A comparative analysis of isotonic versus hypertonic solution volume replacement in septic rats

Abstracts

OBJETIVO: Há controvérsias sobre o melhor fluído a ser utilizado na reposição volêmica no tratamento da sepse. O objetivo do estudo foi comparar a reposição volêmica com solução salina isotônica à 0,9% ou com solução salina hipertônica à 7,5% , em ratos com sepse induzida pela ligadura e punção do ceco. MÉTODOS: Estudo experimental com 30 ratos Wistar, divididos em três grupos: controle (GC, n=10), solução isotônica (GSI, n=10) e solução hipertônica (GSH, n=10). Em todos os grupos foi realizada a ligadura e punção do ceco, sendo avaliadas, após 15 horas, a freqüência respiratória, pressão arterial média, fluxos sanguíneos hepático e renal, peso e coleta de sangue para dosagem de TNF-α. No grupo solução isotônica e grupo solução hipertônica houve reposição volêmica 60 minutos antes com solução salina a 0,9% e solução salina a 7,5%, respectivamente. RESULTADOS: Ocorreram dois óbitos na amostra total. Houve diferença significativa do peso médio dos ratos após 15 horas de sepse (p=0,018), principalmente se comparados GSI e GSH (p=0,003). O fluxo sanguíneo renal também apresentou diferenças significativas entre os grupos GC e GSH (p=0,002), e GC e GSI (p=0,008), mas sem significância entre GSI e GSH. A melhora da PAM com o uso de SSH não foi constatada (p=0,054). As demais variáveis não apresentaram significância para o estudo. CONCLUSÕES: Embora não tenham sido evidenciadas melhorias na pressão arterial média, bem como no fluxo hepático e TNF-α, ratos submetidos à sepse por ligadura e punção do ceco, após 15 horas, apresentaram aumento significativo do fluxo sanguíneo renal independente do uso de solução salina isotônica à 0,9 % ou hipertônica à 7,5%.

Solução salina hipertônica; Soluções isotônicas; Sepse; Ratos Wistar

ORIGINAL ARTICLE

^IScientific Initiation Student of the Discipline of Surgical Technique and Experimental Surgery of the Medical Graduation course of Pontifícia Universidade Católica do Paraná - PUCPR - Curitiba (PR), Brazil

^IIPhD, Titular Professor for the Discipline of Medical Anatomy of Pontifícia Universidade Católica do Paraná - PUCPR - Curitiba (PR), Brazil and Titular Professor for the Discipline of Surgical Technique and Experimental Surgery of Pontifícia Universidade Católica do Paraná - PUCPR - Curitiba (PR), Brazil

^IIIMedical Graduation Students of Pontifícia Universidade Católica do Paraná - PUCPR - Curitiba (PR), Brazil

^IVBiology Graduation Student of Pontifícia Universidade Católica do Paraná - PUCPR - Curitiba (PR), Brazil.

Author for correspondence

ABSTRACT

PURPOSE: Sepsis severity and mortality risk require aggressive therapy which includes hemodynamic support. The best fluid for volume replacement, however, is controversial. This study aimed to compare 0.9% isotonic saline solution versus 7.5% hypertonic saline solution as volume replacement fluid in sepsis induced by cecum ligation plus puncture rats.

METHODS: This experimental trial included 30 rats divided into three groups: Control group (CG, n = 10), isotonic (ISG, n = 10) and hypertonic solution (HSG, n = 10). Fifteen hours after cecum ligation and puncture, all animals underwent respiratory rate, mean arterial pressure, renal and hepatic blood flow and weight evaluation, plus blood collection for TNF-α measurement. The ISG and HSG treatment groups received volume replacement 60 minutes before the procedure with either 0.9% or 7.5% saline solution, respectively.

RESULTS: Two animals died. Significant differences were found for the animals' mean weight after 15 hours (p=0.018), particularly relevant when ISG and HSG are compared (p=0.003). Renal blood flow was also significantly different for the CG versus HSG (p=0.002) and CG versus ISG (p=0.008), but not significantly different for ISG versus HSG. No mean arterial pressure improvement was found for HSG (0.054). Other variables were not significant.

CONCLUSIONS: Although no mean blood pressure, hepatic flow or TNF-α improvements were detected, the rats with sepsis 15 hours after cecum ligation and puncture showed significantly increased renal blood flow which was 0.9% isotonic saline solution or of 7.5% hypertonic solution use independent.

Keywords: Saline solution, hypertonic; Isotonic solutions; Sepsis; Rats, Wistar

INTRODUCTION

Microorganisms or they toxic byproducts in blood stream, hemodynamic changes and local plus generalized inflammatory response are distinctive processes, however together characterize and define sepsis as a systemic inflammatory response syndrome (SIRS) caused by a microorganism infection.^(1,2)

Nevertheless recent diagnosis and therapy progresses, sepsis has still high mortality rates, between 30% and 80%,⁽³⁾ and is the main cause of death in intensive care units (ICU).⁽⁴⁾ In Brazil, according the BASES study,⁽⁵⁾ sepsis and septic shock account for 24.3% and 52.2% of ICU deaths, respectively.

Septic patients show marked hemodynamic disorders, mainly evidenced by its 35% to 40% of the cases progression to septic shock.⁽⁶⁾ Complex changes involve myocardial contractility, micro- and macrocirculation, leading to reduced perfusion and poor tissue oxygen offer.⁽⁷⁾

Therefore, as a frequent, expensive and potentially fatal disease, with little mortality progress evidenced,⁽⁸⁾ aggressive therapy is mandatory, and includes antibiotics therapy plus supportive measures, mainly hemodynamic support, therefore involving volume replacement aimed to improve tissue perfusion.

However, the literature analysis evidences controversy on the best volume replacement fluid. According to the Brazilian Sepsis Consensus (2003),⁽⁹⁾ crystalloids are the first choice; among them, isotonic saline (0.9% NaCl) is most frequently used, however requires large volume infusions. On the other hand, hypertonic solutions improve heart contractility, provide pre-capillary dilation, however have risks of hypertonic conditions development.^(9-11)

Hypertonic saline use in sepsis was poorly studied, and its main mechanisms of action include fast intracellular to extracellular compartment fluid mobilization, endothelial and tissue edema reduction, myocardial contractility increase, cardiac output improvement, arterioles vasodilation, microcirculation improvement, hemodilution and immunomodulation.^(10,11)

Thus, considering the lack of clear definition of hypertonic fluids in sepsis management use, this study was aimed to compare the hemodynamic responses to 0.9% isotonic saline (ISS) versus 7.5% hypertonic saline (HSS) volume replacement in rats with sepsis induced by cecum ligation and puncture (CLP), the most similar to human sepsis abdominal injury animal model.^(1,12)

METHODS

After approval by the Animal Studies Ethics Committee (CEUA) of the Pontifícia Universidade Católica do Paraná (PUCPR), Brazil, an experimental trial was conducted involving 30 Wistar male rats (Rattus norvegicus albinus), provided by the PUCPR's vivarium.

Animals weighting average 310 grams were divided into three groups: control group (CG, n=10), isotonic saline group (ISG, n=10) and hypertonic saline group (HSG, n=10).

All animals underwent cecum ligation and puncture (CLP) procedure, conducted under intramuscular ketamine (90 mg/kg) plus xylasine (10 mg/kg) anesthesia, abdominal trichotomy, weight and respiratory rate (RR) measurement. Next, a supra-umbilical median laparotomy was conducted followed by ligation of the free portion of cecum with a 3-0 cotton thread and three 40-12 needle punctures. The abdominal wall was then sutured in two layers using nylon 4-0 thread, followed by analgesia with Banamine for injection (flunixin meglumine) 0.1 mL in 0.9 mL saline.

All animals were kept in cages with free access to water and food, at room temperature for 15 hours.

Fifteen hours after cecum ligation and puncture, the CG underwent intramuscular ketamine (90 mg/kg) and xylasine (10 mg/kg) anesthesia, weight measurement, 1 cm incision at inguinal region, femoral artery and vein dissection, femoral vein anticoagulation with 5000 IU/mL sodium heparin 0.2 mL femoral artery catheterization with 24G catheter and mean arterial pressure (MAP) measurement using a mercury sphygmomanometer connected with intravenous access tubing. Next, a new laparotomy was conducted for 90 seconds hepatic and renal (left kidney) blood flow evaluation using the LASERFLO Blood Perfusion Monitor BPM², available at the PUCPR's surgical technique laboratory.

After measuring the blood flows, blood was drawn from the femoral artery catheter, centrifuged for 15 minutes at 2600 RPM in a CT-6000R centrifuge obtaining plasma that was frozen at -80ºC for later TNF-α analysis, determined using the Rat TNF-α ELISA Development kit protocol.

Finally, the animals were euthanized with thiopental 250 mg/100g, each 1 g diluted in 40 mL normal saline, and the left kidney, liver and lung removed.

For the ISG and HSG groups the same procedure performed for the CG was conducted after 15 hours plus volume replacement 60 minutes before. For the ISG, 32 mL/kg 0.9% saline solution were subcutaneously infused, while for the HSG group the subcutaneous injection consisted of 4 mL/kg 7.5% saline solution.

The groups' quantitative variables were compared using the non-parametrical Kruskal-Wallis test, being p<0.05 values considered statistically significant.

RESULTS

The experimental procedure was conducted for the three study groups, monitoring RR, MAP and hepatic plus renal blood flow, followed by blood collection and liver, left kidney and lungs removal.

Death before euthanasia occurred in only two rats, both in the ISG group.

Regarding RR, a median increase was observed for the second procedure (RR2), particularly for the HSG, also versus ISG (Figure 1), although it should be highlighted that no statistical significance was found for the groups' comparison, with 0.199 for RR1 and 0.767 for RR2.

A MAP improvement was observed with hypertonic solution, with average 40.9 mmHg for CG, 42.8 mmHg for ISG, and 57.9 mmHg for HSG, however not significant, p=0.054 (Table 1).

TNF-α inflammatory mediator measurement didn't show statistical significance, with p=0.107 for all groups.

Hepatic blood flow evaluation evidenced higher CG flow, median 51.5 mL/min/100g, while for ISG and HSG median liver blood flows of 29 and 30 mL/min/100g, respectively, were shown. However these were not statistically significant, p=0.678 for the three groups.

Finally, significant differences were shown only for renal blood flow and weight variables. For the pairwise groups' comparison, the weight difference between both surgical procedures (Weight 1 by the cecum ligation and puncture procedure time, and Weight 2 by the hemodynamic evaluation procedure time), a median 2.7% weight decrease was found for the CG within the 15 hours, median 315.50 grams before the ligation and 307.0 grams 15 hours later. For the ISG, the weight increased by 0.47% and for HSG, was reduced by 0.85%. On the groups' comparison, these results were statistically significant for Weight 2, p=0.018, particularly for ISG and HSG comparison, p=0.003.

The renal flow had significant differences for CG versus HSG (p=0.002), and CG versus ISG (p=0.008), however was not significant for ISG versus HSG, with median CG 14 mL/min/100 g, ISG 28 mL/min/100g and HSG 30 mL/min/100g (Figure 2).

Table 2 displays mean, median, maximal and minimal, and standard deviations of renal blood flow and Weight 1 and 2 variables. These variables pairwise groups comparison was significant for weight 2 CG versus ISG and HSG comparison, p=0.008 and 0.002, respectively. For the renal blood flow variable, only the ISG versus HSG comparison was statistically significant, p=0.003.

DISCUSSION

Much was discovered on sepsis' pathophysiology,⁽¹³⁾ therefore improving therapeutic perspectives. However, some topics remain unclear,⁽¹⁴⁾ among them hypertonic saline solution volume replacement therapy.⁽¹¹⁾

Aiming to evaluate the literature-described hemodynamic benefits of hypertonic saline solution therapy in sepsis, this study compared volume replacement using hypertonic 7.5% saline solution versus isotonic 0.9% saline solution in cecum ligation and puncture septic rats, using a control non-intervention septic group.

Cecum ligation and puncture was proposed as the most similar to human sepsis animal model, because it has an abscess as local septic focus, mimicking human appendicitis or perforated diverticulitis, in addition of being a simple procedure that provides a bacterial mix, quickly promotes septic shock, although a difficult-to-control sepsis magnitude.⁽¹²⁾ Also, heparinization was required to prevent coagulation during the procedure.⁽¹⁵⁾

Death before euthanasia occurred in only two ISG group animals, only one after cecum ligation and puncture, 6.66% of the total sample, without significant impact on the study results. This was only possible after some pilot experiments, becoming clear that the post-operative period should be reduced from 18 to 15 hours, as discussed in high sample mortality studies.⁽⁷⁾ Otherwise, the sample would be insufficient for a post-volume replacement comparison.

The choice of 32 mL/kg of 0.9% and 4 mL/kg 7.5% saline solutions replacement was to provide approximately similar NaCl amounts for both groups (0.075 g NaCl), neither excessively influencing the hydro-electrolytic balance, nor requiring large volumes infusion.

Thus, to show hypertonic saline solution effects on septic rats volume correction, we measured the respiratory rate, mean arterial pressure, hepatic and renal blood flow, and TNF-α.

The weight difference between the procedures was relevant. For ISG mean 0.47% weight increase from CLP to the after 15 hours evaluation was found. HSG had a mean 0.85% weight reduction, compared to mean 2.7% reduction for CG. A p=0.003 value was found for the ISG versus HSG comparison (statistically significant), in agreement with the literature-reported hypertonic solution benefits.^(10,11) ISG weight may have increased due to broader extracellular space distribution, therefore requiring larger volumes, leading to interstitial overflow and tissue edema.⁽¹¹⁾ The weight reduction for CG was larger than for HSG, as CG had no volume replacement, showing that one of the most important, if not the most important benefit, of hypertonic saline solution is quick intracellular compartment fluids mobilization into the extracellular space, endothelial and tissue edema reduction, without large volumes infusion requirement.^(10,11)

Considering respiratory rate results, all groups had increases, although not statistically significant, thus failing to show the RR improvements reported by Garrido et al.⁽¹⁴⁾ and Friedman et al.⁽¹¹⁾ in a review article, which would characterize improved oxygen extraction. However, in an eventual future study more detailed oxymetry could be interesting.

In a literature review by Friedman et al.,⁽¹¹⁾ MAP improvement from hypertonic saline solution use was described, with CG having mean 40.9 mmHg, ISG mean 42.8 mmHg and HSG mean 57.9 mmHg, however not statistically significant, p=0.054. This shows that, even with no statistical significance, saline solution replacement lead to tentative volume replacement.

Serum TNF-α inflammatory mediator measurement was carefully conducted, however showed no statistical significance (p=0.107). No literature references were found on TNF measurement and hypertonic saline volume replacement in septic rats. TNF is an important cytokine in sepsis, being the first to be identified in circulation,⁽¹⁾ and induces neutrophils release from the bone marrow and muscle catabolism, stimulates angiogenesis, promotes inflammatory proteins synthesis, stimulates coagulation, and additionally, its administration to animals induces a similar to sepsis syndrome.⁽¹⁾

Hepatic blood flow evaluation showed higher CG flow, median 31.5 mL/min/100g, likely due to the sepsis magnitude, as no therapeutic intervention was adopted for these rats, differently from ISG and HSG where lower flows were seen, 29 and 30, respectively. However, no statistical significance for the three groups comparison was found (p=0.678).

The renal blood flow showed significant differences for CG versus HSG and CG versus ISG comparisons, however was not significant for ISG versus HSG, probably reflecting improved renal function. Garrido et al.⁽¹⁴⁾ suggest that hypertonic saline solution is able to improve the blood flow redistribution and microcirculatory perfusion.

CONCLUSION

Although no MAP, hepatic blood flow and TNF-α improvement was shown, septic rats 15 hours after CLP had significant renal blood flow increase, which was independent of isotonic 0.9% or hypertonic 7.5% saline use.

REFERENCES

• 1. Benjamim CF. Atualização sobre mediadores e modelos experimentais de sepse. Medicina (Ribeirão Preto). 2001;34(1):18-26.
• 2. Levy M, Fink MP, Marshall JC, Abraham E, Angus D, Cook D, Cohen J, Opal SM, Vincent JL, Ramsay G; International Sepsis Definitions Conference. 2001 SCCM/ESICM/ACCP/ATS/SIS International Sepsis Definitions Conference. Intensive Care Med. 2003;29(4):530-8.
• 3. Friedman G, Silva E, Vincent JL. Has the mortality of septic shock changed with time. Crit Care Med. 1998;26(12):2078-86.
• 4. Friedman G. Contribuições para o entendimento da principal causa de morte em unidades de tratamento intensivo: a sepse. Rev HCPA & Fac Med Univ Fed Rio Gd do Sul. 1999;19(3):350-75.
• 5. Silva E, Pedro Mde A, Sogayar AC, Mohovic T, Silva CL, Janiszewski M, Cal RG, de Sousa EF, Abe TP, de Andrade J, de Matos JD, Rezende E, Assunção M, Avezum A, Rocha PC, de Matos GF, Bento AM, Corrêa AD, Vieira PC, Knobel E; Brazilian Sepsis Epidemiological Study. Brazilian Sepsis Epidemiological Study (BASES study). Crit Care. 2004;8(4):R251-60.
• 6. Pereira Junior GA, Marson F, Abeid M, Ostini FM, Souza SH, Basile-Filho A. Fisiopatologia da sepse e suas implicações terapêuticas. Medicina (Ribeirão Preto). 1998;31(3):349-62.
• 7. Oliveira RP. Ressuscitação hipertônica com salina/dextran em pacientes sépticos graves estáveis: um estudo randomizado [dissertação]. Porto Alegre: Faculdade de Medicina da Universidade Federal do Rio Grande do Sul; 2001.
• 8. Carvalho PRA, Trotta EA. Avanços no diagnóstico e tratamento da sepse. J Pediatr (Rio J). 2003;79(Supl 2):S195-204.
• ⁹
  Hospital Israelita Albert Einstein; Associação de Medicina Intensiva. Consenso Brasileiro de Sepse - Suporte Hemodinâmico. São Paulo; 2003.
• 10. Oliveira PC. Pressão arterial e manipulação tubular renal de sódio em um modelo de septicemia em ratos [dissertação]. Campinas: Faculdade de Ciências Médicas da Universidade Estadual de Campinas; 2001.
• 11. Friedman G, Soriano FG, Rios ECS. Reposição de volume na sepse com solução salina hipertônica. Rev Bras Ter Intensiva. 2008;20(3):267-77.
• 12. Garrido AG, Figueiredo LFP, Silva MR. Experimental models of sepsis and septic shock: an overview. Acta Cir Bras. 2004;19(2):82-8.
• 13. Bone RC, Fisher CJ Jr, Clemmer TP, Slotman GJ, Metz CA, Balk RA. Sepsis syndrome: a valid clinical entity. Methylprednisolone Severe Sepsis Study Group. Crit Care Med. 1989;17(5):389-93.
• 14. Garrido Adel P, Cruz RJ Jr, Poli de Fiqueiredo LF, Rocha e Silva M. Small volume of hypertonic saline as the initial fluid replacement in experimental hypodynamic sepsis. Crit Care. 2006;10(2):R62.
• 15. Brito MVH, Moura FAS, Carballo MCS, Tavares MLB, Santos LLT, Carvalho RA. Técnica para obtenção de sangue central em ratos. Rev Para Med. 2002;16(4):22-5.

A comparative analysis of isotonic versus hypertonic solution volume replacement in septic rats

Talita Rechetelo Strano^I; Sérgio Luiz Rocha^II; Anna Carolina Botti de Oliveira^III; Débora Bega^III; Guilherme Zammar^III; Misael Gomes Barbosa^IV

Publication Dates

• Publication in this collection
  19 Jan 2011
• Date of issue
  Dec 2010

History

• Received
  17 Aug 2010
• Accepted
  26 Oct 2010