Cerebrovascular carbon dioxide reactivity in children anaesthetized with propofol

Effects of different ventilation on cerebral oxygen saturation and cerebral blood flow before and after modified ultrafiltration in infants during ventricular septal defect repair

OBJECTIVE

To analyse the changes of different ventilation on regional cerebral oxygen saturation and cerebral blood flow in infants during ventricular septal defect repair.

METHODS

Ninety-two infants younger than 1 year were enrolled in the study. End-expiratory tidal pressure of carbon dioxide was maintained at 40-45 and 35-39 mmHg in relative low and high ventilation groups. Regional cerebral oxygen saturation and flow velocity of the middle cerebral artery were recorded after anaesthesia (T0), cut pericardium (T1), separation from cardiopulmonary bypass (T2), the end of modified ultrafiltration, (T3) and at the end of operation (T4).

RESULTS

The relative low ventilation group exhibited a significantly high regional cerebral oxygen saturation at each time point except for T2 (T0:77 ± 4, T1:76 ± 5, T3:76 ± 8, T4:76 ± 8, respectively, p < 0.001). Flow velocity of the middle cerebral artery in the relative low ventilation group was higher compared to the relative high ventilation group at each time point except for T2 (T0:53 ± 14, T1:54 ± 15, T3:53 ± 17, T4:52 ± 16, respectively, p < 0.001). Between the two groups, T2 showed the lowest middle cerebral artery flow velocity (relative low ventilation: 39 ± 15, relative high ventilation: 39 ± 11, p < 0.001).

CONCLUSION

The infants' regional cerebral oxygen saturation and middle cerebral artery flow velocity performed better in the range of 40-45 mmHg end-expiratory tidal pressure of carbon dioxide during CHD surgery. Modified ultrafiltration increased cerebral oxygen saturation. It was important to regulate ventilation in order to balance cerebral oxygen in infants.

Age-related cerebrovascular carbon dioxide reactivity in children with ventricular septal defect younger than 3 years

BACKGROUND

Impaired cerebrovascular reactivity to carbon dioxide was proposed to contribute to neurological morbidity in children undergoing cardiac surgery. The objective of this study was to assess carbon dioxide reactivity and regional cerebral oxygen saturation in children younger than 3 years.

METHODS

This study enrolled children younger than 3 years undergoing ventricular septal defect repair. The cohort was divided into three age groups: younger than 6 months, 6-12 months, and 12-36 months. Under steady-state anesthesia, carbon dioxide reactivity was calculated by measuring changes in middle cerebral artery blood flow velocity using transcranial Doppler sonography. Regional cerebral oxygen saturation changes were measured by near-infrared spectroscopy while endtidal carbon dioxide pressure was adjusted from 30 to 45 mm Hg.

RESULTS

Carbon dioxide reactivity showed a statistically significant increasing relationship with age (younger than 6 months group: 4.42% ± 2.73%, 6-12 months group: 5.86% ± 1.91%, 12-36 months group: 7.58% ± 1.49%; P < .001). Regional cerebral oxygen saturation showed a statistically significant increasing relationship with age (younger than 6 months group: 65% ± 6%, 6-12 months group: 68% ± 5%, 12-36 months group: 70% ± 5%; P = .027). Regional cerebral oxygen saturation showed a statistically significant increasing relationship with endtidal carbon dioxide pressure in all children (P < .001).

CONCLUSION

Abnormal carbon dioxide reactivity is prevalent in children younger than 3 years and the degree varies according to age.

Factors affecting cerebrovascular reactivity to CO2 in premature infants

Background Hypercarbia increases cerebral blood flow secondary to cerebral vasodilatation, while hypocarbia can lead to vasoconstriction with a subsequent decrease in cerebral blood flow. The aim of this study was to examine CO2 cerebral vasoreactivity in a cohort of premature infants and to identify factors which influence this reactivity. Methods We prospectively studied a cohort of hemodynamically stable premature infants [birth weight (BW) <1500 g and gestational age (GA) ≤34 weeks]. Subjects underwent two studies, one in the first 72 h and the second after 1 week of life. Infants were continuously monitored via a physiology station that included transcutaneous CO2 (tcPCO2) monitor, near-infrared spectroscopy (NIRS), arterial pulse oximetry and heart rate. The total hemoglobin (Hb-T) signal of NIRS was used as an indicator of cerebral blood volume (CBV). Correlation between tcPCO2 and Hb-T was performed in each 1-h period using Pearson's correlation. Factors affecting the CO2 cerebrovascular reactivity were examined using bivariate and linear regression analyses. Results A total of 3847 1-h epochs were obtained from 140 studies of 72 premature infants. tcPCO2 correlated positively with Hb-T in 42% of epochs. In regression analysis, factors associated with increased percentage of positive correlation epochs were male sex and younger postmenstrual age (PMA; β = 0.176, 0.169 and P-value = 0.036, 0.047 respectively). Factors associated with increased strength of positive correlation were mechanical ventilation and increased average tcPCO2 (β = 0.198, 0.220 and P-value = 0.024, 0.011 respectively). Conclusion Increased prematurity, male sex, mechanical ventilation and hypercarbia are associated with stronger PCO2 cerebrovascular reactivity in premature infants. This association may explain their role in the pathogenesis of brain injury.

Monitoring and management of brain hemodynamics and oxygenation

While cardiorespiratory monitoring is standard for newborns in the NICU, monitoring of brain hemodynamics and oxygenation is usually sporadic and targeted to newborns with suspected or confirmed neurologic disorders. This is unfortunate, since critically ill newborns, both preterm and term-born, are at high risk of brain injury and would benefit from improved techniques for continuous monitoring of brain hemodynamics and oxygenation, in addition to monitoring of systemic hemodynamics and oxygenation. Near-infrared spectroscopy (NIRS) and, to a lesser extent, Doppler ultrasound are techniques that have been used in research and increasingly for clinical purposes to measure and monitor brain hemodynamics and oxygenation in newborns. NIRS monitoring can be useful for detection of diverse pathologic conditions that occur frequently in very preterm newborns and in selected populations of term newborns at risk for brain injury related to disturbances of systemic hemodynamics. This chapter reviews the current state of the art with regard to brain-monitoring techniques and the research directed at this important area, and it concludes with suggestions for the use of currently available tools to manage newborns at high risk of neurologic injury from disturbances in brain hemodynamics and oxygenation.

Mechanical Ventilation After Bidirectional Superior Cavopulmonary Anastomosis for Single-Ventricle Physiology: A Comparison of Pressure Support Ventilation and Neurally Adjusted Ventilatory Assist

We evaluated the effects of different respiratory assist modes on cerebral blood flow (CBF) and arterial oxygenation in single-ventricle patients after bidirectional superior cavopulmonary anastomosis (BCPA). We hypothesized that preserved auto-regulation of respiration during neurally adjusted ventilatory assist (NAVA) may have potential advantages for CBF and pulmonary blood flow regulation after the BCPA procedure. We enrolled 23 patients scheduled for BCPA, who underwent pressure-controlled ventilation (PCV), pressure support ventilation (PSV), and NAVA at two assist levels for all modes in a randomized order. PCV targeting large V T (15 mL × kg(-1)) resulted in lower CBF and oxygenation compared to targeting low V T (10 mL × kg(-1)). During PSV and NAVA, ventilation assist levels were titrated to reduce EAdi from baseline by 75 % (high assist) and 50 % (low assist). High assist levels during PSV (PSVhigh) were associated with lower PaCO2, PaO2, and O2SAT, lower CBF, and higher pulsatility index compared with those during NAVAhigh. There were no differences in parameters when using low assist levels, except for slightly greater oxygenation in the NAVAlow group. Modifying assist levels during NAVA did not influence hemodynamics, cerebral perfusion, or gas exchange. Targeting the larger V T during PCV resulted in hyperventilation, did not improve oxygenation, and was accompanied by reduced CBF. Similarly, high assist levels during PSV led to mild hyperventilation, resulting in reduced CBF. NAVA's results were independent of the assist level chosen, causing normalized PaCO2, improved oxygenation, and better CBF than did any other mode, with the exception of PSV at low assist levels.

Age-related carbon dioxide reactivity in children after moderate and severe traumatic brain injury

OBJECTIVE The objective of this study is to assess carbon dioxide reactivity (CO2R) in children following traumatic brain injury (TBI). METHODS This prospective observational study enrolled children younger than 18 years old following moderate and severe TBI. Thirty-eight mechanically ventilated children had daily CO2R testing performed by measuring changes in their bilateral middle cerebral artery flow velocities using transcranial Doppler ultrasonography (TCD) after a transient increase in minute ventilation. The cohort was divided into 3 age groups: younger than 2 years (n = 12); 2 to 5 years old (n = 9); and older than 5 years (n = 17). RESULTS Children younger than 2 years old had a lower mean CO2R over time. The 2-5-year-old age group had higher mean CO2R than younger patients (p = 0.01), and the highest CO2R values compared with either of the other age groups (vs > 5 years old, p = 0.046; vs < 2 years old, p = 0.002). Having a lower minimum CO2R had a statistically significant negative effect on outcome at discharge (p = 0.0413). Impaired CO2R beyond Postinjury Day 4 trended toward having an effect on outcome at discharge (p = 0.0855). CONCLUSIONS Abnormal CO2R is prevalent in children following TBI, and the degree of impairment varies by age. No clinical or laboratory parameters were identified as risk factors for impaired CO2R. Lower minimum CO2R values are associated with worse outcome at discharge.

Impact of sevoflurane anesthesia on brain oxygenation in children younger than 2 years

OBJECTIVE/AIM

To assess the impact of sevoflurane and anesthesia-induced hypotension on brain oxygenation in children younger than 2 years.

BACKGROUND

Inhalational induction with sevoflurane is the most commonly used technique in young children. However, the effect of sevoflurane on cerebral perfusion has been only studied in adults and children older than 1 year. The purpose of this study was to assess the impact of sevoflurane anesthesia on brain oxygenation in neonates and infants, using near-infrared spectroscopy.

METHODS

Children younger than 2 years, ASA I or II, scheduled for abdominal or orthopedic surgery were included. Induction of anesthesia was started by sevoflurane 6% and maintained with an expired fraction of sevoflurane 3%. Mechanical ventilation was adjusted to maintain an endtidal CO2 around 39 mmHg. Brain oxygenation was assessed measuring regional cerebral saturation of oxygen (rSO2 c), measured by NIRS while awake and 15 min after induction, under anesthesia. Mean arterial pressure (MAP) variation was recorded.

RESULTS

Hundred and ninety-five children were included. Anesthesia induced a significant decrease in MAP (-27%). rSO2 c increased significantly after induction (+18%). Using children age for subgroup analysis, we found that despite MAP reduction, rSO2 c increase was significant but smaller in children ≤ 6 months than in children >6 months (≤ 6 months: rSO2 c = +13%, >6 months: rSO2 c = +22%; P < 0.0001). Interindividual comparison showed that, during anesthesia at steady-state with comparable CMRO2, rSO2 c values were significantly higher when MAP was above 36 mmHg. And the higher the absolute MAP value during anesthesia was, the higher the rSO2 c was. We observed a rSO2 c variation ≤ 0 in 21 patients among the 195 studied, and the majority of these patients were younger than 6 months (n = 19). No increase or decrease of rSO2 c during anesthesia despite reduction of CMRO2 can be explained by a reduction of oxygen supply. Using the ROC curves, we determined that the threshold value of MAP under anesthesia, associated with rSO2 c variation ≤ 0%, was 39 mmHg in all the studied population (AUC: 0.90 ± 0.02; P < 0.001). In children younger than 6 months, this value of MAP was 33 mmHg, and 43 mmHg in children older than 6 months.

CONCLUSION

Despite a significant decrease of MAP, 1 MAC of sevoflurane induced a significant increase in regional brain oxygenation. But subgroup analysis showed that MAP decrease had a greater impact on brain oxygenation, in children younger than 6 months. According to our results, MAP value during anesthesia should not go under 33 mmHg in children ≤6 months and 43 mmHg in children >6 months, as further changes in MAP, PaCO2 or hemoglobin during anesthesia may be poorly tolerated by the brain.

[How can we determine the best cerebral perfusion pressure in pediatric traumatic brain injury?]

The management of cerebral perfusion pressure (CPP) is the one of the main preoccupation for the care of paediatric traumatic brain injury (TBI). The physiology of cerebral autoregulation, CO2 vasoreactivity, cerebral metabolism changes with age as well as the brain compliance. Low CPP leads to high morbidity and mortality in pediatric TBI. The recent guidelines for the management of CPP for the paediatric TBI indicate a CPP threshold 40-50 mmHg (infants for the lower and adolescent for the upper). But we must consider the importance of age-related differences in the arterial pressure and CPP. The best CPP is the one that allows to avoid cerebral ischaemia and oedema. In this way, the adaptation of optimal CPP must be individual. To assess this objective, interesting tools are available. Transcranial Doppler can be used to determine the best level of CPP. Other indicators can predict the impairment of autoregulation like pressure reactivity index (PRx) taking into consideration the respective changes in ICP and CPP. Measurement of brain tissue oxygen partial pressure is an other tool that can be used to determine the optimal CPP.

Perioperative central nervous system injury in neonates

Anaesthetic-induced developmental neurotoxicity (AIDN) has been clearly established in laboratory animal models. The possibility of neurotoxicity during uneventful anaesthetic procedures in human neonates or infants has led to serious questions about the safety of paediatric anaesthesia. However, the applicability of animal data to clinical anaesthesia practice remains uncertain. The spectre of cerebral injury due to cerebral hypoperfusion, metabolic derangements, coexisting disease, and surgery itself further muddles the picture. Given the potential magnitude of the public health importance of this issue, the clinician should be cognisant of the literature and ongoing investigations on AIDN, and raise awareness of the risks of both surgery and anaesthesia.

Clinical experience with intraoperative jugular venous oximetry during pediatric intracranial neurosurgery

AIM

To report our institutional experience with intraoperative jugular venous oximetry during pediatric intracranial surgery to guide anesthetic care.

BACKGROUND

The utility of intraoperative jugular venous oximetry in adults undergoing intracranial surgery is well known. However, there is a little information on its' application in children during intracranial surgery.

METHODS

After IRB approval, we examined patient, equipment, placement, and sampling characteristics for jugular bulb catheters in children aged <18 years who were monitored with jugular oximetry during elective intracranial surgery between 2006 and 2010. We also determined the prevalence of intraoperative cerebral desaturation (SjvO(2) < 55%), its causes, and the interventions based on jugular oximetry values.

RESULTS

Data from 19 children (10 males and nine females), aged 12 ± 1 years (range 7-17) who underwent craniotomy for arteriovenous malformation (AVM) resection (68%), tumor removal (21%), or aneurysm clipping (11%), were reviewed. We analyzed 88 coincident SjvO(2), PaCO(2), and mean arterial pressure data points. Eleven (58%) patients experienced at least one episode of cerebral desaturation. There were 25 (28%) episodes of cerebral desaturation, six of which we attributed to relative hypotension, four to hypocarbia, and 15 to a combination of both. There were no intraoperative or immediate postoperative (first 24 h) complications because of jugular oximetry.

CONCLUSION

Findings from this series indicate that (i) intraoperative jugular venous oximetry in children is feasible in experienced hands, (ii) cerebral desaturation detected by jugular oximetry is common during pediatric intracranial procedures, and (iii) monitoring jugular venous saturation can impact anesthetic interventions to optimize cerebral physiology.

Gender differences in cerebrovascular reactivity to carbon dioxide during sevoflurane anesthesia in children: preliminary findings

BACKGROUND

Cerebrovascular reactivity to carbon dioxide (CO(2) R) is affected by age, gender and anesthetic agents. While gender differences in CO(2) R are described in adults, there are no such data in children.

AIM

To examine the gender differences in CO(2) R in children during sevoflurane anesthesia.

METHODS

Five girls and five boys <15 years of age and ASA physical status I, undergoing general anesthesia for elective surgery were enrolled. Under steady-state anesthesia with <1.0 MAC sevoflurane, middle cerebral artery blood flow velocity changes were monitored using Transcranial Doppler ultrasound while endtidal carbon dioxide (EtCO(2)) was adjusted from 40 to 30 mmHg (hypocapnia) and then from 40 to 50 mmHg (hypercapnia). CO(2)R was calculated between EtCO(2) ranges 30-40 and 40-50 mmHg. Cerebrovascular resistance (eCVR) was estimated as MAP/Vmca and the change in eCVR (ΔeCVR) between EtCO(2) 30 and 40 mmHg and between EtCO(2) 40 and 50 mmHg was calculated.

RESULTS

There was no gender difference in CO(2)R. However, both CO(2)R and ΔeCVR were lower in the EtCO(2) 40-50 mmHg range compared to EtCO(2) 30-40 mmHg range only in girls (P = 0.01 and P = 0.01, respectively). Vmca increased significantly with increase in CO(2) (P < 0.001) for both boys and girls. The coefficient of nonlinear correlation (r) between Vmca and EtCO(2) was 0.88 in girls vs 0.66 in boys.

CONCLUSION

While there were no gender differences in CO(2)R within the individual EtCO(2) ranges examined, girls but not boys had a significantly lower CO(2)R and ΔeCVR in the higher EtCO(2) range during <1.0 MAC sevoflurane anesthesia.

The effect of a target controlled infusion of propofol on predictability of recovery from anesthesia in children

BACKGROUND

Emergence following termination of a general anesthetic depends on the effect site concentration (C(e)) of the drug declining to an awakening value (C(e)-awake). C(e)-awake has been described in adults, but is unknown in children.

OBJECTIVES

To determine C(e)-awake in children following a target-controlled infusion (TCI) of propofol and to assess a C(e)-driven TCI system's ability to predict times to emergence from anesthesia.

METHODS

Subjects undergoing elective surgery, aged 3 months to <10 years were recruited into three age-stratified groups. A target C(e) of 3-4 microg x ml(-1) was selected for induction and subsequently titrated to patient response and surgical stimulus. Preoperative acetaminophen, a remifentanil infusion and regional anesthesia were permitted for supplemental analgesia. State Entropy (SE) was monitored from induction to emergence. Emergence was defined as the time of first purposeful spontaneous movement (PSM). Time zero was defined as the end of propofol infusion. Based on a pilot study, a C(e)-awake of 1.9 microg x ml(-1) was chosen as the wake-up threshold used by the software to predict emergence times.

RESULTS

Data was collected for 90 of 104 recruited patients. PSM occurred at a mean (sd) C(e) of 2.0 (0.5) microg x ml(-1) and an SE of 79 (11). There were no differences between age groups. A wide variation in emergence time was observed, with a mean (sd) of 16.9 (7) min, and a trend to more rapid emergence in older subjects.

CONCLUSION

A predicted C(e)-awake of 2.0 microg x ml(-1) in children aged 3 months to <10 years was identified with the selected model. For expert users of propofol in children, during shorter surgical procedures, TCI predicted emergence times do not offer significant clinical advantages.

Cerebrovascular pathophysiology in pediatric traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is the leading cause of traumatic morbidity and mortality in children. Although there is increasing information concerning TBI in adults and experimental animal models, relatively little is known regarding cerebrovascular pathophysiology specific to children.

MATERIALS

A review of the pertinent medical literature.

RESULTS

Systemic and cerebral hemodynamic factors such as hypotension, hypoxia, hyperglycemia, and fever are associated with poor outcome in pediatric TBI. Similarly, cerebral autoregulation is often impaired after TBI and may adversely affect outcome, especially if systemic hemodynamics are altered. Furthermore, CO2 vasoreactivity may be altered after pediatric TBI and lead to either cerebral ischemia or hyperemia.

CONCLUSIONS

Understanding the effect of pediatric TBI on the cerebral circulation is needed to potentially develop protocols to improve outcome in this vulnerable population. Specifically, changes in pediatric cerebrovascular physiology and pathophysiology, including CO2 vasoreactivity and pressure autoregulation, must be understood and their mechanism elucidated.

Impact of anesthetic agents on cerebrovascular physiology in children

The role of the pediatric neuroanesthetist is to provide comprehensive care to children with neurologic pathologies. The cerebral physiology is influenced by the developmental stage of the child. The understanding of the effects of anesthetic agents on the physiology of cerebral vasculature in the pediatric population has significantly increased in the past decade allowing a more rationale decision making in anesthesia management. Although no single anesthetic technique can be recommended, sound knowledge of the principles of cerebral physiology and anesthetic neuropharmacology will facilitate the care of pediatric neurosurgical patients.

Cerebral blood flow and autoregulation after pediatric traumatic brain injury

Traumatic brain injury is a global health concern and is the leading cause of traumatic morbidity and mortality in children. Despite a lower overall mortality than in adult traumatic brain injury, the cost to society from the sequelae of pediatric traumatic brain injury is very high. Predictors of poor outcome after traumatic brain injury include altered systemic and cerebral physiology, including altered cerebral hemodynamics. Cerebral autoregulation is often impaired after traumatic brain injury and may adversely impact the outcome. Although altered cerebrovascular hemodynamics early after traumatic brain injury may contribute to disability in children, there is little information regarding changes in cerebral blood flow and cerebral autoregulation after pediatric traumatic brain injury. This review addresses normal pediatric cerebral physiology and cerebrovascular pathophysiology after pediatric traumatic brain injury.

Relationship between age and spontaneous ventilation during intravenous anesthesia in children

BACKGROUND

Maintaining spontaneous ventilation in children, using total intravenous anesthesia (TIVA), is often desirable, particularly for airway endoscopy. The aim of this study was to evaluate the effect of age on the dose of remifentanil tolerated during spontaneous ventilation under anesthesia maintained with infusions of propofol and remifentanil and to provide guidelines for the administration of remifentanil and propofol to maintain spontaneous ventilation in children.

METHODS

Forty-five children scheduled for strabismus surgery were divided by age into three groups (group I: 6 months-3 years, group II: 3 years-6 years, and group III: 6 years-9 years). The propofol infusion was titrated using State Entropy as a pharmacodynamic endpoint and remifentanil infused, using a modified up-and-down method, with respiratory rate depression as a pharmacodynamic endpoint. A respiratory rate of just greater than 10, stable for 10 min, determined the final remifentanil infusion rate. The group mean was estimated from the final remifentanil infusion rate tolerated (RD(50)).

RESULTS

The RD(50) of groups I, II, and III were 0.192 (0.08), 0.095 (0.04), and 0.075 (0.03) microg x kg(-1) x min(-1) respectively. Pair-wise comparisons between the groups for the rate of remifentanil tolerated revealed a statistically significant increase in the RD(50) in children less than 3 years of age compared with older children in groups II and III (P < 0.001). The relationship between remifentanil dose and age, weight or height was not linear.

CONCLUSIONS

Younger children, especially those aged less than 3 years, tolerate a higher dose of remifentanil while still maintaining spontaneous respiration. TIVA with spontaneous ventilation is readily achieved in younger children and infants.

Transcranial Doppler and anesthetics

Transcranial Doppler (TCD) is widely used to investigate the effects of anesthetic drugs on cerebral blood flow. Its repeatability and non-invasivity makes it an ideal, first choice method. Anesthesia providers are required to be conscious of the cerebral hemodynamic effects of drugs given in their practice, especially in neurosurgery and in subjects with impaired brain functions. The purpose of this review is to present the basic concepts of the TCD technique and the effects on cerebral hemodynamics of the most popular anesthetic drugs evaluated using TCD ultrasonography.

Remifentanil Requirements During Propofol Administration to Block the Somatic Response to Skin Incision in Children and Adults

BACKGROUND

During sevoflurane administration, children require a remifentanil infusion rate twofold higher than adults to block responses to skin incision. Similar data concerning remifentanil requirements are unavailable during total IV anesthesia.

METHODS

We prospectively determined the infusion rate (IR) of remifentanil necessary to block the somatic response to skin incision in 50% (IR50) of adults (n = 20, aged 20-60 yr) and children (n = 20, aged 3-11 yr) during propofol anesthesia. In each patient undergoing lower abdominal surgery, a remifentanil infusion was initiated, followed by target-controlled infusion of propofol set at a plasma concentration of 6 mug/mL. After tracheal intubation, propofol was reduced to 3 microg/mL until the end of the study. Remifentanil IR was determined according to Dixon's up-and-down method, with the first patient in each group receiving 0.2 microg x kg(-1) x min(-1) followed by the consecutive patient receiving 0.02 microg x kg(-1) x min(-1) modifications according to the response of the previous patient. The remifentanil IR was kept unchanged for at least 20 min before surgery. At the beginning of surgery, only the skin incision was performed, and the somatic response was observed. If there was any gross movement of extremity the response was considered positive.

RESULTS

The IR50 (CI(95%)) was 0.08 (0.06-0.12) microg x kg(-1) x min(-1) in adults and 0.15 (0.13-0.17) microg x kg(-1) x min(-1) in children (P < 0.001).

CONCLUSION

These results demonstrate that, similar to sevoflurane anesthesia, during total IV anesthesia with propofol, children require a remifentanil IR almost twofold higher than adults to block the somatic response to skin incision.

Effect site concentrations of propofol producing hypnosis in children and adults: comparison using the bispectral index

BACKGROUND

No study has determined the concentration of propofol producing a degree of hypnosis compatible with anaesthesia in children. As a result, concentrations determined in adults are recommended for children. As this can result in an inadequate depth of anaesthesia, we determined the predicted effect site concentration (C(e)) of propofol necessary to obtain a bispectral index (BIS) of 50 in 50% (EC(e50)) of children and adults.

METHODS

Twenty adults (aged 33-44 years) and 20 children (aged 3-11 years) undergoing surgery under general anaesthesia were studied. All were monitored with a BIS monitor, and a target controlled infusion of propofol aiming for a constant C(e) value was started. After 10 min, patients were evaluated using a sedation scale, and the last 5 min was used to determine the mean BIS for this C(e) value. The C(e) value of propofol was defined using the up-and-down method of Dixon and Massey. The first patient in each group received C(e)= 6 microg/ml; thereafter, it was modified in 0.5 microg/ml decrements/increments with positive or negative responses, respectively. A positive response was BIS < 50 and a negative response was BIS > or = 50. The EC(e50) value was compared using unpaired Student's t-test. The prediction probability (P(K)) was used to study the association between BIS and the sedation score.

RESULTS

The mean EC(e50) (95% confidence interval) values were 3.75 microg/ml (2.97-4.75 microg/ml) in adults and 3.65 microg/ml (3.36-3.96 microg/ml) in children (not significant). All patients with BIS < 50 were unarousable with tactile stimulation. The P(K) value was 0.99 in both groups.

CONCLUSIONS

The predicted C(e) value of propofol resulting in BIS = 50 was similar in adults and children aged 3-11 years. The predicted C(e) value of propofol producing hypnosis in adults also seems to be useful in this paediatric population.

Anesthesiological and intensive care considerations in children undergoing extensive cerebral excision procedure for congenital epileptogenic lesions

INTRODUCTION

Epilepsy is a relatively common condition in childhood with a generally favorable prognosis of the affected population. Nevertheless, a significant minority of the treated children do not respond to the medical treatment so that surgical treatment is necessary. While minor surgical procedures have a negligible incidence of mortality, major ones may carry a significant risk of perioperative complications. The leading cause of mortality is represented by hemorrhagic derangements after high intraoperative and postoperative blood loss, mostly in very young patients. Therefore, restoration of euvolemia, detection and correction of related bleeding disorders represent the major concern for pediatric neuroanesthesiologists and intensivists throughout the perioperative period. The present report is focused on the anesthesia and intensive care management of the surgical epileptic patient.

CONCLUSION

Authors recommend that these high-risk procedures should be performed in highly experienced centers where pediatric neurosurgery is performed daily.

Optimizing the intraoperative management of carbon dioxide concentration

PURPOSE OF REVIEW

This review assesses whether there is a carbon dioxide concentration range that provides optimum benefit to the patient intraoperatively. It includes the physiological effects of carbon dioxide on various organ systems in awake and anesthetized individuals and its clinical effects in the ischemia/reperfusion setting. This review will present views on end-tidal or arterial carbon dioxide tension management in the perioperative period.

RECENT FINDINGS

Hypocapnia reduces intracranial pressure and is used by clinicians during acute traumatic brain injury, acute intracranial hemorrhage, and acutely growing brain tumors. There is mounting evidence, however, that hypercapnia improves tissue perfusion and oxygenation. Therefore, clinicians may want to induce mild-to-moderate hypercapnia during reperfusion states such as major vascular surgery, organ transplantation, tissue-graft surgery, and cases managed with low mean arterial pressures to control bleeding. As hypercapnia preserves cerebral blood flow even under relatively low perfusion pressures, it may be beneficial during global reperfusion scenarios. This hypothesis needs to be tested extensively before being considered for clinical applications. From a different perspective, current American Heart Association Guidelines recommend 12-15 breaths/min during cardiopulmonary resuscitation and stress the potential negative role of inadvertent hyperventilation on survival outcome. The importance of this concept is discussed briefly.

SUMMARY

Overall, the benefits of managing carbon dioxide concentration intraoperatively for the maintenance of cardiac output, tissue oxygenation, perfusion, intracranial pressure, and cerebrovascular reactivity are well defined.

Sevoflurane-remifentanil vs isoflurane-remifentanil for the surgical correction of craniosynostosis in infants

BACKGROUND

The aim of the present study was to compare the efficacy of isoflurane-remifentanil and sevoflurane-remifentanil combinations during neurosurgical correction craniosynostosis.

METHODS

Twenty-two infants with craniosynostosis received a slow bolus of remifentanil followed by continuous infusion. The infants were randomly divided into two groups: remifentanil followed by sevoflurane (the 'sevoflurane group'), and remifentanil followed by isoflurane (the 'isoflurane group'). We monitored electrocardiogram (ECG), heart rate (HR), invasive arterial blood pressure (IABP), pulse oximetry saturation (SpO(2)), endtidal CO(2) (P(ECO(2))), inspired fraction of oxygen (FiO(2)) and endtidal volatile agent (PE volatile agent) at 12 time points, from the beginning of surgery (T0) until the cessation of drugs (T11). The volatile agent was stopped prior to skin suture and the remifentanil infusion after skin closure. Subsequently, we evaluated recovery time of spontaneous breathing and spontaneous eye opening and time of extubation at 5, 10, and 15 min after extubation, the Steward Recovery Score (SRS) was assessed. Patients were then transferred to the Pediatric Intensive Care Unit (PICU).

RESULTS

During the surgical procedure the hemodynamic parameters between the two groups did not show statistically significant differences. There were also no significant differences in terms of awakening time or SRS.

CONCLUSIONS

The rapid recovery of the children (confirmed by their high values of SRS) makes it possible to reliably assess the patient's neurological condition immediately after surgery.

The effects of carbon dioxide on oxygenation and systemic, cerebral, and pulmonary vascular hemodynamics after the bidirectional superior cavopulmonary anastomosis

OBJECTIVES

We investigated the effects of different CO(2) tensions on oxygenation, pulmonary blood flow (Qp), cerebral blood flow, and systemic blood flow (Qs) after the bidirectional superior cavopulmonary anastomosis (BCPA).

BACKGROUND

Hypoxemia refractory to management of a high pulmonary vascular resistance index (PVRI) may complicate recovery from the BCPA.

METHODS

After BCPA, CO(2) was added to the inspired gas of mechanically ventilated patients. The Qp, Qs, PVRI, and systemic vascular resistance index (SVRI) were calculated from oxygen consumption, intravascular pressures, and oxygen saturations. Cerebral blood flow was estimated by near infrared spectroscopy and transcranial Doppler.

RESULTS

In nine patients (median age 7.1, range 2 to 23 months), arterial oxygen tension increased significantly (p < 0.005) from 36 +/- 6 mm Hg to 44 +/- 6 to 50 +/- 7 mm Hg at arterial carbon dioxide tensions (PaCO(2)) of 35, 45, and 55 mm Hg, respectively and decreased to 40 +/- 8 mm Hg at PaCO(2) 40 mm Hg. At a PaCO(2) of 55 and 45 compared with 35 mm Hg, Qp, cerebral blood flow, and Qs increased significantly, PVRI, Qp/Qs, and the ratio of Qp to inferior vena caval blood flow were unchanged, but SVRI decreased.

CONCLUSIONS

We have demonstrated that after the BCPA, systemic oxygenation, Qp, Qs, and cerebral blood flow increased and SVRI decreased at CO(2) tensions of 45 and 55 mm Hg compared with 35 mm Hg. We suggest that hypoxemia after the BCPA is ameliorated by a higher PaCO(2) and that low PaCO(2) or alkalosis may be detrimental. Hypercarbic management strategies may allow earlier progression to the BCPA, which may contribute to reducing the interval morbidity in patients with a functional single ventricle.

The effect of nitrous oxide on cerebrovascular reactivity to carbon dioxide in children during propofol anesthesia

Nitrous oxide (N(2)O) increases cerebral blood flow when used alone and in combination with propofol. We investigated the effects of N(2)O on cerebrovascular CO(2) reactivity (CCO(2)R) during propofol anesthesia in 10 healthy children undergoing elective urological surgery. Anesthesia consisted of a steady-state propofol infusion and a continuous caudal epidural block. A transcranial Doppler probe was used to measure middle cerebral artery blood flow velocity. Randomization determined the sequence order of N(2)O (N(2)O/air or air/N(2)O) and end-tidal (ET)CO(2) concentration (25, 35, 45, and 55 mm Hg) using an exogenous source of CO(2). At steady state, three sets of measurements of middle cerebral artery blood flow velocity, mean arterial blood pressure, and heart rate were recorded. A linear preservation of CCO(2)R was observed above 35 mm Hg of ETCO(2), irrespective of N(2)O. A decrease in CCO(2)R to 1.4%-1.9% per millimeters of mercury was seen in the hypocapnic range (ETCO(2) 25-35 mm Hg) with both air and N(2)O. We conclude that N(2)O does not affect CCO(2)R during propofol anesthesia in children. When preservation of CCO(2)R is required, the combination of N(2)O with propofol anesthesia in children would seem suitable. The cerebral vasoconstriction caused by propofol would imply that hyperventilation to ETCO(2) values less than 35 mm Hg may not be required because no further reduction in cerebral blood flow velocity would be achieved.

The effect of nitrous oxide on cerebral blood flow velocity in children anesthetized with propofol

BACKGROUND

Propofol for maintenance of anesthesia by continuous infusion is gaining popularity for use in pediatric patients. Nitrous oxide (N2O) has been shown to increase cerebral blood flow velocity (CBFV) in both children and adults. To determine the effects of N2O on middle cerebral artery blood flow velocity (Vmca) during propofol anesthesia in children, Vmca was measured with and without N2O using transcranial Doppler (TCD) sonography.

METHODS

Thirty ASA I or II children aged 18 months to 6 years undergoing elective urological surgery were enrolled. Anesthesia comprised propofol aimed at producing an estimated steady-state serum concentration of 3 micro g.ml-1 and a caudal epidural block. A transcranial Doppler probe was used to measure middle cerebral artery blood flow velocity. Each patient was randomized to receive a sequence of either Air/N2O/Air or N2O/Air/N2O in 35% oxygen. Fifteen min after each change in the N2O concentration, three measurements of cerebral blood flow velocity, blood pressure and heart rate were recorded. Ventilatory parameters and EtCO2 were kept constant throughout the study period.

RESULTS

CBFV increased by 12.4% when air was replaced by N2O, and returned to baseline when N2O was subsequently removed. There was a 14% decrease in CBFV when N2O was replaced with air, which increased to baseline when air was subsequently replaced with N2O. Mean heart rate and blood pressure remained constant throughout the study period.

CONCLUSION

The effects of nitrous oxide on CBFV are preserved in children during propofol anesthesia.

Propofol decreases cerebral blood flow velocity in anesthetized children

PURPOSE

Propofol, by virtue of its favourable pharmacokinetic profile, is suitable for maintenance of anesthesia by continuous infusion during neurosurgical procedures in adults. It is gaining popularity for use in pediatric patients. To determine the effects of propofol on cerebral blood flow in children, middle cerebral artery blood flow velocity (Vmca) was measured at different levels of propofol administration by transcranial Doppler (TCD) sonography.

METHODS

Twelve ASA I or II children, aged one to six years undergoing elective urological surgery were randomized to receive one of two propofol dosing regimens. Half of the patients received propofol in an escalating fashion, initially targeting an estimated steady-state serum concentration of 3 microg x mL-1, which was then doubled. The other half received propofol designed initially to target the high concentration followed by the lower one. In each child anesthesia was induced and maintained with propofol according to the protocol, rocuronium was given to facilitate tracheal intubation, and a caudal epidural block was performed. A TCD probe was placed appropriately to measure Vmca. Cerebral blood flow velocity (CBFV), mean arterial pressure (MAP) and heart rate (HR) were recorded simultaneously at both levels of propofol administration.

RESULTS

Twelve patients were studied. At the higher estimated target serum propofol concentration there were significant decreases in Vmca (17%, P < 0.001), MAP (6%, P < 0.002) and HR (8%, P < 0.05) when compared to the lower targeted concentration.

CONCLUSION

This study shows that a higher rate of propofol infusion is associated with lower CBFV and MAP values in children. Propofol's cerebral vasoconstrictive properties may be responsible for this finding.