Effect of Propofol and Clonidine on Cerebral Blood Flow Velocity and Carbon Dioxide Reactivity in the Middle Cerebral Artery

Transcranial color-coded duplex sonography assessment of cerebrovascular reactivity to carbon dioxide: an interventional study

Background

The investigation of CO₂ reactivity (CO₂-CVR) is used in the setting of, e.g., traumatic brain injury (TBI). Transcranial color-coded duplex sonography (TCCD) is a promising bedside tool for monitoring cerebral hemodynamics. This study used TCCD to investigate CO₂-CVR in volunteers, in sedated and mechanically ventilated patients without TBI and in sedated and mechanically ventilated patients in the acute phase after TBI.

Methods

This interventional investigation was performed between March 2013 and February 2016 at the surgical ICU of the University Hospital of Zurich. Ten volunteers (group 1), ten sedated and mechanically ventilated patients (group 2), and ten patients in the acute phase (12–36 h) after severe TBI (group 3) were included. CO₂-CVR to moderate hyperventilation (∆ CO₂ -5.5 mmHg) was assessed by TCCD.

Results

CO₂-CVR was 2.14 (1.20–2.70) %/mmHg in group 1, 2.03 (0.15–3.98) %/mmHg in group 2, and 3.32 (1.18–4.48)%/mmHg in group 3, without significant differences among groups.

Conclusion

Our data did not yield evidence for altered CO₂-CVR in the early phase after TBI examined by TCCD.

Trial registration

Part of this trial was performed as preparation for the interventional trial in TBI patients (clinicaltrials.gov NCT03822026, 30.01.2019, retrospectively registered).

Intraventricular Pressure in Non-communicating Hydrocephalus Patients Before Endoscopic Third Ventriculostomy

Background

In patients with non-communicating hydrocephalus impairment of cerebral compliance can occur pre- but also intraoperatively.

Methodology

In such patients (n = 6) undergoing endoscopic third ventriculostomy (ETV), the present study aimed to investigate the effect of ETCO2 (e.g 40 mmHg and 60 mmHg) and positive end-expiratory pressure (PEEP) (e.g. 6 cm and 12 cm H2O) on intraventricular pressure (IVP).

Findings

Before but not after ETV, hypercapnia in contrast to PEEP increased IVP.

before ETV

(PEEP-6/ ETCO2-40: 2.6 ± 2.4 mmHg) vs. (PEEP-6/ ETCO2-60: 12 ± 6.4 mmHg*); (PEEP-12/ ETCO2-40: 4.2 ± 4.1 mmHg) vs. (PEEP-12/ ETCO2-60: 13.7 ± 7.6 mmHg*), * significant, P ≤ 0.05.

after ETV

(PEEP-6/ ETCO2-40: 2.0 ± 1.2 mmHg) vs. (PEEP-6/ ETCO2-60: 4.4 ± 3.1 mmHg); (PEEP-12/ ETCO2-40: 1.6 ± 1.3 mmHg) vs. (PEEP-12/ ETCO2-60: 6.6 ± 2.6 mmHg), * significant, P ≤ 0.05).

Conclusion

Patients with non-communicating hydrocephalus showed that hypercapnia but not PEEP increases significantly IVP before but not after ETV.

A Comparison of Mixed and Central Venous Oxygen Saturation in Patients during and after Cardiac Surgery

Monitoring of mixed venous oxygen saturation (Sv̄O2) allows assessment of the global balance between oxygen supply and demand. Sv̄O2 measurement requires the insertion of a pulmonary artery catheter (PAC) whereas central venous oxygen saturation (ScvO2) monitoring only requires a central venous catheter. The aim of this study was to assess how continuous measurements of ScvO2 relate to simultaneous measurements of Sv̄O2 during and after cardiac surgery. Continuous Sv̄O2 and ScvO2 measurements in 15 patients undergoing elective cardiac surgery were recorded each minute for 24 hours. Bland-Altman analysis of 9,382 paired data points for Sv̄O2 and ScvO2 revealed a mean bias of 4.4% (95% Cl +22.3, −13.6%). Considerable inter- and intra-individual variability was noted. Based on these data and previous studies, ScvO2 and Sv̄O2 are not interchangeable variables.

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.

Clonidine Decreases Stress Response in Patients Undergoing Carotid Endarterectomy Under Regional Anesthesia: A Prospective, Randomized, Double-Blinded, Placebo-Controlled Study

Inadequate analgesia or anxiety may induce an increased stress response in patients undergoing carotid endarterectomy (CEA) under regional anesthesia (RA). Central alpha2 adrenoceptor agonists have significant sedative and analgesic properties, which may attenuate sympathoadrenal activation during CEA and improve the quality of RA. We randomly assigned 80 patients to 2 groups receiving either RA plus placebo (n = 40) or RA plus clonidine 1 microg/kg as the initial loading dose followed by 1 microg.kg(-1).h(-1) (n = 40). RA was performed as combined deep and superficial cervical plexus blockade. Hemodynamic and neurological variables were assessed before, during, and after CEA. Arterial blood samples were collected at defined time points for the determination of plasma concentrations of epinephrine, norepinephrine, cortisol, and creatinine kinase and creatinine kinase-MB. Throughout the study, all patients responded easily to neurological evaluations. Before and during clamping mean arterial blood pressure and heart rate were not different between the groups, but mean arterial blood pressure was lower in the clonidine group (P < 0.01) at skin closure and postoperatively in the intensive care unit. In the placebo group, cortisol, epinephrine, and norepinephrine plasma concentrations were increased significantly (P < 0.05) and more patients required antihypertensive treatment (P < 0.01). Postoperatively the incidence of hypertension (P < 0.001) and development of neurological deficits (P < 0.05) was significantly decreased in the clonidine group. We conclude that 1 microg.kg(-1).h(-1) clonidine suppresses the hyperadrenergic response to CEA without adverse effects on hemodynamics or clinical neurological monitoring.

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.

The role of α2-agonists in neurosurgery

Alpha2-agonists have been extensively used and studied in anaesthesia and intensive care medicine. A list of benefits includes anxiolysis, blood pressure stabilization, analgesia, anaesthetic sparing effects and sedation without respiratory depression or significant cognitive impairment. Fear of inadvertent hypotension, bradycardia or post-operative sedation, and the variability of the haemodynamic response to different doses or rates of administration, have meant that universal acceptance in clinical practice has not yet been seen. Recently, the actions of these agents on the alpha2-adrenoreceptor and the imidazoline receptor have been more accurately identified, helping to explain the differences between the actions of various agents. The two readily available agents, clonidine and dexmedetomidine have already been used in many different anaesthetic situations, for a wide variety of surgical procedures. We believe that both of these alpha2-agonists are useful adjuncts for the management of the neurosurgical patient during surgery, and in the intensive care unit.