None listed
Conditions
Brief summary
Measurement of actual cerebral blood flow during surgery is difficult due to the invasive or unpractical nature of the measurement tools needed. In contrast, cerebral oximetry is the continuous non-invasive measurement of cerebral oxygenation (amount of oxygen in the blood) and perfusion (the delivery of blood to the tissues of the brain). This allows anaesthetists to make critical decisions to maximise oxygen delivery and improve patient outcomes. Cerebral oximetry has been studied for more than 30 years and been commercially available for more than 2 decades. Numerous studies demonstrate that increases in blood carbon dioxide (PaCO2) increase blood flow to the brain. Carbon dioxide is a normal waste product of body metabolism, and is eliminated via the lungs. However, there are no physiological studies to date comparing the effects of normal blood carbon dioxide (normocapnia - defined as PaCO2 levels between 35-40 mmHg) and mildly elevated carbon dioxide levels (mild hypercapnia - defined as PaCO2 levels between 45-55 mmHg) on cerebral oximetry in patients undergoing major surgery. The primary aim of this study is to evaluate the effects of changes in PaCO2 on cerebral oximetry in patients undergoing major surgery. Secondary aims include the evaluation of the effects of normocapnia and mild hypercapnia on acid base blood variables, serum potassium levels, and postoperative delirium. A total of 40 subjects will be included at the Austin Hospital
Interventions
Patient with age greater than 18 years undergoing major surgery of at least 2 hours duration with be treated with controlled ventilation maintaining an arterial CO2 level (PaCO2) between 45 to 55 mmHg. The duration of mild hypercapnia will be from induction of anaesthesia to end of the surgical procedure i.e. skin closure. Controlled ventilation will be managed by the anaesthetist responsible for the conduct of the case. The target CO2 will be achieved by adjusting the minute ventilation on the
Patient with age greater than 18 years undergoing major surgery of at least 2 hours duration with be treated with controlled ventilation maintaining an arterial CO2 level (PaCO2) between 45 to 55 mmHg. The duration of mild hypercapnia will be from induction of anaesthesia to end of the surgical procedure i.e. skin closure. Controlled ventilation will be managed by the anaesthetist responsible for the conduct of the case. The target CO2 will be achieved by adjusting the minute ventilation on the ventilator by changing the respiratory rate, tidal volume, or adjusting both of these variables. These will be adjusted by the treating clinical anaesthetist by following a standardised algorithm:- first the respiratory rate will be adjusted by 2 breaths/min. The blood gas will then be repeated 5-minutes later. Second, if the CO2 is still not within target rage, the tidal volume will be adjusted by 20%. These steps will be repeated until the target CO2 is achieved. Once the target CO2 has been achieved, adherence to the intervention i.e. maintaining an arterial CO2 level between 45 to 55 mmHg, will be verified by the clinical anaesthetist checking the PaCO2 on arterial blood gases at hourly intervals. Blood gases will be performed on a blood gas analyser located in the theatre complex
Sponsors
Deparments of Anaesthesia, Austin Hospital
Study design
Allocation
Randomised controlled trial
Intervention model
Parallel
Primary purpose
Treatment
Masking
Open (masking not used)
Eligibility
Sex/Gender
All
Age
18 Years to No maximum
Healthy volunteers
No
Inclusion criteria
Adult patients (age > 18 years) undergoing major surgery (greater than 2 hours duration) that require the routine use of an arterial line for continuous blood pressure monitoring and intermittent positive pressure ventilation via an endotracheal tube as part of standard anaesthesia care.
Exclusion criteria
1. All patients aged less than 18 years 2. Patients undergoing cardiac surgery 3. Intracranial procedures 4. Glasgow Coma Score < 15 5. Thoracic surgery requiring for one lung isolation 6. Moderate pulmonary hypertension (MPA greater than or equal to 40 mmHg) 7. American Society of Anaesthesiologists (ASA) physical status V
Outcome results
None listed