[The effects of midazolam on oxygen consumption and the level of vigilance. The possibility of the sedative effect of the plexiglas dome (canopy) of the Deltatrac indirect calorimetry device]

OBJECTIVE

To assess the effects of midazolam on oxygen consumption (VO2) and the level of vigilance. To search for a possible "sedative effect" of the canopy of the Deltatrac (Datex) when a placebo is administered instead of midazolam.

STUDY DESIGN

Prospective, comparative, randomized, double-blinded, cross-over study.

PATIENTS

Eight healthy volunteers of ASA physical class 1, not under stress, fasting and at rest.

METHODS

The volunteers were administered at T0 either midazolam (0.07 mg.kg-1, IM), or a placebo at a one week interval in an order at random. The VO2 was measured with a Deltatrac. Circulatory status was monitored with non invasive methods and the level of vigilance assessed using the Ramsay scale. Statistical analysis was obtained with Anova for repeated measurements with two within factors (drug and time).

RESULTS

VO2 decreased similarly and significantly between T0 and T45 min (P < 0.05). The decrease continued only after midazolam until T60 min. However the variation of VO2 between the midazolam and placebo group was not significant. The haemodynamic variables remained unchanged. Midazolam had a stronger sedative effect at T120 min.

[The effect of position on intracranial pressure]

The question as to whether the head and trunk of neurosurgery patients should be elevated remains controversial. This question is particularly important when intracranial hypertension is present. Head up position may have beneficial effects on intracranial pressure (ICP) via changes in mean arterial pressure (MAP), airway pressure, central venous pressure and cerebro spinal fluid displacement. However, in some circumstances, head up position may decrease MAP which in turn will result in a paradoxical rise in ICP through autoregulation mechanisms. Therefore, the degree of head elevation has to be titrated by evaluating the most adequate cerebral perfusion pressure (CPP) for each patient by means of transcranial Doppler or measurement of jugular venous blood oxygen saturation. Head elevation above 30 degrees should be avoided in all cases. In most patients with intracranial hypertension, head and trunk elevation up to 30 degrees is useful in helping to decrease ICP, providing that a safe CPP of at least 70 mmHg or even 80 mmHg is maintained. Patients in poor haemodynamic conditions are best nursed flat. CPP is thus the most important factor in assessment and monitoring when considering head elevation in patients with increased ICP.

[Nutritional aspects of cranial trauma]

In head-injured patients the nutritional support is aimed to prevent denutrition status usually observed. The adequate amount of calories depends on the basal metabolism (as calculated with the Harris Benedict equation). It has to be increased in case of fever (by a 0.1 factor per degree above 37 degrees C), sepsis (by a 0.1 to 0.2 factor) or when sedation is discontinued (by a 0.3 factor). The increased proteolysis is not modified by the associated treatment and results in an inevitable protein loss, whatever the qualitative change in nutritional support. In clinical practice, the nutritional support has to be adjusted continuously to the needs of the patient, to avoid a more pronounced denutrition due to the summation of daily nutritional deficits.

Influence of body temperature, with or without sedation, on energy expenditure in severe head-injured patients

OBJECTIVE

To quantify the effect of body temperature and sepsis on energy expenditure in head-injured patients.

DESIGN

Prospective, nonrandomized, observational study.

SETTING

Neurosurgical intensive care unit.

PATIENTS

Severe head-injured patients.

INTERVENTIONS

Use of an indirect calorimeter to measure energy expenditure.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure (MAP), heart rate (HR), body temperature, and mean hourly energy expenditure were recorded. Twenty-four patients had 1,919 hourly measures of the above parameters. The measurement periods were divided into four groups, according to the anesthetic agents used for sedation: fentanyl and midazolam (group FM); fentanyl, midazolam, and curarization (group C); thiopental (group T); and no sedation (group NS). The energy expenditure/basal energy expenditure ratio (EE/BEE) was significantly lower in group T (1.20 +/- 0.15) than in group FM (1.32 +/- 0.24) or group C (1.32 +/- 0.20) and was significantly higher in group NS (1.60 +/- 0.33). There was a significant correlation between body temperature and EE/BEE (p < .0001, r2 = .27) only in sedated patients. Using the equation of the regression line to correct energy expenditure for differences in body temperatures between groups, the difference in energy expenditure between groups with sedation disappeared. This finding suggested that the low energy expenditure under thiopental was due only to hypothermia. Sepsis significantly increased energy expenditure independently of fever. There was a weak but statistically significant correlation between energy expenditure and HR (p<.01, r2 = .13) but not between energy expenditure and MAP.

CONCLUSIONS

Sedation had a major effect on energy expenditure. In sedated patients, body temperature was the main determinant of energy expenditure; the anesthetic agent used had little influence on the level of energy expenditure. Sepsis increased energy expenditure independently of fever, probably through hormonal changes.

The effect of hemodilution on cerebral blood flow velocity in anesthetized patients

Transcranial Doppler is used to estimate changes in cerebral blood flow, but the effect of hemodilution on cerebral blood flow velocity (CBFV) in anesthetized patients has not been evaluated. The aim of this study was to measure the effect of isovolemic hemodilution on CBFV and lumbar cerebrospinal fluid pressure (P(CSF)) in anesthetized patients without change in other physiological variables that may affect CBFV. Patients undergoing hemodilution were compared with a control group undergoing no hemodilution. With hemodilution, hematocrit decreased from 38% +/- 3% to 30% +/- 2%, arterial oxygen content (Cao2) decreased from 17.5 +/- 1.3 to 13.9 +/- 0.9 mL/dL, and CBFV increased from 50 +/- 10 to 58 +/- 10 cm/s. An equivalent of cerebral arterial O2 transport calculated as Cao2 x CBFV did not significantly change. Over the same time interval, there were no changes in the control group. There was no statistically significant change in P(CSF), pulsatility index, Paco2, blood pressure, heart rate, or body temperature in either group. We conclude that CBFV reflects cerebral blood flow changes after hemodilution.

IMPLICATIONS

Hemodilution increases cerebral blood flow but may change the cerebral artery diameter, which could confound perioperative measurement of cerebral blood flow velocity. This study found transcranial Doppler ultrasonography to accurately assess the effects of hemodilution on the cerebral circulation, but the hematocrit should be taken into account to fully understand perioperative cerebral blood flow velocity changes.

Catheter-related infections following axillary vein catheterization

BACKGROUND

The aim of this study was to determine the rate of infectious complications following axillary vein cannulation and to compare to that observed after internal jugular vein catheterization.

METHODS

A prospective comparative open study was carried out to determine the rate of infectious complications related to the use of catheters inserted via the axillary vein or the internal jugular vein. During the study period all patients submitted to central venous catheterization were evaluated. A total of 141 patients entered and completed the study. Catheter insertion sites were either the axillary vein punctured in the axilla, or the internal jugular vein punctured using an anterior approach. Catheter tips were cultured using a quantitative technique. Clinical information pertaining to the analysis was prospectively collected.

RESULTS

A total of 141 catheters from 141 patients entered was studied. Clinical characteristics and risk factors for catheter infection were similar in both groups. The incidence of catheter-related infection (including catheter-related sepsis, and bacteremia) was not different between the two groups (axillary vein: 8.1%; internal jugular vein: 7.6%). Catheter-related bacteremia were seen at a rate of 3.7% in the internal jugular vein group and a rate of 1.6% in the axillary vein group (NS). The incidence of catheter colonization was similar in both groups (axillary vein: 14.5%; internal jugular vein: 11.4%).

CONCLUSION

Catheter-related infection after axillary vein catheterization was similar to that observed after internal jugular vein catheterization. The chance of developing catheter-related sepsis was less than 10% with either route when catheters were used for the treatment of severely ill patients.

Intraoperative autologous blood transfusion in intracranial surgery

OBJECTIVE

The purpose of this study was to evaluate the benefits of intraoperative autotransfusion of autologous blood on the conservation of allogenic blood, including cost-effectiveness and the consequences for hemoglobin level and coagulation tests.

METHODS

The Hoemonetics Cell Saver 4 autotransfusion system (Hoemonetics Corporation, MA) was used when the estimated blood loss was equal to or more than 500 ml. A total of 472 patients undergoing intracranial surgery were included in the study.

RESULTS

Ninety patients (19%) received transfusions either with autologous blood or allogenic blood. Fifty-five patients (61%) received only autologous blood transfusions, 10 patients (11%) received both autologous and allogenic blood transfusions, and 25 patients (28%) received only allogenic blood transfusions. The amount of autologous blood transfused was 600 +/- 590 ml (range, 230-3000 ml). The amount of allogenic blood transfused was 3 +/- 3 units (range, 2-15 units). Autologous blood represented 68% of all blood products transfused. Mild abnormalities during coagulation tests occurred without clinical bleeding.

CONCLUSION

Autologous blood transfusions were demonstrated to be safe in patients undergoing intracranial surgery and to be more cost-effective than allogenic blood transfusions. Intraoperative autologous blood transfusions may be used alone in more than half of the patients requiring transfusions during intracranial surgery and decrease the amount of allogenic blood used. Improvements in the monitoring for the need of performing this technique, as well as preoperative blood donations, would decrease the amount of allogenic blood transfused.

[Acute Weston Hurst necrotizing hemorrhagic leukoencephalitis]

The clinical and pathological findings of a 43-year-old woman, diagnosed as having acute hemorrhagic leukoencephalitis at postmortem examination, are presented. The acute hemorrhagic leukoencephalitis affects mainly young adults and is the most fulminant from of demyelinating disease. It is frequently preceded by a respiratory infection. Diagnosis is facilitated by CT scanning and MRI, which reveal the massive lesion in the cerebral white matter. Many cases terminate fatally in 2 or 4 days, but in others survival is longer. The pathological findings are distinctive.

[Transfer hypokalemia induced by norepinephrine infusion]

We report a case of a severe hypokalaemia by intracellular shift of potassium in a sedated and ventilated head trauma patient. The kalaemia which was 3.9 mmol.L-1 at admission in the intensive care unit decreased to 1.3 mmol.L-1 during a perfusion of noradrenaline (0.3 micrograms.kg-1.min-1). Following the decrease of the noradrenaline dose, and administration of potassium, the kalaemia rapidly increased to 5.3 mmol.L-1 carrying a risk of arrhythmia. Therefore, kalaemia and ECG should be closely monitored when the noradrenaline doses are reduced. The causes of transcellular shift of potassium are reviewed.

A comparison of extradural and intraparenchymatous intracranial pressures in head injured patients

The reliability of extradural pressure measurements for the measure of intracranial pressure (ICP) is still controversial. This study was undertaken to assess the limits of agreement between extradural and intraparenchymatous pressures using respectively the Plastimed extradural sensor and the Camino fiberoptic system. The study took place in a neurosurgical intensive care unit. Ten head injured patients were included in the study, leading to the comparison of 1032 pairs of hourly ICP values. Although the measures were significantly correlated, there was no agreement between the two methods of ICP monitoring. Extradural pressure was higher than intraparenchymatous pressure (bias 9 mmHg; 95% confidence interval of bias -9.8 to 27.8 mmHg). The lack of agreement between the two methods is probably due to the unreliability of extradural pressure for the measurement of ICP.

Glycosylated and non-glycosylated prolactin forms are increased after opioid administration as part of surgical anaesthesia

OBJECTIVE

Previous studies have shown that non-glycosylated prolactin (NG-PRL) increased more markedly than glycosylated hormone (G-PRL) after TRH or metoclopramide stimulation. The aim of the present study was to determine whether such results could be extended to opioid-induced PRL stimulation.

DESIGN

Open and prospective study. Using a newly developed IRMA specific for NG-PRL, we determined G-PRL and NG-PRL immunoreactivities after administration of 0.8-1.2 mg of the opioid drug phenoperidine as part of an anaesthesia.

PATIENTS

Ten male patients anaesthetized for surgical treatment of a prolapsed lumbar intervertebral disc.

MEASUREMENTS

Samples were obtained hourly pre and post-operatively, and every 15 minutes during operation for determination of plasma PRL, NG-PRL and G-PRL. Plasma cortisol, ACTH and GH levels were measured in an attempt to differentiate the respective roles of stress and opiate agonists in the variations of PRL levels during surgery.

RESULTS

A dramatic increase in PRL levels was observed in all patients from an average of 300 +/- 90 to 1200 +/- 330 mU/l (mean + SEM) 30 minutes after drug administration. The proportion of G-PRL immunoreactivity was not significantly different when basal (25.2%) and stimulated (27%) values were compared (P > 0.05), and when mean increments of NG-PRL and G-PRL were compared (345 and 348%, respectively). The opioid drug induced a significant decrease in cortisol levels after injection and during operation (from 585 +/- 63 to 99 +/- 51 nmol/l) with a concomitant decrease in ACTH levels. GH levels were not significantly altered during anaesthesia but were significantly greater (P < 0.05) after than before surgery (5.0 +/- 1.3 vs 0.98 +/- 0.54 mU/l, respectively).

CONCLUSIONS

We conclude from the present and from previous data that opioid induced anaesthesia is accompanied by an increase in both glycosylated and non-glycosylated PRL and that different PRL secretagogues may induce distinct responses in terms of PRL molecular forms.

[Continuous administration of mivacurium for short procedures. Delayed onset and recovery from neuromuscular blockade]

OBJECTIVE

To assess the delays of onset and spontaneous recovery from neuromuscular block produced by mivacurium administered by continuous infusion for short procedure requiring a deep relaxation.

STUDY DESIGN

Prospective open non comparative study.

PATIENTS

Twenty-nine class ASA I and II adults undergoing a stomatological procedure of short duration were included in the study.

METHOD

General anaesthesia was obtained with a continuous infusion of propofol, supplemented with alfentanil and N2O-O2 mixture. Neuromuscular blockade, assessed with electromyography of the adductor pollicis muscle, was obtained with mivacurium (150 micrograms.kg-1). After restoration of 5% of neuromuscular transmission, mivacurium was administered by continuous infusion in order to maintain a blockade between 91 and 99%.

RESULTS

The delay for decreasing twitch height by 95% was 2.9 +/- 1.0 min. The mean dose for maintenance of blockade was 10.9 +/- 1.5 micrograms.kg-1.min-1. The delay of spontaneous recovery from blockade was 10.2 min, 16.6 min and 21.3 min for obtaining 25, 75 and 95% twitchs respectively. The delay for the twitch increase from 25 to 75% was 6.6 min.

DISCUSSION

Mivacurium in continuous infusion provides rapidly a deep and stable neuromuscular blockade followed by a rapid spontaneous restoration of neuromuscular transmission in patients with normal pseudocholinesterases.

[Patient posture in neurosurgery]

There is still controversy whether neurosurgical patients' head and trunc should be elevated or not, particularly in case of increased intracranial pressure (ICP). Head up position may have beneficial effects on ICP via changes in mean arterial pressure (MAP), airway pressure, central venous pressure and CSF displacement. However, in some circumstances, head up position may decrease MAP, which in turn will result in a paradoxical rise in ICP through autoregulation mechanisms. Therefore, the degree of head elevation has to be titrated by evaluating the most adequate cerebral perfusion pressure (CPP) for each patient by means of transcranial Doppler or measurement of jugular venous blood oxygen saturation. Head elevation above 30 degrees should be avoided in all cases. In most patients with intracranial hypertension, head and trunc elevation up to 30 degrees is useful in helping to decrease ICP, providing that a safe CPP of a least 70 mmHg or even 80 mmHg is maintained. Patients in poor haemodynamic conditions are best nursed flat. CPP is thus a most important factor to evaluate and monitor while considering head elevation in patients with increased ICP.

Energy expenditure and withdrawal of sedation in severe head-injured patients

OBJECTIVES

To determine the outcome of oxygen consumption (VO2) and energy expenditure after cessation of sedation in severe head-injured patients and to assess its usefulness as a predictor of neurologic severity.

DESIGN

Prospective, descriptive study.

SETTING

Neurosurgical intensive care unit (ICU) in a university hospital.

PATIENTS

Fifteen severe head-injured patients with tracheostomies and who were mechanically ventilated and sedated at the time of the study.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

VO2 and energy expenditure were measured, using indirect calorimetry during and after discontinuation of sedation. After the measurement period, the patients were divided into two groups. Group 1 included patients who were completely weaned from sedation; group 2 included patients who had to be sedated again using predetermined criteria. In both groups, energy expenditure was close to basal energy expenditure during sedation, and increased to 150% of basal energy expenditure during the recovery period, with maximum hourly values 80% above basal energy expenditure. In group 1, VO2 and energy expenditure changed from 284 +/- 44 mL/min and 1833 +/- 261 kcal/day during sedation to 390 +/- 85 mL/min and 2512 +/- 486 kcal/day for the period without sedation. During this period, there was a significant correlation between VO2 and mean arterial pressure. For the recovery period, there was no difference in mean or maximum VO2 between the two groups of patients. At 24 and 48 hrs after cessation of sedation, VO2 and energy expenditure decrease to 30% above basal energy expenditure. These changes may be due to the recovery of muscular activity, weaning from mechanical ventilation, or an increase in the amount of circulating catecholamines.

CONCLUSION

In severe head-injured patients, during the first 12 hrs after the discontinuation of sedation, the patients experienced a large increase in VO2, energy expenditure, and mean arterial pressure. Although these changes have no prognostic value in our study, they have potential deleterious effects in head-injured patients. Methods that blunt these changes which have proven efficacious in anesthesia may be effective for intensive care patients.

[Anesthesia in surgery for intracranial aneurysms]

The two major neurological complications of subarachnoid haemorrhage (SAH) due to an intracranial aneurysm are rebleeding and delayed cerebral ischaemia related to cerebral vasospasm. The best way to prevent rebleeding is early surgery. Even when surgery is performed within the first 72 hours posthaemorrhage, the risk of cerebral ischaemia due to vasospasm is high. Conventional medical treatment of cerebral vasospasm includes haemodilution, hypervolaemia and increase of arterial blood pressure. Haemodilution is of limited value as the patients suffering from SAH have usually a low haematocrit. The effectiveness of hypervolaemia is controversial and it may worsen cerebral and pulmonary oedema. Systemic hypertension is an effective therapy of vasospasm, but which can only be used once the aneurysm is controlled. Nimodipine and nicardipine, two calcium antagonists, have a beneficial effect on neurologic outcome following SAH. Today, it is still debated whether the beneficial effect of nimodipine results from the vascular effect of the drug or from a direct cerebral cytoprotective mechanism. Early surgery implies that surgeons operate on brains in acute inflammatory state. Thus, it is mandatory to use peroperative techniques improving cerebral exposure. These techniques include infusion of mannitol, lumbar cerebrospinal fluid (CSF) drainage, administration of anaesthetic agents known to decrease cerebral blood flow (CBF) and hypocapnia. Usually, the effect of CSF drainage is very effective and sufficient by itself. The second objective in the peroperative period is to avoid ischaemia. In areas with decreased flow distal to vasospasm, autoregulation is impaired and CBF is directly dependent on cerebral perfusion pressure. Furthermore, the safe practice of transient clipping of vessels supplying the aneurysm has dramatically reduced the indications of controlled hypotension. During temporary clipping, some authors recommend a pharmacological brain protection using barbiturates, etomidate or propofol, but this practice has not been validated by randomized studies. However, it is generally agreed that the arterial pressure should be increased during temporary clipping to improve collateral blood flow and to maintain it after the aneurysm has been secured. To conclude, together with lumbar CSF drainage and transient clipping, the anaesthetic management of the patients should include: maintenance of the arterial blood pressure close to its preoperative level, maintenance of PaCO2 between 30 and 35 mmHg and of normovolaemia through replacement of fluid and blood losses. After completion of surgery, recovery from anaesthesia should be rapid to allow fast diagnosis of neurological complications. The monitoring of the status of consciousness is the key of the diagnosis of early postoperative complications.

[Use of Diprivan in neurosurgery]

Propofol is an appropriate agent in neurosurgery, where it represents an alternative to the thiopentone-isoflurane anaesthetic technique. Some patients are at risk of hypotension during induction of anaesthesia which may be associated with an important decrease in cerebral perfusion pressure. The administration of propofol as a continuous infusion is therefore preferable in these patients. In the absence of nitrous oxide, propofol anaesthesia allows the monitoring of sensory evoked potentials during spinal surgery. For surgery of epilepsy, it is preferable to avoid giving propofol in the minutes preceding the electroencephalographic location of the areas to be excised.

[Consequences and prevention methods of hemodynamic changes during laryngoscopy and intratracheal intubation]

In patients ranked ASA 1, laryngoscopy and intubation lead to an average increase in blood pressure of 40 to 50%, and a 20% increase in heart rate. These changes, which are greatest one minute after intubation, last for 5 to 10 min. They are due to sympathetic and adrenal stimulation, which may also result in some arrhythmias. About half the patient with coronary artery disease experience episodes of myocardial ischaemia during intubation when no specific prevention is undertaken. Among the different means available for this, narcotics seem to have a reliable and constant effect, but they may be responsible for postoperative respiratory depression. The protective effect of fentanyl starts at 2 micrograms.kg-1, and is at a maximum at 8 micrograms.kg-1. Lidocaine is the drug used most. Recent studies have questioned its efficacy. In clinical practice, it is particularly effective in preventing the pressor response to tracheal intubation, whatever its route of administration (intravenous or intratracheal), but not the increase in heart rate. Beta blockers with bradycardic, antihypertensive, antiarrhythmic and antiischaemic properties, have been advocated. As opposed to lidocaine, these agents are more effective in preventing the changes in heart rate than the pressor response. Because of their depressor effect on the myocardium, their place still remains to be defined, especially in the cardiac risk patient. Short-acting beta blockers should be preferred. Nitroglycerin is specifically indicated in coronary artery disease. Other agents, such as clonidine or calcium blockers, seem to be less effective or less convenient in preventing the haemodynamic alterations. In clinical practice, prevention will first rely on a sufficient dose of narcotics. In some cases, nitroglycerin or beta blockers may be used so as to decrease the doses of narcotics, without altering their efficacy; however, the risk of hypotension should be constantly borne in mind. If preventing measures have not been taken, short-acting antihypertensive agents (beta blockers, calcium blockers) should be used in patients who develop major hypertension during laryngoscopy and intubation.

May-Hegglin anomaly: a rare case of maternal thrombocytopenia in pregnancy

The May-Hegglin anomaly, a rare cause of thrombocytopenia, is an autosomal dominant disorder that may have adverse maternal and fetal consequences. We present herein a case of May-Hegglin anomaly in pregnancy. The characteristic features of this anomaly, clinical presentation, and management options are discussed.