Prehospital Invasive Ventilation: A Scoping Review

1. Introduction

Evidence regarding management of critically ill patients undergoing invasive ventilation in the prehospital setting remains scarce. Practices vary widely due to differences in provider training, protocols, and equipment availability [1]. However, invasive mechanical ventilation (transport ventilator) offers multiple theoretical advantages over manual invasive ventilation (bag-valve with invasive airway) including consistent ventilation, reduced risk of barotrauma or inadequate tidal volume, and allowing the team to focus on other aspects of patient care [2]. The current literature focuses on airway management [3]. While no clear survival benefit has been demonstrated for advanced airway techniques compared with bag-valve-mask ventilation—and in some cases worse outcomes have been reported—these findings depend strongly on provider expertise and system factors [4,5,6]. However, prehospital invasive ventilation, regardless of modality, is a multifaceted intervention whose safety and effectiveness appear to depend more on provider expertise and ventilatory quality rather than the airway device itself [7]. Recent studies increasingly address ventilatory management and lung-protective strategies, but real-world implementation remains heterogeneous [8,9]. Likewise, the comparative effects of manual invasive ventilation versus mechanical invasive ventilation are still unclear and indications for starting prehospital invasive ventilation are poorly defined.

To our knowledge, no prior review has comprehensively mapped the evidence on prehospital invasive ventilation across ventilatory strategies. This scoping review therefore aimed to synthesize the available evidence, describe clinical contexts, and identify knowledge gaps. Given the heterogeneity of the literature and limited randomized evidence, a scoping approach was chosen

2. Materials and Methods

The current review is in line with the methodological guidance of the Joanna Briggs Institute and the guidelines established as the Preferred Reporting Items for Systemic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) [10,11]. No protocol was registered for this review.

This scoping review aimed to provide a literature overview on prehospital invasive ventilation in adults with a focus on clinical outcomes and population specific differences. We used the Population, Concept, Context (PCC) framework as a guiding structure. The PCC identified:

Population

Adult patients (18 years or older) undergoing prehospital invasive ventilation.

Concept

The use of invasive ventilation procedures, regardless of the airway device.

Context

Prehospital settings such as Emergency Medical Services (EMS), mobile emergency teams, Helicopter Emergency Medical Services (HEMS), interfacility transports

Research Questions

• How is prehospital invasive ventilation applied across different patient populations and clinical contexts, and which outcomes are reported?
• What evidence exists regarding the use of mechanical versus manual invasive ventilation in prehospital care?
• What ventilation modalities, targets, and monitoring strategies are described in the prehospital setting?

Search Strategy

A systematic search was conducted in the databases of MEDLINE (via. PubMed), EMBASE and The Cochrane Library in July 2025. Both free-text terms and controlled vocabulary (MeSH and EMTREE) were used. The full search strategy for each database is included in Appendix A.

Inclusion and Exclusion Criteria

Publications were included if they studied prehospital invasive ventilation in adults (≥18 years) evaluating clinical outcomes or specific patient populations. Any controlled clinical study design or observational study was included. Publications were excluded if they studied non-invasive ventilation, pediatric patients (<18 years) or non-prehospital settings (e.g., hospital-based care). Opinion articles, reviews, comments, and editorials were excluded. Publications written in languages other than English were also excluded.

Selection Process

Two independent reviewers (LC and KT) screened titles and abstracts independently based on the inclusion and exclusion criteria. Full-text studies were assessed, and in case of doubt, consensus was sought or a third reviewer (MS) consulted. Rayyan (Rayyan Systems Inc., Cambridge, MA, USA) was used for study selection and Mendeley (Elsevier, Amsterdam, The Netherlands) was used as a reference manager.

Data Charting and Synthesis

Data were charted by two independent reviewers (LC and KT) using a spreadsheet. Charted data included: bibliographic information (first author; year), study characteristics (country of origin; study design; EMS system type), population characteristics (demographics; underlying pathology), intervention details (type of invasive ventilation; technique; comparators, if applicable), and key findings relevant to the research by questions. Disagreements between reviewers were resolved by consensus consulting a third reviewer (MS). Results were summarized in tables and analyzed narratively. No formal critical appraisal of included studies was performed, as the aim of this scoping review was to map the available evidence rather than assess methodological quality

3. Results

Literature Search

The search strategy identified 3461 citations, of which 532 were duplicates. After title and abstract screening, full texts were assessed according to the prespecified inclusion and exclusion criteria.

Using these criteria a total of 25 articles were included (Figure 1).

Characteristics of included studies

There were nine articles which evaluated the use of prehospital invasive ventilation in the setting of out-of-hospital cardiac arrest (OHCA), ten in trauma, one in sepsis and five in mixed pathologies. The characteristics and key findings of these studies are demonstrated in Table 1.

Table 1. Characteristics of included studies.

Out-of-hospital cardiac arrest (OHCA)

First author (year)	Design	Sample size	Setting	Ventilation focus / comparison	Key findings
Benoit (2023)	Retrospective cohort	314	EMS	Capnography derived ventilation rate	Median rate often outside 8–10/min target, only 22% compliant with guidelines; no independent association with ROSC ; poor reliability of measurement through capnography
Drennan (2024)	Before–after	412	EMS	Real-time ventilation feedback	Significant improvement in compliance with target rate and volume; no clear survival effect
Hernández-Tejedor (2023)	Quasi-experimental	150	EMS	Mechanical IPPV vs bag ventilation	Mechanical ventilation improved pCO₂ and pH; no significant neurological survival difference: 15.6% versus 11.3% (p = 0.44%)
Hernández-Tejedor (2025)	Quasi-experimental	521	EMS	CCSV vs IPPV vs bag ventilation	Potential benefit of mechanical ventilation over bag ventilation; no clear superior ventilation mode
Kuisma (2006)	RCT	28	EMS	FiO₂ 30% vs 100% post ROSC	No significant difference in survival (p=0.5134) ; FiO₂ escalation required in 36% of patients
Langhelle (2000)	RCT	17	EMS	500 vs 1000 mL tidal volume during CPR	Higher tidal volume improved CO₂ clearance but did not improve survival
Maertens (2013)	Prospective cohort	98	EMS	Ventilation rate during CPR	Frequent deviation from recommended ventilation rates; 90% in manually ventilated and 92% in mechanical ventilation; hyperventilation common with median rate 20/min
Prause (2023)	RCT	46	EMS	Ventilation rate of 10/min vs 20/min during CPR	No significant difference in survival, median pH or median pC02
Snyder (2023)	Retrospective cohort	1994	EMS	Small vs standard adult BVM	Smaller bags associated with lower ROSC rates; OR 0.74, 95% [CI 0.61 – 0.91]

Trauma

First author (year)	Design	Sample size	Population	Setting	Ventilation focus / comparison	Key findings
McLachlan (2019)	Prospective cohort	20	Major trauma	HEMS	Effectiveness of manual ventilation	Adequate oxygenation in 83.6%, correct ETCO2 in 48.7%
Helm (2003)	RCT	97	Major trauma	HEMS	Capnography-guided vs blind ventilation	Higher incidence of normoventilation with use of ETCO2 monitoring
Warner (2007)	Prospective cohort	492	TBI	EMS + HEMS	Association of normocapnia with mortality	Normocapnia associated with lower mortality (adjusted OR 0.57)
Helm (2002)	Prospective observational	122	TBI	EMS	Quality of prehospital ventilation	Optimal oxygenation achieved in 85.2%, adequate ventilation in 42.6%
Curry (2020)	Retrospective cohort	93	TBI	HEMS	Incidence of eucapnia between manual and mechanical ventilation	Eucapnia in 36% of patients, no difference ventilation types
Davis (2005)	Prospective observational	76	TBI	EMS	Ventilation patterns after paramedic RSI	Inadvertent hyperventilation is common, despite ETCO2 monitoring
Knapp (2023)	Retrospective cohort	308	TBI	HEMS	Adherence to ventilation and SBP targets	45% had PetCO2 in the normal range, only 33% were normocapnic
Bossers (2023)	Prospective observational	1776	TBI	HEMS	Association between prehospital ETCO₂ and 30-day mortality	Increased mortality with ETCO₂ <35 mmHg. No significant association between hypercapnia (≥45 mmHg) and mortality
Herff (2023)	Retrospective cohort	296	Major trauma	HEMS	No/low vs moderate PEEP; association with SBP	No significant correlation between PEEP and mean difference of SBP
Maddry (2018)	Retrospective cohor	650	Major trauma	Air transport	Compliance to ARDSnet protocol	ARDSNet compliance associated with fewer ventilator days and ICU days, lower incidence of ARDS, and lower 30-day mortality

Sepsis

First author (year)	Design	Sample size	Setting	Ventilation focus / comparison	Key findings
Jouffroy (2019)	Retrospective cohort	59	EMS	Association between VTIBW and 28-day mortality	VTIBW <8 mL/kg associated with lower 28-day mortality

Mixed pathologies

First author (year)	Design	Sample size	Setting	Ventilation focus / comparison	Key findings
Moy (2022)	Retrospective cohort	68365	HEMS	Ventilation practices	Majority of subjects had TV set empirically without calculating VTIBW, unclear usage of LPV
Johannigman (1995)	Prospective cohort	160	Transport	Bag vs transport ventilator	No significant difference in arrival ABGs between methods
Singh (2009)	Retrospective cohort	1735	Critical care transport	Ventilation practices	Marked heterogeneity in ventilator settings, 35% of patients at risk ventilated with LPV
Stoltze (2015)	Retrospective cohort	235	HEMS	Influence of prehospital ventilation on inhospital ventilation and ARDS	Prehospital settings influenced ICU settings ; no association with ARDS incidence: P = 0.840
Yang (2022)	Prospective cohort	54	EMS	Respiratory mechanics during manual ventilation	Ventilation 75% within lung-protective range. Most variation in VT and peak pressure during active resuscitation

Studies are grouped according to the primary clinical context in which prehospital invasive ventilation was evaluated. Key outcomes are reported descriptively as presented in the original publications; no quantitative synthesis was performed given the heterogeneity of study designs, populations, ventilation strategies, and outcome definitions. ABG, arterial blood gas; ARDS, acute respiratory distress syndrome; BVM, bag-valve mask; CCSV, chest compression synchronized ventilation; EMS, emergency medical services; ETCO₂, end-tidal carbon dioxide; FiO₂, fraction of inspired oxygen; HEMS, helicopter emergency medical services; IPPV, intermittent positive-pressure ventilation; LPV, lung-protective ventilation; MICU, mobile intensive care unit; MV, mechanical ventilation; OHCA, out-of-hospital cardiac arrest; PBW, predicted body weight; PEEP, positive end-expiratory pressure; PetCO2, end-tidal partial pressure of CO2; ROSC, return of spontaneous circulation; RSI, rapid sequence intubation; TBI, traumatic brain injury; VT, tidal volume; VTIBW, tidal volume indexed to ideal body weight.

Due to the diverse settings and high variability in interventions and outcomes within the selected studies, the results were grouped to the specific pathologies and their key findings.

Out-of-hospital cardiac arrest

Nine studies evaluated invasive ventilation strategies during OHCA.

Ventilation rates

Across studies assessing ventilation rate, compliance with guideline-recommended ventilation rates was low, with most patients ventilated outside target ranges (8-22%). Studies using capnography or device-based measurements demonstrated frequent hyperventilation during resuscitation. Although real-time feedback improved adherence to predefined ventilation targets, no consistent association between ventilation rate and ROSC or survival was demonstrated [12,13,14,15].

Ventilation volumes

In a retrospective observational study, use of smaller adult ventilation bags was associated with lower odds of ROSC (OR 0.74, 95% CI 0.61 – 0.91) [16]. A randomized trial comparing higher versus lower tidal volumes during CPR did demonstrate a higher PaC02 and lower pH with comparing a tidal volume of 500 vs 1000ml; 7.48 kPa (SD 5.25-9.71) versus 3.70 kPa (SD 2.83-4.53) (P=0.002) at 5 minutes post mechanical ventilation and 7.45 kPa (SD 6.26-8.64) versus 3.98 kPa (SD 2.4-5.56) (P0.001) at 10-15 minutes post start of mechanical ventilation. The pH was significantly lower for 500 than 1000 ml at 10–15 min, 7.01 (SD 6.91-7.11) versus 7.20 (SD 7.03-7.37) (P=0.034) [17]. Another study showed that real-time feedback facilitated delivery of target tidal volumes of 6-8ml/kg [15].

Inspired oxygen fraction

One randomized study compared lower versus higher inspired oxygen fractions during OHCA and found no significant difference in clinical outcomes (p=0.5134). In a substantial proportion (36%) of patients initially allocated to lower FiO₂, escalation was required due to hypoxemia [18].

Manual versus mechanical ventilation:

Two papers of the same author were included, which were two phases of the same study [19].

The first paper solely compared IPPV vs bag-valve ventilation while the second added CSSV (Chest Compression Synchronized Ventilation) as a comparator. The data from the first phase was also utilized in the analysis of the second phase.

In phase 1, intermittent positive-pressure ventilation (IPPV) via a mechanical ventilator resulted in significantly improved blood gas parameters compared with bag ventilation, without a statistically significant difference in neurological survival; 15.6% versus 11.3% (p = 0.44%) [20]. Phase 2 introduced chest compression synchronized ventilation (CCSV) and reported differences in physiological and clinical outcomes between ventilation strategies; mechanical ventilation was associated with significantly more ROSC (58.8% versus 49.3% with p = 0.03) and survival (17.0% vs 10.9% with p = 0.03). In shockable rhythms, there was a strong association toward CPC 1 -2 in the mechanical ventilation group than in the manual ventilation group (34.1% versus 20.5% with p = 0.05) [19].

Trauma

Ten studies evaluated prehospital invasive ventilation in trauma patients, including cohorts with severe traumatic brain injury (TBI) and major trauma.

Ventilation patterns

Observational studies reported wide variability in ventilation quality during transport, with normocapnia achieved in only 33–49% of patients on hospital arrival [21,22,23,24]. Most studies found hypocapnia to be the most common, only one study reported the majority of patients (60.2%) to be hypercapnic on hospital admission [23]. In severe TBI, inadvertent hyperventilation remained common even when ETCO₂ monitoring and target ranges were used [25].

Incidence of optimal oxygenation

Two observational studies reported similar incidence of what was defined as optimal oxygenation upon hospital arrival in intubated trauma patients [21,22]. In the prospective HEMS cohort by McLachlan et al., 83.6% of cumulative transport time was reported as spent with adequate oxygen saturations, based on continuous pulse oximetry recordings during manual ventilation [21]. The study does not further specify the exact oxygen saturation threshold used to define adequacy in the published manuscript. In contrast, Helm et al. defined optimal oxygenation as a PaO₂ > 100 mmHg measured on arterial blood gas analysis immediately upon hospital arrival, reporting that this target was achieved in 85.2% of patients with severe head injury [22].

Although both studies report a similarly high proportion of patients meeting their respective oxygenation targets, the definitions and measurement modalities differed substantially, limiting direct comparability between cohorts.

Ventilation targets and mortality

Several studies on major trauma patients demonstrated an association between normocapnia or targeted ventilation and improved survival. In severe TBI cohorts, PaCO₂ on hospital arrival within recommended ranges was associated with lower mortality compared with hypo- or hypercapnia: reported OR of 0.57; ( 95% CI, 0.33-0.99); in another cohort mortality was associated with hypocapnia with OR of 1.89 (95% CI 1.53–2.34) [26,27]. Non-compliance with lung-protective ventilation strategies in major trauma was also associated with worse 30 day mortality in selected cohorts: OR 2.75 (1.17-7.54) [28].

Manual versus mechanical ventilation

Evidence comparing manual and mechanical ventilation in trauma patients was limited. In one HEMS cohort, no significant difference was observed between manual and mechanical ventilation in achieving normocapnia, which was attained in, respectively, 36% and 35% of patients (p = 1.00) [23]. However, interpretation of these findings is constrained by limited data availability due to short transport durations. Furthermore, all patients in whom mechanical ventilation was initiated underwent an initial period of manual ventilation, introducing potential confounding and limiting the ability to isolate the independent effect of ventilation mode.

Capnography-guided ventilation

One randomized controlled trial compared capnography-guided ventilation with ventilation based on estimated weight and age without capnographic monitoring [29]. The study reported a higher proportion of patients at hospital arrival within the normoventilation range (63.2% vs 20% with p<0.0001) and a lower proportion of hypoventilated patients (5.3% vs 37.5% with p<0.0001) in the capnography group.

PEEP and hemodynamics

One retrospective cohort study evaluated the association between prehospital PEEP levels and systolic arterial blood pressure in mechanically ventilated major trauma patients [30]. No significant correlation was found between the mean difference in systolic blood pressure from scene to hospital admission in patients ventilated with low or no PEEP (0-3 cmH₂O) versus moderate PEEP (4–10 cmH₂O) with P = 0.17. In the overall cohort, systolic blood pressure improved modestly in both groups during transport, without significant intergroup differences. However, the observational design precludes causal inference. The observed association may therefore reflect differences in overall resuscitation strategies rather than an independent effect of PEEP level.

Sepsis

One retrospective cohort study evaluated prehospital invasive mechanical ventilation in patients with septic shock [31]. After multivariable adjustment, a tidal volume indexed to ideal body weight (VTIBW) <8 mL/kg was independently associated with lower 28-day mortality (OR adjusted = 0.12 [0.03-0.43]), while VTIBW >8mL/kg was significantly associated with higher mortality (OR adjusted = 8.29 [2.35-34.98]).

Unspecified or mixed pathology

Five studies included heterogeneous adult populations or did not restrict inclusion to a single pathology.

Ventilation practices in HEMS

One retrospective trial reported that lung-protective ventilation was infrequently applied during air medical transport i.e. thirteen percent (13%) of included patients, and that prehospital tidal volume selection influenced subsequent emergency department and ICU ventilator settings. However, there was no clear association of pre-hospital tidal volumes with ARDS incidence with P = 0.840 [32].

Another retrospective trial looked solely at the existing practices of HEMS. It found that tidal volumes were set empirically in the overwhelming majority. Only a small subset (6.1%) of patients had a measured height and thus could have a set tidal volume indexed to predicted body weight [33].

Ventilation practices in EMS

One retrospective observational trial found that the majority (92%) of patients were ventilated with peak pressures of ≤35cmH20 and 22% with PEEP <5cmH20. In the subgroup of patients at risk for acute lung injury, 35% was ventilated according to the arbitrary protective ventilation defined as: PEEP ≥ 5 cmH2O, PIP ≤ 35 cmH2O and Vt ≤ 6.5 mL/kg actual body weight (ABW) [34].

One prospective observational trial evaluated the tidal volumes post intubation per breath and found a mean tidal volume per predicted body weight (PBW) of 7.0ml/kg. Moreover, 75% of breaths were within the 4-10ml/kg PBW range [9]. Both studies had limited reporting of patient-centered outcomes [9,34].

Impact of ventilation on blood gasses

One prospective cohort compared manual bag ventilation with mechanical ventilation in a mixed cohort during interhospital transports and found similar arterial blood gas values on arrival, though interpretation is limited by older technology and practice patterns, as the study was published in 1995 [35].

4. Discussion

This scoping review mapped the breadth of evidence regarding prehospital invasive ventilation in adults and identified substantial heterogeneity in ventilation practices, monitoring strategies, and reported outcomes across clinical contexts.

Interpretation of results

First, ventilation quality during prehospital care is frequently suboptimal, particularly during OHCA and severe trauma. Across multiple cohorts, both hyperventilation and failure to achieve lung-protective tidal volumes were common. Despite widespread recognition of the importance of controlled ventilation, consistent delivery of guideline-concordant ventilation remains challenging in the prehospital environment.

However, our results found no significant improvement in outcomes when ventilation rates were improved to meet the guidelines. This may suggest that the ideal ventilation rate may be different from the ones that are currently proposed in the guidelines.

Second, mechanical ventilation was generally associated with improved physiological control (e.g., pCO₂ and pH) compared with manual bag ventilation. However, the available evidence does not demonstrate a consistent improvement in patient-centered outcomes such as survival or neurological recovery. Most comparative studies were observational or quasi-experimental and therefore subject to confounding by selection bias, transport time, and provider expertise.

Third, observational trauma and septic shock studies suggest that achieving normocapnia and lung-protective tidal volumes may be associated with improved outcomes. These findings are biologically plausible and consistent with in-hospital ventilation literature but remain insufficient to establish causality in the prehospital setting.

Clinical implications

Taken together, the findings suggest that ventilation quality rather than ventilation modality alone may be the key determinant of outcome. Technologies that improve monitoring and feedback—such as continuous capnography and real-time ventilation feedback—consistently improved adherence to target parameters and may represent actionable system-level interventions, but the optimal ventilation strategy may yet have to be determined.

Research implications

This review highlights several important knowledge gaps:

• Few randomized studies comparing manual versus mechanical invasive ventilation
• Inconsistent definitions of adequate ventilation
• Limited reporting of PBW-indexed tidal volumes
• Strong confounding in observational trauma and OHCA cohorts

Future research should prioritize pragmatic, randomized, or well-controlled prospective studies focusing on patient-centered outcomes and standardized ventilation reporting.

Strengths and limitations

A major strength of this review is the comprehensive mapping of invasive ventilation practices across multiple prehospital systems and pathologies. The scoping methodology allowed inclusion of heterogeneous study designs reflective of real-world practice.

Limitations include reliance on predominantly observational data, heterogeneity in outcome definitions, and potential publication bias. No formal quality appraisal was conducted, which limits interpretation of the strength of evidence. Additionally, the inability to perform quantitative synthesis limits causal inference.

5. Conclusions

Prehospital invasive ventilation in adult patients is characterized by substantial heterogeneity in indications, techniques, and monitoring practices. Across OHCA and trauma populations, ventilation outside recommended targets is common, and while mechanical ventilation may improve physiological control, consistent benefits in patient-centered outcomes have not been demonstrated. Current evidence suggests that ventilation quality and monitoring may be more important than ventilation modality alone.