Central airway obstruction

George and colleagues (1992) treated nine patients with malignant central airway obstruction due to tracheal (n=3) or main bronchial ( =6) stenosis with Gianturco stents. All patients suffered from severe dyspnea or asphyxia (four were emergency treatments). All patients had dramatic and rapid reUef of their symptoms after stent insertion. Two patients with intraluminal tumor growth required additional endobronchial measures to control local tumor progression. Patients survived between 3 weeks and 8 months after the intervention. Causes of death were cachexia or pneumonia. 

Figure 17.3 Airway obstruction, (a) Normal, patent airway with radial traction offered to it by surrounding airways. Resistance in this airway is low and air flows through it freely, (b) The airway is obstructed by the presence of excess mucus and airway resistance is increased. Airflow is reduced, (c) Thickening of the airway wall due to inflammation or edema narrows the lumen of the airway. The decrease in airway radius increases airway resistance and decreases airflow, (d) Destruction of surrounding airways results in the loss of interdependence, or radial traction. Without the structural support offered by surrounding airways, the central airway collapses and airflow through it is reduced.

Gl effects Use cautiously in peptic ulcer. Local irritation may occur centrally mediated Gl effects may occur with serum levels greater than 20 mcg/mL. Reduced lower esophageal pressure may cause reflux, aspiration, and worsening of airway obstruction. 

An understanding of common mechanisms of death due to poisoning can help prepare the care-giver to treat patients effectively. Many toxins depress the central nervous system (CNS), resulting in obtundation or coma. Comatose patients frequently lose their airway protective reflexes and their respiratory drive. Thus, they may die as a result of airway obstruction by the flaccid tongue, aspiration of gastric contents into the tracheobronchial tree, or respiratory arrest. These are the most common causes of death due to overdoses of narcotics and sedative-hypnotic drugs (eg, barbiturates and alcohol). 

An increase in the total numbers of T-Iymphocytes is observed in lung parenchyma as well as in peripheral and central airways of patients with COPD a greater increase is observed in CD8 than CD4+ cells (6, 24). A correlation is observed between the numbers of T-cells and the amount of alveolar destruction and the severity of airflow obstruction. Furthermore, the oifly significant difference in the inflammatory cell infiltrate in asymptomatic smokers and smokers with COPD is an increase in T-cells, maiifly CD8+, in patients with COPD. An increase in the absolute number of CD4+ T-cells, albeit in smaller numbers, is evidenced in the airways of smokers with COPD, and these cells express activated STAT-4, which is a transcription factor that is essential for activation and commitment of the Thl lineage, and IFN-y. 

Since the introduction of propranolol, it has been recognized that patients with bronchial asthma treated with beta-adrenoceptor antagonists can develop severe airways obstruction (84), which can be fatal (85) or near fatal (86,87) this has even followed the use of eye-drops containing timolol (88). Beta-blockers upset the balance of bronchial smooth muscle tone by blocking the bronchial beta2-adrenoceptors responsible for bronchodilata-tion. They also promote degranulation of mast cells and depress central responsiveness to carbon dioxide (89,90). 

The parasympathetic division is the dominant portion of the pulmonary autonomic nervous system in all mammals. Airway smooth muscle is richly supplied with muscarinic receptors and stimulation of M3 receptors results in smooth muscle contraction and bronchoconstriction. Cholinergic stimulation is the primary mechanism of bronchospasm in horses with recurrent airway obstruction (Robinson et al 1996). Parasympathetic innervation can be demonstrated throughout the tracheobronchial tree of the horse but smooth muscle contraction evoked by stimulation of cholinergic nerves is more pronounced in the trachea than in the smaller bronchi. It is expected that parasympathetic blockade with a muscarinic antagonist will have the greatest effect in large, central airways. 

Central and Peripheral Deposition. Aerosol deposition in people with obstructive lung disease is shifted toward larger, more central airways. The extent to which airway obstruction reduces delivery to small airways and, thereby, limits drug efficacy is unclear. 

Corticosteroids are used in clinical practice to relieve pressure symptoms caused by many tumor types, notably intracerebral tumors but also those causing airway or central venous obstruction. Their mode of action has been studied in animals (57) and humans (58), and is thought to involve first constriction of tumor vascular volume and then a reduction in water content. Reduced interstitial pressure should increase perfusion and extravascular diffusion rates, and high doses of steroids have been shown to increase blood flow in human colonic tumors transplanted into mice. Uptake of antibody into tumors has been assessed before and after administration of high-dose dexamethasone to decrease tumor interstitial pressure and thus increase antigen accessibility. Three patients with recurrent colorectal carcinoma had two antibody scans each, 72 h apart, and the injected dose was the same for all scans (20 mg). Dexamethasone was started 24 h before the second dose of antibody, with an initial iv dose of 10 mg followed by 4 mg four times daily orally for 48 h. 

C. Cause of Death. In the absence of treatment, death is caused by anoxia resulting from airway obstruction, weakness of the muscles of respiration and central depression of respiration. 

Ophthalmic effects due to direct ocular exposure to OPs include optic neuropathy, retinal degeneration, defective vertical smooth pursuit, myopia, and miosis. Respiratory effects, including muscarinic, nicotinic, and central effects, contribute to respiratory distress in acute and delayed OP toxicity, Muscarinic effects, such as bronchospasm and laiyngeal spasm, can lead to airway obstruction. Nicotinic effects can lead to weakness and paralysis of respiratory oropharyngeal tiiuscles. Central effects can lead to cessation of respiration. 

Topical damage to the respiratory tract may occur due to direct toxic inhalational injury to the airways or alveoli. Cellular damage with consequent airway obstruction, pulmonary interstitial damage, or alveolar-capillary damage ultimately compromises adequate oxygen-carbon dioxide exchange. Some substances are relatively more toxic to the central airways, whereas others are more toxic to the peripheral airways or alveoli. 

However, the bronchodilation which is easily demonstrated in the asthmatic is not evident in CB. Nevertheless, the bronchitic with airways obstruction will report improvement of exercise capability with effective theophylline therapy. Theophylline is a phosphodiesterase inhibitor and results in a decreased breakdown of cAMP. This action in the bronchial tree has not been shown to be of benefit in the pathophysiologic mechanisms of CB. Although the mechanism of action in CB is not clear, benefit may be related to central nervous system stimulation, cardiac action, its modest diuretic activity, or to actions not... 

Appropriate assessment of the location of the tracheal or bronchial obstruction is mandatory to choose the correct stent and to allow proper placement. In the case of a proximal tracheal lesion the distance to the vocal cord has to be assessed and measured. In the case of a distal tracheal lesion the relation to the Carina has to be defined in order to assess whether a single tracheal stent or an additional unilateral or bilateral bronchial stent is required to achieve sufficient luminal diameter in the central airways. In the case of bronchial obstruction, the relation to lobar bronchial orifices has to be analyzed. 

Pulmonary function tests (PFTs) are not helpful (Pherwani et al., 1989 Traub et al., 2002) in this circumstance. A study of schoolchildren exposed to a chlorine gas leak reported a predominantly obstructive pattern on PFTs. This could be explained by congestion and edema narrowing the central airways rather than smaller ones. 

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