Brainstem reflex

Stroke patients who require mechanical ventilation are not necessarily destined for a poor outcome. In a study by Santoli et al., 58 patients underwent mechanical ventilation and 16 survived. Eleven achieved a Barthel Index (BI) score of 60, indicating a good outcome. Within this study population, those patients with bilaterally absent comeal and pupillary reflexes had uniformly poor outcomes, underscoring the need for careful assessment of brainstem reflexes in intubated stroke patients. Other factors that have been associated with poor outcome in intubated stroke patients are advanced age and lower Glasgow Coma Score (GCS) at the time of intubation, as well as seizures and pulmonary edema. ... 

Leis AA, Kofler M, Stokic DS, et al Effect of the inhibitory phenomenon following magnetic stimulation of cortex on brainstem motor neuron excitability and on the cortical control of brainstem reflexes. Muscle Nerve 16 1351-1358, 1993 Lemke MR Effect of carbamazepine on agitation in Alzheimer s inpatients refractory to neuroleptics. J Clin Psychiatry 56 354-357, 1995 Lemus CZ, Robinson DG, Kronig M, et al Behavioral responses to a dopaminergic challenge in obsessive-compulsive disorder. J Anxiety Disord 5 369-373, 1991 Lena C, Changeux JP Allosteric modulations of the nicotinic acetylchohne receptor. Trends Neurosci 16 181-186, 1993... 

All enteral feeds were stopped. The baby was given intravenous glucose, L-arginine, sodium benzoate, and sodium phenylacetate. Hemodialysis was initiated. At this time, there were no spontaneous respirations, there was no response to painful stimuli, and brainstem reflexes were absent. The plasma amino acid results revealed a glutamine level of 1500 pmol/L (normal 254-823), and citrulline was undetectable (normal 10-34 pmol/L). Quantitative carnitine, plasma acylcarnitine, and urine organic acid profiles were normal. The urine orotic acid concen-... 

Ostermann ME et al Coma mimicking brain death following baclofen overdose. Intensive Care Med 2000 26(8) 1144-1146. [PMID 11030173] (Full neurologic recovery in a patient with severe baclofen overdose presenting in deep coma with absent brainstem reflexes.)... 

Nervous System Local anesthetic field block has been associated with transient brain stem paralysis in two adolescent patients undergoing elective foramen magnum decompression for a Chiari type 1 malformation [13 ]. Perioperative field block with levobupivacaine after woxmd closure was closely associated with absent brainstem reflexes and delayed awakening in both patients. The absence of any structural and biochemical pathology per se and the temporal relationship of the occurrence of brainstem symptoms and local anesthetic infiltration make local anesthetic effects the likely cause in the experience of tire authors. 

The current definition of brainstem death is based on coma, absent brainstem reflexes and ap-noea, with the criteria for organ donation listed in Table 5.1.2. 

Opiates activate the chemoreceptor trigger zone in the medulla (by disinhibition) to cause nausea and vomiting, and cough suppression also occurs because of the inhibitory effects of opiates on the brainstem nuclei in the cough reflex pathway. Dextromethorphan is the non-opiate isomer of the opiate levorphanol and is an effective cough suppressant. 

Signals are also transmitted to the reticular formation of the brainstem by way of the spinoreticular tract. The reticular formation plays an important role in the response to pain. First, it facilitates avoidance reflexes at all levels of the spinal cord and, second, it is responsible for the significant arousal effects of pain. Signals from the reticular formation cause an increase in the electrical activity of the cerebral cortex associated with increased alertness. Furthermore, it sends nerve impulses to the hypothalamus to influence its functions associated with sudden alertness, such as increased heart rate and... 

An example of this type of reflex is the baroreceptor reflex (see Figure 1.2). Baroreceptors located in some of the major systemic arteries are sensory receptors that monitor blood pressure. If blood pressure decreases, the number of sensory impulses sent from the baroreceptors to the cardiovascular control center in the brainstem also decreases. As a result of this change in baroreceptor stimulation and sensory input to the brainstem, ANS discharge to the heart and blood vessels is adjusted to increase heart rate and vascular resistance so that blood pressure increases to its normal value. 

Baroreceptors are sensitive to changes in MAP. As VR, CO, and MAP decrease, baroreceptor excitation is diminished. Consequently, the frequency of nerve impulses transmitted from these receptors to the vasomotor center in the brainstem is reduced. This elicits a reflex that will increase HR, increase contractility of the heart, and cause vasoconstriction of arterioles and veins. The increase in CO and TPR effectively increases MAP and therefore cerebral blood flow. Constriction of the veins assists in forcing blood toward the heart and enhances venous return. Skeletal muscle activity associated with simply walking decreases venous pressure in the lower extremities significantly. Contraction of the skeletal muscles in the legs compresses the veins and blood is forced toward the heart. 

The simple or unconditioned salivary reflex occurs when food is present within the oral cavity and causes stimulation of chemoreceptors and pressure receptors. These receptors then transmit impulses to the salivary center in the medulla of the brainstem. Parasympathetic efferent impulses are transmitted back to the salivary glands and secretion is enhanced. 

Startle reflex brainstem auditory evoked response... 

Activity of autonomic nervous system and the modulation of this activity by baroreceptor reflexes and vasomotor centre in the brainstem. 

Benzodiazepines exert central depressant effects on spinal reflexes, in part mediated by the brainstem reticular system.3 For example, chlordiazepoxide depresses the duration of electrical after-discharge in the limbic system. Most benzodiazepines elevate the seizure threshold and therefore may be used as anticonvulsant medications. Diazepam, clonazepam, and clorazepate may be prescribed for this therapeutic purpose. 

Dickerman RD, Jaikumar S. The hiccup reflex arc and persistent hiccups with high-dose anabolic steroids is the brainstem the steroid-responsive locus Clin Neuropharmacol 2001 24(l) 62-4. 

Codeine Many trade names Inhibits cough reflex by direct effect on brainstem cough center... 

Acting in the brainstem, as well as in the respiratory centers of the brain, morphine slows respiration and suppresses the cough reflex. 

In close vicinity of the ARAS the medial longitudinal fasciculus (MLF) and the oculomotor and trochlear nuclei are situated. Combined coma and oculomotor disturbances points to a brainstem lesion (Parvizi and Damasio 2003). Other clinical symptoms like respiratory pattern, pupillary reflex, and position or movement patterns of the limbs may help localize the site of the lesion. 

The pupillary light reflex may help differentiating metabolic cause from structural brainstem lesion in comatose patients (Tokuda et al. 2003). The light reflex is very resistant to metabolic dysfunction. An abnormal light reflex, especially when unilateral, points to a midbrain lesion. Bilateral diencephalic lesions or metabolic coma may cause bilateral small pupils well reacting to light ( diencephalic pupils ). 

Pneumonia is a common complication in elderly patients confined to bed. Chest infection is particularly common after stroke because of impairment in swallow and cough reflex, poor respiratory movement and pulmonary embolism. The risks can be reduced by good nursing and chest physiotherapy. A pharyngeal airway may be required, particularly in drowsy patients or after a brainstem stroke, and ventilation may be considered in certain patients. 

---