Engelhardt, T.; McCheyne, A J.; Karsli, C.; Luginbuehl, I.; Bissonnette, B. Author Information

To determine the effects of nitrous oxide on middle cerebral artery blood flow velocity (CBFV) during sevoflurane anaesthesia in children, CBFV was measured using transcranial Doppler sonography in 16 ASA I or II children. Anaesthesia consisted of 1.0 MAC sevoflurane in 30% oxygen with intermittent positive pressure ventilation maintaining FEco2 at 38 mmHg (5.0 kPa) and a caudal epidural block using 0.25% bupivacaine 1.0 ml.kg-1. The remainder of the inspired gas was varied in one of two sequences either air/nitrous oxide/air or nitrous oxide/air/nitrous oxide. The results showed that CBFV decreased when nitrous oxide was replaced by air (p = 0.03) and returned to its initial value when nitrous oxide was reintroduced. CBFV increased when air was replaced by nitrous oxide (p = 0.04) and returned to its initial value when air was reintroduced. Mean heart rate and blood pressure remained constant. We conclude that nitrous oxide increases cerebral blood flow velocity in healthy children anaesthetised with 1.0 MAC sevoflurane.

BACKGROUNDTo determine whether temperature and haematocrit (Hct) alter the relationship between blood flow (BF) and blood flow velocity (BFV).METHODSUsing a transcranial Doppler apparatus, we measured the peak velocity of whole blood cells pumped by a cardiopulmonary bypass (CPB) circuit, through a 0.15-cm internal diameter segment of rigid tubing. BF and BFV relationships were obtained at temperatures of 19, 28, and 37 degrees C and at Hct of 0.05, 0.22, 0.39, and 0.54, by altering CPB flow over a range from 10 to 100 cc/min. Linear regression analysis was performed.RESULTSThe relationship between velocity and flow for the pooled Hct data was y=(0.43)x+0.86, r2=0.998 and 95% CI (0.999-1) whereas the association for the temperature data was y=(0.42)x+0.02, r2=0.9998 and 95% CI (0.999-0.9997). Changes of blood viscosity had no effect on velocity at a given flow rate. The combined effect of Hct and temperature on velocity for the relationship with flow is expressed by: y=1.3+2.4x.CONCLUSIONIn fixed diameter vessels with laminar flow, the linear relationship between flow and velocity is not affected by changes in temperature and Hct in clinical ranges. These results are explained by the Fahraeus-Lindquist effect. They support the use of transcranial Doppler sonography to estimate cerebral blood flow in infants who may have large variations of Hct and/or temperature during bypass.

To determine the effect of halothane on the cerebral blood flow velocity (CBFV) with increasing then decreasing concentrations, 11 children scheduled for minor surgery were studied. Anaesthesia consisted of halothane, vecuronium, nitrous oxide in oxygen and a caudal block. End-tidal carbon dioxide, temperature, heart rate and systolic arterial pressure were maintained constant. CBFV increased significantly between 0.5 and 1.0 MAC (p <0.001), and 0.5 and 1.5 MAC of halothane (p <0.001), but was not different after increasing concentration from 1.0 to 1.5 MAC. During the decreasing phase, CBFV decreased significantly from 1.5 to 1.0 MAC of halothane (p <0.001), whereas there was no difference in CBFV when decreasing halothane MAC from 1.0 to 0.5 MAC. In children, the decrease in CBFV during decreasing halothane concentration is not superimposable to the increase in CBFV seen when increasing halothane concentration, suggesting the presence of cerebrovascular hysteresis to halothane.

To determine the effect of halothane on cerebral blood flow velocity measured by transcranial Doppler, 23 healthy young children were studied during surgery. Anaesthesia was induced with thiopental, fentanyl and vecuronium, and maintained with halothane in 70% nitrous oxide in oxygen. A continuous epidural anaesthesia with 0. 25% bupivacaine was performed. End-tidal carbon dioxide pressure, temperature, heart rate and systolic blood pressure were kept constant. Three minimal alveolar concentrations (MAC; 0.5, 1.0 and 1. 5) of halothane were administered in stepwise increases. The cerebral blood flow velocity increased significantly at 1.0 (p < 0. 01) and 1.5 MAC (p < 0.001) compared with the value at 0.5 MAC. No further change in cerebral blood flow velocity was seen between 1.0 and 1.5 MAC. These data show that maximal changes in cerebral blood flow velocity are obtained at 1.0 MAC and that further increases in halothane concentration do not modify the cerebral circulation. It is suggested that young children differ from adults in that the maximal effect of halothane occurs at lower concentrations.

OBJECTIVE:To study the effects of mild hypothermia and associated changes in temperature-corrected PaCO2 (cPaCO2) on intracranial pressure (ICP), mean velocity of the middle cerebral artery (Vm), and venous jugular saturation in O2 (SjvO2) in patients with severe traumatic brain injury (TBI).DESIGN:Prospective, observational study.SETTING:Intensive care unit.PATIENTS:Severe TBI patients mechanically ventilated, sedated and paralyzed.INTERVENTIONS:Twenty patients were subjected to four consecutive periods: (a) normocapnia-normothermia; (b) hypocapnia-normothermia, where hypocapnia was induced by an increase in minute volume; (c) hypocapnia-hypothermia, where hypocapnia was induced by hypothermia maintaining the ventilatory settings constant; (d) normocapnia-hypothermia, where normocapnia was achieved by a decrease in minute volume.MEASUREMENTS AND RESULTS:cPaCO2 was 41 +/- 8 mmHg in periods 1 and 4, and 31 +/- 7 mmHg in periods 2 and 3. Core temperature was 37.1 +/- 0.8 degrees C in periods 1 and 2, and 34.1 +/- 1.1 degrees C in periods 3 and 4. End-tidal CO2 and cPaCO2 values showed no difference between periods 1 and 4 and periods 2 and 3. ICP and Vm were dependent on cPaCO2 but independent of core temperature values. SjvO2 was related to cPaCO2 and was significantly higher during period 3 than during period 2 (P < 0.05).CONCLUSION:The decrease in ICP was similar when hypocapnia was induced by hyperventilation or as a result of hypothermia alone. The relationship between cPaCO2 and ICP might predict variations in ICP during changes in core temperature. Further studies are needed to confirm the cerebral metabolic effects of moderate hypothermia in TBI patients.

The combination of vecuronium and atracurium was studied in 60 children of ASA physical status 1 or 2. In part I, the dose–response relationships were determined in 30 children who were randomly assigned to receive a single bolus of 0.02, 0.025 or 0.03 mgkg−1 of vecuronium or 0.075, 0.01 or 0.0125 mgkg−1 of atracurium. The evoked electromyogram of the adductor pollicis brevis muscle to train‐of‐four stimulation was monitored. The speed of onset of the neuromuscular blockade was determined by a 95% depression of the train‐of‐four whereas the recovery index was established at 75% recovery of T1. In part II, 30 children were randomly assigned to receive 2 × ED95 of vecuronium, 2 × ED95 of atracurium, or a combination of 1 × ED95 of vecuronium + 1 × ED95 of atracurium. This study showed that the ED50 and ED95 for vecuronium were 0.021 mgkg−1 and 0.037 mgkg−1 and for atracurium 0.11 mgkg−1 and 0.30 mgkg−1, respectively. The slopes of the dose–response relationships were significantly different (p < 0.001). With vecuronium alone, the speed of onset of neuromuscular blockade was significantly slower (p < 0.001) and the duration of action less (p < 0.001) than that with atracurium alone or with the combination. There were no differences between atracurium and the combination of both medications. The recovery index was similar for all groups. We conclude that the dose–response relationships of vecuronium and atracurium in children undergoing halothane anaesthesia are not parallel and the neuromuscular effects of vecuronium and atracurium are neither additive nor synergistic. While vecuronium has a shorter duration of action than atracurium, this feature is not apparent when it is combined with atracurium in equipotent doses. Recovery is rapid and not prolonged when these two drugs are combined.

Purpose: To evaluate the tracheal intubating conditions when intubation time is determined by the onset time of the neuromuscular block either of the adductor pollicis (AP) or of the orbicularis oculi muscle (OO).Methods: In this prospective, double blind, randomised study, 40 adults ASA I-II undergoing general anaesthesia with tracheal intubation were allocated to two groups (n = 20) according to the reference muscle (AP or OO) used to determine the appropriate intubation time, Induction of anaesthesia was achieved with 5-7 mg . kg(-1) thiopentone, 1.5-2.5 mu g . kg(-1) fentanyl and 0.9 mg . kg(-1) rocuronium (3 x ED95) for muscular relaxation. Supramaximal train of four stimulation of the ulnar and facial nerve every 10 sec was used to monitor the neuromuscular block. After visual loss of AP or OO contraction, tracheal intubation and quality of intubation assessment were performed by two independent anaesthetists, Data are expressed as mean and standard error of the mean (X +/- SEM).Results: Curarisation time of the OO was shorter (110 +/- 4,9 sec) than that of the AP (144 +/- 5,5 sec; P< 0.0001). Intubation conditions were excellent in 95% and good in 5% of the patients in the AP group whereas in the OO group only 65% of the patients had excellent and 20% good intubation conditions (P < 0.05). Coughing was observed in 15% of patients in the OO group during tracheal intubation.Conclusion: Monitoring neuro-muscular activity of the AP using TOF to determine the appropriate tracheal intubation time and conditions in patients paralysed with rocurorium is more clinically relevant than monitoring the OO muscle.

OBJECTIVE:To evaluate the clinical and electromyographic (EMG) effects of ketanserin (K), a serotoninergic receptor antagonist (5-HT2), on postoperative shivering (POS).STUDY DESIGN:Prospective, randomised, double-blind study.PATIENTS:Fifty ASA class 1 and 2 patients with major clinical postoperative tremor were studied.METHODS:POS was assessed clinically (0 = nil, 1 = moderate, 2 = severe). Inclusion criterion was a POS of 2 at admission in the recovery room. The mean arterial blood pressure, rectal temperature, SpO2 were recorded at admission (T0) and subsequently at T5, T10, T15, T30 and T60 minutes. Either 10 mg of K (n = 25) or a corresponding volume of a placebo (P) (n = 25) were intravenously injected. The EMG activity of the deltoid and quadriceps muscles was recorded continuously. Blood lactic acid concentration was measured at the end of POS. Results are expressed as mean +/- SEM. Parametric values were analysed with unpaired Student's t-test, and nonparametric values with chi 2 analysis. P < 0.05 was accepted.RESULTS:Demographic data, duration of anaesthesia, postoperative temperature, oxygen saturation, blood pressure and blood lactate concentration were similar between groups. The POS duration in the K group was significantly shorter than in the P group: 8.8 +/- 1.5 min and 15.5 +/- 1.5 min respectively (P < 0.01). The number of patients in the K group experiencing POS at T5 and T10 was significantly lower, when compared with those who had received the P (P < 0.05).CONCLUSION:At a dose of 10 mg, K administered in patients with POS during recovery, reduced significantly the duration and intensity of the shivering without noticeable side effects. This study suggests that this 5-HT2 antagonist is an efficient therapeutic tool for POS in adults.

Biomechanics can be defined as the physical concepts exploring the effects of mechanical forces in biology. Biomechanics explores the consequences of an alteration in the steady-state normally existing between living tissues and their immediate environment. The application of this science in the field of brain physiopathology and intracranial hypertension is essential to understanding the sequence of events triggered during an alteration of the intracranial volume such as observed with intracranial pathologies. Furthermore, biomechanics allows the development of a logical and rational therapeutic approach, better adapted to the various intracerebral problems anaesthesiologists might be confronted with.

Following subarachnoid haemorrhage, delayed cerebral ischaemia from cerebral vasospasm remains the most important cause of mortality and morbidity in patients with surgically secured aneurysms. Therapy with haemodilution, hypertension and volume expansion has been recommended to prevent and treat delayed cerebral ischaemia in these patients on the basis of uncontrolled clinical series (level of evidence III to V, grade C recommendation). Despite the lack of controlled studies, the maintenance of a cardiac index > 3.5 L . min(-1).m(-2) and a systolic arterial pressure between 120 and 150 mmHg before clipping and 160 to 200 mmHg thereafter is recommended as a prophylactic or therapeutic measure for vasospasm. Close monitoring of neurological and cardiorespiratory status is important to avoid neurologic and systemic complications.

Objectives: To assess that neuromuscular relaxation onset of the adductor pollicis (AP) is related to neuromuscular stimulation rate. To assess that train-of-four (TOF) at 0.05 Hz is a more accurate indicator of optimal tracheal intubation time and conditions, than TOF at 0.08 Hz.Study design: Prospective, comparative, randomized double-blind study.Patients: Forty adults, physical class ASA 1 or 2, undergoing general anaesthesia with tracheal intubation were allocated to two groups (n = 20) according to the sequence of stimulation of the AP : either TOF at 0.05 Hz (test group) or TOF at 0.08 Hz (control group).Methods: Induction of anaesthesia was achieved with thiopentone, fentanyl and vecuronium (0.1 mg . kg(-1)). Neuromuscular monitoring was obtained with force displacement transducers attached to each AP. Tracheal intubation was performed once AP muscular response obtained with TOF at 0.05 Hz for test group and TOF at 0.08 Hz for control group was abolished, Results are expressed as X +/- SEM Fisher exact test was used for intubation conditions comparison. Curarization time between groups was compared with unpaired Student's t test (P < 0.05 accepted).Results: TOF with 0.05 Hz stimulation significantly increased curarization time: 217 +/- 7 versus 162 +/- 6 s (P < 0.001), intubation conditions were excellent in 95% and good in 5% of patients in the study group, compared to 15 and 40% in the control group, respectively (P < 0.01). In 45% of the control group patients coughing at intubation occurred.Conclusion: Low stimulation rate (TOF at 0.05 Hz) of AP is a reliable techique to determine the appropriate intubation time for patients paralyzed with vecuronium.