4 IMPORTANT FACTORS AND THE CORRESPONDING PROPERTIES OF THE LOCAL ANESTHETIC GETTING INFLUENCED:

Risk for Occupational Transmission of HCV

⚠️HCV is not transmitted efficiently through occupational exposures to blood. 

⚠️The average incidence of anti-HCV seroconversion after accidental percutaneous exposure from an HCV-positive source is 1.8% (range: 0%–7%) 

⚠️Transmission rarely occurs from mucous membrane exposures to blood, and no transmission in health care professionals, has been documented from intact or nonintact skin exposures to blood 

⚠️ Environmental contamination with blood containing HCV is not a significant risk for transmission in the health-care setting with the possible exception of the hemodialysis setting where HCV transmission related to environmental contamination and poor infection-control practices have been implicated 

⚠️The risk for transmission from exposure to fluids or tissues other than HCV-infected blood also has not been quantified but is expected to be low.

Reference: Centre for Disease Control June 29, 2001 / Vol. 50 / No. RR-11, Updated U.S. Public Health Service Guidelines for the Management of Occupational Exposuresto HBV, HCV, and HIV and Recommendations for Postexposure Prophylaxis

NEUROTOXICITY OF ANESTHETIC AGENTS IN LONG-TERM

🔹Halothane and Isoflurane: Amyloidogenic properties

🔹Isoflurane : Behavioural changes, apoptosis (Sevo lacks this)

🔹Nitrous oxide: Dose dependent and paradoxical protective and neurotoxic effects 

🔹Opioids @ moderate to high dose: Brain hyper metabolism and damage; Remifentanil doubtful role in genesis of Alzheimer's disease

(Acta Rad, CJA, Proct Natl Acad Sci, Anesth, Lancet)

C⃒L⃒A⃒S⃒S⃒I⃒F⃒I⃒C⃒A⃒T⃒I⃒O⃒N⃒ O⃒F⃒ N⃒E⃒R⃒V⃒E⃒ F⃒I⃒B⃒E⃒R⃒S⃒

BRIEF FUNCTIONAL ANATOMY OF THE BRAIN

✔️Precentral gyrus contains the primary motor cortex

✔️Premotor cortex lies immediately anterior to Primary motor cortex ( Brodmann’s area 6 on the lateral surface of the frontal lobe.)

✔️Premotor cortex is active in response to EXTERNAL visual or somatic sensory cues (e.g. reaching for an object in full view, or identifying an object by touch alone). Also has role in bilateral postural fixation (e.g. stabilization of the hips during walking).

✔️The supplementary motor area occupies a neighbouring part of Brodmann’s area 6 on the medial surface of the frontal lobe.

✔️The supplementary motor area seems to respond to INTERNAL cues, especially intentions to make voluntary movements (even if the movement is not carried out).

✔️Lesions of the supplementary motor cortex are associated with contralateral inability to initiate movements (akinesia).

✔️The inferior frontal gyrus of the dominant hemisphere (usually the left) contains the (Broca’s) motor speech area (Brodmann’s areas 44 and 45)

✔️The somatic sensory cortex, occupies the entire postcentral gyrus (Brodmann’s areas 3, 1 and 2, rostral to caudal).

✔️ Caudal to the somatosensory cortex is the sensory association cortex, which is divided into a superior and an inferior parietal lobule by an intraparietal sulcus.

✔️ The superior lobule is thought to be responsible for conscious awareness of the contralateral half of the body. Lesions of this part of the cortex may result in neglect of the contralateral side of the body.

✔️ The inferior lobule in the dominant (usually left) hemisphere is associated with language functions.

✔️ The cortex adjacent to the parieto-occipital sulcus and the calcarine sulcus, which lies on the medial surface of occipital lobe, constitutes the primary visual cortex (Brodmann’s area 17).

✔️ The superior surface of the temporal lobe contains the primary auditory cortex (Brodmann’s areas 41 and 42), responsible for the conscious perception of sound. Unilateral lesions of the primary auditory cortex will therefore cause partial deafness in both ears.

✔️ The auditory association cortex, known as Wernicke’s area corresponds to Brodmann’s area 22 in the dominant hemisphere. It allows for understanding of the spoken word, and connects with other language areas of the brain.

✔️ The temporal lobe curls inward to form the hippocampus which lies in the floor of the inferior horn of the lateral ventricle, and forms part of the limbic system. Its functions relate to short-term memory and the emotional aspects of behaviour.

✔️ Lying close to the anterior end of the hippocampus is the amygdala. Its a mass of subcortical grey matter that also forms part of the limbic system. It is associated with the conscious appreciation of smells.

✔️ The insula is one of the cortical centres for pain, and is also involved in involuntary activities such as the control of viscera by the autonomic nervous system.

✔️ The basal ganglia includes

• striatum (caudate nucleus, putamen of the lentiform nucleus and the nucleus accumbens) 

• pallidum (globus pallidus of the lentiform nucleus) 

• subthalamic nucleus 

• compact part of the substantia nigra 

✔️ Four basic circuits are known to occur from the cerebral cortex, through the basal ganglia and back to the cortex, by a direct or indirect route: 

-a motor loop is concerned with learned movements;

-a cognitive loop with motor intentions; 

-a limbic loop with emotional aspects of movement and 

-an oculomotor loop with voluntary saccades.

✔️ Limbic system is composed of the the parahippocampal and cingulate gyri, the septal area, the hippocampal formation and the amygdala. Declarative memory (i.e. of new facts and events) may occur as modifications of synapses within the hippocampus.

✔️ Diencephalon comprises, from superior to inferior, the epithalamus, thalamus, subthalamus and hypothalamus.

✔️ The thalamus is the largest component of the diencephalon and is composed of numerous nuclei.

✔️ The epithalamus consists principally of the pineal gland that secretes melatonin and is involved with circadian rhythm and regulation of the onset of puberty and the habenular nuclei.

✔️ The subthalamus contains the subthalamic nucleus which connects to the globus pallidus and substantia nigra and is involved with the control of movement.

✔️ The hypothalamus has important connections with the limbic system, a controlling influence on autonomic nervous system activity and a role in neuroendocrine function.

✔️ The cerebellum coordinates movement by maintenance of equilibrium, posture and muscle tone at an unconscious level. Also concerned with muscular coordination, including trajectory, speed and force of movements.

✔️ The tectum (roof) of the midbrain is formed by four colliculi –the paired superior colliculi are associated with the visual system, and the inferior colliculi with the auditory system.

Reference: The brain: functional divisions, Leo Donnelly, Neurosurgery, Neuroradiology & Neurocritical Care in Anaesthesia

WHAT TO SUSPECT WHEN A PATIENT WITH ANEURYSMAL SAH DEVELOP SEIZURES

✅Vasospasm

✅Rebleeding 

✅Hyponatremia

✅Hydrocephalus 

MECHANISMS THROUGH WHICH HYPERGLYCEMIA WORSENS NEUROLOGICAL OUTCOME

✔️Hyperosmolality 

✔️Lactic acidosis

✔️Alterations in neuronal pH

✔️Increase in excitatory Amino Acids

FACTORS CAUSING FLUID AND ELECTROLYTE DISTURBANCES IN THE NEUROSURGICAL PATIENT

✅POOR ORAL INTAKE LEADING TO DEHYDRATION DUE TO

🔖 Decreased conscious level

🔖 Vomiting

🔖 Bulbar dysfunction 

🔖 Pending surgery 

✅FLUID OVERLOAD DUE TO

🔖overzealous intravenous rehydration 

✅DRUGS

🔖osmotic or loop diuretic therapy as part of the management of raised ICP

✅DISORDERS OF SODIUM-WATER BALANCE ASSOCIATED WITH THE NEUROLOGICAL PATHOLOGY/ SURGERY

🔖Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

🔖Cerebral salt wasting (CSWS) 

🔖Diabetes insipidus

CSF PRESSURES AND VOLUMES

VASOACTIVE AGENTS; DO YOU KNOW ?

Evidence suggests that dopamine can produce mild cerebral vasodilatation.

Phenylephrine can be the drug of choice when the cardiac index (CI) is sufficient but MAP is below the goal

Dobutamine does not have any dopaminergic agonist action.

In case of Labetalol, a reduction in MAP usually occurs when the dose is sufficient to decrease HR

propanolol shifts the hemoglobin-oxygen dissociation curve to the right.

Milrinone can induce thrombocytopenia as well as hypotension.

SNP is associated with the activation of the renin-angiotensin system ; reflex tachycardia can interfere with blood pressure reduction.

Occasionally, patients demonstrate relative resistance to SNP and they are at particular risk for developing cyanide toxicity.

SNP causes more arteriolar than venular vasodilatation, while NTG causes more venular than arteriolar vasodilatation.

Vasopressin increases arterial tone ; it is administered as a constant infusion, and not titrated up to avoid severe complications of distal ischemia.

Reference: Newfield, Philippa; Cottrell, James E., Handbook of Neuroanesthesia, 4th Edition