Plus-Hex CLINICAL
Administration of midazolam reduces the volume of induction agent required and the associated side effects . The use of a benzodiazepine as part of a co-induction protocol also ensures a smooth transition from induction to maintenance .
Once the patient had been induced , topical lidocaine was applied to the larynx before intubation to suppress the cough reflex , which can cause a transient increase in ICP . Induction was smooth and uneventful . The patient was intubated with a size 3.5 mm armoured polyvinylchloride ( PVC ) endotracheal tube with a 1 ml cuff .
Maintenance of anaesthesia
Anaesthesia was maintained using a paediatric circle circuit with sevoflurane on a pressure-controlled ventilator . Sevoflurane was chosen over isoflurane because evidence suggests that it preserves cerebral autoregulation and normotension better than isoflurane at equipotent doses [ 6 ] . Furthermore , sevoflurane ' s comparatively lower blood gas coefficient of 0.69 [ 12 ] means it is less soluble in blood than isoflurane . This enables rapid changes in the depth of anaesthesia , making it easier to ensure adequate depth and analgesia during the procedure [ 13 ] . Although there is currently limited veterinary research on the subject , studies in humans suggest that , due to this lower blood gas coefficient , sevoflurane allows faster , smoother recoveries and permits earlier neurological assessment postoperatively than other gaseous or IV agents [ 14 ] .
Ventilation and monitoring
Following induction , the patient was maintained on a pressure-controlled mechanical ventilator with a mixture of medical air and oxygen throughout the procedure . The mechanical ventilator was set to use a pressure setting , rather than a volume setting , to improve accuracy and reduce the risk of barotrauma , which is trauma to lung tissue due to excessive inflation [ 15 ] .
The mechanical ventilator was used to ensure the patient ' s end-tidal carbon dioxide ( ETCO 2
) remained in the range of 30 – 35 mmHg , as per the intervention plan . It is generally recommended to maintain ETCO 2 between 30 mmHg and 35 mmHg in patients with an increased risk of developing raised ICP [ 16 ] because excessive PaCO 2 leads to vasodilation of the cerebral blood vessels , increasing the cerebral blood volume and therefore causing increased ICP . The opposite is true for hypocapnia . ETCO 2 below 30 mmHg may cause the cerebral vessels to vasoconstrict , reducing cerebral perfusion and risking cerebral hypoxaemia [ 17 ] .
ETCO 2 remained between 27 mmHg and 34 mmHg for the duration of the anaesthetic , so no further interventions were required . This intervention was appropriate to this case and prevented further increases in ICP and associated consequences .
MAP was also closely monitored to ensure normotension was maintained throughout the general anaesthetic . ICP is directly influenced by arterial blood pressure and cerebral blood flow , so blood pressure monitoring is essential in these cases ; it is also important with regard to the maintenance of adequate cerebral perfusion . Hypertension leads to arterial vasoconstriction and increased cerebral blood flow and , consequently , increased ICP . The opposite is true for hypotension [ 17 ] . MAP should be maintained between 80 mmHg and 100 mmHg to ensure adequate cerebral perfusion while avoiding increased ICP [ 4 ] . Blood pressure readings were taken every 3 min using a non-invasive blood pressure measurement device . Throughout the general anaesthetic , there were intermittent periods of hypotension , which were treated accordingly ( see Medications section on page 42 for further details ). Otherwise , the patient ' s blood pressure was largely stable throughout the procedure .
The Cushing ' s reflex is a physiological nervous system response to acute elevations in ICP . The classic Cushing ' s response comprises a triad of clinical signs : increased systolic arterial pressure , bradycardia and respiratory irregularity . Increased ICP leads to diminished perfusion of brain tissue , causing compensatory activation of the sympathetic nervous system to maintain cerebral perfusion by increasing arterial blood pressure . Baroreceptors in the carotid arteries are stimulated by this rise in blood pressure , activating the parasympathetic nervous system , which causes reflex bradycardia . Although this reflex temporarily reduces ICP , in the long term it will lead to raised ICP and further decreased cerebral perfusion [ 5 ] .
It is therefore essential to conduct consistent multiparameter monitoring to evaluate trends in these parameters in order to avoid raised ICP , or identify and correct it quickly if it does occur . Multiparameter monitoring is also vital in monitoring for other general anaesthetic complications such as arrhythmias , hypoxaemia and hypothermia – all of which will have a detrimental effect on the patient . In this patient , electrocardiography , pulse oximetry , capnography , and temperature and MAP monitoring were used throughout the general anaesthetic .
It is also important to ensure normothermia is maintained throughout the procedure because hypothermia may lead to adverse effects such as increased infection risk and surgical blood loss . Anaesthetic-induced hypothermia is known to reduce platelet function and impair enzymes of the coagulation cascade [ 18 ] .
Conversely , excessive hyperthermia increases the cerebral metabolic rate , which increases cerebral blood flow and can lead to raised ICP [ 4 ] . Continuous temperature monitoring was implemented throughout the procedure and an active warming device was used to maintain normothermia in this patient .
Volume 40 ( 1 ) • February 2025
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