Sepsis reduces isoflurane MAC in a normotensive animal model of sepsis

Sedation with propofol and isoflurane differs in terms of microcirculatory parameters: A randomized animal study using dorsal skinfold chamber mouse model

OBJECTIVE

This study aimed to explore the effects of sedative doses of propofol and isoflurane on microcirculation in septic mice compared to controls. Isoflurane, known for its potential as a sedation drug in bedside applications, lacks clarity regarding its impact on the microcirculation system. The hypothesis was that propofol would exert a more pronounced influence on the microvascular flow index, particularly amplified in septic conditions.

MATERIAL AND METHODS

Randomized study was conducted from December 2020 to October 2021 involved 60 BALB/c mice, with 52 mice analyzed. Dorsal skinfold chambers were implanted, followed by intraperitoneal injections of either sterile 0.9 % saline or lipopolysaccharide for the control and sepsis groups, respectively. Both groups received propofol or isoflurane treatment for 120 min. Microcirculatory parameters were obtained via incident dark-field microscopy videos, along with the mean blood pressure and heart rate at three time points: before sedation (T0), 30 min after sedation (T30), and 120 min after sedation (T120). Endothelial glycocalyx thickness and syndecan-1 concentration were also analyzed.

RESULTS

In healthy controls, both anesthetics reduced blood pressure. However, propofol maintained microvascular flow, differing significantly from isoflurane at T120 (propofol, 2.8 ± 0.3 vs. isoflurane, 1.6 ± 0.9; P < 0.001). In the sepsis group, a similar pattern occurred at T120 without statistical significance (propofol, 1.8 ± 1.1 vs. isoflurane, 1.2 ± 0.7; P = 0.023). Syndecan-1 levels did not differ between agents, but glycocalyx thickness index was significantly lower in the isoflurane-sepsis group than propofol (P = 0.001).

CONCLUSIONS

Propofol potentially offers protective action against microvascular flow deterioration compared to isoflurane, observed in control mice. Furthermore, a lower degree of sepsis-induced glycocalyx degradation was evident with propofol compared to isoflurane.

Anesthetic management of patients with sepsis/septic shock

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, while septic shock is a subset of sepsis with persistent hypotension requiring vasopressors to maintain a mean arterial pressure (MAP) of ≥65 mmHg and having a serum lactate level of >2 mmol/L, despite adequate volume resuscitation. Sepsis and septic shock are medical emergencies and time-dependent diseases with a high mortality rate for which early identification, early antibiotic therapy, and early source control are paramount for patient outcomes. The patient may require surgical intervention or an invasive procedure aiming to control the source of infection, and the anesthesiologist has a pivotal role in all phases of patient management. During the preoperative assessment, patients should be aware of all possible organ dysfunctions, and the severity of the disease combined with the patient's physiological reserve should be carefully assessed. All possible efforts should be made to optimize conditions before surgery, especially from a hemodynamic point of view. Anesthetic agents may worsen the hemodynamics of shock patients, and the anesthesiologist must know the properties of each anesthetic agent. All possible efforts should be made to maintain organ perfusion supporting hemodynamics with fluids, vasoactive agents, and inotropes if required.

Minimum alveolar concentration of halogenated volatile anaesthetics in left ventricular hypertrophy and congestive heart failure in rats

BACKGROUND

Although many physiological and pathological conditions affect minimal alveolar concentration (MAC), there are no reliable data on the MAC for halogenated anaesthetics during left ventricular hypertrophy (LVH) and congestive heart failure (CHF). The aim of this experimental study was to determine the MAC values of halothane, isoflurane, and sevoflurane in rats, at early and later stages of cardiomyopathic hypertrophy.

METHODS

LVH was induced by ascending aortic stenosis in 3-4-week-old rats. LVH and CHF in each animal were assessed weekly by echocardiography. MAC of halothane, isoflurane, and sevoflurane was determined using the tail-clamp technique in spontaneously breathing rats from each group. Response vs no-response data were analysed using logistic regression analysis. Data are medians (95% confidence interval).

RESULTS

The MAC of halothane [1.30% (1.26-1.34)], isoflurane [1.52% (1.48-1.57)], and sevoflurane [2.93% (2.78-3.07)] in rats with LVH was not different from sham-operated rats [respectively, 1.23% (1.20-1.26), 1.52% (1.47-1.56), and 2.90% (2.79-3.00)]. Conversely, the MAC of halothane [1.44 (1.39-1.50)] and isoflurane [1.74 (1.69-1.78)], but not sevoflurane [2.99 (2.93-3.06)], was significantly increased in rats with CHF.

CONCLUSIONS

MAC values for halothane, isoflurane, and sevoflurane were unchanged in rats with pressure-induced overload LVH. Conversely, the MAC for halothane and isoflurane, but not sevoflurane, was significantly increased in rats with CHF.

The effect of hypovolemia due to hemorrhage on the minimum alveolar concentration of isoflurane in the dog

OBJECTIVE

To determine the effect of hypovolemia on the minimum alveolar concentration (MAC) of isoflurane in the dog.

STUDY DESIGN

Randomized, cross-over trial.

ANIMAL POPULATION

Six healthy intact mixed breed female dogs weighing 18.2-29.0 kg.

METHODS

Dogs were randomly assigned to determine the MAC of isoflurane in a normovolemic or hypovolemic state with a minimum of 18 days between trials. On both occasions, anesthesia was initially induced and maintained for 40 minutes with isoflurane delivered in oxygen while vascular catheters were placed in the cephalic vein and dorsal metatarsal artery. In dogs assigned to the hypovolemic group, 30 mL kg(-1) of blood was removed at 1 mL kg(-1) minute(-1) from the arterial catheter. All dogs were allowed to recover from anesthesia. Thirty minutes after the discontinuation of isoflurane, anesthesia was re-induced with isoflurane in oxygen delivered by face mask. The tracheas were intubated, and connected to an anesthetic machine with a Bain anesthetic circuit. Mechanical ventilation was instituted at a rate of 10 breaths minute(-1) with the tidal volume set to deliver 10-15 mL kg(-1). Airway gases were monitored continuously and tidal volume was adjusted to maintain an end-tidal carbon dioxide level of 35-40 mmHg (4.67-5.33 kPa). Body temperature was maintained at 37-38 degrees C (98.6-100.4 degrees F). The MAC determination was performed using an electrical stimulus applied to the toe web and MAC was defined as the mean value of end-tidal isoflurane between the concentrations at which a purposeful movement did and did not occur in response to the electrical stimulus. The MAC values were compared between groups using a Student's t-test.

RESULTS

The MAC of isoflurane was significantly less in hypovolemic dogs (0.97 +/- 0.03%) compared with normovolemic dogs (1.15 +/- 0.02%) (p < 0.0079).

CONCLUSIONS AND CLINICAL RELEVANCE

The MAC of isoflurane is reduced in dogs with hypovolemia resulting from hemorrhage. Veterinarians should be prepared to deliver a lower percentage of isoflurane to maintain anesthesia in hypovolemic dogs during diagnostic and therapeutic procedures.

The influence of endotoxemia on the pharmacokinetics and the electroencephalographic effect of propofol in the rat

Endotoxemia decreases the dose requirement for anesthetics but no data are available for propofol. A rat model was used in which the influence of endotoxin administration on the pharmacokinetics and pharmacodynamics of propofol was investigated. Chronically instrumented rats were randomly allocated to either a control (n = 9) or an endotoxin (n = 9) group. Six hours after pretreatment with either endotoxin or its solvent, propofol was infused (150 mg x kg(-1) x h(-1)) until isoelectric periods of 5 s or longer were observed in the electroencephalogram. The changes observed in the electroencephalogram were quantified using aperiodic analysis and used as a surrogate measure of hypnosis. The righting reflex served as a clinical measure of hypnosis. The propofol dose needed to reach the electroencephalographic end point in the endotoxin-treated rats was reduced by almost 50% (p < 0.01). This could be attributed to a decrease in propofol clearance and in distribution volume related to the degree of physiologic and metabolic disturbances induced by endotoxin. To investigate changes in end organ sensitivity, the biphasic electroencephalographic effect versus effect-site concentration relationship was studied. This relationship was characterized by descriptors that showed an increased intrinsic efficacy of propofol in the endotoxin group. The effect-site concentration at the return of righting reflex was lower in the endotoxin group. Our study demonstrates that endotoxin-treated animals need a lower dose of propofol to reach the same degree of anesthetic effect which can mainly be attributed to changes in pharmacokinetics.

Sevoflurane preconditions stunned myocardium in septic but not healthy isolated rat hearts

BACKGROUND

Recent evidence indicates that sevoflurane treatment before prolonged ischaemia reduces infarct size in normal hearts, mimicking ischaemic preconditioning. We examined whether exposure to sevoflurane before brief ischaemia, inducing a 'stunned myocardium', provided such protective effects in an isolated working heart from normal or septic rats.

METHODS

With institutional approval, 91 rats were randomly allocated into one of either caecal-ligation and perforation (CLP: n=50) or sham (Sham: n=41) procedure groups 24 h before the study. After determination of baseline measurements, including cardiac output (CO), myocardial oxygen consumption (mVO(2)) and cardiac efficiency (CE; CO x peak systolic pressure/mVO(2)), each isolated heart was perfused with or without 2% sevoflurane for 15 min before global ischaemia (pre-ischaemia). After 15 min ischaemia and 30 min reperfusion, all hearts were assessed for functional recovery of myocardium (post-reperfusion).

RESULTS

During the pre-ischaemia period, 2% sevoflurane caused a significant reduction of CO in the CLP group compared with the Sham group. During the post-reperfusion period, both CO (16.9 vs 11.0 ml min(-1)) and CE (11.2 vs 7.7 mm Hg ml(-1) ( micro l O(2))(-1)) was higher in the sevoflurane-treated vs -untreated hearts from CLP rats, and was accompanied by lower incidence of reperfusion arrhythmia compared with control hearts (8 vs 32%). In contrast, 2% sevoflurane did not provide cardioprotective effects in normal rats.

CONCLUSIONS

The current study demonstrates that pre-treatment with sevoflurane minimizes myocardial dysfunction and the incidence of reperfusion arrhythmia after brief ischaemic insults in septic hearts.

Influence of sepsis on minimum alveolar concentration of desflurane in a porcine model

The effect of sepsis on the minimum alveolar concentration of desflurane (MAC(DES)) in humans and other animals has not been reported previously. The aim of this study was to test the hypothesis that sepsis might alter MAC(DES) in a normotensive septic porcine model. Twenty-four young healthy pigs were premedicated with ketamine 10 mg kg(-1 )i.m and then anaesthesia was established with propofol 3 mg kg(-1) and the trachea was intubated. Baseline MAC(DES) in each pig was evaluated by pinching with a haemostat applied for 1 min to a rear dewclaw. MAC(DES) was determined by changing desflurane concentrations stepwise until purposeful movement appeared. Pigs were randomly assigned to two groups of 12 animals: the saline group received a 1 h i.v. infusion of saline solution while the sepsis group received a 1 h i.v. infusion of live Pseudomonas aeruginosa. Epinephrine and hydroxyethylstarch were used to maintain normotensive and normovolaemic haemodynamic status. In both groups, MAC(DES) was evaluated 5 h after infusion. Significant increases in heart rate, cardiac output, mean pulmonary artery pressure and pulmonary vascular resistance occurred in the sepsis group. MAC(DES) was 9.2% (95% confidence interval (CI) 6.8-10.6%) for the saline group and 6.7% (95% CI: 4.7-10.4) for the sepsis group (P<0.05). These data indicate that MAC(DES) is significantly decreased in this normotensive hyperkinetic septic porcine model.

Influence of sepsis on sevoflurane minimum alveolar concentration in a porcine model

Sevoflurane is widely used in anaesthetic protocols for patients undergoing surgical procedures. However, there are no reports on the influence of sepsis on minimum alveolar concentration of sevoflurane (MAC(SEV)) in animals or in humans. The aim of this study was to test the hypothesis that sepsis could alter the MAC(SEV) in a normotensive septic pig model. Twenty young, healthy pigs were used. After they had received 10 mg kg(-1) of ketamine i.m. for premedication, anaesthesia was established with propofol 3 mg kg(-1) and the trachea was intubated. Sevoflurane was used as the sole anaesthetic agent. Baseline haemodynamic recording included electrocardiography, carotid artery blood pressure and a pulmonary thermodilution catheter. Baseline MAC(SEV) in each pig was evaluated by pinching with a haemostat applied for 1 min to a rear dewclaw. MAC(SEV) was determined using incremental changes in sevoflurane concentration until purposeful movement appeared. Pigs were assigned randomly to two groups: the saline group (n = 10) received a 1-h i.v. infusion of sterile saline solution while the sepsis group (n = 10) received a 1-h i.v. infusion of live Pseudomonas aeruginosa. Epinephrine and hydroxyethylstarch were used to maintain normotensive and normovolemic haemodynamic status. In both groups, MAC(SEV) was evaluated 5 h after infusion. Significant increases in mean artery pulmonary pressure, filling, epinephrine and vascular pulmonary resistances occurred in the sepsis group. MAC(SEV) for the saline group was 2.4% [95% confidence interval (CI) 2.1-2.55%] and the MAC(SEV) for the sepsis group was 1.35% (95% CI 1.2-1.45%, P<0.05). These data indicate that MAC(SEV) is significantly decreased in this normotensive septic pig model.

Effects of isoflurane, enflurane, and halothane on skeletal muscle microcirculation in the endotoxemic rat

PURPOSE

The cardiovascular effects of volatile anesthetics during sepsis sets patients at high risk for hemodynamic deterioration. We compared the microcirculatory alterations in skeletal muscle under anesthesia with isoflurane, enflurane, and halothane in an endotoxemic rat preparation.

MATERIALS AND METHODS

Twenty-one Sprague-Dawley rats under continuous hemodynamic monitoring and intravital microscopy of the spinotrapezius muscle were studied during two level lipopolysaccharide (0.2 mg/kg and 2 mg/kg) induced sepsis. The effects of equianesthetic concentrations (1.5 minimum alveolar concentration [MAC]) of either isoflurane [n:7], enflurane [n:7], or halothane [n:7] on microcirculatory vasoregulation were measured and histopathologic changes were evaluated.

RESULTS

During low-dose endotoxemia, arteriolar vasodilation under isoflurane was nearly abolished (P < .05). At high-dose endotoxemia, this lack of vasodilatory effect was similar (P < .05). Animals receiving 1.5 MAC of enflurane during low-dose endotoxin presented a significant decrease in arteriolar diameter by -11.3 (+/-2.9%), this response was less during high-dose endotoxemia (-7.0, +/-2.9%). Halothane caused pronounced vasoconstriction by -20 (+/-3.7%) during low-dose endotoxemia and moderate but significant constriction during high-dose endotoxemia (-7.9, +/-2.6%).

CONCLUSIONS

Isoflurane, enflurane, and halothane exert significantly different effects on vasoregulation of skeletal muscle arterioles in the endotoxemic rat.

Severe group A streptococcal infection and streptococcal toxic shock syndrome

PURPOSE

To review the literature on group A streptococcal toxic shock syndrome, (STSS).

DATA SOURCE

Medline and EMBASE searches were conducted using the key words group A streptococcal toxic shock syndrome, alone and in combination with anesthesia; and septic shock, combined with anesthesia. Medline was also searched using key words intravenous immunoglobulin, (IVIG) and group A streptococcus, (GAS); and group A streptococcus and antibiotic therapy. Other references were included in this review if they addressed the history, microbiology, pathophysiology, incidence, mortality, presentation and management of invasive GAS infections. Relevant references from the papers reviewed were also considered. Articles on the foregoing topics were included regardless of study design. Non-English language studies were excluded. Literature on the efficacy of IVIG and optimal antibiotic therapy was specifically searched.

PRINCIPAL FINDINGS

Reports of invasive GAS infections have recently increased. Invasive GAS infection is associated with a toxic shock syndrome, (STSS), in 8-14% of cases. The STSS characteristically results in shock and multi-organ failure soon after the onset of symptoms, and is associated with a mortality of 33-81%. Many of these patients will require extensive soft tissue debridement or amputation in the operating room, on an emergency basis. The extent of tissue debridement required is often underestimated before skin incision.

CONCLUSIONS

Management of STSS requires volume resuscitation, vasopressor/inotrope infusion, antibiotic therapy and supportive care in an intensive care unit, usually including mechanical ventilation. Intravenous immunoglobulin infusion has been recommended. Further studies are needed to define the role of IVIG in STSS management and to determine optimal anesthetic management of patients with septic shock.

Minimum alveolar anesthetic concentration of volatile anesthetics in normal and cardiomyopathic hamsters

Minimum alveolar anesthetic concentrations (MAC) values of volatile anesthetics in cardiovascular diseases remain unknown. We determined MAC values of volatile anesthetics in spontaneously breathing normal and cardiomyopathic hamsters exposed to increasing (0.1%-0.3% steps) concentrations of halothane, isoflurane, sevoflurane, or desflurane (n = 30 in each group) using the tail-clamp technique. MAC values and their 95% confidence interval were calculated using logistic regression. In normal hamsters, inspired MAC values were: halothane 1.15% (1.10%-1.20%), isoflurane 1.62% (1.54%-1.69%), sevoflurane 2.31% (2.22%-2.40%), and desflurane 7.48% (7.30%-7.67%). In cardiomyopathic hamsters, they were: halothane 0.89% (0.83%-0.95%), isoflurane 1.39% (1.30%-1.47%), sevoflurane 2.00% (1.85%-2.15%), and desflurane 6.97% (6.77%-7.17%). Thus, MAC values of halothane, isoflurane, sevoflurane, and desflurane were reduced by 23% (P < 0.05), 14% (P < 0.05), 13% (P < 0.05), and 7% (P < 0.05), respectively in cardiomyopathic hamsters.

IMPLICATIONS

Minimum alveolar anesthetic concentrations of volatile anesthetics were significantly lower in cardiomyopathic hamsters than in normal hamsters.

Septic shock

PURPOSE

Many patients with sepsis require surgery for their management, often on an urgent or emergency basis. Anaesthetists are commonly required to manage patients with sepsis and septic shock in the operating room, past anaesthesia recovery area, and the intensive care unit. Since little has been written in the Anaesthesia literature on sepsis and septic shock, a review of this topic was considered appropriate.

SOURCE

References were obtained from computerized searches on the National Library of Medicine (English language), recent review articles and personal files. PRINCIPLES FINDINGS: Septic shock is a common cause of morbidity and mortality. Its presentation may be subtle or catastrophic. Successful management depends on an understanding of the pathophysiology of the syndrome, allowing rapid, appropriate resuscitation. This often requires aggressive correction of volume deficit, maintenance of adequate perfusion pressure with inotropic and vasopressor therapy, mechanical ventilation and correction of coagulopathy. Appropriate cultures must be taken and antibiotic therapy started, often empirically. Anaesthetic management should include careful haemodynamic monitoring. Anaesthesia induction and maintenance must be tailored to the haemodynamically unstable patient.

CONCLUSIONS

The management of the septic patient in the perioperative period presents a challenge for the anaesthetist. Haemodynamic and respiratory instability should be anticipated. Management requires multisystem intervention and careful anesthetic management.