Noninvasive cerebrovascular autoregulation assessment in traumatic brain injury: validation and utility

A moving correlation index (Mx-CPP) of cerebral perfusion pressure (CPP) and mean middle cerebral artery blood flow velocity (CBFV) allows continuous monitoring of dynamic cerebral autoregulation (CA) in patients with severe traumatic brain injury (TBI). In this study we validated Mx-CPP for TBI, examined its prognostic relevance, and assessed its relationship with arterial blood pressure (ABP), CPP, intracranial pressure (ICP), and CBFV. We tested whether using ABP instead of CPP for Mx calculation (Mx-ABP) produces similar results. Mx was calculated for each hemisphere in 37 TBI patients during the first 5 days of treatment. All patients received sedation and analgesia. CPP and bilateral CBFV were recorded, and GOS was estimated at discharge. Both Mx indices were calculated from 10,000 data points sampled at 57.4Hz. Mx-CPP > 0.3 indicates impaired CA; in these patients CPP had a significant positive correlation with CBFV, confirming failure of CA, while in those with Mx < 0.3, CPP was not correlated with CBFV, indicating intact CA. These findings were confirmed for Mx-ABP. We found a significant correlation between impaired CA, indicated by Mx-CPP and Mx-ABP, and poor outcome for TBI patients. ABP, CPP, ICP, and CBFV were not correlated with CA but it must be noted that our average CPP was considerably higher than in other studies. This study confirms the validity of this index to demonstrate CA preservation or failure in TBI. This index is also valid if ABP is used instead of CPP, which eliminates the need for invasive ICP measurements for CA assessment. An unfavorable outcome is associated with early CA failure. Further studies using the Mx-ABP will reveal whether CA improves along with patients' clinical improvement.     

Dynamic cerebral autoregulation: should intracranial pressure be taken into account?

Summary Background. Although the inclusion of cerebral perfusion pressure (CPP) is a standard feature in static testing of autoregulation after head injury, controversy surrounds the use of CPP versus arterial blood pressure (ABP) in dynamic tests. The aim of our project was to assess the discrepancies between methods of dynamic autoregulation testing based on CPP or ABP, and study possible differences in their prognostic value. Method. Intermittent recordings of intracranial pressure (ICP), ABP and middle cerebral artery blood flow velocity (FV) waveforms were made in 151 anaesthetised and ventilated adult head injured patients as part of their required care. Indices of dynamic autoregulation were calculated as a moving correlation coefficient of 60 samples (total time 3 min) of 6 s mean values of FV and ABP (Mxa) or FV and CPP (Mx). Values of Mx and Mxa were averaged over multiple recordings in each patient and correlated with outcome at 6 months post injury. Findings. Association between Mx and Mxa was moderately strong (r ² = 0.73). However, limit of 95% accordance between both indices was ±0.32. Mxa was significantly greater than Mx (0.22 ± 0.22 versus 0.062 ± 0.28; p < 0.000001). The difference between Mx and Mxa decreased with impairment of autoregulation (r = −0.39; p < 0.000001). Mean value of Mx showed a significant difference between dichotomized outcome groups (better autoregulation in patients with favourable than unfavourable outcome), while Mxa did not. Conclusions. Although relatively similar in a large group of patients, the differences between these two methods of assessment of dynamic autoregulation may be considerable in individual cases. When ICP is monitored, CPP rather than ABP should be included in the calculation of the autoregulatory index.     

Transcranial Doppler sonography in adult hydrocephalic patients

Transcranial Doppler sonography (TCD) is a noninvasive technique for measurement of cerebral blood flow velocity (CBFV) in the major arteries of the circle of Willis. Dynamic changes in the pulsatility index (PI) and the resistance index (RI), as calculated from TCD data, allow for an assessment of the forces acting on the terminal vasculature of the brain. The present study was designed to investigate a possible relationship between TCD parameters and intracranial pressure (ICP) changes in adult patients with hypertensive hydrocephalus. Blood flow velocity in the middle cerebral artery (MCA) was studied by TCD in 29 hydrocephalus patients and in 20 healthy controls. ICP was measured in the patient group before ventricular shunting and was correlated with TCD data. The mean CBFV in hydrocephalic patients prior to ventriculoperitoneal shunting was significantly lower than in the control group. Compared to normal persons, systolic and end-diastolic CBFV values in patients were significantly decreased, suggesting an increased distal cerebrovascular resistance. PI and RI values in patients with elevated ICP prior to shunting were significantly increased in comparison to those of normal persons. There was a statistically significant positive correlation of preshunting ICP and mean preshunting values of RI (r=0.50, P<0.01) in hydrocephalic patients, but no significant correlation between PI and ICP, and between CBFV and ICP. Immediately after shunting, ICP returned to normal, and PI and RI values decreased significantly, while the mean CBFV increased. In a subgroup of hydrocephalic patients with a preshunting ICP value >35 mm Hg (n=6), the changes described above were more pronounced than in the subgroup with preshunting ICP values <35 mm Hg, which suggests an exponential degree of influence of ICP on TCD parameters. In conclusion, TCD may provide a tool for assessment of ICP in adult patients with occlusive hydrocephalus, although an exact noninvasive measurement of ICP by TCD seems impossible. Changes in the RI and PI indices appear to be useful indicators of elevated ICP. Received: 2 June 1998 / Accepted: 26 May 1999     

Association between dynamic cerebral autoregulation and mortality in severe head injury

The objective of the study was to test the hypothesis that dynamic cerebral pressure-autoregulation is associated with the outcome of patients with severe head injury and to derive optimal criteria for future studies on the predictive value of autoregulation indices. Repeated measurements were performed on 32 patients with severe head injury. Arterial blood pressure (ABP) was measured continuously with an intravascular catheter, intracranial pressure (ICP) was recorded with a subdural semiconductor transducer and cerebral blood flow velocity (CBFV) was measured with Doppler ultrasound in the middle cerebral artery. Transfer function analysis was performed on mean beat-to-beat values, using ABP or CBFV as input variables and CBFV or ICP as the output variables. A dynamic index of autoregulation (ARI) ranging between 0 and 9 was extracted from the CBFV step response for a change in ABP. No significant differences between survivors and non-survivors were found due to mean values of ICP, ABP, CPP, CBFV, pCO2, GCS, age or heart rate. The transfer functions between ABP-ICP and CBFV-ICP did not show any significant differences either. The median [lower, upper quartiles] ARI was significantly lower for non-survivors compared with survivors [4.8 (0.0, 5.9) v. 6.9 (5.9, 7.4), p= 0.004]. The correlation between ARI and GOS was also significant (r=0.464, p=0.011). Cohen's coefficient was optimal for a threshold of ARI= 5.86 (kappa 0.51, p=0.0036), leading to a sensitivity for death of 75%, specificity=76.5%, odds ratio =9.75 and overall precision = 75.8%. The difference in ARI values between survivors and non-survivors persisted when results were adjusted for GCS (p = 0.028). A similar analysis for the Marshall CT scale did not reach significance (p = 0.072). A logistic regression analysis confirmed that apart from the ARI, no other variables had a significant contribution to predict outcome. In this group of patients, death following severe head injury could not be explained by traditional indices of risk, but was strongly correlated to indices of dynamic cerebral pressure-autoregulation extracted by means of transfer function analysis. Future studies using a prospective design are needed to validate the predictive value of the ARI index, as estimated by transfer function analysis, in relation to death and other unfavourable outcomes.     

Alteration in brain natriuretic peptide (BNP) plasma concentration following severe traumatic brain injury

Summary Background. Brain natriuretic peptide (BNP) is a potent natriuretic and vasodilator factor which, by its systemic effects, can decrease cerebral blood flow (CBF). In aneurysmal subarchnoid hemorrhage (aSAH), BNP plasma concentrations were found to be associated with hyponatremia and were progressively elevated in patients who eventually developed delayed ischemic deficit secondary to vasospasm. The purpose of the present study was to evaluate trends in BNP plasma concentrations during the acute phase following severe (traumatic brain injury) TBI. Methods. BNP plasma concentration was evaluated in 30 patients with severe isolated head injury (GCS < 8 on admission) in four time periods after the injury (period 1: days 1–2; period 2: days 4–5; period 3: days 7–8; period 4: days 10–11). All patients were monitored for ICP during the first week after the injury. Findings. The initial BNP plasma concentrations (42 ± 36.9 pg/ml) were 7.3 fold (p < 0.01) higher in TBI patients as compared to the control group (5.78 ± 1.90 pg/ml). BNP plasma concentrations were progressively elevated through days 7–8 after the injury in patients with diffused SAH as compared to patients with mild or no SAH (p < 0.001) and in patients with elevated ICP as compared to patients without elevated ICP (p < 0.001). Furthermore, trends in BNP plasma concentrations were significantly and positively associated with poor outcome. Interpretation. BNP plasma concentrations are elevated shortly after head injury and are continuously elevated during the acute phase in patients with more extensive SAH and in those with elevated ICP, and correlate with poor outcomes. Further studies should be undertaken to evaluate the role of BNP in TBI pathophysiology.     

Intracranial pressure levels and single wave amplitudes, Glasgow Coma Score and Glasgow Outcome Score after subarachnoid haemorrhage

Summary Object. To relate intracranial pressure (ICP) levels and single ICP wave amplitudes to the acute clinical state (Glasgow Coma Score, GCS) and final clinical outcome (Glasgow Outcome Score, GOS) in patients with subarachnoid haemorrhage (SAH). Methods. Twenty-seven consecutive patients with severe SAH had their ICP and arterial blood pressure (ABP) continuously monitored during days 1–6 after SAH. The acute clinical state could be assessed in 11 non-sedated cases using the Glasgow Coma Scale, while outcome was assessed in all cases after 6 months using the Glasgow Outcome Scale. The ICP/ABP recordings were stored as raw data files and analyzed retrospectively. For every consecutive 6 seconds time window, mean ICP, mean cerebral perfusion pressure (CPP) and the mean ICP wave amplitude were computed. Results. The GCS during days 1–6 after SAH was significantly related to the mean ICP wave amplitude, but not to the mean ICP or mean CPP. There was also a strong relationship between the mean ICP wave amplitude and GOS 6 months after SAH, with mean ICP wave amplitudes being significantly lower in those with moderate disability/good recovery, as compared with those with severe disability and death. Mean ICP was significantly higher in those who died than in the group with moderate disability/good recovery whereas mean CPP was not different between outcome groups. Conclusions. In this small patient group the mean ICP wave amplitude during days 1–6 after SAH was related to the acute clinical state (GCS) as well as to the clinical outcome (GOS) 6 months after SAH. Similar relationships were not found for mean ICP or the mean CPP, except for a higher mean ICP in those who died than in those with moderate disability/good recovery.     

Indomethacin and cerebral autoregulation in severe head injured patients: a transcranial Doppler study

Summary Objective. To assess the effect of indomethacin on cerebral autoregulation, systemic and cerebral haemodynamics, in severe head trauma patients. Design. Prospective, controlled clinical trial, with repeated measurements. Settings. A 12-bed adult general intensive care unit in a third level referral university hospital. Patients. 16 severely head injured patients, 14 males, age range 17–60. Interventions. Indomethacin was administrated as a load plus continuous infusion. Indomethacin reactivity was assessed as the estimated cerebral blood flow change elicited by the load. Dynamic and static cerebral autoregulation tests were performed before indomethacin administration, and during its infusion. Measurements and main results. Systemic and cerebral haemodynamic changes were assessed through continuous monitoring of mean arterial pressure, transcranial Doppler cerebral blood flow velocity, intracranial pressure, cerebral perfusion pressure, and jugular venous oxygen saturation. Indomethacin loading dose was immediately followed by a cerebral blood flow median decrease of 36 or 29% (p = ns) evaluated by two different methods, by an ICP decrease and by an AVDO₂ increase from 3.52 to 6.15 mL/dL (p = 0.002). Dynamic autoregulation increased from a median of 28 to 57% (p<0.05) during indomethacin infusion; static autoregulation also increased, from a median of 72 to 89% (p = ns). Conclusions. Indomethacin decreased intracranial pressure and cerebral blood flow, and increased cerebral perfusion pressure, while maintaining tissue properties of further extracting O₂. The increase in both autoregulatory values reveals an enhancement of cerebral microvasculature reactivity under indomethacin, during hypertensive and – especially – during hypotensive situations.     

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.      

Evaluation of mechanism of increased intracranial pressure with insufflation

Background: Previous studies have documented an increase in intracranial pressure with abdominal insufflation, but the mechanism has not been explained. Methods: Nine 30–35-kg domestic pigs underwent carbon dioxide insufflation at 1.5 l/min. Intracranial pressure (ICP), lumbar spinal pressure (LP), central venous pressure (CVP), inferior vena cava pressure (IVCP), heart rate, systemic arterial blood pressure, pulmonary arterial pressure, cardiac output, heart rate, respiratory rate, temperature, and end-tidal CO₂ were continuously measured. Mechanical ventilation was used to maintain a constant pCO₂. Measurements were recorded at 0, 5, 10, and 15 mmHg of abdominal pressure with animals in supine, Trendelenburg (T), and reverse Trendelenburg (RT) positions. Prior to recording measurements, the animals were allowed to stabilize for 40 min after each increase in abdominal pressure and for 20 min after each position change. Results: The animals showed a significant increase in ICP (mmHg) with each 5-mmHg increase in abdominal pressure (0 mmHg: 14 ± 1.7; 5 mmHg: 19.8 ± 2.3, p < 0.001; 10 mmHg: 24.8 ± 2.5, p < 0.001; 15 mmHg: 29.8 ± 4.7, p < 0.01). The ICP at 15 mmHg abdominal pressure increased further in the T position (39 ± 4, p < 0.01). Insufflating in the RT position did not significantly reduce the increase in ICP. The IVCP (mmHg) increased with increased abdominal pressure (0 mmHg: 11.5 ± 6.2, 15 mmHg: 22.1 ± 3.5, p < 0.01). This increase correlated with the increase in ICP and LP (r of mean pressures ≥0.95). There was no significant change in CVP. Conclusions: This study suggests that care may be needed with laparoscopy in patients at risk for increased ICP due to head injury or a space occupying lesion. The mechanism of increased ICP associated with insufflation is most likely impaired venous drainage of the lumbar venous plexus at increased intraabdominal pressure. Further studies of cerebral spinal fluid movement during insufflation are currently underway to confirm this hypothesis. Received: 28 March 1997/Accepted: 5 August 1997     

Cerebral autoregulation following head injury.

OBJECT: The goal of this study was to examine the relationship between cerebral autoregulation, intracranial pressure (ICP), arterial blood pressure (ABP), and cerebral perfusion pressure (CPP) after head injury by using transcranial Doppler (TCD) ultrasonography. METHODS: Using ICP monitoring and TCD ultrasonography, the authors previously investigated whether the response of flow velocity (FV) in the middle cerebral artery to spontaneous variations in ABP or CPP provides reliable information about cerebral autoregulatory reserve. In the present study, this method was validated in 187 head-injured patients who were sedated and receiving mechanical ventilation. Waveforms of ICP, ABP, and FV were recorded over intervals lasting 20 to 120 minutes. Time-averaged mean FV and CPP were determined. The correlation coefficient index between FV and CPP (the mean index of autoregulation [Mx]) was calculated over 4-minute epochs and averaged for each investigation. The distribution of averaged mean FV values converged with the shape of the autoregulatory curve, indicating lower (CPP < 55 mm Hg) and upper (CPP > 105 mm Hg) thresholds of autoregulation. The relationship between the Mx and either the CPP or ABP was depicted as a U-shaped curve. Autoregulation was disturbed in the presence of intracranial hypertension (ICP > or = 25 mm Hg) and when mean ABP was too low (ABP < 75 mm Hg) or too high (ABP > 125 mm Hg). Disturbed autoregulation (p < 0.005) and higher ICP (p < 0.005) occurred more often in patients with unfavorable outcomes than in those with favorable outcomes. CONCLUSIONS: Autoregulation not only is impaired when associated with a high ICP or low ABP, but it can also be disturbed by too high a CPP. The Mx can be used to guide intensive care therapy when CPP-oriented protocols are used.     

Comparison of moderate hyperventilation and mannitol for control of intracranial pressure control in patients with severe traumatic brain injury – a study of cerebral blood flow and metabolism

Summary Objective. To compare the respective effects of established measures used for management of traumatic brain injury (TBI) patients on cerebral blood flow (CBF) and cerebral metabolic rates of oxygen (CMRO₂), glucose (CMRGlc) and lactate (CMRLct). Methods. Thirty-six patients suffering from severe traumatic brain injury (TBI) were prospectively evaluated. In all patients baseline assessments were compared with that following moderate hyperventilation (reducing PaCO₂ from 36 ± 4 to 32 ± 4 mmHg) and with that produced by administration of 0.5 gr/kg mannitol 20% intravenously. Intracranial and cerebral perfusion pressure (ICP, CPP), CBF and arterial jugular differences in oxygen, glucose and lactate contents were measured for calculation of CMRO₂, CMRGlc and CMRLct. Results. Following hyperventilation, CBF was significantly reduced (P < 0.0001). CBF remained most often above the ischemic range although values less than 30 ml·100 gr⁻¹·min⁻¹ were found in 27.8% of patients. CBF reduction was associated with concurrent decrease in CMRO₂, anaerobic hyperglycolysis and subsequent lactate production. In contrast, mannitol resulted in significant albeit moderate improvement of cerebral perfusion. However, administration of mannitol had no ostensible effect either on oxidative or glucose metabolism and lactate balance remained mostly unaffected. Conclusions. Moderate hyperventilation may exacerbate pre-existing impairment of cerebral blood flow and metabolism in TBI patients and should be therefore carefully used under appropriate monitoring. Our findings rather support the use of mannitol for ICP control.     

Ultrafiltration Volume Is Associated with Changes in Blood Pressure in Chronically Hemodialyzed Patients

Introduction.?Volume overload is a main factor in development of hypertension in hemodialysis patients. In order to demonstrate impact of ultrafiltration volume on blood pressure during 15-months period in a group of patients undergoing chronic hemodialysis therapy, we conducted this study. We hypothesized that ultrafiltration volume different affects the pre/postdialysis systolic pressure, diastolic pressure, mean arterial pressure (MAP), and pulse pressure (PP) values. Subjects and Methods.?Study subjects were 23 anuric chronically hemodialyzed patients. The overall study time was 15 months, and 136 single hemodialysis treatments were analyzed. Results.?Ultrafiltration was negatively correlated with predialysis systolic blood pressure (r = ?0.169, p = 0.025), postdialysis systolic blood pressure (r = ?0.292, p<0.001), postdialysis MAP (r = ?0.186, p = 0.015), predialysis PP (r = ?0.290, p<0.001), and postdialysis PP (r = ?0.370, p<0.001). Ultrafiltration/dry body mass (UF/W) ratio was negatively correlated with predialysis PP (r = ?0.222, p = 0.005), postdialysis PP (r = ?0.340, p<0.001), and postdialysis systolic blood pressure (r = ?0.243, p = 0.002). We found significant difference in postdialysis PP between dialyses with UF/W ratio ≤0.05 and dialyses with UF/W ratio >0.05 (63.49 ± 20.76 vs. 56.27 ± 16.33 mmHg, p = 0.033). Conclusion.?The ultrafiltration volume strongly affects postdialysis PP values. Evaluation of elevated blood pressure treatment in patients undergoing chronic hemodialysis therapy must be considered in respect of postdialysis PP values, not just depending on pre/postdialysis systolic and diastolic pressure or MAP values.     

Recovery of the blood pressure – cerebral flow relation after carotid stenting in elderly patients

Summary Background. As a sensitive and convenient means for the cerebral hemodynamic monitoring, dynamic cerebral autoregulation testing could be especially useful in medical conditions where less invasive diagnostics and therapies are preferred. This study analysed the effect of carotid stenting on dynamic autoregulation in elderly patients focussing on the relation between blood pressure and cerebral blood flow velocity. Methods. We examined 20 patients age 69 ± 8 years with coexisting cerebrovascular and medical risk factors before and at least six month after stenting of severe carotid stenoses. Data were compared to 24 age-matched healthy controls. Slow spontaneous oscillations were studied in continuous recordings of Transcranial Doppler and beat-to-beat blood pressure. Analysis was based on the “high-pass filter model”, which predicts a positive phase relationship between these oscillations. Findings. Whereas phase shift angles were diminished (20.4 ± 14.1°) before stenting, after stenting these values were significantly increased to normal (48.1 ± 16.6°), to the level of controls (46.7 ± 15.9°). Medical conditions such as coronary artery disease, arterial hypertension, and dyslipidemia did not diminish this recovery. The level of increase was inversely correlated with the initial autoregulatory deficit (r = −0.68) which was largest with insufficient collateral blood supply and symptomatic carotid stenoses. Conclusions. The study showed that an impaired cerebral autoregulation may recover after stent-guided carotid angioplasty even in the elderly with co-existing medical conditions. In this respect to regain vasomotor capability, patients with cerebrovascular risk factors seemed to benefit particularly.     

Opioide,Hirndurchblutung und intrakranieller Druck

The effects of the opioids alfentanil (A), fentanyl (F), and sufentanil (S) on cerebral blood flow (CBF) and intracranial pressure (ICP) have been discussed in several recent publications. The purpose of this review is to describe the results of studies in animals, healthy volunteers, and patients with and without intracranial diseases. Clinical relevance and mechanisms of the reported ICP and CBF increases are analysed. Methods. Approximately 70 original articles and abstracts were retrieved by a systematic literature search using the key word list at the end of this abstract. The cited studies came from computerised database systems like Silver Platter and DIMDI, the SNACC reference list, and the bibliographies of pertinent articles and books. These studies were classified into three groups: significant increase of ICP and/or CBF; no significant or clinically relevant alterations; and significant decreases of ICP and/or CBF. Results. The numerical relationship was 6 : 7 : 3 for A, 7 : 16 : 9 for F, and 5 : 11 : 8 for S. Increases of previously normal or only slightly elevated ICP were registered in some studies in connection with a decrease in mean arterial pressure (MAP). On the other hand, in patients with brain injury and elevated ICP opioids did not further increase ICP despite MAP decreases. In studies monitoring ICP and/or CBF continuously, transient and moderate increases of questionable clinical relevance became apparent a few minutes after bolus injection of opioids. Alterations of systemic and cerebral haemodynamics observed after bolus application were not registered during continuous infusion of A and S. Discussion and conclusions. The cerebral effects of opioids are dependent on several factors, e.g., age, species, ventilation, anaesthesia before and during measurements, systemic haemodynamics, and underlying diseases. The probable mechanism of ICP increase during decreasing MAP is cerebral vasodilatation due to maintained autoregulation. With increasing severity of the cerebral lesion autoregulation is often disturbed. Therefore, ICP often remains unaltered despite MAP decreases. However, the resulting decrease in cerebral perfusion pressure makes such patients more susceptible to develop ischaemic neurological deficits. Induction of somatic rigidity or (with high doses) convulsions, exceeding the upper limit of autoregulation, histamine release, cerebral vasodilatation, increased cerebral oxygen consumption, or carbon dioxide accumulation during spontaneous breathing were discussed as mechanisms for transient ICP/CBF increases. It is concluded that opioids are often beneficial and not generally contraindicated for patients with cerebral diseases and compromised intracranial compliance. However, since negative side effects cannot be excluded, opioid effects and side effects should be monitored (MAP, ICP, cerebrovenous oxygen saturation, transcranial Doppler sonography) in patients at risk. It has to be stressed that opioids should be administered only to patients with stable haemodynamic situations and preferably in well-titrated, continuous infusions. Eingegangen am 3. Januar 1994 / Angenommen am 22. M?rz 1994     

Cerebral effects of nitrous oxide during isoflurane-induced hypotension in the pig

We have studied the effects of nitrous oxide on cerebral bloodflow (CBF), cerebral blood flow velocity (CBFV) and intracranialpressure (ICP) during isoflurane-induced hypotension in 10 pigs.CBF was measured using laser Doppler flowmetry, CBFV in theright middle cerebral artery was calculated using Doppler ultrasoundand ICP was measured using an extradural ICP monitor. Each animalwas studied under four conditions, examined sequentially: (i)mean intra-arterial pressure (MAP) 85 mm Hg, maintained withisoflurane, (ii) MAP 50–55 mm Hg, induced by isofluraneonly, (iii) MAP 85 mm Hg, maintained with isoflurane and 50%nitrous oxide, and (iv) MAP 50–55 mm Hg, induced by isofluraneand 50% nitrous oxide. No significant differences were notedbetween conditions with respect to ICP. There was a significantdifference in CBF during condition (ii) compared with (i) (mean75(SD 21) vs 100(0) %) and during condition (iv) compared with(iii) (90(26) vs 109(13)%). Animals under condition (iv) exhibiteda 20% reduction in CBFV compared with those under condition(iii) (57 vs 69 cm s^–1). For animals under normotensiveconditions, addition of nitrous oxide to isoflurane resultedin a 16% increase in CBFV (69 vs 60 cm s^–1). Comparingisoflurane-induced hypotension ((ii) vs (iv)), there was nostatistical difference in either CBF or CBFV on addition of50% nitrous oxide. The correlation between changes in CBF andCBFV was not significant. We conclude that the use of nitrousoxide during isoflurane-induced hypotension has no significanteffect on CBF, CBFV or ICP compared with the use of isofluranealone.     

Development of a more robust tool for postural stability analysis of laparoscopic surgeons

Background Physical difficulties experienced by surgeons performing minimally invasive surgery (MIS) are being given extensive attention by ergonomic researchers. Postural stability, not commonly addressed, is our prime focus. Center of pressure (COP) alone is used in the few existing postural stability studies. Using COP, we previously correlated postural stability to instrument type, task difficulty, and skill level. This study, including center of mass (COM), sway area analysis, and what we uniquely term postural stability demand (PSD), extends our investigation. Methods Six surgeons from different experience levels were recruited to complete three fundamentals of laparoscopy (FLS^TM) tasks. Standing on two force plates, participants performed each task as a motion capture system recorded body movements. An ellipse was created for sway area analysis of COP, the point where the ground reaction force was located, and COM, the point at which body mass was concentrated. PSD was defined as the mean distance between the COP and COM locations in the anterior–posterior (A–P) or medial–lateral (M–L) directions. Postural parameters and performance time were correlated. Results COM and COP sway areas positively correlated with pegboard transfer performance time (r = 0.928, p < 0.05; r = 0.864, p < 0.05) and also with circle-cutting performance time (r = 0.858, p < 0.05; r = 0.779, p = 0.06). However, COM and COP sway areas negatively correlated with endo-loop placement performance time (r = −0.925, p < 0.05; r = −0.935, p < 0.05). These results indicate unique postural controls based on skill level. During all tasks, PSD in the A–P direction strongly correlated with performance time (r = 0.829, p < 0.05; r = 0.913, p < 0.05; r = 0.880, p < 0.05), indicating that less-skilled participants experienced increased postural demands. Conclusions This study demonstrated that variance in postural adjustments, as evidenced by sway area analysis, correlate to skill level and individual task. Strong correlation between PSD and performance time shows potential as a predictor of skill levels. Combining COM, COP, and PSD data produces a more robust analytic tool for identifying postural adjustments that can be correlated with skill level.     

Age, intracranial pressure, autoregulation, and outcome after brain trauma

OBJECT: The object of this study was to investigate whether a failure of cerebrovascular autoregulation contributes to the relationship between age and outcome in patients following head injury. METHODS: Data obtained from continuous bedside monitoring of intracranial pressure (ICP), arterial blood pressure (ABP), and cerebral perfusion pressure (CPP = ABP - ICP) in 358 patients with head injuries and intermittent monitoring of transcranial Doppler blood flow velocity (FV) in the middle cerebral artery in 237 patients were analyzed retrospectively. Indices used to describe cerebral autoregulation and pressure reactivity were calculated as correlation coefficients between slow waves of systolic FV and CPP (autoregulation index [ARI]) and between ABP and ICP (pressure reactivity index [PRI]). Older patients had worse outcomes after brain trauma than younger patients (p = 0.00001), despite the fact that the older patients had higher initial Glasgow Coma Scale scores (p = 0.006). When age was considered as an independent variable, it appeared that ICP decreased with age (p = 0.005), resulting in an increasing mean CPP (p = 0.0005). Blood FV was not dependent on age (p = 0.58). Indices of autoregulation and pressure reactivity demonstrated a deterioration in cerebrovascular control with advancing age (PRI: p = 0.003; ARI: p = 0.007). CONCLUSIONS: An age-related decline in cerebrovascular autoregulation was associated with a relative deterioration in outcome in elderly patients following head trauma.     

Correlations between perceived stress and depressive symptoms among depressive outpatients

Cognitive distortions associated with depression may amplify the sense of strain and pressure derived from everyday stressors. The Perceived Stress Scale (PSS), designed to assess the degree to which situations are perceived as stressful, was administered before and after open treatment with fluoxetine 20 mg/day for eight weeks to 60 consecutive outpatients with major depression (15 men and 45 women; mean age: 36.9 ± 10.6 years) and to 22 normal controls (11 mean and 11 women; mean age: 34.6 ± 10.1 years). Pretreatment, the mean PSS score among the depressed patients was 38.8 ± 6.4, which was significantly higher (z score: 6.33; p < 0.0001) than that (22.4 ± 7.0) of the group of normal controls. After treatment with fluoxetine, the mean PSS score was 25.1 ± 8.9, not different from controls but significantly different from baseline (paired t-test = 10.8; p < 0.0001). The correlation between PSS and Hamilton Rating Scale for Depression (HAM-D-17) scores was significant both before (r = 0.33; p < 0.02) and after (r = 0.62; p < 0.0001) treatment with fluoxetine. An even greater correlation was found between differences in pre- and post-treatment PSS scores and differences in pre- and posttreatment HAM-D-17 scores (r = 0.65; p < 0.0001).     

The association of bispectral index values and metrics of cerebral perfusion during cardiopulmonary bypass

Study objectiveLow bispectral index (BIS) values have been associated with adverse postoperative outcomes. However, trials of optimizing BIS by titrating anesthetic administration have reported conflicting results. One potential explanation is that cerebral perfusion may also affect BIS, but the extent of this relationship is not clear. Therefore, we examined whether BIS would be associated with cerebral perfusion during cardiopulmonary bypass, when anesthetic concentration was constant.DesignObservational cohort study.SettingCardiac operating room.PatientsSeventy-nine patients with cardiopulmonary bypass surgery were included.MeasurementsContinuous BIS, mean arterial blood pressure (MAP), cerebral blood flow velocity (CBFV), and regional cerebral oxygen saturation (rSO₂) were monitored, with analysis during a period of constant anesthetic. Mean flow index (Mx) was calculated as Pearson correlation between MAP and CBFV. The lower limit of autoregulation (LLA) was identified as the MAP value at which Mx increased >0.4 with decreasing blood pressure. Postoperative delirium was assessed using the 3D-Confusion Assessment Method.ResultsMean BIS was lower during periods of MAP < LLA compared with BIS when MAP>LLA (mean 49.35 ± 10.40 vs. 50.72 ± 10.04, p = 0.002, mean difference = 1.38 [standard error: 0.42]). There was a dose response effect, with the BIS proportionately decreasing as MAP decreased below LLA (β = 0.15, 95% CI for the average slope across all patients 0.07 to 0.23, p < 0.001). In contrast, BIS was relatively unchanged when MAP was above LLA (β = 0.03, 95% CI for the average slope across all patients −0.02 to 0.09, p = 0.22). Additionally, increasing CBFV and rSO₂ were associated with increasing BIS. Patients with postoperative delirium had lower mean BIS and higher percentage of time duration with BIS <45 compared to patients without delirium.ConclusionsThere was an association of BIS and metrics of cerebral perfusion during a period of constant anesthetic administration, but the absolute magnitude of change in BIS as MAP decreased below the LLA was small.     

The Camino intracranial pressure device in clinical practice. Assessment in a 1000 cases

Summary Background. Intracranial pressure (ICP) monitoring has become standard in the management of neurocritical patients. A variety of monitoring techniques and devices are available, each offering advantages and disadvantages. Analysis of large populations has never been performed. Patients and methods. A prospective study was designed to evaluate the Camino^? fiberoptic intraparenchymal cerebral pressure monitor for complications and accuracy. Results. Between 1992–2004 one thousand consecutive patients had a fiberoptic ICP monitor placed. The most frequent indication for monitoring was severe head injury (697 cases). The average duration of ICP monitoring was 184.6 ± 94.3 hours; the range was 16–581 hours. Zero drift (range, −17 to 21 mm Hg; mean 7.3 ± 5.1) was recorded after the devices were removed from 624 patients. Mechanical complications such as: breakage of the optical fiber (n = 17); dislocations of the fixation screw (n = 15) or the probe (n = 13); and failure of ICP recording for unknown reasons (n = 4) were found in 49 Camino^? devices. Conclusions. The Camino ICP sensor remains one of the most popular ICP monitoring devices for use in critical neurosurgical patients. The system offers reliable ICP measurements in an acceptable percentage of device complications and the advantage of in vivo recalibration. The incidence of technical complications was low and similar to others devices.