Thomas Brussel

Effects of positive end-expiratory pressure ventilation on splanchnic oxygenation in humans

OBJECTIVES To examine the influence of positive end-expiratory pressure (PEEP) ventilation on splanchnic oxygenation and lactate production in humans without pulmonary disorders. DESIGN Prospective study. SETTING Single-institutional surgical intensive care unit in a university hospital. PARTICIPANTS Twenty patients who underwent major abdominal surgery. INTERVENTIONS Radial artery, pulmonary artery, and right hepatic vein catheters. Blood samples were collected to determine lactate concentrations and oxygen saturations. MEASUREMENTS AND MAIN RESULTS Six hours postoperatively PEEP levels (5, 10, and 15 cmH2O) were applied in a randomized order, and the following parameters were determined before and at the end of each PEEP level: cardiac output (CO); mean arterial pressure (MAP); arterial (SaO2), mixed venous (SvO2) and hepatic venous oxygen saturation (ShvO2); systemic (C[a-v]O2) and splanchnic (C[a-hv]O2) arterial venous oxygen content difference; and arterial, mixed venous, and hepatic venous lactate concentration. CO and MAP were reduced at PEEP 10 and 15 cmH2O, accompanied by a decrease in SvO2 but unchanged SaO2. A decrease in ShvO2 was seen at PEEP 15 cmH2O. C(a-v)O2 and C(a-hv)O2 were increased at PEEP 15 cmH2O. However, at PEEP 15 cmH2O, the percent increment in C(a-hv)O2 was greater than the increment in C(a-v)O2. Lactate concentrations remained unchanged. CONCLUSIONS Ventilation with PEEP causes reductions in CO and MAP, resulting in a comparable impairment of systemic and splanchnic oxygen. The absence of changes in lactate concentrations indicates that a critical reduction in systemic and splanchnic oxygenation is unlikely during ventilation with low or high PEEP levels.

Gastrointestinal monitoring using measurement of intramucosal Pco2

T he gastrointestinal tract is a major contributor to the pathogenesis of the systemic inflammatory response syndrome, sepsis, and multiorgan dysfunction in critical illness (1). Evidence suggests that this is due to gastrointestinal malperfusion, with consequent damage to the lining of the gut and loss of the barrier preventing bacterial penetration. With its unique blood flow distribution, the gastrointestinal tract is especially vulnerable to ischemia and hypoxia. Therefore, monitoring of the perfusion of the gastrointestinal tract is important in critical illness. Under clinical conditions, the direct determination of the perfusion of the gastrointestinal tract is not feasible. Thus, Fiddian-Green et al. (2,3) introduced gastric tonometry, an indirect measurement of intramucosal Pco, (Pica,) within the lumen of the gastrointestinal tract, which provides information on gastrointestinal blood flow. A decrease of the calculated intramucosal pH (pHi) that results from an increase in Pica, can give information on the adequacy of metabolism and on the perfusion of the gastrointestinal mucosa. Gastrointestinal tonometry has been established as the only minimally invasive procedure for gastrointestinal monitoring routinely used under clinical conditions. In this review, we describe newer techniques for the determination of Pica, and compare these with conventional gastric tonometry. In addition, this article deals with the physiological background of gastric tonometry, .as well as with several problems and misconceptions of this method. Finally, we provide a new hypothesis for the interpretation of data obtained by Pica, measurement.

Cardiopulmonary effects of enoximone or dobutamine and nitroglycerin on mitral valve regurgitation and pulmonary venous hypertension

OBJECTIVE To compare the cardiovascular and pulmonary effects of the phosphodiesterase III inhibitor enoximone (EN) or a combination of dobutamine (DOB) and nitroglycerin (NTG) before and after mitral valve repair or replacement. DESIGN Prospective, randomized, controlled clinical study. SETTING University hospital. PARTICIPANTS Twenty patients with mitral regurgitation and pulmonary venous hypertension scheduled for elective mitral valve surgery. INTERVENTIONS Patients fulfilling the inclusion criteria of the study were randomly allocated into a group treated with EN (group 1, n = 10) or DOB and NTG (group 2, n = 10). A cardiopulmonary status was obtained after induction of anesthesia and mechanical ventilation during stable hemodynamic conditions (control). Then the patients received either EN (bolus dose 1.0 mg/kg followed by a continuous infusion of 10 micrograms/kg/min) or DOB (8.0 micrograms/kg/min) and NTG (1.0 microgram/kg/min) according to the randomization. After a period of 20 minutes, all parameters were measured again. The study drugs were stopped, and cardiac surgery was performed. Infusions of EN (without additional loading dose) or DOB and NTG were started again in the above-described doses 10 minutes before separation from cardiopulmonary bypass (CPB). Respiratory and hemodynamic measurements were made 20 minutes after weaning from CPB and 60 minutes after admission of the patient to the intensive care unit. MEASUREMENTS AND MAIN RESULTS Both groups were comparable regarding preoperative and control data. Before mitral valve surgery, cardiac output (CO) and heart rate (HR) increased by 46% (p < 0.05) and 31% (p < 0.01) during infusion of EN with minor changes of mean systemic arterial pressure (PSA) and gas exchange. Mean pulmonary arterial pressure (PPA) decreased from 32 +/- 11 mmHg to 23 +/- 11 mmHg (p < 0.05). Similar alterations were observed in group 2 (delta CO + 26%, p < 0.05, delta HR + 39%, p < 0.01); however, PPA and calculated pulmonary vascular resistance remained unchanged. After separation from CPB, EN and DOB-NTG achieved comparable effects on CO, HR, and PSA, but PPA was significantly lower in group 1. In addition, venous admixture and alveolo-arterial oxygen tension gradient were lower in EN-treated patients. CONCLUSION Enoximone or DOB and NTG have comparable effects on CO, PSA, and HR in mitral regurgitation and pulmonary hypertension, but EN is more effective in reducing PPA without deterioration of gas exchange.

Early onset of regional intestinal ischemia can be detected with carbon dioxide tension measurement inside the peritoneal cavity.

Methods for detecting regional gastrointestinal ischemia are rare. An early detection of ischemia in the stomach or ileum can be achieved by the continuous intramucosal Pco2 (Pico2) measurement in the region. However, physiological consideration suggests that the placement of a fiberoptic CO2 sensor in the peritoneal cavity should yield comparable results. We tested the hypothesis that a continuous Pco2 measurement in the peritoneal cavity allows the early detection of regional intestinal ischemia. A laparotomy was performed in six pigs (54.7 ± 3.7 kg) with a tourniquet being placed around respective vessels to allow complete ischemia of a 2.75-m part of the ileum. A fiberoptic CO2 sensor (Pico2-ileum) was placed intraluminally in the ileum outside this segment. A second fiberoptic CO2 sensor to measure intraperitoneal Pco2 (i.p.-Pco2) was placed inside the peritoneal cavity in close vicinity to the ischemic gut segment. Gastric Pico2 was determined by using air tonometry. After baseline measurements, ileal ischemia was induced for 180 min followed by a 30-min reperfusion period. Statistics were performed with a Friedman test followed by Wilcoxon Analysis with P < 0.01 considered significant. With the onset of local ileal ischemia, a sudden increase in i.p.-Pco2 from 48.9 (45.0–51.5) mm Hg (mean and 25–75 percentiles) to 94.3 (87.9–95.5;P < 0.01) mm Hg was observed. Gastric Pico2 (49.0 [47.5–51.0]/53.5 [49.0–54.0] mm Hg), and ileal Pico2 (56.4 [44.6–57.0]/54.3 [46.1–57.8] mm Hg) did not change. With reperfusion, the i.p.-Pco2 decreased but stayed above baseline values. Implications Unless systemic changes are induced, regional intestinal perfusion deficits cannot be detected with a Pco2 measurement in the gastric lumen. In pigs, an occlusion of blood flow to an isolated gut segment resulted in a significant increase in intraperitoneal CO2 tension. Thus, the measurement of intraperitoneal Pco2 could allow the early detection of regional intestinal ischemia.

Effects of enflurane and isoflurane on splanchnic oxygenation in humans

STUDY OBJECTIVES To determine the effects of enflurane and isoflurane on hepatic venous oxygen saturation (ShvO2) and splanchnic oxygen (O2) extraction. To measure hemodynamic parameters and ShvO2, mixed venous, and arterial lactate concentrations during enflurane and isoflurane anesthesia. DESIGN Randomized, prospective study. SETTING University hospital. PATIENTS 20 ASA physical status I, II, and III adults, who underwent major abdominal surgery requiring mechanical ventilation a few hours postoperatively. INTERVENTIONS After placement of catheters in the pulmonary artery, radial artery, peripheral and right hepatic vein, one hour postoperatively either enflurane or isoflurane was applied at different minimum alveolar concentration (MAC) of 0.5, 1.0, and 1.5 in a randomized order. MEASUREMENTS AND MAIN RESULTS Before and 10 minutes after administration of each desired end-expiratory anesthetic concentration, the following parameters were determined: hemodynamic parameters, arterial (SaO2), mixed venous (SvO2), and hepatic venous oxygen saturations, systemic and splanchnic O2 extraction, arterial, mixed venous, and hepatic venous lactate concentrations. Cardiac output (CO) and mean arterial pressure (MAP) decreased in a dose dependent manner. SaO2, SvO2, and systemic O2 extraction remained unchanged with enflurane and isoflurane anesthesia. In the enflurane group, but not in the isoflurane group, ShvO2 decreased with increasing inhalational concentrations. This decrease in ShvO2 reflected an increase in splanchnic O2 extraction with enflurane; in contrast to isoflurane. CONCLUSIONS Enflurane causes a decrease in ShvO2, which indicates an impairment of splanchnic perfusion corresponding to the reduction in CO and MAP in a dose-dependent manner. Isoflurane maintains splanchnic perfusion in contrast to enflurane.

The anaesthetist makes a difference: the bottom line matters!

Editor, The editorial by Clergue critically discusses the heterogeneity of the composition of the anaesthesia team in different European countries. On the basis of the survey by Meeusen et al., the author recommends standardisation of the training, responsibilities and limitations of non-physician anaesthesia providers. The editorial further raises a question that is of utmost importance to our specialty: what is the role of non-physician anaesthesia providers in Europe, given the increasing workload combined with an expected shortage of anaesthesiologists and considerable financial restraints?