[Effect of mechanical ventilation guided by transpulmonary pressure on hemodynamics and oxygen metabolism of porcine model of intra-abdominal hypertension]

Abstract

Objective: To assess the effect of mechanical ventilation (MV) guided by transpulmonary pressure (Ptp) on hemodynamics and oxygen metabolism of porcine model of intra-abdominal hypertension (IAH).

Methods: All 6 pigs were anesthetized and received MV. Volume-assist control was set: tidal volume (V(T)) was 10 ml/kg, respiratory rate (RR) was 16 bpm, inhaled oxygen concentration (FiO(2)) was 0.40 and positive end-expiratory pressure (PEEP) was set at 5 cm H(2)O (1 cm H(2)O=0.098 kPa). Following baseline observations, high intra-abdominal pressure (IAP) with intraperitoneal nitrogen inflation was induced in all 6 pigs. The IAP was increased to 25 mm Hg (1 mm Hg=0.133 kPa). Two hours later, PEEP was adjusted to such a level that Ptp during end-expiratory occlusion remained at a level above 0 cm H(2)O for 2 hours by measuring esophageal pressure, and with the rest parameters of breathing machine remaining constant. During the experimental period, hemodynamic parameters including heart rate (HR), mean arterial pressure (MAP), cardiac output index (CI), central venous pressure (CVP), pulmonary arterial wedge pressure (PAWP), and respiratory mechanics index of peak airway pressure (Ppeak), plateau pressure (Pplat), esophageal pressure (Pes) and static compliance (Cst) were continuously recorded with the aid of Swan-Ganz catheter and electrocardiogram. Oxygen partial pressure of arterial blood (PaO(2) ) and carbon dioxide partial pressure of arterial blood (PaCO(2)) were measured by blood-gas analysis. Systemic oxygen delivery (DO(2) )and systemic oxygen consumption(VO(2) )were calculated according to blood-gas analysis of arterial and central venous blood.

Results: No porcine model showed barotrauma and death. Compared with baseline, at 1 hour and 2 hours after induction of IAH in the animals, HR(bpm) increased significantly (134.3±5.8, 127.3±3.3 vs. 117.7±1.5). MAP(mm Hg), CVP (mm Hg) and PAWP (mm Hg) became higher (MAP:120.7±3.8, 117.3±4.8 vs. 100.4±6.6; CVP: 7.3±0.3, 7.6±0.9 vs. 5.6±0.2; PAWP: 14.0±0.6, 14.0±1.0 vs. 12.3±0.3), CI (L×min(-1)×kg(-1)) was lowered (0.150±0.019, 0.137±0.014 vs. 0.179±0.021), Ppeak(cm H(2)O), Pplat (cm H(2)O), Pes (cm H(2)O) were increased significantly (Ppeak: 46.3±2.3, 47.0±3.2 vs. 11.0±1.6; Pplat: 25.7±1.3, 26.0±1.6 vs. 9.0±0.6; Pes: 13.7±0.3, 14.3±0.3 vs. 2.3±0.3), Cst (ml/cm H(2)O), PaO(2) (mm Hg) and DO(2) (ml×min(-1)×kg(-1)) showed significant lowering (Cst: 8.3±0.3, 9.0±0.6 vs. 23.0±1.6; PaO(2) : 142.0±13.2, 140.0±16.0 vs. 166.3±11.3; DO(2) : 19.40±2.90, 19.88 ±4.14 vs. 25.07±6.30, all P<0.05).However, compared to routine ventilation, at 1 hour and 2 hours after PEEP had been adjusted according to measurements of esophageal pressure, PaO(2) , DO(2) and Cst increased significantly (PaO(2) : 161.6±11.9, 164.0±13.6; DO(2) : 21.90±6.21, 21.16±2.78; Cst: 12.0±1.6, 12.7±2.9). CI became lower (0.121±0.013, 0.120±0.012)and Pplat was higher(31.3±3.4, 31.7±3.2, all P<0.05). The lactate (mmol/L) was also decreased significantly (1.60±0.12 vs. 2.70±0.44, 1.67±0.07 vs. 2.27±0.13, both P<0.05). PaCO(2), HR, MAP, CVP and PAWP showed no significant differences compared to IAH pigs ventilated with lower PEEP (all P>0.05).

Conclusion: There were remarkable effects on oxygen metabolism and Cst and less influence on hemodynamics in response to MV guided by Ptp. The results of this study are in favor of setting Ptp according to measurements of esophageal pressure in pigs with IAH.