Diazepam sedation reduces functional residual capacity and alters the distribution of ventilation in man

The neonatal lung--physiology and ventilation

This review article focuses on neonatal respiratory physiology, mechanical ventilation of the neonate and changes induced by anesthesia and surgery. Optimal ventilation techniques for preterm and term neonates are discussed. In summary, neonates are at high risk for respiratory complications during anesthesia, which can be explained by their characteristic respiratory physiology. Especially the delicate balance between closing volume and functional residual capacity can be easily disturbed by anesthetic and surgical interventions resulting in respiratory deterioration. Ventilatory strategies should ideally include application of an 'open lung strategy' as well avoidance of inappropriately high VT and excessive oxygen administration. In critically ill and unstable neonates, for example, extremely low-birthweight infants surgery in the neonatal intensive care unit might be an appropriate alternative to the operating theater. Best respiratory management of neonates during anesthesia is a team effort that should involve a joint multidisciplinary approach of anesthetists, pediatric surgeons, cardiologists, and neonatologists to reduce complications and optimize outcomes in this vulnerable population.

Role of α1- and α2-GABA(A) receptors in mediating the respiratory changes associated with benzodiazepine sedation

BACKGROUND AND PURPOSE

The molecular substrates underlying the respiratory changes associated with benzodiazepine sedation are unknown. We examined the effects of different doses of diazepam and alprazolam on resting breathing in wild-type (WT) mice and clarified the contribution of α1- and α2-GABA(A) receptors, which mediate the sedative and muscle relaxant action of diazepam, respectively, to these drug effects using point-mutated mice possessing either α1H101R- or α2H101R-GABA(A) receptors insensitive to benzodiazepine.

EXPERIMENTAL APPROACH

Room air breathing was monitored using whole-body plethysmography. Different groups of WT mice were injected i.p. with diazepam (1-100 mg·kg(-1) ), alprazolam (0.3, 1 or 3 mg·kg(-1) ) or vehicle. α1H101R and α2H101R mice received 1 or 10 mg·kg(-1) diazepam or 0.3 or 3 mg·kg(-1) alprazolam. Respiratory frequency, tidal volume, time of expiration and time of inspiration before and 20 min after drug injection were analysed.

KEY RESULTS

Diazepam (10 mg·kg(-1) ) decreased the time of expiration, thereby increasing the resting respiratory frequency, in WT and α2H101R mice, but not in α1H101R mice. The time of inspiration was shortened in WT and α1H101R mice, but not in α2H101R mice. Alprazolam (1-3 mg·kg(-1) ) stimulated the respiratory frequency by shortening expiration and inspiration duration in WT mice. This tachypnoeic effect was partially conserved in α1H101R mice while absent in α2H101R mice.

CONCLUSIONS AND IMPLICATIONS

These results identify a specific role for α1-GABA(A) receptors and α2-GABA(A) receptors in mediating the shortening by benzodiazepines of the expiratory and inspiratory phase of resting breathing respectively.

Impact of depth of propofol anaesthesia on functional residual capacity and ventilation distribution in healthy preschool children

BACKGROUND

Propofol is commonly used in children undergoing diagnostic interventions under anaesthesia or deep sedation. Because hypoxaemia is the most common cause of critical deterioration during anaesthesia and sedation, improved understanding of the effects of anaesthetics on pulmonary function is essential. The aim of this study was to determine the effect of different levels of propofol anaesthesia on functional residual capacity (FRC) and ventilation distribution.

METHODS

In 20 children without cardiopulmonary disease mean age (SD) 49.75 (13.3) months and mean weight (SD) 17.5 (3.9) kg, anaesthesia was induced by a bolus of i.v. propofol 2 mg kg(-1) followed by an infusion of propofol 120 microg kg(-1) min(-1) (level I). Then, a bolus of propofol 1 mg kg(-1) was given followed by a propofol infusion at 240 microg kg(-1) min(-1) (level II). FRC and lung clearance index (LCI) were calculated at each level of anaesthesia using multibreath analysis.

RESULTS

The FRC mean (SD) decreased from 20.7 (3.3) ml kg(-1) at anaesthesia level I to 17.7 (3.9) ml kg(-1) at level II (P < 0.0001). At the same time, mean (SD) LCI increased from 10.4 (1.1) to 11.9 (2.2) (P = 0.0038), whereas bispectral index score values decreased from mean (SD) 57.5 (7.2) to 35.5 (5.9) (P < 0.0001).

CONCLUSIONS

Propofol elicited a deeper level of anaesthesia that led to a significant decrease of the FRC whereas at the same time the LCI, an index for ventilation distribution, increased indicating an increased vulnerability to hypoxaemia.

Hypoxaemia and myocardial ischaemia during and after endoscopic cholangiopancreatography: call for further studies

Sixteen non-selected patients undergoing endoscopic cholangiopancreatography (ERCP) after diazepam premedication were monitored for oxygen saturation (SpO2) with a pulse oximeter and for myocardial ischaemia with a Holter tape recorder from 2 h before ERCP to 6 h after the procedure. One patient was excluded from data analysis because of oxygen therapy. Oxygen saturation was significantly decreased (p less than 0.05) both during endoscopy and in the postendoscopy recovery period. Heart rate was significantly increased (p less than 0.05) both during and after the procedure. ST depression occurred in no patients before endoscopy, in 10 patients during, and in no patients after endoscopy. Concurrent ischaemia and episodic hypoxaemia were found in 5 patients, isolated ischaemia in 7 patients, and isolated episodic hypoxaemia in 13 patients. Concurrent ischaemia and tachycardia were found in 10 patients, ischaemia without tachycardia in no patients, and isolated tachycardia in 1 patient. There was no significant correlation between diazepam dose and SpO2 during endoscopy. These results suggest tachycardia to be more important than hypoxaemia in the pathogenesis of myocardial ischaemia during upper gastrointestinal endoscopy. Cardioprotective measures other than oxygen therapy should soon be evaluated before the implications of the new standards of care in endoscopy have become generally adopted.

Effects of repeated doses of benzodiazepines on arterial blood gases and transcutaneous PO2

The effects of repeated doses of benzodiazepines, diazepam and midazolam in combination with meperidine on arterial blood gases and transcutaneous PO2 were studied in eight healthy volunteers. The study was designed to mimic a clinical situation. Initially two doses of either midazolam 0.05 mg/kg or diazepam in fat emulsion 0.15 mg/kg were given in a randomized crossover fashion with a 20-min interval, followed by meperidine 0.5 mg/kg another 20 min later. The opioid effects were then antagonized by naloxone 0.4 mg. The initial doses of benzodiazepines caused an increase in PaCO2 and a decrease in PaO2. The changes in PaO2 were of short duration and recovered to baseline levels between injections. However, they came sooner and were more pronounced after midazolam. The changes in PtcO2 paralleled those in PaO2. The PtcO2 index as a measure of cardiac output and peripheral blood flow adequacy was increased immediately after the first injection of midazolam but was otherwise not different from control. There were no differences between the drugs concerning PtcO2 index. PaCO2 increased after the first benzodiazepine injection and remained so throughout the study. Addition of meperidine caused only small changes in PaO2 and PaCO2. These changes were reversed by naloxone. In spite of different elimination kinetics there was no difference in the duration of respiratory depression between the two benzodiazepines.