The effects of spontaneous and mechanical ventilation on central cardiovascular function and peripheral perfusion during isoflurane anaesthesia in horses.

This scientific study examined the effects of spontaneous breathing versus mechanical ventilation on heart and blood flow functions, as well as muscle and skin blood flow, in horses under isoflurane anaesthesia. It discovered that mechanical ventilation had a negative impact on cardiovascular function compared to natural breathing, causing changes in muscle and skin blood flow, although the underlying mechanisms are not fully understood yet.

Study Methodology

• The research was a prospective controlled study conducted on ten warm-blood trotter horses.
• The horses were prepared by an anaesthetic process using detomidine, induced using intravenous guaifenesin and thiopental, and maintained with isoflurane in oxygen.
• Five animals were allowed to breathe naturally, while the lungs of the other five were mechanically ventilated using intermittent positive pressure ventilation (IPPV).
• The total anesthetic period was 4 hours, with the ventilation type changed after 2 hours. Measurements of various cardiovascular and physiological parameters were conducted throughout the process.

Measurements

• During the anaesthesia, researchers recorded heart rate, cardiac output, stroke volume, systemic arterial blood pressures, and pulmonary arterial pressure.
• Peripheral blood flow was measured in specific muscles and on the horse’s tail skin through laser Doppler flowmetry.
• Blood samples were taken to measure arterial and mixed venous blood gases, pH value, haemoglobin concentration, haematocrit level, and plasma lactate concentration.
• Measurements of oxygen content, venous admixture, oxygen delivery, and oxygen consumption were also calculated.

Results

• The results indicated that during mechanical ventilation, heart rate, arterial blood pressures, pulmonary arterial pressure, cardiac output, stroke volume, venous admixture and carbon dioxide partial pressure were lower compared to spontaneous breathing, while oxygen partial pressure was higher.
• No significant variations were observed in the level of blood flow, oxygen delivery and consumption, haemoglobin concentration, haematocrit level, or plasma lactate concentration between the two modes of ventilation.
• However, when the ventilation mode was altered from mechanical to spontaneous breathing, there was an improvement in blood flow to the left semimembranosus muscle and skin, whereas muscle blood flow was slightly reduced when spontaneous breathing was changed to mechanical ventilation.
• Low-frequency flow motion (a type of blood flow pattern) was noticed twice as often during mechanical ventilation compared to spontaneous breathing.

Conclusions

• The research concluded that, in horses under isoflurane anaesthesia, mechanical ventilation negatively affected cardiovascular function compared to spontaneous breathing.
• Changes in blood flow to muscles and skin occurred with the mode of ventilation, suggesting a need for further studies to understand the underlying mechanisms of these changes.