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Background and Purpose: Conventional angioplasty of cerebral vasospasm combines proximal balloon angioplasty (up to the first segment of cerebral arteries) with chemical angioplasty for distal arteries. Distal balloon angioplasty (up to the second segment of cerebral arteries) has been used in our center instead of chemical angioplasty since January 2015. We aimed to assess the effect of this new approach in patients with aneurysmal SAH., Materials and Methods: The occurrence, date, territory, and cause of any cerebral infarction were retrospectively determined and correlated to angioplasty procedures. Delayed cerebral infarction, new angioplasty in the territory of a previous angioplasty, angioplasty complications, 1-month mortality, and 6- to 12-month modified Rankin Scale ≤ 2 were compared between 2 periods (before-versus-after January 2015, from 2012 to 2017) with adjustment for age, sex, World Federation of Neurosurgical Societies score, and the modified Fisher grade., Results: Three-hundred-ninety-two patients were analyzed (160 before versus 232 after January 2015). Distal balloon angioplasty was associated with the following: higher rates of angioplasty (43% versus 27%, P < .001) and intravenous milrinone (31% versus 9%, P < .001); lower rates of postangioplasty delayed cerebral infarction (2.2% versus 7.5%, P = .01) and new angioplasty (8% versus 19%, P = .003) independent of the rate of patients treated by angioplasty and milrinone; and the same rates of stroke related to angioplasty (3.6% versus 3.1%, P = .78), delayed cerebral infarction (7.7% versus 12.5%, P = .12), mortality (10% versus 11%, P = .81), and favorable outcome (79% versus 73%, P = .21)., Conclusions: Our study suggests that distal balloon angioplasty is safe and decreases the risk of delayed cerebral infarction and the recurrence of vasospasm compared with conventional angioplasty. It fails to show a clinical benefit possibly because of confounding changes in adjuvant therapies of vasospasm during the study period., (© 2019 by American Journal of Neuroradiology.)

Background and Purpose: The management of cervical artery occlusions in hyperacute stroke with tandem cervical/intracranial occlusions has not yet become standardized, especially when the circle of Willis is effective., Methods: We retrospectively analyzed the safety and accuracy of current approaches to manage the cervical occlusion in consecutive patients with tandem occlusions addressed for intracranial mechanical thrombectomy (MT) in our department from January 2012 to May 2017. The different approaches that could be performed in a same patient during the same procedure or hospitalization were analyzed separately., Results: We reported 64 approaches to manage the cervical occlusion in 49 patients with tandem occlusion (14% of MT): medical treatment alone in 16/64 (25%), stenting/angioplasty in 16/64 (25%), occlusion with coils in 12/64 (19%), angioplasty alone in 9/64 (14%), stent-retriever in 8/64 (12%), and/or thromboaspiration in 3/64 (5%). Early ipsilateral embolic recurrence occurred after 9/64 (14%) of them. It was strongly associated with the presence of a cervical intraluminal thrombus (P=0.001) and was then lower after occlusion with coils and stent-retriever compared to medical treatment alone and thromboaspiration (P=0.002). Occlusion with coils had a lower rate of radiological intracranial hemorrhage at 48-hour compared to other approaches (P=0.009). The 3-month rates of favorable outcome (P=0.806) and mortality (P=0.878) were similar. One delayed stroke was imputable to an occlusion with coils, for a median (Q1-Q3) follow-up of 10 (3-20) months., Conclusions: Cervical occlusion with coils and thrombectomy with stent-retrievers may be relevant to prevent early embolic recurrence in cervical occlusions with intraluminal thrombus. Stent-retrievers should be further assessed as a first-line approach, since delayed stroke may occur following occlusion with coils. Medical treatment alone may be sufficient when no cervical intraluminal thrombus is present, the Willis polygon is effective, and the cervical occlusion can be crossed easily to perform the intracranial thrombectomy., (Copyright © 2017. Published by Elsevier Masson SAS.)

Fibro-osseous benign lesions rarely affect the sinonasal tract and are divided into 3 different entities, namely osteoma, fibrous dysplasia and ossifying fibroma. They share several clinical, radiological and histological similarities, but have different behaviours. Ossifying fibroma, and in particular the "juvenile" histological subtype, may have a locally aggressive evolution and a high risk for recurrence if removal is incomplete. The purpose of the present study is to compare the clinical behaviour of ossifying fibroma with the other benign fibro-osseous lesions; highlight different behaviour between the histological subtypes; compare the advantages, limitations and outcomes of an endoscopic endonasal approach with reports in the literature. We retrospectively reviewed 11 patients treated for sinonasal ossifying fibroma at a tertiary care centre. All patients underwent CT scan, and MRI was performed in cases of cranial base involvement or recurrence. Pre-operative biopsy was performed in cases where it was possible to use an endoscopic approach. One patient underwent pre-operative embolisation with ipsilateral visual loss after the procedure. Depending on its location, removal of the tumour was performed using an endoscopic (n = 7), or an external (n = 3) or combined (n = 1) approach. Histopathologically, 5 patients presented the conventional type, 5 the juvenile psammomatoid variant, which was associated in 1 case with an aneurismal bone cyst, and 1 case presented the trabecular juvenile variant. Three patients affected by the juvenile psammomatoid histological variant presented invasion of the skull base and underwent a subtotal removal that subsequently required, due to the regrowth of the remnant, a transbasal approach. Clinical, radiological and histological findings should all be considered to establish differential diagnosis among fibrous osseous lesions. More studies are necessary to conclude if the localisation and extension of the disease at the time of diagnosis is more important than the histological variant. An endoscopic approach is the first choice in most of cases even if an external open approach may be necessary in selected patients.

A polymer based material was developed to act as an embolic agent and drug reservoir for the treatment of arteriovenous malformations (AVM) and hyper vascularized solid tumors. The aim was to combine the blocking of blood supply to the target region and the inhibition of the embolization-stimulated angiogenesis. The material is composed of an ethanolic solution of a linear acrylate based copolymer and acrylate calibrated microparticles containing nanospheres loaded with sunitinib, an anti-angiogenic agent. The precipitation of the linear copolymer in aqueous environment after injection through microcatheter results in the formation of an in-situ embolization gel whereas the microparticles serve to increase the cohesive properties of the embolization agent and to form a reservoir from which the sunitinib-loaded nanospheres are released post-embolization. The swollen state of the microparticles in contact with aqueous medium results in the release of the nanospheres out of microparticles macromolecular structure. After the synthesis, the formulation and the characterization of the different components of the material, anti-angiogenic activity was evaluated in vitro using endothelial cells and in vivo using corneal neovascularization model in rabbit. The efficiency of the arterial embolization was tested in vivo in a sheep model. Results proved the feasibility of this new system for vascular embolization in association with an in situ delivery of anti-angiogenic drug. This combination is a promising strategy for the management of arteriovenous malformations and solid tumors., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Background and Purpose: Parent artery occlusion has long been considered the reference treatment for large/giant or fusiform aneurysms of the carotid siphon. However, meager recent data exist on this technique, which tends to be replaced by stent-assisted reconstructive techniques. In our department since 2004, we have assessed the safety, efficacy, and complication risk factors of parent artery occlusion by using coils for trapping these aneurysms., Materials and Methods: We determined retrospectively the complication rate, factors associated with the occurrence of an ischemic event, changes in symptoms of mass effect, evolution of the aneurysmal size, and the growth of an additional aneurysm after treatment., Results: Fifty-six consecutive patients were included, with a median age of 54 years (range, 25-85 years; 92% women), 48% with giant aneurysms and 75% with infraclinoid aneurysms. There was a permanent morbidity rate of 5% exclusively due to ischemia, a zero mortality rate, an aneurysmal retraction rate of 91%, and an improvement rate for pain of 98% and for cranial nerve palsy of 72%, with a median follow-up of >3 years. Para-/supraclinoid topography of the aneurysm (P = .043) and the presence of cardiovascular risk factors (P = .024) were associated with an excessive risk of an ischemic event, whereas the presence of a mural thrombus had a protective role (P = .033)., Conclusions: In this study, parent artery occlusion by using coils to treat large/giant or fusiform aneurysms of the carotid siphon was safe and effective, especially for giant infraclinoid aneurysms. According to recent meta-analyses, these results suggest that the validation of stent-assisted reconstructive treatments for these aneurysms requires controlled studies with parent occlusion artery., (© 2015 by American Journal of Neuroradiology.)

Background and Purpose: Diaphragms of the internal carotid and vertebral arteries as a cause of ischaemic stroke are reported and stenting of diaphragms as a therapeutic option in stroke secondary prevention is described., Methods: Five patients were cared for in our institution from 2000 to 2011 for recurrent ischaemic strokes which were classified to be of undetermined aetiology after completion of the usual investigations. Because the patients had already had ischaemic strokes in the territory of the same artery, a conventional digital subtracted angiography was performed. A diaphragm was identified on the artery that supplied the territory in which the stroke occurred. The stroke was therefore attributed to the diaphragm. Clinical and radiological data, treatment and the clinical course of the patients was retrospectively reviewed., Results: The diaphragm was located in the vertebral artery in three cases and in the bulb of the internal carotid artery in two. In all cases cerebral MR showed ischaemic strokes of different ages downstream of the diaphragm. Stenting was performed in four cases. No patient had a symptomatic recurrent ischaemic event after stenting., Conclusions: Diaphragms are a rare cause of recurrent embolic strokes which are often not detected with non-invasive imaging. Stenting appears to be a therapeutic option in stroke secondary prevention. These observations suggest that conventional angiography should be performed in cases of recurrent ischaemic strokes in the territory of a single artery and in cases of ischaemic stroke of undetermined aetiology in young adults when the usual investigations are negative., (© 2014 The Author(s) European Journal of Neurology © 2014 EFNS.)

Background and Purpose: Venous drainage of dural arteriovenous fistula (DAVF) with dementia has never been reported. The aim of this study was to discover if specific vascular conditions exist to develop dementia in patients with DAVF., Methods: Venous drainage in patients embolized in our centre between 1996 and 2012 for a DAVF with dementia were qualitatively analyzed and compared with a control group without dementia., Results: Eight patients with dementia and 45 control patients were included. The prevalence of dementia was 4%. Diffuse hemispheric white matter lesions on magnetic resonance imaging (MRI) were consistently associated with dementia. Cognitive symptoms dramatically improved after embolization. The consistent angiographic feature in patients with dementia was drainage of the DAVF into both the straight sinus and the superior sagittal sinuses. Only two patients in the control group had similar abnormalities., Conclusions: The association of a reflux from the fistula into the straight sinus and the superior sagittal sinuses is a necessary condition to develop such a reversible dementia in DAVF. Venous hypertension in the territory of transparenchymal veins may explain this reversal phenomenon. A rapidly progressive dementia with diffuse white matter lesions on MRI should evoke this diagnosis to the physician., (© 2013 The Author(s) European Journal of Neurology © 2013 EFNS.)

Objectives: Convexity subarachnoid and intra-cerebral hemorrhages, in patients aged<50 years, are always a diagnostic challenge. This condition is characterized by acute headaches with or without neurological symptoms and/or seizures, and by the radiological demonstration of subarachnoid and/or intra-cerebral hemorrhages and, more rarely, by the association of ischemic events., Patients and Methods: In a prospective series of 30 consecutive patients (median age 31 years; 22 women) with a subarachnoid and intra-cerebral hemorrhages, 19 were diagnosed with reversible cerebral vasoconstriction syndrome (RCVS), 7 with cerebral venous sinus thrombosis (CVST), and 4 with a bleeding mycotic aneurysm (MA)., Results: RCVS appeared spontaneously in 16 patients and was related to the postpartum period in three cases. Subarachnoid hemorrhage (SAH) was demonstrated in 24 patients as follows: 18 cases were in cortical areas, 4 were in the polygon of Willis, one was inter-hemispheric, and one was inter-hemispheric/intra-cerebral. A convexity pure intra-cerebral hemorrhage (ICH) was recorded in 6 cases. Among the 7 patients suffering from CVST, the superior sagittal sinus was involved in 4 cases, the transverse sinuses (TS) in 2, and the TS plus sigmoid sinus (SS) in one., Conclusion: The three most common causes in this series were RCVS, followed by CVST and bleeding from MA. Because of atypical clinical or radiological presentations, this large spectrum of etiologies can cause diagnostic difficulties. Therefore, careful analysis is needed to ensure correct and prompt diagnosis and to avoid any dangerous delays in management., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Objectives: The goal of the study was to assess whether clinically significant cerebral hypoperfusion in awake patients would be associated with some alterations in the values of the bispectral index (BIS) monitoring., Study Design: Observational study., Population and Methods: We monitored the BIS during endovascular carotid artery occlusion testing in awake patients., Results: Twenty-eight patients were included. Twenty-one adequately tolerated the procedure. Their BIS value remained stable throughout the procedure. Four patients had poor angiographic tolerance, but no clinical symptoms. Their BIS value slightly decreased during the test (minimal BIS: 83 [79-87]). Three patients had poor clinical and angiographic tolerance of the occlusion. They all experienced an immediate and dramatic decrease in their BIS value (minimal BIS: ipsilateral to clamping: 50 [45-60]; contralateral to clamping: 48 [45-52]). In all patients, the clinical symptoms and the BIS normalized after deflating the occlusion balloon., Conclusion: In awake patients, the observed values of the BIS monitoring seem to be associated with clinically relevant cerebral hypoperfusion., (Copyright © 2013 Société française d’anesthésie et de réanimation (Sfar). Published by Elsevier SAS. All rights reserved.)

Objectives: Brain arteriovenous malformations (AVMs) often present with epileptic seizures, but prospective data on the risk of seizures with respect to morphologic AVM characteristics are scarce., Methods: We studied 155 consecutive patients with AVMs from a prospective, single-center database using demographic and morphologic factors based on prospectively coded MRI and digital subtraction angiography (DSA) data. Univariate analysis and multivariate logistic regression models were used to test the effect of demographic (age and sex) and morphologic characteristics (AVM size, anatomic and arterial location, and venous drainage pattern) on seizures as initial presentation in patients with unruptured brain AVMs., Results: Overall, 45 patients with AVMs initially presented with seizures (29%). By univariate comparison, male sex (p = 0.02), increasing AVM size (p < 0,006), frontal lobe localization (p < 0.0001), arterial borderzone location (p < 0.0006), superficial venous drainage (p = 0.0002), and presence of venous ectasia (p = 0.003) were statistically associated with seizures. The multivariate analysis confirmed an independent effect of male sex, frontal lobe AVMs, and arterial borderzone location on seizure occurrence. All patients with seizures showed the presence of a superficial venous drainage component., Conclusions: Our study suggests that seizures mainly occur in AVMs with superficial drainage. Other predisposing factors include male sex, increasing AVM size, and frontal lobe and arterial borderzone location. Whether or not interventional treatment has an effect on the long-term risk of epilepsy remains to be determined.

Background and Purpose: Recently some series have been published about the use of Onyx for the treatment of DAFVs with satisfactory results. Our aim was to describe the treatment of different types of intracranial DAVFs with transcatheter injection of Onyx through an arterial approach., Materials and Methods: At the Department of Interventional Neuroradiology, Hospital Lariboisière Paris, between January 2005 and January 2010, we treated 44 DAVFs in 42 patients. All patients were initially treated by arterial injection of Onyx. The average patient age was 56 years (range, 27-86 years), and there were 17 women and 25 men treated., Results: A total of 58 arterial pedicles were catheterized, with the middle meningeal artery representing the most common site (n = 38). The average time of injection was 30 minutes (range, 15-60 minutes), and the average amount of Onyx was 2.5 mL (range, 0.6-6.5 mL). Of the 20 fistulas with direct venous drainage into a dural sinus (types I and II), we achieved the preservation of the sinus in 7 patients. Of the 44 fistulas embolized, 8 required a second embolization treatment and 1 fistula required a third treatment. In 9 cases, a complementary treatment was performed via transvenous embolization with coils and/or open surgery. Early complications were observed in 6 patients: Four had nerve injury (facial palsy, n = 2, and neuralgia, n = 2), and 2 had complications related to extension of venous thrombosis postembolization. All 6 patients had partial or complete resolution of these symptoms., Conclusions: The treatment of DAVFs by intracranial arterial injection of Onyx is safe, and, in most cases, results in the occlusion of the arterial venous shunt. In DAVFs with direct sinus drainage, sinus preservation was only possible in 7 of 20 patients (35%).

We report the case of an early ISR that was due to platelet aggregation despite correct observance of a standard antiplatelet regimen. Biologic testing showed clopidogrel inefficiency, and ISR disappeared on angiography after a loading dose of clopidogrel. This result suggested that the arterial lumen reduction was due to platelet aggregation rather than in-stent myointimal hyperplasia. This observation emphasizes the importance of verifying the efficacy of clopidogrel before placing a stent.

Objectives: To report clinical characteristics, angiographical findings and results of endovascular treatment of patients presenting with dural carotid-cavernous fistulas (DCCFs)., Method: Retrospective analysis of 27 consecutive patients with DCCF referred to a specialised interventional neuroradiology department., Results: Orbital and neuro-ophthalmological symptoms were the most common clinical presentation at diagnosis (n = 25). The venous drainage of the fistula involved the ipsilateral superior ophthalmic vein in 24 patients, the contralateral cavernous sinus in 6 and a leptomeningeal vein in 5 patients. Thrombosis of at least one petrosal sinus was found in 23 patients. 7 patients did not receive endovascular treatment: 3 had spontaneous DCCF obliteration, and 4 had only minor clinical symptoms and no leptomeningeal venous drainage on an angiogram. 20 patients received endovascular treatment via either a transvenous (n = 16) or a transarterial approach (n = 4). Complete occlusion of the fistula was obtained in 14 of 16 (87%) patients treated by the transvenous approach and in 1 of 4 (25%) patients treated by the transarterial approach. 16 patients had early clinical improvement after endovascular treatment. One patient had a cerebral haemorrhage after transvenous embolisation of a DCCF with leptomeningeal drainage. On follow-up, all patients treated by the transarterial route remained symptomatic, whereas 10 of 14 (71%) patients cured by the transvenous route were asymptomatic., Conclusions: Transvenous embolisation is a safe and efficient endovascular approach to treat patients with DCCF. However, this technique requires a long learning curve.

Three consecutive patients with embolic basilar artery occlusion were treated with endovascular mechanical thrombus extraction. Recanalisation was rapidly obtained in one patient, who had a good initial recovery, and in another patient who made a complete recovery. By contrast, recanalisation failed in the third patient, who made no recovery. No haemorrhagic complications were detected. This technique may have advantages over thrombolysis in both efficacy and safety.

Purpose: To present a modification of both the guiding catheter and stent delivery system to facilitate access into sharply curved supra-aortic vessels during carotid angioplasty., Technique: Access failures during carotid interventions typically occur because either the vessel origin is acutely angled or the stenosis is located proximal to the carotid bifurcation, limiting access to the external carotid artery. We directly catheterized the left common carotid artery or brachiocephalic trunk with a guiding catheter whose tip had been curved by steam-shaping. The tip of the stent delivery system also was molded into a curve by this process so it engaged the curved part of the guiding catheter without pulling it out of the vessel., Conclusions: This simple modification can improve the success rate of carotid cannulation via the femoral approach and does not seem to increase the risk of the intervention.

Summary: Three cases of spontaneously closing dural arteriovenous fistulas (AVFs) are presented, and 11 previously published cases are reviewed. On the basis of clinical and angiographic data, two types of spontaneously regressing dural AVFs are distinguished: posttraumatic and spontaneous. In all cases, the explanation for spontaneous closure is unknown. Some authors have hypothesized that the thrombosis of the draining sinus could be involved. We report three cases of spontaneous dural AVF closure with conservation of sinus patency.

Background and Purpose: Radiation-induced stenoses of the carotid artery are associated with fibrosis of the arterial layers and tissue planes that renders their surgical treatment difficult. We present our clinical experience in carotid angioplasty stenting (CAS) of patients harboring such stenoses., Methods: Seven patients underwent transfemoral CAS of 10 radiation-induced stenoses located on either the common or the internal carotid artery. Six patients presented neurological symptoms. Four patients had undergone previous radical neck dissection, and 3 had permanent tracheostomies. Stenoses were primarily covered with a self-expandable stent before carotid dilation., Results: All interventions were successful, with residual stenoses <20%. No permanent complication occurred. The mean follow-up was 8 months. Patients were symptom free at the last clinical examination, and Doppler control showed no evidence of restenosis., Conclusions: Carotid stenting appears very attractive for such "hostile neck" patients and seems a safe and efficient treatment for radiation-induced stenoses.

An aneurysm of the right renal artery was discovered in a patient suffering from cerebral arterial angiodysplasia and arterial hypertension. The aneurysm was large necked, which made selective endovascular treatment very difficult. To perform the embolization of the aneurysm, a balloon remodelling technique was used. This prevented migration of coils within the arterial lumen.

Following a recent case of adult-type respiratory distress syndrome in a four-year old child, the rare occurrence of this pathology in visceral paediatric surgery is recalled. The few published cases do not allow a comparison of the mortality in paediatric and adult patients. The treatment is discussed, as well as the results of pulmonary function tests performed some time after the acute pulmonary episode.

Three recent cases of surgical closure of ductus arteriosus in very low birth weight infants (less than 1 000 g) are reported. The indications of both surgical and pharmacological closure in very low birth weight premature infants are discussed. The necessity of an early closure of a patent ductus arteriosus is now admitted in the very premature infant, but the use of indomethacin in the first days of life is often impossible because of its side-effects. The use of adapted non-invasive monitoring devices during surgery allows a better control of anaesthesia.

Respiratory effects of nitrous oxide and isoflurane were studied in 13 children (mean age 45.6 +/- 19.3 months, mean weight 14.9 +/- 4.8 kg) during surgery under continuous extradural anaesthesia. Three different anaesthetic states were studied: isoflurane 0.5 MAC in oxygen (27 study periods), isoflurane 0.5 MAC with 50% nitrous oxide (32), isoflurane 1 MAC in oxygen (25). End-tidal carbon dioxide (PE' CO2) and isoflurane, respiratory indices (tidal volume, VT; minute ventilation, VE; mean inspiratory flow, VI; respiratory frequency f, effective inspiratory timing TI/Ttot were measured. The addition of nitrous oxide (comparison of respiratory variables obtained in 25 successive periods at (1) and (2)) produced a significant increase in PE' CO2' significant decreases in VT, VE and VI, a significant increase in f. The increase in alveolar concentration of isoflurane ((1) compared with (3) in 25 successive periods) was associated with a significant increase in PE' CO2' significant decreases in VT, VE, VI and a significant increase in f. The equipotent anaesthetic states (2) and (3) were compared in 21 successive periods. In children, the net result of substituting nitrous oxide for an equal MAC fraction of isoflurane was to produce a smaller decrease in VT responsible for a smaller decrease in VE without significant change in respiratory rate.

The preliminary results of the use of high frequency positive pressure ventilation (HFPPV) in six newborn infants presenting a type III oesophageal atresia during the thoracic stage of surgical repair are reported. HFPPV allowed correct gas exchange during the surgical procedure. In the six cases, a significant decrease in PaCO2 (p less than 0.05) was observed, whereas the effects on PaO2 were variable. The technical problems, mechanism of gas transport during HFPPV and clinical interest of HFPPV in thoracic surgery are discussed.

The present study examines the errors of measurement under working conditions using a capnograph and suggests a methodology to obtain optimal results in a given clinical situation. The authors compare the PCO2 measured with the aid of capnograph using CO2 absorption by infrared, with simultaneous measurements of PCO2 using a mass spectrometer as the reference. The observations measured included static and dynamic responses to a step variation of 5% CO2 and also the PACO2 in normal 9 to 12 year old children. The results show that the errors using a capnograph may reach 45 per cent at the highest respiratory frequencies. The influence of the dimensions of the sampling apparatus and the output of the sampling pump on the measurement of PACO2 are discussed. The static and dynamic calibration allow optimal operating conditions for the requirements of a patient in bed. (In this study children aged 9 to 12, with a respiratory frequency of less than 40/min). The errors after achieving optimal conditions is independent of respiratory frequency and always remained less than 5 per cent. A few simple rules are suggested to avoid the errors we have seen and if proper precautions are taken capnography can be considered as a good method for measuring PACO2 in children.

The changes in ventilatory variables under nitrous oxide isoflurane anaesthesia were studied in 10 children (mean age 46 +/- 13.4 months, mean weight 16.2 +/- 2.1 kg). Measurements of flow and volume were performed by pneumotachography. PE'CO2 was measured by capnography. The following variables (VE, VT, TI/TTOT, VI, PE'CO2) were measured or calculated under three increasing inspired isoflurane concentrations (0.75%, 1.5%, 2.25%). At each level of anaesthesia, ventilatory changes during exposure to an inspired CO2 fraction of 2% were studied. The increase in the inspired concentration of isoflurane was associated with a decrease in alveolar ventilation. PE'CO2 increased significantly with increasing depth of anaesthesia. The respiratory rate was slightly increased under light nitrous oxide isoflurane anaesthesia, but no further changes were observed with increasing depth of anaesthesia, although the children were breathing a mixture of nitrous oxide and oxygen. The ventilatory response to a raised inspired CO2 is markedly decreased under light nitrous oxide isoflurane anaesthesia, and decreases significantly with increasing depth of anaesthesia. In response to a raised CO2, VE, VT and VI increase, but respiratory rate decreases or remains constant and TI/TTOT is unchanged.