Intraoperative Protective Mechanical Ventilation in Dogs: A Randomized Clinical Trial

Objective

To evaluate gas exchange, respiratory mechanics, and hemodynamic impact of mechanical ventilation with low tidal volume (V_T) in dogs with the use of positive end-expiratory pressure (PEEP) or preceded by alveolar recruitment maneuver (ARM).

Study Design

Prospective randomized clinical trial.

Animals

Twenty-one healthy client-owned mesocephalic healthy dogs, 1-7 years old, weighing 10-20 kg, and body condition scores 4-6/9 admitted for periodontal treatment.

Methods

Isoflurane-anesthetized dogs in dorsal recumbency were ventilated until 1 h with a volume-controlled ventilation mode using 8 mL kg^-1 of V_T. The dogs were distributed in 2 groups: in the ARM group, PEEP starts in 0 cmH₂O, increasing gradually 5 cmH₂O every 3 min, until reach 15 cmH₂O and decreasing in the same steps until 5 cmH₂O, maintaining this value until the end; and PEEP group, in which the pressure 5 cmH₂O was instituted from the beginning of anesthesia and maintained the same level up to the end of the anesthesia. Cardiopulmonary, metabolic, oxygenation parameters, and respiratory mechanics were recorded after the anesthesia induction (baseline-BL), 15, 45, and 75 min after BL and during the recovery.

Results

The ARM increased the static compliance (C_st) (15 min after baseline) when compared with baseline moment (24.9 ± 5.8 mL cmH₂0^-1 vs. 20.7 ± 5.4 mL cmH₂0^-1-p = 0.0364), oxygenation index (PaO₂/FIO₂) (505.6 ± 59.2 mmHg vs. 461.2 ± 41.0 mmHg-p = 0.0453) and reduced the shunt fraction (3.4 ± 2.4% vs. 5.5 ± 1.6%-p = 0.062). In the PEEP group, no statistical differences were observed concerning the variables evaluated. At the beginning of the evaluation, the driving pressure (DP) before ARM was significantly greater than all other evaluation time points (6.9 ± 1.8 cmH₂0).

Conclusions and Clinical Relevance

The use of 8 mL kg^-1 of V_T and 5 cmH₂0 PEEP without ARM maintain adequate oxygenation and mechanical ventilation in dental surgeries for up to 1 h. The use of ARM slightly improved compliance and oxygenation during the maneuver.

Scaling of axial muscle architecture in juvenile Alligator mississippiensis reveals an enhanced performance capacity of accessory breathing mechanisms

Quantitative functional anatomy of amniote thoracic and abdominal regions is crucial to understanding constraints on and adaptations for facilitating simultaneous breathing and locomotion. Crocodilians have diverse locomotor modes and variable breathing mechanics facilitated by basal and derived (accessory) muscles. However, the inherent flexibility of these systems is not well studied, and the functional specialisation of the crocodilian trunk is yet to be investigated. Increases in body size and trunk stiffness would be expected to cause a disproportionate increase in muscle force demands and therefore constrain the basal costal aspiration mechanism, necessitating changes in respiratory mechanics. Here, we describe the anatomy of the trunk muscles, their properties that determine muscle performance (mass, length and physiological cross‐sectional area [PCSA]) and investigate their scaling in juvenile Alligator mississippiensis spanning an order of magnitude in body mass (359 g–5.5 kg). Comparatively, the expiratory muscles (transversus abdominis, rectus abdominis, iliocostalis), which compress the trunk, have greater relative PCSA being specialised for greater force‐generating capacity, while the inspiratory muscles (diaphragmaticus, truncocaudalis ischiotruncus, ischiopubis), which create negative internal pressure, have greater relative fascicle lengths, being adapted for greater working range and contraction velocity. Fascicle lengths of the accessory diaphragmaticus scaled with positive allometry in the alligators examined, enhancing contractile capacity, in line with this muscle's ability to modulate both tidal volume and breathing frequency in response to energetic demand during terrestrial locomotion. The iliocostalis, an accessory expiratory muscle, also demonstrated positive allometry in fascicle lengths and mass. All accessory muscles of the infrapubic abdominal wall demonstrated positive allometry in PCSA, which would enhance their force‐generating capacity. Conversely, the basal tetrapod expiratory pump (transversus abdominis) scaled isometrically, which may indicate a decreased reliance on this muscle with ontogeny. Collectively, these findings would support existing anecdotal evidence that crocodilians shift their breathing mechanics as they increase in size. Furthermore, the functional specialisation of the diaphragmaticus and compliance of the body wall in the lumbar region against which it works may contribute to low‐cost breathing in crocodilians.

Non-invasive measurement of abnormal ventilatory mechanics in amyotrophic lateral sclerosis

INTRODUCTION

In this study we investigated non-invasive, effort-independent measurement of ventilatory mechanics in patients with amyotrophic lateral sclerosis (ALS).

METHODS

Ventilatory mechanics were measured by optoelectronic plethysmography (OEP) in ALS patients and matched controls. Analysis determined whether OEP measurements correlated with standard clinical measures.

RESULTS

ALS patients (N = 18) had lower forced vital capacity percent predicted (55.2 ± 22.0 L) compared with controls (N = 15; 104.7 ± 16.2 L) and higher ventilatory inefficiency (49.2 ± 9.0 vs. 40.0 ± 3.5, respectively; P < 0.001 for both measures). Lower tidal volumes within the diaphragm area correlated with the dyspnea subscore calculated from the ALS Functional Rating Scale-revised (P = 0.031), and paradoxical movement of the ribcage compared with the abdominal compartment was seen in the most severe cases.

CONCLUSIONS

Evaluation of ventilatory mechanics in mild to severe ALS reveals dysfunction that is not readily detected by standard testing and ALS functional severity assessment measures. Muscle Nerve 54: 270-276, 2016.