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Anesth Analg 2004;98:1114-1120 © 2004 International Anesthesia Research Society doi: 10.1213/01.ANE.0000100740.07331.A2
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Abstract |
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Endotoxemia is a common problem among critically-ill patients. We previously found that ketamine inhibited hypotension, metabolic acidosis, and increase of plasma cytokines during endotoxemia in rats. Although endotoxic patients often develop hypothermia, it has not been determined whether ketamine retains its antiinflammatory effects during hypothermia. We investigated the effects of ketamine on endotoxemic rats subjected to moderate and mild hypothermia. Male Wistar rats (n = 100) were anesthetized intraperitoneally with pentobarbital sodium and assigned to one of two protocols: one representing moderate hypothermia (30°C–32°C) and the other, mild hypothermia (33°C–35°C). Each protocol included 5 equal groups: 1) Escherichia coli endotoxin (15 mg/kg IV) in normothermia, 2) ketamine (10 mg · kg-1 · h-1 IV) during and after endotoxin injection in normothermia, 3) saline in hypothermia, 4) endotoxin (15 mg/kg IV) in hypothermia, and 5) ketamine (10 mg · kg-1 · h-1 IV) in hypothermia after endotoxin injection. Rats were then warmed or cooled to maintain rectal temperatures as above for 6 h. We assessed hemodynamics, acid-base status, and plasma concentrations of tumor necrosis factor-
, and interleukin-6. Endotoxemic rats developed hypotension and metabolic acidosis as well as increased plasma cytokine concentrations. At 6 h after endotoxin injection, the mean systolic arterial blood pressure decreased by 71% in the saline/normothermia/endotoxin group, whereas it decreased by only 6%, 41%, and 29% in the ketamine/normothermia/endotoxin, saline/moderate hypothermia/endotoxin, and ketamine/moderate hypothermia/endotoxin groups, respectively. Ketamine administration to endotoxemic rats with hypothermia, whether moderate or mild, also attenuated hypotension, metabolic acidosis, and cytokine increase, but these effects were not superior to those of hypothermia alone. Our findings suggest that, during hypothermia, ketamine administration may not have additive beneficial antiinflammatory effects. IMPLICATIONS: Although ketamine administration decreased the severity of hypotension and acidosis in endotoxemic rats, ketamine administration may not have additive beneficial antiinflammatory effects during hypothermia.
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Introduction |
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Endotoxemia and endotoxin shock are common problems in the intensive care unit and carry a very high mortality rate. Cardiovascular dysfunction is common among patients with endotoxemia and is often resistant to aggressive interventions. Endotoxemia increases production of endogenous cytokines, including tumor necrosis factor (TNF)-
, interleukin (IL)-6, and IL-8 (1–4). In addition to endotoxin, cytokines have been implicated in the pathophysiology of endotoxin shock and development of cardiovascular dysfunction in endotoxemia (1–3,5,6). Patients with endotoxemia often require drugs for sedation and analgesia in the intensive care unit, and several investigators have reported on the effects of certain anesthetics on endotoxemia (7–9). In a previous study, we found that administration of ketamine to endotoxemic rats inhibited hypotension, metabolic acidosis, and increase of plasma cytokines such as TNF- and IL-6 (10). Critically-ill patients with endotoxemia often experience hypothermia, and perioperative hypothermia is a common complication of anesthesia and surgery. Therapeutic moderate and mild hypothermia is also an issue; several reports have shown that such treatment after cardiac arrest improves the likelihood of a favorable neurologic outcome (11) and reduces mortality (12,13). Thus, relationships between anesthetics and hypothermia in endotoxemia pose very important unsolved questions. However, whether ketamine retains its antiinflammatory effects during moderate and mild hypothermia has not been determined. We therefore investigated the effects of ketamine on endotoxin-induced shock in rats during moderate and mild hypothermia.
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Methods |
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All experimental procedures were approved by the Animal Care Committee of Kanazawa University and were in accordance with the US National Institutes of Health guidelines for animal use. The method of animal preparation was reported previously (10). Briefly, male Wistar rats (n = 100) weighing 375 ± 11 g (mean ± SD) were anesthetized with an intraperitoneal injection of pentobarbital sodium (30 mg/kg). Ventilation was performed via a tracheotomy. The femoral artery was cannulated to monitor the arterial blood pressure and to draw blood samples. Lactated Ringer’s solution containing a muscle relaxant (pancuronium bromide, 0.02 mg/mL) and pentobarbital sodium (0.5 mg/mL) was infused continuously at a rate of 10 mL · kg-1 · h-1 through a femoral vein cannula. The heart rate (HR) was recorded from lead II of the electrocardiogram. The rats were ventilated by a pressure-controlled ventilator (Servo 900C, Siemens-Elema, Solna, Sweden) delivering 100% oxygen at a frequency of 30 breaths/min with an inspiratory:expiratory ratio of 1:1. The animals then were rested for at least 30 min to allow stabilization of hemodynamic variables, followed by baseline recordings of HR and systolic arterial blood pressure (SAP) as well as arterial blood sampling gas and acid-base analyses (ABL-520; Radiometer, Copenhagen, Denmark).
Moderate Hypothermia
After baseline measurements, 50 rats were allocated randomly to one of five groups, four of which received endotoxin (n = 10 per group).
Saline/Normothermia/Endotoxin Group
Endotoxin shock was induced with a bolus injection of endotoxin (15 mg/kg). We used lipopolysaccharide prepared from Escherichia coli (0111:B4; Difco Laboratories, Detroit, MI) as endotoxin.
Ketamine/Normothermia/Endotoxin Group
This group received an infusion of ketamine (10 mg · kg-1 · h-1). After initiation of the infusion, a bolus of endotoxin (15 mg/kg) was given.
Saline/Moderate Hypothermia/No Endotoxin Group
Animals received a bolus injection of 0.9% saline (1.0 mL/kg) with no exposure to endotoxin.
Saline/Moderate Hypothermia/Endotoxin Group
Endotoxin shock was induced with a bolus injection of endotoxin (15 mg/kg).
Ketamine/Moderate Hypothermia/Endotoxin Group
This group received an infusion of ketamine (10 mg · kg-1 · h-1). After initiation of the infusion, a bolus of endotoxin (15 mg/kg) was given.
Rectal temperatures in the normothermia groups were maintained between 36°C and 38°C with the aid of a heating pad. Immediately after administration of saline or endotoxin, animals in the moderate hypothermia groups were cooled externally so that by 1 h after initiation of cooling the rectal temperature was between 30°C and 32°C. Arterial blood samples (0.25 mL) were drawn 1, 3, and 5 h after endotoxin or saline injection for measurement of arterial pH (pHa), O2 tension (PaO2), and CO2 tension (PaCO2). Additional arterial blood samples (1.5 mL) were drawn for the measurement of plasma cytokine concentrations 2 and 4 h after the endotoxin or saline injection. The total amount of blood drawn from each animal was 4.0 mL over 6 h.
Mild Hypothermia
After baseline measurements, 50 animals were allocated randomly to one of 5 groups (n = 10 per group). Injections, infusions, and blood sampling were performed in each group as in the moderate hypothermia protocol.
Immediately after the administration of saline or endotoxin, animals in the mild hypothermia groups were cooled externally so that by 1 h after initiation of cooling the rectal temperature was between 33 and 35°C.
Sample Analysis
Blood used to measure cytokine concentrations was centrifuged for 10 min at 3000g at 4°C. Plasma was decanted and stored at -70°C until analysis. Cytokine concentrations (TNF- and IL-6) were measured by enzyme-linked immunosorbent assays (BioSource, Camarillo, CA). Lower limits of detection for TNF- and IL-6 were 4.5 pg/mL and 7.0 pg/mL, and the coefficients of variation 3.8% and 6.8%, respectively.
Data are presented as the mean ± SD. Differences between groups at baseline were analyzed with unpaired Student’s t-test and the Mann-Whitney U-test. Hemodynamic variables as well as cytokine concentrations during the study were analyzed using two-way analyses of variance for repeated measures, followed by a post hoc test (Bonferroni’s method). Statistical significance was defined at P < 0.05. Statistical analyses were performed using StatView software (version 5.0 for Macintosh; Abacus Concepts, Berkeley, CA).
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Moderate Hypothermia
Hemodynamics.
No significant differences were noted in baseline HR or SAP among the five groups (Fig. 1). At 6 h after endotoxin injection, the mean SAP decreased by 71% in the saline/normothermia/endotoxin group, whereas it decreased by only 6%, 41%, and 29% in the ketamine/normothermia/endotoxin, saline/moderate hypothermia/endotoxin, and ketamine/moderate hypothermia/endotoxin groups, respectively. The SAP in the ketamine/moderate hypothermia/endotoxin group was higher than that in saline/normothermia/endotoxin group, but it did not differ from that in the ketamine/normothermia/endotoxin and saline/moderate hypothermia/endotoxin groups. Except in the ketamine/normothermia/endotoxin group, endotoxin injection decreased HR significantly (P < 0.05). The HR in the ketamine/moderate hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/moderate hypothermia/endotoxin groups.
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Blood Gases.
PaCO2 and PaO2 showed no significant differences among the five groups at any point during the experimental period (Table 1). The pHa in the saline/normothermia/endotoxin alone decreased. The pHa in the ketamine/moderate hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/moderate hypothermia/endotoxin groups.
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Plasma Cytokine Concentrations.
All baseline values were similar for the five groups (Fig. 2). Endotoxin injection increased the TNF-
concentration 2 h after endotoxin injection, but TNF- in the ketamine/normothermia/endotoxin and ketamine/moderate hypothermia/endotoxin groups was significantly less than that in the saline/normothermia/endotoxin group. TNF- in the ketamine/moderate hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/moderate hypothermia/endotoxin groups. Endotoxin injection increased the IL-6 concentration, but IL-6 was significantly less in the ketamine/normothermia/endotoxin and ketamine/moderate hypothermia/endotoxin groups than in the saline/normothermia/endotoxin group. IL-6 in the ketamine/moderate hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/moderate hypothermia/endotoxin groups.
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Mild Hypothermia
Hemodynamics.
No significant differences were noted in baseline HR or SAP among the five groups (Fig. 3). At 6 h after endotoxin injection, the mean SAP decreased by 72% in the saline/normothermia/endotoxin group, whereas it decreased by only 6%, 53%, and 41% in the ketamine/normothermia/endotoxin, saline/mild hypothermia/endotoxin, and ketamine/mild hypothermia/endotoxin groups, respectively. The SAP in the ketamine/mild hypothermia/endotoxin group was higher than that in saline/normothermia/endotoxin group, but did not differ from that in the ketamine/normothermia/endotoxin and saline/mild hypothermia/endotoxin groups. Except in the ketamine/normothermia/endotoxin group, endotoxin injection decreased HR significantly (P < 0.05). The HR in the ketamine/mild hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/mild hypothermia/endotoxin groups.
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Blood Gases.
PaCO2 and PaO2 showed no significant differences among the five groups at any point during the experimental period (Table 2). The pHa in the saline/normothermia/endotoxin alone decreased. The pHa in the ketamine/mild hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/mild hypothermia/endotoxin groups.
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Plasma Cytokine Concentrations.
All baseline values were similar for the five groups (Fig. 4). Endotoxin injection increased the TNF-
concentration 2 h after endotoxin injection, but TNF- in the ketamine/normothermia/endotoxin and ketamine/mild hypothermia/endotoxin groups was significantly less than that in the saline/normothermia/endotoxin group. TNF- in the ketamine/mild hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/mild hypothermia/endotoxin groups. Endotoxin injection increased the IL-6 concentration, but IL-6 was significantly less in the ketamine/normothermia/endotoxin and ketamine/mild hypothermia/endotoxin groups than in the saline/normothermia/endotoxin group. IL-6 in the ketamine/mild hypothermia/endotoxin group did not differ from that in the ketamine/normothermia/endotoxin and saline/mild hypothermia/endotoxin groups.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Endotoxemia in rats is associated with hypotension and metabolic acidosis as well as increases in plasma cytokine concentrations in normothermic rats. Ketamine prevented these changes in normothermic rats. However, after administration of ketamine, hypothermic, endotoxemic rats, with both moderate and mild hypothermia, continued to show hypotension, metabolic acidosis, and increased plasma cytokines as well as endotoxemic controls. During hypothermia, therefore, ketamine administration in our rat endotoxin model did not have the additive inhibitory effects on inflammatory responses. This was the most important finding of the present study.
In previous studies, ketamine had inhibitory effects, such as cytokine increase and neutrophil activations, on inflammatory responses during endotoxemia without hypothermia (7,8,14). Our previous report, as well as the present one, demonstrated that ketamine administration inhibited hypotension, the increase of TNF- and IL-6, and metabolic acidosis during endotoxemia without hypothermia (10). However, no study had assessed the additive antiinflammatory effects of ketamine on endotoxemia accompanied by hypothermia. Our study showed that ketamine did not have such additional effects during hypothermia.
Various other relationships between ketamine and hypothermia have been studied. Naslund et al. (15) found that ketamine administration during hypothermia was fully neuroprotective in rabbits, reducing deficits from spinal cord ischemia. Yli-Hankala et al. (16) demonstrated that ketamine was useful in combination with hypothermia for improving neurologic outcome after cardiac arrest. However, few reports have addressed the relationship between ketamine and hypothermia during endotoxemia. Our findings suggest that although ketamine may not be as useful as one of the antiinflammatory drugs during hypothermia, ketamine does not deteriorate the hemodynamics and cytokine responses during hypothermia on endotoxemia.
Several investigations concerning relationships between hypothermia and cytokine responses during clinical sepsis demonstrated that hypothermia did not inhibit increases in proinflammatory cytokines such as TNF- or IL-6 concentrations (17). In our experiments, TNF- and IL-6 also remained increased during mild endotoxemia, but IL-6 was inhibited during moderate hypothermia.
In the present study, during both moderate and mild hypothermia, ketamine did not have additive antiinflammatory effects. Two reasons are possible: the actual decrease of the drug’s antiinflammatory effects, and the antiinflammatory effects of hypothermia overshadowing the effects of ketamine. Few reports have analyzed these mechanisms, and further investigations are needed.
One important remaining question concerns the dose-response relationships between ketamine and antiinflammatory effects during hypothermia. In the present study we used 10 mg · kg-1 · h-1 of ketamine because our previous study demonstrated that 10 mg · kg-1 · h-1 of ketamine is the maximally effective dose in endotoxemic rats during normothermia (18). However, few reports have delineated ketamine pharmacokinetics during hypothermia. More generally, several investigations have shown that hypothermia alters the pharmacokinetics of IV anesthetics (11,19). Dose-response properties of ketamine during hypothermia in endotoxemic rats require further investigation.
Critically-ill patients with endotoxemia often experience hypothermia, and perioperative hypothermia is also a common complication of anesthesia and surgery. Therapeutic moderate and mild hypothermia is also an issue; several reports have shown that such treatment after cardiac arrest improves the likelihood of a favorable neurologic outcome (11) and reduces mortality (12,13). Thus, the relationships between anesthetics and hypothermia in endotoxemia pose very important unsolved questions. However, whether ketamine retains its antiinflammatory effects during moderate and mild hypothermia has not been determined. Our findings suggest that during hypothermia, ketamine administration did not have the additive inhibitory effects on inflammatory responses.
In summary, the study presented here showed that although ketamine administration decreased the severity of hypotension and acidosis in endotoxemic rats during normothermia, during moderate and mild hypothermia, ketamine administration may not have additive beneficial antiinflammatory effects.
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References |
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[Abstract/Free Full Text] - Bernard SA, Gray TW, Buist MD, et al. Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia. N Engl J Med 2002; 356: 557–63.
- The Hypothermia After Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. N Engl J Med 2002; 346: 549–56.
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[Abstract/Free Full Text] - Naslund TC, Hollier LH, Money SR, et al. Protecting the ischemic spinal cord during aortic clamping. Ann Surg 1992; 215: 409–15.[Web of Science][Medline]
- Yli-Hankala A, Edmonds HL Jr, Jiang YD, et al. Outcome effects of different protective hypothermia levels during cardiac arrest in rats. Acta Anaeth Scand 1997; 41: 511–5.
- Marik PE, Zaloga GP. Hypothermia and cytokines in septic shock. Intensive Care Med 2000; 26: 716–21.[Web of Science][Medline]
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[Abstract/Free Full Text] - Leslie K, Sessler DI, Bjorksten AR, et al. Mild hypothermia alters propofol pharmacokinetics and increases the duration of action of atracurium. Anesth Analg 1995; 80: 1007–14.[Abstract]
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