Effects of intravenous fat emulsions on lung function in patients with acute respiratory distress syndrome or sepsis

Is parenteral nutrition really that risky in the intensive care unit?

PURPOSE OF REVIEW

Although enteral nutrition is now the mainstay of nutrition delivery within intensive care, there is a blind faith in its benefits and a disregard of its risks. This has led to the belief that parenteral nutrition is no longer required as it is fraught with risks to the patient. This review attempts to dispel these myths and compares and contrasts the risks of enteral nutrition with those of parenteral nutrition in the critically ill.

RECENT FINDINGS

A greater appreciation of the failings and risks associated with the delivery of enteral nutrition combined with improvements in the formulation and use of parenteral nutrition help explain why parenteral nutrition is not as risky as some have believed. Recent evidence has suggested that enteral nutrition in a few selected circumstances may even carry a higher mortality risk. Real outcome benefits have been described with the new glutamine-containing parenteral nutrition formulations.

SUMMARY

Parenteral nutrition remains a valuable yet challenging weapon in our therapeutic armoury in the presence of gastrointestinal feed intolerance or failure. However, it should be used wisely and not indiscriminately because the majority of intensive care unit patients with a fully functional gastrointestinal tract may be fed safely with enteral nutrition.

Effect of a Novel Thromboxane A2 Inhibitor on Right Ventricular-Arterial Coupling in Endotoxic Shock

We investigated the effects of a dual thromboxane (TX)A2 synthase inhibitor and TXA2 receptor antagonist (BM-573) on right ventricular-arterial coupling in a porcine model of endotoxic shock. Thirty minutes before the onset of 0.5 mg/kg endotoxin infusion, six pigs (Endo group) received an infusion with a placebo solution, and six other pigs (Anta group) with BM-573. Right ventricular pressure-volume loops were obtained by the conductance catheter technique. The slope (Ees) of the end-systolic pressure-volume relationship and its volume intercept at 25 mmHg were calculated as measures of right ventricular systolic function. RV afterload was quantified by pulmonary arterial elastance (Ea), and Ees/Ea ratio represented right ventricular-arterial coupling. Mechanical efficiency was defined as the ratio of stroke work and pressure-volume area. In this model of endotoxic shock, BM-573 blunted the early phase of pulmonary hypertension, improved arterial oxygenation, and prevented a decrease in right ventricular myocardial efficiency and right ventricular dilatation. However, the drug could not prevent the loss of homeometric regulation and alterations in right ventricular-arterial coupling. In conclusion, dual TXA2 synthase inhibitor and receptor antagonists such as BM-573 have potential therapeutic applications, improving right ventricular efficiency and arterial oxygenation in endotoxic shock.

Specialized nutrition support in critically ill patients

How nutritional therapy may affect real clinical outcomes is not readily apparent from a superficial reading of current data. Despite great claims in reducing infectious incidence, many studies show little difference in meaningful clinical outcomes. This has led to confusion over the role of nutrition and nutrition practice in intensive care. However, the role that nutrition plays in preventing infection and later how nutrition aids long-term recovery perhaps explain many of the misconceptions and difficulty in understanding the evidence. Encouraging new evidence is starting to show that outcome can be improved by implementing relatively simple therapies well that have an impact on nutrition and metabolic control.

Propofol does not induce pulmonary dysfunction in stressed endotoxic pigs receiving Intralipid

OBJECTIVE

To assess the effect of diisopropyl phenol (propofol), with and without Intralipid, on the cardiopulmonary system and on thromboxane production in endotoxic pigs.

DESIGN

Prospective, randomized animal study.

SETTING

Animal research laboratory at a major teaching hospital.

SUBJECTS

Twenty-four pigs, divided into three groups (n = 8).

INTERVENTIONS

Pulmonary arterial catheters and arterial cannulas were inserted into all pigs. Each pig received a 30 ng/kg bolus of endotoxin at 1 hr, followed by a continuous infusion of endotoxin at 24 ng x kg-1 x hr-1. Diisopropyl phenol at 25, 75, and 200 microg x kg-1 x min-1 was administered to all pigs, beginning at 1, 2, and 3 hrs, respectively. The pigs were divided into three groups to receive 0.25 g x kg-1 x hr-1, 0.08 g x kg-1 x hr-1, or no Intralipid, starting at time t = 0. Heart rate and mean arterial, central venous, and pulmonary arterial pressures were recorded continuously. Core temperature, arterial blood gases, mixed venous oxygen saturation, pulmonary arterial occlusion pressure, and cardiac output were measured intermittently. Thromboxane B(2) concentrations were measured at baseline and at 60, 75, 120, 135, 180, 195, and 240 mins. Data are expressed as mean +/- sd. Groups were compared by using repeated analysis of variance, with p <.05 used for statistical significance.

MEASUREMENTS AND MAIN RESULTS

All pigs completed the 4-hr study. Marked variabilities were noted for individual pigs. Following the infusion of endotoxin, compared with baseline, there was a significant increase in pulmonary vascular resistance and a decrease in Pao(2) (p <.001 and p <.008, respectively). This response was not affected by the increasing dose of diisopropyl phenol, nor were there differences between the Intralipid and control groups. Pao(2) remained significantly lower in all groups, compared with the baseline measurements (p <.001) over the 4 hrs of the experiment. Thromboxane B(2) concentrations remained elevated compared with baseline and were significantly higher (p <.05) in the high-dose Intralipid group, compared with the low-dose and the control groups, during the last hour of the experiment.

CONCLUSIONS

Small doses of endotoxin, when given to pigs, induce major perturbations of cardiopulmonary function. Neither Intralipid, high vs. low dose, nor diisopropyl phenol, at sedating vs. anesthetizing doses, worsened the physiologic derangement associated with the stress of low-dose endotoxemia.

Effects of BM-573, a novel thromboxane A2 inhibitor, on pulmonary hemodynamics in endotoxic shock

Thromboxane A2 is considered to be partially responsible for the increase in pulmonary vascular resistance observed after endotoxin administration and to participate in proinflammatory reactions. The effects of a novel dual TXA2 synthase inhibitor and TXA2 receptor antagonist (BM-573) on pulmonary hemodynamics were investigated in endotoxic shock. 30 mins before the start of a 0.5 mg/kg endotoxin infusion, 6 pigs (Endo group) received a placebo infusion and 6 other pigs (Anta group) received a BM-573 infusion. In Endo group, pulmonary artery pressure increased from 25 +/- 1.8 (T0) to 42 +/- 2.3 mmHg (T60) (p < 0.05) after endotoxin infusion while, in Anta group, it increased from 23 +/- 1.6 (T0) to 25 +/- 1.5 mmHg (T60). This difference is due to a reduction in pulmonary vascular resistance in Anta group while pulmonary arterial compliance changes in Endo group remained comparable with the evolution in Anta group. In Endo group, PaO2 decreased from 131 +/- 21 (T0) to 74 +/- 12 mmHg (T300) (p < 0.05), while in Anta group, PaO2 was 241 +/- 31 mmHg at the end of the experimental period (T300). These results demonstrate that TXA2 plays a major role in pulmonary vascular changes during endotoxin insult. Concomitant inhibition of TXA2 synthesis and of TXA2 receptors by BM-573 inhibited the pulmonary vasopressive response during the early phase of endotoxin shock as well as the deterioration in arterial oxygenation.

Nutrition support in critically ill septic patients

PURPOSE OF REVIEW

Infection and sepsis remain major challenges in the critically ill. How nutritional therapy can effect real clinical outcomes is not easily apparent from the clinical data. Despite reducing infectious incidence, many studies show little difference in meaningful clinical outcomes.

RECENT FINDINGS

Confusion over the role that nutrition and nutrition practice in intensive care plays in preventing infection, and later how nutrition aids recovery from sepsis perhaps explains many of the misconceptions and difficulties with the evidence.

SUMMARY

Encouraging new evidence will help our decision making and shows that outcome can be improved by performing relatively simple therapies well.

Total parenteral nutrition

In recent months, numerous reports concerning total parenteral nutrition in critically ill patients have been published, including the guidelines and recommendations of the American Society for Parenteral and Enteral Nutrition. The old controversy regarding the use of the enteral versus parenteral route still exists. Although the enteral route is indicated in those patients with normal gastrointestinal function, the parenteral route is obviously beneficial in several clinical conditions and appears to be associated with few procedure-related complications when performed by experienced clinicians. There is also continued interest in the supplementation of parenteral formulas with nutrients that were previously considered nonessential, such as arginine, glutamine, and omega-3 fatty acids, but that may become essential in the setting of critical illness.