What Post-Tetanic Count (PTC) means and why it matters in quantitative TOF monitoring

Post-Tetanic Count (PTC) is a quantitative neuromuscular monitoring mode (pattern) designed to assess the neuromuscular block deeper than moderate block (block that is defined by the presence of 1, 2, or 3 of the 4 Twitches in TOF count). Traditionally, clinicians only relied on the number of TOF twitches (TOF count) still present after a dose of neuromuscular blocker. However, even when the TOF count is zero (TOFC=0), respiratory muscles can still be active. The PTC pattern of stimulation will assess deep and profound levels of block (deeper than the TOF count=0), offering valuable insights for precise management during these deep levels of paralysis. 

Our optimized PTC stimulation involves a 5-sec tetanic stimulus applied to the ulnar nerve; this is followed, 3 sec later, by up to 20 single twitch stimulations. The PTC is the total number of detectable muscle responses elicited by the tetanic stimulation. A PTC value can range from 0 to 20, with 0 indicating a total neuromuscular block, and 20 indicating an imminent return of TOF responses (TOFC=1). This measurement scale aligns with the American Society of Anesthesiology’s (ASA) guidelines and is reflected in the all-new TetraGraph Level-of Block Gauge in the next-generation device.

PTC provides critical information about the depth of neuromuscular block, allowing anesthesiologists to tailor the level of relaxation to the specific requirements of a surgical procedure, and also avoid overdosing of neuromuscular blocking agents. This is particularly important during laparoscopic and robotic-assisted surgeries where deep neuromuscular block enhances surgical conditions and patient safety.

One key application of PTC is in assessing the relaxation of the diaphragm, the most resistant muscle to neuromuscular blocking agents. A PTC of 0-1 is typically required to achieve adequate diaphragm relaxation, ensuring optimal conditions for certain procedures. TetraGraph's advanced EMG algorithm offers unparalleled sensitivity and accuracy in detecting and quantifying PTC, even in these challenging scenarios. At the other range of the spectrum, a PTC=0 is indicative of total (profound) block, signaling to the clinician that additional doses of neuromuscular blocking agent are unwarranted, and preventing the possibility of overdose.

The TetraGraph system leverages electromyography (EMG) to measure compound muscle action potentials (CMAPs). Unlike acceleromyography (AMG), which depends on physical movement, EMG provides a direct and reliable measurement of muscle response. This is a crucial advantage, especially when patients' arms are tucked or when other physical constraints limit movement.

Using adhesive sensors placed on the wrist and hand (or ankle and foot, as an alternative), the TetraGraph system stimulates the ulnar nerve (or the posterior tibial nerve at the foot) and records the muscle response. The system then calculates the TOF Ratio (TOFR), TOF Count (TOFC), or PTC, depending on the user’s selected mode and the patient’s neuromuscular depth of block.

What sets TetraGraph apart is its superior sensitivity and ease of use. While other devices may limit PTC measurement to 10 or 15 single twitches, TetraGraph’s PTC algorithm extends up to 20, enhancing precision during all stages of block. This capability makes it easier to predict when TOF responses will return, facilitating timely and accurate decision-making.

1. Enhanced sensitivity: The ability to detect up to 20 responses increases accuracy and resolution.
2. Objective assessment: PTC of 0 provides clear confirmation of complete neuromuscular block, essential for critical procedures, and preventing neuromuscular blocking drug overdose.
3. User-friendly design: Adhesive sensor placement simplifies setup, the EMG technology ensures reliable readings even in constrained positions, and TetraGraph Adaptive PTC in the next-generation device adaptively enters PTC mode when the train-of-four count (TOFC) is zero.
4. Improved patient safety: Accurate monitoring reduces the risk of overdosing, or that of residual paralysis and associated complications.

PTC is an invaluable tool in modern quantitative TOF monitoring, providing anesthesiologists with the data needed to manage profound blocks with confidence. The TetraGraph system’s innovative EMG-based approach ensures the most accurate and reliable assessment, elevating patient care standards during even the most demanding procedures.