CNS and CVS Monitoring in Anaesthesia MCQs

At the point the fourth twitch reappears, still up to 75% to 80% of acetylcholine receptors may be blocked. Adequate reversal (neostigmine–glycopyrrolate) should be given, and clinical signs for return of neuromuscular function should be used to gauge readiness for extubation. Reference: Morgan and Mikhail’s clinical anesthesiology 6th edition pg 134.

Cerebral perfusion pressure is the pressure gradient driving cerebral blood flow. CPP = MAP - (ICP + CVP) Where CPP is cerebral perfusion pressure, CVP is central venous pressure, MAP is the mean arterial pressure and ICP is the intracranial pressure. Reference: Physics, Pharmacology and Physiology for Anaesthetists, Matthew E. Cross, second edition, pg 313.

Noxious stimulation from incisional pain, endotracheal intubation, full bladder, or preoperative discontinuation of anti-hypertensive medication, is usually responsible for increased blood pressure in the recovery area. Adequate analgesia preoperatively given with opioids. Mild to moderate elevations can be treated with intravenous labetalol; an angiotensin-converting enzyme inhibitor, such as enalapril; or a calcium channel blocker, such as nicardipine. The end point for treatment should be consistent with the patient’s own normal blood pressure. Reference: Morgan and Mikhail’s clinical anesthesiology, page no 1300

Ans is 'd' i.e. Chlorhexidine "Chlorhexidine is now the disinfectant recommended for all catheter placement procedures and for routine site cleansing during dressing changes."- Comprehensive Hospital Medicine: An Evidence-Based And Systems Approach By Mark V. Williams, Scott A. Flanders, p320 "Use of antiseptic solution for skin disinfection at the catheter insertion site helps prevent catheter-related infection. Chlorhexidine- based solutions appear to be superior to both aqueous and alcohol- based povidone-iodine in reducing the risk for catheter colonization and catheter-related bloodstream infection. If there is a contraindication to chlorhexidine, tincture of iodine, an iodophor or 70 percent alcohol can be used as alternatives"-uptodate.com

During the delivery of anesthesia, the current standard of care is to measure systemic blood pressure and heart rate every 5 minutes as a minimum. The clinical scenario and phase of the operation may mandate more frequent monitoring, which is up to the judgment of the anesthesia provider. Reference: https://www.asahq.org/standards-and-guidelines/standards-for-basic-anesthetic-monitoring

The human brain is able to maintain neuronal function in the face of decreasing CBF below the normal level of 50 mL/100 g/min. Because O2 delivery is directly related to CBF, EEG evidence of cerebral ischemia will appear if CBF is diminished sufficiently. The CBF reserve, however, is substantial, and the first signs of cerebral ischemia do not appear on EEG until CBF has fallen to approximately 22 mL/100 g/min. When CBF has fallen to 15 mL/100 g/min, the EEG becomes isoelectric. Irreversible membrane damage and cellular death do not occur, however, until CBF falls to 6 mL/100 g/min. Areas of the brain in which CBF falls in the 6 to 15 mL/100 g/min range are referred to as zones of ischemic penumbra. Several hours may elapse in these areas of the brain before irreversible membrane damage occurs. Reference: Miller: Miller's Anesthesia, ed 8, p 410

Indications for intraoperative monitoring of evoked potentials (EPs) include surgical procedures associated with possible neurological injury: spinal fusion with instrumentation, spine and spinal cord tumor resection, brachial plexus repair, thoracoabdominal aortic aneurysm repair, epilepsy surgery, and cerebral tumor resection. Volatile agents decrease the amplitude and increase the latency of evoked potentials. Reference: Morgan and Mikhail’s clinical anesthesiology 6th edition pg 596.

Numerous sites can be used to monitor temperature in the operating room. The tympanic membrane theoretically reflects brain temperature because the auditory canal ' s blood supply is the external carotid artery. Tympanic membrane temperatures reflect core body temperature. After tympanic membrane (perfused by carotid artery) and pulmonary artery measurements, the best reflector of core temperature is bladder temperature. Axillary and skin temperatures are highly prone to errors. Rectal temperature is a poor substitute and probe can induce trauma. Reference: Morgan and Mikhail’s clinical anesthesiology 6th edition pg 132.