Cardiovascular complications of prehospital emergency anaesthesia in patients with return of spontaneous circulation following medical cardiac arrest: a retrospective comparison of ketamine-based and midazolam-based induction protocols

BackgroundHypotension following intubation and return of spontaneous circulation (ROSC) after cardiac arrest is associated with poorer patient outcomes. In patients with a sustained ROSC requiring emergency anaesthesia, there is limited evidence to guide anaesthetic practice. At the Essex & Herts Air Ambulance Trust, a UK-based helicopter emergency medical service, we assessed the relative haemodynamic stability of two different induction agents for post-cardiac arrest medical patients requiring prehospital emergency anaesthesia (PHEA).MethodsWe performed a retrospective database review over a 5-year period between December 2014 and December 2019 comparing ketamine-based and midazolam-based anaesthesia in this patient cohort. Our primary outcome was clinically significant hypotension within 30 min of PHEA, defined as a new systolic BP less than 90 mm Hg, or a 10% drop if less than 90 mm Hg before induction.ResultsOne hundred ninety-eight patients met inclusion criteria. Forty-eight patients received a ketamine-based induction, median dose (IQR) 1.00 (1.00–1.55) mg/kg, and a 150 midazolam-based regime, median dose 0.03 (0.02–0.04) mg/kg. Hypotension occurred in 54.2% of the ketamine group and 50.7% of the midazolam group (p=0.673). Mean maximal HRs within 30 min of PHEA were 119 beats/min and 122 beats/min, respectively (p=0.523). A shock index greater than 1.0 beats/min/mm Hg and age greater than 70 years were both associated with post-PHEA hypotension with ORs 1.96 (CI 1.02 to 3.71) and 1.99 (CI 1.01 to 3.90), respectively. Adverse event rates did not significantly differ between groups.ConclusionPHEA following a medical cardiac arrest is associated with potentially significant cardiovascular derangements when measured up to 30 min after induction of anaesthesia. There was no demonstrable difference in post-induction hypotension between ketamine-based and midazolam-based PHEA. Choice of induction agent alone is insufficient to mitigate haemodynamic disturbance, and alternative strategies should be used to address this.

Large variations of oxygen delivery in self-inflating resuscitation bags used for preoxygenation - a mechanical simulation

Background Self-Inflating Resuscitation Bags (SIRB) are common and essential tools in airway management and ventilation. They are often used in resuscitation and emergency anaesthesia outside the operating theatre. There is a common notion that all SIRBs applied with a tight sealed mask will deliver close to 100 % oxygen during spontaneous breathing. The aim of the study was to measure the oxygen delivery of six commonly used SIRBs in a mechanical spontaneous breathing adult in vitro model. Methods Three SIRBs of each of the six models were evaluated for oxygen delivery during simulated breathing with an adult mechanical lung. The test was repeated three times per device (54 tests in total). The breathing profile was fixed to a minute volume of 10 L/min, a tidal volume of 500 mL and the SIRBs supplied with an oxygen fresh gas flow of 15 L/min. The fraction of delivered oxygen (FDO2) was measured over a three-minute period. Average FDO2 was calculated and compared at 30, 60 and 90 s. Results At 90 s all models had reached a stable FDO2. Average FDO2 at 90 s; Ambu Oval Plus 99,5 %; Ambu Spur II 99,8 %; Intersurgical BVM Resuscitator 76,7 %; Laerdal Silicone 97,3 %; Laerdal The Bag II 94,5 % and the O-Two Smart Bag 39,0 %. All differences in FDO2 were significant apart from the two Ambu models. Conclusions In simulated spontaneous breathing, four out of six (by Ambu and Laerdal) Self-Inflating Resuscitation Bags delivered a high fraction of oxygen while two (Intersurgical and O-two) underperformed in oxygen delivery. These large variations confirm results reported in other studies. It is our opinion that underperforming Self-Inflating Resuscitation Bags might pose a serious threat to patients’ health if used in resuscitation and anaesthesia. Manufacturers of Self-Inflating Resuscitation Bags rarely provide information on performance for spontaneous breathing. This poses a challenge to all organizations that need their devices to deliver adequate oxygen during spontaneous breathing.

Apnoeic oxygenation for emergency anaesthesia of pre-hospital trauma patients

Background Efficient and timely airway management is universally recognised as a priority for major trauma patients, a proportion of whom require emergency intubation in the pre-hospital setting. Adverse events occur more commonly in emergency airway management, and hypoxia is relatively frequent. The aim of this study was to establish whether passive apnoeic oxygenation was effective in reducing the incidence of desaturation during pre-hospital emergency anaesthesia. Methods A prospective before-after study was performed to compare patients receiving standard care and those receiving additional oxygen via nasal prongs. The primary endpoint was median oxygen saturation in the peri-rapid sequence induction period, (2 minutes pre-intubation to 2 minutes post-intubation) for all patients. Secondary endpoints included the incidence of hypoxia in predetermined subgroups. Results Of 725 patients included; 188 patients received standard treatment and 537 received the intervention. The overall incidence of hypoxia (first recorded SpO2 < 90%) was 16.7%; 10.9% had SpO2 < 85%. 98/725 patients (13.5%) were hypoxic post-intubation (final SpO2 < 90% 10 minutes post-intubation). Median SpO2 was 100% vs. 99% for the standard vs. intervention group. There was a statistically significant benefit from apnoeic oxygenation in reducing the frequency of peri-intubation hypoxia (SpO2 < =90%) for patients with initial SpO2 > 95%, p = 0.0001. The other significant benefit was observed in the recovery phase for patients with severe hypoxia prior to intubation. Conclusion Apnoeic oxygenation did not influence peri-intubation oxygen saturations, but it did reduce the frequency and duration of hypoxia in the post-intubation period. Given that apnoeic oxygenation is a simple low-cost intervention with a low complication rate, and that hypoxia can be detrimental to outcome, application of nasal cannulas during the drug-induced phase of emergency intubation may benefit a subset of patients undergoing emergency anaesthesia.

217 The end-tidal and arterial carbon dioxide gradient in serious traumatic brain injury after pre-hospital emergency anaesthesia: a retrospective observational study

Aims/Objectives/BackgroundIn the United Kingdom (UK), 20% of patients with severe traumatic brain injury (TBI) receive pre-hospital emergency anaesthesia (PHEA). Current guidance recommends an end-tidal carbon dioxide (ETCO2) of 4.0–4.5kPa to achieve a low-normal arterial partial pressure of CO2 (PaCO2), and reduce secondary brain injury. This recommendation assumes a 0.5kPa ETCO2-PaCO2 gradient. However, the gradient in the acute phase of TBI is unknown. Our primary aim was to report the ETCO2-PaCO2 gradient of TBI patients at hospital arrival.Methods/DesignA retrospective cohort study of adult patients with serious TBI, who received a PHEA by a pre-hospital critical care team in the East of England between 1st April 2015 to 31st December 2017. Linear regression was performed to test for correlation and reported as R-squared (R2). A Bland-Altman plot was used to test for paired ETCO2 and PaCO2 agreement and reported with 95% confidence intervals (95%CI). ETCO2-PaCO2 gradient data were compared with a two-tailed, unpaired, t-test.Results/Conclusions107 patients were eligible for inclusion. Sixty-seven patients did not receive a PaCO2 sample within 30 minutes of hospital arrival and were therefore excluded. Forty patients had complete data and were included in the final analysis; per protocol.The mean ETCO2-PaCO2 gradient was 1.7 (±1.0) kPa, with only moderate correlation of ETCO2 and PaCO2 at hospital arrival (R2=0.23, p=0.002). The Bland-Altman bias was 1.7 (95%CI 1.4–2.0) kPa with upper and lower limits of agreement of 3.6 (95%CI 3.0–4.1) kPa and -0.2 (95%CI -0.8–0.3) kPa respectively. There was no significant gradient correlation in patients with a co-existing serious thoracic injury (R2=0.13, p=0.10), and this cohort had a larger ETCO2-PaCO2 gradient, 2.0 (±1.1) kPa, p=0.01. Patients who underwent pre-hospital arterial blood sampling had an arrival PaCO2 of 4.7 (±0.2) kPa.Lower ETCO2 targets than previously recommended may be safe and appropriate. The use of pre-hospital PaCO2 measurement is advocated.

Oxygenation strategies prior to and during prehospital emergency anaesthesia in UK HEMS practice (PREOXY survey)

Background Maintaining effective oxygenation throughout the process of Pre-Hospital Emergency Anaesthesia (PHEA) is critical. There are multiple strategies available to clinicians to oxygenate patients both prior to and during PHEA. The optimal pre-oxygenation technique remains unclear, and it is unknown what techniques are being used by United Kingdom Helicopter Emergency Medical Services (HEMS). This study aimed to determine the current pre- and peri-PHEA oxygenation strategies used by UK HEMS services. Methods An electronic questionnaire survey was delivered to all UK HEMS services between 05 July and 26 December 2019. Questions investigated service standard operating procedures (SOPs) and individual clinician practice regarding oxygenation strategies prior to airway instrumentation (pre-oxygenation) and oxygenation strategies during airway instrumentation (apnoeic oxygenation). Service SOPs were obtained to corroborate questionnaire replies. Results Replies were received from all UK HEMS services (n = 21) and 40 individual clinicians. All services specified oxygenation strategies within their PHEA/RSI SOP and most referred to pre-oxygenation as mandatory (81%), whilst apnoeic oxygenation was mandatory in eight (38%) SOPs. The most commonly identified pre-oxygenation strategies were bag-valve-mask without PEEP (95%), non-rebreathable face mask (81%), and nasal cannula at high flow (81%). Seven (33%) services used Mapleson C circuits, whilst there were eight services (38%) that did not carry bag-valve-masks with PEEP valve nor Mapleson C circuits. All clinicians frequently used pre-oxygenation, however there was variability in clinician use of apnoeic oxygenation by nasal cannula. Nearly all clinicians (95%) reported manually ventilating patients during the apnoeic phase, with over half (58%) stating this was their routine practice. Differences in clinician pre-hospital and in-hospital practice related to availability of humidified high flow nasal oxygenation and Mapleson C circuits. Conclusions Pre-oxygenation is universal amongst UK HEMS services and is most frequently delivered by bag-valve-mask without PEEP or non-rebreathable face masks, whereas apnoeic oxygenation by nasal cannula is highly variable. Multiple services carry Mapleson C circuits, however many services are unable to deliver PEEP due to the equipment they carry. Clinicians are regularly manually ventilating patients during the apnoeic phase of PHEA. The identified variability in clinical practice may indicate uncertainty and further research is warranted to assess the impact of different strategies on clinical outcomes.

End-tidal and arterial carbon dioxide gradient in serious traumatic brain injury after prehospital emergency anaesthesia: a retrospective observational study

ObjectivesIn the UK, 20% of patients with severe traumatic brain injury (TBI) receive prehospital emergency anaesthesia (PHEA). Current guidance recommends an end-tidal carbon dioxide (ETCO2) of 4.0–4.5 kPa (30.0–33.8 mm Hg) to achieve a low-normal arterial partial pressure of CO2 (PaCO2), and reduce secondary brain injury. This recommendation assumes a 0.5 kPa (3.8 mm Hg) ETCO2–PaCO2 gradient. However, the gradient in the acute phase of TBI is unknown. The primary aim was to report the ETCO2–PaCO2 gradient of TBI patients at hospital arrival.MethodsA retrospective cohort study of adult patients with serious TBI, who received a PHEA by a prehospital critical care team in the East of England between 1 April 2015 and 31 December 2017. Linear regression was performed to test for correlation and reported as R-squared (R2). A Bland-Altman plot was used to test for paired ETCO2 and PaCO2 agreement and reported with 95% CI. ETCO2–PaCO2 gradient data were compared with a two-tailed, unpaired, t-test.Results107 patients were eligible for inclusion. Sixty-seven patients did not receive a PaCO2 sample within 30 min of hospital arrival and were therefore excluded. Forty patients had complete data and were included in the final analysis; per protocol. The mean ETCO2–PaCO2 gradient was 1.7 (±1.0) kPa (12.8 mm Hg), with moderate correlation (R2=0.23, p=0.002). The Bland-Altman bias was 1.7 (95% CI 1.4 to 2.0) kPa with upper and lower limits of agreement of 3.6 (95% CI 3.0 to 4.1) kPa and −0.2 (95% CI −0.8 to 0.3) kPa, respectively. There was no evidence of a larger gradient in more severe TBI (p=0.29). There was no significant gradient correlation in patients with a coexisting serious thoracic injury (R2=0.13, p=0.10), and this cohort had a larger ETCO2–PaCO2 gradient, 2.0 (±1.1) kPa (15.1 mm Hg), p=0.01. Patients who underwent prehospital arterial blood sampling had an arrival PaCO2 of 4.7 (±0.2) kPa (35.1 mm Hg).ConclusionThere is only moderate correlation of ETCO2 and PaCO2 at hospital arrival in patients with serious TBI. The mean ETCO2–PaCO2 gradient was 1.7 (±1.0) kPa (12.8 mm Hg). Lower ETCO2 targets than previously recommended may be safe and appropriate, and there may be a role for prehospital PaCO2 measurement.

Pre-hospital emergency medicine

This chapter in the Oxford Handbook of Clinical Specialties explores the specialty of pre-hospital emergency medicine. It reviews pre-hospital emergency medicine in general, including activation of the emergency services and major trauma networks in the UK. It gives practical advice on assessment on arrival at the scene, hazards to consider, triage, and initial patient assessment before going into specifics including how to deal with shock, the entrapped patient, pre-hospital analgesia, splintage and manipulation, and injuries to the head, spine, and chest. It explores pre-hospital care of special interest groups and emergency anaesthesia, traumatic cardiac arrest, and how to approach a major incident. It investigates the importance of public health, and how to develop lasting resilience as a member of the pre-hospital emergency team.