Hyperangulated vs. Macintosh Style Blades for Intubation in Obstetric Patients

HyperANGulated Versus Macintosh styLE blaDes for INtubation in OBstetric Patients: a Cluster Randomized Feasibility Study

Cesarean section under general anesthesia requires intubation (insertion of a tube through the mouth into the breathing pipe to support breathing during the surgery). A device called a video laryngoscope is used, which has a smooth, curved, or less curved component called 'a blade' that helps the doctor gently see the voice box and guide the breathing tube safely into place during anesthesia; it is not a sharp tool blade.

There are two types of video laryngoscopes blades: a Macintosh- style blade with a gentle curve, approximately 90 degrees) and a hyperangulated blade (with a more pronounced curve).

Although video laryngoscopes are safe and both types have been used for around 20 years, it is not known whether one type works better that the other in patients undergoing cesarean delivery under general anesthesia. Because general anesthesia is used in only a small proportion (about 5%) of all cesarean deliveries, research in this area is limited.

The main purpose of the study is to assess if a study comparing these two types of blades in the obstetric population is feasible. This is also known as a feasibility study, which aims to test the study plan and determine whether enough participants will join a larger study and accept the study procedures. The results will be used as a guide for a larger study.

Study design and setting.

This will be a single-site, prospective feasibility study conducted within the Department of Anesthesia and Pain management, Mount Sinai Hospital, Toronto, a high-volume tertiary obstetric centre with established expertise in obstetric anesthesia and airway research.

Intervention and Cluster Assignment

Because individual randomization immediately before induction is often impractical in obstetric emergencies, blade assignment will occur by randomized time-based clusters. Randomization will occur in 4 clusters of 4 months each, separated by one-month washout periods. Four consecutive four-month periods will be randomly assigned to use either a hyperangulated or Macintosh-style blade as the default for the first intubation attempt. Clinicians may deviate from the assigned blade for patient safety. The time-block design minimizes contamination associated with rapid decision-making in obstetric emergencies and aligns with real-world workflow on labour and delivery units.

Randomization

Time-block cluster allocation will be generated by a study statistician who is not involved in clinical care, participant enrollment, or study implementation. The allocation schedule will be finalized prior to study initiation and maintained without modification.

Data Collection

A trained research assistant will extract patient demographic and perioperative data from the electronic medical record and confirm key airway variables with the attending anesthesiologist within 72 hours of Cesarean delivery (CD). Patients will be contacted by telephone on postoperative day 3 to assess airway-related morbidity, including minor oral or dental injuries (lacerations of the lips, teeth, tongue, or oral mucosa) and postoperative sore throat.

Outcomes

The primary feasibility outcomes are patient enrollment, intervention adherence, and data completeness .

Each feasibility outcome will be assessed against its predefined threshold to determine whether to proceed to a full-scale randomized controlled trial (RCT), proceed with protocol modifications, or discontinue the study if feasibility cannot be achieved despite modifications. Recruitment strategies will be adapted if enrollment falls below two patients per week for several consecutive weeks. Feasibility will be interpreted using a green/yellow/red framework. Outcomes meeting green thresholds will be considered feasible (>80%); outcomes meeting yellow thresholds will prompt protocol modification (60-79%); and outcomes meeting red thresholds will be considered not feasible (<60%). Secondary exploratory outcomes include first-attempt intubation success, number of intubation attempts, need for rescue airway techniques, and airway-related complications.

Potential risks associated:

This study poses minimal risk to participants, as it compares two standard-of-care video-laryngoscope blades used by experienced clinicians, with no restriction on clinical judgment or rescue airway management. Both hyperangulated and Macintosh-style video-laryngoscope blades are widely used, approved devices and are part of standard clinical practice at Mount Sinai Hospital. No experimental devices or techniques are being introduced. The choice of blade does not expose participants to risks beyond those already inherent to general anesthesia (GA) and tracheal intubation for cesarean delivery.

Sample Size

A pragmatic sample of 100 participants will be enrolled over 19 months. This sample is sufficient to estimate feasibility parameters with acceptable precision but is not powered to detect clinical superiority.

Statistical Analysis

Feasibility outcomes will be summarized descriptively using proportions and 95% confidence intervals and evaluated using the pre-specified green/yellow/red framework to guide progression to a multicentre RCT. Descriptive statistics will be used to summarize patient characteristics and secondary outcomes. Categorical variables will be summarized as frequencies and percentages; continuous variables as means with standard deviation.

Significance/Importance

By establishing feasibility for a definitive multicentre RCT, this study represents a critical step toward optimizing airway management during CD under general anesthesia. Ultimately, this work has the potential to improve first-attempt intubation success, reduce airway-related complications, and enhance maternal and fetal safety nationwide.

Inclusion Criteria:

1. Pregnant patients undergoing emergency or urgent cesarean delivery under general anesthesia requiring tracheal intubation.

Exclusion Criteria:

1. No tracheal intubation performed and (ii) patient refusal of consent.
2. Patients not receiving general anesthesia.
3. Patients that previously participated in the study.