Management of refractory hypoxemia using recruitment maneuvers and rescue therapies: A comprehensive review

Impact of positive end-expiratory pressure and recruitment maneuver on healthy lungs in dogs assessed by functional and anatomical monitoring methods

Introduction

Atelectasis is a common occurrence during anesthesia, and positive end-expiratory pressure (PEEP) ventilation and recruitment maneuvers (RM) can be used to mitigate this. However, both techniques may be associated with side effects in healthy lungs, and close monitoring is indicated. This study aimed to evaluate the effects of PEEP and RM in healthy dogs and to compare functional lung monitoring methods by electrical impedance tomography (EIT), volumetric capnography (VCap), and blood gas analysis with the gold-standard anatomical monitoring provided by computed tomography (CT).

Methods and materials

Nine healthy Beagle dogs underwent anesthesia and mechanical ventilation three times. After 35 min using zero end-expiratory pressure (ZEEP), CT images, VCap, EIT measurements, and arterial blood gas samples were taken. Thereafter, either (1) ZEEP was continued, (2) PEEP initiated or (3) an RM was performed followed by PEEP. Ten minutes after changing the ventilation mode all measurements were repeated. Only one ventilation mode was employed during each anesthesia.

Results

During RM, we found a significant increase in the percentage of overaerated lung (Vhyper) (p < 0.001), while the amount of normally aerated lung (Vnormal), poorly aerated lung and non-aerated lung decreased (p ≤ 0.001). VCap showed an increase in airway dead space (VDaw/VT) (p = 0.002), and a decrease in alveolar dead space (VDalv/VTalv). For PEEP, an increase in airway dead space (p = 0.003) was found. For both groups, the amount of carbon dioxide exhaled per breath (VTCO2,br) decreased (p = 0.001), and EIT showed a shift of the center of ventilation to the dependent lung areas (p = 0.021 and p = 0.046, respectively). Oxygenation was superior in RM compared to ZEEP (p = 0.033). The arterial partial pressure of carbon dioxide decreased in RM (p = 0.012). Positive associations were found between Vhyper and VDaw/VT (p = 0.004), Vhyper and VDaw/VT (p = 0.004), Vhyper and Vnormal with VTCO2,br (p = 0.002 for both). Negative associations were found between Vhyper and VDalv/VTalv (p = 0.004) and non-dependent silent spaces (p = 0.050), and Vnormal with oxygenation (p = 0.030).

Conclusion

While RM may be effective in improving gas exchange, it appears to be not benign in healthy lungs, and PEEP might be the preferable strategy to avoid lung collapse during anesthesia. Functional monitoring - EIT, VCap, blood gas analysis - does not detect changes corresponding to anatomical findings on CT.

Successful management of pulmonary edema secondary to accidental electrocution in a young dog

BACKGROUND

Human records describe pulmonary edema as a life-threatening complication of electric shock. Successful management requires prompt recognition and intensive care. However, in companion animals, electrocutions are rarely reported, even though domestic environments are full of electrical devices and there is always the possibility of accidental injury. Therefore, it is important for veterinarians to know more about this condition in order to achieve successful patient outcomes.

CASE PRESENTATION

A 3-month-old male Labrador Retriever was presented with a history of transient loss of consciousness after chewing on a household electrical cord. On admission, the puppy showed an orthopneic position with moderate respiratory distress. Supplemental oxygen via nasal catheter was provided, but the patient showed marked worsening of respiratory status. Point-of-care ultrasound exams suggested neurogenic pulmonary edema due to electrical shock close to the central nervous system and increased B-lines without evidence of cardiac abnormalities. Mechanical ventilation of the patient was initiated using volume-controlled mode with a tidal volume of 9 to 15 ml/kg until reaching an end-tidal carbon dioxide ≤ 40 mm Hg, followed by a stepwise lung-recruitment maneuver in pressure-controlled mode with increases of the peak inspiratory pressure (15 to 20 cm H2O) and positive end-expiratory pressure (3 to 10 cm H2O) for 30 min, and return to volume-controlled mode with a tidal volume of 15 ml/kg until reaching a peripheral oxygen saturation ≥ 96%. Weaning from the ventilator was achieved in six hours, and the patient was discharged two days after admission without neurological or respiratory deficits.

CONCLUSIONS

We present a rather unusual case of a neurogenic pulmonary edema subsequent to accidental electrocution in a dog. Timely diagnosis by ultrasound and mechanical ventilation settings are described. Our case highlights that pulmonary edema should be considered a potentially life-threatening complication of electrical shock in small animal emergency and critical care medicine.