Ventilation and Oxygenation Considerations During and After Cardiopulmonary Resuscitation

By J. Brady Scott, PhD, RRT, RRT-ACCS, AE-C, FAARC, FCCP

Associate Professor and Program Director, Respiratory Care Program, Department of Cardiopulmonary Sciences, Rush University Medical Center, Chicago

The incidence of in-hospital cardiac arrests tends to vary by country; in the United States, the number of hospital arrests has been reported to be as high as 9.7 per 1,000 hospital admissions.¹ When compared to other countries with available data, it seems that the incidence of in-hospital cardiac arrests in the United States is increasing. The cause for this increase is unknown, but it may be attributed to global cultural differences, infrastructure, and other factors.¹ Regardless of the cause of this increase, the reality is that clinicians caring for patients admitted to the hospital inevitably will encounter a cardiac arrest situation.

Given the inevitability of cardiac arrest situations, numerous clinical trials and guidelines have emerged to offer evidence and recommendations concerning cardiopulmonary resuscitation (CPR), with the aim of enhancing crucial patient outcomes such as survival.^2-6 With a multitude of recommendations spanning from monitoring during CPR to post-arrest targeted temperature management, the specific focus of this article is to review considerations related to ventilation and oxygenation during and after CPR.⁴

Ventilation and Oxygenation During CPR

Ventilation

Current recommendations for ventilation during CPR vary by organization and include providing tidal volumes of approximately 500 mL to 600 mL or enough to provide visible chest rise.^5,6 The goal is to ensure sufficient gas exchange while concurrently preventing elevations in mean intrathoracic pressure and subsequent decreases in venous return to the heart, cardiac output, coronary perfusion pressure, and aortic blood pressure.⁷ Currently, the best method for ventilating a patient during CPR remains unknown as the available data to inform recommendations are limited. Nonetheless, data suggest that clinicians often are unaware of the extent of ventilation they are delivering. It also is clear that hyperventilation during CPR can be harmful.

In 2004, Aufderheide et al published the results of a clinical observation study and an animal study aimed at quantifying excessive ventilation in humans and examining how ventilation rates affected coronary perfusion pressure and survival in pigs. In the human study, they observed an average of 30 ± 3.2 breaths/min in 13 consecutive adults receiving CPR. Interestingly, in six of the first seven patients, the ventilation rate was noted to be 37 ± 4 breaths/min, with a maximum of 49 breaths/min. Noting these high ventilation values, the study investigators retrained the rescuers to provide ventilation to deliver 12 breaths/min during CPR after the establishment of a secured airway, which was in agreement with the American Heart Association (AHA) recommendations at the time of 12-15 breaths/min.^8-10 After the retraining, three of six patients had ventilation rates of ≥ 26 breaths/min, with a maximum of 31 breaths/min.

In the pig study, the investigators randomized pigs to receive four minutes of CPR with one of three ventilation modes: 12 breaths/min with 100% oxygen (O₂); 30 breaths/min with 100% O₂; or 30 breaths/min with 5% carbon dioxide (CO₂) and 95% O₂. Aortic, right atrial, and intrathoracic pressures were recorded during CPR, along with end-tidal CO₂ and O₂ saturations. They noted that increased ventilation rate (30 breaths/min) was associated with significantly higher mean intrathoracic pressures (P < 0.001) and significantly lower coronary artery perfusion pressures (P < 0.03). Notably, the survival rates between the ventilation strategies were different. In the 12 breaths/min with 100% oxygen group, six of seven pigs survived, whereas only 1/7 survived in both the 30 breaths/min with 100% oxygen group and 30 breaths/min with 5% CO₂/95% O₂ group (P = 0.006).

In 2007, O’Neil and Deakin published the first report of actual tidal volumes delivered during CPR.¹¹ Among the 12 patients included in their study, the median tidal volume delivered was 619 mL (range: 374 mL to 923 mL) and the median respiratory rate was 21 (range: 7-37) breaths/min. They also reported median peak inspiratory pressures of 60.6 cm H₂O, noting that airway pressures were positive for 95.3% of the respiratory cycle. The authors concluded that hyperventilation was indeed common but appeared to be more related to respiratory rates rather than excessive tidal volumes. They also noted that while guidelines for respiratory rate were well known, they were not being clinically observed.¹¹

In a cross-sectional study evaluating the delivery of tidal volumes and respiratory rates during simulated resuscitation, Scott et al observed that male study participants administered higher tidal volumes compared to female participants (685 ± 134 mL vs. 587 ± 168 mL, P = 0.05, respectively) when they were unaware of the tidal volume measurements.¹² When allowed to visualize tidal volumes delivered, male participants delivered tidal volumes of 632 ± 105 mL compared to females who delivered 617 ± 153 mL, P = 0.732. Participants with medium-sized gloves delivered smaller tidal volumes than those with large-sized gloves (566 ± 181 mL vs. 728 ± 153 mL, P = 0.020), but did not differ from those with small-sized gloves (566 ± 181 mL vs. 618 ± 114 mL, P = 0.531). No difference was found between groups with large- and small-sized gloves (P = 0.179).

Given the current focus on tidal volume delivery based on predicted body weight, the study authors compared the delivered tidal volumes in the study to the size of the intubated adult male patient simulator (CAE HPS, CAE Healthcare, Sarasota, Florida, USA) with a height of 180 cm. According to the authors, an acceptable tidal volume for most patients falls between 5 mL/kg to 8 mL/kg, which, for the simulated patient, was 375 mL to 600 mL. Throughout their study, only 22 out of 52 (42%) participants delivered tidal volumes within this range during CPR. When queried about the presumed correct tidal volume to administer during CPR, 38 participants (73%) selected a tidal volume of 6 mL/kg to 7 mL/kg and/or 400 mL to 600 mL.¹² The authors concluded that tidal volume delivery appears to vary between sex and glove size, and that it appeared that participants were unaware of how much tidal volume was being delivered.

Currently, the potential harm of hyperventilation during CPR is recognized. We must acknowledge that evidence indicates clinicians frequently deviate from guidelines or struggle to provide optimal tidal volumes, pressures, flow rates, and respiratory rates.¹³ This is not surprising, given that clinicians face the challenge of delivering breaths during highly stressful situations, often without adequate feedback to guide their performance. Although devices designed to offer feedback during manual ventilation have been assessed and show promise, additional studies are required.¹⁴ For the time being, it is reasonable for clinicians to strive to adhere to guidelines, such as those provided by the AHA, regarding ventilation during cardiac arrest.⁵

Oxygenation

Current recommendations indicate that when supplemental oxygen is accessible, it should be administered at the maximal possible amount (i.e., 1.0 fraction of inspired oxygen, or FIO₂) during CPR.⁵ Studies have demonstrated that higher arterial oxygen partial pressures improve the likelihood of return of spontaneous circulation (ROSC) during CPR.^7,15,16 Although delivering the highest achievable FIO₂ during CPR seems ideal, in practice, the optimal amount remains uncertain. Further studies are necessary to determine the most effective FIO₂ or partial pressure of oxygen (and the optimal measurement method) during CPR.⁷

Ventilation and Oxygenation After CPR

Ventilation

Following ROSC, the current AHA recommendations suggest a partial pressure of carbon dioxide (PaCO₂) target of 35 mmHg to 45 mmHg. Similarly, in 2021, the European Resuscitation Council (ERC) recommended that for patients requiring mechanical ventilation after ROSC, normocapnia (PaCO₂ 35 mmHg to 45 mmHg) should be the targeted range. They also advised employing lung-protective mechanical ventilation strategies, aiming for tidal volumes of 6 mL/kg to 8 mL/kg of ideal body weight. More recently, Battaglini et al proposed 10 rules for optimizing ventilatory settings in patients after cardiac arrest.¹⁷ They suggest that tidal volumes should be lung-protective (6 mL/kg to 8 mL/kg predicted body weight), and that plateau pressures be maintained at or below 20 cm H₂O (and corrected for intra-abdominal pressures when indicated). Additionally, they propose that PaCO₂ levels should be between 35 mmHg and 50 mmHg, a goal that can be facilitated by maintaining a respiratory rate in the range of 8-16 breaths/min.¹⁷

Oxygenation

Current AHA recommendations include administering the highest possible FIO₂ until arterial oxygen levels can be reliably measured to prevent hypoxia. However, once oxygen levels are adequately measured (via peripheral blood oxygen saturation), efforts should be focused on avoiding hyperoxemia by adjusting the delivered FIO₂ to achieve oxygen saturations between 92% and 98%.⁵ The ERC also recommends titrating inspired oxygen immediately after ROSC to maintain normoxia (oxygen saturation between 94% and 98%) when arterial blood oxygen saturations can be reliably monitored.⁶ Rule 7 of Battaglini et al’s 10 rules states that in post-cardiac arrest patients, oxygenation should be accurately targeted to normoxia.¹⁷ They maintain that both hypoxemia and hyperoxemia are potentially dangerous. Hypoxemia has been shown to alter cerebral aerobic metabolism, leading to cell death if not corrected. On the other hand, hyperoxemia has been shown to increase the production of reactive oxygen species in mitochondria, causing oxidative damage to brain cells. Additionally, a 2022 meta-analysis revealed that severe hyperoxemia (partial pressure of oxygen, or PaO₂, > 300 mmHg) is associated with poor neurological outcomes and mortality.¹⁸ It is important to note that the effects of hyperoxemia appear to depend on the duration of exposure to high oxygen levels. Regardless, Battaglini et al recommend titrating delivered oxygen to target a PaO₂ of 70 mmHg to 110 mmHg in patients post-cardiac arrest.¹⁷

In a recent review, Latif et al examined various harmful effects of hyperoxia.¹⁹ The authors propose that hyperoxia following ROSC can adversely affect the brain, cardiovascular system, pulmonary system, kidneys, and even mortality. They advocate for the titration of FIO₂ after ROSC to achieve normoxia (PaO₂ 70 mmHg to 100 mmHg; SpO₂ 94% to 96%) in most patients. The authors wisely recommend that oxygen therapy after ROSC should aim to prevent iatrogenic hyperoxia while simultaneously preserving adequate tissue oxygenation through careful and thoughtful oxygen titration. They also suggest that a more conservative approach to oxygen therapy after ROSC appears safe and, most importantly, improves outcomes. However, they concede that more studies are needed to truly understand the effects of hyperoxia, including the dose and duration effects of hyperoxia.

Summary: The Current Landscape

During CPR

1. Ventilation Strategies: Current recommendations suggest providing tidal volumes of approximately 500 mL to 600 mL or enough to ensure visible chest rise. However, the optimal method for ventilating patients during CPR remains unknown, necessitating further research involving both animal and human studies.

2. Hyperventilation Awareness: Clinicians must be aware of the potential harm of hyperventilation during CPR. Studies indicate that deviations from recommended tidal volumes and respiratory rates are common, highlighting the importance of additional research and practical tools for improving adherence.

3. Oxygenation: Administering the highest possible FIO₂ is recommended during CPR. However, the optimal FIO₂ or PaO₂ remains uncertain, emphasizing the need for further studies to determine the most effective oxygenation strategies.

After ROSC

1. Ventilation Targets: Following ROSC, recommendations include maintaining normocapnia and employing lung-protective mechanical ventilation strategies. Individualized approaches, considering patient-specific characteristics, are crucial for optimizing outcomes.

2. Oxygenation Strategies: Recommendations advocate for administering the highest possible FIO₂ until arterial oxygen levels can be reliably measured to prevent hypoxia. Efforts then should focus on avoiding hyperoxemia by adjusting the delivered FIO₂ to achieve oxygen saturations between 92% and 98%.

Future Directions

1. Research Gaps: There is a need for more comprehensive studies, both in animal and human populations, to refine and tailor ventilation and oxygenation strategies. Addressing current limitations, such as the lack of precise recommendations and ongoing challenges in adherence, is crucial for advancing resuscitation science.

2. Individualized Approaches: Moving forward, the focus should be on individualized approaches to ventilation and oxygenation based on patient-specific characteristics.

Current Limitations and the Path Forward

Despite strides in understanding ventilation and oxygenation during and after CPR, persistent limitations warrant further research and guideline refinement. The optimal method for ventilating patients during CPR remains elusive due to limited data, emphasizing the need for comprehensive investigations involving both animal and human studies. Clinicians struggle with adhering to ventilation guidelines, necessitating additional research on practical tools and educational strategies to enhance compliance. Moving forward, comprehensive studies, technological integration, and innovative education are pivotal in addressing limitations and achieving personalized ventilation and oxygenation strategies for improved resuscitation outcomes. It is hoped that a more nuanced and effective approach toward resuscitation someday will enhance outcomes for our patients.

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