Failure of hypertonic saline to resuscitate intestinal ischemia shock in the rat

Crystalloids and colloids for volume replacement

For many years there has been a debate about whether crystalloids or colloids should be used for resuscitation. Some years ago, albumin was the gold standard against which all other solutions were compared. This continues to be the case, despite the fact that other solutions are as effective for volume replacement. This paper stresses the need for a proper understanding of the properties of solutions that may influence the choice for volume replacement. Different classes of solutions are discussed in detail, with special reference to their effects on cardiovascular and oxygen transport parameters. Other important properties such as side-effects and effect on coagulation are also considered.

Haemodynamic effects of volume resuscitation by hypertonic saline-dextran (HSD) in porcine acute cardiac tamponade

BACKGROUND

Hypertonic saline-dextran (HSD) has been utilized for small-volume resuscitation in acute circulatory shock. However, HSD has also been reported to induce myocardial depression. The aim of this study was to examine the effects of HSD on cardiac performance and splanchnic perfusion in a low cardiac output model based on experimental cardiac tamponade.

METHODS

Seven anaesthetized, mechanically ventilated pigs of both sexes (weight 24 +/- 2 kg, mean +/- SEM) completed a randomized, cross-over protocol. A low cardiac output state was established by intrapericardial infusion of dextran. Animals were resuscitated by bolus infusions (4 ml kg(-1) in 2 min) of either 7.5% hypertonic saline-dextran or Ringer's acetated solution (RAc) and then observed during tamponade (20 min) and following its release (40 min). Central haemodynamics, portal venous (QPV) and renal arterial (QRA) flows were measured together with gastric, jejunal, hepatic and renal laser-Doppler flowmetry.

RESULTS

Resuscitation using HSD in a low cardiac output state completely restored QPV and improved gastric, jejunal, hepatic and renal microcirculation as assessed by laser-Doppler flowmetry while no significant effect was observed in QRA. No such beneficial effects could be observed when animals were resuscitated using RAc. The improved haemodynamic state by HSD was maintained following release of cardiac tamponade while perfusion in RAc resuscitated animals returned to baseline or even remained depressed (hepatic and renal microcirculation). No signs of cardiodepression by HSD were observed.

CONCLUSION

Resuscitation using HSD in a low cardiac output state restored splanchnic perfusion and microcirculation without any signs of cardiodepression.

Viabilidade celular da mucosa do intestino delgado de ratos, após correção de choque hipovolêmico com solução de NaCl 7,5%

OBJETIVO: Estudar o efeito da correção volêmica com diferentes tipos de solução, na mucosa do intestino delgado de ratos. MÉTODOS: Foram utilizados 120 ratos Wistar (Rattus norvegicus albinus), machos, adultos, com peso individual entre 310 e 410g, oriundos do Instituto Evandro Chagas de Belém do Pará, submetidos a período de adaptação por 15 dias, recebendo água e ração ad libitum, durante todo o experimento. Os animais foram distribuídos em: Grupo Padrão (P), Grupo Choque (C), Grupo Solução Fisiológica (SF) e Grupo Solução Hipertônica (SH), com 30 animais cada. Estes foram divididos em subgrupos com 10 animais cada, de acordo com o dia de pós-operatório (DPO) previsto para a eutanásia dos animais, (1º, 3º ou 7º DPO), sendo após esta, colhido material para realização de teste de absorvância pelo MTT em todos os animais. RESULTADOS: O grupo SF apresentou menores índices de viabilidade celular comparado aos grupos SH e C (p<0.05). CONCLUSÃO: A correção volêmica com solução de cloreto de sódio a 7.5% levou a manutenção de maior quantidade de células viáveis, no intestino delgado em ratos no 7º dia do experimento.

Hypertonic saline without or with dextran-70 in the treatment of experimental acute myocardial ischemia and reperfusion

OBJECTIVE

To evaluate the effects of treatment with hypertonic saline without (HS) or with dextran (HSD) on cardiac function and myocardial damage during reperfusion after acute myocardial ischemia.

DESIGN

A prospective, randomized, controlled study.

SETTING

Animal laboratory at a university medical center.

SUBJECTS

Three-month-old male, crossbred (Swedish landrace, Yorkshire, and Hampshire) pigs.

INTERVENTIONS

The pigs were anesthetized and catheterized. A mid-sternal thoracotomy was performed, the pericardial sac was opened, and the left anterior descending artery was dissected free and occluded for 45 mins. A 10-min treatment period with 4 mL/kg HS (7.5%), HSD (7.5%/6%), or normal saline (0.9%) was started 5 mins before reperfusion. After a reperfusion period of 240 mins, biopsies from the ischemic area were taken. Thereafter, the hearts were excised and subjected to a staining procedure (triphenyltetrazoliumchloride and Evan's blue), and the left ventricle was sliced for assessment of the size of the infarcted area and the area at risk.

MEASUREMENTS AND MAIN RESULTS

Central hemodynamics and myocardial performance were monitored before, during, and for 240 mins after 45 mins of acute left anterior descending artery occlusion. Alterations in blood chemistry and serum levels of markers of myocardial damage were repeatedly analyzed during the experimental procedure. Biopsies from the injured myocardium were analyzed for adenosine triphosphate, adenosine 5'-diphosphate, adenosine monophosphate, creatine phosphate, lactate, and glucose. Infarct sizes and areas at risk were planimetrically quantified. HS was not found to enhance, but rather to depress, cardiac performance at reperfusion, whereas HSD improved hemodynamics and myocardial contractility. HS or HSD administration was not found to increase the ischemia-induced myocardial damage.

CONCLUSIONS

The administration of HSD but not HS will improve hemodynamics and myocardial performance during reperfusion after 45 mins of myocardial ischemia. The documented myocardial ischemic injury was not affected by any of the fluid therapies. Therefore, the present data do not support previously suggested detrimental effects of HS on myocardial ischemic injury.

[Hemodynamic effects of hypertonic saline solutions]

Haemodynamic effects of hypertonic saline solutions (HSS) have been extensively studied in animals and humans. Hypertonic sodium chloride (7.5%, 2,500 mOsm.L-1) either alone or combined with colloids, remains the standard solution. The haemodynamic response of HSS observed during treatment of hypovolaemic shock is explained by 1) an increase in preload due to the expansion of the plasma volume and a musculocutaneous vasoconstriction and 2) a decrease in systemic vascular resistance and afterload. A myocardial stimulation has been shown in various experimental conditions and in humans. However, the clinical relevance of this inotropic effect is questionable. Haemorrhagic shock is the main indication for small volume resuscitation with HSS. Other potential situations for the use of HSS are volume replacement in perioperative period, septic shock or burn injury and cardiopulmonary resuscitation. Before recommending the clinical use of HSS, additional clinical studies are required to substantiate the benefits of HSS over colloids.

Effects of hypertonic saline on myocardial function and metabolism in nonischemic and ischemic isolated working rat hearts

OBJECTIVE

To study the direct effects of hypertonic saline on the function of non-ischemic and ischemic myocardium by the use of an isolated working rat heart model.

DESIGN

A prospective, randomized, controlled study.

SETTING

Animal laboratory at a university medical center.

SUBJECTS

Adult Wistar rats (n = 32) of both sexes.

INTERVENTIONS

The heart was excised via thoracotomy in anesthetized rats and prepared for antegrade perfusion at a constant heart rate in an antegrade perfusion apparatus at predetermined preloads and afterloads. Hearts were exposed to ischemia, ischemia followed by repeated hypertonic saline treatment, or repeated hypertonic saline without preceding ischemia. Myocardial ischemia was induced by decreasing the mean aortic pressure to 25 mm Hg.

MEASUREMENTS AND MAIN RESULTS

Variables that were measured or calculated included the following: left atrial pressure; mean aortic pressure; heart rate; coronary flow; aortic flow; cardiac output; stroke volume; PO2, electrolyte content, osmolality, and lactate concentration of the perfusate and/or venous effluent; myocardial oxygen extraction; myocardial oxygen consumption; and myocardial lactate efflux. Ischemia resulted in pronounced impairment of myocardial function and metabolism. Hypertonic saline administration during ischemia induced an additional transient myocardial depression. In the nonischemic heart, a transient myocardial-depressant effect after hypertonic saline administration was also seen.

CONCLUSIONS

The present results from an isolated working heart preparation show that hypertonic saline exerts myocardial-depressive effects in the ischemic as well as in the nonischemic heart. Systemic rather than direct myocardial effects may therefore be responsible for the previously reported beneficial hemodynamic effects of hypertonic saline in shock treatment.