electroconvulsive therapy ( ect ) is an established modality of treatment for severe psychiatric illnesses such as depression , drug - resistant bipolar disorder , and schizophrenia . among the various complications associated with ect , oxygen desaturation ( defined as a spo2 < 90% ) the incidence of oxygen desaturation in smaller studies has ranged from 2.5% to 27.5% depending on the inspired oxygen concentration , preoxygenation and ventilation during the seizure . the objective of this study was to establish the incidence of oxygen desaturation during recovery from anesthesia for modified ect and evaluate its risk factors in a large sample . the study was approved by the institutional ethics committee and a written informed consent was obtained from the next of kin of the patient . all patients aged above 15 years who were prescribed a modified ect ( with short acting anesthetic and muscle relaxant ) for their psychiatric illness were prospectively included in this observational study . patients with a history of recent myocardial infarction , pregnancy , intracranial hemorrhage and patients with a baseline oxygen saturation ( spo2 ) < 92% on pulse oximetry were excluded from the study . the clinical and demographic details such as diagnosis , duration of illness , body mass index ( bmi ) , and pharmacotherapy and laboratory investigations were collected for each patient . electroconvulsive therapy protocol and anesthetic management : patients undergoing ect fasted for solids for 6 - 8 h and 2 h for clear fluids . a standard monitoring consisting of an electrocardiogram , noninvasive blood pressure ( bp ) and pulse oximetry ( spo2 ) was established in all patients . the anesthetic regimen consisted of administration of atropine 0.6 mg , thiopentone 3 mg / kg and suxamethonium 0.5 mg / kg for rapid muscle relaxation . during apnea , oxygenation was maintained by administering 8 l / min of o2 through a face mask using manual bag - mask ventilation until spontaneous respiration returned except during stimulus application . passive oxygenation with 8 l / min of o2 through a face mask was continued during the seizures . the ect stimulus was delivered once the muscle fasciculations disappeared using a niviqure ( technonivilak , bangalore , india ) ect machine . a brief - pulse stimulus was delivered using a constant current at 800 ma , with a frequency of 125 pulses / s ( 62.5 hz ) and a pulse width of 1.5 ms ; the duration of the train was altered to adjust the dose . the stimulus charge varied from 30 mc to a maximum of 540 mc and was delivered with either bifrontal or bitemporal electrode placement . the need for a repeat - stimulus was decided by the attending psychiatrist depending on the adequacy of seizure quality and duration . once the patient regained spontaneous respiration and consciousness , he was positioned in the recovery position and an oral suction performed . later , he was shifted to the recovery room for further monitoring and observation . in order to avoid any potential source of bias in data collection , furthermore , to exclude the influence of multiple ect sessions on oxygen saturation in the same patient , only the first session for each patient during the study period was included . the other data that was collected are pre ect ( before administration of anesthesia for ect ) and post - ect ( immediately following termination of ect - induced seizure ) heart rate , bp and oxygen saturation characteristics ( spo2 , time taken for spo2 to return to 95% , the lowest spo2 value ) . ect details ( charge delivered , electrode placement [ bifrontal / bitemporal ] , seizure duration , repeat stimulation ) , and anesthetic variables ( doses of thiopentone , suxamethonium and atropine and anesthetic complications ) were also collected . the primary outcome measure of the study was oxygen desaturation ( defined as spo2 < 90% ) following ect . univariate analysis was carried out to study the association between individual risk factors versus post - ect spo2 and time for spo2 to recover to at least 95% using a pearson 's correlation test for continuous variables and a chi - square test for categorical variables . the parameters were then entered into logistic and linear regression models , to identify the independent predictive factors for post ect oxygen desaturation . univariate analysis was carried out to study the association between individual risk factors versus post - ect spo2 and time for spo2 to recover to at least 95% using a pearson 's correlation test for continuous variables and a chi - square test for categorical variables . the parameters were then entered into logistic and linear regression models , to identify the independent predictive factors for post ect oxygen desaturation . figure 1 shows the changes in the heart rate , mean arterial pressure , and saturation before and after ect [ figure 1 ] . close to 50% ( 45/93 ) of the patients who had desaturation , had spo2 in the range of 80 - 89% . the mean duration for return of saturation to > 95% was 12 s. the incidence of desaturation was 64% ( 14/22 ) in obese patients ( bmi > 30 ) and 27% ( 79/294 ) in nonobese patients ( relative risk = 2.4 [ 95% confidence interval = 1.6 - 3.4 ] p < 0.001 ) . similarly incidence of desaturation was 37% ( 36/97 ) in patients with prolonged seizure duration ( > 45 s ) as compared to 26% ( 57/219 ) in patients with shorter seizure duration ( < 45 s ) [ figure 2 ] . the longest time for spo2 to return to 95% was 150 s in an obese patient with a bmi of 32 . demographic parameters in all patients changes in the heart rate , mean arterial pressure and saturation after electroconvulsive therapy when compared to baseline significant variables associated with desaturation pearson 's correlations between study variables and outcome measures ( parametric analysis ) in 316 patients for 1 session the association of the study variables with post - ect desaturation was also analyzed by nonparametric tests ( chi - square test ) using a predefined cut - off value for each variable [ table 3 ] . in these analyses , age , bmi , dose of thiopentone and suxamethonium and seizure duration correlated with post - ect desaturation . on multivariate analysis ( by bivariate logistic regression and linear regression analysis ) , only bmi and seizure duration were found to be significantly correlated with post - ect desaturation [ tables 4 and 5 ] . significant variables associated with desaturation on univariate analysis in 316 patients for 1 session ( nonparametric analysis ) linear regression analysis in 316 patients for post - ect spo2 logistic regression analysis in 316 patients for post - ect spo2 despite advances in the anesthetic techniques , hypoxic complications during anesthesia for ect are not uncommon . in this study , the incidence of oxygen desaturation during modified ect was significantly high ( 29% ) though the mean duration of desaturation was short ( 12  22 s ) . episodes of oxygen desaturation constitute a potential threat to the safety of the patient undergoing ect procedure . occurrence of oxygen desaturation during perianesthetic period may lead to prolonged stay in the postanesthesia care unit with substantial utilization of manpower and material resources . the cumulative impact of multiple episodes of desaturation on cerebral function , especially in the elderly patients , has not been explored . evidence from similar areas of the study suggests that repeated episodes of oxygen desaturation are associated with impairment of attention and executive function . it would be interesting to explore if cognitive changes associated with ect have an association with the degree of desaturation . furthermore , any damage occurring during ect from these episodes of desaturation may not be apparent until late , when it is likely to be attributed to other causes . oxygen desaturation together with ect - induced autonomic changes may increase the myocardial oxygen demand and compromise the normal cardiac function . quantification of the incidence of hypoxia and identifying the patients at risk and the factors contributing to desaturation will help to improve the safety of patient care . the guidelines for ect published several years ago advocate preoxygenation and ventilation during apnea after suxamethonium until the administration of the ect . lew et al . have demonstrated a significant reduction in the incidence of desaturation by ventilating the lungs during seizure period in a small number of patients . showed that merely increasing the inspired oxygen concentration ( fio2 ) from 30% to 100% did not significantly decrease the incidence of desaturation . on the contrary , high fio2 prolonged the seizure duration , which was an independent risk factor for desaturation in our study . the number of positive breaths administered during suxamethonium apnea seems to be an important factor that affects oxygenation . swindells and simpson observed that desaturation was inversely related to the number of positive pressure ventilations performed after administration of suxamethonium and prior to administration of ect stimulus . thus , it appears that adequate positive pressure ventilation during apnea and not merely increasing the fio2 is the key to prevent desaturation . as regards optimal pco2 , one study demonstrated that hyperventilation lead to prolongation of the seizure . both the above facts taken together , an appropriate ventilatory strategy during ect seems to be one that employs modest increase in fio2 and maintenance of normocapnia . as in our study , lew et al . had also observed a 27.5% incidence of desaturation during 40 ect sessions . a similar incidence in a larger population in our study ( 316 patients ) reaffirms the need to recognize the magnitude of this problem and improve the strategies to minimize it . in this context , the effect of independent predictors namely , bmi and seizure duration on oxygen desaturation needs to be examined in future studies . an important approach to minimize desaturation during ect could be to promote weight reduction in patients prescribed maintenance ect sessions . consideration may also have to be given to prescription of antipsychotic medications that tend to cause weight gain . in our study , we observed that as the seizure duration increased , especially more than 45 s , there was a significant increase in the incidence of post - ect desaturation . it is therefore , advisable to limit the seizure to the minimum duration compatible with good clinical recovery . earlier reports indicate that the efficacy of ect is dependent on administration of 5 - 12 adequately generalized tonic - clonic seizures of at least 20 s duration . we did not monitor end - tidal carbon - dioxide ( etco2 ) pressure during ect as it was not a standard of care in our country at this time . the royal college of psychiatrists recommends preoxygenation only if necessary , leaving open the choice of routine preoxygenation for ect , as is done in elective anesthesia practice . future studies need to examine whether preoxygenation reduces the incidence of desaturation during ect , at least in obese patients and to recommend it as a standard of care during ect . thirdly , we provided only passive oxygenation and not positive pressure during the seizure period as it was done in a previous study that reported a 17% incidence of desaturation . gastric hypomotility can occur from psychiatric illnesses like depression or schizophrenia and also from antipsychotic agents prescribed to treat these conditions . combined with ect - induced convulsions , this may predispose the patients to pulmonary aspiration . traditional recommendation during anesthesia for patients at risk of aspiration includes rapid sequence induction without positive pressure ventilation . endotracheal intubation could be an alternative to protect at - risk patients against this risk . we did not monitor end - tidal carbon - dioxide ( etco2 ) pressure during ect as it was not a standard of care in our country at this time . the royal college of psychiatrists recommends preoxygenation only if necessary , leaving open the choice of routine preoxygenation for ect , as is done in elective anesthesia practice . future studies need to examine whether preoxygenation reduces the incidence of desaturation during ect , at least in obese patients and to recommend it as a standard of care during ect . thirdly , we provided only passive oxygenation and not positive pressure during the seizure period as it was done in a previous study that reported a 17% incidence of desaturation . gastric hypomotility can occur from psychiatric illnesses like depression or schizophrenia and also from antipsychotic agents prescribed to treat these conditions . combined with ect - induced convulsions , this may predispose the patients to pulmonary aspiration . traditional recommendation during anesthesia for patients at risk of aspiration includes rapid sequence induction without positive pressure ventilation . apart from the fear of aspiration , endotracheal intubation could be an alternative to protect at - risk patients against this risk . in this prospective observational study , the incidence of oxygen desaturation during recovery from anesthesia for ect is 29% . this knowledge is likely to help in identifying and optimizing such patients during ect sessions . future studies should evaluate if measures like preoxygenation and intubation in selected patients at risk , will decrease the incidence of desaturation during ect without additional complications .
background and aims : electroconvulsive therapy ( ect ) is an established modality of treatment for severe psychiatric illnesses . among the various complications associated with ect , 
 oxygen desaturation is often under reported . 
 none of the previous studies has evaluated the predictive factors for oxygen desaturation during ect . 
 the objective of this study was to evaluate the incidence of oxygen desaturation during recovery from anesthesia for modified ect and evaluate its risk factors in a large sample.materials and methods : all patients aged above 15 years who were prescribed a modified ect for their psychiatric illness over 1 year were prospectively included in this observational study . 
 the association between age , body mass index ( bmi ) , doses of thiopentone and suxamethonium , stimulus current , ect session number , pre- and post - ect heart rate and mean arterial pressure , seizure duration , and pre- and post ect oxygen saturation , was systematically studied.results:the incidence of oxygen desaturation was 29% ( 93/316 patients ) . 
 seizure duration and bmi were found to be significantly correlated with post ect desaturation.conclusion:in this prospective observational study , the incidence of oxygen desaturation during recovery from anesthesia for ect was high . the study identified obesity and duration of seizure as the independent predictors of this complication . 
 this knowledge is likely to help in identifying and optimizing such patients before subsequent ect sessions .