Ventilatory parameters in children during propofol anaesthesia: a comparison with halothane

Total intravenous anesthesia will supercede inhalational anesthesia in pediatric anesthetic practice

Inhalational anesthesia has dominated the practice of pediatric anesthesia. However, as the introduction of agents such as propofol, short-acting opioids, midazolam, and dexmedetomidine a monumental change has occurred. With increasing use, the overwhelming advantages of total intravenous anesthesia (TIVA) have emerged and driven change in practice. These advantages, outlined in this review, will justify why TIVA will supercede inhalational anesthesia in future pediatric anesthetic practice.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Spontaneous respiration during intravenous anesthesia in children

PURPOSE OF REVIEW

Maintaining spontaneous respiration during intravenous anesthesia for investigative and surgical procedures may avoid the need for airway instrumentation and reduce the risk of desaturation. In addition, when performing airway endoscopic procedures in children, maintaining spontaneous respiration while using intravenous anesthesia can reduce the need for endotracheal intubation. This facilitates improved access to the smaller airway, allows assessment of the dynamic function of the airway, and reduces exposure of personnel to inhaled anesthetic agents.

RECENT FINDINGS

Anesthetic hypnotic and analgesic agents are potent dose-dependent depressants of respiration. Infants have historically been considered to be at a higher risk of respiratory depression, especially from opioid analgesics. However, recent evidence suggests that infants and younger children outside the neonatal period are more resistant to the effects of remifentanil, even when combined with propofol. Spontaneous respiration can be maintained at doses adequate to suppress somatic responses to painful procedures. The large inter-individual variation in respiratory depressant effects necessitates individualized dose titration. The drug dose is more linearly related to variation in the respiratory rhythm and respiratory rate than to minute volume or end-tidal carbon dioxide. Apneic episodes are less likely when respiratory depressant drugs are administered slowly, as this allows time for the end-tidal carbon dioxide level to rise to a new apneic threshold. Hypnotic anesthetics and opioid analgesics act synergistically to cause respiratory depression and suppression of the somatic response.

SUMMARY

Spontaneous respiration can be maintained when anesthetizing children using intravenous anesthesia.

Changes in respiratory and hemodynamic parameters during low-dose propofol sedation in combination with regional anesthesia for herniorrhaphy and genitourinary surgery in children

BACKGROUND

Spontaneous vs mechanical ventilation during propofol sedation has been a subject of debate. We evaluated the safety of low-dose propofol sedation as an adjunct to regional anesthesia during herniorrhaphy and genitourinary surgery in infants and children.

METHODS

The study was conducted in a prospective, nonrandomized manner using a consecutive sample of 62 American Society of Anesthesiologists physical status class I patients between 5 months to 11 years of age in the surgery unit of an urban University Hospital. Propofol sedation (4-8 mg x kg(-1) x h(-1) continuous infusion) was used with regional anesthesia (caudal, ilioinguinal/iliohypogastric nerve or penile block with 0.2-0.375% ropivacaine). All children were spontaneously breathing without an anesthesia circuit. Respiratory and hemodynamic parameters were continuously recorded on all patients. One-way analysis of variance (ANOVA) for repeated measurements was used to analyze changes in respiratory and hemodynamic parameters during the procedure.

RESULTS

Spontaneous ventilation was maintained in all patients with minimal changes in hemodynamic parameters. Heart rate, mean arterial pressure, and P(E)CO(2) remained stable throughout the study period: 23/62 (37%) patients exhibited signs of developing intrinsic endexpiratory pressure (PEEPi) or the presence of PEEPi because of progressive reduction of expiratory time.

CONCLUSIONS

Low-dose propofol sedation in combination with regional anesthesia for elective herniorrhaphy and genitourinary surgery in children maintains spontaneous ventilation and has minimal effects on hemodynamic parameters for sedation lasting <1 h. The presence of PEEPi is a relative contraindication to the use of this regimen in children with asthma or history of upper airway infections.

A Neuronal Mechanism of Propofol-Induced Central Respiratory Depression in Newborn Rats

The neural mechanisms of propofol-induced central respiratory depression remain poorly understood. In the present study, we studied these mechanisms and the involvement of gamma-aminobutyric acid (GABA)A receptors in propofol-induced central respiratory depression. The brainstem and the cervical spinal cord of 1- to 4-day-old rats were isolated, and preparations were maintained in vitro with oxygenated artificial cerebrospinal fluid. Rhythmic inspiratory burst activity was recorded from the C4 spinal ventral root. The activity of respiratory neurons in the ventrolateral medulla was recorded using a perforated patch-clamp technique. We found that bath-applied propofol decreased C4 inspiratory burst rate, which could be reversed by the administration of a GABAA antagonist, bicuculline. Propofol caused resting membrane potentials to hyperpolarize and suppressed the firing of action potentials in preinspiratory and expiratory neurons. In contrast, propofol had little effect on resting membrane potentials and action potential firing in inspiratory neurons. Our findings suggest that the depressive effects of propofol are, at least in part, mediated by the agonistic action of propofol on GABAA receptors. It is likely that the GABAA receptor-mediated hyperpolarization of preinspiratory neurons serves as the neuronal basis of propofol-induced respiratory depression in the newborn rat.

Effect of jaw-thrust and continuous positive airway pressure on tidal breathing in deeply sedated infants

OBJECTIVES

To examine the physiologic impact of the jaw-thrust maneuver or the administration of continuous positive airway pressure (CPAP) on tidal breathing in deeply sedated infants.

STUDY DESIGN

Prospective, non-randomized study of infants undergoing elective fiberoptic bronchoscopy while sedated with intermittent doses of propofol.

METHODS

Spontaneous tidal breathing was measured in the supine position by means of a spirometer attached to a bronchoscopy face mask. Tidal breaths were recorded under the following conditions: (1) neutral sniffing position, (2) jaw-thrust, (3) neutral sniffing position, and (4) CPAP of 5 cm H(2)O. Improvement was defined as a change of more than twice the coefficient of variation of repeated measurements of tidal volume and flows from baseline.

RESULTS

Jaw-thrust increased tidal volume, minute ventilation, and peak tidal inspiratory and expiratory flows significantly in all 13 infants studied (mean +/- SEM age = 8 +/- 2 months). CPAP increased peak tidal inspiratory and expiratory flows by more than twice the coefficient of variation of baseline measurements in 6 patients and tidal volume and minute ventilation in 5 of 10 patients studied.

CONCLUSION

Jaw-thrust and CPAP are effective techniques to improve ventilation of sedated infants undergoing interventions that compromise upper airway patency.

Propofol anesthesia for outpatient oral and maxillofacial surgery

Propofol is a sedative-hypnotic intravenous anesthetic agent that has gained wide use in outpatient oral and maxillofacial surgery since its clinical introduction in 1985. Propofol has several therapeutic advantages that make it an excellent choice for use in all phases of general anesthesia and conscious sedation. It is associated with minimal side effects, a controllable anesthetic state, and rapid recovery. This review of propofol discusses its pharmacologic character, administration, and side effects and presents anesthetic drug interaction information and comparisons.

Can a difference in chest wall mechanics explain the lower respiratory drive during propofol versus halothane anesthesia in children?

This article extends previous work which suggested that respiratory drive was lower during propofol compared with halothane anesthesia. The aim of this study was to assess simultaneously chest wall motion, measured with respiratory inductive plethysmography (RIP), and respiratory drive measured by P0.1 the pressure generated during the initial 100 msec of an occluded inspiratory effort. Ten healthy children age 3 to 6 years who presented for a dental restorative procedure that required in excess of 2.5 hours were recruited. Patients were anesthetized with propofol (2.5 mg x kg(-1); 15 mg x kg(-1) x hr) or halothane (1.25%), in a randomized crossover study design. Following induction of anesthesia, RIP bands were placed at the level of the nipples and the umbilicus for the measurement of rib cage and abdomen excursion, respectively. Flow and airway pressure were measured. A manually operated pneumatic balloon was used for brief airway occlusion. Following a 60-minute washin/out of the anesthetic, the children were removed from mechanical ventilation and spontaneous ventilation was reinstated. The RIP signals were calibrated by the method of simultaneous solution of equations. The phase lag was calculated. During airway occlusion the maximal excursion of the calibrated rib cage trace (RMAX) was measured; a negative value indicated retraction of the rib cage. Respiratory drive was assessed both at a fixed interval (100 msec) (P0.1) and fixed proportion (10%) (P10%) of the occluded inspiratory effort. Significance of differences were assessed with a paired t-test (P-value < 0.05). Thoracoabdominal asynchrony was greater during halothane than propofol anesthesia, as was the amount of rib cage retraction, evidenced by lower values of RMAX; respiratory drive was higher during halothane than propofol anesthesia, as evidenced by higher values of both P0.1, and P10%. We conclude that during halothane anesthesia altered chest wall mechanics may result in a greater respiratory drive than during propofol anesthesia.