Respiratory Effects

Using morphine-hyoscine premedication, Gooding et al. [70] found transient apnoea in 4, and hypoventilation in (totally) 6 of 25 patients. With the same premedication, Morgan et al. [71] compared diazepam-atropine with papaveretum-hyoscine before etomidate induction and observed for 4 minutes without intervention; the incidence of apnoea was 40% after diazepam, compared with 27% after the opiate (n.s.). Zacharias et al [72] found that premedication with pethidine increased the frequence of apnoea compared with unpremedicated patients or those having diazepam premedication. Similar was reported by Carlos and Innerarity [73], who found apnoea in more patients (10 of 25) and of longer duration (in 7 lasting more than 30 sec.) after fentanyl than after diazepam premedication (3 patients with apnoea of less than 15 sec duration among 23 patients). In addition, patients premedicated with fentanyl showed irregular patterns of breathing after the administration of etomidate. Drummond and el-Farhan [74] registered apnoea in 17 of 25 patients given propofol and in 8 of 25 given etomidate. Contrary to these observations, Holdcroft et al. [75] found in a large material of 400 patients a frequency of apnoea of average 10%, that was not affected markedly by premedication (anticholinergics alone or in combination with opiates or diazepam).

For intubation without muscular relaxation, we found that thiopental 5 mg/kg made ventilation necessary in all 6 patients while all 11 patients after etomidate 0.3 mg/kg continued breathing [76]. Using occlusion pressure to indicate the depression of respiratory drive. Kay [77] found that methohexitone produced considerably more respiratory depression than etomidate. In 6 volunteers. Choi et al. [78] registered the ventilatory drive at PCO2 46 mmHg, Following methohexitone 1.5 mg/kg, minute ventilation decreased from baseline 14.6 to 4.3 l/min while it after etomidate 0.3 mg/kg increased from 17.9 to 31.6 l/min. This reveals an experimental study with some stimulation included, though not a noxious one.

Among the non-comparative studies, Colvin et al. [41] found a small increase in respiratory rate, but still a statistically significant increase in pCO2 when etomidate was used after premedication with papaveretum-promethazine; pO2 did not change. 

Rifat et al. [79] observed only discrete changes in resp. parameters when 0.23 mg/kg etomidate were given after atropine premedication. Criado et al. [42] observed a global reduction of the minute volume with minimal effect on the blood gas value. Oxygen uptake also showed a 10% reduction, perhaps related to the reduced metabolic rate. 16 of 36 patients demonstrated audible airway obstruction due to falling back of the tongue. In none of these studies were episodes of apnoea noted. Gooding et al. [40] gave droperidol 5 mg for premedication before  induction of cardiac risk patients with 0.3 mg/kg etomidate, and observed them for 3 minutes. No appreciable changes in arterial blood gases occurred during that time, and intrapulmonary shunt was not altered.