Cerebral oxygenation is affected by filling mode and perfluorochemical volume in partial liquid ventilation of healthy piglets

Mimicking oxygen delivery and waste removal functions of blood

In addition to immunological and wound healing cell and platelet delivery, ion stasis and nutrient supply, blood delivers oxygen to cells and tissues and removes metabolic wastes. For decades researchers have been trying to develop approaches that mimic these two immediately vital functions of blood. Oxygen is crucial for the long-term survival of tissues and cells in vertebrates. Hypoxia (oxygen deficiency) and even at times anoxia (absence of oxygen) can occur during organ preservation, organ and cell transplantation, wound healing, in tumors and engineering of tissues. Different approaches have been developed to deliver oxygen to tissues and cells, including hyperbaric oxygen therapy (HBOT), normobaric hyperoxia therapy (NBOT), using biochemical reactions and electrolysis, employing liquids with high oxygen solubility, administering hemoglobin, myoglobin and red blood cells (RBCs), introducing oxygen-generating agents, using oxygen-carrying microparticles, persufflation, and peritoneal oxygenation. Metabolic waste accumulation is another issue in biological systems when blood flow is insufficient. Metabolic wastes change the microenvironment of cells and tissues, influence the metabolic activities of cells, and ultimately cause cell death. This review examines advances in blood mimicking systems in the field of biomedical engineering in terms of oxygen delivery and metabolic waste removal.

Cerebral blood flow is not affected during perfluorocarbon dosing with volume-controlled ventilation

AIMS

Perfluorocarbon administration increases cerebral blood flow. This can be mitigated by preventing a rise in carbon dioxide by adjusting pressure-controlled ventilation. Volume-controlled ventilation should prevent increases in arterial carbon dioxide and cerebral blood flow. This study aims to determine if cerebral blood flow is increased during administration of 10 mL/kg of perfluorocarbon while using volume-controlled ventilation.

METHODS

Two New Zealand white rabbits, ventilated with volume-control, were each allocated to six dosing events where each dosing event was randomly allocated to one of two dosing strategies: a control group - given a sham dose of air (10 mL/kg) over 20 min; or a partial liquid ventilation group - given 10 mL/kg FC-77 slowly over 20 min. Data were recorded for 1 min before and 30 min after the start of each dosing event. No adjustment of ventilation (except fraction of inspired oxygen) was allowed during each dosing event.

RESULTS

There were no significant changes over time and no differences between groups for carotid blood flow (P = 0.48 at the end of the dose). There were slight increases in cortical cerebral blood flow in both groups; there was no statistically significant difference between groups (P = 0.56 at end dose and P = 0.49 at time of maximum difference). There was no difference between groups for the variability in carotid blood flow or cortical cerebral blood flow.

CONCLUSIONS

Cerebral blood flow was not significantly increased during administration of a dose of 10 mL/kg of perfluorocarbon during commencement of partial liquid ventilation when using volume-controlled ventilation.

Persurf, a new method to improve surfactant delivery: a study in surfactant depleted rats

PURPOSE

Exogenous surfactant is not very effective in adults with ARDS, since surfactant does not reach atelectatic alveoli. Perfluorocarbons (PFC) can recruit atelectatic areas but do not replace impaired endogenous surfactant. A surfactant-PFC-mixture could combine benefits of both therapies. The aim of the proof-of-principal-study was to produce a PFC-in-surfactant emulsion (Persurf) and to test in surfactant depleted Wistar rats whether Persurf achieves I.) a more homogenous pulmonary distribution and II.) a more homogenous recruitment of alveoli when compared with surfactant or PFC alone.

METHODS

Three different PFC were mixed with surfactant and phospholipid concentration in the emulsion was measured. After surfactant depletion, animals either received 30 ml/kg of PF5080, 100 mg/kg of stained (green dye) Curosurf™ or 30 ml/kg of Persurf. Lungs were fixated after 1 hour of ventilation and alveolar aeration and surfactant distribution was estimated by a stereological approach.

RESULTS

Persurf contained 3 mg/ml phospholipids and was stable for more than 48 hours. Persurf-administration improved oxygenation. Histological evaluation revealed a more homogenous surfactant distribution and alveolar inflation when compared with surfactant treated animals.

CONCLUSIONS

In surfactant depleted rats administration of PFC-in-surfactant emulsion leads to a more homogenous distribution and aeration of the lung than surfactant alone.

Effect of the dose volume of perfluorocarbon when starting partial liquid ventilation

OBJECTIVE

Very preterm neonates are prone to brain injury if cerebral blood flow fluctuates. Partial liquid ventilation (PLV) may benefit any lung disease but giving 30 mL/kg of perfluorocarbon when starting PLV increases cortical cerebral blood flow velocity. We aimed to determine if varying the initial dose of perfluorocarbon alters the effect on cerebral blood flow velocity when starting PLV.

METHODS

In this randomised, controlled trial with historical comparison 24 preterm lambs received one of three loading doses of intratracheal perfluorocarbon liquid over 20 min when starting PLV: 20, 30 or 40 mL/kg. Data on respiratory mechanics, haemodynamics and cerebral blood flow velocity, measured with laser Doppler, were collected continuously for 30 min from the start of dosing.

RESULTS

Cortical cerebral blood flow velocity increased over time in all three groups (two-way ANOVA, P= 0.007). There was no difference between groups (two-way ANOVA, P= 0.26). There was no difference between groups in cortical cerebral blood flow velocity variability (P= 0.68), blood pressure (P= 0.96) or heart rate (P= 0.46). The was no statistically significant difference in PaCO(2) between groups measured at baseline and at 30 min after starting PLV (P= 0.51).

CONCLUSIONS

  Cortical cerebral blood flow velocity and its variability are not affected by varying doses of tracheal perfluorocarbon (20, 30 or 40 mL/kg) at the start of PLV in preterm lambs.

Measurements of Evaporated Perfluorocarbon during Partial Liquid Ventilation by a Zeolite Absorber

During partial liquid ventilation (PLV) the knowledge of the quantity of exhaled perfluorocarbon (PFC) allows a continuous substitution of the PFC loss to achieve a constant PFC level in the lungs. The aim of our in vitro study was to determine the PFC loss in the mixed expired gas by an absorber and to investigate the effect of the evaporated PFC on ventilatory measurements.

METHOD

To simulate the PFC loss during PLV, a heated flask was rinsed with a constant airflow of 4 L min(-1) and PFC was infused by different speeds (5, 10, 20 mL h(-1)). An absorber filled with PFC selective zeolites was connected with the flask to measure the PFC in the gas. The evaporated PFC volume and the PFC concentration were determined from the weight gain of the absorber measured by an electronic scale. The PFC-dependent volume error of the CO2SMO plus neonatal pneumotachograph was measured by manual movements of a syringe with volumes of 10 and 28 mL with a rate of 30 min(-1).

RESULTS

Under steady state conditions there was a strong correlation (r2 = 0.999) between the infusion speed of PFC and the calculated PFC flow rate. The PFC flow rate was slightly underestimated by 4.3% (p < 0.01). However, this bias was independent from PFC infusion rate. The evaporated PFC volume was precisely measured with errors < 1%. The volume error of the CO2SMO-Plus pneumotachograph increased with increasing PFC content for both tidal volumes (p < 0.01). However for PFC flow rates up to 20 mL/h the error of the measured tidal volumes was < 5%.

CONCLUSIONS

PFC selective zeolites can be used to quantify accurately the evaporated PFC volume during PLV. With increasing PFC concentrations in the exhaled air the measurement errors of ventilatory parameters have to be taken into account.

Perfluorocarbon species and nebulizer type influence aerosolization rate and particle size of perfluorocarbon aerosol

PURPOSE

Aerosolization of perfluorocarbons (PFC) has been proven beneficial in vivo. The present in vitro study was performed to investigate, how PFC-aerosolization is affected by type of nebulizer and PFC properties.

MATERIALS AND METHODS

Aerosolization rate was studied of 4 different PFC that were nebulized using 3 different jet nebulizers (operating at different flows: 4.1; 7.1; 13 l/min) and one ultrasonic nebulizer. Distribution of aerosol particle size was determined with a laser diffraction device.

RESULTS

Between the studied nebulizers, considerable differences in the aerosolization rate were found. Aerosolization rate was significantly lower for PFOB (0.48-1.24 mL/min), when compared with PF 5080, RM 101 and FC 77 (1.33-4.75 mL/min). The ultrasonic nebulizer did not generate an aerosol but rather PFC vapor. Lowest mass median diameter (MMD) was found for PFOB and varied between the jet nebulizers from 2.2 and 3.7 microm, with a small range in particle size (maximum of 7.3 microm). FC 77 had highest MMD (3.5 to 9.2 microm) and greatest range of particle size of up to 13 microm.

CONCLUSIONS

Our in vitro data show that aerosolization rate depends mainly on density of PFC and the flow of nebulizer. Particle size distribution is affected by PFC properties. Our result may explain controversial results of published in vivo studies.

Changes in FiO2 affect PaO2 with minor alterations in cerebral concentration of oxygenated hemoglobin during liquid ventilation in healthy piglets

OBJECTIVE

To measure the impact of changes in the fraction of inspired oxygen (FiO2) on systemic and cerebral oxygen supply in gas and liquid ventilated healthy animals.

DESIGN

Interventional prospective animal study.

SETTING

University research laboratory.

PARTICIPANTS

Ten healthy, new-born piglets.

INTERVENTIONS

Variations in FiO2 during conventional mechanical ventilation (CMV) followed by partial liquid ventilation (PLV) with two different filling volumes of PF 5080 (10 vs. 30 ml/kg).

MEASUREMENTS AND RESULTS

Arterial blood gases were obtained 15 min after changing FiO2 and concentrations of cerebral oxygenated and total hemoglobin were determined with near infrared spectroscopy. During CMV an increase in FiO2 1.0 was associated with a constant rise in PaO2 but only a small increase in the cerebral concentration of oxygenated Hb. Initiation of PLV (at FiO2 of 1.0) caused a rapid drop in PaO2 towards values that were similar to CMV at FiO2 of 0.5. At FiO2 of 0.5 a reduction in oxygenated Hb was found in the 30 ml/kg filling group. Complete filling of the lungs with PFC caused a significant drop in total cerebral Hb concentration. CONCLUSIONS. According to our data, PLV in healthy lungs should be performed with a FiO2 of 1.0 and a small filling volume to avoid deterioration in cerebral oxygen supply.

Influence of partial liquid ventilation on bacterial growth and alveolar expansion in newborn rabbits with group B-streptococcal pneumonia

Partial liquid ventilation (PLV) with perfluorocarbons has been considered as an alternative therapy for severe inflammatory lung disease. The present study was performed to test whether PLV influences bacterial growth and lung histology in a rabbit model of congenital pneumonia caused by group B streptococci. Near-term newborn rabbits were tracheotomized, inoculated via the airways with group B streptococci, and subsequently ventilated for 5 h with either PLV or conventional ventilation. At 30 min after group B streptococci administration, animals in the PLV group (n = 16) received 30 mL/kg body weight of perfluorocarbon (PF 5080) via the tracheal tube. Evaporative losses were substituted with 20 mL/kg perfluorocarbon at hourly intervals. Identical volumes of air were injected in control animals at the same times (n = 15). The number of colony-forming units in left lung homogenate, evaluated at the end of the experiments, tended to be lower in PLV-treated animals than in controls (6.8 x 109 versus 6.4 x 1010 colony-forming units/g body weight; p = 0.06). Comparison of these numbers with the colony-forming units injected at the beginning of the experiments revealed a reduction in bacterial number in the PLV group and proliferation in the controls (-2.2 x 108 versus +5.6 x 1010 colony-forming units/g body weight; p < 0.05). Histologic examination demonstrated less inflammation and more homogeneous lung expansion in PLV-treated animals. Two animals in the PLV group had focal interstitial emphysema. Our results suggest that PLV with PF 5080 reduces bacterial proliferation in experimental group B streptococcal pneumonia.