Peri-operative respiratory adverse events remain a major cause of morbidity and mortality in children undergoing general anaesthesia; those with asthma are at higher risk. The aim of this feasibility study was to determine whether pre-operative measurements of fractional exhaled nitric oxide and the forced oscillation technique are feasible in children, and to explore whether these measurements can predict peri-operative respiratory adverse events.
We assigned children into respiratory or control groups, according to the presence or absence of respiratory symptoms. We recorded pre-operative measurements of fractional exhaled nitric oxide as well as respiratory mechanics, as determined by the forced oscillation technique. We then recorded the incidence of peri-operative respiratory adverse events.
We enrolled 120 children of which 116 were included. Fractional exhaled nitric oxide and respiratory mechanics (forced oscillation technique) were recorded in 106/116 (91%) and 71/116 (61%), respectively. Peri-operative respiratory adverse events occurred in 17/116 (15%) patients but there was no difference between groups (OR 2.11, 95%CI 0.74–6.55). Pre-operative fractional exhaled nitric oxide levels did not predict the occurrence of peri-operative respiratory adverse events. The measurement of respiratory mechanics using the forced oscillation technique did not predict peri-operative respiratory adverse events.
We have shown the feasibility of study enrolment and pre-operative fractional exhaled nitric oxide measurement but had difficulty obtaining measurements of respiratory mechanics (forced oscillation technique). Neither test improved the prediction of peri-operative respiratory adverse events reliably in this group of patients. A thorough pre-operative clinical history combined with care by an experienced paediatric anaesthetist remains the most reliable means of reducing peri-operative respiratory adverse events.
Intra-operative hypotension is common during cardiopulmonary bypass and may contribute to tissue hypoxia. Tissue hypoxia has been linked to the development of postoperative kidney and brain injury. Vasopressors are used to treat hypotension during and after cardiopulmonary bypass. However, the effects of these drugs on renal and cerebral tissue oxygenation and perfusion are unknown. We tested the effects of four vasopressors on renal and cerebral tissue perfusion and oxygenation in a clinically-relevant ovine model of cardiopulmonary bypass.
We studied 16 sheep before and after induction of anaesthesia and during 2.5 h of cardiopulmonary bypass. After commencing cardiopulmonary bypass at a target non-pulsatile flow of 2.4 l.min-1.m-2, we observed a baseline period with a target mean arterial pressure of 50–60 mmHg, after which we targeted a mean arterial pressure of 75–85 mmHg using a continuous infusion of metaraminol (n = 8); noradrenaline (n = 8); phenylephrine (n = 8); or vasopressin (n = 7). Sheep were allocated randomly to receive two of the four vasopressors.
Compared with the pre-induction state, cardiopulmonary bypass significantly decreased renal medullary tissue perfusion (median (IQR [range]) decrease 55 (4–82 [1–99])%; p = 0.01) and medullary oxygen tension (mean (SD) difference 3.1 (2.5) kPa; p < 0.001). Cardiopulmonary bypass did not significantly alter cerebral tissue perfusion or oxygenation compared with the pre-induction state. Infusing noradrenaline significantly decreased medullary oxygen tension (mean (SD) difference 2.7 (1.6) kPa; p = 0.003). This decrease in medullary oxygen tension was significant compared with vasopressin (mean difference -3.4 kPa, 95%CI -5.7 to -1.0; p = 0.008). No vasopressor infusion significantly altered renal medullary perfusion, cerebral tissue perfusion or oxygenation.
Intra-operative noradrenaline during ovine cardiopulmonary bypass worsens renal medullary tissue oxygenation relative to vasopressin. These findings suggest that the choice of vasopressors may affect renal oxygenation.
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