Pressure autoregulation and positron emission tomography-derived cerebral blood flow acetazolamide reactivity in patients with carotid artery stenosis

OBJECTIVE: Testing autoregulation is of importance in predicting risk of stroke and managing patients with occlusive carotid arterial disease. The use of small spontaneous changes in arterial blood pressure and transcranial Doppler (TCD) flow velocity can be used to assess autoregulation noninvasively without the need for a cerebrovascular challenge. We have previously described an index (called "Mx") that achieves this. Negative or low positive values (<0.4) indicate intact pressure autoregulation, whereas an Mx greater than 0.4 indicates diminished autoregulation. The objective of this study was to compare acetazolamide reactivity of positron emission tomography (PET)-derived cerebral blood flow (CBF) with Mx in patients with carotid arterial disease. METHODS: In 40 patients with carotid arterial disease, we used bilateral TCD recordings of the middle cerebral artery to derive Mx and compared this with PET-derived CBF measurements of acetazolamide reactivity. RESULTS: Mx correlated inversely with baseline PET CBF (P = 0.042, R = -0.349) but not with postacetazolamide CBF or cerebrovascular reactivity to acetazolamide. This may reflect discordance between pressure autoregulation and acetazolamide reactivity. Mx correlated significantly with degree of internal carotid artery stenosis (P = 0.022, R = 0.38), whereas CBF reactivity to acetazolamide did not correlate with Mx (P = 0.22). After the administration of acetazolamide, slow-wave activity in blood pressure and TCD flow velocity recordings was seen to diminish, rendering the calculation of Mx unreliable after acetazolamide. CONCLUSION: The measurement of Mx offers a noninvasive, safe technique for assessing abnormalities of pressure autoregulation in patients with carotid arterial disease.     

The effect of pneumoperitoneum in the steep Trendelenburg position on cerebral oxygenation

Background: daVinci^® robot‐assisted laparoscopic radical prostatectomy (RALP) requires pneumoperitoneum in the steep Trendelenburg position, which results in increased intracranial pressure and cerebral blood flow. The aim of this study was to evaluate the effect of pneumoperitoneum in a 30° Trendelenburg position on cerebral oxygenation using regional cerebral oxygen saturation (rSO₂). Methods: Thirty‐two male patients of ASA I and II physical status without previous episodes of cerebral ischemia or hemorrhage undergoing daVinci^® RALP were enrolled. The rSO₂ was continuously monitored with near‐infrared spectroscopy (INVOS^® 5100^?) during the study period. Measurements were obtained immediately after anesthesia induction (T0; baseline), 5 min after a 30° Trendelenburg position (T1), 5 min after 15 mmHg pneumoperitoneum in a supine position (T2), 30, 60 and 120 min after the pneumoperitoneum in a Trendelenburg position (T3, T4 and T5, respectively) and after desufflation in a supine position (T6). Results: The change in the left and right rSO₂ was statistically significant (Left P=0.004 and Right P=0.023). Both the right and the left rSO₂ increased significantly during pneumoperitoneum in a Trendelenburg position (from T3 to T5) and at T6 compared with the baseline value at T0. The partial pressure of carbon dioxide (PaCO₂) was increased significantly at T2, T3, T5 and T6 compared with the baseline value at T0. Conclusions: During daVinci^® RALP, cerebral oxygenation, as assessed by rSO₂, increased slightly, which suggests that the procedure did not induce cerebral ischemia. The PaCO₂ should be maintained within the normal limit during pneumoperitoneum in a Trendelenburg position in patients undergoing daVinci^® RALP because the rSO₂ increased in conjunctions with the increase in PaCO₂.     

Effects of high positive end‐expiratory pressure on haemodynamics and cerebral oxygenation during pneumoperitoneum in the Trendelenburg position

We investigated the effects of 10 cmH₂O positive end‐expiratory pressure on cerebral haemodynamics and cerebral oxygenation in patients undergoing laparoscopic lower abdominal surgery in the 30° Trendelenburg position during desflurane anaesthesia. Twenty‐six patients were enrolled in this study. After anaesthesia induction, pneumoperitoneum was applied in Trendelenburg position. Twenty minutes later, positive end‐expiratory pressure was applied. There was no change in regional cerebral oxygen saturation (p = 0.376). Cerebral perfusion pressure decreased significantly over time (p < 0.001) and positive end‐expiratory pressure caused a further decrease in cerebral perfusion pressure (p = 0.036). The application of 10 cmH₂O positive end‐expiratory pressure during pneumoperitoneum in the Trendelenburg position preserved regional cerebral oxygen saturation, but cerebral perfusion pressure decreased significantly due to its secondary haemodynamic effects.     

Continuous assessment of cerebral autoregulation in subarachnoid hemorrhage

Cerebral vasospasm remains a leading cause of morbidity and mortality after subarachnoid hemorrhage (SAH). Cerebral ischemia may ensue when autoregulation fails to compensate for spasm. We examined how autoregulation is affected by vasospasm by using transcranial Doppler. The moving correlation coefficient between slow changes of arterial blood pressure and mean or systolic flow velocity (FV), termed "Mx" and "Sx," respectively, was used to characterize cerebral autoregulation. Vasospasm was declared when the mean FV increased to more than 120 cm/s and the Lindegaard ratio was more than 3. This occurred in 15 of 32 SAH patients. On the basis of the bilateral transcranial Doppler recordings of the middle cerebral artery in vasospastic patients, Mx and Sx were calculated for baseline and vasospasm. Mx increased during vasospasm (0.46 +/- 0.32; mean +/- SD) and was significantly higher (P = 0.021) than at baseline (0.21 +/- 0.24). Sx was also increased (0.22 +/- 0.26 vs 0.05 +/- 0.21 at baseline; P = 0.03). Mx correlated with mean FV (r = 0.577; P = 0.025) and the Lindegaard ratio (r = 0.672; P < 0.006). Mx (P = 0.006) and Sx (P = 0.044) were higher on the vasospastic side (Mx, 0.44 +/- 0.27; Sx, 0.24 +/- 0.23) when compared with the contralateral side (Mx, 0.34 +/- 0.29; Sx, 0.16 +/- 0.25). The increased Mx and Sx during cerebral vasospasm demonstrate impaired cerebral autoregulation. Mx and Sx provide additional information on changes in autoregulation in SAH patients. IMPLICATIONS: The moving correlation coefficients between slow changes of arterial blood pressure and mean or systolic flow velocity, termed "Mx" and "Sx," respectively, characterize cerebral autoregulation but have not been applied to subarachnoid hemorrhage. A study in 15 patients revealed that Mx and Sx were significantly increased, indicating impaired autoregulation during vasospasm as compared with baseline, as well as on the side of vasospasm in comparison with the contralateral side.     

Prostatectomia robótica: análise anestesiológica de cirurgias urológicas robóticas: estudo prospectivo

Background and objectives

Although many features of robotic prostatectomy are similar to those of conventional laparoscopic urological procedures (such as laparoscopic prostatectomy), the procedure is associated with some drawbacks, which include limited intravenous access, relatively long operating time, deep Trendelenburg position, and high intra‐abdominal pressure. The primary aim was to describe respiratory and hemodynamic challenges and the complications related to high intra‐abdominal pressure and the deep Trendelenburg position in robotic prostatectomy patients. The secondary aim was to reveal safe discharge criteria from the operating room.

Methods

Fifty‐three patients who underwent robotic prostatectomy between December 2009 and January 2011 were prospectively enrolled. Main outcome measures were non‐invasive monitoring, invasive monitoring and blood gas analysis performed at supine (T₀), Trendelenburg (T₁), Trendelenburg + pneumoperitoneum (T₂), Trendelenburg‐before desufflation (T₃), Trendelenburg (after desufflation) (T₄), and supine (T₅) positions.

Results

Fifty‐three robotic prostatectomy patients were included in the study. The main clinical challenge in our study group was the choice of ventilation strategy to manage respiratory acidosis, which is detected through end‐tidal carbon dioxide pressure and blood gas analysis. Furthermore, the mean arterial pressure remained unchanged, the heart rate decreased significantly and required intervention. The central venous pressure values were also above the normal limits.

Conclusion

Respiratory acidosis and “upper airway obstruction‐like” clinical symptoms were the main challenges associated with robotic prostatectomy procedures during this study.     

Postoperative otorrhagia: an unknown complication of Trendelenburg position during laparoscopic surgery?

Two patients have presented postoperative otorrhagia following gynaecologic laparoscopic procedures. This occurred after uneventful anaesthesia and recovery for surgery performed in forced Trendelenburg position (35 degrees with horizontal position). Different responsible mechanisms are discussed including haemodynamic changes induced by both the Trendelenburg position and the pneumoperitoneum. Particularities of external ear blood supply directly submitted to arterial and venous pressure changes, may also have contributed to the appearance of otorrhagia.     

Effects of Posture and Prolonged Pneumoperitoneum on Hemodynamic Parameters during Laparoscopy

BACKGROUND: The present prospective study was designed to evaluate hemodynamic changes associated with head-down positioning and prolonged pneumoperitoneum during totally endoscopic robot-assisted radical prostatectomy. METHODS: Ten American Society of Anesthesiologists (ASA) physical status I-III patients undergoing totally endoscopic robot-assisted radical prostatectomy were enrolled in the study. Invasive hemodynamic parameters were measured by transpulmonary arterial thermodilution using the PiCCO system with a femoral artery catheter. Cardiac index (CI), heart rate (HR), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), intrathoracic blood volume (ITBV), and central venous pressure (CVP) were recorded with the patient in the supine position, after head-down tilt, intraoperatively after 30 min, 1 h, 2 h, 3 h, and 4 h of pneumoperitoneum at an insufflation pressure of 12 mmHg, after deflation still with head-down positioning, and finally, with the patient in the supine position. RESULTS: Placing the patient in the Trendelenburg (head-down) position caused a significant increase in CVP (from 9.9 +/- 3.4 to 15.1 +/- 2.3 mmHg), whereas all other hemodynamic parameters remained nearly unaffected. The induction of pneumoperitoneum resulted in a significant increase in MAP (from 74.9 +/- 12.9 to 95.4 +/- 11.9 mmHg). No other parameter was affected. Even at 4 h of pneumoperitoneum only mild hemodynamic changes were observed. After release of the pneumoperitoneum with the patient still in the head-down position, HR (49.0 +/- 4 versus 63.9 +/- 12.4 min(-1)) and after placing the patient in the supine position, CI (2.4 +/- 0.2 versus 3.3 +/- 0.7 l min(-1 )m(-2)) increased significantly, whereas CVP returned to baseline values. CONCLUSIONS: Patients undergoing totally endoscopic radical prostatectomy with 4 h of pneumoperitoneum in the Trendelenburg position experienced no significant hemodynamic depression during posture and pneumoperitoneum.     

The Relationship Between Cerebral Blood Flow Autoregulation and Cerebrovascular Pressure Reactivity After Traumatic Brain Injury

BACKGROUND:: Cerebrovascular pressure reactivity is the principal mechanism of cerebral autoregulation. Assessment of cerebral autoregulation can be performed by using the mean flow index (Mx) based on transcranial Doppler ultrasonography. Cerebrovascular pressure reactivity can be monitored by using the pressure reactivity index (PRx), which is based on intracranial pressure monitoring. From a practical point of view, PRx can be monitored continuously, whereas Mx can only be monitored in short periods when transcranial Doppler probes can be applied. OBJECTIVE:: To assess to what degree impairment in pressure reactivity (PRx) is associated with impairment in cerebral autoregulation (Mx). METHODS:: A database of 345 patients with traumatic brain injury was screened for data availability including simultaneous Mx and PRx monitoring. Absolute differences, temporal changes, and association with outcome of the 2 indices were analyzed. RESULTS:: A total of 486 recording sessions obtained from 201 patients were available for analysis. Overall a moderate correlation between Mx and PRx was found (r = 0.58; P < .001). The area under the receiver operator characteristic curve designed to detect the ability of PRx to predict impaired cerebral autoregulation was 0.700 (95% confidence interval: 0.607-0.880). Discrepancies between Mx and PRx were most pronounced at an intracranial pressure of 30 mm Hg and they were significantly larger for patients who died (P = .026). Both Mx and PRx were significantly lower at day 1 postadmission in patients who survived than in those who died (P < .01). CONCLUSION:: There is moderate agreement between Mx and PRx. Discrepancies between Mx and PRx are particularly significant in patients with sustained intracranial hypertension. However, for clinical purposes, there is only limited interchangeability between indices. ABBREVIATIONS:: ABP, arterial blood pressureBF, cerebral blood flowCBV, cerebral blood volumeCPP, cerebral perfusion pressureFV, flow velocityGCS, Glasgow Coma ScaleGOS, Glasgow Outcome ScaleICP, intracranial pressureMx, mean flow indexPRx, pressure reactivity indexROC, receiver operator characteristicTBI, traumatic brain injuryTCD, transcranial Doppler.     

Preservation of static and dynamic cerebral autoregulation after mild hypothermic cardiopulmonary bypass

Background. Dysfunction of cerebral autoregulation might contributeto neurological morbidity after cardiac surgery. In this study,our aim was to assess the preservation of cerebral autoregulationafter cardiac surgery involving cardiopulmonary bypass (CPB). Methods. Dynamic and static components of cerebral autoregulationwere evaluated in 12 patients undergoing coronary artery bypassgraft surgery, anaesthetized with midazolam, fentanyl, and propofol,and using mild hypothermic CPB (31–33°C). Arterialpressure (ABP), central venous pressure (CVP), and blood flowvelocity in the middle cerebral artery (CBFV) were recorded.The cerebral perfusion pressure (CPP) was calculated as a differencebetween mean ABP and CVP. Rapid decrease of CPP was caused bya sudden change of patients' position from Trendelenburg toreverse Trendelenburg. Cerebral vascular resistance (CVR) wascalculated by dividing CPP by CBFV. Index of static cerebralautoregulation (CAstat) was calculated as the change of CVRrelated to change of CPP during the manoeuvre. Dynamic rateof autoregulation (RoRdyn) was determined as the change in CVRper second during the first 4 s immediately after a decreasein CPP, related to the change of CPP. Measurements were obtainedafter induction of anaesthesia, and 15, 30, and 45 min aftertermination of CPB. Results. No significant changes were found in CAstat or RoRdynafter CPB. Significant changes in CVR could be explained byconcomitant changes in body temperature and haematocrit. Conclusion. Autoregulation of cerebral blood flow remains preservedafter mild hypothermic CPB.      

The effects of nicardipine on dynamic cerebral autoregulation in patients anesthetized with propofol and fentanyl

We investigated the effects of nicardipine on dynamic cerebral pressure autoregulation in 13 normal adult patients undergoing gynecologic or orthopedic surgery. Anesthesia was induced and maintained with propofol and fentanyl. Hypotension to a mean arterial pressure of 60-65 mm Hg was induced and maintained with a continuous infusion of nicardipine. Time-averaged mean blood flow velocity in the right middle cerebral artery was measured continuously by using transcranial Doppler ultrasonography. The cerebral autoregulatory responses were activated by releasing thigh cuffs. The actual blood flow velocity in the right middle cerebral artery response to acute change in mean arterial pressure was fitted to 1 of 10 computer-generated curves to determine the dynamic rate of cerebral autoregulation (dRoR), and the best fitting curve was used. The autoregulation test was repeated until two values of dRoR were obtained at baseline and during induced hypotension. Nicardipine significantly reduced dRoR values of 13.1% +/- 3.6%/s at baseline to 8.3% +/- 2.6%/s during hypotension (P: < 0.01). During deliberate hypotension induced by nicardipine, the cerebral dynamic autoregulatory response is impaired in normal adult patients. IMPLICATIONS: During deliberate hypotension induced by nicardipine, the cerebral dynamic autoregulatory response is impaired in normal adult patients.     

Comparação entre ventilação garantida por volume controlado por pressão e ventilação controlada por volume em pacientes obesos durante cirurgia laparoscópica ginecológica na posição de Trendelenburg

Background and objectivesThe aim of this study was to investigate the efficacy of the pressure‐controlled, volume‐guaranteed (PCV‐VG) and volume‐controlled ventilation (VCV) modes for maintaining adequate airway pressures, lung compliance and oxygenation in obese patients undergoing laparoscopic hysterectomy in the Trendelenburg position.MethodsPatients (104) who underwent laparoscopic gynecologic surgery with a body mass index between 30 and 40 kg.m^-2 were randomized to receive either VCV or PCV‐VG ventilation. The tidal volume was set at 8 mL.kg^-1, with an inspired oxygen concentration of 0.4 with a Positive End‐Expiratory Pressure (PEEP) of 5 mmHg. The peak inspiratory pressure, mean inspiratory pressure, plateau pressure, driving pressure, dynamic compliance, respiratory rate, exhaled tidal volume, etCO₂, arterial blood gas analysis, heart rate and mean arterial pressure at 5 minutes after induction of anesthesia in the and at 5, 30 and 60 minutes, respectively, after pneumoperitoneum in the Trendelenburg position were recorded.ResultsThe PCV‐VG group had significantly decreased peak inspiratory pressure, mean inspiratory pressur, plateau pressure, driving pressure and increased dynamic compliance compared to the VCV group. Mean PaO₂ levels were significantly higher in the PCV‐VG group than in the VCV group at every time point after pneumoperitoneum in the Trendelenburg position.ConclusionsThe PCV‐VG mode of ventilation limited the peak inspiratory pressure, decreased the driving pressure and increased the dynamic compliance compared to VCV in obese patients undergoing laparoscopic hysterectomy. PCV‐VG may be a preferable modality to prevent barotrauma during laparoscopic surgeries in obese patients.     

The influence of nicardipine-, nitroglycerin-, and prostaglandin E(1)-induced hypotension on cerebral pressure autoregulation in adult patients during propofol-fentanyl anesthesia.

We investigated the influence of drug-induced hypotension at a mean arterial pressure (MAP) of 60-70 mm Hg on cerebral pressure autoregulation in 45 adult patients during propofol-fentanyl anesthesia. Time-averaged mean blood flow velocity in the right middle cerebral artery (Vmca) was continuously measured at a PaCO(2) of 39-40 mm Hg by using transcranial Doppler ultrasonography. Hypotension was induced and maintained with a continuous infusion of nicardipine, nitroglycerin, or prostaglandin E(1). Cerebral autoregulation was tested by a slow continuous infusion of phenylephrine to induce an increase in MAP of 20-30 mm Hg. From the simultaneously recorded data of Vmca and MAP, cerebral vascular resistance (CVR) was calculated as MAP/Vmca. Furthermore, the index of autoregulation (IOR) was calculated as DeltaCVR/DeltaMAP, where DeltaCVR = change in CVR and DeltaMAP = change in MAP. The test was performed twice for each condition on each patient: baseline and hypotension. The IOR during baseline was similar among the groups. During nitroglycerin- and prostaglandin E(1)-induced hypotension, IOR was not different from baseline. In contrast, during nicardipine-induced hypotension, IOR significantly decreased compared with baseline (0.37 +/- 0.08 versus 0.83 +/- 0.07, P < 0.01). In conclusion, nicardipine, but not nitroglycerin or prostaglandin E(1), significantly attenuates cerebral pressure autoregulation during propofol-fentanyl anesthesia. IMPLICATIONS: Vasodilators may influence cerebral autoregulation by changing cerebral vascular tone. Nicardipine, but not nitroglycerin or prostaglandin E(1), attenuated cerebral pressure autoregulation in normal adult patients during propofol-fentanyl anesthesia.     

The effect of hypocapnia on the autoregulation of cerebral blood flow during administration of isoflurane

Isoflurane impairs autoregulation of cerebral blood flow in a dose-related manner. Previous investigations in several other conditions have demonstrated that impaired autoregulation can be restored by hyperventilation. We hypothesized that hypocapnia may restore cerebral autoregulation impaired by isoflurane anesthesia. We administered isoflurane in 100% oxygen to 12 healthy patients aged 21-59 yr scheduled for elective nonneurological surgery. Isoflurane end-tidal concentration was individualized at 0.1% to 0.2% less than that required to induce short periods of isoelectric electroencephalogram. This resulted in an end-tidal isoflurane concentration of 1.6% +/- 0.2% (mean +/- sd) corresponding to an age-adjusted minimum alveolar anesthetic concentration multiple of 1.4. Mean arterial blood pressure was reduced to <80 mm Hg, by infusion of remifentanil if required. Cerebral autoregulation was assessed by infusing phenylephrine to increase mean arterial blood pressure to 100 mm Hg while monitoring middle cerebral artery blood flow velocity with transcranial Doppler ultrasonography. The change in flow velocity was used to calculate the autoregulation index (ARI). The ARI ranges between 0 and 1 and an ARI < or =0.4 indicates significantly impaired autoregulation. Autoregulation was tested twice in randomized order: once during normocapnia (Paco(2) 38-43 mm Hg) and once during hypocapnia (Paco(2) 27-34 mm Hg). The median (interquartile range) ARI was 0.29 (0.23-0.64) during normocapnia and 0.77 (0.70-0.78) during hypocapnia (P < 0.005). Of the 12 subjects, autoregulation was significantly impaired in 8 subjects during normocapnia and none during hypocapnia (P = 0.001). Hypocapnia restored cerebral autoregulation in normal subjects during isoflurane-induced impairment of autoregulation.     

Effects of pneumoperitoneum and reverse Trendelenburg position on cardiopulmonary function in morbidly obese patients receiving laparoscopic gastric banding

We prospectively evaluated the effects of pneumoperitoneum and reverse Trendelenburg position on cardiopulmonary function in 20 ASA physical status II-III morbidly obese patients (body mass index > 35 kg m(-2)) undergoing laparoscopic gastric banding. After general anaesthesia was induced, patients' lungs were ventilated using intermittent positive pressure ventilation (at measurement times, the following parameters were used: tidal volume 12 mL kg(-1) ideal body weight, respiratory rate of 12 bpm, an inspiratory to expiratory time ratio of 1:2). Haemodynamic variables, blood gas parameters, and lung/chest compliance were recorded: in the supine position, after induction of general anaesthesia (T0, baseline) and induction of pneumoperitoneum (T1); after placing the patient in a 25 degree reverse Trendelenburg position (T2); during the surgical time (T3); before deflating the abdomen (T4); after pneumoperitoneum resolution (T5), and before the end of anaesthesia, with the patient supine (T6). The PaO2, PaO2/FiO2 ratio, and lung/chest compliance decreased during the study. After the pneumoperitoneum had been resolved, lung/chest compliance but not oxygenation parameters returned to baseline values. The arterial to end-tidal CO2 tension difference progressively increased from 0.38+/-0.3 kPa (2.85+/-2.25 mmHg) (T0) to 0.63+/-0.3 kPa (4.73+/-2.25 mmHg) (T6). In morbidly obese patients, undergoing laparoscopic gastric banding, a CO2 pneumoperitoneum markedly affected gas exchange and lung/chest compliance, while positioning the patient in a 25 degree reverse Trendelenburg position had no beneficial effects.     

Secure patient positioning using Badillo/Trendelenburg restraint strap during robotic surgery

Steep Trendelenburg position is routine during robotic urologic and gynecologic surgery in order to optimize exposure of the pelvis. This position requires that the patient be properly secured as to avoid any movement during the procedure. We analyzed the safety and tolerability of a reusable strap with disposable cushions used during robotic assisted radical prostatectomy. The Badillo/Trendelenburg restraint is a harness which is placed on the table prior to patient transfer. The restraint is a Class I FDA-registered device (Pintler Medical, Seattle, WA). Patients were marked at the beginning and end of the case to determine if any movement had occurred. The Badillo/Trendelenburg restraint was employed in 1,200 consecutive RARP cases. The restraint was used by a single surgeon at two institutions. The operating table was marked from edge of the patients shoulder to the end of the head of table at the beginning and end of the case to determine if any movement had occurred. Maximum movement observed was 1 cm. All patients were questioned and a physical examination were done in the post operative period for any shoulder or nerve injury. No reports of shoulder or brachial injury. For patients undergoing robotic surgery with steep Trendelenburg position the Badillo/Trendelenburg restraint provides a secure, reliable and safe means of maintaining proper position without any patient movement.     

Anaesthesia for robotic gynaecological surgery

Robotic surgery is gaining widespread popularity due to advantages such as reduced blood loss, reduced postoperative pain, shorter hospital stay and better visualisation of fine structures. Robots are being used in urological, cardiac, thoracic, orthopaedic, gynaecological and general surgery. Robotic surgery received US Food and Drug Administration approval for use in gynaecological surgery in 2005. The various gynaecological robotic operations being performed are myomectomy, total and supracervical hysterectomy, ovarian cystectomy, sacral colpopexy, tubal reanastomosis, lymph node dissection, surgery of retroperitoneal ectopic pregnancy, Moskowitz procedure and endometriosis surgery. The anaesthetic considerations include difficult access to the patient intraoperatively, steep Trendelenburg position, long surgical duration and the impact of pneumoperitoneum. We highlight the complications encountered in these surgeries and methods to prevent these complications. Robotic gynaecological surgery can be safely performed after considering the physiological effects of the steep Trendelenburg position and of pneumoperitoneum. The benefits of the surgical procedure should be weighed against the risks in patients with underlying cardiorespiratory problems.     

Effects of halothane in low concentrations on cerebral blood flow, cerebral metabolism, and cerebrovascular autoregulation in the baboon

Halothane in anesthetic concentrations causes cerebral vasodilatation and decreases cerebral oxygen consumption (CMRO2). The purpose of this study was to evaluate cerebral blood flow (CBF) and CMRO2 changes associated with low concentrations of halothane. In eight normoventilated baboons with background anesthesia maintained with phencyclidine and nitrous oxide, CBF and CMRO2 were studied during the administration of end-tidal concentrations of halothane (0.125, 0.25, 0.375, 0.5, 0.75, and 1.0 vol%). Arterial blood pressure was supported by an infusion of angiotension II amide at 0.75 and 1.0 vol% of halothane to maintain an adequate cerebral perfusion pressure. In addition, cerebrovascular autoregulation was tested before and during the administration of 0.375, 0.75, and 1.0 vol% of halothane. Cerebrovascular autoregulation was assessed by observing the response of CBF to an acute increase in mean arterial pressure produced by angiotensin. CMRO2 decreased as the concentration of halothane was increased. At low halothane concentrations (0.125-0.375 vol%), CBF decreased; however, at concentrations above 0.375 vol%, CBF increased with a decrease in cerebrovascular resistance. Autoregulation was intact during 0.375 vol% of halothane, but with 0.75 and 1.0 vol% of halothane, CBF was passively dependent on cerebral perfusion pressure, suggesting impaired autoregulation.     

Racemic ketamine does not abolish cerebrovascular autoregulation in the pig

BACKGROUND: Little is known about the influence of racemic ketamine on autoregulation of cerebral blood flow (CBF), and available reports regarding its influence on cerebral hemodynamics are contradictory. This study was designed to evaluate cerebrovascular responses to changes in the mean arterial pressure (MAP) during ketamine anesthesia. METHODS: In eight normoventilated pigs anesthesia was induced with propofol and maintained by i.v. infusion of ketamine (15.0 mg kg(-1) x h(-1)) during measurements. The intra-arterial xenon clearance technique was used to calculate CBF. Balloon-tipped catheters were introduced in the inferior caval vein and mid-aorta, and increases or decreases by up to 40% in mean arterial pressure (MAP) in random order were achieved by titrated inflation of these balloon catheters. Cerebral blood flow was determined at each MAP level. Regression coefficients of linear pressure-flow curves were calculated in all animals. RESULTS: From the mean baseline level (101 mmHg) MAP was reduced by 20% and 40%, and increased by 26% and 43%. The maximal mean increase and decrease in MAP induced a 12% increase and a 15% decrease, respectively, of CBF from the mean baseline level (52.6 ml.100 g(-1) x min1). The 95% confidence interval (-0.02; 0.38) of the mean regression coefficient of individual pressure-flow curves does not include the regression coefficient (0.64) of a linear correlation between MAP and CBF including origo (correlation coefficient 0.99), which indicates complete lack of cerebrovascular autoregulation. CONCLUSIONS: We conclude that autoregulation of CBF is not abolished during continuous ketamine infusion in normoventilated pigs and that previous divergent conclusions are unlikely to be associated with severe impairment of cerebrovascular autoregulation.     

The effect of pneumoperitoneum and Trendelenburg position on acute cerebral blood flow–carbon dioxide reactivity under sevoflurane anaesthesia

This study compared cerebral blood flow–carbon dioxide (CBF–CO₂) reactivities in the supine and modest Trendelenburg position under pnemoperitoneum during sevoflurane anaesthesia. After induction of anaesthesia in 25 patients, mechanical ventilation was adjusted to increase Paco ₂ from 4.7 (T₁) to 6.0 kPa (T₂) in the supine position, and the change in jugular bulb oxygen saturation was measured as an index of CBF. Then, after establishment of pneumoperitoneum and 30° Trendelenburg position, the CO₂ step and measurement of CBF were repeated. The CBF–CO₂ reactivity was 7.5 (3.3) %.kPa^?1 (% change in jugular bulb oxygen saturation per unit change in Paco ₂) in the supine position and 6.8 (2.3) %.kPa^?1 in the 30° Trendelenburg‐pneumoperitoneum condition (p = 0.086). We conclude that CBF–CO₂ reactivity is unchanged by the modest Trendelenburg position under pneumoperitoneum during sevoflurane anaesthesia.     

Cerebral Hemodynamic Effects of Morphine and Fentanyl in Patients with Severe Head Injury: Absence of Correlation to Cerebral Autoregulation

Background: The current study investigates the effects of morphine and fentanyl upon intracranial pressure and cerebral blood flow estimated by cerebral arteriovenous oxygen content difference and transcranial Doppler sonography in 30 consecutive patients with severe head injury in whom cerebrovascular autoregulation previously had been assessed.

Methods: Patients received morphine (0.2 mg/kg) and fentanyl (2 [mu]g/kg) intravenously over 1 min but 24 h apart in a randomized fashion. Before study, carbon dioxide reactivity and autoregulation were assessed. Intracranial pressure, mean arterial blood pressure, and cerebral perfusion pressure were repeatedly monitored for 1 h after the administration of both opioids. Cerebral blood flow was estimated from the reciprocal of arteriovenous oxygen content difference and middle cerebral artery mean flow velocity using transcranial Doppler sonography.

Results: Although carbon dioxide reactivity was preserved in all patients, 18 patients (56.7%) showed impaired or abolished autoregulation to hypertensive challenge, and only 12 (43.3%) had preserved autoregulation. Both morphine and fentanyl caused significant increases in intracranial pressure and decreases in mean arterial blood pressure and cerebral perfusion pressure, but estimated cerebral blood flow remain unchanged. In patients with preserved autoregulation, opioid-induced intracranial pressure increases were not different than in those with impaired autoregulation.