Derivation and validation of an equation to determine the optimal ventilator setting in children undergoing intracranial revascularization surgery: A single-center retrospective study.

BACKGROUND: It can be difficult to determine the appropriate ventilator settings to maintain normocapnia in children undergoing general anesthesia for surgery for moyamoya disease, especially immediately following anesthesia induction. AIM: We conducted this study to attempt to derive an equation to predict the appropriate ventilator settings and subsequently validated the accuracy of the equation. METHODS: A retrospective study of 91 pediatric patients less than 18 years of age who underwent cerebral revascularization for moyamoya disease at our institution. Fifty-eight patients were used to derive the equation, and the subsequent 33 patients were used to validate the equation. We calculated the required respiratory rate to attain normocapnia based on the median of all values of the minute volume during normocapnia (estimated partial pressure of arterial carbon dioxide of 38-42 mm Hg) and the assumption that the tidal volume was 8 mL/kg body weight. We derived the regression equation from the derivation data set where the required respiratory rate to attain normocapnia was represented by age. We simplified the equation by rounding coefficients to the nearest integer. The level of agreement between the respiratory rate predicted from the equation and the actual required respiratory rate was assessed in the validation group using Bland-Altman analysis. RESULTS: The derived equation is tidal volume = 8 mL/kg body weight, respiratory rate = 24-age/min. Bland-Altman analysis in the validation group revealed that the mean bias between the predicted and actual respiratory rate was 0.29 (standard deviation, 3.67). The percentage of cases where the predicted rate was within ± 10% and ± 20% of the actual rate was 42.4% and 66.7%, respectively. CONCLUSIONS: We derived and validated a simple and easily applicable equation to predict the ventilator settings required to attain normocapnia during general anesthesia in children with moyamoya disease.

[Preventing Crying after Revascularization Surgery in Pediatric Patients with Moyamoya Disease:Sedation with Dexmedetomidine].

BACKGROUND: Hyperventilation is a well-known risk factor of ischemic events in pediatric patients with moyamoya disease. For young children, it is important to avoid crying to prevent ischemic events because of their unstable postoperative hemodynamics. To prevent crying in pediatric patients, we used dexmedetomidine(DEX)for sedation immediately after revascularization surgery. OBJECTIVE: We investigated the effects of postoperative DEX use on hemodynamic changes and the avoidance of crying and hypocapnia in pediatric patients with moyamoya disease. CASE: Ten consecutive patients(5 boys and 5 girls)who underwent surgical revascularization were enrolled, and 16 hemispheres(8 boys and 8 girls)were sedated with DEX postoperatively between August 2011 and August 2016. METHODS: During extubation after revascularization, DEX was started at 0.4µg/kg/hr under spontaneous breathing and its dose was increased depending on the degree of consciousness, to maintain sedation of at least 3 on the Ramsay scale. DEX administration was terminated the next morning. RESULTS: Sedation was maintained well in all patients without hypocapnia, and no ischemic complications were observed. One patient cried and needed additional intravenous DEX injections and was immediately re-sedated;no hypocapnia developed. Respiratory depression did not occur and changes in respiratory rate and decreases in SpO2 were not observed. No significant changes in systolic blood pressure and heart rate were observed. CONCLUSION: Dexmedetomidine is safe and useful for postoperative sedation in children with moyamoya disease.

Role of anesthesia in endovascular stroke therapy.

PURPOSE OF REVIEW: Recent randomized clinical trials have demonstrated strong efficacy of endovascular therapy (EVT) for acute ischemic stroke (AIS) from large vessel occlusions; in the USA alone, tens of thousands of patients annually may benefit. The impact of the type of anesthesia used during mechanical thrombectomy on patient outcomes remains controversial. This review discusses the current literature on the effects of anesthesia type on patient outcome following endovascular stroke therapy. RECENT FINDINGS: EVT is the standard of treatment for intracranial large vessel occlusions. Recent studies show that general anesthesia is associated with negative clinical outcome in AIS patients undergoing EVT. Two of the possible mechanisms of this finding are systolic hypotension and hypocapnia. However, the only published randomized controlled studies to date, sedation vs. intubation for endovascular stroke treatment and anesthesia during stroke showed no difference in short-term clinical outcome between EVT patients treated with general anesthesia and conscious sedation and improved longer-term outcome in the general anesthesia group. SUMMARY: Retrospective reports, and the 2015 American Heart Association/American Stroke Association Guideline (focused update of the 2013 guidelines for the early management of patients with AIS regarding endovascular treatment) based on these reports, are in favor of sedation (conscious sedation) over general anesthesia for endovascular stroke thrombectomy. However, the two randomized controlled prospective studies published provide inconclusive evidence as to the best anesthetic practice for endovascular stroke therapy. More randomized clinical trials are needed to optimize anesthetic patient care in AIS.

Episodes of hypo- and hypercapnia in a cohort of mechanically ventilated VLBW infants: the role of adequate staffing.

In preterm neonates, the use of invasive ventilation may be mandatory because of respiratory distress syndrome (RDS). In this short communication, we demonstrate that invasive ventilation in this susceptible cohort may be associated with episodes of both hypo- and hypercapnia, and that inadequate ventilatory support is associated with the occurrence rate of bronchopulmonary dysplasia (BPD; p < 0.05). Also, inadequate mechanical ventilation is aggravated by a shortage of medical staff.

Sympathetic regulation of the human cerebrovascular response to carbon dioxide.

Although the cerebrovasculature is known to be exquisitely sensitive to CO(2), there is no consensus on whether the sympathetic nervous system plays a role in regulating cerebrovascular responses to changes in arterial CO(2). To address this question, we investigated human cerebrovascular CO(2) reactivity in healthy participants randomly assigned to the α(1)-adrenoreceptor blockade group (9 participants; oral prazosin, 0.05 mg/kg) or the placebo control (9 participants) group. We recorded mean arterial blood pressure (MAP), heart rate (HR), mean middle cerebral artery flow velocity (MCA(V mean)), and partial pressure of end-tidal CO(2) (Pet(CO(2))) during 5% CO(2) inhalation and voluntary hyperventilation. CO(2) reactivity was quantified as the slope of the linear relationship between breath-to-breath Pet(CO(2)) and the average MCAv(mean) within successive breathes after accounting for MAP as a covariate. Prazosin did not alter resting HR, Pet(CO(2)), MAP, or MCA(V mean). The reduction in hypocapnic CO(2) reactivity following prazosin (-0.48 ± 0.093 cm·s(-1) · mmHg(-1)) was greater compared with placebo (-0.19 ± 0.087 cm · s(-1) · mmHg(-1); P < 0.05 for interaction). In contrast, the change in hypercapnic CO(2) reactivity following prazosin (-0.23 cm · s(-1) · mmHg(-1)) was similar to placebo (-0.31 cm · s(-1) · mmHg(-1); P = 0.50 for interaction). These data indicate that the sympathetic nervous system contributes to CO(2) reactivity via α(1)-adrenoreceptors; blocking this pathway with prazosin reduces CO(2) reactivity to hypocapnia but not hypercapnia.

Continuous integrated distal capnography in infants ventilated with high frequency ventilation.

OBJECTIVE: To assess within a feasibility study the correlation, agreement, and trending of continuous integrated distal capnography (dCap) with PaCO(2) in infants on HFV. STUDY DESIGN: Sixteen premature infants [median (range) gestational age: 26.5 (24.7-34.7) weeks], ventilated with HFV (mean ± SD airway pressure: 8.1 ± 2.1 cmH(2) O, FiO(2) : 0.39 ± 0.21) for RDS, intubated with a double-lumen endotracheal-tube and whose data were recorded on a bedside computer participated in the study. Side-stream dCap was measured via the extra-port of a double-lumen endotracheal-tube by a Microstream capnograph, with a specially designed software for HFV and compared with simultaneous PaCO(2) . Integrated time-window analysis of the data was performed retrospectively on data collected prospectively. RESULTS: Analysis included 195 measurements. The correlation of dCap with PaCO(2) (r = 0.68, P < 0.0001) and the agreement (bias ± precision: -2.0 ± 10.7 mmHg) were adequate. Area under the ROC curves for dCap to detect high (>60 mmHg) or low (<35 mmHg) PaCO(2) was 0.79 (CI: 0.70-0.89) and 0.87 (CI: 0.73-1.00), respectively; P < 0.0001. Changes in dCap and in PaCO(2) for consecutive measurements within each patient were adequately correlated (r = 0.65, P < 0.0001). CONCLUSIONS: Continuous integrated dCap is feasible in premature infants ventilated with HFV and can be helpful for trends and alarm for unsafe levels of PaCO(2) .

Effects of the transcutaneous electrode temperature on the accuracy of transcutaneous carbon dioxide tension.

AIM: The harmful effect of hypocapnia on the neonatal brain emphasizes the importance of monitoring arterial carbon dioxide tension (PaCO2). Transcutaneous monitoring of carbon dioxide (tcPCO2) reduces the need for arterial blood sampling. Drawbacks are high electrode temperature causing risks of skin burning. The aim was to determine the accuracy and precision of tcPCO2 at reduced electrode temperature. METHODS: Forty newborns (GA 24.9-41.7) were included. Two tc-monitors were applied (TCM4, Radiometer, Copenhagen). Arterial blood gas sampling and monitoring of tcPCO2-level at different electrode temperatures was done simultaneously (39°C, 40°C, 41°C, 42°C, 44°C). Difference of PaCO2 - tcPCO2 was expressed as a percentage of the mean. RESULTS: Mean PaCO2 was 5.8kPa [3,2; 7.9]. Bias (PaCO2 - tcPCO2) increased from 5% at 44°C to 17% at 39°C, but did not differ significantly between 41°C and 40°C. The precision of the tcPCO2 at each temperature ranged from +7-10%. After correction for the temperature-dependent overreading, we found increasing PaCO2 - tcPCO2 difference with increasing PaCO2, approx. 2% pr. kPa increase of CO(2). Only mild transient erythema was observed. CONCLUSION: A lower electrode temperature in tcPCO2-monitoring increases systematic overreading of the tc-electrode. However, in very preterm babies, monitoring at 40°C or 41°C is possible provided a bias correction of 12-15% is applied.

Long-term neurodevelopmental outcomes of congenital diaphragmatic hernia survivors not treated with extracorporeal membrane oxygenation.

BACKGROUND/PURPOSE: Although there has been a marked improvement in the survival of children with congenital diaphragmatic hernia (CDH) in the past 2 decades, there are few reports of long-term neurodevelopmental outcome in this population. The present study examined neurodevelopmental outcomes in 10- to 16-year-old CDH survivors not treated with extracorporeal membrane oxygenation (ECMO). METHODS: Parents of 27 CDH survivors completed questionnaires assessing medical problems, daily living skills, educational outcomes, behavioral problems, and executive functioning. Fifteen CDH survivors and matched full-term controls completed standardized intelligence, academic achievement, phonological processing, and working memory tests. RESULTS: Non-ECMO-treated CDH survivors demonstrated high rates of clinically significant difficulties on standardized academic achievement measures, and 14 of the 27 survivors had a formal diagnosis of specific learning disability, attention deficit hyperactivity disorder, or developmental disability. Specific problems with executive function, cognitive and attentional weaknesses, and social difficulties were more common in CDH patients than controls. Perioperative hypocapnia was linked to executive dysfunction, behavioral problems, lowered intelligence, and poor achievement in mathematics. CONCLUSIONS: Non-ECMO-treated CDH survivors are at substantial risk for neurodevelopmental problems in late childhood and adolescence.

Preconditioning and postinsult therapies for perinatal hypoxic-ischemic injury at term.

Perinatal hypoxic-ischemic encephalopathy can be a devastating complication of childbirth. Herein, the authors review the pathophysiology of hypoxic-ischemic encephalopathy and the current status of neuroprotective strategies to ameliorate the injury centering on four themes: (1) monitoring in the perinatal period, (2) rapid identification of affected neonates to allow timely institution of therapy, (3) preconditioning therapy (a therapeutic that reduces the brain vulnerability) before hypoxic-ischemic encephalopathy, and (4) prompt institution of postinsult therapies to ameliorate the evolving injury. Recent clinical trials have demonstrated the significant benefit for hypothermic therapy in the postnatal period; furthermore, there is accumulating preclinical evidence that adjunctive therapies can enhance hypothermic neuroprotection. Advances in the understanding of preconditioning may lead to the administration of neuroprotective agents earlier during childbirth. Although most of these neuroprotective strategies have not yet entered clinical practice, there is a significant hope that further developments will enhance hypothermic neuroprotection.

[Intra-abdominal hypertension and abdominal compartment syndrome--basic knowledge and anesthesiological aspects]. / Intraabdominelle Hypertonie und abdominelles Kompartmentsyndrom--Basiswissen und anästhesiologische Aspekte.

The increase in intra-abdominal pressure may be followed by a renal, gut, respiratory and cardial dysfunction and an increase in intra-cranial pressure. The review focuses risk factors and pathophysiological consequences of intra-abdominal hypertension and of abdominal compartment syndrome. Patients with intra-abdominal hypertension and abdominal compartment syndrome are critical ill and need special anesthesiological care due to risk of pulmonary aspiration, hemodynamic disturbances and difficult mechanical ventilation.

Evolution of tidal volume requirement during the first 3 weeks of life in infants <800 g ventilated with Volume Guarantee.

BACKGROUND: Volume-targeted ventilation is used in neonates to reduce volutrauma and inadvertent hyperventilation. Little is known about appropriate tidal volume (V(T)) settings in extremely low birthweight (ELBW) infants who remain intubated for extended periods. HYPOTHESIS: The V(T) required to maintain adequate partial pressure of carbon dioxide (P(CO2) levels changes as the underlying disease evolves in infants ventilated for prolonged periods. OBJECTIVE: To obtain normative data for V(T) associated with normocapnia in ELBW infants ventilated with Volume Guarantee over the first 3 weeks of life. DESIGN/METHODS: Set and measured V(T), peak pressure, respiratory rate and blood gas values were extracted from the records of babies <800 g born January 2003 to August 2005 and ventilated with Volume Guarantee. Data were collected at the time of each blood gas measurement during days 1-2, 5-7 and 14-21. Only the V(T) corresponding to P(CO2) values within a defined normal range were included. Descriptive statistics were used to define the patient cohort. Mean V(T) and P(CO2) for each patient during each epoch was calculated, and these values were analysed by repeated-measures analysis of variance. RESULTS: Twenty-six infants, mean (SD) birth weight 615 (104) g, were included. A total of 828 paired blood gas and V(T) sets were analysed: days 1-2 = 251; days 5-7 = 185; days 14-17 = 216; days 18-21 = 176. P(CO2) values (mean (SD)) rose from 44.0 (5.4) mm Hg on days 1-2 to 46.3 (5.2) mm Hg on days 5-7 and remained stable during days 14-17 and 18-21 (53.9 (6.8) and 53.9 (6.2) mm Hg, respectively). Mean exhaled V(T) rose from 5.15 (0.62) ml/kg on day 1 to 5.24 (0.71) ml/kg on days 5-7, 5.63 (1.0) ml/kg on days 14-17, and 6.07 (1.4) ml/kg on days 18-21 (p<0.05). CONCLUSIONS: Despite permissive hypercapnia, V(T) requirement rises with advancing postnatal age in ELBW infants. The increase is greatest during the third week of life, which is probably due to distension of the upper airways (acquired tracheomegaly) and increasing heterogeneity of lung inflation (increased alveolar dead space).

Changes in respiration mediate changes in fear of bodily sensations in panic disorder.

The purpose of the study was to examine whether changes in pCO(2) mediate changes in fear of bodily sensation (as indexed by anxiety sensitivity) in a bio-behavioral treatment for panic disorder that targets changes in end-tidal pCO(2). Thirty-five panic patients underwent 4 weeks of capnometry-assisted breathing training targeting respiratory dysregulation. Longitudinal mediation analyses of the changes in fear of bodily symptoms over time demonstrated that pCO(2), but not respiration rate, was a partial mediator of the changes in anxiety sensitivity. Results were supported by cross lag panel analyses, which indicated that earlier pCO(2) levels predicted later levels of anxiety sensitivity, but not vice versa. PCO(2) changes also led to changes in respiration rate, questioning the importance of respiration rate in breathing training. The results provide little support for changes in fear of bodily sensations leading to changes in respiration, but rather suggest that breathing training targeting pCO(2) reduced fear of bodily sensations in panic disorder.

Recognition and management of complex sleep-disordered breathing.

PURPOSE OF REVIEW: The recent rapid evolution of our understanding of the mechanisms involved in control of respiration during sleep has yielded new insights to guide our care of difficult-to-treat sleep apnea patients with complex sleep-disordered breathing. This review will describe these recent advances in the literature and suggest a model for their incorporation into clinical practice. RECENT FINDINGS: Control of respiration during sleep shows amplified instability relative to that seen during wake in these difficult patients. Baseline (eupneic) carbon dioxide levels as well as the responsiveness of the ventilatory system to changes in carbon dioxide are all-important in this relative instability. Furthermore, the instability seen during sleep varies widely across sleep states. A further refinement of our definition of stable and unstable sleep has been developed that directly informs our understanding of the control of respiration across a night of sleep. SUMMARY: Complex sleep-disordered breathing is a distinct form of sleep apnea. It has recognizable characteristics that are present without, and often worsened during, positive airway pressure treatment. Both sleep state stability and the behavior of the respiratory control system contribute to this complexity. It is only with a clear understanding of the factors contributing to complex sleep-disordered breathing that implementation of truly effective clinical therapy can be achieved for this disorder, which to date is poorly controlled.

Precise control of end-tidal carbon dioxide levels using sequential rebreathing circuits.

Anaesthesiologists have traditionally been consulted to help design breathing circuits to attain and maintain target end-tidal carbon dioxide (P(ET)CO2). The methodology has recently been simplified by breathing circuits that sequentially deliver fresh gas (not containing carbon dioxide (CO2)) and reserve gas (containing CO2). Our aim was to determine the roles of fresh gas flow, reserve gas PCO2 and minute ventilation in the determination of P(ET)CO2. We first used a computer model of a non-rebreathing sequential breathing circuit to determine these relationships. We then tested our model by monitoring P(ET)CO2 in human volunteers who increased their minute ventilation from resting to five times resting levels. The optimal settings to maintain P(ET)CO2 independently of minute ventilation are 1) fresh gas flow equal to minute ventilation minus anatomical deadspace ventilation, and 2) reserve gas PCO2 equal to alveolar PCO2. We provide an equation to assist in identifying gas settings to attain a target PCO2. The ability to precisely attain and maintain a target PCO2 (isocapnia) using a sequential gas delivery circuit has multiple therapeutic and scientific applications.

Controlled versus assisted mechanical ventilation effects on respiratory motor output in sleeping humans.

Central apneas occur after cessation of mechanical ventilation despite normocapnic conditions. We asked whether this was due to ventilator-induced increases in respiratory rate or VT. Accordingly, we compared the effects of increased VT (135 to 220% of eupneic VT) with and without increased respiratory rate, using controlled and assist control mechanical ventilation, respectively, upon transdiaphragmatic pressure in sleeping humans. Increasing ventilator frequency +1 per minute and VT to 165-200% of baseline eupnea eliminated transdiaphragmatic pressure during controlled mechanical ventilation and prolonged expiratory time (two to four times control) after mechanical ventilation. During and after assist control mechanical ventilation at 135-220% of eupneic VT, transdiaphragmatic pressure was reduced in proportion to the increase in ventilator volume. However, every ventilator cycle was triggered by an active inspiration, and immediately after mechanical ventilation, expiratory time during spontaneous breathing was prolonged less than 20% of that observed after controlled mechanical ventilation at similar VT. We conclude that both increased frequency and VT during mechanical ventilation significantly inhibited respiratory motor output via nonchemical mechanisms. Controlled mechanical ventilation at increased frequency plus moderate elevations in VT reset respiratory rhythm and inhibited respiratory motor output to a much greater extent than did increased VT alone.

Improving blood gas control in mechanically ventilated, premature infants through monitoring and evaluation of clinical practice.

Mechanical ventilation causing hypocapnia or hyperoxia carries a risk for the pre-term infant. The aim was to improve blood gas control in our unit. A guideline was written, and all personnel were motivated concerning blood gas control. Case records of all mechanically ventilated premature infants were examined during two 3-month periods, before and after intervention. The hours spent with hypocapnia (pCO2 < 4 kPa) or hyperoxia (PO2 > 12 kPa) were recorded. Case records of 31 infants were examined for a total of 1358 h of mechanical ventilation, 641 h before and 717 h after the intervention. The percentage time of hypocapnia before intervention (7.0%) was reduced significantly (P = 0.044) to less than half (2.9%) after intervention. Hyperoxia was reduced from 14.5% to 8.7% (P = 0.072). Blood gas control of mechanically ventilated premature infants could be improved with little effort, but hyperoxia is too frequent.

Adjustment of sweep gas flow during cardiopulmonary bypass.

Cardiopulmonary bypass (CPB) is one of the major tools of cardiac surgery. However, no clear data are available for the ideal value of sweep gas flow to oxygenator during CPB. The aim of this study was to determine the best value for sweep gas flow during CPB. Thirty patients undergoing isolated CABG were randomly and equally allocated into three groups. Sweep gas flow to oxygenator was kept at 1.35 l/min/m2 in group 1, 1.60 l/min/m2 in group 2, and 2.0 l/min/m2 in group 3. All patients were operated on under the same anaesthetic regime and surgical techniques. Samples for blood gas analysis were collected at T1: before CPB; T2: 5 min after the initiation of CPB; T3: just before rewarning; and T4: at the end of rewarming. Five minutes after the initiation of CPB (T2), pCO2 decreased significantly in groups 2 and 3 compared to group 1 (p < 0.02). With the addition of hypothermia (T3), the changes in the pH and pCO2 became more profound and, in this period, the levels in group 3 patients outranged the physiologic limits, with pCO2 and pH values being 28 +/- 3 mmHg and 7.50 +/- 0.04, respectively. At the end of the rewarming period (T4), in spite of increased carbon dioxide production, pCO2 values were below the physiologic limits in groups 2 and 3. We conclude that sweep gas flow to the oxygenator should be kept between 1.35 and 1.60 l/min/m2 during CPB to avoid hypocapnia, which results in alkalosis and has hazardous effects on lung mechanics, cerebral blood flow, and the cardiovascular system.

A prospective study of the quality of pre-hospital emergency ventilation in patients with severe head injury.

BACKGROUND: Pre-hospital endotracheal intubation for the purpose of controlled ventilation may prevent secondary brain injury in patients with severe head injury. In view of the limited monitoring devices utilized in the pre-hospital setting, little is known about the 'quality' of controlled ventilation initiated in the pre-hospital setting. METHODS: Included in this prospective study were 122 trauma patients with severe head injury (abbreviated injury scale score > or = 3). In all cases, the pre-hospital treatment included endotracheal intubation in the field. Upon hospital admission, and maintaining the same ventilation mode and setting initiated in the pre-hospital setting, arterial blood gas samples were taken. RESULTS: 'Optimal' oxygenation (PaO2 > 100 mm Hg) was achieved in 85.2% and 'adequate' ventilation (PaCO2 35-45 mm Hg) in 42.6% of the patients upon hospital admission. 'Optimal' oxygenation as well as 'adequate' ventilation was achieved in 37.7% of the study population. Hypoxaemia (PaO2 < 60 mm Hg) was observed in 2.5%, hypercapnia (PaCO2 > 45 mm Hg) in 16.4%, and hypocapnia (PaCO2 < 35 mm Hg) in 40.9% of the study patients. The incidence of hypocapnia was significantly more frequent in polytraumatized patients. Hypocapnia as well as hypercapnia was significantly more frequent in patients with associated pulmonary contusion. CONCLUSIONS: Endotracheal intubation and controlled ventilation of the lungs initiated in the pre-hospital setting do not guarantee optimal oxygenaton and ventilation in patients with severe head injury.

Cambios postoperatorios de la función pulmonar / Pulmonary postoperative changes

La anestesia y la cirugía producen cambios en la fisiología pulmonar desde el inicio del acto operatorio. Dichos cambios -reducción de la capacidad residual funcional, de la capacidad de cierre, producción de microatelectasias, alteración del intercambio gaseoso, alteraciones del V/Q, etc. -pueden verse agravados por la presencia de alteraciones mórbidas de los pacientes (hábito de fumar, obesidad, edad) o por causas inherentes al tipo de cirugía (tórax, abdomen superior). Diferentes aspectos del manejo anestésico pueden agravar las condiciones que favorecerán la aparición de complicaciones postoperatorias, si no se tienen en cuenta justamente las características del paciente y de la cirugía por realizarse. El control de la correcta oxigenación, de los valores del CO2, del estado ácidobase, de la administración de líquidos, de la transfusión de sangre, de los volúmenes de gas que ingresan y egresan del árbol broncopulmonar, la elección de modos ventilatorios no habituales, la prevención de broncoespasmos, tromboembolismo, el control del dolor, etc.; en suma, el conocimiento de la fisiología del intraoperatorio y la aplicación de dichos conocimientos en el postoperatorio permiten al anestesiólogo evitar o hacer menos probable la aparición de complicaciones. Las alteraciones pulmonares son más comunes en pacientes y cirugías que reúnen ciertas características: fumadores, obesos, mayores de setenta años, cirugía torácica o del abdomen superior o de larga duración, con antecedentes tromboembólicos, pacientes con enfermedad pulmonar obstructiva crónica o con enfermedad espástica bronquial. Muchas maniobras han sido descriptas en el postoperatorio para evitar las complicaciones pulmonares; las más efectivas incluyen fisioterapia respiratoria, posición semisentada precoz, soporte de O2 para mantener saturaciones periféricas por encima del 93 por ciento o, por lo menos, para alcanzar los valores preoperatorios con una FIO2 del 21 por ciento. (AU)

Carbon dioxide and the critically ill--too little of a good thing?

Permissive hypercapnia (acceptance of raised concentrations of carbon dioxide in mechanically ventilated patients) may be associated with increased survival as a result of less ventilator-associated lung injury. Conversely, hypocapnia is associated with many acute illnesses (eg, asthma, systemic inflammatory response syndrome, pulmonary oedema), and is thought to reflect underlying hyperventilation. Accumulating clinical and basic scientific evidence points to an active role for carbon dioxide in organ injury, in which raised concentrations of carbon dioxide are protective, and low concentrations are injurious. We hypothesise that therapeutic hypercapnia might be tested in severely ill patients to see whether supplemental carbon dioxide could reduce the adverse effects of hypocapnia and promote the beneficial effects of hypercapnia. Such an approach could also expand our understanding of the pathogenesis of disorders in which hypocapnia is a constitutive element.