Capnodynamic end-expiratory lung volume assessment in anesthetized healthy children.

BACKGROUND: Capnodynamic lung function monitoring generates variables that may be useful for pediatric perioperative ventilation. AIMS: Establish normal values for end-expiratory lung volume CO2 in healthy children undergoing anesthesia and to compare these values to previously published values obtained with alternative end-expiratory lung volume methods. The secondary aim was to investigate the ability of end-expiratory lung volume CO2 to react to positive end-expiratory pressure-induced changes in end-expiratory lung volume. In addition, normal values for associated volumetric capnography lung function variables were examined. METHODS: Fifteen pediatric patients with healthy lungs (median age 8 months, range 1-36 months) undergoing general anesthesia were examined before start of surgery. Tested variables were recorded at baseline positive end-expiratory pressure 3 cmH2 O, 1 and 3 min after positive end-expiratory pressure 10 cmH2 O and 3 min after returning to baseline positive end-expiratory pressure 3 cmH2 O. RESULTS: Baseline end-expiratory lung volume CO2 was 32 mL kg-1 (95% CI 29-34 mL kg-1 ) which increased to 39 mL kg-1 (95% CI 35-43 mL kg-1 , p < .0001) and 37 mL kg-1 (95% CI 34-41 mL kg-1 , p = .0003) 1 and 3 min after positive end-expiratory pressure 10 cmH2 O, respectively. End-expiratory lung volume CO2 returned to baseline, 33 mL kg-1 (95% CI 29-37 mL kg-1 , p = .72) 3 min after re-establishing positive end-expiratory pressure 3 cmH2 O. Airway dead space increased from 1.1 mL kg-1 (95% CI 0.9-1.4 mL kg-1 ) to 1.4 (95% CI 1.1-1.8 mL kg-1 , p = .003) and 1.5 (95% CI 1.1-1.8 mL kg-1 , p < .0001) 1 and 3 min after positive end-expiratory pressure 10 cmH2 O, respectively, and 1.2 mL kg-1 (95% CI 0.9-1.4 mL kg-1 , p = .08) after 3 min of positive end-expiratory pressure 3 cmH2 O. Additional volumetric capnography and lung function variables showed no major changes in response to positive end-expiratory pressure variations. CONCLUSIONS: Capnodynamic noninvasive and continuous end-expiratory lung volume CO2 values assessed during anesthesia in children were in close agreement with previously reported end-expiratory lung volume values generated by alternative methods. Furthermore, positive end-expiratory pressure changes resulted in physiologically expected end-expiratory lung volume CO2 responses in a timely manner, suggesting that it can be used to trend end-expiratory lung volume changes during anesthesia.

Fascial plane blocks in children-Scientifically supported or not?

Since the introduction of Fascial Plane Blocks in 2007 there has been an enormous interest and application of Fascial Plane Blocks, evidenced by substantially more than 1000 PubMed items. Despite this gigantic number of publications, also including randomized controlled trials and meta-analyses in children, there is still no clear-cut insight into how much of the purported effect is in fact due to the blockade of nerve structures and how much is merely adding the well-known analgesic and anti-inflammatory effects of the plasma levels of local anesthetics that are achieved with these techniques. Furthermore, Fascial Plane Blocks appear useful only if compared to conventional multi-modal analgesia (no block or placebo) and Fascial Plane Blocks lack the potency to provide surgical anesthesia on their own and appear only to be of value when used for minor-moderate surgery. Despite the huge literature, there has so far not emerged any clinical situations where Fascial Plane Blocks have definitively been shown to be the block of choice, being decisively more effective than other established regional blocks. Lastly, Fascial Plane Blocks may appear as virtually free of complications, but case reports are emerging that point to a real risk for causing local anesthetic systemic toxicity when using Fascial Plane Blocks. This text aims to synthesize the current knowledge base regarding the Fascial Plane Blocks that are relevant to use in the pediatric context. In summary, there does currently not exist any convincing scientific evidence for the continued support for the use of Fascial Plane Blocks in children, except for the rectus sheath block and possibly also the transmuscular quadratus lumborum block.

Spinal anaesthesia in children: A narrative review.

Spinal anaesthesia is an established and frequently used anaesthetic technique in adults. However, this versatile regional anaesthetic technique is less frequently used in paediatric anaesthesia even though it can be used for minor (e.g. inguinal hernia repair) and major (e.g. cardiac surgery) surgical procedures. The aim of this narrative review was to summarize the current literature with regard to technical aspects, surgical context, choice of drugs, potential complications, as well as the effects of the neuroendocrine surgical stress response and potential long-term effects of anaesthesia during infancy. In summary, spinal anaesthesia represents a valid alternative in the paediatric anaesthesia setting also.

Perioperative water and electrolyte balance and water homeostasis regulation in children with acute surgery.

BACKGROUND: Hospital-acquired hyponatremia remains a feared event in patients receiving hypotonic fluid therapy. Our objectives were to assess post-operative plasma-sodium concentration and to provide a physiological explanation for plasma-sodium levels over time in children with acute appendicitis. METHODS: Thirteen normonatremic (plasma-sodium ≥135 mmol/L) children (8 males), median age 12.3 (IQR 11.5-13.5) years participated in this prospective observational study (ACTRN12621000587808). Urine was collected and analyzed. Blood tests, including renin, aldosterone, arginine-vasopressin, and circulating nitric oxide substrates were determined on admission, at induction of anesthesia, and at the end of surgery. RESULTS: On admission, participants were assumed to be mildly dehydrated and were prescribed 50 mL/kg of Ringer's acetate intravenously followed by half-isotonic saline as maintenance fluid therapy. Blood tests, urinary indices, plasma levels of aldosterone, arginine-vasopressin, and net water-electrolyte balance indicated that participants were dehydrated on admission. Although nearly 50% of participants still had arginine-vasopressin levels that would have been expected to produce maximum antidiuresis at the end of surgery, electrolyte-free water clearance indicated that almost all participants were able to excrete net free water. No participant became hyponatremic. CONCLUSIONS: The use of moderately hypotonic fluid therapy after correction of extracellular fluid deficit is not necessarily associated with post-operative hyponatremia. IMPACT: Our observations show that in acutely ill normonatremic children not only the composition but also the amount of volume infused influence on the risk of hyponatremia. Our observations also suggest that perioperative administration of hypotonic fluid therapy is followed by a tendency towards hyponatremia if extracellular fluid depletion is left untreated. After correcting extracellular deficit almost all patients were able to excrete net free water. This occurred despite nearly 50% of the cohort having high circulating plasma levels of arginine-vasopressin at the end of surgery, suggesting a phenomenon of renal escape from arginine-vasopressin-induced antidiuresis.

The Retro Superior Costotransverse Ligament Space as a New Target for Ultrasound-Guided Intertransverse Process Block: A Report of 2 Cases.

An intertransverse process block (ITPB) is a paraspinal thoracic nerve block technique, where the local anesthetic (LA) is injected into the thoracic intertransverse tissue complex posterior to the superior costotransverse ligament (SCTL). Although an ITPB can be ultrasound-guided, it is performed using surrogate bony landmarks without even identifying the SCTL. This report describes a transverse ultrasound imaging technique to identify the retro-SCTL space and perform an ITPB with a retro-SCTL space injection, in 2 patients undergoing video-assisted thoracoscopic surgery. The resultant bilateral, symmetrical, thoracolumbar anesthesia was consistent with epidural spread of the LA and effective for perioperative analgesia.

Cardiac Output Assessments in Anesthetized Children: Dynamic Capnography Versus Esophageal Doppler.

BACKGROUND: The objective of this study was to compare esophageal Doppler cardiac output (COEDM) against the reference method effective pulmonary blood flow cardiac output (COEPBF), for agreement of absolute values and ability to detect change in cardiac output (CO) in pediatric surgical patients. Furthermore, the relationship between these 2 methods and noninvasive blood pressure (NIBP) parameters was evaluated. METHODS: Fifteen children American Society of Anesthesiology (ASA) I and II (median age, 8 months; median weight, 9 kg) scheduled for surgery were investigated in this prospective observational cohort study. Baseline COEPBF/COEDM/NIBP measurements were made at positive end-expiratory pressure (PEEP) 3 cm H2O. PEEP was increased to 10 cm H2O and COEPBF/COEDM/NIBP was recorded after 1 and 3 minutes. PEEP was then lowered to 3 cm H2O, and all measurements were repeated after 3 minutes. Finally, 20-µg kg-1 intravenous atropine was given with the intent to increase CO, and all measurements were recorded again after 5 minutes. Paired recordings of COEDM and COEPBF were examined for agreement and trending ability, and all parameters were analyzed for their responses to the hemodynamic challenges. RESULTS: Bias between COEDM and COEPBF (COEDM - COEPBF) was -17 mL kg-1 min-1 (limits of agreement, -67 to +33 mL kg-1 min-1) with a mean percentage error of 32% (95% confidence interval [CI], 25-37) and a concordance rate of 71% (95% CI, 63-80). The hemodynamic interventions caused by PEEP manipulations resulted in significant decrease in COEPBF absolute numbers (155 mL kg-1 min-1 [95% CI, 151-159] to 127 mL kg-1 min-1 [95% CI, 113-141]) and a corresponding relative decrease of 18% (95% CI, 14-22) 3 minutes after application of PEEP 10. No corresponding decreases were detected by COEDM. Mean arterial pressure showed a relative decrease with 5 (95% CI, 2-8) and 6% (95% CI, 2-10) 1 and 3 minutes after the application of PEEP 10, respectively. Systolic arterial pressure showed a relative decrease of 5% (95% CI, 2-10) 3 minutes after application of PEEP 10. None of the recorded parameters responded to atropine administration except for heart rate that showed a 4% relative increase (95% CI, 1-7, P = .02) 5 minutes after atropine. CONCLUSIONS: COEDM was unable to detect the reduction of CO cause by increased PEEP, whereas COEPBF and to a minimal extent NIBP detected these changes in CO. The ability of COEPBF to react to minor reductions in CO, before noticeable changes in NIBP are seen, suggests that COEPBF may be a potentially useful tool for hemodynamic monitoring in mechanically ventilated children.

Rapid systemic uptake of naloxone after intranasal administration in children.

BACKGROUND: Naloxone has a high affinity for the µ-opioid receptor and acts as a competitive antagonist, thus reversing the effects of opioids. Naloxone is often administrated intravenously, but there is a growing interest in the intranasal route in treating patients with opioid overdose, and in reversing effects after therapeutic use of opioids. As administration is painless and no intravenous access is needed, the intranasal route is especially useful in children. AIM: The aim of this study was to investigate the uptake of naloxone 0.4 mg/ml during the first 20 min after administration as a nasal spray in a pediatric population, with special focus on the time to achieve maximum plasma concentration. METHODS: Twenty children, 6 months-10 years, were included in the study. The naloxone dose administered was 20 µg/kg, maximum 0.4 mg, divided into repeated doses of 0.1 ml in each nostril. Venous blood samples were collected at 5, 10, and 20 min after the end of administration. RESULTS: All patients had quantifiable concentrations of naloxone in venous blood at 5 min, and within 20 min, peak concentration had been reached in more than half of the children. At 20 min after intranasal administration, the plasma naloxone concentrations were within the range of 2-6 nanogram/ml. CONCLUSION: This study confirms the clinical experience that the rapid effect of naloxone after intranasal administration in children was reflected in rapid systemic uptake to achieve higher peak plasma concentrations than previously reported in adults.

Primary spread of caudal blockade in children: the possible limiting role of the lumbar spinal cord enlargement (tumenescence) in combination with the cerebrospinal fluid rebound mechanism.

BACKGROUND: Despite being the most frequently used pediatric nerve block, certain aspects of the initial intraspinal spread of local anesthetics when performing a caudal block need further elucidation. The fact that injected volumes of 0.7-1.3 mL kg-1 initially only reach the thoraco-lumbar junction, with only a few vertebral segments difference despite the huge difference in injected volume, still has no apparent explanation. We hypothesize that the narrowing of the epidural space caused by the lumbar spinal enlargement may provide an anatomical barrier causing this restriction of initial spread, alone or in combination with increased intrathecal pressure caused by the "cerebrospinal fluid rebound mechanism." The aim of this observational study was to find support for or refute this hypothesis. METHODS: Twenty nine MRI scans of the vertebral column, performed in children 0-6 years of age, was identified from the radiographic imaging computer system and analyzed for the vertebral level of the maximum of the lumbar spinal enlargement (Associated anatomical data related to the spinal canal, the dura mater, and the spinal cord were also recorded. RESULTS: The maximum of the lumbar spinal enlargement was found at a median vertebral level of Th 11 (IQR 11-11). CONCLUSION: The maximum of the lumbar spinal enlargement is located at the Th 11 vertebral level. Although not entirely conclusive, the findings of the present study do support the notion that the lumbar spinal enlargement, in combination with the CSF rebound mechanism, may be the factors limiting the initial spread of a caudal block to the thoraco-lumbar junction.

Determination of adequate positive end-expiratory pressure level required for carbon dioxide homeostasis in an animal model of infant laparoscopy.

BACKGROUND: Capnoperitoneum provides a ventilatory challenge due to reduction in end-expiratory lung volume and peritoneal carbon dioxide absorption in both children and adults. The primary aim of this controlled interventional trial was to determine the positive end-expiratory pressure (PEEP) level needed to ensure for adequate carbon dioxide clearance and preservation of carbon dioxide homeostasis in an experimental model of infant laparoscopy. The secondary aim was to evaluate potential effects on cardiac output of PEEP and abdominal pressure level variations in the same setting. METHODS: Eight chinchilla bastard rabbits were anesthetized and mechanically ventilated. Intra-abdominal pressures were randomly set to 0, 6, and 12 mm Hg by carbon dioxide insufflation. Carbon dioxide clearance using volumetric capnography, arterial blood gas data, and cardiac output was recorded, while PEEP 3, 6, and 9 cmH2 O were applied in a random order. RESULTS: A PEEP of 9 cmH2 O showed restoration of carbon dioxide clearance without causing changes in arterial partial pressure of carbon dioxide and bicarbonate and with no associated deterioration in cardiac output. CONCLUSION: The results promote a PEEP level of 9 cmH2 O in this model of infant capnoperitoneum to allow for adequate carbon dioxide removal with subsequent preservation of carbon dioxide homeostasis. The use of high PEEP was not associated with any decrease in cardiac output.

End-expiratory lung volume assessment using helium and carbon dioxide in an experimental model of pediatric capnoperitoneum.

BACKGROUND: Capnoperitoneum during laparoscopy leads to cranial shift of the diaphragm, loss in lung volume, and risk of impaired gas exchange. Infants are susceptible to these changes and bedside assessment of lung volume during laparoscopy might assist with optimizing the ventilation. Thus, the primary aim was to investigate the monitoring value of a continuous end-expiratory lung volume (EELV) assessment method based on CO2 dynamics ( EELV CO 2 ) in a pediatric capnoperitoneum model by evaluating the correlation and trending ability against helium washout (EELVHe ). METHODS: Intra-abdominal pressure (IAP) was randomly varied between 0, 6, and 12 mm Hg with CO2 insufflation, while positive end-expiratory pressure (PEEP) levels of 3, 6, and 9 cm H2 O were randomly applied in eight anesthetized and mechanically ventilated chinchilla rabbits. Concomitant EELV CO 2 and EELVHe and lung clearance index (LCI) were obtained under each experimental condition. RESULTS: Significant correlations were found between EELV CO 2 and EELVHe before capnoperitoneum (r = .85, P < .001), although increased IAP distorted this relationship. The negative influence of IAP was counteracted by the application of PEEP 9, which restored the correlation between EELV CO 2 and EELVHe and resulted in 100% concordance rate between the methods regarding changes in lung volume. EELVHe and LCI showed a curvilinear relationship, and an EELVHe of approximately 20 mL kg-1 , determined with a receiver operating characteristic curve, was associated with near-normal LCI values. CONCLUSION: In this animal model of pediatric capnoperitoneum, reliable assessment of changes in EELV based on EELV CO 2 requires an open lung strategy, defined as EELV above approximately 20 mL kg-1 .

What has happened since the First World Congress on Pediatric Pain in 1988? The past, the present and the future.

The present article summarizes the development within the field of pediatric pain during the last 30 years, with a special focus on pediatric postoperative pain. Insights concerning pain ontogeny, how pain influences the neuro-endocrine stress response and the induction of a "pain memory" is discussed as well as established and new options with regards to treatment of postoperative pain. Lastly, some aspects concerning future development within this field is discussed. It is now well-established that even the unborn fetus reacts with behavioral responses indicative of pain and is also capable of producing a neuro-endocrine stress response if subjected to a painful stimulus. These responses can successfully be treated by opioid administration. The babies stress response if proportional to the magnitude of the surgical procedure and various ways to provide better pain relief to babies undergoing major surgery has been shown to reduce morbidity and mortality. A wide variety of different options exist to treat postoperative pain both in infants and older children. The use of regional anesthetic techniques should be used whenever possible and combined with appropriate systemic options, thereby producing multi-modal analgesia. However, new concepts and drugs are unfortunately few and, thus, progress often lies in using established drugs in more efficient ways. The concept of Enhanced Recovery After Surgery (ERAS) also provides a framework where high-quality postoperative pain relief is of essence for the best possible outcome after both minor and major surgery.

Low Plasma Sodium Concentration Predicts Perforated Acute Appendicitis in Children: A Prospective Diagnostic Accuracy Study.

INTRODUCTION: Early differentiation between perforated and nonperforated acute appendicitis (AA) in children is of major benefit for the selection of proper treatment. Based on pilot study data, we hypothesized that plasma sodium concentration at hospital admission is a diagnostic marker for perforation in children with AA. MATERIALS AND METHODS: This was a prospective diagnostic accuracy study, including previously healthy children, 1 to 14 years of age, with AA. Blood sampling included plasma sodium concentration, plasma glucose, base excess, white blood cell count, plasma arginine vasopressin (AVP), and C-reactive protein. RESULTS: Eighty children with histopathologically confirmed AA were included in the study. Median plasma sodium concentration on admission in patients with perforated AA (134 mmol/L, [interquartile range 132-136]) was significantly lower than in children with nonperforated AA (139 mmol/L, [137-140]). The receiver operating characteristic curve of plasma sodium concentration identifying patients with perforated AA showed an area under the curve of 0.93 (95% confidence interval, 0.87-0.99), with a sensitivity and specificity of 0.82 (0.70-0.90) and 0.87 (0.60-0.98), respectively. Plasma sodium concentrations ≤136 mmol/L resulted in an odds ratio of 31.9 (6.3-161.9) for perforation. The association between low plasma sodium concentration and perforated AA was confirmed in a multivariate logistic regression analysis. Median plasma AVP on admission was higher in patients with perforated (8.6 pg/mL [5.0-14.6]) as compared with nonperforated AA (3.4 pg/mL [2.5-6.6]). CONCLUSION: In children with AA, there is a strong association between low plasma sodium concentration and perforation, a novel and not previously described finding.

Impact of Anesthetics, Analgesics, and Perioperative Blood Transfusion in Pediatric Cancer Patients: A Comprehensive Review of the Literature.

Cancer is the leading cause of death by disease in developed countries. Children and adolescents with cancer need surgical interventions (ie, biopsy or major surgery) to diagnose, treat, or palliate their malignancies. Surgery is a period of high vulnerability because it stimulates the release of inflammatory mediators, catecholamines, and angiogenesis activators, which coincides with a period of immunosuppression. Thus, during and after surgery, dormant tumors or micrometastasis (ie, minimal residual disease) can grow and become clinically relevant metastasis. Anesthetics (ie, volatile agents, dexmedetomidine, and ketamine) and analgesics (ie, opioids) may also contribute to the growth of minimal residual disease or disease progression. For instance, volatile anesthetics have been implicated in immunosuppression and direct stimulation of cancer cell survival and proliferation. Contrarily, propofol has shown in vitro anticancer effects. In addition, perioperative blood transfusions are not uncommon in children undergoing cancer surgery. In adults, an association between perioperative blood transfusions and cancer progression has been described for some malignancies. Transfusion-related immunomodulation is one of the mechanisms by which blood transfusions can promote cancer progression. Other mechanisms include inflammation and the infusion of growth factors. In the present review, we discuss different aspects of tumorigenesis, metastasis, angiogenesis, the immune system, and the current studies about the impact of anesthetics, analgesics, and perioperative blood transfusions on pediatric cancer progression.

Caudal epidural blocks in paediatric patients: a review and practical considerations.

Caudal epidural blockade in children is one of the most widely administered techniques of regional anaesthesia. Recent clinical studies have answered major pharmacodynamic and pharmacokinetic questions, thus providing the scientific background for safe and effective blocks in daily clinical practice and demonstrating that patient selection can be expanded to range from extreme preterm births up to 50 kg of body weight. This narrative review discusses the main findings in the current literature with regard to patient selection (sub-umbilical vs mid-abdominal indications, contraindications, low-risk patients with spinal anomalies); anatomical considerations (access problems, age and body positioning, palpation for needle insertion); technical considerations (verification of needle position by ultrasound vs landmarks vs 'whoosh' or 'swoosh' testing); training and equipment requirements (learning curve, needle types, risk of tissue spreading); complications and safety (paediatric regional anaesthesia, caudal blocks); local anaesthetics (bupivacaine vs ropivacaine, risk of toxicity in children, management of toxic events); adjuvant drugs (clonidine, dexmedetomidine, opioids, ketamine); volume dosing (dermatomal reach, cranial rebound); caudally accessed lumbar or thoracic anaesthesia (contamination risk, verifying catheter placement); and postoperative pain. Caudal blocks are an efficient way to offer perioperative analgesia for painful sub-umbilical interventions. Performed on sedated children, they enable not only early ambulation, but also periprocedural haemodynamic stability and spontaneous breathing in patient groups at maximum risk of a difficult airway. These are important advantages over general anaesthesia, notably in preterm babies and in children with cardiopulmonary co-morbidities. Compared with other techniques of regional anaesthesia, a case for caudal blocks can still be made.

A different perspective: anesthesia for extreme premature infants: is there an age limitation or how low should we go?

PURPOSE OF REVIEW: To put in perspective, the various challenges that faces pediatric anesthesiologists because of the recently lowered limits with regards to the viability of a fetus. Both medical and ethical considerations will be highlighted. RECENT FINDINGS: Issues related to: who should anesthetize these tiny babies; can we provide adequate and legal monitoring during the anesthetic; does these immature babies need hypnosis and amnesia and the moral/ethical implications associated with being involved with care of doubtful long-term outcome are reviewed. SUMMARY: There does currently not exist sufficient research data to provide any evidence-based guidelines for the anesthetic handling of extreme premature infants. Current practice relies on extrapolations from other patient groups and from attempting to preserve normal physiology. Thus, focused research initiatives within this specific field of anesthesia should be a priority. Furthermore, in-depth multiprofessional ethical discussions regarding long-term outcome of aggressive care of extremely premature babies are urgently needed, including the new concepts of disability-free survival and number-need-to-suffer.

Interactive web-based format vs conventional brochure material for information transfer to children and parents: a randomized controlled trial regarding preoperative information.

BACKGROUND: Information transfer to patients is an integral part of modern medicine. Internet-based alternatives represent a new and attractive way for information transfer. METHODS: The study used a prospective observer-blinded design. Children (3-12 years) and parents were instructed to get further preoperative information either through an interactive web-based platform, the Anaesthesia-Web, or conventional brochure material until day of outpatient surgery. On the day of surgery, children and parents were separately asked six different questions. The primary end-point was to compare the total question score in children between the two information options (maximum score = 36). Secondary aims were the total question score for parents and the influence of age, sex, and time between the preoperative visit and day of surgery. RESULTS: A total of 125 children were recruited, of which 103 were included in the final analysis (the Anaesthesia-Web group, n = 49; the brochure material group, n = 54). At the predetermined interim analysis, the total question score in children was found to be substantially higher in the Anaesthesia-Web group than in the brochure material group (median score: 27; IQR: 16.5-33 and median score: 19.5; IQR: 11.25-27.75, respectively, P = 0.0076). The median difference in score was 6; 95% CI: 0-9. The total question score in parents was also higher in the Anaesthesia-Web group than in the brochure material group. Increasing child age was associated with a higher total question score in both groups. Sex did not influence the total question score in the Anaesthesia-Web group, whereas girls scored better than boys in the brochure material group. CONCLUSIONS: Children in the age range 3-12 years of age as well as their parents do better attain preoperative information from an interactive web-based platform compared to conventional brochure material.

Capnodynamic assessment of effective lung volume during cardiac output manipulations in a porcine model.

A capnodynamic calculation of effective pulmonary blood flow includes a lung volume factor (ELV) that has to be estimated to solve the mathematical equation. In previous studies ELV correlated to reference methods for functional residual capacity (FRC). The aim was to evaluate the stability of ELV during significant manipulations of cardiac output (CO) and assess the agreement for absolute values and trending capacity during PEEP changes at different lung conditions. Ten pigs were included. Alterations of alveolar carbon dioxide were induced by cyclic reoccurring inspiratory holds. The Sulphur hexafluoride technique for FRC measurements was used as reference. Cardiac output was altered by preload reduction and inotropic stimulation at PEEP 5 and 12 cmH2O both in normal lung conditions and after repeated lung lavages. ELV at baseline PEEP 5 was [mean (SD)], 810 (163) mL and decreased to 400 (42) mL after lavage. ELV was not significantly affected by CO alterations within the same PEEP level. In relation to FRC the overall bias (limits of agreement) was -35 (-271 to 201) mL, and percentage error 36 %. A small difference between ELV and FRC was seen at PEEP 5 cmH2O before lavage and at PEEP 12 cmH2O after lavage. ELV trending capability between PEEP steps, showed a concordance rate of 100 %. ELV was closely related to FRC and remained stable during significant changes in CO. The trending capability was excellent both before and after surfactant depletion.

Comparison of static end-expiratory and effective lung volumes for gas exchange in healthy and surfactant-depleted lungs.

BACKGROUND: Effective lung volume (ELV) for gas exchange is a new measure that could be used as a real-time guide during controlled mechanical ventilation. The authors established the relationships of ELV to static end-expiratory lung volume (EELV) with varying levels of positive end-expiratory pressure (PEEP) in healthy and surfactant-depleted rabbit lungs. METHODS: Nine rabbits were anesthetized and ventilated with a modified volume-controlled mode where periods of five consecutive alterations in inspiratory/expiratory ratio (1:2-1.5:1) were imposed to measure ELV from the corresponding carbon dioxide elimination traces. EELV and the lung clearance index were concomitantly determined by helium wash-out technique. Airway and tissue mechanics were assessed by using low-frequency forced oscillations. Measurements were collected at PEEP 0, 3, 6, and 9 cm H2O levels under control condition and after surfactant depletion by whole-lung lavage. RESULTS: ELV was greater than EELV at all PEEP levels before lavage, whereas there was no evidence for a difference in the lung volume indices after surfactant depletion at PEEP 6 or 9 cm H2O. Increasing PEEP level caused significant parallel increases in both ELV and EELV levels, decreases in ventilation heterogeneity, and improvement in airway and tissue mechanics under control condition and after surfactant depletion. ELV and EELV exhibited strong and statistically significant correlations before (r=0.84) and after lavage (r=0.87). CONCLUSIONS: The parallel changes in ELV and EELV with PEEP in healthy and surfactant-depleted lungs support the clinical value of ELV measurement as a bedside tool to estimate dynamic changes in EELV in children and infants.