Implementation of a low-titre whole blood transfusion program in a civilian helicopter emergency medical service

BACKGROUND

Early balanced transfusion is associated with improved outcome in haemorrhagic shock patients. This study describes the implementation and evaluates the safety of a whole blood transfusion program in a civilian helicopter emergency medical service (HEMS).

METHODS

This prospective observational study was performed over a 5-year period at HEMS-Bergen, Norway. Patients in haemorrhagic shock receiving out of hospital transfusion of low-titre Group O whole blood (LTOWB) or other blood components were included. Two LTOWB units were produced weekly and rotated to the HEMS for forward storage. The primary endpoints were the number of patients transfused, mechanisms of injury/illness, adverse events and survival rates. Informed consent covered patient pathway from time of emergency interventions to last endpoint and subsequent data handling/storage.

RESULTS

The HEMS responded to 5124 patients. Seventy-two (1.4%) patients received transfusions. Twenty patients (28%) were excluded due to lack of consent (16) or not meeting the inclusion criteria (4). Of the 52 (100%) patients, 48 (92%) received LTOWB, nine (17%) received packed red blood cells (PRBC), and nine (17%) received freeze-dried plasma. Of the forty-six (88%) patients admitted alive to hospital, 35 (76%) received additional blood transfusions during the first 24 h. Categories were blunt trauma 30 (58%), penetrating trauma 7 (13%), and nontrauma 15 (29%). The majority (79%) were male, with a median age of 49 (IQR 27-70) years. No transfusion reactions, serious complications or logistical challenges were reported. Overall, 36 (69%) patients survived 24 h, and 28 (54%) survived 30 days.

CONCLUSIONS

Implementing a whole blood transfusion program in civilian HEMS is feasible and safe and the logistics around out of hospital whole blood transfusions are manageable. Trial registration The study is registered in the ClinicalTrials.gov registry (NCT02784951).

Validation of a point-of-care capillary lactate measuring device (Lactate Pro 2)

Background

The measurement of lactate in emergency medical services has the potential for earlier detection of shock and can be performed with a point-of-care handheld device. Validation of a point-of-care handheld device is required for prehospital implementation.

Aim

The primary aim was to validate the accuracy of Lactate Pro 2 in healthy volunteers and in haemodynamically compromised intensive care patients. The secondary aim was to evaluate which sample site, fingertip or earlobe, is most accurate compared to arterial lactate.

Methods

Arterial, venous and capillary blood samples from fingertips and earlobes were collected from intensive care patients and healthy volunteers. Arterial and venous blood lactate samples were analysed on a stationary hospital blood gas analyser (ABL800 Flex) as the reference device and compared to the Lactate Pro 2. We used the Bland-Altman method to calculate the limits of agreement and used mixed effect models to compare instruments and sample sites. A total of 49 intensive care patients with elevated lactate and 11 healthy volunteers with elevated lactate were included.

Results

There was no significant difference in measured lactate between Lactate Pro 2 and the reference method using arterial blood in either the healthy volunteers or the intensive care patients. Capillary lactate measurement in the fingertip and earlobe of intensive care patients was 47% (95% CI (29 to 68%), p < 0.001) and 27% (95% CI (11 to 45%), p < 0.001) higher, respectively, than the corresponding arterial blood lactate. In the healthy volunteers, we found that capillary blood lactate in the fingertip was 14% higher than arterial blood lactate (95% CI (4 to 24%), p = 0.003) and no significant difference between capillary blood lactate in the earlobe and arterial blood lactate.

Conclusion

Our results showed that the handheld Lactate Pro 2 had good agreement with the reference method using arterial blood in both intensive care patients and healthy volunteers. However, we found that the agreement was poorer using venous blood in both groups. Furthermore, the earlobe may be a better sample site than the fingertip in intensive care patients.

Loss of life years due to unavailable helicopter emergency medical service: a single base study from a rural area of Norway

Background: Despite the potential benefits of physician-staffed Helicopter Emergency Medical Service (HEMS), many dispatches to primary HEMS missions in Norway are cancelled before patient encounter. Information is sparse regarding the health consequences when medically indicated HEMS missions are cancelled and the patients are treated by a GP and ambulance staff only. We aimed to estimate the potential loss of life years for patients in these situations. Method: We included all HEMS requests in the period 2010-2013 from Sogn and Fjordane County that were medically indicated but subsequently cancelled. This provided a selection of patients, with the purpose of studying cancellations independently of the patient's medical status A multidisciplinary expert panel retrospectively assessed each patient's potential loss of life years due to the lack of helicopter transport and intervention by a HEMS physician. Results: The study included 184 patients from 176 missions. Because of unavailable HEMS, seven patients (4%) were anticipated to have lost a total of 18 life years. Three patients suffered from myocardial infarction, three from stroke and one from abdominal haemorrhage. The main contribution from HEMS care in these seven cases might have been rapid transport to definitive care. The probability of a patient losing life years when in need of HEMS evacuation was found to be 0.2%. Conclusion: During the four years period seven patients lost 18 life years. Lack of rapid transport seems to be the primary cause of lost life years in this specific geographical area. Key Points Knowledge about to what extent HEMS contributes to an increased survival and a better outcome for patients is limited. Compared to similar studies on life years gained the estimated loss of life years was minor when HEMS evacuation was unavailable in this rural area. The findings indicates that lack of rapid HEMS transport was the primary cause of the estimated loss of life years.

Comparison of two different intraosseous access methods in a physician-staffed helicopter emergency medical service - a quality assurance study

BACKGROUND

Intravenous access in critically ill and injured patients can be difficult or impossible in the field. Intraosseous access is a well-established alternative to achieve access to a noncollapsible vascular network. We wanted to compare the use of a sternal and tibial/humeral intraosseous device in a physician-staffed helicopter emergency medical service.

METHODS

The helicopter emergency medical service in Bergen, Norway, is equipped with two different intraosseous devices, the EZ-IO and FAST-Responder. We compared insertion time, insertion sites, flow, indication for intraosseous access, and complications between the tibial/humeral and sternal techniques.

RESULTS

In 49 patients, 53 intraosseous insertions were made. The overall intraosseous rate was 1.5% (53 insertions in 3600 patients treated). The main patient categories were cardiac arrest and trauma. Overall, 93.9% of the insertions were successful on the first attempt. The median insertion time using EZ-IO was 15 s compared to 20 s using FAST-Responder. Insertion complications registered using the EZ-IO included extravasation, aspiration failure and insertion time > 30 s. Using FAST-Responder, there were reported complications such as user failure (12.5%) and insertion time > 30 s (12.5%). Regarding the flow, we found that 35.1% of the EZ-IO insertions experienced poor flow and needed a pressure bag. With FAST-Responder, the flow was reported as very good or good in 85.7%, and no insertions had poor flow.

CONCLUSION

Intraosseous access seems to be a reliable rescue technique in our helicopter emergency medical service, with high insertion success rates. EZ-IO was a more rapid method in gaining vascular access compared to FAST-Responder. However, FAST-Responder may be a better method when high-flow infusion is needed. Few complications were registered with both techniques in our service.

Standardised data reporting from pre-hospital advanced airway management - a nominal group technique update of the Utstein-style airway template

Background

Pre-hospital advanced airway management with oxygenation and ventilation may be vital for managing critically ill or injured patients. To improve pre-hospital critical care and develop evidence-based guidelines, research on standardised high-quality data is important. We aimed to identify which airway data were most important to report today and to revise and update a previously reported Utstein-style airway management dataset.

Methods

We recruited sixteen international experts in pre-hospital airway management from Australia, United States of America, and Europe. We used a five-step modified nominal group technique to revise the dataset, and clinical study results from the original template were used to guide the process.

Results

The experts agreed on a key dataset of thirty-two operational variables with six additional system variables, organised in time, patient, airway management and system sections. Of the original variables, one remained unchanged, while nineteen were modified in name, category, definition or value. Sixteen new variables were added. The updated dataset covers risk factors for difficult intubation, checklist and standard operating procedure use, pre-oxygenation strategies, the use of drugs in airway management, airway currency training, developments in airway devices, airway management strategies, and patient safety issues not previously described.

Conclusions

Using a modified nominal group technique with international airway management experts, we have updated the Utstein-style dataset to report standardised data from pre-hospital advanced airway management. The dataset enables future airway management research to produce comparable high-quality data across emergency medical systems. We believe this approach will promote research and improve treatment strategies and outcomes for patients receiving pre-hospital advanced airway management.

Trial registration

The Regional Committee for Medical and Health Research Ethics in Western Norway exempted this study from ethical review (Reference: REK-Vest/2017/260).

Electronic supplementary material

The online version of this article (10.1186/s13049-018-0509-y) contains supplementary material, which is available to authorized users.

Factors influencing on-scene time in a rural Norwegian helicopter emergency medical service: a retrospective observational study

Background

Critically ill patients need to be immediately identified, properly managed, and rapidly transported to definitive care. Extensive prehospital times may increase mortality in selected patient groups. The on-scene time is a part of the prehospital interval that can be decreased, as transport times are determined mostly by the distance to the hospital. Identifying factors that affect on-scene time can improve training, protocols, and decision making. Our objectives were to assess on-scene time in the Helicopter Emergency Medical Service (HEMS) in our region and selected factors that may affect it in specific and severe conditions.

Methods

This retrospective cohort study evaluated on-scene time and factors that may affect it for 9757 emergency primary missions by the three HEMSs in western Norway between 2009 and 2013, using graphics and descriptive statistics.

Results

The overall median on-scene time was 10 minutes (IQR 5–16). The median on-scene time in patients with penetrating torso injuries was 5 minutes (IQR 3–10), whereas in cardiac arrest patients it was 20 minutes (IQR 13–28). Based on multivariate linear regression analysis, the severity of the patient’s condition, advanced interventions performed, mode of transport, and trauma missions increased the on-scene time. Endotracheal intubation increased the OST by almost 10 minutes. Treatment prior to HEMS arrival reduced the on-scene time in patients suffering from acute myocardial infarction.

Discussion

We found a short OST in preselected conditions compared to other studies. For the various patient subgroups, the strength of association between factors and OST varied. The time spent on-scene and its influencing factors were dependent on the patient’s condition. Our results provide a basis for efforts to improve decision making and reduce OST for selected patient groups.

Conclusions

The most important factors associated with increased on-scene time were the severity of the patient’s condition, the need for intubation or intravenous analgesic, helicopter transport, and trauma missions.

Electronic supplementary material

The online version of this article (10.1186/s13049-017-0442-5) contains supplementary material, which is available to authorized users.

Hypoxia and hypotension in patients intubated by physician staffed helicopter emergency medical services - a prospective observational multi-centre study

BACKGROUND

The effective treatment of airway compromise in trauma and non-trauma patients is important. Hypoxia and hypotension are predictors of negative patient outcomes and increased mortality, and may be important quality indicators of care provided by emergency medical services. Excluding cardiac arrests, critical trauma and non-trauma patients remain the two major groups to which helicopter emergency medical services (HEMS) are dispatched. Several studies describe the impact of pre-hospital hypoxia or hypotension on trauma patients, but few studies compare this in trauma and non-trauma patients. The primary aim was to describe the incidence of pre-hospital hypoxia and hypotension in the two groups receiving pre-hospital tracheal intubation (TI) by physician-staffed HEMS.

METHODS

Data were collected prospectively over a 12-month period, using a uniform Utstein-style airway template. Twenty-one physician-staffed HEMS in Europe and Australia participated. We compared peripheral oxygen saturation and systolic blood pressure before and after definitive airway management. Data were analysed using Cochran-Mantel-Haenszel methods and mixed-effects models.

RESULTS

Eight hundred forty three trauma patients and 422 non-trauma patients receiving pre-hospital TI were included. Non-trauma patients had significantly lower predicted mean pre-intervention SpO₂ compared to trauma patients. Post-intervention and admission SpO₂ for the two groups were comparable. However, 3% in both groups were still hypoxic at admission. For hypotension, the differences between the groups were less prominent. However, 9% of trauma and 10% of non-trauma patients were still hypotensive at admission. There was no difference in short-term survival between trauma (97%) and non-trauma patients (95%). Decreased level of consciousness was the most frequent indication for TI, and was associated with increased survival to hospital (cOR 2.8; 95% CI: 1.4-5.4).

CONCLUSIONS

Our results showed that non-trauma patients had a higher incidence of hypoxia before TI than trauma patients, but few were hypoxic at admission. The difference for hypotension was less prominent, but one in ten patients were still hypotensive at admission. Further investigations are needed to identify reversible causes that may be corrected to improve haemodynamics in the pre-hospital setting. We found high survival rates to hospital in both groups, suggesting that physician-staffed HEMS provide high-quality emergency airway management in trauma and non-trauma patients.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT01502111 . Registered 22 Desember 2011.

Targeted temperature management in cardiac arrest: survival evaluated by propensity score matching

Background

Targeted temperature management in cardiac arrest was introduced following evidence of increased survival from two controlled trials published in 2002. We wanted to investigate whether the introduction of targeted temperature management to clinical practice had increased the survival of cardiac arrest patients at Haukeland University Hospital, Norway.

Methods

We included 336 unresponsive patients admitted to the emergency department between December 2003 and December 2008 with return of spontaneous circulation following out-of-hospital cardiac arrest in the analysis. A propensity score model was developed to evaluate the survival of patients receiving intensive care treatment including targeted temperature management, compared with intensive care treatment not including targeted temperature management.

Results

Estimation of the treatment effect revealed an increase of 57 days (95% CI: 12–103, p = 0.01) in restricted mean survival during the first year after cardiac arrest for intensive care treatment including targeted temperature management.

Discussion

As with all observational studies, bias is probable. However, propensity score methodology has been used in order to reduce bias and establish causality. Although residual confounding is likely, our interpretation is that TTM increased survival for comatose OHCA patients in our hospital because survival increased well beyond the level of significance.

Conclusion

The introduction of targeted temperature management to clinical practice is likely to have increased survival for unresponsive patients following out-of-hospital cardiac arrest.

Electronic supplementary material

The online version of this article (doi:10.1186/s13049-017-0373-1) contains supplementary material, which is available to authorized users.

Airway management by physician-staffed Helicopter Emergency Medical Services - a prospective, multicentre, observational study of 2,327 patients

Background

Despite numerous studies on prehospital airway management, results are difficult to compare due to inconsistent or heterogeneous data. The objective of this study was to assess advanced airway management from international physician-staffed helicopter emergency medical services.

Methods

We collected airway data from 21 helicopter emergency medical services in Australia, England, Finland, Hungary, Norway and Switzerland over a 12-month period. A uniform Utstein-style airway template was used for collecting data.

Results

The participating services attended 14,703 patients on primary missions during the study period, and 2,327 (16 %) required advanced prehospital airway interventions. Of these, tracheal intubation was attempted in 92 % of the cases. The rest were managed with supraglottic airway devices (5 %), bag-valve-mask ventilation (2 %) or continuous positive airway pressure (0.2 %). Intubation failure rates were 14.5 % (first-attempt) and 1.2 % (overall). Cardiac arrest patients showed significantly higher first-attempt intubation failure rates (odds ratio: 2.0; 95 % CI: 1.5-2.6; p < 0.001) compared to non-cardiac arrest patients. Complications were recorded in 13 %, with recognised oesophageal intubation being the most frequent (25 % of all patients with complications). For non-cardiac arrest patients, important risk predictors for first-attempt failure were patient age (a non-linear association) and administration of sedatives (reduced failure risk). The patient’s sex, provider’s intubation experience, trauma type (patient category), indication for airway intervention and use of neuromuscular blocking agents were not risk factors for first-attempt intubation failure.

Conclusions

Advanced airway management in physician-staffed prehospital services was performed frequently, with high intubation success rates and low complication rates overall. However, cardiac arrest patients showed significantly higher first-attempt failure rates compared to non-cardiac arrest patients. All failed intubations were handled successfully with a rescue device or surgical airway.

Trial registration

Study registration: www.clinicaltrials.govNCT01502111. Registered 22 December 2011.

Cognitive function and health-related quality of life four years after cardiac arrest

AIM

Neuropsychological testing has uncovered cognitive impairment in cardiac arrest survivors with good neurologic outcome according to the cerebral performance categories. We investigated cognitive function and health-related quality of life four years after cardiac arrest.

METHODS

Thirty cardiac arrest survivors over the age of 18 in cerebral performance category 1 or 2 on hospital discharge completed the EQ-5D-5L and HADS questionnaires prior to cognitive testing using the Cambridge Neuropsychological Test Automated Battery. The results were compared with population norms.

RESULTS

Twenty-nine per cent of patients were cognitively impaired. The pattern of cognitive impairment reflects dysfunction in the medial temporal lobe, with impaired short-time memory and executive function slightly but distinctly affected. There was a significant reduction in quality of life on the EQ-VAS, but not on the EQ index.

CONCLUSION

Cognitive impairment four years after cardiac arrest affected more than one quarter of the patients. Short-term memory was predominantly affected.

A pilot study of angiotensin converting enzyme (ACE) genotype and return of spontaneous circulation following out-of-hospital cardiac arrest

Objective

In the last few years the genetic influence on health and disease outcome has become more apparent. The ACE genotype appears to play a significant role in the pathophysiology of several disease processes. This pilot study aims at showing the feasibility to examine the genetic influence of the ACE genotype on return of spontaneous circulation (ROSC) in out-of-hospital cardiac arrest (OHCA).

Methods

We performed a prospective observational study of all OHCAs of presumed cardiac origin in a well-defined population. We collected prehospital blood samples for the determination of ACE genotype and used this information together with Utstein template parameters in a multivariable analysis to examine the relationship between ROSC and ACE genotype.

Results

We collect blood samples in 156 of 361 patients with OHCA of presumed cardiac origin, 127 samples were analysed (mean age 67 years, 86% male, 79% witnessed OHCA, 80% bystander CPR, 62% had a shockable rhythm, ROSC 77%). Distribution of the ACE gene polymorphisms: insertion polymorphism (II) n=22, 17%, insertion/deletion polymorphism (ID) n=66, 52% and deletion polymorphism (DD) n=39, 31%. We found no significant association between ACE II vs ACE DD/DI and ROSC (OR 1.72; CI 0.52 to 5.73; p=0.38). Other ACE genotype groupings (II/ID vs DD or II vs DD) did not change the overall finding of lack of impact of ACE genotype on ROSC.

Conclusions

This pilot study did not indicate a significant association between ACE gene polymorphism and ROSC. However, it has demonstrated that prehospital genetic studies including blood sampling are feasible and ethically acceptable.

Factors predicting the use of therapeutic hypothermia and survival in unconscious out-of-hospital cardiac arrest patients admitted to the ICU

INTRODUCTION

Therapeutic hypothermia (TH) after out-of-hospital cardiac arrest (OHCA) was adopted early in Norway. Since 2004 the general recommendation has been to cool all unconscious OHCA patients treated in the intensive care unit (ICU), but the decision to cool individual patients was left to the responsible physician. We assessed factors that were associated with use of TH and predicted survival.

METHOD

We conducted a retrospective observational study of prospectively collected cardiac arrest and ICU registry data from 2004 to 2008 at three university hospitals.

RESULTS

A total of 715 unconscious patients older than 18 years of age, who suffered OHCA of both cardiac and non-cardiac causes, were included. With an overall TH use of 70%, the survival to discharge was 42%, with 90% of the survivors having a favourable cerebral outcome. Known positive prognostic factors such as witnessed arrest, bystander cardio pulmonary resuscitation (CPR), shockable rhythm and cardiac origin were all positive predictors of TH use and survival. On the other side, increasing age predicted a lower utilisation of TH: Odds Ratio (OR), 0.96 (95% CI, 0.94 to 0.97); as well as a lower survival: OR 0.96 (95% CI, 0.94 to 0.97). Female gender was also associated with a lower use of TH: OR 0.65 (95% CI, 0.43 to 0.97); and a poorer survival: OR 0.57 (95% CI, 0.36 to 0.92). After correcting for other prognostic factors, use of TH remained an independent predictor of improved survival with OR 1.91 (95% CI 1.18-3.06; P <0.001). Analysing subgroups divided after initial rhythm, these effects remained unchanged for patients with shockable rhythm, but not for patients with non-shockable rhythm where use of TH and female gender lost their predictive value.

CONCLUSIONS

Although TH was used in the majority of unconscious OHCA patients admitted to the ICU, actual use varied significantly between subgroups. Increasing age predicted both a decreased utilisation of TH as well as lower survival. Further, in patients with a shockable rhythm female gender predicted both a lower use of TH and poorer survival. Our results indicate an underutilisation of TH in some subgroups. Hence, more research on factors affecting TH use and the associated outcomes in subgroups of post-resuscitation patients is needed.

Laryngeal tube use in out-of-hospital cardiac arrest by paramedics in Norway

Background

Although there are numerous supraglottic airway alternatives to endotracheal intubation, it remains unclear which airway technique is optimal for use in prehospital cardiac arrests. We evaluated the use of the laryngeal tube (LT) as an airway management tool among adult out-of-hospital cardiac arrest (OHCA) patients treated by our ambulance services in the Haukeland and Innlandet hospital districts.

Methods

Post-resuscitation forms and data concerning airway management in 347 adult OHCA victims were retrospectively assessed with regard to LT insertion success rates, ease and speed of insertion and insertion-related problems.

Results

A total of 402 insertions were performed on 347 OHCA patients. Overall, LT insertion was successful in 85.3% of the patients, with a 74.4% first-attempt success rate. In the minority of patients (n = 46, 13.3%), the LT insertion time exceeded 30 seconds. Insertion-related problems were recorded in 52.7% of the patients. Lack of respiratory sounds on auscultation (n = 100, 28.8%), problematic initial tube positioning (n = 85, 24.5%), air leakage (n = 61, 17.6%), vomitus/aspiration (n = 44, 12.7%), and tube dislocation (n = 17, 4.9%) were the most common problems reported. Insertion difficulty was graded and documented for 95.4% of the patients, with the majority of insertions assessed as being “Easy” (62.5%) or “Intermediate” (24.8%). Only 8.1% of the insertions were considered to be “Difficult”.

Conclusions

We found a high number of insertion related problems, indicating that supraglottic airway devices offering promising results in manikin studies may be less reliable in real-life resuscitations. Still, we consider the laryngeal tube to be an important alternative for airway management in prehospital cardiac arrest victims.

Checklists in the operating room: Help or hurdle? A qualitative study on health workers' experiences

Background

Checklists have been used extensively as a cognitive aid in aviation; now, they are being introduced in many areas of medicine. Although few would dispute the positive effects of checklists, little is known about the process of introducing this tool into the health care environment. In 2008, a pre-induction checklist was implemented in our anaesthetic department; in this study, we explored the nurses' and physicians' acceptance and experiences with this checklist.

Method

Focus group interviews were conducted with a purposeful sample of checklist users (nurses and physicians) from the Department of Anaesthesia and Intensive Care in a tertiary teaching hospital. The interviews were analysed qualitatively using systematic text condensation.

Results

Users reported that checklist use could divert attention away from the patient and that it influenced workflow and doctor-nurse cooperation. They described senior consultants as both sceptical and supportive; a head physician with a positive attitude was considered crucial for successful implementation. The checklist improved confidence in unfamiliar contexts and was used in some situations for which it was not intended. It also revealed insufficient equipment standardisation.

Conclusion

Our findings suggest several issues and actions that may be important to consider during checklist use and implementation.

Capillary leakage in post-cardiac arrest survivors during therapeutic hypothermia - a prospective, randomised study

Background

Fluids are often given liberally after the return of spontaneous circulation. However, the optimal fluid regimen in survivors of cardiac arrest is unknown. Recent studies indicate an increased fluid requirement in post-cardiac arrest patients. During hypothermia, animal studies report extravasation in several organs, including the brain. We investigated two fluid strategies to determine whether the choice of fluid would influence fluid requirements, capillary leakage and oedema formation.

Methods

19 survivors with witnessed cardiac arrest of primary cardiac origin were allocated to either 7.2% hypertonic saline with 6% poly (O-2-hydroxyethyl) starch solution (HH) or standard fluid therapy (Ringer's Acetate and saline 9 mg/ml) (control). The patients were treated with the randomised fluid immediately after admission and continued for 24 hours of therapeutic hypothermia.

Results

During the first 24 hours, the HH patients required significantly less i.v. fluid than the control patients (4750 ml versus 8010 ml, p = 0.019) with comparable use of vasopressors. Systemic vascular resistance was significantly reduced from 0 to 24 hours (p = 0.014), with no difference between the groups. Colloid osmotic pressure (COP) in serum and interstitial fluid (p < 0.001 and p = 0.014 respectively) decreased as a function of time in both groups, with a more pronounced reduction in interstitial COP in the crystalloid group. Magnetic resonance imaging of the brain did not reveal vasogenic oedema.

Conclusions

Post-cardiac arrest patients have high fluid requirements during therapeutic hypothermia, probably due to increased extravasation. The use of HH reduced the fluid requirement significantly. However, the lack of brain oedema in both groups suggests no superior fluid regimen. Cardiac index was significantly improved in the group treated with crystalloids. Although we do not associate HH with the renal failures that developed, caution should be taken when using hypertonic starch solutions in these patients.

Trial registration

NCT00347477.

Respiratory changes during prolonged increased intra-abdominal pressure in pigs

BACKGROUND

Increased intra-abdominal pressure (IAP) elevates thoracic pressure and airway pressures and reduces lung compliance in humans and laboratory animals. We studied respiratory alterations and arterial blood gas changes in pigs with IAP maintained at 20 mmHg or 30 mmHg for 3 h.

METHODS

Domestic pigs of both sexes weighing 30.0 +/- 5.1 kg (mean +/- SD) (n = 21) were divided into three groups. The animals were anesthetized and kept at 20 mmHg IAP (n = 7) or 30 mmHg IAP (n = 7) for 3 h. The third group (n = 7) served as control without an elevated IAP. We recorded respiratory alterations and changes in acid-based parameters at baseline and after 90 min and 180 min of increased IAP.

RESULTS

No significant hypoxia or hypercarbia was found in animals with an IAP of 20 mmHg IAP. At an IAP of 30 mmHg, pO2 decreased to an average 19.6 kPa and pCO2 increased to about 6 kPa, and the animals were slightly acidotic. Airway pressure increased significantly and lung compliance decreased in both groups of elevated IAP.

CONCLUSION

In our porcine model, an IAP of 20 mmHg or higher for 3 h is harmful for the respiratory function of the animals due to deterioration of respiratory parameters, increased airway pressure and decreased lung compliance.

Can the use of methylprednisolone, vitamin C, or α-trinositol prevent cold-induced fluid extravasation during cardiopulmonary bypass in piglets?

OBJECTIVE

Hypothermic cardiopulmonary bypass is associated with capillary fluid leakage, resulting in edema and occasionally organ dysfunction. Systemic inflammatory activation is considered responsible. In some studies methylprednisolone has reduced the weight gain during cardiopulmonary bypass. Vitamin C and alpha-trinositol have been demonstrated to reduce the microvascular fluid and protein leakage in thermal injuries. We therefore tested these three agents for the reduction of cold-induced fluid extravasation during cardiopulmonary bypass.

METHODS

A total of 28 piglets were randomly assigned to four groups of 7 each: control group, high-dose vitamin C group, methylprednisolone group, and alpha-trinositol-group. After 1 hour of normothermic cardiopulmonary bypass, hypothermic cardiopulmonary bypass was initiated in all animals and continued to 90 minutes. The fluid level in the extracorporeal circuit reservoir was kept constant at the 400-mL level and used as a fluid gauge. Fluid needs, plasma volume, changes in colloid osmotic pressure in plasma and interstitial fluid, hematocrit, and total water contents in different tissues were recorded, and the protein masses and the fluid extravasation rate were calculated.

RESULTS

Hemodilution was about 25% after start of normothermic cardiopulmonary bypass. Cooling did not cause any further changes in hemodilution. During steady-state normothermic cardiopulmonary bypass, the fluid need in all groups was about 0.10 mL/(kg.min), with a 9-fold increase during the first 30 minutes of cooling (P <.001). This increased fluid need was due mainly to increased fluid extravasation from the intravascular to the interstitial space at a mean rate of 0.6 mL/(kg.min) (range 0.5-0.7 mL/[kg.min]; P <.01) and was reflected by increased total water content in most tissues in all groups. The albumin and protein masses remained constant in all groups throughout the study.

CONCLUSION

Pretreatment with methylprednisolone, vitamin C, or alpha-trinositol was unable to prevent the increased fluid extravasation rate during hypothermic cardiopulmonary bypass. These findings, together with the stability of the protein masses throughout the study, support the presence of a noninflammatory mechanism behind the cold-induced fluid leakage seen during cardiopulmonary bypass.

Fluid extravasation during cardiopulmonary bypass in piglets--effects of hypothermia and different cooling protocols

BACKGROUND

Hypothermic cardiopulmonary bypass (CPB) is associated with capillary fluid leak and edema generation which may be secondary to hemodilution, inflammation and hypothermia. We evaluated how hypothermia and different cooling strategies influenced the fluid extravasation rate during CPB.

METHODS

Fourteen piglets were given 60 min normothermic CPB, followed by randomization to two groups: 1: rapid cooling (RC-group) ( approximately 15 min to 28 degrees C); 2: slow cooling (SC-group) ( approximately 60 min to 28 degrees C). Ringer's solution was used as CPB prime and for fluid supplementation. Fluid input/losses, plasma volume, colloid osmotic pressures (plasma, interstitial fluid), hematocrit, serum-proteins and total tissue water (TTW) were measured and fluid extravasation rates calculated.

RESULTS

Start of normothermic CPB resulted in a 25% hemodilution. During the first 5-10 min the fluid level of the reservoir fell markedly due to an intravascular volume loss necessitating fluid supplementation. Thereafter a steady state was reached with a constant fluid need of 0.14 +/- 0.04 ml kg-1 min-1. After start of cooling the fluid needs increased in the following 30 min to 0.91 +/- 0.11 ml kg-1 min-1 in the RC group (P < 0.001) and 0.63 +/- 0.10 ml kg-1 min-1 in the SC-group (P < 0.001) with no statistical between-group differences. Fluid extravasation rates after start of hypothermic CPB increased from 0.20 +/- 0.08 ml kg-1 min-1 to 0.71 +/- 0.13 (P < 0.01) and 0.62 +/- 0.13 ml kg-1 min-1 (P < 0.05) in the RC- and SC-groups, respectively, without any changes in degree of hemodilution. TTW increased in most tissues, whereas the intravascular albumin and protein masses remained constant with no between group differences.

CONCLUSION

Hypothermia increased fluid extravasation during CPB independent of cooling strategy. Intravascular albumin and protein masses remained constant. Since inflammatory fluid leakage usually results in protein rich exudates, our data with no net protein leakage may indicate that mechanisms other than inflammation could contribute to fluid extravasation during hypothermic CPB.

Fluid shifts during cardiopulmonary bypass with special reference to the effects of hypothermia

Background

Generalized overhydration, oedema and organ dysfunction occurs in patients undergoing open heart surgery using cardiopulmonary bypass (CPB) and hypothermia. Inflammatory reactions induced by contact between blood and the foreign surfaces of the extracorporeal circuit are commonly held responsible for the disturbances in fluid balance (‘capillary leak syndrome’). Using the CPB circuit reservoir as a fluid gauge (measuring continuous extracorporeal blood volume), fluid shifts between the intravascular and the extravascular space, and differences between normothermic and moderately hypothermic CPB, were examined.

Methods

Piglets were placed on CPB (thoracotomy) under general anaesthesia. In the normothermic group (n = 7) the core temperature was kept at 38°C before and during 2 h on CPB, whereas in the hypothermic group (n = 7) the temperature was lowered to 29°C during bypass. In addition to accurate recording of fluid during operation, the extracorporeal blood volume was kept constant by maintaining a certain blood level in the CPB circuit's reservoir. Acetated Ringer was used as priming solution in the CPB, as maintenance fluid and for adding fluid to the reservoir if necessary.

Results

Cardiac output, serum electrolytes and arterial blood gases were all similar in the two groups. Haematocrit fell significantly following the start of CPB in both groups. The reservoir fluid level fell markedly in both groups necessitating fluid supplementation. This extra fluid requirement was transient in the normothermic group, but persisted in hypothermic animals. At the end of 2 h of CPB the hypothermic animals had received seven times more extra fluid than the normothermic pigs.

Conclusion

There were strong indications of a greater fluid extravasation induced by hypothermia. The model described, using the PBC circuit reservoir as a fluid gauge, provides the opportunity for further study of fluid volume shifts, their causes and potential ways to manipulate fluid pathophysiology related to hypothermia and to PBC.

Determination of plasma volume in anaesthetized piglets using the carbon monoxide (CO) method

Based on measurements of the circulating red blood cell volume (V(RBC)) in seven anaesthetized piglets using carbon monoxide (CO) as a label, plasma volume (PV) was calculated for each animal. The increase in carboxyhaemoglobin (COHb) concentration following administration of a known amount of CO into a closed circuit re-breathing system was determined by diode-array spectrophotometry. Simultaneously measured haematocrit (HCT) and haemoglobin (Hb) values were used for PV calculation. The PV values were compared with simultaneously measured PVs determined using the Evans blue technique. Mean values (SD) for PV were 1708.6 (287.3)ml and 1738.7 (412.4)ml with the CO method and the Evans blue technique, respectively. Comparison of PVs determined with the two techniques demonstrated good correlation (r = 0.995). The mean difference between PV measurements was -29.9 ml and the limits of agreement (mean difference +/-2SD) were -289.1 ml and 229.3 ml. In conclusion, the CO method can be applied easily under general anaesthesia and controlled ventilation with a simple administration system. The agreement between the compared methods was satisfactory. Plasma volume determined with the CO method is safe, accurate and has no signs of major side effects.

Temperature-related fluid extravasation during cardiopulmonary bypass: an analysis of filtration coefficients and transcapillary pressures

BACKGROUND

Cardiopulmonary bypass (CPB) as used for cardiac surgery and for rewarming individuals suffering deep accidental hypothermia is held responsible for changes in microvascular fluid exchange often leading to edema and organ dysfunction. The purpose of this work is to improve our understanding of fluid pathophysiology and to explore the implications of the changes in determinants of transcapillary fluid exchange during CPB with and without hypothermia. This investigation might give indications on where to focus attention to reduce fluid extravasation during CPB.

METHODS

Published data on "Starling variables" as well as reported changes in fluid extravasation, tissue fluid contents and lymph flow were analyzed together with assumed/estimated values for variables not measured. The analysis was based on the Starling hypothesis where the transcapillary fluid filtration rate is given by: JV=Kf [Pc-Pi-sigma(COPp-COPi)]. Here Kf is the capillary filtration coefficient, sigma the reflection coefficient, P and COP are hydrostatic and colloid osmotic pressures, and subscript 'c' refers to capillary, 'i' to the interstitium and 'p' to plasma.

RESULTS AND CONCLUSION

The analysis indicates that attempts to limit fluid extravasation during normothermic CPB should address primarily changes in Kf, while changes in both Kf and Pc must be considered during hypothermic CPB.

Studies on fluid extravasation related to induced hypothermia during cardiopulmonary bypass in piglets

BACKGROUND

Hypothermia, commonly used for organ protection during cardiopulmonary bypass (CPB), has been associated with changes in plasma volume, hemoconcentration and microvascular fluid shifts. Fluid pathophysiology secondary to hypothermia and the mechanisms behind these changes are still largely unknown. In a recent study we found increased fluid needs during hypothermic compared to normothermic CPB. The aim of the present study was to characterize the distribution of the fluid given to maintain normovolemia. In addition, we wanted to investigate the quantity and quality of the fluid extravasated during hypothermic compared to normothermic CPB.

METHODS

Two groups of anesthetized piglets were studied during 2 h of hypothermic (28 degrees C) (n=7) or normothermic (38 degrees C) (n=7) CPB. Net fluid balance (input-output) was recorded. Changes in colloid osmotic pressures of plasma (COPp) and interstitial fluid (COPi), plasma volume (PV), hemoglobin (Hb), hematocrit (HCT), mean corpuscular volume (MCV), s-osmolality, s-albumin and s-total protein was followed throughout the experiments. Fluid extravasation rate was calculated. In addition, total tissue water content was measured and compared with a control group (n=6) (no CPB).

RESULTS

During hypothermic compared with normothermic CPB, the average net positive fluid balance from 10-120 min of extracorporeal circulation was 1.35+/-0.06 ml x kg(-1) x min(-1) and 0.33+/-0.03 ml x kg(-1) x min(-1) respectively (P<0.0001). We found a marked increase in fluid extravasation during hypothermic CPB. The extravasation rate during hypothermia was 1.8+/-0.2 ml x kg(-1) x min(-1), (1st hour) and 1.1+/-0.2 ml x kg(-1) x min(-1) (2nd hour) compared with 0.8+/-0.2 ml x kg(-1) x min(-1), and 0.1+/-(0.1) ml x kg(-1) x min(-1) during normothermia, respectively (P<0.01). The total intravascular protein and albumin masses remained constant in both groups. Following hypothermic CPB, the water content increased significantly in all tissues and organs.

CONCLUSION

During hypothermic CPB an increased extravasation of fluid from the intravascular to the interstitial space was found. As no leakage of proteins could be demonstrated, based on stable values for albumin and protein masses throughout the experiments, the extravasated fluid contained mainly water and small solutes.

Dynamic evaluation of fluid shifts during normothermic and hypothermic cardiopulmonary bypass in piglets

BACKGROUND

Edema, generalized overhydration and organ dysfunction commonly occur in patients undergoing open-heart surgery using cardiopulmonary bypass (CPB) and induced hypothermia. Activation of inflammatory reactions induced by contact between blood and foreign surfaces are commonly held responsible for the disturbances of fluid balance ("capillary leak syndrome"). We used an online technique to determine fluid shifts between the intravascular and the interstitial space during normothermic and hypothermic CPB.

METHODS

Piglets were placed on CPB (fixed pump flow) via thoracotomy in general anesthesia. In the normothermic group (n=7), the core temperature was kept at 38 degrees C prior to and during 2 h on CPB, whereas in the hypothermic group (n=7) temperature was lowered to 28 degrees C during bypass. The CPB circuit was primed with acetated Ringer's solution. The blood level in the CPB circuit reservoir was held constant during bypass. Ringer's solution was added when fluid substitution was needed (falling blood level in the reservoir). In addition to invasive hemodynamic monitoring, fluid input and losses were accurately recorded. Inflammatory mediators or markers were not measured in this study.

RESULTS

Cardiac output, s-electrolytes and arterial blood gases were similar in the two groups in the pre-bypass period. At start of CPB the blood level in the machine reservoir fell markedly in both groups, necessitating fluid supplementation and leading to a markedly reduced hematocrit. This extra fluid need was transient in the normothermic group, but persisted in the hypothermic animals. After 2 h of CPB the hypothermic animals had received 7 times more fluid as compared to the normothermic pigs.

CONCLUSION

We found strong indications for a greater fluid extravasation during hypothermic CPB compared with normothermic CPB. The experimental model using the CPB-circuit reservoir as a fluid gauge gives us the opportunity to study further fluid volume shifts, its causes and potential ways to optimize fluid therapy protocols.

Sampling of interstitial fluid and measurement of colloid osmotic pressure (COPi) in pigs: evaluation of the wick method

The wick method for sampling of interstitial fluid from subcutis was applied in fluid balance studies in young pigs. Colloid osmotic pressure was measured in serum (COPs) and interstitial fluid (COPi) using a membrane colloid osmometer. Our aims were to determine the 'true' COPi, and to find the optimal duration of wick implantation. In series I (n = 6) a 'crossover' experiment was performed using wicks soaked in different priming solutions (non-diluted and diluted serum protein solutions or isotonic salt solution). Circulatory arrest was induced just before wick insertion in order to eliminate the vascular part of the acute inflammation. In series II (n = 6) wicks were removed in sequence after 60, 90, 120 and 180 min sampling time in anaesthetized pigs in vivo. COPs, COPi and haematocrit (HCT) together with haemoglobin (Hgb), serum albumin and total protein concentrations were determined in the same animals. In series I average COPs and COPi were 13.7 (1.4) and 7.2 (1.4) mmHg respectively (SD). In series II the optimal wick implantation times were estimated to be 60-90 min for wicks soaked in diluted protein solution, and 90-120 min for dry and saline-soaked wicks. COPs averaged 13.0 (0.7) mmHg, HCT 30.0 (1.6)%, Hgb 8.3 (0.9) g/dl, s-albumin 22.7 (0.6) g/l and s-protein 47.3 (2.3) g/l. Compared to commonly reported reference values, we found surprisingly low values for most of the measured variables. This may be related to the fact that we used immature pigs. An analysis of the validity of the wick method based on our own results and published reports is presented. We conclude that sampling of interstitial fluid with subcutaneous wicks is easy to perform in young pigs. However, the COP-values measured in wick fluid have to be carefully evaluated especially when sampling is performed in vivo.

Midazolam-fentanyl-isoflurane anaesthesia is suitable for haemodynamic and fluid balance studies in pigs

The domestic pig is a useful model in certain areas of biomedical research. Effective use of this species is often encumbered by lack of reference values in conscious as well as anaesthetized animals. Anaesthesia itself influences physiological and biological variables; the anaesthetic technique often affects experimental results. The relationship between anaesthesia and haemodynamics is well characterized in man, but less established in pigs. We studied the effect of midazolam-fentanyl-isoflurane anaesthesia in six immature, male, domestic pigs (Norwegian landrace). Haemodynamic variables (heart rate, arterial systolic, mean, diastolic pressures, pulmonary systolic, mean, diastolic pressures, pulmonary capillary wedge pressure), tissue perfusion, lymph flow (thoracic duct) were recorded for 3 h in animals with open chest through midline sternotomy. Variables relevant to fluid balance, e.g. interstitial hydrostatic pressure (Pi), serum-colloid osmotic pressure (s-COP) and serum-albumin (s-albumin) and -protein (s-protein) concentrations were measured. With the chosen anaesthetic technique haemodynamic variables, including lymph flow, and laboratory variables remained constant during the study period. Most variables were similar to conditions in humans. In contrast to adult humans exposed to the same anaesthetic technique, these pigs had lower haemoglobin-, s-albumin- and s-protein concentrations. A finding which may reflect immaturity. Liver and lung perfusion decreased significantly during the study period whereas perfusion of the other organs studied remained constant. Lack of responses to defined noxious stimuli during the study period suggest adequate analgesia. We conclude that midazolam, fentanyl and isoflurane provide cardiovascular stability including normal microvascular fluid exchange, which are essential elements for securing the quality of results obtained during cardiovascular research in anaesthetized pigs.