Carbon dioxide retention

Carbon dioxide retention caused by respiratory depression results in cerebral vasodilation. In patients with elevated intracranial pressure, this may lead to lethal alterations in brain function. 

Morphine releases histamine and may cause peripheral vasodilation and orthostatic hypotension (Figure 47.7). The cutaneous blood vessels dilate around the blush areas such as the face, neck, and upper thorax. Morphine causes cerebral vasodilation (due to increased carbon dioxide retention secondary to respiratory depression), and hence, it increases the cerebrospinal fluid pressure. Therefore, morphine should be used cautiously in patients with either meningitis or a recent head injury. When given subcutaneously, morphine is absorbed poorly whenever there is either traumatic or hemorrhagic shock. 

Key findings that have been reported inclnde significant hypoxia, acidosis, and carbon dioxide retention (Sofer et al, 1989). Also hyperglycemia, hypokalemia, and lenkocytosis were observed in a case series of organophosphate exposures (Levy-Khademi et al, 2007). A prospective study done on 17 children with typical organophosphate or carbamate poisoning looked at laboratory abnormalities that are associated with acute pancreatitis. Five of the patients (30%) had laboratory values consistent with pancreatitis with elevated immunoreactive trypsin, amylase, and serum... 

However, an ABG should be obtained after oxygen initiation to monitor carbon dioxide retention owing to hypoventilation. 

A low arterial PO, is termed hypoxia and indicates respiratory impairment. A value less than 8.0 kPa in a patient breathing air at rest is known as respiratory failure. Classically, hypoxia with carbon dioxide retention is called type 2 respiratory failure. Hypoxia without carbon dioxide retention is type I respiratory failure, but these biochemical definitions are not helpful in understanding the pathophysiology of respiratory disease. 

A much better basis than depression of the respiratory center for the explanation of the carbon dioxide retention is the increase in alkaline reserve (1). If one assumes that the body attempts to maintain a constant pH and that the body is still partially successful in this attempt after the administration of morphine, an increase in base must lead to a retention of carbon dioxide to neutralize the base and a further retention to keep the acid-base ratio constant. 

C. Administration of high oxygen concentrations to patients with severe chronic obstructive pulmonary disease and chronic carbon dioxide retention who are dependent on hypoxemia to provide a drive to breathe may result in respiratory arrest. 

The diagnosis of subdural hematoma explains the depressed respirations, which have resulted in carbon dioxide retention and respiratory acidosis. The metabolic system is beginning to buffer the respiratory acids with retention of bicarbonate. The nurse would watch the oxygen levels and respiratory rate closely and continue supplemental oxygen therapy to maintain adequate oxygenation and would prepare to artificially ventilate Ms. Suarez to improve CO removal and total ventilatory effectiveness. 

Butorphanol use in patients with head injury may be associated with carbon dioxide retention and secondary elevation of cerebrospinal fluid pressure, drug-induced miosis, and alterations in mental state. As with other opioids, such use may obscure important clinical signs in patients with head injuries. 

The relative contributions of the bicarbonate and non-bicarbonate buffer systems depend on the nature of the acid load. If the load is due to carbon dioxide retention, the hydrogen ions produced by the addition of carbon dioxide to the blood cannot be buffered by the bicarbonate system. The reason is evident from examination of the chemical reaction ... 

Gorini M, Misuri J, Corrado A, et al. Breathing pattern and carbon dioxide retention in severe chronic obstractive pulmonary disease. Thorax 1996 51 677-683. 

West JB. Causes of carbon dioxide retention in lung disease. N Engl J Med 1971 284 1232-1236. 

Javaheri S, Blum J, Kazemi H. Pattern of breathing and carbon dioxide retention in chronic obstructive lung disease. Am J Med 1981 71 228-234. 

Blood gas analysis shows progressive hypoxaemia and carbon dioxide retention. Pulse oximetry may be helpful but should be used with caution, bearing in mind that it does not give any indication of carbon dioxide levels and may not demonstrate progressive respiratory failure if inspired oxygen levels are high. 

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