Intensive Care Med (1995) 21:6 9 Springer-Verlag 1995 L. Torelli G. Zoccali M. Casarin E Dalla Zuanna E. Lieta G. Conti Comparative evaluation of the haemodynamic effects of continuous negative external pressure (CNEP) and positive end-expiratory pressure (PEEP)in mechanically ventilated trauma patients Received: 3 February 1993 Accepted: 14 December 1993 L. Torelli (~) 9 G. Zoccali 9 M. Casarin E Dalla Zuanna 9 E. Lieta Department of Anesthesia and Intensive Care, Vicenza Hospital, 1-36100 Vicenza, Italy G. Conti Department of Intensive Care, University of Rome "La Sapienza", Rome, Italy Abstract Objective: To compare the haemodynamic effects of identi- cal values of continuous negative external pressure (CNEP) and posi- tive end-expiratory pressure (PEEP) in a group of mechanically ventilat- ed patients 9 Setting: General ICU, Vicenza Hos- pital, Italy. Patients: 15 consecutive patients, admitted after road accident trauma. Methods: We compared the haemodynamic effects of ZEEP, 10 cmH20 of PEEP, and 10 cmH20 CNEP, applied in random order, in 15 head trauma patients under go- ing controlled mechanical ventila- tion; 9 had associated thoracic trau- ma, while 6 did not have lung in- volvement. CNEP was obtained with a "poncho". Results: We observed a significant increase in CI during CNEP, com- pared with both ZEEP and PEEP 10 cmH20. Accordingly the oxygen delivery index significantly increased during CNEP, compared with PEEP 10 cmH20. Conversely, Qs/O.t de- creased with CNEP, if compared with PEEP, both in patients with and without lung damage. Conclusion: CNEP can significantly increase CI in mechanically venti- lated patients in patients with and without associated lung damage. Key words Mechanical ventilation 9PEEP 9 CNEP 9 Poncho 9 Trauma introduction A reduction in lung volume represents the main anatomi- cal and functional characteristic during acute respiratory failure of parenchymal origin. In this condition, arterial oxygen saturation can be increased by augmenting mean airway pressure (by PEEP or CPAP administration) due to a consequent increase of functional residual capacity (FRC) [1]. Conversely, venous return to the heart and car- diac output cannot withstand an increase of airways pres- sure particularly in hypovolemic patients [2]. In order to increase arterial oxygen pressure (PaO2) with less detrimental haemodynamic effects, many au- thors have proposed ventilatory approaches, such as "best" PEEP, moderating the negative consequences on the circulation of continuous positive airways pressure [3]. Considering that FRC is a function of a transpulmo- nary gradient that can be increased either by higher air- ways pressure or by decreasing pleural pressure, it is con- sequent that a negative perithoracic (and abdominal) pressure can increase FRC by decreasing pleural pressure [4, 5]. For many years it has been known that continuous negative external pressure (CNEP) affecting only the thoracoabdominal area and not the whole body (as in tank-type respirators) causes a better venous return to the heart by increasing the peripheral-pleural pressure gradi- ent [5 -7]. The introduction into clinical use of simple de- vices called "ponchos", to provide CNEP, induced us to compare the effects of identical absolute values of PEEP and CNEP on haemodynamic and oxygenation variables in patients mechanically ventilated in control mode.