Failure of the Hering-Breuer reflex to account for tachypnea in anesthetized man: a survey of halothane, fluroxene, methoxyflurane, and cyclopropane

Pulmonary volume-feedback and ventilatory pattern after bilateral lung transplantation using neurally adjusted ventilatory assist ventilation

BACKGROUND

Bilateral lung transplantation results in pulmonary vagal denervation, which potentially alters respiratory drive, volume-feedback, and ventilatory pattern. We hypothesised that Neurally Adjusted Ventilatory Assist (NAVA) ventilation, which is driven by diaphragm electrical activity (EAdi), would reveal whether vagally mediated pulmonary-volume feedback is preserved in the early phases after bilateral lung transplantation.

METHODS

We prospectively studied bilateral lung transplant recipients within 48 h of surgery. Subjects were ventilated with NAVA and randomised to receive 3 ventilatory modes (baseline NAVA, 50%, and 150% of baseline NAVA values) and 2 PEEP levels (6 and 12 cm H₂O). We recorded airway pressure, flow, and EAdi.

RESULTS

We studied 30 subjects (37% female; age: 37 (27-56) yr), of whom 19 (63%) had stable EAdi. The baseline NAVA level was 0.6 (0.2-1.0) cm H₂O μV^-1. Tripling NAVA level increased the ventilatory peak pressure over PEEP by 6.3 (1.8), 7.6 (2.4), and 8.7 (3.2) cm H₂O, at 50%, 100%, and 150% of baseline NAVA level, respectively (P<0.001). EAdi peak decreased by 10.1 (9.0), 9.5 (9.4) and 8.8 μV (8.7) (P<0.001), accompanied by small increases in tidal volume, 8.3 (3.0), 8.7 (3.6), and 8.9 (3.3) ml kg^-1 donor's predicted body weight at 50%, 100%, and 150% of baseline NAVA levels, respectively (P<0.001). Doubling PEEP did not affect tidal volume.

CONCLUSIONS

NAVA ventilation was feasible in the majority of patients during the early postoperative period after bilateral lung transplantation. Despite surgical vagotomy distal to the bronchial anastomoses, bilateral lung transplant recipients maintained an unmodified respiratory pattern in response to variations in ventilatory assistance and PEEP.

CLINICAL TRIAL REGISTRATION

NCT03367221.

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.

Constant positive airway pressure reduces hypoventilation induced by inhalation anesthesia

STUDY OBJECTIVE

To discover if reducing respiratory system impedance would increase tidal volume and improve ventilation during inhalation anesthesia.

DESIGN

Prospective, randomized cross-over study.

SUBJECTS

Nine ASA physical status I and II adult female oncology patients undergoing breast operations with or without lymph node dissection and general anesthesia while breathing spontaneously.

INTERVENTIONS AND MEASUREMENTS

Patients underwent alternating trials of constant positive airway pressure, with or without pressure support. Constant positive airway pressure and pressure support were titrated to maximize respiratory system compliance and equal inspiratory pressure gradient across tracheal tube, respectively. Variables reflecting cardiovascular function, pulmonary mechanics and lung gas exchange, and respired gases and isoflurane concentrations were measured.

MAIN RESULTS

End-tidal concentration of isoflurane (1.3 +/- 0.2%), Fio(2) (0.43 +/- 0.09 ), and CO(2) elimination (209 +/- 42 mL min(-1)) was unchanged throughout study in patients aged 63 +/- 12 years, weighing 72 +/- 12 kg. Constant positive airway pressure (12 +/- 2 cm H(2)O) increased respiratory system compliance from 52 +/- 8 to 80 +/- 9 mL cm H(2)O(-1) (P < .001), tidal volume from 156 +/- 32 to 325 +/- 52 mL (P < .001), and minute ventilation from 4.37 +/- 0.86 to 6.18 +/- 0.92 L min(-1) (P < .001). Respiratory rate decreased from 29 +/- 7 to 19 +/- 2 min(-1) (P < .001), Paco(2) decreased from 54 +/- 8 to 44 +/- 6 mm Hg (P < .001), and Pao(2) increased from 137 +/- 37 to 160 +/- 64 mm Hg (P < .001). Pressure support (3.1 +/- 0.3 cm H(2)O) did not alter ventilation or gas exchange.

CONCLUSION

We conclude that constant positive airway pressure titrated to optimal respiratory system compliance will increase efficiency of inspiratory muscles and improve ventilation. Constant positive airway pressure facilitates a pattern of breathing that minimizes some of the adverse pulmonary effects of inhalation anesthesia.

Breathing pattern and respiratory mechanics in sevoflurane-anesthetized humans

In order to determine the respiratory effects of sevoflurane in humans, breathing pattern and mechanical behavior of respiratory system were investigated in ten subjects at anesthetic depth of 1 MAC (minimum alveolar concentration). Average tidal volume and breathing frequency amounted to 275 ml and 20.9 breaths per minute. Arterial carbon dioxide tension amounted to 45.6 mmHg. Duration of inspiration was 1.06s and that of expiration was 1.92s. Mean inspiratory flow rate amounted to 259 ml.s(-1). Average value of passive respiratory elastance determined by the method of Zin et al. amounted to 21.8 cmH(2)O. l(-1), while those of active respiratory elastance and resistance obtained by the method of Behrakis et al. were 28.0 cmH(2)O. l(-1) and 3.15 cmH(2)O. l(-1).s(-1), respectively. Values of these variables were compared to those reported in halothane and enflurane anesthesia and possible explanations of the differences between the anesthetics are discussed.

[Respiratory effects of increasing doses of alfathesin in the dog]

In 10 dogs the authors studied the effect of increasing doses of alfathesin on ventilation (VE, frequency, VT, blood gases), on the ventilatory pattern (TI, TE, TI/Ttot), on the neurological initiation of ventilation (VT/TI, occlusion pressure at 0.5 seconds), and on the Hering-Beurer reflex (duration of apnoea after occlusion of the airway at the end of inspiration). The results were compared with normal values taken from the literature. The correlation between the dose of alfathesin and the measured or calculated parameters was examined. Ventilation was stimulated by low doses of alfathesin, a stimulation, characterized by tachypnoea without change in tidal volume. Deepening of anaesthesia was accompanied by progressively increasing depression of respiration (diminution of VE, of frequency, of VT/TI and increase of PaCO2 and of the duration of apnoea). The mechanisms of the initial stimulation of ventilation and of respiratory depression are discussed. The authors conclude that the action of alfathesin on the central nervous system is biphasic, with stimulation during light anaesthesia followed by depression with associated depression of ventilation, despite increasing hypoxia and hypercapnia.

Ventilation and chemoreflexes during enflurane sedation and anaesthesia in man

Enflurane sedation and anaesthesia in healthy fit subjects reduced ventilation and the response to carbon dioxide, hypoxaemia and a low dose of doxapram, all in a dose-related fashion. Comparing the three chemoreflexes tested, the response to hypoxaemia and doxapram were the more profoundly impaired; they were nearly totally abolished by anaesthesia. These effects of enflurane on chemoreflex activities are qualitatively similar to those previously observed with halothane.