Effect of aminophylline on ventilatory responses in normal man

The pulmonary physician in critical care . 12: Acute severe asthma in the intensive care unit

Most deaths from acute asthma occur outside hospital, but the at-risk patient may be recognised on the basis of prior ICU admission and asthma medication history. Patients who fail to improve significantly in the emergency department should be admitted to an HDU or ICU for observation, monitoring, and treatment. Hypoxia, dehydration, acidosis, and hypokalaemia render the severe acute asthmatic patient vulnerable to cardiac dysrrhythmia and cardiorespiratory arrest. Mechanical ventilation may be required for a small proportion of patients for whom it may be life saving. Aggressive bronchodilator (continuous nebulised beta agonist) and anti-inflammatory therapy must continue throughout the period of mechanical ventilation. Recognised complications of mechanical ventilation include hypotension, barotrauma, and nosocomial pneumonia. Low ventilator respiratory rates, long expiratory times, and small tidal volumes help to prevent hyperinflation. Volatile anaesthetic agents may produce bronchodilation in patients resistant to beta agonists. Fatalities in acute asthmatics admitted to HDU/ICU are rare.

Lung function, hypoxic and hypercapnic ventilatory responses, and respiratory muscle strength in normal subjects taking oral theophylline

Methylxanthines are known to be respiratory stimulants and are thought by some to augment hypercapnic and hypoxic ventilatory drive and improve respiratory muscle strength. Hypoxic and hypercapnic ventilatory responses were measured in 10 normal subjects before, during, and after administration of theophylline for three and a half days. Pulmonary function, carbon dioxide production, and mouth pressures during maximal static inspiratory and expiratory efforts were also measured. The mean (SD) serum theophylline concentration was 13.8 (3.2) mg/l. Lung volumes and flow rates did not change significantly with theophylline. The mean (SD) values for maximum static inspiratory pressure were 152 (27), 161 (25), and 160 (24) cm H2O, respectively before, during, and after theophylline. Neither these values nor peak expiratory pressure measurements were significantly changed. The slopes of the hypercapnic ventilatory responses were 2.9 (0.9), 3.3 (1.2), and 3.3 (1.4) l/min/mm Hg carbon dioxide tension (PCO2) respectively before, during, and after theophylline administration. The respective values for the slopes of the hypoxic response were -1.4 (0.9), -1.3 (0.8), and -1.1 (0.9) l/min/1% oxyhaemoglobin saturation. None of these values changed significantly with theophylline. Theophylline, however, increased carbon dioxide production (200 to 236 ml/min) and alveolar ventilation (4.7 to 5.7 l/min) significantly, with a concomitant fall of end tidal PCO2 (35.5 to 32.9 mm Hg). It is concluded that in man oral theophylline at therapeutic blood concentrations increases carbon dioxide production and ventilation without changing pulmonary function, respiratory muscle strength, or the hypoxic or hypercapnic ventilatory response significantly.

Effects of theophylline on ventilatory response to hypoxic challenge

The respiratory and arousal responses to mild hypoxia during quiet sleep were studied using inductive plethysmography and transcutaneous gas electrodes in 11 apnoeic infants before and after the administration of oral theophylline (3 mg/kg). Theophylline changed the ventilatory response to a more biphasic pattern--that is, ventilation decreased after an initial increase. The relative ventilatory slope (defined as the decrease in transcutaneous carbon dioxide tension (PCO2) in relation to the fall in transcutaneous oxygen tension (PO2)) decreased significantly after theophylline. Four infants were roused during hypoxia before theophylline administration compared with none after treatment. Theophylline abolished the periodic breathing induced by hypoxia in one of six infants. These findings suggest that methylxanthines may not, as previously thought, enhance the respiratory drive during hypoxia.

Effects of aminophylline on respiratory drive and neuromuscular coupling in normal man and in patients with chronic airflow obstruction

In order to evaluate the separate effects of aminophylline on the neural and muscular components of the respiratory control system, assessed by electromyographic activity of the diaphragm (EMGd) and mouth occlusion pressure (P0.1), respectively, 6 normal subjects and 14 patients with mild or moderate chronic airflow obstruction (8 asthmatics and 6 COPD) were studied during CO2 rebreathing, before and after administration of a therapeutic dose of aminophylline 5.6 mg/kg. Compared to normal subjects, before aminophylline administration both asthmatic and COPD patients exhibited a significantly greater value in EMGd response slope to CO2. In no group did aminophylline modify P0.1 or EMGd activity response slope to CO2, nor did it significantly affect neuromuscular coupling, assessed by plotting change in P0.1 against change in EMGd activity with increasing CO2. The data appear to indicate that aminophylline in therapeutic concentrations does not modify respiratory drive or neuromuscular coupling in normal subjects, or in patients with mild or moderate chronic airflow obstruction.

A comparison of the ventilatory, cardiovascular and metabolic effects of salbutamol, aminophylline and vasoactive intestinal peptide in normal subjects

Intravenous infusion of placebo for 30 min followed by either salbutamol 10 micrograms min-1, aminophylline 0.2 mg kg-1 min-1 or vasoactive intestinal peptide (VIP) 6 pmol kg-1 min-1 for 30 min was performed in a single blind fashion in six normal volunteers. Both salbutamol and aminophylline increased minute ventilation, (P less than 0.05) the mean increase being 26% and 19% respectively. Aminophylline also increased the ventilatory response to carbon dioxide by 47% (P less than 0.05) when measured by hyperoxic rebreathing, whereas salbutamol and VIP were without significant effect. All three drugs caused a tachycardia, mean increase in the pulse being 16, 8 and 2 beats min-1 for salbutamol, aminophylline and VIP respectively, and aminophylline also increased both systolic and diastolic blood pressure, mean arterial pressure increasing by 14 mmHg. VIP caused haemoconcentration and salbutamol the expected changes in plasma biochemistry. Plasma catecholamines increased slightly during drug infusion, although this effect is unlikely to be important.

Acute respiratory failure and chronic obstructive lung disease

Patients with COPD who develop acute respiratory failure require special attention in their management. Patients with severe COPD often have cor pulmonale, complex acid/base compensations, and altered respiratory control mechanisms. These need to be considered when approaching the patient with an acute decompensation. Because of the improving prognosis in this group of patients, aggressive management should be undertaken using combinations of bronchodilator medications, oxygen, bronchial hygiene, and antibiotics.