J. B. Zwischenberger

Immediate positive pressure ventilation with positive end-expiratory pressure (PEEP) improves survival in ovine smoke inhalation injury

BACKGROUNDnThe purpose of this study was to compare the effects of immediate initiation of positive pressure ventilation (PPV) with positive end-expiratory pressure (PEEP) versus the initiation of PPV with PEEP only after hypoxemia ensued following severe smoke inhalation injury.nnnMETHODSnWe prospectively evaluated chronically instrumented adult sheep treated with immediate versus delayed PPV with PEEP and compared oxygen requirements, hemodynamics, pleural fluid formation, postinjury survival, and tracheobronchial pathologic processes among groups. The immediate group (group I; smoke, n = 6; sham, n = 2) underwent tracheostomy and bilateral chest tube placement before they received inhalation injury. They were then immediately placed on PPV with PEEP (12 cm H2O). The animals in the delayed group (group D) (n = 6) were placed on PPV with PEEP when arterial hypoxemia (PaO2 < 80 mm Hg [11.2 kPa] on 0.4 FIO2) or respiratory distress developed.nnnRESULTSnGroups were matched for smoke exposure and peak carboxyhemoglobin. Both groups developed a characteristic decrease in PaO2/FIO2 ratio. Initiation of PPV + PEEP improved PaO2 in the delayed group (69 +/- 7 to 126 +/- 21 mm Hg [9.2 +/- 0.9 to 16.7 +/- 2.8 kPa]). Pleural fluid output was greater in the immediate group compared with the delayed group (1559 +/- 415 vs. 426 +/- 236 mL). At 96 hours after injury five of six animals in the delayed group had died. In contrast, six of six animals in the immediate smoke group survived 96 hours (p < 0.05 versus delayed group). The immediate group had fewer and less extensive tracheobronchial casts at necropsy.nnnCONCLUSIONSnImmediate PPV + PEEP did not prevent the development of hypoxia and was associated with increased pleural fluid formation. Death within 96 hours in the delayed group was the result of respiratory failure aggravated by bronchial cast formation despite vigorous pulmonary toilet. Early positive pressure ventilation with PEEP, preferably initiated immediately after the inhalation insult, significantly increases short-term survival and is associated with decreased tracheobronchial cast formation in this ovine model of severe smoke inhalation injury.

Cerebral autoregulation and gas exchange studied using a human cardiopulmonary model

We have previously developed a model of human cardiopulmonary (CP) system, which included the whole body circulatory system, gas exchange at both lungs and peripheral tissue, and central nervous control of arterial pressure and ventilation. We now add a more detailed description of cerebral circulation, cerebrospinal fluid (CSF) dynamics and brain gas exchange. Two cerebral blood flow (CBF) regulatory mechanisms are included: autoregulation and CO/sub 2/ reactivity. The cerebral model is first validated in an open-loop configuration using input data generated by the cardiopulmonary model as inputs, then is integrated into the CP model to form an integrated CP model. It is this integrated model that we used to study the response to thigh cuff experiment. Our model demonstrated the ability to closely mimic the experimental findings and to provide predictions regarding the state of cerebral autoregulation and brain tissue gas-exchange. With further refinement, it may serve as a useful tool in clinical evaluation of the cerebral autoregulation and brain oxygenation.