Efficacy of tracheal insufflation of oxygen during oleic acid-induced pulmonary edema

Transtracheal oxygen delivery

Tracheal insufflation of oxygen has at least three major uses for chronic oxygen supplementation through a percutaneous catheter, it is an adjunctive measure to enhance gas exchange during mechanical ventilation, and it provides an emergency therapy for oxygen delivery with upper airway obstruction. In this article the mechanisms of gas exchange and techniques of oxygen delivery are described for each of these major uses.

Tetrodotoxin infusion: nonventilatory effects and role in toxicity models

OBJECTIVES

To determine the cardiovascular, autonomic, and neuromuscular effects of an IV infusion of tetrodotoxin (TTX) when ventilation is supported.

METHODS

TTX was infused in 18 anesthetized beagles during conventional mechanical ventilation. TTX infusion continued at a rate of 9.3 micrograms/kg/hr until apnea occurred with 1 minute of ventilator disconnection. Measurements included intravascular pressures, heart rate (HR), cardiac output, blood gases, displacements of the rib cage and abdomen, O2 delivery, and responses to train-of-four and tetanic peripheral nerve stimulation. Results are expressed as mean +/- SD.

RESULTS

During TTX infusion, all the dogs had discoordinate movements of the rib cage, abdomen, and limbs. Vomiting, urination, defecation, and increased salivation occurred. Nicotinic and muscarinic effects, neuromuscular blockade, and cardiovascular depression were produced by TTX. Apnea occurred in 72.0 +/- 17.0 minutes when a total of 119.0 +/- 17.4 micrograms of TTX was infused. At apnea, decreases in arterial pressure, cardiac index, HR, O2 delivery, and systemic vascular resistance occurred, while pulmonary artery pressure and pulmonary vascular resistance increased. Loss of response to tetanic stimulation was closely correlated with the dose of TTX that produced apnea.

CONCLUSION

The clinical symptoms and signs of TTX poisoning are similar to those of anticholinesterase poisons, and TTX dosing as described by this model may serve as a surrogate for organophosphorus poisoning. The model may be useful to determine optimum therapies for TTX poisoning and, since TTX prevents sodium influx into cells, to investigate enhanced survival in animals suffering from ischemia.

Transfer of gas from the acinus during continuous flow and intermittent positive pressure ventilation

We used a technique of measuring Xenon133 washout (XeW) from the alveolar space to evaluate transfer of gas from the acinus (Mackenzie et al., J. Appl. Physiol. 68: 2013-2018, 1990) during 2 min of apnea, 2 min of tracheal insufflation with oxygen (TRIO) and 90 sec of intermittent positive pressure ventilation (IPPV) in 6 anesthetized and paralyzed dogs. Xenon133 dissolved in saline was injected into an occluded acinar region through a pulmonary artery catheter, and XeW was measured by gamma scintillation scanning. With this technique, XeW during apnea represents the contribution of cardiogenic oscillations in regional flow. The XeW rate constant (min-1 +/- SE) was 0.37 +/- 0.03 during apnea. This was not different (P > 0.05) with TRIO (0.29 +/- 0.04). With IPPV, the rate constant increased to 3.49 +/- 0.39, faster than with either apnea or TRIO (P < 0.001). We conclude that: (1) TRIO does not increase convective gas transfer from the acini compared to apnea; and (2) transfer of gas out of the acini due to cardiogenic oscillations is a very small portion of the total gas eliminated during IPPV.

Effects of cardiac oscillations on acinar gas mixing during pulmonary edema

We used a previously reported technique (Mackenzie et al., J. Appl. Physiol. 68: 2013-2018, 1990) to measure the effects of severe pulmonary edema on acinar cardiogenic gas mixing in anesthetized dogs. We also tested how increases in lung volume affected gas mixing in healthy lungs and during pulmonary edema. Cardiogenic gas mixing was evaluated by measurement of the rate of washout of xenon133 injected into an occluded pulmonary artery during apnea. The rate constant of xenon133 washout was 0.40 min-1 (+/- 0.06 SE) in the healthy lung at functional residual capacity. It decreased (P < 0.05) to 0.08 min-1 (+/- 0.03) when lung volume was raised 500 ml. Pulmonary edema was induced by injection of oleic acid (0.06 mg.kg-1) into the right atrium over a 4-min period; clinical signs of severe pulmonary edema were present after 90 min. The rate constant for xenon133 washout (0.07 +/- 0.03 min-1) was less than in the healthy lung (P < 0.05), and was not changed after lung volume was increased (P > 0.05). We conclude that, in the presence of severe pulmonary edema: (1) acinar resistance is increased and/or magnitude of cardiogenic oscillations is decreased; and (2) salutary effects of increased lung volume are not due to enhancement of cardiogenic gas mixing.