Ketamine pharmacology: an update (pharmacodynamics and molecular aspects, recent findings)

For more than 50 years, ketamine has proven to be a safe anesthetic drug with potent analgesic properties. The active enantiomer is S(+)-ketamine. Ketamine is mostly metabolized in norketamine, an active metabolite. During "dissociative anesthesia", sensory inputs may reach cortical receiving areas, but fail to be perceived in some association areas. Ketamine also enhances the descending inhibiting serotoninergic pathway and exerts antidepressive effects. Analgesic effects persist for plasma concentrations ten times lower than hypnotic concentrations. Activation of the (N-Methyl-D-Aspartate [NMDA]) receptor plays a fundamental role in long-term potentiation but also in hyperalgesia and opioid-induced hyperalgesia. The antagonism of NMDA receptor is responsible for ketamine's more specific properties. Ketamine decreases the "wind up" phenomenon, and the antagonism is more important if the NMDA channel has been previously opened by the glutamate binding ("use dependence"). Experimentally, ketamine may promote neuronal apoptotic lesions but, in usual clinical practice, it does not induce neurotoxicity. The consequences of high doses, repeatedly administered, are not known. Cognitive disturbances are frequent in chronic users of ketamine, as well as frontal white matter abnormalities. Animal studies suggest that neurodegeneration is a potential long-term risk of anesthetics in neonatal and young pediatric patients.

Constant-flow insufflation prevents arterial oxygen desaturation during endotracheal suctioning

In mechanically ventilated patients, disconnection from the ventilator and endotracheal suctioning can induce major arterial oxygen desaturation resulting from apnea, changes in inspired oxygen fraction, and decrease in lung volume. The aim of this study was to test the efficacy of a simple method of delivering oxygen and maintaining lung volume during this process. Our study was conducted in two parts. In the first part, constant-flow insufflation of oxygen (CFI) was used in seven patients ventilated for acute respiratory failure (PaO2/FlO2 = 347 +/- 33 mm Hg) as a means of maintaining arterial oxygenation during apnea and disconnection from the ventilator. CFI was administered via a modified endotracheal tube in which small capillaries allowed delivery of a high-velocity jet flow near the tracheal end of the tube during disconnection from the ventilator. In comparison to apnea alone, CFI prevented a fall in arterial oxygen tension (16 +/- 7 mm Hg during CFI versus 117 +/- 27 during apnea, after 90 s of disconnection in the two situations, p less than 0.001), whereas it did not reduce the development of hypercapnia. The efficacy of CFI resulted both from the injection of oxygen into the trachea and from the maintenance of positive alveolar pressure induced by air entrainment (mean 10.4 +/- 1.1 cm H2O), preventing a fall in lung volume usually occurring after disconnection (+338 +/- 88 ml during CFI versus -344 +/- 64 ml during apnea, p less than 0.01). In the second part of the study CFI was used to prevent arterial oxygen desaturation induced by endotracheal suctioning.(ABSTRACT TRUNCATED AT 250 WORDS)

Tachycardia and convulsions induced by accidental intravascular ropivacaine injection during sciatic block

Ropivacaine, a recently introduced local anesthetic of the amide family (1), seems to show less toxicity than bupivacaine (2-4). Nevertheless, both neurologic and cardiovascular toxicities are possible. Six cases of ropivacaine-induced convulsions have previously been reported (5-10), of which three cases also showed cardiovascular toxicity. In three cases, total plasma concentrations were measured (Table 1).

Efficacy and safety of oral ketamine for the relief of intractable chronic pain: A retrospective 5-year study of 51 patients

BACKGROUND

This work summarizes the efficiency, failures and adverse effects of oral administration of ketamine at home for intractable pain.

METHODS

This 5-year retrospective study involved testing ketamine by intravenous in-hospital administration, then a conversion to an oral route, or oral treatment directly administered at home. The daily intravenous dose was increased by steps of 0.5 mg/kg to attain an effective daily dose of 1.5-3.0 mg/kg. Pain was evaluated on a numeric scale from 0 to 10, and evidence of adverse effects was collected every day. The effective daily dose was delivered orally (three to four intakes). If effective, ketamine was continued for 3 months. Short infusions or direct oral treatment began with a 0.5-mg/kg dose, then the daily ketamine dose was increased in 15- to 20-mg increments.

RESULTS

Among 55 cases (51 patients, neuropathic pain 60%), the mean effective oral dose was 2 mg/kg. Ketamine was effective in 24 patients (44%, mean pain reduction 67 ± 17%), partially effective in 20% (mean pain reduction 30 ± 11%), with a mean opioid sparing of 63 ± 32%, and failure in 22%. Half of the patients experienced adverse effects, but only eight had to stop treatment. For patients with opioid therapy, failure of ketamine was less frequent (7% vs. 36%; p < 0.02), with fewer adverse effects (33% vs. 68%; p < 0.01).

CONCLUSIONS

Pain was reduced or abolished in two-thirds of patients under ketamine therapy; ketamine was effective for patients taking opioids and resulted in few adverse effects.

Bronchopulmonary distress associated with toxic epidermal necrolysis

We describe here a patient with severe TEN and respiratory distress and we review the subject of bronchopulmonary symptoms in TEN. Even if pseudostratified ciliated involvement is uncommon, bronchial lesions in the absence of other known causes, should be specifically related to TEN. The mechanisms of pulmonary involvement and ARDS associated with TEN are discussed.

A retrospective study of ketamine administration and the development of acute or post-traumatic stress disorder in 274 war-wounded soldiers

The objective of this study was to explore whether ketamine prevents or exacerbates acute or post-traumatic stress disorders in military trauma patients. We conducted a retrospective study of a database from the French Military Health Service, including all soldiers surviving a war injury in Afghanistan (2010-2012). The diagnosis of post-traumatic stress disorder was made by a psychiatrist and patients were analysed according to the presence or absence of this condition. Analysis included the following covariables: age; sex; acute stress disorder; blast injury; associated fatality; brain injury; traumatic amputation; Glasgow coma scale; injury severity score; administered drugs; number of surgical procedures; physical, neurosensory or aesthetic sequelae; and the development chronic pain. Covariables related to post-traumatic and acute stress disorders with a p ≤ 0.10 were included in a multivariable logistic regression model. The data from 450 soldiers were identified; 399 survived, of which 274 were analysed. Among these, 98 (36%) suffered from post-traumatic stress disorder and 89 (32%) had received ketamine. Fifty-four patients (55%) in the post-traumatic stress disorder group received ketamine vs. 35 (20%) in the no PTSD group (p < 0.001). The 89 injured soldiers who received ketamine had a median (IQR [range]) injury severity score of 5 (3-13 [1-26]) vs. 3 (2-4 [1-6] in the 185 patients who did not (p < 0.001). At multivariable analysis, only acute stress disorder and total number of surgical procedures were independently associated with the development of post-traumatic stress disorder. In this retrospective study, ketamine administration was not a risk factor for the development of post-traumatic stress disorder in the military trauma setting.

[The damage control resuscitation concept]

OBJECTIVE

Damage control is a strategy of care for bleeding trauma patients, involving minimal rescue surgery associated to perioperative resuscitation. The purpose of this review is to draw up a statement on current knowledge available on damage control.

DATA SOURCES

References were obtained from recent review articles, personal files, and Medline database research of English and French publications. All categories of articles on this topic have been selected.

DATA SYNTHESIS

Historical damage control surgery, that consist of abbreviated laparotomy with second-look after resuscitation, is now included in a wider concept called "damage control resuscitation", addressing the lethal triad (coagulopathy, hypothermia and acidosis) at an early phase. Care is focused on coagulopathy prevention. Early resuscitation, or damage control ground zero, has been improved: aggressive management of hypothermia, bleeding control techniques, permissive hypotension concept and early use of vasopressors. Transfusion practices also have evolved: early platelets and coagulation factors administration, use of hemostatic agents like recombinant FVIIa, whole blood transfusion, denote the damage control hematology. Progress in surgical practices and development of arteriographic techniques lead to wider indications of damage control strategy.

Antivenin remains effective against African Viperidae bites despite a delayed treatment

BACKGROUND

Viperidae bites represent a public health issue in Africa and are responsible for a hemorrhagic syndrome with fatal outcome in the short term. A research on Medline database does not reveal any data definitively demonstrating the efficiency of antivenom in case of delayed administration. The aim of this study, based on a 12-year survey of viperine syndromes in Republic of Djibouti, was to compare the normalization of the hemostasis disorders with an early administration of antivenin versus a delayed administration.

METHODS

A retrospective study was conducted from October 1994 to May 2006 in the intensive care unit of the French military Hospital, in Djibouti. Seventy-three Viperidae-envenomed patients were included. Antivenin efficiency in correcting hemostatic disorders was analyzed in relation to time to treatment (before or after the 24th hour after the bite).

RESULTS

Forty-two patients (58%) presented with bleeding. A consumptive coagulopathy was found in 68 patients (93%). Antivenin was observed to be effective in improving hemostasis, and the time to normalization of biologic parameters was similar, whether the treatment was started before or after the 24th hour after the bite.

CONCLUSION

Antivenin should ideally be administered as early as possible. However, in Africa, time to treatment generally exceeds 24 hours. The results of the present evidence-based study confirm an empirical concept: a delayed time to treatment should in no way counterindicate the use of antivenin immunotherapy, in the case of African Viperidae bites.

[Ischaemic stroke secondary to viper envenomation in Morocco in the absence of adequate antivenom]

An ischaemic stroke is a rare complication of viper envenomation that is due to multifactorial pathophysiological mechanisms. The authors describe the case of a 55-year-old patient bitten by the viper Cerastes cerastes. The patient was admitted to the intensive care unit with multiple organ failure, disseminated intravascular coagulopathy, rhabdomyolysis, anuria and elevated troponin level. The persistent disturbance of consciousness has motivated a brain scan which has revealed a bifocal ischemic stroke. The complex venom of the species C. cerastes may induce hypotension, tissue necrosis, acute renal failure, bleeding disorders or DIC. With the cessation of a non-indicated heparintherapy and haemodialysis, the patient recovered in a few weeks despite the initial infusion of an unsuitable antivenom due to the late identification of the reptile. The preventive treatment of the complications of this envenomation is based on the infusion of the polyvalent antivenom Favirept(®).

Severe hypokalaemic paralysis from an unusual cause mimicking the Guillain-Barré syndrome

We report a case of hypokalaemic quadriparesis occurring 37 years after a bilateral ureterosigmoidostomy. The history and physical signs as well as cerebrospinal fluid analysis initially led to a diagnosis of Guillain-Barré syndrome. Acidosis and profound hypokalaemia were present and a dramatic improvement occurred after rapid correction of the potassium depletion. The underlying mechanism of potassium depletion which occurs after this mode of urinary diversion are briefly discussed.

Mechanisms of increased myocardial contractility with hypertonic saline solutions in isolated blood-perfused rabbit hearts

Hypertonic saline improves organ perfusion and animal survival during hemorrhagic shock because it expands plasma volume and increases tissue oxygenation. Because both decreased and increased myocardial performance have been reported with hypertonic saline, the effects of hyperosmolarity and the mechanism accounting for it were investigated in isolated blood-perfused rabbit hearts. Coronary blood flow (CBF), myocardial contractility, relaxation, and oxygen consumption were measured during administration of blood perfusates containing 140-180 mmol sodium concentrations ([Na+]). In two other series of experiments, the role of Na(+)-Ca2+ exchange in the inotropic effect of hyperosmolarity (160 mmol sodium concentration) and hypertonicity (sucrose) were also investigated. Hypertonic [Na+] induced a significant increase in contractility and relaxation, combined with a coronary vasodilation. Myocardial oxygen consumption (MVO2) increased at all hypertonic [Na+] without significant change in coronary venous oxygen tension (PVO2) and content (CVO2). Amiloride (0.3 mmol) inhibited the improved contractility observed with 160 mmol sodium. Similar Na(+)-Ca2+ exchanger blockade did not inhibit the inotropic effect of sucrose. These results confirm the positive inotropic effect of hypertonic [Na+]. The inhibition of this improvement by amiloride suggests that calcium influx through the sarcolemna could be the major mechanism of this effect.

[Pulmonary embolism in the context of severe envenomation by a Moroccan viper]

Heparin, which was widely used thirty years ago for the treatment of viper envenomations, is now contra-indicated during the acute phase, which is at risk for hemorrhage and death. We report a case of pulmonary embolism, a rare situation in the context of viper envenomation. By means of this case report, we want to discuss the pathophysiological links between envenomation and thromboembolic disease, and on the other hand, the potential heparin usefulness, not during the acute, hemorrhagic phase, but as a prophylactic treatment when hemorrhagic risk has been replaced by an inflammatory syndrome, with increased fibrinogen and platelets which are then prothrombotic factors.

Failure of a Mexican antivenom on recovery from snakebite-related coagulopathy in French Guiana

INTRODUCTION

In French Guiana, most snakebites are caused by crotalids, with the main signs being tissue damage and bleeding due to venom-induced coagulopathy. Since December 2014 the Western Guiana Hospital (WGH) has used Antivipmyn Tri ^TM, a Mexican polyvalent antivenom. The aim of the study was to assess its benefit on the correction of snakebite-related coagulopathy.

METHODS

This retrospective study included patients hospitalized at the WGH with snakebite and a coagulopathy defined by: a prothrombin rate (PR) lower than 45%, an activated partial thromboplastin time ratio (aPTTr) greater than 2 or a fibrinogen lower than 100 mg.dL^-1. The antivenom group included patients receiving Antivipmyn Tri ^TM from December 2014 to September 2017. The control group included patients admitted between January 2013 and November 2014 (when antivenom was unavailable) or admitted between December 2014 and September 2017 during times of antivenom shortage. We graphically compared the time courses of PR, aPTTr and fibrinogen between groups. Other endpoints were the length of hospital stay and the need for surgery or dialysis.

RESULTS

84 patients were included: 42 in the antivenom group, 42 in the control group. Both groups were similar for age, sex-ratio, proportion of bleedings, necrosis, and severity. Most patients in the antivenom group received 3 vials. There were no significant differences in recovery of PR, aPTTr and fibrinogen through the first 24 h. Fibrinogen declined again in the control group at 30 h and showed a slower rise to normal concentration. There were no significant differences in any secondary endpoint.

CONCLUSION

Antivipmyn Tri ^TM as currently used did not show any benefit in recovery from coagulopathy.