoxemic episodes.

Hydrolysis of casein accelerates gastrointestinal transit via reduction of opioid receptor agonists released from casein in rats

BACKGROUND

Protein hydrolysate accelerates gastrointestinal transit (GIT) and feeding advancement in preterm infants compared to native protein. In rat pups, opioid receptor agonists released from casein during digestion such as beta-casomorphins slow down GIT. We hypothesized that hydrolysis of casein reduces the opioid activity released during digestion thereby accelerating GIT compared to native casein.

OBJECTIVE

The aim of the present study was to investigate whether casein hydrolysate accelerates GIT compared to native casein and whether pretreatment with naloxone, an opioid receptor blocker, abolishes this difference in rat pups.

METHODS

In a randomized controlled trial following a 2 x 2 factorial design, 216 female Wistar rat pups were fed with pellets based on hydrolyzed or native casein. After pretreatment with naloxone or normal saline, carmine red was administered by oro-gastric gavage as a tracer for GIT velocity measurement. Four hours later the animals were sacrificed, their intestine was removed and the length of the colon from the cecocolonic junction to the anus was measured. GIT was recorded as percentage of the total colonic length (percentage of colonic transit) passed by carmine red. Data were given as mean +/- SD.

RESULTS

GIT was significantly higher with hydrolyzed casein compared to native casein formula (77.4 +/- 17 and 51.2 +/- 20%), but there was no difference after naloxone pretreatment (77.1 +/- 16 and 76.5 +/- 17%).

DISCUSSION

The present data suggest that hydrolysis of casein accelerates GIT via reduction of opioid activity released during digestion. Further studies are required to investigate to which extent these rat pub data apply to preterm infants.

Algorithm for the identification of bacterial pathogens in positive blood cultures by real-time LightCycler polymerase chain reaction (PCR) with sequence-specific probes

We developed real-time polymerase chain reaction (PCR) assays for rapid detection of the most common and clinically relevant bacteria in positive blood culture bottles, including Staphylococcus spp., S. epidermidis, S. aureus, Enterococcus spp. (including differentiation of E. faecalis and E. faecium), Streptococcus spp., Streptococcus agalactiae, Enterobacteriaceae, E. coli, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Acinetobacter spp., Bacteroides spp., Haemophilus influenzae, and Neisseria meningitidis. A total of 507 positive blood cultures were investigated according to a specific PCR algorithm based on the microscopic result of the blood culture, and the PCR results were compared to the culture results. Apart from-cross reactions between E. coli and Chryseomonas luteola and Enterococcus faecium and E. durans, the PCR assay correctly identified all bacteria in the blood cultures and did not show any false-positive results. Regarding blood cultures positive with a single species of bacteria (n = 474), 98.3% of all bacteria were correctly detected by the PCR algorithm within a few hours. However, in mixed infections, the sensitivity was lower. The PCR algorithm is well suited for rapid identification of the most common bacteria in positive blood cultures.

Measurement of interleukin 8 in combination with C-reactive protein reduced unnecessary antibiotic therapy in newborn infants: a multicenter, randomized, controlled trial

OBJECTIVE

Neonatal bacterial infections carry a high mortality when diagnosed late. Early diagnosis is difficult because initial clinical signs are nonspecific. Consequently, physicians frequently prescribe antibiotic treatment to newborn infants for fear of missing a life-threatening infection. This study was designed to test the hypotheses that a diagnostic algorithm that includes measurements of interleukin 8 (IL-8) and C-reactive protein (CRP) 1) reduces antibiotic therapy and 2) does not result in more initially missed infections compared with standard management that does not include an IL-8 measurement.

METHODS

Term and preterm infants who were <72 hours of age and had clinical signs or obstetric risk factors suggesting neonatal bacterial infection but stable enough to wait for results of diagnostic tests were enrolled into the study. A total of 1291 infants were randomly assigned to receive antibiotic therapy according to the guidelines of each center (standard group) or to receive antibiotic therapy when IL-8 was >70 pg/mL and/or CRP was >10 mg/L (IL-8 group). The primary outcome variables were 1) the number of infants treated with antibiotics and 2) the number of infants with infections missed at the initial evaluation.

RESULTS

In the IL-8 group, fewer infants received antibiotic therapy than in the standard group (36.1% [237 of 656] vs 49.6% [315 of 635]). In the IL-8 group, 24 (14.5%) of 165 infants with infection were not detected at the initial evaluation, compared with 28 (17.3%) of 162 in the standard group.

CONCLUSIONS

The number of newborn infants who received postnatal antibiotic therapy can be reduced with a diagnostic algorithm that includes measurements of IL-8 and CRP. This diagnostic strategy seemed to be safe.

Transcutaneous bilirubinometry in very low birthweight infants

AIM

To evaluate whether transcutaneous bilirubinometry (TcB) would be a reliable and efficient screening technique for hyperbilirubinaemia in very low birthweight (VLBW, < or =1500 g) infants in an intensive care unit setting.

METHODS

TcB measurements (Minolta Airshield Jaundice Meter JM-102, Osaka, Japan) were obtained immediately before or within 10 min following routine blood sampling for plasma bilirubin concentration measurements in 124 VLBW infants not receiving phototherapy. The relationship between the two techniques was analysed by linear regression analysis. A plasma bilirubin > or =150 micromol/l was defined as hyperbilirubinaemia. The sensitivity and specificity of possible TcB cut-off readings to detect hyperbilirubinaemia was evaluated.

RESULTS

There was a significant correlation between the measurements of both techniques (p < 0.0001, r = 0.68). In the present study, a TcB cut-off reading of 14 would have reduced the need for plasma bilirubin measurements by 26% without missing true hyperbilirubinaemia.

CONCLUSION

The data suggest that TcB will improve VLBW infant care in an intensive care unit setting by reducing the need for invasive bilirubin concentration measurements.

Whole blood interleukin 8 and plasma interleukin 8 levels in newborn infants with suspected bacterial infection

AIM

To evaluate a new micro-method technique for measurement of interleukin 8 in detergent-lysed whole blood (whole blood IL-8) applicable to capillary blood sampling as a test for bacterial infections in neonates.

METHODS

Whole blood IL-8 was measured at the first suspicion of infection along with IL-8 determined in plasma (plasma IL-8), C-reactive protein and blood cultures in 154 consecutive newborn infants with clinical signs of bacterial infection. Only 20 microl of whole blood were required for the new assay.

RESULTS

Blood culture-proven infections were diagnosed in six infants and clinical infection (defined as a combination of clinical and laboratory signs) in 20 infants. 1000 pg/ml was determined as the suitable threshold for whole blood IL-8 by ROC-curve analysis. At that threshold, whole blood IL-8 detected blood culture-proven infections with a sensitivity of 83% and a specificity of 67%. The areas under the ROC curves were similar for whole blood IL-8 and plasma IL-8.

CONCLUSIONS

Compared with plasma IL-8, whole blood IL-8 offers the advantages that measurements of whole blood IL-8 require a smaller blood sample volume and are not altered by haemolysis. The diagnostic accuracy of whole blood IL-8 remains to be studied in more detail in the future.

Accuracy of pulse oximetry readings in an animal model of low perfusion caused by emerging pneumonia and sepsis

OBJECTIVE

To test the effects of low perfusion caused by emerging sepsis on the performance of two new pulse oximetry techniques: Masimo SET in comparison with Nellcor Oxismart XL.

DESIGN

Cohort study with random allocation of two pulse oximetry devices to two sensor sites. SETTING. University animal research facility.

SUBJECTS

Twenty-five adult, anesthetized, ventilated rabbits.

INTERVENTIONS

Pneumonia/sepsis was induced by tracheal instillation of E. coli.

MEASUREMENTS AND RESULTS

Oxygen saturation was measured by pulse oximetry (SpO(2)) and recorded continuously until death. Arterial oxygen saturation (SaO(2)) was measured hourly by CO oximetry and whenever a difference of >5% between the devices occurred. SpO(2) sensors were positioned at both forelegs and switched hourly. There was no difference in total signal dropout time [median 3.8 min (range 0.4-66.6 min) vs 3.3 min (range 0-94.5 min), Masimo SET vs Oxismart XL]. There were fewer episodes with a false SpO(2) reading [1 (range 0-7) vs 2 (range 0-17)] using the Masimo SET vs the Oxismart XL as verified by CO oximetry; p<0.05. Average bias (SpO(2)-SaO(2)) was significantly different between the two devices, and variability of bias values increased across time with both devices.

CONCLUSIONS

Both devices were capable to measure SpO(2) during most of the experimental time in this model of low perfusion and therefore appear to be highly sensitive to pick up a signal; however, low perfusion caused by emerging sepsis may result in inaccurate measurements with both devices. These episodes were less common with the Masimo SET vs the Oxismart XL.

Hydrolyzed protein accelerates feeding advancement in very low birth weight infants

BACKGROUND

Feeding intolerance is common in very low birth weight (VLBW; <1500 g) infants. Hydrolyzed protein preterm infant formula (HPF) has been shown to accelerate the gastrointestinal transit of formula. The aim of this study was to investigate whether HPF improves early feeding tolerance compared with standard preterm infant formula (SPF). We hypothesized that HPF would accelerate early enteral feeding advancement.

METHODS

Primary outcome was the time from initiation of milk feeds until full feeds (150 mL/kg birth weight/d) were achieved in infants who received <10% human milk (HM) to exclude HM as a confounder. Because the availability of HM was not predictable at the time of enrollment, all eligible VLBW infants (n = 129) were randomly assigned in a randomized, controlled trial to receive HPF or SPF if HM was not available. Infants who received >10% HM (n = 42) were excluded. Milk bolus feeding every 2 to 3 hours was started at the discretion of the attending physician and advanced by 16 mL/kg/d. Preprandial gastric residuals were tolerated up to 5 mL/kg; otherwise, feedings were reduced or withheld. Data are shown as median (5th and 95th percentile).

RESULTS

Forty-six and 41 (HPF vs SPF) infants received <10% HM. There was no significant difference with regard to birth weight, gestational age, and onset of milk feeds (day 3 [1-8] vs 4 [2-6]). The time from initiation of milk feeds to full feeds was significantly shorter with HPF feeding (10 [9-27] vs 12 [9-28] days).

CONCLUSION

HPF improved the feeding tolerance and enabled a more rapid establishment of full enteral feeding in VLBW infants compared with SPF.

Pulse oximetry during low perfusion caused by emerging pneumonia and sepsis in rabbits

OBJECTIVE

This study tested the effects of low perfusion caused by emerging sepsis on the reliability of a new pulse oximetry technology (Masimo SET; IVY 405T) compared with a standard pulse oximeter (Nellcor N-200).

DESIGN

Randomized trial.

SETTING

University animal research facility.

SUBJECTS

Twenty-six anesthetized, ventilated (Fio, 1.0), adult rabbits.

INTERVENTIONS

Pneumonia/sepsis was induced by tracheal instillation of Escherichia coli. Oxygen saturation was measured by pulse oximetry (Spo ) and recorded continuously until death. Arterial oxygen saturation (Sao2) was measured hourly by oximetry and whenever Spo dropped to </=95%, or whenever a difference of >/=5% between devices occurred. Spo2 sensors were positioned at both forelegs and switched hourly.

MEASUREMENTS AND MAIN RESULTS

The total time of signal loss was longer with the N-200 vs. the IVY: 65 (4-299) mins vs. 7 (0-97) mins [median (range)], p < 0.001. Signal loss was more prevalent during the first 80% of the experimental time with the N-200 compared with the IVY. Nineteen of 26 animals had a total of 62 episodes of a falsely low Spo2 value with either one of the two devices associated with hemodynamic deterioration. Median bias (Spo2 - Sao2) was small, but variability of bias values increased toward the end of the experimental time with both devices.

CONCLUSIONS

The pulse oximeter equipped with Masimo SET was less prone to signal loss than the standard pulse oximeter in this sepsis model. Episodes of falsely low Spo2 readings may occur, and deviation of Spo2 from Sao2 may be increased with deteriorating hemodynamics with both devices.

Pulmonary administration of perfluorodecaline- gentamicin and perfluorodecaline- vancomycin emulsions

The aim of this study was to examine pharmacokinetics and pulmonary antibiotic tissue concentrations (PATC) of gentamicin and vancomycin after intrapulmonary administration of a perfluorodecaline (PFD)-gentamicin and a PFD-vancomycin emulsion during partial liquid ventilation (PLV). PLV was initiated in 19 healthy rabbits and 18 surfactant-depleted rabbits. The animals were randomized to receive either 5 mg/kg gentamicin and 15 mg/kg vancomycin intravenously, or 5 mg/kg gentamicin intrapulmonary, or 15 mg/kg vancomycin intrapulmonary. Antibiotic plasma levels were measured after 15, 30, 45, and 60 min, and hourly thereafter. After 5 h animals were sacrificed and lungs were removed to evaluate PATC and histology. PATC were significantly higher after intrapulmonary administration of both gentamicin and vancomycin. In healthy rabbits, peak plasma concentrations were lower and 5 h plasma concentrations were higher after intrapulmonary administration, whereas plasma concentrations were not different in surfactant-depleted rabbits. There were no differences in lung histology, hemodynamics, lung mechanics, or gas exchange between the treatment groups. We conclude that during PLV, higher PATC can be achieved after intrapulmonary administration of PFD-antibiotic emulsions compared with intravenous administration of the same dose without apparent short-term adverse effects. We speculate that intrapulmonary antibiotic administration during PLV may be beneficial in treating severe pneumonia.

Interleukin-8: a valuable tool to restrict antibiotic therapy in newborn infants

This study was conducted to evaluate the accuracy and kinetics of interleukin 8 (IL-8) as a test for early-onset bacterial infections (EOBI) in neonates and to examine whether IL-8 would allow "unnecessary" antibiotic therapy to be reduced. First, IL-8 was measured 378 times on admission, along with C-reactive protein (CRP), immature to total neutrophil ratio (IT ratio) and blood cultures, in full-term and preterm neonates with suspected EOBI. Combined culture-proven and clinical EOBI were detected on admission by the combination of IL-8 > or = 70 pg ml(-1) and/or CRP > 10 mg l(-1) with 92% sensitivity and 74% specificity. An increased IL-8 was found in 62% of the infected infants, while CRP was still normal. In a second study period, IL-8 was determined prospectively in 331 infants who presented clinical signs of EOBI or had a birth history of amniotic infection. Antibiotic therapy was restricted to those infants with suspected infection who also had an increased IL-8 and/or CRP (n = 158). Another 39 infants received antibiotics on the basis of clinical signs despite negative IL-8 and CRP. Of 150 non-infected infants in whom IT ratio, IL-8 and CRP were available, treatment would have been indicated for 93 infants based on IT ratio and/or CRP (n = 77) or clinical signs (n = 16), but was only initiated in 55 infants based on IL-8 and/or CRP (n = 28) or clinical signs (n = 27), an apparent reduction in "unnecessary" antibiotic therapy of 40%.

CONCLUSION

The combination of IL-8 and CRP is a reliable test for the diagnosis of EOBI and may be helpful in enabling antibiotic therapy to be reduced in newborn infants.

Preserved spontaneous breathing improves cardiac output during partial liquid ventilation

The aim of this study was to examine whether preserved spontaneous breathing (SB) supported by proportional-assist ventilation (PAV) would improve cardiac output (CO) during partial liquid ventilation (PLV) in rabbits with and without lung disease if compared with time-cycled, volume-controlled ventilation (CV) combined with muscle paralysis (MP). PLV was initiated in 17 healthy rabbits and 17 surfactant-depleted rabbits using 12 to 15 ml/kg of perfluorodecaline. Both ventilatory modes, SB+PAV and CV+MP, were applied in random sequence using a crossover design. CO was measured by thermodilution. CO was significantly higher during SB+PAV than during CV+MP: 136 +/- 21 ml/kg x min (mean +/- SD) versus 120 +/- 30 ml/kg x min (p = 0.004) in healthy rabbits, and 147 +/- 19 ml/kg x min versus 111 +/- 13 ml/kg x min (p < 0.0001) in surfactant-depleted rabbits, resulting in an improved oxygen delivery. This difference was mainly caused by a larger stroke volume during SB+PAV, whereas there was little change in heart rate. In surfactant-depleted rabbits, SB+PAV resulted in improved arterial blood pressure and arterial and mixed venous pH and in a higher PaO2 at the same level of PEEP and mean airway pressure. We conclude that during PLV, CO is higher during SB+PAV than during CV+MP, resulting in an improved oxygen delivery. In surfactant-depleted rabbits, improved CO, oxygen delivery, and arterial blood pressure resulted in higher pH, possibly reflecting improved tissue perfusion and oxygenation.

Partial liquid ventilation in severely surfactant-depleted, spontaneously breathing rabbits supported by proportional assist ventilation

OBJECTIVE

We hypothesized that partial liquid ventilation (PLV) would improve oxygenation in nonparalyzed, surfactant-deficient rabbits breathing spontaneously while supported by proportional assist ventilation (PAV). This ventilation mode compensates for low pulmonary compliance and high resistance and thereby facilitates spontaneous breathing.

DESIGN

Randomized trial.

SETTING

University animal research facility.

SUBJECTS

Twenty-six anesthetized New Zealand white rabbits weighing 2592 +/- 237g (mean +/- sd).

INTERVENTIONS

After pulmonary lavage (target Pao2 <100 mm Hg on mechanical ventilation with 6 cm H2O of positive end-expiratory pressure [PEEP] and an Fio2 of 1.0), rabbits were randomized to PAV (PEEP of 8 cm H2O) with or without PLV. PLV rabbits received 25 mL/kg of perfluorocarbon by intratracheal infusion (1 mL/kg/min). Pao2, Paco2, tidal volume, respiratory rate, minute ventilation, mean airway pressure, arterial blood pressure, heart rate, pulmonary compliance, and airway resistance were measured. Evaporated perfluorocarbon was refilled every 30 mins in PLV animals. After 5 hrs, animals were killed and lungs were removed. Lung injury was evaluated using a histologic score.

MAIN RESULTS

Pao2 and compliance were significantly higher in PLV rabbits compared with controls (p <.05, analysis of variance for repeated measures). All other parameters were similar in both groups.

CONCLUSIONS

PLV improved oxygenation and pulmonary compliance in spontaneously breathing, severely surfactant-depleted rabbits supported by PAV. The severity of lung injury by histology was unaffected.

Spontaneous breathing during partial liquid ventilation in animals with meconium aspiration

Partial liquid ventilation (PLV) has been shown to improve gas exchange in paralyzed animals and humans with lung disease. The present study tests the hypothesis that PLV improves gas exchange in spontaneously breathing animals with meconium aspiration supported by proportional assist ventilation. Twenty-five adult anesthetized intubated rabbits with experimental meconium aspiration were randomized to gas ventilation (GV) or PLV while being supported by proportional assist ventilation. Minute ventilation, tidal volume, respiratory rate, mean airway pressure, heart rate, and mean arterial and pulmonary arterial pressure were recorded continuously. Every 30 min, arterial blood gases were obtained, and lung compliance, airway resistance, work of breathing, and cardiac output were measured. Animals were sacrificed after 5 h to obtain lung histology. More PLV animals survived until the end of the study period. PaO(2) (14.5 +/- 4.5 versus 25.6 +/- 6.7 kPa; p < 0.01; GV versus PLV) and lung compliance (4.3 +/- 0.4 versus 6.1 +/- 1.2 mL.kPa(-1).kg(-1); p < 0.001) were improved during PLV, resulting in a lower work of breathing (5.3 +/- 2.8 versus 3.5 +/- 1.5 mL.kPa.kg(-1); p < 0.05) and less need for ventilatory support. Minute ventilation and respiratory rate were higher during GV versus PLV, resulting in a slightly lower PaCO(2) (3.9 +/- 0.5 versus 4.5 +/- 0.7 kPa; p < 0.05). Histologic evaluation showed more atelectasis, inflammatory changes, and hemorrhage in GV animals. Other parameters measured were similar. We conclude that PLV improves oxygenation, lung compliance, and survival and results in less lung injury in spontaneously breathing animals with meconium aspiration when supported by proportional assist ventilation.

Meconium passage in extremely low birthweight infants and its relation to very early enteral nutrition

The aim of this study was to evaluate the correlation between the timing of the first and last meconium and feeding tolerance in the very early enteral nutrition of extremely low birthweight (ELBW) infants. Forty-one ELBW infants were fed following a standardized protocol (day 3-14). At 48 h of age bolus gavage feeding with milk was started (12 ml kg(-1) d(-1) increments, 12 meals per day). Gastric residuals up to 2 ml or up to 3 ml were tolerated in infants with a birthweight of < or = 750 g or > 750 g, respectively. No enemas or laxatives were given during the study. The impact of the time until the passage of the first (M-1) and last (M-last) meconium on the feeding volume on day 14 (V14) was evaluated by linear regression analysis. Data are presented as median (range). M-1 was 31 h (0.5-77 h), M-last was 6 d (1.4-22 d) and V14 was 99 (0-156) ml kg(-1). V14 increased with decreasing M-last (p < 0.001) but there was no correlation between V14 and M-1. V14 was 112 (0-156) ml kg(-1) if M-last was shorter than 6 d and 37 (0-147) ml kg(-1) if M-last was longer than 6 d.

CONCLUSION

Rapid meconium evacuation appeared to be a key factor for the feeding tolerance of ELBW infants during the first 14 d of life. Further studies needed to investigate whether meconium passage can be accelerated and whether acceleration of the meconium passage will improve the early feeding tolerance in ELBWW infants.