Relationship between Abdominal Pressure, Pulmonary Compliance, and Cardiac Preload in a Porcine Model

Sánchez-Margallo F, Eugenia Candanosa-Aranda I, Poelaert J, Castellanos G, L. N. G. Malbrain M. The pathophysiological impact of intra-abdominal hypertension in pigs

BACKGROUND

Intra-abdominal hypertension and abdominal compartment syndrome are common with clinically significant consequences. We investigated the pathophysiological effects of raised IAP as part of a more extensive exploratory animal study. The study design included both pneumoperitoneum and mechanical intestinal obstruction models.

METHODS

Forty-nine female swine were divided into six groups: a control group (Cr; n = 5), three pneumoperitoneum groups with IAPs of 20mmHg (Pn20; n = 10), 30mmHg (Pn30; n = 10), 40mmHg (Pn40; n = 10), and two mechanical intestinal occlusion groups with IAPs of 20mmHg (MIO20; n = 9) and 30mmHg (MIO30; n = 5).

RESULTS

There were significant changes (p<0.05) noted in all organ systems, most notably systolic blood pressure (SBP) (p<0.001), cardiac index (CI) (p = 0.003), stroke volume index (SVI) (p<0.001), mean pulmonary airway pressure (MPP) (p<0.001), compliance (p<0.001), pO2 (p = 0.003), bicarbonate (p = 0.041), hemoglobin (p = 0.012), lipase (p = 0.041), total bilirubin (p = 0.041), gastric pH (p<0.001), calculated glomerular filtration rate (GFR) (p<0.001), and urine output (p<0.001). SVV increased progressively as the IAP increased with no obvious changes in intravascular volume status. There were no significant differences between the models regarding their impact on cardiovascular, respiratory, renal and gastrointestinal systems. However, significant differences were noted between the two models at 30mmHg, with MIO30 showing worse metabolic and hematological parameters, and Pn30 and Pn40 showing a more rapid rise in creatinine.

CONCLUSIONS

This study identified and quantified the impact of intra-abdominal hypertension at different pressures on several organ systems and highlighted the significance of even short-lived elevations. Two models of intra-abdominal pressure were used, with a mechanical obstruction model showing more rapid changes in metabolic and haematological changes. These may represent different underlying cellular and vascular pathophysiological processes, but this remains unclear.

NO-Donation Increases Visceral Circulation in a Porcine Model of Abdominal Hypertension

Intraabdominal hypertension (IAH) is negative for outcome after intensive care. Little research has focused on medical intervention to improve visceral circulation during IAH. A nitric oxide (NO)-donor was compared with placebo in 25 pigs; each pig was randomized into three groups: PDNO (NO-donor), Control (placebo), or Sham. IAH was induced by CO2 insufflation to 30 mmHg. Sham group had surgical preparation only. Blood gases, invasive venous and arterial blood pressure, intestinal microcirculation and superior mesenteric blood flow were measured. The PDNO group had significantly increased intestinal microcirculation compared with Controls during IAH (last hour, P = 0.009). The mean arterial pressure and abdominal perfusion pressures (APP) were decreased, and the cardiac index were increased in the PDNO group. Also, systemic and pulmonary vascular resistances were lower in the PDNO group compared with Controls. These experimental findings indicate that NO should be further explored with potential application to improve intestinal microcirculation in IAH patients.

Laparoscopic versus Open Ovariectomy in Bitches: Changes in Cardiorespiratory Values, Blood Parameters, and Sevoflurane Requirements Associated with the Surgical Technique

The aim of this study was to examine the cardiorespiratory and blood changes associated with pneumoperitoneum (PNP) in laparoscopic ovariectomy (LAP Ove), as well as sevoflurane requirements, comparing them to those determined in open surgery (LPT Ove). The study was performed in 16 bitches submitted to LAP or LPT Ove. The cardiorespiratory and end-tidal sevoflurane concentration values were recorded as follows: at the beginning of surgery (T1), after the right ovary resection (T2), after the left ovary resection (T3), and after surgical closure (T4). Blood samples were taken before and after PNP. Among the cardiorespiratory parameters, no differences were observed in the values of end-tidal CO2, minute volume, and heart rate. In the LAP Ove group, a significant increase in inspiratory pressures and a decreased compliance were identified at T2 and T3. Significant higher arterial pressure values were observed in both groups at T2 and T3, with this increase especially marked at T2 in the LPT Ove group. Sevoflurane requirements were significantly higher in the LPT group during ovarian resection. Finally, in terms of the hematochemical parameters, statistical differences were recorded between pre- and post-operative assessments, but not between both surgical groups. The pathophysiological effects associated with PNP seemed to be transient and well-tolerated by healthy dogs.

Pressure-Volume Curve during Capnoperitoneum in Cats

Laparoscopy is a growing field in veterinary medicine, although guidelines are lacking. The objective of this study was to evaluate the pressure-volume curve during capnoperitoneum in cats. A total of 59 female cats were scheduled for routine laparoscopy. Pressure and volume data were recorded and processed, and the yield point of the curve was calculated using a method based on a capacitor discharging function. For the remaining 40 cats, a linear-like pressure-volume curve was observed until a yield point with a mean cutoff pressure (COP) of 6.44 ± 1.7 mmHg (SD) (range, 2.72-13.00 mmHg) and a mean cutoff volume (COV) of 387 ± 144.35 mL (SD) (range, 178.84-968.43 mL) was reached. The mean mL/kg CO₂ value in cats was 208 ± 34.69 mL/kg (range, 100.00-288.46 mL/kg). The COV correlated with COP and body weight but not with body condition score (BCS). COP correlated only with the COV. This study suggests that feline patients have a pressure-volume curve similar to that of canine patients, and the same pressure limit recommendations can be used for both species. After a yield point of 6.44 mmHg is reached, the increment in volume decreases exponentially as the intra-abdominal pressure (IAP) increases.

Effect of moderate elevated intra-abdominal pressure on lung mechanics and histological lung injury at different positive end-expiratory pressures

INTRODUCTION

Intra-abdominal hypertension (IAH) is a well-known phenomenon in critically ill patients. Effects of a moderately elevated intra-abdominal pressure (IAP) on lung mechanics are still not fully analyzed. Moreover, the optimal positive end-expiratory pressure (PEEP) in elevated IAP is unclear.

METHODS

We investigated changes in lung mechanics and transformation in histological lung patterns using three different PEEP levels in eighteen deeply anesthetized pigs with an IAP of 10 mmHg. After establishing the intra-abdominal pressure, we randomized the animals into 3 groups. Each of n = 6 (Group A = PEEP 5, B = PEEP 10 and C = PEEP 15 cmH2O). End-expiratory lung volume (EELV/kg body weight (bw)), pulmonary compliance (Cstat), driving pressure (ΔP) and transpulmonary pressure (ΔPL) were measured for 6 hours. Additionally, the histological lung injury score was calculated.

RESULTS

Comparing hours 0 and 6 in group A, there was a decrease of EELV/kg (27±2 vs. 16±1 ml/kg; p<0.05) and of Cstat (42±2 vs. 27±1 ml/cmH2O; p<0.05) and an increase of ΔP (11±0 vs. 17±1 cmH2O; p<0.05) and ΔPL (6±0 vs. 10±1 cmH2O; p<0.05). In group B, there was no significant change in EELV/kg (27±3 vs. 24±3 ml/kg), but a decrease in Cstat (42±3 vs. 32±1 ml/cmH20; p<0.05) and an increase in ΔP (11±1 vs. 15±1 cmH2O; p<0.05) and ΔPL (5±1 vs. 7±0 cmH2O; p<0.05). In group C, there were no significant changes in EELV/kg (27±2 vs. 29±3 ml/kg), ΔP (10±1 vs. 12±1 cmH2O) and ΔPL (5±1 vs. 7±1 cmH2O), but a significant decrease of Cstat (43±1 vs. 37±1 ml/cmH2O; p<0.05). Histological lung injury score was lowest in group B.

CONCLUSIONS

A moderate elevated IAP of 10 mmHg leads to relevant changes in lung mechanics during mechanical ventilation. In our study, a PEEP of 10 cmH2O was associated with a lower lung injury score and was able to overcome the IAP induced alterations of EELV.

Ventilation in patients with intra-abdominal hypertension: what every critical care physician needs to know

The incidence of intra-abdominal hypertension (IAH) is high and still underappreciated by critical care physicians throughout the world. One in four to one in three patients will have IAH on admission, while one out of two will develop IAH within the first week of Intensive Care Unit stay. IAH is associated with high morbidity and mortality. Although considerable progress has been made over the past decades, some important questions remain regarding the optimal ventilation management in patients with IAH. An important first step is to measure intra-abdominal pressure (IAP). If IAH (IAP > 12 mmHg) is present, medical therapies should be initiated to reduce IAP as small reductions in intra-abdominal volume can significantly reduce IAP and airway pressures. Protective lung ventilation with low tidal volumes in patients with respiratory failure and IAH is important. Abdominal-thoracic pressure transmission is around 50%. In patients with IAH, higher positive end-expiratory pressure (PEEP) levels are often required to avoid alveolar collapse but the optimal PEEP in these patients is still unknown. During recruitment manoeuvres, higher opening pressures may be required while closely monitoring oxygenation and the haemodynamic response. During lung-protective ventilation, whilst keeping driving pressures within safe limits, higher plateau pressures than normally considered might be acceptable. Monitoring of the respiratory function and adapting the ventilatory settings during anaesthesia and critical care are of great importance. This review will focus on how to deal with the respiratory derangements in critically ill patients with IAH.

Large-volume paracentesis effects plasma disappearance rate of indo-cyanine green in critically ill patients with decompensated liver cirrhosis and intraabdominal hypertension

BACKGROUND

Ascites is a major complication of decompensated liver cirrhosis. Intraabdominal hypertension and structural alterations of parenchyma involve decisive changes in hepatosplanchnic blood flow. Clearance of indo-cyanine green (ICG) is mainly dependent on hepatic perfusion and hepatocellular function. As a consequence, plasma disappearance rate of ICG (ICG-PDR) is rated as a useful dynamic parameter of liver function. This study primarily evaluates the impact of large-volume paracentesis (LVP) on ICG-PDR in critically ill patients with decompensated cirrhosis. Additionally, it describes influences on intraabdominal pressure (IAP), abdominal perfusion pressure (APP), hepatic blood flow, hemodynamic and respiratory function.

METHODS

We analyzed LVP in 22 patients with decompensated liver cirrhosis. ICG-PDR was assessed by using noninvasive LiMON technology (Pulsion® Medical Systems; Maquet Getinge Group), and hepatic blood flow was analyzed by color-coded duplex sonography.

RESULTS

Paracentesis of a median volume of 3450 mL ascites evoked significant increases of ICG-PDR from 3.6 (2.8-4.6) to 5.1 (3.9-6.2)%/min (p < 0.001). Concomitantly, we observed a raise in "ICG-Clearance" from 99 (73.5-124.5) to 104 (91-143.5) mL/min/m2 (p = 0.005), while circulating blood volume index was unchanged [2412 (1983-3025) before paracentesis vs. 2409 (1997-2805) mL/m2, p = 0.734]. Sonography revealed a significant impact of paracentesis on hepatic blood flow: Hepatic artery resistance index dropped from 0.74 (0.68-0.75) to 0.68 (0.65-0.71) (p < 0.001) and maximum flow velocity in hepatic vein increased from 24 (17-30) to 30 (22-36) cm/s (p < 0.001). Consistent with previous studies, paracentesis caused significant decreases in IAP from 19.0 (15.0-20.3) to 11.0 (8.8-12.3) mmHg (p < 0.001) and central venous pressure from 22.5 (17.8-29.0) to 17.5 (12.8-24.0) mmHg (p < 0.001) with inverse increases in APP from 63.0 (56.8-69.5) to 71.0 (65.5-78.5) mmHg (p < 0.001). Changes in ICG-PDR were concomitant with changes in IAP (r = - 0.602) and APP (r = 0.576). Moreover, we found a substantial improvement in respiratory function. By contrast, hemodynamic parameters assessed by transpulmonary thermodilution, serum bilirubin and international normalized ratio did not change after paracentesis.

CONCLUSION

Critically ill patients with decompensated cirrhosis and elevated IAP showed dramatically impaired ICG-PDR. Paracentesis evoked an improvement in ICG-PDR in parallel with a decreased IAP and an increased APP, while conventional parameters of liver function did not change. This effect on ICG-PDR is mainly referable to a relief of intraabdominal hypertension and changes in hepatosplanchnic blood flow.

Impact of large volume paracentesis on respiratory parameters including transpulmonary pressure and on transpulmonary thermodilution derived hemodynamics: A prospective study

Introduction

Appropriate mechanical ventilation and prevention of alveolar collaps is mainly dependent on transpulmonary pressure TPP. TPP is assessed by measurement of esophageal pressure EP, largely influenced by pleural and intraabdominal pressure IAP. Consecutively, TPP-guided ventilation might be particularly useful in patients with high IAP.

This study investigates the impact of large volume paracentesis LVP on TPP, EP, IAP as well as on hemodynamic and respiratory function in patients with liver cirrhosis and tense ascites.

Material and methods

We analysed 23 LVP-procedures in 11 cirrhotic patients ventilated with the AVEA Viasys respirator (CareFusion, USA) which is capable to measure EP via an esophageal tube.

Results

LVP of a mean volume of 4826±1276 mL of ascites resulted in marked increases in inspiratory (17.9±8.9 vs. 5.4±13.3 cmH₂O; p<0.001) as well as expiratory TPP (-3.0±4.7 vs. -15.9±10.9 cmH₂O; p<0.001; primary endpoint). In parallel, the inspiratory (2.4±8.7 vs. 14.1±14.5 cmH₂O; p<0.001) and expiratory EP (12.4±6.0 vs. 24.9±11.3 cmH₂O; p<0.001) significantly decreased. The effects were most pronounced for the release of the first 500 mL of ascites. LVP evoked substantial decreases in IAP and central venous pressure CVP. By contrast, mean arterial pressure, cardiac index, global end-diastolic volume index, extravascular lung water index and systemic vascular resistance index did not change.

Among the respiratory parameters we observed an increase in p_aO₂/F_iO₂ (247.7±60.9 vs. 208.3±46.8 mmHg; p<0.001) and a decrease in Oxygenation Index OI (4.8±2.0 vs. 5.8±3.1 cmH₂O/mmHg; p = 0.002). Tidal volume (510±100 vs. 452±113 mL; p = 0.008) and dynamic respiratory system compliance C_dyn (46.8±15.9 vs. 35.1±14.6 mL/cmH₂0; p<0.001) increased, whereas p_aCO₂ (47.3±10.7 vs. 51.2±12.3mmHg; p = 0.046) and the respiratory rate decreased (17.1±7.3 vs. 19.6±7.8 min^-1; p = 0.010).

Conclusions

In mechanically ventilated patients with decompensated cirrhosis, intraabdominal hypertension resulted in a substantially decreased TPP despite PEEP-setting according to the ARDSNet.

In these patients LVP markedly increased TPP and improved respiratory function in parallel with a decline of EP. Furthermore, LVP induced a decrease in IAP and CVP, while other hemodynamic parameters did not change.

The neglected role of abdominal compliance in organ-organ interactions

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency medicine 2016. Other selected articles can be found online at http://www.biomedcentral.com/collections/annualupdate2016. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Intra-abdominal pressure correlates with extracellular water content

Background

Secondary increase in intra-abdominal pressure (IAP) may result from extra-abdominal pathology, such as massive fluid resuscitation, capillary leak or sepsis. All these conditions increase the extravascular water content. The aim of this study was to analyze the relationship between IAP and body water volume.

Material and Methods

Adult patients treated for sepsis or septic shock with acute kidney injury (AKI) and patients undergoing elective pharyngolaryngeal or orthopedic surgery were enrolled. IAP was measured in the urinary bladder. Total body water (TBW), extracellular water content (ECW) and volume excess (VE) were measured by whole body bioimpedance. Among critically ill patients, all parameters were analyzed over three consecutive days, and parameters were evaluated perioperatively in surgical patients.

Results

One hundred twenty patients were studied. Taken together, the correlations between IAP and VE, TBW, and ECW were measured at 408 time points. In all participants, IAP strongly correlated with ECW and VE. In critically ill patients, IAP correlated with ECW and VE. In surgical patients, IAP correlated with ECW and TBW. IAP strongly correlated with ECW and VE in the mixed population. IAP also correlated with VE in critically ill patients. ROC curve analysis showed that ECW and VE might be discriminative parameters of risk for increased IAP.

Conclusion

IAP strongly correlates with ECW.

Effects of paracentesis on hemodynamic parameters and respiratory function in critically ill patients

BACKGROUND

Ascites is a major and common complication of liver cirrhosis. Large or refractory ascites frequently necessitates paracentesis. The aim of our study was to investigate the effects of paracentesis on hemodynamic and respiratory parameters in critically ill patients.

METHODS

Observational study comparing hemodynamic and respiratory parameters before and after paracentesis in 50 critically ill patients with advanced hemodynamic monitoring. 28/50 (56%) required mechanical ventilation.Descriptive statistics are presented as mean ± standard deviation for normally distributed data and median, range, and interquartile range (IQR) for non-normally distributed data. Comparisons of hemodynamic and respiratory parameters before and after paracentesis were performed by Wilcoxon signed-rank tests. Bivariate relations were assessed by Spearman's correlation coefficient and univariate regression analyses.

RESULTS

Median amount of ascites removed was 5.99 L (IQR, 3.33-7.68 L). There were no statistically significant changes in hemodynamic parameters except a decrease in mean arterial pressure (-7 mm Hg; p = 0.041) and in systemic vascular resistance index (-116 dyne·sec/cm5/m2; p = 0.016) when measured 2 hours after paracentesis. In all patients, oxygenation ratio (PaO2/FiO2; median, 220 mmHg; IQR, 161-329 mmHg) increased significantly when measured immediately (+58 mmHg; p = 0.001), 2 hours (+9 mmHg; p = 0.004), and 6 hours (+6 mmHg); p = 0.050) after paracentesis. In mechanically ventilated patients, lung injury score (cumulative points without x-ray; median, 6; IQR, 4-7) significantly improved immediately (5; IQR, 4-6; p < 0.001), 2 hours (5; IQR, 4-7; p = 0.003), and 6 hours (6; IQR 4-6; p = 0.012) after paracentesis.

CONCLUSION

Paracentesis in critically ill patients is safe regarding circulatory function and is related to immediate and sustained improvement of respiratory function.