Peritoneal ventilation: an animal model of extrapulmonary ventilation in experimental adult respiratory distress syndrome

Exploring alternative routes for oxygen administration

Background

Hypoxemia may compromise cell metabolism and organ function. Supplemental oxygen (O₂) at high concentrations may prove ineffective, and issues relating to hyperoxia, barotrauma, mechanical ventilation, and extracorporeal oxygenation are well documented. Old reports suggest the potential safety and efficacy of alternative routes for O₂ administration, such as intravenous or intestinal. We re-explored these routes in rat models of hypoxemia.

Methods

Hypoxemia was induced in spontaneously breathing, anesthetized rats by breathing a hypoxic gas mix (FiO₂ 0.1). Pilot studies infusing pure O₂ gas caused early death, likely due to pulmonary embolism. Instead, rats (n = 6/group) were given intravenous O₂ via a continuous infusion of pre-oxygenated Hartmann’s solution (10 ml/kg/h) for 3 h with normal Ringer’s lactate used in control animals. In separate experiments (n = 8/group), bowel intraluminal oxygenation was assessed with pure O₂ administered through a cannula placed into the jejunal lumen at a dose of a 15 ml/kg bolus followed by a continuous infusion of 50 ml/kg/h; no treatment was given to controls. Echocardiography, arterial blood gas analysis, mean arterial pressure, muscle and liver tPO₂, muscle microvascular perfused vessel density, and urine output were measured.

Results

Administration of oxygenated Hartmann’s solution (PO₂ of solution at end-experiment = 87.5 ± 1.7 kPa) was safe but did not increase either systemic or tissue oxygenation. Similarly, the administration of bowel O₂ was safe but did not improve neither systemic nor liver oxygenation.

Conclusions

In this rat model of hypoxemia, the intravenous infusion of gaseous O₂ was unfeasible as it induced early mortality. Although safe, both intravenous infusion of oxygenated Hartmann’s solution and bowel O₂ administration were unable to improve arterial or tissue oxygenation.

Systemic oxygen delivery by peritoneal perfusion of oxygen microbubbles

Severe hypoxemia refractory to pulmonary mechanical ventilation remains life-threatening in critically ill patients. Peritoneal ventilation has long been desired for extrapulmonary oxygenation owing to easy access of the peritoneal cavity for catheterization and the relative safety compared to an extracorporeal circuit. Unfortunately, prior attempts involving direct oxygen ventilation or aqueous perfusates of fluorocarbons or hemoglobin carriers have failed, leading many researchers to abandon the method. We attribute these prior failures to limited mass transfer of oxygen to the peritoneum and have designed an oxygen formulation that overcomes this limitation. Using phospholipid-coated oxygen microbubbles (OMBs), we demonstrate 100% survival for rats experiencing acute lung trauma to at least 2 h. In contrast, all untreated rats and rats treated with peritoneal oxygenated saline died within 30 min. For rats treated with OMBs, hemoglobin saturation and heart rate were at normal levels over the 2-h timeframe. Peritoneal oxygenation with OMBs was therefore shown to be safe and effective, and the method requires less equipment and technical expertise than initiating and maintaining an extracorporeal circuit. Further translation of peritoneal oxygenation with OMBs may provide therapy for acute respiratory distress syndrome arising from trauma, sepsis, pneumonia, aspiration, burns and other pulmonary diseases.

Peritoneal perfusion with oxygenated perfluorocarbon augments systemic oxygenation

Background

Despite maximal ventilatory support, many patients die from hypoxia in the setting of potentially reversible pulmonary failure. There remains a pressing need for additional pulmonary supportive care measures, especially techniques that do not require systemic anticoagulation. The objective of our experiments was to determine whether systemic oxygenation could be increased in a large animal, with induced hypoxia, by perfusing the abdominal cavity with oxygenated perfluorocarbons.

Methods

Fifteen pigs with a mean (± SD) weight of 45 ± 5 kg were intubated and rendered hypoxic by ventilating them with a blend of nitrogen and oxygen to achieve subatmospheric concentrations of inspired oxygen ranging from 18 to 10%, resulting in baseline mean Pao₂ range of 65.9 ± 9.7 to 26.6 ± 2.8 mm Hg, respectively. Peritoneal perfusion was performed in eight animals with oxygenated perfluorocarbon and in seven control animals with oxygenated saline solution.

Results

The average increase in Pao₂ with oxygenated perfluorocarbon perfusion, compared to oxygenated saline solution perfusion, ranged from 8.1 to 18.2 mm Hg. A common treatment effect was estimated across all fraction of inspired oxygen (Fio₂) values, representing the average mean difference in oxygen uptake between oxygenated perfluorocarbon and saline solution, irrespective of the level of Fio₂. This average was 12.8 mm Hg (95% confidence interval, 7.4 to 18.2; p < 0.001). The most clinically relevant results occurred at an Fio₂ of 14%, resulting in a baseline mean Pao₂ of 39.4 ± 5.0 mm Hg with oxygenated saline solution perfusion, and a mean Pao₂ of 55.3 ± 7.6 mm Hg with oxygenated perfluorocarbon perfusion. This corresponded to an increase in arterial oxygen saturation from 73 to 89%.

Conclusion

These results of our principle experiments demonstrate that the peritoneal cavity can be used for gas exchange and, in our model, yielded clinically relevant increases in systemic arterial oxygen levels. This technique may have the potential for the supportive care of patients dying from hypoxia in the setting of reversible lung injury.

Peritoneal ventilation with oxygen improves outcome after hemorrhagic shock in rats

OBJECTIVE

In experimental pulmonary consolidation with hypoxemia in rabbits, peritoneal ventilation (PV) with 100% oxygen (PV-O2) improved PaO2. We hypothesized that PV-O2 could improve outcome after hemorrhagic shock (HS) with normal lungs, by mitigating dysoxia of the abdominal viscera.

DESIGN

Randomized, controlled, laboratory animal study.

SETTING

University animal research facility.

SUBJECTIVE

Male Sprague-Dawley rats.

INTERVENTIONS

Thirty rats under light anesthesia (N2O/oxygen plus halothane) and spontaneous breathing underwent blood withdrawal of 3 mL/100 g over 15 mins. After volume-controlled HS phase 1 of 60 mins, resuscitation phase 2 of 60 mins included infusion of shed blood and, if necessary, additional lactated Ringer's solution intravenously to control normotension from 60 to 120 mins. This was followed by observation phase 3 for 7 days. We randomized three groups of ten rats each: group I received PV-O2, starting at 15 mins of HS at a rate of 40 inflations/min, and a peritoneal "tidal volume" of 6 mL, until the end of phase 2. Group II received the same PV with room air (PV-Air). Control group III was treated without PV.

MEASUREMENTS AND MAIN RESULTS

During the second half of HS phase 1, mean arterial pressures were higher in the PV-O2 group I compared with the PV-Air group II and control group III (p < .05). All 30 rats survived the 120 mins of phases 1 and 2. Survival to 7 days was achieved by ten of ten rats in PV-O2 group I; by nine of ten in PV-Air group II; and by five of ten in control group III (p < .05 vs. group I; NS vs. group II). Survival times of <7 days were 5 days in the one death of group II and ranged between 6 hrs and 4 days in the five deaths of group III. In 7-day survivors, neurologic deficit scores (0% to 10% = normal, 100% = death) were normal, ranging between zero and 8%. Necropsies of rats that died during phase 3 showed multiple areas of necrosis of the gut, some with perforations. Necropsies in the five survivors to 7 days of group III showed marked macroscopic and microscopic changes (scattered areas of necrosis of stomach and intestine, adhesions, and pale areas in the liver). These changes were absent or less severe in the nine survivors of group II. Viscera appeared normal in all ten rats of PV-O2 group I.

CONCLUSIONS

Peritoneal ventilation with oxygen during and after severe hemorrhagic shock in rats seems to decrease morbidity and mortality by helping preserve viability of abdominal viscera.

Oxygen uptake during peritoneal ventilation in a porcine model of hypoxemia

OBJECTIVES

Peritoneal ventilation (PV) can greatly increase PaO2 in hypoxemic rabbits. We tested the hypothesis that the peritoneum can provide a gas exchange surface for oxygen uptake in larger animals that, like humans, have a smaller relative peritoneal surface area and corresponding blood flow.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University research laboratory.

INTERVENTIONS

In six anesthetized pigs, a modified endotracheal tube (9.0-inner diameter) was inserted into the peritoneal cavity, and the peritoneal cavity was ventilated with oxygen in helium in gas phase. Measurements of peritoneal oxygen uptake and mixed venous oxygen saturation were made over 30 mins of: a) baseline FiO2 0.20, no PV; b) FiO2 0.20, PV; c) FiO2 0.20, PV, dopamine 5 microg/kg/min; d) baseline FiO2 0.15, no PV; e) FiO2 0.15, PV; and f) FiO2 0.15, PV, dopamine 5 microg/kg/min.

MEASUREMENTS AND MAIN RESULTS

Mixed venous oxygen saturation was 61% at the baseline FiO2 of 0.20 and 33% at an FiO2 of 0.15 and did not increase significantly from baseline with PV or with dopamine at either FiO2. Peritoneal oxygen uptake, measured with a waterseal spirometer, was 9.1+/-3.1 (SD) and 11.9+/-3.0 mL/min when lung FiO2 was 0.20 and 0.15, respectively, and 9.7+/-2.8 and 12.2+/-2.7 mL/min when FiO2 was 0.20 and 0.15 and dopamine was infused, respectively.

CONCLUSION

Peritoneal ventilation does not result in clinically significant oxygen uptake or alter mixed venous oxygen saturation in a porcine model of hypoxemia.

Peritoneal ventilation in rabbits: augmentation of gas exchange with cisapride

BACKGROUND

Peritoneal ventilation has been shown to be effective in achieving extrapulmonary oxygenation and carbon dioxide elimination in an animal model of severe adult respiratory distress syndrome (ARDS). Cisapride is a "prokinetic" agent (increases gastric emptying), that may increase the splanchnic circulation and thus favourably affect gas exchange in peritoneal ventilation.

METHODS

Using Doppler ultrasound the effect of cisapride on the portal venous circulation was examined in eight spontaneously breathing rabbits and the effect of cisapride on gas exchange in five rabbits spontaneously breathing room air was compared with that of a control group who did not receive cisapride. Its effect on gas exchange in five rabbits with ARDS being treated with mechanical lung and peritoneal ventilation was compared with that of a control group, and its effect on gas exchange in five rabbits with ARDS treated with conventional ventilation was also compared with that of a control group.

RESULTS

Enteral administration of cisapride increased portal venous blood velocity, as measured ultrasonographically, by a mean of 188% one hour after receiving the drug. In rabbits with ARDS being treated with both peritoneal ventilation and mechanical ventilation to the lungs, those receiving cisapride had arterial oxygen tensions 1.5-3 times that of controls. Cisapride had no effect on arterial blood gas tensions in rabbits who were spontaneously breathing room air, nor in rabbits with ARDS who received only conventional mechanical lung ventilation.

CONCLUSIONS

Cisapride increases arterial oxygenation in rabbits with severe ARDS treated with peritoneal ventilation, probably due to its ability to increase splanchnic circulation. It should be considered as an adjuvant medication to peritoneal ventilation.